Radiotherapy Plus Temozolomide Have No Evident Effect On The Transcriptome Landscape Of Canine Malignant Oral Melanoma

Introduction. Canine oral melanoma (COM) is the most common oral tumor in dogs. It is a very aggressive disease, being locally invasive and having a high chance of metastasizing. Standard therapeutic procedures including surgery, radiotherapy and/or chemotherapy and, recently, immunotherapy do not significantly prolong survival. Nowadays, the RNA sequencing (RNA-Seq) technology allows oncologists to deepen the knowledge on the differential cancer-associated transcriptome, thereby expanding the diagnostic, prognostic and therapeutic opportunities in cancer research. In the present study, we profiled the transcriptome of COM before and after the treatment with radiotherapy and the radiosensitizer temozolomide. Materials and Methods. Following a routine tumor-node-metastasis (TNM) staging, mitotic index (MI) assessment, melanin pigment and nuclear atypia grading, a cohort of twelve COM-diagnosed dogs were prospectively enrolled in this study. Total RNA was isolated from paired blood samples and tumor biopsies before (T0) and after (T1) hypofractionated radiotherapy followed by adjuvant temozolomide. RNA-Seq libraries were prepared, quality-controlled, and then sequenced on an Illumina® HiSeq 2500. The raw data and the subsequent functional analyses were performed using several publicly available tools. Results and Conclusions. RNA-Seq analyses, at the tested conditions, evidenced no differentially expressed genes (DEGs) in tumor biopsies after (compared with before) the radiotherapy and temozolomide treatment (T1 vs T0). However, six genes were moderately (adjusted P<0.1) deregulated in the blood. Based on our results, radiotherapy plus temozolomide does not induce evident transcriptional effects in both primary COM and blood. Advances in the understanding of how cells respond molecularly to ionizing radiation will provide opportunities for the development of new approaches that selectively enhance radiotherapy of COM. Acknowledgements Project supported by grants (IZSVe 11/13 RC) from Veterinary and Public Health Institute (Legnaro, Padua, Italy).