Abstract 1377: DCC-3116, a first-in-class selective inhibitor of ULK1/2 kinases and autophagy, synergizes with encorafenib and cetuximab in BRAF V600E mutant colorectal cancer models
Authors: Bogdan Madhumita , Timson Mary J. , Al-Hashimi Hikmat , Smith Bryan D. , Flynn Daniel L. 
Published: June 2023

Abstract
Background: Cancer cells activate autophagy through ULK1/2 kinases as an adaptive stress response (ASR) mechanism to therapies targeting the RTK/RAS/MAPK/PI3K pathways, limiting antitumor response. BRAF signals through the MAPK pathway while EGFR signals upstream through both the MAPK and PI3K pathways, suppressing ULK1/2 kinases and autophagy. Inhibition of mutant BRAF and EGFR reverses this suppression, activating the autophagy ASR1-4. The BRAF V600E mutation occurs in ~10% of colorectal cancer (CRC) patients. Approved treatments for these patients include the BRAF V600E inhibitor encorafenib in combination with the EGFR antibody, cetuximab. Treatment with encorafenib + cetuximab (E+C) is initially successful, but drug resistance develops either through RTK/MAPK resistant mutations or ASR pathways including autophagy. DCC-3116 is a selective, investigational, potent, first-in-class inhibitor of the ULK1/2 kinases in clinical development in combination with targeted therapies that activate the autophagic ASR pathway. Herein we demonstrate ULK1/2 kinases and autophagy are activated upon treatment with E+C. A combination of E+C with DCC-3116 leads to inhibition of ULK1/2-mediated ATG13 phosphorylation (pATG13) and autophagy in vitro. In a PK/PD model, DCC-3116 inhibits E+C induced pATG13 and leads to synergistic tumor growth inhibition (TGI) in a preclinical model of BRAF V600E mutated CRC.
Methods: ULK1/2 activity was measured in cells using an ELISA for the ULK substrate phospho-ATG13 (pATG13). Autophagic flux was measured by monitoring mCherry/GFP tagged LC3 in HT-29 and Colo-205 cells. Xenograft models were performed at a CRO.
Results: E+C treatment led to the activation of ULK1/2 2-3-fold in BRAF V600E mutated CRC cell lines. DCC-3116 inhibited both E+C -induced and basal pATG13 with IC50 values of 80 nM and 234 nM in HT-29 and Colo-205 cells, respectively. E+C induced autophagic flux ~3-fold which was potently inhibited by DCC-3116 with IC50 values of 65 nM in HT-29 and 40 nM in Colo-205 cells. In a PK/PD model, DCC-3116 inhibited ULK1/2-mediated pATG13 induced by E+C. The combination of DCC-3116 with E+C resulted in greater TGI compared to single agent or the combination of E+C in BRAF V600E models.
Conclusions: These preclinical data demonstrate that BRAF inhibitors in combination with EGFR blockade such as E+C activate ULK-mediated autophagy as an ASR resistance mechanism which can be inhibited by DCC-3116, providing the rationale to study the combination of DCC-3116 with E+C in BRAF V600E mutated CRC patients. DCC-3116 is currently in a Phase 1 clinical trial in patients with advanced solid tumors. (NCT04892017).
References: 1. Bogdan et al. 2021. Mol Cancer Ther 20(12 Suppl):Abstract P084. 2. Gupta et al. 2010. PNAS 107:14333-8 3. Li et al. 2013. Lung Cancer 81:354-61 4. Mehnert et al. 2022. Clin Cancer Res 28:1098-1106
Citation Format: Madhumita Bogdan, Mary J. Timson, Hikmat Al-Hashimi, Bryan D. Smith, Daniel L. Flynn. DCC-3116, a first-in-class selective inhibitor of ULK1/2 kinases and autophagy, synergizes with encorafenib and cetuximab in BRAF V600E mutant colorectal cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1377.