Oncolytic adenovirus CG7870 in combination with radiation demonstrates synergistic enhancements of antitumor efficacy without loss of specificity

Abstract

Conditionally replicating adenoviruses that selectively replicate in tumor cells, but not in normal cells, are being explored as virotherapeutic agents for cancer. A prostate-specific oncolytic adenovirus, CG7870 is currently being evaluated in phase 1/2 clinical trials for the treatment of prostate cancer. To decrease the effective dose and further increase the therapeutic efficacy of CG7870, the combination of virotherapy with radiation therapy was explored in this study. CG7870 is an oncolytic adenovirus in which tumor-specific promoters are driving the expression of E1A and E1B proteins. The effects of combined treatment with CG7870 and radiation on cultured cells were determined in cytotoxicity and virus yield assays. The antitumor efficacy of CG7870 (1 x 10(7) particles/mm3 of tumor), 10 Gy of local radiation or both was evaluated in established subcutaneous LNCaP xenografts in nude mice. In vitro, the dual agent treatment resulted in synergistically enhanced potency at suboptimal doses of radiation and virus. Virus yield in irradiated cells increased relative to yield in nonirradiated cells without compromising the specificity of the vector for its target cell types. In vivo, CG7870 treatment alone suppressed tumor growth and extended tumor nonprogression time. The average tumor-volume of the groups treated with CG7870 only and radiation only was 121 and 126% of baseline, respectively, 39 days after treatment. The average tumor-volume of the combination group was 34% of baseline 39 days after a single dose of treatment. No significant body weight loss was observed in any treatment group. There was a significant drop in serum level of prostate-specific antigen (PSA) in the combination group compared to the group treated with either agent alone. In mice treated with CG7870 only or radiation only, serum PSA levels changed to 26 and 383% of baseline, respectively, by study day 46. In contrast, PSA levels in mice treated with CG7870 plus radiation decreased to less than 11% of baseline by study day 46. Histological analysis of tumor sections collected from the combination group revealed enhanced necrosis and more apoptotic cells. Combination of CG7870 with radiotherapy significantly increased antitumor efficacy compared to either agent alone. These results suggest that CG7870 in combination with radiation has improved antitumor efficacy at lower doses and with no additional side effects.