[DLys(6)]-luteinizing hormone releasing hormone-curcumin conjugate inhibits pancreatic cancer cell growth in vitro and in vivo

Reconnoitering the Therapeutic Role of Curcumin in Disease Prevention and Treatment: Lessons Learnt and Future Directions

Turmeric is a plant with a very long history of medicinal use across different cultures. Curcumin is the active part of turmeric, which has exhibited various beneficial physiological and pharmacological effects. This review aims to critically appraise the corpus of literature associated with the above pharmacological properties of curcumin, with a specific focus on antioxidant, anti-inflammatory, anticancer and antimicrobial properties. We have also reviewed the different extraction strategies currently in practice, highlighting the strengths and drawbacks of each technique. Further, our review also summarizes the clinical trials that have been conducted with curcumin, which will allow the reader to get a quick insight into the disease/patient population of interest with the outcome that was investigated. Lastly, we have also highlighted the research areas that need to be further scrutinized to better grasp curcumin’s beneficial physiological and medicinal properties, which can then be translated to facilitate the design of better bioactive therapeutic leads.

Source and exploration of the peptides used to construct peptide-drug conjugates

Peptide-drug conjugates (PDCs) are a class of novel molecules widely designed and synthesized for delivering payload drugs. The peptide part plays a vital role in the whole molecule, because they determine the ability of the molecules to penetrate the membrane and target to the specific targets. Here, we introduce the source of different kinds of cell-penetrating peptides (CPPs) and cell-targeting peptides (CTPs) that have been used or could be used in constructing PDCs as well as their latest application in delivering drugs. What's more, the approaches of developing CPPs and CTPs and the techniques to discover novel peptides are focused on and summarized in the review. This review aims to help relevant researchers fast understand the research status of peptides in PDCs and carry forward the process of novel peptides discovery.

Synthesis of Radiolabeled Technetium- and Rhenium-Luteinizing Hormone-Releasing Hormone (99mTc/Re-Acdien-LHRH) Conjugates for Targeted Detection of Breast Cancer Cells Overexpressing the LHRH Receptor

Currently, ^186/188Re and ^99mTc are widely used radionuclides for cancer detection and diagnosis. New advancements in modalities and targeting strategies of radiopharmaceuticals will provide an opportunity to enhance imagery and detection of smaller colonies of cancer cells while lowering false-positive diagnoses. To understand the chemistry of agents derived from fac-[^99mTc(CO)₃(H₂O)₃]⁺ species, the nonradioactive [Re(CO)₃(H₂O)₃]⁺ analogue was used. We have designed and synthesized Re-Acdien-LHRH, Re-Acdien-peg-LHRH, and a radiolabeled ^99mTc-Acdien-LHRH (rhenium- and technetium-luteinizing hormone-releasing hormone) conjugates using a tridentate linker to detect cancers overexpressing the LHRH receptor. Re-Acdien-LHRH and Re-Acdien-peg-LHRH were synthesized from non-PEGylated and PEGylated LHRH-Acdien, respectively. Cellular uptake of the compounds ^99mTc-Acdien-LHRH, Re-Acdien-LHRH, and Re-Acdien-peg-LHRH was found to be significantly enhanced compared to that of untargeted ^99mTc alone and unlabeled [Re(CO)₃(H₂O)₃]⁺. In addition, the conjugate compounds showed no difference in cellular toxicity compared to untargeted ^99mTc alone or unlabeled [Re(CO)₃(H₂O)₃]⁺. Further, a competition assay using LHRH indicated selective targeting of Re-Acdien-peg-LHRH toward the LHRH receptor (p < 0.05) compared to that of [Re(CO)₃(H₂O)₃]⁺ alone. Together, our data show the design paradigm and synthesis of targeting radionuclides using the LHRH peptide. Our data suggests that utilizing the LHRH peptide can lead to selective targeting and diagnosis of breast cancers expressing the LHRH receptor.

Novel Crizotinib-GnRH Conjugates Revealed the Significance of Lysosomal Trapping in GnRH-Based Drug Delivery Systems

Several promising anti-cancer drug–GnRH (gonadotropin-releasing hormone) conjugates have been developed in the last two decades, although none of them have been approved for clinical use yet. Crizotinib is an effective multi-target kinase inhibitor, approved against anaplastic lymphoma kinase (ALK)- or ROS proto-oncogene 1 (ROS-1)-positive non-small cell lung carcinoma (NSCLC); however, its application is accompanied by serious side effects. In order to deliver crizotinib selectively into the tumor cells, we synthesized novel crizotinib analogues and conjugated them to a [d-Lys⁶]–GnRH-I targeting peptide. Our most prominent crizotinib–GnRH conjugates, the amide-bond-containing [d-Lys⁶(crizotinib*)]–GnRH-I and the ester-bond-containing [d-Lys⁶(MJ55*)]–GnRH-I, were able to bind to GnRH-receptor (GnRHR) and exert a potent c-Met kinase inhibitory effect. The efficacy of compounds was tested on the MET-amplified and GnRHR-expressing EBC-1 NSCLC cells. In vitro pharmacological profiling led to the conclusion that that crizotinib–GnRH conjugates are transported directly into lysosomes, where the membrane permeability of crizotinib is diminished. As a consequence of GnRHR-mediated endocytosis, GnRH-conjugated crizotinib bypasses its molecular targets—the ATP-binding site of RTKs— and is sequestered in the lysosomes. These results explained the lower efficacy of crizotinib–GnRH conjugates in EBC-1 cells, and led to the conclusion that drug escape from the lysosomes is a major challenge in the development of clinically relevant anti-cancer drug–GnRH conjugates.

Synthesis and Cytotoxic Study of a Platinum(IV) Anticancer Prodrug with Selectivity toward Luteinizing Hormone-Releasing Hormone (LHRH) Receptor-Positive Cancer Cells

Platinum drugs including cisplatin are widely used in clinics to treat various types of cancer. However, the lack of cancer-cell selectivity is one of the major problems that lead to side effects in normal tissues. Luteinizing hormone-releasing hormone (LHRH) receptors are overexpressed in many types of cancer cells but rarely presented in normal cells, making LHRH receptor a good candidate for cancer targeting. In this study, we report the synthesis and cytotoxic study of a novel platinum(IV) anticancer prodrug functionalized with LHRH peptide. This LHRH-platinum(IV) conjugate is highly soluble in water and quite stable in a PBS buffer. Cytotoxic study reveals that the prodrug selectively targets LHRH receptor-positive cancer cell lines with the cytotoxicities 5-8 times higher than those in LHRH receptor-negative cell lines. In addition, the introduction of LHRH peptide enhances the cellular accumulation in a manner of receptor-mediated endocytosis. Moreover, the LHRH-platinum(IV) prodrug is proved to kill cancer cells by binding to the genomic DNA, inducing apoptosis, and arresting the cell cycle at the G₂/M phase. In summary, we report a novel LHRH-platinum(IV) anticancer prodrug having largely improved selectivity toward LHRH receptor-positive cancer cells, relative to cisplatin.

Synthesis and Biological Studies of New Multifunctional Curcumin Platforms for Anticancer Drug Delivery

BACKGROUND

Scientists have extensively investigated curcumin, yielding many publications on treatments of cancer. Numerous derivatives of curcumin were synthesized, evaluated for their anti-oxidant and free-radical scavenging, SAR, ADME properties and tested in anticancer applications.

OBJECTIVE

We decided to exploit curcumin as a bioactive core platform for carrying anticancer drugs, which likely possesses a carboxyl moiety for potential linkage to the carrier for drug delivery.

METHODS

The goal of this work is to develop biolabile multifunctional curcumin platforms towards anticancer drug delivery, including determination of drug release profiling in hydrolytic media, in vitro cytotoxicity, antioxidant properties and blockage of relevant cell survival pathways.

RESULTS

We report on a facile synthesis of the bioactive multifunctional curcumin-based platforms linked to a variety of anticancer drugs like amonafide and chlorambucil, and release of the drugs in a hydrolytic environment. The leading curcumin-based platform has presented antioxidant activity similar to curcumin, but with much more potent cytotoxicity in vitro in agreement with the augmented blockage of the NF-kB cell survival pathway.

CONCLUSION

The approach presented here may prove beneficial for bioactive curcumin-based delivery applications where multiple drug delivery is required in a consecutive and controlled mode.

Cancer-targeted delivery systems based on peptides

There is a growing interest for the discovery of new cancer-targeted delivery systems for drug delivery and diagnosis. A synopsis of the bibliographic data will be presented on bombesin, neurotensin, octreotide, Arg-Gly-Asp, luteinizing hormone-releasing hormone and other peptides. Many of them have reached the clinics for therapeutic or diagnostic purposes, and have been utilized as carriers of known cytotoxic agents such as doxorubicin, paclitaxel, cisplatin, methotrexate or dyes and radioisotopes. In our article, recent advances in the development of peptides as carriers of cytotoxic drugs or radiometals will be analyzed.

Curcumin-Conjugated Gold Clusters for Bioimaging and Anticancer Applications

Curcumin-conjugated gold clusters (CUR-AuNCs) were synthesized using a "green" procedure and utilized as an anticancer and a bioimaging agent. Curcumin is a well-known anticancer agent, which forms a cluster when reacting with a gold precursor under mild alkali condition. A fluorescence spectroscopy analysis showed that the CUR-AuNCs emitted red fluorescence (650 nm) upon visible light (550) irradiation. Fourier transform infrared spectroscopy analysis confirmed the stretching and bending nature between the gold atoms and curcumin. Meanwhile, transmission electron microscopy analysis showed a cluster of approximately 1-3 nm with a uniform size. Time-resolved fluorescence analysis demonstrated that the red fluorescence was highly stable. Moreover, laser confocal imaging and atomic force microscopy analysis illustrated that a cluster was well distributed in the cell. This cluster exhibited less toxicity in the mortal cell line (COS-7) and high toxicity in the cervical cancer cell line (HeLa). The results demonstrated the conjugation of curcumin into the fluorescent gold cluster as a potential material for anticancer therapy and bioimaging applications.

Therapeutic Potential of Curcumin in Treatment of Pancreatic Cancer: Current Status and Future Perspectives

Pancreatic cancer is among the leading cause of deaths due to cancer with extremely poor prognosis. Gemcitabine is being used in the treatment of patient with pancreatic ductal adenocarcinoma (PDAC), although, the response rate is bellow 12%. A recent phase III trial revealed that FOLFIRINOX could be an option for the treatment of metastatic PDAC patients, although it is associated with increased toxicity. Therefore, identification of novel agents that either improves gemcitabine activity, within novel combinatorial approaches, or with a better efficacy than gemcitabine is warranted. The antitumor activity of curcumin in several tumors, including prostate, breast and colorectal cancers have investigated. A recent phase II trial explored the effects of curcumin in advanced pancreatic cancer patient. They found that oral curcumin was well tolerated. Another trial showed the activity of 8,000 mg of curcumin in combination with gemcitabine in patients with advanced pancreatic cancer. This review summarizes the current knowledge about possible molecular mechanisms of curcumin in PDAC with particular emphasis on preclinical/clinical studies in pancreatic cancer treatment. J. Cell. Biochem. 118: 1634-1638, 2017. © 2017 Wiley Periodicals, Inc.

Synthesis, characterization and systematic comparison of FITC-labelled GnRH-I, -II and -III analogues on various tumour cells

Targeted tumour therapy is the focus of recent cancer research. Gonadotropin-releasing hormone (GnRH) analogues are able to deliver anticancer agents selectively into tumour cells, which highly express GnRH receptors. However, the effectiveness of different analogues as targeting moiety in drug delivery systems is rarely compared, and the investigated types of cancer are also limited. Therefore, we prepared selectively labelled, fluorescent derivatives of GnRH-I, -II and -III analogues, which were successfully used for drug targeting. In this manuscript, we investigated these analogues' solubility, stability and passive membrane permeability and compared their cellular uptake by various cancer cells. We found that these labelled GnRH conjugates provide great detectability, without undesired cytotoxicity and passive membrane permeability. The introduced experiments with these conjugates proved their reliable tracking, quantification and comparison. Cellular uptake efficiency was studied on human breast, colon, pancreas and prostate cancer cells (MCF-7, HT-29, BxPC-3, LNCaP) and on dog kidney cells (Madin-Darby canine kidney). Each of the three conjugates was taken up by GnRH-I receptor-expressing cells, but the different cells preferred different analogues. Furthermore, we demonstrated for the first time the high cell surface expression of GnRH-I receptors and the effective cellular uptake of GnRH analogues on human pharynx tumour (Detroit-562) cells. In summary, our presented results detail that the introduced conjugates could be innovative tools for the examination of the GnRH-based drug delivery systems on various cells and offer novel information about these peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

LHRH-Targeted Drug Delivery Systems for Cancer Therapy

Targeted delivery of therapeutic and diagnostic agents to cancer sites has significant potential to improve the therapeutic outcome of treatment while minimizing severe side effects. It is widely accepted that decoration of the drug delivery systems with targeting ligands that bind specifically to the receptors on the cancer cells is a promising strategy that may substantially enhance accumulation of anticancer agents in the tumors. Due to the transformed cellular nature, cancer cells exhibit a variety of overexpressed cell surface receptors for peptides, hormones, and essential nutrients, providing a significant number of target candidates for selective drug delivery. Among others, luteinizing hormonereleasing hormone (LHRH) receptors are overexpressed in the majority of cancers, while their expression in healthy tissues, apart from pituitary cells, is limited. The recent studies indicate that LHRH peptides can be employed to efficiently guide anticancer and imaging agents directly to cancerous cells, thereby increasing the amount of these substances in tumor tissue and preventing normal cells from unnecessary exposure. This manuscript provides an overview of the targeted drug delivery platforms that take advantage of the LHRH receptors overexpression by cancer cells.

Pt-Mal-LHRH, a Newly Synthesized Compound Attenuating Breast Cancer Tumor Growth and Metastasis by Targeting Overexpression of the LHRH Receptor

A new targeting chemotherapeutic agent, Pt-Mal-LHRH, was synthesized by linking activated cisplatin to luteinizing hormone releasing hormone (LHRH). The compound's efficacy and selectivity toward 4T1 breast cancer cells were evaluated. Carboplatin was selected as the comparative platinum complex, since the Pt-Mal-LHRH malonate linker chelates platinum in a similar manner to carboplatin. Breast cancer and normal cell viability were analyzed by an MTT assay comparing Pt-Mal-LHRH with carboplatin. Cells were also treated with either Pt-Mal-LHRH or carboplatin to evaluate platinum uptake by ICP-MS and cell migration using an in vitro scratch-migration assay. Tumor volume and metastasis were evaluated using an in vivo 4T1 mouse tumor model. Mice were administered Pt-Mal-LHRH (carboplatin molar equivalent dosage) through ip injection and compared to those treated with carboplatin (5 (mg/kg)/week), no treatment, and LHRH plus carboplatin (unbound) controls. An MTT assay showed a reduction in cell viability (p < 0.01) in 4T1 and MDA-MB-231 breast cancer cells treated with Pt-Mal-LHRH compared to carboplatin. Pt-Mal-LHRH was confirmed to be cytotoxic by flow cytometry using a propidium iodide stain. Pt-Mal-LHRH displayed a 20-fold increase in 4T1 cellular uptake compared to carboplatin. There was a decrease (p < 0.0001) in 4T1 cell viability compared to 3T3 normal fibroblast cells. Treatment with Pt-Mal-LHRH also resulted in a significant decrease in cell-migration compared to carboplatin. In vivo testing found a significant reduction in tumor volume (p < 0.05) and metastatic tumor colonization in the lungs with Pt-Mal-LHRH compared to carboplatin. There was a slight decrease in lung weight and no difference in liver weight between treatment groups. Together, our data indicate that Pt-Mal-LHRH is a more potent and selective chemotherapeutic agent than untargeted carboplatin.

A conjugate of methotrexate and an analog of luteinizing hormone releasing hormone shows increased efficacy against prostate cancer

LHRH receptor, is over-expressed in a variety of human tumors and, is a potential binding site for targeted metastatic prostate cancer therapy. The objectives of our study were to synthesize a bioconjugate of the LHRH analog [DLys⁶]-LHRH and the anti-tumor agent methotrexate and test the hypothesis that [DLys⁶]-LHRH-MTX targets and inhibits prostate cancer cell growth in vitro and in vivo. The results of in vitro studies, showed that both [DLys⁶]-LHRH-MTX and MTX displayed superior cytotoxicity against prostate cancer cells in a concentration-dependent manners, with IC₅₀ concentrations for PC-3 cells of, 1.02 ± 0.18 μmol/L and 6.34 ± 1.01 μmol/L; for DU-145 cells, 1.53 ± 0.27 μmol/L and 8.03 ± 1.29 μmol/L; and for LNCaP cells, 1.93 ± 0.19 μmol/L and 9.68 ± 1.24 μmol/L, respectively. The IC₅₀ values of [DLys⁶]-LHRH-MTX and MTX were 110.77 ± 15.31 μmol/L and 42.33 ± 7.25 μmol/L, respectively. Finally, [DLys⁶]-LHRH-MTX significantly improved the anti-tumor activity of MTX in nude mice bearing PC-3 tumor xenografts. The inhibition ratios of tumor volume and tumor weight in the [DLys⁶]-LHRH-MTX treated group were significantly higher than those in the MTX-treated group. Tumor volume doubling time was also significantly extended from 6.13 days in control animals to 9.67 days in mice treated with [DLys⁶]-LHRH-MTX. In conclusion, [DLys⁶]-LHRH -MTX may be useful in treating prostate cancer.

Recent Innovations in Peptide Based Targeted Drug Delivery to Cancer Cells

Targeted delivery of chemotherapeutics and diagnostic agents conjugated to carrier ligands has made significant progress in recent years, both in regards to the structural design of the conjugates and their biological effectiveness. The goal of targeting specific cell surface receptors through structural compatibility has encouraged the use of peptides as highly specific carriers as short peptides are usually non-antigenic, are structurally simple and synthetically diverse. Recent years have seen many developments in the field of peptide based drug conjugates (PDCs), particularly for cancer therapy, as their use aims to bypass off-target side-effects, reducing the morbidity common to conventional chemotherapy. However, no PDCs have as yet obtained regulatory approval. In this review, we describe the evolution of the peptide-based strategy for targeted delivery of chemotherapeutics and discuss recent innovations in the arena that should lead in the near future to their clinical application.

One-Step Synthesis of Nanoscale Zeolitic Imidazolate Frameworks with High Curcumin Loading for Treatment of Cervical Cancer

A straightforward nanoprecipitating method was developed to prepare water dispersible curcumin (CCM)-loaded nanoscale zeolitic imidazolate framework-8 (CCM@NZIF-8) nanoparticles (NPs). The as-synthesized CCM@NZIF-8 NPs possess high drug encapsulation efficiency (88.2%), good chemical stability and fast drug release in tumor acidic microenvironments. Confocal laser scanning microscopy and cytotoxicity experiments reveal that NZIF-8 based nanocarriers promote the cellular uptake of CCM and result in higher cytotoxicity of CCM@NZIF-8 than that of free CCM toward HeLa cells. The in vivo anticancer experiments indicate that CCM@NZIF-8 NPs exhibit much higher antitumor efficacy than free CCM. This work highlights the potential of using nanoscale metal organic framworks (NMOFs) as a simple and stable platform for developing a highly efficient drug delivery system in cancer treatment.

An extract of Artemisia dracunculus L. stimulates insulin secretion from β cells, activates AMPK and suppresses inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia dracunculus L. (Russian tarragon) is a perennial herb belonging to the family Compositae and has a history of medicinal use in humans, particularly for treatment of diabetes.

AIM OF THE STUDY

In this study a defined plant extract from A. dracunculus L. (termed PMI-5011) is used to improve beta(β) cells function and maintain β cell number in pancreatic islets as an alternative drug approach for successful treatment of diabetes.

MATERIALS AND METHODS

Mouse and human pancreatic beta cells were treated with defined plant extract of A. dracunculus L. (PMI-5011) to understand the mechanism(s) that influence beta cell function and β cell number.

RESULTS

We found that the PMI-5011 enhances insulin release from primary β cells, isolated mouse and human islets and it maintains β cell number. Insulin released by PMI-5011 is associated with the activation of AMP-activated protein kinase (AMPK), and protein kinase B (PKB). Furthermore, PMI-5011 suppresses LPS/INFγ-induced inflammation and inflammatory mediator(s) in macrophages. PMI-5011 inhibited Nitric oxide (NO) production and expression of inducible nitric oxide synthase (iNOS) at the protein level and also attenuated pro-inflammatory cytokine (IL-6) production in macrophages.

CONCLUSION

PMI-5011 has potential therapeutic value for diabetes treatment via increasing insulin release from β cells and decreases capacity of macrophages to combat inflammation.

Recent advances in pancreatic cancer: biology, treatment, and prevention

Pancreatic cancer (PC) is the fourth leading cause of cancer-related death in United States. Efforts have been made towards the development of the viable solution for its treatment with constrained accomplishment because of its complex biology. It is well established that pancreatic cancer stem cells (CSCs), albeit present in a little count, contribute incredibly to PC initiation, progression, and metastasis. Customary chemo and radiotherapeutic alternatives, however, expands general survival, the related side effects are the significant concern. Amid the most recent decade, our insight about molecular and cellular pathways involved in PC and role of CSCs in its progression has increased enormously. Presently the focus is to target CSCs. The herbal products have gained much consideration recently as they, usually, sensitize CSCs to chemotherapy and target molecular signaling involved in various tumors including PC. Some planned studies have indicated promising results proposing that examinations in this course have a lot to offer for the treatment of PC. Although preclinical studies uncovered the importance of herbal products in attenuating pancreatic carcinoma, limited studies have been conducted to evaluate their role in clinics. The present review provides a new insight to recent advances in pancreatic cancer biology, treatment and current status of herbal products in its anticipation.

Hybrid curcumin compounds: a new strategy for cancer treatment

Cancer is a multifactorial disease that requires treatments able to target multiple intracellular components and signaling pathways. The natural compound, curcumin, was already described as a promising anticancer agent due to its multipotent properties and huge amount of molecular targets in vitro. Its translation to the clinic is, however, limited by its reduced solubility and bioavailability in patients. In order to overcome these pharmacokinetic deficits of curcumin, several strategies, such as the design of synthetic analogs, the combination with specific adjuvants or nano-formulations, have been developed. By taking into account the risk-benefit profile of drug combinations, as well as the knowledge about curcumin's structure-activity relationship, a new concept for the combination of curcumin with scaffolds from different natural products or components has emerged. The concept of a hybrid curcumin molecule is based on the incorporation or combination of curcumin with specific antibodies, adjuvants or other natural products already used or not in conventional chemotherapy, in one single molecule. The high diversity of such conjugations enhances the selectivity and inherent biological activities and properties, as well as the efficacy of the parental compound, with particular emphasis on improving the efficacy of curcumin for future clinical treatments.

Recent developments in delivery, bioavailability, absorption and metabolism of curcumin: the golden pigment from golden spice

Curcumin (diferuloylmethane) is a yellow pigment present in the spice turmeric (Curcuma longa) that has been associated with antioxidant, anti-inflammatory, anticancer, antiviral, and antibacterial activities as indicated by over 6,000 citations. In addition, over one hundred clinical studies have been carried out with curcumin. One of the major problems with curcumin is perceived to be the bioavailability. How curcumin should be delivered in vivo, how bioavailable is it, how well curcumin is absorbed and how it is metabolized, is the focus of this review. Various formulations of curcumin that are currently available are also discussed.

Perspectives on new synthetic curcumin analogs and their potential anticancer properties

Curcumin is the active component of dried rhizome of Curcuma longa, a perennial herb belonging to ginger family, cultivated extensively in south and southeastern tropical Asia. It is widely consumed in the Indian subcontinent, south Asia and Japan in traditional food recipes. Extensive research over last few decades has shown that curcumin is a potent anti-inflammatory agent with powerful therapeutic potential against a variety of cancers. It suppresses proliferation and metastasis of human tumors through regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases and other enzymes. It induces apoptotic cell death and also inhibits proliferation of cancer cells by cell cycle arrest. Pharmacokinetic data has shown that curcumin undergoes rapid metabolism leading to glucuronidation and sulfation in the liver and excretion in the feces, which accounts for its poor systemic bioavailability. The compound has, therefore, been formulated and administered using different drug delivery systems such as liposomes, micelles, polysaccharides, phospholipid complexes and nanoparticles that can overcome the limitation of bioavailability to some extent. Attempts to avoid rapid metabolism of curcumin until now have been met with limited success. This has prompted researchers to look for new synthetic curcumin analogs in order to overcome the drawbacks of limited bioavailability and rapid metabolism, and gain efficacy with reduced toxicity. In this review we provide a summarized account of novel synthetic curcumin formulations and analogs, and the recent progress in the field of cancer prevention and treatment.

Perspectives on new synthetic curcumin analogs and their potential anticancer properties

Curcumin is the active component of dried rhizome of Curcuma longa, a perennial herb belonging to ginger family, cultivated extensively in south and southeastern tropical Asia. It is widely consumed in the Indian subcontinent, south Asia and Japan in traditional food recipes. Extensive research over last few decades has shown that curcumin is a potent anti-inflammatory agent with powerful therapeutic potential against a variety of cancers. It suppresses proliferation and metastasis of human tumors through regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases and other enzymes. It induces apoptotic cell death and also inhibits proliferation of cancer cells by cell cycle arrest. Pharmacokinetic data has shown that curcumin undergoes rapid metabolism leading to glucuronidation and sulfation in the liver and excretion in the feces, which accounts for its poor systemic bioavailability. The compound has, therefore, been formulated and administered using different drug delivery systems such as liposomes, micelles, polysaccharides, phospholipid complexes and nanoparticles that can overcome the limitation of bioavailability to some extent. Attempts to avoid rapid metabolism of curcumin until now have been met with limited success. This has prompted researchers to look for new synthetic curcumin analogs in order to overcome the drawbacks of limited bioavailability and rapid metabolism, and gain efficacy with reduced toxicity. In this review we provide a summarized account of novel synthetic curcumin formulations and analogs, and the recent progress in the field of cancer prevention and treatment.

New perspectives of curcumin in cancer prevention

Numerous natural compounds have been extensively investigated for their potential for cancer prevention over the decades. Curcumin, from Curcuma longa, is a highly promising natural compound that can be potentially used for chemoprevention of multiple cancers. Curcumin modulates multiple molecular pathways involved in the lengthy carcinogenesis process to exert its chemopreventive effects through several mechanisms: promoting apoptosis, inhibiting survival signals, scavenging reactive oxidative species (ROS), and reducing the inflammatory cancer microenvironment. Curcumin fulfills the characteristics for an ideal chemopreventive agent with its low toxicity, affordability, and easy accessibility. Nonetheless, the clinical application of curcumin is currently compromised by its poor bioavailability. Here, we review the potential of curcumin in cancer prevention, its molecular targets, and mechanisms of action. Finally, we suggest specific recommendations to improve its efficacy and bioavailability for clinical applications.

The curcumin analog DM-1 induces apoptotic cell death in melanoma

The main difficulty in the successful treatment of metastatic melanoma is that this type of cancer is known to be resistant to chemotherapy. Chemotherapy remains the treatment of choice, and dacarbazine (DTIC) is the best standard treatment. The DM-1 compound is a curcumin analog that possesses several curcumin characteristics, such as antiproliferative, antitumor, and antimetastatic properties. The objective of this study was to evaluate the signaling pathways involved in melanoma cell death after treatment with DM-1 compared to the standard agent for melanoma treatment, DTIC. Cell death was evaluated by flow cytometry for annexin V and iodide propide, cleaved caspase 8, and TNF-R1 expression. Hoechst 33342 staining was evaluated by fluorescent microscopy; lipid peroxidation and cell viability (MTT) were evaluated by colorimetric assays. The antiproliferative effects of the drugs were evaluated by flow cytometry for cyclin D1 and Ki67 expression. Mice bearing B16F10 melanoma were treated with DTIC, DM-1, or both therapies. DM-1 induced significant apoptosis as indicated by the presence of cleaved caspase 8 and an increase in TNF-R1 expression in melanoma cells. Furthermore, DM-1 had antiproliferative effects in this the same cell line. DTIC caused cell death primarily by necrosis, and a smaller melanoma cell population underwent apoptosis. DTIC induced oxidative stress and several physiological changes in normal melanocytes, whereas DM-1 did not significantly affect the normal cells. DM-1 antitumor therapy in vivo showed tumor burden decrease with DM-1 monotherapy or in combination with DTIC, besides survival rate increase. Altogether, these data confirm DM-1 as a chemotherapeutic agent with effective tumor control properties and a lower incidence of side effects in normal cells compared to DTIC.

After 65 years, research is still fun

In 1946, at the end of World War II, I entered graduate school at Cornell University, where I remained for 44 years. During that time, my laboratory produced more than 300 publications in the field of reproductive biology, including studies on nutrition and reproduction, the role of the hypothalamus in pituitary gonadotropin release, corpus luteum formation and function, hormone assays, and estrous cycle synchronization. At age seventy, I retired from Cornell and accepted the Gordon Cain Endowed Professorship at Louisiana State University, where I continued my work on the bovine corpus luteum and added research on the collection, maturation, in vitro fertilization, and culture of bovine oocytes. In 1994, I moved to the Pennington Biomedical Research Center and soon thereafter started the research that led to development of the lytic peptide-gonadotropin conjugates, which target and destroy cancer cell membranes. I am continuing my work on the development of targeted cancer cell drugs and, yes, research is still fun!

GnRH receptors in cancer: from cell biology to novel targeted therapeutic strategies

The crucial role of pituitary GnRH receptors (GnRH-R) in the control of reproductive functions is well established. These receptors are the target of GnRH agonists (through receptor desensitization) and antagonists (through receptor blockade) for the treatment of steroid-dependent pathologies, including hormone-dependent tumors. It has also become increasingly clear that GnRH-R are expressed in cancer tissues, either related (i.e. prostate, breast, endometrial, and ovarian cancers) or unrelated (i.e. melanoma, glioblastoma, lung, and pancreatic cancers) to the reproductive system. In hormone-related tumors, GnRH-R appear to be expressed even when the tumor has escaped steroid dependence (such as castration-resistant prostate cancer). These receptors are coupled to a G(αi)-mediated intracellular signaling pathway. Activation of tumor GnRH-R by means of GnRH agonists elicits a strong antiproliferative, antimetastatic, and antiangiogenic (more recently demonstrated) activity. Interestingly, GnRH antagonists have also been shown to elicit a direct antitumor effect; thus, these compounds behave as antagonists of GnRH-R at the pituitary level and as agonists of the same receptors expressed in tumors. According to the ligand-induced selective-signaling theory, GnRH-R might assume various conformations, endowed with different activities for GnRH analogs and with different intracellular signaling pathways, according to the cell context. Based on these consistent experimental observations, tumor GnRH-R are now considered a very interesting candidate for novel molecular, GnRH analog-based, targeted strategies for the treatment of tumors expressing these receptors. These agents include GnRH agonists and antagonists, GnRH analog-based cytotoxic (i.e. doxorubicin) or nutraceutic (i.e. curcumin) hybrids, and GnRH-R-targeted nanoparticles delivering anticancer compounds.

Probing the GnRH receptor agonist binding site identifies methylated triptorelin as a new anti-proliferative agent

D-amino acid substitutions at glycine postion 6 in GnRH-I decapeptide can possess super-agonist activity and enhanced in vivo pharmacokinetics. Agonists elicit growth-inhibition in tumorigenic cells expressing the GnRH receptor above threshold levels. However, new agonists with modified properties are required to improve the anti-proliferative range. Effects of residue substitutions and methylations on tumourigenic HEK293_[SCL60] and WPE-1-NB26-3 prostate cells expressing the rat GnRH receptor were compared. Peptides were ranked according to receptor binding affinity, induction of inositol phosphate production and cell growth-inhibition. Analogues possessing D-Trp⁶ (including triptorelin), D-Leu⁶ (including leuprolide), D-Ala⁶, D-Lys⁶, or D-Arg⁶ exhibited agonist and anti-proliferative activity. Residues His⁵ or His⁵,Trp⁷,Tyr⁸, corresponding to residues found in GnRH-II, were tolerated, with retention of sub-nanomolar/low nanomolar binding affinities and EC₅₀s for receptor activation and IC₅₀s for cell growth-inhibition. His⁵D-Arg⁶-GnRH-I exhibited reduced binding affinity and potency, effective in the mid-nanomolar range. However, all GnRH-II-like analogues were less potent than triptorelin. By comparison, three methylated-Trp⁶ triptorelin variants showed differential binding, receptor activation and anti-proliferation potency. Significantly, 5-Methyl-DL-Trp⁶-Triptorelin was equipotent to triptorelin. Subsequent studies should determine whether pharmacologically enhanced derivatives of triptorelin can be developed by further alkylations, without substitutions or cleavable cytotoxic adducts, to improve the extent of growth-inhibition of tumour cells expressing the GnRH receptor.

DM-1, sodium 4-[5-(4-hydroxy-3-methoxyphenyl)-3-oxo-penta-1,4-dienyl]-2-methoxy-phenolate: a curcumin analog with a synergic effect in combination with paclitaxel in breast cancer treatment

This paper describes a new method for the preparation of sodium 4-[5-(4-hydroxy-3-methoxyphenyl)-3-oxo-penta-1,4-dienyl]-2-methoxy-phenolate, DM-1, and 3-oxo-penta-1,4-dienyl-bis (2-methoxy-phenolate), DM-2. The aim of this work was to evaluate the antitumor effects of DM-1 in adjuvant chemotherapy for breast cancer treatment. Mice bearing mammary adenocarcinomas (Ehrlich ascites tumors) were treated with paclitaxel alone, DM-1 alone, and paclitaxel + DM-1. Tumor samples were used to perform cytological analysis by the Papanicolaou method and apoptosis analysis by annexin V and phosphorylated caspase 3. The paclitaxel + DM-1 group had decreased tumor areas and tumor volumes, and the frequency of metastasis was significantly reduced. This caused a decrease in cachexia, which is usually caused by the tumor. Furthermore, treatment with paclitaxel + DM-1 and DM-1 alone increased the occurrence of apoptosis up to 40% in tumor cells, which is 35% more than in the group treated with paclitaxel alone. This cell death was mainly caused through phosphorylated caspase 3 (11% increase in paclitaxel + DM-1 compared to the paclitaxel group), as confirmed by reduced malignancy criteria in the ascitic fluid. DM-1 emerges as a potential treatment for breast cancer and may act as an adjuvant in chemotherapy, enhancing antitumor drug activity with reduced side effects.

Multifaceted roles of curcumin: two sides of a coin!

INTRODUCTION

Curcumin has been a front-line topic of mainstream scientific research for a variety of diseases from cancer to Alzheimer's to infectious diseases. Curcumin suppresses the type 1 immune response, which might lead to alleviation of type 1 immune response disorders. However, the inhibition of type 1 immune response might invite infections with opportunistic pathogens. Considering its low bioavailability, several curcumin derivatives have been designed to improve its functionality.

AREAS COVERED

This is a consolidated review which aims to compare and contrast diverse aspects of curcumin in variety of diseases. The intricate underlying mechanisms and the functional determinants of curcumin are discussed.

EXPERT OPINION

Curcumin being considered as a spicy panacea, is not a remedy for all diseases. However, its ability to act differentially as an anti-oxidant or pro-oxidant akin to that of a double-edged sword/friend turning foe can be either beneficial or harmful for the host. It exhibits anti-oxidant properties at concentrations achievable in the body, making the host vulnerable to infections due to the suppression of innate immune responses. With the increase in knowledge of its functional groups, production of analogues of curcumin is underway to enhance its bioavailability and hence its therapeutic potency.