Using direct-acting agents to target resistant bacteria
Introduction
From 1990–2000, there was a worrying trend in the field of bacterial infections. A surge in resistant strains was observed across the world, with methicillin-resistant Staphylococcus aureus (MRSA) being the most prevalent. Several resistant strains since have been identified, however preventive and curative methods largely remain elusive. Access and unregulated use of antibiotics have further accelerated the risk of antimicrobial resistance (AMR). According to a recent statistical study, the mortality rate due to AMR was twice in India when compared to the United States of America, emphasizing the importance of newer approaches to tackle the problem.
One way the global research ecosystem is exploring enhancement of antimicrobial potency is through research on peptides that act as membrane-active compounds or transport molecules. These antimicrobial peptides (called AMPs) can consist of 5 to 100 amino acids. So far, around 5000 AMPs, classified as small molecules, have been identified from multiple sources [1].
Natural AMPs are found in both eukaryotes and prokaryotes. In animals, tissues exposed to airborne pathogens produce AMPs as a first line of defense. Other tissues like lymph nodes, the digestive track lining, and epithelia cells also produce AMPs, as these tissues interact with foreign particles. Frog skin can be a source of hundreds of different AMPs.
Based on either their biochemical nature or mechanism of action, AMPs can be classified as cationic host defense peptides, anionic antimicrobial peptides/proteins, cationic amphipathic peptides, cationic AMPs, host defense peptides, and α-helical antimicrobial peptides. With respect to mechanism of action, AMPs are broadly classified as either direct-acting small molecules or indirect-acting small molecules.
Direct acting agents
Direct-acting AMPs function to kill their bacterial targets. They directly interact with the external membranes or walls of micro-organisms. This is achieved by varied mechanisms, but a common feature is insertion of AMPs into the membranes to disrupt it in various ways. This insertion can be into both or a single layer of the membrane, in an aggregate manner or as an individual peptide. This insertion of AMPs either thins the membrane (detergent effect) to make cell porous, disrupts the normal functioning of the cell membrane at a localized region, or forms pores killing the microorgansims [2].
As these are proteins with no enzymatic action it is easy to immobilize them on surfaces, modify their structure through recombinant DNA technology, synthesize AMP mimetic antimicrobial peptides, combine them with polymers and organometallic complexes etc. Hence, much scientific innovation is being seen to optimize AMPs and overcome some drawbacks such as easy degradation and cytotoxicity to human tissue.
The approach of conjugating AMPs with functional polymers, to form peptide-polymer conjugates (PPC) has been promising. PPC approach has helped increase biocompatibility, while reducing the cytotoxicity of direct acting AMPs. This makes PPCs a promising antimicrobial class against resistant bacteria [3].
Innovations in AMR
C-CAMP and Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X) have recognized and supported multiple projects in this regard [4]. Gangagen Biotechnologies Pvt Ltd, a drug designing company based in Bangalore was funded by CARB-X for their novel product “klebicins” [5]. Klebicins is an engineered antibiotic protein which targets multi drug-resistant (MDR) Klebsiella pneumoniae, and extended-spectrum beta lactamases (ESBL) expressing K. pneumoniae as well [6].
K. pneumoniae is an opportunistic pathogen that causes pneumonia and neonatal sepsis. MDR K. pneumoniae is of greater health concern in low and middle-income countries as it is airborne and can spread far and wide. Klebicins are narrow spectrum and hence the effect on normal flora is expected to be limited. The drug is in its initial stages of development. In future it will be further developed with the partnership of CARB-X, for the protein engineering and development of klebicins for the treatment of hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) [7].
Most resistant strains were initially identified in Gram-positive bacteria [8]. Tuberculosis caused by Mycobacterium tuberculosis is one of the deadly diseases already shown to have multiple drug MDR types. FNDR Labs along with the support by C-CAMP and BIRAC programs are developing a novel direct acting molecule extracted from the soils of Antarctica [9].
Like Gram-positive bacteria in the 2000’s, 8 drugs were shown to have developed resistance in Gram-negative bacteria leading to need of innovative approaches for tackling this problem [10]. One such product is called “Gyrox” a broad-spectrum, direct acting small molecule developed by Bugworks, supported by C-CAMP and funded by CARB-X. Gyrox, inhibits the enzyme gyrase ( a Type II topoisomerase). Type II topoisomerases are an important DNA replication enzyme and Gyrox inhibits this thus stopping bacterial growth. For Gyrox pre-clinical trials have shown promising efficacy against gram-negative superbugs and is poised to be released for usage in the near future [11].
C-CAMP with its innovative funding and research opportunities have supported multiple research projects to understand and tackle AMR especially focusing on direct acting agents.
PepThera, a drug design company are designing small molecules to target bacterial cell membranes [12]. Abtids by Abgenics, another C-CAMP supported company, uses modified small antibodies derived from camels, that are being used as an efficient platform to deliver a peptide that is toxic for pathogens [13].
Conclusion
Direct acting agents may hold the key to developing next generation of antimicrobials in general and targeted therapies against known resistant pathogens as well. The natural abundance of them in various species and tissues along with the ability to pair them with novel delivery systems and platforms makes this technology unique. The combination of fundamental research to identify naturally occurring peptides and their mechanism of action and innovations in delivery and conjugate systems must be equally supported by the research and innovation eco-systems of the world.
Disclaimer: The blog is a compilation of information on a given topic that is drawn from credible sources; however, this does not claim to be an exhaustive document on the subject. It is not intended to be prescriptive, nor does it represent the opinion of C-CAMP or its partners. The blog is intended to encourage discussion on an important topic that may be of interest to the larger community and stakeholders in associated domains
References:
1. https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001974
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3873676/
3. https://www.hindawi.com/journals/ijps/2022/7610951/
6. https://www.frontiersin.org/articles/10.3389/fimmu.2022.835417/full
7. https://carb-x.org/portfolio/portfolio-companies/
8. https://www.medicalnewstoday.com/articles/gram-positive-vs-gram-negative
9. https://www.fndr.in/portfolio
10. https://www.medicalnewstoday.com/articles/gram-positive-vs-gram-negative
