Inhibitory Effects of Organosulfur Compounds in Garlic on Canine Mammary Tumor Cells
Six organosulfur compounds found in garlic were examined for their ability to alter the growth of canine mammary tumor cells (CMT-13) in culture. S-allyl-cysteine, S-ethyl-cysteine, or S-propyl-cysteine (water soluble organosulfur compounds) did not significantly alter the growth of CMT-13 cells when added at 1.0 mM or less. However, diallyl sulfide, diallyl disulfide, and diallyl trisulfide (oil soluble organosulfur compounds) addition markedly inhibited growth. Diallyl disulfide induced growth depression was accompanied by an increased proportion of cells in the G0/G1 phase compared to untreated cultures. Exposure to diallyl disulfide (1 mM) increased the intracellular glutathione by 57% and the activity of glutathione-S-transferase by 300%. Addition of glutathione prior to diallyl disulfide markedly decreased the severity of the diallyl disulfide-mediated growth inhibition. Simultaneous treatment with sodium selenite (9.6 μM) and diallyl disulfide (1 or 5 μM) enhanced the growth depression compared to that caused by either compound alone. Studies with supplemental glutathione and selenium suggest an involvement of membrane sulfhydryls in the growth inhibition caused by the tested oil soluble sulfhydryls in garlic. These studies document that some sulfhydryls found in garlic are effective inhibitors of the growth of neoplastic cells. Additional studies are warranted to determine the physiological significance of these organosulfur compounds as agents against human tumors.