The Phenoxyphenol Compound 4-HPPP Selectively Induces Antiproliferation Effects and Apoptosis in Human Lung Cancer Cells through Aneupolyploidization and ATR DNA Repair Signaling. Oxid Med Cell Longev. 2020;2020:5167292. [PMID: 32089770 PMCID: PMC7024103 DOI: 10.1155/2020/5167292]

diTFPP, a Phenoxyphenol, Sensitizes Hepatocellular Carcinoma Cells to C2-Ceramide-Induced Autophagic Stress by Increasing Oxidative Stress and ER Stress Accompanied by LAMP2 Hypoglycosylation

Simple Summary

Chemotherapy is the major treatment modality for advanced or unresectable hepatocellular carcinoma (HCC). Unfortunately, chemoresistance carries a poor prognosis in HCC patients. Exogenous ceramide, a sphingolipid, has been well documented to exert anticancer effects; however, recent reports showed ceramide resistance, which limits the development of the ceramide-based cancer treatment diTFPP, a novel phenoxyphenol compound that has been shown to sensitize HCC cells to ceramide treatment. Here, we further clarified the mechanism underlying diTFPP-mediated sensitization of HCC to C₂-ceramide-induced stresses, including oxidative stress, ER stress, and autophagic stress, especially the modulation of LAMP2 glycosylation, the lysosomal membrane protein that is crucial for autophagic fusion. This study may shed light on the mechanism of ceramide resistance and help in the development of adjuvants for ceramide-based cancer therapeutics.

Abstract

Hepatocellular carcinoma (HCC), the most common type of liver cancer, is the leading cause of cancer-related mortality worldwide. Chemotherapy is the major treatment modality for advanced or unresectable HCC; unfortunately, chemoresistance results in a poor prognosis for HCC patients. Exogenous ceramide, a sphingolipid, has been well documented to exert anticancer effects. However, recent reports suggest that sphingolipid metabolism in ceramide-resistant cancer cells favors the conversion of exogenous ceramides to prosurvival sphingolipids, conferring ceramide resistance to cancer cells. However, the mechanism underlying ceramide resistance remains unclear. We previously demonstrated that diTFPP, a novel phenoxyphenol compound, enhances the anti-HCC effect of C₂-ceramide. Here, we further clarified that treatment with C₂-ceramide alone increases the protein level of CERS2, which modulates sphingolipid metabolism to favor the conversion of C₂-ceramide to prosurvival sphingolipids in HCC cells, thus activating the unfolded protein response (UPR), which further initiates autophagy and the reversible senescence-like phenotype (SLP), ultimately contributing to C₂-ceramide resistance in these cells. However, cotreatment with diTFPP and ceramide downregulated the protein level of CERS2 and increased oxidative and endoplasmic reticulum (ER) stress. Furthermore, insufficient LAMP2 glycosylation induced by diTFPP/ceramide cotreatment may cause the failure of autophagosome–lysosome fusion, eventually lowering the threshold for triggering cell death in response to C₂-ceramide. Our study may shed light on the mechanism of ceramide resistance and help in the development of adjuvants for ceramide-based cancer therapeutics.

Zebrafish Model-Based Assessment of Indoxyl Sulfate-Induced Oxidative Stress and Its Impact on Renal and Cardiac Development

Kidney disease patients may have concurrent chronic kidney disease-associated mineral bone disorder and hypertension. Cardiovascular disease (CVD) and neuropathy occur due to kidney failure-induced accumulation of uremic toxins in the body. Indoxyl sulfate (IS), a product of indole metabolism in the liver, is produced from tryptophan by the intestinal flora and is ultimately excreted through the kidneys. Hemodialysis helps renal failure patients eliminate many nephrotoxins, except for IS, which leads to a poor prognosis. Although the impacts of IS on cardiac and renal development have been well documented using mouse and rat models, other model organisms, such as zebrafish, have rarely been studied. The zebrafish genome shares at least 70% similarity with the human genome; therefore, zebrafish are ideal model organisms for studying vertebrate development, including renal development. In this study, we aimed to investigate the impact of IS on the development of zebrafish embryos, especially cardiac and renal development. At 24 h postfertilization (hpf), zebrafish were exposed to IS at concentrations ranging from 2.5 to 10 mM. IS reduced survival and the hatching rate, caused cardiac edema, increased mortality, and shortened the body length of zebrafish embryos. In addition, IS decreased heart rates and renal function. IS affected zebrafish development via the ROS and MAPK pathways, which subsequently led to inflammation in the embryos. The results suggest that IS interferes with cardiac and renal development in zebrafish embryos, providing new evidence about the toxicity of IS to aquatic organisms and new insights for the assessment of human health risks. Accordingly, we suggest that zebrafish studies can ideally complement mouse model studies to allow the simultaneous and comprehensive investigation of the physiological impacts of uremic endotheliotoxins, such as IS, on cardiac and renal development.

The Phenoxyphenol Compound diTFPP Mediates Exogenous C2-Ceramide Metabolism, Inducing Cell Apoptosis Accompanied by ROS Formation and Autophagy in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is a severe disease that accounts for 80% of liver cancers. Chemotherapy is the primary therapeutic strategy for patients who cannot be treated with surgery or who have late-stage HCC. C₂-ceramide is an effective reagent that has been found to inhibit the growth of many cancer types. The metabolism of C₂-ceramide plays a vital role in the regulation of cell death/cell survival. The phenoxyphenol compound 4-{2,3,5,6-tetrafluoro-4-[2,3,5,6-tetrafluoro-4-(4-hydroxyphenoxy)phenyl]phenoxy}phenol (diTFPP) was found to have a synergistic effect with C₂-ceramide, resulting in considerable cell death in the HA22T HCC cell line. diTFPP/C₂-ceramide cotreatment induced a two- to threefold increase in cell death compared to that with C2-ceramide alone and induced pyknosis. Annexin V/7-aminoactinomycin D (7AAD) double staining and Western blotting indicated that apoptosis was involved in diTFPP/C₂-ceramide cotreatment-mediated cell death. We next analyzed transcriptome alterations in diTFPP/C₂-ceramide-cotreated HA22T cells with next-generation sequencing (NGS). The data indicated that diTFPP treatment disrupted sphingolipid metabolism, inhibited cell cycle-associated gene expression, and induced autophagy and reactive oxygen species (ROS)-responsive changes in gene expression. Additionally, we assessed the activation of autophagy with acridine orange (AO) staining and observed alterations in the expression of the autophagic proteins LC3B-II and Beclin-1, which indicated autophagy activation after diTFPP/C₂-ceramide cotreatment. Elevated levels of ROS were also reported in diTFPP/C₂-ceramide-treated cells, and the expression of the ROS-associated proteins SOD1, SOD2, and catalase was upregulated after diTFPP/C₂-ceramide treatment. This study revealed the potential regulatory mechanism of the novel compound diTFPP in sphingolipid metabolism by showing that it disrupts ceramide metabolism and apoptotic sphingolipid accumulation.

Tumor-specific lytic path “hyperploid progression mediated death”: Resolving side effects through targeting retinoblastoma or p53 mutant

A major advance was made to reduce the side effects of cancer therapy via the elucidation of the tumor-specific lytic path “hyperploid progression-mediated death” targeting retinoblastoma (Rb) or p53-mutants defective in G1 DNA damage checkpoint. The genetic basis of human cancers was uncovered through the cloning of the tumor suppressor Rb gene. It encodes a nuclear DNA-binding protein whose self-interaction is regulated by cyclin-dependent kinases. A 3D-structure of Rb dimer is shown, confirming its multimeric status. Rb assumes a central role in cell cycle regulation and the “Rb pathway” is universally inactivated in human cancers. Hyperploidy refers to a state in which cells contain one or more extra chromosomes. Hyperploid progression occurs due to continued cell-cycling without cytokinesis in G1 checkpoint-defective cancer cells. The evidence for the triggering of hyperploid progression-mediated death in RB-mutant human retinoblastoma cells is shown. Hence, the very genetic mutation that predisposes to cancer can be exploited to induce lethality. The discovery helped to establish the principle of targeted cytotoxic cancer therapy at the mechanistic level. By triggering the lytic path, targeted therapy with tumor specificity at the genetic level can be developed. It sets the stage for systematically eliminating side effects for cytotoxic cancer therapy.