University:
West Coast University
Course:
PHAR 837 | IPC Infectious Diseases I
Academic year:

2024
Views:

178

Pages:

54
Author:

Asal A.

Focus onMottand majorsidefents Antimicrobial Agents: Inhibitors of Protein Synthesis Adam Kassan, PhD Associate Professor, Pharmaceutical Sciences West Coast University, School of Pharmacy akassan@westcoastuniversity.edu 323-454-5071 mainenzymetoinhibit Topoisomerase pp Transop Introduction: Ribosomal Structure Bacteria 70S • 30S small subunit • 50S large subunit Eukaryotes 80S • 40S small subunit • 60S large subunit S: Svedberg (sedimentation rate) The 2 subunits: • Composed of  rRNA or formsribosom  proteins • Fit together and work as one to translate mRNA into protein DNA transcription MRNA Translation protein Ribosomeareimparted MRNA fanslate Ribsone inthe ing x Allhaben outgo Introduction: Translation I Initiation SES M Ribosome P Site Ribosomal subunit gym 305 tRNA go I Anticodon Ribosomal subunit mRNA Components needed to begin translation come together. isalways acid firstamino ME Start codon Second codon mRNA On the assembled ribosome, a tRNA carrying the first amino acid is paired with the start codon on the mRNA. The place where this first tRNA sits is called the P site. A tRNA carrying the second amino acid approaches. starts AOG RNAisgoing ÉTransfer conto tostartonthePI Ac Introduction: Translation Elongation peptides prinooitsite A site P Site to New Peptide bond forms P site TonsERNA A site E site E site exits Start codon Second codon I On the assembled ribosome, a tRNA carrying the first amino acid is paired with the start codon on the mRNA. The place where this first tRNA sits is called the P site. A tRNA carrying the second amino acid approaches. mRNA mRNA The second codon of the mRNA pairs with a tRNA carrying the second amino acid at the A site. The first amino acid joins to the second by a peptide bond. This attaches the polypeptide to the tRNA in the P site. Introduction: Translation Elongation EgYterners P site E site at P site tRNA released P site A site A site Growing polypeptide chain A site mRNA E site E site Ribosome moves along mRNA mRNA 1 The ribosome moves along the mRNA until the second tRNA is in the P site. The next codon to be translated is brought into the A site. The first tRNA now occupies the E site. theymoveby 3bases whichis mRNA I coded The second amino acid joins to the third by another peptide bond, and the first tRNA is released from the E site. The ribosome continues to move along the mRNA, and new amino acids are added to the polypeptide. Introduction: Translation ratesandgoback everything set 3 Termination as totheoutsole Polypeptide released P site E site mRNA A site New protein mRNA Stop codon When the ribosome reaches a stop codon, the polypeptide is released. To 30 Finally, the last tRNA is released, and the ribosome comes apart. The released polypeptide forms a new protein. Inhibitors of Protein Synthesis Inhibitors of protein synthesis Agents targeting 30S Aminoglycosides • • • • • • • Streptomycin Gentamicin Neomycin Tobramycin Paromomycin Amikacin Plazomicin Tetracyclines Agents targeting 50S Macrolides Lincosamides Streptogramins Oxazolidinones Pleuromutilins Chloramphenicol Aminoglycosides: Introduction • Streptomycin:  isolated from Streptomyces griseus (1944)  2nd most historically relevant antibiotic to be isolated, after penicillin • Other aminoglycosides  subsequently isolated from various organisms: o Gentamicin (Garamycin) o Neomycin (Mycifradin) o Tobramycin (Tobrex) o Paromomycin (Paromycin)  Semi-synthetic: o Amikacin (1971) (Amikin) o 7Plazomicin (2018) (Zemdri) Amin glucose Aminoglycosides: SAR • A core of 2-deoxystreptamine ring  except streptomycin o streptidine core  to which various amino sugars are attached by glycosidic linkages makeshydrogeBond groups Aminoglycosides: SAR • Lots of polar groups  amino and hydroxyl groups  hydrogen bond with the rRNA e t If wecan Notmatchexactlythebase wi anticodon intheexactaminoacid wewillhavemutation Aminoglycosides: Mechanism of Action ME Protein synthesis site 5' • Irreversible binding to 30S  16s rRNA  selective for bacteria • Ribosomal misreading  protein mutation  membrane alteration 3 • Block 30s movement along mRNA  inhibit protein synthesis U • Bactericidal Growing polypeptide Tunnel Growing polypeptide Chloramphe Translation 50S 50S portion 30S mRNA 3' Three-dimensional detail of the protein synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic ribosome Messenger RNA Streptomycin Changes shape of 30S portion, causing code on mRNA to be read incorrectly Protein synthesis site tRNA 30S portion 70S prokaryotic ribosome Direction of ribosome movement Aminoglycosides: Mechanism of Action • Initially present at low concentrations inside the bacterial cell  taken up poorly by bacteria • Incorporation of incorrect amino acids 1 9519 polypeptides into nascent • The abnormal proteins insert into the bacterial membranes  forming pores and causing membrane damage  allow additional aminoglycoside molecules to flood into the cell • Causing complete inhibition of ribosome activity inactiveAmino Aaas adengliphohydroxyl W E Aminoglycosides: Mechanism of Resistance was enzymes (AMEs) • Aminoglycoside modifying  enzymes that inactivate aminoglycosides by: o acetylation of amino groups o phosphorylation of hydroxyl groups o adenylation of hydroxyl groups 2 • Reduced drug uptake 0583 upregulation of efflux pump  structural changes to the outer membrane of gram –ve (porins)  upregulation of membrane protease o break down the faulty proteins 3 • Mutations in the 30S subunit  drugs unable to bind a Aminoglycosides: Therapeutic Applications bogey astyages Monogram • Narrow spectrum (as monotherapy) of 8D• Synergistic  when administered with agents which disrupts cell wall synthesis o β-lactams, vancomycin o broader spectrum Aminoglycosides: Pharmacokinetics • Polar nature  poor oral absorption o used orally for their local effect within the intestines  do not penetrate BBB or the eye • Administered IM or IV for a systemic effect  septicemia Bipoisoning • Excreted unchanged in the urine  dose adjustment in renal impairment • t½ ~ 2-3 h  24-48 h in case of renal impairment  8-11 h in newborns IthEverslockade a Aminoglycosides: Adverse Effects • Alsoinvoncony Butitshare To All aminoglycosides are ototoxic and nephrotoxic a  special affinity to kidney and sensory cells of the inner ear • Nephrotoxicity (8%-26%)  tubular necrosis  reversible acute renal failure • Ototoxicity  hearing loss  vertigo • 3 Neuromuscular blockade  muscle weakness, respiratory paralysis (apnea)  usually after very high dose  reversible by calcium gluconate Aminoglycosides: Adverse Effects 9 • Avoid during pregnancy  fetal ototoxicity • 5 Avoid concurrent use of other nephrotoxic drugs  amphotericin B, vancomycin, loop diuretics •6 Caution in patients > 60 years of age and those with renal impairment 7 • Do not mix in the same syringe with β-lactams 305 ItsTetracyclines: Introduction • Most widely prescribed antibiotics after penicillins • Characterized by 4 linearly fused six-membered rings • First isolated from Streptomyces aureofaciens  chlortetracycline (Aureomycin) (1948) • Other tetracyclines  subsequently isolated from different natural sources o Tetracycline (Wesmycin) o Doxycycline (Oracea)  semi-synthetic o 3 Minocycline (Minocin) oWTigecycline (Tygacil) Tetracyclines: SAR • Substituents at positions 6 and 7  not essential • Any other substitution g detrimental for activity • Lots of polar groups  amino and hydroxyl groups  hydrogen bond with the rRNA Tetracyclines: Mechanism of Action Protein synthesis site 5' Growing polypeptide Growing polypeptide Translation 50S 50S portion 30S 3' mRNA Three-dimensional detail of the protein synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic ribosome Messenger • Reversible binding to 30S RNA  16s rRNA  selective for bacteria • Block binding of tRNA to the A site  inhibit addition of further amino acids to the nascent peptide 3• Bacteriostatic tRNA 30S portion 70S prokaryotic ribosome Direction of ribosome movement Tetracyclines Interfere with attachment of tRNA to mRNA–ribosome complex RIME Mr Tetracyclines: Resistance • Widespread resistance  used largely in farming • Ribosomal protection protein  prevents binding of tetracycline to ribosomes • Impaired penetration  upregulation of efflux proteins o tetracyclines removal 3 modification of porins o blocking tetracycline penetration •a Enzymatic inactivation Tetracyclines: Newer Drugs Introduction of amino groups in the D-ring • At position 7  minocycline (Minocin)(2002) o improves activity against bacteria that have gained resistance as a result of efflux pump • At position 7 and 9  tigecycline (Tygacil)(2005) o improves activity against bacteria that have gained resistance as a result of - efflux pump - mutation to the ribosomes lots propino Tetracyclines: Chelation • Di- and trivalent cations reduce absorption of tetracyclines  by forming non-absorbable chelates o permanent discoloration in children and infants - contraindicated in pregnancy and children younger than 8 we years old • Incompatible ions must be taken 1h before or 2h after tetracycline Ca++ Al+++ Fe++ Fe+++ Mg++ Tetracyclines: Pharmacokinetics • Absorption after oral administration:  tetracycline 60-70%  doxycycline and minocycline 95-100%  tigecycline poorly absorbed o must be administered IV • Tetracycline should be administered on empty stomach  absorption is inhibited by ~ half if taken with food • Doxycycline and minocycline absorption is not impaired by food Tetracyclines: Pharmacokinetics • Widely distributed  cross the placenta and breast milk  saliva and gingival crevicular fluid (GCF) o concentrations ~4 times serum levels o beneficial for dental use • Stored in dentin and enamel of unerupted teeth • Excreted in urine and bile  except doxycycline and tigecycline o mainly bile (safer with kidney diseases)  No significant CYP450 metabolism o inducers of Cyp40 increase doxycycline metabolism Tetracyclines: Adverse Effects and Drug Interaction I• GI effects  nausea, vomiting, diarrhea  associated with esophageal ulcers  superinfection 2• CNS effects  dizziness •3 Kidney and liver damage •aAntianabolic effects •S Photosensitivity • Tigecycline FDA warning 2013  high rate of mortality  only when alternative treatment are not suitable Bactrastatic s So I go Macrolides: Introduction • Macrolide  large macrocyclic lactone ring • Bacteriostatic • Erythromycin  isolated from Saccharopolyspora erythraea (1952) inhibitproteinsynthesis Macrolides: SAR • 14 membered macrocyclic lactone ring  extensive interaction with A-site • Cladinoseno sugar  hydroxyl group important for activity • DesosamineseeSagar  amine group important for activity  hydroxyl group crucial for activity Macrolides: Erythromycin Acid Sensitivity • Unstable to stomach acids  coated tablets • Acid-catalyzed internal cyclic ketal formation  due to the presence of o ketone o 2 hydroxyl groups Macrolides • • • • Erythromycin (Ery-tab) Incomplete absorption  inactivated by gastric acid Excreted in the bile t1/2 ~1.6h Metabolized by CYP3A4 into different metabolites  inhibit CYP3A4  ↑conc. of numerous drugs • • • • • Haddygroupwasapre se addedmethoxy Clarithromycin (Biaxin) Methoxy analogue of erythromycin  improved oral absorption Hepatic first pass metabolism  reduces bioavailability by 50%-55% Metabolized in the liver into several metabolites  14-hydroxyl-clarithromycin is active 20-40% excreted unchanged in the urine t1/2 ~3-7h (5-9h for the 14-hydroxy) Macrolides Erythromycin (Ery-tab) • • • • Azithromycin (Zithromax) Incorporated N-methyl group  results in 15-membered macrolide  does not inactivate CYP P450 Rapidly absorbed orally with high distribution  including phagocytes Mainly excreted through bile  12% excreted unchanged in urine t1/2 ~40-68h  extensive tissue sequestration and binding Macrolides: Ketolides • • • • • • Telithromycin (Ketek) (2004) Ketolide structure  cladinose sugar replaced with a keto-group The 2 hydroxyl groups replaced by  methoxy group at C6  carbamate ring at C12 Heteroaromatic ring at the end of the extended substituent  form pi-pi interaction with ribosome Rapid oral absorption Metabolized by the liver  eliminated by a combination of biliary and urinary routes Severe hepatotoxicity have limited its use in the US  only for treatment of community-acquired bacterial pneumonia Bindclosetopsite inhibitribosomemovement an Macrolides: Mechanism of Action Tunnel Protein synthesis site Growing polypeptide Growing polypeptide Macrolides Binds to 50S portion and inhibits formation of peptide bond 5' 50S 50S portion 30S P Site Three-dimensional detail of the protein synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic ribosome Messenger RNA Translation Protein synthesis site 3' mRNA tRNA 30S portion Direction of ribosome movement 70S prokaryotic ribosome • Bacteriostatic • Binds close to P-site of the 50S  inhibit ribosome movement ave t Nothsynthesis protein Macrolides: Pharmacokinetics • Usually administered orally  intestinal absorption is limited by the P-glycoprotein (ABCB1) • Excreted in the bile by ABCB1 • Lipophilic and widely distributed in the body • Erythromycin and clarithromycin  metabolized by CYP3A4 in the liver o into active metabolites o excreted mainly in the bile • Azithromycin  not metabolized by CYP3A4 o mostly excreted unchanged into the bile Macrolides: Adverse Reactions I • GI effects  nausea, vomiting, and diarrhea paralysis of promote  most common with erythromycin ppg stomach magnet ao used as prokinetic in patient with gastroparesis •2 Hepatotoxicity (rare but serious)  cholestatic hepatitis  telithromycin is associated with liver failure • 3 Cardiac toxicity  QT interval elongation o effect on potassium ion channels Macrolides: Drug Interactions • Should not be administered with chloramphenicol  bind to the same region of ribosome  mutual antagonism • Erythromycin and clarithromycin  inhibit CYP3A4 o increase statins plasma concentration RIME Macrolides: Resistance • Modification of ribosomal binding site  by chromosomal mutations • Reduced permeability  increased efflux • 3 Production of esterases or phosphotransferases  that modify the macrolide DNA RNA app Macrolides: Fidaxomicin (Dificid) • New addition to the arsenal of clinically useful antibiotics (2011) • Natural product from Dactylosporangium • Non absorbed, narrow-spectrum  good for the GI tract flora • Bactericidal agent for the treatment of only C. difficile • Inhibit RNA polymerase • Classified as macrolide by the FDA Lincosamides: Introduction • Similar spectrum as macrolides • Similar mechanism of action as macrolides • Lincomycin (Lincocin)  first to be discovered  isolated from Streptomyces lincolnensis (1962) • Clindamycin  semi-synthetic  increased activity  associated with C. difficile superinfection Lincosamides: SAR • Contain an unusual 8-carbon sugar  linked by amide to pyrrolidin ring • Propyl substituent  binds near A-site • Sugar ring • binds to a similar region as the desosamine in the macrolides • Hydroxyl groups  hydrogen bonds with nucleotides • Substitution of hydroxyl group with Cl in clindamycin  more lipophilic o better absorption Lincosamides: Resistance • Similar to macrolides (cross-resistance with macrolides):  mutation of the ribosomal binding site  however, not affected by efflux • Should not be combined with macrolides, or chloramphenicol  proximal binding sites Lincosamides: Pharmacokinetics and Adverse Effects as • Nearly completely absorbed after oral administration • t1/2~3h • Widely distributed  including bones  CSF low penetration o but enough to treat toxoplasmosis • Highly protein bound >90% • Accumulates in macrophages and abscesses • Metabolized by the liver CYP3A4  into both active and inactive metabolites o excreted by the urine and the bile • Clindamycin is associated with high risk of C. difficile superinfection agonist fall power y MRSA go Streptogramins I Pristinamycin: • Derived from Streptomyces pristinaespiralis • Mixture of two components  pristinamycin IA Pristinamycin IA  pristinamycin IIA (streptogramin A) • Each binds to 50S subunit and inhibits the elongation process  moderate bacteriostatic activity  combination of both substances o acts synergistically - 100X more active than separate components o leads to a potent bactericidal activity • Poor solubility  limited use by the lack of IV formulation Pristinamycin IIA against powerful MRSA Streptogramins or Quinupristin/dalfopristin (Synercid): • Limited use in the USA • Combination of two antibiotics (30:70 ratio) • Derived from pristinamycin  quinupristin o derived from pristinamycin IA Quinupristin  dalfopristin o from pristinamycin IIA • Synergism (bactericidal)  dalfopristin causes conformational change in the 50S  enhances binding of quinupristin • Water soluble  IV  MRSA and VREF Dalfopristin Streptogramins: Resistance and Toxicity • Enzymatic:  dalfopristin-inactivating acetyltransferase  quinupristin-inactivating hydrolase  loss of synergism (bacteriostatic) • Binding site mutation • Efflux outofthem cat • The principal toxicities are infusion-related events  such as pain at the infusion site psynthe Inhibit atmucheartierstep translation To Oxazolidinones: Mechanism of Action Inhibit protein synthesis at much earlier step than previous agents: • Bind to unique site on 23S RNA of the 50S  no cross resistance with other drug classes • Prevent 70S formation (larger ribosomal-fMet-tRNA complex)  translation cannot start • Resistance is caused by mutation of the binding site on 23S rRNA Oxazolidinones: Adverse Effects mad • Generally well tolerated pope the•A Myelosuppression Reversible apt  thrombocytopenia is the most common (~ 3% of cases)  monitor CBC especially in prolonged treatment •Z Mitochondrial toxicities  with prolonged treatment (>6weeks)  peripheral neuropathy, optic neuritis, lactic acidosis it hyperses tyramine Oxazolidinones: Drug Interactions titmitnathitic ma • Linezolid is an inhibitor of monoamine oxidase A (MOA-A)  caution with patients receiving adrenergic or serotonergic agents (esp. SSRIs) o serotonin syndrome (FDA warning)  caution when eating tyramine-containing food (>100mg/day) o risk of hypertensive crisis • Not CYPs substrates or inhibitors Chloramphenicol: Introduction • Originally isolated from Streptomyces venezuelae  now prepared synthetically • First broad-spectrum oral antibiotic used in the US (1948)  decreased use due to toxicity  no longer available in the US as an oral formulation Chloramphenicol: Mechanism of Action Tunnel Protein synthesis site Growing polypeptide Growing polypeptide Chloramphenicol Binds to 50S portion and inhibits formation of peptide bond P site 5' 50S 50S portion 30S E site Protein synthesis site 3' mRNA Three-dimensional detail of the protein synthesis site showing the 30S and 50S subunit portions of the 70S prokaryotic ribosome Messenger RNA Translation A site tRNA 30S portion Direction of ribosome movement 70S prokaryotic ribosome • Bacteriostatic • Binds reversibly to A-site of the 50S  inhibits ribosome movement Chloramphenicol: Resistance • Enzyme mediated (chloramphenicol acetyltransferase)  catalyzes hydroxyl groups  loss of binding to ribosomes • Escherichia coli is frequently resistant  lack of intracellular accumulation Chloramphenicol: Pharmacokinetics • IV preparation  chloramphenicol succinate o prodrug hydrolyzed by esterase to chloramphenicol in vivo • Well distributed throughout virtually all tissues and body fluids  including CSF • t1/2 ~4h • Metabolized mainly by glucuronidation in the liver  inactive metabolites  excreted in urine Chloramphenicol: Adverse Effects • Bone marrow suppression  aplastic anemia (fatal in ~70% of the cases) • “Gray baby” syndrome  usually 2-9 days after treatment  inability to metabolize the drug Chloramphenicol: Drug Interactions • Potent CYP450 inhibitor  mainly CYP2C19 and CYP3A4  Inhibits metabolism of warfarin, phenytoin…

Inhibitors of Protein Synthesis

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