Cellular uptake of 99mTcN-NOET in human leukaemic HL-60 cells is related to calcium channel activation and cell proliferation
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A major goal of nuclear oncology is the development of new radiolabelled tracers as proliferation markers. Intracellular calcium waves play a fundamental role in the course of the cell cycle. These waves occur in non-excitable tumour cells via store-operated calcium channels (SOCCs). Bis(N-ethoxy, N-ethyldithiocarbamato) nitrido technetium (V)-99m (99mTcN-NOET) has been shown to interact with L-type voltage-operated calcium channels (VOCCs) in cultured cardiomyocytes. Considering the analogy between VOCCs and SOCCs, we sought to determine whether 99mTcN-NOET also binds to activated SOCCs in tumour cells in order to clarify the potential value of this tracer as a proliferation marker.
Uptake kinetics of 99mTcN-NOET were measured in human leukaemic HL-60 cells over 60 min and the effect of several calcium channel modulators on 1-min tracer uptake was studied. The uptake kinetics of 99mTcN-NOET were compared both with the variations of cytosolic free calcium concentration measured by indo-1/AM and with the variations in the SG2M cellular proliferation index.
All calcium channel inhibitors significantly decreased the cellular uptake of 99mTcN-NOET whereas the activator thapsigargin induced a significant 10% increase. In parallel, SOCC activation by thapsigargin, as measured using the indo-1/AM probe, was inhibited by nicardipine. These results indicate that the uptake of 99mTcN-NOET is related to the activation of SOCCs. Finally, a correlation was observed between the tracer uptake and variations in the proliferation index SG2M.
The uptake of 99mTcN-NOET seems to be related to SOCC activation and to cell proliferation in HL-60 cells. These results indicate that 99mTcN-NOET might be a marker of cell proliferation.
KeywordsNuclear imaging Radiopharmaceuticals Tumour imaging 99mTcN-NOET Proliferation marker
The authors wish to thank Prof. M. Villaz, Dr. J. Boutonnat and Dr. L. Riou for their helpful comments and suggestions and P. Champelovier for his expert technical assistance.
Financial support for this work was provided by the Institut National pour la Recherche Scientifique et Médicale (INSERM), by Cis Bio International-Schering SA and by the Association pour la Recherche contre le Cancer (ARC). All experiments were reviewed, approved and performed under the authority of individuals allowed to work on living animals by the French government (D. Fagret, authorisation 38-01).
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