Abstract PR-7: Antitumor activity of the immunomodulatory peptide SCV-07 correlates with changes in macrophage STAT3 signal transduction and cytokine secretion. (2011)

Abstract The synthetic dipeptide gamma-D-glutamyl-L-tryptophan (SCV-07) is able to enhance immune responses in preclinical anti-viral and vaccine models and is currently under clinical evaluation for attenuation of radiation-induced oral mucositis in HNSCC patients. We recently demonstrated that SCV-07 also has anti-tumor efficacy in various syngeneic and nude mouse xenograft models despite lack of direct inhibition of the tumor cell growth in standard proliferation assays. Based on these data, along with observations that SCV-07 enhances a Th1-type immune response in vivo and binds with high affinity to cells and membranes from mouse thymocytes and macrophages, we sought to explore the hypothesis that SCV-07 has anti-tumor activity through modulation of immune cells in the tumor microenvironment. Towards this end we evaluated effects of SCV-07 on signal transduction and biological properties of T cells and macrophages in cell culture and in mouse tumor models. Using phosphoprotein detection arrays broad changes in global phosphorylation patterns were observed upon SCV-07 treatment of Jurkat T cells including STATs 3, 5 and 6, SHP2, several Src family kinases and various cytoplasmic and membrane proteins. We subsequently showed that SCV-07 leads to inhibition of cytokine-induced but not basal STAT3 tyrosine phosphorylation (PY) in Jurkat T cells and this required tyrosine phosphatase activity. New data using phosphospecific antibodies in western blots of Jurkat cells demonstrate that SCV-07 mediates an increase in basal and cytokine-induced phosphorylation of SHP2, a tyrosine phosphatase known to dephosphorylate STAT3. The phosphorylated residue was identified as Tyr542, known to activate SHP2. New findings also demonstrate that SCV-07 inhibits IL-6 stimulated STAT3 PY and induces SHP2 Tyr542 phosphorylation in primary mouse peritoneal macrophages treated in culture, similar to the findings with cell lines. Further evaluation of human PBMC showed that SCV-07 inhibited IL-6, IL-10 and IFNα induced STAT3 PY in monocytes from 2 of 3 PBMC donors. In a syngeneic B16 melanoma model we initially determined that SCV-07 had anti-tumor efficacy and this was accompanied by a decrease in serum CCL2, a cytokine produced by and chemotactic for monocytes/macrophages and which has its expression regulated by STAT3. New results show that SCV-07 can directly inhibit basal and cytokine induced CCL2 secretion from purified primary mouse peritoneal macrophages. Experiments are underway to evaluate the activation state and distribution of tumor infiltrated macrophages and T cells in B16 melanoma xenografts undergoing efficacy response to SCV-07 treatment and these findings will be presented. Taken together our data support a model whereby SCV-07 could mediate an anti-tumor effect by reducing both chemotaxis of tumor-growth promoting macrophages and secretion of tumor growth promoting cytokines in the tumor microenvironment, and also promote a shift from Th2 to Th1 profile of local T cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr PR-7.