Tissue acidosis does not mediate the hypoxia selectivity of [64Cu][Cu(ATSM)] in the isolated perfused rat heart

Abstract

Copper-64-Diacetyl-bis(N4-methylthiosemicarbazone) [64Cu][Cu(ATSM)] is a hypoxia-targeting PET tracer with applications in oncology and cardiology. Upon entering a hypoxic cell, [64Cu][Cu(II)(ATSM)] is reduced to a putative [64Cu][Cu(I)(ATSM)]− species which dissociates to deposit radiocopper, thereby providing hypoxic contrast. This process may be dependent upon protonation arising from intracellular acidosis. Since acidosis is a hallmark of ischemic tissue and tumors, the hypoxia specificity of [64Cu][Cu(ATSM)] may be confounded by changes in intracellular pH. We have therefore determined the influence of intracellular pH on [64Cu][Cu(ATSM)] pharmacokinetics. Using isolated perfused rat hearts, acidosis was induced using an ammonium pre-pulse method, with and without hypoxic buffer perfusion. Cardiac [64Cu][Cu(ATSM)] pharmacokinetics were determined using NaI detectors, with intracellular pH and cardiac energetics monitored in parallel by 31P NMR. To distinguish direct acidotic effects on tracer pharmacokinetics from acidosis-induced hypocontractility, parallel studies used lidocaine perfusion to abolish cardiac contraction. Hypoxic myocardium trapped [64Cu][Cu(ATSM)] despite no evidence of it being acidotic when characterised by 31P NMR. Independent induction of tissue acidosis had no direct effect on [64Cu][Cu(ATSM)] pharmacokinetics in either normoxic or hypoxic hearts, beyond decreasing cardiac oxygen consumption to alleviate hypoxia and decrease tracer retention, leading us to conclude that tissue acidosis does not mediate the hypoxia selectivity of [64Cu][Cu(ATSM)].

Production of copper-64 using a hospital cyclotron: targetry, purification and quality analysis

“…Seven batches of [ 64 Cu]CuCl 2 were manufactured and analysed for the purposes of gathering data in this work; many more have been produced for research applications [9,12,14,33–43,45,51]. The average amount of 64 Ni electroplated for each batch was 9.4 ± 2.1 mg (0.150 ± 0.033 mmol).…”

“…We report analytical and quality control methods that can be used within typical PET radiochemistry production facilities to measure metal ion concentrations and radiometal molar activities. The methods described have been used to produce 64 Cu for several published studies [9,12,14,[33][34][35][36][37][38][39][40][41][42][43][44][45].…”

Detecting Validated Intracellular ROS Generation with 18F-dihydroethidine-Based PET

“…Radiotracer pharmacokinetics were monitored using our custom built triple γ-detector system described previously [ 8 – 13 ]. This system comprises three orthogonally positioned lead-collimated Na/I γ-detectors arrayed around a Langendorff isolated heart perfusion rig.…”

“…It can be used to validate radiotracer behaviour with high levels of experimental control (in terms of perfusion, oxygenation, workload, energy substrate availability, or drug co-administration), monitoring cardiac haemodynamics, contractile performance, and metabolism while retaining the opportunity for post hoc validation using histology, enzyme assays, autoradiography, or Western blotting, etc . as required [ 8 – 13 ].…”

Aerobic exercise-induced up-regulation of HIF-1α ameliorates heart failure by regulating MCT1 and MPC1 expression

“…Metabolic disturbances triggered by myocardial hypoxia lead to abnormal changes in cardiac function (8). In addition, myocardial hypoxia, as a major factor in cardiac ischaemic pathology, is directly implicated in the progression of HF (9). In recent years, the treatment of HF has gradually shifted from traditional approaches such as improving hemodynamics and inhibiting neuroendocrine hyperactivation to myocardial energy metabolism therapy (10,11).…”