Microsatellite Instable Cancer Cells Acquire On-target Resistance Mutations to WRN Helicase Inhibitors

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Werner syndrome helicase (WRN) is a key target for microsatellite instability (MSI) cancers, with multiple clinical trials underway.
• Acquired resistance is a major challenge in targeted cancer therapy, especially in mismatch repair deficient (dMMR) tumors with high mutation rates.

Purpose of the Study:

• To characterize resistance mechanisms against WRN inhibitors in MSI cancer models.
• To identify specific mutations conferring resistance and understand their impact on inhibitor binding.

Main Methods:

• Utilized MSI cell lines and xenograft models with the clinical candidate HRO761 and two novel WRN inhibitors.
• Performed whole-exome sequencing to identify resistance mutations.
• Conducted computational structural analyses to assess the impact of mutations on inhibitor engagement.

Main Results:

• Observed rapid in vitro and in vivo emergence of resistance, linked to clustered mutations in the WRN helicase domain.
• Identified mutations that directly impede inhibitor binding or alter protein conformation.
• Discovered specific resistance mutations (L528S, C727R, F730L) showing chemotype selectivity.

Conclusions:

• On-target resistance to WRN inhibitors develops rapidly in dMMR cancers.
• Resistance profiles suggest opportunities for next-generation inhibitor design and combination therapy strategies.
• Findings support the continued development of WRN-targeted therapies for MSI cancers.