The first small-molecule kinase inhibitor approved as a cancer therapeutic, imatinib mesylate (Gleevec® treatment), has been amazingly successful. However, a thorough understanding of its molecular mechanism of action (MMOA) was not truly obtained until more than ten years after the molecule had been identified.
Understanding the MMOA for a small-molecule inhibitor can play a major role in optimizing a drug’s development. The way a drug actually works–the kinetics of binding to the target molecule and how it competes with endogenous substrates of that target–ultimately determines whether or not a a candidate therapeutic can be useful in the clinic. Drugs that fail late in development are extremely costly.
Drug research and discovery for neglected tropical diseases suffer from a lack of a large commercial market to absorb the costs of late-stage drug development failures. It becomes very important to know as much as possible, simply and quickly, about MMOA for candidate molecules for these diseases that are devastating to large populations.
The phosphotidylinositol 4-kinases (PI 4-kinases) generate phosphotidyl-4-phosphate (PI(4)P) from phosphotylinositol. PI(4)P is an important precursor for other phosphoinositides involved in signaling, such as PI(4,5)P2, which is the substrate of phospholipase C (PLC) and the precursor of DAG and insitol (1,4,5) triphosphate.
There are four different mammalian PI 4-kinases currently described, and these have been divided into two classes based on their sensitivities to wortmannin and adenosine. Type II PI 4-kinases (PI4K2A and PI4K2B) are not sensitive to wortmannin, but are inhibited by the nonspecific inhibitor adenosine; Type III PI 4-kinases (PI4KA and PI4KB) are sensitive to wortmannin.
The functions of the PI 4-kinases and their products are not fully understood. At least one study has shown that PI 4-kinases are important for the proper recycling of synaptic vesicles. The PI 4-kinase from Drosophila, four-wheel drive, is critical for contractile ring formation during cytokinesis. Other studies in yeasts and mammals have shown that PI 4-kinases localize to the Golgi, and in mammals might be critical for proper budding of vesicles from the Golgi. Additionally, type III PI 4-kinases appear to play a role in the replication of hepatitis C virus (HCV) and enteroviruses by participating in the formation of altered host membrane structures. Although, we have hints about their function, to really understand and dissect the precise roles of PI 4-kinases in cells, new tools, such as specific small-molecule inhibitors are required. Continue reading “Identifying and Profiling Inhibitors for PI 4-Kinases Using a Luminescent High-Throughput Screen”
Promega carries a large array of luminescent-based assays to measure cellular events such as viability, cytochrome P450 activity and apoptosis. Recently, we launched a new universal, homogeneous, high-throughput screening method called the ADP-Glo™ Kinase Assay, which measures kinase activity by quantifying the amount of ADP produced during a kinase reaction. While we already offer the Kinase-Glo™ Assays for assessing the quantity of ATP remaining after a kinase reaction, these assays are not ideal for use with low-activity kinases.