Hydrazinonaphthalene and azonaphthalene thrombopoietin mimics are nonpeptidyl promoters of megakaryocytopoiesis

High-throughput screening for the induction of a luciferase reporter gene i n a thrombopoietin (TPO)-responsive cell line resulted in the identificatio n of 4-diazo-3-hydroxy-1-naphthalene-sulfonic acids as TPO mimics. Modifica tion of the core structure and adjustment of unwanted functionality resulte d in the development of (5-oxo-1,5-dihydropyrazol-4-ylidene)hydrazines whic h exhibited efficacies equivalent to those of TPO in several cell-based ass ays designed to measure thrombopoietic activity. Furthermore, these compoun ds elicited biochemical responses in TPO-receptor-expressing cells similar to those in TPO itself, including kinase activation and protein phosphoryla tion. Potencies for the best compounds were high for such low molecular wei ght compounds (MW < 500) with EC50 values in the region of 1-20 nM.