The Design, Synthesis and Functional in-vivo Evaluation of Potent and Selective Small Molecules Targeting KCa Channels

Potassium (K+) channels are important modulators of neuronal excitability and calcium signaling throughout the body. Of particular interest are the calcium-gated K+ channels (KCa). Functional KCa channels are tetramers with six transmembrane segments per subunit and in this case an intracellular C-terminus that is bound to the calcium-binding protein calmodulin. Calcium binding to calmodulin causes a conformational change that opens the channel to allow potassium efflux. This alteration in the protein's conformation results in opening of the channel and with concomitant efflux of potassium ions resulting in the modulation of neuronal excitability, KCa2 channels, and Ca2+ signaling, KCa3.1. Development of modulators of these channels has the potential to treat disease such as epilepsy, ataxia, alcohol abuse and hypertension. Three series of compounds, benzimidiazolone, 2-aminonaphthothiazole and 2-aminonaphthooxazole, were designed and synthesized base on the previous KCa modulator SKA-31. Compounds from all three series modulated KCa2/3 channels. In this dissertation, the chemical synthesis and biological evaluation of these three compound classes are described.;Chapter One, is the introduction to the therapeutic potential of KCa2/3 channels. In this chapter, I discuss the pharmacology of small- and intermediate-conductance potassium channels (KCa2/3). In Chapter Two, I describe why this research project was initiated and how it was design to identify potent and selective KCa2/3 modulators. Since 1-EBIO is a widely used KCa2/3 pharmacological tool compound, derivatives of the benzimidiazolone pharmacophore were synthesized. I discuss the results of this series of compound in Chapter Three.;Chapter Four are the published results of the structure-activity relationship (SAR) study which was aimed at optimizing the benzothiazole pharmacophore of SKA-31 towards KCa3.1 selectivity. We have identified SKA-111 (5-methylnaphtho[1,2- d]thiazol-2-amine), which displays 123-fold selectivity for KCa3.1 (EC50 111 +/- 27 nM) over KCa2.3 (EC50 13.7 +/- 6.9 &mgr;M), and SKA-121 (5-methylnaphtho[2,1-d]oxazol-2-amine), which displays 41-fold selectivity for KCa3.1 (EC50 109 nM +/- 14 nM) over KCa2.3 (EC50 4.4 +/- 1.6 &mgr;M). SKA-121 is a typical positive-gating modulator, which shift the calcium-concentration response curve of KCa3.1 to the left. In blood pressure telemetry experiments SKA-121 (100 mg/kg i.p.) significantly lowered mean arterial blood pressure in normotensive and hypertensive wild-type but not KCa3.1-/- mice. The synthetic optimization of SKA-121 is described in Chapter Six.;Inhibitors of voltage-gated sodium channels have been used as anticonvulsants since the 1940s, while potassium channel activators have only been investigated more recently. We here describe the discovery of SKA-19 (2-amino-6-trifluoromethylthio-benzothiazole), a thioanalog of the neuroprotectant riluzole, as a potent, novel anticonvulsant, which combines the two mechanisms. SKA-19 is a use-dependent NaV channel blocker and an activator of small-conductance Ca2+-activated K+ channels. The discovery of SKA-19 is described in Chapter Five.