Rhodamine‐123 as a new photochemosensitizing agent with the argon laser: “Nonthermal” and thermal effects on human squamous carcinoma cells in vitro

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Abstract
A human squamous carcinoma cell line (P3) was first exposed to a nontoxic dose of Rhodamine‐123 (1 μg/m1 for 1 hour), then subjected to treatment with a single mode argon laser at 514.5 nm. The temperature and energy levels delivered to the target cells were determined by a reproducible method of dosimetry. Cell viability was assessed by the trypan blue exclusion test. Cell duplication and DNA synthesis were measured by the incorporation of 3H‐thymidine at 6 and 24 hours post‐treatment. The results indicate that Rhodamine‐123 at nontoxic doses of 1 μ/m1 enhanced the tumoricidal effects of the argon laser at reduced temperatures as low as 40 °C. Furthermore, at physiological temperature ranges as low as 28 to 39 °C, an immediate and/or delayed inhibition of cell duplication was demonstrated, while cell viability was not affected. These observations, suggest that Rhodamine‐123 can be used effectively as a chemosensitizing agent in the treatment of human tumor cells with the argon laser at 514.5 nm. This new technique of tumor cell targeting by Rhodamine sensitization and specific laser treatment may offer real advantages without the extreme photosensitivity associated with hematoporphyrin derivatives.