Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.
PLoS One. 2011;6(7):e23090. doi: 10.1371/journal.pone.0023090. Epub 2011 Jul 29.
Tumor-derived, circulating proteins are potentially useful as biomarkers for detection of cancer, for monitoring of disease progression, regression and recurrence, and for assessment of therapeutic response. Here we interrogated how a protein's stability, cellular localization, and abundance affect its observability in blood by mass-spectrometry-based proteomics techniques. We performed proteomic profiling on tumors and plasma from two different xenograft mouse models. A statistical analysis of this data revealed protein properties indicative of the detection level in plasma. Though 20% of the proteins identified in plasma were tumor-derived, only 5% of the proteins observed in the tumor tissue were found in plasma. Both intracellular and extracellular tumor proteins were observed in plasma; however, after normalizing for tumor abundance, extracellular proteins were seven times more likely to be detected. Although proteins that were more abundant in the tumor were also more likely to be observed in plasma, the relationship was nonlinear: Doubling the spectral count increased detection rate by only 50%. Many secreted proteins, even those with relatively low spectral count, were observed in plasma, but few low abundance intracellular proteins were observed. Proteins predicted to be stable by dipeptide composition were significantly more likely to be identified in plasma than less stable proteins. The number of tryptic peptides in a protein was not significantly related to the chance of a protein being observed in plasma. Quantitative comparison of large versus small tumors revealed that the abundance of proteins in plasma as measured by spectral count was associated with the tumor size, but the relationship was not one-to-one; a 3-fold decrease in tumor size resulted in a 16-fold decrease in protein abundance in plasma. This study provides quantitative support for a tumor-derived marker prioritization strategy that favors secreted and stable proteins over all but the most abundant intracellular proteins.
肿瘤来源的循环蛋白作为癌症检测的生物标志物具有潜在的应用价值，可用于监测疾病的进展、消退和复发，并评估治疗反应。在此，我们研究了蛋白质的稳定性、细胞定位和丰度如何影响其通过基于质谱的蛋白质组学技术在血液中的可观测性。我们对两种不同的异种移植小鼠模型的肿瘤和血浆进行了蛋白质组学分析。对这些数据的统计分析揭示了可预测蛋白质在血浆中检测水平的特性。尽管在血浆中鉴定出的蛋白质中有 20%是肿瘤来源的，但在肿瘤组织中观察到的蛋白质中只有 5%存在于血浆中。在血浆中观察到了细胞内和细胞外的肿瘤蛋白；然而，在对肿瘤丰度进行归一化后，细胞外蛋白被检测到的可能性要高出七倍。尽管在肿瘤中丰度更高的蛋白质也更有可能在血浆中被观察到，但这种关系是非线性的：光谱计数增加一倍仅将检测率提高了 50%。许多分泌蛋白，即使其光谱计数相对较低，也在血浆中被观察到，但很少有低丰度的细胞内蛋白被观察到。根据二肽组成预测稳定的蛋白质比不稳定的蛋白质更有可能在血浆中被鉴定出来。蛋白质中肽的数量与在血浆中被观察到的蛋白质的机会之间没有显著的相关性。对大肿瘤和小肿瘤的定量比较表明，用光谱计数测量的血浆中蛋白质的丰度与肿瘤大小有关，但这种关系不是一一对应的；肿瘤大小减少 3 倍会导致血浆中蛋白质丰度降低 16 倍。这项研究为一种基于肿瘤来源的标志物优先排序策略提供了定量支持，该策略有利于分泌和稳定的蛋白质，而不是所有除了最丰富的细胞内蛋白质。
