BACKGROUND: Celecoxib, a selective cyclooxygenase 2 (COX-2) inhibitor, blocks growth and promotes apoptosis in breast cancer cells. The PI3K/Akt pathway is important in cell survival, and COX-2 and Akt might promote growth via a positive feedback loop. We have shown that adenoviral delivery of mda-7 (Ad-mda7) in breast cancer down-regulates Akt. We hypothesized that combining Ad-mda7 and celecoxib could mediate tumor suppression in COX-2 overexpressing breast cancer cells. METHODS: Two COX-2 overexpressing human breast cancer cell lines (Her-18 and MDA-MB-436) were treated with celecoxib (20 micromol/L and 50 micromol/L) and Ad-mda7 (multiplicity of infection, 1000 and 2000 viral particles/cell). Adenovirus encoding the luciferase gene was used as a control. We assessed proliferation, cell cycle, apoptosis, prostaglandin E2 production, and changes in protein expression. Statistical analysis was performed by using the Student t test. RESULTS: Regardless of HER-2/neu status, cell growth was markedly inhibited by celecoxib, Ad-mda7, and the combination compared with controls. Celecoxib + Ad-mda7 showed a greater than additive increase in cell death compared with either monotherapy (P < .05) and resulted in cell cycle block and apoptosis (P < .05). Both cell lines showed decreased prostaglandin E2 production after combination treatment compared with controls (P < .05), with decreased expression of COX-2, Akt, and phosphorylated Akt (P < .05). CONCLUSIONS: Enhanced antitumor activity is achieved in breast cancer by combining celecoxib and Ad-mda7 regardless of HER-2/neu status. This occurs through inhibition of COX-2 expression and down-regulation of Akt. Combining Ad-mda7 with COX-2 inhibition provides a novel method of treatment in breast cancer.