Preparation and evaluation of [99mTc]DEPE as a cardiac perfusion agent

Ion-pairing interactions between 99MTc-based myocardial imaging agents and oleic acid

PURPOSE

The purpose was to test the hypothesis that ion-paired facilitated transport is of importance in successful myocardial uptake of cationic imaging complexes. In vitro ion-pairing interactions between oleic acid and seven cationic technetium-99m complexes based on the ligands 1,2-bis[bis(2-ethoxyethyl) phosphino ethane] (tetrofosmin), 1,2-bis(dimethyl phosphino ethane) (DMPE) and 1,2-bis(diethyl phosphino ethane) (DEPE) has been studied. The complexes studied were: [99mTc O2 (tetrafosmin)2]+ (commercially available as myocardial perfusion imaging kit, Myoview), [99mTc O2 (DMPE)2]+, [99mTc O2 (DEPE)2]+, [99mTc Cl2 (DMPE)2]+, [99mTc Cl2 (DEPE)2]+, [99mTc (DMPE)3]+ and [99mTc (DEPE)3]+.

METHODS

Ion-pairing interactions were monitored using a rotating diffusion cell containing a solid supported liquid membrane and by formation of lipid monolayers.

RESULTS

Depletion of complex from the donor phase into an isopropyl myristate model membrane was generally in proportion to distribution coefficient and transfer to the receptor compartment was in all cases very small. However, by the inclusion of 5% w/v oleic acid, which is used in myocardial metabolism, partitioning was enhanced by amounts which varied depending on the tendency to form complex/oleate ion-pairs. Transfer to the receptor compartment was increased for most complexes when given sufficient time to diffuse through the membrane. The complex [99mTc O2 (tetrofosmin)2]+ appeared to form particularly stable ion-pairs with oleic acid. Monolayer formation also indicated ion-pairing interactions.

CONCLUSIONS

The results suggested that whether or not a complex is taken up by the myocyte may depend on its ability to 'hitch a ride' by ion-pairing with the myocytes energy source--a molecule of long chain fatty acid.

Preliminary evaluation in humans of Tc-99m-Q3, a new tracer for myocardial perfusion imaging

Trans[99m-Tc-acac2en(TMPP)2]+, where acac2en is N,N'-ethylenebis(acetylacetone iminate) and TMPP is tris-(3 methoxy propyl) phosphine, (shortened Q3) is a new lipophilic Technetium-99m-labelled compound developed for myocardial perfusion imaging. Encouraging data were obtained in the experimental animal. Aim of this study was to perform a preliminary evaluation of Q3 imaging in humans and to compare it with a reference coronary flow tracer such as Tc-99m microspheres. Eight coronary artery disease patients (males, age 58.5 +/- 10 years) were studied. They were injected with 740 MBq of Q3 and single photon emission computed tomography (SPECT) was performed 90 minutes later. After 3 days 740 MBq of Tc-99m microspheres were injected through a pig-tail catheter in the left ventricle (LV), during heart catheterization, and SPECT was acquired 60 minutes later. Q3 images showed a good target/background activity ratio:LV wall/LV cavity = 4.16 +/- 1.2; myocardium/lung = 3.95 +/- 0.52; the related values with microspheres were 6.36 +/- 2.48 (N.S.) and 4.57 +/- 1.07 (N.S.), respectively. Q3 was cleared by the liver and at the moment of SPECT collection the myocardium/liver activity ratio was 1.54 +/- 0.32. The Q3 LV lateral wall/septum activity ratio showed a good correlation with the corresponding microspheres ratio: Q3 ratio = 0.027 + 0.95 microspheres ratio, r = 0.89, SEE = 1.12, p < 0.005.

Lipophilic 99mTc-nitride radiopharmaceuticals as potential myocardial imaging agents

Monocationic 99mTc-nitrido complexes of a variety of diphosphine ligands have been prepared and the in vivo distribution of such cations has been examined in Sprague-Dawley rats. These complexes show initially high myocardial uptake with subsequent wash-out in this animal model. The lack of myocardial retention can be attributed to the facile in vivo reduction of these cations.

The localization of myocardial ischaemia with technetium-99m methoxy isobutyl isonitrile and single photon emission computed tomography

Thirty-two patients with suspected coronary artery disease were studied by single photon emission computed tomography (SPECT) imaging with oblique reconstructions of the myocardium following the intravenous administration of technetium-99m methoxy isobutyl isonitrile at peak exercise. All patients also underwent three-vessel coronary angiography. The SPECT technique produced very detailed images allowing easy delineation of localized myocardial defects. Segmental myocardial uptake defects were compared with diseased vessels as shown at angiography. A good correlation was shown between right coronary artery (RCA) disease and mid and proximal inferior segments and between left circumflex (LCx) artery disease and mid and proximal lateral segments, allowing accurate localization of a defect to one of these two vessels' territories. Sensitivity and specificity of detection of disease of the RCA and LCx artery were high. Defects associated with a lesion of the left anterior descending vessel were more variable.

Technetium carboxylate complexes--III. A new synthetic route to hexakis-(isonitrile) technetium(I) salts

Hexakis(isonitrile)technetium(I) cations have been prepared from carboxylate based technetium starting materials. The following ligands have been employed: t-butyl, n-butyl, cyclohexyl, and benzyl isonitrile. The products have been characterized by u.v.-visible and i.r. spectroscopy, cyclic voltammetry, fast atom bombardment mass spectrometry and electrophoresis.