Selective isolation of human breast carcinoma cells resistant to the growth-inhibitory effects of retinol

The vitamin A family can significantly decrease the expression of ERbeta of ERs positive breast cancer cells in the presence or absence of ER ligands and paclitaxel

Taxanes have high activity against breast cancer cells either as the single agent or in combination with other anticancer compounds. The aim of the study was to determine the effects of vitamin A compounds on the cytotoxic action of paclitaxel and on the expression of ERs in the MCF-7 breast cancer cells. Retinol and beta-carotene, but not retinoids, added to the culture exerted an effect on paclitaxel activity. However, only beta-carotene significantly reduced the percentage of proliferating cells (40.36% +/- 5.64, p < 0.01). We observed that vitamin A and its derivatives combined with paclitaxel and estradiol decreased the percentage of proliferating cells, but only in comparison to estradiol group, whereas retinol and lycopene administered together with paclitaxel and tamoxifen decrease significantly the percentage of proliferatin cells (36.85% +/- 4.71, p < 0.0001 and 37.22% +/- 1.59, p < 0.0001 respectively, compared with paclitaxel group). We have shown that paclitaxel increases the expression of ERalpha and ERbeta mRNA in MCF-7 line. The strongest effect of transcription inhibition ERalpha (2.5 times) and especially ERbeta (10 times) was observed after addition of 9-cis retinoic acid and paclitaxel. This data suggests a synergistic effect of the compounds on ERbeta down-regulation. Our results support the use of retinoid is treatment of ER positive breast cancer patients.

Alterations in cellular retinol metabolism contribute to differential retinoid responsiveness in normal human mammary epithelial cells versus breast cancer cells

The present study was undertaken to compare ROH growth responsiveness between normal human mammary epithelial cells (HMECs), estrogen receptor positive (MCF-7) and negative (MDA-MB-231) breast cancer cells, and assess whether this responsiveness is correlated with differences in ROH metabolism, particularly RA synthesis. HMECs were markedly more growth sensitive to a physiological dose of ROH than breast cancer cells, exhibiting a significant decrease in cell number by 48h and >70% decrease by 144h. In comparison, numbers of MCF-7s were only decreased 32% by 144h. MDA-MB-231 cells were not affected. However, HMECs and MCF-7 cells displayed similar growth responsiveness to 1 microM RA, while MDA-MB-231 cells were minimally affected. Although the initial rates and extent of ROH uptake were comparable among cell types, ROH levels in HMECs progressively decreased to 20% of the peak by 24h and < or = 10% by 72h. In contrast, ROH levels in the cancer cells remained relatively constant through 48 h. The decrease in HMEC ROH was attributable to greater metabolism as evidenced by rapid and predominant retinyl ester formation. HMECs also produced approximately 5 times more RA from ROH than MCF-7s and approximately 10 times more than MDA MB-231 cells. Our results demonstrate that normal HMECs are markedly more responsive to the growth inhibitory effects of ROH than breast cancer cells, and that this responsiveness is associated with greater ROH metabolism including greater RA synthesis. These data suggest that altered ROH metabolism may be a factor in breast cancer progression.

Metabolic conversion of retinol to retinoic acid mediates the biological responsiveness of human mammary epithelial cells to retinol

The biological effects of vitamin A are mediated in part by retinoic acid (RA) modulation of gene transcription. In this study, we examined whether normal human mammary epithelial cells (HMECs) are biologically responsive to retinol (ROH), the metabolic precursor of RA. While both ROH and tRA resulted in time- and dose-dependent decreases in total cell number, tRA was markedly more potent. Metabolically, treatment of HMECs with physiological doses of ROH resulted in rapid uptake and subsequent production of both retinyl esters and tRA. Although a comparatively minor metabolite, tRA levels peaked at 6 h and remained above endogenous levels for up to 72 h in proportion to cellular ROH concentrations. In HMECs transfected with an RA-responsive luciferase reporter gene, treatment with 3 microM ROH resulted in an increase in luciferase activity to a level intermediate between that observed with 0.001 and 0.01 microM tRA. Citral, an RA-synthesis inhibitor, was also used to examine the biological activity of ROH. Compared to ROH alone, ROH plus citral treatment resulted in three-fold less tRA synthesis and a > 65% attentuation of RA-responsive reporter gene activity which persisted through 72 h. Citral also significantly attenuated the extent of ROH-mediated reductions in total HMEC number. Thus, treatment with physiological concentrations of ROH results in fewer total numbers of HMECs and this response is a consequence of cellular tRA synthesis which can induce RA-responsive gene expression.

Retinoids, carotenoids, and human breast cancer cell cultures: a review of differential effects

Cancer of the breast is the most common incident cancer and cause of death from cancer in women. Several epidemiologic studies have reported a significant inverse relationship between the intake of vitamin A and/or provitamin A-rich foods and the incidence of certain cancers, including breast cancer. A large number of studies have been conducted to determine the effect of retinoids (all-trans-retinoic acid, in particular), and to a lesser extent of carotenoids, on breast cancer using cell culture models. In general, the results of these studies demonstrate beneficial effects of all-trans-retinoic acid on different breast cancer cells. This review compares studies conducted in different laboratories using retinoids and carotenoids as treatments for breast cancer cells and suggests what may be the underlying reasons for the differential effects of these compounds on the same cell lines.

Combined effects of 13-cis-retinoic acid, tamoxifen and interferon on the growth of human breast cancer cells

We studied the effect of 13-cis-retinoic acid (13-cRA) alone and in combination with interferons (IFNs) and tamoxifen (TAM) in two established human breast cancer cell lines: the estrogen-sensitive CG-5 and the estrogen-insensitive MDA-MB-453 cells. 13-cRA (10(-9)-10(-5) M) significantly reduced the growth of both cell lines in a dose-dependent fashion, after 3 and 6 days of treatment. When the retinoid (10(-9)-10(-5) M) was combined with natural beta-IFN (100-1000 IU/ml) for 6 days, we observed a growth inhibition more pronounced than that produced by each of the two single agents in both CG-5 and MDA-MB-453 cells. Only in the former model was the inhibitory effect synergistic at all the drug concentrations used. Association of 13-cRA (10(-9)-10(-5) M) and recombinant alpha2a-IFN (100-1000 IU/ml) or TAM (10(-7)-10(-6) M) did not determine an additive or synergistic effect on the growth of CG-5 cells.

Pretreatment with vitamin A inhibits transforming growth factor alpha stimulation of human mammary carcinoma cells

Vitamin A or retinol is an important agent in the normal differentiation and growth of cells. Retinol is an effective inhibitor of the growth of many transformed cells in vitro and in vivo but its mechanism of action is unclear. Transforming growth factor alpha (TGF alpha) is a known mitogen. We examined the effect of retinol treatment on TGF alpha stimulation of two human mammary carcinoma cell lines, one which is growth inhibited by retinol and one which is not. Pretreatment of both cell lines for 48 hours with retinol resulted in inhibition of TGF alpha stimulation of growth. In the T47D cell line the mechanism was not related to an effect on the cellular content of TGF alpha, epidermal growth factor (EGF) receptor protein, EGF receptor mRNA, or on the binding of TGF alpha to the EGF receptor. However, TGF alpha-induced stimulation of the EGF receptor substrate, phospholipase C-gamma 1, was abrogated in the T47D cell line with retinol pretreatment. In the MDA-MB-468 cell line, pretreatment with retinol resulted in a decrease in tyrosine phosphorylation of the EGF receptor. These results suggest that pretreatment with retinol decreases cellular proliferation seen with TGF alpha treatment by altering phospholipase C-gamma 1 response and/or EGF receptor tyrosine kinase activity. Alteration of phospholipase C-gamma 1 activity does not appear to be responsible for the inhibition of cell growth seen in the absence of TGF alpha stimulation.

Retinoic acid resistance of estradiol-independent breast cancer cells coincides with diminished retinoic acid receptor function

Retinoic acid (RA) strongly inhibits proliferation of the estrogen (E2)-dependent human breast cancer cell lines MCF7, T47D, and ZR75-1, but not the E2-independent and E2 receptor (ER)-negative lines MDA-MB231, MDA-MB468, BT20 and Hs578T. The specific sensitivity of the E2-dependent cell lines seems not to be caused by an inhibitory effect of RA on ER functioning since RA inhibited the proliferative response not only to E2 but also to insulin. Furthermore, endogenous RA receptors (RARs) hardly impaired transcriptional activation of an E2 responsive element-tk-CAT reporter construct. RAR alpha mRNA was highly expressed in the RA-responsive lines, but not in the unresponsive lines, except BT20. With the exception of Hs578T, also RAR beta mRNA expression was low in the unresponsive lines. While in the dependent lines and Hs578T RA activated RA responsive element-dependent transcriptional activity, this response was very low in MDA-MB231, MDA-MB468, and BT20, suggesting that the RA resistance of these latter three ER-negative lines is due to underexpression of functional RARs. Our results suggest that the loss of functional RARs may be a frequent event, leading to RA unresponsiveness of ER-negative breast cancer cells. This implies that both the steroid and retinoid receptor status of breast tumors may be used to predict a successful treatment with retinoids.