Natural Prodrug Research Articles

Nanoparticles Encapsulated γ-Oryzanol as a Natural Prodrug of Ferulic Acid for the Treatment of Oxidative Liver Damage.

Antioxidants are promising therapeutics for treating oxidative stress-mediated liver diseases. Previously, we studied a potent natural antioxidant, ferulic acid, and developed a liposomal formulation of ferulic acid (ferulic-lipo) to improve its solubility. Ferulic-lipo significantly attenuated oxidative damage in the liver by inhibiting reactive oxygenase species (ROS). However, antioxidative liposomes must be less reactive with ROS prior to reaching the target sites to effectively neutralize existing ROS. But ferulic-lipo tends to be oxidized before reaching the liver. Besides, γ-oryzanol has been reported to decompose into ferulic acid in vivo; accordingly, we hypothesized that γ-oryzanol could be employed as a natural prodrug of ferulic acid to improve stability and antioxidative effectiveness. Therefore, in this study, we prepared a liposomal formulation of γ-oryzanol (γ-ory-lipo) and investigated its therapeutic effects in a CCl4-induced rat model of liver injury. We found that γ-ory-lipo has a higher chemical stability than does free γ-oryzanol. Although the antioxidative effect of γ-ory-lipo was lower than that of ferulic-lipo, pretreatment of the HepG2 cells with γ-ory-lipo improved the viability of CCl4-treated cells to a similar level as treatment with ferulic-lipo. γ-Oryzanol was shown to be converted into ferulic acid in vitro and in vivo. Furthermore, intravenous administration of γ-ory-lipo exhibited a similar effectiveness as ferulic-lipo against CCl4-induced hepatotoxicity, which should be the due to the conversion of γ-oryzanol into ferulic acid. These findings demonstrated that γ-ory-lipo could be a good natural prodrug of ferulic acid for eradicating its stability problem.

Nanomedicine as an Emerging Technology to Foster Application of Essential Oils to Fight Cancer.

Natural prodrugs extracted from plants are increasingly used in many sectors, including the pharmaceutical, cosmetic, and food industries. Among these prodrugs, essential oils (EOs) are of particular importance. These biologically active volatile oily liquids are produced by medicinal and aromatic plants and characterized by a distinctive odor. EOs possess high anticancer, antibacterial, antiviral, and antioxidant potential but often are associated with low stability; high volatility; and a high risk of deterioration with exposure to heat, humidity, light, or oxygen. Furthermore, their bioavailability is limited because they are not soluble in water, and enhancements are needed to increase their potential to target specific cells or tissues, as well as for controlled release. Nanomedicine, the application of nanotechnology in medicine, may offer efficient solutions to these problems. The technology is based on creating nanostructures in which the natural prodrug is connected to or encapsulated in nanoparticles or submicron-sized capsules that ensure their solubility in water and their targeting properties, as well as controlled delivery. The potential of EOs as anticancer prodrugs is considerable but not fully exploited. This review focusses on the recent progress towards the practical application of EOs in cancer therapy based on nanotechnology applications.

Delivery of Natural Agents by Means of Mesoporous Silica Nanospheres as a Promising Anticancer Strategy.

Natural prodrugs derived from different natural origins (e.g., medicinal plants, microbes, animals) have a long history in traditional medicine. They exhibit a broad range of pharmacological activities, including anticancer effects in vitro and in vivo. They have potential as safe, cost-effective treatments with few side effects, but are lacking in solubility, bioavailability, specific targeting and have short half-lives. These are barriers to clinical application. Nanomedicine has the potential to offer solutions to circumvent these limitations and allow the use of natural pro-drugs in cancer therapy. Mesoporous silica nanoparticles (MSNs) of various morphology have attracted considerable attention in the search for targeted drug delivery systems. MSNs are characterized by chemical stability, easy synthesis and functionalization, large surface area, tunable pore sizes and volumes, good biocompatibility, controlled drug release under different conditions, and high drug-loading capacity, enabling multifunctional purposes. In vivo pre-clinical evaluations, a significant majority of results indicate the safety profile of MSNs if they are synthesized in an optimized way. Here, we present an overview of synthesis methods, possible surface functionalization, cellular uptake, biodistribution, toxicity, loading strategies, delivery designs with controlled release, and cancer targeting and discuss the future of anticancer nanotechnology-based natural prodrug delivery systems.

Virucidal Action Against Avian Influenza H5N1 Virus and Immunomodulatory Effects of Nanoformulations Consisting of Mesoporous Silica Nanoparticles Loaded with Natural Prodrugs.

BackgroundCombating infectious diseases caused by influenza virus is a major challenge due to its resistance to available drugs and vaccines, side effects, and cost of treatment. Nanomedicines are being developed to allow targeted delivery of drugs to attack specific cells or viruses.Materials and MethodsIn this study, mesoporous silica nanoparticles (MSNs) functionalized with amino groups and loaded with natural prodrugs of shikimic acid (SH), quercetin (QR) or both were explored as a novel antiviral nanoformulations targeting the highly pathogenic avian influenza H5N1 virus. Also, the immunomodulatory effects were investigated in vitro tests and anti-inflammatory activity was determined in vivo using the acute carrageenan-induced paw edema rat model.ResultsProdrugs alone or the MSNs displayed weaker antiviral effects as evidenced by virus titers and plaque formation compared to nanoformulations. The MSNs-NH2-SH and MSNs-NH2-SH-QR2 nanoformulations displayed a strong virucidal by inactivating the H5N1 virus. They induced also strong immunomodulatory effects: they inhibited cytokines (TNF-α, IL-1β) and nitric oxide production by approximately 50% for MSNs-NH2-SH-QR2 (containing both SH and QR). Remarkable anti-inflammatory effects were observed during in vivo tests in an acute carrageenan-induced rat model.ConclusionOur preliminary findings show the potential of nanotechnology for the application of natural prodrug substances to produce a novel safe, effective, and affordable antiviral drug.

Targeted Nano-Drug Delivery of Colchicine against Colon Cancer Cells by Means of Mesoporous Silica Nanoparticles.

Antimitotics are important anticancer agents and include the natural alkaloid prodrug colchicine (COL). However, a major challenge of using COL as an anticancer drug is its cytotoxicity. We developed a novel drug delivery system (DDS) for COL using mesoporous silica nanoparticles (MSNs). The MSNs were functionalized with phosphonate groups, loaded with COL, and coated with folic acid chitosan-glycine complex. The resulting nanoformulation, called MSNsPCOL/CG-FA, was tested for action against cancer and normal cell lines. The anticancer effect was highly enhanced for MSNsPCOL/CG-FA compared to COL. In the case of HCT116 cells, 100% inhibition was achieved. The efficiency of MSNsPCOL/CG-FA ranked in this order: HCT116 (colon cancer) > HepG2 (liver cancer) > PC3 (prostate cancer). MSNsPCOL/CG-FA exhibited low cytotoxicity (4%) compared to COL (~60%) in BJ1 normal cells. The mechanism of action was studied in detail for HCT116 cells and found to be primarily intrinsic apoptosis caused by an enhanced antimitotic effect. Furthermore, a contribution of genetic regulation (metastasis-associated lung adenocarcinoma transcript 1 (MALAT 1), and microRNA (mir-205)) and immunotherapy effects (angiopoietin-2 (Ang-2 protein) and programmed cell death protein 1 (PD-1) was found. Therefore, this study shows enhanced anticancer effects and reduced cytotoxicity of COL with targeted delivery compared to free COL and is a novel method of developing cancer immunotherapy using a low-cost small-molecule natural prodrug.

Chemopreventive efficacy of oral curcumin: a prodrug hypothesis.

Oral consumption of curcumin, a natural polyphenol, is associated with reduced incidence of cancer. Yet, a significant amount of the orally dosed compound is eliminated in the feces, and a major fraction of the absorbed compound is metabolized to inactive glucuronides, resulting in poor bioavailability (<1%). It is not known how oral curcumin exhibits chemopreventive activity. We propose curcumin glucuronide is an inflammation-responsive natural prodrug that is converted back to curcumin on demand at the site of action. Our studies show elevated levels of β-glucuronidase, an enzyme that hydrolyzes the glycosidic bond of glucuronides to generate the parent compound, in human breast cancer. Oral administration of curcumin in mouse tumor models generated significant tumor levels of the polyphenol. Intravenous administration of the glucuronide resulted in the formation of curcumin in the tumor tissue. Chronic daily oral curcumin dosing led to tumor accumulation of curcumin and inhibition of tumor growth in tumor models with high β-glucuronidase activity. Overall, the study presented here provides preliminary evidence for a novel mechanism of action for orally administered curcumin.-Liu, G., Khanna, V., Kirtane, A., Grill, A., Panyam, J. Chemopreventive efficacy of oral curcumin: a prodrug hypothesis.

An update on prodrugs from natural products

A natural prodrug is a chemical compound or substance obtained from plants, microorganism, animal and marine sources. Natural products are small molecule source for Food and Drug Administration approved drugs and major sources for drug discovery. Most of the drugs for different ailment diseases undergo first pass metabolism, resulting in drug inactivation and the generation of toxic metabolites in body. Enormous numbers of prodrugs naturally present in plants, microorganism, animal and marine sources and those prodrugs undergoes chemical reaction to form non-toxic compounds. This review summarizes the list of prodrugs naturally present in the natural product.

A natural prodrug activation mechanism in the biosynthesis of nonribosomal peptides

Highlight describes the recently discovered prodrug activation mechanism found in the biosynthesis of nonribosomally produced peptides and peptide/polyketide hybrids as well as related mechanisms.

First-pass Metabolism of Decursin, a Bioactive Compound of Angelica gigas, in Rats

Decursin is considered the major bioactive compound of Angelica gigas roots, a popular Oriental herb and dietary supplement. In this study, the pharmacokinetics of decursin and its active metabolite, decursinol, were evaluated after the administration of decursin in rats. The plasma concentration of decursin decreased rapidly, with an initial half-life of 0.05 h. It was not detectable at 1 h after intravenous administration at an area under the plasma concentration-time curve of 1.20 µg · mL-1·h, whereas the concentration of decursinol increased rapidly reaching a maximum concentration of 2.48 µg · mL-1 at the time to maximum plasma concentration of 0.25 h and an area under the plasma concentration-time curve of 5.23 µg · mL-1·h. Interestingly, after oral administration of decursin, only decursinol was present in plasma, suggesting an extensive hepatic first-pass metabolism of decursin. The extremely low bioavailability of decursin after its administration via the hepatic portal vein (the fraction of dose escaping first-pass elimination in the liver, FH = 0.11) is indicative of extensive hepatic first-pass metabolism of decursin, which was confirmed by a tissue distribution study. These findings suggest that decursin is not directly associated with the bioactivity of A.gigas and that it may work as a type of natural prodrug of decursinol.

Defining the Mechanism of Action and Enzymatic Selectivity of Psammaplin A against Its Epigenetic Targets

Psammaplin A (11c) is a marine metabolite previously reported to be a potent inhibitor of two classes of epigenetic enzymes: histone deacetylases and DNA methyltransferases. The design and synthesis of a focused library based on the psammaplin A core has been carried out to probe the molecular features of this molecule responsible for its activity. By direct in vitro assay of the free thiol generated upon reduction of the dimeric psammaplin scaffold, we have unambiguously demonstrated that 11c functions as a natural prodrug, with the reduced form being highly potent against HDAC1 in vitro (IC(50) 0.9 nM). Furthermore, we have shown it to have high isoform selectivity, being 360-fold selective for HDAC1 over HDAC6 and more than 1000-fold less potent against HDAC7 and HDAC8. SAR around our focused library revealed a number of features, most notably the oxime functionality to be important to this selectivity. Many of the compounds show significant cytotoxicity in A549, MCF7, and W138 cells, with the SAR of cytotoxicity correlating to HDAC inhibition. Furthermore, compound treatment causes upregulation of histone acetylation but little effect on tubulin acetylation. Finally, we have found no evidence for 11c functioning as a DNMT inhibitor.

Abstract B166: Defining the mechanism of action and enzymatic selectivity of psammaplin A against its epigenetic targets.

Abstract Naturally isolated products continue to play a significant role in anticancer drug discovery. In line with our interest in small molecule compounds which effect epigenetic gene regulation, we are interested in the structural and biological properties of the natural product Psammaplin A. While it has been implicated as an inhibitor of numerous targets such as mycothiol-S-conjugate amidase, topoisomerase II and aminopeptidase N, studies by Crews and co-workers showed it to be an extremely potent inhibitor of both histone deacetylase (HDAC) and DNA methyltransferase (DNMT) enzymes. Our goal was to establish structure-activity relationships around psammaplin A, probing the molecular features responsible for the chemical biology of this natural product. We developed a number of versatile synthetic routes towards small compound libraries based on the psammaplin core [1]. We subsequently assessed the activity of these compounds against a selection of histone deacetylases, DNMT1, and in cell based assays. Analysis of the data revealed psammaplin A to be a natural prodrug; the central disulphide being reduced to a free thiol. Indeed, we showed the corresponding thiol not only to be a potent inhibitor of HDAC1 (IC50 0.001 μM), but to have remarkable selectivity against HDAC6 (IC50 0.360 μM), HDAC7 (IC50 17.4 μM) and HDAC8 (IC50 1.34 μM) in cell-free assays. Cell-based (MCF7) studies confirmed the HDAC targeting potential of psammaplin A and confirmed the selectivity observed in vitro. Curiously, our psammaplin A derivatives demonstrated no activity against DNMT1 in cell-free assays. Taken together with other reports, this data suggests psammaplin A may not be an inhibitor of DNMT1 as previously reported. In conclusion, we have explored the epigenetic activity of psammaplin A and have found it to have significant potency and selectivity against HDACs, whereas we find no evidence for DNMT1 activity. Reference: 1. “New synthetic strategies towards Psammaplin A, access to natural product analogues” Baud, M. G. J.; Leiser, T.; Meyer-Almes, F.-J.; Fuchter, M. J. Org. Biomol. Chem. 2011, 9, 659–662. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B166.

Depsipeptide (FK228) inhibits growth of human prostate cancer cells: Lai MT, Yang CC, Lin TY, Tsai FJ, Chen WC, Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan

FK228 (depsipeptide) is a natural prodrug that inhibits class I histone deacetylases. We aimed to investigate the effects FK228 has on prostate cancer cells in vivo. In non-obese diabetic-severe combined immunodeficient mice implanted with human prostate cancer cells, 50 mg/kg FK228 given orally 3 times a week inhibited tumor growth and metastasis. The median time to the experimental end point [tumor volume 2 cm (3) or death] in the untreated group was 52 days, and average tumor volume was 0.8 ± 0.18 cm (3). At the same time, 94.4% of FK228-treated mice survived and had average tumor volumes of 0.37 ± 0.1 cm (3). All untreated animals died at 98 days, whereas, 61% of treated animal remained alive. Sizeable metastatic tumors positively stained for prostate-specific antigen (PSA), and limited air gaps were found in the lungs of untreated mice. In animals treated with FK228, lung morphology appeared normal. Primary tumors of treated animals were highly positive for PSA, and had an increased level of p21 and the proapoptotic protein Bax. Sections taken from FK228-treated animals and examined under an electron microscope showed condensed chromatin and apoptotic bodies. PSA serum levels were higher in untreated than in treated animals and correlated with tumor volume. Because prolonged oral administration of 50 mg/kg or a single oral dose of 1.2 g/kg FK228 did not cause adverse effects and inhibited proliferation of human prostate cancer cells in vivo, FK228 likely has a potential anticancer effect for prostate cancer.

Depsipeptide (FK228) inhibits growth of human prostate cancer cells

FK228 (depsipeptide) is a natural prodrug that inhibits class I histone deacetylases. We aimed to investigate the effects FK228 has on prostate cancer cells in vivo. In non-obese diabetic-severe combined immunodeficient mice implanted with human prostate cancer cells, 50 mg/kg FK228 given orally 3 times a week inhibited tumor growth and metastasis. The median time to the experimental end point (tumor volume 2 cm 3 or death) in the untreated group was 52 days, and average tumor volume was 0.8 ± 0.18 cm 3. At the same time, 94.4% of FK228-treated mice survived and had average tumor volumes of 0.37 ± 0.1 cm 3. All untreated animals died at 98 days, whereas, 61% of treated animal remained alive. Sizeable metastatic tumors positively stained for prostate-specific antigen (PSA), and limited air gaps were found in the lungs of untreated mice. In animals treated with FK228, lung morphology appeared normal. Primary tumors of treated animals were highly positive for PSA, and had an increased level of p21 and the proapoptotic protein Bax. Sections taken from FK228-treated animals and examined under an electron microscope showed condensed chromatin and apoptotic bodies. PSA serum levels were higher in untreated than in treated animals and correlated with tumor volume. Because prolonged oral administration of 50 mg/kg or a single oral dose of 1.2 g/kg FK228 did not cause adverse effects and inhibited proliferation of human prostate cancer cells in vivo, FK228 likely has a potential anticancer effect for prostate cancer.

Psammaplin A is a natural prodrug that inhibits class I histone deacetylase

Histone deacetylase (HDAC) has been highlighted as one of key players in tumorigenesis and angiogenesis. Recently, several derivatives of psammaplin (Psams) from a marine sponge have been known to inhibit the HDAC activity, but the molecular mechanism for the inhibition has not fully understood. Here, we explored the mode of action of Psams for the inhibition of HDAC activity in the molecular and cellular level. Among the derivatives, psammaplin A (Psam A) showed the potent inhibitory activity in enzyme assay and anti-proliferation assay with IC50 value of 0.003 and 1 muM, respectively. Psam A selectively induced hyperacetylation of histones in the cells, resulting in the upregulation of gelsolin, a well-known HDAC target gene, in a transcriptional level. In addition, reduced Psam A showed a stronger inhibitory activity than that of non-reduced one. Notably, glutathione-depleted cells were not sensitive to Psam A, implying that cellular reduction of the compound is responsible for the HDAC inhibition of Psam A after uptake into the cells. Together, these data demonstrate that Psam A could exhibit its activity under the reduced condition in the cells and be a new natural prodrug targeting HDAC.

Chamazulene Carboxylic Acid and Matricin: A Natural Profen and Its Natural Prodrug, Identified through Similarity to Synthetic Drug Substances

Chamazulene carboxylic acid (1) is a natural profen with anti-inflammatory activity and a degradation product of proazulenic sesquiterpene lactones, e.g., matricin. Both 1 and proazulenes occur in chamomile (Matricaria recutita), yarrow (Achillea millefolium), and a few other Asteraceae species. It was isolated in improved yields, characterized physicochemically, and found to be an inhibitor of cyclooxygenase-2, but not of cyclooxygenase-1. It had anti-inflammatory activity in several animal models with local and systemic application. When human volunteers were given matricin orally, plasma levels of 1 were found to be in the micromolar range. Matricin was converted to 1 in artificial gastric fluid, but not in artificial intestinal fluid. Matricin and the yarrow proazulenes are proposed to be anti-inflammatory through conversion to 1. Intriguingly, the biological activity of the natural compound 1 was found because of its similarity to fully synthetic drug substances. This is the reverse process of the common lead function of natural compounds in drug discovery.

Therapeutic protein transduction of mammalian cells and mice by nucleic acid-free lentiviral nanoparticles

The straightforward production and dose-controlled administration of protein therapeutics remain major challenges for the biopharmaceutical manufacturing and gene therapy communities. Transgenes linked to HIV-1-derived vpr and pol-based protease cleavage (PC) sequences were co-produced as chimeric fusion proteins in a lentivirus production setting, encapsidated and processed to fusion peptide-free native protein in pseudotyped lentivirions for intracellular delivery and therapeutic action in target cells. Devoid of viral genome sequences, protein-transducing nanoparticles (PTNs) enabled transient and dose-dependent delivery of therapeutic proteins at functional quantities into a variety of mammalian cells in the absence of host chromosome modifications. PTNs delivering Manihot esculenta linamarase into rodent or human, tumor cell lines and spheroids mediated hydrolysis of the innocuous natural prodrug linamarin to cyanide and resulted in efficient cell killing. Following linamarin injection into nude mice, linamarase-transducing nanoparticles impacted solid tumor development through the bystander effect of cyanide.

Beta-glucuronidase inhibitory activity and hepatoprotective effect of 18 beta-glycyrrhetinic acid from the rhizomes of Glycyrrhiza uralensis.

An inhibitor of beta-glucuronidase from the rhizomes of Glycyrrhiza uralensis was isolated and its hepatoprotective activity on CCI4-induced hepatotoxicity of rats was investigated. From the water-soluble extract of G. uralensis, glycyrrhizin was isolated as a potent inhibitor of beta-glucuronidase. When glycyrrhizin was orally administered, it had a hepatoprotective activity. However, when glycyrrhizin was intraperitoneally administered, it did not have a hepatoprotective activity. 18 beta-Glycyrrhetinic acid, which is a major metabolite of glycyrrhizin by human intestinal bacteria, was also a potent inhibitor of beta-glucuronidase. When 18 beta-glycyrrhetinic acid was intraperitoneally administered, it also had some hepatoprotective activity. These results suggest that glycyrrhizin may be a natural prodrug for the observed hepatoprotective effect in rats and that serum beta-glucuronidase levels have implications for the liver injury, as reductions of its activity by administration of inhibitors such as G. uralensis or its derived products and silymarin correlate with reductions in biochemical indices of liver injury.