Abstract 3115: High-capacity adenoviral vectors with controlled expression of interleukin 12 as a new strategy against pediatric osteosarcoma

Osteosarcoma (OS) is the most frequent and aggressive primary bone tumor in children and young adults, with a high propensity to metastasize to the lungs. Despite therapeutic efforts, the survival rate for metastatic or relapsed patients in under 30%. For this reason, we need new strategies to halt the progression of primary bone tumor and impede the metastatic stage. Interleukin-12 (IL12) is a cytokine implicated in a variety of immune activities including the stimulation of T and natural killer (NK) cells and the production of high levels of IFNγ. In addition, this process triggers an anti-angiogenic response leading to T reg inhibition and tumor death. This cytokine has shown significant antitumor activity in several animal models and clinical trials. The aim of this work was to evaluate the antisarcoma effect of a high-capacity adenovirus vector carrying the mouse IL12 (mIL12). This vector harbours a mifepristone (RU486)-inducible system for controlled expression of IL12 (HCA-EFZP-IL12) in order to improve the treatment of OS and reduced the systemic toxicity associated with IL12. The murine K7M2 OS cell line was injected intratibially in Balbc mice to induce bone tumor. HCA-EFZP-IL12 was administered intratumorally (two doses 2 days apart) in the orthotopic model with mifepristone induction during two weeks. Blood samples were collected 10 h after the first RU486 induction; mIL12 protein level was measured by ELISA, and tumor volumes were measured using a calliper. At the end of the experiment we collected tibias, lungs and livers for immunohistochemical studies. Our results showed a reduction of local tumor growth and also a significant extended overall survival. Importantly, the treatment led to long-term survivors free of disease. We performed a re-challenge experiment to assess the generation of antitumor memory and we are currently waiting for those results. Immunohistochemical analyses showed an increase in CD3, mainly CD4 and CD8 and a decrease of T-reg cells. Moreover, splenocytes from treated mice produced significant higher amounts of IFNγ than those of control mice. In summary, the role of the microenvironment and the potent antitumor immune response mediated by controlled expression of IL12 by an HC-Ad equipped with a drug-inducible system can be a real therapeutic option for primary pediatrics OS. Citation Format: Marta Zalacain, Virginia Laspieda, Naiara Martinez-Velez, Lucia Marrodan, Maria Bunuales, Marisol Gonzalez-Huarriz, Maider Varela, Montserrat Puigdelloses, Manuela Gonzalez-Aparicio, Marta Maria Alonso, Ruben Hernandez, Ana Patino-Garcia. High-capacity adenoviral vectors with controlled expression of interleukin 12 as a new strategy against pediatric osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3115.