Cyclooxygenase isozymes are expressed in human myeloma cells but not involved in anti‐proliferative effect of cyclooxygenase inhibitors

Abstract

Considering possible tumorigenic activity of cyclooxygenase (COX) isozymes in myeloma, we examined expression levels of COX-1 and -2 in seven human myeloma cell lines (ARH-77, IM-9, RPMI-8226, HPC, HS-Sultan, TSPC-1, and U-266). As analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR), all the cell lines constitutively expressed COX-1, while COX-2 levels markedly varied among different cell lines. Induction of COX-2 by phorbol ester was observed in RPMI-8226 and HPC cells. In contrast, COX-2 was constitutively expressed in ARH-77 and IM-9 cells. Moreover, the high expression level of COX-2 protein in ARH-77 cells was verified by Western blotting. Intact cells of ARH-77 converted 14C-labeled arachidonic acid to prostaglandin E2, F2alpha, and D2, and this activity was dose-dependently inhibited by selective COX-2 inhibitors (SC-58125 and NS-398), a non-selective COX inhibitor (indomethacin), and relatively high concentrations of a selective COX-1 inhibitor (SC-560). These COX inhibitors also suppressed the proliferation of ARH-77 cells, but significant suppression was seen only at 100 microM, a much higher concentration than those sufficient for the COX inhibition. Moreover, proliferation of the myeloma cells lacking COX-2 was also suppressed by 100 microM of SC-58125. These results suggested that the anti-proliferative effect of the COX inhibitors is independent of the inhibition of COX-2.

Thromboxane A2 Receptor Inhibition Suppresses Multiple Myeloma Cell Proliferation by Inducing p38/c-Jun N-terminal Kinase (JNK) Mitogen-activated Protein Kinase (MAPK)-mediated G2/M Progression Delay and Cell Apoptosis

“…However, only the COX-2 inhibitor, NS398, and not the COX-1 inhibitor, SC560, suppressed proliferation of two MM cell lines, indicating that COX-2 suppression plays an inhibitive role in MM cell proliferation. These findings were inconsistent with a previous report that both COX-1 and COX-2 inhibitors suppress proliferation of ARH-77 cells, but the supplementary concentrations in that study are higher (100 M) than those in our study (30 M) or the general dosage (10 M) (12). In addition, TxB 2 production was also decreased by COX-2 inhibitor, but not COX-1 inhibitor, similar to their effects on MM cell proliferation, suggesting that NS398 inhibits TxB 2 synthesis to delay cell proliferation, which is supported by previous findings in lung adenocarcinoma cells (10).…”

“…Li et al (30) have shown that COX-2 siRNA transfection can suppress COX-2 protein expression in RPMI-8226 cells, which leads to growth inhibition and apoptosis independent of Bcl-2. Another study (12) has shown that seven human myeloma cell lines constitutively express COX-1 mRNA, whereas COX-2 levels vary markedly among cell lines and are not detectable in U-266 and RPMI-8226 cells. In the present study, we examined protein level expression of both COX-1 and COX-2 in RPMI-8226 and U-266 cells.…”

“…1A). In addition, we performed cell proliferation assays on RPMI-8226 and U-266 cells with selective COX-1/2 inhibitors SC-560/NS-398, known to repress ARH77 cell growth (12). As shown in Fig.…”

“…Consistent with their role in cancer progression, TxA 2 synthase and TP overexpression has been found in many tumor tissues (11), and their activations stimulate lung cancer cell proliferation via regulating apoptosis or cell cycle progression, whereas the involved signalings are unclear (9). A recent study by Ding et al (12) reveals that COX-1 and COX-2 inhibitors efficiently suppress ARH-77 MM cell proliferation, but the authors do not elucidate the mechanism by which this occurs. Thus, the direct involvement of COX/TxA 2 /TP in RPMI-8226 and U-266 MM cell proliferation and the associated signaling pathways have not yet been explored.…”

Targeting Cyclooxygenase-2 in Hematological Malignancies: Rationale and Promise

“…These observations suggest that Cox-2 selective inhibitors might boost the efficacy of chemotherapeutic treatments already in clinical use. In contrast, investigators performing a similar study showed that ARH-77 and IM-9 MM cell lines expressed Cox-2 mRNA, while RPMI8226, U266 were negative for Cox-2 [45]. ARH-77 cells contained enzymatically active Cox-2 and produced PGE 2 and PGF 2α , whose production was inhibited by Cox-2 selective inhibitors.…”