RETRACTED: Inhibition of rat mammary gland carcinogenesis by simultaneous targeting of cyclooxygenase-2 and peroxisome proliferator-activated receptor γ (Retracted article.: See vol. 65, pg. 8057, 2005)

We examined the effect of celecoxib, a cyclooxygenase-2 (COX-2) inhibitor, and N-(9-fluorenyl-methyloxycarbonyl)-L-leucine(F-L-Leu), a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, separately and combined, on the development of methylnitrosourea (MNU)-induced rat mammary gland carcinogenesis. Celecoxib and F-L-Leu significantly reduced tumor incidence and multiplicity (P < 0.05). Combining both agents exerted higher (synergistic) cancer inhibition than separate treatments (P < 0.05). The effects of the test drugs on COX-2 and PPARgamma expression and on the synthesis of prostaglandin E-2 (PGE(2)) and 15-deoxy-Delta(12,14) -PGJ(2) (15d-PGJ(2)) were examined in rat mammary normal (MNU-untreated), uninvolved, and tumor (MNU-treated) tissues. Celecoxib and F-L-Leu, separately, inhibited COX-2 and up-regulated PPARgamma expression. These effects were paralleled by inhibition of PGE2 synthesis and up-regulation of 15d-PGJ(2). Combined treatment resulted in higher alterations in COX-2 and PPARy transcripts and PG synthesis compared with separate administrations. The effect of the test agents on Bcl(2), BAX, and protein kinase Calpha expression levels were examined in the rat mammary gland and the pro-(BAX:Bcl(2)) and anti-[PKCalpha*(Bcl(2)/BAX)] apoptotic ratios were evaluated. Each drug increased the proapoptotic ratio by 2- to 7-fold and reduced the antiapoptotic ratio by 2- to >8-fold in all tissues. Combined treatment, however, resulted in >9- to 14-fold up-regulation in the proapoptotic processes and 15- to >30-fold down-regulation in the antiapoptotic ones. Analyses were also carried out on the drug-induced modulation of cell cycle regulators and proliferation markers (cyclin-dependent kinase 1 and proliferating cell nuclear antigen). F-L-Leu and celecoxib each reduced the cyclin-dependent kinase 1 and proliferating cell nuclear antigen expression in the tumor. Higher down-regulation was attained in all tissues by combined treatment where cyclin-dependent kinase 1 and proliferating cell nuclear antigen almost retained the expression levels observed in the normal glands. In conclusion, simultaneous targeting of COX-2 and PPARy may inhibit mammary cancer development more effectively than targeting each molecule alone. COX-2 inhibitors and PPARgamma agonists coordinately mediate their anticancer effect via both COX-dependent (inhibition of COX-2, activation of PPARy, and modulation PG synthesis) and COX-independent (induction of proapoptotic factors and inhibition of cell proliferation) pathways.