Inhibitory Effect Of Morphine On Doxorubicin-induced Sh-sy5y Cell Apoptosis

Pain is frequent and severe symptom in advanced cancer. Therefore, pain relief is a fundamental and formidable task in the care of cancer patients. Recently, morphine, an active metabolite of heroin, has gained a prime status in the pain management of cancer patients. Neuroblastoma is the most common malignant sympathetic nervous system tumor of childhood. Doxorubicin, an anthracycline antibiotic, is commonly used to treat this disease.The present study was undertaken to test the hypothesis that morphine might antagonize the antitumor efficacy of doxorubicin. The survival rate was detected by SRB assays and flow cytometry with propidium iodide-stained. Western blotting was used to assess activation of Bax, Bcl-2, cytochrome c and I-κB. Reactive oxygen species generation was evaluated by flow cytometry with dichlorofluorescein and hydroethidine. The translocation of NF-κB was determined by confocal laser scanning microscopy. Studies in cultured SH-SY5Y cells revealed that morphine (≥ 50 μM) suppressed doxorubicin-induced cell proliferation inhibition and programmed cell death in a concentration-dependent manner. However, the inhibitory effects of morphine were not antagonized by naloxone and pertussis toxin, suggesting that the typical opioid receptor-coupled signaling cascade was not involved. Western blot analysis indicated that morphine dramatically inhibited doxorubicin-mediated caspase-3, Bax and Bcl-2 activation and mitochondrial cytochrome c release. Furthermore, we confirmed that doxorubicin could promote production of reactive oxygen species (ROS) and induce nuclear factor-κB (NF-κB) transcriptional activation in association with I-κBα degradation. Our data indicated that morphine at concentration of 200μM blocked intracellular ROS generation, I- κBα degradation and NF-κB transcriptional activation induced by doxorubicin in SH-SY5Y cells.These findings support the hypothesis that morphine, usually used as analgesic treatment, can inhibit doxorubicin-induced apoptosis through inhibition of mitochondrial cytochrome c release and ROS generation, and blockade of NF-kB transcriptional activation. It is suggested that additional studies are needed to determine whether neuroblastoma cancer patients under-...