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Mechanisms of localization and metabolism of iodobenzyl-guanidines, adrenal medullary imaging agents
22x
Around the Nuclear World
29. Iodination Heptadecanoic
Methods for Routine Preparation of 17-(1231)_ Acid and 15( ’ 231-Phenyl)-Pentadecanoic Acid
H. J. MACHULLA and K. DUTSCHKA Universitaetsklinik
der Gesamthochschule,
Essen, Federal
Republic of Germany
For routine preparation of radioiodinated w-phenyl fatty acids, syntheses with high yields and low reaction time are desired. Therefore a new, fast, labelling procedure was developed. 174’ 231)-heptadecanoic acid (IHA) was obtained in a yield of 707,; within 8 min when the I-for-BR exchange was performed in DMFA at 80°C. However, not the yield of the labelling procedure itself, but the over-all yield, is the most important feature for routine productions. Since ‘231-iodide is mainly obtained in aqueous solutions the solvent has to be evaporated and often great losses are observed during this procedure. This can be avoided efficiently with glass beads. Another practical difficulty is the preparation of the injection solution, but if the product is carefully purified by means of HPLC using a reversed phase separation, the product can be dissolved in blood serum of HSA solution practically quantitively. The routine production of l5-(iz3 I)-phenylpentadecanoic acid (IPPA) was also considerably improved. The iodination is performed with yields between 75 and 80”’ ,<, with high reproducibility if water is strictly avoided. The time of preparation is also decreased since the ‘231-iodide is directly distilled out of the irradiated Te-target into the reaction solution. Thus up to 60 mCi of purified product are delivered for medical application each week.
30. Structure-Activity zamide Derivatives
Relationships of 1231 Labeled o-Iodoben-
R. M. BALDWIN, T. H. LIN and H. S. WINCHELL Medi-Physics, Inc., 5801 Christie Ave., Emeryville, CA 94608. U.S.A. o-Iodobenzamide is a stable compound which is labeled quantitatively by heating with no-carrieradded ‘231 NaI in ethanol. The 1231 product is relatively inert biologically, being resistant to in ciw deiodination or hydrolysis, in rats and dogs, for several hours. Furthermore, it appears to be freely diffusible, distributing itself in the body according to the extravascular fluid space, with some localization in the liver, and little tendency for excretion into the urine or bile. The brain uptake and brain-blood ratio is higher than that of iodoantipyrine, and allows imaging the brain in dogs. The product is also taken up by induced myocardial infarcts and transplanted tumors in rats. Substitution of the amide function with single alkyl groups does not alter the in oiuo characteristics except at long-chain length where hepatobiliary excretion predominates. Substitution of both amide hydrogens, however, results in a different pattern, with high blood binding and increased excretion. Conversion to more polar functionalities, such as the hydrazide or hydroxamic acid, also leads to hepatobiliary excretion.
31. Mechanisms of Localization and Metabolism guanidines, Adrenal Medullary Imaging Agents
of Iodobenzyl-
M. C. TUBES, D. L. GILDERSLEEVE,D. M. WIELAND, L. E. BROWN and W. H. BEIERWALTES University of Michigan Hospital. Ann Arbor, MI, U.S.A. Tissue distribution studies of iodine-1254abeled ( 1251)meta (m)-, para (p)-, and ortho (o)guanidines (IBG) have demonstrated different capacities of the isomers to concentrate and in the adrenal medulla, and also different stabilities to in uiuo dehalogenation!‘) Since rently being evaluated clinically as an imaging agent for both the adrenal medulla and the studies were undertaken to evaluate the pharmacokinetics of these IBG isomers.
iodobenzylbe retained IBG is curheart, these
229
Around the Nuclear World
12”I-m-IBG is observed to concentrate in the dog adrenal medulla to a level of 1.20pM. Using a suction technique, we are able to recover 29.81 y/; of the total radioactivity in dog adrenals after i.v. injection of ‘251-m-IBG. This represents a maximum extraction of 32.55:; of pure adrenal medulla. Subcellular fractionation of this extract using a microsedimentation technique demonstrated that 53.52 + 10.08”~~of the radioactivity is in the large chromaffin granule fraction. 480 x g to 12,000 x g. These and other studies support the idea that these compounds may share the same transport pathway as norepinephrine (NE) and accumulate in and displace NE from the chromaffin storage granules. Although analysis of a perchlorate extract of an adrenal homogenate revealed that < 5’?,, of the total radioactivity is in the form of free iodide, the thyroid uptake of radioactivity is suppressed by the administration of oral KI indicating that in ciuo deiodination does occur. Incubation of “51-p-IBG with a 2000 x g supernatant of a dog liver homogenate demonstrated a very slow enzymatic dehalogenation which is stimulated by the addition of glutathione (GSH). These and other studies suggest that this dehalogenation is due to a GSH-S-transferase in the liver. Reference 1.
WIELAND
D.
M. rt ul. J. Nucl. Mud. 21, 349-353 (1980).
32. Analysis of Commercial
’ 251
Fibrinogens
P. H. WATERHOUSE and J. R. MCLEAN* Department of Biology. University of Ottawa and *Radiation
Protection
Bureau, Health
& Welfare
Canada A semi-micro slab gel apparatus was used to analyze 3 commercially available 1251 fibrinogen preparations. The gels were used to detect the presence of high molecular weight labelled aggregates. non-clottable protein impurities and to determine the distribution of 1251 among the component polypeptide chains of fibrinogen. In all preparations, 17 23”,, of the radioactivity was associated largely with high molecular weight aggregates. Their presence could influence the sensitivity of the “‘1 uptake test. The radioactivity associated with the intact fibrinogen was not equally distributed to the component polypeptide subunits and this could influence the rate of clearance of radioactivity from the site of clot formation.
33. Commercial
Production of ‘251-Fibrinogen Injection
L. C. IKENO, B. M. BOWEN and M. DER Chedoke-McMaster
Hospital,
Hamilton,
Ontario,
Canada
in 1975, Health Protection Branch approval was received to distribute ‘2SI-Fibrinogen Injection. Since that time. over 30,000 vials of this drug have been prepared and used in the detection of deep-vein thrombosis. Diagnosis of venous thrombosis with fibrinogen leg scanning depends on the incorporation of ‘251-Fibrinogen into the thrombus, which is then detected by measuring the conscquent increase of overlying surface radioactivity with an isotope detector. The preparation of this drug relies on careful donor selection and preparation of the unlabelled fihrinogen to minimize the chance of transmitting hepatitis and to ensure a high level of clottable protein in each preparation. These methods are described. Approximately 150 mg of fibrinogen having a clottable protein content in excess of 80 % is iodinated using the ICl method. One-half of an atom of iodine per molecule of fibrinogen is added to the protein. The unbound iodide is removed by passing the product through an anion exchange resin column. It is diluted to its final strength with phosphate buffer pH 73, packaged in unit dose vials, then stored at -7O’C until ready for use. Samples stored under various conditions have been examined with respect to their biological half-life and radioactive clottability. The important aspect of any radiopharmaceutical production system is its ability to provide the physician with a product of a consistent high quality with which he may make his clinical assessment of the patient’s condition. The quality control procedures which we tind necessary to ensure this reproducibility are described.
Around the Nuclear World
29. Iodination Heptadecanoic
Methods for Routine Preparation of 17-(1231)_ Acid and 15( ’ 231-Phenyl)-Pentadecanoic Acid
H. J. MACHULLA and K. DUTSCHKA Universitaetsklinik
der Gesamthochschule,
Essen, Federal
Republic of Germany
For routine preparation of radioiodinated w-phenyl fatty acids, syntheses with high yields and low reaction time are desired. Therefore a new, fast, labelling procedure was developed. 174’ 231)-heptadecanoic acid (IHA) was obtained in a yield of 707,; within 8 min when the I-for-BR exchange was performed in DMFA at 80°C. However, not the yield of the labelling procedure itself, but the over-all yield, is the most important feature for routine productions. Since ‘231-iodide is mainly obtained in aqueous solutions the solvent has to be evaporated and often great losses are observed during this procedure. This can be avoided efficiently with glass beads. Another practical difficulty is the preparation of the injection solution, but if the product is carefully purified by means of HPLC using a reversed phase separation, the product can be dissolved in blood serum of HSA solution practically quantitively. The routine production of l5-(iz3 I)-phenylpentadecanoic acid (IPPA) was also considerably improved. The iodination is performed with yields between 75 and 80”’ ,<, with high reproducibility if water is strictly avoided. The time of preparation is also decreased since the ‘231-iodide is directly distilled out of the irradiated Te-target into the reaction solution. Thus up to 60 mCi of purified product are delivered for medical application each week.
30. Structure-Activity zamide Derivatives
Relationships of 1231 Labeled o-Iodoben-
R. M. BALDWIN, T. H. LIN and H. S. WINCHELL Medi-Physics, Inc., 5801 Christie Ave., Emeryville, CA 94608. U.S.A. o-Iodobenzamide is a stable compound which is labeled quantitatively by heating with no-carrieradded ‘231 NaI in ethanol. The 1231 product is relatively inert biologically, being resistant to in ciw deiodination or hydrolysis, in rats and dogs, for several hours. Furthermore, it appears to be freely diffusible, distributing itself in the body according to the extravascular fluid space, with some localization in the liver, and little tendency for excretion into the urine or bile. The brain uptake and brain-blood ratio is higher than that of iodoantipyrine, and allows imaging the brain in dogs. The product is also taken up by induced myocardial infarcts and transplanted tumors in rats. Substitution of the amide function with single alkyl groups does not alter the in oiuo characteristics except at long-chain length where hepatobiliary excretion predominates. Substitution of both amide hydrogens, however, results in a different pattern, with high blood binding and increased excretion. Conversion to more polar functionalities, such as the hydrazide or hydroxamic acid, also leads to hepatobiliary excretion.
31. Mechanisms of Localization and Metabolism guanidines, Adrenal Medullary Imaging Agents
of Iodobenzyl-
M. C. TUBES, D. L. GILDERSLEEVE,D. M. WIELAND, L. E. BROWN and W. H. BEIERWALTES University of Michigan Hospital. Ann Arbor, MI, U.S.A. Tissue distribution studies of iodine-1254abeled ( 1251)meta (m)-, para (p)-, and ortho (o)guanidines (IBG) have demonstrated different capacities of the isomers to concentrate and in the adrenal medulla, and also different stabilities to in uiuo dehalogenation!‘) Since rently being evaluated clinically as an imaging agent for both the adrenal medulla and the studies were undertaken to evaluate the pharmacokinetics of these IBG isomers.
iodobenzylbe retained IBG is curheart, these
229
Around the Nuclear World
12”I-m-IBG is observed to concentrate in the dog adrenal medulla to a level of 1.20pM. Using a suction technique, we are able to recover 29.81 y/; of the total radioactivity in dog adrenals after i.v. injection of ‘251-m-IBG. This represents a maximum extraction of 32.55:; of pure adrenal medulla. Subcellular fractionation of this extract using a microsedimentation technique demonstrated that 53.52 + 10.08”~~of the radioactivity is in the large chromaffin granule fraction. 480 x g to 12,000 x g. These and other studies support the idea that these compounds may share the same transport pathway as norepinephrine (NE) and accumulate in and displace NE from the chromaffin storage granules. Although analysis of a perchlorate extract of an adrenal homogenate revealed that < 5’?,, of the total radioactivity is in the form of free iodide, the thyroid uptake of radioactivity is suppressed by the administration of oral KI indicating that in ciuo deiodination does occur. Incubation of “51-p-IBG with a 2000 x g supernatant of a dog liver homogenate demonstrated a very slow enzymatic dehalogenation which is stimulated by the addition of glutathione (GSH). These and other studies suggest that this dehalogenation is due to a GSH-S-transferase in the liver. Reference 1.
WIELAND
D.
M. rt ul. J. Nucl. Mud. 21, 349-353 (1980).
32. Analysis of Commercial
’ 251
Fibrinogens
P. H. WATERHOUSE and J. R. MCLEAN* Department of Biology. University of Ottawa and *Radiation
Protection
Bureau, Health
& Welfare
Canada A semi-micro slab gel apparatus was used to analyze 3 commercially available 1251 fibrinogen preparations. The gels were used to detect the presence of high molecular weight labelled aggregates. non-clottable protein impurities and to determine the distribution of 1251 among the component polypeptide chains of fibrinogen. In all preparations, 17 23”,, of the radioactivity was associated largely with high molecular weight aggregates. Their presence could influence the sensitivity of the “‘1 uptake test. The radioactivity associated with the intact fibrinogen was not equally distributed to the component polypeptide subunits and this could influence the rate of clearance of radioactivity from the site of clot formation.
33. Commercial
Production of ‘251-Fibrinogen Injection
L. C. IKENO, B. M. BOWEN and M. DER Chedoke-McMaster
Hospital,
Hamilton,
Ontario,
Canada
in 1975, Health Protection Branch approval was received to distribute ‘2SI-Fibrinogen Injection. Since that time. over 30,000 vials of this drug have been prepared and used in the detection of deep-vein thrombosis. Diagnosis of venous thrombosis with fibrinogen leg scanning depends on the incorporation of ‘251-Fibrinogen into the thrombus, which is then detected by measuring the conscquent increase of overlying surface radioactivity with an isotope detector. The preparation of this drug relies on careful donor selection and preparation of the unlabelled fihrinogen to minimize the chance of transmitting hepatitis and to ensure a high level of clottable protein in each preparation. These methods are described. Approximately 150 mg of fibrinogen having a clottable protein content in excess of 80 % is iodinated using the ICl method. One-half of an atom of iodine per molecule of fibrinogen is added to the protein. The unbound iodide is removed by passing the product through an anion exchange resin column. It is diluted to its final strength with phosphate buffer pH 73, packaged in unit dose vials, then stored at -7O’C until ready for use. Samples stored under various conditions have been examined with respect to their biological half-life and radioactive clottability. The important aspect of any radiopharmaceutical production system is its ability to provide the physician with a product of a consistent high quality with which he may make his clinical assessment of the patient’s condition. The quality control procedures which we tind necessary to ensure this reproducibility are described.