INTASYL self-delivering RNAi therapy specifically dual-targeting BRD4 and PD-1 to elicit complete tumor responses and evidence of synergy in a subcutaneous Hepa1-6 model of murine hepatoma in C57BL/6N mice.

e14537 Background: The therapeutic potential of targeting bromodomain and extra-terminal motif (BET) protein BRD4 is supported by promising preclinical data in multiple cancer contexts. However, clinical trials of BET inhibitors (BETi) have overall shown limited clinical efficacy and only passable safety profiles as monotherapy. BET proteins are now also understood to control a wide range of immunoregulatory pathways. Preclinical data suggests a synergistic impact with immune checkpoint blockade (ICB) targeting PD-1. Trials assessing the potential of BETi in rational combination with ICB are underway. The INTASYL platform is a self-delivering RNAi technology enabling efficient delivery into target cells without need for specialized drug delivery systems. INTASYL provides specific, robust, and durable on-target gene silencing. Furthermore, INTASYL moieties targeting multiple specific targets can be formulated together, providing a highly versatile platform for providing multi-targeted combination therapy in a single drug substance. Methods: Here we assessed the efficacy of mouse/human BRD4-targeting INTASYL PH-894 as monotherapy or co-formulated with mouse PD-1 targeting INTASYL mPH-762, in treating a subcutaneous Hepa1-6 model of murine hepatoma in C57BL/6N mice. On-target, specific silencing of BRD4 and PD-1 was demonstrated in vitro. In vivo, mice bearing tumors of ̃150 mm 3 (N = 12/arm) were treated intratumorally on Days 1, 3, 7, 10 & 14 with of PH-894 or mPH-762 as single-agent, or PH-894/mPH-762 in combination at sub-optimal doses (0.1 mg/INTASYL/dose), or with PH-894/mPH-762 at half-suboptimal dose (0.05mg/INTASYL/dose) to assess potential synergistic impacts. Positive control groups received systemic (IP) (+)-JQ-1 (13.33mg/dose; qdx5), anti-mouse PD-1 antibody (75 µg; Days 1, 3, 7, 10, 14), or both treatments. Negative control animals received vehicle only. Tumor volumes and body weights were recorded longitudinally. Results: Compared to vehicle, suboptimal (+)-JQ-1, anti-PD-1, PH-894 or mPH-762 each elicited tumor control but not resolution as expected; while treatment with suboptimal PH-894/mPH-762 combo produced complete response (CR) in 75% (9/12) mice, outperforming combination treatment with (+)-JQ-1 and anti-PD-1 mAb [CR 58% (7/12) of mice]. Treatment with half-suboptimal doses of PH-894/mPH-762 resulted in CR for 42% (5/12) mice and tumor control exceeding that elicited by each monotherapy, suggesting potential synergy of the dual-targeting formulation. Tumors were isolated for mechanistic analyses of immune and tumor cells. Conclusions: These data demonstrate proof-of-concept of the therapeutic potential of rational dual-targeted INTASYL provided as single formulation in vivo, suggesting potential for meaningful clinical therapeutic impact.