Nasopharyngeal carcinoma patient-derived xenograft mouse models reveal potential drugs targeting cell cycle, mTOR, and autophagy pathways

BACKGROUND: Nasopharyngeal carcinoma (NPC) is associated with Epstein–Barr virus (EBV) infection. To test preclinical NPC drugs, we established two patient-derived xenograft (PDX) mouse models, EBV-positive PDX-B13 and EBV-negative PDX-Li41, for drug screening. METHODS: Based on next generation sequencing (NGS) studies, PDX-B13 had CCND1 copy number (CN) gain but CDKN2A CN loss, whereas PDX-Li41 had CDKN2A and RB1 CN loss, TSC1 (negative regulator of mTOR) frameshift deletion mutation, and increased activation of mTOR, a serine/threonine kinase that governs metabolism, autophagy, and apoptosis. Increased mTOR was also associated with poor NPC prognosis. RESULTS: Everolimus, an mTOR inhibitor, suppressed tumor growth in the two PDX NPC models and had an additive antitumor effect with palbociclib, a CDK4/6 inhibitor. PDX tumors treated with various drugs or untreated were subjected to RNA sequencing, transcriptome profile analysis, and selective Western blotting to understand the interactions between these drugs and gene expression profiles. Palbociclib also suppressed EB viral nuclear antigen (EBNA1) expression in PDX-B13. Everolimus together with autophagy inhibitor, hydroxychloroquine, had additive anti-tumor effect on PDX-B13 tumor. Immunohistochemistry revealed that high mTOR levels were correlated with poor overall survival in patients with metastatic NPC (N = 90). CONCLUSIONS: High mTOR levels are a poor prognostic factor in NPC, and cell cycle, mTOR and autophagy pathways may serve as therapeutic targets in NPC. In addition, PDX models can be used for efficiently testing potential NPC drugs.