Overcoming drug resistance in childhood seizure and psychiatric disorders caused by potassium channels
Chief Investigator: Professor Leanne Dibbens
Funding Amount: $100,000
Recipient: University of South Australia
Children with a defective potassium channel (KCNT1) gene have a serious developmental disorder which includes epilepsy and psychiatric features. Affected children experience frequent seizures, even when on anti-epileptic medications, known as ‘drug resistant seizures’. We have identified naturally occurring molecules in the body that modulate the activity of the KCNT1 channel. Depletion of one of these molecules contributes to reduced effectiveness of medication on defective sodium channels in epilepsy. Showing that these molecules can improve the function of defective KCNT1 potassium channels will be a ground breaking step towards offering new treatments for affected children.
Researchers: Leanne Dibbens, Grigori Rychkov, Zeeshan Shaukat
Research Completed: 2021
Research Findings: Mutations in potassium channels contribute to cases of severe epilepsy and psychiatric disturbances in children. To identify potential new drugs to help treat children with drug-resistant epilepsy and psychiatric features, we investigated the effects of two naturally occurring intracellular molecules on a potassium channel. We used cell lines expressing normal and mutant potassium channels and patch clamping in whole cell, cell-attached and inside-out patch modes.
Using inside-out patches we determined that one tested molecule (molecule 1) inhibits the potassium channel in a voltage-dependent manner, with a stronger inhibition at more positive potentials. Intracellular molecule 1 reduces both the open probability and the single channel conductance of normal potassium channels. However, the effect of molecule 1 on single channel conductance is voltage dependent, whereas the effect on the open probability is not. This suggests that molecule 1 inhibits the studied potassium channels through two distinct mechanisms.
To investigate whether epilepsy-causing mutations of the potassium channel affect the molecule 1-mediated block, we characterised basic electrophysiological properties of 10 novel and 4 known potassium mutant channels. Each of these mutated channels has been identified in children with drug resistant epilepsy with some of the children also affected by psychiatric features. Using whole-cell patch clamping we found that each of the epilepsy-causing mutations of the potassium channel produced significantly larger currents than the normal channel, which was expected based on previous studies. One of the novel mutations had a significant effect on the kinetics and rectification of potassium current, but very moderate effect on the current amplitude. Further investigation of this mutation can provide important clues on how larger potassium currents cause epilepsy. Four of the novel mutations were investigated at the single-channel level in inside-out patches, and the results suggested that these mutations do not affect molecule 1 binding in the channel pore.
Investigation of the effects of molecule 2 on the potassium channel in inside-out patches demonstrated that it inhibits the channel with an IC50 of ~3 mM, by decreasing the open time of the channel. The findings in the project have led to a collaboration with a group in Europe and together we are working to identify the binding site so that we may also be able to identify drugs that bind to and act to modulate the channel. In summary, we have confirmed in a cell model that two readily available and non-toxic molecules act to inhibit the action of a potassium channel involved in causing severe epilepsy and psychiatric features in children. We now plan to analyse these molecules in our animal models of childhood epilepsy to look for drugs that bind to a similar region of the potassium channel to test their suitability as potential new treatments for children with severe epilepsy and psychiatric disorders.
Key Outcomes: In this project we have shown that two naturally occurring intracellular molecules act to inhibit the action of a potassium channel involved in causing severe epilepsy and psychiatric features in children. These molecules can now start to be tested as potential new treatments for drug resistant epilepsy in children.
Research Papers: Manuscript in preparation: Rychkov G, Shaukat Z, Hussain R, Lim C X, Ricos MG, Dibbens LM. Inhibition of a potassium channel associated with severe childhood epilepsy and psychiatric disorders: potential new therapies.
Future Outcomes: A key outcome from the project is that we have begun a collaboration with a research pharmacologist in the United Kingdom. Together we are testing the effects of a number of drugs on the ion channel cell models that we have generated in this study to identify those drugs that can reverse the effects of the epilepsy-causing mutations. This has the potential to identify new drugs to treat potassium channel-associated neurological disorders in children.