AML cells do not synthesize cysteine from methionine and, thus, are auxotrophic for this NEAA. (A) Schematic depiction of the metabolic steps in the conversion of methionine (Met) to homocysteine, which proceeds through the TsP to generate cysteine. Cysteine can then be metabolized to generate GSH and taurine (Tau). (B) Relative cell counts at day 2 of HL60 and MOLM13 cells grown with cystine or without cystine (Cys) but in the presence of RPMI-1640 methionine concentrations (0.1 mM) or excess concentrations (1 mM) of methionine. (C) As in panel B but viability is shown. (D) Relative cell counts at day 2 of HL60 and MOLM13 cells grown with or without cystine, or without cystine but in the presence SAM. (E) Relative cell counts at day 1 of MOLM13 cells growth with or without methionine, or without methionine but in the presence SAM. (F) Relative cell counts at day 2 of HL60, MOLM13 and K562 cells grown with or without cystine, or without cystine but in the presence HCY. (G) Normalized expression from the CCLE data set for CBS and CTH in a panel of AML cell lines. (H) EC50 curves for K562 scrambled guide RNA (SCR gRNA) and CTH knockout (KO) cells grown for 3 days in a concentration range of cystine. All experiments: error bars represent mean ± standard error of the mean. Statistical analysis by ordinary 1-way analysis of variance (ANOVA); ∗P < .05, ∗∗P < .01, ∗∗∗P < .001, and ∗∗∗∗P < .0001. Rel., relative.