Making the preclinical case for intratumoral electroporation of DNA-based checkpoint inhibitors

DNA-based antibody gene transfer aims to administer plasmid DNA (pDNA) encoding one or multiple monoclonal antibodies (mAbs). This allows the patient’s body to express the mAbs in vivo for a prolonged period of time, bypassing the expensive and complex production and frequent parenteral administration of proteins. The tumor presents an appealing delivery site, allowing local expression of anticancer drugs, but has not yet been evaluated for DNA-based mAbs. The current study aimed to demonstrate proof of concept for intratumoral (IT) gene transfer of two checkpoint-inhibiting mAbs. These mAbs often induce moderate response rates and carry a high risk of adverse events when delivered intravenously as proteins. To improve the low transfection efficiency of pDNA, we compared electroporation, a technique that employs local electrical pulses to make transient pores in cell membranes, with the pDNA-complexing agent in vivo-jetPEI in a subcutaneous MC38 mouse tumor model. Both methods are evaluated in the clinic for IT gene transfer. IT electroporation of a luciferase reporter pDNA resulted in a strong, local expression in the tumor that remained stable for at least ten days. IT injection of in vivo-jetPEI-pDNA complexes led to two logs lower IT expression that mostly did not exceed the background. Remarkably, expression was also detected in the lungs, presumably due to systemic leakage of the in vivo-jetPEI-pDNA complexes. Accordingly, electroporation was selected as the optimal IT transfection method. To assess the efficacy and pharmacokinetics of IT mAb gene electrotransfer, DNA-based anti-CTLA-4 and anti-PD-1 mAbs, alone or in combination, were delivered to the tumor of MC38-bearing mice. IT mAb expression gave up to 20% complete tumor regressions, with only transient mAb plasma levels in the ng/ml to low µg/ml range. IT gene transfer also generated a systemic anti-tumor response, illustrated by abscopal effects in distant untreated tumors and prolonged protection of cured mice against a tumor rechallenge. In summary, IT electroporation resulted in more efficient and tumor-specific pDNA transfection compared to in vivo-jetPEI. The IT delivery of DNA-based checkpoint inhibitors evoked both local and systemic anti-tumor responses with limited systemic mAb exposure, suggesting a favorable biosafety. Ongoing studies evaluate other (mAb) combination therapies to further improve responses and to demonstrate the versatility of the gene transfer approach.