Despite numerous new cell analysis technologies, contaminating red- and white blood cells remain a central barrier to the efficient characterization of circulating tumor cells. Microbubbles, which capture and separate cells by flotation, recently have been described as an alternative or adjunct to magnetic beads or microfluidic methods for CTC sample preparation. This technology may find particular value in applications where mechanical force needs to be minimized or magnetization of cells needs to be avoided. Here, we evaluate novel RBC-targeting microbubbles for buoyancy-based enrichment of CTCs. Cultured human pancreatic cancer cells (line CFPAC-1, ATCC CRL 1918) were spiked into standardized samples representative of common CTC workflows (106 RBC : 5x104 WBC : 1.5x102 tumor cells). Microbubbles bearing antibodies to human erythrocytes were added at various Bubble:RBC ratios and mixed via trituration for 1 minute. Samples were then centrifuged, the microbubble-captured RBCs removed, and the remaining pelleted cells analyzed for the fraction of RBCs removed and the extent of off-target depletion of tumor cells. Cells were quantified with an automated cell counter, and all experimental conditions were performed in at least triplicate. RBC removal rose with increasing Bubble:RBC ratio ( p < 0.001 ). At a ratio of 1:1, 92 +/- 1% of RBCs were removed with one minute of mixing; at a ratio of 1.5:1, 97 +/- 1% of RBCs were removed. Off-target binding of CFPAC-1 cells was minimal at a Bubble:RBC ratio of 1:1, with 0 +/- 6% of tumor cells captured. Off-target capture increased at a Bubble:RBC ratio of 2:1, with 12 +/- 9% tumor cell loss from the experimental samples. Using a standardized blood sample with a clinically relevant low concentration of cultured tumor cells, microbubbles targeting RBCs and dosed at a ratio of one bubble per target erythrocyte were able to achieve > 90% removal without statistically detectable loss of a cultured cancer line. Higher bubble concentrations resulted in more exhaustive RBC removal, but with some loss of cultured cells. Microbubble-based cell separation may have a useful role in CTC purification protocols.
Citation Format: Thomas Jones, Leo J. Ostruszka, Shamileh Fouladdel, Ebrahim Azizi, Jaroslav Slamecka, Brandon H. McNaughton, John Younger, Max Wicha, Steven McClellan. Microbubble enrichment of CTCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 638.