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 G. GARCIA; LAURA ALANIZ; JORGE B. AQUINO; O GRACIELA SCHAROVSKY; PABLO MATAR; GUILLERMO MAZZOLINI

Rio de Jainer

Simposio; Simposio Sul Americano de terapia genica; 2011

Colorectal carcinoma (CRC) is the second most common cancer worldwide andsurgery is the primary treatment but only it can be performed in 20% of patients.New therapeutic options are needed. Interleukin-12 (IL-12) is animmunostimulatory cytokine with potent antitumor effects in several models buttoxicity has been associated with its systemic application. Gene transfer hasemerged as a tool to express therapeutic genes into the tumor milieu avoidingsystemic toxicity. The aim of this study was to analyze whether sub-therapeuticdoses of an adenovirus encoding IL-12 (AdIL-12) might synergize with single lowor metronomic low doses of cyclophosphamide (Cy) for the treatment of CRCBalb/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. Tumorvolume was measured and samples of peripheral blood and spleen were taken forimmunological studies.Low dose of Cy with AdIL-12 resulted in a potent antitumoral effect higher thaneach agent alone in all of schedules tested. The percentages of complete tumorregressions induced by combined treatment were 50% and 40% both in s.c andliver metastasis models respectively. Metronomic dose of Cy +AdIL-12 was notsuperior to single dose of Cy+AdIL-12. However, both schedules decreased thenumber 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<0,01respectively). Also, the antitumor effect of combined therapy was reverted by invivo administration of Tregs. The combination induced a significant increase in thenumber 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 synergisticantitumor effect against CRC by reversion of suppressive mechanisms andactivation of the specific immune response.