Abstract A04: Targeting immunosuppressive alterations in the tumor microenvironment resulting from therapy-induced DNA damage responses
Authors: Jin Wei , Zhao Aric , Levesque Christine , Colman Ilsa , Nelson Peter S. 
Published: October 2016

Background: Radiation and chemotherapeutics have significantly improved the survival rate among cancer patients although resistance to both treatment approaches commonly develops, particularly in the setting of metastatic disease. It is now recognized that tumor microenvironments (TME) can profoundly influence responses to cytotoxic /genotoxic insults and also alter effective immune-mediated tumor eradication. Major efforts are underway to understand how to improve tumor cell killing within the complex microenvironment of a tumor where tumor-mediated immune suppressive mechanisms have been documented to attenuate immune attack. Senescent/damaged cells have been shown to activate the expression of proinflammatory cytokines, tumor promoting growth factors and proteases which collectively encompass a DNA damage induced secretory program (DDSP). Our preliminary data indicate that genotoxic therapeutics may also generate an immune suppressive microenvironment that could impair an effective immune attack. In this study, we sought to identify the key drivers in the DDSP which hamper the effective-ness of anti-tumor immune responses.

Methods: In this study, we adopted a syngeneic mouse xenograft model to investigate the influence of the DDSP on the immune landscape within the tumor microenvironment (TME) of local and metastatic sites. The Myc-Cap prostate cancer cell line and F4M2 prostate fibroblast line are both derived from FVB mice. We treated F4M2 cells with irradiation (RAD) or genotoxic drugs to induce the DDSP in vitro. The conditional medium (CM) was applied in assays to test the function of different populations of tumor infiltrating lymphocytes (TIL). To further pinpoint the role of Wnt16b, a major component of the DDSP, recombinant protein was used to assess lymphocyte responses.

Results: We hypothesized that the TME DDSP, which is induced by cancer-directed genotoxic treatment, hampers anti-tumor effects by generating an immune suppressive environment. We demonstrated that upon receiving irradiation, DDSP signature genes (IL-6, Wnt16b) were activated in prostate tissue as well as common sites for metastatic prostate cancers. We demonstrated that RAD treated F4M2 CM inhibited T cell proliferation as well as cytotoxic functions of CD8 cells. We further identified that Wnt16b is a key immunosuppressive factor in the CM. In xenograft models, mice transplanted with Myc-Cap/RAD-F4M2 grafts developed significantly larger tumors compared to those receiving sham-treated cell graft (1500mm3 vs. 1023mm3, p=0.039). Mice from the former group exhibited elevated myeloid derived suppressor cells in the periphery as well as reduced numbers of CD8 T cells in the TME.

Conclusions: The DDSP, and particularly the DDSP component Wnt16b, contributes to treatment resistance not only by supporting tumor growth but also creating an immune suppressive TME. Inhibiting the DDSP may enhance anti-tumor effects via the relief of immune suppression.

Citation Format: Wei Jin, Aric Zhao, Christine Levesque, Ilsa Colman, Peter S. Nelson. Targeting immunosuppressive alterations in the tumor microenvironment resulting from therapy-induced DNA damage responses. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A04.