Bone, the tumor microenvironment contributes to cancer invasion, growth and survival and thereby impacts tumor responses to therapy. We here developed an intravital infrared multiphoton imaging model for the multi-parameter visualization of collective cancer cell invasion, guidance by the tumor stroma, and short- and long-term resistance to experimental anti-cancer therapy. Using orthotopic fibrosarcoma and melanoma xenografts, we identify deep invasive growth driven by proliferation concurrent with collective invasion as main local invasion route, which further mediated resistance to high-dose hypofractionated radiation therapy (cumulative dose 2040 Gy). This invasion-associated radioresistance niche comprised several hundreds of cells in close proximity to stromal structures, including collagen, basement vascular and myofibre membranes, and was able to re-establish tumor growth and relapse, thus escaping other imaging modalities but in vivo microscopy. Using simultaneous inhibition of β1 and β3 integrins by RNA interference or combined anti-β1/αV integrin antibody treatment, however, proliferation arrest, anoikis induction was achieved, ablating both tumor lesion and the resistance niche. Thus, the invasion niche represents a microenvironmentally privileged survival niche which provides integrin-dependent therapy resistance.
To establish an model amenable to intravital multiphoton microscopy of bone metastases of prostate cancer (PCa), we implanted engineered humanized neobone into the mouse dermis. After in vivo implantation, TEBC maturation was monitored by μCT, MPM, and histological analysis over time to generate a miniaturized-neobone with defined cortical thickness (5060 mm) surrounding histologically mature murine bone marrow. PCa (PC3) lesions, after implantation into the bone cavity, were longitudinally monitored for growth, niche development and step-wise osteolysis, using multi-parameter recording of collagen/bone matrix, bone surface, blood vessels, stromal phagocytes and steoclasts, and PC3 cells. By combining innovative tissue engineering with optical windows, state-of-the-art fluorescence reporter technology and intravital MPM, this model will provide mechanistic and applied insight into the therapy response of bone metastases.