Vinblastine biosynthesis

Salutaridinol 7-0-acetyltransferase catalyzes the conversion of the phenanthrene alkaloid salutaridinol to salutaridinol-7-Oacetate, the immediate precursor of thebaine along the morphine biosynthetic pathway in P. somniferum (Fig. 10.7).26 Acetyl CoA-dependent acetyltransferases have an important role in plant alkaloid metabolism. They are involved in the synthesis of monoterpenoid indole alkaloids in medicinal plant species such as Rauwolfia serpentina. In this plant, the enzyme vinorine synthase transfers an acetyl group from acetyl CoA to 16-epi-vellosimine to form vinorine. This acetyl transfer is accompanied by a concomitant skeletal rearrangement from the sarpagan- to the ajmalan-type (reviewed in2). An acetyl CoA-dependent acetyltransferase also participates in vindoline biosynthesis in Catharanthus roseus, the source of the chemotherapeutic dimeric indole alkaloid vinblastine (reviewed in2). Acetyl CoA deacetylvindoline 4-O-acetyltransferase catalyzes the last step in vindoline biosynthesis. A cDNA encoding acetyl CoA deacetylvindoline 4-0-acetyltransferase was recently successfully isolated.27... 

Additionally, there had, for many years, been a vast synthetic effort underway aimed at the synthesis of the two monomeric units, where it was anticipated that the two units could be joined to form the vinblastine-type bisindole alkaloids. Coincidentally, as it transpired, 20 years of effort in the areas of synthesis and biosynthesis converged, at almost the same time, on the compound 3, 4 -anhydrovinblastine (8). 

The extremely low yield of vincristine (2) from intact plants has made pursuit of its biosynthesis a very challenging problem, which at this point in time remains unsolved. Kutney et al. have used both anhydrovinblastine (8) (227) and catharanthine N-oxide (107) (233) as precursors to vincristine (2) in a cell-free preparation, but incorporation levels were extremely low. Therefore, the question of whether vinblastine (1) is an in vivo, as well as an in vitro, precursor remains to be answered. Several possibilities exist for the overall oxidation of vinblastine (1) to vincristine (2), including a direct oxidation of the A-methyl group or oxidative loss of the N-methyl group followed by N-formylation. 

A wide variety of other biochemical effects has been reported to be associated with treatment of cells with vinblastine, vincristine, and related compounds (S). These effects include inhibition of the biosynthesis of proteins and nucleic acids and of aspects of lipid metabolism it is not clear whether such effects contribute to the therapeutic or toxic actions of vincristine and vinblastine. Vinblastine and vincristine inhibit protein kinase C, an enzyme system that modulates cell growth and differentiation (9). The pharmacological significance of such inhibition has not been established, however, and it must be emphasized that the concentrations of the drugs required to inhibit protein kinase C are several orders of magnitude higher than those required to alter tubulin polymerization phenomena (10). 

Further information is available on the biosynthesis of vinblastine-type alkaloids (cf. Vol. 11, p. 19 Vol. 10, p. 19). Anhydrovinblastine (61) was found to be metabolized to leurosine (63) and Catharine (64) in cultures of a C. roseus cell-line that do not normally produce these alkaloids.55 Ring-opening in the conversion of the skeleton of anhydrovinblastine (61) into that of Catharine (64) has been suggested to occur by Baeyer-Villiger-type oxidation of an imine las (62). The alternative 21 -imine could give catharinine.56... 

Figure 2.11 Biosynthesis of vindoline, catharanthine and the dimeric alkaloids vinblastine and vincristine. T16H, tabersonine-16-hydroxylase OMT, 5-adenosylmethionine 16-hydroxy-tabersonine-O-methyltransferase NMT, 5-adenosylmethionine 16-methoxy-2,3-dihydro-3-hydroxymethyltabersonine-/ /-methyltransferase D4H, desacetoxy-vindoline-4-dioxygenase DAT, acetylcoenzyme A 4-0-deacetylvindoline-4-0-acetyltransferase.

Baxster RI, Dorschel CA, Lee SL, Scott AI. Biosynthesis of the antitumor cafiiaranfiius alkaloids. Conversion of anhydrovinblastine into vinblastine. J. Chem. Soc. Chem. Comm. 1979 257-259. Gueritte F, Bac NV, Langlois Y, Potier P. Biosynthesis of antitumour alkaloids from Cafiiaranfiius roseus. Conversion of 20 deoxyleurosidine into vinblastine. J. Chem. Soc. Chem. Comm. 1980 452-453. 

This reaction has been extensively studied in the case of the chlopromazine radical (R -mediated aminopyrine (S) oxidation [41], a typical reaction for xenobiotics, as well as in the case of the vindoline radical (R -mediated catharanthine (S) oxidation [42], a key reaction in the biosynthesis of the anticancer drugs, vinblastine and vincristine, which are obtained from Catharanthus roseus. 

The biosynthesis of monoterpenoid indole alkaloids has been intensively investigated since the sixties [76], The great interest in this group of alkaloids is due mainly to the cytotoxic vinblastine and vincristine, which are very useful anticancer drugs, but which are produced by the C. roseus plant in extremely low quantities. It is therefore not surprising that most of the biosynthetic and enzymology studies of monoterpenoid indole bases have been performed to elucidate the biosynthetic pathway of vinblastine and vincristine and its regulation in C. roseus plants. 

Fig. (2). Biosynthesis of vinblastine from the monomeric precursors catharanthine and vindoline. Anhydrovinblastine is the direct product of the dimerization reaction and the precursor of the anticancer drugs. Shaded areas indicate the structural differences between the precursor catharanthine and the deavamine part of...

What is known about the biogenetic routes leading to the biosynthesis of the dimeric akaloids vinblastine and vincristine in C. roseus is represented in Fig. (4) to (6). Enzymes and genes that have been characterized are indicated, and the subcellular compartmentalization of the pathway is presented in Fig. (3). 

Regulation of the biosynthesis of secondary metabolites cannot be seen as separate from the role of these products for the plant. However, in most cases this role is not known. In the case of C. roseus an antifeedant activity against Spodoptora larvae has been reported for vinblastine and catharan-thine 49). A nematocidal effect has been reported for serpentine 50). Antifeedant activity against Spodoptera caterpillars for C. roseus leaf extracts has been described as well 49,51). Luijendijk et al. 52,53) found that besides alkaloids, also nonpolar compounds are involved in the antifeedant... 

For the biosynthesis of a secondary metabolite at least one enzyme is required, changing the primary metabolite into a (specific) secondary product. However, in most cases more enzymes are involved, e.g. the number of enzymes for the biosynthesis of vinblastine, starting from tryptophan and geranyl diphosphate is higher than 25. Plants are thus not only a rich source of complex, biological active, fine-chemicals, but are probably an even more rich source of biocatalysts. Its potential in bioconversions is recognized [2]. 

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