Retraction Note: Structural simulation of adenosine phosphate via plumbagin and zoledronic acid competitively targets JNK/Erk to synergistically attenuate osteoclastogenesis in a breast cancer model.

This article has been retracted at the request of the authors. After publication, the authors found that in Figure 2B-a the first two images in the third row partly overlapped and that there is also overlap between the fourth and fifth image in the second row. The two images were taken from two adjacent wells, treated by ZA 0.3uM-CM or ZA 0.75uM-CM, with or without PL 1.25uM. This overlap may have been caused by mishandling in the imaging process when the authors made microscope observations and so the findings are no longer reliable. All authors agree to this retraction.

Structural simulation of adenosine phosphate via plumbagin and zoledronic acid competitively targets JNK/Erk to synergistically attenuate osteoclastogenesis in a breast cancer model.

The treatment of breast cancer-induced osteolysis remains a challenge in clinical settings. Here, we explored the effect and mechanism of combined treatment with zoledronic acid (ZA) and plumbagin (PL), a widely investigated component derived from Plumbago zeylanica, against breast cancer-induced osteoclastogenesis. We found that the combined treatment with PL and ZA suppressed cell viability of precursor osteoclasts and synergistically inhibited MDA-MB-231-induced osteoclast formation (combination index=0.28) with the abrogation of recombinant mouse receptor activator of nuclear factor-κB ligand (RANKL)-induced activation of NF-κB/MAPK (nuclear factor-κB/mitogen-activated protein kinase) pathways. Molecular docking suggested a putative binding area within c-Jun N-terminal kinase/extracellular signal-regulated kinase (JNK/Erk) protease active sites through the structural mimicking of adenosine phosphate (ANP) by the spatial combination of PL with ZA. A homogeneous time-resolved fluorescence assay further illustrated the direct competitiveness of the dual drugs against ANP docking to phosphorylated JNK/Erk, contributing to the inhibited downstream expression of c-Jun/c-Fos/NFATc-1 (nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1). Then, in vivo testing demonstrated that the combined administration of PL and ZA attenuated breast cancer growth in the bone microenvironment. Additionally, these molecules prevented the destruction of proximal tibia, with significant reduction of tartrate-resistant acid phosphatase (TRAcP)-positive osteoclast cells and potentiation of apoptotic cancer cells, to a greater extent when combined than when the drugs were applied independently. Altogether, the combination treatment with PL and ZA could significantly and synergistically suppress osteoclastogenesis and inhibit tumorigenesis both in vitro and in vivo by simulating the spatial structure of ANP to inhibit competitively phosphorylation of c-Jun N-terminal kinase/extracellular signal-regulated kinase (JNK/Erk).