Abstract 4534: HSK40495, a highly selective PARP1 inhibitor with improved hematopoietic safety for the treatment of HRD cancers

Abstract It is well known that several PARP inhibitors have been approved for tumors with homologous recombination repair deficiencies (HRD), such as BRCA mutations. However, the common side effect of these inhibitors is hematologic toxicity, which limits their therapeutic index and combination potential with first-line chemotherapies. One possible reason is that currently approved PARP inhibitors do not specifically target PARP1, and might also affect other PARP family members. Recent studies have shown that the synthetic lethality caused by PARP trapping with HRD is mainly dependent on PARP1 inhibition, but not other PARP family members. Accordingly, we developed a selective PARP1 inhibitor that effectively inhibits tumor growth with less hematologic toxicity. HSK40495 is a potent PARP1 inhibitor with highly selectivity of PARP2. HSK40495 inhibited PARP1 enzymatic activity with a single digit nanomolar potency and with greater than 5000-fold selectivity against PARP2 in the protein binding assay. In addition, HSK40495 exhibited potent anti-proliferation activity in both DLD1(BRCA KO) cell and MDA-MB-436 cell, while had minimal effects against BRCA-WT DLD1 cell up to 30 µM in an anti-proliferation assay. In a subcutaneous MDA-MB-436 xenograft tumor model, HSK40495 administered orally once daily achieved excellent tumor growth inhibition of 100% at 3mg/kg. HSK40495 demonstrated significant PARylation inhibition in tumor tissues. Importantly, in CD34+ human bone marrow progenitor cell, HSK40495 showed improved cytotoxicity when compare to first-generation PARP inhibitor, Talazoparib. Meanwhile, in a lineage-specific hematotoxicity assay, HSK40495 exhibited improved cytotoxic safety in the process of differentiation of myeloid, erythroid and megakaryocyte compared with Talazoparib treatment. In summary, HSK40495, a highly selective PARP1inhibitor over other PARP family members, exhibits excellent pharmacological and safety properties, and also has the favorable pharmacokinetics profile in preclinical studies. All these findings suggest that HSK40495 has the great potential to be a promising PARP1 inhibitor for further development in the patients with HRD tumors. Citation Format: Fan Li, Xiaoli Gou, Lei Chen, Qingyuan Meng, Yao Li, Hongjiao Dong, Pingming Tang, Ju Wang, Pangke Yan. HSK40495, a highly selective PARP1 inhibitor with improved hematopoietic safety for the treatment of HRD cancers [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 4534.