Abstract 4872: DCC-3116, a first-in-class selective ULK1/2 inhibitor of autophagy, in combination with the KIT inhibitor ripretinib induces complete regressions in GIST preclinical models

Abstract

Abstract Background: Cancer cells activate autophagy as an adaptive stress response (ASR) mechanism to therapies targeting the RTK/RAS/MAPK/PI3K pathways, limiting antitumor response. Autophagy is initiated through ULK1/2 kinases and is triggered by inhibitors of the MAPK and PI3K pathways. Most gastrointestinal stromal tumors (GIST) are driven by mutations in KIT kinase. KIT signals through MAPK/PI3K pathways, suppressing ULK1/2 kinases and autophagy1,2,3. Inhibition of mutant KIT reverses this suppression, activating autophagy and cancer cell survival. Approved therapies for GIST include imatinib, sunitinib, regorafenib, ripretinib, and avapritinib. Treatment with these inhibitors is initially successful, but drug resistance can develop either through KIT secondary mutations or ASR pathways including autophagy. DCC-3116 is a selective, potent, first-in-class investigational inhibitor of the ULK1/2 in clinical development in combination with targeted therapies that activate the autophagic ASR pathway. Herein we demonstrate that ULK1/2 and autophagy are activated upon treatment with ripretinib in KIT mutant GIST models A combination of ripretinib with DCC-3116 inhibits autophagy in vitro and leads to complete tumor regressions in preclinical models of GIST. Methods: Inhibition of ULK1/2 in cell assays was measured using an ELISA for the ULK substrate phospho-ATG13 (pATG13). Autophagic flux was measured by monitoring mCherry/GFP tagged LC3 protein in GIST cells. Xenograft studies were performed at CROs. Results: Ripretinib treatment led to the activation of ULK1/2 by 2-3-fold in mutant KIT GIST cell lines. DCC-3116 inhibited both ripretinib-induced and basal pATG13 with IC50 values of 12-32 nM. Treatment of GIST-T1 cells with ripretinib increased autophagic flux 3-fold. DCC-3116 potently inhibited flux with an IC50 value of 38 nM. Ripretinib also induced pATG13 and autophagic flux (1.5-2.5-fold) in multiple imatinib-resistant cell lines, which was inhibited by DCC-3116 with IC50 values between 8-189 nM. In a GIST T1 PK/PD model, DCC-3116 inhibited ULK1/2-mediated pATG13. The combination of DCC-3116 with ripretinib resulted in complete tumor regressions in comparison to single agent treatment in GIST preclinical models. Conclusions: These data demonstrate preclinically that, like other receptor tyrosine kinase inhibitors1, ripretinib activates ULK1/2-mediated autophagy as an ASR resistance mechanism which is inhibited by DCC-3116, providing the rationale to study the combination of DCC-3116 with ripretinib in GIST patients. DCC-3116 is currently in a Phase 1 clinical trial in patients with advanced solid tumors (NCT04892017).