Fusion proteins comprising a fragment of Vibrio cholerae exotoxin A

Abstract

The invention features recombinant exotoxins from Vibrio cholerae are for the therapeutic treatment of a variety of human diseases, particularly diseases characterized by an abundance or excess of undesired cells.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is the National Stage of International Application No. PCT / US2008 / 008786, filed Jul. 18, 2008, which claims benefit of U.S. Provisional Application No. 60 / 961,308, filed Jul. 20, 2007, each of which is incorporated by reference herein.THE FIELD OF THE INVENTION[0002]The present invention relates to therapies based on Vibrio cholerae exotoxin (VCE), and methods and compositions to utilize the exotoxin and its derivatives as selective cytotoxic or cytostatic agents for selected target cells.BACKGROUND OF THE INVENTION[0003]Selective killing of particular types of cells is desirable in a variety of clinical settings, including the treatment of cancer, which is usually manifested through growth and accumulation of malignant cells. An established treatment for cancer is chemotherapy, which kills tumor cells by inhibiting DNA synthesis or damaging DNA (Chabner and Roberts, Nat. Rev. Cancer 5:65 (2005)). However, such treatments...

AI Technical Summary

Benefits of technology

[0037]The term “protease” as used herein refers to compositions that possess proteolytic activity, and preferably those that can recognize and cleave certain peptide sequences specifically. In one particular embodiment, the specific recognition site is equal to or longer than that of the native furin cleavage sequence of four amino acids, thus providing activation stringency comparable to, or greater than, that of native toxins. A protease may be a native, engineered, or synthetic molecule having the desired proteolytic activity. Proteolytic specificity can be enhanced by genetic mutation, in vitro modification, or addition or subtraction of binding moieties that control activity.

[0046]The term “N-terminal PEGylation” refers to attachment of an optionally substituted PEG moiety to the amino terminus of a protein. Preferred protein fusions or protein hybrids for N-terminal PEGylation have at least one N-terminal amino group. N-terminal PEGylation can be carried out by reaction of an amine-reactive PEG with a protein, or by reaction of a thioester-terminated PEG with an N-terminal cysteine in the reaction known as native chemical ligation, or by reaction of a hydrazide, hydrazine or hydroxylamine terminated PEG with an N terminal aldehyde formed by periodate oxidation of an N-terminal serine or threonine residue. Preferably, a PEG-protein conjugate contains 1-5 PEG substituents, and may be optimized experimentally. Multiple attachments may occur if the protein is exposed to PEGylation reagents in excess. Reaction conditions, including protein:PEG ratio, pH, and incubation time and temperature may be adjusted to limit the number and / or sites of the attachments. Modification at active site(s) within a fusion protein may be prevented by conducting PEGylation in the presence of a substrate, reversible inhibitor, or a binding protein. A fusion protein with the desired number of PEG substitutions may also be obtained by isolation from a more complex PEGylated fusion protein mixture using column chromatography fractionation.

[0051]The term “reversible PEGylation” refers to the reaction of a protein or protein substituent with an optionally substituted PEG moiety through a linker that can be cleaved or eliminated, liberating the PEG moiety. Preferable forms of reversible PEGylation involve the use of linkers that are susceptible to various activities present at the cell surface or in intracellular compartments, and allow the useful prolongation of plasma half-life and / or reduction of immunogenicity while still permitting the internalized or cell-surface-bound protoxin or protoxin proactivator or proactivator activator to carry out their desired action without inhibition or impediment by the PEG substitution. Examples of reversible PEGylation linkers include linkers susceptible to the action of cathepsins, furin / kexin proteases, and lysosomal hydrolases such as neuraminidases, nucleases and glycol hydrolases.

Problems solved by technology

However, such treatments often cause severe systemic toxicity due to nondiscriminatory killing of normal cells.

Because many cancer chemotherapeutics exert their efficacy through selective destruction of proliferating cells, increased toxicities to normal tissues with high proliferation rates, such as bone marrow, gastrointestinal tract, and hair follicles, have usually prevented their use in optimal doses.

Such treatments often fail, resulting in drug resistance, disease relapse, and / or metastasis.

In addition to dose-limiting toxicities, another limitation for chemotherapy is its ineffectiveness for treatment of cancers that do not involve accelerated proliferation, but rather prolonged survival of malignant cells due to defective apoptosis (Kitada et al., Oncogene 21:3459 (2002)).

Consequently, CSCs are thought to be difficult to target and destroy by conventional cancer therapies (Dean et al., Nat. Rev. Cancer 5:275 (2005)).