Evaluation of calibration curve-based approaches to predict clinical inducers and noninducers of CYP3A4 with plated human hepatocytes.

Cytochrome P450 (P450) induction is often considered a liability in drug development. Using calibration curve-based approaches, we assessed the induction parameters R3 (a term indicating the amount of P450 induction in the liver, expressed as a ratio between 0 and 1), relative induction score, Cmax/EC50, and area under the curve (AUC)/F2 (the concentration causing 2-fold increase from baseline of the dose-response curve), derived from concentration-response curves of CYP3A4 mRNA and enzyme activity data in vitro, as predictors of CYP3A4 induction potential in vivo. Plated cryopreserved human hepatocytes from three donors were treated with 20 test compounds, including several clinical inducers and noninducers of CYP3A4. After the 2-day treatment, CYP3A4 mRNA levels and testosterone 6ß-hydroxylase activity were determined by real-time reverse transcription polymerase chain reaction and liquid chromatography-tandem mass spectrometry analysis, respectively. Our results demonstrated a strong and predictive relationship between the extent of midazolam AUC change in humans and the various parameters calculated from both CYP3A4 mRNA and enzyme activity. The relationships exhibited with non-midazolam in vivo probes, in aggregate, were unsatisfactory. In general, the models yielded better fits when unbound rather than total plasma Cmax was used to calculate the induction parameters, as evidenced by higher R(2) and lower root mean square error (RMSE) and geometric mean fold error. With midazolam, the R3 cut-off value of 0.9, as suggested by US Food and Drug Administration guidance, effectively categorized strong inducers but was less effective in classifying midrange or weak inducers. This study supports the use of calibration curves generated from in vitro mRNA induction response curves to predict CYP3A4 induction potential in human. With the caveat that most compounds evaluated here were not strong inhibitors of enzyme activity, testosterone 6ß-hydroxylase activity was also demonstrated to be a strong predictor of CYP3A4 induction potential in this assay model.

Use of the median method to enhance detection of the mismatch negativity in the responses of individual listeners.

The median method was evaluated as an alternative way of expressing the mismatch negativity (MMN). Traditionally, signal averaging has been used to extract these event-related potentials from unwanted background noise. However, mean values are biased by unrejected artifact that skews the relatively small distribution of values on which the MMN is based. Because the median is a more valid measure of central tendency in asymmetric distributions, it may describe MMN data more accurately. Better representation of the signal in the median waveform might enhance detection of the MMN in the responses of individual listeners. Mean and median waveforms were computed from previously recorded MMN data. Visually identified MMNs were validated using area and onset latency criteria. Detectability of the MMN was not improved using median waveforms. Despite this result, a theoretical argument for use of the median is presented.