The Use of Zidovudine Pharmacophore in Multi-Target-Directed Ligands for AIDS Therapy

The concept of polypharmacology embraces multiple drugs combined in a therapeutic regimen (drug combination or cocktail), fixed dose combinations (FDCs), and a single drug that binds to different targets (multi-target drug). A polypharmacology approach is widely applied in the treatment of acquired immunodeficiency syndrome (AIDS), providing life-saving therapies for millions of people living with HIV. Despite the success in viral load suppression and patient survival of combined antiretroviral therapy (cART), the development of new drugs has become imperative, owing to the emergence of resistant strains and poor adherence to cART. 3'-azido-2',3'-dideoxythymidine, also known as azidothymidine or zidovudine (AZT), is a widely applied starting scaffold in the search for new compounds, due to its good antiretroviral activity. Through the medicinal chemistry tool of molecular hybridization, AZT has been included in the structure of several compounds allowing for the development of multi-target-directed ligands (MTDLs) as antiretrovirals. This review aims to systematically explore and critically discuss AZT-based compounds as potential MTDLs for the treatment of AIDS. The review findings allowed us to conclude that: (i) AZT hybrids are still worth exploring, as they may provide highly active compounds targeting different steps of the HIV-1 replication cycle; (ii) AZT is a good starting point for the preparation of co-drugs with enhanced cell permeability.

Co-drug of isoniazid and sulfur containing antioxidant for attenuation of hepatotoxicity and treatment of tuberculosis

The prolonged use of isoniazid (INH) - a highly effective drug in the treatment of tuberculosis - causes fatal liver injury. In order to overcome this adverse effect, a unique amide codrug was designed by covalently linking INH with sulfur-containing antioxidant- alpha-lipoic acid for possible hepatoprotective and antimycobacterial effect. Co-drug LI was prepared by Schotten Baumann reaction and was characterized by spectroscopic analysis. To check the bioreversibility of LI, in vitro release tests were conducted in buffers of specific pH, stomach, and intestinal homogenates of rat employing HPLC. Male Wistar rats were used for the evaluation of the hepatoprotective activity. Liver function markers, oxidative stress markers, and biochemical parameters were estimated. The antimycobacterial efficacy of LI was examined in terms of its ability to decrease the lung bacillary load in Balb/c mice infected intravenously with Mycobacterium tuberculosis. LI resisted hydrolysis in buffers of pH 1.2 (acidic), pH 7.4 (basic), and stomach homogenate of the rat while displayed significant hydrolysis (88.19%) in intestinal homogenates over a period of 6 h. The effect of LI on liver function, antioxidant and biochemical paradigms was remarkable as it reestablished the enzyme levels and restored hepatic cytoarchitecture representing its abrogating effect. The findings of antimycobacterial activity assessment evidently demonstrated that LI was as potent as INH in lowering the mycobacterial load in mice. The outcome of this exploration confirmed that the described co-drug can offer desirable safety and therapeutic benefit in the management of tuberculosis.

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.

Boosting GSH Using the Co-Drug Approach: I-152, a Conjugate of N-acetyl-cysteine and β-mercaptoethylamine

Glutathione (GSH) has poor pharmacokinetic properties; thus, several derivatives and biosynthetic precursors have been proposed as GSH-boosting drugs. I-152 is a conjugate of N-acetyl-cysteine (NAC) and S-acetyl-β-mercaptoethylamine (SMEA) designed to release the parent drugs (i.e., NAC and β-mercaptoethylamine or cysteamine, MEA). NAC is a precursor of L-cysteine, while MEA is an aminothiol able to increase GSH content; thus, I-152 represents the very first attempt to combine two pro-GSH molecules. In this review, the in-vitro and in-vivo metabolism, pro-GSH activity and antiviral and immunomodulatory properties of I-152 are discussed. Under physiological GSH conditions, low I-152 doses increase cellular GSH content; by contrast, high doses cause GSH depletion but yield a high content of NAC, MEA and I-152, which can be used to resynthesize GSH. Preliminary in-vivo studies suggest that the molecule reaches mouse organs, including the brain, where its metabolites, NAC and MEA, are detected. In cell cultures, I-152 replenishes experimentally depleted GSH levels. Moreover, administration of I-152 to C57BL/6 mice infected with the retroviral complex LP-BM5 is effective in contrasting virus-induced GSH depletion, exerting at the same time antiviral and immunomodulatory functions. I-152 acts as a pro-GSH agent; however, GSH derivatives and NAC cannot completely replicate its effects. The co-delivery of different thiol species may lead to unpredictable outcomes, which warrant further investigation.

Design, synthesis and in vitro degradation of a novel co-drug for the treatment of psoriasis

Psoriasis is a common, chronic and relapsing inflammatory skin disease. It affects approximately 2% of the western population and has no cure. Combination therapy for psoriasis often proves more efficacious and better tolerated than monotherapy with a single drug. Combination therapy could be administered in the form of a co-drug, where two or more therapeutic compounds active against the same condition are linked by a cleavable covalent bond. Similar to the pro-drug approach, the liberation of parent moieties post-administration, by enzymatic and/or chemical mechanisms, is a pre-requisite for effective treatment. In this study, a series of co-drugs incorporating dithranol in combination with one of several non-steroidal anti-inflammatory drugs, both useful for the treatment of psoriasis, were designed, synthesized and evaluated. An ester co-drug comprising dithranol and naproxen in a 1:1 stoichiometric ratio was determined to possess the optimal physicochemical properties for topical delivery. The co-drug was fully hydrolyzed in vitro by porcine liver esterase within four hours. When incubated with homogenized porcine skin, 9.5% of the parent compounds were liberated after 24 h, suggesting in situ esterase-mediated cleavage of the co-drug would occur within the skin. The kinetics of the reaction revealed first order kinetics, Vmax = 10.3 μM·min-1 and Km = 65.1 μM. The co-drug contains a modified dithranol chromophore that was just 37% of the absorbance of dithranol at 375 nm and suggests reduced skin/clothes staining. Overall, these findings suggest that the dithranol-naproxen co-drug offers an attractive, novel approach for the treatment of psoriasis.