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

CARPANO, M; PERONA, M; RODRIGUEZ , C; NIEVAS, S; SANTA CRUZ, G; CABRINI, R; BRANDIZZI, D; JUVENAL, G; PISAREV, M; DAGROSA, MA

Tsukuba

Congreso; 15TH International Congress on Neutron Capture Therapy; 2012

Background: 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. Methodos: NIH nude mice of 6-8 weeks were implanted (s.c.) into the back right flank with a 106 of human melanoma cells (MELJ). 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 antibodies Ki67 and CD31. The first one is a marker of proliferative rate and the second is a specific marker of endothelial cells which allow to 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 27.96 ± 1.03, with individual values between 19.87 and 36.03 ppm of 10B at 2 h post injection. Tumor-to-blood and tumor-to-distal skin ratios were 7.4 and 4.2 respectively. Normal tissue temperature correlated with body core temperature with average values of 37 °C. Individual tumor temperatures were always lower 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 core-to-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. Tumors with large areas of viability showed a higher boron uptake. The inmunohistochemistry studies showed a high number of Ki67 positive tumor cells and the presence of vasculature in the peripheral zone with blood vessels of big diameter in tumors which showed a higher boron uptake. Conclusion: We successfully initiated the first BNCT in-vivo studies with the MELJ melanoma cell line in nude mice.These findings seem to indicate a direct correlation between BPA uptake, histology, thermal characteristics, number, type of blood vessels and the growth fraction of a given cell population showing that tumors without necrotic areas have a higher boron uptake and higher heat conductivity than tumors with necrotic regions.