Resistance to FLT3 inhibitors involves different molecular mechanisms and reduces new DNA synthesis

Acute myeloid leukemia (AML) is a challenging hematologic malignancy, frequently characterized by mutations in the FLT3 gene. While patients often respond initially to FLT3 inhibitors, the emergence of drug resistance remains a significant barrier to long-term therapeutic success. To investigate the mechanisms underlying resistance, we developed four AML cell lines resistant to the FLT3 inhibitors gilteritinib or FF-10101, and examined the molecular changes associated with resistance. Additionally, we evaluated the efficacy of a novel inhibitor, Chen-9u, in suppressing cell proliferation.

Each resistant cell line exhibited a distinct resistance mechanism. Common features included reduced FLT3 signaling, enhanced NRAS pathway activity, and diminished DNA synthesis linked to decreased CDK4 activity. Specific resistance mutations were identified: FLT3 C695F and N701K, a novel NRAS G12C mutation, and a possible role for a MYCN mutation in one cell line.

Importantly, Chen-9u effectively inhibited cell growth across all resistant lines, and no resistant clones emerged following prolonged treatment, suggesting a robust barrier to resistance development.

These findings underscore both the adaptability of AML cells in acquiring resistance through diverse mechanisms—even against structurally and mechanistically distinct inhibitors—and the potential of targeting vulnerabilities such as impaired DNA synthesis. Moreover, the resistant cell models described here offer valuable tools for further dissecting the pathways involved in inherent and acquired drug resistance in AML.