Simultaneously targeting Bcl-2 and Akt pathways reverses resistance of nasopharyngeal carcinoma to TRAIL synergistically.
OBJECTIVE
Despite progress in treatment techniques, the five-year survival rate of nasopharyngeal carcinoma (NPC) is disappointing. Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) can selectively induce apoptosis in most tumor cells while sparing normal cells. Given the antiapoptotic functions of Bcl-2 and Akt, we examined the effects of targeting these pathways alone or simultaneously on TRAIL apoptosis in NPC cell lines.


METHODS
We first tested the cytotoxic effect of TRAIL and the expression of death receptors, Bcl-2, Akt, and p-Akt on four NPC cell lines by MTT and Western blotting, respectively. Small interfering RNAs (siRNAs) targeting Bcl-2 and PI3-K inhibitor (LY294002) were used alone or combined with TRAIL in the cell lines and cytotoxicity was examined by MTT. Apoptosis rates, mitochondrial transmembrane potential, and apoptotic pathway signals were detected by flow cytometric analysis, DiOC6(3) assays, and Western blotting after the various combination treatments on CNE-2, the cell line that was most resistant to TRAIL.


RESULTS
Although no direct correlation between the sensitivity to TRAIL and the relative expression levels of Bcl-2 and activated Akt was found in the NPC cell lines examined, siRNA mediated the downregulation of Bcl-2 and LY294002-induced inactivation of Akt, increasing the sensitivity of all examined NPC cell lines to TRAIL. Synergistic enhancement of TRAIL-mediated cytotoxicity was observed in combination treatment of Bcl-2 siRNA and LY294002 compared to cells treated with each treatment alone. The synergistic effects were mediated through increased apoptotic signaling of the mitochondrial pathway, as was evident from the more increased mitochondrial depolarization, activation of caspase-9 and caspase-3, and suppression of XIAP.


CONCLUSIONS
This study provides proof of principle that TRAIL combined with simultaneously targeting the Bcl-2 and Akt signaling pathways may have potential as a novel future treatment strategy for NPC.
Department of Otolaryngology, Head and Neck Surgery, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China.
Shi-Sheng
SS
Li
Qing-Lai
QL
Tang
Shu-hui
SH
Wang
Yue-Hong
YH
Chen
Jia-Jia
JJ
Liu
Xin-Ming
XM
Yang
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000378:metabolism; D015153:Blotting, Western; D002277:Carcinoma / Q000188:drug therapy* / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D005434:Flow Cytometry; D006801:Humans; D009025:Morpholines / Q000494:pharmacology*; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000187:drug effects / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D002867:Chromones; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051057:Proto-Oncogene Proteins c-akt