Plasma Tyrosine Kinase Activity as A Potential Biomarker In BCR-ABL1-Targeted Therapy

In targeted therapy using tyrosine kinase (TK) inhibitors (TKIs), measurement of TK activity could help in diagnosis, identification of potential responders, and monitoring of treatment efficacy. Here we evaluated the feasibility of measuring circulating TK (cTK) activity in plasma in patients with BCR-ABL1-positive leukemia.

Study subjects included 46 patients with newly diagnosed chronic myelogenous leukemia (CML), 24 with multidrug-resistant CML, 24 with BCR-ABL1-positive acute lymphocytic leukemia (ALL), as well as 38 healthy donors. Plasma cTK activity was measured using a chromogenic universal TK assay in which plasma samples and standards were added to wells of a microtiter plate that were coated with synthesized poly(Glu-Tyr) peptide substrates. Specific TK activity was measured by spectrophotometry, with or without addition of TKIs.

cTK activity was significantly higher in CML (median 801.93 U/mL, range 18.10–3932.30 U/mL) and BCR-ABL1-positive ALL patients (median 659.55 U/mL, range 0–1626.90 U/mL) than in healthy donors (median 82.85 U/mL, range 0.63–852.80 U/mL) (P<0.001). Plasma cTK activity was closely correlated with cellular BCR-ABL1 kinase activation, as indicated by phosphorylation of the downstream signaling proteins CRKL (P<0.001) and STAT-5 (P=0.003). However, cTK activity was independent of BCR-ABL1 transcript level and BCR-ABL1 mutation type. Plasma cTK activity was inhibited by imatinib and dasatinib in ex vivo studies; this inhibition was severely diminished in patients harboring T315I mutations.

cTK activity is readily detectable in plasma or serum samples without pre-cleaning or enrichment. Ex vivo testing measuring the effect of TKIs on plasma cTK activity thus hold promise as drug sensitivity tests for predicting and monitoring response to specific TKIs.

Yeh:Quest Diagnostics Inc.: Employment. Abdool:Quest Diagnostics Inc.: Employment. Bruey:Quest Diagnostics Inc.: Employment.