Chip-based analysis of exosomal mRNA mediating drug resistance in glioblastoma

Abstract

Real-time monitoring of drug efficacy in glioblastoma multiforme (GBM) is a major clinical problem as serial re-biopsy of primary tumors is often not a clinical option. MGMT (O6-alkylguanine DNA alkyltransferase) and APNG (alkylpurine-DNA-N-glycosylase) are key enzymes capable of repairing temozolomide-induced DNA damages and their levels in tissue are inversely related to treatment efficacy. Yet, serial clinical analysis remains difficult and when done, primarily relies on promoter methylation studies of tumor biopsy material at the time of initial surgery. Here we present a microfluidic chip to analyze mRNA levels of MGMT and APNG in enriched tumor exosomes obtained from blood. We show that exosomal mRNA levels of these enzymes correlate well with levels found in parental cells and that levels change considerably during treatment of seven patients. We propose that if validated on a larger cohort of patients, the method may be used to predict drug response in GBM patients.

Glycosylated extracellular vesicles released by glioblastoma cells are decorated by CCL18 allowing for cellular uptake via chemokine receptor CCR8

“…MGMT counteracts TMZ effects by direct removal of the O6-methyl group from alkylated guanines [81]. Interestingly, it was reported that GBM EVs from cell lines resistant to TMZ as well as from treatment-refractory patients carry elevated levels of MGMT mRNA, and that these levels are predictive for patient outcome [82]. We therefore do not exclude that EV transfer of MGMT mRNA molecules facilitates, at least partly, the resistance to TMZ observed [60–63].…”

Extracellular vesicles swarm the cancer microenvironment: from tumor–stroma communication to drug intervention

“…Levels of the DNA repair enzymes APNG and MGMT are inversely correlated to response to the gold standard chemotherapeutic temozolomide 30 . EVs containing MGMT mRNA have been demonstrated to accurately reflect the levels of these enzymes in parental cells and in patients throughout treatment and therefore could serve as a potential 'real-time' biomarker of chemotherapy response during drug treatment 70 . Similarly, circulating EVs containing the EGFRvIII splice variant that is thought to be predictive of response to EGFR inhibition were detectable in the serum of GBM patients but not in the 30 matched controls 71 .…”

Spitting out the demons: Extracellular vesicles in glioblastoma

“…51 In addition, as mentioned above, MGMT methylation status in circulating EVs was also found to correspond with the identity of the parental tumor and be predictive of the current response to treatment. 52 Altogether, this recent series of studies hold promise that EVs content may provide a novel tool for early diagnosis and companion biomarkers in combination with the current methods. 10,48 Could EVs be functionally targeted?…”