GBM is the most common primary malignancy of the central nervous system29,30
. Amplification of EGFR is the most frequent genetic abnormality associated with GBM, and EGFR overexpression has been shown in up to 85% of cases29
. GBM also often expresses EGFRvIII, a genomic deletion variant of EGFR that is constitutively active and highly oncogenic31,32
. It is likely that the recent identification of circulating MVs containing EGFRvIII specific RNA5
and GBM associated proteins10
will not only be immediately relevant to this subset of GBM patients, but could also be expanded to other GBM-mutation evaluation. Likewise, circulating MVs may provide new avenues for cancer diagnostics and expand our understanding of cellular communication.
Evaluating circulating MVs could lead to a paradigm shift in clinical care. Phase 1 and phase 2 trials of targeted agents presently require molecular stratification of GBM tumors. In addition, there remains an urgent need to provide sequential indices of tumor molecular response to these agents. While imaging remains useful as a clinical tool, the standard RECIST (Response Evaluation Criteria In Solid Tumors) and volumetric criteria of response are insensitive therapeutic markers in patients receiving vascular-targeted agents such as Avastin. New and more sensitive imaging approaches33–36
are currently in development; however, they are not universally available, are often expensive37
and impractical for rapid sequential evaluations. As a result, there has been intense interest in finding serologic biomarkers for GBM.
Our findings show that GBM-derived circulating MVs can be rapidly detected in clinical blood samples with high sensitivity using a nanotechnology-inspired biosensor. The system combines on-chip micro-filtration and μNMR principles, to enable quantitative detection of MV numbers and protein expression. Measurements are performed on small sample volumes without the need for extensive purification or time-consuming detection techniques. By employing a bioorthogonal targeting approach to specifically target and densely pack MNPs onto MVs, the current platform has achieved a detection sensitivity that surpasses standard ELISA and flow cytometry analyses by several orders of magnitude (). We believe that this could be further enhanced with the use of newer magnetic nanomaterials (with higher magnetization)38
, improved assay types, additional amplification steps, and new bioorthogonal approaches. Likewise, further device optimization are expected. By incorporating differential, multistep filtering system, MVs can be isolated from whole cells; multiple microcoils can be embedded for extensive parallel profiling of a larger number of MV proteins. Such system could realize a comprehensive yet portable lab-on-a-chip for MV analysis.
We further envision other clinical applications in which protein typing of circulating MVs would be useful. The above-described methodology could be extended to examine other primary tumors, particularly since many cancers secrete much greater quantities of circulating MVs than CTCs. It could also be adapted to monitor circulating MVs in a variety of inflammatory and infectious diseases, using blood samples, cerebral spinal fluid, urine, saliva or other biofluids. With its capacity for molecular diagnostics at the bedside, the developed platform could potentially redefine the current standard-of-care for patients.