Abstract B242: Antitumor activity of SEL120: An orally available small-molecule inhibitor of Haspin kinase for standalone and combination therapy with AuroraB inhibitors in colorectal cancer.

The mitotic machinery is a validated target for potential drug therapies in cancer. Anti-mitotic drugs like vinca alkaloids and taxanes interfering with microtubules are important classes of chemotherapeutical agents. However, these agents are not without complications from various side effects, notably neurological and hematological toxicities. There is much interest in identifying new drug targets in mitosis which could lead to safer and more efficacious treatments of cancer. Recently, Haspin has been identified as another important kinase involved in mitosis. Similar to other mitotic kinases such as Polo-like kinase-1 and the Aurora kinases, inhibition of Haspin represents a novel approach in anti-mitotic cancer therapeutics. In this study we report the development of SEL120, a novel ATP competitive inhibitor of Haspin kinase. These small-molecule compounds have binding affinities towards Haspin kinase in the low nM range. SEL120 inhibited proliferation and clonogenic survival of a number of tumor cell lines with particularly good cytostatic activity in colon, lung (NSCLS) and B cell lymphoma cell lines. The only substrate of Haspin reported in literature to date is histone H3. During mitosis Haspin targets a single site in this protein, namely threonine at position T3 (H3T3ph). By using siRNA, we have confirmed that Thr3 phosphorylation of histone H3 could be completely repressed by the knockdown of Haspin in HCT116 colon and A549 (NSCLC) lung cancer cell lines. We also consistently observed decreased phosphorylation of histone H3 (Thr3) in both synchronized and asynchronous cell lines treated with SEL120 inhibitor. Haspin-depleted cells were arrested in the prometaphase as a result of chromosome alignment defects and activation of the mitotic checkpoint. Treatment with SEL120 consistently resulted in mitotic cell cycle arrest in HCT116 and A549 cell lines confirming inhibition of Haspin as the mechanism of action. Furthermore, co-administration of SEL120 with an AuroraB inhibitor, AZD1152, resulted in strong synergistic cytostatic effects. Treatment with both compounds increased the number of cells arrested in mitosis, notably without any signs of polyploidy (cells with >4n) typically observed after inhibition of AuroraB. Oral administration of SEL120 (25mg/kg BID) revealed excellent potency in the HCT116 xenograft model; observed tumor growth inhibition was over 80%. Analysis of pharamcokinetic, ADMET and histopathological parameters afforded encouraging results towards potential development of new therapeutics emerging from our SEL120 program. Presented data validates Haspin as a promising target for anticancer treatments, particularly for colon cancer, lung cancer and lymphomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B242.