title: Pemetrexed indirectly activates the metabolic kinase AMPK in human carcinomas.
abstract: The chemotherapeutic drug pemetrexed, an inhibitor of thymidylate synthase, has an important secondary target in human leukemic cells, aminoimidazolecarboxamide ribonucleotide formyltransferase (AICART), the second folate-dependent enzyme of purine biosynthesis. The purine intermediate aminoimidazolecarboxamide ribonucleotide (ZMP), which accumulates behind this block, transmits an inhibitory signal to the mTORC1 complex via activation of the cellular energy sensor AMP-activated kinase (AMPK). Given that the PI3K-AKT-mTOR pathway is frequently deregulated during carcinogenesis, we asked whether the indirect activation of AMPK by pemetrexed offers an effective therapeutic strategy for carcinomas with defects in this pathway. Activation of AMPK by ZMP in pemetrexed-treated colon and lung carcinoma cells and the downstream consequences of this activation were strikingly more robust than previously seen in leukemic cells. Genetic experiments demonstrated the intermediacy of AICART inhibition and the centrality of AMPK activation in these effects. Whereas AMPK activation resulted in marked inhibition of mTORC1, other targets of AMPK were phosphorylated that were not mTORC1-dependent. Whereas AMPK activation is thought to require AMPKα T172 phosphorylation, pemetrexed also activated AMPK in carcinoma cells null for LKB1, the predominant AMPKα T172 kinase whose deficiency is common in lung adenocarcinomas. Like rapamycin analogs, pemetrexed relieved feedback suppression of PI3K and AKT, but the prolonged accumulation of unphosphorylated 4E-BP1, a tight-binding inhibitor of cap-dependent translation, was seen following AMPK activation. Our findings indicate that AMPK activation by pemetrexed inhibits mTORC1-dependent and -independent processes that control translation and lipid metabolism, identifying pemetrexed as a targeted therapeutic agent for this pathway that differs significantly from rapamycin analogs.
authors.affiliation: Department of Pharmacology & Toxicology and the Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Rothbart
authors.forename: Alexandra C
authors.initials: AC
authors.lastname: Racanelli
authors.forename: Richard G
authors.initials: RG
authors.lastname: Moran
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D051058:Oncogene Protein v-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D000068437:Pemetrexed; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; D004791:Enzyme Inhibitors; D005971:Glutamates; D046912:Multiprotein Complexes; D011506:Proteins; D012265:Ribonucleotides; D000068437:Pemetrexed; D000620:Aminoimidazole Carboxamide; D006147:Guanine; D013940:Thymidylate Synthase; D000076222:Mechanistic Target of Rapamycin Complex 1; D051058:Oncogene Protein v-akt; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D058570:TOR Serine-Threonine Kinases; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide; D020123:Sirolimus