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In the nuclei of hepatocytes, glucokinase regulatory protein (GKRP) modulates the activity of glucokinase (GK), a key regulator of glucose homeostasis. Currently, direct activators of GK (GKAs) are in development for the treatment of type 2 diabetes. However, this approach is generally associated with a risk of hypoglycemia. To mitigate such risk, we target the GKRP regulation, which indirectly restores GK activity. Here we describe a screening strategy to look specifically for GKRP modulators, in addition to traditional GKAs. Two high-throughput screening campaigns were performed with our compound libraries using a luminescence assay format, one with GK alone and the other with a GK/GKRP complex in the presence of sorbitol-6-phosphate (S6P). By a subtraction method in the hit triage process of these campaigns, we discovered two close analogs that bind GKRP specifically with sub-µM potency to a site distinct from where fructose-1-phosphate binds. These small molecules are first-in-class allosteric modulators of the GK/GKRP interaction and are fully active even in the presence of S6P. Activation of GK by this particular mechanism, without altering the enzymatic profile, represents a novel pharmacologic modality of intervention in the GK/GKRP pathway.

Calcimimetics are positive allosteric modulators to the calcium-sensing receptor (CaSR). Activation of the CaSR inhibits the secretion of parathyroid hormone (PTH), stimulates the secretion of calcitonin, and decreases serum calcium (Ca2+). Cinacalcet, a second-generation calcimimetic, is used therapeutically to control PTH in patients with chronic kidney disease who are on dialysis with secondary hyperparathyroidism. A calcimimetic that displays increased separation of PTH versus Ca2+lowering in patients would potentially allow the use of calcimimetics to treat patients in earlier stages of renal disease because hypocalcemia can develop in this population. Toward this end, we developed a third-generation calcimimetic, determined the molecular pharmacological properties of it using an operation model of allosteric modulation/agonism, and measured the compound effects on PTH, serum ionized Ca2+, and calcitonin levels in 5/6 nephrectomized rats. We found the new molecule effectively reduced PTH levels without promoting calcitonin secretion or hypocalcemia. Furthermore, our third-generation molecule was less efficacious at promoting calcitonin secretion from human thyroid carcinoma cells compared with 3-(2-chlorophenyl)-N-((1R)-1-(3-methoxyphenyl)ethyl)-1-propanamine (R-568), a first-generation calcimimetic. These data provide evidence that calcimimetics with increased potency can be used to lower PTH without production of significant hypocalcemia because the threshold for inhibition of PTH secretion is much lower than the threshold for calcitonin secretion.

Calcimimetics are positive allosteric modulators to the calcium-sensing receptor (CaSR). Activation of the CaSR inhibits the secretion of parathyroid hormone (PTH), stimulates the secretion of calcitonin, and decreases serum calcium (Ca(2+)). Cinacalcet, a second-generation calcimimetic, is used therapeutically to control PTH in patients with chronic kidney disease who are on dialysis with secondary hyperparathyroidism. A calcimimetic that displays increased separation of PTH versus Ca(2+) lowering in patients would potentially allow the use of calcimimetics to treat patients in earlier stages of renal disease because hypocalcemia can develop in this population. Toward this end, we developed a third-generation calcimimetic, determined the molecular pharmacological properties of it using an operation model of allosteric modulation/agonism, and measured the compound effects on PTH, serum ionized Ca(2+), and calcitonin levels in 5/6 nephrectomized rats. We found the new molecule effectively reduced PTH levels without promoting calcitonin secretion or hypocalcemia. Furthermore, our third-generation molecule was less efficacious at promoting calcitonin secretion from human thyroid carcinoma cells compared with 3-(2-chlorophenyl)-N-((1R)-1-(3-methoxyphenyl)ethyl)-1-propanamine (R-568), a first-generation calcimimetic. These data provide evidence that calcimimetics with increased potency can be used to lower PTH without production of significant hypocalcemia because the threshold for inhibition of PTH secretion is much lower than the threshold for calcitonin secretion.

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