Abstract The critical role of angiogenesis in tumor development, progression and metastatization has long been appreciated and several anti-angiogenic inhibitors are approved for use in cancer therapy. Recently it has been reported in pre-clinical mouse models that angiogenesis inhibitors, induced transient primary tumor shrinkage followed by an evasive resistance to the therapy eliciting tumor invasiveness and increased distal metastasis formation (1). Therefore it is crucial to identify new angiogenic modulators and uncover the underlying mechanisms in order to design more effective anti-angiogenic combinatory regimens. A growing body of evidences demonstrated an important role of class3 Semaphorins (Sema3s), that act via receptor complexes binding neuropilins 1 and 2 (Nrp1/2) and transducing the signal by plexins, in regulating angiogenesis and tumor growth (2). We have recently demonstrated that Sema3A is an endogenous inhibitor that is lost during tumor progression and its reintroduction into a mouse model of pancreatic neuroendocrine tumors (RIP-Tag2), resulted in reduced vascular density, blood vessel normalization, restoration of cancer normoxia, and inhibition of tumor growth (3). Herein, we show that the treatment of RIP-Tag2 mice and of a mouse model of cervical cancer (HPV16/E2) with Sema3A by somatic gene transfer employing adeno-associated virus (AAV)-8, induced a dramatic reduction of tumor invasiveness, of metastases formation and a modulation of several epithelial-mesenchymal transition (EMT) genes. Then, we sought to investigate whether the administration of Sema3A in tumors was able to overcome the evasive resistance observed upon treatment with Sunitinib, an anti-angiogenic tyrosine kinase receptors inhibitor (1). Notably, we observed a dramatic reduction of cancer invasiveness and distal metastases formation in both RIP-Tag2 and HPV16/E2 mice simultaneously treated with Sema3A and Sunitinib for 4 weeks, compared to Sunitinib-treated controls. Moreover, while Sunitinib-treated tumors were highly hypoxic and displayed few pericyte-covered vessels, the combinatorial regimen of Sema3A with Sunitinib normalized the vasculature and restored tumor normoxia. Remarkably, Real-Time RT-PCR and confocal microscopy, revealed a strong modulation of EMT genes and a dramatic inhibition of several hypoxia-induced molecules in tumors treated with Sema3A and Sunitinib compared to Sunitinib-treated cancers. Thus, treatment of tumors with Sema3A may safely improve the therapeutic potential of anti-angiogenic drugs, by normalizing the vasculature, inhibiting tumor hypoxia, and modulating the expression of hypoxic-induced genes activated by anti-angiogenic treatments. References 1) Paez-Ribes M. et al. Cancer Cell, 2009. 15:220-31 2) Neufeld G. et al. Nat Rev Cancer 2008. 8:632-45 3) Maione F. et al. J.Clin.Invest, 2009. 119:3356-72 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY41-04. doi:1538-7445.AM2012-SY41-04