Susan Ashwell

AZD7762, a novel checkpoint kinase inhibitor, drives checkpoint abrogation and potentiates DNA-targeted therapies

Insights from cell cycle research have led to the hypothesis that tumors may be selectively sensitized to DNA-damaging agents resulting in improved antitumor activity and a wider therapeutic margin. The theory relies on the observation that the majority of tumors are deficient in the G1-DNA damage checkpoint pathway resulting in reliance on S and G2 checkpoints for DNA repair and cell survival. The S and G2 checkpoints are regulated by checkpoint kinase 1, a serine/threonine kinase that is activated in response to DNA damage; thus, inhibition of checkpoint kinase 1 signaling impairs DNA repair and increases tumor cell death. Normal tissues, however, have a functioning G1 checkpoint signaling pathway allowing for DNA repair and cell survival. Here, we describe the preclinical profile of AZD7762, a potent ATP-competitive checkpoint kinase inhibitor in clinical trials. AZD7762 has been profiled extensively in vitro and in vivo in combination with DNA-damaging agents and has been shown to potentiate response in several different settings where inhibition of checkpoint kinase results in the abrogation of DNA damage-induced cell cycle arrest. Dose-dependent potentiation of antitumor activity, when AZD7762 is administered in combination with DNA-damaging agents, has been observed in multiple xenograft models with several DNA-damaging agents, further supporting the potential of checkpoint kinase inhibitors to enhance the efficacy of both conventional chemotherapy and radiotherapy and increase patient response rates in a variety of settings. [Mol Cancer Ther 2008;7(9):2955–66]

DNA Damage Detection and Repair Pathways—Recent Advances with Inhibitors of Checkpoint Kinases in Cancer Therapy

Insights from cell cycle research have led to the hypothesis that tumors may be selectivity sensitized to DNA-damaging agents, resulting in improved antitumor activity and a wider therapeutic margin. The theory relies primarily on the observation that the majority of tumors are deficient in the G1-DNA damage checkpoint pathway, resulting in reliance on S and G2 phase checkpoints for DNA repair and cell survival. The S and G2 phase checkpoints are predominantly regulated by checkpoint kinase 1; thus, inhibition of checkpoint kinase 1 signaling impairs DNA repair and increases tumor cell death. Normal tissues, however, have a functioning G1 checkpoint signaling pathway that allows for DNA repair and cell survival. There is now a large body of preclinical evidence showing that checkpoint kinase inhibitors do indeed enhance the efficacy of both conventional chemotherapy and radiotherapy, and several agents have recently entered clinical trials. Excitingly, additional therapeutic opportunities for checkpoint kinase inhibitors continue to emerge as biology outside their pivotal role in cell cycle arrest is further elucidated.

Keeping checkpoint kinases in line: new selective inhibitors in clinical trials

Background: Checkpoint kinase 1 (Chk1), a serine/threonine kinase, functions as a regulatory kinase in cell cycle progression and is a critical effector of the DNA-damage response. Inhibitors of Chk1 are known to sensitise tumours to a variety of DNA-damaging agents and increase efficacy in preclinical models. Objective: The most advanced agents are now in Phase I clinical trials; the preclinical profiles of these drugs are compared and contrasted, together with a discussion of some of the opportunities and challenges facing this potentially revolutionary approach to cancer therapy. Methods: A review of the publications and presentations on XL-844, AZD7762 and PF-477736. Results/conclusions: Chk kinases are part of the DNA damage recognition and response pathways and as such represent attractive targets. Agents that target checkpoint kinases have demonstrated impressive evidence preclinically that this approach will provide tumour-specific potentiating agents and may have broad therapeutic utility.

Discovery of Checkpoint Kinase Inhibitor (S)-5-(3-Fluorophenyl)-N-(piperidin-3-yl)-3-ureidothiophene-2-carboxamide (AZD7762) by Structure-Based Design and Optimization of Thiophenecarboxamide Ureas.

Checkpoint kinases CHK1 and CHK2 are activated in response to DNA damage that results in cell cycle arrest, allowing sufficient time for DNA repair. Agents that lead to abrogation of such checkpoints have potential to increase the efficacy of such compounds as chemo- and radiotherapies. Thiophenecarboxamide ureas (TCUs) were identified as inhibitors of CHK1 by high throughput screening. A structure-based approach is described using crystal structures of JNK1 and CHK1 in complex with 1 and 2 and of the CHK1-3b complex. The ribose binding pocket of CHK1 was targeted to generate inhibitors with excellent cellular potency and selectivity over CDK1and IKKβ, key features lacking from the initial compounds. Optimization of 3b resulted in the identification of a regioisomeric 3-TCU lead 12a. Optimization of 12a led to the discovery of the clinical candidate 4 (AZD7762), which strongly potentiates the efficacy of a variety of DNA-damaging agents in preclinical models.

Discovery of a novel class of 2-ureido thiophene carboxamide checkpoint kinase inhibitors.

Checkpoint kinase-1 (Chk1, CHEK1) is a Ser/Thr protein kinase that mediates the cellular response to DNA-damage. A novel class of 2-ureido thiophene carboxamide urea (TCU) Chk1 inhibitors is described. Inhibitors in this chemotype were optimized for cellular potency and selectivity over Cdk1.

Preclinical pharmacokinetic/pharmacodynamic models to predict synergistic effects of co-administered anti-cancer agents

PurposePharmacokinetic/pharmacodynamic (PK/PD) models have been shown to be useful in predicting tumor growth rates in mouse xenografts. We applied novel PK/PD models to the published anticancer combination therapies of tumor growth inhibition to simulate synergistic changes in tumor growth rates. The parameters from the PK/PD model were further used to estimate clinical doses of the combination.MethodsA PK/PD model was built that linked the dosing regimen of a compound to the inhibition of tumor growth in mouse xenograft models. Two subsequent PK/PD models were developed to simulate the published tumor growth profiles of combination treatments. Model I predicts the tumor growth curve assuming that the effect of two anticancer drugs, AZD7762 and irinotecan, is synergistic when given in combination. Model II predicts the tumor growth curve assuming that the effect of co-administering flavopiridol and irinotecan is maximally synergistic when dosed at an optimal interval.ResultsModel I was able to account for the synergistic effects of AZD7762 following the administration of irinotecan. When Model II was applied to the antitumor activity of irinotecan and flavopiridol combination therapy, the modeling was able to reproduce the optimal dosing interval between administrations of the compounds. Furthermore, Model II was able to estimate the biologically active dose of flavopiridol recommended for phase II studies.ConclusionsThe timing of clinical combination therapy doses is often selected empirically. PK/PD models provide a theoretical structure useful in the design of the optimal clinical dose, frequency of administration and the optimal timing of administration between anticancer agents to maximize tumor suppression.

Synthesis and Evaluation of Triazolones as Checkpoint Kinase 1 Inhibitors.

Checkpoint kinase 1 (Chk1, CHEK1) is a Ser/Thr protein kinase that plays a key role in mediating the cellular response to DNA-damage. Synthesis and evaluation of a previously described class of Chk1 inhibitors, triazoloquinolones/triazolones (TZs) is further described herein. Our investigation of structure-activity relationships led to the identification of potent inhibitors 14c, 14h and 16e. Key challenges included modulation of physicochemical properties and pharmacokinetic (PK) parameters to enable compound testing in a Chk1 specific hollow fiber pharmacodynamic model. In this model, 16e was shown to abrogate topotecan-induced cell cycle arrest in a dose dependent manner. The demonstrated activity of TZs in this model in combination with a chemotherapeutic agent as well as radiotherapy validates this series of Chk1 inhibitors. X-ray crystal structures (PDB code: 2YEX and 2YER) for an initial lead and an optimized analog are also presented.

Discovery of a novel class of triazolones as checkpoint kinase inhibitors--hit to lead exploration.

Checkpoint Kinase-1 (Chk1, CHK1, CHEK1) is a Ser/Thr protein kinase that mediates cellular responses to DNA-damage. A novel class of Chk1 inhibitors, triazoloquinolones/triazolones (TZs) was identified by high throughput screening. The optimization of these hits to provide a lead series is described.

Chapter 10 – Checkpoint Kinase and Wee1 Inhibitors as Anticancer Therapeutics

Publisher Summary This chapter discusses the checkpoint kinase and Wee1 inhibitors as anticancer therapeutics. DNA damage triggers recruitment of multi-protein complexes (sensors) that then activate the transducers ATM (ataxia telangiectesia mutated) and ATR (ATM and Rad3 related). It is generally accepted that ATR activation is driven by single-strand breaks (SSBs) formed as a result of stalled replication forks, whereas ATM is the main initiator of response to double-strand breaks (DSBs) resulting from ionizing radiation and other types of DNA damage. These mechanisms (collectively termed the DNA-damage response [DDR]) detect DNA lesions, signal their presence and promote their repair by the initiation of cell cycle arrest, repair processes, or apoptotic responses. The DDR is now recognized to be a comprehensive and complex set of responses aimed at safeguarding the genomic integrity of cells. DNA repair processes lay the foundation of this response with additional networks of monitoring leading to the activation of cell cycle checkpoints or apoptosis.

Strategies towards more effective anticancer therapies: targeting DNA damage response pathways

The last decade has seen a tremendous increase in the understanding of the cellular mechanisms that underlie the detection and repair of DNA damage. This gave rise to the hypothesis that inhibition of DNA repair may result in increased efficacy of existing therapies and, more recently, to the idea that some tumor cells may carry additional defects that make them hypersensitive to DNA repair inhibitors as single agents. In order to minimize the potential to cause lesions in normal tissue, strategies have been directed to specific targets or pathways where selectivity for tumor over normal tissue is possible, thus to date most emphasis has been placed on a relatively small number of targets such as the poly(ADP-ribose) polymerase and the checkpoint kinases. Both of these approaches have yielded small molecule inhibitors that are currently in clinical trials.