In vivo studies for the individual application of boron neutron capture therapy (BNCT) to the treatment of the malignant melanoma

CARPANO, M; PERONA, M; NIEVAS, S; SANTA CRUZ, G; JUVENAL, G; PISAREV , M; DAGROSA, MA

Hsinchu, Taiwan

Encuentro; 6th Young Researchers Boron Neutron Capture Therapy Meeting; 2011

National Tsing Hua University

Tumors from different patients with the same histological diagnosis can show different responses to ionizing radiation including to BNCT. Further knowledge about individual tumor characteristics is needed in order to optimize the individual application of this therapy. In previous studies we have shown different patterns of boron intracellular concentration in a number of human melanoma cell lines. The aim of this study was to evaluate the differences in the BPA uptake related to different histological and thermal characteristics of each tumor in nude mice bearing human melanoma. In addition, we studied the vasculature in tumors by immunohistochemistry and their relationship with the BPA uptake. Methodology: We use the human melanoma cell line MELJ, was maintained in RPMI 1640 culture medium containing 10% BFS, under 5% CO2 , at 37 °C. NIH nude mice, aged 6 to 8 weeks were implanted (s.c.) in the back right flank with the tumor cells. To evaluate the BPA uptake, animals were injected with the boron compound at a dose of 350 mg/Kg b.w. (ip) and sacrificed at 0.5, 1, 2, 3 h post administration. Boron measurements in tissues and blood were performed by ICP-OES. For the histological study, samples from the tumors were fixed in buffered 10% formaldehyde and embedded in paraffin. Sections of 5 µm thick were stained with hematoxylin and eosin (HE). Infrared imaging studies were performed twice a week for each animal, measuring the tumor, and body temperatures during tumor growth. Immunohistochemical studies were performed with antibody CD 31, this marker is specific to endothelial cells and allow identify the vasculature. Formaldehyde-fixed paraffin-embedded tissues and avidin biotin complex immunostaining were used. Results: Tumor BPA uptake showed an average maximum concentration of 25.6 ± 2.9, with individual values between 8.2 and 41.4 ppm of B at 2 h post injection. Tumor-to-blood and tumor-to-distal skin ratios were 4.3 and 2.3 respectively. Normal tissue temperature correlated with body temperature with average values of 37 °C. Individual tumor temperatures were always lower temperature and the difference increased with tumor size. Tumor margin temperature was elevated (about 40 °C) during the first three weeks and declined thereafter. A direct correlation between tumor boron uptake and tumor temperature difference (a measure of tumor heat conductivity) was observed. Histological studies showed a wide area of tumor viability with small foci of necrosis. Conclusions: These findings seem to indicate a direct correlation between tumor histology, BPA uptake and thermal characteristics, showing that tumors without necrotic areas have a higher boron uptake and higher heat conductivity than tumors with necrotic regions.