Female C57BL/6 x DBA/2 F1 mice were inoculated with Sarcoma 180 ascites tumor and Pyronin Y (PY) was injected i.p. for 6 days. The dose 15 mg/mouse caused 50% increase in life span.

The long-term survival (clonogenicity) studies were carried out on CHO cells. Exponentially growing CHO cells were seeded at a concentration of 100 and 1000 cells in Petri dishes. 4h were allowed for cell reattachment before Pyronin Y (PY) was added directly to these cultures to give various concentrations. After incubation for 4 h, the cells were washed 2 times with Hanks' balanced salt solution and refed with a fresh prewarmed medium. Stationary CHO cultures were prepared by growing cells to confluence followed by the addition of fresh medium. After a further 2 days, these cultures were treated with various concentrations of PY for 4 h, trypsinized, washed free of PY, and replated at a concentration of 100 or 1000 cells per plate in drug-free medium. The 4-h exposure of exponentially growing CHO cells to 16.7 UMPY reduced clonogenicity by 50% and exposure to 26.7 uM decreased clonogenicity by 99.9%.