Abstract 4532: Discovery of DAT-1000A, a potent Polθ inhibitor that significantly enhances anti-tumor efficacy in combination with PARP inhibitor in homologous-recombination-deficient tumors

Cancers exhibiting homologous recombination (HR) repair deficiencies due to mutations in genes like BRCA1 or BRCA2 rely on alternative DNA damage response (DDR) pathways to uphold genomic integrity. This vulnerability allows for the targeted disruption of these pathways through synthetic lethality approaches. DNA polymerase theta (Polθ, encoded by POLQ) assumes a crucial role in mending DNA double-strand breaks (DSB) via microhomology-mediated end-joining (MMEJ), one of the principal pathways for repairing DNA DSB. Notably, Polθ expression is minimal in normal tissues but becomes upregulated in HR-deficient cancer cells, positioning Polθ as a prime target for synthetic lethality in HRD cancers. Reversion mutations in HR-related genes frequently employ micro-homology deletion mechanisms. Consequently, the inhibition of Polθ holds the potential to thwart the emergence of PARPi resistance, primarily driven by BRCA reversion mutations. In this context, we introduce DAT-1000A, a novel small-molecule Polθ inhibitor exhibiting potent activity with a single-digital nanomolar IC50 value. Its efficacy in MMEJ functional assays validates its on-target cellular activity. Assessments of cell viability in HR-deficient BRCA2-KO DLD-1 cells, compared to their parental counterparts, reveal a striking synthetic lethality window exceeding 500-fold. Additionally, DAT-1000A displays synergistic anti-proliferative effects when combined with PARP inhibitors in BRCA1/2-mutated cells. In BRCA1/2-mutated xenograft models, DAT-1000A demonstrates robust and sustained tumor regression, as evidenced by the level of γH2AX, a common marker for double-strand breaks, which closely correlates with anti-tumor efficacy. Importantly, high-dose DAT-1000A treatment in mice elicits no significant abnormalities, underscoring its excellent tolerability. Collectively, DAT-1000A emerges as a novel Polθ inhibitor, offering both potent activity and a favorable safety profile, and holds promise for advancing therapeutic options in the realm of HRD cancer treatment.

Citation Format: Jingxi Zhang, Huixian Chen, Kevin Zhou. Discovery of DAT-1000A, a potent Polθ inhibitor that significantly enhances anti-tumor efficacy in combination with PARP inhibitor in homologous-recombination-deficient tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4532.

Abstract 1755: Discovery of a novel, selective WRN inhibitor, DAT-5000A, in the treatment of microsatellite-unstable tumors

Werner syndrome ATP-dependent helicase (WRN) is a member of RecQ helicase involved in DNA replication and repair and is identified as a synthetic lethal target in microsatellite instability-high (MSI-H) tumors. MSI-H feature has been found in a variety of tumor types including colorectal, gastric and endometrial cancers. The clinical benefits of immune checkpoint inhibitor (ICI) such as anti-PD-1 or anti-PD-L1 antibodies on MSI-H cancers have been well documented; however, nearly 20-50% of these cancer patients are intrinsically resistant to PD-(L)1 therapies or develop acquired resistance with prolonged treatment. Thus, agents targeting MSI-H tumors are of great interest. Here we described the discovery of a novel non-covalent WRN inhibitor, DAT-5000A, with excellent potency and PK profile. DAT-5000A potently inhibited WRN in vitro activity both on ATPase and unwinding assays and showed good selectivity over BLM, another member of RecQ helicase. DAT-5000A also showed selective killing of MSI-H SW48 but not MSS (microsatellite stability) SW620 tumor cell line. In addition, DAT-5000A demonstrated good drug-like properties including high cell permeability and microsomal metabolic stability, as well as favorable PK profile with low in vivo clearance and optimal oral bioavailability, across multiple species. DAT-5000A exhibited single-agent activity with tumor regression on MSI-H cell-line derived xenograft (CDX) tumor models, meanwhile DAT-5000A did not cause any abnormality on these mice. Our data demonstrated that DAT5000A is a potent, selective WRN inhibitor with sufficient in vivo exposure and acceptable preliminary safety profile, which supports DAT-5000A to be further evaluated in human clinical trials.

Citation Format:

Jingxi Zhang, Huixian Chen, Xi Chen,Kevin Zhou. Discovery of a novel, selective WRN inhibitor, DAT-5000A, in the treatment of microsatellite-unstable tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1755.