The effect of PF-05089771, a selective, peripherally restricted Nav1.7 sodium channel blocker on pain due to diabetic peripheral neuropathy was investigated in a randomised, placebo and active-controlled parallel group clinical trial (NCT02215252). A 1-week placebo-run in the period was followed by a 4-week treatment period and a 1-week placebo run-out/taper-down period. Single-blind placebo was administered throughout run-in and run-out periods. Subjects were randomised to receive either PF-05089771 150 mg twice daily, pregabalin 150 mg twice daily, or placebo during the 4-week treatment period. One hundred thirty-five subjects were randomised. The primary endpoint was the average pain score derived from subjects' Numerical Rating Scale scores over the past 7 days of week 4 of the double-blind treatment period. Predefined efficacy criteria for the trial were the effect of PF-05089771 being >0.5 units better than placebo at interim analysis after completion of the first part of the study. Although a trend for a reduction in the weekly average pain score in the PF-05089771 treatment group was observed, this was not statistically significant when compared with placebo at week 4, with a mean posterior difference of -0.41 (90% credible interval: -1.00 to 0.17). The effect of PF-05089771 was smaller than that seen with pregabalin, which was statistically significant when compared with placebo at week 4, with a mean posterior difference of -0.53 (90% credible interval: -0.91 to -0.20). As predefined efficacy criteria were not met, the study did not proceed to the second part. PF-05089771 was well tolerated. Possible reasons for the modest efficacy observed with PF-05089771 are discussed.

Selective dopamine D(3) receptor (D(3)R) antagonists prevent reinstatement of drug-seeking behavior and decrease the rewarding effects of contextual cues associated with drug intake preclinically, suggesting that they may reduce drug craving in humans. GSK598809 is a selective D(3)R antagonist recently progressed in Phase I trials. The aim of this study was to establish a model, based on the determination of the occupancy of brain D(3)Rs (O(D(3))(R)) across species, to predict the ability of GSK598809 to reduce nicotine-seeking behavior in humans, here assessed as cigarette craving in smokers. Using ex vivo [(125)I](R)-trans-7-hydroxy-2-[N-propyl-N-(3'-iodo-2'-propenyl)amino] tetralin ([(125)I]7OH-PIPAT) autoradiography and [(11)C]PHNO positron emission tomography, we demonstrated a dose-dependent occupancy of the D(3)Rs by GSK598809 in rat, baboon, and human brains. We also showed a direct relationship between O(D(3))(R) and pharmacokinetic exposure, and potencies in line with the in vitro binding affinity. Likewise, GSK598809 dose dependently reduced the expression of nicotine-induced conditioned place preference (CPP) in rats, with an effect proportional to the exposure and O(D(3))(R) at every time point, and 100% effect at O(D(3))(R) values 72%. In humans, a single dose of GSK598809, giving submaximal levels (72-89%) of O(D(3))(R), transiently alleviated craving in smokers after overnight abstinence. These data suggest that either higher O(D(3))(R) is required for a full effect in humans or that nicotine-seeking behavior in CPP rats only partially translates into craving for cigarettes in short-term abstinent smokers. In addition, they provide the first clinical evidence of potential efficacy of a selective D(3)R antagonist for the treatment of substance-use disorders.

Based on the human PK data obtained from the microdose study and subsequent modelling, PF-05089771 provided the best opportunity to explore Nav1.7 blockade for the treatment of acute or chronic pain conditions.

Aims To investigate whether saliva is a useful alternative to plasma for routine monitoring of nicotine and evaluate the predictive performances of saliva and plasma concentration on craving estimated by a Tiffany Questionnaire on Smoking UrgeBrief Form. Methods Thirteen healthy smokers were enrolled in a randomized, two period, crossover trial. Linear and power models were evaluated to predict the plasma nicotine concentrations from the saliva measurements, whereas a population PK/PD indirect response model was used to predict craving using either saliva or plasma nicotine concentration as the independent variable. Results The results of the analysis revealed that the power model was preferred over the linear one The bias on the predicted plasma concentrations was of 0.47 ng ml − 1 with a 95% confidence interval of [-0.57, 1.52] and a precision of 5.68 ng ml − 1 . The placebo effect model was initially fitted to data, then the indirect response approach (with inhibition in k in ) was used to model the craving scores using plasma and saliva nicotine concentrations as independent variables. The two indirect response PK/PD models based on saliva and plasma nicotine concentrations, adequately described the onset, extent, and duration of craving. The maximal inhibition I max was 0.722 and 1 for saliva and plasma concentrations while the estimated nicotine concentrations giving 50% of the maximal inhibition were 269 ng ml − 1 and 24.3 ng ml − 1 for saliva and plasma, respectively. Conclusions A good correlation between plasma and saliva nicotine concentrations has been found using a power model. Comparable values of bias and precision on the model-predicted craving indicate that plasma and saliva concentration can equally well be used to predict the onset of tobacco withdrawal induced craving. Analysis of saliva definitely offers a potentially more attractive way to assess nicotine concentration values, as samples can be collected easily and noninvasively. In addition, saliva sampling avoids the pain and discomfort involved in venepuncture. In studies that assess psychological measures, such as subjective mood, blood collection could present a possible confounding factor because of the anxiety and pain that accompanies it. For these reasons saliva can reasonably be considered as the ideal sampling site for all clinical studies conducted for the evaluation of the potential activity of drugs on nicotine deprivation symptoms.