Mechanism of synergistic action of all-trans- or 9-cis-retinoic acid and interferons in breast cancer cells

Retinoids in biological control and cancer

More than 80 years ago, Wolbach and Howe provided the first evidence suggesting a link between alterations within human cells that lead to malignancies and vitamin A deficiencies (Wolbach and Howe 1925 Nutr. Rev. 36: 16-19). Since that time, epidemiological, preclinical and clinical studies have established a causative relationship between vitamin A deficiency and cancer. Laboratory research has provided insight into the intracellular targets, various signaling cascades and physiological effects of the biologically-active natural and synthetic derivatives of vitamin A, known as retinoids. Collectively, this body of research supports the concept of retinoids as chemopreventive and chemotherapeutic agents that can prevent epithelial cell tumorigenesis by directing the cells to either differentiate, growth arrest, or undergo apoptosis, thus preventing or reversing neoplasia. Continued refinement of the retinoid signaling pathway is essential to establishing their use as effective therapeutics for tumor subtypes whose oncogenic intracellular signaling pathways can be blocked or reversed by treatment with retinoids.

Conversion of Fas-resistant to Fas-sensitive MCF-7 Breast Cancer Cells by the Synergistic Interaction of Interferon-γ and all-TransRetinoic Acid

The membrane receptor Fas (Apo-1/CD95) is an important initiator of programmed cell death induced by anti-Fas antibody or Fas ligand. MCF-7 human breast cancer cells have low levels of Fas receptor (FasR) and are resistant to anti-FasR antibody mediated apoptosis, however two naturally occurring substances, interferon and all-trans retinoic acid (AT), act synergistically to enhance antiproliferative processes in these cells, suggesting this combination may also be an effective means for enhancing FasR expression. When this was studied, it was found that IFN-gamma and AT in combination acted synergistically to induce expression of FasR mRNA and FasR protein in a time-dependent and dose-dependent manner. This induction required continuous protein synthesis, and STAT1 protein, but not PKR or TR1 protein, was induced in a manner quantitatively and temporally related to FasR protein induction, and consistent with STAT1 mediation of the synergistic effect of IFN-gamma and AT on FasR expression. FasR-induced cells were resistant to stimulation of apoptosis by anti-FasR antibody, however treatment with cycloheximide rendered these cells sensitive to antibody-induced apoptosis, suggesting endogenous blockade to signaling. These cells did not express caspase 3, or FLIP(L), but strongly expressed the endogenous inhibitor of apoptosis Bcl-2, indicating a type II Fas signaling pathway. Expression of these proteins was not modulated by IFN/AT, however treatment of Fas-induced cells with Bcl-2 specific small interfering RNA (SiRNA) downregulated Bcl-2 protein expression and rendered these cells sensitive to the cytotoxic effects of anti-Fas antibody. These findings indicate that IFN-gamma+AT in combination modulate Fas signaling and provide a novel mechanism for the promotion of cell death in breast cancer cells.

In vitro inhibition of proliferation of estrogen-dependent and estrogen-independent human breast cancer cells treated with carotenoids or retinoids

Both estrogen-receptor (ER) positive MCF-7 and ER-negative Hs578T and MDA-MB-231 human breast cancer cells were treated with carotenoids (beta-carotene, canthaxanthin and lycopene) and retinoids (all-trans-, 9-cis- and 13-cis-retinoic acid and all-trans-retinol). Among carotenoids, beta-carotene significantly reduced the growth of MCF-7 and Hs578T cells, and lycopene inhibited the growth of MCF-7 and MDA-MB-231 cells. Canthaxanthin did not affect the proliferation of any of the three cell lines. All-trans- and 9-cis-retinoic acid significantly reduced the growth of both MCF-7 and Hs578T cells, whereas 13-cis-retinoic acid and all-trans-retinol had a significant effect only on MCF-7 cells. MCF-7 and Hs578T cells treated with all-trans-retinoic acid (all-t-RA) were further studied for the mechanism behind growth inhibition. Retinoic acid receptors alpha and gamma (RARalpha, gamma) in MCF-7 cells and RARalpha, beta and gamma in Hs578T cells were not induced by all-t-RA treatment at either the protein or mRNA level. Hs578T cells treated with all-t-RA had significantly more cells in the G0/G1 stage of the cell cycle, but the same was not observed for MCF-7 cells. All-t-RA induced a dose-dependent cell death in MCF-7 cells, which may be a necrotic phenomenon. These results demonstrate that ER status is an important, although not essential factor for breast cancer cell response to carotenoid and retinoid treatments, and the mode of action of all-t-RA in MCF-7 and Hs578T cells is not through the induction of RAR. Other mechanistic pathways that are either followed by or concomitant with growth inhibition are possible.

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.

Kinetics of plasma and tissue distribution of 9-cis-retinoic acid in rat

The biotransformation and tissue distribution of 9-cis-retinoic acid was investigated in hairless rats. Indeed, only limited information is available about the pharmacokinetics of 9-cis-retinoic acid. Assuming that the target site for retinoids is the skin, tissue distribution study is therefore particularly justified. Following single oral administration of 30 mg/kg of 9-cis-retinoic acid, the parent drug and five metabolites were detected in plasma. Additionally, concentrations of 9-cis-retinoic acid and metabolites were determined in the skin and seven other tissues. The distribution of 9-cis-retinoic acid was rapid in all of the organs studied (T(max) </=2 h). In skin, unchanged 9-cis-retinoic acid was still measurable up to 168 h after administration and was undetectable in other organs and plasma after 48 h.

Retinoic acid modulates prolactin receptor expression and prolactin-induced STAT-5 activation in breast cancer cells in vitro

Two recent papers demonstrate that prolactin plays an important role in the induction and progression of mammary tumours. Retinoids have been shown to be potent inhibitors of breast carcinogenesis. We studied expression of prolactin receptor mRNA in human breast cancer cell lines MCF-7, SKBR-3, T47D and BT-20 treated with and without retinoids using Northern blot and a quantitative polymerase chain reaction (PCR) method. In all cell lines, all-trans- and 9-cis-retinoic acid, as well as the retinoic acid receptor gamma (RAR-gamma) selective agonists CD2325 and CD437 (1 microM), were able to down-regulate prolactin receptor. After 1 h, a significant reduction was detectable and maximal effect was achieved after 24 h of treatment. Pretreatment with retinoic acid also reduced the prolactin-/prolactin receptor-dependent signal transduction and activation of transcription 5 (STAT-5) activation in T47D cells. Cycloheximide failed to abrogate the retinoic acid-induced decline in prolactin receptor mRNA levels, indicating that this effect was not dependent upon continuing protein synthesis. Similarly, no change in the stability of prolactin receptor mRNA was observed during 12 h of retinoic acid treatment. In conclusion, our results demonstrate that retinoids are able to inhibit the expression of prolactin receptor message, which encodes an important growth factor receptor in breast cancer cells. This action could be responsible for the anti-tumour effects of retinoids.

Pharmacokinetics and pharmacodynamics of 9-cis-retinoic acid in healthy men

A double-blind, placebo-controlled, randomized study using single ascending oral doses of 5 mg, 15 mg, 40 mg, 80 mg, and 150 mg of 9-cis-retinoic acid was performed to assess the single-dose pharmacokinetics, tolerability, and pharmacodynamic effects of 9-cis-retinoic acid in healthy men. Forty participants received treatment (six taking the active treatment and two taking placebo for each dose level). The pharmacokinetics of 9-cis-retinoic acid were linear over the dose range studied. Peak plasma concentrations were achieved within 3 to 4 hours on average. The half-life was in the range of 1.3 to 2.4 hours. Metabolism was the major pathway of elimination. 4-Oxo-9-cis-retinoic acid, one of four metabolites measured, which included all-trans-retinoic acid and 13-cis-retinoic acid, was the main metabolite in plasma, achieving peak plasma levels of 41% to 83% of those of 9-cis-retinoic acid. Dose-/concentration-dependent reductions of retinol in plasma, with a maximum of 30% from baseline, were observed 24 hours after administration. Baseline levels were recovered after 5 days. Concentrations of retinol binding protein remained unchanged. Overall, the drug was well tolerated at all dose levels. Adverse events observed were consistent with findings of other retinoids (all-trans-retinoic acid and 13-cis-retinoic acid) and included headache and xeroderma at high dose levels.

Activity of retinoic acid receptor-gamma selectively binding retinoids alone and in combination with interferon-gamma in breast cancer cell lines

Retinoids modulate several cell functions and especially inhibit the growth of a wide variety of cells including breast cancer. Retinoic acid receptor-gamma (RAR-gamma) has been shown to mediate the antiproliferative activity of retinoids. To further test this hypothesis we examined the effects of different RAR-gamma selectively binding retinoids (CD2325, CD2247, CD666 and CD437) on breast cancer cell lines. With exception of CD2247, all retinoids inhibited proliferation of MCF-7, SKBR-3, T47D and ZR-75-1 breast cancer cell lines, similar to the natural compound all-trans retinoic acid (ATRA). In addition, all 4 compounds were able to act synergistically with interferon-gamma (IFN-gamma) in all breast cancer cell lines including the retinoid-resistant BT-20 and 734-B lines. In functional transactivation assays we demonstrated that only in the MCF-7 cell line, TPA-mediated AP-1 activity was suppressed only by ATRA and CD2325, whereas in SKBR-3, another RA-sensitive breast cancer cell line, it was not. The synergistic antiproliferative activity involving retinoids and IFN-gamma could not be explained by an enhanced anti-AP-1 activity. No correlation was found between expression of RARs and cellular retinoic acid binding proteins (CRABPs) and antiproliferative effects of the retinoids. RAR-gamma selectively binding retinoids are potent inhibitors of breast cancer cell proliferation, alone and in combination with IFN-gamma. For this reason and because of a possible low toxicity, as compared with retinoic acid, we speculate that these RAR-gamma selective binding retinoids might be of clinical importance.

All-trans-retinoic acid blocks cell cycle progression of human ovarian adenocarcinoma cells at late G1

We prepared single cell clones from two ovarian carcinoma cell lines, CA-OV3 and SK-OV3, and analyzed the effect of all-trans-RA treatment on cell division, DNA synthesis, and cell cycle stage distribution of these single cell clones. Our results show that despite the well-known heterogeneous nature of these cell lines, all single cell clones of SK-OV3 cells are resistant to the growth inhibitory effects of all-trans-RA. In contrast, all single cell clones of CA-OV3 cells were growth inhibited by all-trans-RA. However, the extent of growth inhibition did vary somewhat from clone to clone. Additional studies employing flow cytometry showed that all-trans-RA blocked CA-OV3 cell cycle progression in the G1 stage. Finally, all-trans-RA was able to inhibit G1 progression in growth-arrested CA-OV3 cells following stimulation with fetal bovine serum, insulin, IGF-1, or estrogen. Since each of these growth factors is known to act via distinct signal transduction pathways, our results suggest that all-trans-RA blocks G1 progression by targeting a downstream process or event which occurs at a point after the insulin/IGF-1, estrogen, and serum signal transduction pathways converge.

Pharmacokinetics and effects on plasma retinol concentrations of 13-cis-retinoic acid in melanoma patients

The pharmacokinetics of 13-cis-retinoic acid (13cisRA) and its effects on retinol plasma levels were investigated after the first and the last doses in melanoma patients, who participated in a study run to assess tolerance over a long period of a treatment schedule of 13cisRA associated with recombinant interferon alpha2a (rIFN-alpha2a). Melanoma patients with regional node metastases after radical surgery were randomized to be treated for 3 months with rIFN-alpha2a, 3 x 10(6) IU s.c. every other day, associated with oral 13cisRA at doses of 20 mg day(-1) (five patients) or 40 mg every other day (seven patients). Maximum 13cisRA blood concentrations usually occurred 4 h after drug administration, with average values of 406 and 633 ng ml(-1) (i.e. 1.3 and 2.1 microM) after the 20 and 40 mg dose respectively. The average half-life (t(1/2)) was approximately 30 h. The maximum concentration, the t(1/2) and the area under the concentration-time curves from 0 to 48 h (AUC(0-48)) of 13cisRA did not change after multiple dosing, whereas the AUC(0-48) of its major blood metabolite, 4-oxo-13-cis-retinoic acid, increased. Immediately after 13cisRA treatment, retinol plasma levels started to decline and they reached the lowest values (approximately 20% reduction) shortly after the time of maximum 13cisRA concentrations (i.e. 4-12 h after drug intake). Afterwards, values returned to baseline. The amount of retinol reduction in time was correlated with 13cisRA maximum concentrations.

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.

Experimental basis of cancer combination chemotherapy with retinoids, cytokines, 1,25-dihydroxyvitamin D3, and analogs

Retinoids, cytokines as well as 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and analogs possess properties known to contribute potentially to cancer chemopreventive and chemotherapeutic effects. They induce cell differentiation, inhibit cell proliferation, suppress expression of viral oncogenes, and inhibit angiogenesis necessary for tumor growth. Since clinical combination chemotherapy of cytotoxic agents has proven superior to monotherapy, this modality might also be useful for other classes of antitumor drugs. A series of retinoids, such as all-trans-, 13-cis-, 9-cis retinoic acid, and acitretin, cytokines, 1,25(OH)2D3, and analogs have been investigated in model systems of differentiation, proliferation, viral oncogenes, and angiogenesis. The three classes of compounds have common effects but nevertheless show a variance depending on the particular representative of each class. Combination of compounds of the different classes led in the various models to a higher efficacy compared with the compounds given alone. Cytokines such as IFN alpha, IFN gamma, G-CSF, TNF alpha, IL-1, and IL-4 markedly potentiate the differentiation-inducing effect of retinoids. Cytokines as well as retinoids combined with 1,25(OH)2D3 and analogs synergistically enhanced differentiation induction in human transformed hemopoietic cell lines. On a series of human transformed epithelial cell lines a panel of cytokines, such as IFN alpha, IFN gamma, TNF alpha, TGF beta, and EGF acted synergistically with retinoids on inhibition of proliferation. This was also observed by combining retinoids with 1,25(OH)2D3 and analogs. Retinoids as well as interferons alpha and gamma have the capacity to suppress the oncogene expression of human papilloma viruses which are involved in induction and growth of certain malignancies such as cervical cancer.(ABSTRACT TRUNCATED AT 250 WORDS)