Protein Binding-dependent Decreases in hERG Channel Blocker Potency Assessed by Whole-Cell Voltage Clamp in Serum:

Machine learning and deep learning approaches for enhanced prediction of hERG blockade: a comprehensive QSAR modeling study

BACKGROUND

Cardiotoxicity is a major cause of drug withdrawal. The hERG channel, regulating ion flow, is pivotal for heart and nervous system function. Its blockade is a concern in drug development. Predicting hERG blockade is essential for identifying cardiac safety issues. Various QSAR models exist, but their performance varies. Ongoing improvements show promise, necessitating continued efforts to enhance accuracy using emerging deep learning algorithms in predicting potential hERG blockade.

STUDY DESIGN AND METHOD

Using a large training dataset, six individual QSAR models were developed. Additionally, three ensemble models were constructed. All models were evaluated using 10-fold cross-validations and two external datasets.

RESULTS

The 10-fold cross-validations resulted in Mathews correlation coefficient (MCC) values from 0.682 to 0.730, surpassing the best-reported model on the same dataset (0.689). External validations yielded MCC values from 0.520 to 0.715 for the first dataset, exceeding those of previously reported models (0-0.599). For the second dataset, MCC values fell between 0.025 and 0.215, aligning with those of reported models (0.112-0.220).

CONCLUSIONS

The developed models can assist the pharmaceutical industry and regulatory agencies in predicting hERG blockage activity, thereby enhancing safety assessments and reducing the risk of adverse cardiac events associated with new drug candidates.

Plasma Protein-Mediated Uptake and Contradictions to the Free Drug Hypothesis: A Critical Review

According to the free drug hypothesis (FDH), only free, unbound drug is available to interact with biological targets. This hypothesis is the fundamental principle that continues to explain the vast majority of all pharmacokinetic and pharmacodynamic processes. Under the FDH, the free drug concentration at the target site is considered the driver of pharmacodynamic activity and pharmacokinetic processes. However, deviations from the FDH are observed in hepatic uptake and clearance predictions, where observed unbound intrinsic hepatic clearance (CL_int,u) is larger than expected. Such deviations are commonly observed when plasma proteins are present and form the basis of the so-called plasma protein-mediated uptake effect (PMUE). This review will discuss the basis of plasma protein binding as it pertains to hepatic clearance based on the FDH, as well as several hypotheses that may explain the underlying mechanisms of PMUE. Notably, some, but not all, potential mechanisms remained aligned with the FDH. Finally, we will outline possible experimental strategies to elucidate PMUE mechanisms. Understanding the mechanisms of PMUE and its potential contribution to clearance underprediction is vital to improving the drug development process.

The utility of hERG channel inhibition data in the derivation of occupational exposure limits

Inhibition of the human ether-à-go-go (hERG) channel may lead to QT prolongation and fatal arrhythmia. While pharmaceutical drug candidates that exhibit potent hERG channel inhibition often fail early in development, many drugs with both cardiac and non-cardiac indications proceed to market. In this study, the relationship between in vitro hERG channel inhibition and published occupational exposure limit (OEL) was evaluated. A total of 23 cardiac drugs and 44 drugs with non-cardiac indications with published hERG channel IC₅₀ and published OELs were identified. There was an apparent relationship between hERG IC₅₀ potency and the OEL for cardiac and non-cardiac drugs. Twenty cardiac and non-cardiac drugs were identified that had a potent hERG IC₅₀ (≤25 μM) and a contrastingly large OEL value (≥100 μg/m³). OELs or hazard banding corresponding to ≤100 μg/m³ should be sufficiently protective of effects following occupational exposure to the majority of APIs with hERG IC₅₀ values ≤ 100 μM. It is important to consider hERG IC₅₀ values and possible cardiac effects when deriving OEL values for drugs, regardless of indication. These considerations may be particularly important early in the drug development process for establishing exposure control bands for drugs that do not yet have full clinical safety data.

Observations on conducting whole-cell patch clamping of the hERG cardiac K+ channel in pure human serum

Inhibition of the human ether-a-go-go-related gene (hERG) K⁺ channel by drugs leads to QT prolongation on the electrocardiogram and can result in serious cardiac arrhythmia. For this reason, screening of drugs on hERG is mandatory during the drug development process. Patch clamp electrophysiology in a defined physiological saline solution (PSS) represents the standard method for assaying drug effects on the channel. To make the assay more translatable to clinical studies, we have conducted whole-cell patch clamping of hERG using pure human serum as the extracellular medium. Pure human serum had little effect on the hERG channel waveform or the current-voltage relationship when compared to PSS. hERG current recordings were highly stable in serum at room temperature, but prolonged recordings at the physiological temperature required prior heat inactivation of the serum. Compared to PSS, the IC₅₀ values, conducted at room temperature, of the classic hERG blocking drugs cisapride, moxifloxacin, and terfenadine were shifted to the right by an extent predicted by their known plasma protein binding, but we did not detect any differences in IC₅₀ s between male and female serum. Total plasma levels of these drugs associated with clinical QT prolongation corresponded to small (<15%) inhibition of hERG current in pure serum suggesting that minor inhibition of the channel leads to observable pharmacodynamic effects. Conducting whole-cell patch clamping of hERG in human serum has the potential to make the assay more translatable to clinical studies and improve its predictive value for safety testing. Copyright © 2016 John Wiley & Sons, Ltd.