Tumor vessel normalization has been proposed as a therapeutic paradigm. However, normal microvessels are hierarchical and vasoreactive with single file transit of red blood cells through capillaries. Such a network has not been identified in malignant
tumors. We tested whether the chaotic
tumor microcirculation could be reconfigured by the mesenchyme-selective
growth factor, FGF9. Delivery of FGF9 to renal
tumors in mice yielded microvessels that were covered by pericytes, smooth muscle cells, and a
collagen-fortified basement membrane. This was associated with reduced pulmonary
metastases. Intravital microvascular imaging revealed a haphazard web of channels in control
tumors but a network of arterioles, bona fide capillaries, and venules in FGF9-expressing
tumors. Moreover, whereas vasoreactivity was absent in control
tumors, arterioles in FGF9-expressing
tumors could constrict and dilate in response to
adrenergic and
nitric oxide releasing agents, respectively. These changes were accompanied by reduced
hypoxia in the
tumor core and reduced expression of the
angiogenic factor VEGF-A. FGF9 was found to selectively amplify a population of PDGFRβ-positive stromal cells in the
tumor and blocking PDGFRβ prevented microvascular differentiation by FGF9 and also worsened
metastases. We conclude that harnessing local mesenchymal stromal cells with FGF9 can differentiate the
tumor microvasculature to an extent not observed previously.