Molecular mechanisms underlying synergistic interactions between Australian propolis and doxorubicin in MCF7 breast adenocarcinoma cells : multiomics study

The combination of natural products with standard chemotherapeutic agents offers a promising strategy to enhance the efficacy or reduce the side effects of standard chemotherapy. We explored the synergistic interactions between Australian propolis extract (AP−1) and doxorubicin (DOX) in the MCF7 cells. Five prenylated stilbenes were identified as the key metabolites in the most active AP−1 fraction. Strong synergy was observed validated by different synergy quantitation models when AP−1 was combined with DOX in the ratio of 100:0.29 (w/w). AP−1 enabled the reversal of DOX-mediated necrosis to programmed cell death, which may be advantageous to decline DOX-related side effects. AP−1 also significantly enhanced the apoptotic effect of DOX after 24 h of treatment with significant upregulation of catalase, HTRA2/Omi, FADD together with DR5 and DR4 TRAIL-mediated apoptosis, contributing to the antiproliferative activity of AP−1. Significant upregulation of pro-apoptotic p27, PON2 and catalase with downregulated antiapoptotic XIAP, HSP60 and HIF-1α, and increased antioxidant proteins (catalase and PON2) may be associated with the improved apoptosis and oxidative status of the synergistic combination-treated MCF7 cells compared to the mono treatments. Shotgun proteomics identified 21 significantly dysregulated proteins in the synergistic combination-treated cells versus the mono treatments. These proteins were involved in the TP53/ATM-regulated non-homologous end-joining pathway and double-strand breaks repairs, recruiting the overexpressed BRCA1 and suppressed RIF1 encoded proteins. The overexpression of UPF2 was noticed in the synergistic combination treatment, which could assist in overcoming doxorubicin resistance-associated long non-coding RNA and metastasis of the MCF7 cells. In conclusion, we identified the significant synergy and highlighted the key molecular pathways in the interaction between AP−1 and DOX in the MCF7 cells together with the AP−1 anticancer metabolites. Further in vivo and clinical studies are warranted on this synergistic combination.