In vitro activity: PF0325901 shows higher permeability than CI-1040, another MEK inhibitor. PD0325901 should be able to achieve higher systemic exposures than CI-1040. PD0325901 is exquisitely specific and highly potent against purified MEK, revealing a Kiapp of 1 nM against activated MEK1 and MEK2. PD0325901 is roughly 500-fold more potent than CI-1040 with respect to its cellular effects on phosphorylation of ERK1 and ERK2, displaying subnanomolar activity. PD0325901 prevents the growth of melanoma cell lines. PD0325901 inhibits the growth of TPC-1 cells and K2 cells with GI50 of 11 nM and 6.3 nM, respectively.  PD0325901 significantly prevents the the growth of PTC cells harboring a BRAF mutation at very low concentration (10 nM) and only moderately increases the growth of the PTC cells carrying the RET/PTC1 rearrangement at the same concentration. PD0325901 effectively inhibits the phosphorylation of ERK1/2 in multiple PTC cell lines.

Kinase Assay: Incorporation of 32P into myelin basic protein (MBP) is assayed in the presence of a glutathione S-transferase fusion protein containing p44MAP kinase (GST-MAPK) and a glutathione S-transferase protein containing p45MEK (GST-MEK). The assay solution contained 20 mM HEPES, pH 7.4, 10 mM MgCl2, 1 mM MnCl2, 1 mM EGTA, 50 mM [gamma-32P]ATP, 10 mg GST-MEK, 0.5 mg GST-MAPK and 40 mg MBP in a final volume of 100 mL. Reactions are stopped after 20 minutes by addition of trichloroacetic acid and filtered through a GF/C filter mat. 32P retained on the filter mat is determined using a 1205 Betaplate. PD0325901 is assessed at various dose ranges in order to determine dose response curves.

Cell Assay: PTC cells (1 × 104) are seeded in 24-well plates with 1 mL of medium for 4 days in a 37 °C incubator. MEK inhibitor PD0325901 at varying concentrations is added to the cells in triplicate on day 0. MTT dissolved in 0.8% NaCl solution at 5 mg/mL is added to each well (0.2 mL) on day 2 to test GI50 or every day for cell growth curves. The cells are incubated at 37 °C for 3 hours with MTT. The liquid is then aspirated from the wells and discarded. Stained cells are dissolved in 0.5 mL of DMSO and their absorption at 570 nm is measured using a Synergy HT multidetection microplate reader. For GI50, cell growth is calculated as 100 × (T − T0)/(C − T0), where T is the optical density of the wells treated with inhibitors after a 48-hour period, T0 is the optical density at time zero, and C is the control optical density with DMSO only.