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Summarising the evidence from animal models of neurological disease: Are there any babies in the bathwater?
Malcolm MacleodUniversity of Edinburgh
• Lots of drugs seem to work in animal models of stroke
• Some of these drugs have been around for ages, and are probably safe
• Rather than spend billions developing a novel drug, why not test something we already know works in animals?
Where we started …
What do we already know works in animals?
• Lots of individual promising studies• Little in the way of research
synthesis
So …• Review the field systematically• Pick a target and synthesise the
evidence
1026
1026 interventions in experimental stroke
1026603
1026 interventions in experimental stroke
Tested in focal ischaemia
1026883374
1026 interventions in experimental stroke
Effective in focal ischaemia
1026883550
97 18
1026 interventions in experimental stroke
Tested in clinical trial
1026883550
97 171 3
1026 interventions in experimental stroke
Effective in clinical trial
Outline
• Review the internal validity of animal studies
• Review the external validity of animal studies
• Explore the potential uses of this approach– Mechanisms research– Biomarker validation– Bibliometrics
Methodological approach
• Written review protocol – hypothesis, inclusion and exclusion criteria, analyses prespecified
• Standardised search strategy – 3 online databases, conference abstracts, dual screening
• Data extraction to bespoke database/analysis tool• Random effects weighted mean difference
stratified meta-analysis or meta-regression• Publication bias by Funnel plot, Egger regression,
Trim and Fill
There is nothing new under the sun …
“…you will meet with several observations and experiments which, though communicated for true by candid authors or undistrusted eye-witnesses, or perhaps recommended by your own experience, may, upon further trial, disappoint your expectation, either not at all succeeding, or at least varying much from what you expected”
Robert Boyle (1693)Concerning the Unsuccessfulness of Experiments
Focal cerebral ischaemia
• Emily Sena• David Howells• Tori O’Collins• Bart van der Worp• Philip Bath
Internal validity …
• the extent to which an experiment accurately describes what happened in that model system
• may be confounded bySelection Bias (Randomisation)Performance Bias (Allocation Concealment)Detection Bias (Blinded outcome assessment)Attrition bias (Reporting drop-outs/ ITT analysis)False positive report bias (Adequate sample sizes)
NXY-059 in animal stroke models
9 publications, 29 experiments, 408 animals 44% (35-53%) improvement in outcome
External validity
• Has the intervention been tested under a range of circumstances similar to those which might be encountered in clinical practice?
• Are the data you know about representative of all data? (what is the likelihood of publication bias)
Hypertension in studies of NXY-059 in experimental stroke
Hypertension:– 7% of animal studies– 77% of patients in the
(neutral) SAINT II study
Hypertension in studies of tPA in experimental stroke
Comorbidity
“Normal” BP
Effi
cacy
-2%25%
Infarct Volume:– 113 publications– 212 experiments– 3301 animals– Improved outcome by 24% (20-28)
Hypertension:– 9% of animal studies– Specifically exclusion criterion in (positive)
NINDS study
The importance of Time to Treatment
• Both tPA and tirilazad appear to work in animals
• tPA works in humans but tirilazad doesn’t
• Time to treatment: tPA:– Animals – median 90 minutes– Clinical trial – median 90 minutes
• Time to treatment: tirilazad– Animals – median 10 minutes– Clinical trial - >3 hrs for >75% of patients
Publication bias in experimental stroke
• Only 11/525 publications (2.2%) reported no significant treatment effects
• Trim and Fill suggested ~16% (214/1573) of experiments remain unpublished
• Best estimate of magnitude of problem – Observed efficacy 31.3% (29.7-32.8)– Adjusted efficacy 23.8% (22.2-25.5)
Publication bias
Randomisation Co-morbidity
bias
Reported efficacy
24%32% 18% 4%
There are multiple drivers of bias
Dopamine agonists in PD models
• Evelien Rooke• Hanna Vesterinen• Kieren Egan• Emily Sena
Systematic review
Internal validity in PD models
Blinded outcome assessment Composite quality
Experimental allergic encaphalomyelitis
• Hanna Vesterinen• Emily Sena
Publications identified in review
Outcomes reported
Efficacy – for what it’s worth
Internal validity
External validity
Demyelination
Axon loss
Neurobehaviour
31%
32%
14%
Relationship between endpoints
Transgenic models of AD
• Kieren Egan
Systematic Review
8495
409
8086 Excluded
381 Full publications
28 Abstracts
284 papers have histologicaldata extracted
69 Papers have data on the MWM extracted
Study Quality
RandomisationBlinded
Outcome AssessmentSample
Size calculation
Stroke 36% 29% 3%
MND 31% 20% <1%
AD 14% 22% 0%
PD 16% 15% <1%
EAE 8% 16% <1%
Glioma 14% 0% 0%
Effect Size Amyloid beta 40, All fractions (Standard Deviations)
-12 -8 -4 0 4 8 12 16 20 24 28
Eff
ect
Siz
e A
ß42
, A
ll fr
actio
ns (
Sta
ndar
d D
evia
tions
)
-8
-4
0
4
8
12
16
20
24
28 R2 = 0.74
Is there a relationship between efficacy for Aß 40 and Aß 42?
Amyloid beta 42 = 0.5321 x amyloid beta 40 + 0.3685
Efficacy is higher in younger animals
Time at Administration (Days)
1-10
1
102-
195
196-
335
>335
Eff
ect
Siz
e (S
tan
dar
d D
evia
tio
ns)
0.0
0.5
1.0
1.5
2.0
Summarising data from more fundamental research
• The interval validity of findings– Are they the product of bias?
• The validity of research summaries– Have the authors of “pivotal” reviews
considered all relevant data?
• The external validity of findings– Do these findings hold only in limited
highly controlled situations, or only one species, or are they generally applicable across biology?
Perplexing pathways
The added value of a systematic approach …
• Identifying, and explaining, heterogeneity
• Developing a systematic evidence base for understanding biological pathways
• Providing the components for mathematical models predicting the response to interventions
The role of Th17 cells in the development of EAE
Immunisation EAETh17
Th1
CD4+
- = +
- 6
= 3
+ 6 1
EAE
Th
1
- = +
- 11 1
= 1
+ 2 2
EAE
Th
17
Surrogate outcomes and biomarkers
Surrogate outcomes and biomarkers
Surrogate outcome
Functional outcome
Can animal models help?
• In animal studies– Does structural outcome predict functional
outcome?– Does this relationship hold across
interventions?
• Inclusion criteria: – Reports of the efficacy of a candidate stroke
drug in an animal model of focal cerebral ischaemia
– Structural and functional outcome reported from the same cohort of animals
– Simultaneous measurement of structural and functional outcome
Data
1047
257
16
71
131
71
21
25
110
13
110
12
24
18
26
9
Experiments reporting any
outcome
299TOTAL
58Stem Cells
11Other Thrombolytics
20Nicotinamide
54Thrombolytics
16NOS Inhibitors
8FK506
0NOS Donors
42Hypothermia
4Melatonin
51Growth Factors
3NXY-059
7Enriched Environment
16Tirilazad
8Minocycline
1IL1-RA
Experiments reporting structural and
functional outcomesDrug Group
Raw correlation
Raw correlation coefficient = 0.439
adjusted r2=0.301
∆ F
un
ctio
nal
ou
tco
me
∆ Structural outcome
Better
Better
Worse
Structural Outcome
Coefficient 95% CI
Constant (tPA) 23.9 17.1-30.7
Other lytics 19.3 2.93-35.7
FK506 19.9 1.62-38.1
Tirilazad 21.4 7.91-34.9
Nicotinamide 23.4 6.75-40.2
Hypothermia 26.1 15.9-36.4
NXY 059 29.1 0.43-57.8
Delay to assessment (days) -0.01 -0.02-0.00
% improvement (SO) = 23.9 + f(drug) -0.01*(days to assessment)
Adjusted r2 = 0.24
Functional Outcome
Coefficient 95% CI
Structural outcome (Infarct Volume) 0.47 0.37 to 0.56
Stem cells 10.0 1.9 to 18.1
Hypothermia 11.2 2.4 to 19.9
FK506 18.4 4.2 to 32.6
Minocycline 18.5 5.1 to 31.9
Nicotinamide 19.9 10.1 to 29.7
NOS Inhibitors 20.7 10.4 to 30.9
Tirilazad 22.9 8.1 to 37.9
Delay to assessment (days) 0.58 0.36 to 0.82
Delay to treatment (hours) -0.96 -1.44 to -0.48
% improvement (FO) = 0.47*SO + f(drug) + 0.58*(days to assessment) – 0.96*(hours to drug administration)
Adjusted r2 = 0.56
Summary
Structural Outcome Functional Outcome Independent effects on both
tPA Stem cells FK506
Other lytics Minocycline Tirilazad
NXY 059 NOS Inhibition Nicotinamide
Hypothermia
Delay to treatment (-ve)Delay to assessment
(-ve SO, +ve FO)
Lesion Structural Outcome Functional Outcome
Summary
Structural Outcome Functional Outcome Independent effects on both
tPA Stem cells FK506
Other lytics Minocycline Tirilazad
NXY 059 NOS Inhibition Nicotinamide
Hypothermia
Delay to treatment (-ve)Delay to assessment
(-ve SO, +ve FO)
Lesion Structural Outcome Functional Outcome
Summary
Structural Outcome Functional Outcome Independent effects on both
tPA Stem cells FK506
Other lytics Minocycline Tirilazad
NXY 059 NOS Inhibition Nicotinamide
Hypothermia
Delay to treatment (-ve)Delay to assessment
(-ve SO, +ve FO)
Lesion Structural Outcome Functional Outcome
Summary
Structural Outcome Functional Outcome Independent effects on both
tPA Stem cells FK506
Other lytics Minocycline Tirilazad
NXY 059 NOS Inhibition Nicotinamide
Hypothermia
Delay to treatment (-ve)Delay to assessment
(-ve SO, +ve FO)
Lesion Structural Outcome Functional Outcome
Key findings
• Structural outcome explains around 30% of the variation in functional outcome
• Crucially, this relationship is different for different interventions
• Surrogate outcome measures in Phase II are likely to be intervention specific rather than disease specific
• Nonetheless, this approach might help with rational selection of combination therapies
Summary
• The internal and external validity of animal experiments is limited
• Conclusions from such experiments are confounded by many biases
• There is no reason to believe that more “pathophysiological” experiments are any better
Does journal impact factor reflect validity of the presented work?
• 500 publications in focal cerebral ischaemia
• Modelling of Impact factor• IF = 3.7 + 2.4(Conflict of Interest
Statement) + 1.2(Allocation Concealment):
• adjusted r2 = 0.06
Future directions
• Qualitative systematic research• Quantitative systematic research
– Study quality issues– Evidence based pathways– Strategic research targeting
Are there any babies in the bathwater?
• MRC Trials Methodology Hub• Chief Scientist Office• MS Society• NHS R&D Methodology Program
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