Prodrug Design to Improve Pharmacokinetic and Drug Delivery Properties: Challenges to the Discovery Scientists

The prodrug design is a versatile, powerful method that can be applied to a wide range of parent drug molecules, administration routes, and formulations. Clinically, the majority of prodrugs are used with the aim of enhancing drug permeation by increasing lipophilicity, or by improving aqueous solubility. Prodrug design may improve the bioavailability of parent molecule, and thus can be integrated into the iterative process of lead optimization, rather than employing it as a post-hoc approach. The purpose of this review is to provide an update of advances and progress in the knowledge of current strategic approaches of prodrug design, along with their real-world utility in drug discovery and development. The review covers the type of prodrugs and functional groups that are amenable to prodrug design. Various prodrug approaches for improving oral drug delivery are discussed, with numerous examples of marketed prodrugs, including improved aqueous solubility, improved lipophilicity, transporter-mediated absorption, and prodrug design to achieve site-specific delivery. Tools employed for prodrug screening, and specific challenges in prodrug research and development are also elaborated. This article is intended to encourage discovery scientists to be creative and consider a rationally designed prodrug approach during the lead optimization phase of drug discovery programs, when the structure activity relationship (SAR) for the drug target is incompatible with pharmacokinetic or biopharmaceutical objectives. Keywords: Absorption, bioavailability, carrier-mediated transport, drug targeting, permeability, prodrug, solubility, transporter, lipophilicity, transporter-mediated absorption, structure ac-tivity relationship (SAR), pharmacokinetic properties, intestinal epithelium, blood-brain barrier, distribution, metabolism, and excretion (ADME), Bioprecursor, sulindac, Losartan, Oxidative, cyclophosphamide, antiproliferative agent, neoplastic cells, hypoxia, antiparasitic, nitroarenes, metronidazol, antimicrobial prodrugs, antitubercular, nitroimidazooxazine, cytotoxic agents, Bopindolol, Dipivefrine, Glaucoma, Spirapril, Melevodapa, Mestranol, Nitazoxamide, Terfenadine, Viramidine, omeprazole action, Carrier-linked prodrugs, oseltamivir, bambuterol, bacampicillin, oximes, Quinapril, Enalapril, angiotensin-converting enzyme (ACE), Phosphate Ester Prodrugs, Acyloxyalkyl Prodrugs, Carbamate Prodrugs, Docarpamine, Schiff Base Prodrugs, γ-aminobutyric acid (GABA), P-glycoprotein, enterocyte, protease inhibitors, desglymidodrine, Gabapentin, colonic mucosa, Chemical delivey System (CDS), Sulfasalazine, Tumour Targeting, Capecitabine, antibody-directed enzyme prodrug therapy (ADEPT), gene-directed enzyme prodrug therapy (GDEPT), Nitroreductase, nucleoside monophosphonate (NMP), 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA), Simvastatin, Lovastatin, Caco-2, nalbuphine, fosphenytoin, hydroxyethylnicotinamide, adefovir dipivoxil, polymorphism, tenofovir disoproxil, Acyclovir, Hepatic clearance, Gancyclovir