Interaction of Vinca Alkaloids with Tubulin:  A Comparison of Vinblastine, Vincristine, and Vinorelbine

Vinca alkaloids are antimitotic drugs that inhibit microtubule assembly and induce tubulin self-association into coiled spiral aggregates. Previous sedimentation velocity results with vinblastine have been interpreted by a mechanism involving isodesmic ligand-mediated or ligand-mediated plus ligand-...

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Bibliographic Details
Published in:Biochemistry (Easton) 1996-05, Vol.35 (21), p.6806-6814
Main Authors: Lobert, Sharon, Vulevic, Bojana, Correia, John J
Format: Article
Language:English
Subjects:
Animals
Antineoplastic Agents, Phytogenic - chemistry
Antineoplastic Agents, Phytogenic - metabolism
Brain
Guanosine Diphosphate - metabolism
Guanosine Triphosphate - metabolism
Kinetics
Light
Scattering, Radiation
Swine
Thermodynamics
Tubulin - chemistry
Tubulin - isolation & purification
Tubulin - metabolism
Vinblastine - analogs & derivatives
Vinblastine - metabolism
Vincristine - metabolism
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Summary:Vinca alkaloids are antimitotic drugs that inhibit microtubule assembly and induce tubulin self-association into coiled spiral aggregates. Previous sedimentation velocity results with vinblastine have been interpreted by a mechanism involving isodesmic ligand-mediated or ligand-mediated plus ligand-facilitated self-association [Lobert et al. (1995) Biochemistry 34, 8050−8060]. In this study, we compare the vincristine- or vinorelbine-induced self-association of porcine brain tubulin with our prior vinblastine studies in the presence of 50 μM GDP or 50 μM GTP. Vincristine demonstrates the highest overall affinity for tubulin, K 1 K 2, and vinorelbine the lowest (vincristine > vinblastine > vinorelbine). These are the first quantitative studies comparing the interaction of a new vinca alkaloid derivative, vinorelbine (Navelbine), with other vinca alkaloids. The relative binding affinities reported here correlate with the weekly drug doses used clinically in cancer chemotherapy, where vincristine is used at the lowest dosages and vinorelbine at the highest. Surprisingly, K 1, the affinity of drug for tubulin heterodimers, is identical for all three drugs. When data are fit with the ligand-mediated model, the differences in overall affinity are due to effects on K 2, the affinity of liganded heterodimers for spiral polymers. When data are fit with the ligand-mediated plus -facilitated model, affinity differences are also reflected in K 3, the binding of the drug to unliganded polymers. We find that GDP enhances self-association in the presence of all three drugs 3−5-fold over GTP. The enhancement is manifested in K 2 and K 3 and amounts to an average of 0.90 ± 0.17 kcal/mol. Thus, nucleotide enhancement is linked to the self-association step. Data collected at 5, 25, and 36 °C for all three drugs show increased maximum s̄ 20,w values with increasing temperature and are consistent with an entropically driven reaction for the overall process. To investigate these results further, stopped-flow light scattering experiments have been conducted. Relaxation times are longest for the largest vincristine polymers and shortest for the smallest vinorelbine polymers, consistent with a cascade of events corresponding to successive dissociation events from spiral polymers, the larger the polymers the longer the relaxation time. Relaxation times for any single drug decrease with increasing tubulin concentration, consistent with the occurrence of oligomer annealing in additio
ISSN:0006-2960
1520-4995
DOI:10.1021/bi953037i