detella pertussis toxin (PTx), also known as islet-activating protein, induces insulin secretion by ADP-ribosylation of inhibitory G proteins. PTx-induced insulin secretion may result either from inactivation of G␣o proteins or from combined inactivation of G␣o, G␣i1, G␣i2, and G␣i3 isoforms. However, the specific role of G␣i2 in pancreatic ␤-cells still remains unknown. In global (G␣i2 Ϫ/Ϫ ) and ␤-cell-specific (G␣ i2 ␤cko ) gene-targeted G␣i2 mouse models, we studied glucose homeostasis and islet functions. Insulin secretion experiments and intracellular Ca 2ϩ measurements were used to characterize G␣i2 function in vitro. G␣i2Ϫ/Ϫ and G␣i2 ␤cko mice showed an unexpected metabolic phenotype, i.e., significantly lower plasma insulin levels upon intraperitoneal glucose challenge in G␣i2 Ϫ/Ϫ and G␣i2 ␤cko mice, whereas plasma glucose concentrations were unchanged in G␣ i2 Ϫ/Ϫ but significantly increased in G␣i2 ␤cko mice. These findings indicate a novel albeit unexpected role for G␣i2 in the expression, turnover, and/or release of insulin from islets. Detection of insulin secretion in isolated islets did not show differences in response to high (16 mM) glucose concentrations between control and ␤-cellspecific G␣ i2-deficient mice. In contrast, the two-to threefold increase in insulin secretion evoked by L-arginine or L-ornithine (in the presence of 16 mM glucose) was significantly reduced in islets lacking G␣ i2. In accord with a reduced level of insulin secretion, intracellular calcium concentrations induced by the agonistic amino acid L-arginine did not reach control levels in ␤-cells. The presented analysis of gene-targeted mice provides novel insights in the role of ␤-cell G␣ i2 showing that amino acid-induced insulin-release depends on G␣i2. G␣ i2; insulin secretion; ␤-cell; L-arginine; GPCR GLUCOSE IS THE PRINCIPAL STIMULATOR of insulin secretion from pancreatic ␤-cells. Together with regulators such as other nutrients or hormones, it adjusts insulin secretion according to physiological demands. A disruption of this tightly controlled process can lead to diabetes mellitus and its comorbidities. Physiological regulators of insulin release include not only glucose but also other nutrients such as free fatty acids or amino acids on the one hand, and hormones including glucagon and norepinephrine on the other hand. They all have in common that they signal via seven-transmembrane G proteincoupled receptors (GPCR) present on the surface of pancreatic ␤-cells (1, 28, 33). Upon ligand binding, GPCRs activate heterotrimeric G proteins, thereby modulating the activity of cellular effectors. It is widely accepted that insulin release from pancreatic ␤-cells can be triggered via G␣ s -and/or G q /G 11 -dependent mechanisms (2, 41). Studies in isolated systems and in animals, using pertussis toxin (PTx), also known as isletactivating protein, suggest G␣ i /G␣ o -dependent signaling as being important for inhibition of insulin secretion (11,14,15). PTx specifically catalyzes the ADP-ribosylation of a cysteine residue locat...

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The mitogen-activated protein kinase (MEK) inhibitor zapnometinib is in development to treat acute viral infections like COVID-19 and influenza. While the antiviral efficacy of zapnometinib is well documented, further data on target engagement/pharmacodynamics (PD) and pharmacokinetics (PK) are needed. Here, we report zapnometinib PK and PD parameters in mice, hamsters, dogs, and healthy human volunteers. Mice received 25 mg/kg/day zapnometinib (12.5 mg/kg p. o. twice daily, 8 h interval). Syrian hamsters received 30 mg/kg (15 mg/kg twice daily) or 60 mg/kg/day once daily. Beagle dogs were administered 300 mg/kg/day, and healthy human volunteers were administered 100, 300, 600 and 900 mg zapnometinib (once daily p. o.). Regardless of species or formulation, zapnometinib maximum plasma concentration (Cmax) was reached between 2–4 h after administration with an elimination half-life of 4–5 h in dogs, 8 h in mice or hamsters and 19 h in human subjects. Doses were sufficient to cause up to 80% MEK inhibition. Across all species approximately 10 μg/ml zapnometinib was appropriate to inhibit 50% of peripheral blood mononuclear cells (PBMC) MEK activity. In mice, a 50%–80% reduction of MEK activity was sufficient to reduce influenza virus titer in the lungs by more than 90%. In general, while >50% MEK inhibition was reached in vivo at most doses, 80% inhibition in PBMCs required significantly higher doses and appeared to be the practical maximal level obtained in vivo. However, the period of reduced phosphorylated extracellular-signal regulated kinase (pERK), a measure of MEK inhibition, was maintained even after elimination of zapnometinib from plasma, suggesting a sustained effect on MEK consistent with regulatory effects or a slow off-rate. These data suggest a target plasma Cmax of at least 10 μg/ml zapnometinib in further clinical studies.