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Rhodamine Dyes as Potential Agents for Photochemotherapy of Cancer in Human Bladder Carcinoma Cells¹

Wellman Laboratories of Photomedicine, Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114

The phototoxicity in vitro of rhodamine 123 and tetrabromo rhodamine 123 (TBR) was compared, in order to assess their photochemotherapeutic potential. Exposure to 514.5-nm radiation from an argon ion laser caused phototoxicity in MGH-U1 bladder carcinoma cells previously treated with either dye at 10 µM for 30 min. As assessed by colony formation and cellular morphology, TBR was markedly more phototoxic than rhodamine 123, reflecting increased intersystem crossing of TBR to the triplet manifold via spin-orbital coupling induced by the heavy bromine atoms. Photoreactions of TBR very efficiently generated singlet oxygen (¹O₂) in solution; furthermore, irradiation of TBR-treated cells was significantly more toxic when performed in the presence of deuterium oxide, an enhancer of damage caused by ¹O₂. Retention of fluorescence in TBR-treated cells was enhanced by irradiation, indicating that a stable photoproduct may be formed in reaction with cellular components.

¹ This work was sponsored under the Office of Naval Research Contract N0014-86-K-0117 and by the Arthur O. and Gullan M. Wellman Foundation.

² To whom requests for reprints should be addressed.

Received 9/ 8/88. Revised 3/13/89. Accepted 4/20/89.

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