BIOSYNTHESIS OF TAXOL AND RELATED COMPOUNDS

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Taxol, a diterpene derivative isolated from Taxus brevifolia and other Taxus species, is an important new anti-cancer agent. It has been approved by the FDA for treatment of ovarian cancer and also shows promise against breast, lung and other cancers. Taxotere, a semisynthetic analog, is also undergoing clinical evaluation with, so far, excellent results. These clinical successes have raised the problem of securing adequate commercial supplies of these drugs. The complexity of the structures does not bode well for an economically viable total synthesis of these drugs, and even after the imminent replacement of new bark extraction by semisynthesis from a more abundant taxane, 10-deacetylbaccatin-III, as the commercial source of taxol, the supply of these and future generation taxane-based drugs will depend on biosynthesis of at least the functionalized taxane ring system for years to come. It is the long-term goal of this project to elucidate, at the chemical, enzymatic and eventually, genetic level, the biosynthetic pathway by which taxol and related taxanes are assembled in the yew plant. We propose to (1) establish the mode of formation of the taxane ring system from its presumed precursor, geranylgeranyl pyrophosphate, (2) map the sequence of reactions leading from the initial hydrocarbon precursor to the fully functionalized taxane moiety of taxol, (3) gain mechanistic insight into the transformation of phenylalanine into the phenylisoserine and benzoate moieties of taxol and (4) confirm the model and stage of attachment of the C-13 side chain to the ring system and isolate the enzyme(s) catalyzing this process. As a tool for these studies we will also develop and optimize Taxus cell cultures to levels of taxane production useful for biosynthetic experiments. It is anticipated that the information generated will help provide the knowledge base for efforts to develop alternative biotechnological processes for the commercial production of these important new antitumor drugs.