Biodistribution of rhodamine-123 in nude mice heterotransplanted with human squamous cell carcinomas.

Rhodamine-123 uptake and release was determined in nu/nu mice heterotransplanted with P3 human squamous carcinomas to assess its value as an in vivo laser photosensitizer for treatment of solid tumors. Following intraperitoneal injection of Rh-123 (1 micrograms/g of body weight), mice were killed at 2, 4, 6 and 24 hours, and 3 and 7 days postinjection. The peak concentrations of Rh-123 per milligram of tissue measured by fluorescence spectrophotometry was distributed as follows: kidneys greater than spleen greater than intestine greater than stomach greater than liver greater than tumor greater than skin greater than skeletal muscles greater than lung greater than heart greater than blood greater than brain. No preferential uptake or retention of Rh-123 by tumors was observed. However, a longer retention with higher concentrations of the dye was seen in normal skin as opposed to P3 tumors from 4 hours to 7 days postinjection with Rh-123. The elimination of Rh-123 was rapid, with the dye falling to less than 2% of peak concentration at 7 days postinjection. Knowledge of Rh-123 biodistribution in tumors and other tissues suggests that optimal timing after injection of this dye may allow selective photodiagnosis and photodynamic therapy of tumors with the argon laser.