Animesh Dhar

DNA methyltransferases: a novel target for prevention and therapy

Cancer is the second leading cause of death in US. Despite the emergence of new, targeted agents, and the use of various therapeutic combinations, none of the available treatment options are curative in patients with advanced cancer. Epigenetic alterations are increasingly recognized as valuable targets for the development of cancer therapies. DNA methylation at the 5-position of cytosine, catalyzed by DNA methyltransferases (DNMTs), is the predominant epigenetic modification in mammals. DNMT1, the major enzyme responsible for maintenance of the DNA methylation pattern is located at the replication fork and methylates newly biosynthesized DNA. DNMT2 or TRDMT1, the smallest mammalian DNMT is believed to participate in the recognition of DNA damage, DNA recombination, and mutation repair. It is composed solely of the C-terminal domain, and does not possess the regulatory N-terminal region. The levels of DNMTs, especially those of DNMT3B, DNMT3A, and DNMT3L, are often increased in various cancer tissues and cell lines, which may partially account for the hypermethylation of promoter CpG-rich regions of tumor suppressor genes in a variety of malignancies. Moreover, it has been shown to function in self-renewal and maintenance of colon cancer stem cells and need to be studied in several cancers. Inhibition of DNMTs has demonstrated reduction in tumor formation in part through the increased expression of tumor suppressor genes. Hence, DNMTs can potentially be used as anti-cancer targets. Dietary phytochemicals also inhibit DNMTs and cancer stem cells; this represents a promising approach for the prevention and treatment of many cancers.

Crocetin: an Agent Derived from Saffron for Prevention and Therapy for Cancer

Cancer is one of the leading causes of death in the United States and accounts for approximately 8 million deaths per year worldwide. Although there is an increasing number of therapeutic options available for patients with cancer, their efficacy is time-limited and non-curative. Approximately 50-60% cancer patients in the United States utilize agents derived from different parts of plants or nutrients (complementary and alternative medicine), exclusively or concurrently with traditional therapeutic regime such as chemotherapy and/or radiation therapy. The need for new drugs has prompted studies evaluating possible anti-cancer agents in fruits, vegetables, herbs and spices. Saffron, a spice and a food colorant present in the dry stigmas of the plant Crocus sativus L., has been used as an herbal remedy for various ailments including cancer by the ancient Arabian, Indian and Chinese cultures. Crocetin, an important carotenoid constituent of saffron, has shown significant potential as an anti-tumor agent in animal models and cell culture systems. Crocetin affects the growth of cancer cells by inhibiting nucleic acid synthesis, enhancing anti-oxidative system, inducing apoptosis and hindering growth factor signaling pathways. This review discusses the studies on cancer preventive potential of crocetin and its future use as an anticancer agent.

Crocetin inhibits pancreatic cancer cell proliferation and tumor progression in a xenograft mouse model

Crocetin, a carotenoid compound derived from saffron, has long been used as a traditional ancient medicine against different human diseases including cancer. The aim of the series of experiments was to systematically determine whether crocetin significantly affects pancreatic cancer growth both in vitro and/or in vivo. For the in vitro studies, first, MIA-PaCa-2 cells were treated with crocetin and in these sets of experiments, a proliferation assay using H3-thymidine incorporation and flow cytometric analysis suggested that crocetin inhibited proliferation. Next, cell cycle proteins were investigated. Cdc-2, Cdc-25C, Cyclin-B1, and epidermal growth factor receptor were altered significantly by crocetin. To further confirm the findings of inhibition of proliferation, H3-thymidine incorporation in BxPC-3, Capan-1, and ASPC-1 pancreatic cancer cells was also significantly inhibited by crocetin treatment. For the in vivo studies, MIA-PaCa-2 as highly aggressive cells than other pancreatic cancer cells used in this study were injected into the right hind leg of the athymic nude mice and crocetin was given orally after the development of a palpable tumor. The in vivo results showed significant regression in tumor growth with inhibition of proliferation as determined by proliferating cell nuclear antigen and epidermal growth factor receptor expression in the crocetin-treated animals compared with the controls. Both the in vitro pancreatic cancer cells and in vivo athymic nude mice tumor, apoptosis was significantly stimulated as indicated by Bax/Bcl-2 ratio. This study indicates that crocetin has a significant antitumorigenic effect in both in vitro and in vivo on pancreatic cancer. [Mol Cancer Ther 2009;8(2):315–23]

Cellular energetics in hemorrhagic shock: Restoring adenosine triphosphate to the cells

BACKGROUND This is a review of studies with two agents, glutamine and crocetin, which have been found to enhance recovery of cellular adenosine triphosphate (ATP) and adenosine diphosphate after hemorrhagic shock. METHODS The studies used a sublethal (30 minutes) reservoir shock model in 300- to 350-g, male, Sprague-Dawley rats, using either ketamine-xylazine or isoflurane anesthesia. Glutamine was given as a 3% (21 mmol/L) solution in Ringers lactate (630 mg/kg). Crocetin was given as a 500 nmol/L solution in Ringers lactate (2 mg/kg). RESULTS Both glutamine and crocetin caused recovery of ATP to baseline levels (9.0 micromol/g) within 60 to 120 minutes after resuscitation. Xanthine levels returned more rapidly to baseline (0.1 micromol/g). Both agents prevented the elevation in apoptosis seen in controls at 24 and 48 hours. CONCLUSION Glutamine is a metabolic substrate and a precursor of ATP synthesis. Crocetin enhances oxygen diffusivity in plasma. Both agents restore cellular energy stores to normal after hemorrhagic shock and produce a marked diminution in the extent of apoptosis postshock. Their mechanism of action probably involves prevention of mitochondrial damage.

Glutamine administration during total parenteral nutrition protects liver adenosine nucleotides during and after subsequent hemorrhagic shock.

BACKGROUND Glutamine supplementation of total parenteral nutrition (TPN) in stressed patients has been advocated. To determine whether glutamine supplementation affects the host response to conditions of stress, animals were given TPN with or without glutamine for 7 days. They were then subjected to the acute stress of hemorrhagic shock, which results in marked loss of hepatic adenosine triphosphate (ATP) and adenosine diphosphate (ADP), with accumulation of adenosine monophosphate (AMP) and the metabolites adenosine, inosine, hypoxanthine, and xanthine. This loss of ATP and accumulation of metabolites contributes to subsequent tissue damage. The hypothesis of the study was that glutamine supplementation would significantly improve restoration of hepatic adenosine nucleotides before and after hemorrhagic shock. METHODS Sprague-Dawley rats were given TPN for 7 days. One half of the animals (n = 8) received TPN supplemented with glutamine, while one half received TPN with an isonitrogenous mixture of alanine and glycine. Animals were subjected to hemorrhagic shock for 30 minutes and then resuscitated using only heparinized shed blood. Liver biopsies were taken pre- and post-shock, and at 30 and 60 minutes after resuscitation. ATP, ADP, AMP, and their metabolites were measured using gradient high-performance liquid chromatography. RESULTS After 7 days of TPN, baseline values of ATP, ADP, AMP, and metabolites were similar between the 2 groups before the initiation of shock. Glutamine-treated animals manifested a 40% decrease in ATP level immediately after shock and recovered to 90% of baseline within 60 minutes. By contrast, the control animals manifested a 66% decrease in ATP level after the shock period and recovered only to 60% of baseline at 1 hour postresuscitation. Similar changes were observed in ADP levels and were accompanied by corresponding changes in AMP and adenosine metabolites, all of which rose during shock and fell after resuscitation. CONCLUSIONS Glutamine supplementation significantly protected the liver from tissue damage caused by hemorrhagic shock. ATP levels remained higher during shock and recovered more rapidly after resuscitation. Glutamine supplementation may help to protect cellular energy stores in the stressed organism and may offer opportunities for therapeutic intervention during and after stress.

Honokiol radiosensitizes colorectal cancer cells: enhanced activity in cells with mismatch repair defects

DNA mismatch repair is required for correcting any mismatches that are created during replication and recombination, and a defective mismatch repair system contributes to DNA damage-induced growth arrest. The colorectal cancer cell line HCT116 is known to have a mutation in the hMLH1 mismatch repair gene resulting in microsatellite instability and defective mismatch repair. Honokiol is a biphenolic compound that has been used in traditional Chinese medicine for treating various ailments including cancer. This study was designed to test the hypothesis that honokiol enhances the radiosensitivity of cancer cells with mismatch repair defect (HCT116) compared with those that are mismatch repair proficient (HCT116-CH3). We first determined that the combination of honokiol and γ-irradiation treatment resulted in dose-dependent inhibition of proliferation and colony formation in both cell lines. However, the effects were more pronounced in HCT116 cells. Similarly, the combination induced higher levels of apoptosis (caspase 3 activation, Bax to Bcl2 ratio) in the HCT116 cells compared with HCT116-CH3 cells. Cell cycle analyses revealed higher levels of dead cells in HCT116 cells. The combination treatment reduced expression of cyclin A1 and D1 and increased phosphorylated p53 in both cell lines, although there were significantly lower amounts of phosphorylated p53 in the HCT116-CH3 cells, suggesting that high levels of hMLH1 reduce radiosensitivity. These data demonstrate that honokiol is highly effective in radiosensitizing colorectal cancer cells, especially those with a mismatch repair defect.

Crocetinic acid inhibits hedgehog signaling to inhibit pancreatic cancer stem cells

Pancreatic cancer is the fourth leading cause of cancer deaths in the US and no significant treatment is currently available. Here, we describe the effect of crocetinic acid, which we purified from commercial saffron compound crocetin using high performance liquid chromatography. Crocetinic acid inhibits proliferation of pancreatic cancer cell lines in a dose- and time-dependent manner. In addition, it induced apoptosis. Moreover, the compound significantly inhibited epidermal growth factor receptor and Akt phosphorylation. Furthermore, crocetinic acid decreased the number and size of the pancospheres in a dose-dependent manner, and suppressed the expression of the marker protein DCLK-1 (Doublecortin Calcium/Calmodulin-Dependent Kinase-1) suggesting that crocetinic acid targets cancer stem cells (CSC). To understand the mechanism of CSC inhibition, the signaling pathways affected by purified crocetinic acid were dissected. Sonic hedgehog (Shh) upon binding to its cognate receptor patched, allows smoothened to accumulate and activate Gli transcription factor. Crocetinic acid inhibited the expression of both Shh and smoothened. Finally, these data were confirmed in vivo where the compound at a dose of 0.5 mg/Kg bw suppressed growth of tumor xenografts. Collectively, these data suggest that purified crocetinic acid inhibits pancreatic CSC, thereby inhibiting pancreatic tumorigenesis.

Molecular basis of protective effect by crocetin on survival and liver tissue damage following hemorrhagic shock.

Hemorrhagic shock (HS) causes reduction of cellular energy stores, as measured by levels of ATP and ADP. Furthermore, energy depletion may cause mitochondrial damage, which in turn leads to cell death by apoptosis. The hypothesis of the present study is that by enhancing the recovery of cellular ATP and ADP and mitochondrial damage can be reduced, and the extent of apoptosis minimized. Crocetin, a carotenoid compound, appears to enhance the diffusion of oxygen in aqueous solution, and hence may improve energy stores both to the cell and within it. HS was produced in Sprague–Dawley rats by withdrawing blood from the carotid cannula until a mean arterial pressure of 35–40 mm Hg was reached, and then maintained by further withdrawals of blood for 30 and 60 min. Crocetin was administered 2–4 mg/kg in resuscitation fluid through venus cannula and the animals survived for 24–48 h after HS. Experiments designed to promote tissue reconstitution of ATP using crocetin indicate that these approaches are successful in increasing ATP post-hemorrhage and survival. Crocetin treatment also inhibited cellular damage as indicated by increase of Bcl-2 following decrease in cytosolic cytochrome c and caspase-3 after resuscitation. The prolonged energy deficit seen after hemorrhagic shock can produce late damage and rapid restoration of ATP levels to baseline can reduce apoptosis. In conclusions, crocetin can minimize the cellular damage as evidenced by apoptosis and increased the survival of rats. (Mol Cell Biochem 278: 139–146, 2005)

Quinomycin A targets Notch signaling pathway in pancreatic cancer stem cells

Cancer stem cells (CSCs) appear to explain many aspects of the neoplastic evolution of tumors and likely account for enhanced therapeutic resistance following treatment. Dysregulated Notch signaling, which affects CSCs plays an important role in pancreatic cancer progression. We have determined the ability of Quinomycin to inhibit CSCs and the Notch signaling pathway. Quinomycin treatment resulted in significant inhibition of proliferation and colony formation in pancreatic cancer cell lines, but not in normal pancreatic epithelial cells. Moreover, Quinomycin affected pancreatosphere formation. The compound also decreased the expression of CSC marker proteins DCLK1, CD44, CD24 and EPCAM. In addition, flow cytometry studies demonstrated that Quinomycin reduced the number of DCLK1+ cells. Furthermore, levels of Notch 1–4 receptors, their ligands Jagged1, Jagged2, DLL1, DLL3, DLL4 and the downstream target protein Hes-1 were reduced. The γ-secretase complex proteins, Presenilin 1, Nicastrin, Pen2, and APH-1, required for Notch activation also exhibited decreased expression. Ectopic expression of the Notch Intracellular Domain (NICD) partially rescued the cells from Quinomycin mediated growth suppression. To determine the effect of Quinomycin on tumor growth in vivo, nude mice carrying tumor xenografts were administered Quinomycin intraperitoneally every day for 21 days. Treatment with the compound significantly inhibited tumor xenograft growth, coupled with significant reduction in the expression of CSC markers and Notch signaling proteins. Together, these data suggest that Quinomycin is a potent inhibitor of pancreatic cancer that targets the stem cells by inhibiting Notch signaling proteins.

Bitter melon extracts enhance the activity of chemotherapeutic agents through the modulation of multiple drug resistance.

Recently, we demonstrated that extracts of bitter melon (BME) can be used as a preventive/therapeutic agent in colon cancers. Here, we determined BME effects on anticancer activity and bioavailability of doxorubicin (DOX) in colon cancer cells. BME enhanced the effect of DOX on cell proliferation and sensitized the cells toward DOX upon pretreatment. Furthermore, there was both increased drug uptake and reduced drug efflux. We also observed a reduction in the expression of multidrug resistance conferring proteins (MDRCP) P-glycoprotein, MRP-2, and BCRP. Further BME suppressed DOX efflux in MDCK cells overexpressing the three efflux proteins individually, suggesting that BME is a potent inhibitor of MDR function. Next, we determined the effect of BME on PXR, a xenobiotic sensing nuclear receptor and a transcription factor that controls the expression of the three MDR genes. BME suppressed PXR promoter activity thereby suppressing its expression. Finally, we determined the effect of AMPK pathway on drug efflux because we have previously demonstrated that BME affects the pathway. However, inhibiting AMPK did not affect drug resistance, suggesting that BME may use different pathways for the anticancer and MDR modulating activities. Together, these results suggest that BME can enhance the bioavailability and efficacy of conventional chemotherapy.