TRAIL gene therapy and oncolytic adenovirotherapy have been investigated in xenografic human tumor models established in nude mice. However, the effects of these therapies on syngeneic murine tumors in immunocompetent settings were not well documented. We hypothesized that TRAIL gene therapy used with an oncolytic adenovirus would overcome the weaknesses of the two therapies used individually. In this study, we performed XTT assay to evaluate the antitumor effects of Delta24, in both human and murine breast cancer cell lines. We also analyzed the effects of TRAIL gene therapy combined with oncolytic virotherapy in these cancer cells. We determined the combination index (CI) at different MOIs in each cell line with CalcuSyn software .We established syngeneic breast cancer models using 4T1 cells in immunocompetent Balb/c mice, and measured the tumor size after different treatments. Our results showed that Delta24 can replicate and help the E1-deleted adenovector replicate in murine cancer cells. We found that Ad/TRAIL-F/RGD plus Delta24 had greater antitumor activity than either one alone in both human and murine breast cancer cells lines. At 300 MOI(virus particle per cell), the cell viability of 4T1 in the two therapies combined groups( 6.7±1% ) were significantly lower than Ad/TRAIL-F/RGD (38.9±9%) or Delta24 (45.0±16%) individually. We also found that in the MDA-MB-231, 4T1, and LM2 cells, the combination of Delta24 with Ad/TRAIL-F/RGD led to a strong synergism (CI <0.3) in most doses. In contrast, the Delta24 plus Ad/TRAIL-F/RGD treatment had an antagonistic effect on the MDA-MB-435 cells for all the doses tested (CI >1.1). In the syngeneic murine breast cancer models, at 19 days after the first treatment, the relative tumor volume(compared to the volume before treatment) of Ad/TRAIL-F/RGD plus Delta24 was 4.5±1.0, Ad/TRAIL-F/RGD 6.9±1.2, Delta24 7.0±0.6,respectively. Moreover, Delta24 viroherapy alone and Ad/TRAIL-F/RGD plus Delta24 dramatically reduced the spontanous liver metastasis that originated in the subcutaneous 4T1 tumor estalished in Balb/c mice. These findings provide important considerations in the development and preclinical assessments of oncolytic virotherapy.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]