Modulation of Calcium-activated K-channels in T cells: A novel therapeutic approach?

LS Madsen, PhD a,b, M Hertz, PhD c, D Strøbæk, PhD a, P Christophersen, PhD a, FA Sløk, PhD a, A Gautam, PhD c BS Jensen, PhD a

a Section of Ion channel Pharmacology, NeuroSearch A/S, Ballerup, Denmark, b Poseidon Pharmaceuticals, Ballerup, Denmark, c Pharmexa A/S, Hørsholm, Denmark.

T cells respond to antigens by a transient peak increase in intracellular calcium, [Ca2+]i, followed by a sustained high level, which is obligatory to the proliferation and production of cytokines. K-channels have been implicated in hyperpolarizing the T-cell and thereby in the maintenance of a large driving force for Ca-influx possibly via CRAC-like Ca-channels. Without K-channel activation, the sustained calcium influx is reduced, resulting in impaired or absent cytokine production and T cell proliferation. T cell K-channels therefore represent a potential molecular target for immune suppression. Upon activation, T cells dramatically up-regulate the expression of K-channels, especially the Ca2+-activated, intermediate-conductance K-channel (IK channel), pointing towards an essential role of this channel subtype in the regulation of T-cell proliferation. To assess the role of the IK-channel as a target for immune suppression, we have cloned and expressed the human IK-channel in HEK-293 cells and characterized it pharmacologically using the whole cell patch clamp technique. Using potent IK-channel blockers (clotrimazole, nitrendipine, charybdotoxin) it was demonstrated that these compounds effectively impair proliferation of T cell hybridomas in vitro and inhibit the release of cytokines from T cells during a mixed lymphocyte reaction. None of these compounds have a therapeutic potential for immune suppression, however, and we have therefore initiated a chemical optimization program targeted at the IK channel. Highly potent compounds have been developed (structures not disclosed) and the overall correlation between electrophysiological data and T-cell inhibition support the notion that the IK-channel play a pivotal role in activation of T-cells in vitro.

KEY WORDS: patch clamp, IK channel, charybdotoxin, clotrimazole, nitrendipine, cytokine release.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Novel Therapies, Part 1.