Efficacy of atovaquone on EpCAM⁺CD44⁺ HCT‑116 human colon cancer stem cells under hypoxia

Abstract

Tumor hypoxia contributes to the development of resistance to chemotherapeutic drugs in several human cancer cell lines. Atovaquone, an anti-malaria drug approved by the US Food and Drug Administration, has recently demonstrated anti-cancer effects in vitro and in vivo in several cancer models. To assess the potential of atovaquone as an anti-cancer agent under hypoxia in colorectal carcinoma, EpCAM + CD44 + colon cancer stem cells were isolated from HCT-116 human colon cancer cells through magnetic-activated cell sorting. The efficacy of atovaquone on cytotoxicity, tumorsphere formation, apoptosis, invasion and cell-cycle progression under hypoxic conditions were evaluated. MTS assays indicated that atovaquone inhibited the proliferation of EpCAM + CD44 + HCT-116 cells with a half-maximal inhibitory concentration of 15 µM. Atovaquone inhibited tumorsphere formation and cell proliferation by causing cell-cycle arrest in S-phase, which induced apoptosis of EpCAM + CD44 + HCT-116 cells, as detected by Annexin V-FITC/PI double staining assays, and caused mitochondrial membrane potential depolarization, as determined by a JC-1 staining assay. Reverse transcription-quantitative PCR demonstrated increased expression of Bax and downregulation of Bcl-2. Transwell invasion assays indicated that atovaquone inhibited the invasiveness of EpCAM + CD44 + HCT-116 cells under hypoxia, which was associated with upregulation of MMP-2 and-9 and increased expression of tissue inhibitor of MMPs (TIMP)-1. Taken together, atovaquone reduced the tumorsphere formation and invasion ability of EpCAM + CD44 + HCT-116 cells, at least in part by increasing the expression of TIMP-1 and downregulating the expression of MMP-2 and-9, as well as the cells' viability by inducing cell-cycle arrest in S-phase and induction of apoptosis via the Bcl-2/Bax pathway under hypoxic conditions. Further studies are warranted to explore the mechanisms of action of atovaquone as a promising anticancer agent in the treatment of colorectal carcinoma.

Gel-Free 3D Tumoroids with Stem Cell Properties Modeling Drug Resistance to Cisplatin and Imatinib in Metastatic Colorectal Cancer

“…Interestingly, Xie et al reported that overexpressing microRNA-34a overcame ABCG2-mediated drug resistance to 5-FU in SP cells from colon cancer via suppressing DLL1 [29]. Another study showed the efficacy of atovaquone on EpCAM + CD44 + HCT-116 human colon cancer stem cells under hypoxia [40]. In this study, the EpCAM + CD44 + CSC also expressed increased mRNA levels of pluripotency genes such as Nanog, Sox2, Oct4 (aka.…”

The Potential Role of CD44 and CD133 in Colorectal Stem Cell Cancer

“…Fu et al (2020) stated that atovaquone, which usually treats malaria infection, can be used against positive CD44 and EpCAM cancer cells. Atovaquone stopped the proliferation by blocking S-phase under hypoxia, which causes apoptosis to CSCs, but the authors stated that the study has some limitations during the trial process, which may affect the apoptotic rate; this calls for further research to be conducted [ 37 ].…”

The Role of Altered Mitochondrial Metabolism in Thyroid Cancer Development and Mitochondria-Targeted Thyroid Cancer Treatment

“…Recently, atovaquone was reported as a promising anti-cancer agent that is effective against cancer cells and cancer stem cells. The application of atovaquone increase radiosensitivity by alleviating tumour hypoxia, thus suggesting its high potential in combination with other anti-cancer drugs [ 93 , 94 ]. In ATC and FTC cell cultures, atovaquone decreases growth, migration, and survival by inhibiting mitochondrial complex III activity and subsequently reducing ATP production.…”