3598

The cyclooxygenase-2 (COX-2) inhibitor, celecoxib, exhibits anticancer activity in both preclinical studies and clinical practice. However, celecoxib has relatively weak apoptosis-inducing activity and modest cancer therapeutic efficacy. Therefore, efforts have been made to develop derivatives of celecoxib with superior anticancer activity. Dimethyl-celecoxib (DMC) is just such a derivative which lacks COX-2-inhibitory activity. Several preclinical studies have demonstrated that DMC has better apoptosis-inducing activity than celecoxib albeit with undefined mechanisms and exhibits anticancer activity in animal models. In this study, we examined the effects of DMC on the growth of human lung cancer cells as well as its cooperative effect with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on induction of apoptosis and the underlying mechanisms. By comparing the effects of DMC and celecoxib on the growth of a group of human lung cancer cell lines, we found that DMC decreased cell survival with IC50s ranging from 10 μM to 20 μM, whereas celecoxib did so with IC50s ranging between 20 and 30 μM, indicating that DMC is more effective than celecoxib in decreasing the survival of lung cancer cells. When cells were treated with the combination of DMC and TRAIL, enhanced or synergistic effects in reduction of cell survival and induction of apoptosis including activation of caspases were observed in comparison with the effects in cells exposed to each agent alone. To understand the mechanisms underlying this synergy, we also analyzed the effects of DMC on modulation of several apoptosis-related genes. We found that DMC rapidly increased DR5 levels and reduced c-FLIP (both FLIPL and FLIPS) levels starting from 2 h post treatment while having limited effects on modulating the levels of other proteins including DR4, Bcl2, Bcl-XL and Bax. Importantly, enforced expression of FLIPL or silencing of DR5 expression using DR5 small interfering RNA (siRNA) abrogated the enhanced effects on induction of apoptosis by the combination of DMC and TRAIL, indicating that both DR5 upregulation and c-FLIP reduction contribute to cooperative induction of apoptosis by the combination of DMC and TRAIL. Collectively, we conclude that DMC sensitizes TRAIL-induced apoptosis in human lung cancer cells via induction of DR5 and downregulation of c-FLIP.(Supported by GCC Distinguished Cancer Scholar award and DOD grant W81XWH-04-1-0142-VITAL)

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA