Abstract 1277: Discovery of novel CDC7 inhibitors that disrupt cell cycle dynamics and show anti-proliferative effects in cancer cells

Introduction: CDC7 is a serine/threonine protein kinase that phosphorylates the MCM2-7 helicase complex, a required step in DNA replication initiation. CDC7 has emerged as an attractive target for cancer treatment because of high expression in a number of tumors (e.g. ovarian, lung, and oral) which is thought to be linked to their proliferative capacity and ability to bypass DNA damage responses. Consistent with this, disruption of CDC7 activity in cancer cells results in delayed DNA replication, mitotic abnormalities and cell death whereas non-transformed, p53 wildtype cells are protected from cytotoxicity due to G1 cell cycle arrest. Due to the low ATP Km of CDC7, very potent inhibitor molecules are required to effectively block CDC7 activity and drive cancer cells into apoptosis. We have identified novel potent and selective CDC7 inhibitors targeting the ATP binding site that are active in biophysical, biochemical and cellular assays as well as in vivo CDX models. Results: Our lead compounds show potent picomolar (pM) inhibition of CDC7 in a biochemical kinase activity assay, pM affinity in SPR assay and complete inhibition of MCM2 (S53) phosphorylation in COLO205, A427, MV-4-11 and SW48 cancer cell lines. In a broad kinase selectivity panel, the novel inhibitors showed good selectivity for CDC7 kinase. Mechanistic studies show that our CDC7 inhibitors induced apoptosis, disrupted DNA replication and cell cycle dynamics with accumulation of polyploid cells after 48 h of treatment of cancer cells with minimal effects on human fibroblast cell lines. Our compounds have shown potent anti-proliferative and cytotoxic effects in a panel of more than a 100 cancer cell lines of varying origin including COLO205, SW48, A427, MOLM-13, and SUM149. Comparison of CDC7 inhibitors with other oncology drugs in a panel of cancer cell lines revealed a unique mechanism of action. In vivo, our compounds reduced tumor cell MCM2 (S53) phosphorylation in the mouse COLO205 xenograft model and showed strong tumor growth inhibition. We have also examined the effect of CDC7 inhibitors on cancer cell proliferation in combination with other anti-cancer agents, including other DNA damage response (DDR) targeting agents. Conclusions: We have identified novel potent ATP-competitive CDC7 inhibitors that show target engagement in cells and CDX tumors and have shown strong inhibition of cancer cell proliferation in vitro and tumor growth in vivo. CDC7 inhibitors show promise for use in com