Tumor necrosis factor-related apoptosis-inducing ligand's antitumor activity in vivo is enhanced by the chemotherapeutic agent CPT-11.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in a wide variety of transformed human cells in vitro. In this study, the antitumor activity of recombinant TRAIL was analyzed in mice bearing human colon carcinoma tumors. We found that these tumors displayed a differential sensitivity to TRAIL in vivo that paralleled their susceptibility to TRAIL-induced apoptosis in vitro. Treatment of TRAIL-sensitive tumors 3 days after tumor challenge resulted in a dose-dependent inhibition of growth and the elimination of tumors in many mice. Colon carcinoma cell lines could be further sensitized to TRAIL-induced apoptosis in vitro by the addition of the chemotherapeutic agent camptothecin. Moreover, the combination of TRAIL and CPT-11, a water-soluble analogue of camptothecin, greatly enhanced the antitumor activity of TRAIL in vivo. TRAIL plus CPT-11 treatment of both 3- and 10-day established TRAIL-sensitive tumors resulted in both a significant inhibition of tumor growth and a high proportion of complete tumor regressions. Treatment of TRAIL-resistant tumors with TRAIL and CPT-11 dramatically slowed tumor growth and induced a transient tumor regression. These data demonstrate that TRAIL alone is a potent antitumor agent in vivo, and its activity can be significantly enhanced in combination with the chemotherapeutic agent CPT-11.