Differential Effects of Selective COX-2 Inhibitors on Cell Cycle Regulation and Proliferation of Glioblastoma Cell Lines

Abstract

B i o s c i e n c e . N o t f o r d i s t r i b u t i o n .[Cancer Biology & ACKNOWLEDGEMENTSWe are grateful to the following people for providing plasmids or cell lines: Frank B. Furnari, Webster K. Cavenee, William R. Taylor, and Toshio Nikaido. The technical assistance of Susan Su is acknowledged.This work was supported in part by the Kriegel Foundation (A.K.; T.C.C.). NOTE ADDED IN PROOFUsing prostate cancer cell lines, Johnson et al. (Adv Enzyme Regul 2001; 41:221-35) observed differential effects of selective COX-2 inhibitors on apoposis induction. Similar to our data presented here, they found celecoxib to be the most potent compound. Research Paper Differential Effects of Selective COX-2 Inhibitors on Cell Cycle Regulation and Proliferation of Glioblastoma Cell Lines ABSTRACTIt is well established that traditional NSAIDs, which inhibit cyclooxygenase (COX) 1 and COX-2, have the potential to reduce the risk of colorectal cancer. New generation COX inhibitors have been developed that selectively inhibit COX-2, which might cause less side effects while still retaining their therapeutic potential. As patients with brain tumors, such as glioblastoma, exhibit a very poor prognosis, we began to explore whether COX inhibitors could be useful for the treatment of this type of tumor. We found that celecoxib inhibited the proliferation of various glioblastoma cell lines in vitro much more potently than traditional NSAIDs. In addition, although several different selective COX-2 inhibitors potently reduced PGE2 levels in these cells, none of them exerted anti-proliferative effects that were comparable to celecoxib. The addition of external PGE2 to celecoxib-treated cells did not restore proliferation, indicating that growth inhibition by celecoxib was not mediated via the blockage of PGE2 production. In an effort to determine the underlying molecular processes that might mediate celecoxib's potent anti-proliferative effects, we found a loss of the activity of cyclin-dependent kinases, the essential regulators of cell proliferation, which was due to the transcriptional downregulation of cyclin A and cyclin B expression. Taken together, our results show that celecoxib exerts COX-2-independent anti-proliferative effects on glioblastoma cell growth, which are more potent than those of other selective COX-2 inhibitors or traditional NSAIDs, and which are mediated via the transcriptional inhibition of two essential components of the cell cycle machinery, cyclin A and cyclin B.

Dimethyl-Celecoxib (DMC), a derivative of celecoxib that lacks cyclooxygenase-2-Inhibitory function, potently mimics the anti-tumor effects of celecoxib on burkitt’s lymphoma in vitro and in vivo

“…As controls, cell lysates were also prepared from U87, LN229, and A172 glioblastoma cell lines. As previously established, 29 the expression level of COX-2 in these glioblastoma cell lines is: U87 → highly elevated; LN229 → elevated; A172 → not detectable. All lysates were subjected to Western blot analysis with an antibody specific to COX-1 (top panel).…”

“…31,32,70,71 This was true even for cancer cell lines with greatly varying levels of COX-2 expression, i.e., the amount of intracellular COX-2 enzyme did not appear to modulate the potency of celecoxib. 29,72 While the details of these differential sensitivities certainly deserve further investigation, these results further indicate that growth inhibition by celecoxib might be mediated by targets other than COX-2. In this regard, we envision that DMC presents a useful tool for the further exploration of these COX-2 independent effects.…”

“…U87 cells, which overexpress COX-2 and display elevated levels of PGE 2 (ref. 29 and Fig. 3), were cultured in the presence or absence (Control) of 40 µM DMC for 24 hours.…”

“…In the case of celecoxib, it has been generally observed that the effective anti-proliferative concentration in vitro is higher (>10 µM) [28][29][30][31][32] than the concentration of drug measured in patients or experimental animals (well below 10 µM). 33,34 Based on this discrepancy, it has been suggested that in vitro effects of celecoxib might be an artifact and are not reflective of the mechanisms taking place in vivo.…”

Proteomic Profiling Identifies Cyclooxygenase-2-Independent Global Proteomic Changes by Celecoxib in Colorectal Cancer Cells

“…Third, concentration of celecoxib needed for growth inhibition in vitro is several orders of magnitude higher than the concentration at which COX-2 is inhibited (15,16). And finally, derivatives of celecoxib devoid of the COX-2 inhibitory activity have recently been shown to mimic celecoxib by affecting processes such as cell cycle progression, apoptosis, neovascularization, growth inhibition in vitro, and tumor formation in vivo (17)(18)(19)(20). Clearly, a better understanding of the molecular targets of celecoxib involved in its COX-2-dependent and/or COX-2-independent antiproliferative functions is of considerable clinical significance and would be helpful in enhancing its chemopreventive potential.…”