Abstract 1783: Distinctive effects of the Src-inhibitor, saracatinib (AZD0530), on T-cell activation and differentiation: A basic study to combine Src-inhibitor and vaccine based-cancer immunotherapy
Authors: Takai Shinji , Schlom Jeffrey , Greiner John W. 
Published: August 2014

Targeted inhibitors have become attractive as novel therapies against cancer. Inhibition of Src-family kinases (SFK) is attractive since they have been implicated in tumor progression. Saracatinib is a selective inhibitor of SFKs which is undergoing clinical investigation in NSCLC and breast cancer. Emerging preclinical data have also indicated possible immune-potentiating effects when some inhibitor-based therapies are combined with immunotherapy. However, combination of a SFK inhibitor with immune-based therapy is particularly challenging since SFKs are expressed in immune cells and play a central role in T-cell activation. The primary aim of this study was to investigate the effects of a SFK inhibitor – saracatinib – on tumor and T cells in vitro and the development of antigen-specific cell mediated immunity.

Treatment of murine colon, lung and pancreatic tumor cells with saracatinib (0.3-10 µM) inhibited SFK and resulted in increased apoptosis. Although similar findings were observed in naive T-cells, activated T-cells were resistant to the cytotoxic effects of saracatinib at intermediate doses (up to 3 µM). In fact, low dose (0.3-1 µM) saracatinib enhanced IFN-γ production by 50% in activated CD8+ T-cells and increased central memory (CD44+/CD62L+) CD8+ T-cells after cognate peptide stimulation. These immune-potentiating effects on CD8+ T-cells were observed when the T cells expressed CD44 (i.e. activated T-cells). Furthermore, these effects by saracatinib might be due to inhibition of molecule other than SFK since results from IP-western blot and kinase activity assays for Src, Lck and Fyn in extracts from activated T-cells showed that Src kinase was not activated and neither Lck or Fyn were inhibited by 1 µM of saracatinib. This hypothesis was further supported in other studies in which treatment with dasatinib, another SFK-inhibitor, suppressed IFN-γ production, yet failed to change central memory cell generation at any doses. These findings suggest distinctive effects of saracatinib at lower doses and timing with respect to T-cell activation and differentiation. In vivo saracatinib daily administration (10mg/kg) after rV/rF-flu-NP34 vaccine had no adverse effects on the generation of Ag-specific CD8+ T-cells and increased the number of central memory CD8+ T-cells compared with vaccine alone. Moreover, splenocytes from saracatinib treated mice showed enhanced IFN-γ production upon ex vivo stimulation by peptide.

These immune-potentiating effects on CD8+ T-cells by low dose of saracatinib might afford better protection from cancer progression when combined with cancer vaccine. The dose and timing for administration of saracatinib with cancer vaccine should be optimized to obtain better results in preclinical study as well as future translational studies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1783. doi:10.1158/1538-7445.AM2011-1783