Zwitterionic polymer-coated immunobeads for blood-based cancer diagnostics

Both total plasma and tumor-derived microvesicle (TMV)-associated miRNAs have been proposed as potential blood-based biomarkers for cancer diagnosis. However, there has been no comparison of the two types of miRNAs for biomarker discovery because of technological challenges of isolating TMVs from human plasma. The effective isolation of TMVs can be hardly achieved with conventional immunobead-based methods due to the high content of plasma proteins. In the current study, zwitterionic sulfobetaine-conjugated immunobeads are prepared using cluster of differentiation 83 (CD83) as a candidate protein marker for breast cancer-derived microvesicles. The zwitterionic immunobeads are more than 10-fold efficient for isolating TMVs from clinical plasma samples by suppressing nonspecific protein binding than conventional immunobeads. Early-stage breast cancer can be distinguished from benign breast disease by using the sulfobetaine-modified immunobeads, whereas conventional immunobeads show poor discriminatory performance. Further, we demonstrate that miRNAs in the form of TMVs offer a major improvement over total plasma miRNAs for early cancer detection. The analyses of miRNA expression levels show that in total, 6 miRNAs are significantly upregulated in the CD83-positive microvesicles of breast cancer patients, whereas differential miRNA expression is not detected on using total plasma RNA. The results indicate that our zwitterionic immunobead platform may constitute a powerful tool to identify circulating biomarkers and open a new avenue for highly sensitive blood-based cancer diagnostics.