BACH1 Stabilization by Antioxidants Stimulates Lung Cancer Metastasis.

For tumors to progress efficiently, cancer cells must overcome barriers of oxidative stress. Although dietary antioxidant supplementation or activation of endogenous antioxidants by NRF2 reduces oxidative stress and promotes early lung tumor progression, little is known about its effect on lung cancer metastasis. Here, we show that long-term supplementation with the antioxidants N-acetylcysteine and vitamin E promotes KRAS-driven lung cancer metastasis. The antioxidants stimulate metastasis by reducing levels of free heme and stabilizing the transcription factor BACH1. BACH1 activates transcription of Hexokinase 2 and Gapdh and increases glucose uptake, glycolysis rates, and lactate secretion, thereby stimulating glycolysis-dependent metastasis of mouse and human lung cancer cells. Targeting BACH1 normalized glycolysis and prevented antioxidant-induced metastasis, while increasing endogenous BACH1 expression stimulated glycolysis and promoted metastasis, also in the absence of antioxidants. We conclude that BACH1 stimulates glycolysis-dependent lung cancer metastasis and that BACH1 is activated under conditions of reduced oxidative stress.

Intussusceptive Angiogenesis in Human Metastatic Malignant Melanoma.

Angiogenesis supplies oxygen and nutrients to growing tumors. Inhibiting angiogenesis may stop tumor growth, but vascular endothelial growth factor inhibitors have limited effect in most tumors. This limited effect may be explained by an additional, less vascular endothelial growth factor-driven form of angiogenesis known as intussusceptive angiogenesis. The importance of intussusceptive angiogenesis in human tumors is not known. Epifluorescence and confocal microscopy was used to visualize intravascular pillars, the hallmark structure of intussusceptive angiogenesis, in tumors. Human malignant melanoma metastases, patient-derived melanoma xenografts in mice (PDX), and genetically engineered v-raf murine sarcoma viral oncogene homolog B1 (BRAF)-induced, phosphatase and TENsin homolog deleted on chromosome 10 (PTEN)-deficient (BPT) mice (BrafCA/+Ptenf/fTyr-Cre+/0-mice) were analyzed for pillars. Gene expression in human melanoma metastases and PDXs was analyzed by RNA sequencing. Matrix metalloproteinase 9 (MMP9) protein expression and T-cell and macrophage infiltration in tumor sections were determined with multiplex immunostaining. Intravascular pillars were detected in human metastases but rarely in PDXs and not in BPT mice. The expression of MMP9 mRNA was higher in human metastases compared with PDXs. High expression of MMP9 protein as well as infiltration of macrophages and T-cells were detected in proximity to intravascular pillars. MMP inhibition blocked formation of pillars, but not tubes or tip cells, in vitro. In conclusion, intussusceptive angiogenesis may contribute to the growth of human melanoma metastases. MMP inhibition blocked pillar formation in vitro and should be further investigated as a potential anti-angiogenic drug target in metastatic melanoma.

Cellular Redox Homeostasis.

Cellular redox homeostasis is an essential and dynamic process that ensures the balance between reducing and oxidizing reactions within cells and regulates a plethora of biological responses and events. The study of these biochemical reactions has proven difficult over time, but recent technical and methodological developments have contributed to the rapid growth of the redox field and to our understanding of its importance in biology. The aim of this short review is to give the reader an overall understanding of redox regulation in the areas of cellular signaling, development, and disease, as well as to introduce some recent discoveries in those fields.

Mitochondria-Targeted Antioxidants MitoQ and MitoTEMPO Do Not Influence BRAF-Driven Malignant Melanoma and KRAS-Driven Lung Cancer Progression in Mice.

Cancer cells produce high levels of mitochondria-associated reactive oxygen species (ROS) that can damage macromolecules, but also promote cell signaling and proliferation. Therefore, mitochondria-targeted antioxidants have been suggested to be useful in anti-cancer therapy, but no studies have convincingly addressed this question. Here, we administered the mitochondria-targeted antioxidants MitoQ and MitoTEMPO to mice with BRAF-induced malignant melanoma and KRAS-induced lung cancer, and found that these compounds had no impact on the number of primary tumors and metastases; and did not influence mitochondrial and nuclear DNA damage levels. Moreover, MitoQ and MitoTEMPO did not influence proliferation of human melanoma and lung cancer cell lines. MitoQ and its control substance dTPP, but not MitoTEMPO, increased glycolytic rates and reduced respiration in melanoma cells; whereas only dTPP produced this effect in lung cancer cells. Our results do not support the use of mitochondria-targeted antioxidants for anti-cancer monotherapy, at least not in malignant melanoma and lung cancer.

Antioxidants Promote Intestinal Tumor Progression in Mice.

Dietary antioxidants and supplements are widely used to protect against cancer, even though it is now clear that antioxidants can promote tumor progression by helping cancer cells to overcome barriers of oxidative stress. Although recent studies have, in great detail, explored the role of antioxidants in lung and skin tumors driven by RAS and RAF mutations, little is known about the impact of antioxidant supplementation on other cancers, including Wnt-driven tumors originating from the gut. Here, we show that supplementation with the antioxidants N-acetylcysteine (NAC) and vitamin E promotes intestinal tumor progression in the ApcMin mouse model for familial adenomatous polyposis, a hereditary form of colorectal cancer, driven by Wnt signaling. Both antioxidants increased tumor size in early neoplasias and tumor grades in more advanced lesions without any impact on tumor initiation. Importantly, NAC treatment accelerated tumor progression at plasma concentrations comparable to those obtained in human subjects after prescription doses of the drug. These results demonstrate that antioxidants play an important role in the progression of intestinal tumors, which may have implications for patients with or predisposed to colorectal cancer.

Genomic profiling of the transcription factor Zfp148 and its impact on the p53 pathway.

Recent data suggest that the transcription factor Zfp148 represses activation of the tumor suppressor p53 in mice and that therapeutic targeting of the human orthologue ZNF148 could activate the p53 pathway without causing detrimental side effects. We have previously shown that Zfp148 deficiency promotes p53-dependent proliferation arrest of mouse embryonic fibroblasts (MEFs), but the underlying mechanism is not clear. Here, we showed that Zfp148 deficiency downregulated cell cycle genes in MEFs in a p53-dependent manner. Proliferation arrest of Zfp148-deficient cells required increased expression of ARF, a potent activator of the p53 pathway. Chromatin immunoprecipitation showed that Zfp148 bound to the ARF promoter, suggesting that Zfp148 represses ARF transcription. However, Zfp148 preferentially bound to promoters of other transcription factors, indicating that deletion of Zfp148 may have pleiotropic effects that activate ARF and p53 indirectly. In line with this, we found no evidence of genetic interaction between TP53 and ZNF148 in CRISPR and siRNA screen data from hundreds of human cancer cell lines. We conclude that Zfp148 deficiency, by increasing ARF transcription, downregulates cell cycle genes and cell proliferation in a p53-dependent manner. However, the lack of genetic interaction between ZNF148 and TP53 in human cancer cells suggests that therapeutic targeting of ZNF148 may not increase p53 activity in humans.

Antioxidants can increase melanoma metastasis in mice.

Antioxidants in the diet and supplements are widely used to protect against cancer, but clinical trials with antioxidants do not support this concept. Some trials show that antioxidants actually increase cancer risk and a study in mice showed that antioxidants accelerate the progression of primary lung tumors. However, little is known about the impact of antioxidant supplementation on the progression of other types of cancer, including malignant melanoma. We show that administration of N-acetylcysteine (NAC) increases lymph node metastases in an endogenous mouse model of malignant melanoma but has no impact on the number and size of primary tumors. Similarly, NAC and the soluble vitamin E analog Trolox markedly increased the migration and invasive properties of human malignant melanoma cells but did not affect their proliferation. Both antioxidants increased the ratio between reduced and oxidized glutathione in melanoma cells and in lymph node metastases, and the increased migration depended on new glutathione synthesis. Furthermore, both NAC and Trolox increased the activation of the small guanosine triphosphatase (GTPase) RHOA, and blocking downstream RHOA signaling abolished antioxidant-induced migration. These results demonstrate that antioxidants and the glutathione system play a previously unappreciated role in malignant melanoma progression.