Inhibition of Rat Mammary Gland Carcinogenesis by Simultaneous Targeting of Cyclooxygenase-2 and Peroxisome Proliferator-activated Receptor γ

Abstract

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 ␥ (PPAR␥) 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 PPAR␥ expression and on the synthesis of prostaglandin E 2 (PGE 2 ) and 15-deoxy-⌬ 12,14 -PGJ 2 (15d-PGJ 2 ) were examined in rat mammary normal (MNUuntreated), uninvolved, and tumor (MNU-treated) tissues. Celecoxib and F-L-Leu, separately, inhibited COX-2 and up-regulated PPAR␥ expression. These effects were paralleled by inhibition of PGE 2 synthesis and up-regulation of 15d-PGJ 2 . Combined treatment resulted in higher alterations in COX-2 and PPAR␥ transcripts and PG synthesis compared with separate administrations. The effect of the test agents on Bcl 2 , BAX, and protein kinase C␣ expression levels were examined in the rat mammary gland and the pro-(BAX:Bcl 2 ) and anti-[PKC␣*(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 (cyclindependent 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 PPAR␥ may inhibit mammary cancer development more effectively than targeting each molecule alone. COX-2 inhibitors and PPAR␥ agonists coordinately mediate their anticancer effect via both COX-dependent (inhibition of COX-2, activation of PPAR␥, and modulation PG synthesis) and COX-independent (induction of proapoptotic factors and inhibition of cell proliferation) pathways.

Chemopreventive Effect of Peroxisome Proliferator–Activated Receptor γ on Gastric Carcinogenesis in Mice

“…Recently, Badawi et al reported that PPARg mRNA and protein levels were lower in MNU-induced rat mammary tumors than in normal tissues (47). Our present study showed the suppressed expression of PPARg in MNU-induced carcinomas, showing a consistent pattern of PPARg expression.…”

15(S)-Hydroxyeicosatetraenoic Acid Induces Angiogenesis via Activation of PI3K-Akt-mTOR-S6K1 Signaling

“…A body of data accumulated in the past several years indicates that the COX, LOX, and CYP metabolites of arachidonic acid are involved in the maintenance of survival and proliferative capacities of various types of normal and cancer cells and play (2,4,5,(12)(13)(14)(15)(16)(17)(18)(19)(20). Despite these evidences linking arachidonic acid metabolites to the development of various cancers including colon and prostate cancers and vessel wall diseases, very little is known with regard to the mechanisms by which eicosanoids influence these lesions.…”

“…In addition, these lipid molecules have been reported to mediate various intracellular signaling events in response to different stimulants (7)(8)(9)(10)(11)(12). Studies over the past several years also suggest that the COX, LOX, and CYP metabolites of arachidonic acid stimulate the proliferative capacity of various cell types and play a role in tumor progression (13)(14)(15)(16)(17)(18)(19)(20). In addition, eicosanoids have been shown to be associated with the pathogenesis of vascular diseases such as atherosclerosis and restenosis (21,22).…”

Enhanced expression of peroxisome proliferator-activated receptor gamma in epithelial ovarian carcinoma

“…In addition, PPARg ligands have been shown to inhibit transcriptional activation of COX-2 in human epithelial cells (Badawi et al, 2004). In certain cancer cells, ligand activation of PPARg results in the inhibition of the release of inflammatory cytokines by cancer cells (Leung et al, 2004).…”