Taxanes are powerful
chemotherapy agents that target the microtubule cytoskeleton, leading to mitotic arrest and cell death; however, their clinical efficacy has been hampered due to the development of drug resistance. Therefore, other
proteins involved in spindle assembly are being examined as potential targets for anticancer
therapy. The mitotic
kinesin, Eg5 is critical for proper spindle assembly; as such, inhibition of Eg5 leads to mitotic arrest making it a potential anticancer target. We wanted to validate Eg5 as a therapeutic target and determine if Eg5 inhibitors retain activity in
Taxol-resistant cells. Using affinity chromatography we first show that the compound
HR22C16 is an Eg5 inhibitor and does not interact with other microtubule motor
proteins tested. Furthermore,
HR22C16 along with its analogs, inhibit cell survival in both
Taxol-sensitive and -resistant
ovarian cancer cells with at least 15-fold greater efficacy than
monastrol, the first generation Eg5 inhibitor. Further analysis with HR22C16-A1, the most potent
HR22C16 analog, showed that it retains efficacy in PgP-overexpressing cells, suggesting that it is not a PgP substrate. We further show that HR22C16-A1 induces cell death following mitotic arrest via the intrinsic apoptotic pathway. Interestingly, the combination of HR22C16-A1 with
Taxol results in an antagonistic antiproliferative and
antimitotic effect, possibly due to the abrogation of
Taxol-induced mitotic spindles by HR22C16-A1. Taken together, our results show that Eg5 inhibitors have promising anticancer activity and can be potentially used to overcome
Taxol resistance in the clinical setting.