monastrol and dimethylenastron

Human kinesin Eg5, which plays an essential role in mitosis by establishing the bipolar spindle, has proven to be an interesting drug target for the development of cancer chemotherapeutics. Here, we report the crystal structures of the Eg5 motor domain complexed with enastron, dimethylenastron, and fluorastrol. By comparing these structures to that of monastrol and mon-97, we identified the main reasons for increased potency of these new inhibitors, namely the better fit of the ligand to the allosteric binding site and the addition of fluorine atoms. We also noticed preferential binding of the S-enantiomer of enastron and dimethylenastron to Eg5, while the R-enantiomer of fluorastrol binds preferentially to Eg5. In addition, we performed a multidrug resistance (MDR) study in cell lines overexpressing P-glycoprotein (Pgp). We showed that one of these inhibitors may have the potential to overcome susceptibility to this efflux pump and hence overcome common resistance associated with tubulin-targeting drugs.

Topics: Antimitotic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Cell Line; Cell Line, Tumor; Cell Proliferation; Crystallography, X-Ray; Drug Resistance, Multiple; Humans; Kinesins; Models, Molecular; Protein Conformation; Protein Structure, Tertiary; Pyrimidines; Quinazolines; Stereoisomerism; Structure-Activity Relationship; Thiones

The inhibition of kinesin Eg5 by small molecules such as monastrol is currently evaluated as an approach to develop a novel class of antiproliferative drugs for the treatment of malignant tumours. Therefore, we studied the effects of the new monastrol analogues enastron, dimethylenastron and vasastrol VS-83 on the proliferation of human glioblastoma cells in the kinetic crystal violet assay. Compared to monastrol, the new cell cycle specific compounds showed an at least one order of magnitude higher anti proliferative activity against U-87 MG, U-118 MG, and U-373 MG glioblastoma cells. The compounds were neither inactivated by hydrolysis nor by binding to serum proteins. Moreover, we demonstrated the characteristic monoaster formation after incubation of cells with the new compounds by confocal laser scanning microscopy. We also showed that the arrangement of beta-actin and tubulin, vital components of the cyto-skeleton of mitotic and quiescent cells, were not affected by the new compounds. Due to the necessity of overcoming the blood-brain barrier in the treatment of brain tumours, we investigated if the new monastrol analogues are modulators or substrates of the p-glycoprotein (p-gp) 170 by a flow cytometric calcein-AM efflux assay. The tested compounds showed no modulating effects on the p-gp function. With respect to the treatment of primary and secondary CNS tumours, the results of our experiments suggest that the new monastrol analogues represent an interesting class of potential anticancer drugs, predicted to be less neurotoxic in comparison to classical tubulin inhibitors.

Topics: Acridines; Antineoplastic Agents, Phytogenic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Cell Line, Tumor; Cell Proliferation; Cell Survival; Cysteine; Dose-Response Relationship, Drug; Flow Cytometry; Fluoresceins; Glioblastoma; Humans; Insecticides; Kinesins; Molecular Structure; Paclitaxel; Pyrimidines; Quinazolines; Rotenone; Spindle Apparatus; Tetrahydroisoquinolines; Thiones; Time Factors; Tubulin; Tubulin Modulators; Vinblastine