Establishing an Ex Vivo Skin-Like Microenvironment Using Hydrogels to Study Macrophage-Tumor Interactions

Cancers are among the leading causes of morbidity and mortality worldwide. The disease manifests as mutations in native cells disrupt natural cellular proliferative or apoptotic mechanisms. Cancers form and mature in numerous tissue types. Variation between individual cases stems from the genes disrupted by the mutation and from the tissue in which it exists. Despite the potential for variation, research has shown numerous features and behaviors of the disease to be conserved. Strong correlations between cancer and the nature of the immune response it elicits are an important example of a conserved component. Research concerning links between cancer and the immune system, related to both progression and treatment, has established a relationship between the disease and host defense network. In contrast to its role in fighting the disease, the immune system can aid in its progression and is sometimes the primary cause of cancer. Research efforts establishing the oncogenesis-promoting potential of inflammation (Colotta, Allavena, Sica, Garlanda & Mantovani, 2009; Hanahan & Weinberg, 2011) were a response to observations of increased cancer risk in chronically inflamed organs. In addition to its role in tumor development, inflammation significantly contributes in the process of tumor progression (Hanahan & Weinberg, 2011). Efforts to identify the cause of these and other tumor-promoting immune system-based features such as extracellular matrix (ECM) modifications to promote migration and acquired resistance to anti-cancer treatments have identified populations of macrophages peripheral to the tumor as the basis for nearly all tumor promoting actions resulting from immune system dysfunction (Mantovani & Sica, 2010; Solinas, Germano, Mantovani & Allavena, 2009). Macrophages incorporated into the microenvironmental architecture of tumors are identified as tumor-associated macrophages (TAMs). An established TAM population is capable of masking the tumor from immune surveillance and aid in its maturation through directed modulation of the immune system. TAMs can also protect against anti-tumor treatments. The underlying mechanisms for how tumor cells modulate immune response remain unclear. This is partly due to lack of ex vivo models that can monitor macrophage-cancer interaction. The goal of this research project was to establish a 3D culture system reflecting features of a natural microenvironment and evaluate its potential for the study of crosstalk between TAMs and tumor cells. As modulation of immune cell activation has emerged as a potential means to target cancer cells, future work may identify a tool for the development of immunotherapies for tumor treatments. In order to reveal the nature of the crosstalk while maximizing the extent to which ex vivo observations might translate to in vivo mechanisms, this research relied on a TAMs-tumor relationship based on a form of melanoma. The use of melanoma was based on our ability to reproduce the ECM-based microenviornmental features of skin. Through the analysis of both melanoma and macrophage cell populations following periods of co-culture, this work endeavored to reveal key features of the mechanistic basis for tumor-directed macrophage polarization. This was achieved through the development of a custom co-culture platform, the value of which was challenged by directly comparing it against an established commercial product. Ultimately we determined our platform has the potential to serve as a valuable research tool and used it to assess the roles of key signaling mechanisms in tumor-directed macrophage polarization