Enhancement of the therapeutic outcome of radio-immunotherapy by combination with whole-body mild hyperthermia T. Saga a, *, H. Sakahara b , Y. Nakamoto a , N. Sato a , T. Ishimori a , M. Mamede a , H. Kobayashi a , S. Masunaga c , K. Sasai d , M. Kuroki e , J. Konishi a a Department of Nuclear Medicine and Diagnostic Imaging, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan d Department of Therapeutic Radiology and Oncology, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan c Radiation Oncology Research Laboratory, Research Reactor Institute, Kyoto University, Osaka, Japan b Department of Radiology, Hamamatsu University School of Medicine, Hamamatsu, Japan e First Department of Biochemistry, Fukuoka University, Fukuoka, Japan Received 14 November 2000; received in revised form 26 February 2001; accepted 29 March 2001 Abstract To enhance the effect of radio-immunotherapy for solid cancers, whole-body mild hyperthermia was added, and its effects on the pharmacokinetics of radiolabelled antibody, outcome of radio-immunotherapy, and radiosensitivity of the tumour were investi- gated. Nude mice bearing human colon cancer xenografts were heated to 40  C for 3 or 6 h. After heating, mice received intravenous (i.v.) injections of [ 131 I]-labelled anti-carcinoembryonic antigen (CEA) monoclonal antibody. Although 6-h heating did not alter the biodistribution of the radiolabelled antibody, and alone did not show any therapeutic effect on tumour growth, when combined with radio-immunotherapy, the therapeutic effect on tumour growth was significantly enhanced. Three-hour heating also sig- nificantly enhanced the effect of radio-immunotherapy. Colony formation assay showed that the radiosensitivity of the tumour was significantly enhanced after heating, which was achieved by a reduction of the hypoxic fraction of the tumour. In conclusion, the addition of whole-body mild hyperthermia significantly enhanced the therapeutic effect of radio-immunotherapy by increasing the radiosensitivity of the tumour. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radio-immunotherapy; Whole-body hyperthermia; Radiolabelled monoclonal antibody; Carcinoembryonic antigen; Hypoxia 1. Introduction In spite of the progress made in radio-immunotherapy techniques, solid cancers are still hard to cure [1]. To obtain satisfactory results, radio-immunotherapy is combined with various therapeutic modalities [2–5]. In the present study, the effect of combined whole-body mild hyperthermia on the therapeutic outcome of radio- immunotherapy was investigated along with its effect on the pharmacokinetics of the radiolabelled antibody and radiosensitivity of the tumour, using nude mice bearing human colon cancer xenografts. 2. Materials and methods 2.1. Human colon cancer xenograft Carcinoembryonic antigen (CEA)-expressing human colon cancer cells LS174T, (American Type Culture Collection, Rockville, MD, USA), were grown in Ros- well Park Memorial Institute (RPMI) 1640 medium (Nissui Pharmaceutical Co., Tokyo, Japan) supple- mented with 10% fetal calf serum (GIBCO Labora- tories, Grand Island, NY, USA) and 0.03% L- glutamine, in a 5% CO 2 environment. A single-cell suspension of 310 6 LS174T cells was subcutaneously (s.c.) injected into the left thighs of female BALB/c nu/nu mice. Ten to 12 days later, s.c. tumours reached the optimal size (300–500 mg) for further study. 0959-8049/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0959-8049(01)00138-1 European Journal of Cancer 37 (2001) 1429–1434 www.ejconline.com * Corresponding author. Tel.: +81-75-751-3762; fax: +81-75-771- 9709. E-mail address: saga@kuhp.kyoto-u.ac.jp (T. Saga).