Equilibrium binding of 5-(Sx8)-F in cultured acute leukemia cells and in blasts from two acute leukemia patients. Cells were incubated with graded concentrations of 5-(Sx8)-F (0.5 to 30 nmol/L), and then cell-associated 5-(Sx8)-F was measured by flow cytometry, as the mean fluorescence intensity in each sample determined by flow analysis of 10,000 cells. Nonspecific binding of 5-(Sx8)-F was determined in a parallel set of samples that were pretreated with 5 μmol/L NBMPR to occupy es transporter sites. The data were subjected to mass law analysis by the method of Scatchard to yield the K_d and B_max values (±SD) shown. (A) OCI/AML-2 cells; (B) blasts from AML patient H.M.; (C) CEM cells; (D) blasts from ALL patient T.Z.