Prediction of Therapy Response and Prognosis in Leukemias by Flow Cytometric MDR Assays

Multidrug resistance (MDR) is an unwanted phenomenon, that may cause therapy failure in several neoplasms including hematological malignancies. The purpose of any type of laboratory MDR assay is to reliably identify such patients and to provide useful data to clinicians with a relatively short turnaround time. MDR can be multicausal and several previous data identified a group of transmembrane proteins - the ATP-binding casette (ABC) proteins - that may be involved in MDR in various hematological malignancies. The prototype of these proteins is the P-glycoprotein (Pgp, MDR1, ABCB1) that is a seven-membrane spanning transmembrane protein capable of extruding several cytotoxic drugs that are of key importance in the treatment of hematological disorders. Similarly other ABC proteins - Multidrug resistance associated protein 1 (ABCC1) and breast cancer resistance protein (ABCG2) are both capable of pumping out cytotoxic drugs. Here, we present flow cytometric methods to identify MDR proteins by antigen and activity assays. The advantage of flow technology is the short turnaround time and its relative easiness compared to nucleic acid based technologies. However, for the activity assays, it should be noted, that these functional tests require live cells, thus adequate results can only be provided if the specimen transport can be completed within 6 hours of sample collection. Identification of MDR proteins provides prognostic information and may modulate therapy, thus signifies a clinically useful information in the evaluation of patients with leukemias.