Molecular analysis of compensatory mechanism which tumor cells exert in VEGF deficent/RipTag mouse

当我们从加州大学弗朗西斯科分校转移RipTag小鼠时，我们发现日本的肿瘤形成显著减少。已知RipTag小鼠中肿瘤的形成对遗传背景敏感。尽管我们试图通过将其回交到C57 B1/6 N或DBA背景中来解决该问题，但我们没有观察到肿瘤形成的显著恢复。后来，它已被揭示，在UCSF的原始小鼠群体中观察到相同的现象。RipTag小鼠中可能发生了一些基因组变化。目前正在考虑重建转基因小鼠。同时，对来自RipTag/VEGF-/-小鼠的存档胰腺样品的分析显示，存在具有相当低的微血管密度的残留肿瘤，没有明显的坏死。我们发现残余肿瘤含有广泛的缺氧区。这一发现表明，抑制血管生成导致缺氧区域的出现以及肿瘤形成的减少。在这些缺氧肿瘤中，凋亡并没有明显增加，肿瘤细胞似乎通过适应缺氧微环境而存活。从临床角度来看，这些结果提出了一个严重的问题，即抗血管生成治疗可能通过选择耐缺氧的癌细胞而诱导耐药。随后，我们开始研究恶性肿瘤细胞耐缺氧的分子机制。我们发现各种细胞系可以在缺氧条件下维持几周。这些肿瘤细胞是活的，但没有观察到增殖或细胞死亡。我们专注于mTOR信号转导，已知其在缺氧中被抑制，但其后果尚未阐明。我们发现，抑制mTOR信号传导对于它们在长时间缺氧条件下的存活至关重要。

While we transferred RipTag mice from university of California at San Francisco, we found profound reduction of tumor formation in Japan. Formation of tumor in RipTag mouse is known to be sensitive to the genetic background. Although we tried to resolve the problem by backcrossing it into C57B1/6N or DBA background, we did not observe remarkable recovery of tumor formation. Afterwards, it has been revealed that the same phenomenon was observed in the original mouse colony in UCSF. It is likely that some genomic change in RipTag mouse occurred. Re-establishment of the transgenic mouse is now under consideration. Meanwhile, analysis of the archive pancreas samples from RipTag/VEGF-/- mice revealed that there were residual tumors with quite low microvessel density without apparent necrosis. We found that the residual tumors contains broad hypoxic region. This finding suggests that inhibiting angiogenesis results in emergence of hypoxic region as well as reduction of tumor formation. In these hypoxic tumors, apoptosis was not significantly increased, tumor cells seems to survive by adapting to the hypoxic microenvironment. From clinical point of view, the results offered a serious issue that anti-angiogenesis therapy might induce drug resistance by selecting hypoxia tolerant cancer cells. Then, We started to investigate the molecular mechanism of hypoxia tolerance of malignant cells. We found various cell lines can be maintained in hypoxic conditions for a couple of weeks. These tumor cells were alive but no proliferation nor cell death was observed. We focused on the mTOR signaling, which is know to be suppressed in hypoxia, but the consequence has not been clarified yet. We revealed that suppression of mTOR signaling is critical for their survival under prolonged hypoxic conditions.