Anticancer activity of Celastrol in combination with ErbB2-targeted therapeutics for treatment of ErbB2-overexpressing breast cancers

Tualang honey promotes apoptotic cell death induced by tamoxifen in breast cancer cell lines

Tualang honey (TH) is rich in flavonoids and phenolic acids and has significant anticancer activity against breast cancer cells comparable to the effect of tamoxifen (TAM), in vitro. The current study evaluated the effects of TH when used in combination with TAM on MCF-7 and MDA-MB-231 cells. We observed that TH promoted the anticancer activity of TAM in both the estrogen receptor-(ER-)responsive and ER-nonresponsive human breast cancer cell lines. Flow cytometric analyses indicated accelerated apoptosis especially in MDA-MB-231 cells and with the involvement of caspase-3/7, -8 and -9 activation as shown by fluorescence microscopy. Depolarization of the mitochondrial membrane was also increased in both cell lines when TH was used in combination with TAM compared to TAM treatment alone. TH may therefore be a potential adjuvant to be used with TAM for reducing the dose of TAM, hence, reducing TAM-induced adverse effects.

Oral bioavailability and gender-related pharmacokinetics of celastrol following administration of pure celastrol and its related tablets in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Celastrol is a natural compound extracted from the traditional Chinese medicinal herb, Thunder God Vine (TGV). Owing to its potential anti-inflammatory and antitumor effects, celastrol has been considered as a promising candidate for drug development.

AIM OF THE STUDY

To establish a sensitive LC-MS/MS method to investigate the pharmacokinetic properties of celastrol in rats. Key pharmacokinetic issues of celastrol including oral bioavailability, comparative pharmacokinetics between pure compound and tablet preparation, as well as gender-related pharmacokinetic difference are to be addressed for the first time.

MATERIALS AND METHODS

Sprague-Dawley rats were administrated an intravenous dose (100 μg kg(-1)) of pure celastrol and an oral dose (1000 μg kg(-1)) of pure celastrol and TGV tablets (corresponding to 534 μg kg(-1) of celastrol), respectively. At different time points, the concentration of celastrol in rat plasma was determined by a sensitive and well-validated LC-MS/MS method. Main pharmacokinetic parameters including area under the plasma concentration-time curve (AUC), maximal plasma concentration (Cmax), the time for maximal concentration (Tmax) and mean residence time (MRT) were estimated by Drug and Statistic1.0 pharmacokinetic software (Chinese Pharmacological Association, Anhui, PR China). Statistical analysis was performed using two one-side t test with p-values less than 0.05 as the level of significance.

RESULTS

The standard curve of celastrol showed good linearity in the concentration range of 0.11~54.3 ng mL(-1) in our current method, with acceptable selectivity, precision, recovery, and stability. The oral absolute bioavailability of celastrol significantly increased from 17.06% for pure celastrol to 94.19% for TGV tablets containing equivalent celastrol. After oral administration of TGV tablets, the Cmax and AUC values of celastrol in female rats were (32.03±8.41) μg L(-1) and (379.49±118.19) μg h L(-1), which were significantly higher (p<0.01) than that in males with the values of (14.31±7.33) μg L(-1) and (188.17±92.33) μg h L(-1).

CONCLUSION

Celastrol administered orally in the rat was poorly absorbed into the systemic circulation. However, the poor absorption of celastrol could be greatly improved when celastrol-containing TGV tablets orally administered, and thereby the oral bioavailability of celastrol was significantly increased. As for gender difference, female rats showed significantly better absorption of celastrol than males.

Beta-catenin mediates the apoptosis induction effect of celastrol in HT29 cells

AIM

We evaluated the apoptosis induction effects of celastrol in human colorectal cancer cell line HT29 in WNT/beta-catenin pathway.

MAIN METHODS

HT29 cells were treated with various concentrations (10-100μM) for 24h, MTT assay was performed to examine the effect of celastrol on growth inhibition of HT29 cells. Beta-catenin siRNA was used for transfection of cells. Cell apoptosis was detected through both DNA laddering analysis and Tdt-mediated dUTP nick end labeling (TUNEL) assay. Western blot analysis and real-time reverse transcription polymerase chain reaction technologies were applied to assess the expression level of c-Myc, Bax, and Bcl-2 in HT29 cells.

KEY FINDINGS

Treatment of HT29 cells with celastrol resulted in a growth inhibition effect, and the IC(50) value was 56μM. Celastrol induced HT29 cells apoptosis, and increased the nuclear translocation of beta-catenin. Apoptosis induction effects of celastrol were significantly attenuated by beta-catenin siRNA transfection. Beta-catenin siRNA markedly increased mRNA and protein levels of c-Myc compared with control siRNA. Beta-catenin siRNA significantly inhibited the expression of Bax and Bcl-2 in celastrol-treated HT29 cells.

SIGNIFICANCE

Beta-catenin mediates the apoptosis induction effects of celastrol in HT29 cells.

Perturbing pro-survival proteins using quinoxaline derivatives: a structure-activity relationship study

In HeLa cells the combinatorial knockdown of Bcl-xL and Mcl-1 is sufficient to induce spontaneous apoptosis. Quinoxaline derivatives were screened for the induction of Mcl-1 dependent apoptosis using a cell line without functional Bcl-xL. Quinoxaline urea analog 1 h was able to specifically induce apoptosis in an Mcl-1 dependent manner. We demonstrate that even small changes to 1h results in dramatic loss of activity. In addition, 1 h and ABT-737 synergistically inhibit cell growth and induce apoptosis. Our results also suggest that 1h could have therapeutic potential against ABT-737 refractory cancer.

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: potential role in prevention and therapy of cancer

Over the last two decades, extensive research on plant-based medicinal compounds has revealed exciting and important pharmacological properties and activities of triterpenoids. Fruits, vegetables, cereals, pulses, herbs and medicinal plants are all considered to be biological sources of these triterpenoids, which have attracted great attention especially for their potent anti-inflammatory and anti-cancer activities. Published reports in the past have described the molecular mechanism(s) underlying the various biological activities of triterpenoids which range from inhibition of acute and chronic inflammation, inhibition of tumor cell proliferation, induction of apoptosis, suppression of angiogenesis and metastasis. However systematic analysis of various pharmacological properties of these important classes of compounds has not been done. In this review, we describe in detail the pre-clinical chemopreventive and therapeutic properties of selected triterpenoids that inhibit multiple intracellular signaling molecules and transcription factors involved in the initiation, progression and promotion of various cancers. Molecular targets modulated by these triterpenoids comprise, cytokines, chemokines, reactive oxygen intermediates, oncogenes, inflammatory enzymes such as COX-2, 5-LOX and MMPs, anti-apoptotic proteins, transcription factors such as NF-κB, STAT3, AP-1, CREB, and Nrf2 (nuclear factor erythroid 2-related factor) that regulate tumor cell proliferation, transformation, survival, invasion, angiogenesis, metastasis, chemoresistance and radioresistance. Finally, this review also analyzes the potential role of novel synthetic triterpenoids identified recently which mimic natural triterpenoids in physical and chemical properties and are moving rapidly from bench to bedside research.

Synthesis and evaluation of indole-based chalcones as inducers of methuosis, a novel type of nonapoptotic cell death

Methuosis is a novel caspase-independent form of cell death in which massive accumulation of vacuoles derived from macropinosomes ultimately causes cells to detach from the substratum and rupture. We recently described a chalcone-like compound, 3-(2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one (i.e., MIPP), which can induce methuosis in glioblastoma and other types of cancer cells. Herein, we describe the synthesis and structure-activity relationships of a directed library of related compounds, providing insights into the contributions of the two aryl ring systems and highlighting a potent derivative, 3-(5-methoxy, 2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one (i.e., MOMIPP) that can induce methuosis at low micromolar concentrations. We have also generated biologically active azide derivatives that may be useful for future studies aimed at identifying the protein targets of MOMIPP by photoaffinity labeling techniques. The potential significance of these studies is underscored by the finding that MOMIPP effectively reduces the growth and viability of Temozolomide-resistant glioblastoma and doxorubicin-resistant breast cancer cells. Thus, it may serve as a prototype for drugs that could be used to trigger death by methuosis in cancers that are resistant to conventional forms of cell death (e.g., apoptosis).

Celastrol inhibits tumor cell proliferation and promotes apoptosis through the activation of c-Jun N-terminal kinase and suppression of PI3 K/Akt signaling pathways

Celastrol, a plant triterpene has attracted great interest recently, especially for its potential anti-inflammatory and anti-cancer activities. In the present report, we investigated the effect of celastrol on proliferation of various cancer cell lines. The mechanism, by which this triterpene exerts its apoptotic effects, was also examined in detail. We found that celastrol inhibited the proliferation of wide variety of human tumor cell types including multiple myeloma, hepatocellular carcinoma, gastric cancer, prostate cancer, renal cell carcinoma, head and neck carcinoma, non-small cell lung carcinoma, melanoma, glioma, and breast cancer with concentrations as low as 1 μM. Growth inhibitory effects of celastrol correlated with a decrease in the levels of cyclin D1 and cyclin E, but concomitant increase in the levels of p21 and p27. The apoptosis induced by celastrol was indicated by the activation of caspase-8, bid cleavage, caspase-9 activation, caspase-3 activation, PARP cleavage and through the down regulation of anti-apoptototic proteins. The apoptotic effects of celastrol were preceded by activation of JNK and down-regulation of Akt activation. JNK was needed for celastrol-induced apoptosis, and inhibition of JNK by pharmacological inhibitor abolished the apoptotic effects. Overall, our results indicate that celastrol can inhibit cell proliferation and induce apoptosis through the activation of JNK, suppression of Akt, and down-regulation of anti-apoptotic protein expression.

Mechanisms of Trastuzumab resistance in ErbB2-driven breast cancer and newer opportunities to overcome therapy resistance

The Human Epidermal Growth Factor Receptor 2 (Her2, ErbB2 or Neu) is overexpressed in about 20 – 25% of breast cancers and is causally linked to oncogenesis, providing opportunities for targeted therapy. Trastuzumab (Herceptin^™, Genentech Inc, San Francisco, CA), a humanized monoclonal antibody against ErbB2, is a successful example of this concept and has vastly improved the response to treatment and overall survival in a majority of ErbB2+ breast cancer patients. However, lack of response in some patients as well as relapse during the course of therapy in others, continue to challenge researchers and clinicians alike towards a better understanding of the fundamental mechanisms of Trastuzumab action and resistance to treatment. The exact in vivo mechanism of action of Trastuzumab remains enigmatic, given its direct effects on the ErbB2 signaling pathway as well as indirect contributions from the immune system, by virtue of the ability of Trastuzumab to elicit Antibody-Dependent Cellular Cytotoxicity. Consequently, multiple mechanisms of resistance have been proposed. We present here a comprehensive review of our current understanding of the mechanisms, both of Trastuzumab action and clinical resistance to Trastuzumab-based therapies. We also review newer strategies (based on ErbB2 receptor biology) that are being explored to overcome resistance to Trastuzumab therapy.

The main anticancer bullets of the Chinese medicinal herb, thunder god vine

The thunder god vine or Tripterygium wilfordii Hook. F. is a representative Chinese medicinal herb which has been used widely and successfully for centuries in treating inflammatory diseases. More than 100 components have been isolated from this plant, and most of them have potent therapeutic efficacy for a variety of autoimmune and inflammatory diseases. In the past four decades, the anticancer activities of the extracts from this medicinal herb have attracted intensive attention by researchers worldwide. The diterpenoid epoxide triptolide and the quinone triterpene celastrol are two important bioactive ingredients that show a divergent therapeutic profile and can perturb multiple signal pathways. Both compounds promise to turn traditional medicines into modern drugs. In this review, we will mainly address the anticancer activities and mechanisms of action of these two agents and briefly describe some other antitumor components of the thunder god vine.

Engineered biological entities for drug delivery and gene therapy protein nanoparticles

The development of genetic engineering techniques has speeded up the growth of the biotechnological industry, resulting in a significant increase in the number of recombinant protein products on the market. The deep knowledge of protein function, structure, biological interactions, and the possibility to design new polypeptides with desired biological activities have been the main factors involved in the increase of intensive research and preclinical and clinical approaches. Consequently, new biological entities with added value for innovative medicines such as increased stability, improved targeting, and reduced toxicity, among others have been obtained. Proteins are complex nanoparticles with sizes ranging from a few nanometers to a few hundred nanometers when complex supramolecular interactions occur, as for example, in viral capsids. However, even though protein production is a delicate process that imposes the use of sophisticated analytical methods and negative secondary effects have been detected in some cases as immune and inflammatory reactions, the great potential of biodegradable and tunable protein nanoparticles indicates that protein-based biotechnological products are expected to increase in the years to come.