ARRY-649, a member of a novel class of Eg5 kinesin inhibitors

Abstract

13045 Background: Inhibitors of the Eg5 motor kinesin selectively disrupt mitotic spindles in dividing cells. This selective targeting of microtubule dynamics in dividing cells is expected to translate to broad-spectrum anti-tumor activity while avoiding neuropathic side effects caused by taxanes. To date, quinazolinone Eg5 inhibitors, exemplified by ispinesib, represent the only Eg5 inhibitors reported in clinical trials. Methods: We used X-ray crystallography, biochemical and cell-based assays, pharmacokinetic profiling and in vivo efficacy studies to identify and optimize a potent series of Eg5 inhibitors. Results: We have discovered a distinct series of potent Eg5 inhibitors, exemplified by ARRY-649. ARRY-649 inhibited Eg5 with an IC50 of 0.7 nM, blocked phosphorylation of histone H3 in HeLa cells with an IC50 of 0.3 nM and showed sub-nanomolar activity against a broad panel of human tumor cells lines in in vitro viability assays. Further evaluation of mechanism-of-action in tumor cell lines revealed that ARRY-649 induced a monopolar spindle phenotype and subsequent apoptosis characteristic of Eg5 inhibition. In contrast to paclitaxel, ARRY-649 retained potent activity against multi-drug resistant human tumor cells lines selected to overexpress P-glycoprotein. ARRY-649 demonstrated robust efficacy in the HT-29 human colon tumor xenograft model and was well-tolerated at efficacious doses and schedules. Durable complete- and partial-regressions were observed upon intraperitoneal administration on a 5 mg/kg q4dx3 schedule in the HT-29 model. Similar results were obtained using the HL-60 myelomonocytic xenograft model. Conclusions: ARRY-649 represents a distinct class of potent Eg5 inhibitors with robust activity in preclinical models of human cancer. Based on these observations, we have progressed novel Eg5 inhibitors toward clinical development. [Table: see text]