Unit 2.5.1 Preclinical Studies in Drug Development.pdf

Medicinal chemistry

1. Unit2.5.1 Pre-Clinical Studies
in Drug Development
Lecture Notes in Medicinal Chemistry (PMY4330)
Prepared by:
Ronald Kampamba Mutati, MSc.,BPharm.
Course Organizer & Lecturer in Medicinal Chemistry
June 2020
Revised-1: 18May2021

2. 2.5.1 Pre-clinical Studies:
•2.5.1.1 Toxicity Testing:
•2.5.1.2 Pharmacokinetics & Drug
Metabolism Studies:
•2.5.1.3 Pharmacology
(Pharmacodynamics):

3. 2.5.1.1 Toxicity Testing:
•2.5.1.1(a) Objectives of Toxicity Testing:
•2.5.1.1(b) In-vitro and In-vivo Toxicity
Testing:
•2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•2.5.1.1(d) Sub-chronic & Chronic Toxicity
Studies:
•2.5.1.1(e) Carcinogenicity Studies:
•2.5.1.1(f) Reproductive Studies:
•2.5.1.1(g) Genotoxicity (Mutagenic)
Studies:

4. 2.5.1.1(a) Objectives of Toxicity Testing:
•(a) Pre-clinical drug safety evaluation
(or toxicity) tests are performed to
determine:
•(i) the potential of the drug candidate
for toxicity with short-term use (acute
toxicity) or long term use (chronic
toxicity);

5. 2.5.1.1(a) Objectives of Toxicity Testing:
•(ii) the potential of the drug candidate
for specific organ toxicity;
•(iii) the mode, site and degree of
toxicity;
•(iv) the dose-response relationship for
low, intermediate and high doses over
a specified time;

6. 2.5.1.1(a) Objectives of Toxicity Testing:
•(v) gender, reproductive or teratogenic
toxicity;
•(vi) the carcinogenic potential of the
drug candidate; and
•(vii) the genotoxic (or mutagenic)
potential of the drug candidate;

7. 2.5.1.1(b) In-vitro and In-vivo Toxicity
Testing:
•(b) Toxicity tests are undertaken in-
vitro and in-vivo:
•(i) In-vitro toxicity tests are performed
on isolated organs, tissues or cells;

8. 2.5.1.1(b) In-vitro and In-vivo Toxicity
Testing:
•(ii) In-vivo toxicity tests are performed
in transgenic and other laboratory
animals such as mice (or rats), guinea
pigs, rabbits (and dogs);

9. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Acute toxicity studies are conducted to
determine the short-term toxic effects
of the drug candidate when
administered in a single dose and/or
multiple doses over a short period of
time –usually 24 hours;

10. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Acute toxicity tests are performed in-
vivo on laboratory animals;
•Different animal species are used in
the study;

11. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•The route of administration used for in-
vivo toxicity studies usually represents
the route intended for administration in
humans;

12. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•The drug candidate is administered in
low, intermediate and high dose
levels;
•Then toxicity signs are observed for:
onset, progression (or reversal)
severity, mortality and rates of
incidence;

13. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Doses are varied so as to determine:
•-largest single dose (of the drug
candidate) that will not produce a toxic
effect,
•-the dose level at which severe toxicity
or death occurs, and
•-intermediate toxicity levels;

14. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Animals are observed and compared
with controls for various signs of
toxicity for about 30 days post dose;
•Blood, urine and faeces specimens are
collected and clinical laboratory tests
are performed to determine toxicity;

15. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Animal deaths are recorded;
•Dead animals are dissected and
tissues and organs are subjected to
histology, pathology and statistical
evaluation;
•

16. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Evaluation is made on the basis of:
•-dose-response,
•-age,
•-gender,
•-intra-species and inter-species
finding, and
•-in comparison with controls;

17. 2.5.1.1(c) Acute (Short-term) Toxicity
Studies:
•Surviving animals are killed , dissected
and similarly evaluated;

18. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(i) Sub-Chronic Toxicity Studies:
•Sub-chronic (or sub-acute) toxicity
tests are designed to establish
relationship with projected human
studies;

19. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(i) Sub-Chronic Toxicity Studies:
•For example: to support the initial
administration of a single dose in
human clinical testing, animal toxicity
studies for at least two weeks of daily
drug administration at three or more
dosage levels to two animal species
are required;

20. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(i)Sub-Chronic Toxicity Studies:
•The initial human dose is usually one
tenth (at most) of the highest non-toxic
dose shown during animal studies –in
milligrams per kilogram of the
subject’s weight;

21. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(ii) Chronic Toxicity Studies:
•Chronic toxicity studies are
undertaken for drug candidates
intended to be administered to humans
for a week or more;
•For which animal studies for 90 to 180
days must demonstrate safety;

22. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(ii) Chronic Toxicity Studies:
•When the drug is intended for chronic
human illness, animal studies must be
performed for at least on year to
support human use;

23. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(ii) Chronic Toxicity Studies:
•In some cases, animal toxicity studies
are undertaken for two years or longer
to facilitate corroboration of findings
obtained during human clinical trials.

24. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(iii) Factors evaluated in Sub-chronic and
Chronic Toxicity Studies:
•Various factors are evaluated in sub-
chronic and chronic studies, including:
•-comparative data of test and control
animal species;
•-strain,
•-sex,
•-age;

25. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(iii) Factors evaluated in Sub-chronic
and Chronic Toxicity Studies:
•-dose levels and ranges,
•-routes of administration,
•-duration of treatment,
•-observed effects,
•-mortality;

26. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(iii) Factors evaluated in Sub-chronic
and Chronic Toxicity Studies:
•-body weight changes,
•-food and water intake/consumption;
•-physical examination (e.g. ECG, e.g.
ophthalmology);

27. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(iii) Factors evaluated in Sub-chronic
and Chronic Toxicity Studies:
•-haematology,
•-clinical chemistry,
•-Urinalysis,
•-Gross pathology,
•-Neoplastic pathology,
•-histopathology,

28. 2.5.1.1(d) Sub-chronic & Chronic
Toxicity Studies:
•(iii) Factors evaluated in Sub-chronic
and Chronic Toxicity Studies:
•-ADME data,
•-Other factors;

29. 2.5.1.1(e) Carcinogenicity Studies:
•Carcinogenicity testing is undertaken
when a drug candidate has shown
sufficient promise to enter human
clinical trials,
•Carcinogenicity testing is usually done
as part of chronic testing on a limited
number of female and male rats and
mouse strains;

30. 2.5.1.1(e) Carcinogenicity Studies:
•In carcinogenicity testing, high,
intermediate and low doses are used over
a 90 day period;
•The high dose in carcinogenicity testing
is the maximum tolerated dose that is just
high enough to induce toxicity (if any);
•Such that there is no significant change in
the life span of the test animal except due
to carcinogenicity(if any);

31. 2.5.1.1(e) Carcinogenicity Studies:
•Carcinogenicity tests are long-term -
lasting 18-24 months;
•Surviving animals during toxicity
testing are sacrificed at defined weeks
during the test period;

32. 2.5.1.1(e) Carcinogenicity Studies:
•The animals are evaluated with respect
to:
•-causes of death (other than killing);
•-tumor incidence, type and site;
•-necropsy data are collected and
evaluated;
•-any preneoplastic lesions and tissue
specific proliferation effects are
included in the evaluations;

33. 2.5.1.1(e) Carcinogenicity Studies:
•If a drug candidate shows any signs of
carcinogenicity, it is excluded from
further investigations;
•-------------------------------------------------------

34. 2.5.1.1(f) Reproductive Studies:
•Reproductive tests are done to assess
the drug candidate for any effects on
mammalian reproduction;

35. 2.5.1.1(f) Reproductive Studies:
•Reproductive tests include: fertility,
mating behavior;
•Reproductive tests also include: early
embryonic, prenatal, and postnatal
development, multi-generation effects,
and teratology;

36. 2.5.1.1(f) Reproductive Studies:
•Thus, the combined reproductive tests
cover exposure of the test animals to
the drug candidate from conception to
sexual maturity;

37. 2.5.1.1(f) Reproductive Studies:
•As such, reproductive studies facilitate
detection of immediate and latent
effects through complete life cycles
and through successive generations;

38. 2.5.1.1(f) Reproductive Studies:
•Evaluations are made for anatomical
abnormalities, growth and
development of the maternal parents,
fetus, neonates, and weaning
offspring;

39. 2.5.1.1(f) Reproductive Studies:
•In addition to the use of the same
species of animals used in other
toxicity tests (usually rats), embryonic
studies normally require the use of a
second mammalian species -for which
a rabbit is preferred for practical
reasons and because of the
knowledge already accumulated on
the rabbit;

40. 2.5.1.1(f) Reproductive Studies:
•Other testing principles and
approaches regarding dose selection,
route of administration, dose intervals,
in reproductive studies are similar to
those used in other toxicity studies;
•------------------------------------------------------

41. 2.5.1.1(g) Genotoxicity (Mutagenic)
Studies:
•Genotoxicity (or mutagenicity) studies
are performed to assess the drug
candidate for any effects on gene
mutation or for any cause of
chromosome damage or DNA damage;
•Mutation detection assays have
routinely included the use of
Salmonella typhimurium ;
•----------------------------------------------------

42. 2.5.1.2 Pharmacokinetics & Drug
Metabolism Studies:
•2.5.1.2 (1) Pharmacokinetics:
•Pharmacokinetic studies are
undertaken to evaluate the Absorption,
Distribution, Metabolism (or
Biotransformation ) and Excretion –
the ADME processes -of the drug
candidate;

43. 2.5.1.2 (1) Pharmacokinetics:
•Pharmacokinetic studies of a drug
candidate are performed on a series of
laboratory animals to determine the
following:

44. 2.5.1.2 (1) Pharmacokinetics:
•(a) the extent and rate of absorption of
the drug candidate from various routes
of administration including that
intended for human use;
•(b) the rate and extent of distribution
throughout the body and the site(s)
and duration of residence;

45. 2.5.1.2 (1) Pharmacokinetics:
•(c) the rate, primary and secondary
sites, and mechanism of metabolism of
the drug candidate in the body;
•(d) the chemistry and pharmacology of
metabolites;
•(e) the proportion of the administered
dose eliminated from the body and
rate and route of elimination;

46. 2.5.1.2 (1) Pharmacokinetics:
•At least two animal species are used in
pharmacokinetic studies –a rodent
and another, usually a dog;

47. 2.5.1.2 (1) Pharmacokinetics:
•ADME assessments are done by timely
collection and analysis of samples of
urine, blood, feaces;
•ADME assessments also include
careful examination of animal tissues
and organs following autopsy;

48. 2.5.1.2 (1) Pharmacokinetics:
•Also included in ADME studies are
special studies to determine:
•-any presence of the drug candidate
and its metabolites in milk of lactating
animals;
•-whether the drug candidate crosses
placental barrier and enters foetal
circulation; and
•-any long term retention of the drug
candidate and its metabolite;
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49. 2.5.1.2 (2) Drug Metabolite Studies
•Drug metabolism studies are, by
definition, part of pharmacokinetic
studies, which focus on the evaluation
of the biotransformation product
(metabolites) of the drug candidate
with regard to their pharmacological
activity, safety profile, distribution,
elimination, and other such metabolite
evaluation;

50. 2.5.1.2 (2) Drug Metabolite Studies
•To facilitate effective drug metabolism
studies the drug candidate is labeled
with radioactive isotopes which can be
detected in small quantities by
measuring theirβradiation;
•----------------------------------------------------

51. 2.5.1.3 Pharmacology
(Pharmacodynamics):
•By the time of drug candidate
development a lot of pharmacological
studies will have been done on the lead
compound during lead discovery and
lead optimization (drug design);

52. 2.5.1.3 Pharmacology
(Pharmacodynamics):
•However it is necessary to carry out
further pharmacology studies on the
drug candidate for the purposes of:

53. 2.5.1.3 Pharmacology
(Pharmacodynamics):
•(a) determining whether the drug
candidate has activity at other targets
other than the intended one;
•(b) gaining a better insight into the
drug candidate’s mechanism of action;

54. 2.5.1.3 Pharmacology (Pharmacodynamics):
•(c) determining dose response
relationships;
•(d) defining the duration of action of the
drug candidate;
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