Abstract 5374: LY-GSK-3i, a novel glycogen synthase kinase-3 inhibitor, potentiates the apoptotic activity of cytotoxic agents in combination chemotherapy protocols inin vitroandin vivotumor models

Combination chemotherapy regimens for the treatment of cancer arise from the need to either enhance single agent activity, circumvent drug resistance or reduce toxicity by allowing lower dosing of cytotoxic agents. Glycogen synthase kinase 3 (GSK-3) is a constitutively active protein kinase with two highly homologous isoforms, GSK-3α and GSK-3β. Elevated GSK-3 activity has been described in a variety of tumors types and pharmacological or genetic inhibition of this kinase has been shown to reduce the survival of these tumors. In order to explore the potential for GSK-3 inhibitors in cancer therapy we developed LY-GSK-3i, which potently inhibits the enzymatic activity of GSK-3α and GSK-3β with IC50s of 1.5 nM and 0.9nM respectively and reduces the phosphorylation (Ser-396) of its substrate protein, Tau, with an EC50 of 1.4 nM. Here we report the novel and potent chemo-potentiating activity of LY-GSK-3i in a broad range of tumor models in combination with cytotoxic agents having different mechanisms of action. In in vitro caspase 3 activation assays, LY-GSK-3i enhances the apoptotic activity of pemetrexed, a multi-targeted anti-folate, in the NCI-H460 NSCLC cell line. The LY-GSK-3i/ pemetrexed combination enhances apoptotic activity 4-fold over the additive effect of each individual chemotherapeutic agent. DNA damaging agents such as platinum containing cytotoxics are also subject to chemopotentiation by LY-GSK-3i. In the NCI-H460 model, LY-GSK-3i potentiates the action of carboplatin 2 fold. Similarly, in the FaDu and SiHa squamous carcinoma cell lines, a 2-3 fold increase in apoptotic activity is observed with the combination treatment of LY-GSK-3i and cisplatin relative to treatment with either agent alone. Camptothecin is a DNA topoisomerase I inhibitor with modest apoptotic activity in the A2780, ovarian tumor cell line. The combination of camptothecin with LY-GSK-3i resulted in significant elevation in caspase 3 activation. Interestingly, commercially available GSK3/CDK inhibitors, such as SB216763, LiCl, alsterpaullone and purvalanol A have modest chemo-potentiating effect on Camptothecin toxicity compared to LY-GSK-3i. In vivo xenograft growth studies indicated that administration of LY-GSK-3i significantly improved the antitumor efficacy of cisplatin against Colo-205 colorectal tumors. Furthermore, LY-GSK-3i also potentiated in vivo the antitumor activity of carboplatin, or a combination of carboplatin/pemetrexed in NCI-H460 xenografts. Taken together, these data provide evidence for the potential therapeutic utility of LY-GSK-3i, in combination with cytotoxic agents, for the treatment of cancer. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5374.