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.

Metabolic signatures of amyotrophic lateral sclerosis reveal insights into disease pathogenesis.

Metabolic dysfunction is an important modulator of disease course in amyotrophic lateral sclerosis (ALS). We report here that a familial mouse model (transgenic mice over-expressing the G93A mutation of the Cu/Zn superoxide dismutase 1 gene) of ALS enters a progressive state of acidosis that is associated with several metabolic (hormonal) alternations that favor lipolysis. Extensive investigation of the major determinants of H(+) concentration (i.e., the strong ion difference and the strong ion gap) suggests that acidosis is also due in part to the presence of an unknown anion. Consistent with a compensatory response to avert pathological acidosis, ALS mice harbor increased accumulation of glycogen in CNS and visceral tissues. The altered glycogen is associated with fluctuations in lysosomal and neutral α-glucosidase activities. Disease-related changes in glycogen, glucose, and α-glucosidase activity are also found in spinal cord tissue samples of autopsied patients with ALS. Collectively, these data provide insights into the pathogenesis of ALS as well as potential targets for drug development.

Carbohydrate-mediated polyethylene glycol conjugation of TSH improves its pharmacological properties.

Thyrogen (thyrotropin alfa for injection), recombinant human TSH (rhTSH), has been successfully used to enhance diagnostic radioiodine scanning and thyroglobulin testing in the follow-up of patients with thyroid cancer and as an adjunctive treatment for radioiodine thyroid remnant ablation. However, the short half-life of rhTSH in the circulation requires a multidose regimen. We developed novel sialic acid-mediated and galactose-mediated conjugation chemistries for targeting polyethylene glycol (PEG) to the three N-linked glycosylation sites on the protein, to prolong plasma half-life by eliminating kidney filtration and potential carbohydrate-mediated clearance. Conjugates of different PEG sizes and copy numbers were screened for reaction yield, TSH receptor binding, and murine phamacokinetics/pharmacodynamics studies. The best performing of these products, a 40-kDa mono-PEGylated sialic acid-mediated conjugate, exhibited a 3.5-fold longer duration of action than rhTSH in rats, as a 5-fold lower affinity was more than compensated by a 23-fold extension of circulation half-life. Biochemical characterization confirmed conjugation through the sialic acids. Correlation of PEG distribution on the three N-linked glycosylation sites and the PEG effect on receptor binding supported the previously reported structure-function relationship of rhTSH glycosylation. This long-acting rhTSH has the potential to significantly improve patient convenience and provider flexibility while reducing potential side effects associated with a sudden elevation of serum TSH.