Animal experiment:

Mice[1] To demonstrate that the observed glucose lowering by MK-4256 is SSTR3-dependent, the effect of a maximally efficacious dosage of MK-4256 on blood glucose excursion during an oGTT was investigated in SSTR3 KO mice. Administration of MK-4256 (1 mg/kg) and compound A (1 mg/kg; des-F-sitagliptin, a DPP-4 inhibitor included as a positive control) to age-matched C57BL/6N male WT mice significantly inhibits blood glucose excursion by 112 and 91%, respectively.

MK-4256 is a potent and selective SSTR3 antagonist with IC50s of 0.66 nM and 0.36 nM in human and mouse receptor binding assays, respectively.

MK-4256 has excellent selectivity against other SSTR subtypes based on in vitro assays. In human receptor binding assays, MK-4256 has IC50s >2 μM for SSTR1 and SSTR2. Although the binding IC50 values on SSTR4 and SSTR5 are below 1 μM, there is still >500-fold selectivity. MK-4256 is tested in functional antagonist assays against SSTR4 and SSTR5. The IC50 values are greater than 5 μM (at least 5000-fold selectivity)[1]. MK-4256 inhibits radiolabeled MK-499 binding of the hERG channel with an IC50=1.74 μM. In a functional patch clamp assay, MK-4256 exhibits 50% blockade of hERG at 3.4 μM concentration[2].

MK-4256 reduces glucose excursion in a dose-dependent fashion with maximal efficacy achieves at doses as low as 0.03 mg/kg po. MK-4256 demonstrates exceptional SSTR3-mediated glucose-lowering efficacy in the mouse oGTT model with minimal hypoglycemia risk. MK-4256 achieves complete ablation of glucose excursion (109%) at 1 mg/kg po. MK-4256 reduces the glucose excursion from 0.003 to 10 mg/kg in a dose-dependent manner. The plasma Cmax of MK-4256 is determined from parallel mouse PK studies. At 0.01, 0.1, and 1 mg/kg oral dose, MK-4256 achieves Cmax of 7, 88, and 493 nM, respectivley[1].

[1]. He S, et al. The Discovery of MK-4256, a Potent SSTR3 Antagonist as a Potential Treatment of Type 2 Diabetes. ACS Med Chem Lett. 2012 May 7;3(6):484-9. [2]. He S, et al. Investigation of Cardiovascular Effects of Tetrahydro-β-carboline sstr3 antagonists. ACS Med Chem Lett. 2014 Apr 21;5(7):748-53.