BRCA1-deficient breast cancer cell lines are resistant to MEK inhibitors and show distinct sensitivities to 6-thioguanine

Synergistic effects of sequential treatment with doxorubicin and zoledronic acid on anticancer effects in estrogen receptor-negative breast cancer cells

Zoledronic acid (ZA), a bisphosphonate, is commonly used in breast cancer patients with bone metastases to treat hypercalcemia and osteolysis. Recent studies showed the anti-cancer effects of ZA in breast cancer. This study further explored the synergistic effects of sequential and nonsequential ZA and doxorubicin (DOX) administration on estrogen receptor (ER)-positive and -negative breast cancer cell lines. Anti-cancer and anti-invasion effects were evaluated using MTT and Matrigel invasion assays. The synergistic effects were analyzed using the Chou-Talalay method. The protein levels of invasive and angiogenic factors were assessed by western blot. ZA was found to inhibit the proliferation of ER-positive and -negative breast cancer cells in a concentration-dependent manner. When ZA and doxorubicin (DOX) were sequentially combined at nontoxic concentrations, synergistic effects were observed in sequential administrations with DOX followed by ZA only in ER-negative breast cancer cells. Conversely, the sequential and nonsequential treatments did not significantly differ in ER-positive breast cancer cells. Moreover, this sequential treatment significantly reduced cell invasion and MMP9, pNF-κB, and FGF2 protein levels in ER-negative cells. The results suggest that ZA potentially inhibits ER-negative cells by suppressing the canonical NF-κB pathway and its downstream proteins, MMP9 and FGF2. Furthermore, DOX pretreatment enhanced the ZA effect and increased cell sensitivity to ZA, leading to improved outcomes with lower concentrations and shorter drug exposure durations. When combined with DOX, ZA produced synergistic effects on cell proliferation and invasion when administered sequentially in ER-negative breast cancer cells.

Genomic Features of Homologous Recombination Deficiency in Breast Cancer: Impact on Testing and Immunotherapy

Genomic instability is one of the well-established hallmarks of cancer. The homologous recombination repair (HRR) pathway plays a critical role in correcting the double-stranded breaks (DSB) due to DNA damage in human cells. Traditionally, the BRCA1/2 genes in the HRR pathway have been tested for their association with breast cancer. However, defects in the HRR pathway (HRD, also termed 'BRCAness'), which has up to 50 genes, have been shown to be involved in tumorigenesis and treatment susceptibility to poly-ADP ribose polymerase inhibitors (PARPis), platinum-based chemotherapy, and immune checkpoint inhibitors (ICIs). A reliable consensus on HRD scores is yet to be established. Emerging evidence suggests that only a subset of breast cancer patients benefit from ICI-based immunotherapy. Currently, albeit with limitations, the expression of programmed death-ligand 1 (PDL1) and tumor mutational burden (TMB) are utilized as biomarkers to predict the favorable outcomes of ICI therapy in breast cancer patients. Preclinical studies demonstrate an interplay between the HRR pathway and PDL1 expression. In this review, we outline the current understanding of the role of HRD in genomic instability leading to breast tumorigenesis and delineate outcomes from various clinical trials. Furthermore, we discuss potential strategies for combining HRD-targeted therapy with immunotherapy to achieve the best healthcare outcomes in breast cancer patients.

Molecular, Cellular, and Technical Aspects of Breast Cancer Cell Lines as a Foundational Tool in Cancer Research

Breast cancer comprises about 30% of all new female cancers each year and is the most common malignant cancer in women in the United States. Breast cancer cell lines have been harnessed for many years as a foundation for in vitro analytic studies to understand the use of cancer prevention and therapy. There has yet to be a compilation of works to analyze the pitfalls, novel discoveries, and essential techniques for breast cancer cell line studies in a scientific context. In this article, we review the history of breast cancer cell lines and their origins, as well as analyze the molecular pathways that pharmaceutical drugs apply to breast cancer cell lines in vitro and in vivo. Controversies regarding the origins of certain breast cancer cell lines, the benefits of utilizing Patient-Derived Xenograft (PDX) versus Cell-Derived Xenograft (CDX), and 2D versus 3D cell culturing techniques will be analyzed. Novel outcomes from epigenetic discovery with dietary compound usage are also discussed. This review is intended to create a foundational tool that will aid investigators when choosing a breast cancer cell line to use in multiple expanding areas such as epigenetic discovery, xenograft experimentation, and cancer prevention, among other areas.

Anticancer effects of alpelisib on PIK3CA-mutated canine mammary tumor cell lines

Canine mammary tumors (CMTs) are commonly observed in old and unspayed female dogs. Recently, dogs have been increasingly spaying at a young age to prevent mammary tumors. These CMTs require extensive local excision and exhibit a high probability of metastasis to the regional lymph nodes and lungs during malignancy. However, the molecular and biological mechanisms underlying CMT development have not been fully elucidated, and research in this area is limited. Therefore, in this study, we established new CMT cell lines by isolating cells from tumor tissues and investigated phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), a target for human breast cancer. PIK3CA mutations were observed at a similar loci as in the human PIK3CA gene in half of all canine samples. Furthermore, we investigated whether alpelisib, a PIK3CA inhibitor approved by the U.S. Food and Drug Administration for human breast cancer treatment, along with fulvestrant, is effective for CMT treatment. Alpelisib exerted stronger anticancer effects on cell lines with PIK3CA mutations than on the wild-type cell lines. In conclusion, we established new CMT cell lines with PIK3CA mutations and confirmed the efficacy of alpelisib for CMT treatment in vitro.

Validation of Dual-Action Chemo-Radio-Labeled Nanocarriers with High Efficacy against Triple-Negative Breast Cancer

Identification and selectivity of molecular targets with prolonged action for difficult-to-target cancer such as triple-negative breast cancer (TNBC) represent a persisting challenge in the precision delivery of therapeutics. In the quest to target undruggable sites, this study validates the bioavailability of polydopamine-sealed mesoporous silica nanocarriers (PDA-mSiO2) for in vivo drug delivery to TNBC. For controlled transport and release, the chemotherapeutic drug doxorubicin was encapsulated in mSiO2 nanocarriers coated with a PDA layer serving as a stimuli-responsive gatekeeper or seal. For unifying targeting and treatment modalities, these nanocarriers were covalently conjugated to a macrocyclic chelator (DOTA) and folate (FA-mSiO2.) that enabled incorporation of radionuclides and identification of FR Alpha (FolRα) receptors present on TNBC cells. The robust chemical design of FA- and DOTA-functionalized PDA-coated mSiO2 nanocarriers constitutes mild reaction conditions to avoid the loss of surface-bound molecules. The radiolabeling studies with the theranostic pair 68Ga and 177Lu showed quantitative trends for radiochemical efficacy and purity. Nanocarriers equipped with both radiolabels and affinity ligands were optimally stable when incubated with human serum for up to 120 h (177Lu), demonstrating hydrophilicity with a partition coefficient (log P) of -3.29 ± 0.08. Specifically, when incubated with TNBC cells, the cells received significant FA-mSiO2 carriers, demonstrating efficient carrier internalization and time-dependent uptake. Moreover, in vivo results visualize the retention of drug-filled carriers at the tumor sites for a long time, which holds promise for therapeutic studies. This research work demonstrates for the first time the successful dual conjugation of nanocarriers through the colocation of radionuclides and anticancer drugs that is promising for both live molecular imaging and enhanced therapeutic effect for TNBC.

Emerging potential of ubiquitin-specific proteases and ubiquitin-specific proteases inhibitors in breast cancer treatment

Breast cancer is the most frequently diagnosed cancer in women, accounting for 30% of new diagnosing female cancers. Emerging evidence suggests that ubiquitin and ubiquitination played a role in a number of breast cancer etiology and progression processes. As the primary deubiquitinases in the family, ubiquitin-specific peptidases (USPs) are thought to represent potential therapeutic targets. The role of ubiquitin and ubiquitination in breast cancer, as well as the classification and involvement of USPs are discussed in this review, such as USP1, USP4, USP7, USP9X, USP14, USP18, USP20, USP22, USP25, USP37, and USP39. The reported USPs inhibitors investigated in breast cancer were also summarized, along with the signaling pathways involved in the investigation and its study phase. Despite no USP inhibitor has yet been approved for clinical use, the biological efficacy indicated their potential in breast cancer treatment. With the improvements in phenotypic discovery, we will know more about USPs and USPs inhibitors, developing more potent and selective clinical candidates for breast cancer.

Auger Emitter Conjugated PARP Inhibitor for Therapy in Triple Negative Breast Cancers: A Comparative In-Vitro Study

Simple Summary

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer, with a high recurrence rate. Since treatment of BRCA^mut TNBC patients with PARP inhibitor (PARPi), targeting the nuclear protein PARP1, shows varied responses, its therapeutic efficacy is currently evaluated in combination with chemotherapy. Auger emitters (AEs) are radionuclides that can cause DNA damage when delivered close to the DNA. Due to the nuclear location of PARP1, radiolabelling of PARPi with AEs provide an efficient nuclear delivery mechanism. This study shows the radiosynthesis of an AE radiolabelled PARPi ([¹²⁵I]-PARPi-01) and its therapeutic effect as monotherapy or in combination with chemotherapeutics in a panel of TNBC cell lines. We found that [¹²⁵I]-PARPi-01 efficiently induces DNA damage with therapeutic effect irrespective of BRCA mutation. All responsive cell lines have homologous recombination deficiency. Short pretreatment with doxorubicin significantly reduces clonogenic survival of both responsive and resistant cell lines.

Abstract

PARP1 inhibitors (PARPi) are currently approved for BRCA^mut metastatic breast cancer, but they have shown limited response in triple negative breast cancer (TNBC) patients. Combination of an Auger emitter with PARPis enables PARP inhibition and DNA strand break induction simultaneously. This will enhance cytotoxicity and additionally allow a theranostic approach. This study presents the radiosynthesis of the Auger emitter [¹²⁵I] coupled olaparib derivative: [¹²⁵I]-PARPi-01, and its therapeutic evaluation in a panel of TNBC cell lines. Specificity was tested by a blocking assay. DNA strand break induction was analysed by γH2AX immunofluorescence staining. Cell cycle analysis and apoptosis assays were studied using flow cytometry in TNBC cell lines (BRCA^wt/mut). Anchorage independent growth potential was evaluated using soft agar assay. [¹²⁵I]-PARPi-01 showed PARP1-specificity and higher cytotoxicity than olaparib in TNBC cell lines irrespective of BRCA their status. Cell lines harbouring DNA repair deficiency showed response to [¹²⁵I]-PARPi-01 monotherapy. Combined treatment with Dox-NP further enhanced therapeutic efficiency in metastatic resistant BRCA^wt cell lines. The clonogenic survival was significantly reduced after treatment with [¹²⁵I]-PARPi-01 in all TNBC lines investigated. Therapeutic efficacy was further enhanced after combined treatment with chemotherapeutics. [¹²⁵I]-PARPi-01 is a promising radiotherapeutic agent for low radiation dosages, and mono/combined therapies of TNBC.

Interactions of BRCA1-mutated Breast Cancer Cell Lines with Adipose-derived Stromal Cells (ADSCs)

Lipofilling may constitute a technique to assist reconstruction of breasts following prophylactic mastectomy for patients with mutated BRCA1 or BRCA2 genes. However, to date it is not clear whether adipose-derived stromal cells (ADSCs) increase the risk of tumor initiation and progression in this situation. Therefore, the interactions of BRCA1 mutated breast cancer cell lines with normal ADSCs were investigated in the present study. Characteristics of MDA-MB-436 (BRCA1 c.5277 + 1G > A) and HCC1937 (BRCA1 p.Gln1756.Profs*74) were compared to MDA-MB-231 and T47D BRCA1/2 wild-type breast cancer cell lines. ADSCs were cultivated from lipoaspirates of a panel of BRCA1/2- wildtype patients. Interactions of conditioned medium (CM) of these cells with the breast cancer lines were studied using proliferation and migration assays as well as adipokine expression western blot arrays. CM of ADSCs exhibit a dose-dependent stimulation of the proliferation of the breast cancer cell lines. However, of the ADSC preparations tested, only 1 out of 18 samples showed a significant higher stimulation of BRCA1-mutated MDA-MB-436 versus wildtype MDA-MB-231 cells, and all CM revealed lower stimulatory activity for BRCA1-mutated HCC1937 versus wildtype T47D cells. Additionally, migration of breast cancer cells in response to CM of ADSCs proved to be equivalent or slower for BRCA1/2 mutated versus nonmutated cancer cells and, with exception of angiopoietin-like 2, induced expression of adipokines showed no major difference. Effects of media conditioned by normal ADSCs showed largely comparable effects on BRCA1-mutated and wildtype breast cancer cell lines thus advocating lipofilling, preferentially employing allogeneic non-mutated ADSCs.

Multi-omics data integration reveals correlated regulatory features of triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive type of breast cancer with very little treatment options. TNBC is very heterogeneous with large alterations in the genomic, transcriptomic, and proteomic landscapes leading to various subtypes with differing responses to therapeutic treatments. We applied a multi-omics data integration method to evaluate the correlation of important regulatory features in TNBC BRCA1 wild-type MDA-MB-231 and TNBC BRCA1 5382insC mutated HCC1937 cells compared with non-tumorigenic epithelial breast MCF10A cells. The data includes DNA methylation, RNAseq, protein, phosphoproteomics, and histone post-translational modification. Data integration methods identified regulatory features from each omics method that had greater than 80% positive correlation within each TNBC subtype. Key regulatory features at each omics level were identified distinguishing the three cell lines and were involved in important cancer related pathways such as TGFβ signaling, PI3K/AKT/mTOR, and Wnt/beta-catenin signaling. We observed overexpression of PTEN, which antagonizes the PI3K/AKT/mTOR pathway, and MYC, which downregulates the same pathway in the HCC1937 cells relative to the MDA-MB-231 cells. The PI3K/AKT/mTOR and Wnt/beta-catenin pathways are both downregulated in HCC1937 cells relative to MDA-MB-231 cells, which likely explains the divergent sensitivities of these cell lines to inhibitors of downstream signaling pathways. The DNA methylation and RNAseq data is freely available via GEO GSE171958 and the proteomics data is available via the ProteomeXchange PXD025238.

A review on genotoxicity in connection to infertility and cancer

Genotoxicity has been identified as the main cause of infertility and a variety of cancers. The mechanisms affect the structure, quality of the information or the segregation of DNA and are not inherently correlated with mutagenicity. The concept of genotoxicity, the chemical classes that cause genetic damage and the associated mechanisms of action are discussed here. Hazardous effects of pharmaceuticals, cosmetics, agrochemicals, industrial compounds, food additives, natural toxins and nanomaterials are, in large part, identified by genotoxicity and mutagenicity tests. These are critical and early steps in industrial and regulatory health assessment. Though several in vitro experiments are commonly used and approval by regulatory agencies for commercial licensing of drugs, their accuracy in human predictions for genotoxic and mutagenic effects is frequently questioned. Treatment of real and functional genetic toxicity problems depends in detail on the knowledge of mechanisms of DNA damage in the molecular, subcellular, cellular and tissue or organ system levels. Current strategies for risk assessment of human health need revisions to achieve robust and reliable results for optimizing their effectiveness. Additionally, computerized methods, neo-biomarkers leveraging '-omics' approaches, all of which can provide a convincing genotoxicity evaluation to reduce infertility and cancer risk.

Combined treatment with auranofin and trametinib induces synergistic apoptosis in breast cancer cells

Auranofin is a gold complex used as an anti-rheumatic agent and may act as a potent anticancer drug against breast tumors. Trametinib is a specific mitogen-activated protein kinase inhibitor, approved for the treatment of metastatic melanoma. The aim of this study was to examine the synergistic effects of auranofin and trametinib on apoptosis in MCF-7 human breast cancer cells. The combination treatment inhibited cancer cell proliferation and induced cell cycle arrest at the sub-G1 phase and apoptosis via poly (ADP-ribose) polymerase cleavage and caspase-3/7 activation. It is noteworthy that this treatment significantly increased p38 mitogen-activated protein kinase (MAPK) phosphorylation to induce mitochondrial stress, subsequently promoting cancer cell apoptosis through release of apoptosis-inducing factor. Further data demonstrated that combined treatment significantly induced increase in nuclear translocation of AIF. These results indicated that activation of the p38 MAPK signaling pathway and mitochondrial apoptosis may contribute to the synergistic consequences in MCF-7 cells. Collectively, our data demonstrated that combined treatment with auranofin and trametinib exhibited synergistic breast cancer cell death and this combination might be utilized as a novel therapeutic strategy for breast cancer.

Synthesis and Biological Evaluations of Electrophilic Steroids Inspired by the Taccalonolides

Natural products have served as inspirational scaffolds for the design and synthesis of novel antineoplastic agents. Here we present our preliminary efforts on the synthesis and biological evaluation of a new class of electrophilic steroids inspired by the naturally occurring taccalonolides. We demonstrate that these simplified analogs exhibit highly persistent antiproliferative properties similar to the taccalonolides and retain activity against resistant cancer cell lines that warrants further preclinical development.

Thioguanine Induces Apoptosis in Triple-Negative Breast Cancer by Regulating PI3K-AKT Pathway

Triple-negative breast cancer (TNBC) is notoriously difficult to treat due to the lack of biological targets and poor sensitivity to conventional therapies. Chemotherapy is the main clinical therapy, but the effective screening strategy for chemotherapy drugs is poorly investigated. Drug repositioning has been the center of attention in recent years attracting numerous studies. Here, we firstly found multiple common features between leukemia and TNBC by analyzing the global transcriptome profiles based on the transformed comparison data from NCI60. Therefore, we investigated the role of the classic leukemia drug thioguanine (6-TG) in TNBC cancer cells. Our results indicated that 6-TG inhibited cell proliferation and tumor cell progression by suppressing PI3K–AKT pathway via downregulating the DNA methylation level of PTEN. Moreover, apoptosis was induced via the activation of PI3K-AKT downstream TSC1 and the downregulation of methylation levels of DAXX, TNF, FADD and CASP8etc. These findings indicated 6-TG exerts its anti-tumor effects in vitro and in vivo through regulating the DNA methylation levels of genes involved in PI3K–AKT and apoptosis pathway. Meanwhile, our study suggested that transcriptome-based drug screening has potential implications for breast cancer therapy and drug selection.

β-hCG-induced mutant BRCA1 ignites drug resistance in susceptible breast tissue

β-hCG expression in breast cancer is highly controversial with reports supporting both protective and tumorigenic effects. It has also been reported that risk of breast cancer at an early age is increased with full-term pregnancies if a woman is a BRCA1 mutation carrier. We have already demonstrated that BRCA1-defective cells express high levels of β-hCG and that when BRCA1 is restored, β-hCG level is reduced. Also, BRCA1 can bind to the promoter and reduce the levels of β-hCG. β-hCG induces tumorigenicity in BRCA1-defective cells by directly binding to TGFBRII and induces TGFBRII-mediated cell proliferation. In this study, we analyzed the mechanism of action of β-hCG on BRCA1 expression and its influence on drug sensitivity in breast cancer cells. We demonstrate that β-hCG induces mutant BRCA1 protein expression in BRCA1 mutant cells; however, in BRCA1 wild-type cells, β-hCG reduced wild-type BRCA1 protein expression. Transcriptionally, β-hCG could induce Slug/LSD1-mediated repression of wild-type and mutant BRCA1 messenger RNA levels. However, β-hCG induces HSP90-mediated stabilization of mutant BRCA1 and hence the overexpression of mutant BRCA1 protein, resulting in partial restoration of homologous recombination repair of damaged DNA. This contributes to drug resistance to HSP90 inhibitor 17AAG in BRCA1-defective cancer cells. A combination of HSP90 inhibitor and TGFBRII inhibitor has shown to sensitize β-hCG expressing BRCA1-defective breast cancers to cell death. Targeting the β-hCG-HSP90-TGFBRII axis could prove an effective treatment strategy for BRCA1-mutated breast tumors.

Transcriptomics Analysis of the Tumor-Inhibitory Pathways of 6-Thioguanine in MCF-7 Cells via Silencing DNMT1 Activity

Background

6-thioguanine (6-TG), as a conventional “ancient” drug for the treatment of acute leukemia, has been proved to have extensive anti-tumor roles. This study was created to investigate the hidden function of 6-TG on the MCF-7 breast cancer cell line (ER+, PR+) and its mechanisms.

Methods

MCF-7 cells were treated with 6-TG, and the IC50 value was measured by a cell counting kit-8 assay. Differentially expressed genes (DEGs) were confirmed by RNA-seq analysis. Apoptosis and cell cycle consequences were determined by flow cytometry and Western blot analyses.

Results

The results showed that colony formation decreased markedly and the percentage of cell apoptosis increased after 6-TG treatment. DNMT1 mRNA and protein expression decreased, and FAS expression increased. Moreover, 6-TG also induced MCF-7 cells to undergo G2/M phase cell cycle arrest and upregulated CDKN1A (p21).

Conclusion

Overall, our results suggest that 6-TG may induce FAS-mediated exogenous apoptosis and p21-dependent G2/M arrest by inhibiting the activity of DNMT1 in MCF-7 breast cancer cells.

Apoptosis Induction via ATM Phosphorylation, Cell Cycle Arrest, and ER Stress by Goniothalamin and Chemodrugs Combined Effects on Breast Cancer-Derived MDA-MB-231 Cells

Goniothalamin (GTN), a styryl-lactone, exhibits inhibitory effects on many kinds of cancer cells in vitro. The objectives of this study were to investigate the anticancer activities of GTN and molecular signaling pathways associated with cell death in human breast cancer MDA-MB-231 cell line. GTN inhibited the growth of MDA-MB-231 cells. Apoptosis was confirmed by annexin V-FITC and PI staining, and apoptotic morphology was observed by microscopy. Reduction of mitochondrial transmembrane potential and enhanced caspases activities were found in GTN-treated MDA-MB-231 cells. GTN significantly altered apoptosis-related protein expressions, including Noxa, PUMA, Bax, Bim, Bad, Bcl-2, Bcl-xL, and DIABLO, which was related to the gene expression levels. Mitochondrial calcium released to the cytosol and ER stress related proteins increased, which correlated with increases in ER stress gene expression levels. GTN induced hydrogen peroxide and superoxide anion radicals in MDA-MB-231 cells associated with cell cycle arrest in G2/M phase, which was induced by phosphorylation and ATM gene expression. Moreover, GTN had synergistic effects when combined with cyclophosphamide, 5-fluorouracil, paclitaxel, and vinblastine, and additive effect with methotrexate through caspases enzyme-acceleration. In conclusion, goniothalamin-induced MDA-MB-231 cell apoptosis occurred via intrinsic and extrinsic pathways, along with ER stress. These pathways provide new targeted drug strategies for advancements in anticancer medicine.

FePt-Cys nanoparticles induce ROS-dependent cell toxicity, and enhance chemo-radiation sensitivity of NSCLC cells in vivo and in vitro

FePt-Cys nanoparticles (FePt-Cys NPs) have been well used in many fields, despite their poor solubility and stability. We synthetized a cysteine surface modified FePt NPs, which exhibited good solubility, stability and biocompatibility. We explored the insight mechanisms of the antitumor effects of this new nanoparticle system in lung cancer cells. In the in vitro study, FePt-Cys NPs induced a reactive oxygen species (ROS) burst, which suppressed the antioxidant protein expression and induced cell apoptosis. Furthermore, FePt-Cys NPs prevented the migration and invasion of H1975 and A549 cells. These changes were correlated with a dramatic decrease in MMP-2/9 expression and enhanced the cellular attachment. We demonstrated that FePt-Cys NPs promoted the effects of chemo-radiation through activation of the caspase system and impairment of DNA damage repair. In the in vivo study, no severe allergies or drug-related deaths were observed and FePt-Cys NPs showed a synergistic effect with cisplatin and radiation. In conclusion, with good safety and efficacy, FePt-Cys NPs could therefore be potential sensitizers for chemoradiotherapy.

MEK inhibitor, PD98059, promotes breast cancer cell migration by inducing β-catenin nuclear accumulation

Abnormal activation of the RAF/MEK/ERK signaling pathway has been observed in breast cancer. Thus, a number of MEK inhibitors have been designed as one treatment option for breast cancer. Although some studies have found that these MEK inhibitors inhibit the growth of a variety of human cancer cells, some trials have shown that the use of MEK inhibitors as a treatment for breast cancer does not adequately improve survival for unknown reasons. In the present study, MEK inhibitor PD98059 was used to evaluate its anticancer effects on human breast cancer MCF-7 and MDA-MB-231 cells and to explore the possible mechanism of action. Our results revealed that MEK inhibitor PD98059 exhibited antiproliferative effects in a dose- and time-dependent manner in MCF-7 and MDA-MB-231 breast cancer cells. Conversely, incubation of MCF-7 and MDA-MB-231 cells with PD98059 promoted their migration. Further investigation disclosed that the enhanced ability of migration promoted by PD98059 was dependent on β-catenin nuclear translocation in the MCF-7 and MDA-MB‑231 cells. Subsequent experiments documented that activation of EGFR signaling induced by PD98059 increased the amount of β-catenin in the nucleus. Taken together, our findings may elucidate a possible mechanism explaining the ineffectiveness of MEK inhibitors in breast cancer treatment and improve our understanding of the role of MEK in cancer.

A c-Jun N-terminal kinase inhibitor, JNK-IN-8, sensitizes triple negative breast cancer cells to lapatinib

Triple negative breast cancers (TNBC) have poor prognosis compared to other breast cancer subtypes and represent 15-20% of breast cancers diagnosed. Unique targets and new molecularly-targeted therapies are urgently needed for this subtype. Despite high expression of Epidermal Growth Factor Receptor, inhibitors such as lapatinib have not shown therapeutic efficacy in TNBC patients. Herein, we report that treatment with the covalent JNK inhibitor, JNK-IN-8, synergizes with lapatinib to cause cell death, while these compounds as single agents have little effect. The combination significantly increases survival of mice bearing xenografts of MDA-MB-231 human TNBC cells. Our studies demonstrate that lapatinib treatment increases c-Jun and JNK phosphorylation indicating a mechanism of resistance. Combined, these compounds significantly reduce transcriptional activity of Nuclear Factor kappa B, Activating Protein 1, and Nuclear factor erythroid 2-Related Factor 2. As master regulators of antioxidant response, their decreased activity induces a 10-fold increase in reactive oxygen species that is cytotoxic, and is rescued by addition of exogenous antioxidants. Over expression of p65 or Nrf2 also significantly rescues viability during JNK-IN-8 and lapatinib treatment. Further studies combining JNK-IN-8 and lapatinib may reveal a benefit for patients with TNBC, fulfilling a critical medical need.