Summary A large body of evidence indicates that chronic inflammation is one of key risk factors for cancer initiation, progression, and metastasis. However, the underlying mechanisms responsible for the contribution of inflammation and inflammatory mediators to cancer remain elusive. Here we present genetic evidence showing that loss of CXCR2 dramatically suppresses colonic chronic inflammation and colitis-associated tumorigenesis through inhibiting infiltration of myeloid-derived suppressor cells (MDSCs) into colonic mucosa and tumors in a mouse model of colitis-associated cancer. CXCR2 ligands were elevated in inflamed colonic mucosa and tumors and induced MDSC chemotaxis via its receptor, CXCR2. Adoptive transfer of wild type MDSCs into Cxcr2−/− mice restored AOM/DSS-induced tumor progression. MDSCs accelerated tumor growth by inhibiting CD8+ T cell cytotoxic activity.

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Although DNA methylation is one of the critical ways for silencing tumor suppressor and DNA repair genes during tumor initiation and progression, the mechanisms underlying DNA methylation in cancer remain unclear. Here we show that prostaglandin E2 (PGE2) silences certain tumor suppressor and DNA repair genes via DNA methylation to promote tumor growth. These findings uncover a previously unrecognized role for PGE2 in the promotion of tumor progression.

Hepatocyte growth factor (HGF), a natural ligand for the c-met protooncogene product, exhibits mitogenic, motogenic, and morphogenic activities for regeneration of the liver, kidney, and lung. Recently, HGF was clearly shown to enhance neurite outgrowth in vitro. To determine whether HGF has a neuroprotective action against the death of neurons in vivo, we studied the effect of HGF on delayed neuronal death in the hippocampus after 5-minute transient forebrain ischemia in Mongolian gerbils. Continuous postischemic intrastriatal administration of human recombinant HGF (10 or 30 micrograms) for 7 days potently prevented the delayed death of hippocampal neurons under both anesthetized and awake conditions. Even when HGF infusion started 6 hours after ischemia (i.e., in a delayed manner), HGF exhibited a neuroprotective action. We conclude that HGF, a novel neurotrophic factor, has a profound neuroprotective effect against postischemic delayed neuronal death in the hippocampus, which may have implications for the development of new therapeutic strategies for ischemic neuronal damage in humans.

Homeodomain-only protein X (HOPX)-β promoter methylation was recently shown to be frequent in human cancers and was suggested as tumor suppressor gene in esophageal and gastric cancer. The aim of this study was to investigate the mechanistic roles of HOPX-β promoter methylation and its clinical relevance in colorectal cancer (CRC). HOPX-β promoter methylation was assessed in human CRC cell lines and 294 CRC tissues. HOPX mRNA and protein levels were measured in relation to HOPX-β promoter methylation. The effects of forced HOPX expression on tumorigenesis were studied using in vitro and in vivo assays. The association between HOPX-β promoter methylation and clinical relevance of CRC patients was determined. HOPX-β promoter methylation is cancer-specific and frequently found in CRC cell lines and tissues, resulting in the down-regulation of HOPX mRNA and protein levels. In CRC cell lines, forced expression of HOPX suppressed proliferation, invasion, and anchorage-independent growth. DNA microarray analyses suggested critical downstream genes that are associated with cancer cell proliferation, invasion or angiogenesis. In a mouse xenograft model, HOPX inhibited tumorigenesis and angiogenesis. Finally, HOPX-β promoter methylation was associated with worse prognosis of stage III CRC patients (hazard ratio= 1.40, P = .035) and also with poor differentiation (P = .014). In conclusion, HOPX-β promoter methylation is a frequent and cancer-specific event in CRC progression. This epigenetic alteration may have clinical ramifications in the diagnosis and treatment of CRC patients.

Bone marrow (BM)-derived hematopoietic cells, which are major components of tumor stroma, determine the tumor microenvironment and regulate tumor phenotypes. Cyclooxygenase (COX)؊2 and endogenous prostaglandins are important determinants for tumor growth and tumor-associated angiogenesis; however, their contributions to stromal formation and angiogenesis remain unclear. In this study, we observed that Lewis lung carcinoma cells implanted in wild-type mice formed a tumor mass with extensive stromal formation that was markedly suppressed by COX-2 inhibition, which reduced the recruitment of BM cells. Notably, COX-2 inhibition attenuated CXCL12/CXCR4 expression as well as expression of several other chemokines. Indeed, in a Matrigel model, prostaglandin (PG) E 2 enhanced stromal formation and CXCL12/CXCR4 expression. In addition, a COX-2 inhibitor suppressed stromal formation and reduced expression of CXCL12/CXCR4 and a fibroblast marker (S100A4) in a micropore chamber model. Moreover, stromal formation after tumor implantation was suppressed in EP3 ؊/؊ mice and EP4 ؊/؊ mice, in which stromal expression of CXCL12/ CXCR4 and S100A4 was reduced. The EP3 or EP4 knockout suppressed S100A4 Recent advances in tumor biology have identified the stroma as an important regulator of carcinogenesis and a potentially valuable therapeutic target. Although interactions between the epithelium and stroma have long been considered to be important in tumor progression, the efficacy of targeting stromal components as a therapeutic strategy has not been established, because the specific regulators of such interactions remain unclear. In addition to endothelial cells, macrophages and fibroblasts 1 are the major stromal components of the tumor microenvironment, and they play key roles in the enhancement of angiogenesis. It has recently been established that bone marrow (BM)-derived hematopoietic cells are the major components of the stroma of tumors, and that they determine the tumor microenvironment [2][3][4][5][6][7][8] ; however, the specific factors that enhance the functions of BM-derived precursor cells, and the mechanism of recruitment of these cells during tumor angiogenesis, are not fully understood. Tumor-associated angiogenesis in the tumor stroma is a prerequisite for invasive growth of a tumor larger than 2 to 3 mm in diameter, and then metas-

Development of solid cancer depends on escape from host immunosurveillance. Various types of immune cells contribute to tumor-induced immune suppression, including tumor associated macrophages, regulatory T cells, type 2 NKT cells, and myeloid-derived suppressor cells (MDSCs). Growing body of evidences shows that MDSCs play pivotal roles among these immunosuppressive cells in multiple steps of cancer progression. MDSCs are immature myeloid cells that arise from myeloid progenitor cells and comprise a heterogeneous immune cell population. MDSCs are characterized by the ability to suppress both adaptive and innate immunities mainly through direct inhibition of the cytotoxic functions of T cells and NK cells. In clinical settings, the number of circulating MDSCs is associated with clinical stages and response to treatment in several cancers. Moreover, MDSCs are reported to contribute to chemoresistant phenotype. Collectively, targeting MDSCs could potentially provide a rationale for novel treatment strategies in cancer. This review summarizes recent understandings of MDSCs in cancer and discusses promissing clinical approaches in cancer patients.

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