Stephen John Davies

Drug Targeting to Monocytes and Macrophages Using Esterase-Sensitive Chemical Motifs

The therapeutic and toxic effects of drugs are often generated through effects on distinct cell types in the body. Selective delivery of drugs to specific cells or cell lineages would, therefore, have major advantages, in particular, the potential to significantly improve the therapeutic window of an agent. Cells of the monocyte-macrophage lineage represent an important target for many therapeutic agents because of their central involvement in a wide range of diseases including inflammation, cancer, atherosclerosis, and diabetes. We have developed a versatile chemistry platform that is designed to enhance the potency and delivery of small-molecule drugs to intracellular molecular targets. One facet of the technology involves the selective delivery of drugs to cells of the monocyte-macrophage lineage, using the intracellular carboxylesterase, human carboxylesterase-1 (hCE-1), which is expressed predominantly in these cells. Here, we demonstrate selective delivery of many types of intracellularly targeted small molecules to monocytes and macrophages by attaching a small esterase-sensitive chemical motif (ESM) that is selectively hydrolyzed within these cells to a charged, pharmacologically active drug. ESM versions of histone deacetylase (HDAC) inhibitors, for example, are extremely potent anticytokine and antiarthritic agents with a wider therapeutic window than conventional HDAC inhibitors. In human blood, effects on monocytes (hCE-1-positive) are seen at concentrations 1000-fold lower than those that affect other cell types (hCE-1-negative). Chemical conjugates of this type, by limiting effects on other cells, could find widespread applicability in the treatment of human diseases where monocyte-macrophages play a key role in disease pathology.

Monocyte and macrophage selective anti-inflammatory kinase inhibitors

Appending appropriate esters to anti-inflammatory compounds leads to monocyte/macrophage selectivity. This has been demonstrated in p38α MAP kinase in which we observe differential inhibition of phosphorylation of the substrate MAPKAPK2 in stimulated cells. This selectivity is due to differential expression of carboxylesterases within the cells, which cause the active form of the compounds to accumulate with the cells.

Abstract 1242: A broad activity screen in support of a chemogenomic map for kinase signaling research and drug discovery

Since protein kinases play a fundamental role in cell signaling, especially as components of critical growth and differentiation pathways linked to cancer, kinase inhibitors have been commercialized as both therapeutics and research tools. This has been enabled to some degree by the chemical tractability of protein kinase ATP binding pockets, the automation of activity measurements, and the correlation of in vitro, cellular, and in vivo activities. Despite the development of a number of efficacious kinase inhibitors, the strategies for rational design of these compounds have been limited by target promiscuity. In an effort to better understand the nature of structure and activity across the kinome, especially as it relates to off-target effects, we screened a well-defined collection of kinase inhibitors using “gold standard” radiometric assays for inhibitory activity toward 234 kinases, which represent all branches of the kinome tree. We screened 158 small molecules initially identified in the literature as potent and specific inhibitors of kinases important from a therapeutic target as well as a signal transduction biology perspective. We performed hierarchical clustering of these benchmark kinase inhibitors based upon their kinome activity profiles and illustrate how they relate to chemical structure similarities; this provides new insights into inhibitor specificity and potential applications for probing new targets. Additionally, we developed a selectivity score for each kinase which we believe reflects general binding site accessibility to small molecules. Knowledge of such scoring indices can play an important role in therapeutic target selection and drug discovery strategies. Using this broad set of data, we provide a framework for assessing polypharmacology. Examples will be shown to demonstrate that we not only identify likely off-target inhibitor activities but also potential new uses for known small molecules. Moreover we demonstrate how activity data can be used to help explain the effects of small molecules observed in phenotypic screening. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1242. doi:1538-7445.AM2012-1242