From radiolabeling to receptor quantification: Preclinical assessment of [⁹⁹ᵐTc]Tc-carvedilol as a cardiac β-adrenoceptor probe

Hala F Azhari^*

• Umm al-Qura University, Mecca, Saudi Arabia

Accurate cardiac adrenoceptor assessment is crucial for managing cardiovascular diseases. This study introduces a novel radiotracer, technetium-99m-labeled carvedilol ([⁹⁹ᵐTc]Tccarvedilol), which advances non-invasive cardiac receptor evaluation by improving traceability and myocardial tissue selectivity. Aimed at strengthening diagnostic precision, it optimizes a selective radioligand for quantifying cardiac adrenergic receptor sites. Methods: [⁹⁹ᵐTc]Tc-carvedilol was synthesized via direct radiolabeling with technetium-99m, key parameters were optimized to maximize radiolabeling efficiency and ensure a reliable and reproducible [⁹⁹ᵐTc]Tc-carvedilol complex. Biodistribution was rigorously evaluated in vitro and in vivo, emphasizing cardiac uptake, receptor occupancy, biodistribution, and clearance kinetics. Comparative analysis with [ 131 I]iodocarvedilol and 99m Tc-sestamibi provided insights into advancements in detection efficiency and translational potential. Results: [⁹⁹ᵐTc]Tc-carvedilol showed a radiolabeling efficiency of 96.5 ± 2.87%, with serum stability > 92% at 24 h. Biodistribution studies in Swiss Albino mice (24 mice, aged 10-12 weeks, weighing 25 ± 3 g) revealed peak cardiac uptake (27.533 ± 0.931% injected dose per gram of tissue (ID/g) within 15 min post-injection, alongside efficient blood clearance and minimal non-target tissue uptake (5.972 ± 0.131% ID/g organ) by 120 min. Docking analysis confirmed robust β1-adrenoceptors (-9.2 kcal/mol) via hydrogen bonds and hydrophobic and electrostatic interactions. Compared to [ 131 I]iodocarvedilol and 99m Tc-sestamibi, [⁹⁹ᵐTc]Tc-carvedilol exhibited superior stability, targeting accuracy, and pharmacokinetics. Discussion: The enhanced selective cardiac uptake and favorable pharmacokinetics of [⁹⁹ᵐTc]Tc-carvedilol position it as a promising agent for non-invasive cardiac receptor mapping, with the potential to improve diagnostic accuracy and specificity. Further clinical validation is essential to confirm its efficacy in detecting and evaluating cardiac pathologies.