an evaluation of the use of 125i-labeled proteins to examine adme characteristics of iodinated...

An Evaluation of the Use of 125I-Labeled Proteins to Examine ADME Characteristics of Iodinated Compounds

Eric Solon, PhD - QPS, LLC

INTRODUCTION

Radiolabeled pharmaceutical compounds have been used to examine the absorption, distribution, metabolism and excretion (ADME) patterns of new drugs for decades.These studies rely on the ability to obtain accurate quantitative data that are directly related to the drug (parent molecule and metabolites) in vivo. Small molecule test drugs are most often radiolabeled with 14C because it can be synthesized to reside in specific molecular positions, it is often very stable in vivo, it has a good signal for quantitation and imaging, and it is relatively safe to use. In the last 5 years, the biotech community, who develop therapeutic large molecules (e.g., peptides, enzymes, antibodies, proteins), are increasingly asked to also determine ADME properties for the new biotech drugs they are developing. Stable radiolabeling large molecules with 14C is often difficult and expensive. Most often large molecules are labeled with 125I, which is relatively quick, easy and much less expensive. HOWEVER!!!

September 27, 2012 Confidential 2

125I labeled proteins have issues that investigators need to be aware of.

The stability of 125I on proteins is highly variable in vivo due to biodehalogenation.

Anywhere from 5% to 80% of the radiolabel can detach from a labeled protein after it’s dosed to an animal.

Quantitative and qualitative results can be confounded by the detection of free 125I that is practically always produced as a result of biodehalogenation.

Therefore ADME studies using 125I-labeled large molecules must account for biodehalogenation and investigators and regulators must understand how that effects the interpretation of the ADME data.

September 27, 2012 Confidential

INTRODUCTION

3

INTRODUCTION

Effect of biodehalogenation of 125I-Proteins and co-administration with “cold”

Iodide


Mouse given IV dose of 125I-Protein

Mouse given IV dose of 125I-Protein and NaI in drinking water.

Thyroid

4

The objectives of this study were to evaluate the use of 125I in ADME studies, which include the determination of mass balance (MB) of total radioactivity from an 125I-labeled protein (125I-IgGrat), and tissue distribution (TD) of the drug-derived radioactivity using quantitative whole-body autoradiography (QWBA).


INTRODUCTION

5

INTRODUCTION

This evaluation included:

A determination of the upper and lower limits of quantitation for phosphor imaging technology (used for QWBA).

To examine and parameterize the effect of high concentrations of 125I in closely associated tissues during QWBA image analysis (a.k.a. radioactive “flaring”) to determine tissue concentrations.

To determine the effect of administering NaI via drinking water to saturate iodine-organifying tissues (e.g. thyroid, skin, salivary gland), and iodine transporters (kidney, stomach).

A comparison of the MB and TD of Sodium-125Iodide (125I-Na) to 125I-IgGrat.

A sample large molecule (125I-IgGrat) ADME study to examine the effect of biodehalogenation on determining ADME properties of iodinated large molecules.


Evaluation of Standards for QuantitationCreate a set of 125I-spiked blood standards

Expose calibration standards for 1, 2, 3, 4, and 7 days

Evaluate calibration curves for linearity

Evaluate background and compare to lowest standard imaged to determine lower limit of quantitation (LLOQ)


STUDY DESIGN

Block of frozen CMC with holes drilled, filled with 125I-blood at serial dilutions

Sections collected on 3M 8210 tape at 40 µm thickness w/ Leica CM3600 cryomicrotome set to maintain -20˚C

Calibration standards were attached to cardboard supports and covered by low density polyethylene wrap

7

STUDY DESIGN

Evaluation of “Flare” effect on tissue quantitation by image analysis

Examine and measure image density values of calibration standards and regions immediately adjacent to them using histogram module of MCID Image analysis software.

Red circle outlines the original sample limits

Grey scale adjustments do not cause any change in the data

Will the flare affect adjacent target during quantitation?


STUDY DESIGN

In Vivo Studies

GroupNumber/ Sample

StudyTarget

Dose Level(mg/kg)

TargetRadioactivity

Level(µCi/kg)

Samples

1 / 125I-rIgG QWBAw/NaI in H2O

2 20Terminal plasma and carcass

2 / 125I-rIgG QWBAw/out NaI in H2O

2 20Terminal plasma and carcass

3 / 125I-rIgG MB w/NaI in H2O 2 20

Urine, feces, cage residue at intervals to 72 h; 1 carcass for

QWBA, 2 carcasses for MB

4 / 125I-rIgG MB w/out NaI in H2O 2 20



5 / Na125I MB w/ NaI in H2O 10 20



6 / Na125IQWBA

w/NaI in H2O10 20

Terminal plasma and carcass

7 / Na125IQWBA

w/out NaI in H2O10 20

Terminal plasma and carcass


STUDY DESIGN - METHODS

QWBA and Mass Balance analyses were performed using standard methods

QWBA - carcass freezing, embedding, sectioning @ 40 µm, phosphor imaging, and image analysis to determine tissue concentrations of 125I radioactivity

Mass Balance – amount of 125I in urine (@ 0-8h, 8-24h, 24-48h, 48-72h), homogenized feces (@ 24 h intervals), cages residues (@ 24 h intervals), and homogenized carcasses (@72h) were determined using gamma counting and % of administered 125I was determined.

Properties of the test article need to be considered (e.g., sticking to formulation container, and/or infusions lines, cross-calibration of gamma counters)

Plasma Precipitation to assess biodehalogenation – plasma was treated with/without Trichloroacetic acid (TCA) precipitation followed by gamma counting) to determine concentration and free and bound 125I.


RESULTS

Calibration Curves and Limits of Quantitation

Image Analysis and Influence of “Flare” effect

Biodehalogenation and In Vivo Radiostability (TCA results)

Mass Balance of 125I and 125I-IgG

QWBA Tissue Concentrations of 125I and 125I-IgG


Image Displayed “Flare” at high concentrations

Calibration curves were generated after different exposure durations (1, 2, 3, 4, and 7 days)

Observed variability among different exposure times

Lower calibration standards on the shorter exposures were unacceptable and were difficult to differentiate from background

Questions:

What is effect of “Flare” and how do we cope with it?

How will the LLOQ and ULOQ be determined?

RESULTS – Flare & Calibration


RESULTS – Calibration & LOQ

1- and 2-day exposures did not pass with the lower calibration standards included (0.0001 – 0.0005 µCi/g)

Passed when lower standards removed

3-, 4-, and 7-day Exposures passed acceptance with all standards

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

0 0.5 1 1.5 2 2.5 3 3.5

µCi/g

MDC/m

m2

1 Day

2 Day

3 Day

4 Day

7 Day

y = 1E+06x + 3679.2R2 = 0.9999

y = 749562x - 2876R2 = 0.9999

y = 596272x + 926.26R2 = 1

y = 386432x - 211.42R2 = 1

y = 201950x + 523.75R2 = 1


RESULTS - Background & LLOQ

Multiple methods suggested for LLOQ

Mean of background readings

Mean of background readings + (3 x Standard Deviation)

Mean of background readings + (5 x Standard Deviation)

Lowest Calibration Standard used in curve

Backgrounds of different sizes 5mm x 5 mm and 25 mm x 25 mm



Variable background readings detected Background readings dependent on the individual exposure conditions and area size of sampled image (5 mm2, 10 mm2, 15 mm2)

µCi/g

24 h

exposure72 h

exposure168 h

exposure

Average Background 5x5 mm 0.000077 0.000040 0.000004

Average Background 25x25 mm 0.000033 0.000048 0.000000

Average Background 5x5 mm at 5 mm away from highest standard 0.002096 0.002205 0.002060



Lowest Standard used for Calibration Curve 0.000968 0.000107 0.000107



µCi/g

72 h exposure

Average Background 5x5mm 0.000040

Average Background 25x25mm 0.000048

5x5 mm; X + 3xSD 0.000136

5x5 mm; X + 5xSD 0.000200

25x25 mm; X + 3xSD 0.000151

25x25 mm; X + 5xSD 0.000219

Lowest Standard used for Calibration Curve 0.000107

Mean of multiple background readings + (x)SD produces an LLOQ comparable to the lowest standard in the calibration curve


Determination of ULOQ is ongoing

Report limits and identify tissue concentration values above the highest standard in the curve

Phosphor Imaging detection of radioactivity is inherently linear across at least 5-6 orders of magnitude.



RESULTS – Flare Effect at 24 h

24 h Exposure - Standard 1

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 12 14

mm

uCi/g


0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14

mm

uCi/g


-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 2 4 6 8 10 12

mm

uCi/g


-0.002

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

-1 1 3 5 7 9 11 13

mm

uCi/g

-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0 2 4 6 8 10 12 14

uCi/g

mm

24 h Exposure - Standard 5 24 h Exposure - Standard 6

-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0 2 4 6 8 10 12 14

mm

uCi/g


-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0 2 4 6 8 10 12 14 16

mm

uCi/g


-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0 2 4 6 8 10 12 14 16

mm

uCi/g

Lowest 2 StandardsFailed Acceptance

Flare/ScatterDistance ca. 1-1.5 mm from the high standards

Red Bars



0

0.5

1

1.5

2

2.5

3

3.5

4 6 8 10 12 14 16 18 20

mm

uCi/g


0

0.2

0.4

0.6

0.8

1

1.2

4 6 8 10 12 14 16 18 20

mm

uCi/g


-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

4 6 8 10 12 14 16 18 20

mm

uCi/g

Flare/ScatterDistance ca. 1-1.5 mm fromthe highstandards

Red Bars


-0.002

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

4 6 8 10 12 14 16 18 20

mm

uCi/g


-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

4 6 8 10 12 14 16 18 20

mm

uCi/g


-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

4 6 8 10 12 14 16 18

mm

uCi/g


-0.0006

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

4 6 8 10 12 14 16

mm

uCi/g


-6.00E-04

-4.00E-04

-2.00E-04

0.00E+00

2.00E-04

4.00E-04

6.00E-04

8.00E-04

1.00E-03

1.20E-03

1.40E-03

4 6 8 10 12 14 16

mm

uCi/g



-0.0004

-0.0003

-0.0002

-0.0001

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

3 5 7 9 11 13 15 17 19

mm

uCi/g


-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

9 11 13 15 17 19 21 23 25

mm

uCi/g


-0.0006

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

3 5 7 9 11 13 15 17

mm

uCi/g

Flare/ScatterDistance ca. 1-1.5 mm from the High standards

Red Bars


-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

9 11 13 15 17 19 21 23 25

mm

uCi/g


-0.002

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

9 11 13 15 17 19 21 23 25

mm

uCi/g


-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

9 11 13 15 17 19 21 23 25

mm

uCi/g


0

0.2

0.4

0.6

0.8

1

1.2

9 11 13 15 17 19 21 23 25

mm

uCi/g


0

0.5

1

1.5

2

2.5

3

3.5

9 11 13 15 17 19 21 23 25

mm

uCi/g

Flaredistance does not increase with exposure time duration

Background Readings at Different DistancesFrom the Highest Standard at 168 h Exposure

10% at 1 mm, 7% at 1.5 mm, < 1 % at 3 mm

0.1

1

10

100

0 1 2 3 4 5 6

Distance from source (mm)

% of Rad

iation Source

% Radiation of Flare A

% Radiation of Flare B

RESULTS – Flare Effect Distance



Stability of label of 125I-Protein

Biodehalogenation of 125I test articles results in significant free 125I in plasma and at least some tissues, which is measured along with the iodinated test article.

Choroid plexus, epidermis, kidney, mammary, prostate, salivary gland, stomach, thymus, and thyroid, contain receptors for free 125I and/or an iodine symporter, which is involved in the organification and/or transport of Iodine.

Amount of free 125I in tissues can mislead investigators, thus quantitation using 125I test articles is semi-quantitative unless proven in vivo radiostability.

RESULTS – Biodehalogenation




Treatment Time Point % 125I-Protein125I-IgG w/NaI 1h 96.5

48h 96.272h 95.9

125I-IgG alone 1h 95.548h 97.172h 96.2

125I-Na w/NaI 1h 13.548h BQL72h BQL

125I-Na alone 1h 26.148h BQL

Stability of label of 125I-Protein in Plasma

Rat 125I-IgG appeared to be stably labeled in this experiment 125I-Na appeared to associate with plasma proteins in vivo!

What about other labeled proteins???

23



# of Protiens Time % of 125I-Protein in PlasmaExamined point 10-20% 20-30% 30-40% 40-50% ~50-60% 60-70% 70-80% 80-90% 90-100%

n=11 5 min 1 2 1 2 2 2 1n=5 30 min 3 2

n=11 1h 1 3 2 2 3n=11 6h 3 2 1 1 2 1 1n=5 24h 1 1 1 2

Survey of other 125I-Proteins in Plasma (w/ NaI)

TCA precipitation results vary widely and may depend on the method of iodination and/or protein structure.

Appears most are relatively stable at early time points.

Biodehalogenation appears to peak at ~0.5 – 6 h.

Later time points show primarily labeled proteins.

Co-administration of NaI doesn’t seem to effect Biodehalogenation.

24


RESULTS – Mass Balance (125I-IgG w/NaI)

Specimen Time Mean % Recovered SD Cumulative

Feces Pre-dose 0.00 0.00 0.00

0-24 h 0.35 0.20 0.35

24-48 h 0.27 0.13 0.62

48-72 h 0.29 0.19 0.92

Sub-total 0.92 0.27

Urine Pre-dose 0.00 0.00 0.00

0-8 h 4.88 0.99 4.88

8-24 h 13.65 1.06 18.53

24-48 h 6.11 0.71 24.64

48-72 h 4.50 0.23 29.14

Sub-total 29.14 0.56

Cage Rinse 24 h 0.83 0.24 0.83

48 h 0.42 0.09 1.26

Cage Wash 72 h 0.90 0.02 2.16

Cage Residue Sub-total 2.16 0.26

Carcass 72 h 61.23 NC (n=2)

Total 93.04 1.00

25


Specimen Time Mean % Recovery SD Cumulative


0-24 h 0.45 0.16 0.45

24-48 h 0.50 0.12 0.95

48-72 h 0.42 0.01 1.36

Sub-total 1.36 0.03


0-8 h 0.69 0.45 0.69

8-24 h 4.84 0.53 5.53

24-48 h 2.80 0.11 8.32

48-72 h 2.09 0.03 10.41


Cage Rinse 24 h 0.68 0.18 0.68

48 h 0.39 0.03 1.07

Cage Wash 72 h 1.14 0.25 2.20

Cage Residue Sub-total 2.20 0.04

Carcass 72 h 65.52 NC (n=2)

Total 79.49 NC

RESULTS – Mass Balance (125I-IgG alone)

26


RESULTS – Mass Balance (125I-Na w/NaI)

Collection % of Dose Recovered

Specimen Time Mean SD Cumulative


0-24 h 0.44 0.12 0.44

24-48 h 0.07 0.06 0.52

48-72 h 0.01 0.01 0.53

Sub-total 0.51 0.16


0-8 h 35.16 13.32 35.16

8-24 h 50.05 6.98 85.32

24-48 h 1.35 0.48 86.56

48-72 h 2.10 2.50 88.65


Cage Rinse 24 h 2.05 0.97 2.05

48 h 0.45 0.21 2.51

Cage Wash 72 h 2.10 1.65 4.61

Cage Residue 72 h 1.54 1.96 6.15

Total 95.32 2.90

27


RESULTS – Mass Balance (125I-Na w/NaI)

Test article did not have issues of sticking to glassware, but a minimal amount may have stuck in syringe.

Gamma Counters at QPS and Vitrax were cross-calibrated to ensure uniform counting of stock Test Article material.

Mass Balance was improved with co-administration of NaI in drinking water.

Loss of radioactivity in group treated with 125I-IgG alone may have been due to carcass digestion in strong KOH where some 125I was volatilized.

28


RESULTS – QWBA (Autoradioluminographs)

29

RESULTS – 125I-Na QWBA (µCi/g)

Tissue 125I-Na w/NaI

125I-Na 1 h 48 h 72 h 1 h 48 h

Blood 0.013 BQL BQL 0.013 BQLSpleen 0.008 BQL BQL 0.006 BQLThymus 0.007 BQL BQL 0.004 BQLRenal Cortex 0.010 BQL BQL 0.007 BQLRenal Medulla 0.012 BQL BQL 0.007 BQLLiver 0.009 BQL BQL 0.005 BQLUrinary Bladder 0.204 BQL BQL 0.064 BQLUrinary Bladder (contents) 0.220 0.001 0.001 0.078 0.001Adrenal Gland 0.012 BQL BQL 0.005 BQLThyroid Gland 0.026 0.003 0.013 0.136 0.317Salivary Gland 0.014 BQL BQL 0.007 BQLAdipose (brown) 0.010 BQL BQL 0.005 BQLSkin 0.013 0.001 0.001 0.014 0.004Prostate Gland 0.014 BQL BQL 0.042 BQLHeart 0.009 BQL BQL 0.006 BQLSkeletal Muscle 0.004 BQL BQL 0.002 BQLLung 0.014 BQL BQL 0.009 BQLLarge Intestine 0.011 BQL BQL 0.000 BQLSmall Intestine 0.011 BQL BQL 0.019 BQLStomach (gastric mucosa) 0.197 BQL BQL 0.155 BQLStomach (contents) 0.081 BQL BQL 0.202 0.001

TCA Results (% Bound) 13.50 NC NC 26.10 NC

TCA results suggest that we need to examine more time points between 0-6 h.

Kidney & Urine results suggest that co-dosing shunts more free 125I through thus faster clearance.

Thyroid has much less 125I uptake with NaI co-administration.

Concentrations in Skin, & stomach with and without NaI are similar.

Prostate gland has higher radioactivity in rat without co-administration of NaI.


RESULTS – QWBA (Autoradioluminographs)

31

RESULTS – 125I-IgG QWBA (µCi/g)

uCi/g

Tissue 125I-IgG w/NaI 125I-IgG

1 h 48 h 72 h 1 h 48 h 72 hBlood 0.098 0.037 0.032 0.091 0.034 0.031Spleen 0.031 0.010 0.007 0.036 0.009 0.008Thymus 0.009 0.005 0.004 0.003 0.005 0.004Renal Cortex 0.014 0.008 0.007 0.020 0.008 0.006Renal Medulla 0.016 0.009 0.008 0.025 0.009 0.007Liver 0.027 0.008 0.006 0.030 0.008 0.005Urinary Bladder 0.015 0.011 0.015 0.022 0.012 0.014Urinary Bladder (contents) 0.048 0.007 0.004 0.018 0.001 0.002Adrenal Gland 0.015 0.007 0.009 0.031 0.010 0.005Thyroid Gland 0.011 0.006 0.010 0.077 1.747 1.808Salivary Gland 0.034 0.015 0.012 0.005 0.009 0.006Adipose (brown) 0.020 0.018 0.015 0.011 0.009 0.009Skin 0.004 0.008 0.012 0.004 0.010 0.011Prostate Gland 0.011 0.007 0.008 0.014 0.006 0.008Heart 0.025 0.016 0.014 0.026 0.015 0.012Skeletal Muscle 0.002 0.003 0.002 0.002 0.003 0.002Lung 0.051 0.026 0.021 0.067 0.017 0.015Large Intestine 0.004 0.006 0.018 0.006 0.005 0.006Small Intestine 0.009 0.005 0.004 0.007 0.005 0.005Stomach (gastric mucosa) 0.011 0.004 0.004 0.009 0.005 0.005Stomach (contents) 0.005 0.001 0.001 0.008 0.003 0.003TCA Results (% Bound) 96.50 96.20 95.50 95.50 97.10 96.20

Kidney & Urine results suggest that co-dosing does not shunt more 125I through, but this is probably because of low biodehalogenation of 125I-IgG.

Thyroid has much less 125I uptake with NaI co-administration.

Concentrations in skin, stomach, and prostate with and without NaI are similar, which is probably due to stably labeled 125I-IgG.


RESULTS – QWBA (µCi/g)

Free 125I was eliminated from tissues much faster than the 125I-IgG (expected if stable radiolabel).

Co-administration of NaI increased elimination rate of free 125I and blocked uptake in symporter tissues, thus enabling improved image analysis by decreasing areas of “flare” effect.

Co-administration did not seem to effect the concentration of free 125I in skin or stomach.

Co-administration of NaI with 125I-proteins that are resistant to biodehalogenation will still be helpful to reduce the “Flare” effect near tissue such as thyroid.

33

Conclusions – Image Calibration

Acceptable calibration curves were obtained after 3-, 4-, and 7-day exposure periods.

Background measurements vary depending on the size of the sampled areas, and the individual exposure conditions (time, background radiation present in lab and from samples)

LLOQ based on the lowest standard is efficient and effective without relying on background.

High concentration calibration standards need to be placed away from other standards to avoid influence of “Flare” effect (at least 15 mm).

More work is need to establish a more reliable ULOQ.

IV and PO Doses of 10-20 µCi/kg worked fine for this study.


Conclusions – “Flare” Effect

The “Flare” distance from source did not change appreciably with longer exposure times

Most flare within 1 to 1.5 mm from source (10% at 1 mm, 7% at 1.5 mm, < 1 % at 3 mm)

Co-administration of NaI in drinking water reduces localization of free 125I in tissues thus reducing “hot” spots like thyroid and improves image sampling of surrounding tissues.

Relatively larger animal models should be considered when performing tissue distribution by QWBA to facilitate tissue sampling of small tissues and to reduce effect of “Flare” on quantitation. (i.e., rat instead of mouse).


Conclusions – Biodehalogenation

Most biodehalogenation was observed at 0-6 h post-dose.

Biodehalogenation or stability of 125I label can vary widely among different proteins and doesn’t seem to be predictable.

TCA precipitation (or another method; e.g., Gel analysis) should be performed on plasma and/or tissues of interest for each animal being analyzed (by QWBA and/or gamma counting).

Co-administration of “cold” iodine helps reduce free 125I in tissues, thus reducing influence on tissue concentration data and “Flare” effect from thyroid and/or other tissues that uptake iodine.

Co-administration of “cold” iodine did not reduce biodehalogenation.

Animals that have voided their urinary bladder before or during euthanasia will make image analysis of surrounding tissues easier and more accurate.

Biohalogenation of endogenous proteins can occur after administration of 125I.


Conclusions – Mass Balance

Cross-calibration of gamma counters from radiolabeling lab and in-life labs is important.

All formulation storage containers and dose administration instruments should be included in mass balance sample analysis if sticking is suspected.

125I may be lost (volatilized?) during carcass digestion using strong KOH.

Co-administration of “cold” iodine decreases the amount of free 125I and improved recovery at 72 h post-dose. (Did not achieve mass balance from rats given 125I-IgG alone at 72 h post-dose).


Conclusions – Tissue Distribution

Proteins typically have much longer tissue half-lives than free 125I, except for thyroid, which uptakes most free 125I, so caution is needed when interpreting concentration data for that tissue.

Co-administration of “cold” iodine did not seem to have an effect on the tissue concentrations observed in skin and/or stomach, but caution should still be observed because free 125I was observed in these tissues for a relatively long time post-dose (up to 72 h).

Co-administration of “cold” iodine appears to shunt free 125I to urine relatively quickly (0-6 h) thereby reducing confounding effect of flare and from “background” free 125I.

Tissue image measurements should be obtained at least 3 mm away from tissue with high concentrations to avoid “Flare” effect. Or tissues with suspected high levels (i.e. thyroid) can be removed from the section before imaging to avoid the “flare” effect altogether.


Questions??


When 125I is removed from the protein the Specific Activity will change. Biodehalogenation occurs to a great extent during 0-6 h. What is the effect on tissue concentration data?

What other choices are available to label proteins more stably and at a reasonable cost? 35S?, 3H?

Other questions??

39

Thank You and Support

Helen Shen

Alfred Lordi

Jared Lander

Tony Srnka

I would like to thank QPS, LLC and the following people for their support and contributions during the planning and conduct of this experiment


an evaluation of the use of 125i-labeled proteins to examine adme characteristics of iodinated...

Health & Medicine

adme data

adme studies

iggrat adme study

therapeutic large molecules

sample large molecule

effect ofbiodehalogenation

new biotech drugs

drinking water