Targeting a miRNA–mRNA Regulatory Network to Overcome Radioresistance in Head and Neck Cancer: Identification of I-OMe-AG-538 via Transcriptome-Guided Drug Repurposing

Radioresistance is a major obstacle to successful radiotherapy in head and neck cancer (HNC), leading to treatment failure, recurrence, and poor patient outcomes. MicroRNAs (miRNAs) are key post-transcriptional regulators implicated in radiosensitivity, but comprehensive miRNA–mRNA networks driving radioresistance in HNC remain poorly defined. Here, we established isogenic radioresistant (RR) sublines from OECM1 and Detroit HNC cells through long-term fractionated irradiation and performed global miRNA profiling to identify a consistent 25-miRNA signature (12 upregulated oncogenic miRNAs [OncomiRs] and 13 downregulated tumor-suppressive miRNAs [TSmiRs]) associated with radioresistance. Integrative target prediction, pathway enrichment, and network construction revealed that these miRNAs converge on oncogenic modules including receptor tyrosine kinase (RTK) signaling, cell motility, and stress/cancer stemness pathways, with central hubs such as EGFR, IGF1R, and MYC. The refined miRNA–mRNA network (68 interaction pairs) highlighted key regulatory miRNAs (e.g., miR-199b-5p, miR-522-3p), whose ectopic overexpression significantly enhanced radiosensitivity in HNC cells. Transcriptome-guided drug repurposing via the Connectivity Map platform prioritized I-OMe-AG-538, an IGF1R inhibitor (τ = –87), as the top candidate radiosensitizer. Validation showed that I-OMe-AG-538 dose-dependently suppressed IGF1R and Erk phosphorylation, reprogrammed the RR miRNA profile by downregulating OncomiRs and upregulating TSmiRs, elevated intracellular ROS levels, and synergistically increased radiosensitivity in clonogenic assays. TCGA-HNSC analysis confirmed that high IGF1R expression correlates with poor prognosis and upregulation of ROS-scavenging genes. These findings delineate a coordinated miRNA–mRNA regulatory network underlying radioresistance in HNC and identify I-OMe-AG-538 as a promising radiosensitizer that disrupts oncogenic signaling and redox homeostasis through inhibiting IGF1R and miRNAs, offering a potential strategy to enhance radiotherapy efficacy in refractory HNC.