Inhibition of the downstream pathways of the IGF-1R by PPP. (A) IGF-1R isolated from 5T33MM cell lysates was incubated with different concentrations of PPP for 30 minutes, before kinase activation. IGF-1R autophosphorylation was detected by a sandwich ELISA. (B) 5T33MM cells were preincubated with 1 μM PPP for 4 hours before stimulation with IGF-1 (100 ng/mL for 10 minutes). Equivalent amounts of lysates were immunoblotted with anti–P-ERK1/2 and reblotted with anti-ERK1/2 to confirm equal loading. One experiment representative of 3 is shown.