Abstract 1384: Stearoyl-CoA desaturase confers cell density-dependent resistance to ferroptosis induced by inhibition of glutathione peroxidase 4 in melanoma cells
Authors: Shirahama Hitomi , Tani Yuri , Tsukahara Satomi , Okamoto Yuka , Hasebe Akiko , Dan Shingo , Tomida Akihiro 
Published: April 2023

Abstract
Ferroptosis, one of the programmed cell deaths, is induced by accumulation of lipid peroxidation. To protect from ferroptosis, cells possess a wide range of reduction systems including glutathione peroxidase 4 (GPX4), which reduces lipid peroxides to non-toxic lipid alcohols. Indeed, inhibiting GPX4 leads to ferroptosis in various cancer cells, but cellular sensitivity to GPX4 inhibition often varies depending on cell conditions. Some previous studies reported that an increase in cell density induces resistance to GPX4 inhibition, but the mechanisms of cell density-dependent resistance are not fully understood.
In this study, we have also found that several melanoma cell lines become resistant to ferroptosis induced by GPX4 inhibition in a density-dependent manner. For example, a selective GPX4 inhibitor, RSL3, immediately induced cell death at low cell density of A375 within 6-8 hours, but did not at high density even after 24 hours. The acute cell death at low density was rescued by ferroptosis inhibitors (lipid peroxidation inhibitors or iron chelator), but not those of apoptosis and necrosis, supporting that this type of cell death is ferroptosis.
To elucidate the mechanisms of ferroptosis resistance at high density, we first conducted transcriptome and metabolome analyses using the difference between low and high densities of A375. The gene ontology analysis on upregulated genes at high density indicated an increase in fatty acid metabolism. In contrast, nutritional stress was not implied from the transcriptional analysis, resulting from frequent changes of culture medium to avoid nutrition starvation. The enrichment analysis based on upregulated metabolites at high density similarly suggested increased de novo lipogenesis. Particularly, gene and protein levels of stearoyl-CoA desaturase (SCD) were induced in a density-dependent manner. Similar induction of SCD was observed in several melanoma cell lines.
We further examined the role of SCD in density-dependent ferroptosis resistance. With this aim, pharmacological inhibition or genetic knockout of SCD was conducted on A375 at different densities (low and high) treated with RSL3. The result showed that SCD inhibition reduced RSL3 resistance at high density while having no effect on RSL3 sensitivity at low density. In summary, we found that SCD is upregulated in melanoma cells at high density and protects cells from ferroptosis induced by GPX4 inhibition. It is known that metastasizing melanomas in the blood are sensitive to ferroptosis, resembling cells at low density. This report might provide an explanation for the ferroptosis sensitivity of metastasizing melanomas and a strategy for ferroptosis-based therapy.
Citation Format: Hitomi Shirahama, Yuri Tani, Satomi Tsukahara, Yuka Okamoto, Akiko Hasebe, Shingo Dan, Akihiro Tomida. Stearoyl-CoA desaturase confers cell density-dependent resistance to ferroptosis induced by inhibition of glutathione peroxidase 4 in melanoma 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 1384.