Electrophilic tuning of the chemoprotective natural product sulforaphane.
Sulforaphane [1-isothiocyanato-4-(methylsulfinyl)butane], a naturally occurring isothiocyanate derived from cruciferous vegetables, is a highly potent inducer of phase 2 cytoprotective enzymes and can protect against electrophiles including carcinogens, oxidative stress, and inflammation. The mechanism of action of sulforaphane is believed to involve modifications of critical cysteine residues of Keap1, which lead to stabilization of Nrf2 to activate the antioxidant response element of phase 2 enzymes. However, the dithiocarbamate functional group formed by a reversible reaction between isothiocyanate of sulforaphane and sulfhydryl nucleophiles of Keap1 is kinetically labile, and such modification in intact cells has not yet been demonstrated. Here we designed sulforaphane analogs with replacement of the reactive isothiocyanate by the more gentle electrophilic sulfoxythiocarbamate group that also selectively targets cysteine residues in proteins but forms stable thiocarbamate adducts. Twenty-four sulfoxythiocarbamate analogs were synthesized that retain the structural features important for high potency in sulforaphane analogs: the sulfoxide or keto group and its appropriate distance to electrophilic functional group. Evaluation in various cell lines including hepatoma cells, retinal pigment epithelial cells, and keratinocytes as well as in mouse skin shows that these analogs maintain high potency and efficacy for phase 2 enzyme induction as well as the inhibitory effect on lipopolysaccharide-induced nitric oxide formation like sulforaphane. We further show in living cells that a sulfoxythiocarbamate analog can label Keap1 on several key cysteine residues as well as other cellular proteins offering new insights into the mechanism of chemoprotection.
Ahn
Young-Hoon
YH
Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Hwang
Yousang
Y
Liu
Hua
H
Wang
Xiu Jun
XJ
Zhang
Ying
Y
Stephenson
Katherine K
KK
Boronina
Tatiana N
TN
Cole
Robert N
RN
Dinkova-Kostova
Albena T
AT
Talalay
Paul
P
Cole
Philip A
PA
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D001688:Biological Products / Q000737:chemistry* / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004583:Electrons; D017879:Isothiocyanates; D000072019:Kelch-Like ECH-Associated Protein 1; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D015394:Molecular Structure; D009569:Nitric Oxide / Q000378:metabolism; D012867:Skin / Q000187:drug effects / Q000378:metabolism; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013454:Sulfoxides; D013861:Thiocyanates / Q000737:chemistry* / Q000494:pharmacology*
D048868:Adaptor Proteins, Signal Transducing; D001688:Biological Products; D003598:Cytoskeletal Proteins; D017879:Isothiocyanates; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D013438:Sulfhydryl Compounds; D013454:Sulfoxides; D013861:Thiocyanates; D009569:Nitric Oxide; C016766:sulforaphane