Response of LUAD cells to LCS3

High-throughput phenotype-based screening of large libraries of compounds can identify small molecules that elicit a desired cellular response, but additional approaches are required to find and characterize their targets and mechanisms of action. Here we show that a compound termed lung cancer screen 3 (LCS3), previously selected for its ability to impair the growth of human lung adenocarcinoma (LUAD) cell lines, but not normal lung cells, induces oxidative stress and activates the NRF2 signaling pathway by generating reactive oxygen species (ROS) in sensitive LUAD cell lines. To identify the effector that mediates this effect, we applied thermal proteome profiling (TPP) and uncovered the disulfide reductases GSR and TXNRD1 as LCS3 targets. Through enzymatic assays using purified protein, we confirmed that LCS3 inhibits disulfide reductase activity through a reversible, uncompetitive mechanism. Further, we demonstrate that LCS3-sensitive LUAD cells are correspondingly sensitive to the synergistic inhibition of glutathione and thioredoxin pathways. Lastly, a genome-wide CRISPR screen identified the loss of NQO1 as a mechanism of LCS3 resistance. This work highlights the power of TPP to uncover targets of small molecules identified by high-throughput screens and demonstrates the potential utility of inhibiting disulfide reductases in treatment of LUAD. Two LUAD cell lines (H1650 and H23) sensitive to LCS3 were treated with the 3uM LCS3 or DMSO (0.1%) and RNA harvested at the points indicated for expression analysis using Affymetrix arrays. In total, two biological replcates were analyzed for each cell line for each treatment condition/time point.