Abstract 2838: Intratumoral-regulated expression of IL-12 as a potential immunotherapeutic strategy for the treatment of breast cancer.
Authors: Barrett John A. , Sun Lei , Grigoriadis Maria , Fulan-Freguia Christan , Chan Tim , Fogler Bill , Humeau Laurent , Khosravi-Far Roya , Morgan Robert A. , Youssoufian Hagop 
Published: August 2014

Abstract
A major obstacle for the development of immunotherapeutics is the ability of tumors to escape the immune system coupled with toxicity associated with systemic administration of cytokines. To overcome these challenges we have developed an adenoviral vector with regulated expression of IL-12, Ad-RTS-mIL-12 (Ad), was administered intratumorally under the control of the RheoSwitch Therapeutic System® (RTS®) expression platform. Previously we have shown that a single intratumoral injection of Ad combined with oral administration of the activator ligand, INXN-1001 (AL), led to significant inhibition of tumor growth and increased survival. Herein, we show that localized delivery of IL-12 is well tolerated and its mechanism of action is through an increase in tumor infiltrating leukocytes concomitant with a reduction in tumor growth. In vitro studies using HT1080 human fibrosarcoma cells transduced with Ad and incubated with AL have shown a concentration-related increase in IL-12 mRNA concomitant with an increase in expression of IL-12 protein. Removal of AL from the media resulted in return of IL-12 expression to baseline within 48 hours. In the 4T1 BALB/c mouse model, oral administration of AL elicited a dose- related increase in plasma AL levels which correlated with increasing tumor levels of AL. The increase in tumoral AL in turn activated the RheoSwitch® portion of the adenoviral vector leading to a dose-related increase in tumor IL-12 production with virtually no increase in systemic IL-12. The maximal tumoral IL-12 protein level of ∼280 pg/mg protein was achieved on Day 4 of AL dosing with a concomitant serum IL-12 level of 0.5 pg/mg protein following a single intratumoral injection of Ad-RTS-mIL-12 (1x1010 vp) on Day 1 combined with once daily oral administration of AL at 150 mg/m2 on Days 1-7. This increase in tumoral IL-12 levels correlated with a dose-related increase in tumor-infiltrating CD4-positive and CD-8 positive lymphocytes in and adjacent to the tumor, coupled with an increase in apoptotic marker caspase 3 in the tumor when compared with vehicle. No increase in IL-12 protein expression in mice treated with Ad or AL alone was observed. Moreover, this 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.
These results support our hypothesis that localized delivery of IL-12 is well tolerated and results in an increase in tumor infiltrating leukocytes concomitant with a reduction in tumor growth. These findings suggest the applicability of our immunotherapeutic strategy for the treatment of metastatic breast cancer.
Citation Format: John A. Barrett, Lei Sun, Maria Grigoriadis, Christan Fulan-Freguia, Tim Chan, Bill Fogler, Laurent Humeau, Roya Khosravi-Far, Robert A. Morgan, Hagop Youssoufian. Intratumoral-regulated expression of IL-12 as a potential immunotherapeutic strategy for the treatment of breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2838. doi:10.1158/1538-7445.AM2013-2838