Chronic phase chronic myeloid leukemia patients with low OCT-1 activity randomized to high-dose imatinib achieve better responses and have lower failure rates than those randomized to standard-dose imatinib.

Background: The functional activity of the organic cation transporter 1 (OCT-1) protein (OCT-1 activity) is an excellent predictor of molecular response and progression-free survival in patients with newly diagnosed chronic phase chronic myeloid leukemia treated with imatinib as front-line therapy.

Design And Methods: In this study the predictive value of OCT-1 activity in patients treated with imatinib 400 mg/day or 800 mg/day was evaluated in relation to trough imatinib plasma levels assessed in 100 patients enrolled in the Tyrosine Kinase Inhibitor Optimization and Selectivity (TOPS) trial.

Results: The rate of major molecular responses by 24 months in patients on imatinib 400 mg/day was significantly higher in those with high OCT-1 activity than in those with low OCT-1 activity (low OCT-1 activity, 57% of patients; high OCT-1 activity, 100%; P < 0.

The poor response to imatinib observed in CML patients with low OCT-1 activity is not attributable to lower uptake of imatinib into their CD34+ cells.

The functional activity of the organic cation transporter 1 (OCT-1) protein in chronic myeloid leukemia (CML) mononuclear cells (MNCs) is highly predictive of molecular response in imatinib treated patients. Here we investigate whether the MNC OCT-1 activity (OA) provides a surrogate indicator of effective targeting of the more immature CD34(+) cells. While confirming our previous findings that high MNC OA is significantly associated with the achievement of major molecular response (MMR; P = .

Functional activity of the OCT-1 protein is predictive of long-term outcome in patients with chronic-phase chronic myeloid leukemia treated with imatinib.

Purpose: Organic cation transporter-1 (OCT-1) activity (OA), a measure of the OCT-1-mediated influx of imatinib into CML mononuclear cells (MNCs), is predictive of major molecular response (MMR) at 12 and 24 months in patients with untreated CML. We now report the impact of OA on loss of response, disease transformation, and survival after 5 years of imatinib.

Patients And Methods: OA is defined as the difference in intracellular concentration of carbon-14-imatinib with and without OCT-1 inhibition.

Dasatinib cellular uptake and efflux in chronic myeloid leukemia cells: therapeutic implications.

Purpose: The organic cation transporter OCT-1 mediates active transport of imatinib. We recently showed that low OCT-1 activity is a major contributor to suboptimal response in chronic myeloid leukemia (CML) patients treated with imatinib. The relevance of OCT-1 activity and efflux pumps in determining intracellular uptake and retention (IUR) of dasatinib was assessed.