CBIO-15. LOSS OF WILLIAMS SYNDROME TRANSCRIPTION FACTOR (WSTF) LEADS TO IMPROVED TEMOZOLOMIDE SENSITIVITY IN HUMAN GLIOBLASTOMA CELLS IRRESPECTIVE OF MGMT EXPRESSION

The prognosis for glioblastoma multiforme (GBM) patients is poor with a median survival of approximately 15 months. The DNA repair protein O⁶-methylguanine-DNA methyltransferase (MGMT) counteracts the effects of temozolomide (TMZ) chemotherapy and is thus associated with poor outcome in GBM patients. Williams Syndrome Transcription Factor (WSTF) has been suggested to regulate the DNA damage response pathway (DDR) in both an indirect (through chromatin remodeling) and direct manner (by phosphorylating H2AX at Tyr142). However, whether WSTF has any role in the development of resistance against chemotherapy through its functions in the DDR in GBMs, is so far unknown. In this study, we investigated whether a loss of WSTF sensitizes different MGMT-proficient and -deficient GBM cell lines to TMZ treatment.

We generated WSTF knockout clones from both MGMT-proficient (LN18, T98G) and -deficient GBM cell lines (U-251) using CRISPR/Cas9 gene-editing technology with lentiviral vectors. The PCR-based screening results combined with the T7 endonuclease mismatch assay for bi-allelic monoclonal knockouts were verified via sequencing and immunoblotting to identify candidate knockout clones. Colony formation assays were performed to determine the survival ability in response to TMZ treatment. Statistical analysis was performed using two-way ANOVA.

WSTF knockout clones showed a significant decrease in colony formation after TMZ-treatment compared to the corresponding control groups (non-target single guide RNA) (LN18: Clone 59 vs control: p= 0.0456, T98G: All three studied clones vs control: p< 0.0001, U-251: Clone 7/35.1/70.2 vs control: p< 0.0001/p= 0.0107/p= 0.0119).

WSTF is an important factor in both MGMT de- and proficient GBM cell lines for response against TMZ chemotherapy. The loss of WSTF leads to a significantly increased TMZ sensitivity in clinically relevant concentrations for all the studied cell lines. Ongoing studies are investigating the underlying mechanisms and potential alterations in the DDR pathway caused by WSTF loss.