Optimization of methods for the detection of BCR-ABL activity in Philadelphia-positive cells

ObjectiveThe recent success in treating chronic myeloid leukemia (CML) with tyrosine kinase inhibitors (TKI), such as imatinib mesylate (IM), has created a demand for reproducible methods to accurately assess inhibition of BCR-ABL activity within CML cells, including rare stem and progenitor cells, either in vitro or in vivo. The purpose of this study was to develop an enzyme-linked immunosorbent (ELISA) method to measure total tyrosine phosphorylation (P-Tyr) in small samples of cells that express BCR-ABL and to compare to more established methods.Materials and MethodsThe assay was first validated in BCR-ABL wild-type and mutant vs BCR-ABL–negative cell lines. P-Tyr levels were then measured by ELISA in primary CD34+ CML cells treated with IM.ResultsIn vitro exposure to TKI resulted in decreases in the level of P-Tyr, in both BCR-ABL–positive cell lines and primary CD34+ CML samples, which were comparable to the reduction in P-Tyr by flow cytometry and phosphorylation of CrkL by either Western blot or flow cytometry.ConclusionWe have developed an accurate ELISA method to measure BCR-ABL activity within Ph+ cells, which is comparable to other in vitro BCR-ABL assessment techniques in terms of sensitivity and could be adapted for high throughput.