PHAR3B Q&A Session Notes

Selective Toxicity

• Central to chemotherapy is selective toxicity, where drugs target invading organisms or cancer cells while being relatively harmless to the host.
• This relies on biochemical differences between target cells and the host.

Different Classes of Antibiotics

• Aminoglycosides
  • Often bacteriostatic, restricting growth and reproduction.
  • Examples: Streptomycin, neomycin, kanamycin, paromomycin.
  • Mode of action: Inhibit protein synthesis, leading to cell death.
• Glycopeptides
  • Bactericidal, causing bacterial cell death.
  • Examples: Vancomycin, teicoplanin.
  • Mode of action: Inhibit bacterial cell wall biosynthesis.
• Ansamycins
  • Bactericidal, causing bacterial cell death.
  • Examples: Geldanamycin, rifamycin, naphthomycin.
  • Mode of action: Inhibit RNA synthesis by bacteria.
• Streptogramins
  • Bactericidal, causing bacterial cell death. Act synergistically.
  • Examples: Pristinamycin IIA, Pristinamycin IA.
  • Mode of action: Inhibit protein synthesis by bacteria.
• β-Lactams
  • Most widely used antibiotics.
  • Examples: Penicillins (amoxicillin, flucloxacillin), Cephalosporins (cefalexin).
  • Mode of action: Inhibit bacterial cell wall biosynthesis.
• Sulfonamides
  • First commercial antibiotics.
  • Examples: Prontosil, sulfanilamide, sulfadiazine, sulfisoxazole.
  • Mode of action: Prevent bacterial growth and multiplication; can cause allergic reactions.
• Tetracyclines
  • Becoming less popular due to resistance.
  • Examples: Tetracycline, doxycycline, limecycline, oxytetracycline.
  • Mode of action: Inhibit protein synthesis by bacteria.
• Macrolides
  • Second most prescribed antibiotics.
  • Examples: Erythromycin, clarithromycin, azithromycin.
  • Mode of action: Inhibit protein synthesis, occasionally leading to cell death.
• Oxazolidinones
  • Potent antibiotics, commonly used as 'drugs of last resort'.
  • Examples: Linezolid, posizolid, tedizolid, cycloserine.
  • Mode of action: Inhibit protein synthesis by bacteria.
• Quinolones
  • Resistance evolves rapidly.
  • Examples: Ciprofloxacin, levofloxacin, trovafloxacin.
  • Mode of action: Interfere with bacterial DNA replication and transcription.
• Lipopeptides
  • Instances of resistance are rare.
  • Examples: Daptomycin, surfactin.
  • Mode of action: Disrupt multiple cell membrane functions, leading to cell death.
• Chloramphenicol
  • Commonly used in low-income countries.
  • Mode of action: Inhibit synthesis of proteins, preventing growth. No longer a first line drug due to increased resistance and worries around safety.

Chemotherapy Toxicity

• Chemotherapeutic agents should ideally be toxic to pathogens or cancer cells, but harmless to the host (selective toxicity).
• All toxicity is dosage-dependent.
• Chemotherapy without any side effects is theoretically impossible.
• Acceptable toxicity is balanced against the benefit, depending on alternative options and disease severity.

Selectivity by Drug Target

• Unique target in pathogen: Identified through comparative genomics (e.g., haemoglobin degradation by Plasmodium).
• Different importance of target: Target present in host and pathogen, but essential only in the pathogen.
• Different stability of target protein: Target present and essential in host and pathogen, but target enzyme quickly replaced by host.
• Drug has higher affinity for parasite than for host enzyme: Low drug concentrations inhibit pathogen enzymes first (selective inhibitor).

Antimicrobial Drug Targets

• Cell surfaces
• Proteolytic enzymes
• Energy metabolism
• Protein synthesis
• Nucleic acid synthesis
• Nucleic acid replication

Penicillin Inhibition of Cell Walls

• Penicillin inhibits the transpeptidase that cross-links peptide chains in the cell wall, thus inhibiting cell wall construction.
• Irreversible deactivation of the enzyme occurs via binding to a specific serine residue in the binding pocket (covalent bond).
• Penicillin mimics the D-alanyl-D-alanine residues that would normally bind to this site.

Limitations of Antibiotics

• Ineffective against viruses.
• Mostly ineffective against protozoan parasites and helminths.
• Often effective only against a subclass of bacteria.
• Difficult to synthesise/derivatise.
• Antibiotic resistance is guaranteed.

Ergosterol Biosynthesis

• Ergosterol is essential for fungi, making its biosynthesis a valid drug target.
• Unique pathway not present in mammalian cells.
• Complex biosynthesis route with many essential enzymes.
• Targets: Statins, Azoles, Azasterols, Terbinafine

Targeting Aspartic Proteases in Antiparasite Drug Discovery

• Validated drug targets
• Good experimental tools available
• Large body of data on host and some other enzymes
• Expertise exists in academia and industry
• Possibility of ‘piggy-backing’ on existing programmes (HIV, hypertension, Alzheimer’s)
• Potential for multi-target drugs (minimizing resistance)
• Multi-disease drugs are a possibility (reducing cost)

Adaptations of Parasites for Glucose Metabolism

• Intracellular parasites are not exposed to high glucose levels and use mostly amino acids for energy (Leishmania, Trypanosoma cruzi, Toxoplasma).
• Anaerobic protozoa (amitochondriate) use variations on glycolysis and anaerobic re-oxidation of NAD+ (Trichomonas, Giardia, Entamoeba).

Metronidazole Activation

• Metronidazole is activated by metabolic reduction within the hydrogenosome.
• PFOR = pyruvate:ferredoxin oxidoreductase; Fd = ferredoxin
• R-NO2 \rightarrow Metronidazol{red} (free \ radical)

Chloramphenicol

• Binds to the large (50S) subunit of the bacterial ribosome.
• Inhibits the peptidyl transferase step of protein synthesis by binding to 23S rRNA (residues A2451 and A2452).
• Peptidyl transferase is a ribozyme.
• Blocks the elongation of the growing peptide chain by inhibiting the transfer of the chain to the next amino acid / tRNA unit.
• Bacteriostatic, broad-spectrum antibiotic (Gram-positive and Gram-negative).

Folate Synthesis

• Dihydropteroate synthase; inhibited by PABA analogues such as sulphonamides (‘sulpha’).
• Dihydrofolate reductase; inhibited by folate analogues such as Pyrimethamine and Cycloguanil.
• Plasmodium: folates are synthesised from GTP and PABA and are essential for nucleotide metabolism.
• Synthesis of Thymidine MP requires Methylated tetrahydro-folate.

Retroviral Life Cycle (e.g., HIV)

• Targets for inhibitors: Integrase inhibitors, Protease inhibitors, Reverse transcriptase inhibitors, Fusion/entry inhibitors.

Drug Resistance: General Mechanisms

• Reduced drug uptake into the organism.
• Increased efflux of drug.
• Increased breakdown of drug.
• Alterations in drug target (decreased binding/inhibition).
• Increased production of target.

Drug Transporters in Trypanosoma brucei

• HAPT/AQP2: transports Pentamidine, Melarsomine
• TbAT1/P2: transports Adenosine, Pentamidine, Melarsomine, Diminazene
• TbAAT6 : transports Ornithine, Eflornithine

Major Targets of Antibiotics

• Cell Wall Synthesis: Beta Lactams, Penicillins, Cephalosporins, Carbapenems, Monobactams, Vancomycin, Bacitracin
• Cell Membrane: Polymyxins
• Folate Synthesis: Sulfonamides, Trimethoprim
• Nucleic Acid Synthesis: Quinolones (DNA Gyrase), Rifampin (RNA Polymerase)
• Protein Synthesis: Macrolides, Clindamycin, Linezolid, Chloramphenicol, Streptogramins, Tetracyclines, Aminoglycosides

Intrinsic vs. Extrinsic Resistance

• Intrinsic resistance: Innate ability of a bacterial species to resist an antimicrobial agent through its inherent structural or functional characteristics; a natural trait (e.g., anaerobic bacteria showing intrinsic resistance to aminoglycosides).
• Extrinsic resistance: Acquired ability of a microbe to resist an antimicrobial agent to which it was previously susceptible, acquired through mutation or DNA transfer.

Mechanisms of Antiviral Resistance

• Prodrugs: Resistance can be overcome by failing to activate them.
• Allosteric inhibitors: Resistance can be overcome by binding site mutations.
• Competitive inhibitors: Resistance can be overcome by increased substrate specificity or changing to a different substrate.
• Host factors modification: Resistance can be overcome by using alternative factors.

Cytotoxic Drugs

• Target proliferating cells through inhibition of/interference with DNA metabolism.
• Examples: Methotrexate, Mercaptopurine, Thioguanine, 5-Fluorouracil, Gemcitabine, Ara-C, Cisplatin, Nitrogen mustards, Camptothecins, Vinblastine, Paclitaxel, Docetaxel

Hallmarks of Cancer

• Refer to Hanahan D, Weinberg RA. Cell. 2011 extract for more information.

Cancer Chemotherapy Toxicity

• Common toxicities: Vomiting, Alopecia, Nausea, Diarrhoea, Immunosuppression, Anaemia
• Dose-limiting organs: Bone marrow, Intestinal crypts, Hair follicle
• Other effects: Weight loss, Pain, Cognition, Fatigue, Infertility, Memory loss, Edema, Dysgeusia, Neuropathies, Skin rash, Xerostomia, Urinary problems, Appetite loss, Inflammation, Liver/kidney functions

Impact of Microbiome in Drug Pharmacokinetics

• Drug absorption: Bioaccumulation/uptake, bile salt metabolism modification, altered drug uptake.
• Drug metabolism: Activate pro-drug or inactivate/metabolise drug.
• Drug excretion: Removal of glucuronides/sulfates, entry into enterohepatic circulation.
• Drug toxicity: Conversion of parent drug/metabolite into active/toxic form.

Summary of Key Points

• Selective toxicity: Drugs kill pathogens/cancer cells while sparing host cells.
• Employed in antimicrobial pharmacology against bacteria, parasites, fungi, and viruses.
• Drugs target cell surfaces, proteases, energy metabolism, protein/nucleic acid synthesis/replication.
• Resistance mechanisms evolved (e.g., altered expression of transporters).
• Cancer chemotherapy: Evolved from cytotoxic drugs to targeted therapies.
• Resident microbes influence drug PK and response.

PHAR3B Lectures Feedback

• No specific questions were asked about the lectures.

PHAR3B Labs/Workshops Feedback

• No specific questions were asked about the labs or workshops.

PHAR3B Tutorials Feedback

• Hopefully, everyone had 5 tutorials in Semester 2.

PHAR3B Assessments Feedback

• Literature reviews are due on Mon 24 March at 5 pm.
• Mol Methods grades have been released, and feedback will follow.
• Poster grades and feedback will be available in early April.
• Only the Creative Assignment and exams remain.
• There will be an exam preparation session the following week.

Generic Feedback on Lab Reports

• Follow the provided guidance.
• Read scientific papers to learn appropriate terminology.
• Avoid unnecessary details (e.g., calibration).
• Report drug concentrations instead of volumes added.
• Avoid reporting results at individual concentrations in the text.
• Think about the meaning of results and compare them with existing data.
• Explain discrepancies and avoid attributing them to experimental error.
• Give intracellular mechanisms underlying observed effects.
• Do not draw conclusions based on things you didn’t measure (e.g., Ca2+, NO).

Generic Feedback on Posters

• Presentations were marginally better than posters in most cases.
• Many posters had too much text or too few illustrations.
• Keep the design simple and consistent.
• Ensure proper alignment and natural flow.
• Pay attention to citations and referencing.
• Know your topic and have additional information.
• Understand the illustrations and their purpose.
• Avoid reading the poster and using notes.
• Listen carefully to questions and take your time to answer.

GPS Event - Tue 25 March

• "Redefining the landscape of drug discovery: innovative approaches to treat malaria, neurodegeneration and asthma"
• 25th March 2025 at the University of Glasgow.
• Speakers: Prof. Graeme Milligan and Prof. Andrew Tobin.

Creative Assignment

• Worth 5% of the total marks for PHAR3B.
• Group work is recommended in teams of students to produce a piece of creative work that reflects your knowledge of pharmacology from the L3 course.
• Guidance and sources of inspiration will be released on Tue 25 March.
• The assignment will be introduced, undertaken, presented, and assessed on Wed 26 March. in Room 201, McIntyre Building

L3 Pharmacology Event

• Social event in Wolfson Link Atrium from 5:00-7:00 pm on Wed 26 March.
• For L3 students, core teaching staff, and GTAs.

Feedback from Staff

• Attendance has been increasingly poor at teaching sessions recently; staff all know who attends / engages and who doesn’t
• EvaSys course evaluation is open for PHAR3B.
• Semester 2 SSLC is on Fri 21 March.

Week 11 Sessions

• L3 Pharmacology exam prep session: Tue 25 March at 1:00 pm.
• L4 Pharmacology information session: Tue 25 March at 12:00 pm.