The Change of Intracellular pH is Involved in the Cisplatin-Resistance of Human Lung Adenocarcinoma A549/DDP Cells

Abstract

We had reported that the intracellular pH (pH_i) 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 pH_i and cisplatin-resistance of A549 /DDP cells was further studied by altering pH_i in consequence of the change of CO₂ concentration of the incubator. The pH_i alterations of the cells were monitored by using the fluorescence probe of BCECF-AM. The results indicated that the pH_i 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 pH_i in especially more acidic compartments in A549/DDP cells involves their cisplatin resistance.

• A549/DDP Cells
• pH_i
• Cisplatin
• MDR