Detection of ERK and phospho-ERK in leukemic marrow samples from 4 selected patients obtained before therapy (baseline) and at weekly intervals during R115777 administration.

ERK expression was detected before and after treatment in marrow samples from all 4 patients, and phospho-ERK as detected in 3 samples at baseline. Of note, phospho-ERK disappeared following R115777 treatment in samples from 2 of the 3 patients whose marrow populations exhibited baseline phospho-ERK expression.