Antibacterial Drugs - Advanced Pharmacology Sem 1 2024-2025 PDF

PHARMACOLOGY Antibacterial drugs ADVANCED AHBS 4378 Current strategy in drug discovery antibiotics? Penicillium notatum, the source of penicillin. penicillin had clinical potential, both as a topical anti...

PHARMACOLOGY Antibacterial drugs ADVANCED AHBS 4378 Current strategy in drug discovery antibiotics? Penicillium notatum, the source of penicillin. penicillin had clinical potential, both as a topical antiseptic and as an injectable antibiotic, if it could be isolated and purified. R-side chain Thiazolide ring Beta lactam ring  Beta-Lactams Beta-lactams are a wide range of antibiotics, the first of which to be discovered was penicillin, which Alexander Fleming identified in 1928. All beta-lactam antibiotics contain a beta-lactam ring; they include penicillins, such as amoxicillin, and cephalosporins. They work by interfering with the synthesis of peptidoglycan, an important component of the bacterial cell wall, and are mostly used against gram-positive bacteria. Bacteria can, however, develop resistance to beta- lactams via several routes, including the production of enzymes that break down the beta-lactam ring. In the NHS, penicillins are the most commonly prescribed antibiotics, with amoxicillin being the most common in the class.  Sulfonamides Prontosil, a sulfonamide, was the first commercially available antibiotic, developed in 1932. A significant number of sulfonamide antibiotics were subsequently developed, defined as broad- spectrum antibiotics capable of acting on both Gram-positive and Gram-negative bacteria. Unlike the beta-lactams, they do not act by directly killing the bacteria, but by inhibiting bacterial synthesis of the B vitamin folate, thus preventing the growth and reproduction of the bacteria. In the present day, sulfonamides are rarely used, partially due to the development of bacterial resistance, but also due to concern about unwanted effects such as hepatotoxicity.  Aminoglycosides Aminoglycosides inhibit the synthesis of proteins in bacteria, eventually leading to cell death. They are only effective against certain Gram-negative bacteria, as well as some Gram-positive bacteria, but are not absorbed during digestion, so must be injected. In the treatment of tuberculosis, streptomycin was the first drug found to be effective; however, due to issues with toxicity of aminoglycosides, their present-day use is limited.  Tetracyclines Tetracyclines are broad-spectrum antibiotics, active against both Gram-positive and Gram- negative bacteria. Like the sulfonamides, they inhibit protein synthesis, inhibiting the growth and reproduction of bacteria. Their use is decreasing due to increasing instances of bacterial resistance; however, they still find use in the treatment of acne, urinary tract, and respiratory tract infections, as well as chlamydia infections. They must be taken in isolation, often two hours before or after eating, as they can easily bind with food, reducing their absorption.  Chloramphenicol Another broad-spectrum antibiotic, chloramphenicol also acts by inhibiting protein synthesis, and thus growth and reproduction of bacteria. However, it is also bactericidal against a limited number of bacteria. Due to the possibility of serious toxic effects, in developed countries it is generally only used in cases where infections are deemed to be life-threatening, although it is also occasionally used in the treatment of eye infections. Despite this, it is a much more common antibiotic in developing countries due to its low cost and availability, and is recommended by the World Health Organisation as an effective first-line treatment for meningitis in those countries with a low income.  Macrolides Much like the beta-lactams, the macrolides are mainly effective against Gram-positive bacteria; however, they act in a bacteriostatic manner, preventing growth and reproduction by inhibiting protein synthesis. Their effectiveness is marginally broader than that of penicillins, and they are effective against several species of bacteria that penicillins are not. Whilst some bacterial species have developed resistance to macrolides, they are still the second most commonly prescribed antibiotics in the NHS, with erythromycin being the most commonly prescribed in the class.  Glycopeptides Glycopeptides include the drug vancomycin – commonly used as a ‘drug of last resort’, when other antibiotics have failed. Whilst this used to be the last line of defence against infections, particularly MRSA, the more recent development of newer antibiotics in other classes has provided other options. Nonetheless, there remain strict guidelines on the circumstances in which vancomycin can be used to treat infections, to delay the development of resistance. The bacteria against which glycopeptides are active are otherwise somewhat limited, and in most, they inhibit growth and reproduction rather than killing bacteria directly.  Oxazolidinones Oxazolidinones are active against Gram-positive bacteria and act by inhibiting protein synthesis, and hence growth and reproduction. Linezolid, approved for use in 2000, was the first marketed antibiotic in the class, although the compound cycloserine has been used as a second- line tuberculosis treatment since 1956. Whilst linezolid is expensive, resistance seems to be developing relatively slowly since its introduction.  Ansamycins This class of antibiotics are effective against Gram-positive bacteria, as well as some Gram- negative bacteria. They inhibit the production of RNA, which has important biological roles inside the cells of the bacteria, and as such leads to the death of the bacterial cells. A subclass of antibiotics, rifamycins, are used to treat tuberculosis and leprosy. Uncommonly, ansamycins can also demonstrate anti-viral activity.  Quinolones Quinolones are bactericidal compounds that interfere with the replication and transcription of DNA in bacteria cells. They are broad-spectrum antibiotics and are widely used for urinary tract infections, as well as other hospital-acquired infections where resistance to older classes of antibiotics is suspected. Additionally, their use for veterinary purposes is widespread; a use that has been criticised in some quarters for hastening the development of resistance. Resistance to quinolones can be particularly rapid in its development; in the US, they were the most commonly prescribed antibiotics in 2002, and their prescription for unrecommended conditions or viral infections is also thought to be a significant contributor to the development of resistance.  Streptogramins Streptogramins are unusual in that they are usually administered as a combination of two antibiotic drugs from the different groups within the class: streptogramin A and streptogramin B. On their own, these compounds only show growth-inhibiting activity, but combined they have a synergistic effect and are capable of directly killing bacteria cells, by inhibiting the synthesis of proteins. They are often used to treat resistant infections, although resistance to the streptogramins themselves has also developed.  Lipopeptides Discovered in 1987, lipopeptides are the most recent class of antibiotics and are bactericidal against Gram-positive bacteria. Daptomycin is the most commonly used member of the class; it has a unique mechanism of action, disrupting several aspects of cell membrane function in bacteria. This unique mechanism of action also seems to be advantageous in that, currently, incidences of resistance to the drug seem to be rare – though they have been reported. It is given via injection, and commonly used to treat infections in the skin and tissue. mechanism of actions Beta lactam  Beta lactam Green Thumbs Garden Cafe | Gardening for Food Beta lactam N-acetylmuramic acid (NAM N-acetylglucosamine (NAG) Green Thumbs Garden Cafe | Gardening for Food Beta lactam N-acetylmuramic acid (NAM N-acetylglucosamine (NAG) Green Thumbs Garden Cafe | Gardening for Food Beta lactam Penicillin binding protein bind the amino acids producing bridge Green Thumbs Garden Cafe | Gardening for Food Beta lactam beta-lactam inhibit PBPs thus inhibit the cross bridge to form peptidoglycan Green Thumbs Garden Cafe | Gardening for Food Beta lactam Green Thumbs Garden Cafe | Gardening for Food DD transpeptidase (part of PBP) - a bacterial enzyme which cross-links the peptidoglycan chains to form rigid cell walls. Beta lactam Green Thumbs Garden Cafe | Gardening for Food penicillin binds to transpeptidase, prevent the enzyme to bind to peptidoglycan peptide beta lactam beta-lactamase cleaved beta-lactam ring Green Thumbs Garden Cafe | Gardening for Food beta lactam beta-lactamase cleaved beta-lactam ring Green Thumbs Garden Cafe | Gardening for Food  beta lactam mutation in PBP gene Green Thumbs Garden Cafe | Gardening for Food Sulphonamides sulphonamides sulphonamides have almost similar structure to PABA sulphonamides PABA needed to produce folic acids in bacteria sulphonamides folic acids needed for DNA replication - cell division. sulphonamides interruption of folic acids reduce DNA replication - thus reduce cell division. sulphonamides mutation in both enzymes reduce the action of the drugs - alternative pathway; by passing enzyme dependent step sulphonamides overproduction of PABA - to outcompete sulphonamides for enzyme binding sulphonamides activate efflux pump Aminoglycosides  aminoglycoside Green Thumbs Garden Cafe | Gardening for Food aminoglycoside Fact about aminoglycoside! Its uptake through cells Green Thumbs Garden Cafe | membrane require energy derived Gardening for Food from aerobic metabolism Thus not effective for anaerobes! aminoglycoside Fact about aminoglycoside! Effective against Gram negative Green Thumbs Garden Cafe | over Gram positive Gardening for Food Less able to penetrate thick peptidoglycan  aminoglycoside Green Thumbs Garden Cafe | Gardening for Food aminoglycoside mutation ribosome hinder Green Thumbs Garden Cafe | binding with AG Gardening for Food aminoglycoside produce enzyme to Green Thumbs Garden Cafe | methylate ribosome - prevent binding Gardening for Food aminoglycoside produce modification (AME) Green Thumbs Garden Cafe | enzyme - covalently modify the hydroxyl or amino Gardening for Food groups AG AME - aminoglycoside modifying enzyme aminoglycoside Green Thumbs Garden Cafe | modify cell membrane - less Gardening for Food permeable for AG  aminoglycoside activate efflux pump Green Thumbs Garden Cafe | Gardening for Food Tetracyclines  tetracycline Green Thumbs Garden Cafe | Gardening for Food  tetracycline Green Thumbs Garden Cafe | Gardening for Food tetracycline (a) Tetracyclines bind to repressor protein Tet(R), which results in its Green Thumbs Garden Cafe | dissociation from mRNA and facilitates the expression of Gardening for Food tetracycline-specific efflux pumps  tetracycline (b) Ribosomal protection proteins (RPPs) can prevent Green Thumbs Garden Cafe | the binding of tetracyclines to the Gardening for Food ribosome, allowing translation to proceed. Chloramphenicol  Chloramphenicol Green Thumbs Garden Cafe | Gardening for Food  binds to peptidyl transferase - prevent peptide binding - stop translation  Acetylation of Chloramphenicol chloramphenicol by chlorampenicol acyltransferase Green Thumbs Garden Cafe | Reduce ability chloramphenicol to Gardening for Food binds to peptidyl transferase Macrolides  macrolides Green Thumbs Garden Cafe | Gardening for Food  Binds near the peptidyltransferase center → prevents peptidyl transferase from adding amino acids to a growing peptide (prevents transpeptidation) macrolides Methylation of macrolides binding site prevent the binding of macroides to the 50S ribosome subunit Glycopeptides Glycopeptides Glycopeptides glycopeptides binds to peptides (alanine changed into lactate) Glycopeptides Bacteria modify the D-Ala-D-Ala target site, replacing it with D-Ala-D-Lactate Glycopeptides reduce binding affinity of vancomycin Oxazolidinones Oxazolidinones Oxazolidinones prevent the formation of 70s complex (interaction between 50s and 30s subunit) -initial step in translation Oxazolidinones Mutation in 23srRNA of 50s subunit prevent oxazolinidone to its target Quinolones fluroquinolones 1. Quinolone binds to cleavage complex of topoisomerase-DNA template DNA can't be resealed in presence of quinolone fluroquinolones 2&3 If the cleavage complex is not resolved, replication and transcription cannot happen, which causes slow bacterial cell death fluroquinolones 4&5 topoisomerase removed, double- strand break is free, left unrepaired, leads to the fragmentation of the chromosome, which causes rapid bacterial cell death fluroquinolones 6 removal of the topoisomerase from the cleavage complex, might lead to the accumulation of reactive oxygen species (ROS) that can cause rapid fluroquinolones 6 Fact about quinolones! removal of the topoisomerase from Gram-negative bacteria have porins the cleavage that allow easier penetration of the complex, might leaddrug into the cell, whereas Gram- to the accumulation positive bacteria have thicker of reactive oxygen peptidoglycan layers and may have species (ROS) that reduced permeability can cause rapid fluroquinolones mutation in gyrase gene (type II topoisomerase) - reduce affinity of fluroquinolones to gyrase enzyme Streptogramins Streptogramins Quinupristin (Group A) interferes with the early stage of protein elongation by preventing the incorporation of amino acids into the growing peptide chain. This disrupts the synthesis of proteins in the bacteria. Dalfopristin (Group B) prevents the release of the synthesized protein from the ribosome, effectively causing premature termination of protein synthesis. Streptogramins acetyltransferases can acetylate the drug, and phosphotransferases can phosphorylate it, preventing it from binding to the ribosome. can use efflux pumps to actively pump the streptogramins out of the bacterial cell, Lipopeptides Lipopeptides 1) Oligomerization of 14-16 units of daptomycin in the presence of calcium (Ca 2+ ). 2) Interaction of daptomycin micelle with the cell membrane. 3) Dissociation of the daptomycin. 4) Insertion of daptomycin in the membrane via lipid tail. 5) Oligomerization of the daptomycin in the membrane and 6) Pore formation, depolarization, and cell death. Lipopeptides increase the negative charge on the membrane or alter the expression of phosphatidylglycerol, he membrane component that interacts with the lipopeptide, Polymyxins  bactericidal action of polymyxin by targeting lipopolysaccharide on outer membrane and inner membrane Gram-negative bacteria.  Binding to the Outer Membrane: Polymyxins are cationic (positively charged) and lipophilic (fat-soluble) molecules, allowing them to interact with the lipopolysaccharide (LPS) layer of the outer membrane of Gram- negative bacteria. The LPS layer is a major component of the bacterial outer membrane and carries a negative charge.  Disruption of the Outer Membrane: Once bound to the LPS, polymyxins insert into the membrane and disrupt its structure. They displace calcium and magnesium ions that help stabilize the membrane. This destabilization causes membrane disruption and increased permeability, which leads to leakage of cellular contents such as ions, proteins, and other essential molecules.  Damage to the Inner Membrane: In addition to disrupting the outer membrane, polymyxins can also affect the inner membrane (cytoplasmic membrane) of the bacteria. This further exacerbates the loss of cellular integrity and impairs the cell's ability to maintain its internal environment.  Bactericidal Effect: The disruption of the membrane and the resulting leakage of cellular contents leads to cell death. This makes polymyxins bactericidal, meaning they actively kill the bacteria rather than merely inhibiting their growth.  Modification of the LPS can reduce its negative charge, making it less likely to interact with the cationic polymyxin. Addition of aminoarabinose or phosphoethanolamine groups to the LPS can reduce the binding affinity of polymyxins, preventing them from disrupting the membrane. mechanism of antibiotics resistance https://www.imr.gov.my/images/uploads/NSAR/2021/NSAR-2021_to- be-uploaded.pdf  What is antimicrobial resistance (AMR)? AMR - when the germs (bacteria, virus, fungi, parasite) no longer can be killed or inhibited by the available antimicrobial drugs  What is antimicrobial resistance (AMR)? AMR - when the germs (bacteria, virus, fungi, parasite) no longer can be killed or inhibited by the available antimicrobial drugs Top 5 AMR organisms (AMROs) urgent threat: Carbapenem-resistant Acinetobacter Candida auris Clostridiodes difficile Carbapenem-resistant Enterobactericiae Drug-resistant Neisseria gonorrhea  Why has AMR become a global concern? AMR - when the germs (bacteria, virus, fungi, parasite) no longer respond to the available antimicrobial drugs  Pe 19 19 nic 42 illi Pe 41 nic n illi n 19 Te 50 tra cyc lin e antimicrobial drugs 19 respond to the available Ery 53 Te thr tra 1 om virus, fungi, parasite) no longer AMR - when the germs (bacteria, cyc 959 yci lin ne e Me 1 thi 96 19 cil 2 Me 60 lin thi cil lin Ery thr 1 19 om 968 Ge 67 ici nta n mi cin Ge 19 nta 19 Va 72 mi 79 nc cin om yci n Antibiotic resistance Antibiotic introduced Ce 19 fta 19 zid 87 Im 85 im Va e Ce ipen fta em nc 19 zid & om 88 im Lev yci e ofl 19 n ox 96 ac 19 in Lev 96 Im 1 ofl ipe 99 ox ne 8 ac m in 20 Lin 00 ezo lid Lin 20 Ce ez 01 fta o2li0 rol d11 20 ine Ce 10 fta Why has AMR become a global concern? Ventola, 2015 rol Udin et al., 2021 ine Why has AMR become a global concern? Multi-drug or pan-drug pathogen, that are not treatable with the existing antimicrobial drugs rapidly spread to human population Why has AMR become a global concern? Multi-drug or pan-drug pathogen, that are not treatable with the existing antimicrobial drugs rapidly spread to human population In 2019, WHO declared AMR as among top 10 public health threat on human population Global cases of antimicrobial resistance  WHO report of 2019: AMR responsible for >700 000 death Estimation 20 million cases in 2050  CDC Antibiotic Resistance Threats report 2019: > 2.8 million antibiotic- resistance infections/ year in US causing >35,000 deaths  European Antimicrobial Resistance Surveillance Networks (EARS-Net): Methycillin Resistant Staphylococcus aureus (MRSA) affect > 119, 000 people in US >19, 000 fatal case  Pe 19 19 nic 42 illi Pe 41 nic n illi n 19 Te 50 tra cyc lin e 19 Ery 53 Te thr tra 1 om cyc 959 yci lin ne e Me 1 thi 96 19 cil 2 Me 60 lin thi cil lin Ery thr 1 19 om 968 Ge 67 ici nta n mi cin Ge 19 nta 19 Va 72 mi 79 nc cin om yci n Antibiotic resistance Antibiotic introduced Ce 19 fta 19 zid 87 Im 85 im Va e Ce ipen fta em nc 19 zid & om 88 im Lev yci e ofl 19 n ox 96 ac 19 in Lev 96 Im 1 ofl ipe 99 ox ne 8 ac m in 20 Lin 00 ezo lid Lin 20 Ce ez 01 fta o2li0 rol d11 20 When antimicrobial resistance occur? ine Ce 10 fta Ventola, 2015 rol Udin et al., 2021 ine How antimicrobial resistance developed? How antimicrobial resistance developed? Natural process in microbes in adapting the surroundings (Selective pressure eg. exposure to antibiotic): How antimicrobial resistance developed? Natural process in microbes in adapting the surroundings (Selective pressure eg. exposure to antibiotic): Genetic modification (mutation on antibiotic target) eg. Mutation in Penicillin Binding Protein (PBP) results in inability of the penicillin to bind to cell How antimicrobial resistance developed? Natural process in microbes in adapting the surroundings (Selective pressure eg. exposure to antibiotic): Genetic modification Resistance gene transfer (mutation on antibiotic target) (to other microbes) eg. Mutation in Penicillin Binding Protein (PBP) results in inability of the penicillin to bind to cell  Natural process occurs within control rate. But the AMR become issues because of drastic cases of AMR involved various types of organism, antimicrobial drugs and human population globally How antimicrobial resistance developed? Natural process in microbes in adapting the surroundings (Selective pressure eg. exposure to antibiotic): Genetic modification (mutation on Ab critical target) eg. Mutation in Penicillin Binding Protein (PBP) cause the penicillin cannot bind to the cell Genetic resistance gene transfer (to other microbes) What influence the selective pressure? What influence the selective pressure? Inaccurate diagnosis and Overuse of prescription of antibiotic antibiotics What influence the selective pressure? Inaccurate diagnosis and Overuse of prescription of antibiotic antibiotics Expose to antibiotics trigger the mutagenesis in microbes. Antibiotic given not effective towards target pathogen, killed the non-target bacteria which could be useful to protect from pathogen. Resistant strains dominated the site, multiply and spreads. Graham et al., 2019  Current strategies to overcome AMR  Combination strategy Develop new drug Target resistance mechanism Use antimircobial peptides Nanotechnology Phage therapy Antibiotic stewardship  Combination Therapy Using two or more antibiotics or drugs together to enhance efficacy and reduce resistance development. Combination antibiotic therapy is used in critically ill patients due to widespread emergence of multidrug resistance organisms (MDR). Multidrug resistance is defined as lack of susceptibility to at least one agent in three or more antibiotic categories. Examples: Beta-lactams + Aminoglycosides: Effective for gram-negative bacteria (e.g., Pseudomonas infections). Vancomycin + Rifampin: Used for multidrug-resistant gram-positive infections.  Development of New Antibiotics Discover novel compounds that bacteria have not yet encountered. Examples: Siderophore Cephalosporins (e.g., Cefiderocol): Target iron uptake systems in Gram-negative bacteria. Teixobactin: A new antibiotic class effective against Gram- positive pathogens.  siderophore is a small, high-affinity iron-chelating molecule secreted by microorganisms, such as bacteria and fungi, to acquire iron from their environment.  Mechanism of Siderophore-Enhanced Cephalosporin Uptake Iron Scavenging Mimicry: Siderophores are naturally produced by bacteria to bind iron (Fe³⁺), an essential nutrient. Siderophore-cephalosporins mimic these natural siderophores by including a siderophore-like structure in their molecular design. Binding to Iron: The siderophore moiety in the antibiotic chelates ferric iron (Fe³⁺), forming a siderophore-iron complex. Recognition by Bacterial Transport Systems: Gram-negative bacteria have specialized outer membrane receptors for siderophores. The siderophore-iron complex is recognized by these receptors and actively transported into the bacterial cell. Drug Delivery to the Periplasm: Once inside, the cephalosporin component of the drug is released and reaches its target: penicillin- binding proteins (PBPs). This disrupts bacterial cell wall synthesis, leading to cell death.  Use of Antimicrobial Peptides (AMPs) AMPs disrupt bacterial membranes or inhibit essential pathways. It is a short, naturally occurring peptides that form part of the innate immune defense in many organisms Examples: Polymyxins: Effective against multidrug-resistant gram- negative bacteria. Natural peptides (e.g., defensins, cathelicidins).  Figure 4. Models of action for extracellular AMP activity. (a) Barrel-stave model: AMPs aggregate into multimers and insert into the lipid bilayer, aligning parallel to the phospholipids and forming transmembrane channels. (b) Toroidal pore Model: AMPs embed perpendicularly into the membrane, bending to form a continuous pore through the lipid bilayer. (c) Carpet model: AMPs accumulate on the membrane surface, acting similarly to detergents, leading to membrane disruption and cell lysis  Phage Therapy Using bacteriophages (viruses that infect bacteria) to target and kill specific bacterial strains. Advantages: Highly specific, minimizing damage to normal flora. Effective against multidrug-resistant bacteria.  Targeting Resistance Mechanisms Inhibitors for Efflux Pumps: Inhibit bacterial efflux pumps to retain antibiotics inside the cell. Example: Relebactam, used with imipenem-cilastatin. Inhibitors for Biofilm Formation: Disrupt biofilms that shield bacteria from antibiotics. Example: Enzymes like DNase or quorum-sensing inhibitors. Increase the drug reaches: Use compounds to increase permeability of Gram-negative bacteria. Example: Polymyxins combined with other antibiotics. Silence resistance genes: Use antisense RNA to bind to bacterial mRNA, disrupt translation and silence the production of resistance protein.  Nanotechnology in Antibacterial Therapy Use nanoparticles to deliver antibiotics directly to bacteria. Examples: Silver nanoparticles disrupting bacterial membranes. Liposomal formulations for targeted delivery. Mechanisms of action of NPs. Destruction of bacterial cell wall and cell membrane, Over production of reactive oxygen species (ROS) that produce oxidative stress and damage vital intracellular macromolecules, as well as inflict protein damage. Enzyme damage, mitochondrial damage, DNAdamage, alteration in membrane permeability, prevent extrusion of drug through damage of efflux pump, inhibition of electron transport chain and prevent and disrupt biofilm  Antibiotic Stewardship Rational use of antibiotics to minimize unnecessary exposure and resistance. Reduce usage of antibiotic in agriculture Enforce hygiene protocol; handwashing, isolation, sterilization Key Practices: Prescribe narrow-spectrum antibiotics when possible. Avoid misuse, such as using antibiotics for viral infections.