Abstract 5348: In vivo and in vitro alveolar rhabdomyosarcoma cell growth is affected by TNK2 expression

Abstract

Abstract Rhabdomyosarcoma is the most common pediatric soft tissue tumor. The two major histologic subtypes are embryonal (ERMS) and alveolar rhabdomyosarcoma (ARMS); which have different genetic alterations: 11p15 LOH in ERMS and PAX3 (or PAX7)-FOXO1 translocation in ARMS. Despite utilization of aggressive multimodal therapy, patients with recurrent or metastatic disease remain essentially incurable. This is particularly true in patients with alveolar rhabdomyosarcoma. New therapies are needed to improve outcomes in this disease. To detect genes that are critical for rhabdomyosarcoma cell growth and survival, we performed a loss-of-function shRNA screen in ARMS and ERMS cell lines using a regulated shRNA library that was delivered to RMS cells using retrovirus. We hypothesized that genes whose loss of function significantly influence the growth and survival of ARMS cells with relatively no impact on ERMS cells represent a critical vulnerability or “Achilles’ heel” for ARMS. We sorted our gene list using this approach. In this study, we identified TNK2 (tyrosine kinase, non-receptor 2; also known as ACK1) as a critical gene is ARMS cell survival and as a potential therapeutic target. TNK2 is a non-receptor tyrosine kinase that integrates signals from different membrane receptors, including integrins, EGFR and IGFR. Reported downstream targets include CDC42 and AKT. The TNK2 gene is located at 3q29. TNK2 amplification has been described in prostate, lung and breast cancer and its role in invasion and metastasis has recently been suggested. However, its role in rhabdomyosarcoma has not been previously explored. We initially confirmed that TNK2 is uniformly expressed RMS. In addition, analysis of TNK2 expression in primary tumor samples of RMS using a publicly available database indicated that rhabdomyosarcomas with higher TNK2 expression show lower overall survival. We used a tetracycline-inducible shRNA construct to knock down TNK2 expression in rhabdomyosarcoma cells. TNK2 knock down resulted in significant decrease in cell growth in ARMS. We characterized the specificity of our findings using 5 different shRNA sequences targeting this gene delivered via lentivirus. In addition, we have been able to rescue the effect of an shRNA targeting the 3’UTR of this gene using TNK2 cDNA. We validated our in vitro data in an in vivo model using tumor xenografts. Downstream pathways under investigation include but are not limited to AKT, MAPK and CDC42. These data suggest that TNK2 could represent a therapeutic target in ARMS and highlight the role of loss of function shRNA screens to improve the understanding of tumor biology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5348. doi:10.1158/1538-7445.AM2011-5348