title: Modification of cysteine 179 of IkappaBalpha kinase by nimbolide leads to down-regulation of NF-kappaB-regulated cell survival and proliferative proteins and sensitization of tumor cells to chemotherapeutic agents.
abstract: Reverse pharmacology, also called the "bedside to bench" approach, that deals with new uses for a well known molecular entity has been used extensively in cancer drug development to identify novel compounds and delineate their mechanisms of action. Here, we show that nimbolide, a triterpenoid isolated from Azadirachta indica, enhanced the apoptosis induced by inflammatory cytokines and chemotherapeutic agents in tumor cells. This limonoid abrogated the expression of proteins associated with cell survival (Bcl-2, Bcl-xL, IAP-1, and IAP-2), proliferation (cyclin D1), invasion (MMP-9), and angiogenesis (VEGF), all regulated by nuclear factor (NF)-κB. Nimbolide inhibited the activation of NF-κB induced by carcinogens and inflammatory stimuli. Constitutively active NF-κB found in most tumor cells was also inhibited. We found that suppression of NF-κB activation by nimbolide was caused by inhibition of IκB kinase (IKK), which led to suppression of IκBα phosphorylation and degradation, nuclear translocation, DNA binding, and gene transcription. Reducing agent reversed the action of the limonoid, suggesting the involvement of a cysteine residue. Replacement of Cys(179) of IKK-β with alanine abolished the effect of nimbolide, suggesting that Cys(179) plays a critical role in inhibiting the NF-κB activation. Overall, our results indicate that nimbolide can sensitize tumor cells to chemotherapeutic agents through interaction with IKK, leading to inhibition of NF-κB-regulated proteins.
authors.affiliation: Cytokine Research Laboratory, Department of Experimental Therapeutics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Subash C
authors.initials: SC
authors.lastname: Gupta
authors.forename: Sahdeo
authors.initials: S
authors.lastname: Prasad
authors.forename: Simone
authors.initials: S
authors.lastname: Reuter
authors.forename: Ramaswamy
authors.initials: R
authors.lastname: Kannappan
authors.forename: Vivek R
authors.initials: VR
authors.lastname: Yadav
authors.forename: Jayaraj
authors.initials: J
authors.lastname: Ravindran
authors.forename: Padmanabhan S
authors.initials: PS
authors.lastname: Hema
authors.forename: Madan M
authors.initials: MM
authors.lastname: Chaturvedi
authors.forename: Mangalam
authors.initials: M
authors.lastname: Nair
authors.forename: Bharat B
authors.initials: BB
authors.lastname: Aggarwal
mesh_terms: D019943:Amino Acid Substitution; D017209:Apoptosis / Q000187:drug effects; D031601:Azadirachta / Q000737:chemistry; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D019938:Cyclin D1 / Q000378:metabolism; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D057809:HEK293 Cells; D018922:HL-60 Cells; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism*; D019169:Jurkat Cells; D020014:K562 Cells; D036701:Limonins / Q000737:chemistry / Q000494:pharmacology*; D015394:Molecular Structure; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D020298:U937 Cells; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D036701:Limonins; D016328:NF-kappa B; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D042461:Vascular Endothelial Growth Factor A; D019938:Cyclin D1; C042198:nimbolide; D051550:I-kappa B Kinase; D020169:Caspases; D003545:Cysteine