Silver(I) Complexes Bearing S-Alkyl Thiosalicylic Acid Derivatives: DNA/BSA Binding and Antitumor Activity In Vitro and In Vivo

<b>Background/Objectives:</b> In recent years, silver complexes have shown strong antibacterial, antifungal, and antitumor activity with high selectivity toward cancer cells. Their cytotoxic effects are mainly linked to apoptosis induction, DNA damage, and enzyme inhibition, while the antitumor activity of silver(I) complexes with S-alkyl thiosalicylic acid derivatives remains unexplored. <b>Methods:</b> Silver(I) complexes with S-alkyl derivatives of thiosalicylic acid (<b>C1</b>-<b>C5</b>) were obtained through the direct reaction of silver(I) nitrate, the corresponding ligand of thiosalicylic acid, and a sodium hydroxide solution. The interactions between the complexes and CT-DNA/BSA were studied using UV-Vis, fluorescence spectroscopy, and molecular docking studies. The cytotoxic capacity of the newly synthesized complexes was assessed by an MTT assay. <b>Results</b>: Complexes <b>C1</b>-<b>C5</b> exhibited strong cytotoxicity against murine and human breast (4T1, MDA-MB-468), colon (CT26, HCT116), and lung (LLC1, A549) cancer cell lines. The <b>C3</b> complex significantly diminished tumor progression in an orthotropic mammary carcinoma model while demonstrating good systemic tolerance. <b>Conclusions</b>: The tested complex <b>C3</b> triggered apoptosis in 4T1 cells by altering the delicate balance between pro- and anti-apoptotic Bcl-2 family members, increasing reactive oxygen species (ROS) levels, and reducing mitochondrial membrane depolarization. Moreover, the <b>C3</b> arrested the 4T1 cell cycle in G0/G1 phase, decreasing the expression of cyclin D3 and increasing the expression of p16, p21, and p27.