131‐Oxophorbine protopheophorbide A from Ziziphus lotus as a novel mesenchymal‐epithelial transition factor receptor inhibitory lead for the control of breast tumor growth in vitro and in vivo

: The failure of chemotherapy especially in triple negative breast cancer (TNBC) patients has been correlated with the overexpression of the mesenchymal-epithelial transition factor (c-Met) receptor. Thus, the hepatocyte growth factor (HGF)/c-Met signaling axis has gained considerable attention as a valid molecular target for breast cancer therapy. This study reports for the first time the discovery of the 131 -oxophorbines pheophorbide A and protopheophorbide A along with chlorophyllide A from Ziziphus lotus, an edible typical Tunisian plant, as the potent antiproliferative compounds against the human breast cancer cells MDA-MB-231 and MCF-7. Compared to other compounds, protopheophorbide A exerted the highest light-independent antiproliferative effect against the metastatic TNBC MDA-MB-231 cells (IC50  = 6.5 μM). In silico, this compound targeted the kinase domain of multiple c-Met crystal structures. It potently inhibited the kinase domain phosphorylation of wild and mutant c-Met in Z-LYTE kinase assay. Protopheophorbide A inhibited HGF-induced downstream c-Met-dependent cell proliferation, survival, adhesion and migration through RAF/MEK/ERK and PI3K/PTEN/AKT signaling pathways modulation, ROS generation and activation of JNK and p38 pathways. Interestingly, this compound impaired the ability of the MDA-MB-231 cells to adhere at different extracellular matrix proteins by reducing the HGF-induced expression of integrins αv, β3, α2, and β1. Moreover, protopheophorbide A exhibited anti-migratory properties (IC50  = 2.2 μM) through impacting the expression levels of E-cadherin, vimentin, β-catenin, FAK, Brk, Rac, and Src proteins. Importantly, treatment with protopheophorbide A significantly inhibited the MDA-MB-231 tumor growth in vivo. Our results suggest that protopheophorbide A could be a novel c-Met inhibitory lead with promise to control c-Met/HGF-dependent breast malignancies.