Identification of Causative Genetic Networks in Angiosarcoma

Malignant vascular tumors are a type of sarcoma that originates from transformed endothelial cells. While the disease is rare (2% of all sarcomas), these tumors are highly invasive and display low survival (50% lethality / year). Unlike the vast majority of cancers, the identification of causative genes in angiosarcoma is lagging behind other tumor types and therefore, advancements in early diagnostic markers, generation of animal models for the disease and development of therapeutic approaches has been severely impaired. An additional emerging concern has been the raising incidence of angiosarcoma in patients exposed to radiotherapy for breast cancer treatment. In this application, we propose experiments to identify the critical circuitry of mutations that are necessary to trigger endothelial cell transformation and emergence of angiosarcoma. The approach follows on the footsteps of preliminary data obtained from mouse genetic screens and exome sequencing of human patients and it is intended to pursue therapeutic targets. The mouse genetic screen identified a series of 81 potential causative (driver) genes that were mutated in angiosarcoma after transposon-induced endothelial-specific targeting. These genes were selected as potential drivers only when mutated in at least three independent angiosarcoma lesions (in a cohort of 257 lesions evaluated and 337 mice). Exome sequencing of 16 human angiosarcoma specimens collected in collaboration with our clinical colleagues from three distinct hospitals, guided our selection of candidates. Subsequent network analysis allowed us to establish biological relationships and narrow our original list to 11 mutated genes. Replication of several of these mutations in normal endothelium elicits transformation, including anchorage-independent growth in soft agar assays. As a natural evolution of this project, our next objective is to develop reagents and test these mutated genes in an in vivo experimental platform. Thus, the central hypothesis in this application is that some endothelial mutations predispose, but are only transforming when additional genes are also mutated. Our goal here is to determine the temporal order of the mutations and minimal combination required to trigger endothelial transformation. Ultimately, we hope to identify the critical regulatory nodes operative in human angiosarcoma to develop targeted therapy. Considering the poor survival rate of individuals with this disease and the rising incidence of this tumor type as a consequence of radiation therapy, we believe that the development of an animal model in which to study the onset and evolution of angiosarcoma in the context of causative genetic mutations is long overdue. Such animal model would provide a valuable platform in which to explore potential therapeutic avenues to advance research in this area and lead to the improvement of clinical care for patients with angiosarcoma.