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

19th Thursday, 2012  |   Others  |  no comments


Abstract
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-?B, 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.
Source:
Shanmugam MK, Nguyen AH, Kumar AP, Tan BK, Sethi G. Cancer Lett. 2012 Mar 7.

Are Cancer Stem Cells Ready for Prime Time?

18th Wednesday, 2012  |   Others  |  no comments

 

Untitled Document

 
A flood of new discoveries has refined our definition of cancer stem cells. Now it’s up to human clinical trials to test if they can make a difference in patients.
The Scientist. Suling Liu, Hasan Korkaya, and Max S. Wicha | April 1, 2012

Photo Researchers, Inc., David McCarthy

In the 30-year battle waged since the initiation of the “war on cancer,” there have been substantial victories, with cures for childhood malignancies among the most important. Our ever-expanding understanding of cellular and molecular biology has provided substantial insights into the molecular underpinnings of the spectrum of diseases we call cancer. Yet, while researchers view this as tremendous progress, many patients have seen only limited improvement. In fact, the relatively modest gains achieved in treating the most common malignancies have caused some to say that we are actually losing the war on cancer.1

Based on new intelligence, oncologists are making informed battle plans to attack a particularly pernicious enemy—the cancer stem cell. Controversial though they are, cancer stem cells are an incredibly promising target. If treatment-resistant cancer, and the metastases that transplant the cancer throughout the body, could be attributed to the actions of a single cell type, it could explain many of the treatment failures and provide a novel way to attack the disease.

The idea that cancers are driven by cells with “embryonic features” is an old one. Many cancers regress to a less differentiated state, expressing proteins that are usually expressed only in the embryo or during early development. It is only in the past 20 years or so, however, that additional observations led to the hypothesis that these embryonic-like cells were a separate subpopulation that fueled tumor expansion, much the same way that stem cells churn out the cells that make up a particular organ.

A number of groups, including our own, have identified cancer stem cell markers enabling the isolation and characterization of these cells. In addition, the development of in vitro and mouse functional assays has led to a veritable explosion of research on cancer stem cells from both blood-derived malignancies and solid tumors.2,3 However, the limitations of these markers and assays have generated heated debate regarding which tumors follow a stem cell model, and which do not. New data from our lab and from others is helping to clarify some of these areas of debate with the goal of better understanding how these cells can be identified and characterized.

Clarifying the debate

A cancer stem cell (CSC) is defined as a cell that has the ability to self-renew, dividing to give rise to another malignant stem cell, as well as to produce the phenotypically diverse, differentiated tumor cells that form the bulk of the tumor. Evidence for CSCs was first documented in leukemia, where it was clear that only a small subset of cancer cells was capable of perpetuating the cancer upon serial transplantation from one mouse to another. Extensive knowledge of normal blood stem cells facilitated our recognition and understanding of leukemia stem cells. Evidence for CSCs in solid tumors has been more controversial, because it is more technically challenging to divide a solid mass into individual cells without damage or alteration, and knowledge of the properties of normal-tissue stem cells in these organs is more limited. However, some of the areas of contention may be resolved by continuing research into the biology of these CSCs.

Relatively modest gains achieved in treating the most common malignancies have caused some to say that we are actually losing the war on cancer.

One of the points of confusion in CSC biology is the question of where these cells come from. Do they arise from normal stem cells that have become cancerous through mutation, or do they arise from partially differentiated tissue-progenitor cells that have acquired the ability to self-renew? Recent evidence suggests CSCs may arise from either source.

A second misconception is that the definition of CSCs precludes the possibility that cancers arise from sequential mutations that accumulate over many cell generations and are selected for through a Darwinian process—the so-called “clonal evolution model.” Some have proposed that the “CSC model” is a competing theory of carcinogenesis. In fact, both models may be correct. There is evidence that CSCs may also be genetically unstable, resulting in clonal evolution that generates several distinct CSC clones in a tumor.

While the identification of CSC markers and the development of in vitro and mouse models have led to important advances in the field, each of these markers and models has limitations that have fueled debate. Markers used to isolate cancer stem cells, such as CD44, CD24, CD133, aldehyde dehydrogenase (ALDH), and Hoechst dye exclusion, have proven useful for identifying these cell populations in tumor samples. However, expression of these markers is highly dependent on experimental conditions such as culture medium and oxygen concentration. Similarly, in vitro assays that rely on the ability to form spherical colonies in suspension can be useful, but are notoriously inaccurate. Since the definition of CSCs is ultimately an operational one, the most reliable assay for these cells has been their ability to initiate tumors when transplanted into mouse models. Because the immune system will reject any implanted foreign tissue, researchers have had to use immunosuppressed mice to test for human CSCs. In some tumor types, such as melanoma, the proportion of cells capable of initiating tumors is dependent on the degree of immunosuppression in the mouse models utilized. However, the more immunosuppressed mouse models may actually overestimate the true frequency of CSCs.

Recent studies have indicated that CSCs have the ability to evade immune surveillance, even when the same immune cells can detect and destroy bulk tumor cells. If this is truly the case, then highly immunosuppressed models of cancer may not reliably simulate the behavior of the immune system in the microenvironment of a patient’s tumor. Indeed, CSCs isolated from transgenic mouse tumors have been transplanted successfully into mice with intact immune systems, demonstrating the existence of CSCs and providing further support for relevance of these cells in patients.

Another misconception is that the cancer stem cell hypothesis requires that CSCs be rare. In fact, studies suggest that the percentage of CSCs may vary significantly in different types of cancer, as well as within each cancer type. In acute leukemia, CSCs appear to be rare, constituting less than 0.1 percent of the total cancer cell population. In some solid tumors, such as breast cancer, their numbers are reported to represent approximately 1–10 percent, while in some tumors, such as melanoma, they may be even more common, leading some investigators to propose that some cancers follow a stem cell model while others don’t. While this is debatable, identifying populations of CSCs in tumors in which these cells are abundant, or in the majority, may be of less importance, since any effective therapy would primarily target the CSCs.

Developmentally informed

Some researchers have focused on defining CSCs from a genetic and developmental perspective. Researchers including Robert Weinberg and colleagues from the Whitehead Institute for Biomedical Research have noted that when cancer cells adopt a genetic program responsible for the epithelial-to-mesenchymal transition (EMT), they convert to a CSC phenotype.4 EMT is known to developmental biologists as the transition from a non-motile, epithelial-like cell to one that can detach from the surrounding tissue and migrate. Cellular migration is important in development, and it is also a defining characteristic of aggressive tumors that metastasize to new sites in the body. Both inflammatory immune responses and a hypoxic tumor microenvironment induce EMT in cancers. It is also increasingly recognized that EMT plays an important role in therapeutic resistance.5

Infographic: The Two Faces of Metastasis

In contrast, other studies have suggested that the EMT state, although associated with tumor invasion, is characterized by cellular quiescence, or an inability to replicate, creating a paradox. How can cells which are associated with aggressive metastatic behavior be quiescent? Recent observations by our group and others have suggested an additional mechanism that could explain both observations: CSCs may in fact flip-flop between an EMT state and its converse, the mesenchymal-to-epithelial transition (MET), in which cells re-attach to the matrix and become highly proliferative, thus generating tumors at sites of metastasis.

These results suggest that CSCs, such as those found in breast cancers, have plasticity and can exist in two alternative states: an EMT-like state of CSCs expressing surface markers CD44 but not CD24 (CD44+CD24), and an MET-like population expressing the CSC marker ALDH. Previous studies taken together with our current work suggest that CSCs located inside the primary tumor mass exist predominantly in the MET state in which they are highly proliferative and express ALDH. In contrast, tumor cells that migrate into the circulation and metastasize are characterized as CD44+CD24—highly invasive but quiescent EMT CSCs.5 This scenario is supported by studies showing that in women with breast-cancer-derived, bone micrometastases express the EMT CSC markers CD44+CD24.5 These micrometastases are largely quiescent, as indicated by their lack of expression of markers of cellular proliferation such as Ki67.5 In order to enter a proliferative state, EMT CSC cells must undergo an MET transition in which they lose their invasive characteristics and acquire self-renewal capacity.

Clinical implications of cancer stem cell models

The effectiveness of the majority of cancer chemotherapeutic agents has been judged by their ability to cause tumor regression, as ascertained by direct measurement or through radiographic imaging. Since tumor size is largely determined by bulk cell populations, however, it follows that tumor regression reflects changes in this population rather than in the rarer CSCs, which may be the real drivers of tumor growth and metastasis. This could explain why in many cancers tumor regression does not translate to increased patient survival. There is substantial evidence in preclinical models that most CSCs are relatively resistant to chemotherapeutic agents and radiation therapy. In addition, CSCs may display resistance to molecularly targeted therapeutics. For example, one of the greatest advances within targeted therapeutics has been the development of imatinib (Gleevec) for chronic myelogenous leukemia (CML). Almost all patients treated with this molecularly targeted tyrosine kinase inhibitor enter clinical remission. However, disease quickly recurs following discontinuation of the drug, and CML cancer stem cells have been demonstrated to be resistant to this agent. This has led to experimental approaches that target CSCs using agents such as sirtuin inhibitors6 or interferon.

Another targeted therapy is trastuzumab (Herceptin), the development of which has represented a major advance in therapy for breast cancers that overexpress the human epidermal growth factor receptor 2 (HER2). Unfortunately, only some 20 percent of women with breast cancer have this genetic alteration. In 2008, however, researchers from the University of Pittsburgh published clinical trial results showing that women who were HER2-negative also appeared to benefit from treatment when the drug was part of the chemotherapy cocktail given after surgery to prevent recurrence. This puzzling finding could have huge implications for the majority of breast cancers that are currently not being treated with the drug. When we looked further into HER2 expression patterns, we found that this receptor also increased the self-renewal of breast CSCs.7 This may provide an explanation for the remarkable efficacy of the drug, which blocks HER2.8 Our ongoing preclinical studies indicate that trastuzumab can kill the CSCs in tumors that express this receptor only on their CSCs, and would thus be classified as HER2-negative.9

New Horizon for Cancer Treatment

The cancer stem cell (CSC) hypothesis offers explanations for many of the frustrating failures of cancer therapy in the clinic. The resistance of CSCs to chemotherapy, radiation, and many targeted therapies, may explain why cancers come back after the tumor mass has been removed and the patient has gone into remission. As such, CSCs offer a new target for attack.

Chemo catch-22:Although chemotherapy is still considered to be the most effective treatment for many cancers, the drugs may act on a tumor’s surrounding tissue in a way that spurs the production of more stem cells. In fact, increases in CSC numbers have been observed in tumors after chemo or radiation. These treatments can create inflammation in the tissue surrounding the tumor as well as hypoxia, or loss of oxygen, which activates Wnt signaling. Inflammatory mediators such as IL-8, IL-6, and Wnt signaling spur CSCs to self-renew or increase in number, thus driving tumor growth.

Antiangiogenic agents are another treatment whose administration may need to be rethought in light of what we now know about CSC biology. The development of antiangiogenic agents such as bevacizumab (Avastin) and sunitinib (Sutent) represented an area of significant promise in cancer. However, recent clinical trials have produced relatively disappointing results. Although these agents delay tumor progression, they do not significantly increase patient survival. Our group has demonstrated that in mouse models, these antiangiogenic agents actually increase CSC populations through generation of tumor hypoxia, or low oxygenation,which drives the proliferation of CSCs by triggering the Akt and Wnt pathways.10 This suggests that, to be clinically effective, these agents may require additional therapies capable of targeting CSC populations.

Over the past decade, a number of developmental pathways that regulate the self-renewal of normal stem cells have been elucidated. These include the developmental pathways Wnt, Notch, and Hedgehog, and the cell division and proliferation pathways PI-3K, NF-kB and Jak/STAT. Interestingly, these pathways are dysregulated in many human cancers, leading to uncontrolled self-renewal of CSCs.11 These pathways may provide excellent targets for developing drugs against CSCs.

In addition to the regulation of CSCs by intrinsic signals, elements in the tumor microenvironment or niche also play a role in regulation of the stem cells. In tumors, this niche contains a variety of cellular elements, including inflammatory cells, fibroblasts, endothelial cells, and mesenchymal stem cells.12 Iterative crosstalk between cancer stem cells, their differentiated progeny, and the microenvironment regulates cellular function through paracrine cell signaling. Some of these interactions include the Wnt, Notch, and Hedgehog pathways. In addition, inflammatory cells, fibroblasts, and mesenchymal stem cells may interact with CSCs and increase their production and replication via cytokine loops. Several inflammatory cytokines, including IL-6 and IL-8, have been demonstrated to increase breast cancer stem cell self-renewal in mouse models and in vitro. In addition, chemotherapy-induced cellular toxicity increases local IL-8 production, which may contribute to increased cancer stem cell populations following chemotherapy. High serum levels of IL-6 and IL-8 in patients with advanced breast cancers have been associated with development of metastasis and poor outcome.11 These studies suggest that developing strategies to interfere with these loops may provide a novel way to target CSCs. Interestingly, statins, which have anti-inflammatory effects, have been reported to decrease breast cancer risk.13

We have also recently demonstrated that blocking IL-8 with antibodies or drugs targets breast CSCs in mouse models and inhibits tumor growth and metastasis.11 Repertaxin, a drug that blocks the IL-8 receptor, was developed to prevent graft rejection and has been reported to be relatively nontoxic in phase I clinical trials. We have recently begun a clinical trial combining Repertaxin with chemotherapy in women with advanced breast cancer.

In the past 5 years there has been an exponential increase in CSC research. This research has helped to resolve a number of controversies regarding identification of these cells and their role in driving tumor growth and mediating treatment resistance. Despite these advances, the CSC field is still in its relative infancy, and many questions and challenges remain. More than a dozen biotechnology and pharmaceutical companies are now vigorously pursuing CSC research. As a result, a number of early-phase clinical trials targeting CSCs are in progress. These studies and the later-stage efficacy trials that follow them should indicate whether successful targeting of CSCs significantly improves outcomes in cancer patients. If this is found to be the case, it may usher in the beginning of a new era of cancer therapy.

Suling Liu, Hasan Korkaya, and Dr. Max S. Wicha, Director, UM Cancer Center, are all at the University of Michigan Comprehensive Cancer Center.

References

  1. C. Leaf, “Why we’re losing the war on cancer (and how to win it),” Fortune, 149:76-82, 84-86, 88 passim., 2004. ?
  2. A. Larochelle et al., “Identification of primitive human hematopoietic cells capable of repopulating NOD/SCID mouse bone marrow: Implications for gene therapy,” Nat Med, 2:1329-37, 1996. ?
  3. M. Al-Hajj et al., “Prospective identification of tumorigenic breast cancer cells,” PNAS, 100:3983-88, 2003. ?
  4. S.A. Mani et al., “The epithelial-mesenchymal transition generates cells with properties of stem cells,” Cell, 133:704-15, 2008. ?
  5. S. Liu et al., “Role of microRNAs in the regulation of breast cancer stem cells,” J Mammary Gland Biol Neoplasia, DOI: 10.1007/s10911-012-9242-8, 2012. ?
  6. L. Li et al., “Activation of p53 by SIRT1 inhibition enhances elimination of CML leukemia stem cells in combination with imatinib,” Cancer Cell, 21:266-81, 2012. ?
  7. H. Korkaya et al., “HER2 regulates the mammary stem/progenitor cell population driving tumorigenesis and invasion,” Oncogene, 27:6120-30, 2008. ?
  8. S. Paik et al., “HER2 status and benefit from adjuvant trastuzumab in breast cancer,” N Engl J Med, 358:1409-11, 2008. ?
  9. S. Liu, M.S. Wicha “Targeting breast cancer stem cells,” J Clin Oncol, 25:4006-12, 2010. ?
  10. S.J. Conley et al., “Antiangiogenic agents increase breast cancer stem cells via the generation of tumor hypoxia,” PNAS, 109:2784-89, 2012. ?
  11. H. Korkaya et al., “Breast cancer stem cells, cytokine networks, and the tumor microenvironment,” J Clin Invest, 121:3804-09, 2011. ?
  12. A. Albini, M.B. Sporn, “The tumour microenvironment as a target for chemoprevention,” Nat Rev Cancer, 7:139-47, 2007. ?
  13. R. Kochhar et al.,”Statins reduce breast cancer risk: a case control study in US female veterans,” J Clin Oncol, ASCO Annual Meeting Proceedings 23:514, 2005. ?

 

Psoralidin, an Herbal Molecule from Psoralea corylifolia, Inhibits Phosphatidylinositol 3-Kinase–Mediated Akt Signaling in Androgen-Independent Prostate Cancer Cells

18th Wednesday, 2012  |   Herb or Compound, Prostate Cancer  |  no comments

Kumar R, Srinivasan S, Koduru S, et al. Cancer Prev Res March 2009 2; 234. doi: 10.1158/1940-6207.CAPR-08-0129

The protein kinase Akt plays an important role in cell proliferation and survival in many cancers, including prostate cancer. Due to its kinase activity, it serves as a molecular conduit for inhibiting apoptosis and promoting angiogenesis in most cell types. In most of the prostate tumors, Akt signaling is constitutively activated due to the deletion or mutation of the tumor suppressor PTEN, which negatively regulates phosphatidylinositol 3-kinase through lipid phosphatase activity. Recently, we identified a natural compound, psoralidin, which inhibits Akt phosphorylation, and its consequent activation in androgen-independent prostate cancer (AIPC) cells. Furthermore, ectopic expression of Akt renders AIPC cells resistant to chemotherapy; however, psoralidin overcomes Akt-mediated resistance and induces apoptosis in AIPC cells. While dissecting the molecular events, both upstream and downstream of Akt, we found that psoralidin inhibits phosphatidylinositol 3-kinase activation and transcriptionally represses the activation of nuclear factor-?B and its target genes (Bcl-2, Survivin, and Bcl-xL, etc.), which results in the inhibition of cell viability and induction of apoptosis in PC-3 and DU-145 cells. Interestingly, psoralidin selectively targets cancer cells without causing any toxicity to normal prostate epithelial cells. In vivo xenograft assays substantiate these in vitro findings and show that psoralidin inhibits prostate tumor growth in nude mice. Our findings are of therapeutic significance in the management of prostate cancer patients with advanced or metastatic disease, as they provide new directions for the development of a phytochemical-based platform for prevention and treatment strategies for AIPC.

PI3K/Akt signaling is a major component of the cell signaling network, as it is a focal point for a number of prosurvival pathways that modulate numerous transcriptional factors and genes involved in the regulation of cell proliferation, cell survival, angiogenesis, and tissue invasion (27). PTEN is a negative regulator of Akt, which often gets mutated or deleted in AIPC, resulting in Akt-mediated survival signaling, which confers chemotherapeutic resistance in AIPC (28). To effectively target PTEN-negative prostate tumors, more selective therapeutic approaches are needed; however, the low degree of specificity of compounds that are currently under investigation has been an impediment in realizing this goal (29). In this study, we have identified a chloroform-extractable natural compound, psoralidin, from Rasagenthi Lehyam, an herbal preparation, and have found it to be effective for the treatment of AIPC (30). Psoralidin is one of the active ingredients in the Psoralea corylifolia plant, which is extensively used in traditional medicines against many diseases, including cancer. We found that psoralidin targets PI3K-mediated Akt signaling, resulting in the inhibition of cell survival and induction of apoptosis in AIPC cells.

Our findings suggest that psoralidin inhibits pAkt (Ser473) in PC-3 and DU-145 cells without altering total levels of Akt. Our results also indicate that psoralidin inhibits pAkt after shorter exposure (3 hours), compared with commercially available Akt inhibitors. The complete down-regulation of pAkt by psoralidin suggests that it could be an excellent candidate to inhibit Akt-mediated signaling in prostate cancer. Psoralidin also inhibits Akt kinase activation, and as a result its direct substrate GSK-3 (31). Akt has been shown to phosphorylate GSK-3 (Ser21/9), which via the regulation of genes involved in cell cycle progression and survival plays a role in cell proliferation. Psoralidin inhibits the kinetics of pGSK-3?/? in a dose-dependent manner, thereby revealing that GSK-3 is directly regulated by Akt in AIPC cells. Further, GSK-3 is involved in the phosphorylation and degradation of the cell cycle regulatory protein, cyclin D1 (32), and our results showed that psoralidin down-regulates cyclin D1 in both the prostate cancer cell lines, suggesting that psoralidin is capable of inhibiting the complete Akt signaling pathway in prostate cancer cells, including its downstream targets. Further, overexpression of myr-Akt induces Akt phosphorylation and enhances cell growth in PC-3 and DU-145 (results not shown). Psoralidin, however, overcomes Akt-mediated resistance and induces apoptosis in Akt-overexpressed AIPC cells. Recently, it was found that phosphorylation and activation of Akt correlates with prostate tumor invasiveness (33) and high Gleason grade prostate cancers (34). As we know that Akt is involved in tumor aggressiveness and metastasis, psoralidin-mediated inhibition of Akt signaling might possess a therapeutic potential in sensitizing prostate cancer to apoptosis.

PI3K is one of the key activators of Akt signaling, and accumulating evidence implicates the involvement of the PI3K/Akt signaling as having a critical role in the development of several human malignancies, including prostate cancer (35, 36). Our results show that psoralidin inhibits the constitutive levels of PI3K p110 and p85 in a dose- and time-dependent manner. Our results also reveal that psoralidin blocks PI3K activation in both PC-3 and DU-145 cells. Several studies suggested that inhibition of the PI3K signaling results in the induction of apoptosis in AIPC (37, 38) and the PI3K pathway is currently a major therapeutic target for the treatment of cancer (39, 40); we believe that psoralidin is also one such compound that targets the PI3K/Akt pathway in AIPC cells.

We have previously shown that activation of NF-?B confers resistance to current treatments in AIPC (25), as activated NF-?B promotes tumor growth and curtails induction of apoptosis in AIPC (41, 42). Interestingly, psoralidin-mediated inhibition of NF-?B activation occurred in both PC-3 and DU-145 cells, suggesting that psoralidin not only selectively inhibits Akt but also targets other prosurvival signaling in prostate cancer. Although Akt-driven NF-?B activation is well established in many cancer cell types, epidermal growth factor receptor– and Her-2–mediated NF-?B activation via casein kinase II (CK-2) has also been reported in AIPC (43, 44). Inhibition of NF-?B activation by psoralidin suggests that not only Akt-mediated activation of NF-?B but also epidermal growth factor receptor– or Her-2–mediated NF-?B might be suppressed in prostate cancer.

In unstimulated conditions, NF-?B is sequestered in the cytoplasm as a heterodimer by the inhibitory protein I?B-? (45). In response to external stimuli, I?B? is rapidly phosphorylated, allowing the active dimers to translocate to the nucleus, thereby activating the target genes. In our results, we observed that psoralidin degrades the p65 in the cytosolic and nuclear fractions of both PC-3 and DU-145 cells. Recently, it was reported that PDLIM2 causes ubiquitination and degradation of p65 in several cell types (46) and, hence, it might be possible that psoralidin activates PDLIM2, thereby degrading p65 in AIPC cells. Interestingly, decreased expression of p50 was observed only in cytosol but not in nuclear extract of both the cell lines. This may be due to the fact that p50 is constitutively bound to the ?B binding sites in the promoter regions of the target genes, thereby inhibiting NF-?B activation in these cell lines (47). Additionally, NF-?B binding as well as promoter activation studies clearly suggested that psoralidin regulates NF-?B at the promoter level.

NF-?B regulates many prosurvival genes such as members of the Bcl-2 and IAP families, which suppress apoptosis (48). Therefore, we speculated that inhibition of NF-?B by psoralidin might result in the down-regulation of antiapoptotic Bcl-2 and Bcl-xL proteins; our results confirmed that there is indeed a complete inhibition of prosurvival signaling in both PC-3 and DU-145 cells. Down-regulation of endogenous as well as ectopic expression of Bcl-2 protein might lead to an alteration in the Bcl-2 to Bax ratio, which could trigger apoptosis through the mitochondrial pathway in these cells. Survivin, also a member of the inhibitor of apoptosis family, is overexpressed in the AIPC (49), and treatment with psoralidin resulted in a decrease in survivin expression over time (undetectable levels in both PC3 and DU-145 cells after 12 hours). Survivin has been shown to inhibit apoptosis by binding to active caspase-3 and caspase-7 (50). Thus, we observed that treatment of both the prostate cancer cell lines with psoralidin resulted in increased expression of active caspase-3 and caspase-7, which resulted in the induction of apoptosis.

In summary, this study shows that direct modulation of PI3K/Akt/NF-?B signaling activity by psoralidin causes apoptosis induction in AIPC cells, which could provide the molecular basis for therapeutic targeting of advanced prostate cancer with this compound. Considering the pivotal role of PI3K/Akt signaling in the pathogenesis of human prostate cancer, these findings may have significant clinical relevance, in the context that psoralidin could be developed as an agent for the management of prostate cancer, as a novel chemoprevention strategy, and/or as an effective therapeutic approach. Ongoing studies focus on fully dissecting the mechanism of action of psoralidin in a physiologic setting in the AIPC models and functionally linking the antitumor action of this (relatively safe and well-tolerated) phytochemical with the prevention of prostate cancer during prostate tumor progression to metastatic disease using in vivo model systems. The observations made in our in vivo studies may also enable us to conduct clinical trials with psoralidin to determine its chemotherapeutic and chemopreventive effects in human subjects.

Curcumin induces the apoptosis of human monocytic leukemia THP-1 cells via the activation of JNK/ERK Pathways

17th Tuesday, 2012  |   Herb or Compound  |  no comments


Curcumin is a principal compound of turmeric, commonly used to treat tumors and other diseases. However, its anti-cancer activity in human acute monocytic leukemia THP-1 cells is not clear. This study aimed to study the anti-cancer effect and action of curcumin on THP-1 cells.
Methods
THP-1 parental cells and PMA-treated THP-1 cells, were used as in vitro models to evaluate the anti-cancer effect and mechanism of curcumin. Apoptosis and its mechanism were evaluated by WST-1, flow cytometry and Western blotting. MAPK inhibitors were used to further confirm the molecular mechanism of curcumin-induced THP-1 cell apoptosis.
Results
Curcumin induced cell apoptosis of THP-1 cells as shown by cell viability, cell cycle analysis and caspase activity. Curcumin significantly increased the phosphorylation of ERK, JNK and their downstream molecules (c-Jun and Jun B). Inhibitor of JNK and ERK reduced the pro-apoptotic effect of curcumin on THP-1 cells as evidenced by caspase activity and the activation of ERK/JNK/Jun cascades. On the contrary, the pro-apoptotic effect of curcumin was abolished in the differentiated THP-1 cells mediated by PMA.
Conclusions
This study demonstrates that curcumin can induce the THP-1 cell apoptosis through the activation of JNK/ERK/AP1 pathways. Besides, our data suggest its novel use as an anti-tumor agent in acute monocytic leukemia.
Source:
Chu-Wen Yang, Chi-Lun Chang, Hsin-Chen Lee, Chin-Wen Chi, Jia-Ping Pan and Wen-Chin Yang. BMC Complementary and Alternative Medicine 2012, 12:22 doi:10.1186/1472-6882-12-22

Interleukin 6; Inflammation, Cancer and Immunomodulatory Drugs [IMiDs]

17th Tuesday, 2012  |   Others  |  no comments


INTRODUCTION
Chronic inflammation induced by biological, chemical, and physical factors has been associated with increased risk of human cancer at various sites. Inflammation activates a variety of inflammatory cells, which induce and activate several oxidant-generating enzymes such as NADPH oxidase, inducible nitric oxide synthase, myeloperoxidase, and eosinophil peroxidase. Interleukin-6 [IL-6] is a pro-inflammatory cytokine secreted by T cells and macrophages with a well-documented role in cancer. IL-6 and cancer morbidity in prostate and ovarian cancers, cancer reoccurrence rates and cancer symptoms such as cachexia and depression are all well recognised.
Therapeutic targeting of IL-6 and other inflammatory cytokines and their receptors in cancer has strong biologic rationale, and there is preliminary evidence suggesting that targeting of the IL-6 system may be beneficial in the treatment of cancer. Chinese herbal medicine (CHM) has a strong role to play in the regulation of IL-6 and can be used as an adjunctive compound along with chemo and radiotherapies. The use of CHM, herb formulas and extracts has been demonstrated to reduce IL-6, TNF-a and other inflammatory cytokines and help treat a variety of tumours and the symptoms of cancer.
METHODOLOGY
A retrospective review was performed using the following key words inflammation, cancer, IL-6, VEGF and TNF-a on the Medline database. A total of 58 manuscripts were sourced in Medline and a further 79 Chinese language journals, books and Internet sources were utilised. Inclusion criteria included prostate cancer, breast cancer and gastric cancer since all have been shown to have chronic inflammation associated with their angiogenesis and/or re-occurrence. This review has focused on recent articles (year 2000 or later) and some older historical references for background.
RESULTS
A number of herbs have been reported to reduce IL-6, TNF-a and VEGF including rheum palmatum / da huang (rabbits, small numbers), propolis / feng jiao (rat), euphorbia kansui / gan sui (rat), ganoderma lucidum / ling zhi (mice), phytolacca acinosa / shang lu (human), chrysanthemum indicum / ye ju hua (rabbits), Coptidis / huang lian (mice), Oldenlandiae diffusa / bai hua she she cao (in vitro), and epimedium sagittatum / yin yang huo (human). These studies were principally evaluating IL-6 levels in inflammatory processes and the effects on tumours and cancer symptoms and are generally limited by small numbers or animal models.
Several herbs have shown specific anti-cancer activities in regard to lowering the activity and/or blocking receptors of IL-6. Berberine, a compound extracted from Coptidis down-regulates IL-6 and has an anti-cachetic effect. One of the anti-inflammatory mechanisms of Pulsatilla could suppress the secretion of TNF, IL-1 and IL-6 from Kupffler Cells stimulated by Lipopolysaccharide. Further research studies suggest that Ganoderma has pro-apoptotic and anti-inflammatory functions, as well as inhibitory effects on cytokine expression during early inflammation in colonic carcinoma cells, which may be of significance in the use of Chinese herbal medicines.
CONCLUSION
CHM may play a role in modulating inflammatory markers, particularly IL-6. Several CHM extracts have shown anti-tumoural, apoptotic and anti-angiogenetic activities via down regulation of IL-6 and other inflammatory cytokines. These herbs may have a role in the treatment of a variety of cancers and their symptoms.

Daniel Weber