Chemotherapeutic Agents

1. Chemotherapeutic Agents

2. Definitions Chemotherapeutic agent: any chemical used to treat disease Antimicrobial agent: any chemical used to treat infection Antibiotic: compound produced by one micro-organism that kills/inhibits another Antiseptic: antimicrobial that is too toxic for internal use Disinfectant: chemical so toxic that it is used only on inanimate objects

3. “The right drug for the right bug” The Golden Rule

4. Soluble in body Stable in body Selectively toxic Consistent Toxicity Non-allergic Bacterial resistance difficult to develop Long shelf life Reasonable cost Ideal Antimicrobial Agent

5. a chemical substance produced by certain molds and bacteria that kills or inhibits the growth of another microorganism Bacteriostatic inhibits Bacteriocidal kills Altough initially isolated as natural products of microorganims, can now also be synthesized in the lab Antibiotic

6. Fungi Bacillus species Actinomycetes Antibiotic producers

7. Discovery of Penicillin • Flemming • in 1928 observed inhibition of Staphylococcus by Penicillium mold • 1930’s • Clinical trials of penicillin • 1940’s • Developed mass production of penicillin due to need for it in World War II S. aureus Penicillium

8. Bacillus sp. • Bacillus sp. • Gram-positive • Spores-formers

9. Streptomyces • member of the bacterial order Actinomycetales • most successful genus in Streptomyces • Over 500 species • Actinomycetes • Gram-positive bacteria. • resemble fungi, but are true bacteria • prokaryotic cells • unlike eukaryotic fungal cells. • non-motile, filamentous • form spores from aerial filaments • distinct from bacterial endospores. • Produce numerous antibiotics • Streptomyces species are found worldwide in soil

10. Selective Toxicity Spectrum of Activity Mode of Action Side Effects Resistance Terms/Concepts of Antimicrobial Agent

11. Concentration that eliminates pathogen Therapeutic dosage level Concentration that causes damage to host Toxic dosage level Chemotherapeutic index = Maximum tolerable dose (per Kg body weight) Minimum therapeutic dose (per Kg body weight) __ High for Penicillin (bacteria) low for heavy metal compounds (worm parasite) Selective Toxicity

12. Range of microorganisms that are affected by agent Broad spectrum Wide range, e.g. both gram-pos & gram-neg Used when infective bacterial agent on is not precisely identified Narrow spectrum Limited number, or specific group of bacteria Used to prevent development of resistance Less of an affect on normal bacterial flora Spectrum of Activity

13. Antibiotic Spectrum Obligate intracellular microorganisms Chlamydia – tiny, non-motile, spherical bacteria Rickettsia – small, non-motile, gram-negative bacteria

14. Antibiotic Mode of Action • Cell Wall • Cell membrane • Protein synthesis • Nucleic Acid Synthesis • Antimetabolites

15. Some clinically important antibiotics

16. Bacteria have a high internal osmotic pressure Without a sturdy cell wall, this pressure will cause membrane to burst Antibiotics can interfere with formation of the cell wall Results in cell death by cell bursting open Cell Wall Disruption

17. Cell Wall penicillin • Penicillin has a 4-member ring • “looks like” part of the cell wall to the cross-linking enzyme • Penicillin competes with the normal cell wall component for the cross-linking enzyme, i.e. competitive inhibition • Prevents this enzyme from cross-linking cell wall

18. Penicillin G is the natural penicillin Produced by Penicillium notatum Administered by injection because is degraded by stomach acids Rapidly absorbed into blood & rapidly excreted Used against:streptococcus, meningococcus, pneumonococcus, spirochetes, clostridia, aerobic gram-positive rods, some staphylococcus and gonococcus Active in urine; so used for urinary tract infections Generally nontoxic Problems Allergic reaction (~5% in adults) Bacterial resistance Penicillin

19. Add a side-chain to the penicillin structure Alters: Chemical characteristics Spectrum of activity Development of bacterial resistance Methicillin Penicillinase resistant resistance by an different mechanism developed Ampicillin broad spectrum ( gram-neg & gram-pos) acid resistant, i.e. oral administration Semi-synthetic Penicillins

20. Cell Wall - Polypeptide Antibiotics • Bacitracin • Produced by Bacillus licheniformis • Small polypeptide • Inhibits cell wall formation • Used on lesions & wounds because: • Poorly absorbed in body • Toxic to kidneys • Vancomycin • Streptomyces • Very narrow spectrum • Used against Staphylococcus that is resistant to penicillin • Vancomycin resistance is now developing

21. Isoniazid (INH) Inhibits synthesis of mycolic acid in cell wall of Mycobacteria Tuberculosis Administered with other antibiotics to prevent development of resistance Ethambutanol Inhibits incorporation of mycolic acid into cell wall Weak drug– just used secondarily to avoid development of resistance to INH Rifampin (inhibits mRNA synthesis) Hits alternative target in cell Cell Wall - Antimycobacterial

22. IsoniazidComplications • Competitive inhibitor of Vitamin B6 • Prevents enzymes from converting Vitamin B6 to useful molecules • Often supplement patient’s diet with extra Vitamin B6 during treatment

23. Echinocandins First new class of antifungals in 40 years Fungal cell walls contain glucans (polysaccharide) Echinocandins inhibit synthesis of glucans So inhibits synthesis of fungal cell wall Cell Wall - Antifungals

24. Act as detergent Distort cell membrane Bind to phospholipids Membrane loses function Selective transport Especially effective against gram-negatives because of their high lipid content in outer membrane Can adversely affect host cells Cell Membrane Disruption

25. From soil bacterium, Bacillus polymyxa Targets prokaryotic membrane Usually for skin infections by gram-negatives Toxic so used internally only under close medical supervision Kidney damage Respiratory arrest Polymyxins

26. Gramicidin • Bacillus brevis • Gram-positive infections • Topical ointment • highly toxic • cannot be administered internally • used only on the skin as a lotion or ointment. • Interacts with bacterial membrane to form channel • Interferes with membrane function • increases the permeability of the bacterial cell membrane

27. Many used for topical application only, due to toxicity for superficial fungal infections only Systemic fungal infections Can be toxic to the animal host Toxicity due to adverse effect on specific tissues kidneys, bone marrow Antifungal antibiotics

28. Amphotericin B • Streptomyces • inhibits membrane function of fungi • selective transport • cell shape • binds to sterols in the cell membranes of fungi • degradation of membrane integrity and cell lysis • Fungal cell membrane contain ergosterol • Animal cells contain cholesterol

29. DNA synthesis inhibition Metronidazoles add functional groups to DNA Makes DNA weak and prone to strand breakage antibacterial and antiprotozoal drug Amebiasis, giardiasis, Helicobacterer pylorii (ulcers) Side effects: nausea, vomiting, diarrhea Nalidixic acid & quinolines specifically bind to enzymes necessary for DNA synthesis DNA gyrase, that uncoils and coils the DNA Prevents DNA replication Bacteria die out Inhibit Nucleic Acid Synthesis

30. Rifampin Streptomyces binds to bacterial RNA polymerase blocks bacterial DNA from transferring its information to RNA Used in U.S. for TB and meningococcus treatment Can cause liver damage Inhibit mRNA synthesis - Transcription

31. Flucytosine Analogue of cytosine Fungi have enzyme to convert Flucytosine to 5-Flurouracil 5-Flurouracil is incorporated into RNA in place of cytosine Disrupts protein synthesis because: Either incorrect amino acid or no amino acid is put into protein protein synthesis stops RNA synthesis disruption - Antifungals

32. RNA translation to protein bacterial ribosomes read the mRNA code bring in the tRNA which holds the anti-codons Carries in proper amino acid to add to polypepetide Antimicrobial agents target the large and small subunits of bacterial ribosomes. because ribosomes of prokaryotes are different from those of eukaryotes (70S vs 80S) Therefore specific to prokaryotic ribosomes Less toxic to eukaryotic host Protein Synthesis - Translation

33. Peptide chain elongation • Streptomycin, kanamycin, tetracycline & neomycin • bind to the smaller 30S ribosomal subunit, • Chloramphenicol, erythromycin & streptogramins • bind to the 50S ribosome • Streptogramins used with vancomycin-resistant pathogens • Can be toxic to kidney & inner ear (ringing) • Tetracycline stains teeth • Chloramphenicol can damage bone marrow • Aplastic anemia • low RBC’s & platelets count

34. Anti-metabolites PABA • Sulfonilamides, or Sulfa drugs • First antimicrobial agent • Folic acid analogue (= similar structure) • Coenzyme necessary for metabolic pathways • Similar structure to a precursor of folic acid • Competitive inhibition • Inhibit synthesis of folic acid • Humans require their folic acid in their diet • humans do not synthesize folic acid • So human metabolism is not inhibited by sulfonilamides • Allergies can develop Sulfanilamide

35. Antiviral • Purine & pyrimidine analogs • Inhibit viral replication • The most effective ones are incorporated more rapidly into viral-infected cells than uninfected cells Purine vidarabine pyrimidine idoxuridine

36. Acyclovir • a guanosine analog • Acyclovir is phosphorylated by viral enzyme • becomes a “false nucleotide” • Viral enzyme has a higher affinity for acyclovir than does host enzyme • If false nucleotide is used by DNA polymerase • will halt DNA synthesis

37. Acyclovir and Thymine Kinase nucleotide nucleoside Nucleoside kinase DNA Polymerae Acyclovir Acyclovir phosphate Nucleoside kinase DNA Polymerae DNA Synthesis stops

38. Interferon • Naturally synthesized by infected host cell • Prevents surrounding cell from being infected • Helps to limit infection

39. Antiprotozoal • Quinines • Malaria; Plasmodium vivax • Interfers with protein synthesis • Especially red blood cells • Prevents parasite from metabolizing hemoglobin as an energy and carbon source • Metranidazole • causes breakage of DNA strands • Trichomonas infections, Giardiasis,

40. Niclosamide Interfers with carbohydrate metabolism tapeworms Mebendazole Interfers with glucose uptake roundworms Piperazine Neurotoxin Paralyzes muscles of worm Can cause convulsions pinworms Antihelminthic

41. Toxicity Allergy Disrupt Normal Flora Superinfection Overgrowth More likely with broad spectrum antibiotics Resistance Side Effects

42. Antibiotic resistance • New enzymes • Degrade or alter antibiotic • Alter Target • can’t bind won’t work • Ribosomes, enzymes • Alter membrane • Prevent transport in • Actively pump out • Bypass affected pathway by using an alternative pathway

43. Destroy Antibiotic

44. Penicillin resistance • Bacteria obtains gene for production of the enzyme lactamase • Breaks covalent bond of the lactam ring of penicillin

45. Resistance by ribosome alteration • A bacterium alters the antibiotic's target • the 50S ribosomal subunit. • The drug is no longer able to bind to the ribosome • Can’t block protein synthesis. Normal ribosome Altered ribosome

46. Alter antibiotic’s transport protein

47. Efflux Mechanism– Pump Antibiotic out

48. Development of Antibiotic Resistance

49. Transferring Antibiotic Resistance

50. Increase in Antibiotic Resistance