Intramuscular allopregnanolone and ganaxolone in a mouse model of treatment‐resistant status epilepticus

Abstract

Allopregnanolone (5α-pregnan-3α-ol-20-one) and its synthetic 3β-methyl analog, ganaxolone, are positive allosteric modulators of synaptic and extrasynaptic γ-aminobutyric acid (GABA) receptors that exhibit antiseizure activity in diverse animal seizure models, including models of status epilepticus (SE). The 2 neuroactive steroids are being investigated as treatments for SE, including as a treatment for SE induced by chemical threat agents. Intramuscular injection is the preferred route of administration in the prehospital treatment of SE. The objective of this study was to assess the efficacy of intramuscular allopregnanolone and ganaxolone in the treatment of SE induced by the chemical threat agent tetramethylenedisulfotetramine (TETS). The test agents were administered 40 minutes after the onset of SE when mice are refractory to treatment. Allopregnanolone and ganaxolone (each at 3 mg/kg) terminated SE in, respectively, 92% and 75% of animals, and prevented mortality in 85% and 50% of animals; the mean times to termination of behavioral seizures were, respectively, 172 ± 16 and 447 ± 52 seconds. In a separate series of experiments, mice were dosed with the neuroactive steroids by intramuscular injection, and plasma and brain levels were sampled at various time points following injection to estimate pharmacokinetic parameters. Plasma C (maximum concentration) values for allopregnanolone and ganaxolone were 645 and 550 ng/mL, respectively. Brain exposure of both steroids was approximately 3-fold the plasma exposure. Two-compartment pharmacokinetic analysis revealed that the central compartment V (volume of distribution), CL (clearance), t (terminal half-life), and F (intramuscular bioavailability) values for allopregnanolone and ganaxolone were, respectively, 4.95 L/kg 12.88 L/kg/h,16 minutes, 97%, and 5.07 L/kg, 8.35 L/kg/h, 25 minutes, 95%. Allopregnanolone and ganaxolone are effective in the treatment of TETS-induced SE when administered by the intramuscular route. Allopregnanolone is more rapidly acting and modestly more effective, possibly because it has greater potency on GABA receptors.

A Rationale for Allopregnanolone Treatment of Alcohol Use Disorders: Basic and Clinical Studies

“…Given that GABAergic neuroactive steroids have potent anticonvulsant effects in several animal models (Devaud et al, ; Reddy and Rogawski, ), and potent modulatory actions at extrasynaptic GABA A receptors (Belelli and Lambert, ), they may be valuable therapeutic agents. Indeed, allopregnanolone and its synthetic 3β‐methyl analog ganaxolone both proved effective in rodent (mostly males) models of treatment‐resistant status epilepticus (Rogawski et al, ; Zolkowska et al, ). Furthermore, case reports, limited to 2 young girls and 2 young adult men, suggested that intravenous allopregnanolone may be therapeutic for status epilepticus in a number of individuals (Broomall et al, ; Vaitkevicius et al, ).…”

Intravenously Administered Ganaxolone Blocks Diazepam-Resistant Lithium-Pilocarpine–Induced Status Epilepticus in Rats: Comparison with Allopregnanolone

“…Improvements in PK characteristics were extended to improvements in duration of antiseizure activity, with a 2-to 4-fold longer duration of action than that of ALLO. Note that in a recent report ALLO was found to produce a faster onset of action and a better antiepileptic response than GNX in a mouse model of SE (Zolkowska et al, 2018). However, this study was conducted with i.m.…”

Comparison of the toxicokinetics of the convulsants picrotoxinin and tetramethylenedisulfotetramine (TETS) in mice

“…For the long-term PK study, we utilized the so-called "TETS SE model", in which adult male NIH-NCI Swiss mice are pretreated with riluzole 10 min prior to TETS administration (Zolkowska et al 2018). Riluzole was prepared in 10% Captisol® (Ligand Technology, La Jolla, CA) and 90% saline at 10 mg/mL and further diluted 1:10 in sterile saline for i.p.…”

“…To our surprise, we observed that TETS serum concentrations basically "flat-lined" at ~ 600 nM in blood samples taken at 1 min, 5 min, 10 min, 20 min, 40 min, 60 min instead of decreasing with the normally observed mono-or biexponential decay. To further investigate this persistence, we next designed a long-term PK experiment in the "TETS SE model", in which adult male NIH-NCI Swiss mice are pretreated with riluzole 10 min prior to TETS administration (Zolkowska et al 2018). The riluzole pretreatment prevents mice from succumbing to tonic hindlimb extension, and thus the majority of animals go into a prolonged status epilepticus following i.p.…”