PD-0325901 is an orally bioavailable inhibitor of mitogen-activated protein kinase kinases (MAPK/ERK kinases or MEK) with potential antineoplastic activity. MEK inhibitor PD325901, a derivative of MEK inhibitor CI-1040, selectively binds to and inhibits MEK, which may result in the inhibition of the phosphorylation and activation of MAPK/ERK and the inhibition of tumor cell proliferation. PD-0325901 is tested in clinical trials against non-small cell lung cancer, neurofibromatosis, melanoma and breast cancer.

Selumetinib (AZD6244 or ARRY-142886) is a potent, selective, and ATP-uncompetitive inhibitor of Ras-Raf-mitogen-activated protein kinase kinase (MEK1/2). This inhibition can prevent ERK activation, disrupt downstream signal transduction, and inhibit cancer cell proliferation and survival. Selumetinib has shown tumour suppressive activity in multiple rodent models of human cancer including melanoma, pancreatic, colon, lung, and breast cancers. AstraZeneca is responsible for development and commercialization of selumetinib.

Cobimetinib is an orally active, potent and highly selective small molecule inhibiting mitogen-activated protein kinase kinase 1 (MAP2K1 or MEK1), and central components of the RAS/RAF/MEK/ERK signal transduction pathway. It has been approved in Switzerland and the US, in combination with vemurafenib for the treatment of patients with unresectable or metastatic BRAF V600 mutation-positive melanoma. Preclinical studies have demonstrated that Cobimetinib is effective in inhibiting the growth of tumor cells bearing a BRAF mutation, which has been found to be associated with many tumor types. A threonine-tyrosine kinase and a key component of the RAS/RAF/MEK/ERK signalling pathway that is frequently activated in human tumors, MEK1 is required for the transmission of growth-promoting signals from numerous receptor tyrosine kinases. Cobimetinib is used in combination with vemurafenib because the clinical benefit of a BRAF inhibitor is limited by intrinsic and acquired resistance. Reactivation of the MAPK pathway is a major contributor to treatment failure in BRAF-mutant melanomas, approximately ~80% of melanoma tumors becomes BRAF-inhibitor resistant due to reactivation of MAPK signalling. BRAF-inhibitor resistant tumor cells are sensitive to MEK inhibition, therefore cobimetinib and vemurafenib will result in dual inhibition of BRAF and its downstream target, MEK. Cobimetinib specifically binds to and inhibits the catalytic activity of MEK1, resulting in inhibition of extracellular signal-related kinase 2 (ERK2) phosphorylation and activation and decreased tumor cell proliferation. Cobimetinib and vemurafenib target two different kinases in the RAS/RAF/MEK/ERK pathway. Cobimetinib is used for the treatment of patients with unresectable or metastatic melanoma with a BRAF V600E or V600K mutation. Cobimetinib is used in combination with vemurafenib, a BRAF inhibitor. Cobimetinib is marketed under the trade name Cotellic.

Trametinib is a reversible and specific inhibitor of mitogen-activated protein kinase kinases MEK1 and MEK2 which are involved in a RAS/RAF/MEK/ERK signaling pathway and control cell growth, survival, and differentiation. By inhibiting MEK1 and MEK2 trametinib blocks dual phosphorylation of ERK1/2 and stops cell cycling. In addition, trametinib blocks BRAF pathway in the cells with BRAF V600E mutations. Trametinib (as a single agent and in combination with dabrafenib) is approved for the treatment of unresectable or metastatic melanoma with BRAF V600E or V600K mutations.

Refametinib (RDEA-119, BAY- 869766) is a highly potent and selective inhibitor of mitogen-activated ERK kinase (MEK1/2) activity, Refametinib binds to an allosteric pocket adjacent to the ATP binding site, locking the enzyme in a catalytically inactive conformation. This compound is highly efficacious at inhibiting cell proliferation in several tumor cell lines in vitro. In vivo, Refametinib exhibits potent activity in xenograft models of cancers. Ardea Biosciences (a subsidiary of AstraZeneca) and Bayer HealthCare are developing refametinib for the treatment of cancer. The sulfonamide agent was originally developed by Valeant Pharmaceuticals International. Refametinib is in phase II development for hepatocellular carcinoma, and phase I/II development for pancreatic cancer and other solid tumours.

RO4987655 is a highly selective non-competitive small molecule inhibitor of MEK. RO4987655 has a strong anti-proliferation efficacy in various tumor cells including COLO205, HT29, QG56, MIA and C32 with IC50 values of 0.86nM, 1.7nM, 9.5nM, 3.3nM and 8.4nM, respectively. In addition, RO4987655 is found to have antitumor activity in a wide range of human cancer xenograft models. In the HT-29 human colon cancer xenograft, RO4987655 shows a strong inhibition of pERK formation as well as tumor regression. RO4987655 shows clinical activity in both patients with BRAF wild-type melanoma and BRAF V600-mutated melanoma. It is also efficacious in patients with KRAS-mutated non-small cell lung cancer but not KRAS-mutated colorectal cancer.

TAK-733 had been developed by Millennium Pharmaceuticals (subsidiary of Takeda) for the treatment of adult patients with advanced non-hematological malignancies. In 2015, Takeda discontinued this studies. TAK-733 is an inhibitor of MEK that exhibits anticancer chemotherapeutic activity. In tumor explant models, TAK-733 induces tumor regression. In colorectal cancer cells and melanoma cells, this compound suppresses cell growth. Additionally, TAK-733 decreases tumor growth and weight in animal models of lung cancer and melanoma.

DC-0623 is an orally active, selective and ATP-uncompetitive MEK inhibitor with potential antineoplastic activity. GDC-0623 specifically inhibits mitogen-activated protein kinase kinase (MEK or MAP/ERK kinase), resulting in inhibition of growth factor-mediated cell signaling and tumor cell proliferation. In a panel of mutant cancer cell lines, GDC-0623 inhibits cellular proliferation with EC50 values in the low nanomolar range. In vivo, GDC-0623 (40 mg/kg, p.o.) causes potent tumor growth inhibition (TGI) in mouse MiaPaCa-2 (120%), A375 (102%) and HCT116 (115%) xenografts. GDC-0623 had been in phase I clinical trials by Genentech, Inc. for the treatment of Advanced or Metastatic Solid Tumors. However, the clinical development of GDC-0623 was discontinued.

CI 1040 is an inhibitor of the mitogen-activated protein (MAP) kinase signal transduction pathway and has been shown to specifically inhibit MAP kinase kinase (MEK). CI 1040 was being developed by Parke-Davis (formerly a division of WarnerLambert, Now Pfizer) as an anticancer agent. It was the initial MEK inhibitor to undergo clinical evaluation based on promising preclinical activity. However, its development has been discontinued.