Published in Cancer Detection and Prevention 2000; 24(Supplement 1).

Increase of sensitivity on radioresistant procaryote, Deinococcus radiodurans, using hyperthermia and heavy ion beam

M Imamura MD 1, S Sawada MD 2, K Harima MD 1, T Shiga MD 1, S Kariya MD 3, T Shiraishi MD 3, K Harada PhD 4

1 Kansai Medical University Kohri Hospital, Neyagawa, Osaka;, 2 Kansai Medical University, Moriguchi, Osaka;, 3 Ishikiri Seiki Hospital, Higashi, Osaka;, 4 Nara Medical University, Kashihara, Nara; Japan,

AIM: We researched the sensitivity against hyperthermia including acid heating and heavy ion beam on radioresistant procaryote, Deinococcus radiodurans, for the purpose of cancer therapy. METHODS: We examined the decreases of survival rate and molecular weight of DNA purified from the cells by acid heat treatment. Also, we investigated the relation between LET (linear energy transfer) and RBE (relative biological effectiveness) on the cells using AVF cyclotron at JAERI-Takasaki, and Kyoto University Research Nuclear Reactor in Japan. The cells were irradiated with carbon ion beam at LET of about 100 keV/µm etc., and alpha-particles of boron 10 neutron captured beam. Further, the combination effect with heavy ion beam and hyperthermia was researched. RESULTS: The decrease of survival rate and the low molecular pattern of DNA from the cells were recognized by heating at 55C below pH 5.0. Then, we assumed that the decrease in survival in vivo and the damage to DNA in vitro by acid heating were due to the depurination. Next, we found that the peak at about 100 keV/µm in the figure of the relation between LET and RBE on the cells. Third, the combination treatment with 4.8 kGy of alpha-particles and hyperthermia at 52C caused the synergistic killing effect on the cells. Being dissimilar to the case of gamma-irradiation, the interval incubation at 30C in the medium between the both treatments did not restore the cell survival. CONCLUSION: We recognized that the resistance of D. radiodurans disappeared by the treatment with acid heating only, or heavy ion beam plus hyperthermia. Therefore, we assumed that these treatments were effective to cancer therapy.

KEY WORDS: Deinococcus radiodurans, hyperthermia, acid heating, heavy ion beam, cancer therapy.

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Paper presented at the International Symposium on Impact of Biotechnology on Cancer Diagnostic & Prognostic Indicators; Geneva, Switzerland; October 28 - 31, 2000; in the section on synergistic therapies.