Synthesis of 123I-16-iodo-9-hexadecenoic acid and derivatives for use as myocardial perfusion imaging agents

Radioiodinated p-phenylene bridged fatty acids as new myocardial imaging agents: syntheses and biodistribution in rats

Due to the inhibition of beta-oxidation, radiolabeled long-chain fatty acids with substituents in the alkyl chain often can enhance the retention of myocardial radioactivity. In this connection the synthesis and biodistribution of 12 new radioiodinated omega-(p-iodophenyl)fatty acids is described featuring a p-phenylene group as an inhibiting group. Phenyl fatty acid esters were acylated (Friedel-Crafts) with omega-(p-halophenyl)fatty acid chlorides, reduced and hydrolyzed (Wolff-Kishner) to form the omega-(p-halophenyl)-p-phenylene-fatty acid (PHIPA) derivatives. The peak heart uptake and the loss of radioactivity from the myocardium of fasted Sprague-Dawley rats depended on the alkyl-chain length and p-phenylene position. Thus, compared to radioiodinated 15-(p-iodophenyl)pentadecanoic acid (IPPA) some of the 131I labeled PHIPA derivatives with 12, 13 or 14 methylene groups proved to show an about equal initial heart uptake (about 5% inj. dose/g at 2.5 min). This was especially true for those PHIPA derivatives with a p-phenylene moiety close to the carboxylic acid group. The retention of radioactivity in the heart was also significantly prolonged when the p-phenylene group was in this position. Among the PHIPA derivatives investigated, 13-(p[131I]iodophenyl)-3-(p-phenylene)tridecanoic acid (PHIPA 3-10) and 14-(p-[131I] iodophenyl)-4-(p-phenylene)tetradecanoic acid (PHIPA 4-10) showed the most promising characteristics for potential use as new myocardial imaging agents. Both agents showed an initial heart/blood activity ratio of about 10 which increased to 15 after 10-30 min. This high value was maintained for at least 4 h.

omega-Iodophenyl fatty acids: a convenient method of radioiodination

A solid-phase radioiodination technique for omega-iodophenyl fatty acids using ammonium sulfate is described. The radioiodinations are regioselective, high in yield (95%), short in reaction time (1 h) and capable of yielding high specific activity products although at lower yields. Purification is exceptionally simple: a single passage through an ion exchange column to remove unreacted I- is all that is required. Syntheses of several omega-iodophenyl fatty acids are also described.

Radioiodinated fatty acids for cardiological diagnosis

The development of fatty acids labelled with iodine-123 is reviewed. The variety of methods for producing 123I and introducing radioiodine into the molecule is discussed and the important points of the biochemical background are recalled with the aim of finding a broad application for 123I-labelled fatty acids. The results of the pharmacokinetic studies and biochemical analyses are presented as they prove that both 17-123I-heptadecanoic acid (IHA) and 15-(p-123I-phenyl)pentadecanoic acid (IPPA) exhibit analogous behaviour to that of the naturally occurring fatty acids. Clinical applications demonstrated two fields of importance: applications solely for imaging the heart and assessment of myocardial turnover rates of fatty acids for functional diagnosis. Moreover, very recent studies show that the provision of information about prognosis of myocardial diseases and the applied cardiological therapy appear to be possible.

Synthesis of high purity 11C labeled palmitic acid for measurement of regional myocardial perfusion and metabolism

Palmitic acid is a major physiological substrate of the myocardium and its role in myocardial metabolism is well understood. 11C labeled palmitic acid may be used with a positron emission tomograph (PET) to obtain high contrast images of transverse sections of the heart. A rapid and reliable method for producing [11C]palmitic acid from [11C]carbon dioxide by the Grignard synthesis is described. All interfering long chain nonradioactive impurities are removed by the purification procedure. As a result, this [11C]palmitic acid may be used as a tracer for pure palmitic acid in the measurement of regional myocardial function.

Role of cardiovascular nuclear medicine in evaluating trauma and the postoperative patient

In the patient with cardiac trauma, radionuclide imaging may provide important information about cardiac mechanical function, vascular anatomy and integrity, myocardial perfusion, and myocardial metabolism. Studies require only minimal patient cooperation, can be performed relatively rapidly and often at the bedside, and may be repeated at frequent intervals for serial evaluations. These studies provide valuable adjunctive knowledge when selected and interpreted with knowledge of the mechanism of injury, timing of the examination relative to the time of injury, and most likely differential diagnoses.

Simple labeling of omega-phenylfatty acids by iodine isotope exchange

Within 1 h 15-(p-iodophenyl)-pentadecanoic acid (p-IPPA) can easily be labeled with 123I by iodine-isotope exchange. In contrast to the electrophilic aromatic substitution procedure this method enables a 95% radiochemical yield. The so formed p-123IPPA can be used without the application of any complicated separation techniques. By comparison with commercially available 17-[123I]iodoheptadecanoic acid (123IHA) p-123IPPA shows a remarkably higher uptake in a rabbit heart. Additionally the background activity of p-123IPPA proved to be lower than that measured with 123IHA. p-123IPPA thus indicating its suitability for routine applications in nuclear medical heart diagnosis.

I-123 labeled hexadecenoic acid in comparison with Thallium-201 for myocardial imaging in coronary heart disease. A preliminary study

The imaging properties of 123I-16-iodo-9-hexadecenoic acid (123I-HA), a terminally iodinated 17-carbon atom fatty acid analogue, were compared with Thallium-201 (201Tl). Because of its shorter half-life, favourable photon-energy and rapid myocardial turnover rate, 123I-HA possesses potential advantages in the study of regional myocardial perfusion and metabolism. Twelve patients with documented coronary artery disease (CAD) were studied; eight patients sustained an acute myocardial infarction, four patients suffered from unstable angina. Visually assessed, a similar distribution pattern and comparable imaging quality was demonstrated with both radionuclides. The scintigraphic results were also correlated with coronary arteriographic findings. A good relationship was found between the perfusion defects and the location of the coronary artery lesions in the patients with acute myocardial infarction. We conclude that 123I-HA is comparable to 201Tl in detecting areas of reduced myocardial perfusion in patients with CAD with the advantage of studying myocardial metabolism.

A comparison between terminally radioiodinated hexadecenoic acid (I-HA) and 201Tl-thallium chloride in the dog heart. Implications for the use of I-HA for myocardial imaging

The regional myocardial distribution of 131I-16-iodo-9-hexadecenoic acid (131I-HA) and 201Tl-thallium chloride (201TlCl) was determined in normal dogs and after occlusion of a coronary artery. The uptake of 131I-HA was about 20% lower than that of 201TlCl but the ratio 201Tl/131I was the same for the whole myocardium within narrow limits for normal as well as infarcted tissue. The potential of 123I-HA as a radiopharmaceutical for diagnosis of myocardial defects is discussed.