Production of polyketides

Abstract

Recombinant Myxococcus host cells can be used to produce polyketides, including epothilone and epothilone analogs that can be purified from the fermentation broth and crystallized.

Description

FIELD OF THE INVENTION [0001] The present invention provides recombinant methods and materials for producing polyketides in recombinant host cells; recombinant host cells that produce polyketides; novel polyketides related in structure to the epothilones; methods for purifying epothilones; and crystalline forms of epothilone D. In a preferred embodiment, the recombinant host cells of the invention are from the suborder Cystobacterineae, preferably from the genera Myxococcus and Stigmatella, which have been transformed with recombinant DNA expression vectors of the invention that encode modular or iterative polyketide synthase (PKS) genes. The recombinant host cells produce known and novel polyketides, including but not limited to epothilone and epothilone derivatives. The invention relates to the fields of agriculture, chemistry, medicinal chemistry, medicine, molecular biology, and pharmacology. BACKGROUND OF THE INVENTION [0002] Polyketides constitute a class of structurally diver...

AI Technical Summary

Benefits of technology

[0131] In a preferred and illustrative embodiment, the recombinant host cell of the invention produces epothilone or an epothilone derivative. The naturally occurring epothilones (including epothilone A, B, C, D, E, and F) and non-naturally occurring compounds structurally related thereto (epothilone derivatives or analogs) are potent cytotoxic agents specific for eukaryotic cells. These compounds have application as anti-fungals, cancer chemotherapeutics, and immunosuppressants, and generally for the treatment of inflammation or any hyperproliferative disease, such as psoriasis, multiple sclerosis, atherosclerosis, and blockage of stents. The epothilones are produced at very low levels in the naturally occurring Sorangium cellulosum cells in which they have been identified. Moreover, S. cellulosum is very slow growing, and fermentation of S. cellulosum strains is difficult and time-consuming. One important benefit conferred by the present invention is the ability simply to produce an epothilone or epothilone derivative in a non-S. cellulosum host cell. Another advantage of the present invention is the ability to produce the epothilones at higher levels and in greater amounts in the recombinant host cells provided by the invention than possible in the naturally occurring epothilone producer cells. Yet another advantage is the ability to produce an epothilone derivative in a recombinant host cell. Thus, the present invention provides recombinant host cells that produce a desired epothilone or epothilone derivative. In a preferred embodiment, the host cell produces the epothilone or epothilone derivative at equal to or greater than 10 mg / L. In one embodiment, the invention provides host cells that produce one or more of the epothilones or epothilone derivatives at higher levels than produced in the naturally occurring organisms that produce epothilones. In another embodiment, the invention provides host cells that produce mixtures of epothilones that are less complex than the mixtures produced by naturally occurring host cells that produce epothilones.

[0132] In an especially preferred embodiment, the host cells of the invention produce less complex mixtures of epothilones than do naturally occurring cells that produce epothilones. As one example, certain host cells of the invention can produce epothilone D in a less complex mixture than is produced by a naturally occurring Sorangium cellulosum, because epothilone D is a major product in the former and a minor product in the latter. Naturally occurring Sorangium cellulosum cells that produce epothilones typically produce a mixture of epothilones A, B, C, D, E, F, and other very minor products, with only epothilones A and B present as major products. The Table 1 below summarizes the epothilones produced in different illustratrive host cells of the invention. TABLE 1Epothilones NotCell TypeEpothilones ProducedProduced*1A, B, C, DE, F2A, CB, D, E, F3B, DA, C, E, F4A, BC, D5C, DA, B6BA, C, D, E, F7DA, B, C, E, F*or produced only as minor products

[0133] Thus, the recombinant host cells of the invention also include host cells that produce as a major product only one desired epothilone or epothilone derivative.

[0134] Based solely on an analysis of the domains of the epothilone PKS, one could predict that the PKS enzyme catalyzes the production of epothilones arbitrarily designated “G” and “H”, the structures of which are shown below:

[0135] These compounds differ from one another in that epothilone G has a hydrogen at C-12 and epothilone H has a methyl group at that position. The variance at the C-12 position is predicted to arise from the ability of the corresponding AT domain (extender module 4) of the PKS to bind either malonyl CoA, leading to hydrogen, or methylmalonyl CoA, leading to methyl. However, epothilones G and H have not been observed in nature or in the recombinant host cells of the invention. Instead, the products of the PKS are believed to be epothilones C and D, which differ from epothilones G and H, respectively, by having a C-12 to C-13 double bond and lacking a C-13 hydroxyl substituent. Based on the expression of the epothilone PKS genes in heterologous host cells and the products produced by genetic alteration of those genes, as described more fully below, the dehydration reaction that forms the C12-C13 double bond in epothilones C and D is believed to be carried out by the epothilone PKS itself. Epothilones A and B are formed from epothilones C and D, respectively, by epoxidation of the C-12 to C-13 double bond by the epoK gene product. Epothilones E and F may be formed from epothilones A and B, respectively, by hydroxylation of the C-21 methyl group or by incorporation of a hydroxymalonyl CoA instead of a malonyl CoA by the loading module of the epothilone PKS, as discussed further below.

[0136] Thus expression of the epothilone PKS genes and the epoK gene in a host cell of the invention leads to the production of epothilones A, B, C, and D. If the epoK gene is not present or is rendered inactive or partially inactive by mutation, then epothilones C and D are produced as major products. If the AT domain of extender module 4 is replaced by an AT domain specific for malonyl CoA, then epothilones A and C are produced, and if there is no functional epoK gene, then epothilone C is produced as the major product. If the AT domain of extender module 4 is replaced by an AT domain specific for methylmalonyl Co A, then epothilones B and D are produced as major products, and if there is no functional epoK gene, then epothilone D is produced as the major product.

Problems solved by technology

While such methods are valuable and highly useful, certain polyketides are expressed only at very low levels in, or are toxic to, the heterologous host cell employed.

Despite the success of these efforts, the chemical synthesis of the epothilones is tedious, time-consuming, and expensive.

Indeed, the methods have been characterized as impractical for the full-scale pharmaceutical development of any epothilone as an anticancer agent.

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