a-d, Measurement of ROS levels (a), intracellular levels of cystine (b), NADP+/NADPH ratios (c), and cell death (d) of UMRC6 cells cultured in glucose-containing or glucose-free medium with or without treatment of TEMPO or Trolox. e-g, Measurement intracellular levels of cystine (e), NADP+/NADPH ratios (f), and cell death (g) of UMRC6 cells cultured in glucose-containing or glucose-free medium with or without treatment of 2 mM NAC. h-j, Measurement intracellular levels of cystine (h), NADP+/NADPH ratios (i), and cell death (j) of UMRC6 cells cultured in glucose-containing or glucose-free medium with or without treatment of 1 mM 2ME, 2 mM D-Penicillamine or L-Penicillamine. k-m, Measurement intracellular levels of cystine (k), NADP+/NADPH ratios (l), and cell death (m) of UMRC6 cells cultured in glucose-containing or glucose-free medium with or without treatment of TCEP. n-p, Measurement intracellular levels of cystine (n), NADP+/NADPH ratios (o), and cell death (p) of UMRC6 cells cultured in glucose-containing or glucose-free medium with or without treatment of 1 mM 2ME. All p values were calculated using two-tailed unpaired Student’s t-test. Detailed statistical tests are described in the Methods. All error bars are mean± s.d., n=3 independent experiments. Numeral data are provided in Statistics Source Data Fig. 4.