量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Purpose/Objective (s): Radiation therapy for cancer often has severe side effects that limit its efficacy. Because these side effects are in part determined by p53-mediated apoptosis, temporary suppression of p53 has been suggested as a therapeutic strategy to relieve the damage of normal tissues during treatment of p53-deficient tumors. On the other hand, it is known that dissociation of a zinc ion, which is coordinated to metal ion binding site of p53, could induce p53 denaturation, hence we evaluated some zinc chelators as radioprotective p53 inhibitor. As a result, we found 5-chloro-8-quinolinol (KH-3) as a radioprotector that can protect mice from a sublethal dose of 7.5 Gy total-body irradiation (TBI). In this study, we investigated the effects and mechanism of KH-3 comparatively to a known radioprotective p53 inhibitor, PFTm.
Materials /Methods: Imprinting control region (ICR) female mice, aged 8-week old, were total-body irradiated with an X-ray generator (Pantak-320S, Shimadzu) operated at 200 kV at a dose rate of 0.66 Gy/min. KH-3 (35 mg/kg) or vehicle was ip injected 30 minutes before 7.5 Gy TBI. In cell analysis, highly radiosensitive cell line MOLT-4, derived from human T-cell leukemia, was used and 10 Gy-irradiated. The suppressive effect of KH-3 and the reference compound PFTm on radiation-induced MOLT-4 apoptosis was evaluated using Annexin V-FITC or MitoTracker Red staining. To examine the specificity of KH-3 for p53-mediated apoptosis, we used MOLT-4 cells and their derivatives, namely, p53-knockdown transformant and p53 revertant which re-expressed p53 using shRNA-resistant FLAG-tagged p53-expressing plasmid. To elucidate the mechanism of action of KH-3 in p53-mediated apoptotic pathway, we mainly investigated the expression of p53 target-genes, p21 and PUMA, using quantitative real-time PCR and immunoblotting analyses.
Results: For the 30-day survival study, half of the animals in the KH-3-treated group survived, whereas all the mice receiving only TBI died within 14 days (P < 0.01). Cell death analysis revealed that KH-3 had a higher inhibitory effect on cell death and lower toxicity than that of PFTm in the MOLT-4 cells. KH-3 was ineffective against the radiation-induced apoptosis of p53-knockdown transformant, but suppressed that of p53 revertant. Results indictated that suppression of radiation-induced apoptosis by KH-3 was specifically mediated through p53 signaling pathways. Furthermore, KH-3 modulated p53 target-gene expression without affecting p53 expression. In particular, p21, which has anti-apoptotic activity, was markedly up-regulated by KH-3.
Conclusion: KH-3 is a novel kind of radioprotector that modulates p53 transcription. The radioprotective effect of KH-3 may be associated with its ability to up-regulate p21 expression.
会議概要（会議名, 開催地, 会期, 主催者等）
American Society for Radiation Oncology (ASTRO) Annual Meeting
The mechanism of a novel radioprotector, 8-quinolinol derivative KH-3
