In-vivo Studies Towards Optimizing the Application of BNCT to the Individual Treatment of Malignant Melanoma

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

Buenos Aires

Congreso; 14th International Congress of Neutron Capture Therapy; 2010

CNEA, UNSAM, ROFFO

Introduction: Melanoma is an aggressive tumor which can be controlled with the conventional treatments in early diagnosed patients. However, in advanced stages the effectiveness of the usual therapies is poor. Tumors from different patients with the same histological diagnosis can show different responses to ionizing radiation. BNCT has been used for the treatment of melanoma in different countries around the world but without considering the individual patients’ characteristics. With this goal in mind, we have developed an in vivo model by transplanting the human melanoma cell line MELJ into nude mice, measuring tumor growth, performing BPA biodistribution studies and following the animals with infrared imaging. Materials and Methods: 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 and weighing 20 to 25 g were implanted (s.c.) in the back right flank with different concentrations of tumor cells. The size of the tumors was measured with a caliper twice a week and the volume was calculated measuring the major and minor diameters. To evaluate the BPA uptake, animals were injected with the boron compound at a dose of 350 mg/Kg b.w. (i.p.) and sacrificed at 0.5, 1, 2, 3 h post administration. After that, boron measurements in tissues and blood were performed by ICP-OES. Histological preparations were made from the tumor and the surrounding skin. Infrared imaging studies were performed twice a week for each animal, measuring the tumor, tumor margin and body core temperatures during tumor growth. Results and Discussion: the animals implanted with 4x106 cells showed an exponential tumor growth at 25 days post implantation reaching a maximum volume of 923 mm3 at day 30. Histological studies showed a wide area of tumor viability with small foci of necrosis. BPA uptake showed an average maximum concentration of 29.76 ± 1.34 mg/kg, with individual values between 9.48 and 40.03 mg/kg of 10B at 2 h post injection. Tumor-to-blood and tumor-to-distal skin ratios were 5.88 and 3.65 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. 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 tumor histology, BPA uptake and thermal characteristics, showing that tumors with few necrotic areas have a higher boron uptake and higher heat conductivity than tumors with large necrotic regions.