4-(4-Chlorophenyl)-4-hydroxy-N-methyl-α,α-diphenyl-1-piperidinebutanamide; R 20905

A metabolite of Loperamide; a new and improved PET radiotracer for imaging P-gp function. N-Desmethyl loperamide is a prodrug of loperamide, which is a peripherally acting μ-opioid receptor agonist. It has been shown to be effective in reducing the uptake of radiation in wild-type mice. This drug also inhibits p-glycoprotein (p-gp), and has been shown to reduce the uptake of pyridinium ions and amide substrates. N-Desmethyl loperamide has been shown to have anticancer properties, including resistance to radiation, inhibition of tumor growth and metastasis, and induction of apoptosis, which may be due to its ability to inhibit cellular proliferation and induce cell death. The mechanism by which this drug functions is not yet clear but it may involve inhibition of the expression or function of p-gp or other efflux pumps in cells that are sensitive to these drugs.