HILPDA Confers Radiotherapy Resistance In Nasopharyngeal Carcinoma By Promoting Cardiolipin-dependent Mitophagy

Background: Radiotherapy resistance is a major cause for treatment failure in nasopharyngeal carcinoma(NPC),leading to tumor recurrence or metastasis.According to previous research,abnormal metabolic status is a typical phenotype of malignancies,and greatly contributed to tumor progression and resistance to anti-cancer therapies.Therefore,in this study,we aim to explore whether and how aberrant lipid metabolism in tumor cells is involved in the development of radio-resistance and a potential therapeutic target to reverse radio-resistance and promote radiotherapy responses.Methods: Radio-resistant human NPC cell lines were firstly established for further explorations.Then we assessed lipid droplet(LD)accumulation by oil red O staining and Bodipy staining.Then we screened the potential molecules which may function in the lipid droplets accumulation that may induce development of radio-resistance.Subsequently,by conducting lipidomics sequencing,mitochondrial function and mitochondrial autophagy(mitophagy)and other subsequent experiments,we ensured the pathways and mechanisms that induced radio-resistance development.Moreover,we used xenograft NPC models to verify these results.Also,human NPC tissues were applied for immunohistochemistry staining and clinicopathological analysis for further determination of lipid metabolism related radio-resistance development.Results: Increasing LDs was observed in radio-resistant NPC and hypoxia inducible lipid droplet associated protein(HILPDA)was proved to be closely associated with tumor sensitivity to irradiation.Then we found that HILPDA up-regulated mitophagy by increasing cardiolipin(CL)level,thereby conferring to radio-resistance.Further,we deemed that HILPDA stabilized the expression of cardiolipin synthase 1(CLS1)by inhibiting PTEN-induced putative kinase 1(PINK1)ubiquitination,to increase CL level.Finally,the above results were verified in human NPC tissues by analyzing related clinical data.Conclusions: Our findings identify HILPDA as an essential role in promoting nasopharyngeal carcinoma radio-resistance in vitro and in vivo,by increasing mitophagy in irradiated tumor cells.