The effect of intracellular pH on hERG inhibition

The challenge

A valued client, BugWorks Research, approached ApconiX to help them investigate the effect of intracellular pH on the inhibition of hERG potassium channel.  At different pH, molecules might carry a different charge, depending on their structure.  This may affect the molecule’s activity at hERG. Their enquiry followed some unexpected hERG inhibition by their compounds and the discovery of a paper published in 2016 by Wang et al.  The paper showed that dofetilide, a known hERG blocker, had a quicker onset of effect at lower intracellular pH than under standard conditions.  As shown in Figure 1.

Figure 1: Decreased time to effect of dofetilide at intracellular pH 6.2 versus pH 7.2 (from Wang et al., 2016)

The science

Electrophysiology experiments were performed on the Patchliner automated patch-clamp system (Nanion Technologies).  These experiments showed no significant difference in the onset of dofetilide inhibition at lower intracellular pH, as illustrated in figure 2.

Figure 2: No change in time to effect of dofetilide on hERG current at pH 6.3 versus pH 7.3.

There is limited literature in this area. ApconiX found a second paper by Du et al., 2011, which reported no effect of intracellular pH on hERG inhibition by dofetilide, contesting Wang’s original data.

The outcome

Based on data from ApconiX and others, it is unlikely that intracellular pH is affecting the onset of hERG inhibition. Changes in intracellular pH that might affect the charge of a molecule does not, in this case, explain unexpected hERG inhibition.

Du et al (2011) Enhanced inhibitory effect of acidosis on hERG potassium channels that incorporate the hERG1b isoform. Biochem Biophys Res Comm 405, 222–7

Wang et al. (2016) Role of the pH in state-dependent blockade of hERG currents. Scientific Reports 6: 32536

The Testimonial

A Company Focused on Novel Oncology Targets

The challenge

Our client had identified a clinical candidate aimed at a novel tumour target, with promising activity against a range of cancers.  Upon completion of suitable GLP toxicity studies, the company intended to move into Phase I in patients, in combination with chemotherapy. There were a number of pressing issues, including choice of the appropriate nonclinical species, dosing schedule, achieving adequate exposure as well as the potential for greater target organ toxicity when dosed in combination.

The solution

ApconiX joined the client’s project team by providing a dedicated project toxicologist, supported by our other experts.  With a clear understanding of the project goals and clinical objectives, we delivered a bespoke, focussed nonclinical safety package designed to ensure the right data were provided for regulatory success and rapid initiation of the Phase I patient studies.

A study that provided safety and DMPK data on the novel agent dosed with chemotherapy was also designed and conducted. Although not a regulatory requirement, this allowed a better understanding of the impact of the combination and supported a higher start dose in combination with chemotherapy.

ApconiX managed all aspects of the preclinical safety package, working closely with CROs to ensure appropriate study design, costs, dose level selection, data interpretation as well as timely delivery of quality study reports.  Concurrently, we authored the nonclinical sections of the regulatory submission documents and represented the client at a regulatory agency meeting.

The benefit

With ApconiX as part of the team, our client benefited from our many years of collective experience in preclinical safety, DMPK and drug development.   The package was designed to ensure regulatory and clinical objectives were met, keeping to budget and agreed timelines.

The outcome

The Clinical Trial Authorisation was approved, allowing the compound to move into clinical trials, in combination with chemotherapy.  During this phase, we also assisted in the out-licencing of this asset to a third party.   We continue to work with the new owners to ensure its further success.