Characterization of tumorous and normal tissue using a pH-sensitive fluorescence indicator (5,6-carboxyfluorescein) in vivo.

The pH of the interstitial fluid of malignant tumours tends to be lower than that of normal tissue and is depressed by glucose administration. This study aimed to evaluate the effectiveness of dual-wavelength fluorometry using a pH-dependent indicator (5,6-carboxyfluorescein: 5,6-CF) for the detection of tumour areas in vivo. 5,6-CF has two main characteristics: it has two wavelengths of maximum absorbance (465 and 490 nm) and its fluorescence emission (maximum, 515 nm) increases as a function of pH in the physiological pH range of 6-7.4. The experimental study was performed on 28 CDF mice bearing lymphoid leukaemia P388 grafted subcutaneously. The tissue pH values were evaluated from the ratio of the fluorescence intensities (I490/I465) on the basis of a calibration curve linking pH measurements performed within the tissue using a microelectrode and values of the fluorescence intensity ratio. The fluorescence intensity reached its maximum value 60 min after 5,6-CF and glucose administration, followed by a plateau (90 min) when the ratios remained constant at 1.79 +/- 0.05 for normal tissue and 1.35 +/- 0.04 for tumour tissue (p less than 0.005). These results were correlated with the pH measurements in accordance with the calibration curve. This study validates the relevance of dual-wavelength fluorometry using a pH-dependent indicator to characterize in vivo normal and tumour tissues after glucose administration.