Genomic instability at the 13q31 locus and somatic mtDNA mutation in the D-loop site correlate with tumor aggressiveness in sporadic Brazilian breast cancer cases

Somatic Mutations in Latin American Breast Cancer Patients: A Systematic Review and Meta-Analysis

(1) Background: Somatic mutations may be connected to the exposome, potentially playing a role in breast cancer's development and clinical outcomes. There needs to be information regarding Latin American women specifically, as they are underrepresented in clinical trials and have limited access to somatic analysis in their countries. This study aims to systematically investigate somatic mutations in breast cancer patients from Latin America to gain a better understanding of tumor biology in the region. (2) Methods: We realize a systematic review of studies on breast cancer in 21 Latin American countries using various databases such as PubMed, Google Scholar, Web of Science, RedAlyc, Dianlet, and Biblioteca Virtual en Salud. Of 392 articles that fit the criteria, 10 studies have clinical data which can be used to create a database containing clinical and genetic information. We compared mutation frequencies across different breast cancer subtypes using statistical analyses and meta-analyses of proportions. Furthermore, we identified overexpressed biological processes and canonical pathways through functional enrichment analysis. (3) Results: 342 mutations were found in six Latin American countries, with the TP53 and PIK3CA genes being the most studied mutations. The most common PIK3CA mutation was H1047R. Functional analysis provided insights into tumor biology and potential therapies. (4) Conclusion: evaluating specific somatic mutations in the Latin American population is crucial for understanding tumor biology and determining appropriate treatment options. Combining targeted therapies may improve clinical outcomes in breast cancer. Moreover, implementing healthy lifestyle strategies in Latin America could enhance therapy effectiveness and clinical outcomes.

Mitochondrial mutations and mitoepigenetics: Focus on regulation of oxidative stress-induced responses in breast cancers

Epigenetic regulation of mitochondrial DNA (mtDNA) is an emerging and fast-developing field of research. Compared to regulation of nucler DNA, mechanisms of mtDNA epigenetic regulation (mitoepigenetics) remain less investigated. However, mitochondrial signaling directs various vital intracellular processes including aerobic respiration, apoptosis, cell proliferation and survival, nucleic acid synthesis, and oxidative stress. The later process and associated mismanagement of reactive oxygen species (ROS) cascade were associated with cancer progression. It has been demonstrated that cancer cells contain ROS/oxidative stress-mediated defects in mtDNA repair system and mitochondrial nucleoid protection. Furthermore, mtDNA is vulnerable to damage caused by somatic mutations, resulting in the dysfunction of the mitochondrial respiratory chain and energy production, which fosters further generation of ROS and promotes oncogenicity. Mitochondrial proteins are encoded by the collective mitochondrial genome that comprises both nuclear and mitochondrial genomes coupled by crosstalk. Recent reports determined the defects in the collective mitochondrial genome that are conducive to breast cancer initiation and progression. Mutational damage to mtDNA, as well as its overproliferation and deletions, were reported to alter the nuclear epigenetic landscape. Unbalanced mitoepigenetics and adverse regulation of oxidative phosphorylation (OXPHOS) can efficiently facilitate cancer cell survival. Accordingly, several mitochondria-targeting therapeutic agents (biguanides, OXPHOS inhibitors, vitamin-E analogues, and antibiotic bedaquiline) were suggested for future clinical trials in breast cancer patients. However, crosstalk mechanisms between altered mitoepigenetics and cancer-associated mtDNA mutations remain largely unclear. Hence, mtDNA mutations and epigenetic modifications could be considered as potential molecular markers for early diagnosis and targeted therapy of breast cancer. This review discusses the role of mitoepigenetic regulation in cancer cells and potential employment of mtDNA modifications as novel anti-cancer targets.

Overview of mitochondrial germline variants and mutations in human disease: Focus on breast cancer (Review)

High lactate production in cells during growth under oxygen-rich conditions (aerobic glycolysis) is a hallmark of tumor cells, indicating the role of mitochondrial function in tumorigenesis. In fact, enhanced mitochondrial biogenesis and impaired quality control are frequently observed in cancer cells. Mitochondrial DNA (mtDNA) encodes 13 subunits of oxidative phosphorylation (OXPHOS), is present in thousands of copies per cell, and has a very high mutation rate. Mutations in mtDNA and nuclear DNA (nDNA) genes encoding proteins that are important players in mitochondrial biogenesis and function are involved in oncogenic processes. A wide range of germline mtDNA polymorphisms, as well as tumor mtDNA somatic mutations have been identified in diverse cancer types. Approximately 72% of supposed tumor-specific somatic mtDNA mutations reported, have also been found as polymorphisms in the general population. The ATPase 6 and NADH dehydrogenase subunit genes of mtDNA are the most commonly mutated genes in breast cancer (BC). Furthermore, nuclear genes playing a role in mitochondrial biogenesis and function, such as peroxisome proliferators-activated receptor gamma coactivator-1 (PGC-1), fumarate hydratase (FH) and succinate dehydrogenase (SDH) are frequently mutated in cancer. In this review, we provide an overview of the mitochondrial germline variants and mutations in cancer, with particular focus on those found in BC.

Relative levels of let-7a, miR-17, miR-27b, miR-125a, miR-125b and miR-206 as potential molecular markers to evaluate grade, receptor status and molecular type in breast cancer

MicroRNAs (miRNAs/miRs) are a class of short, single‑stranded nucleic acids, which have been investigated as potential molecular markers for various types of cancer. The gold‑standard and most sensitive method for comparing miRNA levels in cancer tissues is reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). This technique uses stably expressed genes for normalisation. The aim of the present study was to improve this model of analysis in the context of RT‑qPCR results. A total of six known miRNAs (let‑7a, miR‑17, miR‑27b, miR‑125a, miR‑125b and miR‑206), RNU6B RNA and five mRNAs [erb‑b2 receptor tyrosine kinase 2 (ERBB2), hydroxymethylbilane synthase and polymerase (RNA) II (DNA directed) polypeptide A] were analysed pair‑wise, in order to determine which biomarker pairs best correlated with the histological groups of 27 breast cancer samples. The lowest P‑values and the highest area under the curve values in the receiver operating characteristic analysis were used to select the optimum ratios for discrimination among groups. Among the 21 pairs, miR‑17/miR‑27b and miR‑125a/RNU6B best discriminated three groups of samples with different tumour grades (G classification). miR‑125b/miR‑206 best discriminated two groups of samples with different tumour sizes (pT), let‑7a/RNU6B best discriminated two groups of samples with different lymph node status (pN), and let‑7a/miR‑125b best discriminated groups of samples with negative and positive oestrogen and progesterone receptor status. No pair of miRNAs was found to discriminate well between groups with either a negative or positive human epidermal growth factor receptor 2 (HER2) status. However, one miRNA/mRNA pair, miR‑125a/ERBB2, discriminated HER2‑negative from HER2‑positive groups. The breast cancer samples investigated in the present study were grouped by immunohistological methods into three molecular classes: Luminal, HER2 positive and basal (L, H and B, respectively). In order to discern L from H and L from B, two miRNA pairs were selected: miR‑125a/miR‑125b and miR‑125a/miR‑206. In conclusion, the pair‑wise method of RT‑qPCR data analysis may be a reasonable alternative to the standard method of using stably expressed reference genes, such as RNU6B RNA, for normalisation. This method may increase the classification power of miRNA biomarkers in breast cancer diagnostics.

Targeting mitochondrial function for the treatment of breast cancer

There are many approaches used to control breast cancer, although the most efficient strategy is the reactivation of apoptosis. Since mitochondria play an important role in cellular metabolism and homeostasis, as well as in the regulation of cell death pathways, we focus here on metabolic remodeling and mitochondrial alterations present in breast tumor cells. We review strategies including classes of compounds and delivery systems that target metabolic and specific mitochondrial alterations to kill tumor cells without affecting their normal counterparts. We present here the arguments for the improvement of already existent molecules and the design of novel promising anticancer drug candidates that target breast cancer mitochondria.

Mitochondria and familial predisposition to breast cancer

Mitochondrial genome and functional alterations are related to various diseases including cancer. In all cases, the role of these organelles is associated with defects in oxidative energy metabolism and control of tumor-induced oxidative stress. The present study examines the involvement of mitochondrial DNA in cancer and in particular in breast cancer. Furthermore, since mitochondrial DNA is maternally inherited, hereditary breast cancer has been focused on.