Discovery of (R)‑N‑Benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide [(R)-AS‑1], a Novel Orally Bioavailable EAAT2 Modulator with Druglike Properties and Potent Antiseizure Activity In Vivo

(R)-7 [(R)-AS-1] showed broad-spectrum antiseizure activity across in vivo mouse seizure models: maximal electroshock (MES), 6 Hz (32/44 mA), acute pentylenetetrazol (PTZ), and PTZ-kindling. A remarkable separation between antiseizure activity and CNS-related adverse effects was also observed. In vitro studies with primary glia cultures and COS-7 cells expressing the glutamate transporter EAAT2 showed enhancement of glutamate uptake, revealing a stereoselective positive allosteric modulator (PAM) effect, further supported by molecular docking simulations. (R)-7 [(R)-AS-1] was not active in EAAT1 and EAAT3 assays and did not show significant off-target activity, including interactions with targets reported for marketed antiseizure drugs, indicative of a novel and unprecedented mechanism of action. Both in vivo pharmacokinetic and in vitro absorption, distribution, metabolism, excretion, toxicity (ADME-Tox) profiles confirmed the favorable drug-like potential of the compound. Thus, (R)-7 [(R)-AS-1] may be considered as the first-in-class small-molecule PAM of EAAT2 with potential for further preclinical and clinical development in epilepsy and possibly other CNS disorders. ■ INTRODUCTION Epilepsy is a common neurological disorder characterized by spontaneous and recurrent seizures, often accompanied by a spectrum of neuropsychiatric symptoms. It is also a very heterogeneous disease with multifactorial and complex etiology. There are many different types of epilepsies, and the disease affects more than 70 million patients globally. 1 Progress in epilepsy research has led to the approval and marketing authorization of more than 30 antiseizure drugs (ASDs) over recent decades. Yet, despite this unquestionable therapeutic success, approximately one-third of epilepsy patients still experience uncontrolled and debilitating seizures. 2 These patients are considered as having the so-called drug-resistant epilepsy, which is defined as the failure of adequate trials of two tolerated and appropriately chosen ASD schedules (whether as monotherapies or in combination) to achieve seizure freedom. 3 The mechanisms underlying drug resistance in epilepsy are complex and still relatively poorly understood, which in combination with the multifactorial etiology and pathophysiology of epilepsy immensely complicate the rational selection of ASDs for optimal therapy. As such, drug-resistant epilepsy creates an urgent unmet medical need and propels ongoing drug discovery and development programs globally. Currently approved ASDs work through a number of mechanisms to restore the disturbed balance between excitatory and inhibitory neurotransmission responsible for seizure generation. 4 Such drugs target mainly ion channels (e.g., sodium or potassium channels), excitatory and inhibitory receptors, or presynaptic neurotransmitter release mechanisms. So far, only a few ASDs target neurotransmitter uptake mechanisms, mainly γ-aminobutyric acid (GABA) uptake (i.e., tiagabine). However, glutamate uptake dysregulation, which is not yet specifically targeted by ASDs, emerges as one of the critical drivers of excitotoxicity and seizures.