Assessment of 18F-labeled mitochondrial complex I inhibitors as PET myocardial perfusion imaging agents in rats, rabbits, and primates.

PURPOSE: Myocardial extractions of mitochondria complex I (MC-I) inhibitors were high and well correlated with flow. This study assessed the potential of MC-I inhibitors to be developed as myocardial perfusion imaging (MPI) agents. METHODS: RP1003, RP1004, and RP1005 representing three classes of MC-I inhibitor were synthesized and radio-labeled with (18)F. These agents were evaluated for IC(50) values, tissue biodistribution, and cardiac PET imaging. (18)F-RP1004 was further examined for first-pass extraction and by imaging in non-human primates (NHP) and rats following coronary ligation. RESULTS: RP1003, RP1004, and RP1005 exhibited high MC-I inhibitory activity with IC(50) of 3.7, 16.7, and 14.4 nM. Heart uptakes in rats (percent injected dose per gram tissue) at 15 and 60 min after injection were 3.52 +/- 0.36 and 2.68 +/- 0.20 for (18)F-RP1003, 2.40 +/- 0.21 and 2.67 +/- 0.27 for (18)F-RP1004, and 2.28 +/- 0.12 and 1.81 +/- 0.17 for (18)F-RP1005. The heart to lung and liver uptake ratios were favorable for cardiac imaging with these agents. In isolated perfused rabbit hearts, the uptake of (18)F-RP1004 increased from 0.74 +/- 0.19 to 1.68 +/- 0.39 mL/min/g at flow rates of 1.66 to 5.06 mL/min/g. These values were higher than or similar to that of (99m)Tc-sestamibi. Cardiac imaging with these agents in rats and rabbits allowed visualization of the heart with minimal lung interference and rapid liver activity clearance. Imaging with (18)F-RP1004 also showed clear myocardium and marked liver activity washout in the NHP and clear detection of the perfusion-deficit area associated with left coronary artery ligation in the rat. CONCLUSION: MC-I inhibitors have the potential to be a new class of MPI agent.

(S)-N-(5-Chlorothiophene-2-sulfonyl)-beta,beta-diethylalaninol a Notch-1-sparing gamma-secretase inhibitor.

Accumulation of beta-amyloid (Abeta), produced by the proteolytic cleavage of amyloid precursor protein (APP) by beta- and gamma-secretase, is widely believed to be associated with Alzheimer's disease (AD). Research around the high-throughput screening hit (S)-4-chlorophenylsulfonyl isoleucinol led to the identification of the Notch-1-sparing (9.5-fold) gamma-secretase inhibitor (S)-N-(5-chlorothiophene-2-sulfonyl)-beta,beta-diethylalaninol 7.b.2 (Abeta(40/42) EC(50)=28 nM), which is efficacious in reduction of Abeta production in vivo.

A new 18F-labeled myocardial PET tracer: myocardial uptake after permanent and transient coronary occlusion in rats.

UNLABELLED: Conventional myocardial perfusion PET tracers require onsite tracer production because of their short radioactive half-lives. To investigate the potential of a new (18)F-labeled pyridazinone analog ((18)F-BMS-747158-02), we characterized this tracer in a rat model of permanent and transient coronary occlusion using small-animal PET. METHODS: Myocardial (18)F-BMS-747158-02 distribution in healthy rats (n = 7), rats with transient (3-min) left coronary artery occlusion (n = 11), and rats with permanent left coronary occlusion (n = 11) was analyzed with a dedicated small-animal PET scanner. RESULTS: Normal hearts demonstrated intense and almost homogeneous tracer uptake throughout the left ventricle for more than 2 h. During permanent coronary occlusion, PET demonstrated perfusion defects, which remained unchanged (37.6% +/- 8.8%, 37.4% +/- 10.2%, and 36.2% +/- 9.8% left ventricle at 15, 45, and 115 min, respectively, after tracer injection). After transient ischemia, the induced defect size decreased significantly after reperfusion (16.2% +/- 9.3%, 6.0% +/- 6.5%, and 1.4% +/- 1.3% left ventricle). Tracer reinjection after transient ischemia resulted in normalization of the induced defect. CONCLUSION: Coronary occlusion yielded distinct myocardial (18)F-BMS-747158-02 uptake defects in the area of ischemia, which demonstrated normalization of activity after reperfusion and reinjection. These promising kinetic parameters may allow for assessment of flow using exercise-rest protocols similar to those used in combination with exercise and rest perfusion SPECT.

Initial characterization of an 18F-labeled myocardial perfusion tracer.

UNLABELLED: PET allows for quantitative, regional myocardial perfusion imaging. The short half-lives of the perfusion tracers currently in use limit their clinical applicability. Here, the biodistribution and imaging quality of a new 18F-labeled myocardial perfusion agent (18F-BMS-747158-02) in an animal model are described. METHODS: The biodistribution of 18F-BMS-747158-02 was determined at 10 and 60 min after injection. The first-pass extraction fraction of the tracer was measured in isolated rat hearts perfused with the Langendorff method. Small-animal PET imaging was used to study tracer retention. RESULTS: The biodistribution at 10 min after injection demonstrated high myocardial uptake (3.1 percentage injected dose per gram [%ID/g]) accompanied by little activity in the lungs (0.3 %ID/g) and liver (1.0 %ID/g). The tracer showed a high and flow-independent myocardial first-pass extraction fraction, averaging 0.94 (SD = 0.04). PET imaging provided excellent delineation of myocardial structures. The heart-to-lung activity ratio increased from 4.7 to 10.2 between 1 and 15 min after tracer injection (at rest). Adenosine infusion (140 microg/kg/min) led to a significant increase in myocardial tracer retention (from 1.68 [SD = 0.23]) s(-1) to 3.21 [SD = 0.92] s(-1); P = 0.03). CONCLUSION: The observation of a high and flow-independent first-pass extraction fraction promises linearity between tracer uptake and myocardial blood flow. Sustained myocardial tracer uptake, combined with high image contrast, will allow for imaging protocols with tracer injection at peak exercise followed by delayed imaging. Thus, 18F-BMS-747158-02 is a promising new tracer for the quantitative imaging of myocardial perfusion and can be distributed to imaging laboratories without a cyclotron.

Amino Acid derived enamides: synthesis and aminopeptidase activity.

Recently developed copper-catalyzed coupling methodology has been applied to the synthesis of amino acid derived enamides. Bond formation proved to be strongly influenced by protection strategy and vinyl iodide substitution while tolerant of limited side chain functionality. Assessment of aminopeptidase activity revealed a preference for (E)-1,2-disubstituted constructs.

Mechanism of uptake and retention of F-18 BMS-747158-02 in cardiomyocytes: a novel PET myocardial imaging agent.

BACKGROUND: BMS-747158-02 is a novel fluorine 18-labeled pyridazinone derivative designed for cardiac imaging. The uptake and retention mechanisms of F-18 BMS-747158-02 in cardiac myocytes were studied in vitro, and the biodistribution of F-18 BMS-747158-02 was studied in vivo in mice. METHODS AND RESULTS: Fluorine 19 BMS-747158-01 inhibited mitochondrial complex I (MC-I) in bovine heart submitochondrial particles with an IC(50) of 16.6 +/- 3 nmol/L that was comparable to the reference inhibitors of MC-1, rotenone, pyridaben, and deguelin (IC(50) of 18.2 +/- 6.7 nmol/L, 19.8 +/- 2.6 nmol/L, and 23.1 +/- 1.5 nmol/L, respectively). F-18 BMS-747158-02 had high uptake in monolayers of neonatal rat cardiomyocytes (10.3% +/- 0.7% of incubated drug at 60 minutes) that was inhibited by 200 nmol/L of rotenone (91% +/- 2%) and deguelin (89% +/- 3%). In contrast, an inactive pyridaben analog, P-070 (IC(50) value >4 micromol/L in MC-1 assay), did not inhibit the binding of F-18 BMS-747158-02 in cardiomyocytes. Uptake and washout kinetics for F-18 BMS-747158-02 in rat cardiomyocytes indicated that the time to half-maximal (t((1/2))) uptake was very rapid (approximately 35 seconds), and washout t((1/2)) for efflux of F-18 BMS-747158-02 was greater than 120 minutes. In vivo biodistribution studies in mice showed that F-18 BMS-747158-02 had substantial myocardial uptake (9.5% +/- 0.5% of injected dose per gram) at 60 minutes and heart-to-lung and heart-to-liver ratios of 14.1 +/- 2.5 and 8.3 +/- 0.5, respectively. Positron emission tomography imaging in the mouse allowed clear cardiac visualization and demonstrated sustained myocardial uptake through 55 minutes. CONCLUSIONS: F-18 BMS-747158-02 is a novel positron emission tomography cardiac tracer targeting MC-I in cardiomyocytes with rapid uptake and slow washout. These characteristics allow fast and sustained accumulation in the heart.

BMS-747158-02: a novel PET myocardial perfusion imaging agent.

BACKGROUND: BMS-747158-02 is a fluorine 18-labeled pyridaben derivative designed as a new myocardial perfusion imaging agent for use with positron emission tomography (PET). This study evaluated BMS-747158-02 in animal models of cardiac perfusion and compared it with established single photon emission computed tomography agents. METHODS AND RESULTS: In a rat biodistribution study, BMS-747158-02 (15 microCi) had substantially higher myocardial uptake than technetium 99m sestamibi (100 microCi) at 15 minutes (3.5% +/- 0.3% %ID/g vs 1.9% +/- 0.1% %ID/g) and 120 minutes (3.2% +/- 0.4% of injected dose per gram vs 1.8% +/- 0.0% of injected dose per gram) after intravenous administration. Uptake ratios of heart to lung and liver at 60 minutes were also higher for BMS-747158-02 (12.7 +/- 1.4 and 3.7 +/- 0.2, respectively) than Tc-99m sestamibi (5.9 +/- 0.5 and 2.4 +/- 0.4, respectively). In an isolated rabbit heart model at flow rates of 1.66 to 5.06 mL x min(-1).g(-1) wet left ventricular weight, the net BMS-747158-02 heart uptake increased proportionally (0.93 +/- 0.15 to 2.44 +/- 0.40 mL.min(-1) x g(-1)) and to a greater extent than that of thallium 201 (0.76 +/- 0.02 to 1.11 +/- 0.02 mL x min(-1) x g(-1)) or Tc-99m sestamibi (0.49 +/- 0.03 to 0.77 +/- 0.08 mL x min(-1) x g(-1)). PET imaging with BMS-747158-02 showed a clear and sustained cardiac uptake in rats, rabbits, and nonhuman primates with minimal lung interference and rapid liver clearance. Myocardial perfusion deficit zones created by either permanent left coronary ligation or reperfusion after ligation in rats were both clearly identified on PET cardiac images of BMS-747158-02 and had good agreement with in vitro histology. CONCLUSIONS: BMS-747158-02 exhibited high and sustained cardiac uptake that was proportional to blood flow, and it represents a new class of PET myocardial perfusion imaging agent.