Potentiation of paclitaxel cytotoxicity in lung and esophageal cancer cells by pharmacologic inhibition of the phosphoinositide 3-kinase/protein kinase B (Akt)-mediated signaling pathway.
BACKGROUND
Constitutive activation of the phosphoinositide 3-kinase/protein kinase B survival signal transduction pathway influences the intrinsic chemoresistance of cancer cells. This study evaluates the effect of LY294002, a pharmacologic inhibitor of phosphoinositide 3-kinase, on the sensitivity of lung and esophageal cancer cells to paclitaxel (Taxol) in vitro. Materials and methods Cell viability and apoptosis of cancer cells treated with paclitaxel + LY294002 combinations were quantitated by methyl-thiazol-diphenyl-tetrazolium and terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling-based ApoBrdU assays, respectively. The effect of LY294002-mediated phosphoinositide 3-kinase inhibition on protein kinase B (Akt) activation and nuclear factor-kappaB signaling was determined by Western blot analysis. Nuclear factor-kappaB transcription activity in cultured cancer cells either at baseline or after treatments with LY294002 or BAY11-0782 (a pharmacologic inhibitor of nuclear factor-kappaB) was determined by the nuclear factor-kappaB-Luciferase reporter system.


RESULTS
A 4- to more than 20-fold reduction of paclitaxel IC(50) values was observed in cancer cells treated with paclitaxel + LY294002 combinations. This was paralleled with synergistic induction of apoptosis. LY294002 treatment caused a significant dose-dependent inhibition of protein kinase B (Akt) activation and suppression of nuclear factor-kappaB transcriptional activity that was accompanied by elevation of IkappaB, the intrinsic inhibitor of nuclear factor-kappaB, and concomitant reduction of nuclear factor-kappaB-regulated antiapoptotic proteins cIAP1, cIAP2, and BclXL. Direct inhibition of nuclear factor-kappaB activity by BAY11-0782 also resulted in profound enhancement of paclitaxel sensitivity and paclitaxel-mediated induction of apoptosis in lung and esophageal cancer cells.


CONCLUSIONS
LY294002-mediated inhibition of the phosphoinositide 3-kinase/protein kinase B-dependent survival pathway with secondary suppression of nuclear factor-kappaB transcriptional activity was associated with enhancement of paclitaxel cytotoxicity in lung and esophageal cancer cells. Direct inhibition of nuclear factor-kappaB by BAY11-0782 also sensitized these cancer cells to paclitaxel, indicating that nuclear factor-kappaB may be the crucial intermediary step connecting phosphoinositide 3-kinase/protein kinase B (Akt) to the intrinsic susceptibility of cancer cells to chemotherapeutic agents.
Nguyen
Dao M
DM
Section of Throacic Oncology, Surgery Branch, Center for Cancer Research, National Cancer Center, National Institutes of Health, Bethesda, MD, USA. Dao_Nguyen@nih.gov
Chen
G Aaron
GA
Reddy
Rishindra
R
Tsai
Wilson
W
Schrump
William D
WD
Cole
George
G
Schrump
David S
DS
D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000201:enzymology; D002470:Cell Survival / Q000187:drug effects; D002867:Chromones / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004359:Drug Therapy, Combination; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D004938:Esophageal Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000201:enzymology; D009025:Morpholines / Q000008:administration & dosage; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D017239:Paclitaxel / Q000008:administration & dosage / Q000633:toxicity*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects* / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000187:drug effects* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects*; D013223:Statistics as Topic; D013997:Time Factors; D017211:Treatment Failure; D014407:Tumor Cells, Cultured
D000972:Antineoplastic Agents, Phytogenic; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D016328:NF-kappa B; D017239:Paclitaxel; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human