Abstract 2901: Targeting <i>miR-19b</i>/PPP2R5E regulatory axis to enhance alkylating agent efficacy: a new avenue to counteract temozolomide resistance in recurrent glioblastomas

Abstract Glioblastoma (GBM), the most aggressive primary brain tumor, notorious for its inevitable recurrence despite standard of care, presents a pressing need for novel treatment paradigms. Temozolomide (TMZ), a frontline DNA alkylating agent, induces extensive DNA damage. However, TMZ response is counteracted by intricate or acquired survival mechanisms. Through functional TMZ-resistance screens using microRNAs, we uncovered a novel mechanism involving the miR-19b target, PPP2R5E, a subunit of PP2A serine-threonine phosphatase, in TMZ response. Specifically, the induced expression of PPP2R5E, resulting from miR-19b attenuation, triggers genotoxic stress, priming GBM cell lines and primary GBM cells for heightened TMZ cytotoxicity. Elevated DNA damage in PPP2R5E-overexpressing cells is attributed to increased nuclear and mitochondrial ROS production, which is accompanied by enhanced ROS-mediated senescence and ferroptosis. Of note, all these phenotypes are reversed in GBM cells with concomitant miR-19b and PPP2R5E attenuation, indicating that miR-19b exerts its role in TMZ resistance by targeting PPP2R5E. In line with this finding, our orthotopic human-derived GBM stem cell xenograft model confirmed that PPP2R5E attenuation not only decreases TMZ cytotoxicity in the brain, but also at the spinal metastatic location. Consistently, treating cells with the PP2A-activating drug FTY720 or knocking down endogenous PP2A-inhibiting proteins mirrors the effects of miR-19b attenuation in enhancing TMZ cytotoxicity. This intricate interplay between miR-19b and PPP2R5E underscores a novel strategy to modulate the TMZ response, highlighting promising results in our pre-clinical models. Intriguingly, PP2A inhibiting proteins CIP2A and ANP32A (PHAP1) are upregulated in TMZ-resistant GBM cells and recurrent GBM tumors following TMZ treatment, suggesting a role of the PPP2R5E axis in TMZ resistance. In conclusion, our findings advocate for the therapeutic targeting of the miR-19b/PPP2R5E axis as a promising strategy to overcome TMZ resistance in GBM, indicating a potential novel strategy in the pursuit of effective therapeutic interventions for the formidable recurrent GBM tumors. Citation Format: Erik Vassella, Elham Kashani. Targeting miR-19b/PPP2R5E regulatory axis to enhance alkylating agent efficacy: a new avenue to counteract temozolomide resistance in recurrent glioblastomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2901.