Osalmid inhibits lung adenocarcinoma progression and enhances EGFR-TKI responses: a preclinical and translational study

Background: Therapeutic resistance to current treatment strategies indicates the need for more effective agents to treat lung adenocarcinoma (LUAD). RRM2 dysregulation has been implicated in LUAD progression and therapeutic resistance. However, whether pharmacological inhibition of ribonucleotide reductase regulatory subunit M2 (RRM2) by osalmid may suppress LUAD growth and enhance epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) responses remains unclear. We sought to explore the antitumor effects of osalmid and investigate potential combinatorial approaches with third-generation EGFR-TKIs to treat LUAD patients with EGFR mutations.

Methods: Patient data were used to analyze survival based on RRM2 expression. In vitro and in vivo experiments explored the antitumor effects of AZD9291 (Osimertinib), osalmid, and AST2818 (Alflutinib) as single agents and in combination. The combination index (CI) was conducted to assess the synergy effect of two drugs. Ferroptosis-related data obtained via CRISPR screens and western blotting were used to explore the relationships between RRM2 and ferroptosis suppressor genes (GPX4 and SLC7A11). Immunohistochemical analysis of 4-hydroxynonenal (4-HNE) was conducted to evaluate lipid peroxidation in tumor tissues after treatment with osalmid.

Results: Patients with high RRM2 expression had poorer survival than patients with low RRM2 expression (P<0.001). RRM2 knockdown or osalmid treatment decreased the proliferation and colony formation of LUAD cell lines. When AST2818 and osalmid were combined, the half-maximal inhibitory concentration (IC₅₀) values of AST2818 and AZD9291 were significantly decreased. CI values of AST2818 and osalmid ranged 0.22 to 0.82. EGFR-TKI exposure reduced RRM2 expression, although partial RRM2 rebound was observed under prolonged AST2818 treatment, suggesting potential adaptive regulation. In vivo, AST2818 plus osalmid achieved a higher tumor-suppression rate than AST2818 monotherapy in NCI-H1975 xenografts (89% vs. 70%, P<0.001).

Conclusions: Our findings suggest that osalmid exerts antitumor activity in LUAD and may enhance EGFR-TKI responses, particularly in EGFR-mutant or RRM2-dependent contexts. Further validation in biomarker-selected models is warranted.