Pharmacology: Mode of Action of a Drug

Study Notes

Naloxone and Mode of Action of a Drug

Determining the mode of action of a drug is crucial, despite knowing the target, to understand the drug's effect on the body
Mode of action studies can be either molecular target-based or phenotype-based

Sulfonamides: The First Mode of Action Study

Sulfonamides were the first widely-used antibacterials
Prontosil was shown to be a prodrug in 1935
The mode of action of sulfanilamide was discovered by adding extra nutrients, such as yeast extract, to bacteria, which made them withstand sulfanilamide better
The "Factor" in yeast extract that protects against sulfanilamide was found to be para-aminobenzoic acid
Sulfanilamide and p-aminobenzoic acid compete for the same active site of dihydropteroate synthase

Aspirin: Mode of Action

Aspirin was developed from salicylic acid to reduce gastric irritation
Aspirin confers its effect by inhibiting prostaglandin production
John Vane's assay used strips of animal tissue to measure the contraction or relaxation of muscles in response to molecules like bradykinin, histamine, and ovalbumen
Aspirin inhibits the production of prostaglandin E2 (PGE2) in the lungs

Aspirin Acetylation

Aspirin acetylates biomolecules, with some specificity
Incubating a biological sample with aspirin containing a radioactive acetyl group and running it on an SDS-PAGE gel can detect the acetylated protein
The molecular weight of the peak is approximately 85,000 Da

Protein Polyacrylamide Gel Electrophoresis (PAGE)

SDS-PAGE is used to separate and detect proteins based on their size and charge
The protein is denatured and complexed with SDS, which conveys a negative charge and keeps the protein unfolded
The sample is then subjected to an electric field, and the migration distance is proportional to the size of the protein

Initial Focus of Chem390

The initial focus of Chem390 is on experiments and data interpretation, including experimental methods and qualitative and quantitative data interpretation.
The course aims to build confidence in interpreting data, which is essential in real science, where the focus is not just on finding the correct answer, but also on how to figure it out.

Background and Prerequisites

The course builds on previous material taught by Professors Sarojini and Barker.
Students come from varied backgrounds, including MedChem, Biology, or MedSci, and some may have taken many biology classes but not some chemistry classes, while others may have taken chemistry classes but not biology classes.

Interpreting Data

Interpreting standard errors (S.E. or S.E.M.) is important, and standard deviations and confidence intervals are different from standard errors.
Understanding dose-response curves, including how to judge if a drug candidate is effective and how to determine the mechanism of action (MOA) of a medicine.

Ligand-Receptor Binding

The behavior of [LP] can be described by the formula: [P] = [P]T - [LP].
The dissociation constant (KD) can be calculated from a curve: KD = L [P] / [LP].
Ligand-receptor binding curves can appear sigmoidal or hyperbolic, depending on the x-axis (linear vs logarithmic).

Enzyme Kinetics

Enzyme kinetics are similar to receptor-ligand kinetics, with the equation: E + S ⇋ ES ⟶ E + P.
The Michaelis-Menten (or Henri) equation is: V = Vmax [S] / (KM + [S]).
Lineweaver-Burke plots can be used to analyze enzyme kinetics.

Enzyme Inhibition

Enzyme inhibition can be competitive or non-competitive, and double-reciprocal plots can be used to determine the type of inhibition.
Competitive inhibition plots on "normal" axes and double-reciprocal plots.

Determining the Mode of Action of a Medicine

Determining the mode of action of a medicine is important because it helps to understand how the medicine works and to identify potential targets for new medicines.
Molecular target-based and phenotype-based approaches can be used to determine the mode of action.

Historical Example: Sulfonamides

Sulfonamides were the first widely-used antibacterials, and Prontosil was shown to be a prodrug in 1935.
The mode of action of sulfanilamide was discovered by adding extra nutrients to bacteria, which made them withstand sulfanilamide better.
The "Factor" in the yeast that protected against sulfanilamide was found to be para-aminobenzoic acid, which competes with sulfanilamide for the same active site.

Description

This quiz explores the concept of determining the mode of action of a drug, including the use of molecular target-based and phenotype-based approaches. It also touches on the reversibility of naloxone binding.