ANTIMITOTIC AND TUBULIN-INTERACTING PROPERTIES OF VINFLUNINE, A NOVELFLUORINATED VINCA ALKALOID

This study aimed to define the mechanism of action of vinflunine, a no vel Vinca alkaloid synthesised from vinorelbine using superacidic chem istry and characterised by superior in vivo activity to vinorelbine in preclinical tumour models. In vitro vinflunine cytotoxicity proved de pendent on concentration and exposure duration, with IC50 values (72-h r exposures) generally ranging from 60-300 nM. Vinflunine induced G(2) + M arrest, associated with mitotic accumulation and a concentration- dependent reduction of the microtubular network of interphase cells, a ccompanied by paracrystal formation. These effects, while comparable t o those of vincristine, vinblastine or vinorelbine, were achieved with 3-to l7-fold higher vinflunine concentrations. However, vinflunine an d the other Vincas all inhibited microtubule assembly at micromolar co ncentrations. Vinflunine, like vinblastine, vincristine and vinorelbin e, appeared to interact at the Vinca binding domain, as judged by prot eolytic cleavage patterns, and induced tubulin structural changes favo uring an inhibition of GTP hydrolysis. However, vinflunine did not pre vent [H-3]vincristine binding to unassembled tubulin at concentrations less than or equal to 100 mu M, and only weakly inhibited binding of [H-3]vinblastine or [ [H-3]vinorelbine. Indeed, specific binding of [H -3]vinflunine to tubulin was undetectable by centrifugal gel filtratio n. Thus, the comparative capacities of these Vincas to bind to or to i nterfere with their binding to tubulin could be classified as: vincris tine > vinblastine > vinorelbine > vinflunine. By monitoring alkylatio n of sulfhydryl groups, differential effects on tubulin conformation w ere identified with vinflunine and vinorelbine acting similarly, yet d istinctively from vinblastine and vincristine. Overall, vinflunine app ears re, function as a definite inhibitor of tubulin assembly, while e xhibiting quantitatively different tubulin binding properties to the c lassic Vinca alkaloids. (C) 1998 Elsevier Science Inc.