Preferential cytotoxicity for multidrug-resistant K562 cells using the combination of a photosensitizer and a cyanine dye

The cyanine dye 1,1',3,3,3',3'-hexamethylindodicarbocyanine iodide (TPPS2) protects K562 leukemia cells from photodynamic membrane damage caused by ci s-di (4-sulfonatophenyl) diphenylporphine (TPPS2) and 420 nm light. This wa velength of light is chosen because it is absorbed by TPPS2, but not by HID C. The photodynamic system studied may be useful as a model for antineoplas tic therapy. A subline of K562 leukemia (K562/DOX), expressing the multidru g-resistance (MDR) phenotype, is found to accumulate smaller amounts of HID C than the parent cell line and thus has less photoprotection. In the absen ce of added HIDC, the K562/DOX cell line is more resistant to photodynamic cytotoxicity than the K562 cell line. The resistance of the K562/DOX cell l ine is not due to a smaller accumulation of TPPS2 than the K562 cell line. However? when both cell lines are incubated with HIDC and TPPS2, and then e xposed to light, the K562/DOX cell line becomes more sensitive to photodyna mic cell damage than the K562, cell line. The combination of a photosensiti zer with a cationic or lysomorphotropic photoprotector represents a novel s trategy for the eradication of malignant cells expressing the MDR phenotype . (C) 2000 Elsevier Science S.A. All rights reserved.