Polyphenols inhibit indoleamine 3,5-dioxygenase-1 enzymatic activity--a role of immunomodulation in chemoprevention.

Metastasis is one of the cancer hallmarks described by Hanahan and Weinberg. Emerging evidence shows that it requires interplays between cancer cells and micro-environmental biofactors. Indoleamine 3,5-dioxygenase-1 (IDO-1) produced by cancer, local lymph nodes, and satellite cells have been demonstrated as one of the biofactors. Aberrant IDO-1 activity has partially contributed to immunosuppressive environment by repressing T lymphocyte and natural killer cell activities, and activating regulatory T cells (Treg, CD4+CD25+). Clinical investigations further show a negative correlation between the enzyme activity and prognosis in patients with various cancer types. The findings suggest a possible role of IDO-1 inhibitor in restoring host anti-tumor immunity and attenuating cancer metastasis. Data from preclinical and phase I/II clinical studies with IDO-1 inhibitors support this hypothesis. Polyphenols as antioxidants are shown to exhibit anticancer activities. However, the underlying mechanism has not been entirely characterized. We recently found that certain flavone molecules profoundly inhibit the enzymatic activity of IDO-1 but not mRNA expression in human neuronal stem cells (hNSC) confirmed by cell-based assay and qRT-PCR. To further the investigation, we studied additional anti-cancer phytochemicals including chalcone, flavonol, isoflavone, and diterpene. Here we summarize the results and show that the inhibitory sensitivity depends on the molecular structure in the following order: apigenin > wogonin > chrysin > biacalein ~ genistein > quercetin. Curcumin and isoliquiritigenin (a chalcone) exhibited toxicity to hNSCs. Although oridonin (a diterpene) showed a null toxicity toward hNSCs, it repressed the enzymatic function only marginally in contrast to its potent cytotoxicity in various cancer cell lines. While the mode of action of the enzyme-polyphenol complex awaits to be investigated, the sensitivity of enzyme inhibition was compared to the anti-proliferative activities toward three cancer cell lines. The IC50s obtained from both sets of the experiments indicate that they are in the vicinity of micromolar concentration with the enzyme inhibition slightly more active. These results suggest that attenuation of immune suppression via inhibition of IDO-1 enzyme activity may be one of the important mechanisms of polyphenols in chemoprevention or combinatorial cancer therapy.

Advances in the treatment of ovarian cancer: a potential role of antiinflammatory phytochemicals.

Epithelial ovarian cancer (EOC) is the leading cause of death among gynecological malignancies worldwide. The five-year survival rates for stage IIIC and IV patients are 29% and 13%, respectively. Type-2 EOC cells have been found to be associated with this late stage disease. In contrast, women diagnosed in stage 1 disease, which mostly exhibits type-1 cells, have a high 5-year survival rate (90%). Recent progress in understanding the pathogenesis of EOC and inflammatory signaling pathways revealed that type-2 cells frequently express a deleted or mutated TP53 (60-80%), or aberrations in BRCA1 (30-60%) and BRCA2 (15-30%). The deletion or mutation of TP53 results in a dysregulated inflammatory signal network and contributes to an immunosuppressive microenvironment. Thus, to be effective, EOC therapy may be necessary to cover two areas: (1) direct cytotoxic killing of cancer cells; (2) reversion of the immunosuppressive microenvironment. Presently the first strategy is advancing rapidly while the second strategy remains behind. Isolation and characterization of cancer stem cells (CSCs) have helped to confirm the dynamic role of the tumor microenvironment in promoting cancer metastasis and recurrence. Based on widely published in vitro and mouse-model data, some anti-inflammatory phytochemicals appear to exhibit activity in modulating the tumor microenvironment. Specifically, apiegenin, baicalein, curcumin, EGCG, genistein, luteolin, oridonin, quercetin, and wogonin repress NF-kappaB (NF-κB, a proinflammatory transcription factor) and inhibit proinflammatory cytokines such as TNF-α and IL-6. Additionally, most of these phytochemicals have been shown to stabilize p53 protein, sensitize TRAIL (TNF receptor apoptosis-inducing ligand) induced apoptosis, and prevent or delay chemotherapy-resistance. Recent studies further indicate that apigenin, genistein, kaempferol, luteolin, and quercetin potently inhibit VEGF production and suppress ovarian cancer cell metastasis in vitro. Lastly, oridonin and wogonin were suggested to suppress ovarian CSCs as is reflected by down-regulation of the surface marker EpCAM. Unlike NSAIDS (non-steroid anti-inflammatory drugs), well documented clinical data for phyto-active compounds are lacking. In order to evaluate objectively the potential benefit of these compounds in the treatment of ovarian cancer, strategically designed, large scale studies are warranted.

PC-SPES: Molecular mechanism to induce apoptosis and down-regulate expression of PSA in LNCaP human prostate cancer cells.

PC-SPES is an eight-herbal mixture which has activity against prostate cancer cells and can reduce the serum level of prostate specific antigen (PSA) in more than 80% of individuals with prostate cancer. We conducted this study to begin to clarify the molecular mechanism by which PC-SPES inhibited the growth of prostate cancer cells and down-regulated expression of PSA. Western blot analysis, luciferase reporter assay using a variety of promoters of the PSA gene and the isolated androgen receptor response elements (ARE), as well as electrophoretic mobility shift assay (EMSA) were employed to study the effect of PC-SPES on DHT-induced expression of PSA in LNCaP androgen-dependent human prostate cancer cells. Also, Western blot analysis and luciferase reporter assay using 12-0-tetradecanoylphorbol-13-acetate response elements were employed to study the ability of PC-SPES to activate the c-Jun NH2-terminal kinase (JNK)/c-Jun/AP-1 signal pathway in these cells. Reporter studies showed that PC-SPES inhibited DHT-induced PSA promoter/enhancer-luciferase activity via inhibition of ARE transcriptional activity. Western blot analysis showed that PC-SPES down-regulated DHT-induced expression of PSA without decreasing DHT-induced nuclear level of AR. EMSA demonstrated that PC-SPES inhibited the binding of DHT-activated AR to ARE. Moreover, we found that PC-SPES phosphorylated JNK, increased levels of phosphorylated and unphosphorylated forms of c-Jun, and enhanced AP-1 transcriptional activity in LNCaP cells. Interestingly, when LNCaP cells were stably tranfected with the dominant negative JNK binding domain (JBD) of JNK-interacting protein-1 (JIP-1), these cells no longer underwent apoptosis and growth inhibition in the presence of PC-SPES. But, PC-SPES still decreased levels of PSA in the LNCaP-JIP-1 cells. Taken together, PC-SPES inhibited binding of DHT-activated AR to AREs of PSA gene resulting in down-regulation of ARE transcriptional activity and expression of PSA, and this occurred independently of the JNK/c-Jun/AP-1 signal pathway. Also, PC-SPES activated the JNK/c-Jun/AP-1 signal pathway resulting in growth arrest and apoptosis of prostate cancer cells.

Oridonin induces growth inhibition and apoptosis of a variety of human cancer cells.

PC-SPES is an eight herbal mixture that was shown to have activity against prostate cancer. Recently, we purified oridonin from Rabdosia rubescens, one component of PC-SPES, by high performance liquid chromatography (HPLC). The ability of oridonin to inhibit the proliferation of cancer cells was examined by MTT assay. Oridonin effectively inhibited the proliferation of a wide variety of cancer cells including those from prostate (LNCaP, DU145, PC3), breast (MCF-7, MDA-MB231), non-small cell lung (NSCL) (NCI-H520, NCI-H460, NCI-H1299) cancers, acute promyelocytic leukemia (NB4), and glioblastoma multiforme (U118, U138) with ED50s ranging from 1.8 to 7.5 micro g/ml. TUNEL assay and cell cycle analysis showed that oridonin induced apoptosis and G0/G1 cell cycle arrest in LNCaP prostate cancer cells. In addition, expression of p21waf1 was induced in LNCaP and NCI-H520 cells in a p53-dependent manner. Interestingly, when p53 was suppressed by over-expression of E6 from human papilloma virus type 16 (HPV-16), these cells lost their sensitivity to oridonin-induced growth inhibition and apoptosis. Taken together, oridonin inhibited the proliferation of cancer cells via apoptosis and cell cycle arrest with p53 playing a central role in several cancer types which express the wild-type p53 gene. Oridonin may be a novel, adjunctive therapy for a large variety of malignancies and probably represents one of the major, active components of PC-SPES.