Richard J. Boyce

Modulating Protein-Protein Interactions of the Mitotic Polo-like Kinases to Target Mutant KRAS

Summary Mutations activating KRAS underlie many forms of cancer, but are refractory to therapeutic targeting. Here, we develop Poloppin, an inhibitor of protein-protein interactions via the Polo-box domain (PBD) of the mitotic Polo-like kinases (PLKs), in monotherapeutic and combination strategies to target mutant KRAS. Poloppin engages its targets in biochemical and cellular assays, triggering mitotic arrest with defective chromosome congression. Poloppin kills cells expressing mutant KRAS, selectively enhancing death in mitosis. PLK1 or PLK4 depletion recapitulates these cellular effects, as does PBD overexpression, corroborating Poloppins mechanism of action. An optimized analog with favorable pharmacokinetics, Poloppin-II, is effective against KRAS-expressing cancer xenografts. Poloppin resistance develops less readily than to an ATP-competitive PLK1 inhibitor; moreover, cross-sensitivity persists. Poloppin sensitizes mutant KRAS-expressing cells to clinical inhibitors of c-MET, opening opportunities for combination therapy. Our findings exemplify the utility of small molecules modulating the protein-protein interactions of PLKs to therapeutically target mutant KRAS-expressing cancers.

Abstract 4090: Preclinical pharmacokinetics of CASC-578, a novel, selective, potent, and orally bioavailable small molecule checkpoint kinase 1 inhibitor

Introduction: Checkpoint kinase 1 (Chk1) is a serine/threonine protein kinase that regulates cell division in response to genotoxic stress by arresting cell cycle progression in the S & G2 phases. Pharmacological inhibition of Chk1 is proposed to selectively uncouple the completion of DNA replication from G2/M phase transition in tumor cells that have impaired DNA damage response networks, resulting in mitotic catastrophe and cell death. CASC-578 is a novel small molecule inhibitor of Chk1 that is selective, highly potent and orally bioavailable in multiple preclinical species. Methods: The in vitro ADME properties of CASC-578 were evaluated, including in vitro intrinsic microsomal clearance, Caco2 permeability, plasma protein binding and stability, blood to plasma partitioning, cytochrome P450 inhibition and induction, and transporter inhibition. Pharmacokinetic studies of CASC-578 were conducted in mice, rats, and cynomolgus monkeys as either single dose (IV and/or PO) or repeat dose (PO only). Multiple oral dose pharmacokinetic studies were conducted in mice, rats and cynomolgus monkeys for 5-7 days. Results: CASC-578 is highly bound in plasma protein across all species. The apparent permeability is high in Caco2 bi-directional transport study and correlated well with a rapid absorption profile observed in vivo. CASC-578 is not a substrate of P-glycoporotein (efflux =1). There was no direct nor time dependent inhibition on human CYP450 enzymes, and only a slight induction of CYP3A4 was seen at 10 uM drug concentration in a transporter cell-based induction assay. In all animal species, CASC-578 exhibited species-dependent systemic clearance resulting from both phase I and phase II metabolism, and a moderate to high volume of distribution. The elimination kinetics appeared to be monophasic. Oral bioavailability was high in all species studied (>60% F). There was no significant difference in the pharmacokinetics of the drug between genders. Maximal plasma concentration and total drug exposure (AUC) appeared to be proportional from repeat dose studies. Overall, CASC-578 has very desirable drug-like properties and ideal pharmacokinetics for an oral once daily drug, and represents a suitable candidate for clinical development as a novel potential therapeutic approach for the treatment of solid and hematological malignancies Citation Format: Dina Leviten, Teresa Sierra, Ashley Dozier, Richard Boyce, Bob Boyle, Scott Peterson, Alex C. Vo. Preclinical pharmacokinetics of CASC-578, a novel, selective, potent, and orally bioavailable small molecule checkpoint kinase 1 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4090. doi:10.1158/1538-7445.AM2017-4090

Abstract 2721: Discovery and development of orally available subnanomolar potent checkpoint kinase 1 inhibitors as potential anticancer therapies

Checkpoint kinase 1 (Chk1) is a serine/threonine protein kinase that regulates cell division by arresting progression in the S & G2 phases of the cell cycle in response to genotoxic stress. Pharmacological inhibition of Chk1 selectively uncouples the completion of DNA replication from G2/M phase transition in tumor cells lacking parallel cell cycle checkpoint controls, resulting in mitotic catastrophe and cell death. These properties make Chk1 inhibition a unique therapeutic approach as a single agent or as a means to enhance the efficacy of DNA-targeted chemotherapeutic drugs. In this report, we describe our progress in the development of orally bioavailable, potent and selective Chk1 inhibitors derived from an aminopyrazole chemical scaffold. Starting with the lead compound, ONT-2409 (IC50 of Citation Format: Alex C. Vo, Janelle Taylor, Robert Rosler, Dina Leviten, Teresa Sierra, Richard Boyce, Robert Boyle, Scott Peterson, Kevin Klucher. Discovery and development of orally available subnanomolar potent checkpoint kinase 1 inhibitors as potential anticancer therapies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2721.