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Hypericin (HYP) is used after instillation as a diagnostic tool for the fluorescence detection of CIS in the human bladder.
In this study the in vitro cellular accumulation and intraspheroidal distribution of HYP and three analogues (OH1, OH2,
OH3) with gradually increasing hydrophilicity were studied. E-cadherin negative (T24-C1-) and E-cadherin positive
(T24-H3++) human bladder cancer cells were used.
We report that in the presence of FBS all compounds were taken up by the monolayer cells to the same limited extent,
whereas the overall intracellular accumulation was substantially higher when the incubation of the different dyes took
place using cell medium not supplemented with FBS. The results of this study therefore confirm the competition
between cellular uptake of HYP and analogues and binding to FBS constituents.
Investigating the permeation of the compounds in spheroids, it was found that all HYP analogues diffused dramatically
better through the three-dimensional cell layers than HYP itself. This enhanced ability of hydrophilic HYP analogues to
permeate through the cell layers in the presence of FBS can be explained in terms of a preferred binding to HDL as
compared to LDL. The results further show that all compounds, including LDL-binding HYP, substantially permeated
better in T24-C1- spheroids than in T24-H3++ spheroids. The data therefore support the hypothesis that a lowered cellular
cohesion is the key to understand the selective uptake of hypericin and its analogues in malignant urothelial cells.
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