Carbidopa: a selective Ah receptor modulator (SAhRM).

The aryl hydrocarbon receptor (AhR) was discovered as the intracellular receptor that bound with high affinity to the environmental toxicant 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD), and the AhR is required for mediating the toxicity induced by TCDD. Subsequent studies show that the AhR binds structurally diverse chemicals including plant-derived compounds that promote health and several AhR-active pharmaceuticals that exhibit anticancer activity. In this issue, there is a report that carbidopa, a drug used for treating Parkinson's disease, is also an AhR ligand, and this compound inhibits pancreatic cancer cell and tumor growth. These results are consistent with activities of other AhR-active compounds that inhibit carcinogenesis. Like carbidopa, these chemicals are selective AhR modulators with potential clinical applications that are AhR-dependent.