Fig. 7. l-Arginine decreases the DNA damage repair capacity of cancer cells.

(A) DNA synthesis capacity determined by 5-bromo-2′-deoxyuridine (BrdU) incorporation in MDA-MB-231 cells exposed to vehicle or l-arginine for 60 min with or without the NOS inhibitor L-NMMA. (B) Representative images of nuclear γH2AX and 53BP1 foci in MDA-MB-231-BrM2 cells exposed to vehicle, l-arginine, ionizing radiation, or the combination. (C) DNA damage levels assessed by comet assay in MDA-MB-231-BrM2 cells exposed to vehicle or l-arginine for 60 min followed by ionizing radiation (4 Gy). DNA damage was assessed at 60 min following l-arginine administration (baseline, before irradiation) and at 30 min and 4 hours following irradiation. (D) DNA damage levels in MDA-MB-231-BrM2 cells exposed to vehicle or l-arginine for 1 hour followed by etoposide for 2 hours. DNA damage was assessed by comet assay at 1 hour after vehicle or l-arginine administration, at 2 hours after etoposide treatment, and at 1.5 and 6 hours after drug washing (recovery). (E) Intratumor lactate concentration in the murine 4T1 TNBC orthotopic model. Mice were treated with vehicle or a mouse-equivalent dose of l-arginine administered by oral gavage, and tumor lactate content was measured after 60 min by nuclear magnetic resonance (NMR). (F) Experimental design (left) to determine γH2AX levels by flow cytometry in tumor cells (middle) and CD45⁺ tumor-associated lymphocytes (right) isolated from the murine 4T1 TNBC orthotopic model. Mice were treated with vehicle or a mouse-equivalent dose of l-arginine followed by ionizing radiation (2 Gy). Data are shown in viable cells (cleaved caspase-3^NEG). *P < 0.01, **P < 0.001, and ***P < 0.0001. ns, not significant.