Psora 4

EC50: 3 nM

Psora 4 is a Kv1.3 blocker.

The voltage-gated Kv1.3 channel and the Ca2+-activated IKCa1 channel has been reported to promote and sustain Ca2+ signaling in human T cells via providing the driving force for Ca2+ entry through voltage-independent Ca2+ channels. Selective blockade of Kv1.3 and/or IKCa1 leads to membrane depolarization, reduced Ca2+ entry, as well as diminished cytokine proliferation and production.

In vitro: Psora-4 could block Kv1.3 in a dose-dependent manner. Psora-4 was found to be the most potent small-molecule Kv1.3 blocker known. Psora-4 exhibited 17- to 70-fold selectivity for Kv1.3 over Kv1-family channels including Kv1.1, Kv1.2, Kv1.4, and Kv1.7 and also showed no effect on human ether-a-go-go-related channel, Kv3.1, or the neuronal NaV1.2 channel. In addition, Psora-4 could suppress the proliferation of rat and human myelin-specific effector memory T cells with EC50 values of 60 and 25 nM, respectively, without persistently suppressing the peripheral blood naive and central memory T cells [1].

In vivo: In a study of in vivo toxicity in rats, Psora-4 was found not to show any signs of acute toxicity following five daily subcutaneous injections at 33 mg/kg body weight [1].

Clinical trial: N/A

Reference:
[1] Vennekamp J,Wulff H,Beeton C,Calabresi PA,Grissmer S,Hnsel W,Chandy KG.  Kv1.3-blocking 5-phenylalkoxypsoralens: a new class of immunomodulators. Mol Pharmacol.2004 Jun;65(6):1364-74.

Psora-4, a Kv1.3 Blocker, Enhances Differentiation and Maturation in Neural Progenitor Cells.[Pubmed:25976092]

CNS Neurosci Ther. 2015 Jul;21(7):558-67.

AIM: The self-repair ability of neural progenitor cells (NPCs) has been found to be activated and protected in several therapies helpful in multiple sclerosis (MS), an inflammatory demyelinating disease of the CNS. As a potential therapeutic target in MS, the role of the ion channel Kv1.3 in NPC self-repair has received limited attention. The aim of this study was to explore the effects of a selective Kv1.3 blocker on NPC neuronal differentiation and maturation. METHODS: A small-molecule selective blocker for Kv1.3, Psora-4, was added to the differentiation medium of cultured mouse NPCs to assess its effect on NPC differentiation efficiency. Both a polypeptide Kv1.3 blocker and Kv1.3-specific RNA interference were used in parallel experiments. Further, the maturity of newborn neurons in the presence of Psora-4 was measured both by morphological analysis and by whole-cell patch clamping. RESULTS: Psora-4 induced a significant increase in the percentage of neurons. Knockdown of Kv1.3 in NPCs also promoted neuronal differentiation. Both morphological and electrophysiological analyses suggested that NPC-derived neurons in the presence of Psora-4 were more mature. CONCLUSION: Our studies reveal a crucial role for the ion channel Kv1.3 in the regulation of NPC differentiation and maturation, making Psora-4 a promising candidate molecule for MS treatment.

Voltage-gated potassium channel Kv1.3 regulates GLUT4 trafficking to the plasma membrane via a Ca2+-dependent mechanism.[Pubmed:16403947]

Am J Physiol Cell Physiol. 2006 Feb;290(2):C345-51.

Kv1.3 is a voltage-gated K(+) channel expressed in insulin-sensitive tissues. We previously showed that gene inactivation or pharmacological inhibition of Kv1.3 channel activity increased peripheral insulin sensitivity independently of body weight by augmenting the amount of GLUT4 at the plasma membrane. In the present study, we further examined the effect Kv1.3 on GLUT4 trafficking and tested whether it occurred via an insulin-dependent pathway. We found that Kv1.3 inhibition by margatoxin (MgTX) stimulated glucose uptake in adipose tissue and skeletal muscle and that the effect of MgTX on glucose transport was additive to that of insulin. Furthermore, whereas the increase in uptake was wortmannin insensitive, it was completely inhibited by dantrolene, a blocker of Ca(2+) release from intracellular Ca(2+) stores. In white adipocytes in primary culture, channel inhibition by Psora-4 increased GLUT4 translocation to the plasma membrane. In these cells, GLUT4 protein translocation was unaffected by the addition of wortmannin but was significantly inhibited by dantrolene. Channel inhibition depolarized the membrane voltage and led to sustained, dantrolene-sensitive oscillations in intracellular Ca(2+) concentration. These results indicate that the apparent increase in insulin sensitivity observed in association with inhibition of Kv1.3 channel activity is mediated by an increase in GLUT4 protein at the plasma membrane, which occurs largely through a Ca(2+)-dependent process.

Design of PAP-1, a selective small molecule Kv1.3 blocker, for the suppression of effector memory T cells in autoimmune diseases.[Pubmed:16099841]

Mol Pharmacol. 2005 Nov;68(5):1254-70.

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.

Kv1.3-blocking 5-phenylalkoxypsoralens: a new class of immunomodulators.[Pubmed:15155830]

Mol Pharmacol. 2004 Jun;65(6):1364-74.

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.