Does the same fit for all? A new method to determine pontnib plasmatic concentration

Background: Ponatinib is a 3rd generation tyrosine kinase inhibitor (TKI)very effective in Chronic Myeloid Leukemia (CML); nevertheless, cardiovascular (CV) adverse events represent a major issue during therapy and some groups proposed to reduce the drug dose for avoiding CV complications. It has been established that the therapeutic plasmatic concentration of Ponatinib must be ≥ 20 ng/mL, but little is known about the relationship between drug dose, plasmatic concentration and toxicity or response to treatment. Aim: We present here a new high resolution mass spectrometry-based method to determine Ponatinib plasma concentration. Method: We collected 15 peripheral blood samples from 11 CML patients (6 males and 5 female, mean age 44) in treatment with Ponatinib at different doses (from 45 mg daily to 30 mg weekly). The reason for switch to Ponatinib was toxicity in 4 and resistance in 7 cases. In the resistant cohort, Ponatinib allowed to reach major (MMR) and deep molecular response (DMR) in 28.5% and 71.5% of cases, respectively. Samples were analyzed by LC/HRMS (Ultimate 3000 LC system with TurboFlow technology coupled to a Q-Exactive system). After deproteinization with an acetonitrile/methanol solution (75/25), the samples were injected directly into the system, using Tracefinder® software for quantification analysis. The procedure was validated and successfully applied to the blood samples in routine laboratory analyses and can be considered fast and easy. Results: The method proves to be reliable with both precision and accuracy higher than 85% and showing a very good specificity and sensitivity. The therapeutic Ponatinib concentration of 20.0 ng/mL was reached in 73.3% of tested samples, regardless of the dosage scheme (15, 30 or 45 mg daily), except for 2 samples from the same patient treated with a very-low dose (30 mg weekly) because of a very-high cardiovascular risk. Conclusions: 1) even if on a small series, our data confirm the high response rate achievable with Ponatinib; 2) the achievement of the minimal therapeutic concentration regardless of the dosing regimen can explain the dose-independent Ponatinib efficacy also reported in the OPTIC Trial; 3) the method resulted to be accurate and easily applicable for a patient-tailored treatment in clinical practice. In the further steps, we’ll investigate if the cytochromeP450 or efflux-pump polymorphisms might condition the Ponatinib plasma levels.