Design and Synthesis of New Heterocyclic-Chitosan Loaded Gold Nanoparticles That Induce Cancer Cell Death

Abstract Objective: This work involved the synthesis of novel polymer nanocomposites based on chitosan/Schiff bases and coated gold nanoparticles (AuNPs) 5a–5b via sequential methods, examining their antibacterial activity, and screening their potential as in vitro anticancer agents. Methods: The synthesis of the polymer nanocomposites 5a–5b involved a multi-step process. Initially, the symmetrical substituted 1,2,4-triazole-4-amine was prepared through a cyclization reaction of 4-methoxybenzohydrazide in DMSO, followed by a condensation reaction with syringaldehyde or 3,4,5-trimethoxybenzaldehyde, refluxing in dry benzene and AcOH, resulting in the formation of Schiff bases 2a–2b. The addition reaction of acid chloride with 2a–2b in dry benzene yielded N-acyl derivatives 3a–3b. Modified chitosan derivatives 4a–4b were prepared through the reaction between 3a–3b with chitosan in EtOH. In a blended matrix, AuNPs were bonded to chitosan/Schiff bases 4a–4b via a simple and green chemical reaction in good yield. The new compounds were tested for their antibacterial and antitumor activities. Moreover, an in vivo acute oral toxicity study was conducted in mice to evaluate the safety profile of the nanocomposite 5a using three doses from 5000 to 20000 mg/kg. Results and Discussion: The structures of the prepared compounds were confirmed by FT-IR, 1H NMR spectroscopy, and FESEM. Comparative analysis with amoxicillin as a standard antibiotic revealed that all the prepared compounds demonstrated moderate to excellent antibacterial activities against E. coli (Gramnegative) and Staphylococcus aureus (Grampositive). Additionally, the cytotoxic effect of the novel polymer nanocomposite 5a against an Iraqi patient-derived breast cancer cell line (AMJ13) was evaluated to estimate antitumor activity at serial concentrations ranging from 5 to 0.0195 µg/mL, and the results were compared with the effect against normal rat embryonic fibroblasts (REF) cell line. The nanocomposite 5a exhibited excellent inhibition of cancer cell proliferation. The cytotoxicity test of this nanocomposite showed no toxic effect in normal cells. Measurements of cytochrome c oxidase activity and apoptotic figures were used to estimate the capacity to induce apoptosis, which showed the ability of the nanocomposite to induce apoptosis in cancer cells with a lesser effect on normal cells. The acute toxicity results showed no mortality at 5000 mg/kg and only mild toxicity at higher doses, with an estimated LD50 greater than 20000 mg/kg, indicating a high safety margin. These findings corroborate the in vitro data, confirming the low toxicity of 5a in normal biological systems. Conclusions: The effective antitumor activity, biocompatibility, and low in vivo toxicity of the synthesized nanocomposite 5a further support its potential for safe clinical translation in cancer therapy.