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Peregrine Pharmaceuticals (NASDAQ: PPHM [FREE Stock Trend Analysis]) today announced data from studies validating the immune-stimulatory mechanism of action of bavituximab and demonstrating that the combination of a preclinical phosphatidylserine (PS)-targeting antibody with the immune checkpoint inhibitors anti-CTLA-4 or anti-PD-1 antibodies yielded superior anti-tumor immune responses in animal models of melanoma and colon cancer compared to anti-CTLA-4 and PD-1 antibodies alone. These data were presented yesterday and today as a late-breaking poster presentation and a poster presentation, respectively at the 105th Annual Meeting of the American Association for Cancer Research (AACR) being held in San Diego, California from April 5-9, 2014. Bavituximab is an investigational immunotherapy currently being evaluated in second-line, non-small cell lung cancer (NSCLC) as part of the SUNRISE pivotal Phase III clinical trial. "Data from these combination studies are compelling as they provide further evidence that support the immune-stimulatory effects of bavituximab in reducing the prevalence of key immunosuppressive checkpoints in the tumor environment, reducing tumor-suppressive factors, reducing immune suppressor cells and providing increased tumor-specific immunity," said Jeff T. Hutchins, Ph.D., vice president of preclinical research at Peregrine. "These data also show that when combined with downstream immune checkpoint inhibitors such as anti-CTLA-4 and anti-PD-1, PS targeting mediates an improved protective tumor-specific immunity following tumor rechallenge. While these new downstream checkpoint inhibitors have been shown to strengthen the tumor-killing activity of T-cells and thus extend survival in some patients, there remains a need to increase the number of responders that mount anti-tumor T-cell responses in order to maximize the effects of these downstream checkpoint inhibitors. We believe a PS-targeting antibody, such as bavituximab, plays a key role in reducing tumor suppression and driving a more inclusive immune-mediated response. Insights from these data will influence our future clinical development plans including the soon to be opened investigator-sponsored trial assessing the potential of bavituximab and an anti-CTLA-4 antibody in patients with advanced melanoma." In a poster titled: "Targeting of Phosphatidylserine by Monoclonal Antibodies Enhances Activity of Immune Checkpoint Inhibitors in Tumors," scientists from Peregrine Pharmaceuticals, led by Bruce Freimark, Ph.D., director of pre-clinical research oncology, reported that animals treated with the PS-targeting antibody ch1N11, the preclinical equivalent to bavituximab, in combination with anti-CTLA-4 or anti-PD-1 in melanoma and colon cancer tumor models demonstrated greater delayed tumor growth and suppression than anti-CTLA-4 or anti-PD-1 alone. Results also showed that the combination with anti-CTLA-4 reduced M2 macrophages in the melanoma tumor model, an important cell type responsible for facilitating tumor growth and proliferation. In addition, in the preclinical melanoma model, the combination of ch1N11 with anti-CTLA-4 or anti-PD-1 antibody developed protective tumor-specific immunity to tumor re-challenge than either the anti-CTLA-4 or anti-PD-1 antibody alone. Lastly, results showed that the combination treatment of ch1N11 and anti-PD-1 led to a proportional increase in tumor infiltrating cytotoxic T-cells, while decreasing PD-L1 expression on tumor derived CD45 cells such as tumor, endothelial and stromal cells as compared to anti-PD-1 alone. "We now have compelling evidence from these preclinical studies in multiple tumor models that PS-targeting antibodies mediate a fundamental immune-stimulatory shift in the tumor environment, facilitating increased antigen presenting cells as well as tumor-specific cytotoxic T-cells," said Peregrine's Dr. Freimark. "With the use of immunohistochemical staining, we have seen that tumors from animals treated with ch1N11 in combination with anti-PD-1 antibody showed faster and more complete T-cell and macrophage tumor infiltration rates, which correlate with decreased tumor cells, than anti-PD-1 alone. We look forward to further exploring the potential of the bavituximab with other immune checkpoint inhibitors." In a poster titled: "Phosphatidylserine-Targeting Antibody Synergizes with anti-PD-1 Antibody to Inhibit Tumor Growth in K1735 Mouse Melanoma Model," researchers from the University of Texas Southwestern Medical Center summarized their findings that PS-targeting antibodies block PS-mediated tumor immunosuppression while reactivating tumor immunity at multiple levels. Specifically, results showed that a PS-targeting antibody repolarized tumor-associated macrophages (TAM) from an M2 to a M1-phenotype, decreased the presence of myeloid-derived suppressor cells (MDSC), promoted dendritic cell maturation into cells having the phenotype of functional antigen presenting cells and elicited antitumor T cell immunity. In addition, statistically signifcant differences were seen in T-cell mediating markers IL-2 and gamma-interferon with the ch-1N11 and PD-1 combination. 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