CYTOTOXIC EFFECT OF CALCEIN ACETOXYMETHYL ESTER ON HUMAN TUMOR-CELL LINES - DRUG-DELIVERY BY INTRACELLULAR TRAPPING

Calcein acetoxymethyl ester (calcein/AM) and some related cellular dye s with a cytoplasmic distribution were investigated with respect to ce llular hydrolysis, accumulation, efflux and cytotoxicity in a panel of established human cell lines, including multidrug resistant (MDR) phe notypes. At 0.1-1 mu g/ml, calcein/AM was highly cytotoxic against sev eral cell lines, even after short-term exposure (30 min). Calcein/AM i nduced no immediate loss (3 h) of membrane integrity and the drug was more active against low compared with high density plated cells, In ce ll lines with the MDR phenotype and in the renal carcinoma cell line A CHN, the drug was considerably less active, Non-esterified calcein had no effect and calcein/AM was significantly more potent than other str ucturally related fluorescein analogs and AM esters tested. Although M DR cell lines showed a decreased cellular hydrolysis and accumulation of the dye, there was no strict relationship between cytoplasmic calce in exposure and cytotoxic activity, The rate of efflux was low in the two most sensitive cell lines, the human lymphoma U-937-GTB and its vi ncristine (ver) resistant subline U-937/vcr10, while the remaining cel l lines showed similar biphasic efflux patterns, including cell lines of the MDR phenotype. The results show that calcein/AM has cytotoxic a ctivity against human tumor cell lines at low concentrations, The effe ct appears dependent on the intracellular trapping of the drug, althou gh the specific cellular target remains unknown, Due to its cytotoxic efficacy and unique principle of cellular drug delivery, further inves tigation of calcein/AM and related compounds as potentially new antica ncer agents seems warranted.