Abstract: Compounds are provided that complex with the modulating domain of erythropoietin receptor (EPO-R) for use with EPO-R to determine the presence of EPO-R, the ability of other molecules to bind to the modulating domain in competitive assays and to induce a signal by EPO-R into a cell when bound by the subject compounds in a physiological environment. The compounds are characterized by having a six-membered heterocyclic ring comprising at least one nitrogen atom and include substituted triazolopyrimidine, pyridazinone, pyridine and piperidine.

Abstract: Oligopeptides having an amino acid sequence corresponding to a receptor's extracellular domain, and having sequence similarity to regulatory peptides from MHC class I antigens, enhance the physiological response of ligand binding to the corresponding receptor. The oligopeptides are used in diagnosis and therapy of diseases that involve inadequate or inappropriate receptor response as well as in the screening of drug candidates that affect surface expression of receptors. Also useful for drug screening is a modified receptor molecule, where the sequence corresponding to the regulatory peptide is modified or deleted.