title: Inhibition of IkappaB kinase by a new class of retinoid-related anticancer agents that induce apoptosis.
abstract: The transcription factor NF-kappaB is overexpressed or constitutively activated in many cancer cells, where it induces expression of antiapoptotic genes correlating with resistance to anticancer therapies. Small molecules that inhibit the NF-kappaB signaling pathway could therefore be used to induce apoptosis in NF-kappaB-overexpressing tumors and potentially serve as anticancer agents. We found that retinoid antagonist MX781 inhibited the activation of NF-kappaB-dependent transcriptional activity in different tumor cell lines. MX781 was able to completely inhibit tumor necrosis factor alpha-mediated activation of IkappaB kinase (IKK), the upstream regulator of NF-kappaB. Inhibition of IKK activity resulted from direct binding of MX781 to the kinase, as demonstrated by in vitro inhibition studies. Two other molecules, MX3350-1 and CD2325, which are retinoic acid receptor gamma-selective agonists, were capable of inhibiting IKK in vitro, although they exerted variable inhibition of IKK and NF-kappaB activities in intact cells in a cell type-specific manner. However, N-(4-hydroxyphenyl)-retinamide, another apoptosis-inducing retinoid, and retinoic acid as well as other nonapoptotic retinoids did not inhibit IKK. Inhibition of IKK by the retinoid-related compounds and other small molecules correlated with reduced cell proliferation and increased apoptosis. Reduced cell viability was also observed after overexpression of an IKKbeta kinase-dead mutant or the IkappaBalpha superrepressor. The induction of apoptosis by the retinoid-related molecules that inhibited IKK was dependent on caspase activity but independent of the retinoid receptors. Thus, the presence of an excess of retinoic acid or a retinoid antagonist did not prevent the inhibition of IKK activation by MX781 and CD2325, indicating a retinoid receptor-independent mechanism of action.
authors.affiliation: Sidney Kimmel Cancer Center, Department of Pharmacology, University of California-San Diego School of Medicine, San Diego, California, USA.
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Bayon
authors.forename: Maria A
authors.initials: MA
authors.lastname: Ortiz
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Lopez-Hernandez
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: Michael
authors.initials: M
authors.lastname: Karin
authors.forename: Magnus
authors.initials: M
authors.lastname: Pfahl
authors.forename: F Javier
authors.initials: FJ
authors.lastname: Piedrafita
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004987:Ethers / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D051550:I-kappa B Kinase; D016328:NF-kappa B / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D012176:Retinoids / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D004987:Ethers; C115167:MX 781; D016328:NF-kappa B; D012176:Retinoids; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human; D020169:Caspases