Sensitivity to halichondrin analog E7389 and hemiasterlin analog E7974 correlates with βIII tubulin isotype expression in human breast cancer cell lines

Abstract

2012 Background: Resistance to tubulin-targeted agents has been associated with differential tubulin isotype expression in cancer cells. In this study we investigated whether β-tubulin isotype composition of tumor cells affects their sensitivity to 2 natural product-based antitubulin agents: halichondrin analog E7389 and hemiasterlin analog E7974. Methods: Antiproliferative effects of E7389, E7974, paclitaxel and vinblastine against a panel of human breast cancer cell lines were determined by methylene blue-based or MTT-based cell growth inhibition assays. Cell lines were tested for evidence of PgP expression by monitoring effects of the PgP blocker verapamil on paclitaxel sensitivity. Using quantitative PCR with specific primers, expression levels of the seven human β-tubulin isotypes were determined (I, II, III, IVa, IVb, V, and VI). Results: No evidence for PgP expression was found in any of the cell lines tested. In growth inhibition studies, interdrug correlations were seen between sensitivities to the 3 microtubule polymerization inhibitors E7974, E7389 and vinblastine, but not between the microtubule stabilizer paclitaxel and the other agents. All 7 β-tubulin isotypes were detected at different levels in each cell line, with isotypes I and IVb showing the least variation while isotypes II, III, and IVa showed the greatest variability between the cell lines. A significant correlation was demonstrated between β III tubulin expression levels and sensitivity to both E7389 and E7974. Conclusions: These findings in cancer cell lines suggest that tumors expressing higher levels of βIII tubulin isotype may be more responsive to treatment with E7389 and E7974. If confirmed clinically, such preclinical insights may lay the foundation for selection of patient populations with enhanced sensitivities to these 2 natural product-based antitubulin agents. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Eisai Medical Research Institute