Description Application Calcein-AM is a non-fluorescent cell permeable derivative of calcein that becomes fluorescent upon hydrolysis within the cytosol. Calcein-AM is used as a cell viability stain and as a neutral substrate for multidrug (MDR) efflux transporters. Non-fluorescent cell permeable derivative of calcein, becomes fluorescent on hydrolysis. Used as a neutral substrate for multidrug resistance protein, MRP; employed in tumor research.