Vitamin A Enhances Antitumor Effect of a Green Tea Polyphenol on Melanoma by Upregulating the Polyphenol Sensing Molecule 67-kDa Laminin Receptor

BACKGROUND: Green tea consumption has been shown to have cancer preventive qualities. Among the constituents of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG) is the most effective at inhibiting carcinogenesis. However, the concentrations of EGCG that are required to elicit the anticancer effects in a variety of cancer cell types are much higher than the peak plasma concentration that occurs after drinking an equivalent of 2-3 cups of green tea. To obtain the anticancer effects of EGCG when consumed at a reasonable concentration in daily life, we investigated the combination effect of EGCG and food ingredient that may enhance the anticancer activity of EGCG on subcutaneous tumor growth in C57BL/6N mice challenged with B16 melanoma cells. METHODOLOGY/PRINCIPAL FINDINGS: All-trans-retinoic acid (ATRA) enhanced the expression of the 67-kDa laminin receptor (67LR) and increased EGCG-induced cell growth inhibition in B16 melanoma cells. The cell growth inhibition seen with the combined EGCG and ATRA treatment was abolished by treatment with an anti-67LR antibody. In addition, the combined EGCG and ATRA treatment significantly suppressed the melanoma tumor growth in mice. Expression of 67LR in the tumor increased upon oral administration of ATRA or a combined treatment of EGCG and ATRA treatment. Furthermore, RNAi-mediated silencing of the retinoic acid receptor (RAR) alpha attenuated the ATRA-induced enhancement of 67LR expression in the melanoma cells. An RAR agonist enhanced the expression levels of 67LR and increased EGCG-induced cell growth inhibition. CONCLUSIONS/SIGNIFICANCE: Our findings provide a molecular basis for the combination effect seen with dietary components, and indicate that ATRA may be a beneficial food component for cancer prevention when combined with EGCG

IFN-alpha2b and retinoic acid combined treatment affects proliferation and gene expression of human cervical carcinoma cells

The in vivo and in vitro antitumor effectiveness of IFNs is well documented. Their combination with differentiating agents, such as retinoic acid, has been demonstrated to be a promising therapy for patients with advanced squamous cell cancer of the skin and the cervix. However, the mechanisms that mediate these antitumor responses are not yet known. We studied the epidermoid cell line ME 180 derived from human cervical carcinoma to test its responsiveness to IFN-alpha-2b (INTRON A) and all-trans-retinoic acid (RA), Both agents have demonstrated ability to inhibit the growth of ME 180 cells in a dose- and time-dependent manner, The antiproliferative effect was further increased by the treatment with IFN alpha-2b and RA combined, In accordance with this result, we found that the combination of the two agents has the effect of increasing the expression of the 2-5A synthetase gene, which is thought to play a key role in antigrowth responses to IFNs. At increased levels of 2-5A synthetase mRNA corresponds a significant increase in 2-5A synthetase activity. Although RA per se has no effect on the 2-5A synthetase expression, when it is combined with IFN-alpha-2b it appears to be able to potentiate the IFN-induced 2-5A synthetase expression. Moreover, the combination of IFN-alpha-2b and RA produces a similar effect also on the expression of the HLA-AZ gene, which has been shown to be induced in ME 180 cells both by IFN-alpha-2b and RA alone. In view of the possible mechanisms of action of the two agents, it is interesting to note that their combination increases, although transiently, the expression of IRF(1), which codes for a transcription factor that regulates IFN gene expression and is thought to be involved in the regulation of IFN-induced effects and in mediating cell death or apoptosis

Retinoic acid and interferon inhibition of cell proliferation is associated with apoptosis in squamous carcinoma cell lines. Role of IRF-1 and TGAseII-dependent pathways

Both retinoids and IFNs are known to inhibit proliferation of many normal and transformed cells and to have an in vivo antitumor effect against a variety of cancers, including squamous cell carcinoma, Because the combination of IFNs and all-trans retinoic acid (RA) could improve their antitumor effectiveness (depending on the histological origin and state of differentiation of the cells), we compared the activity of RA and/or IFN-alpha 2b with regard to the mechanism of growth inhibition of ME180 and SiHa cell lines, derived from squamous cervix carcinoma at different stages of differentiation, We reported previously that, in the ME180 cell line, the combined treatment significantly increased the growth inhibitory effect of the single agents, Here, we show that the SiHa cell line appears more sensitive to IFN-alpha 2b than the ME180 cell line, and resistant to RA, which does not significantly inhibit SiHa cell growth, Induction of apoptotic cell death clearly occurs and correlates with the inhibition of cell proliferation in both cell lines, It is interesting that the induction of the transcription factor IFN regulatory factor 1 correlates with the subsequent induction of apoptosis, whereas TGase I and II expression does not, In particular, TGase I and II appear differentially expressed in the ME180 and SiHa cell lines; i.e., TGase I is expressed in ME180 and specifically inhibited by RA, whereas TGase II is expressed in SiHa, It is interesting that both IFN-alpha and RA are able to increase TGase II expression and activity in this cell line