Discovery of 2,4-diaryl-2,5-dihydropyrrole inhibitors of the mitotic kinesin KSP

Proc Amer Assoc Cancer Res, Volume 46, 2005 SY13-1 Mitotic kinesins are involved in bipolar spindle assembly, maintenance and elongation, chromosome alignment and segregation, and microtubule depolymerization, among other functions during cell division. KSP is a mitotic kinesin that causes centrosome separation, a process required for bipolar spindle formation and maintenance. Inhibition of KSP results in collapse of bipolar spindles and gives rise to monopolar spindle arrays, referred to as monoasters. Importantly, this phenotype is accompanied by cell cycle arrest in mitosis, and prolonged mitotic arrest in tumor cells can lead to apoptosis. KSP inhibitors therefore have potential as general antiproliferative agents useful for the treatment of cancer. Additionally, KSP inhibition represents a novel and specific mechanism by which to target the mitotic spindle that may be devoid of the neuropathy-associated, mechanism-based side effects common to the taxanes and other natural products that target microtubules. KSP inhibitors may also offer advantages over these agents with regard to formulation and tumor resistance. In this presentation, we disclose the development of 2,4-diaryl-2,5-dihydropyrroles as novel, potent and selective inhibitors of KSP. The evolution of this class from a 3,5-diaryl-4,5-dihydropyrazole lead structure will be described with emphasis on modifications to the N-1 substituent of the dihydropyrrole nucleus that provided potency and aqueous solubility simultaneously. Initial optimization efforts in this series led to the identification of compound 1 (KSP IC50 = 2.0 nM). Compound 1 caused mitotic arrest in vitro in A2780 human ovarian carcinoma cells (EC50 = 8.6 nM) and upon prolonged exposure activated caspase-3 (EC50 = 11 nM) and induced apoptosis as determine by FACS analysis. Furthermore, compound 1 caused mitotic arrest, induced apoptosis and inhibited tumor growth in vivo in A2780 tumors in mice. An analysis of the novel binding mode of compound 1 will be provided along with a summary of its physiochemical properties and pharmacokinetics in animals. A scalable asymmetric synthetic route to compound 1 will also be highlighted in this presentation.