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Atypical teratoid rhabdoid tumors (ATRTs) are fatal pediatric brain tumors that warrant improved therapies urgently. ATRTs are characterized by loss of INI1, a subunit of the SWI/SNF chromatin-remodeling complex. ATRTs grow aggressively despite majority of primary tumors expressing p53, suggesting inactivation of this tumor suppressor pathway. Reactivation of p53 could be a potential therapeutic strategy for inhibiting ATRT growth. Our laboratory specializes in researching mechanisms contributing to ATRT pathogenesis and potential therapies. In line with this, we investigated an anti-malarial drug called quinacrine that has been safely used in children for decades and can induce p53 in renal cell carcinoma. We used 5 patient-derived ATRT cell lines (BT-37, BT-12, CHLA-06, CHLA-266, CHLA-05) for our studies. We show that ATRT cell lines treated with quinacrine for 6 hours show increased expression of p53, suggesting its activation. Treatment of ATRT cell lines with increasing doses of quinacrine for 24 hours showed dose-dependent decrease in cell growth and proliferation (assessed by MTS assay and BrdU incorporation, P&amp;lt;0.05) and increase in apoptotic cell death (CC-3 and cleaved PARP expression). Nude mice harboring flank tumors of ATRT cell lines and treated with quinacrine for 3 weeks showed significant reduction in tumor growth compared to control animals (P&amp;lt;0.05). Since quinacrine is a substrate for the drug-efflux proteins P-gp/BCRP, we used quinacrine in combination with elacridar (Pgp/BCRP inhibitor) in our intracranial xenograft experiments to increase quinacrine’s retention in the brain. Mice harboring intracranial xenografts of ATRT cells showed increased survival when treated with quinacrine and elacridar (median survival 46 days) compared to control animals (median survival 25 days). These results suggest that quinacrine inhibits ATRT growth, partly by activating p53. Our studies are the first to show quinacrine’s effect on ATRTs and our current experiments include further investigation of quinacrine’s mechanism.

ATRT-05. REPURPOSED ANTI-MALARIAL QUINACRINE ACTIVATES P53 AND INHIBITS ATRT TUMORIGENICITY