Various imaging methods have been employed for the extracorporeal detection of malignant
tumors in the human body, such as scintigraphy and PET; however, none is sufficiently accurate and all are also very expensive. To resolve these issues, we attempted to develop a new imaging technique of photodynamic diagnosis (PDD) with
acridine orange (AO). AO has the ability to rapidly and specifically accumulate in malignant
tumors and emit
brilliant green fluorescence after blue light excitation. In this study, we investigated the feasibility of PDD utilizing the fluorovisualization effect of AO, for the extracorporeal detection of mouse
osteosarcoma inoculated into the soft tissues. At 2 h after
intravenous administration of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 mg/kg AO, the
tumor and the surrounding normal tissues were illuminated by blue light. The visual fluorescence contrast and ratio (X) of the difference in fluorescence intensity between the
tumor and the surrounding normal tissues were evaluated using a high-resolution digital camera equipped with an absorption filter. In addition, the fluorescence contrast was also detected sequentially at 0.5, 1, 2, 3, 6 and 12 h after
intravenous administration of AO at 1.0 mg/kg. The results revealed that the optimal condition for clear detection of the
tumor was evaluation 2 h after
intravenous injection of AO at 0.1 mg/kg, because it provided the best visual contrast on the digital images, and the fluorescence intensity as well as the value of X were higher as compared to the values under other conditions of dose and timing. Based on the results of an acute toxicity study of AO, the estimated LD50 of this substance following
intravenous administration was 27.30 mg/kg. In conclusion, we believe that PDD using AO administered intravenously may be feasible for the detection of human musculoskeletal
sarcomas in the soft tissues at extremities, and this technique might be a less invasive, less expensive, quicker and more accurate imaging modality than other previously reported imaging methods for this purpose.