Fig. 8: Lysine restriction and its mimetic boost the therapeutic efficacy.

A Sensitivity of TGS04 cells cultured in a lysine-restricted medium to TMZ was measured by the sphere formation assay (n = 4 technical replicates). B Illustration for the mechanism of homoarginine action on lysosomal function, in which homoarginine induces nitric oxide as a substrate of nitric oxide synthase. C Nitric oxide level in TGS04 cells was detected with DAF-FM DA after treatment with 30 mM homoarginine (hArg) for 16–24 h with flow cytometry. D, E Lysosomal proteolytic activity was detected after treatment with homoarginine (25 mM) for 16–24 h in TGS04 cells with confocal fluorescence microscopy (D) (n = 30 cells/group) and with flow cytometry (E). F Sensitivity of TGS04 to TMZ in combination of hArg (n = 4 technical replicates). G Sensitivity of TGS04 cells overexpressing MGMT to TMZ with or without homoarginine was measured (n = 3 technical replicates). H Sensitivity of KGS23 cells, which naturally express MGMT, to TMZ with or without homoarginine was measured (n = 3 technical replicates). I Quantification of the number of spheres formed by neural progenitor cells treated with TMZ and hArg (n = 3 technical replicates). J Screening for drugs synergized with homoarginine to suppress GBM cell viability using a clinically available anticancer drug library consisting of 174 compounds. TGS04 cells were treated with 3 doses of anticancer drugs and 25 mM homoarginine for 2 days before cell viability assay. K, L Sensitivity of TGS04 cells to the indicated drugs in the presence or absence of homoarginine (hArg) (n = 3 technical replicates). M Sensitivity of TGS04 cells to X-ray in the presence or absence of hArg (n = 4 technical replicates). Data are presented as the means ± SD. Statistic comparison (A, F–I, K–M) using a two-way ANOVA. Statistic comparison (D) using unpaired two-tailed Student’s t-tests. ns, not significant, ****p < 0.0001. Experiments (I, K–M) were repeated at least two times with similar results, other experiments were repeated at least three times with similar results. Source data are provided with this paper.