“Green Synthesis of Silver Nanoparticles using Cowpea Pods and the Evaluation of anticancer effects in vitro

Abstract

Cancer remains a major global health burden, and the number of cases is expected to double by 2040. Current treatments such as surgery, chemotherapy and radiotherapy have shown improved health and survival rates but are limited by several drawbacks. Chemotherapy and radiotherapy may result in adverse effects and drug resistance, while surgery is primarily effective on solid and tissue confined tumours. Consequently, there is a pressing demand for novel cancer therapies that are effective and have less adverse side effects. Nanotechnology has shown potential to develop novel anticancer strategies that incorporate materials on the nanoscale range. Metallic nanoparticles, particularly silver nanoparticles (AgNPs) have demonstrated impressive anticancer properties, and a potential to be effective in both localized and metastatic cancers. Their effectiveness is due to their physicochemical properties such as large surface area, tuneable size and shape, making them valuable for various biological applications such as biotechnology, medicine, microbiology and pharmaceuticals. The physical and chemical synthesis methods of AgNPs are costly, energy-intensive, and use environmentally harmful chemicals. Green synthesis using agricultural waste like cowpea pods (CP) provides sustainable, more affordable, and environmentally friendly alternatives. In this study, CP aqueous extract was obtained through maceration in distilled water and used as a reducing and stabilizing agents in the biosynthesis of CP-AgNPs. The CP-AgNPs were synthesized by optimizing reaction parameters such as pH, temperature, CP-Extract concentration, AgNO3 concentration and reaction time. CP-AgNPs were characterized using Ultraviolet-visible (UV-Vis) spectroscopy, Dynamic Light Scattering (DLS), High Resolution-Transmission Electron Microscopy (HR-TEM) and Attenuated Total Reflectance Fourier Transform Infrared (ATR- FTIR). The stability of CP-AgNPs was evaluated in biological media such as, Phosphate Buffered Saline (PBS), Roswell Park Memorial Institute (RPMI) 1640 and Dulbecco’s Modified Eagle’s Medium (DMEM) with supplements (complete) and without supplements (incomplete). The total phenolic content (TPC) of CP-Extract and CP-AgNPs was determined by Folin-Ciocalteu (FC) assay using Gallic acid as a reference standard. The anticancer effects of CP-Extract, CP-AgNPs, free doxorubicin (Dox), and co-treatment of CP-AgNPs with Dox were evaluated on normal skin fibroblast (KMST-6), pancreatic cancer (Panc-1) and prostate cancer (PC-3) cell lines using the WaterSoluble Tetrazolium Salts-1 (WST-1) assay. The CP-AgNPs had a surface plasmon resonance peak at 420 nm. DLS revealed a hydrodynamic diameter of 64.94 ± 4.293 nm (PDI 0.2596 ± 0.0152), while HR-TEM displayed an average core size of 10.99 ± 2.6 nm confirming synthesis of small CP-AgNPs. The ATR- FTIR identified the functional groups involved in the reduction of Ag+ to CP-AgNPs. CP-Extract was non-toxic to all the cell lines. CP-AgNPs reduced the cell viability of Panc-1 cells to ~58%, with minimal toxicity against KMST-6 and PC-3 cells. The co-treatment of CP-AgNPs and Dox did not show synergistic effects as the cell viability after co-treatment was similar to when the treatments were used on their own. In conclusion, the CP-AgNPs showed favourable cytotoxic effects against Panc-1 cells thus indicating that agricultural waste can be used as a sustainable source of reducing and stabilizing agents for green synthesis of bioactive AgNPs.