OBJECTIVETo investigate the treatment efficiency of a new photodynamic therapeutic(PDT) drug synthesized by our laboratory toward MGC803 cells and related mechanisms.

METHODSBleaching method was used to evaluate the photostability of drug upon repetitive illumination. MTT assay was used to determine the ability of new drug killing MGC803 cells after PDT. Laser scanning confocal microscopy (LSCM) was applied to investigate the subcellular localization of drug in MGC803 cells (mitochondria and/or lysosomes). Hoechst staining and flow cytometry(Annexin V/PI double-staining) were performed to detect the death mode of MGC803 cells after PDT.

RESULTSThis new PDT drug had good stability to light irradiation after repetitive illumination. MTT assay showed no cytotoxicity towards MGC803 cells only by drug or only by irradiation(P>0.05), but intense lethal effect was observed with drug and light combination(P<0.05). The phototoxicity of medicine increased with the elevation of concentration, the LD50 was 1.74 μmol/L, and reaching plateau at the concentration of 3.12 μmol/L, even increasing the concentration. LSCM found that drug localized in lysosomes of MGC803 cells. Hoechst staining showed that the death mode of cells was mainly necrosis and Annexin V/PI double-staining proved this result further.

CONCLUSIONThis new PDT drug is an effective PDT sensitizer for MGC803 cells and the death mode of cells is mainly necrosis.