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 μg/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>spleen>intestine> stomach>liver>tumor>skin>skeletal muscles> lung>heart>blood>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.