The causes of sporadic human cancer are seldom recognized, but it is estimated that carcinogen exposure and chronic inflammation are two important underlying conditions for tumour development, the latter accounting for approximately 20% of human cancer. Whereas the causal relationship between carcinogen exposure and cancer has been intensely investigated, the molecular and cellular mechanisms linking chronic inflammation to tumorigenesis remain largely unresolved. We proposed that activation of the nuclear factor kappaB (NF-kappaB), a hallmark of inflammatory responses that is frequently detected in tumours, may constitute a missing link between inflammation and cancer. To test this hypothesis, we studied the Mdr2-knockout mouse strain, which spontaneously develops cholestatic hepatitis followed by hepatocellular carcinoma, a prototype of inflammation-associated cancer. We monitored hepatitis and cancer progression in Mdr2-knockout mice, and here we show that the inflammatory process triggers hepatocyte NF-kappaB through upregulation of tumour-necrosis factor-alpha (TNFalpha) in adjacent endothelial and inflammatory cells. Switching off NF-kappaB in mice from birth to seven months of age, using a hepatocyte-specific inducible IkappaB-super-repressor transgene, had no effect on the course of hepatitis, nor did it affect early phases of hepatocyte transformation. By contrast, suppressing NF-kappaB inhibition through anti-TNFalpha treatment or induction of IkappaB-super-repressor in later stages of tumour development resulted in apoptosis of transformed hepatocytes and failure to progress to hepatocellular carcinoma. Our studies thus indicate that NF-kappaB is essential for promoting inflammation-associated cancer, and is therefore a potential target for cancer prevention in chronic inflammatory diseases.

As a result of deprivation of oxygen (hypoxia) and nutrients, the growth and viability of cells is reduced. Hypoxia-inducible factor (HIF)-1alpha helps to restore oxygen homeostasis by inducing glycolysis, erythropoiesis and angiogenesis. Here we show that hypoxia and hypoglycaemia reduce proliferation and increase apoptosis in wild-type (HIF-1alpha+/+) embryonic stem (ES) cells, but not in ES cells with inactivated HIF-1alpha genes (HIF-1alpha-/-); however, a deficiency of HIF-1alpha does not affect apoptosis induced by cytokines. We find that hypoxia/hypoglycaemia-regulated genes involved in controlling the cell cycle are either HIF-1alpha-dependent (those encoding the proteins p53, p21, Bcl-2) or HIF-1alpha-independent (p27, GADD153), suggesting that there are at least two different adaptive responses to being deprived of oxygen and nutrients. Loss of HIF-1alpha reduces hypoxia-induced expression of vascular endothelial growth factor, prevents formation of large vessels in ES-derived tumours, and impairs vascular function, resulting in hypoxic microenvironments within the tumour mass. However, growth of HIF-1alpha tumours was not retarded but was accelerated, owing to decreased hypoxia-induced apoptosis and increased stress-induced proliferation. As hypoxic stress contributes to many (patho)biological disorders, this new role for HIF-1alpha in hypoxic control of cell growth and death may be of general pathophysiological importance.

Adult neovascularization relies on the recruitment of circulating cells, but their angiogenic roles and recruitment mechanisms are unclear. We show that the endothelial growth factor VEGF is sufficient for organ homing of circulating mononuclear myeloid cells and is required for their perivascular positioning and retention. Recruited bone marrow-derived circulating cells (RBCCs) summoned by VEGF serve a function distinct from endothelial progenitor cells. Retention of RBCCs in close proximity to angiogenic vessels is mediated by SDF1, a chemokine induced by VEGF in activated perivascular myofibroblasts. RBCCs enhance in situ proliferation of endothelial cells via secreting proangiogenic activities distinct from locally induced activities. Precluding RBCCs strongly attenuated the proangiogenic response to VEGF and addition of purified RBCCs enhanced angiogenesis in excision wounds. Together, the data suggest a model for VEGF-programmed adult neovascularization highlighting the essential paracrine role of recruited myeloid cells and a role for SDF1 in their perivascular retention.

Hormone refractory metastatic prostate cancer remains an incurable disease. We found that high expression levels of the chemokine receptor CXCR4 correlated with the presence of metastatic disease in prostate cancer patients. Positive staining for CXCL12, the ligand for CXCR4, was mainly present in the tumor-associated blood vessels and basal cell hyperplasia. Subcutaneous xenografts of PC3 and 22Rv1 prostate tumors that overexpressed CXCR4 in NOD/SCID mice were two- to threefold larger in volume and weight vs. controls. Moreover, blood vessel density, functionality, invasiveness of tumors into the surrounding tissues, and metastasis to the lymph node and lung were significantly increased in these tumors. Neutralizing the interactions of CXCL12/CXCR4 in vivo with CXCR4 specific antibodies inhibited the CXCR4-dependent tumor growth and vascularization. In vitro, CXCL12 induced the proliferation and VEGF secretion but not migration of PC3 and 22Rv1 cells overexpressing CXCR4. Similar effects of CXCR4 overexpression on tumor growth in vivo were also noted in two breast cancer lines, suggesting that the observed effect of CXCR4 is not unique to prostate tumor cells. Thus high levels of the chemokine receptor CXCR4 induce a more aggressive phenotype in prostate cancer cells and identify CXCR4 as a potential therapeutic target in advanced cases of metastatic prostate cancer.

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