Curcumin, a component of turmeric (Curcuma longa), has been shown to exhibit chemopreventive activity. Whether analogs of curcumin (Cur), such as demethoxycurcumin (DMC), bisdemethoxycurcumin (BDMC), tetrahydrocurcumin (THC) and turmerones, modulate inflammatory signaling and cell proliferation signaling to same extent as curcumin was investigated. The results indicate that the relative potency for suppression of tumor necrosis factor (TNF)-induced nuclear factor-kappaB (NF-kappaB) activation was Cur > DMC > BDMC; thus suggesting the critical role of methoxy groups on the phenyl ring. THC, which lacks the conjugated bonds in the central seven-carbon chain, was completely inactive for suppression of the transcription factor. Turmerones also failed to inhibit TNF-induced NF-kappaB activation. The suppression of NF-kappaB activity correlated with inhibition of NF-kappaB reporter activity and with down-regulation of cyclooxygenase-2, cyclin D1 and vascular endothelial growth factor, all regulated by NF-kappaB. In contrast to NF-kappaB activity, the suppression of proliferation of various tumor cell lines by Cur, DMC and BDMC was found to be comparable; indicating the methoxy groups play minimum role in the growth-modulatory effects of curcumin. THC and turmerones were also found to be active in suppression of cell growth but to a much lesser extent than curcumin, DMC and BDMC. Whether suppression of NF-kappaB or cell proliferation, no relationship of any of the curcuminoid was found with reactive oxygen species (ROS) production. Overall, our results demonstrated that different analogs of curcumin present in turmeric exhibit variable anti-inflammatory and anti-proliferative activities, which do not correlate with their ability to modulate the ROS status.

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Identification of the active component and mechanisms of action of traditional medicines is highly desirable. We investigated whether zerumbone, a sesquiterpene from tropical ginger, can enhance the anticancer effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We found that zerumbone potentiated TRAIL-induced apoptosis in human HCT116 colon cancer cells and that this correlated with the up-regulation of TRAIL death receptor (DR) 4 and DR5. Induction of DRs occurred at the transcriptional level, and this induction was not cell-type specific, as its expression was also up-regulated in prostate, kidney, breast, and pancreatic cancer cell lines. Deletion of DR5 or DR4 by small interfering RNA significantly reduced the apoptosis induced by TRAIL and zerumbone. In addition to up-regulating DRs, zerumbone also significantly down-regulated the expression of cFLIP but not that of other antiapoptotic proteins. The induction of both DRs by zerumbone was abolished by glutathione and N-acetylcysteine (NAC), and this correlated with decreased TRAIL-induced apoptosis, suggesting a critical role of reactive oxygen species. Inhibition of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase but not of Jun NH 2 -terminal kinase abolished the effect of zerumbone on DR induction. Zerumbone also induced the p53 tumor suppressor gene but was found to be optional for DR induction or for enhancement of TRAIL-induced apoptosis. Both bax and p21, however, were required for zerumbone to stimulate TRAIL-induced apoptosis. Overall, our results show that zerumbone can potentiate TRAIL-induced apoptosis through the reactive oxygen species-mediated activation of extracellular signal-regulated kinase 1/2 and p38 mitogenactivated protein kinase leading to DR4 and DR5 induction and resulting in enhancement of the anticancer effects of TRAIL. [Cancer Res 2009;69(16):6581-9]

Many studies have been performed with the aim of developing effective resistance modulators to overcome the multidrug resistance (MDR) of human cancers. Potent MDR modulators are being investigated in clinical trials. Many current studies are focused on dietary herbs due to the fact that these have been used for centuries without producing any harmful side effects. In this study, the effect of tetrahydrocurcumin (THC) on three ABC drug transporter proteins, P-glycoprotein (P-gp or ABCB1), mitoxantrone resistance protein (MXR or ABCG2) and multidrug resistance protein 1 (MRP1 or ABCC1) was investigated, to assess whether an ultimate metabolite form of curcuminoids (THC) is able to modulate MDR in cancer cells. Two different types of cell lines were used for P-gp study, human cervical carcinoma KB-3-1 (wild type) and KB-V-1 and human breast cancer MCF-7 (wild type) and MCF-7 MDR, whereas, pcDNA3.1 and pcDNA3.1-MRP1 transfected HEK 293 and MXR overexpressing MCF7AdrVp3000 or MCF7FL1000 and its parental MCF-7 were used for MRP1 and MXR study, respectively. We report here for the first time that THC is able to inhibit the function of P-gp, MXR and MRP1. The results of flow cytometry assay indicated that THC is able to inhibit the function of P-gp and thereby significantly increase the accumulation of rhodamine and calcein AM in KB-V-1 cells. The result was confirmed by the effect of THC on [(3)H]-vinblastine accumulation and efflux in MCF-7 and MCF-7MDR. THC significantly increased the accumulation and inhibited the efflux of [(3)H]-vinblastine in MCF-7 MDR in a concentration-dependent manner. This effect was not found in wild type MCF-7 cell line. The interaction of THC with the P-gp molecule was clearly indicated by ATPase assay and photoaffinity labeling of P-gp with transport substrate. THC stimulated P-gp ATPase activity and inhibited the incorporation of [(125)I]-iodoarylazidoprazosin (IAAP) into P-gp in a concentration-dependent manner. The binding of [(125)I]-IAAP to MXR was also inhibited by THC suggesting that THC interacted with drug binding site of the transporter. THC dose dependently inhibited the efflux of mitoxantrone and pheophorbide A from MXR expressing cells (MCF7AdrVp3000 and MCF7FL1000). Similarly with MRP1, the efflux of a fluorescent substrate calcein AM was inhibited effectively by THC thereby the accumulation of calcein was increased in MRP1-HEK 293 and not its parental pcDNA3.1-HEK 293 cells. The MDR reversing properties of THC on P-gp, MRP1, and MXR were determined by MTT assay. THC significantly increased the sensitivity of vinblastine, mitoxantrone and etoposide in drug resistance KB-V-1, MCF7AdrVp3000 and MRP1-HEK 293 cells, respectively. This effect was not found in respective drug sensitive parental cell lines. Taken together, this study clearly showed that THC inhibits the efflux function of P-gp, MXR and MRP1 and it is able to extend the MDR reversing activity of curcuminoids in vivo.

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The 170 kDa plasma membrane P-glycoprotein (Pgp) causes the efflux of chemotherapeutic drugs from cells and is believed to be an important mechanism in multidrug resistance (MDR) in human cancer. This study demonstrates that some putative flavonoids, i.e., flavonols (quercetin and kaempferol) and isoflavones (genistein and daidzein) markedly increase the sensitivity of the multidrug-resistant human cervical carcinoma KB-V1 cells (high Pgp expression) to vinblastine and paclitaxel dose-dependently, and also decrease the relative resistance of these anti-cancer-drugs in KB-V1 cells. None of the flavonoids had a significant effect on vinblastine and paclitaxel cytotoxicity in wildtype drug-sensitive KB-3-1 cells (lacking Pgp). These flavonoids also caused an increase in intracellular accumulation, and reduced the efflux of Rh123 and 3[H]vinblastine in KB-V1 cells, but not in KB-3-1 cells. The flavonols increased the inhibitory effectiveness of Pgp activity in MDR KB-V1 cells more than isoflavones. Only treatment with flavonols up to 48 h was able to significantly decrease the Pgp expression in a dose-dependent manner in KB-V1 cells. These findings provide evidence that flavonols reduced Pgp expression and function resulting in the inhibition of Pgp activity, but isoflavones modulated intracellular drug levels by inhibiting Pgp function with no effect on Pgp expression. Among the flavonoids tested, flavonols, particularly kaempferol, exhibit the most potent MDR reversing property in KB-V1 cells.

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Curcumin (curcumin I), demethoxycurcumin (curcumin II), and bisdemethoxycurcumin (curcumin III) are the major forms of curcuminoids found in the turmeric powder, which exhibit anticancer, antioxidant, and anti-inflammatory activities. In this study, we evaluated the ability of purified curcuminoids to modulate the function of either the wild-type 482R or the mutant 482T ABCG2 transporter stably expressed in HEK293 cells and drug-selected MCF-7 FLV1000 and MCF-7 AdVp3000 cells. Curcuminoids inhibited the transport of mitoxantrone and pheophorbide a from ABCG2-expressing cells. However, both cytotoxicity and [ 3 H]curcumin I accumulation assays showed that curcuminoids are not transported by ABCG2. Nontoxic concentration of curcumin I, II, and III sensitized the ABCG2-expressing cells to mitoxantrone, topotecan, SN-38, and doxorubicin. This reversal was not due to reduced expression because ABCG2 protein levels were unaltered by treatment with 10 Mmol/L curcuminoids for 72 hours. Curcumin I, II, and III stimulated (2.4-to 3.3-fold) ABCG2-mediated ATP hydrolysis and the IC 50 s were in the range of 7.5 to 18 nmol/L, suggesting a high affinity of curcuminoids for ABCG2. Curcuminoids also inhibited the photolabeling of ABCG2 with P]8-azidoATP to ABCG2, suggesting that they do not interact with the ATP-binding site of the transporter. Collectively, these data show that, among curcuminoids, curcumin I is the most potent modulator of ABCG2 and thus should be considered as a treatment to increase the efficacy of conventional chemotherapeutic drugs.