Structure-Activity Relationships of α-, β1-, γ-, and δ-Tomatine and Tomatidine against Human Breast (MDA-MB-231), Gastric (KATO-III), and Prostate (PC3) Cancer Cells

Partial acid hydrolysis of the tetrasaccharide (lycotetraose) side chain of the tomato glycoalkaloid alpha-tomatine resulted in the formation of four products with three, two, one, and zero carbohydrate side chains, which were separated by high-performance liquid chromatography (HPLC) and identified by thin-layer chromatography (TLC) and liquid chromatography ion-trap time-of-flight mass spectrometry (LCMS-IT-TOF). The inhibitory activities in terms of IC50 values (concentration that inhibits 50% of the cells under the test conditions) of the parent compound and the hydrolysates, isolated by preparative HPLC, against normal human liver and lung cells and human breast, gastric, and prostate cancer cells indicate that (a) the removal of sugars significantly reduced the concentration-dependent cell-inhibiting effects of the test compounds, (b) PC3 prostate cancer cells were about 10 times more susceptible to inhibition by alpha-tomatine than the breast and gastric cancer cells or the normal cells, (c) the activity of alpha-tomatine against the prostate cancer cells was 200 times greater than that of the aglycone tomatidine, and (d) the activity increased as the number of sugars on the aglycone increased, but this was only statistically significant at p < 0.05 for the normal lung He1299 cell line. The effect of the alkaloids on tumor necrosis factor alpha (TNF-alpha) was measured in RAW264.7 macrophage cells. There was a statistically significant negative correlation between the dosage of gamma- and alpha-tomatine and the level of TNF-alpha. alpha-Tomatine was the most effective compound at reducing TNF-alpha. The dietary significance of the results and future research needs are discussed.