Insulin levels are inadequate to maintain euglycemia in patients with type-2 diabetes (T2D), which is due in part to perturbations in pancreatic ꞵ-cell Ca2+ homeostasis. TALK-1 K+ channels are key regulators of ꞵ-cell electrical excitability, Ca2+ handling and glucose-stimulated insulin secretion (GSIS). KCNK16, which encodes TALK-1 is the most abundant ꞵ-cell K+ channel transcript and also the most islet-restricted ion channel transcript. Furthermore, a nonsynonymous coding sequence polymorphism in KCNK16 causes a predisposition for developing T2D. However, the ability to utilize TALK-1 as a therapeutic target to normalize ꞵ-cell Ca2+ homeostasis in T2D has not been determined. Here, we optimized a high throughput fluorescence-based thallium (TI+) flux assay (z’ =0.64) to screen for TALK-1 inhibitors, which resulted in identification of 286 TALK-1 inhibitors with potent drug-like properties (from a 50,000 compound screen). Of these hits, 78 exhibit TALK-1 selectivity and do not influence the activity of other K+ channels including TALK-2, TREK-2, TASK-1, TASK-3, KATP or hERG channels. We then performed dose response curve analyses and identified 9 potent inhibitors with IC50s < 2.5μM that inhibit TALK-1 activity (>65%). To test the efficacy of the inhibitors for their ability to augment islet function, we assessed their impact on mouse islet Ca2+ handling. TALK-1 inhibitors significantly increased islet Ca2+ oscillation frequency (e.g., VU0233408, 2.47 peaks/min vs. DMSO, 1.82 peaks/min, p-value= 0.011), similar to what was previously observed in TALK-1 KO islets. Moreover, the inhibitors did not increase glucose-stimulated Ca2+ oscillation frequency in TALK-1 KO islets. Thus, pharmacological inhibition of TALK-1 is predicted to increase GSIS.
In conclusion, we have identified the first potent and selective TALK-1 inhibitors that can be utilized to assess the role of TALK-1 during human ꞵ-cell GSIS under physiological and diabetic conditions.
A.Y. Nakhe: None. P. Dadi: None. D. Westover: None. E. Days: None. J. Denton: None. D. Jacobson: None.
National Institute of Diabetes and Digestive and Kidney Diseases (R01DK115620VDC); Vanderbilt University Diabetes and Research Training Center (P60DK20593)