Isolation and structures of novel fungal metabolites as chemokine receptor (CCR2) antagonists

The chemokine receptor, CCR2, is predominantly expressed on monocytes/rnacrophages, and on a subset of memory T cells. It binds to several CC type chemokines of the monocyte chemoattractant protein (MCP) family of which MCP-1 exhibits the highest affinity. CCR2/MCP-1 expression/association in monocyte/macrophage/T cells has been associated with inflammatory processes such as rheumatoid arthritis, multiple sclerosis and atherosclerosis. Neutralization of CCR2 with either a peptide or receptor antagonist results in the prevention of joint swelling in rodent models of arthritis. In this paper, bioassay-guided discovery of CCR2 receptor antagonists derived from natural product extracts are reported. These antagonists belong to two main classes exemplified by bis-thiodiketopiperazines and cytochalasins. Six compounds, including emestrin, two new emestrin analogs, and chaetomin represent the first group of compounds. These compounds inhibited the binding of MCP-1 to CCR2 (CHO membrane) with IC50 values of 0.8 to 9 mu M and exhibited good activity in a whole cell assay using MCP-1. and human monocytes with IC50/s ranging from 4 similar to 9 mu M. Cytochalasins A and B represented the second group and inhibited the binding activity with IC50 values of 5 and 188 mu M, respectively. This is the first report of natural product antagonists of the CCR2 receptor.