Combination screen in multi-cell type tumor spheroids reveals interaction between aryl hydrocarbon receptor antagonists and E1 ubiquitin-activating enzyme inhibitor

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates the expression of genes involved in drug transport and the metabolism of xenobiotics, facilitating their detoxification. In cancer biology, AhR plays a dual role, capable of both promoting and suppressing tumor development by influencing malignant behaviors in tumor cells and modulating anti-tumor immunity. The impact of AhR activity varies depending on the tumor type and its developmental stage, prompting the development of selective AhR modulators, such as BAY 2416964, currently under clinical investigation.

To explore potential small molecule anticancer agents that could complement AhR antagonists in cancer treatment, researchers conducted a high-throughput combination screening. This screening utilized multi-cell-type tumor spheroids, comprising malignant cells, endothelial cells, and mesenchymal stem cells. The AhR-selective antagonists—BAY 2416964, GNF351, and CH-223191—were evaluated both as monotherapies and in combination with 25 different anticancer agents. As standalone treatments, BAY 2416964 and CH-223191 exhibited limited activity, whereas GNF351 reduced the viability of certain spheroid models at concentrations above 1 µM.

For most combinations, the observed effects aligned with the single-agent activity of the partnered anticancer agents, indicating little added benefit from the AhR antagonists. However, all three antagonists enhanced the sensitivity of tumor spheroids to TAK-243, an inhibitor of the E1 ubiquitin-activating enzyme. These synergistic effects were observed in spheroids derived from various tumor types, including bladder, breast, ovarian, kidney, pancreatic, colon, and lung cancers. Additionally, AhR antagonists potentiated the activity of pevonedistat, a selective inhibitor targeting the NEDD8-activating enzyme E1 regulatory subunit, across several tumor spheroid models.