Many sarcomas and leukemias carry non-random chromosomal translocations encoding mutant fusion transcription factors that are essential to their molecular pathogenesis. These novel, tumor-specific proteins provides a unique opportunity for the development of highly selective anticancer drugs that has yet to be exploited. A particularly clear example is provided by Ewing's Sarcoma Family Tumors (ESFT) which contain a characteristic t(11;22) translocation leading to expression of the oncogenic fusion protein EWS-FLI1. EWS-FLI1 is a disordered protein that precluded standard structure-based small molecule inhibitor design. Using surface plasmon resonance screening, we discovered a lead compound, NSC635437. A derivative compound, YK-4-279, blocks RHA binding to EWS-FLI1, induces apoptosis in ESFT cells, and reduces the growth of ESFT orthotopic xenografts. These findings provide proof of principle that inhibiting the interaction of mutant cancer-specific transcription factors with the normal cellular binding partners required for their oncogenic activity provides a promising strategy for the development of uniquely effective, tumor-specific anticancer agents.

Clinical trials repurposing lysosomotropic chloroquine (CQ) derivatives as autophagy inhibitors in cancer demonstrate encouraging results, but the underlying mechanism of action remains unknown. Here, we report a novel dimeric CQ (DC661) capable of deacidifying the lysosome and inhibiting autophagy signifi cantly better than hydroxychloroquine (HCQ). Using an in situ photoaffi nity pulldown strategy, we identifi ed palmitoyl-protein thioesterase 1 (PPT1) as a molecular target shared across monomeric and dimeric CQ derivatives. HCQ and Lys05 also bound to and inhibited PPT1 activity, but only DC661 maintained activity in acidic media. Knockout of PPT1 in cancer cells using CRISPR/Cas9 editing abrogates autophagy modulation and cytotoxicity of CQ derivatives, and results in signifi cant impairment of tumor growth similar to that observed with DC661. Elevated expression of PPT1 in tumors correlates with poor survival in patients in a variety of cancers. Thus, PPT1 represents a new target in cancer that can be inhibited with CQ derivatives. SIGNIFICANCE:This study identifi es PPT1 as the previously unknown lysosomal molecular target of monomeric and dimeric CQ derivatives. Genetic suppression of PPT1 impairs tumor growth, and PPT1 levels are elevated in cancer and associated with poor survival. These fi ndings provide a strong rationale for targeting PPT1 in cancer.

Lysosomes serve dual roles in cancer metabolism, executing catabolic programs (i.e. autophagy and macropinocytosis), while promoting mTORC1-dependent anabolism. Antimalarial compounds such as chloroquine or quinacrine have been used as lysosomal inhibitors, but fail to inhibit mTOR signaling. Further, the molecular target of these agents has not been identified. We report a screen of novel dimeric antimalarials that identifies dimeric quinacrines (DQs) as potent anticancer compounds, which concurrently inhibit mTOR and autophagy. Central nitrogen methylation of the DQ linker enhances lysosomal localization and potency. An in situ photoaffinity pulldown identified palmitoyl-protein thioesterase 1 (PPT1) as the molecular target of DQ661. PPT1 inhibition concurrently impairs mTOR and lysosomal catabolism through the rapid accumulation of palmitoylated proteins. DQ661 inhibits the in vivo tumor growth of melanoma, pancreatic, and colorectal cancer mouse models and can be safely combined with chemotherapy. Thus, lysosome-directed PPT1 inhibitors represent a new approach to concurrently targeting mTORC1 and lysosomal catabolism in cancer.

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