Blood vessel networks form in a 2-step process of sprouting angiogenesis followed by selective branch regression and stabilization of remaining vessels. Pericytes are known to function in stabilizing blood vessels, but their role in vascular sprouting and selective vessel regression is poorly understood. The endosialin (CD248) receptor is expressed by pericytes associated with newly forming but not stable quiescent vessels. In the present study, we used the Endosialin ؊/؊ mouse as a means to uncover novel roles for pericytes during the process of vascular network formation. We demonstrate in a postnatal retina model that Endosialin ؊/؊ mice have normal vascular sprouting but are defective in selective vessel regression, leading to increased vessel density. Examination of the Endosialin ؊/؊ mouse tumor vasculature revealed an equivalent phenotype, indicating that pericytes perform a hitherto unidentified function to promote vessel destabilization and regression in vivo in both physiologic and pathologic angiogenesis. Mechanistically, Endosialin ؊/؊ mice have no defect in pericyte recruitment. Rather, endosialin binding to an endothelial associated, but not a pericyte associated, basement membrane component induces endothelial cell apoptosis and detachment. The results of the present study advance our understanding of pericyte biology and pericyte/endothelial cell cooperation during vascular patterning and have implications for the design of both proand antiangiogenic therapies. (Blood. 2012;120(7):1516-1527) IntroductionThe expansion of existing blood vessels, known as angiogenesis, is a critical process that occurs in response to an insufficient supply of nutrients and oxygen during development and tissue regeneration. The deregulated generation and abnormal remodeling of blood vessels can promote the expansion of tumors or fail to restore tissue oxygenation adequately, contributing to ischemic disease progression (eg, in diabetic retinopathy). Therefore, the identification of the cellular and molecular targets for therapeutic strategies to influence vascular network formation and remodeling is of considerable clinical importance. 1,2 Angiogenesis is initiated in response to local production of proangiogenic factors, in particular VEGF-A, which promote new vascular sprout formation by the induction and migration of leading tip cells and by stimulating the proliferation of neighboring stalk cells. In addition, VEGFmediated regulation of the Delta-like 4/Notch1 signaling pathway ensures the correct spatiotemporal coordination of tip versus stalk cell specialization required for organized patterning of new vascular networks. 3 Subsequent to sprouting angiogenesis, the initial vascular plexus is remodeled extensively. Key to this remodeling is the pruning of unwanted capillaries through selective branch regression. The remaining vessels mature and are stabilized, which marks the end of vessel plasticity and reflects the quiescent state of the new hierarchical vascular network. With the exception of the complete regr...

Recent studies have revealed a role for macrophages and neutrophils in limiting chemotherapy efficacy, however the mechanisms underlying therapeutic benefit of myeloid-targeting agents in combination with chemotherapy are incompletely understood. Here, we show that targeting tumor-associated macrophages by colony-stimulating factor-1 receptor (CSF-1R) blockade in the K14cre;Cdh1 F/F ;Trp53 F/F transgenic mouse model for breast cancer stimulates intratumoral type I interferon (IFN) signaling which enhances the anti-cancer efficacy of platinum-based chemotherapeutics. Notably, anti-CSF-1R treatment also increased intratumoral expression of type I IFN-stimulated genes in cancer patients, confirming that CSF-1R blockade is a powerful strategy to trigger an intratumoral type I IFN response. By inducing an inflamed, type I IFN-enriched tumor microenvironment and by further targeting immunosuppressive neutrophils during cisplatin therapy, anti-tumor immunity was activated in this poorly immunogenic breast cancer mouse model. These data illustrate the importance of breaching multiple layers of immunosuppression during cytotoxic therapy to successfully engage anti-tumor immunity in breast cancer.

PARP inhibitors have been proposed as a potential targeted therapy for patients with triple-negative (ER-, PR-, HER2-negative) breast cancers. However, it is as yet unclear as to whether single agent or combination therapy using PARP inhibitors would be most beneficial. To better understand the mechanisms that determine the response to PARP inhibitors, we investigated whether enzymes involved in metabolism of the PARP substrate, β-NAD+, might alter the response to a clinical PARP inhibitor. Using an olaparib sensitization screen in a triple-negative (TN) breast cancer model, we identified nicotinamide phosphoribosyltransferase (NAMPT) as a non-redundant modifier of olaparib response. NAMPT is a rate-limiting enzyme involved in the generation of the PARP substrate β-NAD+ and the suppression of β-NAD+ levels by NAMPT inhibition most likely explains these observations. Importantly, the combination of a NAMPT small molecule inhibitor, FK866, with olaparib inhibited TN breast tumour growth in vivo to a greater extent than either single agent alone suggesting that assessing NAMPT/PARP inhibitor combinations for the treatment of TN breast cancer may be warranted.