BMED 450 Chs 8-10 (+ lecture)

Define the terms

NOEL (no observed effect level) is the highest dose or exposure of a compound at which no toxicity is observed. NOAEL (no adverse effect level) is the maximum dose or exposure level of a compound that can be employed without creating unmanageable toxicity. NOAEL is also called the maximum tolerable dose.

What is the maximum tolerable dose (MTD) of a compound?

MTD is the highest dose of a compound that can be employed without creating unmanageable toxicity.

What is a mechanism-based toxicity?

Also known as target-based toxicity, it is toxicity that arises from the intended action of a drug on its biological target and leads to unintended harmful effects due to the target’s normal role in the body. Increase in target activity equals increase in toxicity

Why is a compound’s activity at the hERG channel an important aspect of its safety profile? How can changes in metabolism impact the importance of hERG channel activity?

The hERG channel is key for cardiac repolarization. Blocking it delays repolarization, increases QT interval, and can cause arrhythmia or sudden cardiac death. Metabolism can convert a safe compound into a metabolite that blocks hERG, creating risk.

What is a hapten? How does it evoke a biochemical response?

A hapten is a molecule that produces an immune response only when covalently bound to a carrier protein. The hapten–protein adduct is recognized as foreign, triggering antibody production and an immune response.

What is the difference between acutely toxic compounds and chronically toxic compounds?

Acutely toxic compounds cause effects after a single or short-term exposure, while chronically toxic compounds cause effects after prolonged or repeated exposure over time.

What is the purpose of the MTT human hepatotoxicity assay?

Used to assess cytotoxicity by monitoring the conversion of MTT to formazan, indicating cell viability.

What is the purpose of the AMES assay?

Assess a compound’s ability to cause mutagenesis (carcinogenic) by looking at histidine production. AMES positive means compound causes mutations

What is the purpose of the micronucleus assay?

Used to identify compounds that cause chromosomal damage by measuring formation of micronuclei.

What does the comet assay detect?

Detects DNA strand breaks by observing migration of fragmented DNA during electrophoresis.

How do drug–drug interactions occur?

They occur when one drug alters the metabolism of another, leading to toxicity not seen when used alone.

What are the limitations of the [3H]-dofetilide hERG assay?

It only detects binding at the dofetilide site and cannot detect interactions at other hERG binding sites.

What are some major cardiovascular parameters examined in safety assessments?

Heart rate, blood pressure, contractile force, and ejection fraction.

What animal model can identify compounds with sedation risk?

The rotarod assay.

If a compound is teratogenic, what risks are associated?

It can disrupt fetal development, causing malformations, growth retardation, functional deficits, or death.

Provide a definition of a clinical trial.

A biomedical or behavioral experiment in humans designed to answer questions about a therapeutic agent’s safety and efficacy.

What are the general goals of phase I, II, and III clinical trials?

Phase I: safety and pharmacokinetics. Phase II: initial efficacy and safety. Phase III: large-scale efficacy and risk–benefit evaluation.

What is polymorphism?

The ability of a solid compound to exist in multiple crystalline forms.

Why develop new synthesis methods for commercial scale?

Lab methods may be impractical or inefficient at industrial scale and require modification.

What are delivery methods for drugs?

Oral (PO), intravenous (IV), intraperitoneal (IP), subcutaneous (SC), intramuscular (IM), transdermal, intranasal.

What is the purpose of an enteric coating?

Allows tablets to pass through the stomach unchanged and dissolve in the intestines.

What is an excipient?

A non-active ingredient added to aid drug delivery (e.g., fillers, binders).

What is the purpose of the push chamber in an osmotic pump?

It expands with water influx and pushes drug out of the delivery system.

What are the three sections of an IND application?

Animal pharmacology/toxicology, CMC (chemistry manufacturing controls), and clinical protocols.

What is the purpose of an IRB?

Ensures clinical trials are ethical and properly conducted.

What is allometric scaling?

A method to estimate human dosing from animal data using PK parameters and NOAEL.

What is a “3 + 3” phase I study?

Groups of three receive increasing doses until toxicity defines the MTD.

What is the purpose of an interim analysis?

To evaluate data mid-trial and determine whether to continue the study.

What is the purpose of a stopping rule?

Predetermined criteria to stop a trial when risk outweighs benefit.

Why run a phase III equivalency trial?

When the drug is not more effective but offers advantages like safety or convenience.

What are the advantages of a cross-over study?

Patients serve as their own controls, requiring fewer subjects.

How are adaptive trials different?

They allow modifications based on interim data during the trial.

What is translational medicine?

Application of basic science discoveries to develop therapies (bench-to-bedside).

What are the two categories of translational medicine?

(1) Applying lab discoveries to human trials (2) Improving adoption of best clinical practices.

What is the focus of T1–T4?

T1: link basic science to humans. T2: clinical impact. T3: real-world use. T4: policy/practice improvement.

What is a biomarker?

A measurable indicator of biological processes, disease, or drug response.

What are biomarker categories?

Target engagement, mechanism, outcome, toxicity, pharmacogenomic, diagnostic.

What qualities should a biomarker have?

Easily measured, reproducible, quantitative, objective, predictive.

What is a surrogate endpoint?

A biomarker used instead of a clinical endpoint to predict outcomes.

Benefits of surrogate endpoints and biomarkers?

Reduce cost, time, and patient risk.

What imaging technologies are used?

CT, PET, SPECT, MRI, fMRI, ultrasound.

Why is radioactive decay important in PET?

Short half-life reduces signal quickly, requiring rapid use.

Why develop alternate PET synthesis?

To incorporate radioisotopes quickly or enable labeling when original synthesis is unsuitable.

Why is low non-specific binding important?

Prevents background noise and improves signal clarity.

Desired PK properties of PET/SPECT ligands?

Rapid uptake, short half-life, minimal Pgp efflux.

Safety pharmacology

The study of a candidate compound’s impact on normal physiological function. Best drug candidate substantially outweighs the risk leaving the condition or disease untreated AND the risk associated with the compound itself.

Off-target effects

Not tied to mechanism of target, lack of target specificity

metabolite effects

molecule itself does not induce safety or toxicity issues. It can be altered by metabolic enzymes which may interact with other molecular targets.

Cytotoxicity

capable of killing healthy cells

carcinogenic (mutation causing)

alteration in metabolism or DNA damage/mutations causes unchecked proliferation of malignant cells.

genotoxic

damage to the genetic information within a cell. Single and double strand DNA breaks, apoptosis.

mutagenicity

subset of genotoxicity in which the DNA is mutated.

Chromosomal aberration assay

Easily observe chromosomal damage, identify unrepaired single/double strand breaks, assesses genotoxicity

Comet Assay (single-cell gel electrophoresis SCGE)

detects single and double strand breaks, assesses genotoxicity

Assessing drug-drug interactions

Metabolism screening with CYP enzymes

hERG competitive binding assay

radio labeled hERG substrate and measures displacement by candidate compound. con is Multiple binding sites on the hERG channel and no assessment of electrophysiological impact

hERG rubidium efflex assay

load cells with a potassium mimic (rubidium), then measure how fast it leaks out through hERG channels. Slower leakage means stronger hERG channel blockade

Patch clamp

gold standard, provides electrophysiology data

Cardiovascular derisking

Cardiovascular target libraries and animal models are needed. Langendorff preparation: perfuse animal heart model with candidate compound and asses changes in cardiac function.

In vivo cardiovascular assessment

surgically implant telemetry equipment (heart rate, blood pressure, contraction force and ejection fraction devices) and administer dose and monitor. Very expensive, done with most promising derisked candidates

CNS safety and toxicity

Off target effects include hallucinations, insomnia, sedation, etc. Can test with novel object recognition, contextual fear conditioning, rotarod test

Assessing teratogenicity

conversion of ESC into cardiomyocytes and assessing MSC cell adhesion, movement, communication, divison, etc. Zebrafish development assay to asses malformed, missing, or dysfunctional organs

GLP

Good lab practices, a set of conditionals and protocols to ensure proper experimental control and data variability.

In Vivo toxicity and safety studies

general health, system and organ function, and histology

In vivo - SAD study

single ascending dose study, determine the MTD, NOEL, NOAEL to demonstrate therapeutic index. (Acute)

In vivo - Chronic dosing studies

Determine MTD, NOEL, NOAEL, and therapeutic index to study extended administration