Targeting AVIL, a novel oncogene in rhabdomyosarcoma

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Rhabdomyosarcoma (RMS) is the most common pediatric soft-tissue cancer. Despite treatment intensification, the outcome for patients with advanced stage RMS has remained dismal. As of now, no targeted therapy is available. Better understanding and treatment are clearly needed. In our preliminary study, we identified a novel oncogene, AVIL in RMS. We found that, 1) AVIL forms a fusion with a house-keeping gene MARS in some RMS; 2) AVIL is overexpressed in the majority of remaining RMS we tested, yet hardly detectable in mesenchymal stem cells or normal muscle tissues; 3) RMS cells are addicted to AVIL dysregulation in that silencing MARS- AVIL (in RMS cells that harbor the fusion) or silencing AVIL (in AVIL overexpressed RMS) nearly eradicated the cells, and dramatically inhibited in vivo xenografts, but had no effect on control cells; 4) conversely, overexpressing AVIL promoted cell proliferation and migration, enabled fibroblasts to form foci, and transformed mesenchymal stem cells; 5) sarcoma patients with increased AVIL expression have worse prognosis; and 6) RMS cells are sensitive to our small molecules inhibiting AVIL. Based on these observations, our long-term hypothesis is that AVIL is an Achilles heel of RMS, and targeting it may be an effective approach for treating the disease. In this application, we propose the systematic investigation of AVIL as a novel target against RMS. Aim 1: Determine the efficacy of targeting AVIL in vitro. We will investigate its role in an expanded list of cell lines and short-term explants of RMS PDX cultures. We will test the efficacy of tet-inducible shRNAs targeting AVIL, and small molecule compounds we identified through small molecule screen. Since last submission, we also generated over 70 novel compounds derivative of the initial hit compounds. We will test their efficacy in vitro. In addition, we will determine whether AVIL expression serves as a biomarker for sensitivity to AVIL inhibition. Aim 2: Determine the efficacy of targeting AVIL in animal RMS models. We will use shRNA and small-molecule inhibitors in xenograft models to test both the efficacy and safety of targeting AVIL in vivo. In addition, we have generated both Avil transgenic and knockout models. We will cross Avil transgenic with various Cre strains to test whether Avil overexpression is sufficient for RMS tumorigenesis. We will also use Avil knockout mouse model by crossing them with RMS mouse models to test whether Avil expression is necessary for RMS tumorigenesis in mouse. Aim 3: Investigate the downstream targets and mechanisms of AVIL inhibition and identify potential pharmacodynamic biomarkers. We will investigate molecular mechanism under which AVIL regulates FOXM1 stability, and determine the domain and exact activity on F-actin that are responsible for its oncogenic activity. Aim 4: Assess AVIL-targeting lead compounds for optimal ADME (absorption, distribution, metabolism, elimination), bioavailability, and pharmacokinetic properties. The proposed study will have a significant impact on the understanding and treatment of RMS. The findings will pave ways to target AVIL as a novel oncogene, and lead to the development of novel therapeutic approaches for the desperate disease.