Transcriptome analysis of canine histiocytic sarcoma tumors and cell lines reveals multiple targets for therapy

Histiocytic sarcoma (HS) is a highly aggressive malignancy characterized by excessive proliferation of histiocytes in dogs and humans. A subset of dog breeds, including the Bernese mountain dog (BMDs) show a remarkably high prevalence of HS, thus provide opportunities for insight into the molecular pathogenesis of the disease. Previous work by our lab and others has identified somatic driver mutations of HS in the PTPN11 and KRAS genes that activate the MAPK pathway in about 60% of canine HS cases. However, no somatic driver mutations have been identified in the remaining 40%. Here, we report our whole transcriptome analysis of eighteen well-characterized BMD HS tumor tissues, as well as three HS cell lines, allowing us to gain further insight into the molecular basis of HS tumorigenesis. Our analysis reveals significant upregulation of molecular pathways involving the FOXM1, AURKB, PLK1, and E2F genes, providing new information regarding pathways that may be targeted with inhibitors. In addition, we document the expression of multiple checkpoint genes, suggesting the option of treatment with small molecule inhibitors together with checkpoint inhibitors. Further, we show that the transcriptomes of three canine HS cell lines mirror those of canine patient tumors, further highlighting their potential use in drug efficacy studies. Finally, we demonstrate, for the first time, that aurora kinase inhibitors are effective in curtailing growth of HS cells in vitro and show synergism with MAPK inhibition. This study provides the most detailed analysis of the canine HS transcriptome to date, highlighting key pathways in its pathogenesis and suggesting new avenues for both single and combination treatment strategies which may be pertinent to treatment of human HS. RNA-seq profiling of 18 HS tumors samples from BMDs as well as 3 canine HS cell lines to investigate the HS transcriptome and to find significantly affected molecular pathways and gene expression in HS affected dogs.