Abstract 2329: Variable HPV E6 levels among oropharyngeal cancers govern therapy response via the PGC1/ERR axis

Abstract

Abstract BACKGROUND: Elevated mitochondrial antioxidant defenses contribute to progression and therapy resistance of some poor prognosis cancer types. By contrast, HPV+ oropharyngeal squamous cell carcinomas (OPSCCs) are generally sensitive to oxidative damage from radiation plus cisplatin, which are often curative. It is unknown whether the subset of HPV+ OPSCCs with poor outcomes exploit antioxidant capacity provided by high mitochondrial mass to evade therapy. It is also unclear whether the wide range of HPV oncoprotein expression among them contributes to diversity in mitochondrial mass and treatment outcomes. AIMS: (1) evaluate HPV+ OPSCCs for associations between mitochondrial mass and clinical outcome (2) elucidate relationships among HPV oncoprotein levels, mitochondrial mass, and therapy response (3) delineate mechanisms by which variable HPV oncoprotein levels govern therapy response. METHODS/RESULTS: High expression of genes involved in oxidative metabolism was associated with decreased survival in three patient cohorts. In PDX and cell line models, cisplatin resistance positively correlated with mitochondrial mass (MTCO1/B2M), oxidative metabolism (basal OCR), and antioxidant capacity (NADPH/NADP+). Among the HPV oncoproteins, only full length E6 (fl-E6) was linked to these features, showing negative correlation with mitochondrial mass in the cell lines, PDXs, and patient tumors. Fl-E6 levels also positively correlated with cisplatin response in the PDXs and cell lines. To test whether fl-E6 can mediate such effects, lentiviral fl-E6 expression in HPV+ cancer cell lines with low endogenous fl-E6 was used to increase levels to the high end of the range seen in human tumors. Doing so reduced MTCO1/B2M, basal OCR, and NADPH/NADP+ while sensitizing to radiation and cisplatin in vitro and in vivo. The same effects on mitochondrial biogenesis were maintained in nTERT/E7 keratinocytes. Using luciferase reporter assays, fl-E6 was shown to repress the PGC-1/ERR axis for mitochondrial biogenesis by attenuating p53-dependent PGC1α promoter activity. The prediction of PGC1/ERR axis activation in tumors with low fl-E6 was confirmed in PDXs and patient cohorts, where high ERRα was negatively prognostic. CONCLUSIONS: These results reveal a novel ability of E6-mediated p53 downregulation to contribute to treatment sensitivity by depleting mitochondrial antioxidant capacity. They also provide evidence that differing fl-E6 levels across HPV+ cancers variably repress the PGC1/ERR pathway, leading to diversity in mitochondrial mass that impacts therapy response. Therapy-refractory features may prove identifiable using expression-based biomarkers in the PGC1/ERR axis and be mitigated through targetable nodes in this pathway. In addition, HPV+ OPSCCs may find competitive advantage in down-regulating fl-E6 upon acquiring alternate drivers to compensate decrease in its oncogenic functions. Citation Format: Malay K. Sannigrahi, Pavithra Rajagopalan, Ling Lai, Xinyi Liu, Varun Sahu, Hiroshi Nakagawa, Robert Brody, Iain M. Morgan, Bradford E. Windle, Xiaowei Wang, Phyllis A. Gimotty, Daniel P. Kelly, Elizabeth A. White, Devraj Basu. Variable HPV E6 levels among oropharyngeal cancers govern therapy response via the PGC1/ERR axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2329.