Ferrauto Giuseppe, Di Gregorio Enza, Auboiroux Vincent, Petit Manuel, Berger François, Aime Silvio, Lahrech Hana
Molecular Imaging Center, Department of Molecular Biotechnologies and Health Sciences, University of Torino, Turin, Italy.
Clinatec CEA, Grenoble, France.
NMR Biomed. 2018 Nov;31(11):e4005. doi: 10.1002/nbm.4005. Epub 2018 Sep 5.
In glioma, the acidification of the extracellular tumor microenvironment drives proliferation, angiogenesis, immunosuppression, invasion and chemoresistance. Therefore, quantification of glioma extracellular pH (pHe) is of crucial importance. This study is focused on the application of the YbHPDO3A (ytterbium 1,4,7-triscarboxymethyl-1,4,7,10-tetraazacyclododecane) probe for in vivo glioma pHe quantification using chemical exchange saturation transfer (CEST)-MRI and its correlation with tumor metabolism assessed by immunohistochemistry. The U87 glioma mouse model was used (n = 18) and MRI performed at 4.7 T. CEST-MRI of YbHPDO3A solutions at different pH values showed two resolved CEST spectra at 71 ppm and 99 ppm, both sensitive to pH variations, allowing therefore calculation of the ratiometric curve for in vivo pH quantification. In vivo MRI sequences consisted of T for tumor localization, T * to assess YbHPDO3A biodistribution by exploiting its magnetic susceptibility effect and CEST for glioma pHe mapping. T * images show that YbHPDO3A extravasates in tumor in regions with damaged blood-brain barrier. The pHe is calculated only in these regions. Hematoxylin/eosin histology and Ki-67, CA-IX (carbonic anhydrase 9) and NHE-1 immunohistochemical staining were performed; their expression rates were compared with the in vivo pHe values. On the basis of the cell proliferation marker Ki-67, two groups were defined: one group with a lower mitotic index (MI% < 20% = mean value) and a mean pHe value of 7.00 (low-proliferation/high-pH group) and the other with MI% > 20% and an acidic pHe of 6.6 (high-proliferation/low-pH group). CA-IX and NHE-1 were over-expressed in the high-proliferation/low-pH group (CA-IX, 92 ± 7% versus 30 ± 13%; NHE-1, 84 ± 8% versus 35 ± 11%), indicating an acidic/hypoxic microenvironment. These immunohistochemical results are consistent with our pHe mapping (Pearson correlation coefficient > 0.70) and provide evidence for the feasibility of the CEST-MRI method with the YbHPDO3A probe for glioma pHe quantification at 4.7 T. Importantly, the YbHPDO3A probe has similar chemical and biological properties to the clinically approved MRI contrast agent GdHPDO3A. This makes the method promising for a clinical translation.
在胶质瘤中，细胞外肿瘤微环境的酸化会促进肿瘤增殖、血管生成、免疫抑制、侵袭和化疗耐药。因此，定量测定胶质瘤细胞外pH值（pHe）至关重要。本研究聚焦于镱1,4,7-三羧甲基-1,4,7,10-四氮杂环十二烷（YbHPDO3A）探针在体内利用化学交换饱和转移（CEST）-磁共振成像（MRI）定量测定胶质瘤pHe中的应用，以及其与通过免疫组织化学评估的肿瘤代谢的相关性。使用U87胶质瘤小鼠模型（n = 18），并在4.7 T磁场下进行MRI检查。不同pH值的YbHPDO3A溶液的CEST-MRI显示在71 ppm和99 ppm处有两个分辨的CEST谱，两者均对pH变化敏感，因此可计算用于体内pH定量的比率曲线。体内MRI序列包括用于肿瘤定位的T1、通过利用其磁化率效应评估YbHPDO3A生物分布的T2以及用于胶质瘤pHe映射的CEST。T2图像显示YbHPDO3A在血脑屏障受损区域的肿瘤中渗出。仅在这些区域计算pHe。进行苏木精/伊红组织学检查以及Ki-67、碳酸酐酶9（CA-IX）和钠氢交换体1（NHE-1）免疫组织化学染色；将它们的表达率与体内pHe值进行比较。根据细胞增殖标志物Ki-67，定义了两组：一组有丝分裂指数较低（MI% < 20% = 平均值），平均pHe值为7.00（低增殖/高pH组），另一组MI% > 20%，酸性pHe为6.6（高增殖/低pH组）。CA-IX和NHE-1在高增殖/低pH组中过度表达（CA-IX，92 ± 7%对30 ± 13%；NHE-1，84 ± 8%对35 ± 11%），表明存在酸性/缺氧微环境。这些免疫组织化学结果与我们的pHe映射结果一致（皮尔逊相关系数> 0.70），并为在4.7 T磁场下使用YbHPDO3A探针的CEST-MRI方法定量测定胶质瘤pHe的可行性提供了证据。重要的是，YbHPDO3A探针具有与临床批准的MRI造影剂钆1,4,7-三羧甲基-1,4,7,10-四氮杂环十二烷（GdHPDO3A）相似的化学和生物学特性。这使得该方法有望实现临床转化。
