Immunomodulatory preconditioning with cyclophosphamide enhances the inhibitory effect of adenovirus gene transfer of IL-12 on growth and metastasis of colorectal carcinoma in mice

MARIANA MALVICINI; FLAVIA PICCIONI; JUAN BAYO; ESTEBAN FIORE; CATALINA ATORRASAGASTI; MARIANA GARCÍA; LAURA ALANIZ; JORGE B. AQUINO; O. GRACIELA SCHAROVSKY; PABLO MATAR; GUILLERMO MAZZOLINI

Río de Janeiro

Simposio; Simpósio Sul-Americano de Terapia Gênica; 2011

Instituto Nacional do Câncer (Inca)

Colorectal carcinoma (CRC) is the second most common cancer worldwide and surgery is the primary treatment but only it can be performed in 20% of patients. New therapeutic options are needed. Interleukin-12 (IL-12) is an immunostimulatory cytokine with potent antitumor effects in several models but toxicity has been associated with its systemic application. Gene transfer hasemerged as a tool to express therapeutic genes into the tumor milieu avoiding systemic toxicity. The aim of this study was to analyze whether sub-therapeutic doses of an adenovirus encoding IL-12 (AdIL-12) might synergize with single low or metronomic low doses of cyclophosphamide (Cy) for the treatment of CRC Balb/c mice were injected with CT26 cells intrahepatic or subcutaneously (day 0); distributed in groups (day 7) and treated with: saline; Cy 50 mg/Kg i.p (single dose, day 7); AdIL-12 109 TCID50 i.t (day 8); Cy single dose + AdIL-12; Cy 25 mg/kg i.p. (metronomic dose, 3 times a week) or Cy metronomic dose + AdIL-12. Tumor volume was measured and samples of peripheral blood and spleen were taken for immunological studies. Low dose of Cy with AdIL-12 resulted in a potent antitumoral effect higher than each agent alone in all of schedules tested. The percentages of complete tumor regressions induced by combined treatment were 50% and 40% both in s.c and liver metastasis models respectively. Metronomic dose of Cy +AdIL-12 was not superior to single dose of Cy+AdIL-12. However, both schedules decreased the number of regulatory T cells (Tregs) in peripheral blood and spleen of treated micein comparison with untreated or single agent-treated mice (p<0,05 and p<0,01 respectively). Also, the antitumor effect of combined therapy was reverted by in vivo administration of Tregs. The combination induced a significant increase in the number of dendritic cells and lead to development of specific IFN-γ-secreting CD4+ T-lymphocytes response. No signs of toxicity were observed in treated animals. Our results suggest that AdIL-12 in combination with Cy induce a potent synergistic antitumor effect against CRC by reversion of suppressive mechanisms and activation of the specific immune response.