(150g) Breast Cancer CSC Display Novel In Vivo Imaging Features, Reminiscent of Development, During Early Tumor Progression

Virtually nothing is known about how nascent tumors form from cancer stem cells (CSC) and mammary stroma, yet this is essential for advancing breast cancer stem cell biology and developing molecular imaging and therapeutic strategies directed towards CSC. With this in mind, we developed a novel in vivo intravital imaging system designed to both image across the entire mammary gland and stroma. Importantly, this allowed us to identify new, rapidly developing, in vivo, quantitative imaging features at high resolution/sensitivity, not appreciable with conventional techniques. Using the developing mouse as a model for early tumor growth, we imaged and mapped the same fluorescent mammary gland at 3 and 4.5 weeks, and demonstrated rapid, spatially restricted growth; certain branches displayed a 400% increase in area over 1.5 weeks and maintained branching architecture, while neighboring ducts within 500µm displayed a 200% decrease. While examining stromal elements responsible for duct growth, we identified that normal mammary buds in virgin females displayed frequent microvascular interactions, and surprisingly, 77.7 % ± 6.4 (mean ± SD) of buds strongly interacted with the microvasculature (n=3, total terminal end buds =120). Notably, this stroma imaging feature was “conserved” in the 3 week old developing mouse, where we found 33/40 (83%) of mammary buds displayed analogous microvascular interactions. We then applied these imaging features to interpret a CSC tumor model designed to simulate early tumor formation from CSC. Two weeks after direct injection of 2500 CSC (or Tumorigenic) or non-CSC (non-Tumorigenic) cells from FvB MMTV-Wnt1 mice derived tumors into the developing GFP mammary gland, we observed new imaging features from the host mammary glands and host vasculature of the CSC populations only, including a 170% increase (p <0.28) in side branching of endogenous, eGFP+ ducts, with maintained host microvascular-bud interactions. Lastly, two weeks after transplantation of dye-labeled CSC and non-CSC , we observed a 240% increase in overall angiogenesis (p < 0.027), and quantifiable imaging features of normal growth (p < 0.005), including selective bud and duct outgrowths supplied with vasculature, and invasion by loosely organized neovasculature. Overall, our data suggests that CSC populations display several rapidly developing imaging features involving CSC and the underlying stroma, some of which are seen in developing mammary gland, which can be potentially useful for early radiologic identification of CSC in tissues, identification of new targets for molecular probes, monitoring therapy, or understanding the biology of CSC-stromal interactions.