KTP LASER AND NEUTRAL RED PHOTOTHERAPY OF HUMAN SQUAMOUS-CELL CARCINOMA

Neutral red (NR) is a cationic, nontoxic vital dye employed as a histo logic stain for proliferating cells; it has been used clinically for p hotodynamic treatment of herpes simplex virus lesions. NR is selective ly taken up and concentrated by mitotic cells, an important characteri stic for more effective antineoplastic agents. In the present study, U CLA-SO-P3 human squamous carcinoma cells displayed minimal toxicity wh en incubated with up to 50 mu g/ml NR in the absence of light. However cells incubated with greater than 0.5 mu g/ml NR followed by exposure to KTP laser light at 532 nm exhibited nearly 100% tumor cell death. The degree of cell toxicity was proportional to NR dose and laser ligh t fluence. This study demonstrates that NR is an excellent cancer cell photosensitizer in vitro, and, after adding additional in vivo precli nical testing, may prove to be a useful agent in photodynamic destruct ion of head and neck tumors.