1. Introduction
The breast cancer is the most common cancer newly diagnosed for women in United States in 2020 [
1]. Breast cancer is a heterogeneous disease with different molecular subtypes defined by distinct molecular classes associated to prognosis: claudin-low, normal-like, luminal A, luminal B, HER2 and basal [
2] and confirmed by gene quantification in pam50 classification [
3]. Breast cancer is the second leading cause of mortality in woman due to rapid metastasis and disease recurrence [
4]. The breast tissue is in a unique microenvironment with plentiful adipocytes infiltrating. Previous studies have shown that adipocytes can regulate fatty acid metabolism, enhance the invasion and metastasis of breast cancer [
5]. Ferroptosis is an iron-dependent regulated form of cell death caused by the accumulation of lipid-based reactive oxygen species (ROS) [
6]. Prerequisites for ferroptosis include iron metabolism, mitochondrial metabolism, synthesis of polyunsaturated fatty acid phospholipid (PUFA-PL) and lipid peroxidation [
7]. Targeting ferroptosis have been proposed to treat breast cancer. There is increasing evidence that ferroptosis can inhibit breast cancer cell growth, improve the sensitivity of chemotherapy and radiotherapy and inhibit distant metastases [
5]. From 2001 to 2003, the Stockwell Lab performed a screen to identify compounds that kill cells engineered to be tumourigenic (harbouring the RAS mutant), without killing their isogenic parental precursors. One of the most efficient compounds was identified and named “erastin” after its ability to “Eradicate RAS-and Small T transformed cells” [
8]. Subsequently, they identified RSL3, which was also named after its “oncogenic-RAS-selective lethal” property in 2008 [
9]. Small molecule–induced ferroptosis has been shown to have a strong inhibitory effect on tumor growth in a drug-resistant environment, which may increase the sensitivity of the tumor to chemotherapeutic treatment [
10]. Ferroptosis is also considered an important cell death mechanism caused by a number of therapies, including chemotherapy, radiotherapy (RT), targeted therapy and immunotherapy [
11], but in opposite way, the tumor cells with ferroptosis could diminish anti-tumor immune response by inhibiting the antigen presenting cells [
12]. The tumor microenvironment (TME) plays a notable role in cancer progression. It includes pH and oxygen levels, the extracellular matrix (ECM), connective tissue, infiltrating immune cells, and the vasculature of the tumor. Interaction between the ECM and the tumor cells activates key signaling pathways that promote tumor proliferation, invasion, and metastasis. This notably influences many tumors as the ECM can comprise up to 60% of the tumor mass [
13].
In the present work, by a text-mining approach integrated in transcriptome experiments, a link between Ferroptosis and ECM remodeling was done through gene related regulation in adverse prognosis of breast cancer but also in TNBC cellular model stimulated by ferroptosis activators.
2. Materials and Methods
Using keyword “Ferroptosis in breast” keyword, a co-occurrence of citations with coding gene identifiers was searched in the article abstracts of the PUBMED database was searched with the "Génie" algorithm [
14]. Bioinformatics analyses were realized in R software environment version 4.2.1. False Discovery Rate (FDR) of the significant associated genes were analyzed by qqplot visualization with qqman R package version 0.1.8 [
15]. Further investigations of text-mining associations with gene identifiers have been confirmed with the “GeneValorization” application [
16] on the National Center for Biotechnolgy Information (NCBI) database [
17]. The results of this text-mining were drawn as circleplot of gene-keywords co-occurrence with circlize R-package version 0.4.15 and as alluvial plot.
Fragments Per Kilobase of transcript sequence per Millions base pairs sequenced (FPKM) Transcript quantification performed by original pipeline of dataset GSE173905 [
19] were downloaded at the following address:
https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE173905 (accessed on 2023, may 18
th). After sequencing on Illumina NovaSeq 6000 technology, the original pipeline aligned reads on human genome with the reference genome was built using Hisat2 v2.0.5 [
20] and paired-end clean reads were aligned to the reference genome using Hisat2 v2.0.5 software and FPKM, expected number of Fragments Per Kilobase of transcript sequence per Millions base pairs sequenced were computed on counts obtained with Feature Counts v1.5.0-p3 software [
21]. On selected genes for Ferroptosis/Extracellular matrix remodeling signature, unsupervised principal component analysis was performed with FactoMiner R package version 2.8 [
22].
Distant relapse free survival (DRFS) from dataset GSE25066 [
18] was used as outcome to performed iterative univariate Cox analysis against expression of the genes identified as being significantly associated with the keyword "ferroptosis in breast". During trial follow-up of adjuvant therapy in breast cancer, distant relapse–free survival (DRFS) could be used as endpoint [
18]. DRFS was defined as the interval from initial diagnostic biopsy until diagnosis of distant metastasis or death from breast cancer, non-breast cancer, or unknown causes [
23]. This iteration of univariate Cox analysis was automatized with loopcolcox R-package version 1.0.0 available at the following address:
https://github.com/cdesterke/loopcolcox (accessed on 2023, may 18
th). Univariate Kaplan Meier and survival optimal threshold on variables were performed with survminer R-package version 0.4.9 and survival R-package version 3.3.1. On genes with adverse prognosis association a functional enrichment was performed with CPG signature from MsigDb database [
24] through Toppgene online application [
25]. A breast cancer related signature network was drawn with Cytoscape standalone software version 3.9.1 [
26]. An expression molecular score related to Ferroptosis/Extracellular matrix remodeling functionalities was done by computing the sum of the product between Cox beta coefficients and expression of the eleven selected genes. For the eleven genes belonging to the Ferroptosis/Extracellular matrix remodeling signature a multi-ROC analysis was done against estrogen/progesterone receptors status detected in immunohistochemistry with the R-package multirocauc version 1.0.0 available at the address:
https://github.com/cdesterke/multirocauc (accessed on 2023, may 18
th) (
Supplemental Figure 1A). A multivariate Cox model was built with DRFS as outcome and with incorporation of molecular score and relevant clinical parameters. This DRFS multivariate model was assessed by testing linearity of residuals at global level and for each individual included parameters with Schoenfeld tests. Calibration of the DRFS multivariate model at 10 months of follow-up was done by 500 iterations of bootstrap with rms R-package version 6.7.0. Nomogram validated at 10 months of follow-up was drawn for DRFS multivariate model with regplot R-package version 1.1.
4. Discussion
During this study, by text mining approach, a list of genes was defined as related to ferroptosis cellular functionality known as important way cellular death implicated in tumor response to therapies [
10]. Surprisingly, in transcriptome of breast tumors under therapies (GSE173905) [
18], the majority of ferroptosis-related genes were found having expression associated with adverse distant relapse free survival: 171 of 252 significant genes were found with univariate hazard ratio over 1 (
Supplemental Table 1). With an independent text mining application querying NCBI database: GeneValorization [
16], it could be able to establish a Ferroptosis/ECM remodeling molecular score in basal breast cancer [
18] based on the expression of eleven related genes: TNF, IL6, SET, CDKN2A, EGFR, HMGB1, KRAS, MET, LCN2, HIF1A, TLR4. Except CDKN2A and TNF, the majority of these implicated genes have been validated as been expressed in TNBC cellular model MDA-MB-231 and regulated by ferroptosis activators: erastin and RSL3 [
8,
9].
HIF-1α is an important regulator of the lipid metabolism [
29]. Hypoxia-induced lipid metabolism reprogramming results in fatty acid accumulation, which promotes tumor growth and survival upon reoxidation [
30]. Ferroptosis induction with erastin or RSL3 showed a significant up regulation of HIF1A in TNBC cell line. In the context of increased hypoxia/HIF1A and ECM stiffness in chemoresistant tumors, high expression of HIF1A could be adverse because its is leading to upregulation of ITGA5, activation of the downstream FAK/Src signaling pathways and repression of miR-326 which targets fibronectin (FN1), an extracellular matrix (ECM) central chemoresistance driver gene [
31]. The adipokine Lipocalin-2 (LCN2) has been demonstrated to be an ECM regulator through its association with the ECM protease matrix metalloproteinase-9 (MMP-9) [
32]. It has been shown that LCN2 knockout in human breast cancer cell line MDA-MB-231 ameliorates erastin-mediated ferroptosis and increases cisplatin vulnerability [
33].
Adipocytes constitute the main cell component of ECM in breast cancer [
34]. Cancer-associated adipocytes (CAAs) are localized at the invasive front of breast tumor and exhibit a modified phenotype, a loss of lipid content, a decrease in late adipocyte differentiation markers and overexpression of inflammatory cytokines and proteases [
35]. IL6 up regulation was promoted by ferroptosis activators in MDA-MB-231 TNBC cellular model (
Figure 6D). In breast tumors, IL6 is secreted by CAAs which play essential roles in favor of proliferation, angiogenesis, dissemination, invasion and metastasis of breast cancer [
36]. In breast cancer, the pleiotropic cytokine IL-6 production is related to the development of stem cell phenotype, angiogenesis, cachexia, and resistance to therapy [
37].
EGFR overexpression was found under ferroptosis stimulation in MDA-MB-231 cells (
Figure 6D). EGFR promoted TNBC cell clustering and blockade of EGFR successfully abolished tumor cell cluster formation [
38]. It has been shown that inhibition of EGFR signaling pathway significantly suppressed cell viability of TNBC cells and reduced fraction of CSCs with intracellular enhancement of lipid peroxidation when TNBC cells exposed to erastin [
39].
MET is known to be implicated in chemotherapy resistance especially resistance to targeted therapies, including those targeting EGFR, BRAF and MEK but also contributes to cytotoxic chemotherapy resistance [
40]. Its ligand, HGF is a pleiotropic factor produced by mesenchymal cells in the stroma and as such is widely distributed in the extracellular matrix of most tissues [
41]. Dysregulation of the MET/HGF pathway leads to uncontrolled cell proliferation and oncogenesis and is observed in multiple tumour types [
42]. There is few link between MET and ferroptosis except that HGF exacerbated pancreatic cancer cell ferroptosis resistance [
43]. In the present work, it was observed that RSL3 ferroptosis activator induced overexpression of MET in MDA-MB-231 TNBC cellular model.
In MDA-MB-231, it was observed a significant down regulation of High-mobility group box 1 (HMGB1). HMGB1 control chromosomal structure and is considered as a redox-sensitive protein. HMGB1 is implicated in regulating stress responses to oxidative damage and cell death, which are closely related to the pathology of inflammatory diseases such as cancer. HMGB1 can also be released into the extracellular space and function as a damage-associated molecular pattern protein during ferroptosis [
44]. HMGB1 is known to act via the NRF2/GPX4 axis to repress ferroptosis in mesangial cells in response to high glucose [
45].
In ER-positive breast cancer, SET overexpression reduced tamoxifen-induced antitumor effects and may contribute to the failure of the tamoxifen treatment by modulating the ER signaling [
46]. In MDA-MB-231 TNBC cellular model, ferroptosis activation shown a major repression of SET proto-oncogene.
Ferroptosis activators induced repression of KRAS oncogene expression in MDA-MB-231 TNBC cellular model. KRAS mutations are known as very infrequent in triple-negative breast tumors [
47], but in basal breast cancer, KRAS have been shown to promote the mesenchymal features of this aggressive cancer [
48].
Overexpression of Toll-like receptor-4 (TLR4) in human tumors often correlates with chemoresistance and metastasis. Depletion of TLR4 in naturally overexpressing MDA-MB-231 cells downregulated prosurvival genes concomitant with 2- to 3-fold reduced IC(50) to paclitaxel in vitro and a 6-fold decrease in recurrence rate in vivo [
49]. Effect of ferroptosis activators Erastin and RSL3 on MDA-MB-231 showed an opposite effect on TLR4 expression.
In the present work, by a text mining approach integrated in distinct transcriptome dataset, we could elucidate an adverse molecular program which crosstalk between ferroptosis and extracellular remodeling functionalities during basal breast cancer. This adverse regulated program allowed to compute a molecular expression score that could be promising to evaluate response of ferroptosis target therapies in breast cancer.