MGMT genomic rearrangements contribute to chemotherapy resistance in gliomas.

Temozolomide (TMZ) is an oral alkylating agent used for the treatment of glioblastoma and is now becoming a chemotherapeutic option in patients diagnosed with high-risk low-grade gliomas. The O-6-methylguanine-DNA methyltransferase (MGMT) is responsible for the direct repair of the main TMZ-induced toxic DNA adduct, the O6-Methylguanine lesion. MGMT promoter hypermethylation is currently the only known biomarker for TMZ response in glioblastoma patients. Here we show that a subset of recurrent gliomas carries MGMT genomic rearrangements that lead to MGMT overexpression, independently from changes in its promoter methylation. By leveraging the CRISPR/Cas9 technology we generated some of these MGMT rearrangements in glioma cells and demonstrated that the MGMT genomic rearrangements contribute to TMZ resistance both in vitro and in vivo. Lastly, we showed that such fusions can be detected in tumor-derived exosomes and could potentially represent an early detection marker of tumor recurrence in a subset of patients treated with TMZ.We would like to acknowledge Claudia Savini, Susana Garcia, and Hector Peinado for the help and discussion on the exosome isolation and analysis. We thank MCarmen Martin Guijarro and Francisco Jose Moya for performing the FISH staining. We thank Manuel Perez and Gadea Mata for their assistance with the high-throughput microscopy analysis. We also thank Alvaro Ucero for the help with the isolation of the blood from the mice. We are very grateful to Anne Harttrampf and Lilianne Massade for sharing treatment information of the medulloblastoma patient, in which they identified the ASAP2-MGMT fusion. This research was supported by funds from the Seve Ballesteros Foundation and the Asociacion Espanola Contra el Cancer (AECC) to M.S. This work was also supported by Natural Science Foundation of China (NSFC)/Research Grants Council (RGC) Joint Research Scheme (81761168038 to TJ and N_HKUST606/17 to J.W.), RGC-ECS grant 26102719, the NSFC grant (No. 31922088), ITC grant (ITCPD/17-9), Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (ZYLX201708), Beijing Municipal Administration of Hospitals' Mission Plan (SML20180501), Beijing Nova Program (Z171100001117022) and Beijing Talents Foundation from Organization department of Municipal committee of the CPC (2017000021223ZK32).S