The PPAR Agonist Rosiglitazone Suppresses Syngeneic Mouse SCC (Squamous Cell Carcinoma) Tumor Growth through an Immune-Mediated Mechanism

Recent evidence suggests that PPAR agonists may promote anti-tumor immunity. We show that immunogenic PDV cutaneous squamous cell carcinoma (CSCC) tumors are rejected when injected intradermally at a low cell number (1 x 10(6)) into immune competent syngeneic hosts, but not immune deficient mice. At higher cell numbers (5 x 10(6) PDV cells), progressively growing tumors were established in 14 of 15 vehicle treated mice while treatment of mice with the PPAR agonist rosiglitazone resulted in increased tumor rejection (5 of 14 tumors), a significant decrease in PDV tumor size, and a significant decrease in tumor cell Ki67 labeling. Rosiglitazone treatment had no effect on tumor rejection, tumor volume or PDV tumor cell proliferation in immune deficient NOD.CB17-Prkdc(SCID)/J mice. Rosiglitazone treatment also promoted an increase in tumor infiltrating CD3(+) T-cells at both early and late time points. In contrast, rosiglitazone treatment had no significant effect on myeloid cells expressing either CD11b or Gr-1 but suppressed a late accumulation of myeloid cells expressing both CD11b and Gr-1, suggesting a potential role for CD11b(+)Gr-1(+) myeloid cells in the late anti-tumor immune response. Overall, our data provides evidence that the PPAR agonist rosiglitazone promotes immune-mediated anti-neoplastic activity against tumors derived from this immunogenic CSCC cell line.