Fig. 1.

External cystine requirement for the growth of tumor cells. a The percent growth inhibition of cancer cells after 5 days of growth in special RPMI-1640 medium (10% FBS) with and without amino acids. For the complete medium, L-glutamine (2.05 mM) and L-methionine (100 μM) were added at their normal concentration present in the regular RPMI-1640 medium. L-cystine (84 μM) at its physiological concentration was added to the medium. + and − symbols indicate presence or absence of the amino acids in the medium. ∗ p < 0.001, ∗∗ p ≤ 0.003. b Representative photomicrographs of FaDu cells treated with various concentration of MSG with and without BME in special RPMI-1640. Cells were treated for 24 h, rinsed with sterile PBS and fresh medium was added. Cells were further incubated for 72 h and pictures were captured with 100 × magnification using inverted microscope. c Percent growth inhibition of FaDu cells treated with different concentrations (100, 150 and 180 μM) of MSG alone and in combination with BME. Special RPMI-1640 medium was used. ∗ p ≤ 0.005, ∗∗ p ≤ 0.001.