Asparagine Promotes Breast Cancer Metastasis

Asparagine influences breast cancer metastasis; abstract:

Using a functional model of breast cancer heterogeneity, we previously showed that clonal sub-populations proficient at generating circulating tumour cells were not all equally capable of forming metastases at secondary sites. A combination of differential expression and focused in vitro and in vivo RNA interference screens revealed candidate drivers of metastasis that discriminated metastatic clones. Among these, asparagine synthetase expression in a patient's primary tumour was most strongly correlated with later metastatic relapse. Here we show that asparagine bioavailability strongly influences metastatic potential. Limiting asparagine by knockdown of asparagine synthetase, treatment with l-asparaginase, or dietary asparagine restriction reduces metastasis without affecting growth of the primary tumour, whereas increased dietary asparagine or enforced asparagine synthetase expression promotes metastatic progression. Altering asparagine availability in vitro strongly influences invasive potential, which is correlated with an effect on proteins that promote the epithelial-to-mesenchymal transition. This provides at least one potential mechanism for how the bioavailability of a single amino acid could regulate metastatic progression.

Cytoplasmic DNA And Metastasis

Chromosomal instability results in DNA in the cytoplasm, which is of course not normal, DNA being normally found only in the nucleus.  This misplaced cytoplasmic DNA triggers a pathway that simulates cell signaling that can promote metastasis.  This could in theory be targeted to inhibit metastasis (keep in mind that cancer mortality is for the most part due to metastasis).  Abstract:

Chromosomal instability is a hallmark of cancer that results from ongoing errors in chromosome segregation during mitosis. Although chromosomal instability is a major driver of tumour evolution, its role in metastasis has not been established. Here we show that chromosomal instability promotes metastasis by sustaining a tumour cell-autonomous response to cytosolic DNA. Errors in chromosome segregation create a preponderance of micronuclei whose rupture spills genomic DNA into the cytosol. This leads to the activation of the cGAS-STING (cyclic GMP-AMP synthase-stimulator of interferon genes) cytosolic DNA-sensing pathway and downstream noncanonical NF-κB signalling. Genetic suppression of chromosomal instability markedly delays metastasis even in highly aneuploid tumour models, whereas continuous chromosome segregation errors promote cellular invasion and metastasis in a STING-dependent manner. By subverting lethal epithelial responses to cytosolic DNA, chromosomally unstable tumour cells co-opt chronic activation of innate immune pathways to spread to distant organs.

Plant Compound Against Breast Cancer

A plant-derived natural compound inhibits breast cancer cell growth and metastasis by repressing Wnt signaling.  Abstract:

Metastatic breast cancer is the leading cause of worldwide cancer-related deaths among women. Triple negative breast cancers (TNBC) are highly metastatic and are devoid of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) amplification. TNBCs are unresponsive to Herceptin and/or anti-estrogen therapies and too often become highly chemoresistant when exposed to standard chemotherapy. TNBCs frequently metastasize to the lung and brain. We have previously shown that TNBCs are active for oncogenic Wnt10b/β-catenin signaling and that WNT10B ligand and its downstream target HMGA2 are predictive of poorer outcomes and are strongly associated with chemoresistant TNBC metastatic disease. In search of new chemicals to target the oncogenic WNT10B/β-CATENIN/HMGA2 signaling axis, the anti-proliferative activity of the diterpene Jatrophone (JA), derived from the plant Jatropha isabelli, was tested on TNBC cells. JA interfered with the WNT TOPFLASH reporter at the level between receptor complex and β-catenin activation. JA efficacy was determined in various subtypes of TNBC conventional cell lines or in TNBC cell lines derived from TNBC PDX tumors. The differential IC50 (DCI50) responsiveness was compared among the TNBC models based on etiological-subtype and their cellular chemoresistance status. Elevated WNT10B expression also coincided with increased resistance to JA exposure in several metastatic cell lines. JA interfered with cell cycle progression, and induced loss of expression of the canonical Wnt-direct targets genes AXIN2, HMGA2, MYC, PCNA and CCND1. Mechanistically, JA reduced steady-state, non-phosphorylated (activated) β-catenin protein levels, but not total β-catenin levels. JA also caused the loss of expression of key EMT markers and significantly impaired wound healing in scratch assays, suggesting a direct role for JA inhibiting migration of TNBC cells. These results indicate that Jatrophone could be a powerful new chemotherapeutic agent against highly chemoresistant triple negative breast cancers by targeting the oncogenic Wnt10b/β-catenin signaling pathway.

Different Roles Of Dkk1 In Cancer Metastasis

Wnt signaling is involved in the development and progression of a variety of cancers, and researchers have typically approached Wnt-targeted therapeutics with the aim of suppressing this signaling. Dkk1 is an inhibitor of Wnt signaling, and so this molecule has been thought to be useful with respect to cancer therapy.  But in the paper linked here, it was shown that while Dkk1 inhibits metastasis of lung cancer, it can actually promote metastasis of breast cancer to bone.  This demonstrates that particular therapeutic approaches may need to be specifically targeted to particular cancer types; it also suggests that suppression of signaling is not always the best approach.  There has been some work suggesting boosting cell signaling to abnormally high levels can cause cancer cell death as well; this is a topic worth revisiting in the future.  Abstract:

Metastatic cancer is a systemic disease, and metastasis determinants might elicit completely different effects in various target organs. Here we show that tumour-secreted DKK1 is a serological marker of breast cancer metastasis organotropism and inhibits lung metastasis. DKK1 suppresses PTGS2-induced macrophage and neutrophil recruitment in lung metastases by antagonizing cancer cell non-canonical WNT/PCP-RAC1-JNK signalling. In the lungs, DKK1 also inhibits WNT/Ca2+-CaMKII-NF-κB signalling and suppresses LTBP1-mediated TGF-β secretion of cancer cells. In contrast, DKK1 promotes breast-to-bone metastasis by regulating canonical WNT signalling of osteoblasts. Importantly, targeting canonical WNT may not be beneficial to treatment of metastatic cancer, while combinatory therapy against JNK and TGF-β signalling effectively prevents metastasis to both the lungs and bone. Thus, DKK1 represents a class of Janus-faced molecules with dichotomous roles in organotropic metastasis, and our data provide a rationale for new anti-metastasis approaches.

Intermittent Fasting Problem?

While there are a number of studies supporting benefits for of intermittent calorie restriction (ICR), a disturbing new study in mice suggests negative effects of ICR: an increase in cancer stem cells (CSCs) and enhancement of epithelial to mesenchymal transition, which promotes metastasis.  Keeping the mice in “continuous calorie restriction had no effect on tumor weight, metastasis, or the number of CSCs in tumors or blood” – not bad but not good either.  Speaking for myself, I eat three healthy meals per day (with approximately 12 hours between dinner and the subsequent breakfast), avoid overweight/obesity, and avoid any “fad diets.”  That’s what I’m doing, that is not necessarily a recommendation to anyone else.  Abstract:

The effect of intermittent calorie restriction (ICR) on cancer is controversial. In this study, we examined the effects of ICR and food content in syngeneic BALB/c mice injected with CT26 mouse colon cancer cells. Mice were subjected to 24-h fasting once a week for 4 weeks, and then provided with a control, high-calorie, or trans fatty acid-rich diet. While ICR resulted in increases in tumor weights, metastasis and in the number of cancer stem cells (CSCs) in the tumors or blood of mice fed the control and high-fat diets, it had no effect on body weight after 4 weeks. In particular, we detected increases in the numbers of CSCs in the tumor or blood on the day after starvation, when food overconsumption was detected. Conversely, continuous calorie restriction had no effect on tumor weight, metastasis, or the number of CSCs in tumors or blood. In the post-starvation period, energy metabolism in the tumor was altered from oxidative phosphorylation to glycolysis/lactate fermentation, with the acquisition of the epithelial-mesenchymal transition (EMT) phenotype. Hyperglycemia at the post-starvation period induced the expression of insulin-like growth factor-1, hypoxia-induced factor-1α and Nanog, as well as the phosphorylation of Stat3. Taken together, these findings suggest that ICR induces an increase in the number of CSCs and enhances EMT by promoting the Warburg/Crabtree effect following post-fasting food overconsumption.

Gut Microbiota And Metastasis

Remarkably, not only are primary colorectal cancers colonized by particular strains of bacteria from the gut microbiota, but distal metastases of those tumors have the same strains as well.  Therefore, tumor-associated bacteria “go along for the ride” when metastasis occurs; in particular, Fusobacterium nucleatum is associated with both the primary and metastatic tumors, illustrating stability of bacteria-cancer association.  Mouse xenografts of human primary colorectal cancers exhibited maintenance of the bacteria, and antibiotic treatment “reduced Fusobacterium load, cancer cell proliferation and overall tumor growth.”  One wonders if the bacterial actually promote metastasis as well, and are not just “along for the ride;” it would seem reasonable to suppose that at least the bacteria help the metastasis get established and grow at its new location.  All of this highlights the link between gut microbiota and cancer; note also that diet affects the microbiota, possibly in a clinically-relevant manner.  Abstract:

Colorectal cancers comprise a complex mixture of malignant cells, non-transformed cells and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer tissues. Here we show that colonization of human colorectal cancers with Fusobacterium and its associated microbiome, including Bacteroides, Selenomonas and Prevotella species, is maintained in distal metastases, demonstrating microbiome stability between paired primary-metastatic tumors. In situ hybridization analysis revealed that Fusobacterium is predominantly associated with cancer cells in the metastatic lesions. Mouse xenografts of human primary colorectal adenocarcinomas were found to retain viable Fusobacterium and its associated microbiome through successive passages. Treatment of mice bearing a colon cancer xenograft with the antibiotic metronidazole reduced Fusobacterium load, cancer cell proliferation and overall tumor growth. These observations argue for further investigation of antimicrobial interventions as a potential treatment for patients with Fusobacterium-associated colorectal cancer.

Biomarkers For Metastatic Colon Cancer Treatment

Metastatic colon cancer patients would benefit from having biomarkers analyzed, to judge potential response to certain therapeutic approaches.  This makes sense, as variation in signaling pathways can affect response to treatments, particularly those that target the altered pathways or other pathways that communicate with those altered.  Abstract:

BACKGROUND:

Metastatic colorectal cancer (mCRC) patients with mutant KRAS or NRAS are ineligible for anti-epidermal growth factor receptor (anti-EGFR) therapy, as RAS mutations activate downstream pathways independently of EGFR and induce primary resistance. However, even among RAS wild-type (WT) patients, only a fraction responds to anti-EGFR therapy, suggesting that other mechanisms of resistance exist. We hypothesise that different (epi)genetic alterations can lead to primary anti-EGFR resistance and that the crucial end point is the activation of protein signalling pathways.

METHODS:

We analysed the expression and activation of proteins involved in cell signalling, using reverse phase protein arrays, on a multicentre French cohort of RAS WT mCRC treated with anti-EGFR treatment.

RESULTS:

We identify activated EGFR and HER3 as protein biomarkers predictive for better overall survival. Active EGFR signalling and downstream PI3K, but not MAPK, pathway activation are associated with response to anti-EGFR treatment. Left-sided mCRC displays active ErbB2/3 and Wnt pathways and a better response to anti-EGFR therapy compared to right-sided mCRC.

CONCLUSIONS:

We identify active EGFR and PI3K signalling as a key factor for response to anti-EGFR treatment in mCRC and highlight the importance of developing these biomarkers in clinical practice for the selection of RAS WT mCRC patients that would benefit from anti-EGFR treatment. British Journal of Cancer advance online publication 12 October 2017; doi:10.1038/bjc.2017.353 www.bjcancer.com.