Abstract 983: Identification of potent, highly selective and orally available ATR inhibitor BAY 1895344 with favorable PK properties and promising efficacy in monotherapy and combination in preclinical tumor models

The integrity of the genome of eukaryotic cells is secured by complex signaling pathways, known as DNA damage response (DDR). Recognition of DNA damage activates DDR pathways resulting in cell cycle arrest, suppression of general translation, induction of DNA repair, cell survival or even cell death. Proteins that directly recognize aberrant DNA structures recruit and activate kinases of the DDR pathway, such as ATR (ataxia telangiectasia and Rad3-related). ATR responds to a broad spectrum of DNA damage, including double-strand breaks (DSB) and lesions derived from interference with DNA replication as well as increased replication stress (e.g. in oncogene-driven tumor cells). Therefore, inhibition of ATR kinase activity could be the basis for a novel anti-cancer therapy in tumors with increased DNA damage, deficiency in DNA damage repair or replication stress. Herein we report the identification of the potent, highly selective and orally available ATR inhibitor BAY 1895344 by a collaborative effort involving medicinal chemistry, pharmacology, DMPK and computational chemistry. The chemical structures of lead compound BAY-937 and clinical candidate BAY 1895344 as well as the main SAR trends within this novel class of naphthyridine derivatives will be disclosed for the first time. The novel lead compound BAY-937 revealed promising inhibition of ATR (IC50 = 78 nM) and high kinase selectivity in vitro. In cellular mechanistic assays BAY-937 inhibited hydroxyurea-induced H2AX phosphorylation (IC50 = 380 nM) demonstrating the anticipated mode of action. Moreover, BAY-937 was shown to inhibit proliferation of a variety of tumor cell lines with low- to sub-micromolar IC50 values. In initial xenograft studies, BAY-937 revealed moderate activity in monotherapy and in combination with cis-platin. However, BAY-937 also revealed low aqueous solubility, low bioavailability (rat) and activity in the hERG patch clamp assay. Extensive lead optimization efforts led to the identification of the novel, orally available ATR inhibitor BAY 1895344. In vitro, BAY 1895344 was shown to be a very potent and highly selective ATR inhibitor (IC50 = 7 nM), which potently inhibits proliferation of a broad spectrum of human tumor cell lines (median IC50 = 78 nM). In cellular mechanistic assays BAY 1895344 potently inhibited hydroxyurea-induced H2AX phosphorylation (IC50 = 36 nM). Moreover, BAY 1895344 revealed significantly improved aqueous solubility, bioavailability across species and no activity in the hERG patch-clamp assay. BAY 1895344 also demonstrated very promising efficacy in monotherapy in DNA damage deficient tumor models as well as combination treatment with DNA damage inducing therapies. The start of clinical investigation of BAY 1895344 is planned for early 2017. Citation Format: Ulrich T. Luecking, Julien Lefranc, Antje Wengner, Lars Wortmann, Hans Schick, Hans Briem, Gerhard Siemeister, Philip Lienau, Christoph Schatz, Benjamin Bader, Gesa Deeg, Franz von Nussbaum, Michael Brands, Dominik Mumberg, Karl Ziegelbauer. Identification of potent, highly selective and orally available ATR inhibitor BAY 1895344 with favorable PK properties and promising efficacy in monotherapy and combination in preclinical tumor models [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 983. doi:10.1158/1538-7445.AM2017-983