Martin G R, Jain R K
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213.
Cancer Res. 1994 Nov 1;54(21):5670-4.
The tumor interstitial pH and its modification play a significant role in cancer treatment. Current in vivo pH measurement techniques are invasive and/or provide poor spatial resolution. Therefore, there are no data on perivascular interstitial pH gradients in normal or tumor tissue. We have optically measured interstitial pH gradients with high resolution in normal and tumor (VX2 carcinoma) tissue in vivo by combining a fluorescence ratio imaging microscopy technique and the rabbit ear chamber preparation. The strengths of our approach include the ability to follow pH in the same location for several weeks and to relate these measurements to local blood flow and vascular architecture. Our results show: (a) tumor interstitial pH (6.75 units; N = 6 animals, n = 324 measurements) is significantly (P < 0.001) less than normal interstitial pH (7.23; N = 5, n = 274). This increased acidity in the tumor interstitium is in agreement with the previously reported data on this tumor; (b) with respect to pH spatial gradients in normal tissue, the interstitial pH decreased by approximately 0.32 pH units over a distance of 50 microns away from the blood vessel, while in tumor tissue, interstitial pH decreased by approximately 0.13 units over the same distance. Although the pH gradient near the vessel wall was steeper in normal tissue compared to tumor, the proton concentration gradient in normal tissue was less than that in the tumor. The approximate increase in proton concentration from 0-50 microns from the vessel was 4.5 x 10(-8)M in normal versus 5.7 x 10(-8)M in tumor tissue; (c) a simple one-dimensional diffusion-reaction model suggested that tumor tissue was producing protons at a rat 65-100% greater than normal tissue; (d) feasibility studies of temporal dynamics resulting from hyperglycemia (6 g/kg) or hypercapnia (10% CO2) led to significant (P < 0.05) interstitial pH reductions. During hyperglycemia, pH dropped by more than 0.2 pH units in about 90 min in tumor tissue but remained constant in normal tissue. Hypercapnia dramatically reduced pH by approximately 0.3 pH units in tumor tissue. Our limited studies on hyperglycemia and hypercapnia are in agreement with the previously published studies and demonstrate the capability of fluorescence ratio imaging microscopy to measure spatial as well as temporal changes in interstitial pH. Fluorescence ratio imaging microscopy should permit noninvasive evaluation of new pH-modifying agents and offer unique mechanistic information about tumor pathophysiology in tissue preparations where the surface of the tissue can be observed.
肿瘤间质pH值及其调节在癌症治疗中起着重要作用。目前的体内pH测量技术具有侵入性且/或空间分辨率较差。因此，尚无关于正常或肿瘤组织中血管周围间质pH梯度的数据。我们通过结合荧光比率成像显微镜技术和兔耳室制备方法，在体内对正常组织和肿瘤（VX2癌）组织中的间质pH梯度进行了高分辨率光学测量。我们方法的优势包括能够在同一位置跟踪pH值数周，并将这些测量结果与局部血流和血管结构相关联。我们的结果表明：（a）肿瘤间质pH值（6.75单位；N = 6只动物，n = 324次测量）显著低于正常间质pH值（7.23；N = 5，n = 274）（P < 0.001）。肿瘤间质中这种酸度增加与先前关于该肿瘤的报道数据一致；（b）关于正常组织中的pH空间梯度，在距血管50微米的距离内，间质pH值下降约0.32个pH单位，而在肿瘤组织中，在相同距离内间质pH值下降约0.13个单位。尽管正常组织中血管壁附近的pH梯度比肿瘤组织中的更陡，但正常组织中的质子浓度梯度小于肿瘤组织中的。从血管0 - 50微米处质子浓度的近似增加在正常组织中为4.5×10⁻⁸M，而在肿瘤组织中为5.7×10⁻⁸M；（c）一个简单的一维扩散 - 反应模型表明，肿瘤组织产生质子的速率比正常组织高65 - 100%；（d）高血糖（6 g/kg）或高碳酸血症（10% CO₂）引起的时间动态可行性研究导致间质pH值显著降低（P < 0.05）。在高血糖期间，肿瘤组织中的pH值在约90分钟内下降超过0.2个pH单位，而在正常组织中保持恒定。高碳酸血症使肿瘤组织中的pH值显著降低约0.3个pH单位。我们对高血糖和高碳酸血症的有限研究与先前发表的研究一致，并证明了荧光比率成像显微镜测量间质pH值空间和时间变化的能力。荧光比率成像显微镜应允许对新的pH调节药物进行非侵入性评估，并在可以观察组织表面的组织制剂中提供有关肿瘤病理生理学的独特机制信息。
