1. Studies on the mechanism of the inhibition of human leukaemia cell growth by dietary isothiocyanates and their cysteine adducts in vitro.
- Author
-
Xu K and Thornalley PJ
- Subjects
- Anticarcinogenic Agents chemistry, Apoptosis, Caspase 3, Caspase 8, Caspase 9, Caspases metabolism, Cell Division drug effects, Chemoprevention, Cysteine chemistry, DNA, Neoplasm biosynthesis, Food Preservatives pharmacology, HL-60 Cells, Humans, Hydrolysis, Isothiocyanates chemistry, Leukemia, Lymphocytes cytology, Lymphocytes drug effects, RNA, Neoplasm biosynthesis, Tumor Cells, Cultured, Anticarcinogenic Agents pharmacology, Cysteine pharmacology, Diet, Isothiocyanates pharmacology
- 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.
- Published
- 2000
- Full Text
- View/download PDF