Tissue autofluorescence spectroscopy: An intermediate endpoint for chemopreventive agents

We report on the fluorescence spectroscopy of a multicellular tumor spheroid treated and non-treated with β-all-trans retinoic acid. Following ten days of treatment with RA (10 ^-6M), reproducible fluorescent changes were measured using a Mediscience CD scanner. The most significant changes included an increase in emission at 520 nm in the RA treated spheroids when excited at 340 nm. When investigating fluorescence emission at 450 nm, a blue shift in the excitation profile was noted. Molecular alterations induced by RA and as measured by optical fluorescence spectroscopy may arise from qualitative and/or quantitative changes in a number of key molecules involved in cellular differentiation, proliferation and/or electron transfer, i.e. NADH at (450 nm emission), flavins (520 nm), or cytokeratins (520 nm). To further explore alterations of cytokeratins, immunohistochemical staining showed an increase in AE1 positive cells induced by RA which paralleled the increased 520 nm. signal. Our results indicate that certain vitamin derivatives are capable of modulating the intrinsic fluorescence profile emitted by neoplastic mucosa. Tissue autofluorescence may represent a significant marker for the biologic effect of cancer preventing agents in clinical trials.