Objective Delonix regia (L.) (Caesalpiniaceae) is one of the plants that have been used for centuries to prevent cancer. D. regia has been described as a strong anti-inflammatory, antibacterial, and analgesic. Also, the cytotoxicity of this plant has been proved due to its flavonoid compounds. Besides, silver (Ag) nanoparticles have been proved to be promising in cancer treatment. Methods The synergistic effect of medicinal plant extracts with silver antibacterial nanoparticles on cancer cell inhibition was investigated. Cytotoxic effect of D. regia extract with silver NPs on MCF-7 and Panc-1 cancer cells was investigated by cell viability analysis, morphological changes, apoptosis induction, and TUNEL assay. Results Results showed the cells treated with D. regia extract containing AgNPs exhibited a considerable reduction in viability percent in comparison with control cells. Analysis of MTT demonstrated that the IC50 value of D. regia extract and AgNPs on both cell lines observed in 0.5 mg/mL for 24 h. The results demonstrated that the maximum inhibition of both cell lines growth was observed in 1.5 mg/L and 0.2 mg/L in the presence with D. regia and AgNPs, respectively. Also, morphological characteristics of cells indicated that D. regia extract and silver NPs induce cell death by apoptosis and it is confirmed by TUNEL assay. Conclusion Interestingly, D. regia extract and Ag NPs had no significant cytotoxicity against normal cells. It can be con- cluded that Delonix regia plant and silver nanoparticles have an inhibitory potential on two cancer cell lines, but in the use of synergism of D. regia extract and AgNPs, the induction of apoptosis in MCF-7 and Panc-1 was increased. Interestingly, in normal cells, no significant negative effect was observed as control.
