Abstract 5276: Exploration of the cachectic phenotype
Authors: Penet Marie-France , Winnard Paul T. , Marik Radharani , Nimmagadda Sridhar , Pomper Martin G. , Bhujwalla Zaver M. 
Published: June 2012

Abstract
The complexities of cancer, and cachexia induced by cancer, dictate the necessity of studying this disease in the context of its microenvironment as well as in the context of interactions between the tumor and the body, i.e., the ‘macroenvironment’. In the present study, we are applying molecular and functional imaging to understand cancer cachexia and develop clinically translatable indices for early detection of this condition. As models, we are using cachectic (MAC16) and non-cachectic (MAC13) murine colon adenocarcinoma cells. MAC16 tumors induce extensive weight loss in tumor-bearing animals, whereas MAC13 tumors, although histologically similar, do not induce weight loss. By using in vivo 1H MRSI, we detected a high level of total choline in cachectic tumors compared to non-cachectic ones but no differences in lactate levels in tumor extracts. We then performed [18F]fluorodeoxyglucose positron emission tomography studies and observed a significant increase in glucose uptake in the cachectic tumors compared to the non-cachectic ones. To detect the early onset of cachexia inducing signals, we have created a cell based optical biosensor using genetically engineered myoblasts that are injected into the gastrocnemius skeletal muscle. Glucocorticoids induce the expression of a muscle specific ubiquitin ligase (MuRF1), which has been shown to be involved with the catabolism of muscle proteins during cachexia. The up-regulation of MuRF1 occurs by the specific activation of the glucocorticoid receptor (GR) upon hormone binding. Activated GR then translocates to the nucleus and directly binds to its response element (GRE) within the MuRF1 promoter. Importantly, increased expression of MuRF1 has been shown to be an early event in cachexia processes. We have constructed a fluorescent protein reporter gene that is linked to a portion of the MuRF1 promoter containing the GRE, to report on the initial stages of the induction of cachexia. This reporter system was tested and optimized in mouse C2C12 myoblast cells, a well-established muscle cell model system. C2C12 myoblast cells were transfected with constitutively expressed green fluorescent protein (GFP) and MURF1 promoter driven tdTomato red fluorescent protein (RFP). RFP expression can then be induced by dexamethasone treatment through MURF1 promoter transactivation by GR. Stably transfected C2C12 myoblasts will be used as cell based optical biosensors. Regulatory changes occurring in engrafted C2C12 muscle cells in cachectic mice will be compared to analogous grafts on non-cachectic mice to identify the sequence of events in the cachexia cascade. These studies are part of our ongoing work to obtain a comprehensive characterization of the ‘cachectic phenotype’ using noninvasive multimodality imaging that will allow us to detect cancer induced cachexia and identify new targets to prevent or reverse this condition.
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 5276. doi:10.1158/1538-7445.AM2011-5276