Abstract 3503: CCT241533 is a novel, potent and selective inhibitor of CHK2 and potentiates the cellular effects of PARP inhibitors

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Abstract CHK2 is a checkpoint kinase involved in the ATM-mediated response to double stranded DNA breaks (DSB). Detection of DSB by the MRE11-RAD50-NBS1 (MRN) complex leads to activation of ataxia telangiectasia mutated (ATM) kinase, which can then phosphorylate CHK2 on threonine 68. This facilitates CHK2 to dimerisation and autophosphorylation in trans at threonine 383/387, resulting in full activation and subsequent phosphorylation in cis at serine 516, a biomarker read out of CHK2 activation. Once activated, CHK2 phosphorylates a range of targets involved in DNA damage repair, cell cycle arrest and apoptosis. It has been suggested that inhibitors of CHK2 may increase the efficacy of genotoxic cancer therapies. However, the evidence so far is inconsistent. We have therefore developed a CCT241533, a potent and selective inhibitor of CHK2, as a molecular tool and potential therapeutic agent (the structure will be disclosed in the presentation). The co-crystal structure of CCT241533 bound to the kinase domain of CHK2 confirms that the compound binds the ATP binding pocket. CCT241533 inhibits CHK2 with an IC50 of 3 nM and shows minimal inhibitory activity against a panel of known kinases at 1 μM, including CHK1 (IC50 = 245 nM). We show that CCT241533 blocks CHK2 activity in three human tumor cell lines (HT29, HeLa, MCF7) in which we have confirmed functional activation of CHK2. We also show that CCT241533 potentiates the growth inhibitory effect of two structurally distinct Poly (ADP-ribose) polymerase (PARP) inhibitors in p53 defective human cancer cells. We further demonstrate that this cellular effect correlates with inhibition of PARP inhibitor-mediated induction of CHK2 activity, as assessed by the phospho-serine 516 biomarker and CHK2 mobility shift. This adds strength to the conclusion that the potentiation between the two compounds is due to their effects on CHK2. To summarize, we have developed a potent and selective CHK2 inhibitor and show, for the first time, potentiation between CHK2 inhibition and PARP inhibition. 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 3503.