Quantitative combination effects between sulforaphane and 3,3′-diindolylmethane on proliferation of human colon cancer cells in vitro

Abstract

Isothiocyanates (ITCs) and indoles derived from cruciferous vegetables possess growth-inhibiting and apoptosis-inducing activities in cancer cell lines in vitro. ITCs like sulforaphane (SFN) are cytotoxic, whereas indoles including indole-3-carbinol or its condensation product 3,3'-diindolylmethane (DIM) are acting by cytostatic mechanisms in human colon cancer cell lines. In the present study, we have investigated the impact of defined combinations of SFN and DIM (ratio 1:4, 1:2, 1:1, 2:1 and 4:1) on cell proliferation, cell-cycle progression and apoptosis induction in cultured 40-16 colon carcinoma cells. Calculations of combination effects were based on the method of Chou et al. (1984) Adv. Enzyme Regul., 22, 27-55, and were expressed as a combination index (CI) with CI < 1, CI = 1 or CI > 1 representing synergism, additivity or antagonism, respectively. Interestingly, at a total drug concentration of 2.5 microM, all combinations of SFN and DIM were antagonistic. With increasing concentrations, the antagonistic effect gradually turned into a synergistic interaction at the highest combined cytotoxic concentration of 40 microM. Cell-cycle analyses with SFN:DIM ratios of 1:1, 1:2 and 1:4 and total concentrations between 10 and 25 microM confirmed antagonism at low and additive effects at higher doses. SFN (10 microM) in combination with DIM (10 microM) resulted in strong G(2)/M cell-cycle arrest, which was not observed with either compound alone. Our results indicate that cytotoxic concentrations of SFN:DIM combinations affect cell proliferation synergistically. At low total concentrations (below 20 microM), which are physiologically more relevant, the combined broccoli compounds showed antagonistic interactions in terms of cell growth inhibition. These data stress the need for elucidating mechanistic interactions for better predicting beneficial health effects of bioactive food components.

Dietary polyphenol quercetin targets pancreatic cancer stem cells

“…The intake of dietary supplements produced from broccoli sprout extracts are available at concentrations of 30 mg glucoraphanin per tablet. Nevertheless, as suggested by the data of the present study and by findings of others (14,15,26) dietary agents act best in concert. Thus, upon intake of isolated dietary supplements the beneficial effects may be much weaker and more unspecific than with a natural occuring mixure of bioactive plant ingredients.…”

“…These plant substances have recently been demonstrated to inhibit self-renewal of breast CSCs (14). Most importantly, quantitative combination effects between e.g., curcumin and piperine, and sulforaphane and 3,3-diindolylmethane, another broccoli ingredient, were observed (14,15).…”

The Anti-Carcinogenic Effect of Indole-3-Carbinol and 3, 3'-Diindolylmethane and their Mechanism of Action

“…The anti-proliferative effect of DIM was mediated by G1 arrest followed by induction of apoptosis. Interestingly, DIM also inhibited the growth of primary thyroid goiter cells by 70% [91]. These studies provide a strong rational for the clinical exploration of DIM as an adjuvant to surgery in thyroid proliferation diseases.…”

“…Dietary indoles has been documented as inhibiting tumorigenesis in various target organs including colon [89][90][91], thyroid [92], pancreas [93], liver [94], cervix [95,96], melanoma [97], and lung [98,99].…”

Inhibitory effect of the low‑toxic exogenous aryl hydrocarbon receptor modulator 3'3‑diindolylmethane on gastric cancer in mice

“…DIM is an acid-catalyzed condensation product of indole-3-carbinol, a constituent of cruciferous vegetables (11). DIM has been identified as an anti-cancer agent involved in various solid malignancies, including ovarian (12), prostate (13), colon (14) and pancreatic cancer (15). The anti-cancer effects of DIM include suppressing cancer cell proliferation (16)(17)(18) and promoting cancer cell apoptosis (19)(20)(21).…”