The numerous side effects of platinum based chemotherapy has led to the design of new therapeutics with platinum replaced by another transition metal. Here, we investigated the interactions of previously reported copper(II) complexes containing S-isoalkyl derivatives, the salicylic acid with guanosine-5′-monophosphate and calf thymus DNA (CT-DNA) and their antitumor effects, in a colon carcinoma model. All three copper(II) complexes exhibited an affinity for binding to CT-DNA, but there was no indication of intercalation or the displacement of ethidium bromide. Molecular docking studies revealed a significant affinity of the complexes for binding to the minor groove of B-form DNA, which coincided with DNA elongation, and a higher affinity for binding to Z-form DNA, supporting the hypothesis that the complex binding to CT-DNA induces a local transition from B-form to Z-form DNA. These complexes show a moderate, but selective cytotoxic effect toward colon cancer cells in vitro. Binuclear complex of copper(II) with S-isoamyl derivative of thiosalicylic acid showed the highest cytotoxic effect, arrested tumor cells in the G2/M phase of the cell cycle, and significantly reduced the expression of inflammatory molecules pro-IL-1β, TNF-α, ICAM-1, and VCAM-1 in the tissue of primary heterotopic murine colon cancer, which was accompanied by a significantly reduced tumor growth and metastases in the lung and liver.

Background/Objectives: 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. Methods: Silver(I) complexes with S-alkyl derivatives of thiosalicylic acid (C1–C5) 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. Results: Complexes C1–C5 exhibited strong cytotoxicity against murine and human breast (4T1, MDA-MB-468), colon (CT26, HCT116), and lung (LLC1, A549) cancer cell lines. The C3 complex significantly diminished tumor progression in an orthotropic mammary carcinoma model while demonstrating good systemic tolerance. Conclusions: The tested complex C3 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 C3 arrested the 4T1 cell cycle in G0/G1 phase, decreasing the expression of cyclin D3 and increasing the expression of p16, p21, and p27.

New zinc(II)-complexes with S-alkyl derivatives of thiosalicylic acid (alkyl = benzyl-(L1), methyl-(L2), ethyl-(L3), propyl-(L4), butyl-(L5)) have been synthesized and characterized by elemental microanalysis, IR spectroscopy, and ¹H and ¹³C NMR spectroscopy. The S-alkyl derivatives of thiosalicylic acid were prepared by alkylation of thiosalicylic acid by adding alkyl halides to an alkaline water-ethanol solution, while the corresponding zinc(II)-complexes were obtained via the direct reaction of ZnCl₂ with S-alkyl derivatives of thiosalicylic acid in water. Based on the microanalysis results and the IR and NMR spectra of the S-alkyl derivatives of thiosalicylic acid and the corresponding zinc(II)-complexes, we concluded that the ligands are bidentately coordinated to the zinc(II)-ion.