Discovery of new AMR drugs targeting modulators of antimicrobial activity using in vivo silkworm screening systems

The Journal of Antibiotics https://doi.org/10.1038/s41429-024-00788-2 REVIEW ARTICLE Discovery of new AMR drugs targeting modulators of antimicrobial activity using in vivo silkworm screening systems Fumiaki Tabuchi1 Kazuhiro Mikami1,2 Masanobu Miyauchi1 Kazuhisa Sekimizu ● ● ● 3 ● Atsushi Miyashita 1 1234567890();,: 1234567890();,: Received: 1 April 2024 / Revised: 27 October 2024 / Accepted: 30 October 2024 © The Author(s) 2024. This article is published with open access Abstract Global concerns about drug-resistant bacteria have underscored the need for new antimicrobial drugs. Emerging strategies in drug discovery include considering the third factors that influence drug activity. These factors include host-derived elements, adjuvants, and drug combinations, which are crucial in regulating antimicrobial efficacy. Traditional in vivo assessments have relied on animal models to study drug absorption, distribution, metabolism, excretion, and toxicity (ADMET). Alternative models, such as silkworms, are being explored to overcome the ethical and financial barriers associated with mammalian models. The silkworm has been proven effective in evaluating ADMET and in highlighting the therapeutic potential enhanced by third factors. Host factors (either mammalian or non-mammalian) enhance the antimicrobial activity of antimicrobial agents such as lysocin E. Additionally, using D-cycloserine to potentiate vancomycin has successfully combated vancomycin-resistant infections in silkworms. Leveraging silkworms in drug discovery could establish a novel screening method incorporating interactions with third factors, whether host related or non-host-related, thus promising new pathways for identifying antimicrobial drugs with unique mechanisms of action. Introduction Currently, the spread of pathogens resistant to multiple drugs, known as Antimicrobial Resistance (AMR), poses a global clinical challenge and has become a significant societal issue [1]. Examples of such drug-resistant bacteria include Methicillin-resistant Staphylococcus aureus (MRSA), Multidrug-resistant Pseudomonas aeruginosa (MDRP), and the pathogenic fungus Candida auris. Alongside the proliferation of these drug-resistant pathogens, there is a concerning trend towards a decrease in the number of new antimicrobial drugs reaching the market [1, 2], raising fears of a depletion of effective antimicrobial treatments available for clinical use. Therefore, there is an urgent need to develop drugs with new mechanisms of action. To address this challenge, accelerating infectious disease drug discovery through novel approaches different from traditional methods is crucial [1–3]. Enhancing the efficiency of exploratory research, particularly in the initial phase of drug discovery, is essential to prepare for the emergence of new drug-resistant bacteria and to expand the foundation for generating a diverse array of seed compounds. This review focuses on the development of drugs targeting factors that regulate the activity of antimicrobials, with the aim of overcoming infections caused by drugresistant bacteria. Traditional antimicrobial drug discovery strategies and their limitations * Atsushi Miyashita 1 Teikyo University Institute of Medical Mycology, Hachioji, Tokyo, Japan 2 Graduate School of Medical Care and Technology, Teikyo University, Itabashi, Tokyo, Japan 3 Faculty of Pharma-Science, Teikyo University, Itabashi, Tokyo, Japan Recently, in addition to the “bilateral interaction” between pathogens and antimicrobial agents, the existence of a third factor that synergistically interacts with antimicrobials has been highlighted [4]. The third factor in this context is defined as a substance other than the antimicrobial agent and its target, which influences the therapeutic effect of the antimicrobial agent. Incorporating this third factor into the traditional bilateral F. Tabuchi et al. interaction is expected to pave the way for new discoveries in infectious disease drug development; however, the lack of sufficient knowledge regarding this concept, apart from a few attempts (e.g., see [5]), remains a challenge. One of the challenges in infectious disease drug discovery based on bilateral interactions is that many seed compounds identified in exploratory research demonstrate antimicrobial activity in vitro but fail to show therapeutic efficacy in vivo. Mechanisms contributing to this discrepancy traditionally include factors such as absorption, distribution, metabolism, and excretion within the body, and potential toxicity [6, 7]. Therefore, it is crucial to gather information on pharmacokinetics and toxicity early in the exploration phase to identify promising compounds. In recent years, the significance of substances that interact with antimicrobials to enhance their therapeutic activity has grown. Examples of such third factors include apolipoprotein A-I, which can influence antimicrobial activity [4]. Failure to consider these factors during screening may lead to overlooking potential antimicrobial agents. Moreover, the requirement for candidate compounds to have low toxicity in vivo means that traditional screening methods based solely on the interaction between pathogens and drugs are inefficient in discovering effective drugs. Combination antimicrobial drugs Antibiotics such as penicillin and streptomycin were administered as single agents at the time of their development. However, antibiotics are now given in combination to enhance antibacterial activity and combat the emergence of drug-resistant bacteria. The presence of combination drugs also affects the action of antimicrobial agents. The combination of sulfamethoxazole and trimethoprim is a typical antimicrobial combination, which is known to act synergistically in terms of antimicrobial activity [8]. The simultaneous administration of sulfamethoxazole and trimethoprim, which inhibit different enzymes in the folic acid synthesis pathway, is known to synergistically exhibit antimicrobial activity against pathogenic bacteria [9]. Moreover, the combination of amoxicillin and gentamicin has been shown to have a synergistic therapeutic effect on mice infected with penicillin-resistant Streptococcus pneumoniae, making the combination of antimicrobial drugs an important strategy for overcoming drug-resistant bacterial infections [10]. Additionally, colistin, known for disrupting cell membranes, acts synergistically with various antibiotics against colistin-resistant Enterobacteriaceae species [11]. A model diagram of the molecular mechanism of the interaction between the antimicrobial agent and the other factor described is shown (Fig. 1a & Table 1). Factors influencing the activity of antimicrobial drugs Host endogenous factors One interaction factor that affects the activity of antimicrobial drugs is host endogenous factors. Certain antimicrobial drugs have been suggested to have capability of interacting with host molecules, leading to enhancement (...truncated)