Vinblastine binding

The answer is d. (Hardman, p 1258. Katzung, pp 935-9.36.) Vinblastine binds to tubulin and blocks the protein from polymerizing to microtubules. The drug-tubulin complex binds to the developing microtubule, resulting in inhibition of microtubule assembly and subsequent depolymerization. 

Affinity determined by displacement of pig brain tubulin-bound [ H]vinblastine. Data are relative to vinblastine binding (1.00, K, = 106). 

Earlier studies indicated that vinblastine binding to tubulin dimers involves interaction of two molecules of vinblastine with each dimeric pro-... 

Bruggemann EP, Currier SJ, Gottesman MM, et al. Characterization of the azido-pine and vinblastine binding site of P-glycoprotein. J Biol Chem 1992 267 (29) 21020-21026. 

Ferry DR, Malkhandi PJ, Russell MA, et al. Allosteric regulation of [3H]vinblastine binding to P-glycoprotein of MCF-7 ADR cells by dexniguldipine. Biochem Pharmacol 1995 49(12) 1851-1861. 

Malkhandi J, Ferry DR, Boer R, et al. Dexniguldipine-HCl is a potent allosteric inhibitor of [3H]vinblastine binding to P-glycoprotein of CCRF ADR 5000 cells. Eur J Pharmacol 1994 288(1) 105-114. 

Fig. 4 Diagram of the crystal structure of the T2R complex showing the binding sites of MT-destabilizing drugs (PDB entry 1Z2B) [13]. Protein subunits are represented as ribbons. RB3-SLD is colored orange, a-tubulin is purple, and p-tubulin is green. Small-molecule ligands are represented as spheres (vinblastine orange, colchicine red, GTP yellow, and GDP magenta). Colchicine binds to the p-subunit at the intradimer interface. Vinblastine binds at the interdimer interface...

Fig. 4 Left, location of the vinblastine and colchicine binding sites in tubulin (1Z2B structure), a- and (3-tubulin are represented as yellow and magenta ribbons, respectively vinblastine and DAMA-colchicine are represented as green and cyan spheres, respectively GTP and GDP are represented as pink sticks. Vinblastine binds at the interdimer interface, whereas colchicine binds at the intradimer interface. Right, zoom on the vinblastine binding site. Secondary structure elements contacting vinblastine are colored blue...

The exact binding site of vinca alkaloids remained unknown until 2005, when the crystal structure of vinblastine bound to tubulin complexed with colchicine and with the stathmin-like domain of RB3 was determined (PDB entry 1Z2B) [3], The structure revealed that vinblastine binds to curved tubulin at the interface between two a/p-tubulin heterodimers (interdimer interface, Fig. 4), introducing a wedge that interferes with tubulin assembly. The vinblastine binding site is defined by loop T7, helix H10 and strand S9 in the a subunit of the first heterodimer, and by helix H6 and loops T5 and H6-H7 in the p subunit of the second heterodimer. In microtubules, this region is located toward the inner lumen and is... 

Fig. 5 Interaction of antimitotic peptides and depsipeptides with the vinca domain with respect to the vinblastine binding site (1Z2B structure). Residues supposed to interact with the peptides are represented as blue sticks, vinblastine is represented as green sticks. Tubulin ribbons are colored as in Fig. 4...

Ekins et al. built QSAR models using Catalyst software to rank and predict inhibitors for P-gp substrate transport. In their first attempt, four different pharmacophores were derived from the analysis of inhibitors of digoxin transport, vinblastine binding, or intracellular accumulation of vinblastine and calcein [61]. These data were then combined with experiments using verapamil as inhibitor and led to the construction of a unique pharmacophore consisting of one hydrogen-bond acceptor, one aromatic ring, and two hydrophobic centers [62]. 

Martin, C., Higgins, C.F., and Callaghan, R. (2001) The vinblastine binding site adopts high- and low-affinity conformations during a transport cyde of P-glycoprotein. Biochemistry, 40 (51), 15733-15742. 

Cryptophycin-52 (26a), a member of the cryptophycin family developed by Eli Lilly and produced by total chemical synthesis [76], was selected from diverse synthetic analogues displaying superior potency, stability and amenability of clinical formulation [77,76]. Cryptophycin-52 in vitro binds non-covalently to tubulin at a single high affinity site, which presumably overlaps with the Vinblastine binding site [75]. Proliferation of diverse tumour cell lines was inhibited with IC50 values of 13 pM to 232 pM, minimally affected by P-gp or MRP overexpression [78]. Data from phase I and II trials showed severe toxicities as long... 

Rai S, Wolff J. Localization of the vinblastine-binding site on p-tubulin. j Biol Chem 1996 271 14707-14711. 

Wilson, L, Creswell, KM and Chin, D (1975) The mechanism of action of vinblastine. Binding of [acetyl- H]vinblastine to embryonic chick brain tubulin and tubulin from sea urchin sperm tail outer doublet microtubules. Biochemistry, 14, 5586-5592. 

Using the digoxin transport model to predict 51 of the molecules from the vinblastine binding, vinblastine accumulation, and verapamil accumulation data sets results in a correlation of observed versus predicted values (r = 0.63) and a Spearmans rho ranking correlation coefficient of 0.75 p = < 0.0001, Figure 6). This is quite acceptable as a computational model for drug discovery where large databases need to be filtered in a cost-effective manner. 

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