Live single cell mass spectrometry reveals cancer-specific metabolic profiles of circulating tumor cells

Abstract

Recently, there has been increased attention on the analysis of circulating tumor cells (CTCs), also known as liquid biopsy, owing to its potential benefits in cancer diagnosis and treatment. Circulating tumor cells are released from primary tumor lesions into the blood stream and eventually metastasize to distant body organs. However, a major hurdle with CTC analysis is their natural scarcity. Existing methods lack sensitivity, specificity, or reproducibility required in CTC characterization and detection. Here, we report untargeted molecular profiling of single CTCs obtained from gastric cancer and colorectal cancer patients, using live single cell mass spectrometry integrated with microfluidics-based cell enrichment techniques. Using this approach, we showed the difference in the metabolomic profile between CTCs originating from different cancer groups. Moreover, potential biomarkers were putatively annotated to be specific to each cancer type.

Keywords: cancer biomarker; circulating tumor cells; liquid biopsy; mass spectrometry; single cell analysis.

Figure 1

Schematic of single‐cell analysis of circulating tumor cells (CTCs) using live single‐cell mass spectrometry. Blood samples were collected from gastric cancer and colorectal cancer patients. CTCs were isolated and enriched using a microfluidics technique. Single CTCs were sampled and analyzed using the live single‐cell mass spectrometry system. Data processing and statistical analysis (t test and principle component analysis) was done. RBC, red blood cell

Figure 2

Principle component analysis of circulating tumor cells (CTCs) and lymphocytes. A, The difference in the metabolic profile between CTCs and lymphocytes collected from gastric cancer patients. B, Metabolic profile of CTCs and lymphocytes from colorectal cancer patients. Each dot corresponds to a single cell

Figure 3

Heatmap of significant peaks found in all collected circulating tumor cells (CTCs) in comparison with lymphocytes. The P value of each annotated peak is shown above the figure

Figure 4

Single cell profiling of gastric cancer (GC) and colorectal cancer (CRC) circulating tumor cells (CTCs). A, Principle component analysis‐discriminant analysis discriminating between GC CTCs, CRC CTCs, and blank. Each dot corresponds to a single cell. B, Histogram of the frequency of peak distribution across the m/z scale of different cancer types

Figure 5

Characterization of significant peaks found in both gastric cancer and colorectal cancer circulating tumor cells (CTCs). A, Heatmap of significant peaks found in both gastric cancer and colorectal cancer CTCs. The P value of each annotated peak is shown above the figure. B, Histogram showing the frequency of the unique peaks (potential biomarkers) to each cancer type distribution across the m/z scale of the two cancer types