Cell experiment:

MDA-MB-468 and MCF7 cells are seeded in growth medium into 96-well plates at 1000 and 4000 cells/well, respectively. Sixteen hours after plating, MELK-8a are added and incubated for 7 days. For each well, ATPLite reagent is added and incubated. Luminescence is measured on an multilabel plate reader[1].

Animal experiment:

Mice: For pharmacokinetic studies, the intravenous and oral dose is prepared in a solution containing 5% ethanol, 100% PG, 5% CremophorEL, and 80% PBS. The subcutaneous dose is formulated in 10% PG and 25% (20%, v/v) Solutol. Plasma samples are collected at specified time points and stored frozen (–20 ℃) until MELK-8a analysis. An LC–MS/MS method is used to quantitate MELK-8a drug levels in plasma[1].

MELK-8a hydrochloride is a novel maternal embryonic leucine zipper kinase (MELK) inhibitor with an IC50 of 2 nM.

MELK-8a remains very potent (IC50=140 nM) when the ATP concentration in the biochemical assay is shifted from 20 μM to 2 mM. Its potency is well tracked between full-length MELK versus catalytic domain construct (5 nM versus 2 nM). It only inhibits seven off-target kinases in addition to MELK with >85% inhibition of binding at 1 μM demonstrating great selectivity. The compound is at least 90-fold more selective in targeting MELK in all cases. MELK-8a is fairly soluble (0.22 g/L at pH 6.8) and shows a good permeability in the Caco-2 assay. MELK-8a inhibits the growth of MDA-MB-468 cells and MCF-7 cells with an IC50 of approximately 0.06 and 1.2 μM, respectively[1].

Subcutaneous administration of MELK-8a at 30 mg/kg in C57BL/6 mice results in good plasma exposure. The compound adsorption into the systemic circulation is rapid (Tmax=0.4 h) and peak plasma concentration reaches 6.6 μM. An ascending dose PK study in female athymic nude mice shows that the rate of compound release is maximal at 120 mg/kg and all clearance mechanisms can be saturated at 240 mg/kg. However, when administered orally at 10 mg/kg in C57BL/6 male mice, it shows very poor PK (3.6% oral bioavailability) consistent with very high in vivo clearance[1].

[1]. Touré BB, et al. Toward the Validation of Maternal Embryonic Leucine Zipper Kinase: Discovery, Optimization of Highly Potent and Selective Inhibitors, and Preliminary Biology Insight. J Med Chem. 2016 May 26;59(10):4711-23.