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We have previously reported1 that human peripheral blood mononuclear cells (PBMC) contain type II estrogen binding sites (type II EBS). In this study, the fluctuations of type IIEBS during the menstrual cycle were analyzed in 6 normally menstruating women.Approximately 3 times higher levels of type II EBS were found in the period periovulatory with respect to both follicular and luteal phases. In postmenopausal women the mean type II EBS levels were similar to those observed in the follicular phase of the cycle. However, in 3 postmenopausal patients a short course of estrogen or tamoxifen resulted in a marked increase of type II EBS levels. Tamoxifen was also found to compete with 17 β-estradiol for type II EBS in PBMC, although to a lesser extent than diethylstilbestrol.

It is well recognized that growth hormone (GH) may act as a growth and differentiation factor for the thymus gland. Recently, it has been reported that Pit-1/GHF-1 transcription factor, which controls the expression of both GH and prolactin, is expressed in stromal (not lymphoid) cells of human thymus. Here, we demonstrated by immunohistochemistry and in situ hybridization the presence of distinct GH-producing epithelial cell subsets in human thymus. The cells positive for GH mRNA and GH-immunoreactive substance are both located in the same thymus compartments, i.e., along the thymus capsule, in the subcapsular cortex, and within the septa. Local concentration of GH higher than systemic ones, in combination with other factors, may be important in regulating the thymic microenvironment necessary for T-lymphocyte differentiation.

This study demonstrates that the flavonoid quercetin (Q), a plant-derived compound with low toxicity in vivo, greatly potentiates the growth-inhibitory activity of Adriamycin (ADR) on MCF-7 ADR-resistant human breast cancer cells. The effect of Q was dose-dependent at concentrations ranging between 1 and 10 µM. Since ADR resistance in these cells is associated with the expression of high levels of P-glycoprotein (Pgp), we evaluated the effect of Q and related flavonoids of Pgp activity in cytofluorographic efflux experiments with the fluorescent dye rhodamine 123 (Rh 123). Our results indicate that Q and 3-OMe Q (3',4',7-trimethoxyquercetin) but not the 3-rhamnosylglucoside of Q (rutin) inhibit the Pgp pump-efflux activity in a dose-related manner. Moreover, 10 µM Q reduces the expression of the immunoreactive Pgp in MCF-7 ADR-resistant cells as evaluated by cytofluorimetric assay. In conclusion, these findings provide a further biological basis for the potential therapeutic application of Q as an anticancer drug either alone or in combination with ADR in multidrug-resistant breast tumor cells.

It has been demonstrated that the flavonoid quercetin (3,3',4',5,7-pentahydroxyflavone; Q) inhibits the growth of several cancer cell lines. There is evidence suggesting that the antiproliferative activity of this substance is mediated by the so-called type II estrogen-binding, site (type II EBS). We looked for the presence of type II EBS and the effect of Q on the proliferation of an Adriamycinresistant estrogen-receptor-negative human breast-cancer cell line (MCF-7 ADRr). By whole-cell assay using estradiol labelled with 6,7-tritium ([3H]-E2) as a tracer, we demonstrated that MCF-7 ADRr cells contain type II EBSs. Competition analysis revealed that diethylstilbestrol (DES) and Q competed with similar potency for [3H]-Es binding to type II EBSs. The antiestrogen tamoxifen (TAM) competed for type II EBSs, albeit to a lesser extent than either DES or Q. Growth experiments demonstrated that Q and DES exerted a dose-dependent inhibition of cell proliferation in the range of concentrations between 10 nM and 10 µm, whereas TAM was less effective. Q could also inhibit colony formation in a clonogenic assay. Our results indicate that multidrug-resistant estrogen-receptor-negative MCF-7 cells express, type II EBSs and are sensitive to the inhibitory effect of Q. This substance could be the parent compound of a novel class of anticancer agents.

To investigate the possibility that canthaxanthin inhibits cancer cell growth by inducing apoptosis, human WiDr colon adenocarcinoma and SK-MEL-2 melanoma cells were treated with two different doses of the carotenoid for 48 h. Canthaxanthin was incorporated and/or associated to cells. The treatment with the carotenoid caused growth inhibition in both cell types. Concomitantly, apoptosis was induced. Increasing time of exposure and carotenoid concentration, this effect was more pronounced. At 48 h, the percentages of apoptotic cells were 13 and 15, using 1 microM canthaxanthin, and 18 and 20, using 10 microM canthaxanthin in WiDr and SK-MEL-2 cells, respectively. This study represents the first demonstration that canthaxanthin is able to induce apoptosis in tumour cells.