99m Tc-HL91

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Abstract
Background 99m Tc-HL91 is a potential imaging agent that has demonstrated increased uptake in hypoxic tumor cells. The purpose of this study was to determine if 99m Tc-HL91 demonstrates increased uptake and retention in ischemic and hypoxic myocardium. Methods and Results 99m Tc-HL91 (11.1 MBq) was infused over 10 minutes, followed by a 60-minute clearance phase. Activity was monitored by using an NaI detector. Three groups were studied using Krebs-Henseleit buffer (KH): controls (12 mL/min, n=6), low-flow ischemic (1 mL/min, n=7), and hypoxic (12 mL/min, n=8). Two groups were perfused with KH, red blood cells, and albumin: controls (6 mL/min, n=6) and low-flow ischemic (0.5 mL/min, n=6). For the KH hearts, the 99m Tc-HL91 peak uptake progressively increased from control (6.3±0.5 μCi, mean±SEM) to hypoxic (9.1±1.0 μCi) to low flow (44.0±2.6 μCi; P <.01). The peak uptake low-flow/control ratio was 7:1. Final retention increased progressively from control (0.8±0.1 μCi) to hypoxic (2.9±0.5 μCi) to low flow (10.9±1.3 μCi; P <.01). The final low-flow/control activity ratio was 13.6:1. Similar results were observed in the red blood cell–perfused control and low-flow groups. Conclusions This study introduces a new myocardial “hot spot” imaging agent, 99m Tc-HL91. This agent demonstrates increased myocardial uptake and retention in hypoxic and low-flow ischemic models. Further in vivo imaging studies are warranted to determine the clinical potential of this agent.

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