a, Mammosphere assay of TNBC cells grown in ultra-low attachment plates in control or methionine-free mammosphere media (0% Met) with or without cycloleucine (CL, 50 mM). Top panel, representative images showing mammospheres at day 7. Bottom panel, mammospheres were scored in ten fields from each well (mean ± SEM, n =3) ***, P < 0.001 versus mammospheres grown in control media without cycloleucine. b, TNBC cells were cultured in ultra-low attachment plates in control or methionine-free mammosphere media (0% Met) with or without CL (50 mM) for 5 days. Apoptosis was measured by Annexin V labeling using flow cytometry. c, TNBC cells were cultured in ultra-low attachment plates in control or methionine-free mammosphere media (0% Met) with or without SAM (100 μM), CL (50 mM), or both for 7 days. Mammospheres were scored in ten fields from each well (mean ± SEM, n =3) *, P < 0.05, ***, P < 0.001 versus mammospheres grown in control media or the indicated comparisons.