The investigation of novel anti-tumor agents that preferentially select for malignant cells with a tolerable toxicity level has been the focus of anti-cancer drug discovery. Our laboratories have previously reported that certain N-alkylthiolated β-lactams had DNA-damaging and apoptosis-inducing activity in various tumor lines but not in nontransformed cells. In the current study, we further delineated the effects of substitutions at C3 or N1 of the lactam ring for cell death-inducing capability with close attention paid to a discernible structure-activity relationship (SAR). We found that two β-lactam analogs (JG-5 and JG-19), both containing a branched-chain moiety at C3 of the lactam ring, exhibit potent apoptosis-inducing activity. Additionally, JG-5 exhibited superior in vitro biological activity over JG-19 owing to structural modifications made to substituents at the N1 and C3 positions of the lactam ring. Furthermore, the branched β-lactams were able to inhibit growth of mice bearing breast cancer xenografts, associated with induction of DNA damage and apoptosis in tumor tissues. Our results strongly warrant further investigation into these novel β-lactams as potential anti-cancer therapeutics.
β-lactams; structure-activity relationship; apoptosis; DNA damage; tumor cell death
An elevated level of copper (Cu), which is necessary for the growth and metastasis of tumor cells, has been found in many types of cancer, including breast, prostate, lung and brain. Although its molecular basis is unclear, this tumor-specific Cu elevation has been proposed to be a novel target for developing selective anti-cancer therapies. We previously reported that 8-hydroxylquinoline (8-OHQ) is able to form a Cu complex that inhibits the proteasome and induces apoptosis in cultured cancer cells. Toward the goal of discovering novel 8-OHQ analogs as potential anti-copper and anti-cancer drugs, in the current study we synthesized several 8-OHQ analogs and their copper complexes and evaluated their biological activities in human breast cancer cells. We report that when substitutions are made on the hydroxyl group of 8-OHQ, their copper mixtures have profound effects on the proteasome-inhibitory and apoptosis-inducing abilities in breast cancer MDA-MB-231 cells. In addition, the proteasome-inhibitory and apoptosis-inducing activities of 8-OHQ analog-copper mixtures are determined by both the polarity and position of the substituents. Finally, a synthetic complex of 8-OHQ analog-copper was able to inhibit the proteasome activity, induce cell death and suppress the growth selectively in breast cancer MDA-MB-231 cells, but not in normal immortalized human breast MCF-10A cells. Our results support the concept that human cancer cells and tissues, which contain an elevated copper level and are highly dependent on proteasome activity for their survival, should be sensitive to treatment with anti-copper drugs such as the novel 8-OHQ analogs described here.
8-hydroxylquinoline; copper; anti-copper drugs; structure activity relationship; proteasome inhibitors; apoptosis
Tea, next to water, is the most popular beverage in the world. It has been suggested that tea consumption has the cancer-preventive effects. Epidemiological studies have indicated decreased cancer occurrence in people who regularly drink green tea. Research has also discovered numerous mechanisms of action to explain the biological effects of tea. The most abundant and popular compound studied in tea research is (−)-epigallocatechin-3-gallate or (−)-EGCG, which is a powerful antioxidant and can inhibit a number of tumor cell proliferation and survival pathways. Tea polyphenols are known to inhibit metaloproteonases, various protein kinases, and proteins that regulate DNA replication and transformation. We also reported that ester bond-containing tea polyphenols, for example, (−)-EGCG, potently and specifically inhibited the tumor proteasomal activity. We further demonstrated that methylation on green tea polyphenols under physiological conditions decreased their proteasome-inhibitory activity, contributing to decreased cancer-preventive effects of tea consumption. Since (−)-EGCG is unstable under physiological conditions, we also developed the peracetate-protected or prodrug form of (−)-EGCG, Pro-EGCG (1), and showed that Pro-EGCG (1) increases the bioavailability, stability, and proteasome-inhibitory and anti-cancer activities of (−)-EGCG in human breast cancer cells and tumors, demonstrating its potential use for cancer prevention and treatment.
Despite an initial response from androgen deprivation therapy, most prostate cancer patients relapse to a hormone-refractory state where tumors still remain dependent on androgen receptor (AR) function. We have previously shown that AR breakdown correlates with the induction of cancer cell apoptosis by proteasome inhibition. However, the involvement of AR in modulating the cell death pathway has remained elusive. To investigate this, we used an experimental model consisting of parental PC-3 prostate cancer cells that lack AR expression and PC-3 cells stably overexpressing wild type AR gene. Here, we report that both chemotherapeutic drugs (cisplatin) and proteasome inhibitors induced caspase-3-associated cell death in parental PC-3 cells whereas non-caspase-3 associated cell death in PC3-AR cells. The involvement of AR in modulating tumor cell death was further confirmed in PC-3 cells transiently expressing AR. Consistently, treatment with the clinically used proteasome inhibitor Bortezomib (Velcade/PS-341) of (AR+) LNCaP prostate cancer cells caused AR cleavage and cell death with low levels of caspase activation. However, co-treatment with Bortezomib and the AR antagonist Bicalutamide (Casodex) caused significant decrease in AR expression associated with an increase in caspase-3 activity in both LNCaP and PC3-AR cells. Thus our results provide compelling evidence for involvement of AR in deciding types of tumor cell death upon cytotoxic stimuli, and specifically, blockade of AR activities could change necrosis to apoptosis in tumor cells. Our findings may help guide clinicians based on AR status in the design of favorable treatment strategies for prostate cancer patients.
Androgen receptor; proteasome inhibitor; cell death; caspase-3; necrosis; calpain
(−)-Epigallocatechin gallate [(−)-EGCG] has been implicated in cancer chemoprevention and has been shown as an inhibitor of tumor proteasomal chymotrypsin-like activity in vitro and in vivo. However, EGCG is subjected to rapid biotransforming modifications such as methylation by catechol-O-methyltransferase (COMT) that limits its action. We recently reported that structure 7, an EGCG analog which should be resistant to COMT-mediated methylation and inactivation in cells, was able to inhibit the activity of purified 20S proteasome and cellular 26S proteasome. However, the involved molecular mechanism is unknown. Herein, we applied computational solution to understand the possible interaction between EGCG analogs including structure 7 and the proteasome β5 subunit which is responsible for the chymotrypsin-like activity. We report that the ester carbonyls at C2 and C3 carbon atoms may be the active sites for nucleophilic attack in structure 7 and 5. Equally spaced carbon atoms in COMT-resistant structure 7 give more stable conformation and lower docked free energy than other EGCG analogs. The absence of a second gallate group in structure 16 and 21 significantly decreases the ability to inhibit the proteasome.
catechol-O-methyltransferase; methylation; proteasome inhibitor; (−)-epigallocatechin gallate; computational docking; cancer
Tea is one of the most popular beverages in the world and has been studied extensively as a health-promoting beverage that may act to prevent a number of chronic diseases and cancers. (-)-Epigallocatechin gallate [(-)-EGCG], a major component in green tea, is unstable under physiological conditions and methylation of (-)-EGCG by catechol-O-methyltransferase (COMT) is a modification that reduces the biological activity of (-)-EGCG. In the current study, we hypothesized that suppression of COMT activity in human breast cancer cells could increase the proteasome-inhibitory potency of (-)-EGCG and therefore enhance its tumor cell growth-inhibitory activity. We first determined the COMT genotype and basal levels of COMT activity in various human breast cancer cell lines. Furthermore, when breast cancer MDA-MB-231 cells containing high COMT activity were tested, the diminished COMT activity apparently increased the effectiveness of (-)-EGCG via augmented proteasome inhibition and apoptosis induction. This study supplements the previous findings that methylated (-)-EGCG is less bioactive and supports the notion that COMT inhibition may increase the anti-cancer properties of tea polyphenols and the combination may serve as a novel approach or supplemental treatment for breast cancer chemotherapy.
epigallocatechin gallate; catechol-O-methyltransferase; proteasome inhibition; apoptosis; breast cancer
The molecular mechanisms of triptolide responsible for its antitumor properties are not yet fully understood. The ubiquitin/proteasome system is an important pathway of protein degradation in cells. This study investigated whether triptolide may inhibit proteasomal activity and induce apoptosis in human cancer cells.
Materials and Methods
In vitro proteasome inhibition was measured by incubation of a purified 20S proteasome with triptolide. Human breast and prostate cancer cell lines were also treated with different doses of triptolide for different times, followed by measurement of proteasome inhibition (levels of the chymotrypsin-like activity, ubiquitinated proteins and three well-known proteasome target proteins, p27, IκB-α and Bax) and apoptosis induction (caspase-3 activity and PARP cleavage).
Triptolide did not inhibit the chymotrypsin-like activity of purified 20S proteasome. However, treatment of triptolide was able to cause decreased levels of cellular proteasomal chymotrypsin-like activity and accumulation of ubiquitinated proteins and three well-known proteasome target proteins in human breast and prostate cancer cells, associated with apoptosis induction.
It is possible that at least one of metabolites of triptolide has proteasome-inhibitory activity.
Triptolide; medicinal compounds; proteasome inhibitors; apoptosis; cancer therapy
Emerging evidence clearly suggests the potential chemopreventive and anti-tumor activity of a well known “natural agent” curcumin. However, studies have shown that curcumin is not readily bioavailable, and thus the tissue bioavailability of curcumin is also poor except for gastrointestinal track. Because of the potential biological activity of curcumin, many studies have attempted for making a better analog of cucumin that is equally effective or better with increased bioavailability, which was the purpose of our current study.
We have designed and synthesized new difluoro Knoevenagel condensates of curcumin and Schiff bases along with their copper (II) complexes and evaluated their biological activities with respect to the inhibitory effects on purified rabbit 26S proteasome, and growth inhibition and induction of apoptosis in colon and pancreatic cancer cell lines.
All copper complexes possess distorted square planar geometries with 1:1 metal to ligand stoichiometry with reversible copper redox couple. The difluoro compound CDF exhibited inhibitory effects on purified rabbit 20S proteasome or cellular 26S proteasome, and caused both growth inhibition of cancer cell lines and induced apoptotic cell death in our preliminary assessment.
Our results suggest that our newly synthesized classes of curcumin analogs could be useful as chemopreventive and/or therapeutic agents against cancers.
apoptosis; cancer cells; cell growth; curcumin; difluoro Knoevenagel condensates of curcumin
Polypyridyl pentadentate ligands N4Py (1) and Bn-TPEN (2), along with their respective iron complexes, have been investigated for their ability to inhibit the purified 20S proteasome. Results demonstrated that the iron complexes of both ligands are potent inhibitors of the 20S proteasome (IC50 = 9.2 μM for [FeII(OH2)(N4Py)]2+ (3) and 4.0 μM for [FeII(OH2)(Bn-TPEN)]2+ (4)). Control experiments showed that ligand 1 or FeII alone showed no inhibition, whereas 2 was moderately active (IC50 = 96 μM), suggesting that iron, when bound to these ligands, plays a key role in proteasome inhibition. Results from time-dependent inactivation studies suggest different modes of action for the iron complexes. Time-dependent decay of proteasome activity was observed upon incubation in the presence of 4, which accelerated in the presence of DTT, suggesting reductive activation of O2 and oxidation of the 20S proteasome as a mode of action. In contrast, loss of 20S proteasome activity was not observed with 3 over time, suggesting inhibition through direct binding of the iron complex to the enzyme. Inhibition of the 20S proteasome by 4 was not blocked by reactive oxygen species scavengers, consistent with a unique oxidant being responsible for the time-dependent inhibition observed.
Epidemiological studies have shown that a diet rich in fruits and cruciferous vegetables is associated with a lower risk of prostate cancer. Indole-3-carbinol (I3C) and its dimeric product 3,3′-diindolylmethane (DIM) have been shown to exhibit anti-tumor activity both in vitro and in vivo. Recently, we have reported that a formulated DIM (B-DIM) induced apoptosis and inhibited growth, angiogenesis, and invasion of prostate cancer cells by regulating Akt, NF-κB, VEGF and the androgen receptor (AR) signaling pathway. However, the precise molecular mechanism(s) by which B-DIM inhibits prostate cancer cell growth and induces apoptosis have not been fully elucidated. Most importantly, it is not known how B-DIM affects cell cycle regulators and proteasome activity, which are critically involved in cell growth and apoptosis. In this study, we investigated the effects of B-DIM on proteasome activity and AR transactivation with respect to B-DIM-mediated cell cycle regulation and induction of apoptosis in both androgen-sensitive LNCaP and androgen-insensitive C4-2B prostate cancer cells. We believe that our results show for the first time the cell cycle-dependent effects of B-DIM on proliferation and apoptosis of synchronized prostate cancer cells progressing from G1 to S phase. B-DIM inhibited this progression by induction of p27Kip1 and down-regulation of AR. We also show for the first time that B-DIM inhibits proteasome activity in S phase, leading to the inactivation of NF-κB signaling and induction of apoptosis in LNCaP and C4-2B cells. These results suggest that B-DIM could be a potent agent for the prevention and/or treatment of both hormone sensitive as well as hormone-refractory prostate cancer.
Since androgen receptor (AR) plays an important role in prostate cancer development and progression, androgen-ablation has been the frontline therapy for treatment of advanced prostate cancer even though it is rarely curative. A curative strategy should involve functional and structural elimination of AR from prostate cancer cells. We have previously reported that apoptosis induced by medicinal proteasome-inhibitory compound celastrol is associated with a decrease in AR protein levels. However celastrol-stimulated events contributing to this AR decrease have not been elucidated. Here, we report that a variety of chemotherapeutic agents, including proteasome inhibitors, a topoisomerase inhibitor, DNA–damaging agents and docetaxel that cause cell death, decrease AR levels in LNCaP prostate cancer cells. This decrease in AR protein levels was not due to the suppression of AR mRNA expression in these cells. We observed that a proteolytic activity residing in cytosol of prostate cancer cells is responsible for AR breakdown and that this proteolytic activity was stimulated upon induction of apoptosis. Interestingly, proteasome inhibitor celastrol- and chemotherapeutic drug VP-16-stimulated AR breakdown was attenuated by calpain inhibitors calpastatin and N-Acetyl-L-leucyl-L-leucyl-L-methioninal. Furthermore, AR proteolytic activity pulled down by calmodulin-agarose beads from celastrol-treated PC-3 cells showed immunoreactivity to a calpain antibody. Taken together, these results demonstrate calpain involvement in proteasome inhibitor-induced AR breakdown, and suggest that AR degradation is intrinsic to the induction of apoptosis in prostate cancer cells.
proteasome inhibitors; anticancer drugs; prostate cancer; apoptosis; cell death
Schiff bases have been intensively investigated due to their antibacterial and antitumor properties. Copper is a cofactor essential for the tumor angiogenesis processes, whereas other transition metals are not. Consistently, high serum or tissue levels of copper were found in many types of human cancer including breast, prostate, colon, lung, and brain, supporting the idea that copper could be used as a novel selective target for cancer therapies. In the current study we hypothesize that a synthetic taurine Schiff base copper complex (Compound 1) could suppress tumor cell growth via the direct inhibition of proteasome activity. Compound 1 potently inhibits the activity of purified 20S and 26S proteasome in human breast cancer MDA-MB-231 and leukemia Jurkat T cells. Inhibition of tumor cellular proteasomal activity by Compound 1 results in the accumulation of ubiquitinated protein and the proteasome target proteins p27 and Bax, followed by the induction of apoptosis. Our results strongly suggest that taurine Schiff base copper complexes, as potent proteasome inhibitors, have great potential to be developed into novel anticancer drugs.
taurine; Schiff base; copper; proteasome inhibitor; apoptosis; cancer
An ongoing strategy for cancer treatment is selective induction of apoptosis in cancer over normal cells. N-thiolated β-lactams were found to induce DNA damage, growth arrest and apoptosis in cultured human cancer cells. However, whether these compounds have a similar effect in vivo has not been studied. We report here that treatment with the β-lactam L-1 caused a significant inhibition of tumor growth in a breast cancer xenograft mouse model, associated with induction of DNA damage and apoptosis in vivo. These results suggest that the synthetic antibiotic N-thiolated β-lactams hold great potential to be developed as novel anti-cancer drugs.
β-Lactam; DNA damage; Apoptosis; Anti-tumor activity; Breast cancer
Flavonoids are polyphenolic compounds widely distributed in the plant kingdom. Compelling research indicates that flavonoids have important roles in cancer chemoprevention and chemotherapy possibly due to biological activities that include action through anti-inflammation, free radical scavenging, modulation of survival/proliferation pathways, and inhibition of the ubiquitin-proteasome pathway. Plant polyphenols including the green tea polyphenol, (-)-epigallocatechin gallate or (-)-EGCG, and the flavonoids apigenin, luteolin, quercetin, and chrysin have been shown to inhibit proteasome activity and induce apoptosis in human leukemia cells. However, biotransformation reactions to the reactive hydroxyl groups on polyphenols could reduce their biological activities. Although methylated polyphenols have been suggested to be metabolically more stable than unmethylated polyphenols, the practical use of methylated polyphenols as a cancer preventative agent warrants further investigation. In the current study, methylated and unmethylated flavonoids were studied for their proteasome-inhibitory and apoptosis-inducing abilities in human leukemia HL60 cells. Methylated flavonoids displayed sustained bioavailability and inhibited cellular proliferation by arresting cells in the G1 phase. However, they did not act as proteasome inhibitors in either an in vitro system or an in silico model and only weakly induced apoptosis. In contrast, unmethylated flavonoids exhibited inhibition of the proteasomal activity in intact HL60 cells, accumulating proteasome target proteins and inducing caspase activation and poly (ADP-ribose) polymerase cleavage. We conclude that methylated flavonoids lack potent cytotoxicity against human leukemia cells and most likely have limited ability as chemopreventive agents.
Methylated flavonoids; Proteasome inhibitors; Apoptosis; Cell cycle progression
The ubiquitin–proteasome system (UPS) degrades 80 – 90% of intracellular proteins. Cancer cells take advantage of the UPS for their increased growth and decreased apoptotic cell death. Thus, the components that make up the UPS represent a diverse group of potential anti-cancer targets. The success of the first-in-class proteasome inhibitor bortezomib not only proved that the proteasome is a feasible and valuable anti-cancer target, but also inspired researchers to extensively explore other potential targets of this pathway.
This review provides a broad overview of the UPS and its role in supporting cancer development and progression, especially in aspects of p53 inactivation, p27 turnover and NF-κB activation. Also, efforts toward the development of small molecule inhibitors (SMIs) targeting different steps in this pathway for cancer treatment are reviewed and discussed.
Whereas some of the targets in the UPS, such as the 20S pro-teasome, Nedd8 activating enzyme and HDM2, have been well-established and validated, there remains a large pool of candidates waiting to be investigated. Development of SMIs targeting the UPS has been largely facilitated by state-of-the-art technologies such as high-throughput screening and computer-assisted drug design, both of which require a better understanding of the targets of interest.
cancer therapy; deubiquitinases; E3 ligases; proteasome; small molecule inhibitors; ubiquitin
The conventional approach toward anticancer drug development is a time-consuming and expensive procedure.
One approach to expedite this process and achieve more affordable means is to discover new applications of existing drugs, since their pharmacokinetics and pharmacological profiles are well known.
Our encouraging findings in recent studies reveal anticancer activities of several copper-binding ligands including disulfiram (an antialcoholism drug), clioquinol (used to treat Alzheimer’s and Huntington’s diseases) and diethyldithiocarbamate (an agent for HIV-1 infection treatment).
These in vitro and in vivo studies have demonstrated that these archaic drugs can target and react with tumor cellular copper, forming complexes that act as potent proteasome inhibitors and apoptosis inducers.
Antitumor activity; clioquinol; copper; disulfiram; dithiocarbamate; proteasome inhibitors
We have previously reported on a gold(III) complex, namely [AuBr2(DMDT)] (N,N-dimethyldithiocarbamate) showing potent in vitro and in vivo growth inhibitory activities toward human cancer cells and identifying the cellular proteasome as one of the major targets. However, the importance of the oxidation state of the gold center and the involved mechanism of action has yet to be established. Here we show that both gold(III)- and gold(I)-dithiocarbamato species, namely [AuBr2(ESDT)] (AUL12) and [Au(ESDT)]2 (AUL15), could inhibit the chymotrypsin-like activity of purified 20S proteasome and 26S proteasome in human breast cancer MDA-MB-231 cells, resulting in accumulation of ubiquitinated proteins and proteasome target proteins, and induction of cell death, but at significantly different levels. Gold(I) and gold(III) compounds-mediated proteasome inhibition and cell death induction were completely reversed by the addition of a reducing agent, dithiothreitol or N-acetyl-l-cysteine, suggesting the involvement of redox processes. Furthermore, treatment of MDA-MB-231 cells with gold(III) compound (AUL12), but not the gold(I) analogue (AUL15), resulted in the production of significant level of reactive oxygen species. Our study provides strong evidence that the cellular proteasome is an imporant target of both gold(I) and gold(III) dithiocarbamates, but distinct cellular mechanisms of action are responsible for their different overall effect.
Apoptosis; gold compounds; proteasome inhibitor; redox; reactive oxygen species
The ubiquitinproteasome system is involved in various cellular processes, including transcription, apoptosis, and cell cycle. In vitro, in vivo, and clinical studies suggest the potential use of proteasome inhibitors as anticancer drugs. Cadmium (Cd) is a widespread environmental pollutant that has been classified as a human carcinogen. Recent study in our laboratory suggested that the clinically used anti-alcoholism drug disulfiram (DSF) could form a complex with tumor cellular copper, resulting in inhibition of the proteasomal chymotrypsin-like activity and induction of cancer cell apoptosis. In the current study, we report, for the first time, that DSF is able to convert the carcinogen Cd to a proteasome-inhibitor and cancer cell apoptosis inducer. Although the DSF–Cd complex inhibited the chymotrypsin-like activity of a purified 20S proteasome with an IC50 value of 32 μmol/L, this complex was much more potent in inhibiting the chymotrypsin-like activity of prostate cancer cellular 26S proteasome. Inhibition of cellular proteasome activity by the DSF–Cd complex resulted in the accumulation of ubiquitinated proteins and the natural proteasome substrate p27, which was followed by activation of calpain and induction of apoptosis. Importantly, human breast cancer MCF10DCIS cells were much more sensitive to the DSF–Cd treatment than immortalized but non-tumorigenic human breast MCF-10A cells, demonstrating that the DSF–Cd complex could selectively induce proteasome inhibition and apoptosis in human tumor cells. Our work suggests the potential use of DSF for treatment of cells with accumulated levels of carcinogen Cd.
Cadmium; Disulfiram; Proteasome inhibitor; Calpain; Apoptosis
Tumor drug resistance significantly limits the success of chemotherapy in the clinic. Tumor cells utilize multiple mechanisms to prevent the accumulation of anticancer drugs at their intracellular site of action. In this study, we investigated the anticancer efficacy of doxorubicin in combination with photodynamic therapy using methylene blue in a drug-resistant mouse tumor model. Surfactant-polymer hybrid nanoparticles formulated using an anionic surfactant, Aerosol-OT™ (AOT), and a naturally occurring polysaccharide polymer, sodium alginate, were used for synchronized delivery of the two drugs. Balb/c mice bearing syngeneic JC tumors (mammary adenocarcinoma) were used as a drug-resistant tumor model. Nanoparticle-mediated combination therapy significantly inhibited tumor growth and improved animal survival. Nanoparticle-mediated combination treatment resulted in enhanced tumor accumulation of both doxorubicin and methylene blue, significant inhibition of tumor cell proliferation, and increased induction of apoptosis. These data suggest that nanoparticle-mediated combination chemotherapy and photodynamic therapy using doxorubicin and methylene blue has significant therapeutic potential against drug-resistant tumors.
Chemotherapy; Nanoparticles; Photosensitizer; Drug efflux; Drug resistance; Reactive oxygen species
Zinc and copper are trace elements essential for proper folding, stabilization and catalytic activity of many metalloenzymes in living organisms. However, disturbed zinc and copper homeostasis is reported in many types of cancer. We have previously demonstrated that copper complexes induced proteasome inhibition and apoptosis in cultured human cancer cells. In the current study we hypothesized that zinc complexes could also inhibit the proteasomal chymotrypsin-like activity responsible for subsequent apoptosis induction. We first showed that zinc(II) chloride was able to inhibit the chymotrypsin-like activity of a purified 20S proteasome with an IC50 value of 13.8 μM, which was less potent than copper(II) chloride (IC50 5.3 μM). We then compared the potencies of a pyrrolidine dithiocarbamate (PyDT)-zinc(II) complex and a PyDT-copper(II) complex to inhibit cellular proteasomal activity, suppress proliferation and induce apoptosis in various human breast and prostate cancer cell lines. Consistently, zinc complex was less potent than copper complex in inhibiting the proteasome and inducing apoptosis. Additionally, zinc and copper complexes appear to use somewhat different mechanisms to kill tumor cells. Zinc complexes were able to activate calpain-, but not caspase-3-dependent pathway, while copper complexes were able to induce activation of both proteases. Furthermore, the potencies of these PyDT-metal complexes depend on the nature of metals and also on the ratio of PyDT to the metal ion within the complex, which probably affects their stability and availability for interacting with and inhibiting the proteasome in tumor cells.
Zinc; Copper; Proteasome inhibitor; Apoptosis; Calpain; Pyrrolidine dithiocarbamate
Tea is the most popular beverage in the world, second only to water. Tea contains an infusion of the leaves from the Camellia sinensis plant rich in polyphenolic compounds known as catechins, the most abundant of which is (−)-EGCG. Although tea has been consumed for centuries, it has only recently been studied extensively as a health-promoting beverage that may act to prevent a number of chronic diseases and cancers. The results of several investigations indicate that green tea consumption may be of modest benefit in reducing the plasma concentration of cholesterol and preventing atherosclerosis. Additionally, the cancer-preventive effects of green tea are widely supported by results from epidemiological, cell culture, animal and clinical studies. In vitro cell culture studies show that tea polyphenols potently induce apoptotic cell death and cell cycle arrest in tumor cells but not in their normal cell counterparts. Green tea polyphenols were shown to affect several biological pathways, including growth factor-mediated pathway, the mitogen-activated protein (MAP) kinase-dependent pathway, and ubiquitin/proteasome degradation pathways. Various animal studies have revealed that treatment with green tea inhibits tumor incidence and multiplicity in different organ sites such as skin, lung, liver, stomach, mammary gland and colon. Recently, phase I and II clinical trials have been conducted to explore the anticancer effects of green tea in humans. A major challenge of cancer prevention is to integrate new molecular findings into clinical practice. Therefore, identification of more molecular targets and biomarkers for tea polyphenols is essential for improving the design of green tea trials and will greatly assist in a better understanding of the mechanisms underlying its anti-cancer activity.
Tea polyphenols; Molecular targets; Cancer prevention; Cancer treatment
The purpose of the current study was to assess the effect of newly synthesized Curcumin analogs on COX-2 protein by molecular docking studies and by assessments of the effect of one such analog (CDF) on nuclear factor NF-κB and PGE2. In addition, we have determined the pharmacokinetics and tissue distribution of CDF in mice compared to Curcumin.
Molecular docking on COX-2 protein was assessed by standard computer modeling studies. PGE2 assay in conditioned media was done utilizing high sensitivity immunoassay kit following manufacturer’s instructions, while NF-κB was done by routine EMSA. Serum pharmacokinetics and tissue distribution studies were carried out using the validated high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) methods.
The molecular docking showed that fluorocurcumin analogs do not introduce any major steric changes compared to the parent Curcumin molecule, which was consistent with down-regulation of NF-κB and reduced PGE2 levels in cells treated with CDF. Pharmacokinetic parameters revealed that CDF had better retention and bioavailability and that the concentration of CDF in the pancreas tissue was 10-fold higher compared to Curcumin.
Our observations clearly suggest that the bioavailability of CDF is much superior compared to Curcumin, suggesting that CDF would be clinically useful.
COX-2; curcumin; fluorocurcumin; pharmacokinetics
Metals are essential cellular components selected by nature to function in several indispensable biochemical processes for living organisms. Metals are endowed with unique characteristics that include redox activity, variable coordination modes, and reactivity towards organic substrates. Due to their reactivity, metals are tightly regulated under normal conditions and aberrant metal ion concentrations are associated with various pathological disorders, including cancer. For these reasons, coordination complexes, either as drugs or prodrugs, become very attractive probes as potential anticancer agents. The use of metals and their salts for medicinal purposes, from iatrochemistry to modern day, has been present throughout human history. The discovery of cisplatin, cis-[PtII(NH3)2Cl2], was a defining moment which triggered the interest in platinum(II)- and other metal-containing complexes as potential novel anticancer drugs. Other interests in this field address concerns for uptake, toxicity, and resistance to metallodrugs. This review article highlights selected metals that have gained considerable interest in both the development and the treatment of cancer. For example, copper is enriched in various human cancer tissues and is a co-factor essential for tumor angiogenesis processes. However the use of copper-binding ligands to target tumor copper could provide a novel strategy for cancer selective treatment. The use of nonessential metals as probes to target molecular pathways as anticancer agents is also emphasized. Finally, based on the interface between molecular biology and bioinorganic chemistry the design of coordination complexes for cancer treatment is reviewed and design strategies and mechanisms of action are discussed.
Cancer; metal; zinc; copper; platinum; metal complex; DNA; proteasome
RNF115, or Breast Cancer-Associated Gene 2 (BCA2), encodes a RING-finger ubiquitin E3 ligase, expression of which was associated with estrogen receptor (ER)-positive status in human breast tumors. Although the BCA2 promoter contains several estrogen response element (ERE) half-sites, the role of ER in the regulation of BCA2 transcription has not been reported. The aim of this study is to investigate the molecular mechanism by which estrogen regulates BCA2 transcription. BCA2 mRNA and protein levels were examined by RT-PCR and Western blot analysis, respectively, and localization was assessed by immunofluorescence. BCA2 promoter activity in response to E2 was tested by a dual luciferase reporter assay and ER binding to the BCA2 promoter was examined by chromatin immunoprecipitation assay. We found that BCA2 mRNA and protein levels are regulated by estrogen in ER-positive MCF7 breast cancer cells and MDA MB 231 cells stably transfected with ER. Estrogen treatment in hormonal depleted MCF7 and MDA MB 231/ER stably transfected cells resulted in increased nuclear ER and cytoplasmic and nuclear BCA2 staining. Cycloheximide is not able to inhibit BCA2 mRNA levels, suggesting potential BCA2 regulation at the transcriptional level. Anti-estrogens like tamoxifen and ICI 182 178 counteracted E2-induced BCA2 protein and knockdown of ER by ER siRNA resulted in a significant decrease in BCA2 protein and a lower nuclear expression pattern. Estrogen treatment lead to a significant increase in BCA2 promoter response, associated with increased binding of ER to the ERE region of the BCA2 promoter. BCA2 is therefore a newly identified transcriptional target of estrogen receptor.
Breast cancer; Estrogen receptor (ER); Breast cancer-associated gene 2 (BCA2); Estrogen (E2); Estrogen response element (ERE); Tamoxifen and ICI 182 178 (ICI)
Emerging evidence demonstrates that targeting the tumor proteasome is a promising strategy for cancer therapy.
This review summarizes recent results from cancer clinical trials using specific proteasome inhibitors or some natural compounds that have proteasome-inhibitory effects.
A literature search was carried out using PubMed. Results about the clinical application of specific proteasome inhibitors and natural products with proteasome-inhibitory activity for cancer prevention or therapy were reviewed.
Bortezomib, the reversible proteasome inhibitor that first entered clinical trials, has been studied extensively as a single agent and in combination with glucocorticoids, cytotoxic agents, immunomodulatory drugs and radiation as treatment for multiple myeloma and other hematological malignancies. The results in some cases have been impressive. There is less evidence of bortezomib's efficacy in solid tumors. Novel irreversible proteasome inhibitors, NPI-0052 and carfilzomib, have also been developed and clinical trials are underway. Natural products with proteasome-inhibitory effects, such as green tea polyphenol (−)-epigallocatechin-3-gallate (EGCG), soy isoflavone genistein, and the spice turmeric compound curcumin, have been studied alone and in combination with traditional chemotherapy and radiotherapy against various cancers. There is also interest in developing these natural compounds as potential chemopreventive agents.
clinical trials; combinational therapy; hematological malignancies; natural products; proteasome inhibitors; solid tumors