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

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.

Rational Design of 5-(4-(Isopropylsulfonyl)phenyl)-3-(3-(4-((methylamino)methyl)phenyl)isoxazol-5-yl)pyrazin-2-amine (VX-970, M6620): Optimization of Intra- and Intermolecular Polar Interactions of a New Ataxia Telangiectasia Mutated and Rad3-Related (ATR) Kinase Inhibitor

The DNA damage response (DDR) is a DNA damage surveillance and repair mechanism that can limit the effectiveness of radiotherapy and DNA-damaging chemotherapy, commonly used treatment modalities in cancer. Two related kinases, ataxia telangiectasia mutated (ATM) and ATM and Rad3-related kinase (ATR), work together as apical proteins in the DDR to maintain genome stability and cell survival in the face of potentially lethal forms of DNA damage. However, compromised ATM signaling is a common characteristic of tumor cells, which places greater reliance on ATR to mediate the DDR. In such circumstances, ATR inhibition has been shown to enhance the toxicity of DNA damaging chemotherapy to many cancer cells in multiple preclinical studies, while healthy tissue with functional ATM can tolerate ATR inhibition. ATR therefore represents a very attractive anticancer target. Herein we describe the discovery of VX-970/M6620, the first ATR inhibitor to enter clinical studies, which is based on a 2-aminopyrazine core first reported by Charrier ( J. Med. Chem. 2011 , 54 , 2320 - 2330 , DOI: 10.1021/jm101488z ).

Abstract 1644: VX-970, the first-in-class inhibitor of the DNA damage repair enzyme ATR

Proficient repair of DNA damage is important for cancer cell survival and is a leading cause for the poor response many patients experience when treated with DNA-damaging drugs or ionizing radiation. The protein kinase ataxia telangiectasia mutated and Rad3 related (ATR) regulates an important DNA damage response pathway that is most commonly activated by replication stress (RS). RS arises during S-phase when the cell's DNA replication machinery attempts to copy through an unresolved damage lesion. Such events are common after cells are treated with DNA-damaging agents. Unresolved RS often leads to double strand breaks, which in turn may cause DNA mutations, chromosomal rearrangements or cell death. Pre-clinical data suggests a reliance on ATR for survival is a common feature in cancer cells. This may occur when there are defects in other DNA damage repair pathways or high levels of background RS.

VX-970 is the first potent (Ki <0.3nM) and highly selective ATR inhibitor to enter clinical trials (EUDRACT: 2012-003126-250). In pre-clinical studies, it markedly increases the cytotoxic activity of multiple DNA damaging agents across large panels of cancer cell lines. In contrast, normal cells tolerate inhibition of ATR by activating compensatory repair signaling for example the pathway mediated by ATM. Defects in this ATM pathway, most notably as a result of mutations in the TP53 gene that encodes p53 (a principle substrate for ATM) is found to be a predictive marker for cell sensitivity in cancer cell lines. In mouse xenograft models VX-970 strongly potentiates the anti-cancer activity of DNA damaging drugs that include cisplatin, carboplatin, irinotecan and gemcitabine. Combinations are generally well tolerated and have been shown to provide better anti-cancer activity than the cytotoxic alone at its MTD. In addition, VX-970 has marked cytotoxic activity when combined with inhibitors of PARP (base excision repair protein) in multiple cancer cell lines, but is well tolerated by normal cells. Emerging data suggests that the cancer cell specificity for this combination may again be associated, at least in part, with defective ATM-p53 pathway signaling. Finally, VX-970 has potential as a monotherapy since potent single agent cytotoxic activity is observed in certain cancer cell lines. The basis for sensitivity to monotherapy may require both defects in alternative repair pathways and high background replication stress levels.

VX-970 is currently in Phase 1 clinical studies as monotherapy and in combination with gemcitabine, cisplatin and carboplatin.

Note: This abstract was not presented at the meeting.

Citation Format: John Pollard, Philip Reaper, Julie Jones, Christopher Barnes, Scott Gladwell, Stuart Hughes, Adele Peak, Hakim Djeha, Amy Hall, David Newsome, Yuxin Wang, Diane Boucher, Brenda Eustace, Yong Gu, Brian Hare, Mac Johnson, Sean Milton, Cheryl Murphy, Darin Takemoto, Crystal Tolman, Mark Wood, Brinley Furey, Marina Penney, Howard Li, Christopher Defranco, Mohammed Asmal, Scott Fields. VX-970, the first-in-class inhibitor of the DNA damage repair enzyme ATR. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1644. doi:10.1158/1538-7445.AM2015-1644

Abstract LB-299: Comprehensive preclinical evaluation of VE-822, the first ATR-targeted drug candidate: a novel approach to transforming the efficacy of DNA damaging agents

DNA damaging agents have been the cornerstone of cancer therapy for decades yet they provide only modest benefit for most patients. For example, standard of care for patients with non-small cell lung cancer (NSCLC) is dominated by the use of platinating drugs and ionizing radiation (IR), however outcome remains very poor with 5-year survival rates of <15% for patients that present with advanced disease. Such poor responses to DNA damaging treatment reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). The DDR detects double strand breaks and replication stress, the most lethal forms of DNA damage, and acts to enforce checkpoints to halt cell cycle progression, and to stimulate repair. Key regulators of the DDR are the phosphoinositol 3-kinase-like serine/threonine protein kinase (PIKK) family members ATR and ATM. Recent pre-clinical data has suggested that a reliance on ATR for survival from DNA damage may be a common feature of cancer. This can arise either as a consequence of high replicative stress, for example from expression of certain oncogenes, from a hypoxic microenvironment, or from defects elsewhere in DNA damage surveillance and repair pathways. Most notably inhibition of ATR has been shown to be synthetic lethal with loss of the ATM-p53 pathway. In NSCLC defective ATM signaling, from loss of ATM expression or from defects in p53 has been reported in about 50% of tumors. Here we describe the comprehensive in vitro and in vivo profile for VE-822 a novel highly potent and selective inhibitor of ATR.

VE-822 potently inhibits ATR in biochemical assays with Ki <0.3nM and in cell assays with IC50 of 20nM. Against a large panel of NSCLC lines, low concentrations of VE-822 sensitized many lines to the cytotoxic effects of multiple DNA damaging agents; for example >90% of lines showed >3-fold shifts in IC50 for cisplatin in the presence of VE-822, with ~50% of lines showing >10-fold increases in cisplatin cytotoxicity. In contrast normal cells tolerate inhibition of ATR. In a panel of mouse xenograft models, derived from various primary human NSCLC tumor tissues, oral or IV administration of VE-822 strongly sensitized tumors to cisplatin treatment. In many cases, combinations including VE-822 led to tumor regression or extensive tumor growth delay. Inhibition of ATR activity and accumulation of DNA damage by VE-822 was observed coincident with efficacy. When administered alone or in combination with cisplatin VE-822 was well tolerated in mice at doses that block ATR activity.

These data support the potential for ATR inhibitors to substantially increase the efficacy of standard-of-care agents in diseases such as NSCLC.

Citation Format: Diane Boucher, Peter Charlton, Jean-Damien Charrier, Brinley Furey, Yong Gu, Amy Hall, Brian Hare, Howard Li, Sean Milton, Cheryl Murphy, Philip Reaper, Darin Takemoto, Taturo Udagawa, Yuxin Wang, Mark Wood, John Pollard. Comprehensive preclinical evaluation of VE-822, the first ATR-targeted drug candidate: a novel approach to transforming the efficacy of DNA damaging agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-299. doi:10.1158/1538-7445.AM2013-LB-299

Abstract 5501: Evaluation of the first potent and highly selective inhibitor of ATR kinase: An approach to selectively sensitize cancer cells to ionizing radiation and hypoxia

DNA damaging agents, such as ionizing radiation (IR), have provided a basis for the treatment of solid tumors for decades, yet they provide only modest benefit for most patients. This reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). The ATR, ATM and DNA-PK phosphoinositol 3-kinase-like serine/threonine protein kinases (PIKKs) are the key regulators of the DDR to IR-induced double-strand DNA breaks. This acts to detect the DNA lesions, enforce checkpoints to arrest cell cycle progression, and stimulate repair. Various components of the DDR have been shown to be commonly defective in cancer cells. These cells are widely hypothesized to become dependent on their remaining DDR pathways for survival from DNA damage. The tumor microenvironment has been reported to induce a DDR and in particular, ATR-mediated signaling in response to severe hypoxia.

While inhibitors of a number of DDR enzymes, including ATM, DNA-PK, Chk1 and PARP, have been reported, there have been no reports of drug-like ATR inhibitors. Using the first potent and selective ATR inhibitor (VE-821), we now characterize the effects of ATR inhibition on the cellular response to IR and hypoxia. VE-821 sensitizes many cancer cell lines to IR in both clonogenic and short-term (MTS) assays. For example, VE-821 reduced the surviving fraction of MiaPaca-2 cells treated with 6 Gy IR by 3-fold. Consistent with this, ATR inhibition ablated both RAD51 focus formation and phosphorylation of Chk1 (but not Chk2) after IR treatment, delayed the IR-induced G2/M arrest analyzed by flow cytometry and slowed down DNA replication rates measured using DNA fiber technology. Furthermore, we provide evidence that a basis for the sensitization of cancer cell lines to IR with VE-821 is a synthetic lethal interaction between loss of ATM signaling (a frequent event in cancer resulting from loss of function of proteins such as ATM or p53) and ATR inhibition when cells are treated with IR. In keeping with these results, normal cells (with functional ATM) do not appear sensitized to IR by ATR inhibition. In this case a compensatory DDR is activated, which in turn leads to checkpoint arrest and a strong survival response. Importantly, ATR inhibition also sensitized cancer cells to IR under hypoxic conditions, and to anoxia alone.

These studies show for the first time that a selective ATR inhibitor can preferentially sensitize cancer cells to ionizing radiation under both normoxic and hypoxic conditions and exploit a synthetic lethal interaction between ATM and ATR signaling. This underpins the broad potential of ATR inhibition as a highly promising new strategy to improve the efficacy of DNA damaging therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5501. doi:10.1158/1538-7445.AM2011-5501

Abstract 5491: Evaluation of the first potent and highly selective inhibitor of ATR kinase: An approach to selectively sensitize cancer cells to genotoxic drugs

DNA damaging agents have been the cornerstone of solid cancer therapy for decades yet they provide only modest benefit for patients with many tumor types. This reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). Key regulators of the DDR are the phosphoinositol 3-kinase-like serine/threonine protein kinase (PIKK) family members ATR, ATM and DNA-PK. The DDR acts to detect DNA lesions, enforce checkpoints to halt cell cycle progression, and stimulate repair. Recent data have shown that elements of the DDR are commonly defective in cancer cells. It is widely believed that these cells become dependent on the remaining DDR pathways for survival from DNA damage. Inhibitors have been reported for a number of DDR enzymes, including ATM, DNA-PK, CHK1 and PARP, however there are no reports of drug-like ATR inhibitors.

Here we disclose the in vitro characterization of a potent and highly selective ATR inhibitor (VE-821). This compound selectively blocks ATR signaling in cells (IC50 = 0.7 µM), but has little impact on ATM or DNA-PK signaling (IC50 >10 µM). Treatment with 10 µM VE-821 for 144 h causes little cell death in normal cell lines (5-11 %) but markedly higher death in cancer cell lines (28-46 %). VE-821 also dramatically sensitizes many cancer cells to multiple classes of genotoxic agents including antimetabolites, topoisomerase inhibitors and crosslinking agents; with over 10-fold increases genotoxic potency observed in some cases. In a panel of 36 lung cancer cell lines, VE-821 sensitized the cytotoxic effect of cisplatin to a far greater magnitude and over a broader subset of these lines than potent inhibitors of ATM, Chk1, or PARP. In over half of these cell lines, the IC50 of cisplatin was reduced by greater than 5 fold upon the addition of VE-821.

We show that a basis for the cancer-selective effects of VE-821 is a synthetic lethal interaction between loss of ATM signaling (a frequent event in cancer resulting from loss of function of proteins such as ATM or p53) and ATR inhibition when cells encounter DNA damage. In keeping with this, ATR inhibition does not sensitize normal cells (with functional ATM) to the cytotoxic effects of genotoxic therapy. In this case a compensatory DDR is activated that is associated with marked activation of ATM, which in turn leads to reversible checkpoint arrest and a strong survival response.

These studies show for the first time that a selective ATR inhibitor can preferentially sensitize cancer cells to genotoxic drugs by exploiting a synthetic lethal interaction between ATM and ATR signaling. This underpins the broad potential of ATR inhibition as a highly promising new strategy to improve the efficacy of genotoxic therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5491. doi:10.1158/1538-7445.AM2011-5491