Preclinical evaluation of drug

Pharmacology and Toxicology

Pharmacological Screening

of Drugs

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S K Kanthlal

Amrita School of

Pharmacy

Drug Development process

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Preclinical trial - a laboratory test of a new drug

or a series of chemicals, usually done on animal

subjects, to see if the hoped-for treatment really

works and if it is safe to test on humans.

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File for approval as an Investigational New Drug (IND)

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Establish Effective and Toxic Doses

Screen the Drug in the Assay

Develop a Bioassay

Indentify a Drug Target

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Get idea for drug target

Develop a bioassay

Screen chemical compounds in assay

Establish effective and toxic amounts

File for approval as an Investigational New Drug

(IND) (leads to clinical trials)5

Screening of drugs

A thorough investigation to

Get pharmacological activity of new/chemically undefined

substances

Investigate the functions of endogenous mediators

Measure/ define the toxicity and/or unwanted actions

• A test or group of test believed to permit the detection of physiological activityScanning

• To reduce the uncertainty of scanning

Evaluation6

Programmed

Blind

Simple

Is the substance active?

(1/2 similar testing)

Is there any

Biological activity ?

In what ways compound(s) acts ?

Main activity ?.,,,,, Subsidiary activity?

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SIMPLE SCREENING

◦ One or 2 similar test to find substances having a

particular property

◦ To find the substance are active in a single way

◦ No need for battery/ series of test

◦ Inexpensive and less time consuming

◦ Select only suitable method

◦ Not Sufficiently accuracy in results

Eg. Hypoglycemic testing: Ability of a compound to

diminish the Blood glucose levels.

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BLIND SCREENING

◦ Only for the series of new chemical substances with no

prior pharmacological history.

◦ New chemical entity or isolated naturals

◦ Provides a road towards fields of activity if they exists

◦ To demonstrate whether new group of substances is worthy

for further attention?

◦ Point out the most potent chemical with interesting

pharmacological activity

◦ Requires planning and skillful execution of test (Nature,

economical, time & money)

◦ Toxicological pathway is essential for every library of

compounds

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PROGRAMMED SCREENING

◦ Provide information “what compounds are active in what

ways?”

◦ A new drug of specific type (known) and/or series of

chemicals is to be investigated for some particular

pharmacological activity.

Eg. System or organ specific

◦ A series of testing program is required to provide

information on the compounds on specific targets

◦ Explores main activity and subsidiary activity

◦ Potency can be compared with known compounds which

lead the investigator to proceed or to terminate.

◦ More limited than blind, precision is expected

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Preclinical Studies

Invitro Invivo

Pharmacological

Studies

Toxicological

studies

SafetyEfficacy

Dose conversion

Determination of

starting dose

Receptor Characterization

Receptor binding assay

Enzyme inhibition

20 Messenger analysis

Cytotoxic activity

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METHODS OF SCREENING• Invitro :

▫ Experimental process in a given procedure which is mainly

done outside the body in a controlled condition

Activity assays (screen the activity)

Bioassays (define the molecular mechanism)

Toxicity assays (Toxicity of chemicals)

Types: Biological assay using isolated tissues/organs

(skeletal/smooth muscles, aorta, heart etc.,)

Chemical Assay using regents

Cell culture studies

Antioxidant assays

Xanthine oxidase activity

Antiglycation activity

DNA, protein, RNA level

assays

Immunological assays

Toxicity(cyto) assays

Immunological assays

Cancer cell line studies

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• Exvivo:

▫ Experimental process which is performed outside the living

body in an ‘artificial invivo environment’

▫ This usually lasting up to 24 hrs

• In vivo

▫ Experimental process which is performed in the living body

using laboratory animals

• Insilico

▫ Process which is performed on computer or via computer

simulator

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Techniques employed for the determination of the potency of

chemical and biological agents like drugs, hormones, ions,

etc., by means of biological indicators using whole animals,

isolated organs and tissues or using cell lines

Biological Indicators:

Body temperature

Blood glucose level

Behavioral responses

Serum parameters

Contraction/relaxation

Growth/inhibition of cells14

STEP I

◦ Toxicological assessment of chemicals

◦ LD50 estimation

Using Acute/sub-acute, chronic etc., studies

STEP II (

◦ Evaluation of 10 & 20Pharmacological activity

◦ Animal models of induced disease and injury

STEP III

◦ ADME Studies

Absorption studies

Tissue/organ/fluid conc. estimation

Histopathological studies

Serum estimation of biological indicators for drug & metabolites

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Factors:SpeciesStrainsSexAgeDiseaseInductionEnvironmental

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•In Vitro Toxicology

•In Vivo Toxicology

AT PRESANT

What is Toxicology?

Toxicology is the study of the adverse /unwanted

effects of chemical, physical, or biological agents on

people, animals, and the environment

Why Do Toxicology Testing?

Need to prove new drugs are safe:

Before first administration to humans

Before later clinical trials 17

In V

itro

To

xic

olo

gy

In vitro toxicology

The bridge exists between new drug discovery and drug

development.

Provide information on mechanism(s) of action of a drug

Provides an early indication of the potential for some kinds of

toxic effects, allowing a decision to terminate or to proceed

further.

In vitro methods are widely used for:

Screening and ranking chemicals

Get a platform for animal studies for physiological actions

Studying cell, tissue, or target specific effects

Improve subsequent study design

Advs & Disadvs.

Faster than in vivo studies

Less expensive to run

Less predictive of toxicity in intact organisms 18

Cytotoxicity

◦ Toxicity to cells

◦ Liver cells, blood cells, bacteria, fungi, yeast

Structural – e.g., effects on membrane integrity

Functional – e.g., effects on mitochondrial function

Cell proliferation – decreases or increases

Protein binding

◦ Receptor/enzyme interactions

CYP inhibition/induction

◦ Using hepatic enzymatic reaction

Membrane permeability

Immunotoxicity

◦ Drug induced cytokine, histamine release etc.,

Metabolism and Kinetics

◦ Information about pathways and metabolites (toxic nature)19

Invivo Toxicological studies

Expected results should, at a minimum:

Establish a safe starting dose for clinical studies

To determine the dose levels for future prospects

Provide information on a drug-therapy regimen that

would produce the least toxicity

Assess target organ toxicity and its reversibility

Provide insight into biomarkers for clinical

monitoring

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Studies to be performed before clinical trials

Pharmacodynamics

Pharmacokinetics

Single dose toxicity in two species

Repeated dose toxicity in two species,

Chronic Toxicity/Carcinogenicity

Safety Pharmacology

Local tolerance

Genotoxicity

Reproductive Toxicity/ Teratogenicity study

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