MICRORNA DEGRADATION ENHANCES GLIOBLASTOMA INTRA-TUMORAL HETEROGENEITY TO AUGMENT ACQUIRED TEMOZOLOMIDE RESISTANCE

INTRODUCTION O6 methyl-guanine methyltransferase (MGMT) restores alkylated DNA to its undamaged form and dictates clonal evolution in response to chemotherapy. As such, MGMT is a major determinant of glioblastoma resistance to the standard-of-care chemotherapy temozolomide. miR-181d is a MGMT suppressing microRNA, whose expression inversely correlate with survival expectation after temozolomide treatment. Here, we characterize the expression of miR-181d and MGMT in response to temozolomide treatment. Method: Laboratory characterization, single cell analysis, and murine modeling RESULTS Treatment of glioblastoma cells with temozolomide (TMZ) induced a feed-forward cascade resulting in an ataxia telangiectasia and Rad3 (ATR) and polyribonucleotide nucleotidyl transferase 1 (PNPT1) dependent degradation of miR-181d. Single-cell analyses revealed such miR-181d degradation: 1) increased mean level of MGMT expression in a cell population and 2) enhanced cell-to-cell variability in MGMT expression to increase intra-tumoral heterogeneity in DNA repair capacity. This increased intra-tumoral heterogeneity enhanced glioblastoma resistance to temozolomide through a mechanism distinct from lowering the mean MGMT expression of the tumor population. Suppression of this heterogeneity by exogenous miR-181d over-expression enhanced the tumoricidal activity of temozolomide against glioblastomas. CONCLUSION We identified an interface between DNA damage response and miRNA degradation that mediate intra-tumoral heterogeneity and subsequent temozolomide resistance. This resistance mechanism is distinct from modulation of the mean MGMT expression of the population.