Pharmacologic stimulation of insulin granule acidification increases β-cell zinc content and augments β-cell-targeted drug delivery

Pathologic loss of insulin-producing pancreatic β-cells is a hallmark of diabetes that is potentially reversible through regenerative therapy. However, existing replication-promoting compounds lack β-cell specificity, limiting their clinical application. To overcome this challenge, we generated βRepZnC, a zinc-chelating replication compound designed to leverage the uniquely high zinc content of β-cells for targeted delivery. Herein, we identify pharmacological agents that boost β-cell zinc and improve the targeted delivery and bioactivity of βRepZnC. Using a high-content, image-based screen with the zinc fluorophore TSQ, we identified GR-46611 as a pharmacologic enhancer of β-cell zinc levels. Time-lapse TSQ imaging revealed that GR-46611 rapidly elevated intracellular zinc, prompting further mechanistic studies that showed increased zinc accumulation through the transporter ZnT8. This effect was mediated by enhanced V-ATPase-driven vesicle acidification via cAMP-PKA signaling inhibition. Supporting this mechanism, multiple PKA inhibitors also increased β-cell zinc content. Importantly, zinc enhancement significantly increased βRepZnC accumulation in both mouse and human primary islets, with FACS sorting and mass spectrometry confirming selective drug retention in β-cells over non-β-cells. To evaluate effects on bioactivity, we performed complementary on-treatment and post-treatment islet replication assays, measuring replication either concurrent with or 48 hours after drug exposure, respectively. Zinc elevation via GR-46611 or the PKA inhibitor H89 selectively potentiated βRepZnC-induced β-cell replication in both contexts. Notably, only βRepZnC-unlike non-zinc-binding replication compounds-elicited a sustained replication response after drug withdrawal. This work defines a new pharmacologic strategy for manipulating β-cell zinc levels that can be exploited for durable β-cell-targeted therapeutic delivery.