VIII-Ⅱ-3. Original Research

OR1

Reducing Intratumor Acute Hypoxia through Bevacizumab Treatment,
Referring to Distant Metastatic Potential

S. Masunaga, H. Tanaka, Y. Sakurai, M. Suzuki,
N. Kondo, M. Narabayashi, A. Maruhashi and K. Ono
Research Reactor Institute, Kyoto University
BACKGROUNDS AND PURPOSES: It was believedthat antiangiogenic therapy prevents the tumor vascular
growth and proliferation, thus depriving the tumor ofoxygen and nutrients necessary for survival [1]. Subsequent study, however, suggested that antiangiogenic
therapy may also “normalize” the tumor vasculature for ashort period of time, thereby providing a window of opportunity for improved drug delivery and enhanced sensitivity to radiation [1,2]. Tumor hypoxia results from either limited oxygen diffusion (chronic hypoxia) or limited perfusion (acute hypoxia) [3]. Further, it was reported that acute and cyclic, but not chronic, hypoxia significantly increased the number of spontaneous lung metastases, and that this effect was due to the influence ofacute hypoxia treatment on the primary tumor [4,5]Here, we tried to analyze on hypoxia in solid tumors
after the administration of the vascular endothelial
growth factor (VEGF) inhibitor bevacizumab, using theacute hypoxia-releasing agent nicotinamide combinedwith -ray irradiation, in terms of both local tumor response and lung metastasis compared with irradiation
combined with mild temperature hyperthermia (MTH),
already shown to have the potential to release tumor cells
from diffusion-limited chronic hypoxia [6,7]. In addition,
concerning the local tumor response, the effect not only
on the total (= proliferating (P) + quiescent (Q)) tumor
cell population but also on the Q cell population wasevaluated using our original method for detecting theresponse of Q cells in solid tumors [8].
MATERIALS AND METHODS: B16-BL6 melanoma
tumor-bearing C57BL/6 mice were continuously given
5-bromo-2’-deoxyuridine (BrdU) to label all proliferating(P) cells. They received -ray irradiation following treatment with the acute hypoxia-releasing agent nicotinamide
or MTH with or without the administration of
bevacizumab under aerobic conditions or totally hypoxic
conditions achieved by clamping the proximal end of thetumors. Immediately after the irradiation, cells from sometumors were isolated and incubated with a cytokinesis
blocker. The responses of the Q and total cell populations
were assessed based on the frequency of micronuclei
using immunofluorescence staining for BrdU. In othertumor-bearing mice, 17 days after irradiation, macroscopic lung metastases were enumerated.
RESULTS: Three days after bevacizumab administration,acute hypoxia-rich total cell population in the tumor
showed the remarkably enhanced radio-sensitivity to-rays, and the hypoxic fraction (HF) was reduced, evenafter MTH treatment. However, the HF was not reduced
after nicotinamide treatment. With or without -ray irradiation, bevacizumab administration showed some potential to reduce the number of lung metastases as well as
nicotinamide treatment.
CONCLUSION: Bevacizumab has the potential to reduce the perfusion-limited acute hypoxia and some potential to cause the decrease in the number of lung metastases as well as nicotinamide [9].

REFERENCES:[1] R.F. Jain, Science 307 (2005) 58-62.
[2] F. Winkler, et al., Cancer Cell 6 (2004) 553-563.
[3] J.M. Brown, Br. J. Radiol. 2 (1979) 650-656.
[4] B.A. Cairns, et al., Cancer Res. 61 (2001)
8903-8908.
[5] E.K. Rofstad, et al., Clin. Cancer Res. 13 (2007)
1971-1978.
[6] S. Masunaga, et al., Int. J. Hyperthermia 13 (1997)
401-411.
[7] S. Masunaga, et al, Clin. Exp. Metastasis 26 (2009)693-700.
[8] S. Masunaga and K. Ono, J. Radiat. Res. 43 (2002)
11-25.
[9] S. Masunaga et al., Br. J. Radiol. 84 (2011)
1131–1138.

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ベバシツマブ処置による腫瘍内急性低酸素細胞分画低下作用と遠隔肺転移抑制効果について 独自研究
（京大・原子炉）増永慎一郎、田中浩基、櫻井良憲、鈴木実、近藤夏子、楢林正流、丸橋 晃、小野公二