Ursolic Acid Analogs as Potential Therapeutics for Cancer.

Ursolic acid (UA) is a pentacyclic triterpene isolated from a large variety of vegetables, fruits and many traditional medicinal plants. It is a structural isomer of Oleanolic Acid. The medicinal application of UA has been explored extensively over the last two decades. The diverse pharmacological properties of UA include anti-inflammatory, antimicrobial, antiviral, antioxidant, anti-proliferative, etc. Especially, UA holds a promising position, potentially, as a cancer preventive and therapeutic agent due to its relatively non-toxic properties against normal cells but its antioxidant and antiproliferative activities against cancer cells. Cell culture studies have shown interference of UA with multiple pharmacological and molecular targets that play a critical role in many cells signaling pathways. Although UA is considered a privileged natural product, its clinical applications are limited due to its low absorption through the gastro-intestinal track and rapid elimination. The low bioavailability of UA limits its use as a therapeutic drug. To overcome these drawbacks and utilize the importance of the scaffold, many researchers have been engaged in designing and developing synthetic analogs of UA via structural modifications. This present review summarizes the synthetic UA analogs and their cytotoxic antiproliferative properties reported in the last two decades.

Design, Synthesis, and Molecular Docking Studies of Curcumin Hybrid Conjugates as Potential Therapeutics for Breast Cancer.

Curcumin (CUR) has received great attention over the past two decades due to its anticancer, anti-inflammatory, and antioxidant properties. Similarly, Dichloroacetate (DCA), an pyruvate dehydrogenase kinase 1 (PKD1) inhibitor, has gained huge attention as a potential anticancer drug. However, the clinical utility of these two agents is very limited because of the poor bioavailability and unsolicited side effects, respectively. We have synthesized fusion conjugates of CUR and DCA with an amino acids linker to overcome these limitations by utilizing the molecular hybridization approach. The molecular docking studies showed the potential targets of Curcumin-Modified Conjugates (CMCs) in breast cancer cells. We synthesized six hybrid conjugates named CMC1-6. These six CMC conjugates do not show any significant toxicity in a human normal immortalized mammary epithelial cell line (MCF10A) in vitro and C57BL/6 mice in vivo. However, treatment with CMC1 and CMC2 significantly reduced the growth and clonogenic survival by colony-formation assays in several human breast cancer cells (BC). Treatment by oral gavage of a transgenic mouse BC and metastatic BC tumor-bearing mice with CMC2 significantly reduced tumor growth and metastasis. Overall, our study provides strong evidence that CUR and DCA conjugates have a significant anticancer properties at a sub-micromolar concentration and overcome the clinical limitation of using CUR and DCA as potential anticancer drugs.

The andean anticancer herbal product BIRM causes destabilization of androgen receptor and induces caspase-8 mediated-apoptosis in prostate cancer.

BIRM is an anticancer herbal formulation from Ecuador. Previous study established its antitumor and antimetastatic activity against prostate cancer models. The activity of BIRM against human prostate cancer (PCa) cells was investigated to uncover its mechanism of antitumor activity. In androgen receptor (AR)-expressing PCa cells BIRM was 2.5-fold (250%) more cytotoxic in presence of androgen (DHT) compared to cells grown in the absence of DHT. In AR-positive cells (LAPC-4 and LNCaP) BIRM caused a dose and time-dependent down-regulation of AR and increased apoptosis. Exposing cells to BIRM did not affect the synthesis of AR and AR promoter activity but increased degradation of AR via proteasome-pathway. BIRM caused destabilization of HSP90-AR association in LAPC-4 cells. It induced apoptosis in PCa cells by activation of caspase-8 via death receptor and FADD-mediated pathways. A synthetic inhibitor of Caspase-8 cleavage (IETD-CHO) aborted BIRM-induced apoptosis. The effect of BIRM on AKT-mediated survival pathway in both AR+ and AR- negative (PC-3 and DU145) showed decreased levels of p-AKTser 473 in all PCa cell lines. BIRM dosed by oral gavage in mice bearing PC-3ML tumors showed selective efficacy on tumor growth; before tumors are established but limited efficacy when treated on existing tumors. Moreover, BIRM inhibited the LNCaP tumor generated by orthotropic implantation into dorsal prostate of nude mice. Partial purification of BIRM by liquid-liquid extraction and further fractionation by HPLC showed 4-fold increased specific activity on PCa cells. These results demonstrate a mechanistic basis of anti-tumor activity of the herbal extract BIRM.

Bioactive natural products for chemoprevention and treatment of castration-resistant prostate cancer.

Prostate cancer (PCa), a hormonally-driven cancer, ranks first in incidence and second in cancer related mortality in men in most Western industrialized countries. Androgen and androgen receptor (AR) are the dominant modulators of PCa growth. Over the last two decades multiple advancements in screening, treatment, surveillance and palliative care of PCa have significantly increased quality of life and survival following diagnosis. However, over 20% of patients initially diagnosed with PCa still develop an aggressive and treatment-refractory disease. Prevention or treatment for hormone-refractory PCa using bioactive compounds from marine sponges, mushrooms, and edible plants either as single agents or as adjuvants to existing therapy, has not been clinically successful. Major advancements have been made in the identification, testing and modification of the existing molecular structures of natural products. Additionally, conjugation of these compounds to novel matrices has enhanced their bio-availability; a big step towards bringing natural products to clinical trials. Natural products derived from edible plants (nutraceuticals), and common folk-medicines might offer advantages over synthetic compounds due to their broader range of targets, as compared to mostly single target synthetic anticancer compounds; e.g. kinase inhibitors. The use of synthetic inhibitors or antibodies that target a single aberrant molecule in cancer cells might be in part responsible for emergence of treatment refractory cancers. Nutraceuticals that target AR signaling (epigallocatechin gallate [EGCG], curcumin, and 5α-reductase inhibitors), AR synthesis (ericifolin, capsaicin and others) or AR degradation (betulinic acid, di-indolyl diamine, sulphoraphane, silibinin and others) are prime candidates for use as adjuvant or mono-therapies. Nutraceuticals target multiple pathophysiological mechanisms involved during cancer development and progression and thus have potential to simultaneously inhibit both prostate cancer growth and metastatic progression (e.g., inhibition of angiogenesis, epithelial-mesenchymal transition (EMT) and proliferation). Given their multi-targeting properties along with relatively lower systemic toxicity, these compounds offer significant therapeutic advantages for prevention and treatment of PCa. This review emphasizes the potential application of some of the well-researched natural compounds that target AR for prevention and therapy of PCa.

Polyphenol-rich extract of Pimenta dioica berries (Allspice) kills breast cancer cells by autophagy and delays growth of triple negative breast cancer in athymic mice.

Bioactive compounds from edible plants have limited efficacy in treating advanced cancers, but they have potential to increase the efficacy of chemotherapy drugs in a combined treatment. An aqueous extract of berries of Pimenta dioica (Allspice) shows promise as one such candidate for combination therapy or chemoprevention. An aqueous extract of Allspice (AAE) was tested against human breast cancer (BrCa) cells in vitro and in vivo. AAE reduced the viability and clonogenic growth of several types of BrCa cells (IC50 ≤ 100 µg/ml) with limited toxicity in non-tumorigenic, quiescent cells (IC50 >200 µg/ml). AAE induced cytotoxicity in BrCa was inconsistent with apoptosis, but was associated with increased levels of autophagy markers LC3B and LC3B-positive puncta. Silencing the expression of autophagy related genes (ATGs) prevented AAE-induced cell death. Further, AAE caused inhibition of Akt/mTOR signaling, and showed enhanced cytotoxicity when combined with rapamycin, a chemotherapy drug and an inhibitor of mTOR signaling. Oral administration (gavage) of AAE into athymic mice implanted with MDA-MB231 tumors inhibited tumor growth slightly but not significantly (mean decrease ~ 14%, p ≥ 0.20) if mice were gavaged post-tumor implant. Tumor growth showed a significant delay (38%) in tumor palpability and growth rate (time to reach tumor volume ≥ 1,000 mm3) when mice were pre-dosed with AAE for two weeks. Analysis of tumor tissues showed increased levels of LC3B in AAE treated tumors, indicating elevated autophagic tumor cell death in vivo in treated mice. These results demonstrate antitumor and chemo-preventive activity of AAE against BrCa and potential for adjuvant to mTOR inhibition.

A multi-targeted approach to suppress tumor-promoting inflammation.

Cancers harbor significant genetic heterogeneity and patterns of relapse following many therapies are due to evolved resistance to treatment. While efforts have been made to combine targeted therapies, significant levels of toxicity have stymied efforts to effectively treat cancer with multi-drug combinations using currently approved therapeutics. We discuss the relationship between tumor-promoting inflammation and cancer as part of a larger effort to develop a broad-spectrum therapeutic approach aimed at a wide range of targets to address this heterogeneity. Specifically, macrophage migration inhibitory factor, cyclooxygenase-2, transcription factor nuclear factor-κB, tumor necrosis factor alpha, inducible nitric oxide synthase, protein kinase B, and CXC chemokines are reviewed as important antiinflammatory targets while curcumin, resveratrol, epigallocatechin gallate, genistein, lycopene, and anthocyanins are reviewed as low-cost, low toxicity means by which these targets might all be reached simultaneously. Future translational work will need to assess the resulting synergies of rationally designed antiinflammatory mixtures (employing low-toxicity constituents), and then combine this with similar approaches targeting the most important pathways across the range of cancer hallmark phenotypes.

Medicinal properties of the Jamaican pepper plant Pimenta dioica and Allspice.

The Caribbean tropical tree, Pimenta dioica has been used for a variety of human endeavors, such as in perfumery industry, food spice, as a natural pesticide, and in folk medicine. Discovered in Jamaica during the voyages of Christopher Columbus, the dried unripe berries of P. dioica also known as Allspice can be found in all continents with unique names in over 50 languages. Systematic investigation of aromatic constituents of Pimenta leaves and its unripe berries, Allspice, have resulted in discovery of many and novel aromatic compounds, mostly glycosides and polyphenols that show antibacterial, hypotensive, anti-neuralgic and analgesic properties. Recent studies have shown two of the known compounds isolated from Allspice, Eugenol and Gallic acid have selective antiproliferative and anti-tumor properties on human cancer cells and their animal models. New characterization of novel compounds such as Ericifolin from the aqueous extract of Allspice berries show potent anti-prostate cancer and anti-breast cancer properties that can be verified in vitro as well as in vivo. Considering its purity, mostly available as "organically grown" berries, availability at low cost, wide acceptance in culinary delights of many cultures world-wide, Allspice may have an additional space in most households, in their medicine cabinets.

Achyranthes aspera (Apamarg) leaf extract inhibits human pancreatic tumor growth in athymic mice by apoptosis.

ETHNOPHARMACOLOGICAL RELEVANCE: Achyranthes aspera (Family Amaranthacea) is used for cancer therapy by ayurvedic medical practitioners in India. However, due to the non formal nature of its use, there are no systematic studies validating its medicinal properties. Thus, it's utility as an anti cancer agent remains anecdotal. Earlier, we demonstrated A. aspera to exhibit time and dose-dependent preferential cytotoxicity to cultured human pancreatic cancer cells. In this report we validate in vivo anti tumor properties of A. aspera. MATERIALS AND METHODS: The in vivo anti tumor activity of leaf extract (LE) was tested by intraperitoneal (IP) injections into athymic mice harboring human pancreatic tumor subcutaneous xenograft. Toxicity was monitored by recording changes in behavioral, histological, hematological and body weight parameters. RESULTS: Dosing LE to athymic mice by I.P. injection for 32 days showed no adverse reactions in treated mice. Compared to the control set, IP administration of LE to tumor bearing mice significantly reduced both tumor weight and volume. Gene expression analysis using Real time PCR methods revealed that LE significantly induced caspase-3 mRNA (p<0.001) and suppressed expression of the pro survival kinase Akt-1 (p<0.05). TUNEL assay and immunohistochemistry confirmed apoptosis induction by activation of caspase-3 and inhibiting Akt phosphorylation in treated sets. These results are in agreement with RT PCR data. CONCLUSION: Taken together, these data suggest A. aspera to have potent anti cancer property.

Inhibition of cyclooxygenase (COX)-2 expression by Tet-inducible COX-2 antisense cDNA in hormone-refractory prostate cancer significantly slows tumor growth and improves efficacy of chemotherapeutic drugs.

PURPOSE: Overexpression of the proinflammatory enzyme cyclooxygenase (COX)-2 is associated with the progression of various malignancies; the role of COX-2 in prostate cancer is less clear. The significance of COX-2 in prostate cancer growth and response to chemotherapy was investigated in an androgen-refractory prostate cancer cell line using a Tet-inducible antisense COX-2 expression system. EXPERIMENTAL DESIGN: An antisense COX-2 cDNA construct under the control of a doxycycline-inducible promoter was transfected into a prostate cancer cell line, PC-3ML. Modulations of cell growth, apoptosis, and chemosensitivity in the presence or absence of doxycycline were analyzed. Tumor incidence, growth rate, and response to two cytotoxic drugs, COL-3 [chemically modified tetracycline-3-(6-demethyl-6-deoxy-4-dedimethylamino-tetracycline)] and Taxotere (docetaxel), were investigated in tumor xenografts. Apoptotic incidences and tumor microvessel density in tumors were determined by immunohistochemistry. RESULTS: Conditional suppression of COX-2 in PC-3ML caused reduced cell proliferation, decreased levels of phosphorylated AKT, G(0)-G(1) arrest, and increased apoptosis and caspase-3 activity. Suppression of COX-2 increased Bax protein and decreased Bcl-x(L) protein in vitro. COX-2 antisense-expressing PC-3ML tumors showed a 57% growth delay compared with nontransfected or vector controls. Oral administration of COL-3 (40 mg/kg, oral gavage) or Taxotere (2.3 mg/kg, intraperitoneally; 3x per week) in tumor-bearing mice further slowed tumor growth (65% and approximately 94%, respectively). Compared with the control group, the occurrence of apoptosis in antisense COX-2 tumors was eight times higher, and the tumor microvessel density was three times lower. CONCLUSIONS: These results provide direct evidence that constitutive expression of COX-2 in prostate cancer has both angiogenic and cytoprotective functions. Suppression of tumor cell COX-2 is sufficient to enhance chemotherapy response in prostate cancer.