Abstract LB-175: Concomitant radiotherapy (RT) and TGFβ neutralizing antibodies alters tumor microenvironment and promotes tumor regression

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Transforming growth factor-β (TGFβ) has a broad range of pro-tumorigenic activities and immunosuppressive functions that have drawn considerable interest in cancer, especially since pharmaceutical inhibitors are in clinical trials. It is not clear how best to release the considerable potential of TGFβ inhibitors. Radiation induces TGFβ activity that promotes effective response to DNA damage, which protects cancer cells from radiation-induced cell death. Radition therapy is quite effective in eliciting immunogenic signals but is itself a source of immunosuppressive effects in the tumor microenvironment. Here we demonstrate that inhibition of TGFβ in pre-clinical models of breast and lung cancer creates a systemic environment that relieves the tumor-driven immune-suppression and creates a tumor microenvironment that promotes tumor regression. Balb/c and C57/BL6 mice were inoculated with TSA breast cancer cells and Lewis lung cancer cells respectively into the flank and injected with 10mg/kg i.p preclinical TGFβ neutralizing antibody 1D11 or control antibody 13C4, both provided by Genzyme, Inc., beginning on day 13 post tumor cell implantation and continuing on alternate days to experiment termination. Radiotherapy (RT) was initiated on day 14 in 5 daily, 6Gy fractions. Tumor growth was caliper-measured thrice/week. Flow cytometry analysis and ex vivo cultures were used to assess frequency and functional characteristics of immune cells. TGFβ neutralizing antibody monotherapy had no effect on tumor growth, however when combined with RT, tumor growth was substantially decreased relative to radiation treatment alone in both tumor models (p< 0.001). Notably, more than half of mice achieved complete tumor regression in the breast cancer model, suggesting activation of tumor immunity. TGFβ blockade decreases a splenic reservoir of CD11b+ myeloid-derived suppressor cells that mediate immunosuppression in the tumor microenvironment as well as CD11b+Gr1+/intF4/80+ precursors of tumor-associated macrophages in both tumor models. Immunoactivating IL12 was upregulated upon TGFβ inhibition while immunosuppressive IL10 and pro-angiogenic CXCL1 decreased. The number of splenic CD11c+ MHC Class I+ antigen presenting cells was dramatically reduced from either irradiated TSA and LLC tumor-bearing mice, but unaffected in mice receiving 1D11 antibody concomitant with RT. Tumor cell MHC Class I overexpression, which is induced by in vitro irradiation, was impaired after co-culture with splenocytes from irradiated mice but not from mice receiving the dual treatment or 1D11 alone. Thus, TGFβ blockade, which sensitizes tumor cells to RT, also alleviates tumor suppressive consequences of radiation systemically and creates a pro-immunogenic signal. Together, these actions can achieve persistent tumor control. Citation Format: Ilenia Pellicciotta, Shisuo Du, Silvia Formenti, Mary Helen Barcellos-Hoff. Concomitant radiotherapy (RT) and TGFβ neutralizing antibodies alters tumor microenvironment and promotes tumor regression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-175. doi:10.1158/1538-7445.AM2014-LB-175