CD73 is a cell surface 5 0 -nucleotidase that converts AMP to adenosine, an immune suppressive molecule. CD73 may promote immune escape in cancer by contributing to the degradation of extracellular ATP released by dying cancer cells in hypoxic tumors or following chemotherapy. However, whether CD73 exerts a critical oncogenic function during tumorigenesis is unknown. In this study, we used genetically deficient mice to investigate its contribution to autochthonous tumor formation. CD73 deficiency suppressed the development of 3-methylcholanthrene (MCA)-induced fibrosarcomas through a mechanism relying upon IFN-g, natural killer (NK) cells, and CD8 þ T cells. Similarly, CD73 deficiency also suppressed prostate tumorigenesis in TRAMP transgenic mice.Importantly, treatment with an anti-CD73 monoclonal antibody effectively suppressed growth of established MCA-induced tumors or TRAMP-C1 prostate tumors and inhibited the development of TRAMP-C1 lung metastases. The therapeutic activity of anti-CD73 monoclonal antibody against primary tumors was dependent on CD8 þ T cells, whereas its antimetastatic activity was dependent on host CD73 expression independent of T cells or NK cells. Taken together, our findings indicate that CD73 is a critical factor in tumorigenesis and that anti-CD73 antibodies may offer a novel generalized strategy to blunt immune escape and treat cancer. Cancer Res; 72(9); 2190-6. Ó2012 AACR.

ABSTRACT

Tumor hypoxia induces the up-regulation of Hif-1alpha which in turn induces the expression of genes including VEGF to recruit new blood vessel outgrowth, enabling tumor growth and metastasis. Interference with the Hif-1 pathway and neoangiogenesis is an attractive anti-tumor target. The hydroxylation of Hif-1alpha by PHD proteins during normoxia serves as a recognition motif for its proteasomal degradation. However, under hypoxic conditions, hydroxylation is inhibited and furthermore, PHD proteins are themselves poly-ubiquitylated and degraded by Siah ubiqiuitin ligases. Our data demonstrate for the first time that inhibition of the interaction between Siah and PHD proteins using a peptide derived from a Drosophila protein interferes with the PHD degradation. Furthermore, cells stably expressing the inhibitor display reduced up-regulation of Hif-1alpha protein levels and Hif-1 mediated gene expression under hypoxia. In a syngeneic mouse model of breast cancer, the inhibitor reduced tumor growth and neoangiogenesis and prolonged survival of the mice. In addition, levels of Hif-1alpha and its target Glut-1 are reduced in the inhibitor expressing tumors. These data demonstrate, in a proof-of-principle study, that Siah protein, the most upstream component of the hypoxia pathway yet identified, is a viable drug target for anti-tumor therapies.

Tumor hypoxia is associated with resistance to antiangiogenic therapy and poor prognosis. The Siah E3 ubiquitin ligases regulate the hypoxic response pathway by modulating the turnover of the master proangiogenic transcription factor hypoxia-inducible factor-1a . In this study, we show that genetic deficiency in the Siah family member Siah2 results in vascular normalization and delayed tumor growth in an established transgenic model of aggressive breast cancer. Tumors arising in a Siah2À/À genetic background showed increased perfusion and pericyte-associated vasculature, similar to that occurring with antiangiogenic therapy. In support of the role of Siah2 in regulating levels of Hif-1a, expression of angiogenic factors was decreased in Siah2tumors. Blood vessel normalization in Siah2 À/À tumors resulted in an increased response to chemotherapy and prolonged survival. Together, our findings offer a preclinical proof of concept that targeting Siah2 is sufficient to attenuate Hif-1a-mediated angiogenesis and hypoxia signaling, thereby improving responses to chemotherapy.

Background Gene promoter methylation is an important regulator of expression and is a key epigenetic factor in tumorigenesis. DNA methylation is mediated by DNA methyltransferases (DNMTs), of which three active forms have been identified: DNMT1, DNM3A and DNMT3B. The C→T transition polymorphism (C46359T) in the promoter of the DNMT3B gene, which significantly increases transcriptional activity, has been postulated to increase the propensity for promoter-hypermethylation-mediated silencing of tumour suppressor genes.