In-beam light absorption measurement of anthracyclines in cells with a flow-through system

A flow-through cuvette in which cells attach as a monolayer to a quartz plate was developed for measurement of the light absorbance of anthracyclines in cells. Despite the drawback of a short path-length (of the order of the cell diameter), a dynamic flow-through set-up and baseline storage made it possible to measure intracellular absorbance and obtain spectral data for daunomycin and carminomycin. Stopping the flow and allowing the drug to equilibrate between medium and cells led to a 20% decrease of molar light absorption of cellular anthracycline, which permitted measurement of the total cellular concentration. Furthermore, accumulation and efflux kinetics were determined for H35 rat hepatoma cells. On the basis of the reported formation constant of the iro-complex of carminomycin, which is of the order of 10³⁴, we expected to find this complex within the cells. However, the spectrum of cellular drug did not show absorbance bands characteristic of the complex. A red shift and hypochromism were found in the daunomycin spectrum after intracellular binding, which corresponds with the spectral change observed after intercalation of daunomycin into DNA.