Preclinical Autism Consortium for Therapeutics: Developing a Platform for Medications Discovery

Background:  Recent discoveries that mutations associated with autism spectrum disorder occur in genes that mediate the formation and functioning of synapses raised the possibility that effective interventions could target real-time synaptic events.  We sought to develop a rigorous strategy for evaluating therapeutic targets based on synaptic mechanisms, by assembling a standardized set of assays with maximum relevance to the diversity of symptoms of autism, applied to multiple mouse and rat models of autism. 

Objectives: The overarching goal of our Autism Speaks PACT initiative is to improve the early phases of medicines discovery and development for treating autism spectrum disorder.  In vivo approaches were sought to validate mechanistic targets, speed the discovery of viable new medications, and increase the success rate of clinical trials for the diagnostic symptoms of autism. Specific objectives: (1) Identify mouse and rat lines with mutations in the same gene to provide cross-species corroboration; (2) Design assays relevant to the diagnostic and associated symptoms of autism spectrum disorder for relatively high-throughput analysis of symptom reversals by pharmacological treatments; (3) Replicate studies within and across sites to maximize the robustness and reliability of findings.

Methods:  (a) We first considered the full range of available mouse and rat models of autism with mutations in the same gene.  The two-species approach became feasible through the newly available knockout rats generated by Sage Research Labs with support from Autism Speaks.  (b) We next considered which well-validated rodent behavioral assays maximize face validity to the diagnostic and associated symptoms of autism.  (c) We then considered the strength of biochemical, neuroanatomical, and physiological biomarkers in the literature, to identify rodent biological assays with maximal construct validity and feasibility.  External academic and industry colleagues contributed advice.

Results: (a) Based on published phenotypes of all mouse mutant models in which rat mutant models are also available, the initial four models we selected are Cntnap2, Shank3, Pten and Fmr1.  (b) Behavioral assays selected include social approach, reciprocal social interactions with associated ultrasonic vocalizations, exploration of social olfactory cues, spontaneous motor stereotypies, repetitive behaviors, water T-maze reversal, open field exploration, elevated plus-maze, light/dark transitions, acoustic startle and prepulse inhibition, hot plate, novel object recognition, and contextual and cued fear conditioning.  Protocols and order of behavioral tests follow the same fixed sequence in both mice and rats, and are conducted across developmental ages. (c) Global physiological analyses were selected as feasible, relevant in vivo biomarkers, including EEG epileptiform and gamma oscillations, and telemetry for sleep patterns and circadian rhythms.  Preliminary behavioral and physiological data will be presented for the Cntnap2 model.

Conclusions:  The PACT initiative has defined a strong set of standardized behavioral and physiological assays to evaluate potential new medicines targeting synaptic pathophysiology associated with mutations in risk genes for autism.  Internal replications within each species, and corroborations across two species, have been designed to provide an unprecedented level of reliability.  Our platform will be made available to industrial partners to advance novel medicines with the aim of expanding and improving the pipeline from preclinical evaluation of synaptic targets to clinical trials.