Introduction:

Detalimogene voraplasmid (formerly known as EG-70) is a novel, investigational, non-integrating, non-viral gene therapy that was specifically designed to elicit local stimulation of anti-tumor immune response in the bladder while mitigating the risk of systemic toxicities from immune stimulation. Detalimogene voraplasmid is administered by intravesical instillation (IVI) to eligible patients with non-muscle-invasive bladder cancer (NMIBC) to drive bladder-localized expression of innate (retinoic acid-inducible gene I [RIG-I] agonists) and adaptive (interleukin-12 [IL-12]) immune regulators and remodel the tumor microenvironment. LEGEND is an ongoing Phase 1/2 study (ClinicalTrials.gov: NCT04752722) investigating the safety and efficacy of detalimogene voraplasmid in patients with BCG-unresponsive NMIBC. We now present preclinical data supporting the mechanism of action of detalimogene voraplasmid, which involves immune cell recruitment, tumor microenvironment remodeling and, ultimately, immune training on neoantigens and tumor clearance.

Methods:

Preclinical evaluation of detalimogene voraplasmid efficacy was conducted in an orthotopic syngeneic mouse model of bladder cancer to recapitulate a physiological tumor microenvironment in immunocompetent C57BL/6 mice. Luciferase-expressing MB49 cells were instilled in the bladder on study Day 1; following confirmation of tumor engraftment by in vivo bioluminescence imaging on Day 9, mice received two weekly IVIs of mEG-70 (a murine surrogate of EG-70) on Days 10 and 17. Efficacy of mEG-70 was assessed post-dosing by flow cytometry, MSD immunoassays, immunohistochemistry, bioluminescence in vivo imaging, bladder weight evaluation and overall survival. Animal experimentation was approved by the Institutional Animal Care Committee (IACC) and conducted in accordance with the guidelines of the Canadian Council on Animal Care (CCAC). In the Phase 1 part of the LEGEND study, detalimogene voraplasmid was assessed in patients with high-risk BCG-unresponsive NMIBC with carcinoma in situ (CIS).

Results:

Immune profiling revealed a profound remodeling of the tumor microenvironment from an immunosuppressive phenotype to a pro-inflammatory milieu supportive of tumor clearance. Accordingly, administration of mEG-70 was associated with marked reduction in tumor burden and marked improvement in survival in mice. As demonstrated by either bladder or flank tumor cell rechallenge, the anti-tumor immune response in surviving tumor-free mice resulted in durable protection against subsequent tumor re-challenge, and systemic immune memory.

Conclusion:

These preclinical findings demonstrate that detalimogene voraplasmid delivers genetically encoded immunostimulatory payloads locally to the bladder. The mechanism of action described preclinically has been translated into the clinic in the Phase 1 part of the LEGEND study, in which detalimogene voraplasmid treatment of patients with BCG-unresponsive NMIBC with CIS was generally well tolerated, with an overall complete response rate of 73%.

Funding: Funding for this research was provided by enGene, Inc.