Study of arsenic trioxide-induced vascular shutdown and enhancement with radiation in solid tumor

PURPOSE: Arsenic trioxide (ATO) has been reported to be an effective chemotherapeutic agent for acute promyelocytic leukemia (APL), and, recently, anti-tumor effect has been demonstrated in solid tumors. However, little is known about the mechanism of action of the ATO effect on solid tumor. We investigated the anti-vascular effect of ATO and the potential of combining ATO with radiation therapy. MATERIALS AND METHODS: We studied the anti-vascular effect of ATO and radiosensitization of squamous cell carcinoma (SCC) VII murine tumors of C3H mice. The anti-vascular effect was examined using magnetic resonance imaging(MRI), and radiosensitivity was studied by clonogenic assay and tumor growth delay. Histopathological changes of the tumors after various treatments were also observed with hematoxylin and eosin (H&E) staining. RESULTS: Necrosis and blood flow changes in the central region of tumors in the hind limbs of the animals were observed on T2-weighted imaging after an i.p. injection of 8 mg/kg of ATO alone. ATO exposure followed by radiation decreased the clonogenic survival of SCC VII cells compared with either treatment alone. Tumor growth delay after 10-20 Gy of radiation alone was increased slightly compared with control tumors, but the combination of ATO injection 2 hours before exposure to 20 Gy of radiation significantly prolonged tumor growth delay by almost 20 days. CONCLUSION: The results suggest that ATO and radiation can enhance the radiosensitivity of solid tumor.