Identification of a New Class of Inhibitors of the Voltage-Gated Potassium Channel, K_v1.3, with Immunosuppressant Properties

Abstract

The voltage-gated potassium channel, K(v)1.3, is a novel target for development of immunosuppressants. Using a functional (86)Rb(+) efflux assay, a new class of high-affinity K(v)1.3 inhibitors has been identified. The initial active in this series, 4-phenyl-4-[3-(2-methoxyphenyl)-3-oxo-2-azaprop-1-yl]cyclohexanone (PAC), which is representative of a disubstituted cyclohexyl (DSC) template, displays a K(i) of ca. 300 nM and a Hill coefficient near 2 in the flux assay and in voltage clamp recordings of K(v)1.3 channels in human T-lymphocytes. PAC displays excellent specificity as it only blocks members of the K(v)1 family of potassium channels but does not affect many other types of ion channels, receptors, or enzyme systems. Block of K(v)1.3 by DSC analogues occurs with a well-defined structure-activity relationship. Substitution at the C-1 ketone of PAC generates trans (down) and cis (up) isomer pairs. Whereas many DSC derivatives do not display selectivity in their interaction with different K(v)1.x channels, trans DSC derivatives distinguish between K(v)1.x channels based on their rates of C-type inactivation. DSC analogues reversibly inhibit the Ca(2+)-dependent pathway of T cell activation in in vitro assays. Together, these data suggest that DSC derivatives represent a new class of immunosuppressant agents and that specific interactions of trans DSC analogues with channel conformations related to C-type inactivation may permit development of selective K(v)1.3 channel inhibitors useful for the safe treatment of autoimmune diseases.

Kv1.3-Blocking 5-Phenylalkoxypsoralens: A New Class of Immunomodulators

“…In contrast to Psora-4, most known peptide and small-molecule Kv1.3 blockers have Hill coefficients of 1, consistent with a 1:1 stoichiometry of interaction between blocker and channel protein (Nguyen et al, 1996;Hanner et al, 1999;Hanson et al, 1999;Chandy et al, 2001). The Hill coefficient of 2 observed for Psora-4 and its analogs suggests that two molecules of blocker interact with one Kv1.3 channel tetramer, as has been reported recently for PAC and its derivatives (Schmalhofer et al, 2002(Schmalhofer et al, , 2003. Psora-4 has a log P value of 4.33, well in the range for a therapeutic, exhibits 16-to 70-fold selectivity for Kv1.3 over closely related Kv1 channels, and does not affect other K ϩ channels (HERG, BK Ca , IKCa1, and SKCa3) or the neuronal sodium channel Na V 1.2.…”

Investigation of the Phenylalkylamine Binding Site inhKv1.3 (H399T), a Mutant with a Reduced C-Type Inactivated State

“…In addition, fits of the corresponding (Ϯ)-emopamil dose-response curve indicated a 2:1 ligand/receptor stoichiometry. So far, the binding of two small molecule inhibitors to hKv1.3 has been demonstrated only for disubstituted cyclohexyl compounds (Schmalhofer et al, 2002(Schmalhofer et al, , 2003 and 5-phenylalkoxypsoralens (Vennekamp et al, 2004). To investigate the importance of the methoxy groups in more detail, we examined the effects of (Ϯ)-gallopamil, which has an additional methoxy group at R 3 , and (Ϫ)-devapamil, that lacks the methoxy group at R 2 Ј .…”

K+ Channel Expression during B Cell Differentiation: Implications for Immunomodulation and Autoimmunity

“…In proof-of-concept studies in rats, Kv1.3 blockers have been shown to ameliorate adoptive experimental autoimmune encephalomyelitis induced by myelin-specific memory T cells (16,70), a model for MS, and to prevent inflammatory bone resorption in experimental periodontal disease caused mainly by memory cells (81). Several small-molecule Kv1.3 inhibitors with nanomolar potency have been developed over the last decade (WIN-17317, CP-339818, U.K.-78,282, correolide, trans-N-propylcarbamoyloxy-PAC, sulfamidebenzamidoindanes, tetraphenylporphyrins, dichlorophenylpyrazolopyrimidines, chalcones, and Psora-4 (6,7,31,69,82,83)), and the continuing development of more selective and potent Kv1.3 blockers may make Kv1.3-based immunomodulation for autoimmune disorders a reality.…”