Masunaga Shin-Ichiro, Nagasawa Hideko, Gotoh Keiko, Sakurai Yoshinori, Uto Yoshihiro, Hori Hitoshi, Nagata Kenji, Suzuki Minoru, Maruhashi Akira, Kinashi Yuko, Ono Koji
Radiation Oncology Research Laboratory, Research Reactor Institute, Kyoto University, 2-1010, Asashiro-nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan.
Radiat Med. 2006 Feb;24(2):98-107. doi: 10.1007/BF02493275.
To evaluate the usefulness of 5 new 10B-compounds (TX-2091, TX-2095, TX-2097, TX-2100, and TX-2110) as 10B-carriers in boron neutron capture therpy (BNCT). They were conjugates that had been synthesized from a hypoxia-specific cytotoxic bioreductive agent, quinoxaline oxide TX-402, and a clinically used 10B-carrier, sodium borocaptate-10B (BSH).
The 5 new compounds were hybrid compounds that have both a hypoxic cytotoxin unit and a thermal neutron-sensitizing unit, BSH. These new compounds and BSH were administered intraperitoneally to SCC VII tumor-bearing mice. Then, the 10B concentrations in the tumors and normal tissues were measured by gamma-ray spectrometry. Subsequently, SCC VII tumor-bearing mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all proliferating (P) cells in the tumors, then treated with TX-2100, which was chosen based on the results of the above-mentioned biodistribution analyses, or BSH in the same manner as in the biodistribution studies. Right after irradiation, during which intratumor 10B concentrations were kept at levels similar to each other, the tumors were excised, minced, and trypsinized. The tumor cell suspensions thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labeling [= quiescent (Q) cells] was determined using immunofluorescence staining for BrdU. Meanwhile, the MN frequency in the total (P+Q) tumor cell population was determined from the tumors that were not pretreated with BrdU. Clonogenic cell survival was also determined in mice given no BrdU.
10B biodistribution analyses in tumors, brain, skin, muscles, blood, and liver indicated that TX-2100 has the most favorable characteristics for concentrating a sufficient amount of 10B in tumors and maintaining a high enough 10B concentration during irradiation. In addition, TX-2100 had a significantly stronger radio-sensitizing effect with reactor thermal neutron beams than BSH on both total and Q cells in solid tumors. Further, TX-2100 clearly exhibited a radio-sensitizing effect with gamma-rays not only on total cells but also on Q and hypoxic tumor cells, which was not achieved by BSH.
A 10B-carrier that acts as a hypoxic cytotoxin on tumor cells as well as having the potential to keep 10B in tumors and sensitize tumor cells more markedly than conventional 10B-carriers, such as TX-2100, is a promising candidate for use in BNCT.
评估5种新型10B化合物（TX - 2091、TX - 2095、TX - 2097、TX - 2100和TX - 2110）作为硼中子俘获疗法（BNCT）中10B载体的效用。它们是由一种对缺氧具有特异性细胞毒性的生物还原剂喹喔啉氧化物TX - 402与一种临床使用的10B载体硼卡醇钠 - 10B（BSH）合成的共轭物。
这5种新型化合物是兼具缺氧细胞毒素单元和热中子敏化单元BSH的杂合化合物。将这些新型化合物和BSH腹腔注射给荷SCC VII肿瘤的小鼠。然后，通过γ射线光谱法测量肿瘤和正常组织中的10B浓度。随后，给荷SCC VII肿瘤的小鼠连续注射5 - 溴 - 2'-脱氧尿苷（BrdU）以标记肿瘤中所有增殖（P）细胞，然后按照上述生物分布分析的结果选择TX - 2100或采用与生物分布研究相同的方式给予BSH进行治疗。在照射后立即将肿瘤切除、切碎并胰蛋白酶消化，照射期间肿瘤内10B浓度保持在彼此相似的水平。将由此获得的肿瘤细胞悬液与细胞松弛素B（一种胞质分裂阻滞剂）一起孵育，并使用针对BrdU的免疫荧光染色测定未标记BrdU的细胞[=静止（Q）细胞]中的微核（MN）频率。同时，从不预先用BrdU处理的肿瘤中测定总（P + Q）肿瘤细胞群体中的MN频率。在未给予BrdU的小鼠中也测定克隆形成细胞存活率。
在肿瘤、脑、皮肤、肌肉、血液和肝脏中进行的10B生物分布分析表明，TX - 2100具有最有利的特性，能够在肿瘤中富集足够量的10B并在照射期间保持足够高的10B浓度。此外，在实体瘤的总细胞和Q细胞上，TX - 2100对反应堆热中子束的放射增敏作用明显强于BSH。此外，TX - 2100不仅对总细胞，而且对Q细胞和缺氧肿瘤细胞都明显表现出γ射线放射增敏作用，而BSH未达到此效果。
一种10B载体，如TX - 2100，对肿瘤细胞具有缺氧细胞毒素作用，并且有可能使10B保留在肿瘤中并比传统的10B载体更显著地使肿瘤细胞敏感，是BNCT中一种有前景的候选物。
