Developing a Multimodal miR-15a Mimic to Overcome PARP Inhibitor Resistance in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is characterized by high relapse rates and the development of drug resistance, driven by adaptive DNA repair and survival pathways. Here, we develop a multimodal, chemically engineered miRNA therapeutic, MTX-5-FU-Gem-miR-15a, that integrates tumor-suppressive miR-15a activity with chemotherapeutic modifications and tumor-targeting capability. This modified miRNA exhibits potent nanomolar activity across diverse EOC models, including PARP inhibitor-resistant cells, without requiring delivery vehicles. Mechanistically, MTX-5-FU-Gem-miR-15a induces replication stress while suppressing G2/M checkpoint regulators (WEE1 and CHK1), resulting in genomic instability and apoptotic cell death. Transcriptomic and protein-level analyses revealed coordinated suppression of resistance-associated and oncogenic signaling pathways, alongside activation of DNA damage coupled with checkpoint abrogation and potential innate immune response. MTX-5-FU-Gem-miR-15a also demonstrates strong synergy with olaparib and robust antitumor efficacy in vivo. These findings establish a multimodal miRNA-based therapeutic strategy that targets replication stress and checkpoint dependency to overcome PARPi resistance in ovarian cancer.