Genetic Interpretation of the Impacts of Honokiol and EGCG on Apoptotic and Self-Renewal Pathways in HEp-2 Human Laryngeal CD44^high Cancer Stem Cells

Abstract

Most current larynx cancer therapies are generally aimed at the global mass of tumor, targeting the non-tumorigenic cells, and unfortunately sparing the tumorigenic cancer stem cells (CSCs) that are responsible for sustained growth, metastasis, and chemo- and radioresistance. Phytochemicals and herbs have recently been introduced as therapeutic sources for eliminating CSCs. Therefore, we assessed the anti-tumor effects of two herbal ingredients, the green tea extract “Epigallocatechin-3-gallate (EGCG)” and Honokiol (HNK), on parental cells or CD44^high CSCs of the human laryngeal squamous cell carcinoma cell line HEp-2. Results revealed that EGCG had a preeminent apoptotic potential on HEp-2 laryngeal CSCs. HNK conferred higher cytotoxic impacts on parental cells mostly by necrosis induction, especially with higher doses, but apoptosis induction with lower doses was also observed. The Notch signaling pathway genes were more potently suppressed by EGCG than HNK. However, HNK surpassed EGCG in downregulating the β-catenin and the Sonic Hedgehog signaling pathways genes. On a genetic basis, both agents engaged the BCL-2 family-regulated and caspase-dependent intrinsic apoptotic pathway, but EGCG and HNK triggered apoptosis via p53-independent and p53-dependent pathways, respectively. Taken together, EGCG and HNK eradicated HEp-2 human larynx cancer cells through targeting multiple self-renewal pathways and activating diverse cell death modalities.

Acknowledgments

We are grateful to members of the Medical Experimental Research Center (MERC) at Mansoura University for their great assistance with cell culturing, immunomagnetic cell sorting, tumor sphere formation, CFU, and cell proliferation assays. We thank Ayman Ali from the molecular biology unit at the Mansoura Research Center for Cord Stem Cells (MARC-CSC) for his great assistance with total RNA extraction, cDNA synthesis, and qRT-PCR. Special thanks go to the director of MERC, Prof. Mohamed Salama, and the director of MARC-CSC, Prof. Farha El-Chennwai, for their technical supervision and support. We also thank members of the cell culture and cell analysis unit at the Egyptian Liver Research Institute and Hospital (ELRIAH) for their assistance with flow cytometry analysis.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.