Pharmacokinetic and pharmacodynamic end points during therapy in leukemia blasts obtained from 1 representative patient. Leukemic blasts were obtained before treatment (D0-Pre), after end of infusion clofarabine (D1-EOI), and on day 1 following clofarabine followed by CY 2 hours after CY EOI (D1 After), and clofarabine-TP was extracted and analyzed (▩) using high-pressure liquid chromatography. Samples were obtained prior to pretreatment of clofarabine (D1-Before), after end of infusion clofarabine (D1-EOI), after end of infusion cyclophosphamide (D1-EOI), and on day 1 following clofarabine followed by CY 2 hours after CY EOI (D1 After) for dATP quantitation (■). Additional samples were obtained for γH2AX (□) and analyzed as described in Figure 1.