Systems pharmacology modeling in neuroscience: Prediction and outcome of PF-04995274, a 5-HT4 partial agonist, in a clinical scopolamine impairment trial

Background: 5-HT4receptors in cortex and hippocampus area are considered as a possible target for modulation of cognitive functions in Alzheimer’s disease (AD). A systems pharmacology approach was adopted to evaluate the potential of the 5-HT4 modulation in providing beneficialeffects on cognition in AD. Methods: A serotonergic synaptic cleft model was developed by integrating serotonin firing, release, synaptic half-life, drug/tracer properties (affinity and agonism) as inputs and5-HT4 activity as output. The serotonergic model was calibrated using bothinvivo data on free 5-HT levels in preclinical models and human imaging data. The model was further expanded to other neurontransmitter systems and incorporated into a computer-based cortical network model which implemented the physiology of 12 different membrane CNS targets. A biophysically realistic, multi-compartment model of 80 pyramidal cells and 40 interneurons was further calibrated usingdata reported for working memory tasks in healthyhumans and schizophrenia patients. Model output was the duration of the network firing activity in response to an external stimulus. Alzheimer’s disease (AD) pathology, in particular synapse and neuronal cell loss in addition to cholinergic deficits, was calibrated to align with the natural clinical disease progression. The model was used to provide insights into the effect of 5-HT4 activation on working memory and to prospectively simulate the response of PF- 04995274, a 5-HT4partial agonist, in a scopolamine-reversal trial in healthy human subjects. Results: The model output suggested a beneficial effect of 5-HT4
agonism on working memory. The model also projected no effect or an exacerbation of scopolamine impairment for low in- trinsic activity 5-HT4agonists, which was supported by the subsequent human trial outcome. The clinical prediction of the disease model strongly suggests that 5-HT4 agonists with high intrinsic activity may have a beneficial effect on cognition in AD patients.