Major obstacles for the development of immunotherapeutics are the ability of tumors to escape the immune system coupled with toxicity associated with systemic administration. To overcome these challenges, we have developed an adenoviral vector, Ad-RTS-IL-12 (AD), administered intratumorally (IT) under control of the RheoSwitch Therapeutic System® (RTS) technology platform. Expression of IL-12 mRNA and IL-12 protein is tightly regulated by the oral administration of a small molecule activator ligand, veledimex (AL).

We have previously demonstrated a concentration-related increase in IL-12 mRNA concomitant with increase in expression of IL-12 protein in HT1080 cells transduced with AD and incubated with AL. Removal of AL from the media resulted in a return to baseline IL-12 expression within 48 hours. Results from the subcutaneous 4T1 syngeneic BALB/c mouse mammary tumor model demonstrated an AL dose-related increase in tumor IL-12 mRNA and IL-12 protein expression with the maximum IL-12 tumor protein level of 280 ng/mg achieved at 150 mg/m2 AL + 1e10 vp AD. In addition, a return to baseline IL-12 mRNA and IL-12 protein expression was observed on cessation of AL.

The effect of AD + AL on tumor growth rate was evaluated in a subcutaneous 4T1 syngeneic BALB/c mouse mammary tumor model. A single intratumoral injection of 1e10 vp AD combined with oral administration of AL (15, 30, 75 or 150 mg/m2) on a Q1Dx5 schedule led to significant AL dose-related tumor growth inhibition with tumor size reduction of 27%, 37%, 57% and 60%, respectively when compared to vehicle on Day 33. Neither AD or AL alone had an effect on tumor growth rate relative to vehicle control. No change in clinical signs or body weight was observed when compared to vehicle alone. Tumor growth inhibition correlated with an increase in tumor IL-12 levels, a decrease in Tregs, and an increase in cytotoxic T cells. Results from a phase 1 study in melanoma have shown dose-related production of IL-12 and clinical activity in injected and non-injected lesions at 100 and 160 mg of AL.

Cytotoxic agents at low doses have been shown to prime the immune system and combination with immunotherapy may augment tumor specific T-cell immune responses resulting in enhanced efficacy. In the 4T1 mouse mammary tumor model Ad-RTS-mIL12 (1e10vp) + AL (30 mg/m2) combined with palifosfamide (40 or 120 mg/m2 QD IP for 3 days) significantly inhibited tumor growth (∼71-90% vs. control) concomitant with increased median survival when compared to the single agents alone. Based on these findings in a multicenter, open-label, randomized, phase 2 study evaluating the safety and efficacy of AD + AL alone or in combination with cytotoxic agents in subjects with recurrent/metastatic breast cancer with accessible tumor(s) is ongoing. This study assesses AD + AL administered as a monotherapy and a combination therapy. In the monotherapy arm, AD is administered IT on Day 1 and AL 140 mg is administered orally on either a Q1Dx7 or QODx14 schedule. In the combination arm, palifosfamide 120 mg/m2 IV Q1Dx3 is be administered with AD + AL QODx14 (28 day cycle). Preliminary data show that AD + AL is safe and well tolerated. Preclinical and clinical data will be presented.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-02-01.