SLC7A11 and glioblastoma: However, current evidence has shown that GBM cells, such as U87, U251, and U373 cells, are highly insensitive to treatment with SAS or erastin (72, 97), a phenotype that could be related to resistance mechanisms mediated by ATF4 and Nrf-2 that favor overexpression of SLC7A11 (21, 97, 98).