Abstract 1340: Assessing autophagic flux in cell culture models with a novel plate-based assay

The importance of autophagy in normal cell health and diseased states, including cancer, immunology and inflammation, has become quite clear. Given the growing interest in screening for autophagy modulators, we have developed a homogeneous plate-based assay to measure autophagic flux in cell culture models using NanoLuc® Binary Technology (NanoBiT™). LC3B (Atg8) protein was tagged on its N-terminus with an 11 amino acid peptide, (HiBiT), as well as an intervening “spacer” sequence. When expressed at low-to-moderate levels in mammalian cell lines, this LC3-based reporter is subject to degradation by the autophagic pathway. Changes in reporter levels following cell treatment are determined by addition of a lytic reagent containing Large BiT (LgBiT), which rapidly associates with HiBiT to produce a bright, luciferase activity in the presence of added substrate. In stable U2OS reporter cells, mTORC inhibitor treatment decreased assay signal by 25% (rapamycin) to 60% (PP242, AZD8055), consistent with compound stimulation of autophagic flux and degradation of the autophagy reporter. In contrast, treatment with autophagy inhibitors (bafilomycin A1, chloroquine) produced a 70-80% increase in assay signal, consistent with accumulation of autophagy reporter following blockade of basal autophagy. Similar results were obtained in HEK293 cells stably expressing the reporter, as well as in cells in which autophagy reporter was transiently expressed via simple, one-step transduction with BacMam viral particles. Mechanism of action of autophagy modulators was confirmed through blockade of effects by 50nM bafilomycin A1 cotreatment. Multiplex with a cell necrosis detection agent allowed for same-well determination of cytotoxic effects that might undermine analysis of a compound9s discrete effects on autophagic flux. When assayed in 384-well plates with automation, U2OS and HEK293 autophagy reporter cells produced Z9 values of 0.6-0.7 in response to autophagy induction (PP242), and Z9 values of 0.7-0.8 by subsequent blockade of autophagy (PP242 + bafilomycin A1). Therefore, using this novel plate-based assay system for the determination of autophagic flux, it is possible to screen test agents and quantitatively assess their effects in cell culture models. Citation Format: Dan F. Lazar, Ryan W. Kessens, Amani A. Gillette, Braeden L. Butler, Christopher T. Eggers, Brock F. Binkowski, Gediminas Vidugiris, Michael R. Slater, Dongping Ma, James J. Cali. Assessing autophagic flux in cell culture models with a novel plate-based assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1340.