The Cyclooxygenase-2 Inhibitor Celecoxib Induces Apoptosis by Blocking Akt Activation in Human Prostate Cancer Cells Independently of Bcl-2

Abstract

This study investigates the apoptotic activity of the cyclooxygenase-2 (COX-2) inhibitor celecoxib in prostate carcinoma cells. COX-2 is constitutively expressed in androgen-responsive LNCaP and androgen-nonresponsive PC-3 cells. Exposure of these cells to celecoxib induces characteristic features of apoptosis, including morphological changes, DNA laddering, and caspase-3 activation, whereas piroxicam, a COX-1-specific inhibitor, displays no appreciable effect on either cancer cell line even after prolonged exposure. Moreover, the potency of celecoxib in apoptosis induction is significantly higher than that of other COX-2 inhibitors examined despite the observation that these inhibitors exhibit similar IC 50 in COX-2 inhibition. It is noteworthy that normal human prostate epithelial cells, expressing a marginally detectable level of COX-2, are insensitive to the induction of apoptosis by celecoxib. These data suggest a correlation between COX-2 expression and sensitivity to the apoptotic effect of the COX-2 inhibitor. In an effort to delineate the underlying mechanism, we examined the effect of celecoxib on the expression of Bcl-2 as well as the activation of the key anti-apoptotic kinase Akt. In contrast to an earlier report that attributed the apoptotic activity of NS398 in LNCaP cells to Bcl-2 down-regulation, we provide evidence that the induction of apoptosis by celecoxib in LNCaP and PC-3 cells is independent of Bcl-2. First, treatment with celecoxib does not alter the cellular Bcl-2 level in both cell lines. Second, enforced Bcl-2 expression in PC-3 cells does not confer protection against the induction of apoptosis by celecoxib. Our data show that celecoxib treatment blocks the phosphorylation of Akt. This correlation is supported by studies showing that overexpression of constitutively active Akt protects PC-3 cells from celecoxib-induced apoptosis. Nevertheless, how celecoxib down-regulates Akt is not clear because the drug does not adversely affect phosphoinositide 3-kinase activity in vivo and okadaic acid, a protein phosphatase 2A inhibitor, cannot rescue the inhibition. In summary, our data demonstrate that inhibition of Akt activation may play a crucial role in the induction of apoptosis by celecoxib.An expanding body of information has suggested the potential application of nonsteroidal anti-inflammatory drugs (NSAIDs) 1 in cancer chemoprevention (1-3). Epidemiological studies indicate that the use of aspirin and other NSAIDs reduces the risk of colorectal cancer by 40 -50% (4 -7) and, to a lesser extent, the risk of breast cancer (6,8). The fact that all NSAIDs in clinical use are cyclooxygenase (COX) inhibitors provides a putative link between the inhibition of COX activity and the chemopreventive effect of NSAIDs (1, 2, 9). Two isoforms of COX have been identified, each of which displays a distinct physiological profile. COX-1, constitutively expressed in almost all tissues, is important for the maintenance of homeostatic function, whereas COX-2, an inducible isozyme, is dramatically up-regula...

Cyclooxygenase inhibitors modulate the p53/HDM2 pathway and enhance chemotherapy-induced apoptosis in neuroblastoma

“…Mitogeninduced activation of PI3-kinase and its downstream target Akt results in phosphorylation of HDM2 on ser166 and 168 and enhanced HDM2 nuclear localization (Mayo and Donner, 2001;Ashcroft et al, 2002). Interestingly, a number of studies have demonstrated that COX-2 inhibitors induce apoptosis by blocking Akt activation in adult carcinomas (Hsu et al, 2000;Arico et al, 2002). However, in this study, we did not observe any early changes in Akt or Akt phosphorylation that could have explained the downregulation of phosphorylated HDM2 mediated by COX inhibitors as early as 2 h. In contrast, we observed dose-dependent reduction of Akt levels after 24 h of COX inhibitor treatment (data not shown) and these late effects may account for the observed sustained downregulation of P-HDM2 up to 48 h by COX inhibitors in neuroblastoma.…”

Dual treatment with COX-2 inhibitor and sodium arsenite leads to induction of surface Fas Ligand expression and Fas-Ligand-mediated apoptosis in human melanoma cells

“…These levels can only be achieved in normal cells by stimulation with growth factors and cytokines [29,70,71]. Active anti-apoptotic functions of COX-2 in cancer cells have been widely reported [72][73][74]. Furthermore, COX-2 is one of the several important genes, which mediate breast cancer metastasis to the lung [75].…”

Celecoxib derivatives induce apoptosis via the disruption of mitochondrial membrane potential and activation of caspase 9

“…26 Studies in human prostate cancer cell lines indicate that celecoxib induces apoptosis by blocking Akt and Erk2 activation, through the mitochondrial pathway, independent of COX-2 activity and Bcl-2. 8,29,30 This has led to the design of celecoxib derivatives that optimize the apoptosis-inducing potency, separate from the COX inhibiting activity of celecoxib. 8,[31][32][33] Recent studies with the first and second generation derivatives of celecoxib in the PC-3 human prostate cell line suggests that apoptosis is mediated through the blockade of Akt activation by derivative inhibition of 3-phosphoinositide dependent kinase-1 (PDK1).…”