No abstract

Summary Tumor inflammation promotes angiogenesis, immunosuppression and tumor growth, but the mechanisms controlling inflammatory cell recruitment to tumors are not well understood. We found that a range of chemoattractants activating G-protein coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and Toll-like/IL-1 receptors (TLR/IL1Rs) unexpectedly initiate tumor inflammation by activating the PI3-kinase isoform p110γ in Gr1+CD11b+ myeloid cells. Whereas GPCRs activate p110γ in a Ras/p101 dependent manner, RTKs and TLR/IL1Rs directly activate p110γ in a Ras/p87-dependent manner. Once activated, p110γ promotes inside-out activation of a single integrin, α4β1, causing myeloid cell invasion into tumors. Pharmacological or genetic blockade of p110γ suppressed inflammation, growth and metastasis of implanted and spontaneous tumors, revealing an important therapeutic target in oncology.

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a low five-year survival rate, yet new immunotherapeutic modalities may offer hope for this and other intractable cancers. Here we report that inhibitory targeting of PI3Kγ, a key macrophage lipid kinase, stimulates anti-tumor immune responses, leading to improved survival and responsiveness to standard-of-care chemotherapy in animal models of PDAC. PI3Kγ selectively drives immunosuppressive transcriptional programming in macrophages that inhibits adaptive immune responses and promotes tumor cell invasion and desmoplasia in PDAC. Blockade of PI3Kγ in PDAC-bearing mice reprograms tumor-associated macrophages to stimulate CD8+ T cell-mediated tumor suppression and to inhibit tumor cell invasion, metastasis and desmoplasia. These data indicate the central role that macrophage PI3Kγ plays in PDAC progression and demonstrate that pharmacological inhibition of PI3Kγ represents a new therapeutic modality for this devastating tumor type.

Recent studies have shown that lymphangiogenesis or the growth of lymphatic vessels at the periphery of tumors promotes tumor metastasis to lymph nodes. We show here that the fibronectin-binding integrin α4β1 and its ligand fibronectin are novel functional markers of proliferative lymphatic endothelium. Tumors and lymphangiogenic growth factors, such as vascular endothelial growth factor-C (VEGF-C) and VEGF-A, induce lymphatic vessel expression of integrin α4β1. Integrin α4β1 then promotes growth factor and tumor-induced lymphangiogenesis, as genetic loss of integrin α4β1 expression in Tie2Cre+ α4 loxp/loxp mice or genetic loss of α4 signaling in α4Y991A knock-in mice blocks growth factor and tumor-induced lymphangiogenesis, as well as tumor metastasis to lymph nodes. In addition, antagonists of integrin α4β1 suppress lymphangiogenesis and tumor metastasis. Our studies show that integrin α4β1 and the signals it transduces regulate the adhesion, migration, invasion, and survival of proliferating lymphatic endothelial cells. As suppression of α4β1 expression, signal transduction, or function in tumor lymphatic endothelium not only inhibits tumor lymphangiogenesis but also prevents metastatic disease, these results show that integrin α4β1-mediated tumor lymphangiogenesis promotes metastasis and is a useful target for the suppression of metastatic disease.

Tumor-associated macrophages promote tumor growth by stimulating angiogenesis and suppressing anti-tumor immunity. Thus, therapeutics that inhibit macrophage recruitment to tumors may provide new avenues for cancer therapy. Here we show how the chemoattractants SDF-1α and IL-1β collaborate with myeloid cell integrin α4β1 to promote tumor inflammation and growth. We found that SDF-1α and IL-1β are highly expressed in the microenvironments of murine lung, pancreatic and breast tumors; surprisingly, SDF-1α was expressed only by tumor cells, while IL-1β was produced only by tumor-derived granulocytes and macrophages. In vivo, both factors directly recruited pro-angiogenic macrophages to tissues, while antagonists of both factors suppressed tumor inflammation, angiogenesis and growth. Signals induced by IL-1β and SDF-1α promoted the interaction of talin and paxillin with the cytoplasmic tails of integrin α4β1, thereby stimulating myeloid cell adhesion to endothelium in vitro and in vivo. While inhibiting integrin α4β1, SDF-1α or IL-1β was sufficient to block tumor inflammation and growth, the combined blockade of these molecules greatly accentuated these effects. Furthermore, antagonists of integrin α4β1 inhibited chemotherapy-induced tumor inflammation and synergized with chemotherapeutic agents to suppress tumor inflammation and growth. These results demonstrate that targeting myeloid cell recruitment mechanisms can be an effective approach to suppress tumor progression.

Endothelial progenitor cell (EPC) transplantation has beneficial effects for therapeutic neovascularization; however, only a small proportion of injected cells home to the lesion and incorporate into the neocapillaries. Consequently, this type of cell therapy requires substantial improvement to be of clinical value. Erythropoietin-producing human hepatocellular carcinoma (Eph) receptors and their ephrin ligands are key regulators of vascular development. We postulated that activation of the EphB4/ephrin-B2 system may enhance EPC proangiogenic potential. In this report, we demonstrate in a nude mouse model of hind limb ischemia that EphB4 activation with an ephrin-B2-Fc chimeric protein increases the angiogenic potential of human EPCs. This effect was abolished by EphB4 siRNA, confirming that it is mediated by EphB4. EphB4 activation enhanced P selectin glycoprotein ligand-1 (PSGL-1) expression and EPC adhesion. Inhibition of PSGL-1 by siRNA reversed the proangiogenic and adhesive effects of EphB4 activation. Moreover, neutralizing antibodies to E selectin and P selectin blocked ephrin-B2-Fc-stimulated EPC adhesion properties. Thus, activation of EphB4 enhances EPC proangiogenic capacity through induction of PSGL-1 expression and adhesion to E selectin and P selectin. Therefore, activation of EphB4 is an innovative and potentially valuable therapeutic strategy for improving the recruitment of EPCs to sites of neovascularization and thereby the efficiency of cell-based proangiogenic therapy.

Background-Proangiogenic cell therapy based on administration of bone marrow-derived mononuclear cells (BMCs) or endothelial progenitor cells (EPCs) is now under investigation in humans for the treatment of ischemic diseases. However, mechanisms leading to the beneficial effects of BMCs and EPCs remain unclear. Methods and Results-BMC-and CD34ϩ -derived progenitor cells interacted with ischemic femoral arteries through SDF-1 and CXCR4 signaling and released nitric oxide (NO) via an endothelial nitric oxide synthase (eNOS)-dependent pathway. BMC-induced NO production promoted a marked vasodilation and disrupted vascular endothelial-cadherin/ ␤-catenin complexes, leading to increased vascular permeability. NO-dependent vasodilation and hyperpermeability were critical for BMC infiltration in ischemic tissues and their proangiogenic potential in a model of hindlimb ischemia in mice. Conclusions-Our results propose a new concept that proangiogenic progenitor cell activity does not rely only on their ability to differentiate into endothelial cells but rather on their capacity to modulate the function of preexisting vessels.

Abstract-Cell-based therapy is a promising approach designed to enhance neovascularization and function of ischemic tissues. Interaction between endothelial and smooth muscle cells regulates vessels development and remodeling and is required for the formation of a mature and functional vascular network. Therefore, we assessed whether coadministration of endothelial progenitor cells (EPCs) and smooth muscle progenitor cells (SMPCs) can increase the efficiency of cell therapy. Unilateral hindlimb ischemia was surgically induced in athymic nude mice treated with or without intravenous injection of EPCs (0.5ϫ10 6 ), SMPCs (0.5ϫ10 6 ) and EPCsϩSMPCs (0.25ϫ10 6 ϩ0.25ϫ10 6 ). Vessel density and foot perfusion were increased in mice treated with EPCsϩSMPCs compared to animals receiving EPCs alone or SMPCs alone (PϽ0.001). In addition, capillary and arteriolar densities were enhanced in EPCϩSMPC-treated mice compared to SMPC and EPC groups (PϽ0.01). We next examined the role of Ang-1/Tie2 signaling in the beneficial effect of EPC and SMPC coadministration. Small interfering RNA directed against Ang-1-producing SMPCs or Tie2-expressing EPCs blocked vascular network formation in Matrigel coculture assays, reduced the rate of incorporated EPCs within vascular structure, and abrogated the efficiency of cell therapy. Production of Ang-1 by SMPCs activates Tie2-expressing EPCs, resulting in increase of EPC survival and formation of a stable vascular network. Subsequently, the efficiency of EPC-and SMPC-based cotherapy is markedly increased. Therefore, coadministration of different types of vascular progenitor cells may constitute a novel therapeutic strategy for improving the treatment of ischemic diseases.