Effect of adenoviral p53 (Ad-p53) tumor suppressor immune gene therapy on checkpoint inhibitor resistance and abscopal therapeutic efficacy.

Abstract

e14610 Background: Immune checkpoint inhibitors represent an important advance in cancer therapeutics. However, most cancer patients do not respond or become resistant to this form of immune therapy. Methods: We evaluated the ability of Ad-p53 to reverse immune checkpoint inhibitor resistance and induce abscopal effects in the immune therapy resistant murine B16F10 melanoma tumor model. To mimic clinical conditions of checkpoint inhibitor resistance, animals with established tumors were treated with anti-PD-1 before initiating Ad-p53 intra-tumoral therapy. Results: Anti-PD-1 had minimal therapeutic efficacy compared to control treatment. A statistical analysis of variance (ANOVA) comparison of tumor volumes revealed that the combined effect of Ad-p53 and anti-PD-1 treatment was synergistic and superior to either therapy alone (p = 0.0001). Surprisingly, there was a statistically significant abscopal effect with decreased growth of contralateral tumors not injected with Ad -p53. The Ad- p53 alone (p = 0.046) and Ad- p53 + anti-PD-1 (p = 0.0243) treatment groups both demonstrated a statistically significant decreased abscopal tumor growth compared to treatment with anti-PD-1 alone. Combined Ad- p53 and anti-PD-1 therapy demonstrated a statistically significant increase in survival compared to Ad- p53 therapy alone (p = 0.0167) and anti-PD-1 therapy alone (p < 0.001) by the log rank test. We have initiated a Phase 1 clinical trial of Ad-p53 intra-hepatic arterial therapy in combination with capecitabine for patients with solid tumor liver metastases. In the first cohort of patients at a dose of 2 x 1012viral particles, treatment has been well tolerated with transient fever, chills and rigors. In one patient, decreased SUV uptake on PET scans of distant lymph node metastases suggested possible abscopal effects. Conclusions: These results suggest that Ad-p53 tumor suppressor immune gene therapy may reverse immune checkpoint inhibitor resistance and induce abscopal effects supporting the planned clinical evaluation of combined Ad-p53 and anti-PD-1 therapy in patients resistant to immune checkpoint inhibitor therapy. Clinical trial information: NCT02842125.