4-Phenoxybutoxy-substituted heterocycles--a structure-activity relationship study of blockers of the lymphocyte potassium channel Kv1.3.

The voltage-gated potassium channel Kv1.3 constitutes an attractive pharmacological target for the treatment of effector memory T cell-mediated autoimmune diseases such as multiple sclerosis and psoriasis. Using 5-methoxypsoralen (5-MOP, 1), a compound isolated from Ruta graveolens, as a template we previously synthesized 5-(4-phenoxybutoxy)psoralen (PAP-1, 2) which inhibits Kv1.3 with an IC(50) of 2nM. Since PAP-1 is more than 1000-fold more potent than 5-MOP, we here investigated whether attaching a 4-phenoxybutoxy side chain to other heterocyclic systems would also produce potent Kv1.3 blockers. While 4-phenoxybutoxy-substituted quinolines, quinazolines and phenanthrenes were inactive, 4-phenoxybutoxy-substituted quinolinones, furoquinolines, coumarins or furochromones inhibited Kv1.3 with IC(50)s of 150 nM to 10 microM in whole-cell patch-clamp experiments. Our most potent new compound is 4-(4-phenoxybutoxy)-7H-furo[3,2-g]chromene-7-thione (73, IC(50) 17 nM), in which the carbonyl oxygen of PAP-1 is replaced by sulfur. Taken together, our results demonstrate that the psoralen system is a crucial part of the pharmacophore of phenoxyalkoxypsoralen-type Kv1.3 blockers.

Different curcuminoids inhibit T-lymphocyte proliferation independently of their radical scavenging activities.

PURPOSE: We investigated the inhibitory effects of curcumin, curcumin derivatives and degradation products on OKT3-induced human peripheral blood mononuclear cell (PBMC) proliferation and the role of their radical scavenging activity. METHODS: OKT3-induced human PBMC proliferation was determined by measuring 3H-thymidine incorporation. Radical scavenging activity was evaluated by using an in vitro DPPH assay. RESULTS: OKT3-induced PBMC proliferation was inhibited by curcumin, isocurcumin, bisdesmethoxy-, diacetyl-, tetrahydro-, hexahydro-, and octahydrocurcumin as well as by vanillin, ferulic acid, and dihydroferulic acid with IC50-values of 2.8, 2.8, 6.4, 1.0, 25, 38, 82, 729, 457, and >1,000 microM, respectively. The investigated substances with the strongest effect on radical scavenging were tetrahydro-, hexahydro-, and octahydrocurcumin with IC50 values of 10.0, 11.7, and 12.3 microM, respectively. IC50-values of dihydroferulic acid, ferulic acid, and curcumin were 19.5, 37, and 40 microM. The substances with the lowest radical scavenging activities were vanillin, isocurcumin, diacetylcurcumin, and bisdesmethoxycurcumin with IC50 values higher than 100 microM each. CONCLUSIONS: Curcuminoid-induced inhibition of OKT3-induced PBMC proliferation depends on the number of carbon atoms and double bonds of the 1,6-heptadiene-3,5-dione structure as well as on the phenolic ring substitutes of the curcuminoids but is not correlated to their respective radical scavenging activity.

The human Ca2+-activated K+ channel, IK, can be blocked by the tricyclic antihistamine promethazine.

Phenothiazines can be used as psychopharmaceutical agents and are known to cause many side effects during treatment since they interfere with many different cellular systems. Recently, phenothiazines were reported to block Ca(2+)-activated potassium channels of the SK type. Therefore we investigated their effect on the functionally related class of Ca(2+)-activated potassium channels of the IK type. The representative phenothiazine derivative promethazine (PTZ) blocked IK channels almost independently from the extracellular pH(o) with an IC(50) of 49 +/- 0.2 microM (pH(o) 7.4, n = 5) and 32 +/- 0.2 microM (pH(o) 6.2, n = 5) in whole cell experiments. The extracellularly applied membrane impermeable PTZ analogue methyl-promethazine (M-PTZ) had a strongly reduced blocking potency compared to PTZ. In contrast, intracellularly applied PTZ and M-PTZ had the same blocking potency on IK channels in excised inside out patch clamp experiments (K(d) = 9.3 +/- 0.5 microM for PTZ, n = 7 and 6.7 +/- 0.4 microM for M-PTZ, n = 5). The voltage dependency of the PTZ and M-PTZ block was investigated in excised inside out patch clamp experiments at a concentration of 100 microM. For both compounds the block was more pronounced at positive membrane potentials. The steepness of the voltage dependency was found to be 70 +/- 10 mV (for PTZ) and 61 +/- 6 mV (for M-PTZ) indicating that both compounds sensed approximately 40% of the entire membrane spanning electrical field from the inside. We conclude that PTZ and M-PTZ bind to a side in IK channels, which is located within the electrical field and is accessible from the intracellular side.

Design of PAP-1, a selective small molecule Kv1.3 blocker, for the suppression of effector memory T cells in autoimmune diseases.

The lymphocyte K+ channel Kv1.3 constitutes an attractive pharmacological target for the selective suppression of terminally differentiated effector memory T (TEM) cells in T cell-mediated autoimmune diseases, such as multiple sclerosis and type 1 diabetes. Unfortunately, none of the existing small-molecule Kv1.3 blockers is selective, and many of them, such as correolide, 4-phenyl-4-[3-(methoxyphenyl)-3-oxo-2-azapropyl]cyclohexanone, and our own compound Psora-4 inhibit the cardiac K+ channel Kv1.5. By further exploring the structure-activity relationship around Psora-4 through a combination of traditional medicinal chemistry and whole-cell patch-clamp, we identified a series of new phenoxyalkoxypsoralens that exhibit 2- to 50-fold selectivity for Kv1.3 over Kv1.5, depending on their exact substitution pattern. The most potent and "drug-like" compound of this series, 5-(4-phenoxybutoxy)psoralen (PAP-1), blocks Kv1.3 in a use-dependent manner, with a Hill coefficient of 2 and an EC50 of 2 nM, by preferentially binding to the C-type inactivated state of the channel. PAP-1 is 23-fold selective over Kv1.5, 33- to 125-fold selective over other Kv1-family channels, and 500- to 7500-fold selective over Kv2.1, Kv3.1, Kv3.2, Kv4.2, HERG, calcium-activated K+ channels, Na+,Ca2+, and Cl- channels. PAP-1 does not exhibit cytotoxic or phototoxic effects, is negative in the Ames test, and affects cytochrome P450-dependent enzymes only at micromolar concentrations. PAP-1 potently inhibits the proliferation of human TEM cells and suppresses delayed type hypersensitivity, a TEM cell-mediated reaction, in rats. PAP-1 and several of its derivatives therefore constitute excellent new tools to further explore Kv1.3 as a target for immunosuppression and could potentially be developed into orally available immunomodulators.

[Photosensitization due to drugs: adverse reaction and beneficial effect]. / Photosensibilisierung durch Arzneistoffe. Unerwünschte Wirkung und therapeutischer Effekt.

In all areas of everyday life men get in touch with photosensitizers which increase the susceptibility to solar light. Dermal reactions arise after exposure to a photosensitizer and light. Quality and intensity depend on the compound and the radiation dose. Many drugs provoke these responses appearing as an adverse reaction during conventional treatment or as beneficial effect in the context of photodynamic therapy (PDT) or photochemotherapy (PUVA, ECP). Basic mechanisms and clinical aspects are reviewed.

Kv1.3-blocking 5-phenylalkoxypsoralens: a new class of immunomodulators.

The lymphocyte potassium channel Kv1.3 is widely regarded as a promising new target for immunosuppression. To identify a potent small-molecule Kv1.3 blocker, we synthesized a series of 5-phenylalkoxypsoralens and tested them by whole-cell patch clamp. The most potent compound of this series, 5-(4-phenylbutoxy)psoralen (Psora-4), blocked Kv1.3 in a use-dependent manner, with a Hill coefficient of 2 and an EC50 value of 3 nM, by preferentially binding to the C-type inactivated state of the channel. Psora-4 is the most potent small-molecule Kv1.3 blocker known. It exhibited 17- to 70-fold selectivity for Kv1.3 over closely related Kv1-family channels (Kv1.1, Kv1.2, Kv1.4, and Kv1.7) with the exception of Kv1.5 (EC50, 7.7 nM) and showed no effect on human ether-a-go-go-related channel, Kv3.1, the calcium-activated K+ channels (IKCa1, SK1-SK3, and BKCa), or the neuronal NaV1.2 channel. In a test of in vivo toxicity in rats, Psora-4 did not display any signs of acute toxicity after five daily subcutaneous injections at 33 mg/kg body weight. Psora-4 selectively suppressed the proliferation of human and rat myelin-specific effector memory T cells with EC50 values of 25 and 60 nM, respectively, without persistently suppressing peripheral blood naive and central memory T cells. Because autoantigen-specific effector memory T cells contribute to the pathogenesis of T cell-mediated autoimmune diseases such as multiple sclerosis, Psora-4 and other Kv1.3 blockers may be useful as immunomodulators for the therapy of autoimmune disorders.

Khellinone derivatives as blockers of the voltage-gated potassium channel Kv1.3: synthesis and immunosuppressive activity.

The voltage-gated potassium channel Kv1.3 constitutes a promising new target for the treatment of T-cell-mediated autoimmune diseases such as multiple sclerosis. In this study, we report the discovery of two new classes of Kv1.3 blockers based on the naturally occurring compound khellinone, 5-acetyl-4,7-dimethoxy-6-hydroxybenzofuran: (1) khellinone dimers linked via the alkylation of the 6-hydroxy groups and (2) chalcone derivatives of khellinone formed by Claisen-Schmidt condensation of the 5-acetyl group with aryl aldehydes. In particular, the chalcone 3-(4,7-dimethoxy-6-hydroxybenzofuran-5-yl)-1-phenyl-3-oxopropene (16) and several of its derivatives inhibited Kv1.3 with K(d) values of 300-800 nM and a Hill coefficient of 2, displayed moderate selectivity over other Kv1-family K(+) channels, suppressed T-lymphocyte proliferation at submicromolar concentrations, and showed no signs of acute toxicity in mice. Because of their relatively low molecular weight and lipophilicity and their high affinity to Kv1.3, aryl-substituted khellinone derivatives represent attractive lead compounds for the development of more potent and selective Kv1.3 blocking immunosuppressants.

Folate-synthesizing enzyme system as target for development of inhibitors and inhibitor combinations against Candida albicans-synthesis and biological activity of new 2,4-diaminopyrimidines and 4'-substituted 4-aminodiphenyl sulfones.

The paper describes the design, synthesis, and testing of inhibitors of folate-synthesizing enzymes and of whole cell cultures of Candida albicans. The target enzymes used were dihydropteroic acid synthase (SYN) and dihydrofolate reductase (DHFR). Several series of new 2,4-diaminopyrimidines were synthesized and tested as inhibitors of DHFR and compared with their activity against DHFR derived from mycobacteria and Escherichia coli. To test for selectivity, also rat DHFR was used. A series of substituted 4-aminodiphenyl sulfones was tested for inhibitory activity against SYN and the I(50) values compared to those obtained previously against Plasmodium berghei- and E. coli-derived SYN. Surprisingly, QSAR equations show very similar structural dependencies. To find an explanation for the large difference in the I(50) values observed for enzyme inhibition (SYN, DHFR) and for inhibition of cell cultures of Candida, mutant strains with overexpressed efflux pumps and strains in which such pumps are deleted were included in the study and the MICs compared. Efflux pumps were responsible for the low activity of some of the tested derivatives, others showed no increase in activity after pumps were knocked out. In this case it may be speculated that these derivatives are not able to enter the cells.