AST-001 Improves Social Deficits and Restores Dopamine Neuron Activity in a Mouse Model of Autism

Population pharmacokinetic and pharmacodynamic model guided weight-tiered dose of AST-001 in pediatric patients with autism spectrum disorder

AST-001, a novel syrup formulation of L-serine, was developed for the treatment of autism spectrum disorders (ASD) in pediatric patients. This study aimed to establish a pharmacokinetic (PK)-pharmacodynamic (PD) model to elucidate the effect of AST-001 on adaptive behavior in children with ASD. Due to the absence of PK samples in pediatric patients, a previously published population PK model was used to link the PD model by applying an allometric scale to body weight. The time courses of Korean-Vineland Adaptive Behavior Scale-II Adaptive Behavior Composite (K-VABS-II-ABC) scores were best described by an effect compartment model with linear drug effects (Deff, 0.0022 L/μg) and linear progression, where an equilibration half-life to the effect compartment was approximately 15 weeks. Our findings indicated a positive correlation between the baseline K-VABS-II-ABC score (E0, 48.51) and the rate of natural progression (Kprog, 0.015 day-1), suggesting enhanced natural behavioral improvements in patients with better baseline adaptive behavior. Moreover, age was identified as a significant covariate for E0 and was incorporated into the model using a power function. Based on our model, the recommended dosing regimens for phase III trials are 2, 4, 6, 10, and 14 g, administered twice daily for weight ranges of 10-13, 14-20, 21-34, 35-49, and >50 kg, respectively. These doses are expected to significantly improve ASD symptoms. This study not only proposes an optimized dosing strategy for AST-001 but also provides valuable insights into the PK-PD relationship in pediatric ASD treatment.

Pathogenic gating pore current conducted by autism-related mutations in the NaV1.2 brain sodium channel

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by social and communication deficits and repetitive behaviors. The genetic heterogeneity of ASD presents a challenge to the development of an effective treatment targeting the underlying molecular defects. ASD gating charge mutations in the KCNQ/KV7 potassium channel cause gating pore currents (Igp) and impair action potential (AP) firing of dopaminergic neurons in brain slices. Here, we investigated ASD gating charge mutations of the voltage-gated SCN2A/NaV1.2 brain sodium channel, which ranked high among the ion channel genes with mutations in individuals with ASD. Our results show that ASD mutations in the gating charges R2 in Domain-II (R853Q), and R1 (R1626Q) and R2 (R1629H) in Domain-IV of NaV1.2 caused Igp in the resting state of ~0.1% of the amplitude of central pore current. The R1626Q mutant also caused significant changes in the voltage dependence of fast inactivation, and the R1629H mutant conducted proton-selective Igp. These potentially pathogenic Igp were exacerbated by the absence of the extracellular Mg2+ and Ca2+. In silico simulation of the effects of these mutations in a conductance-based single-compartment cortical neuron model suggests that the inward Igp reduces the time to peak for the first AP in a train, increases AP rates during a train of stimuli, and reduces the interstimulus interval between consecutive APs, consistent with increased neural excitability and altered input/output relationships. Understanding this common pathophysiological mechanism among different voltage-gated ion channels at the circuit level will give insights into the underlying mechanisms of ASD.