Synergistic anticancer effect of green synthesized nickel nanoparticles and quercetin extracted from Ocimum sanctum leaf extract

Leaf extract of medicinally important plant Ocimum sanctum (O. sanctum) has been used for the synthesis of nickel nanoparticles (NiGs) and extraction of quercetin (Qu). Qu has been conjugated with NiGs for enhanced anticancer effect on human breast cancer MCF–7 cells. Extracted Qu was conjugated with polyethylene glycol (PEG) coated NiGs (Qu–PEG–NiGs) which was used as carriers for breast cancer treatment. Anticancer activity of Qu–PEG–NiGs was evaluated by assessing cell viability, reactive oxygen species (ROS) production, caspase activity, mitochondrial membrane potential (MMP) and changes in nuclear morphology (staining methods). 0.85 mg of quercetin was extracted from 1 g of leaves with retention time (R_t) of 2.914 min. Loading and encapsulation efficiency of quercetin onto PEG–NiGs was 15.04% and 82% respectively and Qu–PEG–NiGs has shown a sustained release of Qu of about 84% after 48 h. Qu and Qu–PEG–NiGs showed dose dependent (1.56–50 μg/mL) anticancer effect against MCF–7 cells with IC₅₀ values of 50 and 6.25 μg/mL respectively which was mediated by oxidative stress due to ROS over-production that induced loss of mitochondrial membrane potential, capsase -9, -7 activities leading to apoptosis. The present study validates that Qu–PEG–NiGs can be used as a potential anticancer agent for cancer therapy.