Effect of NBI-31772, a small-molecule inhibitor of the binding of insulin-like growth factor (IGF)-1 to IGF-binding proteins, on 125I-labeled IGF-1 binding to human osteoarthritic chondrocytes. Confluent chondrocytes were incubated with 1 × 105 dpm 125I-labeled IGF-1 with or without excess (150 nM) IGF-1 or 10 μM NBI-31772 for 1 hour at 4°C. Medium was harvested and cells were washed three times with Dulbecco's phosphate-buffered saline. Cells were lysed in 1 N NaOH. The percentage of 125I-labeled IGF-1 bound to the cells was calculated as dpm in NaOH-treated cells over total dpm. Data are expressed as the means and SEM of four replicates from a representative experiment (out of two independent cultures).