Abstract 5110: Initial characterization of an optical reporter myoblast cell line for non-invasive imaging in a cancer cachexia model in mice

Cancer associated cachexia affects a majority of patients during cancer progression, compromising therapeutic interventions and contributing to decreased survival rates. Identifying factors involved in the onset of cachexia will provide a better understanding of early treatment strategies. To this end, we developed a mouse model system that allows for real time longitudinal monitoring of cancer induced wasting and has the potential of identifying early cachectic events. Several attributes of our system are new. 1) The construction of a dual optical reporter vector with green fluorescence protein (GFP) expression constitutively driven from an EF1α promoter and red fluorescence protein (tdTomato) expression driven by an engineered skeletal muscle specific inducible promoter. The latter is a synthetic sequence of a triple-tandem repeat of the glucocorticoid-FOXO1 response element region from the proximal promoter of the human MuRF1 gene. 2) Generation of a rat L6 myoblast optical reporter cell line (To3B cells) with stable integration of the dual reporter vector construct, which provides living reporter grafts within mouse muscle. 3) A human pancreatic cancer cell line (Pa04C) that as an orthotopic or subcutaneous xenograft causes weight loss in male SCID mice. In preliminary studies, we tested several human pancreatic cancer cell lines as orthotopic xenografts in male SCID mice. We found that red fluorescence signals were reproducibly detected in live mice only from To3B grafts in mice undergoing weight loss, while graft size and viability were readily monitored by imaging GFP fluorescence in all animals. In addition, mice bearing Pa04C tumors lost the most weight while mice bearing Panc1 tumors gained weight. Therefore, Pa04C and Panc1 cells were used for subcutaneous xenografts in male SCID mice and weight loss was followed with optical monitoring of To3B grafts. Importantly, in weight losing mice, we found that red fluorescence could be detected and quantified at a nascent stage of the syndrome; e.g., unambiguous red fluorescent signals were quantified at weight losses of only 1.2 to 2.7% at very low tumor burdens of only ∼0.079 to ∼0.170 cm3. Red fluorescence remained very low to undetectable in mice that gained weight. Tumor sizes were comparable between groups, which was an indication that factors independent of tumor growth were involved in switching on red fluorescence. Ex vivo fluorescence microscopy confirmed a robust presence of red fluorescence only in To3B grafts in skeletal muscle from Pa04C tumor bearing mice. The evidence from this initial development of a unique optical reporter myoblast cell line indicates the potential to detect the onset of cancer cachexia. These studies set the ground work for future research aimed at identifying initiating systemic as well as local molecular events in the muscle of cachectic mice. Supported by NIH P50CA103175 Citation Format: Paul T. Winnard, Marie-France Penet, Yelena Mironchik, Flonne Wildes, Anirban Maitra, Zaver M. Bhujwalla. Initial characterization of an optical reporter myoblast cell line for non-invasive imaging in a cancer cachexia model in mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5110. doi:10.1158/1538-7445.AM2015-5110