Cellular uptake of (99m)TcN-NOET in human leukaemic HL-60 cells is related to calcium channel activation and cell proliferation

Abstract

Purpose: 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 ((99m)TcN-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 (99m)TcN-NOET also binds to activated SOCCs in tumour cells in order to clarify the potential value of this tracer as a proliferation marker.

Methods: Uptake kinetics of (99m)TcN-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 (99m)TcN-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.

Results: All calcium channel inhibitors significantly decreased the cellular uptake of (99m)TcN-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 (99m)TcN-NOET is related to the activation of SOCCs. Finally, a correlation was observed between the tracer uptake and variations in the proliferation index SG2M.

Conclusion: The uptake of (99m)TcN-NOET seems to be related to SOCC activation and to cell proliferation in HL-60 cells. These results indicate that (99m)TcN-NOET might be a marker of cell proliferation.