ch156_lecture5 autoradiography

7/22/2019 CH156_Lecture5 Autoradiography

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Chemistry 156: Chemistry of Positron Emission Tomography

Lecture 4:

Autoradiography


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Autoradiography - Background

Autoradiography is any technique used to produce an image of the

2D distribution of a radioactive substance.

-The first autoradiography was obtained

accidently around 1867 when ablackening was produced on emulsions

of silver chloride and iodide by uranium

salts.

- uc s u es an e wor o e ur es

in 1898 demonstrated autoradiography

before, and contributed directly to, the

discovery of radioactivity.

-The development of autoradiography as a

biological technique really started tohappen after World war II with the

development of photographic

emulsions and then stripping film made

of silver halide.


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Autoradiography First use for drug binding

- Determined binding of a [3

H]-labeled opioid peptide, [3H]-

morphine, and derivatives

- Pretreated with opioid drugs todetermine specific binding


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General Methods for Autoradiography

Two General Types of Experiments:

1) In-vivoautoradiography - receptors are labeled in intact living tissue by systemicadministration of the radioligand (like in PET). Tissue is removed, processed, and

visualized.

2) In-vitroautoradiography - slide-mounted tissue sections are incubated withradioligand so that receptors are labeled under very controlled conditions

Radionuclide Half-life Theoretical SA(Ci/mmol)

Decay mode

14C 5730 years 0.0624

3H 12.43 years 28.8*

35S 87.4 days 1494

32P 14.3 days 9131

125I 60.0 days 2176

131I 8.04 16240


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General Technique

- Map anatomical location of radiolabelled ligands to visualize andquantify receptors in tissue

- Trace neurons by axonal transport of radioactively labeled aminoacids, certain sugars, or transmitter substances

- Measure DNA production (e.g., 3H-thymidine)

Examples uses for autoradiography:

Board 1


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Important considerations: Validation of Protocol

- Binding must be linear with respect to receptor density over the

range in which the assay will be used.

- The stability of the ligand should be measured to make sure it stays

intact over the time-course of the experiment

- The stability at integrity of the target (receptor/enzyme/etc) should

e ver e . or examp e, oes ssue process ng mpac n ng .

Board 2


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Kinetics of Binding

Unlike PET imaging in vivo, we have control over the

timing of the experiment and can verify that equilibrium

is reached.

Boards 3-8


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Autoradiography Detection with Film

Grain

Autoradiographic film is typically composed of 4 layers.

1- An upper protective coat.

2- A layer of gelatin that contains silver halide (AgBr, AgCl, or AgI)

crystals. (The type and proportions of the different silver halides

determining the speed of the film.)

3- The film base, usually made from a flexible polymer.

4- An anti-halation backing to prevent light from reflecting back

onto the emulsion.


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-particles

Film before exposure

Exposure of film to sample

Formation of latent image

Fixing removes unreacted silver halides

from the emulsion.

Development changes silver ions to

metallic silver


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Boards 9-12


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Radiotracer of the Day [18F]-FMISO

[18F]Fluoromisonidazole is a hypoxia marker.

Hypoxia (oxygen deprivation) in malignant tumors can affectthe outcome of anti-cancer treatments. Malignant tumors are

relatively resistant to chemotherapy and irradiative therapybecause of their lack of oxygen, a potent radiosensitizer.


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Radiotracer of the Day [18F]-FMISO

Brain Tumor - Glioblastoma

FMISO FDG MRI

Nonsmall Cell Lung Carcinoma

FMISOFDG CT

ch156_lecture5 autoradiography

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