PD98059 – THE MOST COMMON MEK INHIBITOR

by Selleckchem | Mar 20 2012

Introduction: The Mitogen-Activated Protein Kinase

Protein kinases are responsible for much of the activation, control and regulation of the cell cycle processes, such activities as cell division, cell migration, gene transcription and apoptosis. Typical a kinase cascade exists where a trans membrane kinase is activated by an extra cellular factor such as growth factors, mitogens, stress factors and cytokines. The top level of the MAP kinases are referred to as MAP kinase kinase kinases and examples are the Raf series of proteins, MLK3, TAK, MEKK1, 2,3 &4 which trigger signaling cascades down to the next level of proteins usually located either bonded to the inner membrane or in the cell cytosole. Second level kinases examples are MEK1/2 or 5, MKK3/4 or 6/7. The last level MAP kinases are usually located in the mitochondria / nucleus membranes or in either the mitochondria / nucleus themselves. The extensive nature of the MAPK pathways means that they are significantly involved in the normal and abnormal growth patterns of the mammalian system. In terms of the abnormal activity the MAPK’s have been linked to a variety of different cancer forms which indicates that inhibition of the MAPK levels to be crucial in future treatment profiles. One of the developed molecules for the specific inhibition of the MAPK level is PD98059, which is a specific inhibitor for the MEK1&2 upstream of ERK a key regulator of cellular growth, differentiation and developmental processes.

PD98059: Properties and Availability

PD98059 MEK1 inhibitor consists of a benzopyranone and methoxyphenyl linked segments and is used extensively in research for the inhibition of MEK1 and MEK2. Sensitivity of the PD98059 MEK2 inhibitor is 10 fold lower than for MEK1 but specificity is very high with no other kinases demonstrating activity. PD98050 IC50 has been determined for the purified MEK proteins and is 4 µM for MEK1 and 50µM for MEK2. PD98059 prices from a large number of PD98059 suppliers varies greatly ($44 - $286 for just 5 mg) while the purity does not reflect the cost (99% pure - $44; 95% pure – $286). Caution is recommended for researchers wanting to buy PD98059. Like most tyrosine kinase inhibitors this molecule is poorly soluble in water limiting the buffer concentrations to 50-100 µM. However, PD98059 solubility in ethanol reasonable at 1 mg/ml and in DMSP 25 mg/ml solutions can be achieved. Expiration data on this molecule is limited but standard conditions (-20°C / 2 years) is recommend for PD98059 stability.

PD98059: Preclinical Investigations

Developed in the mid 1990’s preclinical investigation with this molecule PD98059 revealed that it was potently active against the MAP Kinases, more specifically the MEK1/2 isoforms. Also demonstrated was that PD98059 effective against the mutant forms of MEK1/2 (S217E, S221E) [1]. Conversely PD98059 irreversible inhibition of these kinases was dependant on the strength of the signal received from the upstream proteins in the cascade. Sufficiently strong signals were found to be sufficiently powerful to over ride the inhibition and signaling proceeded as normal. In addition to the murine models PD98059 was tested in vitro on UM-SCC-1 cell line derived from a head and neck cancer forms, PD98059 did not slow the rate of tumour progression but significantly reduced the migration of cells from the primary tumour site. Poor pharmacokinetics and solubility of PD98059 inhibited the in vivo use of this molecule but liposomes capsules were used successfully in animal models [2] Used in research for mapping out the molecular mechanisms of the protein kinase PD98059 has become invaluable in determining the aspects of the cell cycle mechanism [3]. In light of these results PD98059 was not carried forward into PD98059 clinical trials as a single therapy drug. Tested against in vitro models in combination with other protein kinase blockers demonstrated a mold anti tumor activity but efficacy was compromised due to extensive redundant factors [3;4].

References

1. Alessi DR, Cuenda A et al. PD 098059 is a specific inhibitor of the activation of mitogen-activated protein kinase kinase in vitro and in vivo. J Biol Chem 1995; 270(46):27489-27494.

2. Simon C, Hicks MJ et al. PD 098059, an inhibitor of ERK1 activation, attenuates the in vivo invasiveness of head and neck squamous cell carcinoma. Br J Cancer 1999; 80(9):1412-1419.

3. Cross DA, Smythe C. PD 98059 prevents establishment of the spindle assembly checkpoint and inhibits the G2-M transition in meiotic but not mitotic cell cycles in Xenopus. Exp Cell Res 1998; 241(1):12-22.

4. Moon DO, Park C et al. PD98059 triggers G1 arrest and apoptosis in human leukemic U937 cells through downregulation of Akt signal pathway. Int Immunopharmacol 2007; 7(1):36-45.