Abstract 5921: PH027-1, a potent and selective small-molecule WRN inhibitor that targets MSI-H tumors
Authors: Gao Feng , Liu Bin , Jing Liandong , Wang Jing , Wu Yongyong , Wan Jun , Zhang Pengzhi , Gao Yu , Li Zhizhong , Guo Yongqi 
Published: March 2024

Abstract
Background: High microsatellite instability (MSI-H) is highly prevalent across many cancer types including endometrium, gastric, ovary and colorectal cancer. It is well known that there is a clear synthetic lethality (SL) interaction between MSI-H and Werner syndrome protein (WRN) inhibition. WRN is a member of RecQ helicase family and involved in the maintenance of genome integrity. Different from other RecQ family members, WRN has two activity centers responsible for helicase and exonuclease activity, respectively. Further studies confirmed that an inhibition on helicase activity, but not exonuclease activity, is responsible for SL interaction with MSI-H. Also, Recent clinical observations supported that though loss-of-function of WRN could cause an early-aged disease Werner syndrome, selective loss of helicase but not exonuclease leads to only mild to moderate symptoms, suggesting a selective inhibitor of helicase activity has the potential to induce the SL interaction with MSI-H and keep patients safe.
Methods: Biochemical assays and cell-based assays were performed to evaluate in vitro activity and selectivity of PH027-1. The in vivo anti-tumor efficacy was tested in two cell-derived xenograft (CDX) mouse models with tumors harboring MSI-H. The in vivo pharmacokinetics (PK) properties were evaluated in mice, rats and dogs, and other in vitro and in vivo PK and safety properties were assessed with corresponding assay methods.
Results: Biochemical assays showed that PH027-1 potently inhibited helicase activity of WRN (IC50, 0.8 nM), but had no effect on other RecQ family members even at the highest tested concentration of 10 μM (IC50, all≥10 μM for BLM, RecQ4 and RecQ5). At the same time, PH027-1 did not affect the exonuclease activity of WRN at all tested concentrations. In cell-based assays, PH027-1 potently inhibited cell viability of MSI-H cancer cells SW48 and HCT116 at tens of nM, but had no effect on MSS cells (HT29 cancer cells and CD34+ hematopoietic stem cells) even at 10 μM. The tests were further expanded to 18 cancer cell lines covering uterus, gastric, ovary and colorectal cancer. Nine of twelve MSI-H cell lines were very sensitive to WRN inhibition, and all six MSS cell lines were totally resistant to the treatment. PH027-1 possessed excellent PK profiles as shown by in vivo PK studies, with absolute bioavailability of 58%~102% in mice, rats and dogs. In two CDX models (SW48 and HCT116), oral administration of PH027-1 dose-dependently inhibited tumor growth, and a nearly complete inhibition was observed at a dose of 20 mg/kg QD. Tumor regression was clearly shown at higher doses. All other in vitro and in vivo PK and safety tests showed favorable results and supported for preclinical development of PH027-1.
Conclusion: As a highly selective and potent inhibitor on helicase activity of WRN, PH027-1 has the potential to become a novel and safe approach for treatment of MSI-H tumors.
Citation Format: Feng Gao, Bin Liu, Liandong Jing, Jing Wang, Yongyong Wu, Jun Wan, Pengzhi Zhang, Yu Gao, Zhizhong Li, Yongqi Guo. PH027-1, a potent and selective small-molecule WRN inhibitor that targets MSI-H 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 5921.