Abstract:
The stromal cells of the tumour microenvironment play a critical role in tumour progression, and are therefore an attractive target for cancer therapy. Communication between cancer cells and the non-malignant stromal cells maintaining this tumour-favouring environment is complex, and not completely understood. Techniques to further understand these interactions and how they may be perturbed are critically needed, to enable evaluation and development of stromal targeting agents. An ideal stromal targeting agent would be effective against primary tumours as well as metastases; therefore better understanding of the metastatic microenvironment is also important. The primary objective of this thesis is to establish multi-modal experimental platforms to dissect the tumour-stroma interactions in the microenvironment of primary and metastatic melanoma, and how they can be perturbed with stromal targeting agents. As proof-of-principle of this approach, the effects of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) were examined in a xenograft (A375) model and syngeneic (B16) murine models of melanoma. Antitumour activity was assessed by growth inhibition studies and histology. Immunofluorescence-based techniques, including flow cytometry and immunohistochemistry, were used to determine the stromal composition of subcutaneous A375 and B16-F10 tumours, as well as intracranial and pulmonary B16-F10 metastases. Stromal and cancer cell cytokines were measured at the protein level by Multiplex assay and compared to microarray data measured from the same samples. In A375 xenografts, DMXAA showed excellent antitumour activity, including rapid haemorrhagic necrosis, recruitment and activation of innate immune cells, likely mediated by induced production of proinflammatory cytokines and chemokines by stromal cells and melanoma cells. B16-F10 murine melanomas grown as subcutaneous, intracranial or pulmonary tumours differed in the presence and extent of lymphocyte infiltration, but the presence of monocytic myeloid cells was common at all sites, many of which resembled tissue-specific macrophages. DMXAA induced haemorrhagic necrosis in B16 tumours, but antitumour activity overall was modest. DMXAA induces innate immunity against A375 xenografts, but this activity may be reduced in poorly immunogenic and aggressive B16 melanomas. Nevertheless, this multi-modal experimental platform allowed distinction between signals produced by cancer cells and those produced by stromal cells, and could be applied to investigate other tumour models and anti-cancer agents.