Restoration of sensitivity to STI571.

Phosphotyrosine (p-Tyr) immunoblot of LAMA84-s (S), LAMA84-r (R), and resistant cells grown in the absence of STI571 for 234 days (R^234d) exposed to 1 μ μM STI571 for 2 hours, as compared with nonexposed aliquots. Densitometric analysis of the p210 Bcr-Abl band corrected for the actin control showed a 2.1-fold decrease in phosphorylation of LAMA84-s and a 3.0-fold for the LAMA84-R^234d line upon treatment with STI571. As previously shown,4 LAMA84-r cells kept continuously in the presence of STI571 have an elevated phosphotyrosine content.