Abstract 369: Antitumor activity of M4344, a potent and selective ATR inhibitor, in monotherapy and combination therapy

Abstract

The protein kinase ataxia telangiectasia mutated and Rad3-related ATR is one of the key mediators of the DNA damage response. ATR is recruited to regions of single-stranded DNA, which most commonly arise during replication stress (RS). RS occurs during S-phase when the cell’s DNA replication machinery encounters problems such as unresolved DNA lesions. In addition, treatment of cells with DNA-damaging agents can lead to RS as cells progress to S-phase without resolving damage incurred by such agents. Elevated levels of RS are evident in some cancer cells, even in the absence of a DNA-damaging agent resulting from expression of oncogenes that drive dysregulated replication, a hypoxic environment, or from defects in other repair pathways. RS in cancer cells can drive reliance on ATR for survival and, accordingly, ATR inhibitors may have benefit as monotherapy. M4344 was determined to be an adenosine triphosphate (ATP)-competitive, highly potent, and tight-binding inhibitor of ATR with a Ki of < 150 pM. Minimal inhibitory activity was observed against a large panel of unrelated protein kinases, with 308 of 312 kinases tested having a measured Ki corresponding to more than 100-fold selectivity. M4344 potently inhibits ATR-driven phosphorylated checkpoint kinase-1 (P-Chk1) phosphorylation with an IC50 of 8 nM. Profiling on a selected set of cancer cell lines showed synergy with several types of DNA damaging chemotherapeutics as well as PARP1/2 and CHK1 inhibitors. In monotherapy efficacy studies M4344 showed tumor stasis to regression in tumor models with alternative lengthening of telomeres (ALT). In combination with PARP inhibitors, tumor regression could be observed in triple-negative breast cancer xenograft models. A dose-escalation phase 1 study in patients with advanced solid tumors is currently ongoing. Citation Format: Frank T. Zenke, Astrid Zimmermann, Heike Dahmen, Brian Elenbaas, John Pollard, Philip Reaper, S Bagrodia, M E. Spilker, C Amendt, Andree Blaukat. Antitumor activity of M4344, a potent and selective ATR inhibitor, in monotherapy and combination therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 369.

RP-3500: A Novel, Potent, and Selective ATR Inhibitor that is Effective in Preclinical Models as a Monotherapy and in Combination with PARP Inhibitors

“…In this first disclosure, we show that RP-3500 is a highly potent and selective ATRi in biochemical and cell-based assays with a preclinical pharmacology profile that justifies clinical evaluation. In cell assays, RP-3500 inhibits ATR with an IC 50 of 0.33 nM, and is 30-fold selective over mTOR and >2,000-fold selective over other PIKK family members including ATM, DNA-PK, and the related kinase PI3K, showing that RP-3500 is among the most potent ( 9) and selective published ATRi (5,10,(40)(41)(42). RP-3500 is orally bioavailable in vivo with compelling efficacy when administered daily as a single agent in the LoVo model with an MED of 7 mg/kg QD compared with the published MED for AZD6738 of 25 mg/kg QD in the same model (5).…”

Progress towards a clinically-successful ATR inhibitor for cancer therapy

“…M4344, formerly known as VX-803, is another orally bioactive ATR inhibitor which was originally developed by Vertex pharmaceuticals but has now been acquired by Merck KGaA, Germany (in addition to M6620) for further development. M4344 is by far the most potent ATR inhibitor reported, strongly inhibiting ATR activity both in cell free assays (ATR IC 50 ​= ​0.15 ​nM) and in cellular assays (ATR IC 50 ​= ​8 ​nM), with over 100-fold selectivity against a panel of 308 kinases, including ATR homologs and PI3K kinases ( Zenke et al., 2019 ). Preclinical data for M4344 has not been extensively reported ( Zenke et al., 2019 ), but M4334 was reported to exhibit synergy with several DNA-damaging chemotherapeutics, PARP and CHK1 inhibitors in a panel of 92 cancer cell lines, and has also demonstrated tumour regression in tumour models in vivo .…”

“…M4344 is by far the most potent ATR inhibitor reported, strongly inhibiting ATR activity both in cell free assays (ATR IC 50 ​= ​0.15 ​nM) and in cellular assays (ATR IC 50 ​= ​8 ​nM), with over 100-fold selectivity against a panel of 308 kinases, including ATR homologs and PI3K kinases ( Zenke et al., 2019 ). Preclinical data for M4344 has not been extensively reported ( Zenke et al., 2019 ), but M4334 was reported to exhibit synergy with several DNA-damaging chemotherapeutics, PARP and CHK1 inhibitors in a panel of 92 cancer cell lines, and has also demonstrated tumour regression in tumour models in vivo . While M4344 has entered two phase I clinical trials as a monotherapy or in combination with carboplatin and cisplatin for advanced solid tumours (NCT02278250), and in combination with niraparib (a PARP inhibitor) against PARP-resistant recurrent ovarian cancer (NCT04149145), at the time of writing, no clinical data has been reported.…”

“…Interestingly, despite the mTOR inhibition observed at sub-micromolar concentrations (IC 50 ​= ​35 ​nM), it was observed to inhibit the PI3K/AKT/mTOR pathway with over 60-fold selectivity compared to its ATR inhibition. However, despite some level of ATR selectivity reported with BAY1895344, it is the least potent and least selective of the ATR inhibitors currently being evaluated in clinical trials (the other drugs being M6620, AZD6738, and M4334) ( Fokas et al., 2012 ; Foote et al., 2018 ; Zenke et al., 2019 ).…”

Clinical Candidates Targeting the ATR–CHK1–WEE1 Axis in Cancer

“…There are currently four candidates in clinical trials acting as ATR-kinase inhibitors ( Table 1 ). Two of them were developed by Vertex Pharmaceuticals, Inc., but are presently under maintenance of Merck KGaA (berzosertib and M4344); AstraZeneca PLC and Bayer AG operate with ceralasertib and BAY1895344, respectively [ 112 , 113 , 114 , 115 ]. Of these, berzosertib and ceralasertib are the most studied candidates, paving the way for others [ 116 , 117 ].…”