A method for screening of an in vitro display library within a cell

Abstract

A method for screening of an in vitro display library for binding within a cell of a small-molecule chemical compound binding entity of the library to a protein or RNA target of interest in order to identify at least one individual chemical compound binding entity of the library that is capable of binding within the cell to the protein or RNA target of interest.

Description

TITLE: A METHOD FOR SCREENING OF AN IN VITRO DISPLAY LIBRARY WITHIN A CELLFIELD OF THE INVENTION:The present invention relates to a method for screening of an in vitro display library for binding within a cell of a small-molecule chemical compound binding entity of the library to a protein or RNA target of interest in order to identify at least one individual chemical compound binding entity of the library that is capable of binding within the cell to the protein or RNA target of interest.BACKGROUNDDisplay technologies have been developed to combine information storage and amplification capabilities of nucleic acids with the functional activities of other compounds. Display technologies rely on an association between a functional binding entity (i.e. phenotype) and a nucleic acid sequence informative (genotype) about the structure of the binding entity. Note: Nucleic acid aptamer technology is considered a display technology although a special case as the pheno- and genotype consist of the same molecule (DNA or RNA).An advantage of such methods is that very large libraries can be constructed and probed for a desired activity of the functional binding entities. Library members having the desired activity can then be partitioned from library members not having the desired activity, thus creating an enriched library with a higher fraction of members having the desired activity. This process is called selection or enrichment. Some display technologies allow for rounds of selections, where the enriched library from one round is amplified and used to prepare a new enriched display library and used in a next round of selection and so forth. The structures of the library members in the enriched library can then be identified by their cognate nucleic acid sequence, thus allowing identification even from minute amounts of material.Herein relevant libraries may according to the art be termed“in vitro display libraries”.The term“in vitro display library” shall herein be understood according to the art - i.e. as a library comprising numerous different binding entities wherein each binding entity is attached to a nucleic acid molecule and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the binding entity - i.e. once one knows the specific nucleic acid sequence information of the nucleic acid molecule one directly knows the structure of the specific binding entity attached to the nucleic acid molecule - the structure of the binding entity (i.e. phenotype) attached to the nucleic acid molecule (genotype) is herein termed B-structure.When the attached nucleic acid molecule is a DNA molecule - the term“ in vitro display library” may in the art sometimes be referred to as“DNA-encoded library (DEL)”.The term“binding entity” may in the art sometimes be referred to as“ligand”.The prior art describes a number of different methods to make such in vitro display libraries - herein suitable examples include e.g. EP1809743B1 (Vipergen - YoctoReactor® (yR) library technology), EP1402024B1 (Nuevolution), EP1423400B1 (David Liu), Nature Chem. Biol. (2009), 5:647-654 (Clark), WO 00 / 23458 (Harbury), Nature Methods (2006), 3(7), 561-570, 2006 (Miller), Nat. Biotechnol. 2004; 22, 568-574 (Melkko), Nature. (1990); 346(6287), 818- 822 (Ellington), or Proc Natl Acad Sci USA (1997). 94 (23): 12297-302 (Roberts),WO06053571A2 (Rasmussen).As described in e.g. above-mentioned prior art - one can today make in vitro display libraries comprising very many (e.g. 1015) specific binding entities (e.g. 1015different chemical compounds).In view of this high number of specific binding entities - it is evident that theselection / enrichment step of such libraries to make an enriched library is important - e.g. to efficient be able to identify the structure of a specific binding entity (e.g. a chemical compound) that binds to a target of interest (e.g. a medical important receptor molecule).In figure 3 of EP2622073B1 (Vipergen) is shown an example of the in vitro display technology as described in EP1809743B1 (Vipergen - YoctoReactor® (yR) library technology) - as can be seen in this figure 3 of EP2622073B1 , the selection step of this example is performed by immobilizing the target (e.g. a receptor) to a solid surface (e.g. a bead or a glass plate) and non-binders and low affinity binders are typically washed away, whereas the population enriched for binders are recovered from the solid support. Numerous examples of such solid support based selection / enrichment methods are described in the art.EP2622073B1 (Vipergen) relates as such to an improved in vitro display based method in order to make an enriched library, which is termed Enrichment by Co-Compartmentalization (ECC) or alternatively termed Binder Trap Enrichment® (BTE) - see e.g. figures 1-2 of EP2622073B1 or the Vipergen company home-page: http: / / www. vipergen .comAs discussed above, in many prior arts described“in vitro display library” methods - the selection / enrichment step of binding specific binding entity (e.g. a chemical compound) to a target of interest (e.g. a medical important receptor molecule) is performed in way that may be termed to rely on purified, heterologously expressed proteins in a not natural artificial context - such as e.g. by immobilizing the target (e.g. a receptor) to a solid surface (e.g. abead or a glass plate).In relation to binding / selection in such so-called artificial context - the article of Lynn MM et al. (“Identification of Ligand-Target Pairs from Combined Libraries ofSmall Molecules and Unpurified Protein Targets in Cell Lysates”; J. Am. Chem. Soc. 2014, 136, 3264-3270) reads“the results of selections on immobilized targets may lack biological relevance for proteins that adopt non-native conformations or lack binding partners or cofactors essential for their function when taken out of the cellular context.”.In view of this, the article of Lynn describes a so-called interaction determination using unpurified proteins (IDUP) method to identify ligand+target pairs from one-pot mixtures of DNA-linked ligands and unpurified protein targets in cell lysates.The article of Zining Wu et al. (“Cell-Based Selection Expands the Utility of DNA-Encoded Small-Molecule Library Technology to Cell Surface Drug Targets..”; ACS Comb. Sci. 2015, 17, 722-731) describes a cell-based selection method for identifying high affinity and selective ligands against cell surface targets from small-molecule DNA-Encoded Libraries (DELs) - i.e. where the binding is made on cells surfaces, which is not within the cell as such.The article of M. Schurmann et al. (“Small-Molecule Target Engagement in Cells”; Cell Chemical Biology 23, April 21 , 2016) describes that a single specific small-molecule chemical compound may be introduced into a cell and it sometimes may then be possible to identify / detect if this single (one specific) chemical compound binds to a target (e.g. a receptor).As understood by the skilled person in the present context - this M. Schurmann article does not relate to a method for screening an in vitro display library (such as e.g. a DNA-EncodedLibrary) - i.e. a library comprising numerous (e.g. 1010) different binding entities.In short, this M. Schurmann article essentially relates to a situation where one already knows that the small-molecule of interest binds to the target (e.g. a receptor) of interest and one essentially simply wants to confirm this within a cell of interest or one wants to study where (e.g. in which compartment) of the cell the binding physically takes place.In summary and without being limited to theory - the present inventors believe that no prior art document directly and unambiguously describes a method for screening an in vitro display library (e.g. a DNA-Encoded Library (DEL)) for binding within a cell of a small-molecule chemical compound binding entity of the library to a protein or RNA target of interest - i.e. where the library selection / enrichment step of binding specific binding entity (e.g. a chemical compound) to a target of interest (e.g. a medical important receptor molecule) is performed within a cell.SUMMARY OF THE INVENTIONThe problem to be solved by the present invention may be seen as to provide an improved method for screening an in vitro display library for binding of a small-molecule chemical compound of interest to a target of interest (e.g. a medical relevant receptor).Most previous examples of DNA-encoded library (DEL) screenings are performed on recombinant, purified proteins that are taken out of a cellular context. The purified proteins may lack binding partners or cofactors essential for their function and adopt non-native conformations. Chemical binding entities identified in DEL screenings on purified proteins outside a cellular context may therefore lack biological relevance. In the present invention, DEL screenings are performed on proteins expressed within the cell. Within the cell, the protein of interest can interact with essential binding partners and cofactors in a native environment. Chemical binding entities identified from DEL screenings inside the cell therefore has a higher chance of being biologically active. The latter is particularly important for chemical binding entities which will be applied for drug discovery.The present invention allows for DEL screenings to be performed on proteins expressed within the cell. The present invention is therefore not dependent on laborious protocols to obtain recombinantly expressed and purified proteins, which are required for most previous examples of DEL screenings.In working Example herein is described how the present inventors successfully performed a screening of an in vitro display library (DNA-encoded library) within a cell (i.e. a Xenopus laevis oocyte) and identified a number of individual chemical compound binding entities (ligand) of the library that are capable of binding within the cell to the protein target of interest.As discussed above and without being limited to theory - the present inventors believe that no prior art document directly and unambiguously describes such a“within the cell” method - i.e. where the library selection / enrichment step of binding specific binding entity (e.g. a chemical compound) to a target of interest (e.g. a medical important receptor molecule) is performed within a cell. Without being limited to theory - it was not prima facie obvious for the present inventors that is was possible to obtain the in working Example herein described“within the cell” very positive screening results - see e.g. the Conclusions of Example 1 herein.One reason for this relates to that it is known in the art that the“protein density” within a cell isvery high, since the cell comprises numerous proteins and other compartments - for instance reads the article of Ron Milo (“What is the total number of protein molecules per cell volume?..”; Bioessays 35: 1050-1055, 2013):“we estimate a range of 2-4 million proteins per cubic micron (i.e. 1 fl_) in bacteria, yeast, and mammalian cells”.In relation to a method for screening an in vitro display library of the present invention - the high“protein density” within a cell would by the skilled person prima facie be considered a problem, since an in vitro display library comprises numerous (e.g. 1010) different chemical compound binding entities and it would prima facie be considered not plausible that a substantial amount of“good binders” within the library, actually would be able find the target (e.g. a receptor) of interest and thereby bind the target of interest.Said in other words, before the disclosure of the present“within the cell” invention - one could prima facie have believed that none (or only very few) of the library chemical compound binding entities would actually be able to find and thereby bind the target (e.g. a receptor) of interest within a cell - i.e. in such a scenario would library binder screening“within the cell” not be technical relevant / useful, since one would not identify a representative amount of good binders compounds of the library.As discussed herein - by using a“within the cell” library screening method of the present invention, the present inventors identified a number of individual different good binder chemical compound binding entities - i.e. an acceptable representative high number of good binder compounds of the library.Accordingly, one relevant technical contribution of the present invention may be seen as relating to the fact that the present invention demonstrated that it is actually possible to successfully perform a screening of an in vitro display library (DNA-encoded library) within a cell and thereby identify an acceptable representative high number of individual chemical compound binding entities (ligand) of the library that are capable of binding within the cell to the protein target of interest.In working Example herein, the cell used was a Xenopus laevis oocyte.However, the“protein density” within a cell possible problem / issue discussed above may be seen as a matter not only relevant for a Xenopus laevis oocyte - to the contrary, it may be seen as a general matter of concern for virtually any cell of interest.Accordingly, it is believed that the fact that working Examples herein demonstrate that the method of the present invention works for Xenopus laevis oocyte makes it plausible that it would also work in a substantial amount of other different cell types (e.g. other eukaryotic cell types such as e.g. a human (e.g. CHO) cell).Accordingly, a first aspect of the invention relates to a method for screening of an in vitro display library for binding within a cell of a small-molecule chemical compound binding entity of the library to a protein or RNA target of interest in order to identify at least one individual chemical compound binding entity of the library that is capable of binding within the cell to the protein or RNA target of interest and wherein the method comprises the steps of:(i): expressing at least one target Tn, wherein n = 1 or more, in a cell and wherein the at least one target is a protein or RNA - the structure of the target is herein termed T-structure;(ii): introducing an in vitro display library into the cell of (i), wherein:(a): the library is a library of at least 1000 different binding entities Bn, wherein n = 1000 or more, wherein each binding entity is attached to a nucleic acid molecule and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the binding entity - wherein once one knows the specific nucleic acid sequence information of the nucleic acid molecule one directly knows the structure of the specific binding entity attached to the nucleic acid molecule and wherein the binding entities of the library are chemical compounds with an average molecular weight MW below 10000 dalton - the structure of the binding entity attached to the nucleic acid molecule is herein termed B- structure; and(b): the library is introduced into the cell under binding conditions, which are conditions where a B-structure containing a binding entity capable of binding to a target molecule, binds more efficiently to the corresponding T-structure, than a B-structure containing a binding entity not capable of binding to the same target do and wherein one within the cell gets binding of at least one of the binding entities to at least one target thereby creating within the cell a complex comprising a B-structure bound to a T-structure, which is termedBBoundToT-stmcture;(iii): making lysis of the cell of (ii) to breaking down the membrane of cells in order to:(A): get the BBOundToT-structures of (ii) out of the cell and thereby obtain a solution comprising BBOundToT-structures, wherein the BBoundToT-structures are not within the cells; or (B): get B-structures out of the cells that had bound to target in step (ii) and have been marked before step (iii) in a way that makes it possible to distinguish the marked B- structures from a B-structure that has not bound to target in step (ii) and thereby obtain a solution comprising binder marked B-structures, wherein the binder marked B-structures are not within the cells; and(iv): identifying, via use of the solution of (iii) and the nucleic acid molecules that comprises the specific nucleic acid sequence information allowing to identify the binding entity of the B-structures, at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.Step (i) relating to expressing at least one target in a cell may be done according to the art - it is routine work for the skilled person to express a protein or RNA target of interest in a cell of interest.Many times, it may be preferred that the target is a heterologous expressed target.According to the art - the term "heterologous" relates to a target (e.g. a protein) that is experimentally put into a cell that does not normally make (i.e. expresses) that target (e.g. a protein).However, in some cases it may be preferred that the target is a target naturally expressed in the cell - e.g. a human receptor target naturally expressed in a human (e.g. CHO) cell. In some cases, it may be preferred that the target is expressed in cells originating from a transgenic host - e.g. a modified version of a human receptor target.As discussed above, the prior art describes a number of different methods to make an in vitro display library as such - accordingly making the in vitro display library as such of step (ii) may be done according to known prior art techniques for making such in vitro display libraries.Step (ii) refers to“introducing an in vitro display library into the cell of (i)” - essentially this step may be made based on prior art know techniques.As discussed in working Example herein - when the cell is a Xenopus laevis oocyte may the library be introduced into the oocyte cell via prior art known injection techniques and there is no reason to believe that injection (e.g. micro-injection) would not work in a substantial amount of other mammalian cell types.Alternatively, and depending on the cell type of interest - it may e.g. be done by transfection (e.g. electroporation or chemical based).It is routine work for the skilled person to identify suitable“binding conditions” according to step (ii)(b).Essentiality, the“binding conditions” of step (ii)(b) are generally the natural binding conditions within the cell - i.e. one of the advantages of the present invention is that the binding entity (ligand) can bind the target under“binding conditions” of step (ii)(b) that may be natural within the cell binding conditions.Step (iii) refers to“making lysis of the cell of (ii) to breaking down the membrane of cells” - essentially this step may be made based on prior art know techniques.Also step (iv) may be made by based on prior art know techniques as e.g. discussed above.In short and as discussed in further detail herein, this“identifying... at least one individual binding entity that binds within the cell of (ii) to at least one target of interest” of step (iv) may be made in different ways and based on the common general knowledge and the technical teaching herein, it is routine work for the skilled person to perform this step (iv).In short, based on the detailed description herein and the common general knowledge - the skilled person may perform all of the individual steps (i) to steps (iv) of the first aspect in a number of different ways / embodiments.Embodiments of the present invention are described below, by way of examples only.DRAWINGSFigure 1 : Illustrative example of an embodiment of the method of first aspect (i.e. claim 1) herein.Figure 2: Illustrative example of an embodiment of the method of first aspect (i.e. claim 1) herein, where used Prey-BaitFigure 3: Results of working Example 1 herein - for further details see the Example 1.DETAILED DESCRIPTION OF THE INVENTIONStep (i) of first aspectAs discussed above, step (i) reads:“(i): expressing at least one target Tn, wherein n = 1 or more, in a cell and wherein the at least one target is a protein or RNA - the structure of the target is herein termed T-structure”The target may be any suitable protein or RNA target of interest.As discussed above, it is routine work for the skilled person to express a protein or RNA target of interest in a cell of interest.As discussed in working Examples herein and as known in the art - when the cell is a Xenopus laevis oocyte, the expression of the target may be done by injection of mRNA and itmay be preferred.However, expression of the target in the cell may be done in other well know suitable ways, such as via routine recombinant expression (via e.g. use of an expression vector made of e.g. DNA) of the target of interest in the cell of interest.Many times, it may be preferred that the target is a heterologous expressed target.According to the art - the term "heterologous" relates to a target (e.g. a protein) that is experimentally put into a cell that does not normally make (i.e. expresses) that target (e.g. a protein).In some cases, it may be preferred that the target is heterologously expressed in a specific cellular compartment within the cell - e.g. in the nucleus. For the skilled person, this can be done be installing a leader sequence or signal sequence in the target construct.Preferably, the target is a protein.As known in the art - a suitable target could e.g. be a receptor molecule present in e.g. the human body and one would be interested in identifying a binding entity (e.g. a chemical compound) that can bind to the receptor.Accordingly, the target may preferably be a receptor such as e.g. a receptor protein molecule.In accordance with the prior art - suitable examples may be wherein the target is an autoantigen, a bacterial protein, a blood protein, a cell adhesion protein, a cytokine, a cytoskeleton protein, a DNA-binding protein, a developmental protein, an engineered protein, an enzyme, an extracellular matrix protein, a GTP-binding protein regulator, a glycoprotein, a growth factor, a heat shock protein, a lipoprotein, a membrane protein, a metalloprotein, a motor protein, a phosphoprotein, a prion, a protein complex, a protein domain, a RNA-binding protein, a receptor, a recombinant protein, a seed storage protein, a structural protein, a transcription coregulator protein, a transport protein, a viral protein or fragments hereof.In short, the skilled person is aware of numerous different possible targets than could be of interest in the present context. In some cases, it may be preferred to modify the expressed target protein - e.g. by phosphorylation, methylation, acetylation or dephosphorylation. By the skilled person, this can be done by co-expressing a modifying enzyme - e.g. a kinase, methyltransferase, acetyltransferase or a phosphatase - together with the target protein.As discussed above, it is believed that the fact that working Examples herein demonstrate that the method of the present invention works when the cell is a Xenopus laevis oocyte makes it plausible that it would also work in a substantial amount of other different cell types (e.g. other eukaryotic cell types such as e.g. a human (e.g. CHO) cell).Preferably, the cell is a eukaryotic cell such as e.g. mammalian cell, preferably wherein the mammalian cell is a human (e.g. CHO).In working Examples herein is shown that it is possible to introduce (via injection) into one single individual cell (i.e. a Xenopus laevis oocyte) an in vitro display library comprising numerous different binding entities.Accordingly, in a preferred embodiment, the cell is a Xenopus oocyte, such as e.g. Xenopus tropicalis oocyte or Xenopus laevis oocyte- most preferably the cell is a Xenopus laevis oocyte.The term“a cell” of step (i) may be a single cell (e.g. when the cell is a Xenopus laevis oocyte).However, as understood by the skilled person in the present context - the term“a cell” of step (i) may in practice many times refer to a population of cells, wherein individual cells of the population recombinantly express the target of interest.For instance, wherein the target is expressed by use of e.g. an expression vector in a standard / routine recombinant expression of target in a cell type of interest (e.g. human CHO cells), this will generally give a population of cells, wherein individual cells of the population recombinantly express the target of interest.Step (i) of first aspect reads“at least one target Tn, wherein n = 1 or more”.An advantage of the method as described herein is that one in an efficient and rapid way can simultaneous screen for binding entities that could bind to e.g. two or more targets.For instance - the targets could be two different receptor molecules and the method as described herein could then simultaneous identify one binding entity that binds to one of the receptors and another binding entity that binds to the other receptor.In the example above (with two different e.g. receptor targets) we would have a situation, wherein the target Tn (n = 2) or alternatively expressed T2.In line of above - it may be relevant to have at least two different targets in step (i) [i.e. Tn (n = 2 or more], or to at least three different targets in step (i) [i.e. Tn (n = 3 or more], or to have at least ten different targets in step (i) [i.e. Tn (n = 10 or more], or to at least hundred different targets in step (i) [i.e. Tn (n = 100 or more].Without being limited to theory it may be difficult to have more than 1000 different targets in step (i) - i.e. more than 1000 different T-structures in the cell.Step (ii) of first aspectAs discussed above, step (ii) relates to:“(ii): introducing an in vitro display library into the cell of (i), wherein:(a): the library is a library of at least 1000 different binding entities Bn, ... and wherein the binding entities of the library are chemical compounds with an average molecular weight MW below 10000 dalton; and(b): the library is introduced into the cell under binding conditions,...”Step (ii) refers to“introducing an in vitro display library into the cell of (i)” - essentially this step may be made based on prior art know techniques.As discussed in working Example herein - when the cell is a Xenopus laevis oocyte may the library be introduced into the oocyte cell via prior art known injection techniques and there is no reason to believe that injection (e.g. micro-injection) would not work in a substantial amount of other mammalian cell types.Alternatively, and depending on the cell type of interest - it may e.g. be done by transfection (e.g. electroporation or chemical based).In working Examples herein is shown that it is possible to introduce (via injection) into one single individual cell (i.e. a Xenopus laevis oocyte) an in vitro display library comprising numerous (approx. 108) different binding entities.The term“the cell” of step (ii) may be a single cell (e.g. when the cell is a Xenopus laevis oocyte).However, as discussed above - the term“a cell” of step (i) may in practice many times refer to a population of cells and in such a case term“the cell” of step (ii) may in practice be the population of cells of step (i).As understood by the skilled person in the present context - if one in step (ii) e.g. introduces an in vitro display library of e.g. 106different binding entities into population of cells of step (i) (e.g. human CHO with recombinantly expressed target) by e.g. transfection then there may be introduced different numbers of binding entities into each cell of the population - such as e.g. some cells of the population may comprise less than 5 binding entities (e.g. one binding entity) and other cells of the population may comprises more than 1000 different binding entities.The term“in vitro display library” shall be understood according to the art - i.e. as a library comprising numerous different binding entities wherein each binding entity is attached to a nucleic acid molecule and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the binding entity - i.e. once one knows the specific nucleic acid sequence information of the nucleic acid molecule one directly knows the structure of the specific binding entity attached to the nucleic acid molecule - the structure of the binding entity (i.e. phenotype) attached to the nucleic acid molecule (genotype) is herein termed 13- structure.When the attached nucleic acid molecule is a DNA molecule - the term“in vitro display library” may in the art sometimes be referred to as“DNA-encoded library (DEL)”.The term“binding entity” may in the art sometimes be referred to as“ligand”.As discussed herein - the prior art describes a number of different methods to make such in vitro display libraries - i.e. an in vitro display library of step (i).Said in other words, it is today routine work for the skilled person to properly make a structure of the binding entity (i.e. phenotype) attached to the nucleic acid molecule (genotype) - i.e. what is herein termed a“B-structure”.As known in the art - binding entity (i.e. phenotype) may be attached to the nucleic acid molecule (genotype) by e.g. a covalent binding or e.g. a high affinity non-covalent binding.It may herein be preferred that the binding entity (i.e. phenotype) is attached to the nucleic acid molecule (genotype) by a covalent binding.An in vitro display library of step (i) comprises a number of different B-structures - i.e. in line of above it is routine work for the skilled person to make an in vitro display library of step (i).Herein suitable examples include e.g. EP1809743B1 (Vipergen), EP1402024B1(Nuevolution), EP1423400B1 (David Liu), Nature Chem. Biol. (2009), 5:647-654 (Clark), WO00 / 23458 (Harbury), Nature Methods (2006), 3(7), 561-570, 2006 (Miller), Nat. Biotechnol. 2004; 22, 568-574 (Melkko), Nature. (1990); 346(6287), 818-822 (Ellington), or Proc Natl Acad Sci USA (1997). 94 (23): 12297-302 (Roberts).Said in other words, the in vitro display library of step (i) of first aspect may be made in a number of ways as described in the prior art.Without being limited to theory - herein suitable examples of in vitro display library technologies include DNA Encoded Chemical Library technologies, Aptamer technologies, RNA / DNA display technologies such as CIS display, Ribosome display, mRNA display or bead display system (using nucleic acids for encoding).As described in the prior art (see e.g. EP1809743B1 (Vipergen)) - the nucleic acid molecule of the B-structure may e.g. be PNA, LNA, RNA, DNA or combinations thereof. Preferably, the nucleic acid molecule of the B-structure is DNA.In a preferred embodiment of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may be a double stranded nucleic acid molecule.In a preferred embodiment of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may be at least 0 % double stranded (i.e. single stranded), may be at least 10 % double stranded, at least 20 % double stranded, at least 30 % double stranded, at least 40 % double stranded, at least 50 % double stranded, at least 60 % double stranded, at least 70 % double stranded, at least 80 % double stranded, at least 90 % double stranded, or 100 % double stranded.In a preferred embodiment of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may contain a PCR priming site or a fraction hereof.In a preferred embodiment of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may contain 2 PCR priming sites or fractions hereof.In a preferred embodiment of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may contain at least 3 PCR priming sites or fractions hereof.In some embodiments of the present invention a fraction of a PCR priming site comprises at least 5 nucleotides, at least 6 nucleotides, at least 7 nucleotides, at least 8 nucleotides, at least 9 nucleotides, at least 10 nucleotides, at least 11 nucleotides, at least 12 nucleotides, at least 13 nucleotides, at least 14 nucleotides, at least 15 nucleotides, at least 16 nucleotides, at least 17 nucleotides, at least 18 nucleotides, at least 19 nucleotides, or at least 20 nucleotides.In some embodiments of the present invention the nucleic acid molecule (genotype) attached to the binding entity (phenotype) in the B-structure may contain a single stranded overhang reverse complement to a single stranded overhang of another relevant nucleic acid molecule (genotype) used in the method as described herein (e.g. a nucleic acid molecule attached to a bait as discussed below). The overhang may preferentially be 1 nucleotide, 2 nucleotides, 3 nucleotides, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, or 10 nucleotides long.The Binding entity may be any suitable binding entity of interest, wherein the binding entities of the library are chemical compounds with an average molecular weight MW below 10000 dalton, more preferably an average molecular weight MW below 5000 dalton, even more preferably an average molecular weight MW below 1000 dalton.Suitable examples of a herein relevant chemical compound binding entity may be found in the prior art - see e.g. EP1809743B1 (Vipergen), EP1402024B1 (Nuevolution), EP1423400B1 (David Liu), Nature Chem. Biol. (2009), 5:647-654 (Clark), WO 00 / 23458 (Harbury), Nature Methods (2006), 3(7), 561-570, 2006 (Miller), Nat. Biotechnol. 2004; 22, 568-574 (Melkko), Nature. (1990); 346(6287), 818-822 (Ellington), or Proc Natl Acad Sci USA (1997). 94 (23): 12297-302 (Roberts).In short, the skilled person is aware of numerous different possible binding entities that could be of interest in the present context.Step (ii) of first aspect reads“at least 1000 different binding entities Bn, wherein n = 1000 or more”.In practice, there may many times be many more different binding entities present in the library of step (i) - such as e.g. at least 104, at least 106or at least 108different binding entities - i.e. where n= at least 104, n= at least 106or n= at least 108.In working Examples herein is shown that it is possible to introduce (via injection) into one single individual cell (i.e. a Xenopus laevis oocyte) an in vitro display library comprising numerous (approx. 108) different binding entities.Accordingly, in a theoretical situation, wherein the library comprises exactly 104different binding entities - one may herein express this as Bn(n = 104) or B104. Without being limited to theory it may be difficult to make a library with more than 1020different binding entities.Step (ii)(b) reads:“(b): the library is introduced into the cell under binding conditions, which are conditions where a B-structure containing a binding entity capable of binding to a target molecule, binds more efficiently to the corresponding T-structure, than a B-structure containing a binding entity not capable of binding to the same target do and wherein one within the cell gets binding of at least one of the binding entities to at least one target thereby creating within the cell a complex comprising a B-structure bound to a T-structure, which is termed BeoundToT-structure”The term“binds more efficiently” shall be understood according to common practice e.g. higher affinity, faster on rate, or slower dissociation rate. As known to the skilled person - in the present context it is routine work for the skilled person to perform step (ii)(b) under conditions, wherein one get this“binds more efficiently” effect.It would be routine work for the skilled person to optimize the binding conditions of step (ii)(b) in order to get the required“binds more efficiently” effect of step (ii)(b).As discussed above, the“binding conditions” of step (ii)(b) are generally the natural binding conditions within the cell - i.e. one of the advantages of the present invention is that the binding entity (ligand) can bind the target under“binding conditions” of step (ii)(b) that may be natural within the cell binding conditions.As known to the skilled person - herein relevant optimization parameters may e.g. be inonic strength, temperature etc.Accordingly, under any practical herein relevant circumstance - the skilled person would not be in any reasonable doubt if he (after e.g. proper routine adjustment of the binding conditions) would work under binding conditions of step (ii)(b) or not.In a preferred embodiment, step (ii)(b) is performed under binding conditions, wherein a B- structure containing a binding entity capable of binding to a target molecule, binds 10 fold(more preferably 100 fold, even more preferably 1000 fold) more efficiently to thecorresponding T-structure, than a B-structure containing a binding entity not capable of binding to the same target do.The method as described herein allows optimizing for major binding characteristic for binding of binding entity to target. For example, potency (affinity), association rate (on rate) or dissociative half-life of binding entity and target (off rate).Affinity based selection is achieved in binding step (ii)(b) e.g. by using equilibrium conditions and controlled by the target concentration in the binding step - for instance, binding conditions wherein 90% of the molecules of a binding entity in the display library having a K equal to 10 times smaller than the target concentration are target bound or binding conditions wherein 90% of the molecules of a binding entity in the display library having a Kdequal to 2 times smaller than the target concentration are target bound.In a preferred embodiment of the present invention - the concentration of T-structures in the “binding step step(ii)(b)” is at least 1015M, at least 1014M, at least 1013M, at least 1012M, at least 1011M, at least 1010M, at least 109M, at least 108M, at least 107M, at least 106M, at least 105M, or at least 104M.In working example herein (see below) the concentration of T-structures in the“binding step” step(ii)(b) was around 200 x 109M.Alternatively, association rate based selection is achieved by controlling the time allowed for the binding step step(ii)(b) - accordingly, the“binding step” may be performed for a time period shorter than the time needed to reach binding equilibrium conditions.Step (iii) of first aspectAs discussed above, step (iii) reads:“(iii): making lysis of the cell of (ii) to breaking down the membrane of cells in order to:(A): get the BBOundToT-structures of (ii) out of the cell and thereby obtain a solution comprising BBOundToT-structures, wherein the BBoundToT-structures are not within the cells; or(B): get B-structures out of the cells that had bound to target in step (ii) and have been marked before step (iii) in a way that makes it possible to distinguish the marked B- structures from a B-structure that has not bound to target in step (ii) and thereby obtain a solution comprising binder marked B-structures, wherein the binder marked B-structures are not within the cells”Step (iii) refers to“making lysis of the cell of (ii) to breaking down the membrane of cells” - essentially this step may be made based on prior art know techniques such as e.g. by mechanical crushing (e.g. centrifugation or pipetting) or by chemical lysis (e.g. by use of SDS to dissolve the membrane).In view of the common general knowledge of the skilled person and the technical teaching herein (see e.g. below) - the skilled person may perform step (iii) in numerous different suitable ways.As understood by the skilled person and discussed herein - whether one uses option step(iii)(A) or step (iii)(B) may be seen as relating to how one prefers to make the identifying step(iv). It may be preferred that step (iii) is step (iii)(A).As illustrated in Figure 1 herein - in a situation wherein step (iii) is step (iii)(A) it may e.g. be that step (iv) is done by:- binding BBOundToT-structures of the solution (iii)(A) of to a solid support via binding of target of the BeoundToT-stmctures to the solid support and remove B-structures not bound to target and thereby not bound to the solid support; and- identifying, via use of the specific nucleic acid sequence information allowing to identify the binding entity of the BBOundToT-structures bound to the solid support, at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.As illustrated in Figure 2 herein and in working Example herein - in a situation wherein step (iii) is step (iii)(A), the method as described herein may preferably be done by a method wherein:- the T-structure of (i) of the first aspect comprises a prey (e.g. a target-prey fusion protein) and there in step (ii) of the first aspect is also introduced a bait attached to a nucleic acid molecule (which e.g. has complementary cohesive ends to the nucleic acid molecule of the B- structure) and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the specific target and wherein the bait binds to the prey of the target in step (ii) and thereby creates BBoundToT-structures with the bait bound to the prey of target; - after lysis step (iii)(A) - fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBoundToT-structures with the bait bound to the prey of target, wherein the fused nucleic acid molecules comprise the sequence information allowing to identify binding entity and target; and- identifying in step (iv) via use of the specific nucleic acid sequence information allowing toidentify the binding entity and target of the fused (e.g. ligated) nucleic acid molecules of the preceding step at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.Before the“fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBoundToT-structures with the bait bound to the prey of target” step it may be preferred to make a dilution step (e.g. a dilution step of the solution (e.g. supernatant) obtained from cell lysis step (iii).It may be preferred that the dilution step of the solution (e.g. supernatant) obtained from cell lysis step (iii) (preferably step (iii)(A)) is a diluting the solution of at least 102fold, such as at least 103fold, at least 104fold, or at least 105fold.In working example herein (see below) the diluting the solution was around 104fold.An advantage of this diluting step is that not bound B and T-structures (i.e. B and T-structures alone as such) may after dilution be even further physically apart from each other in the solution and there will then less“false positives” after the“fusing the nucleic acid molecules of the BeoundToT-structures” step.After the“fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBoundToT-structures with the bait bound to the prey of target” step it may be preferred to make a purification of the fused (e.g. ligated) nucleic acid molecules - e.g. in order to have more pure nucleic acid molecules (e.g. DNA) for e.g. a subsequent amplification (e.g. via PCR) step.The skilled person in the art can routinely identify numerous different strategies in order to purify nucleic acid molecules (e.g. DNA) of interest, without being limited for example by: agarose gel electrophoresis, polyacrylamid gel electrophoresis, spin-columns, etc.The“identifying” step (iv) preferably comprises a step, wherein the fused nucleic acid molecules that comprise the sequence information for binding entity and for target are amplified (preferably by use of polymerase chain reaction (PCR)).As evident, if there is only one target (i.e. n = 1 in step (i), then is the identifying of at least one individual binding entity essentially done by use of the specific nucleic acid sequence information allowing to identify the binding entity.The prior art within the herein relevant field of biotechnology describes numerous herein suitable“prey-bait” systems, such as e.g.:- prey: tetrameric streptavidin and bait: biotin;- prey: monomeric streptavidin (e.g. mSA2) and bait: biotin;- prey: His-tag and bait: NTA;- prey: SNAP-tag® and bait: benzyl guanin (BG);- prey: Halo-Tag® and bait: reactive chloroalkane linker bound to a functional group;- prey: carbonic anhydrase IX (CAIX) and bait: VD11-4-2; or- prey: maltose binding protein (MBP) and bait: maltose or maltotriose.In working Example herein is the“prey-bait” system - prey: carbonic anhydrase IX (CAIX) and bait: VD11-4-2 - accordingly, this is preferred“prey-bait” system.The“prey-bait” system - prey: carbonic anhydrase IX (CAIX) and bait: VD11-4-2 is described in e.g. the article of V. Dudutiene et al. (“Discovery and Characterization of Novel Selective Inhibitors of Carbonic Anhydrase IX”; J. Med. Chem. 2014, 57, 9435-9446), where it is described that VD11-4-2 is the small chemical compound with the structure:VD11-4-2Preferably, the T-structure of (i) of the first aspect that comprises a prey is obtained by expressing a target-prey fusion protein (e.g. target-CAIX) within the cell - see e.g. working Example herein for an example of this.It is routine work for the skilled person to express a target-prey fusion protein within a cell of interest.A possible embodiment could be where the bait actually binds to binding site of target, which is different to binding site of binding entity (i.e. ligand). In the present context“fusing (e.g. by ligating) the nucleic acid molecules of the BBoundToT- structures with the bait bound to the prey of target” shall be understood as joining the genetic information carried by the two genotypes (i.e. nucleic acid molecule with sequence information for binding entity and nucleic acid molecule with sequence information for target). As known to the skilled person (see e.g.

[0166] of EP2622073B1 (Vipergen)), this“fusing” can be accomplished in several ways such as e.g:a) information transfer by e.g. overlap PCR or overlap genome extension;b) information joining catalyzed by an enzyme forming an amplifiable facilitating bond - e.g. by a DNA ligase where a phosphordiester bond between at least one of the strands from eachnucleic acid molecule is formed.Preferably, the fusing is done by ligating via use of a ligase. If a e.g. a ligase enzyme is used to get the fusing of nucleic acid molecules - then one does not need to have any base pairing overlapping regions between the nucleic acid molecules.However, it may be preferred (independently if e.g. ligase is used or not) that the nucleic acid molecule attached to the bait is a nucleic acid molecule, which has complementary cohesive ends to the nucleic acid molecule of the B-structure - more preferably, wherein there are phosphorothioate bonds at the complementary cohesive ends of the nucleic acid molecules of both the nucleic acid molecule of the B-structure and the nucleic acid molecule attached to the bait.Preferably, there are phosphorothioate bonds installed in the phosphate backbone at the complementary cohesive ends of the nucleic acid molecule of the B-structure and the nucleic acid molecule attached to the bait. The number of phosphorothioate bonds may for each nucleic acid molecule preferentially be at least 1 phosphorothioate bond, at least 2 phosphorothioate bonds or more preferably at least 3 phosphorothioate bonds.In working Example 1 herein was used 3 phosphorothioate bonds and the results of Example 2 herein demonstrate that use of 3 phosphorothioate bonds gives surprising significant technically advantages in the present context as compared to use of unmodified DNA (i.e. zero phosphorothiate bonds).In some cases, it may be preferred that the number of phosphorothioate bonds may for each nucleic acid molecule preferentially be at least 4 phosphorothioate bonds, such as at least 10 phosphorothioate bonds or at least 20 phosphorothioate bonds.Similar to the B-structure - the nucleic acid molecule attached to the bait is e.g. PNA, LNA, RNA, DNA or combinations thereof - preferably, the nucleic acid molecule is DNA.Other preferred embodiments for the nucleic acid molecule of the B-structure as discussed above (e.g. may be a double stranded nucleic acid molecule; may contain a PCR priming site; etc.) may also be preferred embodiments for the nucleic acid molecule attached to the bait. The“fusing (e.g. by ligating) the nucleic acid molecules” may be done wherein there is a significant binding of the binding entities to target of the BBOundToT-structures - an example of this is illustrated in Figure 2 herein and working example herein.However, as discussed in e.g. EP2622073B1 (Vipergen) - the“fusing (e.g. by ligating) thenucleic acid molecules” may be done wherein there is essentially no binding of the binding entities to target of the BBOundToT-structures - i.e. this is also a possible option in relation to the method as described herein.Accordingly and in line with e.g. EP2622073B1 (Vipergen), the after lysis step (iiiA) step of fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBoundToT- structures with the bait bound to the prey of target may be performed according to steps (iv) to (vi) of claim 1 of EP2622073B1 (Vipergen) - i.e. by:(A): applying the created BBoundToT-structures with the bait bound to the prey of target to an in vitro compartmentalization system - under binding conditions, which are conditions where a B-structure containing a binding entity capable of binding to a target molecule, binds more efficiently to the corresponding T-structure, than a B-structure containing a binding entity not capable of binding to the same target do - preferably, wherein the compartmentalization system comprises at least 2 times more individual compartments than the number of B-structures introduced in step (ii) under conditions wherein the B- structures, T-structures and BBoundToT-structures enter randomly into the individual compartments; and(B): fusing the nucleic acid molecules of a B-structure and a T-structure which are both present within the same individual compartment - which is fusing the nucleic acid molecule of the B-structure to the nucleic acid molecule of the T-structure - this structure is herein termed BTFused-structure and the BTFused-structure comprises the specific nucleic acid sequence information allowing to identify the binding entity and the specific nucleic acid sequence information allowing to identify the specific target; and(C): combining the content of the individual compartments of step (B) under conditions wherein there is no fusing of the nucleic acid molecules of a B-structure and a T-structure - wherein there is not created any new BTFused-structure not already created in step (B) - in order to get a library of BTFused-structures, wherein the library is an enriched library of species of BTFused-structures originating from binding pairs of target and binding entity when compared to BTFused-structures originating from nonbinding pairs of target and binding entity; andwherein the BBoundToT-structures remain suspended in solution in the individual compartments of step (A); and / orwherein the method does not rely on target immobilization on a solid support; and wherein the nucleic acid of BTFused-structures present in the enriched library of step (C) are amplified.It may be preferred that step (iii) of the first aspect is step (iii)(B).When step (iii) is step (iii)(B), the method as described herein may preferably a method, wherein- the T-structure of (i) of first aspect comprises an enzyme fused to the target and this enzyme is due to the proximity created by the binding of the binding entity and target of the BBoundToT- structures of (ii) of first aspect capable of making an reaction on the B-structure of the BBoundToT-structure that marks B-structure and thereby makes it possible to distinguish the B- structure of the BBOundToT-structure from a B-structure that not have bound to target.An example may e.g. be, wherein the enzyme fused to the target is a ligase and wherein there in step (ii) of first aspect is also introduced nucleic acid molecules that have complementary cohesive ends to the nucleic acid molecule of the B-structure and wherein the ligase due to the proximity ligates the introduced nucleic acid molecules to the nucleic acid molecule of the B-structure and thereby marks the B-structure.Another example may e.g. be, wherein the enzyme fused to the target is an enzyme that due to the proximity is capable of using the nucleic acid molecule of the B-structure as a substrate to make a reaction and thereby marks the B-structure - an example could e.g. be an enzyme that could biotinylate the nucleic acid molecule.Step (iv) of first aspectAs discussed above, step (iv) reads:“(iv): identifying, via use of the solution of (iii) and the nucleic acid molecules that comprises the specific nucleic acid sequence information allowing to identify the binding entity of the B- structures, at least one individual binding entity that binds within the cell of (ii) to at least one target of interest”As understood by the skilled person - use of the specific nucleic acid sequence information allowing to identify the binding entity will preferably require some kind of sequencing.It is or course routine work for the skilled person to sequence a nucleic acid molecule of interest.Step (iv) may be made by based on prior art know techniques as e.g. discussed herein.As understood by the skilled person and discussed herein - whether one uses option step(iii)(A) or step (iii)(B) may be seen as relating to how one prefers to make the identifying step(iv).The“identifying” step (iv) of the first aspect preferably comprises a step, wherein the nucleic acid molecules that comprises the specific nucleic acid sequence information allowing to identify the binding entity of the B-structures are amplified. The skilled person in the art can routinely identify numerous different strategies in order to amplify the nucleic acid in the fused genotypes, for example without being limited: PCR (United States Patent 4,683,202; Mullis), Emulsion PCR (Nakano et al., J Biotechnol.2003;102(2):117-24), Digital PCR (Vogelstein, B; Kinzler KW (1999). "Digital PCR". Proc Natl Acad Sci U S A. 96 (16): 9236-41), NASBA (Compton J. Nucleic acid sequence-based amplification. Nature. 1991 ;350(6313):91 -2), or Rolling Circle Amplification (American Journal of Pathology. 2001 ;159:63-69)Preferably, the nucleic acid molecules are amplified via PCR. It may be preferred that there in the identifying step (iv) are identified at least two (such as e.g. at least 3 or at least 6 or at least 10) different individual binding entities that binds within the cell of (ii) to at least one target of interest.In working example herein (see below) was there in the identifying step (iv) identified around 10 different individual binding entities.It is evident that in order to be able to identify e.g. at least 10 different individual binding entities in this step (iv) - it is required that:- the solution of step (iii)(A) comprises more than 10 different BBOundToT-structures; or- the solution of step (iii)(B) comprises more than 10 different“binder marked B-structures”.EXAMPLESExample 1 :In-cell screening and comparative in vitro (i.e. not within a cell) screening of p38 against a YoctoReactor library containing approx. 10sdifferent binding entitiesFor overview see Figures 1 and 2.MethodsDNA oligonucleotides usedvip7460AAAGCTGGGAGACACCA*A*T*G(* = phosphorothioated DNA bases)vip7461T*T*G*GTGTCTCCCAGCTTTGA(* = phosphorothioated DNA bases)vip7442A*G*C*ACTAAGCCTTGATGGCCACATTCCTACTTCTCCCTAAGGTGCAGTTTTGCCAAGG(* = phosphorothioated DNA bases)vip7463xCCTTGGCAAAACTGCACCTTAGGGAGAAGTAGGAATGTGGCCATCAAGGCTTAGTGC*T *C*A(x = 5'-aminomodifier C6; * = phosphorothioated DNA bases)Preparation of YoctoReactor library (Lib027b_TA01)The YoctoReactor library was constructed in a trimer format essentially as described elsewhere (Hansen et al. J. Am. Chem. Soc., 2009, 131 (3), pp 1322-1327) with the following modification: a 20-mer adapter nucleic acid molecule (consisting of oligonucleotides vip7460 and vip7461) was ligated onto the YoctoReactor library thereby generating an adapter modified library, i.e. Lib027b_TA01. The constructed YoctoReactor DNA has an overlapping region (2 nucleotide 3’-overhang) which is complementary to the overlapping region (2 nucleotide 3’-overhang) on the target DNA.MaterialsProprietary Vipergen YoctoReactor library (batch Lib027b, approx. 1.1 *108different molecules)Oligonucleotides vip7460 and vip7461 (100pM stock prepared; Eurofins Genomics)NaCI (4M stock prepared; Sigma-Aldrich)HEPES, pH 7.5 (1 M; Sigma-Aldrich)Tris-HCI, pH 7.5 (1 M; Sigma-Aldrich)Glycogen (20mg / ml_; Thermo Fisher Scientific)Ethanol (96%; Honeywell)MgCI2(2M; Sigma-Aldrich)PEG4000 (50%; Thermo Fisher Scientific)ATP (100mM stock prepared; Sigma-Aldrich)T4 DNA ligase (30 Weiss U / pl; Thermo Fisher Scientific)Water (molecular biology grade; Sigma-Aldrich)20% TBE-PAGE gels (Kem-En-Tec)NucleoSpin Gel and PCR Clean-up columns (Macherey-Nagel)Qubit dsDNA HS Assay Kit (Thermo Fisher Scientific)Quant-iT PicoGreen dsDNA Assay Kit (Thermo Fisher Scientific)ProtocolThe 20-mer nucleic acid adapter molecule was prepared by annealing vip7460 and vip7461 according to a published protocol(https: / / eu.idtdna.com / pages / education / decoded / article / annealing-oligonucleotides). The annealed oligos were precipitated by addition of 20pl 4M NaCI, 1 pl glycogen and 1 ml ice-cold ethanol to a 300pl annealing reaction and centrifugation (20,000g at 4°C for at least 30min). The pellet was washed twice with 80% ethanol, air-dried at room temperature and dissolved in water to a concentration of 100pM. The concentration was confirmed by Qubit assay (according to manufacturer’s protocol) and the integrity of the 20-mer nucleic acid adapter was verified on 20% TBE-PAGE (200V, 55min, 20°C).The 20-mer nucleic acid adapter was ligated to a proprietary YoctoReactor library (batch Lib027b) by mixing the YoctoReactor library (Lib027b) and the annealed adapter (2-fold molar excess) in a total of 200pL water followed by addition of 200pL 2X ligation master mix (80mM Tris-HCI pH 7.5, 20mM MgCI2, 4% PEG4000, 2mM ATP and 60U T4 DNA ligase). The ligation was allowed to proceed overnight at room temperature. The ligated YoctoReactor library was precipitated by adding 1 .2ml_ ice-cold ethanol, 1 pL glycogen and 40mI_ 4M NaCI. The mixture was stored 1 h at -20°C before being pelleted by centrifugation (20,000g at 4°C for at least 30min) and air-dried at room temperature. To eliminate excess of the 20-mer nucleic acid adapter, the ligated YoctoReactor library was purified on NucleoSpin Gel and PCR Clean-up columns. The purified adapter modified YoctoReactor library was precipitated (NaCI, glycogen, and ice-cold ethanol) and dissolved in buffer (5mM Tris-HCI pH 7.5, 20mM NaCI, 0.001 % Tween20) at a concentration of 47.9mM (determined by PicoGreen Assay according to manufacturer’s protocol). Importantly, the adapter modified YoctoReactor library (i.e. Lib027b_TA01) was 100% competent in ligation to vip7442 / vip7463 target DNA.Preparation of CAIX-binder (i.e. bait = VD11-4-2) attached to target DNA (TD_VD11-4-2)The small molecule CAIX-binder, VD11-4-2, was covalently attached to a 60-mer oligonucleotide (vip7463). The oligonucleotide was hereafter assembled with a reverse complementary oligonucleotide (vip7442), forming a double stranded nucleic acid molecule (i.e. target DNA) attached to the bait compound, VD11-4-2. The constructed target DNA (i.e. TD_VD11-4-2) has an overlapping region (2 nucleotide 3’-overhang) which is complementary to the overlapping region (2 nucleotide 3’-overhang) on the YoctoReactor DNA.MaterialsPentafluorophenylsulfonamide (Fluorochem, 034664)8-Mercaptooctanoic acid (Sigma-Aldrich, 675075)Anhydrous methanol (Fisher Scientific, 10499560; stored over 4A MS)Triethylamine (Sigma-Aldrich, 90340)Hydrogen peroxide solution (Sigma-Aldrich, 95321)Cyclooctyl amine (Sigma-Aldrich, C110604)HPLC grade water (Fisher Scientific, 10221712)Triethylammonium acetate (Sigma-Aldrich, 90358)Acetonitrile (Fisher Scientific, 106291 12)DMSO (Sigma-Aldrich, D8418)Ethyl-(N’,N’-dimethylamino)propylcarbodiimide hydrochloride (EDC; Sigma-Aldrich, E6383) N-hydroxysuccinimide (NHS; Sigma-Aldrich, 130672)N-Methylpyrrolidone (NMP; Sigma-Aldrich, 494496)ProtocolAn analogue of VD1 1-4-2 was prepared using an adapted procedure from V. Dudutiene et al. (“Discovery and Characterization of Novel Selective Inhibitors of Carbonic Anhydrase IX”; J. Med. Chem. 2014, 57, 9435-9446). Instead of 2-mercaptoethanol, 8-mercaptooctanoic acid was used, and an analogue carrying a distal carboxylic acid was produced:VD11-4-2 Analogue of VD11-4-2The HPLC purified product (3.3 mg) was subsequenty activated using ethyl-(N’,N’- dimethylamino)propylcarbodiimide hydrochloride (EDC, 1.2 mg) and N-hydroxysuccinimide (NHS, 0.7 mg) in N-methylpyrrolidine (NMP, 60 pL). The crude activation mixture (50 pL) was added to a premixed solution of vip7463 (10 nmol; 100 pL of 100 pM), HEPBS buffer (100 pL, 1 M stock), NMP (200 pL) and water (50 pL).After coupling for 16h, the DNA was EtOH precipitated and the crude conjugate purified by RP-HPLC using triethylammonium acetate in water / MeCN. Fractions with desired conjugate were concentrated by lyophilization and final product dissolved in water. QC by LCMS (ESI; neg mode): obs m / z 19322, calc 19324.6 (see HPLC chromatogram below).The purified single-stranded conjugate, i.e. vip7463_VD11-4-2, was subsequently hybridized to the reverse complementary DNA oligonucleotide vip7442, hereby generating double stranded target DNA attached to VD11-4-2 (i.e. TD_VD11-4-2). In vitro screening on p38 conjugated to DNA outside oocytes (e1 ; reference)An in vitro screening (i.e. not within a cell) on recombinant p38 protein conjugated to DNA against Lib027b_TA01 (i.e. the same YoctoReactor library applied for in-cell screenings) was performed for reference. Conjugation of p38 protein to target DNA, and subsequent screening against Lib027b_TA01 (20nM p38 conjugated to target DNA was screened against approx. 5.6*1012library molecules per pi) was performed essentially as described previously (Petersen et al.,“Novel p38a MAP kinase inhibitors identified from YoctoReactor DNA-encoded small molecule library”, Med. Chem. Commun., 2016, 7, 1332-1339).In-cell screening on p38 expressed in oocytes (e2 and e3)Expression of target-prey fusion protein (e.q. CAIX-P38) in Xenopus leavis oocytesA gene encoding p38 (UniProt accession code: Q16539) N-terminally fused via a 6-amino acid linker to the catalytic domain of human CAIX was synthesized and sub-cloned between the Hindlll and BamHI sites in the pSP64 expression vector (Eurofins Genomics). The vector was linearized with EcoRI, and mRNA was synthesized with the Ambion mMESSAGE mMACHINE SP6 transcription kit (Thermo Fisher Scientific). mRNA was purified via RNeasy columns (Qiagen).Approx. 50ng of CAIX-p38 mRNA was injected in a volume of 50nl_ (diluted in water) into Xenopus leavis oocytes (Ecocyte Bioscience) using a Nanoliter 2010 injector (World Precision Instruments). The oocytes were maintained at 18°C in Modified Barth’s Medium (in mM, 88 NaCI, 1 KCI, 0.4 CaCI2, 0.33 Ca(N03)2, 0.8 MgS04, 5 Tris-HCI, 2.4 NaHC03, pH 7.4) until experiments.Quantification of expressed target-prey fusion protein (e.q. CAIX-P38) in Xenopus leavis oocytesFour days after injection of mRNA, expression of CAIX-p38 protein inside Xenopus leavis oocytes was quantified by using a human CAIX DuoSet ELISA assay (Bio-techne). As control, uninjected Xenopus leavis oocytes were processed in parallel. Briefly, one Xenopus leavis oocyte was crushed in 25pl buffer (1 mM EDTA, 0.5% Triton X-100, 5mM NaF in PBS) by centrifugation (20,000g for 2min at 4°C), supernatant was transferred to an ELISA plate coated with CAIX-capture antibody and incubated for 1 h at RT. All wells were washed (three times in wash buffer; 0.05% Tween20 in PBS), and biotinylated CAIX-detection antibody was added. The plate was incubated for 1 h at RT, and all wells were washed. Streptavidine conjugated to horseradishperoxidase (streptavidine-HRP) was added, and the plate was incubated for 20min at RT in the dark. All wells were washed before addition of the HRP substrate TMB SENS (Kem-En-Tec). The plate was incubated for 5min at RT in the dark before the reaction was stopped by addition of 2M H2S04. The optical density at 450nm was determined on a DTX880 Multimode Detector (Beckman Coulter). Based on a CAIX standard curve, which was generated in parallel with recombinant CAIX protein, the concentration of CAIX-p38 protein expressed inside Xenopus leavis oocytes was determined to be approx. 200nM.Introduction of target DNA and YoctoReactor library into Xenopus leavis oocytesA diverse YoctoReactor library (Lib027b_TA01) consisting of approx. 1.1 *108different molecules (i.e. potential binders coupled to double stranded nucleic acid molecule) was mixed with TD_VD11-4-2 (i.e. target DNA covalently attached to bait compound, VD1 1-4-2), and the mixture was injected into Xenopus leavis oocytes expressing CAIX-p38 protein. Injection of YoctoReactor library and TD_VD11-4-2 was done 4 days after injection of mRNA encoding CAIX-p38. A total of 50nL, consisting of a total of approx. 6.6*1011YoctoReactor library molecules and 1.5*1011TD_VD11-4-2 molecules, was injected into each oocyte (e2). In parallel experiments, the Lib027b_TA01 / TD_VD11-4-2 mix was supplemented with 0.1 pg / ml RNaseA before injections (e3). Injection of RNaseA was done to digest endogenous RNA that could potentially affect the selection process inside the oocytes.The Xenopus leavis oocytes were incubated at 18°C for 2-4h. Within this period, the expressed CAIX-p38 protein was allowed to bind to: 1) YoctoReactor library ligands (binding to the protein of interest, p38), and 2) TD_VD11-4-2 (binding to CAIX-tag).Breaking of Xenopus leavis oocyte membrane and DNA ligationThe membrane of the Xenopus leavis oocyte was broken in order to release the binding complexes from the cell, i.e. CAIX-p38 bound to: 1) YoctoReactor library ligands and 2) TD_VD11-4-2. The DNA fragments associated to the CAIX-p38 protein (i.e. target DNA and YoctoReactor DNA, respectively) have overlapping regions resulting in the potential assembly of the two fragments to combined fragments by DNA ligation. The ligation will be driven byproximity when both DNA fragments are associated to the CAIX-p38 protein, thus creating an enriched library with a higher fraction of members having the desired binding activity.For breaking of the Xenopus leavis oocyte membrane, one oocyte was centrifuged (20,000g for 2min at 4°C) in 600pl ligation buffer without ATP and ligase. The supernatant (600pl) was diluted in two sequential steps into a total of 11 ml_ ligation buffer (50mM Tris-HCI, 50mM NaCI, 0.1 % Triton X-100, 0.75% BSA, 9mM KCI, 4.5% glycerol, 1 mM DTT, 5mM MgCI2, 1 mM ATP, pH 7.4) supplemented with 300 Weiss units T4 DNA ligase (Thermo Fisher Scientific). The binding complex was thereby diluted approx. 104-fold in total, and ligation was allowed to proceed for 4min at 16°C. Then, T4 DNA ligase was inactivated by addition of 11 ml_ stop buffer (NTI buffer supplemented with 50mM EDTA, 0.2pg / pl Proteinase K, 0.2% N-lauryl sarcosine) and the resulting mixture was subsequently incubated at 65°C for 1 h. After cooling to RT, DNA was purified on NucleoSpin Gel and PCR Clean-up columns (Macherey-Nagel).Amplification of ligated DNAThe ligated and purified DNA fragments were treated with Lambda Exonuclease (to remove free, unligated 5’-phosphorylated DNA fragments) and amplified by PCR.PCR mixture (final concentrations):25pl purified ligated DNA (PCR template)1X Vent (-exo) PCR buffer (New England Biolabs)0.4mM CleanAmp dNTP (tebu-bio)6mM MgCI2(Sigma-Aldrich)3% DMSO (Sigma-Aldrich)0.25pM forward PCR primer0.25pM backward PCR primer1 U Vent (-exo) polymerase (New England Biolabs)Water to a total of 10OplThe mixture was subjected to thermal cycling by applying the following program in a PCR machine:95°C 10min, 27 cycles of (95°C 30sec, 62°C 30sec, 72°C 2min30sec), 72°C 2minThe resulting library of DNA fragments was purified on NucleoSpin Gel and PCR Clean-up columns (Macherey-Nagel), and subjected to a second round of PCR to introduce priming sites for lllumina sequencing.PCR mixture:5mI purified amplified DNA (PCR template)1X Vent (-exo) PCR buffer (New England Biolabs)0.2mM dNTP (Thermo Fisher Scientific)6mM MgCI2(Sigma-Aldrich)0.5M betaine (Sigma-Aldrich)0.25mM forward lllumina primer0.25mM backward lllumina primer1 U Vent (-exo) polymerase (New England Biolabs)Water to a total of 10OmIThe mixture was subjected to thermal cycling by applying the following program in a PCR machine:92°C 2min, 10 cycles of (92°C 30sec, 62°C 30sec, 72°C 2min30sec), 72°C 2minThe resulting library of DNA fragments was purified by Agencourt AMPure XP (Beckman Coulter Life Sciences) and preparative 10% TBE-PAGE (Kem-En-Tec) and submitted for lllumina DNA sequencing (Fulgent Genetics). Analysis of enrichment by DNA sequencing using lllumina sequencing technologyDNA sequencing data was decoded and analyzed as described elsewhere (Petersen et al., “Novel p38a MAP kinase inhibitors identified from yoctoReactor DNA-encoded small molecule library”, Med. Chem. Commun., 2016, 7, 1332-1339).By counting how many times a given library member was observed within a sequencing sample, hits that were enriched above the random ligation events could be identified. Library members observed many times are target binders (hits) whereas compounds observed only a few times are dominantly results of the random events (background). The number of observations based on random event represents a linear decay line on a logarithmic scale (red spheres in signal plot). Thus, library members with observation number above the transition from decay phase to signal phase are thus above the mathematical threshold (MT, green spheres in signal plot). From three individual selection experiments (e1-e3), signal plots were produced (panel A-C on Figure 3 herein). Signal plot A originate from screening on p38 conjugated to target DNA against YoctoReactor library Lib027b_TA01 (e1 , reference), and signal plots B or C are from in-cell screenings on p38 expressed in oocytes without (e2) or with co-injection of RNaseA (e3). From screening against approx. 1.1 *108different molecules in e1-e3, we identified a total of 39 hits above MT (green spheres). The 39 hits were combined and annotated for number of observations in the three data pools from DNA sequencing (panel D on Figure 3). The 39 hits were observed above MT in at least one of the three experiments. A significant number of hits were found in both the reference experiment (e1) and in the two in-cell screening experiments (e2 or e3). Hit ID #31 was a previously validated p38a inhibitor (vpc00249; IC500.51 mM; Petersen et al.,“Novel p38a MAP kinase inhibitors identified from yoctoReactor DNA-encoded small molecule library”, Med. Chem. Commun., 2016, 7, 1332-1339).ConclusionsAs discussed above, based on an in vitro display library of around 108different binding entities - in this“within the cell” screening example was there in the identifying step (corresponding to identifying step (iv) of the first aspect) identified around 10-30 different individual good binder chemical compound binding entities, including a previously validated p38 inhibitor together with several non-validated hits. In the present context this is considered an acceptable representative high number of good binder compounds of the library.A reason for that the identified number of good binder entities are considered acceptable relates to that for this target (i.e. p38) was, as discussed above, made a comparative in vitro (i.e. not within a cell) screening of the same in vitro display library and there was identified around 10 different individual good binders, i.e. the number identified binders of the“within the cell” screening was at least comparable to the comparative in vitro screening - i.e. it was considered acceptable.Further, the individual good binders identified in the within the cell screening of the present invention corresponded to the good binders identified in the comparative in vitro screening.If there for instance only would have been identified one or two individual good binder chemical compound binding entities in the“within the cell” screening of this example, then would it not have been considered as good as the around 10 different individual good binders actually identified in this example. One reason for this relates to that if only 1 -2 individual good binders would have been identified, then there could maybe have been a risk of losing possible relevant good binders - i.e. loosing valuable good binder information.As discussed, some the identified good binders of the“within a cell” and comparative in vitro screening were the same and some of the good binders of the“within a cell” screening were not identified in the comparative in vitro screening - a reason for this may relate to that some of the in“real life” good binders maybe could only be identified under the natural“within the cell” binding conditions (i.e. step (ii)(b) of the first aspect) of the“within the cell” screening method of this example - i.e. a method of the present invention.Example 2:Comparative example - use of 3 phosphorothioate bonds have been compared against unmodified DNA (i.e. zero phosphorothiate bonds)MethodsDNA oligonucleotides used (schematic illustration)Double stranded nucleic acid molecules (i.e. target DNA. ID) injected into Xenopus leavis oocytes:Note: TD_001 , TD_002 and TD_003 contain a 2-nt overhang in 3'-end of lower strand, which iscomplementary to the 2-nt overhang on ligation DNA (i.e. LDJJG1).Double stranded nucleic acid ligation molecule (i.e. ligation DNA. LD):LD_GQ1unmodifiedNote: LD_001 contain a 2-nt overhang in 3'-end of upper strand, which is complementary to the 2-nt overhang on target DNA (i.e. TD_001, TD_002, TD_003).Evaluation of ligation potential of target DNA with or without phosphorothioate bonds after injection into and extraction from Xenopus leavis oocytesTarget DNA with or without phosphorothioated DNA bases (i.e. TD_001 , TD_002 and TD_003) was injected into Xenopus leavis oocytes. The target DNA was incubated inside oocytes for increasing time intervals before the membrane of the Xenopus leavis oocyte was broken and the injected target DNA was recovered. The ligation potential of the recovered target DNA was examined in a DNA ligation reaction with ligation DNA (i.e. LD_001). Note, retaining the ligation potential of target DNA after incubation inside a cell is a critical parameter in the present context of in-cell screenings.Injection of target DNA into Xenopus leavis oocytesApprox. 1 -2pmol of target DNA with or without phosphorothioate bonds (i.e. TD_001 , TD_002 or TD_003) was injected in a volume of 50nl_ (diluted in water) into Xenopus leavis oocytes (Ecocyte Bioscience) using a Nanoliter 2010 injector (World Precision Instruments). The oocytes were maintained at 18°C in Modified Barth’s Medium (in mM, 88 NaCI, 1 KCI, 0.4 CaCI2, 0.33 Ca(N03)2, 0.8 MgS04, 5 Tris-HCI, 2.4 NaHC03, pH 7.4). The oocytes were incubated for increasing time intervals before the membrane was broken and the injected target DNA was recovered (as detailed below).Breaking of Xenopus leavis oocyte membrane and recovery of injected target DNAThe membrane ef the Xenopus leavis eecyte was broken in erder te recever the injected target DNA. For breaking of the Xenopus leavis oocyte membrane, five oocytes were centrifuged (20,000g for 2min at 4°C) in 200mI crushing buffer (10mM Tris-HCI, 150mM NaCI, 0.01 % Tween-20). The recovered target DNA (originating from five oocytes) was purified onNucleoSpin Gel and PCR Clean-up columns. The purified target DNA was precipitated (NaCI, glycogen, and ice-cold ethanol) and pelleted by centrifugation (20,000g at 4°C for at least 30min). The DNA pellet was air-dried at room temperature and dissolved in water.DNA ligationThe ligation potential of the recovered target DNA was evaluated by applying it in a DNA ligation reaction together with ligation DNA, i.e. LD_01. The purified target DNA (originating from five oocytes) was mixed with approx. 2pmol of LD_01 ligation DNA in ligation buffer (50mM Tris-HCI, 50mM NaCI, 0.1 % Triton X-100, 0.75% BSA, 9mM KCI, 4.5% glycerol, 2mM DTT, 10mM MgCI2, 2mM ATP, pH 7.4) supplemented with approx. 1 Weiss units T4 DNA ligase (Thermo Fisher Scientific). The ligation reaction was allowed to proceed for 1-2h at 16°C. The ligation mixture was applied to native PAGE (10% TBE-PAGE, 200V, 35min, room temperature) to allow for evaluation of the ligation potential of the recovered target DNA. The ligation potential of unmodified target DNA (i.e. TD_001) was lost after incubation inside a Xenopus leavis oocyte in a time-dependent manner. Specifically, 50% of ligation potential was lost after incubation for 30min and ligation potential was almost completely lost after incubation for 1 h inside the oocyte. For target DNA with phosphorothioate bonds installed in one strand (i.e. TD_002), approx. 50% of the ligation potential was lost after incubation for 2h inside the oocyte. In contrast, when phosphorothioate bonds were installed in both strands of the target DNA (i.e. TD_003), the ligation potential was almost not affected after incubation for 2h inside the oocyte.ConclusionsThe results of this example demonstrate that use of 3 phosphorothioate bonds gives surprising significant technically advantages in the present context as compared to use of unmodified DNA (i.e. zero phosphorothiate bonds).REFERENCE LIST1 : EP1809743B1 (Vipergen)2: EP1402024B1 (Nuevolution)3: EP1423400B1 (David Liu)4: Nature Chem. Biol. (2009), 5:647-654 (Clark)5: WO 00 / 23458 (Harbury)6: Nature Methods (2006), 3(7), 561-570 7: 2006 (Miller)7: Nat. Biotechnol. 2004; 22, 568-574 (Melkko)8: Nature. (1990); 346(6287), 818-822 (Ellington)9: Proc Natl Acad Sci USA (1997). 94 (23): 12297-302 (Roberts)10: W02006 / 053571 A2 (Rasmussen)11 : EP2622073B1 (Vipergen)12: Lynn MM et al. (“Identification of Ligand-Target Pairs from Combined Libraries of Small Molecules and Unpurified Protein Targets in Cell Lysates”; J. Am. Chem. Soc. 2014, 136, 3264-3270)13: Zining Wu et al. (“Cell-Based Selection Expands the Utility of DNA-Encoded Small- Molecule Library Technology to Cell Surface Drug Targets..”; ACS Comb. Sci. 2015, 17, 722-731)14: M. Schurmann et al. (“Small-Molecule Target Engagement in Cells”; Cell ChemicalBiology 23, April 21 , 2016)15: Ron Milo (“What is the total number of protein molecules per cell volume?..”; Bioessays 35: 1050-1055, 2013)16: V. Dudutiene et al. (“Discovery and Characterization of Novel Selective Inhibitors of Carbonic Anhydrase IX”; J. Med. Chem. 2014, 57, 9435-9446)17. Petersen et al. (“Novel p38a MAP kinase inhibitors identified from yoctoReactor DNA- encoded small molecule library”, Med. Chem. Commun., 2016, 7, 1332-1339)

Claims

CLAIMS1. A method for screening of an in vitro display library for binding within a cell of a small- molecule chemical compound binding entity of the library to a protein or RNA target of interest in order to identify at least one individual chemical compound binding entity of the library that is capable of binding within the cell to the protein or RNA target of interest and wherein the method comprises the steps of:(i): expressing at least one target Tn, wherein n = 1 or more, in a cell and wherein the at least one target is a protein or RNA - the structure of the target is herein termed T-structure;(ii): introducing an in vitro display library into the cell of (i), wherein:(a): the library is a library of at least 1000 different binding entities Bn, wherein n = 1000 or more, wherein each binding entity is attached to a nucleic acid molecule and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the binding entity - wherein once one knows the specific nucleic acid sequence information of the nucleic acid molecule one directly knows the structure of the specific binding entity attached to the nucleic acid molecule and wherein the binding entities of the library are chemical compounds with an average molecular weight MW below 10000 dalton - the structure of the binding entity attached to the nucleic acid molecule is herein termed 13- structure; and(b): the library is introduced into the cell under binding conditions, which are conditions where a B-structure containing a binding entity capable of binding to a target molecule, binds more efficiently to the corresponding T-structure, than a B-structure containing a binding entity not capable of binding to the same target do and wherein one within the cell gets binding of at least one of the binding entities to at least one target thereby creating within the cell a complex comprising a B-structure bound to a T-structure, which is termedBBoundToT-stmcture; (iii): making lysis of the cell of (ii) to breaking down the membrane of cells in order to:(A): get the BBOundToT-structures of (ii) out of the cell and thereby obtain a solution comprising BBOundToT-structures, wherein the BBoundToT-structures are not within the cells; or(B): get B-structures out of the cells that had bound to target in step (ii) and have been marked before step (iii) in a way that makes it possible to distinguish the marked B- structures from a B-structure that has not bound to target in step (ii) and thereby obtain a solution comprising binder marked B-structures, wherein the binder marked B-structures are not within the cells; and(iv): identifying, via use of the solution of (iii) and the nucleic acid molecules that comprisesthe specific nucleic acid sequence information allowing to identify the binding entity of the 13- structures, at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.

2. The method of claim 1 , wherein the target T is a protein and wherein the cell is a eukaryotic cell.

3. The method of any of the preceding claims, wherein the cell is a Xenopus oocyte.

4. The method of claim 3, wherein the cell is a Xenopus laevis oocyte.

5. The method of any of claims 3 to 4, wherein the introducing of the in vitro display library into the cell of step (ii) of claim 1 is done via injection of the in vitro display library into the Xenopus oocyte; andwherein the in vitro display library of step (ii) of claim 1 is a library of at least 106different binding entities Bn, wherein n = 106.

6. The method of any of the preceding claims, wherein the concentration of T-structures in the binding step step(ii)(b) of claim 1 is at least 1010M.

7. The method of any of the preceding claims, wherein the step (iii) of claim 1 is step (iii)(A).

8. The method of claim 7, wherein step (iv) of claim 1 is done by:- binding BBOundToT-structures of the solution (iii)(A) of to a solid support via binding of target of the BeoundToT-stmctures to the solid support and remove B-structures not bound to target and thereby not bound to the solid support; and- identifying, via use of the specific nucleic acid sequence information allowing to identify the binding entity of the BBOundToT-structures bound to the solid support, at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.

9. The method of claim 7, wherein the method is a method wherein:- the T-structure of (i) of claim 1 comprises a prey (e.g. a target-prey fusion protein) and there in step (ii) of claim 1 is also introduced a bait attached to a nucleic acid molecule (which e.g. has complementary cohesive ends to the nucleic acid molecule of the B-structure) and the nucleic acid molecule comprises specific nucleic acid sequence information allowing to identify the specific target and wherein the bait binds to the prey of the target in step (ii) of claim 1 and thereby creates BBoundToT-structures with the bait bound to the prey of target;- after lysis step (iii)(A) - fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBOundToT-structures with the bait bound to the prey of target, wherein the fused nucleicacid molecules comprise the sequence information allowing to identify binding entity and target; and- identifying in step (iv) of claim 1 via use of the specific nucleic acid sequence information allowing to identify the binding entity and target of the fused (e.g. ligated) nucleic acid molecules of the preceding step at least one individual binding entity that binds within the cell of (ii) to at least one target of interest.

10. The method of claim 9, wherein the cell is a Xenopus oocyte, preferably wherein the cell is a Xenopus laevis oocyte.

11. The method of any of claims 9 to 10, wherein there before the“fusing (e.g. by ligating via use of a ligase) the nucleic acid molecules of the BBOundToT-structures with the bait bound to the prey of target” step is made a dilution step of the solution (e.g. supernatant) obtained from cell lysis step (iii) and wherein the dilution is a diluting the solution of at least 102fold; and wherein there is only one target (n = 1) in step (i) of claim 1 ; and wherein the“identifying” step (iv) comprises a step, wherein the fused nucleic acid molecules that comprise the sequence information for binding entity and for target are amplified, preferably by use of polymerase chain reaction (PCR); and wherein the“prey-bait” system is:- prey: tetrameric streptavidin and bait: biotin;- prey: monomeric streptavidin (e.g. mSA2) and bait: biotin;- prey: His-tag and bait: NTA;- prey: SNAP-tag® and bait: benzyl guanin (BG);- prey: Halo-Tag® and bait: reactive chloroalkane linker bound to a functional group;- prey: carbonic anhydrase IX (CAIX) and bait: VD11-4-2; or- prey: maltose binding protein (MBP) and bait: maltose or maltotriose; and wherein the nucleic acid molecule attached to the bait is DNA and the nucleic acid molecule of the B-structure is DNA.

12. The method of any of claims 9 to 11 , wherein the nucleic acid molecule attached to the bait is a nucleic acid molecule which has complementary cohesive ends to the nucleic acid molecule of the B-structure; andwherein there are phosphorothioate bonds installed in the phosphate backbone at the complementary cohesive ends of the nucleic acid molecule of the B-structure and the nucleic acid molecule attached to the bait; andthe number of phosphorothioate bonds is for each nucleic acid molecule at least 2 phosphorothioate bonds.

13. The method of any of claims 1 to 6, wherein the step (iii) of claim 1 is step (iii)(B); and wherein method is a method, wherein- the T-structure of (i) of claim 1 comprises an enzyme fused to the target and this enzyme is due to the proximity created by the binding of the binding entity and target of the BBoundToT- structures of (ii) of claim 1 capable of making an reaction on the B-structure of the BBoundToT- structure that marks B-structure and thereby makes it possible to distinguish the B-structure of the BBoundToT-structure from a B-structure that not have bound to target; andwherein the enzyme fused to the target is a ligase and wherein there in step (ii) of first aspect is also introduced nucleic acid molecules that have complementary cohesive ends to the nucleic acid molecule of the B-structure and wherein the ligase due to the proximity ligates the introduced nucleic acid molecules to the nucleic acid molecule of the B-structure and thereby marks the B-structure.

14. The method of any of the preceding claims, wherein the“identifying” step (iv) of claim 1 comprises a step, wherein the nucleic acid molecules that comprises the specific nucleic acid sequence information allowing to identify the binding entity of the B-structures are amplified, preferably the nucleic acid molecules are amplified by use of polymerase chain reaction (PCR).

15. The method of any of the preceding claims, wherein there in the identifying step (iv) of claim 1 are identified at least 6 different individual binding entities that binds within the cell of (ii) to at least one target of interest; andwherein there is only one target (n = 1) in step (i) of claim 1 .

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