Highly Sensitive Hill-Type Small-Molecule pH Probe That Recognizes the Reversed pH Gradient of Cancer Cells
作者:Xiao Luo、Haotian Yang、Haolu Wang、Zhiwei Ye、Zhongneng Zhou、Luyan Gu、Jinquan Chen、Yi Xiao、Xiaowen Liang、Xuhong Qian、Youjun Yang
DOI:10.1021/acs.analchem.8b00218
日期:2018.5.1
A hallmark of cancer cells is a reversed transmembrane pH gradient, which could be exploited for robust and convenient intraoperative histopathological analysis. However, pathologically relevant pH changes are not significant enough for sensitive detection by conventional Henderson–Hasselbalch-type pH probes, exhibiting an acid–base transition width of 2 pH units. This challenge could potentially be addressed by a pH probe with a reduced acid–base transition width (i.e., Hill-type probe), appropriate pKa, and membrane permeability. Yet, a guideline to allow rational design of such small-molecule Hill-type pH probes is still lacking. We have devised a novel molecular mechanism, enabled sequential protonation with high positive homotropic cooperativity, and synthesized small-molecule pH probes (PHX1–3) with acid–base transition ranges of ca. 1 pH unit. Notably, PHX2 has a pKa of 6.9, matching the extracellular pH of cancer cells. Also, PHX2 is readily permeable to cell membrane and allowed direct mapping of both intra- and extracellular pH, hence the transmembrane pH gradient. PHX2 was successfully used for rapid and high-contrast distinction of fresh unprocessed biopsies of cancer cells from normal cells and therefore has broad potentials for intraoperative analysis of cancer surgery.
癌细胞的一个特征是跨膜 pH 梯度反转,可利用这一特征进行可靠、便捷的术中组织病理学分析。然而,传统的亨德森-哈塞尔巴赫(Henderson-Hasselbalch)型 pH 探针的酸碱转换宽度为 2 个 pH 单位,其病理相关的 pH 变化不够显著,无法进行灵敏检测。酸碱转换宽度减小的 pH 探针(即希尔型探针)、适当的 pKa 和膜渗透性有可能解决这一难题。然而,目前仍缺乏合理设计此类小分子希尔型 pH 探针的指导原则。我们设计了一种新的分子机制,实现了具有高正向同向合作性的顺序质子化,并合成了酸碱转换范围约为 1 个 pH 单位的小分子 pH 探针(PHX1-3)。值得注意的是,PHX2 的 pKa 值为 6.9,与癌细胞细胞外的 pH 值相符。此外,PHX2 易于渗透到细胞膜上,可直接绘制细胞内和细胞外的 pH 值,从而形成跨膜 pH 梯度。PHX2 成功地用于快速、高对比度地区分未经处理的新鲜活检癌细胞和正常细胞,因此在癌症手术的术中分析方面具有广泛的潜力。