Abstract 481: In vivo imaging identifies that myf5+ embryonal rhabdomyosarcoma-propagating cells are dynamically reorganized during tumor growth

Abstract

Abstract Embryonal rhabdomyosarcoma (ERMS) is a devastating pediatric cancer with specific features of muscle differentiation. Here, we use a transgenic zebrafish model of RAS-induced ERMS and show that myf5+ ERMS cells possess self-renewal potential, confirming that ERMS is a cancer stem cell driven disease. The ERMS-initiating cell is molecularly similar to an activated satellite cell and expresses myf5, m-cadherin, and c-met. To directly visualize tumor-initiating cells in vivo, fluorescent transgenic zebrafish were created that express myf5-GFP, myogenin-h2b-mRFP, and mylz2-lyn-cyan. These transcription factors are expressed during distinct stages of muscle/ERMS development and transgenic reporter lines using these gene promoters allow self-renewing cells to imaged in live animals by confocal microscopy. myf5-GFP+ ERMS-initiating cells from early stage tumors lie in immediate proximity to muscle fibers where normal satellite cells reside. However, as tumors grow, the niche is greatly expanded with the number of myf5-GFP+ cells increasing by 10-fold per fiber. By late stages of tumor growth, myf5-GFP+ ERMS cells are re-localized into a new tumor-specific stem cell niche that is no longer associated with fibers and is separated from more differentiated myogenin+ and myogenein/mylz2 double positive tumor cells. Analysis of human ERMS showed that tumors also contain regional niches of differentiated and undifferentiated cells. Time-lapse imaging of live zebrafish showed that myf5-GFP+ ERMS cells move only locally within the tumor and remain largely confined to stable self-renewing niches. By contrast, myogenin+ cells move dynamically throughout tumors and colonize new areas for tumor growth by both migration through the tissue and entry into the vasculature system. Following colonization by myogenin+ cells, self-renewing myf5+ cells are recruited to new areas of tumor growth. Our findings reconcile the clinical observation that myogenin-positivity in RMS correlates with poor outcome, because it is these cells that intravasate into blood vessels, invade new areas of tumor growth, and recruit slow moving self-renewing cells to newly colonized areas. Taken together, our in vivo imaging studies provide unprecedented access to directly visualize tumor growth in real-time and to define the kinetics of self-renewal and tumor dissemination as has never been assessed in any experimental model. 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 481. doi:10.1158/1538-7445.AM2011-481