Gambogic Acid Efficiently Kills Stem-Like Colorectal Cancer Cells by Upregulating ZFP36 Expression

Abstract

Background/Aims: Gambogic acid (GA), the main active compound of Gamboge hanburyi, has been reported to be a potential novel antitumor drug. Whether GA inhibits putative cancer stem cells (CSCs), which are considered to be the major cause of cancer treatment failure, remains largely unknown. This study investigated whether GA inhibits the CSCs of colorectal cancer (CRC) and its possible mechanisms. Methods: We performed CCK8 and tumor sphere formation assays, percentage analysis of both side population and CD133⁺CD44⁺ cells, and the detection of stem cells markers, in order to assess the role of GA in inhibiting the stem celllike features of CRC. An mRNA microarray was performed to identify the downstream gene affected by GA and rescue assays were performed to further clarify whether the downstream gene is involved in the GA induced decrease of the stem cell-like CRC population. CRC cells were engineered with a CSC detector vector encoding GFP and luciferase (Luc) under the control of the Nanog promoter, which were utilized to investigate the effect of GA on putative CSC in human tumor xenograft-bearing mice using in vivo bioluminescence imaging. Results: Our results showed that GA significantly reduced tumor sphere formation and the percentages of side population and CD133⁺CD44⁺ cells, while also decreasing the expression of stemness and EMT-associated markers in CRC cells in vitro. GA killed stem-like CRC cells by upregulating the expression of ZFP36, which is dependent on the inactivation of the EGFR/ ERK signaling pathway. GFP+ cells harboring the P_Nanog-GFP-T2A-Luc transgene exhibited CSC characteristics. The in vivo results showed that GA significantly inhibited tumor growth in nude mice, accompanied by a remarkable reduction in the putative CSC number, based on whole-body bioluminescence imaging. Conclusion: These findings suggest that GA significantly inhibits putative CSCs of CRC both in vitro and in vivo by inhibiting the activation of the EGFR/ ERK/ZFP36 signaling pathway and may be an effective drug candidate for anticancer therapies.

<p>MicroRNA-423 Drug Resistance and Proliferation of Breast Cancer Cells by Targeting ZFP36</p>

“…28 In recent years, there have been more and more reports of ZFP36 in tumors, which were shown to inhibit tumorigenesis and affect the malignant phenotype of tumors. 29 However, the current report of ZFP36 in breast cancer was rare, and its expression regulation and specific mechanism of action were still unclear. The results indicated that downregulation of miR-423 significantly enhanced wt-ZFP36-3ʹUTR luciferase activity, confirming the existence of a targeted relationship between miR-423 and ZFP36.…”

AU-rich element-binding proteins in colorectal cancer

“…Furthermore, the loss of TTP in CRC ( e.g ., HCT116 and SW480 cells) correlates with an increase in stemness markers ( i.e ., Bmi-1, ALDH-1 and ABCG2)[137], thus indicating that TTP is a critical regulator of colon cancer cell differentiation. Some cell adhesion molecules (CAMs) are negatively regulated by TTP[138], and thus their overexpression following TTP loss will contribute to the establishment of a metastatic phenotype.…”

“…Finally, EGFR/ERK signaling has been implicated in TTP loss, since Gambogic acid from the Indian Gambodge tree induces TTP expression through the downregulation of EGFR/ERK pathway signaling[137]. Other compounds of natural origin have also been reported to induce TTP expression in colon cancer cells.…”

The Tristetraprolin Family of RNA-Binding Proteins in Cancer: Progress and Future Prospects

“…TTP has also been identified as one of the eight genes functionally related to the NF-κB pathway that were highly downregulated in lethal prostate cancer [63]. Gambogic acid, a polyprenylated xanthone, was demonstrated to significantly inhibit cancer stem cells in colorectal carcinoma, both in vitro and in vivo, by inhibiting EGFR-ERK signaling, resulting in upregulation of TTP [38]. TTP has also been demonstrated to be a post-transcriptional regulator of aryl hydrocarbon receptor repressor (AHRR) in breast cancer cells [23].…”