The change of intracellular pH is involved in the cisplatin-resistance of human lung adenocarcinoma A549/DDP cells.

We had reported that the intracellular pH (pHi) of human lung adenocarcinoma A549 cells, which is sensitive to cisplatin, was more acidic than that of cisplatin-resistant A549/DDP cells. The correlation between the change of the pHi and cisplatin-resistance of A549/DDP cells was further studied by altering pHi in consequence of the change of CO2 concentration of the incubator. The pHi alterations of the cells were monitored by using the fluorescence probe of BCECF-AM. The results indicated that the pHi was more alkaline at lower CO2 concentration (2% CO2 in the incubator) and more acidic at higher CO2 concentration (8% CO2 in the incubator) for both A549 and A549/DDP cells compared with those of both A549 and A549/DDP cells cultured at 5% CO2 as the normal condition. Accumulation of bodipy-cisplatin, a fluorescence probe used for drug resistance assays, in A549 cells incubated at 2%, 5%, and 8% CO2 was increased 8.4%, 17.4%, and 23.5% compared to A549/DDP cells, respectively. Intracellular sequestration and distribution of bodipy-cisplatin imaged by laser scanning confocal microscopy indicated that bodipy-cisplatin was more encapsulated in acidic compartments of A549/DDP cells as shown with acridine orange, a dye that specifically labels acidic organelles in the cells. These results can be further confirmed in liposome systems with different pH gradients. It is proposed from the above results that the change of pHi in especially more acidic compartments in A549/DDP cells involves their cisplatin resistance.