Fluorescence Imaging of Human Cells with a Novel Conjugate of the Antifungal Nystatin

The antitumor activity of antibacterial and antifungal compounds has been of interest in the past. In several investigations glycopeptide antibiotics like bleomycin and antifungal agents like itraconazole have shown direct positive results whereas antifungal polyenes such as amphotericin B have been shown to potentiate the effects of antitumor agents. After having investigated the fluorescence-marked antibacterial glycopeptides vancomycin and ramoplanin on various malignant and healthy human cells in previous studies, the present work is focused on the antifungal polyene nystatin. We coupled nystatin to the fluorescent dye fluorescein isothiocyanate (FITC). After confirming the correct mass by mass spectrometry the effect of the conjugate on nine different human cell lines (two benign and seven tumor cell lines) was examined. The character of the uptake was determined by confocal laser scanning microscopy (CLSM) and the uptake was quantified by fluorescence activated cell sorting (FACS). The addition of propidium iodide (PI) allowed for detection and quantification of cell membrane disruption caused by the fluorescein-nystatin conjugate. Uptake of the conjugate was found to vary among the nine cell lines investigated. Conjugate uptake was strongest after 6 hours in most cell lines. Only the two prostate carcinoma cell lines PC3 and LNCaP showed further increase in uptake after long-time (24h) incubation. PI staining in general correlated well with the conjugate FITC staining values. The Colo205 colon carcinoma cell line and the U373 and LN18 glioblastoma cell lines exhibited very low conjugate uptake and PI staining. The results indicate that this conjugate shows potential for future imaging studies on certain human cancer cells.