Improving Existing Drugs for Long QT Syndrome type 3 (LQT3) by hiPSC Disease-in-Dish Model
This project uses patient hiPSC-derived cardiomyocytes to develop a safe and effective drug to treat a serious heart health condition. This research and product development will provide a novel method for a human genetic heart disorder characterized by long delay (long Q-T interval) between heart beats caused by mutations in the Na+ channel α subunit. Certain patients are genetically predisposed to a potentially fatal arrhythmogenic response to existing drugs to treat LQT3 since the drugs have off-target effects on other important ion channels in cardiomyocytes. We will use patient-derived hiPSC-cardiomyocytes to develop a safer drug (development candidate, DC) that will retain efficacy against the "leaky" Na+-channel yet minimize off-target effects in particular against the K+ hERG channel that can be responsible for the existing drug’s pro-arrhythmic effect. Since this problem is thought to occur severely in patients with the common KCHN2 variant, K897T (~33% of the white population), removing the off-target liability addresses a serious unmet clinical need. Futher, since we propose to modify an existing drug (i.e., do drug rescue), the path from patient-specific hiPSCs to clinic might be easier than for a completely new chemical entity. Lastly, an appealing aspect is that the hiPSCs were derived from a child to test his therapy, & we aim to produce a better drug for his treatment. Our goal is to complete development of the DC and initiate IND-enabling in vivo studies.
In the US, an estimated 850,000 adults are hospitalized for arrhythmias each year, making arrhythmias one of the top five causes of healthcare expenditures in the US with a direct cost of more than $40 billion annually for diagnosis, treatment & rehabilitation. The State of California has approximately 12% of the US population which translates to 102,000 individuals hospitalized every year for arrhythmias. Another 30,000 Californians die of sudden arrhythmic death syndrome every year. Arrhythmias are very common in older adults and because the population of California is aging, research to address this issue is important for human health and the State economy. Most serious arrhythmias affect people older than 60. This is because older adults are more likely to have heart disease & other health problems that can lead to arrhythmias. Older adults also tend to be more sensitive to the side effects of medicines, some of which can cause arrhythmias. Some medicines used to treat arrhythmias can even cause arrhythmias as a side effect. In the US, atrial fibrillation (a common type of arrhythmia that can cause problems) affects millions of people & the number is rising. Accordingly, the same problem is present in California. Thus, successful completion of this work will not only provide citizens of California much needed advances in cardiovascular health technology & improvement in health care but an improved heart drug. This will provide high paying jobs & significant tax revenue.
The project objective is to design, synthesize and test a sodium-channel inhibitor analog that selectively inhibits the sodium channel and not the potassium channel in patient-derived IPSCs. The strategy is to first work out the approach with wild-type human IPSCs in advance of the patient-derived cells. The status is that the milestones for Year 1 have largely been accomplished. The achievements for this reporting period include nearly locking down the IPSC protocol, developing ultra high throughput kinetic analysis of human cardiomyocytes, developing an enantioselective synthesis of sodium-channel inhibitors and analogs and identifying from a pool of only 49 compounds, a promising sodium-channel inhibitor that provides insight into selective sodium channel inhibition.
We have been successful with a cardiovascular drug re-purposing. The parent drug possesses significant adverse off-target properties and pharmacological liabilities. We have synthesized new drug candidates that showed improved potency compared to the parent drug molecule. The new compounds showed greater than 50-100-fold improvement in the on-target versus off-target effects compared to the currently used drug treatment. We have found that minor chemical changes to the position of key substituents on the molecule had a great impact on potency and off-target effects. This improvement in potency for the on-target effects of the molecule may lead to lower doses and/or greater therapeutic efficacy of the new drug candidate compared to the currently used drug.
We have nominated a small subset as lead compounds and advanced these compounds into pre-clinical testing that included chemical and metabolic stability studies. The results from chemical stability studies showed the lead drug candidates to be stable with a half-life of degradation of greater than 30 days. We have tested one of the lead compounds in liver microsomes to monitor potential hepatic metabolism of the compound. In addition, we studied the lead compounds in an in vitro measure of cytotoxicity and found the compounds are sufficiently non-toxic to move forward. The results showed one lead compound to have sufficient stability against metabolic enzymes of the liver to move the molecule forward into more advanced in vivo pre-clinical studies, including safety studies and efficacy studies.