National Library of Medicine) - Indole-3-carbinol

The current options for treating breast cancer are limited to excision surgery, general chemotherapy, radiation therapy, and, in a minority of breast cancers that rely on estrogen for their growth, antiestrogen therapy. The naturally occurring chemical indole-3- carbinol (I3C), found in vegetables of the Brassica genus, is a promising anticancer agent that we have shown previously to induce a G1 cell cycle arrest of human breast cancer cell lines, independent of estrogen receptor signaling. Combinations of I3C and the antiestrogen tamoxifen cooperate to inhibit the growth of the estrogen-dependent human MCF-7 breast cancer cell line more effectively than either agent alone. This more stringent growth arrest was demonstrated by a decrease in adherent and anchorage- independent growth, reduced DNA synthesis, and a shift into the G1 phase of the cell cycle. A combination of I3C and tamoxifen also caused a more pronounced decrease in cyclin-dependent kinase (CDK) 2- specific enzymatic activity than either compound alone but had no effect on CDK2 protein expression. Importantly, treatment with I3C and tamoxifen ablated expression of the phosphorylated retinoblastoma protein (Rb), an endogenous substrate for the G1 CDKs, whereas either agent alone only partially inhibited endogenous Rb phosphorylation. Several lines of evidence suggest that I3C works through a mechanism distinct from tamoxifen. I3C failed to compete with estrogen for estrogen receptor binding, and it specifically down-regulated the expression of CDK6. These results demonstrate that I3C and tamoxifen work through different signal transduction pathways to suppress the growth of human breast cancer cells and may, therefore, represent a potential combinatorial therapy for estrogen-responsive breast cancer.

Dose-ranging study of indole-3-carbinol for breast cancer prevention.

Indole-3-carbinol is made from indole-3-glucosinolate by the enzyme myrosinase.

Indole-3-carbinol (C 9 H 9 N O) is produced ..

Indole-3-carbinol inhibits the expression of cyclin-dependent kinase- 6 and induces a G1 cell cycle arrest of human breast cancer cells independent of estrogen receptor signaling.


Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables such as cabbage, broccoli, and Brussels sprouts, has been shown to reduce the incidence of spontaneous and carcinogen-induced mammary tumors. Treatment of cultured human MCF7 breast cancer cells with I3C reversibly suppresses the incorporation of [3H]thymidine without affecting cell viability or estrogen receptor (ER) responsiveness. Flow cytometry of propidium iodide-stained cells revealed that I3C induces a G1 cell cycle arrest. Concurrent with the I3C-induced growth inhibition, Northern blot and Western blot analyses demonstrated that I3C selectively abolished the expression of cyclin-dependent kinase 6 (CDK6) in a dose- and time-dependent manner. Furthermore, I3C inhibited the endogenous retinoblastoma protein phosphorylation and CDK6 phosphorylation of retinoblastoma in vitro to the same extent. After the MCF7 cells reached their maximal growth arrest, the levels of the p21 and p27 CDK inhibitors increased by 50%. The antiestrogen tamoxifen also suppressed MCF7 cell DNA synthesis but had no effect on CDK6 expression, while a combination of I3C and tamoxifen inhibited MCF7 cell growth more stringently than either agent alone. The I3C-mediated cell cycle arrest and repression of CDK6 production were also observed in estrogen receptor-deficient MDA-MB-231 human breast cancer cells, which demonstrates that this indole can suppress the growth of mammary tumor cells independent of estrogen receptor signaling. Thus, our observations have uncovered a previously undefined antiproliferative pathway for I3C that implicates CDK6 as a target for cell cycle control in human breast cancer cells. Moreover, our results establish for the first time that CDK6 gene expression can be inhibited in response to an extracellular antiproliferative signal.

Indole-3-carbinol works as a strong , thereby protecting the DNA and other cell structures.

Indole-3-carbinol « New Drug Approvals

BACKGROUND: The oxidative metabolism of estrogens in humans is mediated primarily by cytochrome P450, many isoenzymes of which are inducible by dietary and pharmacologic agents. One major pathway, 2- hydroxylation, is induced by dietary indole-3-carbinol (I3C), which is present in cruciferous vegetables (e.g., cabbage and broccoli). PURPOSE: Because the pool of available estrogen substrates for all pathways is limited, we hypothesized that increased 2-hydroxylation of estrogens would lead to decreased activity in competing metabolic pathways. METHODS: Urine samples were collected from subjects before and after oral ingestion of I3C (6-7 mg/kg per day). In the first study, seven men received I3C for 1 week; in the second study, 10 women received I3C for 2 months. A profile of 13 estrogens was measured in each sample by gas chromatography-mass spectrometry. RESULTS: In both men and women, I3C significantly increased the urinary excretion of C-2 estrogens. The urinary concentrations of nearly all other estrogen metabolites, including levels of estradiol, estrone, estriol, and 16alpha-hydroxyestrone, were lower after I3C treatment. CONCLUSIONS: These findings support the hypothesis that I3C-induced estrogen 2-hydroxylation results in decreased concentrations of several metabolites known to activate the estrogen receptor. This effect may lower estrogenic stimulation in women. IMPLICATIONS: I3C may have chemopreventive activity against breast cancer in humans, although the long-term effects of higher catechol estrogen levels in women require further investigation.

Benzyl Carbinol | Spectrum Chemical

Sixty women at increased risk for breast cancer were enrolled in a placebo-controlled, double-blind dose-ranging chemoprevention study of indole-3-carbinol (I3C). Fifty-seven of these women with a mean age of 47 years (range 22-74) completed the study. Each woman took a placebo capsule or an I3C capsule daily for a total of 4 weeks; none of the women experienced any significant toxicity effects. The urinary estrogen metabolite ratio of 2-hydroxyestrone to 16 alpha- hydroxyestrone, as determined by an ELISA assay, served as the surrogate endpoint biomarker (SEB). Perturbation in the levels of SEB from baseline was comparable among women in the control (C) group and the 50, 100, and 200 mg low-dose (LD) group. Similarly, it was comparable among women in the 300 and 400 mg high-dose (HD) group. Regression analysis showed that peak relative change of SEB for women in the HD group was significantly greater than that for women in the C and LD groups by an amount that was inversely related to baseline ratio; the difference at the median baseline ratio was 0.48 with 95% confidence interval (0.30, 0.67). No other factors, such as age and menopausal status, were found to be significant in the regression analysis. The results in this study suggest that I3C at a minimum effective dose schedule of 300 mg per day is a promising chemopreventive agent for breast cancer prevention. A larger study to validate these results and to identify an optimal effective dose schedule of I3C for long-term breast cancer chemoprevention will be necessary.

Synthesis of trifluoromethyl carbinols

A major obstacle to successful chemotherapy is the development of multidrug resistance (MDR) by cancer cells. MDR is characterized by enhanced cellular efflux of many structurally and functionally diverse compounds, including many anticancer drugs, due to overexpression of the MDR-1 gene product, P-glycoprotein. We hypothesized that the phytochemical, indole-3-carbinol (I3C), and some of its acid-condensation derivatives may inhibit P-glycoprotein- mediated transport due to their aromatic and nitrogen components, thus increasing the accumulation and efficacy of anticancer drugs and acting as a dietary adjuvant to conventional chemotherapy. I3C was subjected to acid conditions similar to those occurring in the stomach following ingestion and three acid-condensation products; a dimer, a noncyclic trimer, and a cyclic trimer were isolated and purified by high-performance liquid chromatography. The ability of I3C and its acid-condensation derivatives to reverse MDR was investigated using murine B16 melanoma cells that were transfected with the human MDR-1 gene (B16/hMDR-1 cells) and were cross-resistant to vinblastine and doxorubicin. The I3C acid-condensation product mixture, but not I3C, sensitized B16/hMDR-1 transfectants to the toxicity of vinblastine and doxorubicin. All three I3C acid- condensation products also increased the accumulation of the P- glycoprotein substrate, doxorubicin, in B16/hMDR-1 transfectants to levels comparable to parental B16 cells. The I3C acid-condensation product mixture competed with azidopine for binding to P- glycoprotein, suggesting that the observed MDR-reversing effect of the acid-condensation products was due to direct interaction with P- glycoprotein. The ability of p.o. administered I3C to reverse MDR was also tested in vivo. The resistance of B16/hMDR-1 transfectants to vinblastine and doxorubicin was preserved after i.p. injection and growth in nude mice. Tumor mass in mice that were provided with 333 or 500 mg/kg mouse/day I3C in their diet and injected s.c. with the anticancer drugs doxorubicin or vinblastine was significantly reduced as compared to tumor mass in mice provided with standard diet and injected with these anticancer drugs or mice provided with 500 mg/kg mouse/day I3C and not injected with anticancer compound. The concentrations of I3C used had no effect on survival or the general appearance and behavior of the mice. Collectively, these results indicate that ingestion of the common dietary constituent I3C results in its conversion to acid-condensation derivatives that sensitized MDR tumors to chemotherapeutic drugs without eliciting direct toxicity to the host.