Legal Information Sold for research purposes under agreement from Pfizer Inc. Biochem/physiol Actions PD184352 (CI-1040) is a highly selective non-competitive inhibitor of MEK (MKK1; MAPK kinase) and the closely related MKK2. It has anti-cancer activity, suppresses the ERK pathway, and has been used along with other classes of inhibitors to establish embryonic stem cell lines.