title: PDE5 inhibitors enhance the lethality of pemetrexed through inhibition of multiple chaperone proteins and via the actions of cyclic GMP and nitric oxide.
abstract: Phosphodiesterase 5 (PDE5) inhibitors prevent the breakdown of cGMP that results in prolonged protein kinase G activation and the generation of nitric oxide. PDE5 inhibitors enhanced the anti-NSCLC cell effects of the NSCLC therapeutic pemetrexed. [Pemetrexed + sildenafil] activated an eIF2α - ATF4 - CHOP - Beclin1 pathway causing formation of toxic autophagosomes; activated a protective IRE1 - XBP-1 - chaperone induction pathway; and activated a toxic eIF2α - CHOP - DR4 / DR5 / CD95 induction pathway. [Pemetrexed + sildenafil] reduced the expression of c-FLIP-s, MCL-1 and BCL-XL that was blocked in a cell-type -dependent fashion by either over-expression of HSP90 / GRP78 / HSP70 / HSP27 or by blockade of eIF2α-CHOP signaling. Knock down of PKGI/II abolished the ability of sildenafil to enhance pemetrexed toxicity whereas pan-inhibition of NOS using L-NAME or knock down of [iNOS + eNOS] only partially reduced the lethal drug interaction. Pemetrexed reduced the ATPase activities of HSP90 and HSP70 in an ATM-AMPK-dependent fashion that was enhanced by sildenafil signaling via PKGI/II. The drug combination activated an ATM-AMPK-TSC2 pathway that was associated with reduced mTOR S2448 and ULK-1 S757 phosphorylation and increased ULK-1 S317 and ATG13 S318 phosphorylation. These effects were prevented by chaperone over-expression or by expression of an activated form of mTOR that prevented autophagosome formation and reduced cell killing. In two models of NSCLC, sildenafil enhanced the ability of pemetrexed to suppress tumor growth. Collectively we argue that the combination of [pemetrexed + PDE5 inhibitor] should be explored in a new NSCLC phase I trial.
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Laurence
authors.initials: L
authors.lastname: Booth
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Jane L
authors.initials: JL
authors.lastname: Roberts
authors.affiliation: Department of Medicine, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Poklepovic
authors.affiliation: Department of Medicine, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Gordon
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298-0035, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
mesh_terms: D000072283:A549 Cells; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D045744:Cell Line, Tumor; D006152:Cyclic GMP / Q000378:metabolism*; D004357:Drug Synergism; D000091342:Endoplasmic Reticulum Chaperone BiP; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D000068437:Pemetrexed / Q000494:pharmacology*; D058986:Phosphodiesterase 5 Inhibitors / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; C000717248:Hspa5 protein, mouse; D018832:Molecular Chaperones; D058986:Phosphodiesterase 5 Inhibitors; D000068437:Pemetrexed; D009569:Nitric Oxide; D006152:Cyclic GMP
keywords: autophagy; chaperone; lung cancer; pemetrexed; sildenafil