Differential in vitro association of vinca alkaloid-induced tubulin spiralfilaments into aggregated spirals

Vinblastine, vincristine, vindesine, and vinorelbine, the four vinca alkalo ids used in cancer therapy, differ in their antitumoral spectra and toxicit ies, but not in their inhibitory effects on microtubule assembly in vitro. At higher drug concentrations, vinca alkaloids induce the assembly of spira l filaments of tubulin, which, in turn, can interact laterally and form par acrystals. Using methods that distinguish spiral filaments and paracrystals (aggregated spirals), we found that spiral filament formation was largely independent of the incubation temperature, of the alkaloid used, and of the presence or absence of microtubule-associated proteins (MAPs). In contrast , the formation of aggregated spirals was markedly dependent on the alkaloi d used, on the incubation temperature, and on the absence or presence of MA Ps. Aggregated spirals failed to assemble in the presence of high concentra tions of MAP-1A or MAP-1B, whereas they assembled readily with tau and MAP- 2. Differences in patterns of turbidity development using pure tubulin allo wed the classification of thirteen cytotoxic vinca alkaloids into five dist inct groups, with centrifugal recovery of aggregated spirals in close agree ment with the various turbidity patterns. With microtubule protein, i.e. tu bulin preparations containing MAPs, only four groups were defined by turbid ity patterns, and centrifugal protein recovery was more divergent. Vinblast ine, vincristine, vindesine, and vinorelbine fell into distinct groups unde r both reaction conditions, and thus they appear to have qualitatively dist inguishable in vitro interactions with tubulin. These differential effects on spiral filament and aggregated spiral assembly revealed that the four dr ugs induce different constraints on the tubulin molecule. BIOCHEM PHARMACOL 58;6:959-971, 1999. (C) 1999 Elsevier Science Inc.