Effects of the garlic compound diallyl disulfide on the metabolism, adherence and cell cycle of HT-29 colon carcinoma cells: evidence of sensitive and resistant sub-populations

Diallyl disulfide (DADS) is a major organosulphur compound present in garli c with an anti-mitotic potential against colon neoplasic lesions in vivo an d colon tumour cell growth in vitro. Using the human colon adenocarcinoma H T-29 Glc(-/+) cell line we identified sub-populations of tumoural cells wit h markedly different characteristics in terms of metabolic capacities, adhe sion properties and distribution in the cell cycle phases. After 1 and 2 da ys treatment with 100 muM DADS HT-29 cells were largely released into the c ulture medium. These floating cells accumulated in the G(2)/M phase and wer e characterized by a 5-fold reduction in cell capacity for de novo protein synthesis. Polyamine metabolism, which is necessary for intestinal epitheli al cell attachment and growth, was also severely affected, since 3-fold red uctions in polyamine biosynthesis and net accumulation of putrescine were m easured after DADS treatment. However, oxidation of L-glutamine, the main p recursor of the tricarboxylic acid cycle in these cells, and de novo synthe sis of glutathione, a tripeptide involved in tumoural cell chemoresistance, were not affected by DADS treatment. In contrast, the adherent sub-populat ion of HT-29 cells, although partially accumulated in G(2)/M phase, were ch aracterized by unaffected metabolic capacities when compared with control c ells except for putrescine accumulation, which was transiently decreased, a nd L-glutamine oxidation, which was increased 2-fold. DADS-resistant cells selected within 5 days were then able to proliferate at a similar rate to c ontrol untreated cells. The DADS-induced changes in HT-29 metabolic capacit ies, adhesion properties and the cell cycle are discussed from a causal per spective.