Abstract 3101: Discovery of helical sulfonyl-γ-AApeptides targeting LC3 in cancer cells

Abstract

Abstract Introduction: Autophagy pathway activation and upregulation is an important mechanism for cancer cell survival upon exposure to chemotherapeutic agents. LC3, a ubiquitin-like protein, plays a key role in the regulation of cargo selection and autophagosome formation. Given small molecule inhibitors have not been well developed to target LC3, we aim to design and synthesize an LC3 binder and evaluate its activity in the inhibition of autophagy pathway in cancer cells. Methods: The crystal structure of LC3 and p62 complex (PDB: 2ZJD) was used to assist our design of helical sulfonyl-γ-AApeptides to the LC3 interacting region of p62. The peptidomimetics were synthesized on the solid phase and purified by HPLC. We used fluorescent polarization assay to assess the binding affinity of the peptidomimetics to LC3. We then utilized an LC3 HiBiT reporter cell line (U2OS) from Promega, which was engineered to have a fused human LC3-HiBiT with a HaloTag in between to study the effect of the lead LC3 binder on autophagic flux. In addition, confocal microscopy enabled direction visualization of the colocalization of FITC-labeled LC3 binder with LC3 and lysosome, respectively. Cytotoxicity of LC3 binder was evaluated in colorectal cancer cell line HCT116. Results: We designed and synthesized 6 helical sulfonyl-γ-AApeptides (JC1-6) to target the binding interface of LC3 and p62. These peptidomimetic compounds were designed to retain essential LC3 and p62 interactions at the W and L regions and yet have different functional groups on the helical scaffold. Compounds JC1 and JC6 have binding affinity of Kd 280 nM and 150 nM with LC3, respectively. FITC-labelled JC6 was able to penetrate U2OS and HCT116 cells. It had intracytoplasmic colocalization with not only lysosomes but also LC3 aggregates. Direct visualization of intracytoplasmic LC3 aggregates showed that JC6 at 50 µM significantly inhibited the autophagic degradation of LC3 aggregates. This effect was augmented by the presence of 2 µM autophagy activator PP242. Lastly, JC6 demonstrated cytotoxicity with IC50 approximately 50 µM in HCT116 cells bearing baseline autophagy activation compared to lack of cytotoxicity in U2OS cells with no baseline autophagy activity. Conclusion: We designed and synthesized novel helical sulfonyl-γ-AApeptide LC3 binders. With the ability of cellular penetration, they demonstrated inhibition of autophagic flux and preliminary cytotoxicity in cancer cells. Future studies may focus on structural activity relationship and further evaluation of its mechanisms of action in cancer cells. Citation Format: Mentalla Mahmoud, Jianyu Chen, Jianfeng Cai, Hao Xie. Discovery of helical sulfonyl-γ-AApeptides targeting LC3 in cancer cells [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 3101.