Selumetinib (AZD6244) (AZD6244) is an effective, specific inhibitor of MEK1 and ERK1/2 phosphorylation (IC50: 14/10 nM).

The IC50 of Selumetinib (AZD6244; ARRY-142886) was 14 nmol/L against purified MEK1. Treatment with ARRY-142886 resulted in the growth inhibition of several cell lines containing B-Raf and Ras mutations but had no effect on a normal fibroblast cell line [1]. For the time course and dose-response experiments, primary 2-1318 cells were treated with vehicle and escalating doses of Selumetinib (AZD6244) for 24 and 48 h. A 50% reduction in cell viability was seen at a dose of <0.5 μmol/L after 48-h incubation [2]. 5 of 31 breast cancer cell lines and 15 of 43 NSCLC cell lines were sensitive against Selumetinib (IC50s: <1 micromol/L) [3].

When dosed orally, ARRY-142886 was capable of inhibiting both ERK1/2 phosphorylation and growth of HT-29 xenograft tumors in nude mice. Tumor regressions were also seen in a BxPC3 xenograft model. In addition, tumors remained responsive to growth inhibition after a 7-day dosing holiday [1]. AZD6244, when given p.o. to mice bearing these xenografts, resulted in a dose-dependent inhibition of tumor growth [2]. In vivo administration of AZD6244, doxorubicin, or the combination of AZD6244 and doxorubicin in mice bearing 5-1318 HCC xenografts resulted in approximately 52%, 12%, and 76% growth inhibition, respectively [4].

NH2-terminal hexahistidine tagged, constitutively active MEK1 was expressed in baculovirus-infected Hi5 insect cells and purified by immobilized metal affinity chromatography, ion exchange, and gel filtration. The activity of MEK1 was assessed by measuring the incorporation of [γ-33P]phosphate from [γ-33P]ATP onto ERK2. The assay was carried out in a 96-well polypropylene plate with an incubation mixture (100 μL) composed of 25 mmol/L HEPES (pH 7.4), 10 mmol/L MgCl2, 5 mmol/L β-glycerolphosphate, 100 μmol/L sodium orthovanadate, 5 mmol/L DTT, 5 nmol/L MEK1, 1 μmol/L ERK2, and 0 to 80 nmol/L compound (final concentration of 1% DMSO). The reactions were initiated by the addition of 10 μmol/L ATP (with 0.5 μC k[γ-33P]ATP/well) and incubated at room temperature for 45 min. An equal volume of 25% trichloracetic acid was added to stop the reaction and precipitate the proteins. Precipitated proteins were trapped onto glass fiber B filter plates, excess labeled ATP was washed off with 0.5% phosphoric acid, and radioactivity was counted in a liquid scintillation counter. ATP dependence was determined by varying the amount of ATP in the reaction mixture. The data were globally fitted using SigmaPlot. Values were calculated using the following equation for noncompetitive inhibition: v = [Vmax × S / (1 + I / Ki)] / (Km + S) [1].

Primary HCC cells were plated at a density of 2.0 × 10^4 per well in growth medium. After 48 h in growth medium, the cell monolayer was rinsed twice with MEM. Cells were treated with various concentrations of AZD6244 (0, 0.5, 1.0, 2.0, 3.0, and 4.0 μmol/L) for 24 or 48 h. Cell viability was determined by the MTT assay. Cell proliferation was assayed using a bromodeoxyuridine kit as described by the manufacturer. Experiments were repeated at least thrice, and the data were expressed as mean ± SE [2].

HT-29 human colon carcinoma or BxPC3 human pancreatic tumor fragments were implanted s.c. in the flank of nude mice and allowed to grow to 100 to 150 mg. Mice (n = 10 per group) were randomized to treatment groups to receive vehicle (10 mL/kg and 10% ethanol/10% cremophor EL/80% D5W) or ARRY-142886 (10, 25, 50, or 100 mg/kg, oral, BID) on days 1 to 21. Tumors [(W^2 × L) / L] were measured twice weekly. Tumor growth inhibition was calculated as 1 ? (tumor sizetreated / tumor sizevehicle) on each measurement day. Four hours after the last dose on day 21, three mice per group were euthanized to evaluate pharmacokinetic/pharmacodynamic responses. Tumors were excised and flash frozen. Homogenates were analyzed for phospho-ERK1/2 and ERK1/2 expression by Western blotting as described above. For the HT-29 study, monitoring of tumor regrowth was continued for the remaining seven mice per group until tumors reached 1,000 mm^3, when mice would be sacrificed. There were two BxPC3 tumor xenograft studies. For the first study, one group of mice was treated with the clinical standard of care, gemcitabine, at 160 mg/kg, i.p., every 3rd day for a total of four doses. This dose was determined to be the maximum tolerated dose for gemcitabine in the BxPC3 model on this dosing schedule. To evaluate whether previously treated tumors would be refractory to a second cycle of treatment, a second BxPC3 xenograft study was carried out. Mice were treated with vehicle or ARRY-142886 at 25 or 50 mg/kg, BID, for 21 days. Treatment was stopped and tumors were allowed to grow for an additional 7 days before treatment resumed for another 21-day cycle [1].