ATRT-18. SHH-SUBTYPE ATYPICAL TERATOID/RHABDOID TUMORS ARE SELECTIVELY SENSITIVE TO GEMCITABINE TREATMENT

Atypical Teratoid Rhabdoid Tumors (ATRT) are highly malignant embryonal tumors of the central nervous system with a dismal prognosis. ATRT can be divided into three molecular subgroups of which the Sonic Hedgehog (SHH) subgroup is most prevalent. In this study, we developed and validated a novel patient-derived ATRT model, which we used along a panel of other primary ATRT models for large scale drug discovery assays. We found that ATRTs are selectively sensitive to the nucleoside analogue gemcitabine, with SHH-subtype ATRTs being the most sensitive subgroup. Gene expression profiles and protein analysis indicated that gemcitabine treatment causes degradation of Sirtuin 1 (SIRT1), which causes ATRT specific cell-death through NF-kB and p53 activation. Furthermore, we found that this gemcitabine induced loss of SIRT1 results in a nucleus-to-cytoplasm shift of the SHH signaling activator Gli, explaining the additional gemcitabine sensitivity in SHH-subtype ATRT. Treatment of SHH-subgroup ATRT xenograft-bearing mice resulted in a >40% increase in median survival (p<0.01, log-rank test) and long-term survivors in two independent models. To prepare translation of our findings to the clinic, we investigated potential gemcitabine induced resistance mechanisms by conducting kinome-wide CRISPR/Cas9 knockout screens in primary ATRT cells. Through these experiments we found that low-dose gemcitabine treatment combined with inhibition of protein kinase C zeta (PKCζ) prevents regrowth of resistant ATRT subclones. Together, these findings show that ATRT are highly sensitive to gemcitabine treatment; and as such we suggest that gemcitabine may be rapidly incorporated into future treatment regimens for SHH-ATRT.