NEW YORK, April 9, 2013 (GLOBE NEWSWIRE) -- ZIOPHARM Oncology, Inc. (Nasdaq:ZIOP), a biopharmaceutical company focused on the development and commercialization of new cancer therapies, announced today the presentation of results from a study in a breast cancer murine model demonstrating the anti-tumor effects and tolerability of Ad-RTS-mIL-12, a viral vector DNA-based therapeutic for the controlled, local expression of IL-12, an important protein for enhancing antitumor immunity. The data were presented at the American Association for Cancer Research 2013 Annual Meeting (AACR 2013) taking place April 6-10, 2013 in Washington, D.C. The study was conducted jointly by ZIOPHARM and Intrexon Corporation, a synthetic biology company that utilizes its proprietary technologies to provide control over cellular function. ZIOPHARM is Intrexon's exclusive channel partner for the development of in vivo therapeutics in oncology. For the study, intratumoral administration of Ad-RTS-mIL-12 (Ad) was examined in a 4T1 BALB/c mouse breast carcinoma model. Production of murine IL-12 was controlled using Intrexon's RheoSwitch Therapeutic System ® (RTS ®) platform and oral administration of the activator ligand INXN-1001 (AL). Oral administration of AL was found to elicit a dose-related increase in plasma AL levels, which correlated with increasing tumor levels of AL. The increase in tumor AL levels in combination with Ad in turn resulted in a dose-related increase in expression of mIL-12 in the tumor, with minimal increase in serum mIL-12. This increase in AL-regulated tumor IL-12 levels correlated with an increase in tumor-infiltrating CD4 + and CD8 + T cells in and adjacent to the tumor, concomitant with a decrease in tumor regulatory T cells. This resulted in a dose-related decrease in tumor growth rate. Moreover, the therapeutic strategy appears to be well tolerated, as no change in clinical signs or body weight was observed in the treated animals when compared with vehicle alone. Samuel Broder, M.D., Chairman of Intrexon's Therapeutic Opportunities Committee and former Director of the NCI (National Cancer Institute), stated, "Two major obstacles for the development of immunotherapeutics in the treatment of cancer are the ability of tumors to evade the anti-cancer capabilities of the immune system and the toxicity often associated with the systemic administration of immunomodulating agents. To overcome these challenges, we have developed Ad-RTS-IL-12, a DNA-based system for the regulated expression of IL-12, that allows for localized, controlled expression of immunomodulating cytokines and activation of their corresponding anti-tumor effects. This strategy is now being tested in the clinic, with the recent launch of a Phase 2 Study of Ad-RTS-IL-12 combined with palifosfamide in the treatment of advanced breast cancer."