Figure 1.

Changes in P-glycoprotein function during chemotherapy in two B-cell lymphoma canine patients. P-glycoprotein activity, as determined by the calcein assay (MAF values), was monitored during therapy (treatments are indicated by arrows). Flow cytometry histograms show the calcein fluorescence of cancer cells incubated with (blue) and without (red) the Pgp inhibitor verapamil. (a) Patient 1 showed the typical kinetics of acquired multidrug resistance. (b) In the case of Patient 2, MDR was reversed by a 33-day-long (unplanned) drug holiday. The immunophenotype of the lymphoma remained identical during the treatment in both case (results show data of the final measurement).