Pulsatilla Saponins Inhibit Experimental Lung Metastasis of Melanoma via Targeting STAT6-Mediated M2 Macrophages Polarization

by Selleckchem | Aug 21 2023

Pulsatilla saponins (PS) extracts from Pulsatilla chinensis (Bge.) Regel, are a commonly used traditional Chinese medicine. In the previous study, we found Pulsatilla saponins displayed anti-tumor activity without side effects such as bone marrow suppression. However, the mechanism of the anti-tumor effect was not illustrated well. Since M2-like tumor-associated macrophages (TAMs) that required activation of the signal transducer and activator of transcription 6 (STAT6) for polarization are the important immune cells in the tumor microenvironment and play a key role in tumor progress and metastasis, this study aimed to confirm whether Pulsatilla saponins could inhibit the development and metastasis of tumors by inhibiting the polarization of M2 macrophages. We investigated the relevance of M2 macrophage polarization and the anti-tumor effects of Pulsatilla saponins in vitro and in vivo. In vitro, Pulsatilla saponins could decrease the mRNA level of M2 marker genes Arg1, Fizz1, Ym1, and CD206, and the down-regulation effect of phosphorylated STAT6 induced by IL-4; moreover, the conditioned medium (CM) from bone marrow-derived macrophages (BMDM) treated with Pulsatilla saponins could inhibit the proliferation and migration of B16-F0 cells. In vivo, Pulsatilla saponins could reduce the number of lung metastasis loci, down-regulate the expression of M2 marker genes, and suppress the expression of phosphorylated STAT6 in tumor tissues. Furthermore, we used AS1517499 (AS), a STAT6 inhibitor, to verify the role of PS on M2 macrophage polarization both in vitro and in vivo. We found that Pulsatilla saponins failed to further inhibit STAT6 activation; the mRNA level of Arg1, Fizz1, Ym1, and CD206; and the proliferation and migration of B16-F0 cells after AS1517499 intervention in vitro. Similar results were obtained in vivo. These results illustrated that Pulsatilla saponins could effectively suppress tumor progress by inhibiting the polarization of M2 macrophages via the STAT6 signaling pathway; this revealed a novel mechanism for its anti-tumor activity.

Comments:

The study you described aimed to investigate the potential anti-tumor effects of Pulsatilla saponins (PS) extracted from Pulsatilla chinensis (Bge.) Regel, a traditional Chinese medicine. The researchers focused on understanding the mechanism by which PS inhibits tumor development and metastasis by targeting M2-like tumor-associated macrophages (TAMs) and their polarization.

M2 macrophages are a specific type of immune cells found in the tumor microenvironment and are known to contribute to tumor progression and metastasis. These M2 macrophages require activation of a signaling protein called signal transducer and activator of transcription 6 (STAT6) for their polarization. The researchers hypothesized that PS might inhibit M2 macrophage polarization by targeting the STAT6 signaling pathway, thus suppressing tumor growth.

The study involved both in vitro and in vivo experiments. In the in vitro experiments, the researchers treated bone marrow-derived macrophages (BMDM) with PS and observed a decrease in the mRNA levels of M2 marker genes (Arg1, Fizz1, Ym1, and CD206) as well as a reduction in phosphorylated STAT6 induced by interleukin-4 (IL-4). Moreover, the conditioned medium (CM) collected from PS-treated BMDMs inhibited the proliferation and migration of B16-F0 cells, a cell line commonly used to study melanoma.

In the in vivo experiments, PS administration resulted in a reduction in the number of lung metastasis loci and down-regulation of M2 marker gene expression in tumor tissues. Additionally, the expression of phosphorylated STAT6 was suppressed in the tumor tissues of mice treated with PS.

To further validate the role of PS in inhibiting M2 macrophage polarization via the STAT6 pathway, the researchers used AS1517499 (AS), a STAT6 inhibitor. They found that when AS was used to inhibit STAT6 activation, PS failed to provide additional inhibition of STAT6 or further down-regulate the mRNA levels of M2 marker genes. Similarly, the proliferation and migration of B16-F0 cells were not affected by PS when combined with AS. These findings were consistent in both in vitro and in vivo experiments.

Overall, the results of the study suggest that Pulsatilla saponins derived from Pulsatilla chinensis can effectively suppress tumor progression by inhibiting the polarization of M2 macrophages through the STAT6 signaling pathway. This provides a novel mechanistic understanding of the anti-tumor activity of PS and highlights its potential as a therapeutic agent in cancer treatment.