Structural Analogs of the GABAkine KRM-II-81 Are Orally Bioavailable Anticonvulsants without Sedation

Abstract

To provide back-up compounds to support the development of the GABA_A receptor (GABAAR) potentiator KRM-II-81, three novel analogs were designed: replacing the pyridinyl with 2'-Cl-phenyl (FR-II-60), changing the positions of the N and O atoms in the oxazole ring with addition of an ethyl group (KPP-III-34 and KPP-III-51), or substituting a Br atom for the ethynyl of KRM-II-81 (KPP-III-34). The compounds bound to brain GABAARs. Intraperitoneal administration of FR-II-60 and KPP-III-34 produced anticonvulsant activity in mice [maximal electroshock (MES)-induced seizures or 6 Hz-induced seizures], whereas KPP-III-51 did not. Although all compounds were orally bioavailable, structural changes reduced the plasma and brain (FR-II-60 and KPP-III-51) exposures relative to KRM-II-81. Oral administration of each compound produced dose-dependent increases in the latency for both clonic and tonic seizures and the lethality induced by pentylenetetrazol (PTZ) in mice. Since KPP-III-34 produced the highest brain area under the curve (AUC) exposures, it was selected for further profiling. Oral administration of KPP-III-34 suppressed seizures in corneal-kindled mice, hippocampal paroxysmal discharges in mesial temporal lobe epileptic mice, and PTZ-induced convulsions in rats. Only transient sensorimotor impairment was observed in mice, and doses of KPP-III-34 up to 500 mg/kg did not produce impairment in rats. Molecular docking studies demonstrated that all compounds displayed a reduced propensity for binding to α1His102 compared with the sedating compound alprazolam; the bromine-substituted KPP-III-34 achieved the least interaction. Overall, these findings document the oral bioavailability and anticonvulsant efficacy of three novel analogs of KRM-II-81 with reduced sedative effects. SIGNIFICANCE STATEMENT: A new non-sedating compound, KRM-II-81, with reduced propensity for tolerance is moving into clinical development. Three new analogs were orally bioavailable, produced anticonvulsant effects in rodents, and displayed low sensorimotor impairment. KPP-III-34 demonstrated efficacy in models of pharmacoresistant epilepsy. Docking studies demonstrated a low propensity for compound binding to the α1His102 residue implicated in sedation. Thus, three additional structures have been added to the list of non-sedating imidazodiazepine anticonvulsants that could serve as backups in the clinical development of KRM-II-81.

Fig. 1.

Structures of KRM-II-81 and the structural analogs reported in this manuscript.

Fig. 2.

Pharmacokinetic profiles and calculated parameters of FR-II-60 in plasma and brain after oral gavage in adult male Sprague-Dawley rats (n = 3 per time point) at dose of 2 mg/kg. T_max, time of maximum concentration; t_1/2 - terminal elimination half-life.

Fig. 3.

Pharmacokinetic profiles and calculated parameters of KPP-III-34 in plasma and brain after oral gavage in adult male Sprague-Dawley rats (n = 3 per time point) at dose of 2 mg/kg. T_max, time of maximum concentration; t_1/2 - terminal elimination half-life.

Fig. 4.

Pharmacokinetic profiles and calculated parameters of KPP-III-51 in plasma and brain after oral gavage in adult male Sprague-Dawley rats (n = 3 per time point) at dose of 2 mg/kg. T_max, time of maximum concentration; t_1/2 - terminal elimination half-life.

Fig. 5.

Effects of orally administered FR-II-60, KPP-III-34, or KPP-III-51 on the latency to produce clonic (left panels) or tonic (right panels) seizures after 75 mg/kg PTZ s.c. in male C57BL/6N mice. *P < 0.05, **P < 0.01, and ***P < 0.001 compared with respective vehicle control value. n = 6–9 mice per group.

Fig. 6.

Effects of KPP-III-34 in male C57/Bl6 mice that were created to exhibit spontaneous recurrent hippocampal discharges. *P < 0.05; n = 8 mice per group.

Fig. 7.

Effect of orally administered diazepam (5 mg/kg), FR-II-60, and KPP-III-34 on sensorimotor coordination in female Swiss Webster mice as assessed by rotarod performance. Data are means ± S.E.M. (n = 10 per group). *P < 0.05 or ***P < 0.001 compared with vehicle-treated mice at the same time point.

Fig. 8.

(A) Showing best pose of compound FR-II-60 (goldenrod) docked in 6HUO. (B) Showing best pose of compound FR-II-60 (goldenrod) docked in 6HUO, overlay with bound alprazolam (gray) in 6HUO. α1 (aquamarine) and γ2 (orchid) subunits of α1β3γ2L GABA_A receptor 6HUO. Dashed lines indicate π–π, hydrogen bond, and halogen bond interactions.

Fig. 9.

(A) Showing best pose of compound KPP-III-34 (purple) docked in 6HUO. (B) Showing best pose of compound KPP-III-34 (purple) docked in 6HUO, overlay with bound alprazolam (gray) in 6HUO. α1 (Aquamarine) and γ2 (orchid) subunits of α1β3γ2L GABA_A receptor 6HUO. Dashed lines indicate π–π, hydrogen bond, and halogen bond interactions.