In Vitro and In Vivo Evaluations of a Hydrophilic ⁶⁴Cu-Bis(Thiosemicarbazonato)–Glucose Conjugate for Hypoxia Imaging

Abstract

A water-soluble glucose conjugate of the hypoxia tracer 64 Cudiacetyl-bis(N 4 -methylthiosemicarbazone) ( 64 Cu-ATSM) was synthesized and radiolabeled ( 64 Cu-ATSE/A-G). Here we report our initial biological experiments with 64 Cu-ATSE/A-G and compare the results with those obtained for 64 Cu-ATSM and 18 F-FDG. Methods: The uptake of 64 Cu-ATSE/A-G and 64 Cu-ATSM into HeLa cells in vitro was investigated at a range of dissolved oxygen concentrations representing normoxia, hypoxia, and anoxia. Small-animal PET with 64 Cu-ATSE/A-G was performed in male BDIX rats implanted with P22 syngeneic carcinosarcomas. Images of 64 Cu-ATSM and 18 F-FDG were obtained in the same model for comparison. Results: 64 CuATSE/A-G showed oxygen concentration-dependent uptake in vitro and, under anoxic conditions, showed slightly lower levels of cellular uptake than 64 Cu-ATSM; uptake levels under hypoxic conditions were also lower. Whereas the normoxic uptake of 64 Cu-ATSM increased linearly over time, 64 Cu-ATSE/A-G uptake remained at low levels over the entire time course. In the PET study, 64 CuA-TSE/A-G showed good tumor uptake and a biodistribution pattern substantially different from that of each of the controls. In marked contrast to the findings for 64 Cu-ATSM, renal clearance and accumulation in the bladder were observed. 64 Cu-ATSE/A-G did not display the characteristic brain and heart uptake of 18 F-FDG. Conclusion: The in vitro cell uptake studies demonstrated that 64 Cu-ATSE/A-G retained hypoxia selectivity and had improved characteristics when compared with 64 Cu-ATSM. The in vivo PET results indicated a difference in the excretion pathways, with a shift from primarily hepatointestinal for 64 Cu-ATSM to partially renal with 64 Cu-ATSE/A-G. This finding is consistent with the hydrophilic nature of the glucose conjugate. A comparison with 18 F-FDG PET results revealed that 64 Cu-ATSE/A-G was not a surrogate for glucose metabolism. We have demonstrated that our method for the modification of Cu-bis(thiosemicarbazonato) complexes allows their biodistribution to be modified without negating their hypoxia selectivity or tumor uptake properties.

Hypoxia Imaging Using PET and SPECT: The Effects of Anesthetic and Carrier Gas on [64Cu]-ATSM, [99mTc]-HL91 and [18F]-FMISO Tumor Hypoxia Accumulation

“…[ 64 Cu]-CuATSM was prepared from H 2 ATSM as previously described [11]. Briefly, to 40 µL of H 2 ATSM stock solution (1 mg/mL) was added 50 µL of dimethyl sulfoxide (DMSO) and 50 µL of aqueous [ 64 Cu]Cu(OAc) 2 (100 MBq).…”

Nitroimidazole conjugates of bis(thiosemicarbazonato)64Cu(II) – Potential combination agents for the PET imaging of hypoxia

“…Ex vivo biodistribution results from mice bearing EMT6 tumors showed high accumulation in the liver, suspected to be a consequence of the high lipophilicity or hydrolytic instability of the complexes. We have also studied a glucose conjugate of 64 Cu-ATSM/A [34]. This hydrophilic complex showed improved in vitro hypoxia selectivity in HeLa cells in comparison to 64 Cu-ATSM, due to a reduced level of uptake under normoxic conditions.…”

Pre-clinical Positron Emission Tomography Reconstruction Algorithm Effect on Cu-64 ATSM Lesion Hypoxia

“…All reconstruction algorithms showed increased magnitude of mean SUV max and mean T/B with time frame measured, reflecting known uptake characteristics of Cu-64 ATSM for hypoxia measurements ( 20 ), thus offering some level of assurance that reconstruction algorithms were functioning appropriately. In order to assist characterizing reconstruction effects using different algorithms, we identified general trends from SUV max and T/B results acquired at time frames specified.…”