Current Topics in Medicinal Chemistry - Volume 21, Issue 24, 2021

Drug development is a very time, capital, and labor-intensive process. It was anticipated that bringing a novel chemical entity to market would take over a billion dollars and around 14 years [1]. In addition, drug development is characterized by a very high attrition rate both in preclinical and clinical studies. It was reported that only 40% of drug candidates with the most drug-like properties could make their way into clinical trials, and only 10% of these can eventually reach FDA approval [2]. After analyzing the data from seven UK128;based pharmaceutical companies from 1964 through 1985, Prentis et al. found that 39% of failure was attributed to poor pharmacokinetic (PK) profiles in humans, 29% was attributed to a lack of clinical efficacy, 21% was attributed to toxicity and adverse effects, and about 6% was attributed to commercial limitations [3]. When a drug candidate is identified with one of these issues (except the commercial limitations), normally, a new round of structureactivity or structure-property relationship (SAR/SPR) studies is carried out to generate a new chemical entity with improved profiles, and in most cases, such a process is time and labor-intensive. Alternatively, prodrug strategy can be leveraged to efficiently address associated drug developability issues without making enormous derivatives. Prodrug strategy has been demonstrated to be very successful and fruitful in drug development, with around 20% of approved drugs from 2008 through 2020 being clarified as prodrugs [4]. In recent years, prodrug strategy has also been leveraged to address the delivery issues associated with gasotransmitters, including NO, H2S, CO as well as SO2 [5-8]. In this thematic issue, six excellent reviews were included, focusing on varied prodrug strategies in addressing different drug developability issues associated with anticancer drugs, central nervous system (CNS) drugs, and gasotransmitters....

Prodrug design is an effective method proven to improve the drug-like properties of a molecule, and it has been widely used in the drug development of various diseases. Due to the complexity of the central nervous system (CNS), the development of CNS drugs has high requirements related to the pharmaceutical, pharmacokinetic, and pharmacodynamic properties of the molecules. Prodrug design has now been widely and successfully applied to improve these properties. We conducted a mini-review to promote the use of the prodrug strategies in CNS drug development. To facilitate the description, we chose drug indications as a clue, then presented and discussed some representative CNS prodrugs. Finally, a brief summary and outlook about this area were presented.

Amino acids derived prodrugs emerged as an attractive approach to improve oral delivery of drugs with low solubility and permeability. Conjugation of amino acids with parent drug molecules resulted in several-fold increases in water solubility. Acceptability of the amino acids derived prodrug approach increases day by day to fulfill the different characteristics needed to get the desired pharmacological or therapeutic activity. Due to the significant structural diversity of amino acids, various amino acids can be employed as a carrier to provide desirable Pharmacokinetic-Pharmacodynamic (PK-PD) characteristics. The present review focused on using amino acids as a carrier moiety to improve approved drugs' bioavailability. Attempts have been made to cover amino acid conjugated clinically available drugs.

Cancer is the second leading cause of human death after cardiovascular disease, and the most used drugs in clinics are cytotoxic agents. However, these drugs have some inherent disadvantages, such as the risk of toxicity, low selectivity, poor solubility, and so on. To overcome these shortcomings, a variety of drug delivery strategies based on prodrugs have been developed. The application of drug delivery systems can optimize ADME properties of cytotoxic agents and improve their selectivity at the target, thereby greatly enhancing the anticancer effect in clinics. At present, it has become mainstream in drug design. This review systematically summarized the studies of prodrug- based drug delivery systems over the past five to ten years, according to four aspects, solubility, controlled release, in situ concentration, and targeting.

Uncaging chemistry catalyzed by transition metals is developed from deprotection reactions and metal-organic catalytic reactions. Also, it has the characteristics of high efficiency, simplicity and rapidity in the living biological system. In the past decade, metal encapsulation systems (such as nanoparticles) and metal complexes have been developed to reveal the reactivity of transition metals (including palladium, ruthenium, and gold) in biological systems. Metal nanostructures provide huge possibilities for targeted drug delivery, detection, diagnosis and imaging. So far, palladium, ruthenium and gold nano-architectures have dominated the field, but there are some problems that hinder their wide application in clinical practice. In this review, based on palladium, ruthenium, gold and their complexes, the application of prodrug design through uncaging reaction has been widely discussed.

Biofilms are among the most important causes of nosocomial and recurrent infections as biofilms confer antibiotic resistance to pathogenic bacteria and protect them from the host’s immune system. Thus, it is imperative to investigate effective therapeutic agents to counteract biofilms. As an important signaling molecule, Nitric Oxide (NO) plays a crucial role in various biological and pathological processes. NO could disperse biofilm and restore the drug sensitivity by reducing intracellular cyclic-diguanosine monophosphate (c-di-GMP) levels. This review highlights recent advances on antibacterial and antibiofilm effects of NO when NO was co-administered with other antimicrobial agents. A significant improvement in drug permeability and biofilm cell targeting and reduced cytotoxicity could be attained with this strategy. In this review, we briefly lay out challenges and propose future directions in this appealing avenue of research on NO-based therapy for biofilm eradication.

Hydrogen sulfide (H2S), as one of the endogenous gasotransmitters, has shown great potential in treating cardiovascular diseases (CVDs). H2S plays a protective role in CVDs by removing reactive oxygen species (ROS), promoting vasodilation, inhibiting myocardial hypertrophy, preventing thrombosis, and protecting mitochondria. However, there still exist some problems for H2S as drugs such as challenging delivery, uncontrollable release rate, and other drug developability issues. Addressing these problems, the prodrug strategy shows great potential. Therefore, a key issue on the H2S-based therapeutics is developing appropriate H2S prodrugs. In this review, we mainly discussed the mechanism of H2S against CVDs and reviewed the cardiovascular effects of current H2S prodrugs.