Fluorescent verapamil analogue for monitoring acidic intracellular organelles in Multidrug resistant and sensitive cells

Resistance to chemotherapeutic agent is a major cause of treatment failure in patients with cancer. In many cases, the primaly mechanism leading to a multidrug-resistant phenotype is the plasma-membrane localized overexpression of drug efflux transporters, such as P-glycoprotein. However, acidic intracellular organelles seem also to participate in resistance to chemotherapeutic drugs and the determination of the pH of these organelles is of importance. In the present study we have used a new fluorescent derivative of verapamil, 2-2-diphenyl-5-[(methylaminomethyl)anthracene] pentanenitrile (EDP 96), and show that it is an efficient inhibitor of the P-gp-mediated efflux of anthracycline in K562 resistant cells. The fluorescence of EDP 96 is environmental and pH sensitive. EDP 96 is a weak base (pKa = 6.0) and its aceumulation into K562 cells is accompanied by a significant fluorescence increase due to its entry of the drug into acidic regions in the cells. We have used this properties to develop a new method to accurately determine the pH of acidic organelle. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.