# Astragalin Attenuates Bone Destruction and the Progression of Bone Metastasis in Breast Cancer

## TL;DR

Astragalin, a natural compound, reduces bone destruction and breast cancer bone metastasis by inhibiting tumor growth and osteoclast activity.

## Contribution

This study reveals astragalin's novel anti-metastatic effects in breast cancer through ER stress and AKT pathway inhibition.

## Key findings

- Astragalin attenuates bone destruction and tumor growth in breast cancer bone metastasis.
- Astragalin induces apoptosis in breast cancer cells and inhibits osteoclast formation.
- Astragalin's effects are mediated through ER stress-induced Ddit3 upregulation and AKT pathway inhibition.

## Abstract

Astragalin (AS) showed potential anti-tumor properties in various cancers; however, it is still unclear whether it affects the progression of bone metastasis in breast cancer (BC). In this study, AS markedly attenuated bone destruction and tumor growth. Further studies confirmed that AS can regulate the development of BC cells and osteoclasts. Flow cytometry indicated that AS can induce the apoptosis of both MDA-MB-231 and 4T1 cells in vitro. Transcriptome data indicated that Ddit3 was significantly upregulated by AS. Consistently, Ddti3 knockdown reversed the effects of AS on BC cells. Mechanically, AS-induced ER stress inhibited the activation of the AKT pathway. On the other hand, AS also directly inhibited osteoclastogenesis partly by inhibiting AKT. Our study revealed that AS is a promising treatment for bone metastasis in BC.

Background: Bone metastasis of breast cancer (BC) is a key reason for poor prognosis. Recently, natural ingredients derived from plants have been found to exert a broad anti-tumor effect and are considered to be promising candidates for adjuvant therapy. Astragalin (AS) was found to inhibit the progression of several types of tumors; however, the role of AS in regulating the bone metastasis of BC is still unclear. Methods: The effects of AS on the progression of bone metastasis of BC were detected in vivo through safranin O and fast green staining, in vivo living imaging and microCT. The BrdU assay and Annexin V-PI analysis were used to detect the effects of AS on the growth of BC cells. Furthermore, TRAP staining was performed to examine the formation of osteoclasts regulated by AS. A transcriptome was performed to explore the downstream effects of AS on regulating the growth of BC cells, and the mechanism was further confirmed by Western blot and real-time PCR. Results: Administration of AS could effectively attenuate the bone destruction and the progression of bone metastasis of BC. The growth of BC cells can be inhibited by AS by inducing ER stress-mediated upregulation of Ddit3. In addition, AS can also prevent osteoclastogenesis through inhibiting the activation of the AKT pathway. Conclusions: Our studies suggest that AS could be an ideal adjuvant therapy for attenuating the progression of bone metastasis of BC, since it can directly restrict the growth of tumor, as well as attenuate osteolysis.