title: MEK inhibition enhances paclitaxel-induced tumor apoptosis.
abstract: The anti-cancer drug paclitaxel (Taxol) alters microtubule assembly and activates pro-apoptotic signaling pathways. Previously, we and others found that paclitaxel activates endogenous JNK in tumor cells, and the activation of JNK contributes to tumor cell apoptosis. Here we find that paclitaxel activates the prosurvival MEK/ERK pathway, which conversely may compromise the efficacy of paclitaxel. Hence, a combination treatment of paclitaxel and MEK inhibitors was pursued to determine whether this treatment could lead to enhanced apoptosis. The inhibition of MEK/ERK with a pharmacologic inhibitor, U0126, together with paclitaxel resulted in a dramatic enhancement of apoptosis that is four times more than the additive value of the two drugs alone. Enhanced apoptosis was verified by the terminal transferase-mediated dUTP nick end labeling assay, by an enzyme-linked immunosorbent assay for histone-associated DNA fragments, and by flow cytometric analysis for DNA content. Specificity of the pharmacologic inhibitor was confirmed by the use of (a) a second MEK/ERK inhibitor and (b) a transdominant-negative MEK. Enhanced apoptosis was verified in breast, ovarian, and lung tumor cell lines, suggesting this effect is not cell type-specific. This is the first report of enhanced apoptosis detected in the presence of paclitaxel and MEK inhibition and suggests a new anticancer strategy.
authors.affiliation: Lineberger Comprehensive Cancer Center, Department of Microbiology and Immunology, Department of Surgery, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: MacKeigan
authors.forename: T S
authors.initials: TS
authors.lastname: Collins
authors.forename: J P
authors.initials: JP
authors.lastname: Ting
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D002070:Butadienes / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005419:Flavonoids / Q000494:pharmacology; D005434:Flow Cytometry; D005799:Genes, Dominant; D006657:Histones / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D009570:Nitriles / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D002070:Butadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D006657:Histones; D009570:Nitriles; C113580:U 0126; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D017239:Paclitaxel; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one