The results showed no big difference in the sequences obtained from IR and K562 K562 cells, ruling out the Abl kinase domain mutation since the mechanism of resistance to imatinib in IR K562 cells. In the pres-ence of just one M celecoxib, the % inhibition in the development of IR K562 cells was greater at all concentrations of imatinib studied than in the cells grown in its absence. Consequently, the IC50 of imatinib for IR K562 cells was decreased from 1-0 to 6 M in PF299804 1110813-31-4 the clear presence of 1 M celecoxib. Celecoxib showed stronger inhibition in the development of IR K562 cells than in K562 cells, as shown in Dining table 2. Ergo, IR K562 cells tend to be more sensitive to celecoxib than K562 cells, either alone or in conjunction with imatinib. We next examined the mechanism associated with celecoxibinduced cytotoxicity in IR K562 cells. Apoptosis was quantified by propidium iodide binding assay using flow cytometer. Treatment of IR K562 cells with 10 M imatinib resulted in 25-room cells undergoing apoptosis, while with celecoxib at 10 M alone showed 400-watt of IR K562 cells undergoing apoptosis. Papillary thyroid cancer Interestingly, when cells were treated with both imatinib and celecoxib, there was a substantial escalation in the % apoptosis of IR K562 cells. Furthermore, DNA fragmentation analysis and ugly microscopic analysis also confirmed the celecoxib induced apoptosis in IR K562 cells and its synergy with imatinib. We next examined whether celecoxib inhibits the kinase activity and/or mRNA expression of BCR/ABL. As shown in the Fig. 5a and b, celecoxib showed no effect on tyrosine phosphorylation of BCR/ABL kinase and also on its expression at mRNA level in IR K562 cells. Imatinib at 1-0 M, but, inhibited the phosphorylatedBCR/ABLin IR K562 cells. Take-n together, these results indicate that celecoxibinduced apoptosis of IR K562 cells is through a mechanism not involving direct Tipifarnib 192185-72-1 inhibition of BCR/ABL kinase. Recent reports demonstrated that celecoxib induced apoptosis in K562 cells is through the down regulation of COX 2 and development of drug resistance in K562 cells is due to up regulation of MDR 1. The existence of a causal link between COX 2 and MDR 1 has been implicated in kidney cancer by Patel et al.. In the light of the, IR K562 cells were confronted with celecoxib, a selective COX 2 inhibitor, and the expression of COX 2 and MDR 1 was monitored by Western blot and RT PCR analysis. The results indicate the down-regulation in the expression of MDR 1 and COX 2 by celecoxib, equally at mRNA and protein levels. The PGE2 release from IR K562 cellswas determined by ELISA technique, to examine more closely the involvement of COX 2. The outcome plainly show a significant increase in the levels in IR K562 cells com-pared to K562 cells and a significant decline in the levels of PGE2 in cells treated with celecoxib.