title: Studies on the mechanism of the inhibition of human leukaemia cell growth by dietary isothiocyanates and their cysteine adducts in vitro.
abstract: The dietary isothiocyanates and cancer chemopreventive agents phenethyl isothiocyanate and allyl isothiocyanate and their cysteine conjugates inhibited the growth and induced apoptosis of human leukaemia HL60 (p53-) and human myeloblastic leukaemia-1 cells (p53+) in vitro. The median growth inhibitory concentration (GC(50)) values were in the range 1.49-3.22 microM in cultures with 10% serum. Isothiocyanates and cysteine conjugates had increased potency against HL60 cells in serum-free medium, with GC(50) values of 0.8-0. 9 microM. The potency of the compounds decreased with increased serum content of the medium, but that of the cysteine conjugates decreased more markedly. Growth inhibition and toxicity was characterised by either a rapid interaction of the isothiocyanate with the cells in the first hour of culture or exposure to isothiocyanate liberated from the cysteine conjugate in the initial 3 hr of culture, inhibition of macromolecule synthesis, and a commitment to apoptosis which developed in the initial 24 hr. Activities of caspase-3 and caspase-8 were increased during isothiocyanate-induced apoptosis, but caspase-1 activity was not. The general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone and the specific caspase-8 inhibitor N-benzyloxycarbonyl-Ile-Glu(OMe)-Thr-Asp(OMe)-fluoromethylketone inhibited apoptosis, but specific caspase-1 and caspase-3 inhibitors did not. The antiproliferative activities were limited by hydrolysis of the isothiocyanate. This suggests that caspase-8 has a critical role, and caspase-3 a supporting role, in isothiocyanate-induced apoptosis in which p53 is not an obligatory participant. Isothiocyanate-induced apoptosis may suppress the growth of preclinical tumours and contribute to the well-established decreased cancer incidence associated with a vegetable-rich diet.
authors.affiliation: Department of Biological Sciences, University of Essex, Central Campus, Wivenhoe Park, CO4 3SQ, Essex, Colchester, UK.
authors.forename: K
authors.initials: K
authors.lastname: Xu
authors.forename: P J
authors.initials: PJ
authors.lastname: Thornalley
mesh_terms: D016588:Anticarcinogenic Agents / Q000737:chemistry / Q000494:pharmacology*; D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D018890:Chemoprevention; D003545:Cysteine / Q000737:chemistry / Q000494:pharmacology*; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004032:Diet; D005520:Food Preservatives / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D006868:Hydrolysis; D017879:Isothiocyanates / Q000737:chemistry / Q000494:pharmacology*; D007938:Leukemia; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects; D012334:RNA, Neoplasm / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
chemical_list: D016588:Anticarcinogenic Agents; D004273:DNA, Neoplasm; D005520:Food Preservatives; D017879:Isothiocyanates; D012334:RNA, Neoplasm; C058305:phenethyl isothiocyanate; C004471:allyl isothiocyanate; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D003545:Cysteine