Positive Allosteric Modulation of AMPA Receptors from Efficacy to Toxicity: The Interspecies Exposure-Response Continuum of the Novel Potentiator PF-4778574

Abstract

a-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) positive allosteric modulation (i.e., "potentiation") has been proposed to overcome cognitive impairments in schizophrenia, but AMPAR overstimulation can be excitotoxic. Thus, it is critical to define carefully a potentiator's mechanismbased therapeutic index (TI) and to determine confidently its translatability from rodents to higher-order species. Accordingly, the novel AMPAR potentiator N-{(3R,4S)-3-[4-(5-cyano-2-thienyl) phenyl]tetrahydro-2H-pyran-4-yl}propane-2-sulfonamide (PF-4778574) was characterized in a series of in vitro assays and single-dose animal studies evaluating AMPAR-mediated activities related to cognition and safety to afford an unbound brain compound concentration (C b,u )-normalized interspecies exposure-response relationship. Because it is unknown which AMPAR subtype(s) may be selectively potentiated for an optimal TI, PF-4778574 binding affinity and functional potency were determined in rodent tissues expected to express a native mixture of AMPAR subunits and their associated proteins to afford composite pharmacological values. Functional activity was also quantified in recombinant cell lines stably expressing human GluA2 flip or flop homotetramers. Procognitive effects of PF-4778574 were evaluated in both rat electrophysiological and nonhuman primate (nhp) behavioral models of pharmacologically induced N-methyl-D-aspartate receptor hypofunction. Safety studies assessed cerebellum-based AMPAR activation (mouse) and motor coordination disruptions (mouse, dog, and nhp), as well as convulsion (mouse, rat, and dog). The resulting empirically derived exposure-response continuum for PF-4778574 defines a single-dose-based TI of 8-to 16-fold for self-limiting tremor, a readily monitorable clinical adverse event. Importantly, the C b,u mediating each physiological effect were highly consistent across species, with efficacy and convulsion occurring at just fractions of the in vitro-derived pharmacological values.

Induced Pluripotent Stem Cell Models to Enable In Vitro Models for Screening in the Central Nervous System

“…Table 2 illustrates several types of iPSC-based physiological models, in which iPSCs may be used to recapitulate neural cell interactions with other cells and their environment. Several functional interactions can be assessed [48][49][50][51][52][53][54]; these include modeling (1) blood-brain barrier, (2) synaptic networks, (3) neuron-astrocyte interactions, (4) oligodendrocyte myelination, (5) peripheral myelination, (6) retinal processes, (7) developmental processes, and (8) immunological interactions [55][56][57][58]. With the advent of numerous protocols for deriving iPSCs from multiple patientderived cell sources, academic and industry partnerships should be used to derive large and comprehensive repositories for iPSCs from well-characterized sibling controls and patients suffering from a range of CNS indications.…”

“…Some of the endpoints being assessed include the ability of chemicals to affect neuronal proliferation and differentiation [86], neuronal crest migration [87,88], and neuronal firing [48,51,52,89]. In addition, iPSCderived differentiated cell populations from patients with neurological disorders such as Parkinson's disease are being used to test for the possibility of differential chemical sensitivity [90,91] Through the advancement of human-based iPSC models, we are now able to capture, to some extent, genetic variability and susceptibility of response to drugs, pollutants, and other environmental chemicals, which is currently not possible using classical, animal toxicological studies.…”

AMPA Receptor-Positive Allosteric Modulators for the Treatment of Schizophrenia: An Overview of Recent Patent Applications

“…In a 2013 publication Pfizer describe the detailed pharmacological profile of cyanothiophene PF-4778578 (13) [75]. In vitro the compound is a potent ligand for the AMPA receptor with a binding affinity of 85 nM (rat) and shows positive modulation in a number of cellular assays.…”

Translating depression biomarkers for improved targeted therapies

“…The AMPA potentiator, LY451395, showed benefit on the Neuropsychiatric Inventory in a trial targeting cognitive deficits in Alzheimer's disease (Chappell et al, 2007), and efficacy in a primary depression study has not been reported. Augmentation of AMPA receptors can M a n u s c r i p t 26 cause convulsions and this has limited development of certain classes of AMPA potentiators (Shaffer et al, 2013).…”