Arunasree Kalle M, Roy Karnati R, Anilkumar Kotha, Aparna A, Reddy Gorla Venkateswara, Reddanna Pallu
Department of Animal Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India.
Leuk Res. 2008 Jun;32(6):855-64. doi: 10.1016/j.leukres.2007.11.007. Epub 2008 Feb 20.
Selective inhibition of the BCR/ABL tyrosine kinase by imatinib (STI571, Glivec/Gleevec) is the therapeutic strategy in patients with chronic myelogenous leukemia (CML). Despite significant hematologic and cytogenetic responses with imatinib, mainly due to the mutations in the Abl kinase domain, resistance occurs in patients with advanced disease. In the present study on imatinib-resistant K562 cells (IR-K562), however, no such mutations in the Abl kinase domain were observed. Further studies revealed the over-expression of COX-2 and MDR-1 in IR-K562 cells suggesting the possible involvement of COX-2 in the development of resistance to imatinib. So, we sought to examine the effect of celecoxib, a selective COX-2 inhibitor, on IR-K562 cells. The results clearly indicate that celecoxib is more effective in IR-K562 cells with a lower IC50 value of 10 microM compared to an IC50 value of 40 microM in K562 cells. This increase in the sensitivity of IR-K562 cells towards celecoxib suggests that the development of resistance in IR-K562 cells is COX-2 dependent. Further studies revealed down-regulation of MDR-1 by celecoxib and a decline in p-Akt levels. Celecoxib-induced apoptosis of IR-K562 cells led to release of cytochrome c, PARP cleavage and decreased Bcl2/Bax ratio. Also, celecoxib at 1 microM concentration induced apoptosis in IR-K562 cells synergistically with imatinib by reducing the IC50 value of imatinib from 10 to 6 microM. In conclusion, the present study indicates over-expression of COX-2 and MDR-1 in IR-K562 cells and celecoxib, a COX-2 specific inhibitor, induces apoptosis by inhibiting COX-2 and down-regulating MDR-1 expression through Akt/p-Akt signaling pathway.
伊马替尼（STI571，格列卫）对BCR/ABL酪氨酸激酶的选择性抑制是慢性粒细胞白血病（CML）患者的治疗策略。尽管伊马替尼能带来显著的血液学和细胞遗传学反应，但主要由于Abl激酶结构域的突变，晚期疾病患者仍会出现耐药。然而，在本项针对伊马替尼耐药的K562细胞（IR-K562）的研究中，未观察到Abl激酶结构域存在此类突变。进一步研究发现IR-K562细胞中COX-2和MDR-1过表达，提示COX-2可能参与了对伊马替尼耐药的发生。因此，我们试图研究选择性COX-2抑制剂塞来昔布对IR-K562细胞的作用。结果清楚地表明，塞来昔布对IR-K562细胞更有效，其IC50值为10微摩尔，而K562细胞的IC50值为40微摩尔。IR-K562细胞对塞来昔布敏感性的增加表明，IR-K562细胞耐药的发生是COX-2依赖性的。进一步研究发现塞来昔布可下调MDR-1并降低p-Akt水平。塞来昔布诱导IR-K562细胞凋亡导致细胞色素c释放、PARP裂解以及Bcl2/Bax比值降低。此外，1微摩尔浓度的塞来昔布与伊马替尼协同诱导IR-K562细胞凋亡，将伊马替尼的IC50值从10微摩尔降至6微摩尔。总之，本研究表明IR-K562细胞中COX-2和MDR-1过表达，而COX-2特异性抑制剂塞来昔布通过抑制COX-2并通过Akt/p-Akt信号通路下调MDR-1表达来诱导细胞凋亡。
