Abstract 2086: Intratumorally administrated encapsulated IL-12 (PCX12) promotes anti-tumor immune response in GL-261 murine orthotopic glioma model
Authors: Lakshmikanthan Sribalaji , Diaz Damaris , Kolli Prasad , Thiagalingam Arunthi , Gonzales Paul M. , Sepulveda Mario , Dalsing-Hernandez Jessica , Lebel Francois , Barrett John A. 
Published: June 2022

Glioblastoma (GBM) is inherently immunosuppressed (cold). Short term localized controlled immune activation has been shown to increase cytotoxic T cell infiltrate, resulting in reduced tumor growth and prolonged survival (Barrett et al. 2018). We have developed an encapsulated-mouse IL-12 formulation (mPCX12), using a sustained IL-12 release platform (Egilmez et al. 2000) to facilitate short term localized immune activation in the tumor without systemic toxicity. mPCX12 elicited a sustained dose-related IL-12 release concomitant with downstream IFNγ in mouse splenocytes, demonstrating mPCX12’s biologic activity. Similar results were observed with hPCX12 in human PBMCs. In an orthotopic murine glioma model, C57B6/L mice were inoculated with 3 × 105 GL-261 glioma cells in the frontal lobe via intracranial injection with drug treatment on Day 5. Mice were randomly assigned (n=22/group) to receive a single intratumoral dose of mPCX12 at 0.5, 0.75 and 1 mg, or mrIL-12 1µg (equivalent to mPCX12 1mg), or empty shells or vehicle. In addition, lomustine (6 mg/kg, QD×5 i.p.) was also assessed. The results showed that mPCX12 treatment increased tumor IL-12 and downstream IFNγ levels in a dose dependent manner. At 1mg mPCX12, tumor IL-12 and IFNγ levels were 2069±631 and 646±8 pg/mg, respectively, on Day 3. Low levels of IL-12 and IFNγ were observed in the systemic circulation of mPCX12 and mrIL-12 groups. mPCX12 tumor IL-12 level persisted, while mrIL-12 returned to baseline by Day 7. Flowcytometric immunophenotyping of tumors showed increased cytotoxic T cells in mPCX12 treated gliomas. These increases in local cytokine levels translated into a dose-related prolongation of survival compared to the median survival in the groups treated with vehicle and empty shells (~19 days), lomustine (20 days), and mrIL-12 (37 days). mPCX12 elicited a dose-related increase in survival. For mPCX12 at 1mg, the median survival was &gt;90 days. At Day 90, 41%, 45% and 55% of the animals that received doses of 0.5, 0.75 or 1mg mPCX12, respectively, were alive with median survival &gt;90 days (last day of study). At the end of the study, a portion of the surviving mice subgroups were euthanized, and those animals treated with mPCX12 were tumor free. The remaining surviving mPCX12-treated animals from the 0.75 mg and 1 mg mPCX12 groups were reinoculated with 3 × 105 GL261 cells in the ipsilateral side of the brain and compared with age-matched control vehicle or empty shells. The median survival in control groups was 27 days, and all rechallenged mPCX12-treated groups survived at Day 90, demonstrating memory T cell activation.

In summary, short-term controlled release of locally administered IL-12 via PCX12 resulted in turning cold tumors hot, resulting in enhanced overall survival in an orthotopic GBM model. Thus, short term controlled locally administered PCX12 warrants further investigation in GBM patients.

Citation Format: Sribalaji Lakshmikanthan, Damaris Diaz, Prasad Kolli, Arunthi Thiagalingam, Paul M. Gonzales, Mario Sepulveda, Jessica Dalsing-Hernandez, Francois Lebel, John A. Barrett. Intratumorally administrated encapsulated IL-12 (PCX12) promotes anti-tumor immune response in GL-261 murine orthotopic glioma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2086.