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![Page 1: SI and non-SI units for Biological · PDF fileSI and non-SI units for Biological quantities Adrian F. Bristow ... – The unit of insulin can only be described in terms of a reference](https://reader036.vdocument.in/reader036/viewer/2022081521/5a9ec59d7f8b9a76178bd6b6/html5/thumbnails/1.jpg)
National Institute for Biological Standards and Control
Assuring the quality of biological medicines
SI and non-SI units for Biological quantities
Adrian F. Bristow
National Institute for Biological Standards and control
(Health Protection Agency)
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Assignment of quantities to biological medicines:
An old problem re-discovered
Assignment of quantities to biological medicines:
An old problem re-discovered
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On March 13th 2006, 6 healthy male volunteers were given low doses of
TGN1412, an experimental monoclonal antibody which was under clinical
trial as a potential immune-activating agent, through agonistic
(stimulatory) interaction with the CD28 T-cell receptor.
All developed rapid, life-threatening adverse reactions, leading to multiple
organ dysfunction. This was later confirmed to arise from a toxic
“cytokine storm”. Thanks to rapid intervention the men all survived, but
at least some will have persistent, irreversible sequelae.
The dose (mg/kg) used was 500 times lower than the dose that had been
safe in monkeys
Assignment of quantities to biological medicines:
An old problem re-discovered
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Assignment of quantities to biological medicines:
An old problem re-discovered
![Page 5: SI and non-SI units for Biological · PDF fileSI and non-SI units for Biological quantities Adrian F. Bristow ... – The unit of insulin can only be described in terms of a reference](https://reader036.vdocument.in/reader036/viewer/2022081521/5a9ec59d7f8b9a76178bd6b6/html5/thumbnails/5.jpg)
Assignment of quantities to biological medicines:
An old problem re-discovered
![Page 6: SI and non-SI units for Biological · PDF fileSI and non-SI units for Biological quantities Adrian F. Bristow ... – The unit of insulin can only be described in terms of a reference](https://reader036.vdocument.in/reader036/viewer/2022081521/5a9ec59d7f8b9a76178bd6b6/html5/thumbnails/6.jpg)
Assignment of quantities to biological medicines:
An old problem re-discovered
Why have I told you this?
TGN1412 is a super-agonist for the CD28 T-cell receptor.
It is meant to stimulate release of T-cell cytokines
It could be argued that qualitatively the response was not unexpected.
What was unexpected was the magnitude of the response. What the
clinical trial lacked was any reference framework for relating the dose
quantity (mg) to the magnitude of the response in humans.
In medicine, numbers, quantities and units matter.
They make the difference between lack of efficacy, effective therapy and
over-dose
They make the difference between mis-diagnosis and accurate diagnosis
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.
Assignment of quantities to biological medicines:
An old problem re-discovered
Measurement of quantities in medicine
Therapeutic intervention Diagnosis
Most drugs (eg aspirin) are dosed in
units of the SI (mg)
A significant minority, the
“biologicals”, are in arbitrary units
Several hundred quantities are
measured in the diagnosis of disease
About 20% are measured in units of the
SI (mg or mol)
The majority are “biologicals”, and not
traced to the SI
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Assignment of quantities to biological medicines:
An old problem re-discovered
What, in this context, is a “biological” medicine ?
and
Why is it an old problem re-discovered?
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Consider insulin:
A story of successful quantification of an unknown quantity
Biological assays and standardization in
medicine: Historical background
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Diabetes Voice (Kambaskovic, D., June
2002 Volume 47 Issue 2) describes two diabetics with remarkably long life spans
Hazel Davies, who had lived for 80 years on insulin therapy after being diagnosed in 1921, and Roy Cross, who lived to be >100 after being diagnosed in 1938
This suggests that insulin was a well-controlled drug
however:
Even now it would be impossible to assign any kind of value in SI to the 1925 insulin.
How did they do it then so successfully?
HPLC of therapeutic insulin
1925 1995
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Even with today’s technology, the 1920’s preparation would be too
impure to assay by an HPLC method
(Insulin structure determined by Sanger in the 1950’s)
Paradox:
Insulin is a drug whose dose needs to be precisely controlled +/- 10%
This was clearly achieved (Hazel Davies lived to be >100)
How was this possible?
The Insulin Story: accurate quantification of an unknown quantity
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How do you measure, to within 10%, the potency of insulin in 1925?
You have to assign a precise figure to the biological activity of insulin
preparations, even when you don’t know what insulin is
•What do you know?
– It lowers blood sugar
•Can you measure blood sugar?
– Yes but not easily
•What can you measure?
– You can count!
- Mouse convulsion insulin assay:
Injecting fasting mice with insulin will cause some to go into hypoglycaemic
convulsions. The number that do appears to be related to the amount of
insulin you inject
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Convulsion-inducing activity compared
to reference standard
A comparative mouse convulsion insulin assay (N = 24)
SL Standard low dose (30mU/ml)
SH Standard high dose (60mU/ml)
TL Test low dose ?
TH Test high dose ? (2 x TL)
Assay 1
SH = 20/24
SL = 8/24
TH = 21/24
TL = 6/24
30 60
30
20
10
0
Standard
Test
Statistical analysis is based on calculations of a common slope, then chi-squared for deviations for parallelism and linearity
Assay 1: 97.0% (75-126)
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Convulsion-inducing activity compared
to reference standard
A comparative mouse convulsion insulin assay (N = 24)
SL Standard low dose (30mU/ml)
SH Standard high dose (60mU/ml)
TL Test low dose ?
TH Test high dose ? (2 x TL)
Assay 1
SH = 20/24
SL = 8/24
TH = 21/24
TL = 6/24
30 60
30
20
10
0
Standard
Test
Statistical analysis is based on calculations of a common slope, then chi-squared for deviations for parallelism and linearity
30 60
30
20
10
0
Standard
Test
Assay 2
SH = 8/24
SL = 1/24
Th = 9/24
Tl = 2/24
Sir Henry Dale established that a unit of insulin can only effectively be described in
terms of a reference material, not in terms of an absolute response
Assay 1: 97.0% (75-126) Assay 2: 111.3% (74.0-181)
Combination: 100.75% (80.2 – 126)
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The Insulin Story exemplifies all aspects of a
“biological” as the term is used in medicine:
• The medicinal substance was isolated from a biological source
(extracts of animal pancreata – bovine, porcine)
• Accurate quantification of the active principle was achieved by
quantifying its activity in a test measuring function rather than
quantity of substance
– i.e. what it does, rather than what it is
• Quantification is dependent on the science of biological
standardization
– The unit of insulin can only be described in terms of a reference material,
not in terms of an absolute response (eg. number of convulsions)
– Statistical combination of independent assays can produce precise
numbers from an inherently imprecise and irreproducible method
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Clotting factors
Thrombolytics
Hormones
Cytokines and growth factors
Enzymes
Vaccines
Micobiological antigens
Toxins
Antisera and immunoglobulins
Genomic DNA, cDNA and RNA
WHO Biological reference materials
Established by NIBSC (>400)
Include:
“Biologicals” and Biological Reference materials:
the current portfolio
Examples
Blood Coagulation factor VIII
Tissue plasminogen activator
Follicle stimulating hormone
Interferon
Thrombin
Whole cell Pertussis vaccine
Hepatitis B antigen
Botulinum toxin
Anti-HPV-16 Ab
HIV clade 1 genetic reference panel
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Clotting factors
Thrombolytics
Hormones
Cytokines and growth factors
Enzymes
Vaccines
Micobiological antigens
Toxins
Antisera and immunoglobulins
Genomic DNA, cDNA and RNA
WHO Biological reference materials
Established by NIBSC
Number > 400, including:
Stimulation of cell proliferation in vitro
Protection of test animals against microbiological challenge
Clot lysis in vitro
Animal or cell death
Examples of quantitative measurement
methods (bioassay)
“Biologicals” and Biological Reference materials:
the current portfolio
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Assignment of quantities to biological medicines:
An old problem re-discovered
Chemical drugs Biological drugs
Where the dose or clinical effect
can be related to a fundamental
physical constant, measuring
quantity or effect
Where the dose or clinical effect can only be
related to the response in a complex
measurement system such as an animal or a
living cell, and can be traced only to the
effect produced by a reference material
(bioassay)
This complexity is irreducible!
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A “biological” analytes is considered by WHO as one
“…of biological origin,
which cannot be characterized adequately by chemical
and/or physical means alone…”
(WHO, Tech. Rep. Ser. 800, 1990, 181-213).
This is a practical definition, relating the structural complexity of the
material being standardised to the current utility of analytical methods.
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Assignment of quantities to biological medicines:
An old problem re-discovered
Does this paradigm really still reflect analytical reality in the
second decade of the 21st century?
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It is true that our understanding of what meets
the definition of a “biological is changing
• Aspirin 180
• Adrenaline 333
• Ampicillin 371
• Oestradiol 376
• Insulin 5808
• Growth hormone 22K
• Rec Hep-B vaccine 28K
• Erythropoietin ~30.6K
• Tissue plasminogen activator ~65K
• Albumin 67K
• Anti-TNF receptor MAb 150K
• Clotting factor VIII ~280K
• Viral gene delivery vectors >100kb DNA
• Meningococcus vaccine
• Stem cells
• Organs
1950 2007m.w 1950 2010
Biological
Non-biological
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Assignment of quantities to biological medicines:
An old problem re-discovered
Although the last twenty years has seen a progressive move towards
physcichemical analytical methods for many smaller proteins, the
“new” medicine, based on biotechnology encompasses therapeutic
interventions such as engineered antibodies, complex glycoproteins,
gene-therapy delivery vectors, stem cells, and engineered vaccines.
These are comfortably below the “biologicals” cut-off line and their
measurement remains dependant on complex biological systems.
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A “biological” analytes is considered by WHO as one
“…of biological origin,
which cannot be characterized adequately by chemical
and/or physical means alone…”
(WHO, Tech. Rep. Ser. 800, 1990, 181-213).
This is a practical definition, relating the structural complexity of the
material being standardised to the current utility of analytical methods.
Assignment of quantities to biological medicines:
An old problem re-discovered
Is this definition still valid?
The short answer is yes!
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Assignment of quantities to biological medicines:
An old problem re-discovered
Description of the amount of material in terms of basic physical constant is
complicated by:
Extreme complexity
Heterogeniety
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Assignment of quantities to biological medicines:
An old problem re-discovered
Insulin
51 amino acids,
5.8kD
Growth hormone
191 amino acids
22kD
Clotting factor VIII
2361 amino acids
268kD (protein)
Glycosylated
1 Complexity
Consider clotting factor VIII, a large (ish) glycoprotein used
to treat haemophilia
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Assignment of quantities to biological medicines:
An old problem re-discovered
Peptide mapping is a front-line technique for analysing proteins
Somatropin
Tryptic peptides:
3-10 14
11-20 5
>20 1
Factor VIII
Tryptic peptides:
3-10 108
11-20 53
>20 28
Irresolvable in one dimension
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Assignment of quantities to biological medicines:
An old problem re-discovered
A single subunit globular glycoprotein, 165 amino acids
3 N-linked and 1 O-linked glycosylation sites
Mr Approx 30,600 (ie 35% CHO)
Kidney-derived hormone maintaining erythrocyte maturation in vivo
Used in treatment of anaemia associated with renal failure and other conditions
Erythropoietin: a therapeutic glycoprotein
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Sialic acid
SulphateGalactose
GalNac
N-acetyl glucosamine
Mannose
Asparagine
Glycosylation: N-linked glycan structures
biantennary
triantennary
tetraantennary
Glycosylation: a non-template-directed process which
produces heterogeneous products
Charge based fractionation of
pharmaceutical erythropoietin
products
2 Heterogeneity
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Assignment of quantities to biological medicines:
An old problem re-discovered
For heterogeneous glycoproteins, quantification by mass (mg) is
meaningless – the structures all have different molecular weights
Quantification in mol protein is feasible, but -
200 250 300 350
0
50
100
150
200
In v
ivo
bio
log
ica
l a
cti
vit
y
Terminal glycosylatyion (Z)
Mol protein is not a
measurement that reflects the
biological activity of the
molecule
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Assignment of quantities to biological medicines:
An old problem re-discovered
Complexity of vaccines
Proteomics-based identification of antigenically-active components present in OMV
Vaccines against Meningococcal group B disease
-At least 30 different antigens can be identified
in this vaccine
-The relationship between antigen quantity and
protective immunity is not understood
-Protective immunity can only be measured in a
(biological) challenge protection assay
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Assignment of quantities to biological medicines:
An old problem re-discovered
So description of quantity in terms of basic physical constants is
both difficult and misleading.
What about description of function in terms of basic physcal
constants?
Most pharmacologically active biologicals exert their actions by
interacting with a receptor
Can this be an analytical target for expressing function in terms
of physical constants?
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Assignment of quantities to biological medicines:
An old problem re-discovered
Analysis of receptor binding by
surface plasmon resonanceInteraction of active bio-molecules with their
receptors can be measured and described in
physico-chemical terms by techniques such
as surface plasmon resonance
Receptor binding is a good analogue of
biological activity in cell bioassays in vitro
What’s the problem?
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Assignment of quantities to biological medicines:
An old problem re-discovered
200 250 300 350
0
50
100
150
200
In v
ivo
bio
log
ica
l a
cti
vit
y
Terminal glycosylatyion (Z)
In v
itro
bio
log
ica
l a
cti
vit
y
Terminal glycosylatyion (Z)
200 250 300 350
0
100
200
300
400
Erythropoietin: relationships between glycosylation and biological activity
In vitro activity (receptor binding) In vivo activity
Factors affecting the ability of erythropoietin to bind to its receptor are not
the same as those affecting its ability to stimulate red blood cell formation in
a whole organism
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Assignment of quantities to biological medicines:
An old problem re-discovered
Activity-determining factors
In vitro In vivo
Amount of substance
Receptor affinity
Signal Transduction in
responsive cells
Amount of substance
Receptor affinity
Signal Transduction in
responsive cells
Access to target tissue
Plasma half life
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Assignment of quantities to biological medicines:
An old problem re-discovered
-Insulin analogues with up to 10-fold higher receptor affinity, or with similarly
reduced receptor affinity have been produced (eg B-10 Asp insulin)
-The receptor-binding properties of such analogues are reflected in their in vivo
potency
-It is not reflected in the in vivo potency, which is usually similar to the parent
molecule
-Similarly, insulin analogues with reduced receptor binding do not show reduced
activity in vivo
-??
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Assignment of quantities to biological medicines:
An old problem re-discovered
Ribel et al(1990) Diabetes 39 10333-1039
Maintenance of the biological blood glucose-lowering activity action
of insulin in vivo depends on the circulating plasma levels
The main route of clearance of insulin in vivo is through its receptor
Increasing the affinity for the receptor increases the rate of removal
from the plasma compartment and vice versa
Changes in receptor affinity are not reflected in changes in in vivo
activity (and therefore in clinical efficacy)
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Assignment of quantities to biological medicines:
An old problem re-discovered
Chemical drugs Biological drugs
Where the dose or clinical effect
can be related to a fundamental
physical constant, measuring
quantity or effect
Where the dose or clinical effect can only be
related to the response in a complex
measurement system such as an animal or a
living cell, and can be traced only to the
effect produced by a reference material
(bioassay)
This complexity is irreducible!
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Assignment of quantities to biological medicines:
An old problem re-discovered
-There is a need for robust and accurate quantitation in all areas of
medicine, including biological medicines
-Although some progress has been made in applying measurement
science to bio-molecules, much of this area of medicine remains
beyond its scope present capacities
-The use of complex measurement systems based on biological
responses remains embedded in the approach to controlling this type
of medicine
-A reductionist approach to measurement in this field, breaking down
the system into measurable components, seems unpromising –
biological systems are not the sum of their parts
-Developing a metrology for complex systems seems overdue!
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Thank you for your attention
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