Abstract
P1066
Introduction: Myocardial perfusion imaging evaluates various heart conditions such as myocardial infarction and coronary artery disease. Current positron emission tomography (PET) practice utilizes either [13N]NH3 (9.9 min), [82Rb]RbCl (75 sec), or [15O]H2O (2 min) to perform stress test. Given the shorter half-lives of the PET probes, myocardial perfusion imaging with PET is limited to large medical centers equipped with onsite cyclotron facility only. In this study, we aimed to develop and evaluate novel cardiac targeting peptide (CTP) based radiotracer [68Ga]Ga-NOTA-CTP as a myocardial perfusion imaging PET probe in normal CD-1 mice that could be produced without the need for an onsite cyclotron.
Methods: A 12-amino acid based cardiac targeting peptide1-2 (CTP) was conjugated with a bifunctional chelator 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA-Bn-NCS) at the N-terminus. Conjugation of NOTA-Bn-NCS with CTP was characterized by mass spectrometry. Radiolabeling was performed with generator produced [68Ga]GaCl3, at room temperature in sodium acetate buffer at pH 4.5-5.0 for 10 min. Product formation was checked on r-TLC in 0.1M sodium citrate and also by rad-HPLC (Rt 11.5 min) using a gradient method of 0.1%TFA- water and 0.1%TFA- acetonitrile3-6. Stability of the developed tracer was also measured in final formulation over time using rad-TLC. Obtained product was formulated in 0.9% saline solution and filtered through a 0.2 µm filter before performing tail vein injection to CD-1 mice. A dynamic 30 min PET imaging followed 60 min and 120 min static PET imaging were performed post-injection (p.i.) using microPET scanner. PET images were analyzed and scaled to SUV by image analysis software. After PET imaging at 120 min animals were euthanized and organs/tissues were collected to measure standardized uptake value (SUV) in major organs.
Results: NOTA-CTP was successfully synthesized, characterized and radiolabeled with [68Ga]GaCl3 at room temperature with >98% radiolabeling yield (n=6) in 10 min after optimization. Obtained product showed high radiochemical purity >97 % on rad-HPLC. The molar activity (Am) of [68Ga]Ga-NOTA-CTP was found to be 0.71±0.18 (n=6) GBq/µmole. Stability analysis using rad-TLC showed >98 stability at 2h and >96% stability at 4h post radiosynthesis.
In-vivo evaluation of [68Ga]Ga-NOTA-CTP in CD-1 mice, showed uptake (SUV) in liver (1.17 ± 0.14), heart (0.93 ± 0.15), and kidneys (L: 2.41 ± 0.60, R: 2.31 ± 0.61), at 0-5 min time points. After 5 min radiotracer started washing out from all major organs and by 30 min it was only visible in liver, cecum, and urinary bladder, and at 60 min and 120 min it was predominantly present in urinary bladder with extremely small quantities in cecum and small intestine. Interestingly, we also noticed uptake of this tracer in gallbladder at 60 min timepoint. Ex vivo biodistribution performed at 120 min postinjection showed similar results as observed in PET/CT imaging with major radioactivity present in urinary bladder (48.2 ± 28.3, n=6), kidney (0.73 ± 0.28, n=6) and intestine (0.38 ± 0.34, n=6).
Conclusions: Radiosynthesis of [68Ga]Ga-NOTA-CTP was performed successfully in a high radiolabeling yield (>98%) at room temperature. Rad-TLC and rad-HPLC methods were also developed to measure radiolabeling yield and radiochemical purity, respectively. The developed PET probe showed high uptake in myocardium at 0-5 min time point followed by fast renal clearance within 30 min making it a suitable radiotracer for further evaluation in infarcted heart mouse model.
Acknowledgement
This study was funded by the Division of Nuclear Medicine and Department of Cardiology, Mayo Clinic, Rochester, MN USA.
In this issue
Jump to section
Related Articles
Cited By...
- No citing articles found.