VIII-Ⅱ-1. Project Research
Project 4

PR4-1The Effect of Boron Neutron Capturetreatment Targeting Tumor Endohtelial Cellsof Clinically Relevant Radioresistant Tumors

Y. Kuwahara, M. Fukumoto, Y. Sakurai1, M. Suzuki1, K.
Ono1 and M. Fukumoto.
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University.
1
Department of Radiation Life Science and Radiation
Medical Science, Research Reactor Institute, Kyoto University
INTRODUCTION: Radiotherapy is one of the major
therapeutic modalities for eradicating malignant tumors.
However, the existence of radioresistant cells remains
one of the most critical obstacles in radiotherapy. To understand the characteristics of radioresistant cells and todevelop more effective radiotherapy, we have establishedclinically relevant radioresistant (CRR) cell lines. The
density of blood vessels in tumor tissues of CRR cells
transplanted into nude mice was higher compared with
their radiosensitive parental cell lines. Therefore, weperformed boron neutron capture treatment (BNCT) targeting tumor endothelial cells using PEG-10B.
EXPERIMENTS: Three days before experiments, 1x106
cells of HeLa and HeLa-R were injected subcutaneously
into hind legs of male Balb/c nude mice (4 weeks old).
Tumor size was determined by caliper measurements.
The day of BNCT treatment tumor diameter was approximately 3-4 mm and was measured every 2 days.
For irradiation of tumor endothelial cells by α-particles,
PEG-10B was administered. The compound was suspended in physiological saline at a concentration of 2,500
ppm and was injected via the tail vein. Three hours
after the administration, mice were exposed to neutron-radiation at the Research Reactor Institute, Kyoto
University (RRIKU). The calculated dose of α-particles
was 8 Gy-Eq. Endothelial cells of blood vessels in tumor
tissues were immunohistochemically stained for CD34
and CD31. Pericytes were detected by immunohistochemistry for Type Ⅳ collagen and functional bloodvessels was determined by tomatolectin injected from thetail vain. We counted the number of vessels in 10 highpower field (x400) and calculated the average (n=3).

RESULTS: Within 24 days after BNCT, the size ofHeLa-R tumors was not significantly different fromHeLa-R tumors without BNCT. But the size of HeLa
tumors was significantly smaller compared with HeLa
tumors without BNCT. Mice were sacrificed on day 30
after BNCT. Histological examination showed that thetumor blood vessel density of HeLa-R tumors were larger
compared with their radiosensitive HeLa tumors. CD34
positive blood vessels were also more abundant in SAS-R
tumors than in SAS-tumors (Data not shown). After
BNCT using PEG-10B, the density of CD31 positive
blood vessels of HeLa-R tumors recovered more rapidly
than HeLa tumors on 7 days. However, 4 weeks afterBNCT, the density of CD34 positive blood vessels wasalmost the same between tumor with BNCT and without
BNCT in both HeLa-R tumors and HeLa tumors.
DISCUSSION: Our preliminary experiments showedthat the density of blood vessels in SAS-R tumors washigher than that in SAS tumors. In order to determine thesignificance of blood vessel concentration inradiorsistance, we tried to target tumor endothelial cellsby selective exposure of endothelial cells to α-particles,
using BNC with PEG-10B.
Seven days after BNC the density of CD31 positive
blood vessels were destroyed in HeLa tumor exposed toα-particles compared to control HeLa tumor but did notin HeLa-R tumor irrespective of α-particles exposure.
Moreover, to our surprise, 4 weeks after BNCT the desityof CD34 positive blood vessels were almost same
irrspective of α-particles exposure in both HeLa-R tumorand HeLa. Therefore, further studies are needed to confirm how blood vessel density contributes to tumor radiotherapy.

採択課題番号 23P4-3 腫瘍内の血管は腫瘍の放射線耐性にどのように関わっているのか（東北大・加齢研）桑原義和、福本 基、福本 学（京大・原子炉）桜井良憲、鈴木 実、小野公二