Characterization and Radiosensitivity of HPV-Related Oropharyngeal Squamous Cell Carcinoma Patient-Derived Xenografts

Abstract

The purpose of this study was to create a number of patient-derived xenografts (PDXs) reflecting the heterogeneity of oropharyngeal squamous cell carcinoma (OPSCC) and compare the models with the corresponding human original tumors. Also, we aimed to determine if the PDX model is suitable for radiation therapy research. Fresh tumor biopsies from patients with primary, untreated OPSCC were implanted subcutaneously in immunodeficient mice. PDX tumors were serially transplanted and expanded, producing generations of PDX tumors with identical origin. PDX tumors and their corresponding human original were compared using histology, immunohistochemistry, gene expression profiling and next-generation sequencing (NGS). Radiosensitivity was assayed by subjecting PDX tumors to low-dose irradiation in a growth delay assay (4-8 Gy, single fraction). Tumor specimens from 34 OPSCC patients were xenografted, resulting in tumor growth in 20 cases (59%). However, 8 PDX models had a lymphoma-like histologic and immunohistochemical appearance and were disregarded. Further studies were conducted on 12 valid PDX models that retained histological and immunohistochemical features, yielding a final take-rate of 35%. No differences were noted between the full patient cohort and patients giving rise to valid PDXs with regard to HPV status, smoking or tumor characteristics. Although NGS revealed that valid PDX tumors had a mean of 22 genetic variants more than the original tumor (P<.02), there was a high concordance between PDXs and original tumors, with more than half of genetic variants retained in the PDX, including important driver mutations in TP53, PIK3CA, KMT2D, KMT2C and NOTCH1. Gene expression analysis revealed high concordance between PDX and original tumors with regard to expression of HPV oncogenes E6 and E7. However, there were notable differences in tumor microenvironment parameters with PDX tumors showing higher expression of hypoxia-related genes and lower expression of genes related to inflammation and low-dose irradiation of PDX tumors resulted in a reproducible growth delay. Radiosensitivity studies revealed that the most radiosensitive PDX models were HPV-positive, although one HPV-positive PDX model was relatively radioresistant. It is possible to generate PDX models from OPSCC patients that reflect differences in etiology with regard to HPV and smoking. Most PDX models retain histological and immunohistochemical features as well as important driver gene alterations. There are some differences related to tumor microenvironment and immune response. Overall, the PDX model is a promising high-fidelity research tool that may aid in development of personalized medicine. Perspectives include biomarker development, testing of targeted therapies, and improvement of radiation therapy.