Mutual prodrug concept: Fundamentals and applications

Enzymatic Synthesis of Thymol Octanoate, a Promising Hybrid Molecule

Interest in the synthesis and application of thymol esters has increased in recent years due to the numerous applications associated with its biological activities. The enzymatic synthesis of thymol octanoate by esterification of thymol and octanoic acid was explored using soluble lipases and immobilized lipase biocatalysts in solvent-free systems. Candida antarctica lipase B in its soluble form was the most active biocatalyst for this reaction. Different thymol and lipase feeding strategies were evaluated to maximize thymol octanoate production. The results suggest that there could be lipase inhibition by the ester product of the reaction. In this way, the optimal reaction condition was given using a thymol/acid molar ratio of 1:4 mol/mol. Under these conditions the conversion of thymol was close to 94% and the lipase maintained more than 90% of its initial activity after the reaction, showing the potential of the enzyme to be used in successive reaction cycles.

Strategies and progresses for enhancing targeted antibiotic delivery

Antibiotic resistance is a global health issue and a potential risk for society. Antibiotics administered through conventional formulations are devoid of targeting effect and often spread to various undesired body sites, leading to sub-lethal concentrations at the site of action and thus resulting in emergence of resistance, as well as side effects. Moreover, we have a very slim antibiotic pipeline. Drug-delivery systems have been designed to control the rate, time, and site of drug release, and innovative approaches for antibiotic delivery provide a glint of hope for addressing these issues. This review elaborates different delivery strategies and approaches employed to overcome the limitations of conventional antibiotic therapy. These include antibiotic conjugates, prodrugs, and nanocarriers for local and targeted antibiotic release. In addition, a wide range of stimuli-responsive nanocarriers and biological carriers for targeted antibiotic delivery are discussed. The potential advantages and limitations of targeted antibiotic delivery strategies are described along with possible solutions to avoid these limitations. A number of antibiotics successfully delivered through these approaches with attained outcomes and potentials are reviewed.

The effects of L-carnitine-loaded solid lipid nanoparticles on performance, antioxidant parameters, and expression of genes associated with cholesterol metabolism in laying hens

The purpose of this study was to investigate the production performance, antioxidant parameters, egg yolk cholesterol content, and expression of genes related to cholesterol metabolism in laying hens fed L-carnitine (LC) and L-carnitine-loaded solid lipid nanoparticles (LC-SLNs). A total of 350 Hy-Line (w-36) laying hens at 50 wk of age (1520.0 ± 0.7 g) were randomly assigned to 35 units (5 replicates and 50 hens in each treatment) with seven dietary treatments as a completely randomized design. The dietary treatments were corn-soybean meal-based diets, including 1) Control (basal diet); 2) Basal diet +50 mg/kg LC (50LC); 3) Basal diet +100 mg/kg LC (100LC); 4) Basal diet +150 mg/kg LC (150LC); 5) Basal diet +50 mg/kg LC-SLNs (50LC-SLNs); 6) Basal diet +100 mg/kg LC-SLNs (100LC-SLNs) and 7) Basal diet +150 mg/kg LC-SLNs (150LC-SLNs). Results showed that the 50LC-SLNs had the least feed conversion ratio (FCR) in all groups (P < 0.05). The dietary supplementation of 100LC-SLNs decreased (P < 0.01) the egg yolk cholesterol concentration from 14.71 to 11.76 mg/g yolk (25%). The 50LC-SLNs group produced the most total antioxidant capacity with a difference of 58.44% compared to the control group (P < 0.01). The greatest amount of total superoxide dismutase was found for 50LC-SLNs (P < 0.05), while the glutathione peroxidase was not affected by the experimental treatments (P > 0.05). Serum malondialdehyde levels were reduced by 50.52% in laying hens fed 50LC-SLNs compared to the control group (P < 0.05). The transcript level of 3-hydroxy-3-methylglutaryl coenzyme A reductase was significantly decreased (P < 0.01) in the LC and LC-SLNs groups. The expression of cholesterol 7α-hydroxylase was significantly increased (P < 0.01) in the plain LC (∼83%) and LC-SLNs (∼91%) groups. The inclusion of LC-SLNs in the diet increased (P < 0.05) the villus height and decreased villus width in all three parts of the small intestine. Dietary inclusion of LC was found to reduce egg yolk and serum cholesterol content by improving the production performance and antioxidant status. The LC-SLNs groups were more affected than the plain LC groups, which may be attributed to the increased bioavailability of LC.

Novel mutual prodrug of 5-fluorouracil and heme oxygenase-1 inhibitor (5-FU/HO-1 hybrid): design and preliminary in vitro evaluation

In this work, the first mutual prodrug of 5-fluorouracil and heme oxygenase1 inhibitor (5-FU/HO-1 hybrid) has been designed, synthesised, and evaluated for its in vitro chemical and enzymatic hydrolysis stability. Predicted in silico physicochemical properties of the newly synthesised hybrid (3) demonstrated a drug-like profile with suitable Absorption, Distribution, Metabolism, and Excretion (ADME) properties and low toxic liabilities. Preliminary cytotoxicity evaluation towards human prostate (DU145) and lung (A549) cancer cell lines demonstrated that 3 exerted a similar effect on cell viability to that produced by the reference drug 5-FU. Among the two tested cancer cell lines, the A549 cells were more susceptible for 3. Of note, hybrid 3 also had a significantly lower cytotoxic effect on healthy human lung epithelial cells (BEAS-2B) than 5-FU. Altogether our results served as an initial proof-of-concept to develop 5-FU/HO-1 mutual prodrugs as potential novel anticancer agents.

Enzyme Models-From Catalysis to Prodrugs

Enzymes are highly specific biological catalysts that accelerate the rate of chemical reactions within the cell. Our knowledge of how enzymes work remains incomplete. Computational methodologies such as molecular mechanics (MM) and quantum mechanical (QM) methods play an important role in elucidating the detailed mechanisms of enzymatic reactions where experimental research measurements are not possible. Theories invoked by a variety of scientists indicate that enzymes work as structural scaffolds that serve to bring together and orient the reactants so that the reaction can proceed with minimum energy. Enzyme models can be utilized for mimicking enzyme catalysis and the development of novel prodrugs. Prodrugs are used to enhance the pharmacokinetics of drugs; classical prodrug approaches focus on alternating the physicochemical properties, while chemical modern approaches are based on the knowledge gained from the chemistry of enzyme models and correlations between experimental and calculated rate values of intramolecular processes (enzyme models). A large number of prodrugs have been designed and developed to improve the effectiveness and pharmacokinetics of commonly used drugs, such as anti-Parkinson (dopamine), antiviral (acyclovir), antimalarial (atovaquone), anticancer (azanucleosides), antifibrinolytic (tranexamic acid), antihyperlipidemia (statins), vasoconstrictors (phenylephrine), antihypertension (atenolol), antibacterial agents (amoxicillin, cephalexin, and cefuroxime axetil), paracetamol, and guaifenesin. This article describes the works done on enzyme models and the computational methods used to understand enzyme catalysis and to help in the development of efficient prodrugs.

Bicyclic Diazepinones as Dual Ligands of the α2δ-1 Subunit of Voltage-Gated Calcium Channels and the Norepinephrine Transporter

The synthesis and pharmacological activity of a new series of bicyclic diazepinones with dual activity toward the α2δ-1 subunit of voltage-gated calcium channels (Ca_vα2δ-1) and the norepinephrine transporter (NET) are reported. Exploration of the positions amenable for substitution on a nonaminoacidic Ca_vα2δ-1 scaffold allowed the identification of favorable positions for the attachment of NET pharmacophores. Among the patterns explored, attachment of the 2-ethylamino-9-methyl-6-phenyl-6,7,8,9-tetrahydro-5H-pyrimido[4,5-e][1,4]diazepin-5-one framework to the meta-position of the phenyl ring of the 3-methylamino-1-phenylpropoxy and 3-methylamino-1-thiophenylpropoxy moieties provided dual compounds with excellent NET functionality. Alternative bicyclic frameworks were also explored, and some lead molecules were identified, which showed a balanced dual profile and exhibited good ADMET properties.

4-Aryl-1-oxa-4,9-diazaspiro[5.5]undecane Derivatives as Dual μ-Opioid Receptor Agonists and σ1 Receptor Antagonists for the Treatment of Pain

The synthesis and pharmacological activity of a new series of 1-oxa-4,9-diazaspiro[5.5]undecane derivatives as potent dual ligands for the sigma-1 receptor (σ1R) and the μ-opioid receptor (MOR) are reported. The different positions of the central scaffold, designed using a merging strategy of both target pharmacophores, were explored using a versatile synthetic approach. Phenethyl derivatives in position 9, substituted pyridyl moieties in position 4 and small alkyl groups in position 2 provided the best profiles. One of the best compounds, 15au, showed a balanced dual profile (i.e., MOR agonism and sigma antagonism) and a potent analgesic activity, comparable to the MOR agonist oxycodone in the paw pressure test in mice. Contrary to oxycodone, as expected from the addition of σ1R antagonism, 15au showed local, peripheral activity in this test, which was reversed by the σ1R agonist PRE-084. At equianalgesic doses, 15au showed less constipation than oxycodone, providing evidence that dual MOR agonism and σ1R antagonism may be a useful strategy for obtaining potent and safer analgesics.

Disulfide based prodrugs for cancer therapy

Advances in the tumor microenvironment have facilitated the development of novel anticancer drugs and delivery vehicles for improved therapeutic efficacy and decreased side effects. Disulfide bonds with unique chemical and biophysical properties can be used as cleavable linkers for the delivery of chemotherapeutic drugs. Accordingly, small molecule-, peptide-, polymer- and protein-based multifunctional prodrugs bearing cleavable disulfide bonds are well accepted in clinical settings. Herein, we first briefly introduce a number of prodrugs and divide them into three categories, namely, disulfide-containing small molecule conjugates, disulfide-containing cytotoxic agent–targeted fluorescent agent conjugates, and disulfide-containing cytotoxic agent–macromolecule conjugates. Then, we discuss the complex redox environment and the underlying mechanism of free drug release from disulfide based prodrugs in in vivo settings. Based on these insights, we analyze the impact of electronics, steric hindrance and substituent position of the disulfide linker on the extracellular stability and intracellular cleavage rate of disulfide containing prodrugs. Current challenges and future opportunities for the disulfide linker are provided at the end.

This review summarizes the progress in disulfide linker technology to balance extracellular stability and intracellular cleavage for optimized disulfide-containing prodrugs.

Design, Synthesis, and in Vitro Biological Evaluation of 14-Hydroxytylophorine-dichloroacetate Co-drugs as Antiproliferative Agents

Co-drug, or mutual-prodrug, is a drug design approach consisting of covalently linking two active drugs so as to improve the pharmacokinetics and/or pharmacodynamics properties of one or both drugs. Co-drug strategy has proven good success in overcoming undesirable properties such as absorption, poor bioavailability, nonspecificity, and gastrointestine tract (GIT) side effects. In this work, we successfully developed a co-drug of 14-hydroxytylophorine, a phenanthroindolizidine derivative with remarkable antiproliferative activity, and dichloroacetate, a known inhibitor of pyruvate dehydrogenase kinase. Dichloroacetate steers tumour cell metabolism from glycolysis back to glucose oxidation, which in turn reverses the Warburg effect and renders tumour cells with a proliferative disadvantage. The obtained co-drugs retained the cytotoxicity of 14-hydroxytylophorine. However, they showed similar unselectivity towards normal cells.

Separation of epimeric aromatic acid (-)-menthol esters by countercurrent chromatography using hydroxypropyl-β-cyclodextrin as an additive

The separation of ten epimeric aromatic acid (-)-menthol esters by countercurrent chromatography with hydroxypropyl-β-cyclodextrin as the mobile phase additive was investigated, and methods for the analysis of all the epimeric esters by reversed-phase high-performance liquid chromatography were established. A biphasic solvent system composed of n-hexane/20-70% methanol containing 50 mmol/L of hydroxypropyl-β-cyclodextrin (1:1, v/v) was selected, which provided high separation factors for five of the epimeric esters, and successful separations by countercurrent chromatography were achieved. The complete separation of five pairs of epimeric ester was obtained with the purity being over 98% for each peak fractions, as determined by high-performance liquid chromatography. The recovery of each analyte from the eluted fractions reached around 80-88%.

Application of bis(oxazoline) in asymmetric β-amination of chalcones

A variety of β-imidoketone derivatives containing various functional groups were obtained with high enantioselectivities.

Synthesis and quantitative analysis of diastereomeric linked ester conjugates with remote stereocenters using high-field NMR and chiral HPLC

A stereochemically safe high-yielding procedure for linking unprotected as well as protected hydroxycarboxylic acids to chiral secondary alcohols via glycolic acid linker is proposed. L-menthol has been linked with both enantiomers of mandelic, malic, and methoxyphenylacetic acid using bromo- or iodoacetyl group as a precursor of the glycolic acid linker. High-field nuclear magnetic resonance (NMR) and chiral high-performance liquid chromatography (HPLC) determination of high diastereomeric ratio (dr) (>99%) of the products bearing remote stereocenters was explored. Chiral HPLC allowed quantitation of the diastereomers up to dr 99.9/0.1. High-field NMR quantitation of the diastereomeric and parent alcoholic impurities in esters was demonstrated at the molar 0.3% and 0.03% levels, respectively. These analyses were done via comparison of integral intensities from major component (13)C satellites in (1)H or even in (13)C spectra to the (1)H or (13C signals of impurities. Despite lower sensitivity, the last option generally has much better selectivity. In this way the dynamic resolution is brought down by two orders.

Design, synthesis, hydrolysis kinetics and phamacodynamic profiles of histidine and alanine conjugates of aceclofenac

The gastrointestinal toxicity associated with aceclofenac can be reduced by condensing its carboxylic acid group with methyl esters of amino acids like histidine and alanine to give amide linkage by the Schotten-Baumann method. Physicochemical characterization of the conjugates was carried out by various analytical and spectral methods. The synthesized conjugates were also subjected to in vitro hydrolysis in simulated gastric fluid (SGF) at pH 1.2, simulated intestinal fluid (SIF) at pH 7.4 and SIF+ 80% human plasma at pH 7.4. The release of free aceclofenac from histidine and alanine conjugated aceclofenac showed negligible hydrolysis in SGF compared to SIF. This indicated that the conjugates do not break in stomach, but release aceclofenac in SIF. Both synthesized conjugates showed excellent pharmacological response and encouraging hydrolysis rate in SIF and SIF + 80% human plasma. Marked reduction of the ulcer index and comparable increase in analgesic and anti-inflammatory activities were obtained in both cases compared to aceclofenac alone. These findings suggest that the conjugates are better in action compared to the parent drug and have fewer gastrointestinal side-effects.