What Is the Structure/Function Relationship? What Do We Know?

The Structure/Function
Relationship: What do we know?
What would we like to know?
Brian R. Berridge, DVM, PhD, DACVP
GlaxoSmithKline
Research Triangle Park, NC
brian.x.berridge@gsk.com
919-315-6592
Outline
• A (very) brief overview of the structure and function of
the cardiovascular system?
• What data are we integrating and where do we get it?
• Connecting the dots
• What do we still need to learn?
We know a fair bit about the cardiovascular system as an
integration of form and function
Blood vessels conduct
blood to the heart itself as
well as the rest of the
body.
Rhythmic waves of
electrical activity ensure
coordinated contraction
of different regions of the
heart.
Cardiomyocytes are
contractile cells with
immense energy needs
A muscular pump and its
delivery system.
Heart valves ensure
unidirectional flow of blood.
We know something about what cardiovascular toxicity
looks like!
Nonclinical CV Toxicity
Clinical CV Toxicity
“Adverse CV events”
(Vioxx, Darvocet)
vascular injury
cardiomyocyte injury
Congestive Heart Failure
(TZDs, TKIs)
cellular
biochemistry
valvulopathy
morphology
Decreased EF
(TKIs)
ultrastructural injury
Valvulopathy
(Fen-Phen)
function
∆cardiac mass
QT prolongation
Non-QT arrhythmias
Increased blood pressure
(Torcetrapib)
QT prolongation/TdP risk
∆ BP
∆ HR
∆contractility
Possible Cardiac Adverse Effects of Drugs
Primary functional effects ±
morphological consequences
Primary effect on cardiac structures ±
secondary functional effects
Adverse effects on cardiac
function
Effects on vascular
motricity
Exaggerated vasodilation
and reflex activation of
heart
Arrhythmias ±
conduction
impairment
Direct effect on cardiac
structure
Effect on
contractile protein
or Ca channels
Myocardial
degeneration
Valvular
proliferation
e.g. QT prolongation
Acute
Myocardial
necrosis
e.g. isoproterenol
Chronic
Cardiac fibrosis
Cardiac hypertrophy
e.g. minoxidil
Decreased/impaired cardiac
contractility
e.g. doxorubicin
Impairment of
atrioventricular and/or
arterial flows
e.g. anorexigenic drugs
Exacerbation of pre-existing dz- 1o, 2o
Not in the Hanton scheme
Adapted from Hanton, G. Drugs R D 2007: 8(4):213
Possible Cardiac Adverse Effects of Drugs
Primary functional effects ±
morphological consequences
Primary effect on cardiac structures ±
secondary functional effects
Adverse effects on cardiac
function
Effects on vascular
motricity
Exaggerated vasodilation
and reflex activation of
heart
Arrhythmias ±
conduction
impairment
Direct effect on cardiac
structure
Effect on
contractile protein
or Ca channels
Myocardial
degeneration
Valvular
proliferation
e.g. QT prolongation
Acute
Myocardial
necrosis
e.g. isoproterenol
Chronic
Cardiac fibrosis
Cardiac hypertrophy
e.g. minoxidil
Decreased/impaired cardiac
contractility
e.g. doxorubicin
Impairment of
atrioventricular and/or
arterial flows
e.g. anorexigenic drugs
Exacerbation of pre-existing dz- 1o, 2o
Not in the Hanton scheme
Adapted from Hanton, G. Drugs R D 2007: 8(4):213
We know we generate a lot of relevant
data in relatively sensitive ways?
In vitro screening for ion channel and receptor
binding activity
•Prospective opportunity for identifying putative risks
•Retrospective opportunity to define pathogenesis/mechanism
In vivo studies
Current paradigms in preclinical safety assessment
Acute/Single Dose Safety Pharmacology Studies
Functional
endpoints
Multiple species
In vitro/Ex vivo
Rodents
Early Development CV Fxn
Patch clamp ion channel assays
Rabbit wedge assay
Translatable biomarkers
Non-Rodents
FTIH-enabling GLP CV Study
•Telemetered rat
•Telemetered dog or
•Heart rate
monkey
•ECG (quantitative)
•Heart rate
•No QT
•ECG (quantitative)
•Blood pressure
•Blood pressure
•± surrogate
•± surrogate
measures of
measures of
contractility- LVP, QA
contractility- LVP, QA
Current paradigms in preclinical safety assessment
In Vivo Repeat-Dose General Toxicity Studies
Rodents
4 days
Multiple species
Non-Rodents
Repeat-dose studies of increasing length at super-pharmacologic
doses
Morphologic
endpoints
Organ weight
Gross
Microscopic
- light microscopy
- ultrastructure
Blood/urine
biomarkers
Serum chemistry
Hematology
2 years
Functional
endpoints
Heart rate
ECG (qualitative)
Hemostasis
Urinanalysis
Translatable biomarkers
* Repeat dose studies biased toward morphologic endpoints
Morphologic Evaluation- Gross to Microscopic
Light microscopy of myocardium
Ultrastructure of myocardium
Gross examination of the intact rodent heart
Evaluation of atrioventricular valve of “opened” non-rodent (dog) heart
Light microscopy of atrioventricular valve
Standard clinical pathology endpoints in repeat-dose
toxicity studies
• Serum chemistry
Biomarkers of hepatobiliary injury- ALT, AST, Tbili, ALP, GGT
Biomarkers of muscle injury- CK, AST, Potassium
Biomarkers of renal injury- BUN, Cr, Urine Sp Gr, Urine Total Protein
Biomarkers of metabolic health- glucose, triglycerides, cholesterol,
electrolytes, total protein, albumin, globulins
– Biomarkers of calcium-phosphorus balance – calcium, inorganic phosphorus
–
–
–
–
• Hematology
– Biomarkers of inflammation, hematologic dyscrasia, hematopoiesis – CBC,
reticulocyte count, blood smear review
– Biomarkers of coagulation- PT, APTT, fibrinogen, platelet count
• Urinanalysis
– Biomarkers of renal health, metabolic health - pH, protein, glucose, blood,
bilirubin, ketones, urobilinogen, urine sediment, urine specific gravity, renal
electrolytes
Endpoints with particular relevance to CV injury
Compliments of A. Eric Schultze
Novel CV Biomarker Interests
• Cardiac troponins
• Natriuretic peptides
• H-FABP
• Novel contexts of use for troponins or natriuretic
peptides
• Imaging
• miRNAs
We know what we’re looking for!
•
Changes in serum chemistry
–
–
•
Changes in function
–
•
•
Vacuolation
Degeneration
Necrosis
Apoptosis
Hypertrophy
Myocardial injury
–
–
–
•
•
Inotropy, chronotropy, rhythmicity
Changes in heart mass with our without proportional changes in chamber volumes
Cellular injury
–
–
–
–
–
•
Increases in cTn, NTproANP/BNP, CK, K+
Altered coagulation parameters
Hemorrhage
Inflammation
Fibrosis
Valvular injury
Vascular injury
*Important to recognize that the heart, like many target
organs, has a finite number of ways to respond to altered
physiology or noxious stimuli.
And what it looks like!
• 4 mg/kg s.c. in F344 rats
2-4 hr
Temporal
pathogenesis of
isoproterenolinduced injury in
the rat heart
24 hr
48 hr
2 weeks
Vascular responses to injury
Vasoconstrictor/hypertension injury
Medial hypertrophy/hyperplasia
Periarterial fibrosis
Fibrinoid necrosis
Compliments of H. Thomas
We know what to do with the data when we get it:
Integrated Interpretation of Histopathology Data
Light microscopy
Vascular injury
Myocardial injury
Is the injury reversible or
irreversible (e.g. necrosis,
fibrosis)
Is there a correlative
change in blood pressure?
NO
reversible
YES
Possible translational
biomarker or screening
parameter
NO
Generally not
monitorable = Dose and
development limiting
irreversible
Is there a correlative
functional change?
Possible direct
vasculotoxin and
more difficult
development
challenge
Valvulopathy
YES
Is there a correlative
increase in cTnI?
NO
Is the molecule an ergot alkaloid
or have ALK 5 inhibitory activity?
YES
SAR screen
May be dose &/or
development
limiting
Re-examine time
of sampling
Translational
biomarkers
Reporting translational
biomarker
Monitorability and exposure margins
significantly impact progression opportunity!
We know
can
leadPressure
to structural
Effect functional
of Minoxidilchanges
on Arterial
Blood
and Heart Rate
in Conscious
Rat
injuries: Minoxidil as a model
cardiovascular
toxicant in
rats
•Minoxidil is a vasodilating K+ channel blocker
7d repeat-dose rat CV study
•
Mean absolute (relative to BW) heart
weight
– Gp. 2- +7.8% (+3.6%)
– Gp. 3- +21.1% (+13.4%)
– Gp. 4- +13.3% (+6.7%)
Multifocal myocardial
necrosis
Arterial injury in the
mesentery
Single dose rat CV study
Minoxidil (mg/kg)
MAP
HR
3
Maximal decrease of 22 mmHg
Effect last ~22 h
Maximal increase of 70 beats/min
Effect last ~6 h
30
Maximal decrease of 23 mmHg
Effect last ~24 h
Maximal increase of 181 beats/min
Effect last ~24 h
100
Maximal decrease of 33 mmHg
Effect last ~24 h
Maximal increase of 138 beats/min
Effect last ~24 h
PDE4 inhibitors can do it too!
Subendocardial necrosis
Vascular injury
*no HW ∆ reported
What I would like to know?
Every
Function
Structure
Study
•Logistical challenges
•Technological challenges
•How do we get these relationships from the ‘right’
studies?
We need to understand the complexity of our target patients better!
Attributes of a diabetic
patient population
•Concurrent medications
•Ischemic heart dz
•Stroke
•Heart failure
•Renal disease
•Hyperglycemia
•Hypertension
•Dyslipidemia
How do we model diabetic patients
preclinically?
Baseline characteristics of patients with diabetes studied in the RECORD trial. Lancet 373:2125-2135, 2009
We need to know how to better model our target patients!
Drug-induced vascular injury- place for a significant
safety pharmacology contribution??
Gap = there are no biomarkers of ‘vasoactivity’ on these lists!
Thank you!
Questions?