Mitochondrial serine/threonine phosphatase, phosphoglycerate mutase 5 (PGAM5) is a novel target to promote abdominal radiotherapy

Pancreatic cancer patients frequently undergo radiotherapy, which carries a significant risk of toxicity to the small bowel and gastrointestinal tissues. Therapeutic outcomes in pancreatic cancer often depend on delivering higher radiation doses, and thus strategies that minimize gastrointestinal toxicity without compromising tumor radiosensitivity would be profoundly beneficial to patients. Radiation induced oxidative stress plays a significant role in radiation induced toxicity in intestinal epithelial cells. However, mitigation of gastrointestinal toxicity requires reduction of oxidative stress and stimulation of epithelial regeneration through activation of WNT/beta-catenin signaling. Mitochondrial serine/threonine phosphatase, phosphoglycerate mutase 5 (PGAM5), is involved in activation of oxidative stress along with inhibition of WNT/beta-catenin signaling. PGAM5, located in the mitochondrial membrane, inhibits nuclear translocation of NRF2 and thereby represses NRF2-dependent antioxidant gene expression. Moreover, PGAM5 induces beta-catenin degradation by dephosphorylating DVL2, a beta-catenin destruction complex . We have observed PGAM5 expression significantly increased in intestinal epithelium in response to irradiation. Pharmacological inhibition of PGAM5 using a novel small molecule-based modulator LFHP-1c (3 mg/kg BW, subcutaneous) at 24 hours post irradiation mitigates gastrointestinal toxicity. Mice exposed to partial body irradiation (PBI) with 2.5% bone marrow shielding (LD100/15) followed by LFHP-1c treatment demonstrated significant improvement of mice survival (90% mice survived beyond 30 day) (p< 0.00002) compared to irradiated control where all the mice died within 14 days. Histopathological analyses demonstrated preservation of crypt-villus structures in the jejunum sections of LFHP-1c-treated mice compared to untreated irradiated mice. LFHP-1c treatment significantly (p<0.005) induced stabilization and nuclear translocation of NRF2, along with increased nuclear localization of beta-catenin, indicating activation of the WNT/beta-catenin signaling pathway in the irradiated intestinal epithelium. LFHP-1c treatment in irradiated organoids from Lgr5/eGFP-IRES-Cre-ERT2; R26-ACTB-tdTomato-EGFP mice intestine demonstrated mitigation of radiation induced toxicity and significant improvement in Lgr5+ve intestinal stem cell survival. In mice model of Pancreatic tumors, LFHP-1c treatment did not compromise the radiosensitivity of Kras positive KPC cells. In conclusion, our studies using mice model of radiation induced genotoxic stress and ex vivo organoid model demonstrated that PGAM5 can be a potential target to promote therapeutic ratio for abdominal radiotherapy.