HER2 Signaling Drives DNA Anabolism and Proliferation through SRC-3 Phosphorylation and E2F1-Regulated Genes

DLGAP5 upregulates E2F1 to promote prostate adenocarcinoma neuroendocrine differentiation

AIMS

DLGAP5 plays a significant role in promoting cancer progression across various cancers. However, the specific role of DLGAP5 in neuroendocrine differentiation (NED) of prostate cancer (PCa) remains elusive. Our objective is to explore the mechanism by which DLGAP5 mediates NED in PCa.

MATERIALS AND METHODS

Utilizing diverse public databases, we conducted bioinformatics analysis to examine DLGAP5 expression in PCa. We confirmed aberrant DLGAP5 expression in various PCa cell lines through Western blotting. Functional assays both in vivo and in vitro have validated the oncogenic role of DLGAP5 in PCa. Furthermore, we sought to identify downstream key genes to elucidate the mechanisms underlying DLGAP5-mediated NED in PCa. We also identified a small molecule drug, AAPK-25, which specifically targets DLGAP5.

KEY FINDINGS

DLGAP5 was highly expressed in NEPC. The suppression of AR signaling promoted DLGAP5 transcription. DLGAP5 endowed PCa cells with a robust ability to proliferate and migrate. E2F1 was an important downstream target of DLGAP5. DLGAP5 mediated the NED of PCa through E2F1. AAPK-25, as an inhibitor of DLGAP5, inhibited PRAD proliferation by repressing the DLGAP5/E2F1 axis both in vitro and in vivo.

SIGNIFICANCE

We identified the AR/DLGAP5/E2F1 signaling pathway as a pivotal mechanism that facilitates the transition of PCa towards a neuroendocrine phenotype. This pathway may represent a promising therapeutic target for NEPC patients.

Adaptive Proteomic Changes in Protein Metabolism and Mitochondrial Alterations Associated with Resistance to Trastuzumab and Pertuzumab Therapy in HER2-Positive Breast Cancer

HER2 (human epidermal growth factor receptor 2) is overexpressed in approximately 15-20% of breast cancers, leading to aggressive tumour growth and poor prognosis. Anti-HER2 therapies, such as trastuzumab and pertuzumab, have significantly improved the outcomes for patients with HER2-positive breast cancer by blocking HER2 signalling. However, intrinsic and acquired resistance remains a major clinical challenge, limiting the long-term effectiveness of these therapies. Understanding the mechanisms of resistance is essential for developing strategies to overcome it and improve the therapeutic outcomes. We generated multiple HER2-positive breast cancer cell line models resistant to trastuzumab and pertuzumab combination therapy. Using mass spectrometry-based proteomics, we conducted a comprehensive analysis to identify the mechanisms underlying resistance. Proteomic analysis identified 618 differentially expressed proteins, with a core of 83 overexpressed and 118 downregulated proteins. Through a series of advanced bioinformatics analyses, we identified significant protein alterations and signalling pathways potentially responsible for the development of resistance, revealing key alterations in the protein metabolism, mitochondrial function, and signalling pathways, such as MAPK, TNF, and TGFβ. These findings identify mitochondrial activity and detoxification processes as pivotal mechanisms underlying the resistance to anti-HER2 therapy. Additionally, we identified key proteins, including ANXA1, SLC2A1, and PPIG, which contribute to the tumour progression and resistance phenotype. Our study suggests that targeting these pathways and proteins could form the basis of novel therapeutic strategies to overcome resistance in HER2-positive breast cancer.

Inhibition of METTL14 overcomes CDK4/6 inhibitor resistance driven by METTL14-m6A-E2F1-axis in ERα-positive breast cancer

CDK4/6i, the first-line drug for treating ERα-positive breast cancer, significantly improves clinical outcomes. However, CDK4/6i resistance often develops and remains a major hurdle, and the underlying mechanisms remain challenging to fully investigate. Here, we used Genome-wide CRISPR/Cas9 library screening combined with single-cell sequencing to screen for molecules mediating CDK4/6i resistance and identified METTL14 as a determinant of CDK4/6i sensitivity. Clinical samples and datasets were analyzed and in vitro and in vivo experiments were performed to confirm the critical function of METTL14 in CDK4/6i resistance. Mechanistically, METTL14 can induce an increase in E2F1 expression in breast cancer cells via an m6A IGF2BP2-dependent mechanism and thus promote CDK4/6i resistance. Furthermore, through a small molecule screen, a novel METTL14 inhibitor named WKYMVM, which can restore sensitivity to CDK4/6i in CDK4/6i-resistant breast cancer cells, was identified. Treatment with folate-conjugated liposomes targeting breast cancer cells that contained both a CDK4/6i and WKYMVM revealed the synergistic effect of METTL14 inhibition with CDK4/6i therapy in a CDK4/6i-resistant PDX model. Together, our findings reveal the mechanism of CDK4/6i resistance and provide a strategy for overcoming CDK4/6i resistance via METTL14 inhibition.

CDK4/6 Inhibitor Resistance in ER+ Breast Cancer

The cyclin-dependent kinases 4 and 6 inhibitors are the mainstay of treatment for patients with hormone receptor-positive and HER2-negative breast cancer. The ability of these drugs to improve the outcome of patients both in the metastatic and the early setting has been largely demonstrated. However, resistance, either de novo or acquired, represents a major clinical challenge. In the past years, efforts have been made to identify biomarkers that might help in a better selection of patients or to unravel the mechanisms leading to resistance in order to develop new therapeutic strategies to overcome it. Alterations of cell cycle-related genes and proteins are among the best characterized markers of resistance, and pathways impacting the cell cycle, including nuclear and growth factor receptors signaling, have been thoroughly investigated. Despite this, to date, cyclin-dependent kinases 4 and 6 inhibitors are administered based only on the hormone receptor and HER2 status of the tumor, and patients progressing on therapy are managed with currently available treatments. Here we summarize present knowledge on the cyclin-dependent kinases 4 and 6 inhibitors' mechanisms of action, efficacy data, and mechanisms of resistance.

E2F1-Associated Purine Synthesis Pathway Is a Major Component of the MET-DNA Damage Response Network

Various lines of investigation support a signaling interphase shared by receptor tyrosine kinases and the DNA damage response. However, the underlying network nodes and their contribution to the maintenance of DNA integrity remain unknown. We explored MET-related metabolic pathways in which interruption compromises proper resolution of DNA damage. Discovery metabolomics combined with transcriptomics identified changes in pathways relevant to DNA repair following MET inhibition (METi). METi by tepotinib was associated with the formation of γH2AX foci and with significant alterations in major metabolic circuits such as glycolysis, gluconeogenesis, and purine, pyrimidine, amino acid, and lipid metabolism. 5'-Phosphoribosyl-N-formylglycinamide, a de novo purine synthesis pathway metabolite, was consistently decreased in in vitro and in vivo MET-dependent models, and METi-related depletion of dNTPs was observed. METi instigated the downregulation of critical purine synthesis enzymes including phosphoribosylglycinamide formyltransferase, which catalyzes 5'-phosphoribosyl-N-formylglycinamide synthesis. Genes encoding these enzymes are regulated through E2F1, whose levels decrease upon METi in MET-driven cells and xenografts. Transient E2F1 overexpression prevented dNTP depletion and the concomitant METi-associated DNA damage in MET-driven cells. We conclude that DNA damage following METi results from dNTP reduction via downregulation of E2F1 and a consequent decline of de novo purine synthesis.

SIGNIFICANCE

Maintenance of genome stability prevents disease and affiliates with growth factor receptor tyrosine kinases. We identified de novo purine synthesis as a pathway in which key enzymatic players are regulated through MET receptor and whose depletion via MET targeting explains MET inhibition-associated formation of DNA double-strand breaks. The mechanistic importance of MET inhibition-dependent E2F1 downregulation for interference with DNA integrity has translational implications for MET-targeting-based treatment of malignancies.

Lead Compound Development of SRC-3 Inhibitors with Improved Pharmacokinetic Properties and Anticancer Efficacy

Steroid receptor coactivator 3 (SRC-3) is a critical mediator of many intracellular signaling pathways that are crucial for cancer proliferation and metastasis. In this study, we performed structure-activity relationship exploration and drug-like optimization of the hit compound SI-2, guided by in vitro/in vivo metabolism studies and cytotoxicity assays. Our efforts led to the discovery of two lead compounds, SI-10 and SI-12. Both compounds exhibit potent cytotoxicity against a panel of human cancer cell lines and demonstrate acceptable pharmacokinetic properties. A biotinylated estrogen response element pull-down assay demonstrated that SI-12 could disrupt the recruitment of SRC-3 and p300 in the estrogen receptor complex. Importantly, SI-10 and SI-12 significantly inhibited tumor growth and metastasis in vivo without appreciable acute toxicity. These results demonstrate the potential of SI-10 and SI-12 as drug candidates for cancer therapy, given their potent SRC-3 inhibition and promising pharmacokinetic and toxicity profiles.

Metabolic heterogeneity affects trastuzumab response and survival in HER2-positive advanced gastric cancer

BACKGROUND

Trastuzumab is the only first-line treatment targeted against the human epidermal growth factor receptor 2 (HER2) approved for patients with HER2-positive advanced gastric cancer. The impact of metabolic heterogeneity on trastuzumab treatment efficacy remains unclear.

METHODS

Spatial metabolomics via high mass resolution imaging mass spectrometry was performed in pretherapeutic biopsies of patients with HER2-positive advanced gastric cancer in a prospective multicentre observational study. The mass spectra, representing the metabolic heterogeneity within tumour areas, were grouped by K-means clustering algorithm. Simpson's diversity index was applied to compare the metabolic heterogeneity level of individual patients.

RESULTS

Clustering analysis revealed metabolic heterogeneity in HER2-positive gastric cancer patients and uncovered nine tumour subpopulations. High metabolic heterogeneity was shown as a factor indicating sensitivity to trastuzumab (p = 0.008) and favourable prognosis at trend level. Two of the nine tumour subpopulations associated with favourable prognosis and trastuzumab sensitivity, and one subpopulation associated with poor prognosis and trastuzumab resistance.

CONCLUSIONS

This work revealed that tumour metabolic heterogeneity associated with prognosis and trastuzumab response based on tissue metabolomics of HER2-positive gastric cancer. Tumour metabolic subpopulations may provide an association with trastuzumab therapy efficacy.

CLINICAL TRIAL REGISTRATION

The patient cohort was conducted from a multicentre observational study (VARIANZ;NCT02305043).

Reviewing the significance of dendritic cell vaccines in interrupting breast cancer development

Breast cancer is a heterogeneous disease and is the most prevalent cancer in women. According to the U.S breast cancer statistics, about 1 in every 8 women develop an invasive form of breast cancer during their lifetime. Immunotherapy has been a significant advancement in the treatment of cancer with multiple studies reporting favourable patient outcomes by modulating the immune response to cancer cells. Here, we review the significance of dendritic cell vaccines in treating breast cancer patients. We discuss the involvement of dendritic cells and oncodrivers in breast tumorigenesis, highlighting the rationale for targeting oncodrivers and neoantigens using dendritic cell vaccine therapy. We review different dendritic cell subsets and maturation states previously used to develop vaccines and suggest the use of DC vaccines for breast cancer prevention. Further, we highlight that the intratumoral delivery of type 1 dendritic cell vaccines in breast cancer patients activates tumor antigen-specific CD4+ T helper cell type 1 (Th1) cells, promoting an anti-tumorigenic immune response while concurrently blocking pro-tumorigenic responses. In summary, this review provides an overview of the current state of dendritic cell vaccines in breast cancer highlighting the challenges and considerations necessary for an efficient dendritic cell vaccine design in interrupting breast cancer development.

Clinical considerations of CDK4/6 inhibitors in HER2 positive breast cancer

Deregulation of cell cycles can result in a variety of cancers, including breast cancer (BC). In fact, abnormal regulation of cell cycle pathways is often observed in breast cancer, leading to malignant cell proliferation. CDK4/6 inhibitors (CDK4/6i) can block the G1 cell cycle through the cyclin D-cyclin dependent kinase 4/6-inhibitor of CDK4-retinoblastoma (cyclinD-CDK4/6-INK4-RB) pathway, thus blocking the proliferation of invasive cells, showing great therapeutic potential to inhibit the spread of BC. So far, three FDA-approved drugs have been shown to be effective in the management of advanced hormone receptor positive (HR+) BC: palbociclib, abemaciclib, and ribociclib. The combination strategy of CDK4/6i and endocrine therapy (ET) has become the standard therapeutic regimen and is increasingly applied to advanced BC patients. The present study aims to clarify whether CDK4/6i can also achieve a certain therapeutic effect on Human epidermal growth factor receptor 2 positive (HER2+) BC. Studies of CDK4/6i are not limited to patients with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced BC, but have also expanded to other types of BC. Several pre-clinical and clinical trials have demonstrated the potential of CDK4/6i in treating HER2+ BC. Therefore, this review summarizes the current knowledge and recent findings on the use of CDK4/6i in this type of BC, and provides ideas for the discovery of new treatment modalities.

Bibliometric analysis and visualization of endocrine therapy for breast cancer research in the last two decade

Background

Breast cancer endocrine therapy research has become a crucial domain in oncology since hormone receptor-positive breast cancers have been increasingly recognized, and targeted therapeutic interventions have been advancing over the past few years. This bibliometric analysis attempts to shed light on the trends, dynamics, and knowledge hotspots that have shaped the landscape of breast cancer endocrine therapy research between 2003 and 2022.

Methods

In this study, we comprehensively reviewed the scientific literature spanning the above-mentioned period, which included publications accessible through the database of the Web of Science (WOS) and the National Center for Biotechnology Information (NCBI). Next, a systematic and data-driven analysis supported by sophisticated software tools was conducted, such that the core themes, prolific authors, influential journals, prominent countries, and critical citation patterns in the relevant research field can be clarified.

Results

A continuous and substantial expansion of breast cancer endocrine therapy research was revealed over the evaluated period. A total of 1,317 scholarly articles were examined. The results of the analysis suggested that research on endocrine therapy for breast cancer has laid a solid basis for the treatment of hormone receptor-positive breast cancer. From a geographical perspective, the US, the UK, and China emerged as the most active contributors, illustrating the global impact of this study. Furthermore, our analysis delineated prominent research topics that have dominated the discourse in the past two decades, including drug therapy, therapeutic efficacy, molecular biomarkers, and hormonal receptor interactions.

Conclusion

This comprehensive bibliometric analysis provides a panoramic view of the ever-evolving landscape of breast cancer endocrine therapy research. The findings highlight the trajectory of past developments while signifying an avenue of vast opportunities for future investigations and therapeutic advancements. As the field continues to burgeon, this analysis will provide valuable guidance for to researchers toward pertinent knowledge hotspots and emerging trends, which can expedite the discoveries in the realm of breast cancer endocrine therapy.

Multiplexed and reproducible high content screening of live and fixed cells using Dye Drop

High-throughput measurement of cells perturbed using libraries of small molecules, gene knockouts, or different microenvironmental factors is a key step in functional genomics and pre-clinical drug discovery. However, it remains difficult to perform accurate single-cell assays in 384-well plates, limiting many studies to well-average measurements (e.g., CellTiter-Glo®). Here we describe a public domain Dye Drop method that uses sequential density displacement and microscopy to perform multi-step assays on living cells. We use Dye Drop cell viability and DNA replication assays followed by immunofluorescence imaging to collect single-cell dose-response data for 67 investigational and clinical-grade small molecules in 58 breast cancer cell lines. By separating the cytostatic and cytotoxic effects of drugs computationally, we uncover unexpected relationships between the two. Dye Drop is rapid, reproducible, customizable, and compatible with manual or automated laboratory equipment. Dye Drop improves the tradeoff between data content and cost, enabling the collection of information-rich perturbagen-response datasets.

Targeting Cell Cycle Progression in HER2+ Breast Cancer: An Emerging Treatment Opportunity

The development of HER2-targeted therapies has dramatically improved patient survival and patient management and increased the quality of life in the HER2+ breast cancer patient population. Due to the activation of compensatory pathways, patients eventually suffer from resistance to HER2-directed therapies and develop a more aggressive disease phenotype. One of these mechanisms is the crosstalk between ER and HER2 signaling, especially the CDK4/6-Cyclin D-Rb signaling axis that is commonly active and has received attention for its potential role in regulating tumor progression. CDK 4/6 inhibitors interfere with the binding of cell-cycle-dependent kinases (CDKs) with their cognate partner cyclins, and forestall the progression of the cell cycle by preventing Rb phosphorylation and E2F release that consequentially leads to cancer cell senescence. CDK 4/6 inhibitors, namely, palbociclib, ribociclib, and abemaciclib, in combination with anti-estrogen therapies, have shown impressive outcomes in hormonal receptor-positive (HR+) disease and have received approval for this disease context. As an extension of this concept, preclinical/clinical studies incorporating CDK 4/6 inhibitors with HER2-targeted drugs have been evaluated and have shown potency in limiting tumor progression, restoring therapeutic sensitivity, and may improving the management of the disease. Currently, several clinical trials are examining the synergistic effects of CDK 4/6 inhibitors with optimized HER2-directed therapies for the (ER+/-) HER2+ population in the metastatic setting. In this review, we aim to interrogate the burden of HER2+ disease in light of recent treatment progress in the field and examine the clinical benefit of CDK 4/6 inhibitors as a replacement for traditional chemotherapy to improve outcomes in HER2+ breast cancer.

Intercepting Premalignant, Preinvasive Breast Lesions Through Vaccination

Breast cancer (BC) prevention remains the ultimate cost-effective method to reduce the global burden of invasive breast cancer (IBC). To date, surgery and chemoprevention remain the main risk-reducing modalities for those with hereditary cancer syndromes, as well as high-risk non-hereditary breast lesions such as ADH, ALH, or LCIS. Ductal carcinoma in situ (DCIS) is a preinvasive malignant lesion of the breast that closely mirrors IBC and, if left untreated, develops into IBC in up to 50% of lesions. Certain high-risk patients with DCIS may have a 25% risk of developing recurrent DCIS or IBC, even after surgical resection. The development of breast cancer elicits a strong immune response, which brings to prominence the numerous advantages associated with immune-based cancer prevention over drug-based chemoprevention, supported by the success of dendritic cell vaccines targeting HER2-expressing BC. Vaccination against BC to prevent or interrupt the process of BC development remains elusive but is a viable option. Vaccination to intercept preinvasive or premalignant breast conditions may be possible by interrupting the expression pattern of various oncodrivers. Growth factors may also function as potential immune targets to prevent breast cancer progression. Furthermore, neoantigens also serve as effective targets for interception by virtue of strong immunogenicity. It is noteworthy that the immune response also needs to be strong enough to result in target lesion elimination to avoid immunoediting as it may occur in IBC arising from DCIS. Overall, if the issue of vaccine targets can be solved by interrupting premalignant lesions, there is a potential to prevent the development of IBC.

CDK4/6 and PI3K inhibitors: A new promise for patients with HER2-positive breast cancer

BACKGROUND

HER2-positive (HER2+) breast cancer represents a heterogeneous breast cancer subtype, including both oestrogen receptor (ER) positive and negative tumours. A deeper understanding of the crosstalk between ER and HER2 receptor pathways has led to the development of treatment strategies consisting of a simultaneous blockade of both signalling pathways, as a reasonable approach to prevent the onset of mechanisms of resistance.

METHODS

This review was based on the material searched on PubMed, MEDLINE and Embase databases and on conference proceedings from major oncology conferences up to 15 December 2020. The search strategy included the following keywords: 'HER2-positive breast cancer', 'CDK4-6 inhibitors' and 'PI3K inhibitors', and was adapted for use with different bibliographic databases.

RESULTS

CDK4/6 and PI3K inhibitors are two classes of agents already approved in patients with hormone receptor positive, HER2-negative breast cancer. Recently, promising data with their use have been also shown in HER2+ disease. Results from preclinical and clinical studies are shedding light on the role of these classes of agents in HER2+ breast cancer, and are paving the road for a forthcoming change in clinical practice.

CONCLUSIONS

Treatment landscape for HER2+ breast cancer is rapidly changing, and CDK4/6 and PI3K inhibitors represent a new promising strategy to improve patients' outcomes.

HER2-PI9 and HER2-I12: two novel and functionally active splice variants of the oncogene HER2 in breast cancer

In this study, two novel alternative splice variants of HER2, named HER2-PI9 and HER2-I12, were identified in breast cancer cell lines and breast tumour tissues. Whilst HER2-P19 arises from the inclusion of an 117 bp cassette-exon of intron 9 of HER2, HER2-I12 results from intron 12 inclusion. In silico analyses were performed to predict the amino acid sequences of these two HER2 novel variants. To confirm their protein expression, plasmid vectors were generated and transfected into the HER2 negative breast cancer cell line, MCF-7. Additionally, their functional properties in oncogenic signalling were confirmed. Expression of HER2-PI9 and HER2-I12 was successful and matched the in silico predictions. Importantly, these splice variants can modulate the phosphorylation levels of extracellular signal-related kinase 1/2 (ERK1/2) and Akt/protein kinase B (Akt) signalling in MCF-7 breast cancer cells. Enhanced cellular proliferation, migration and invasion were observed in the case of the HER2-I12 expressing model. In human tissues and breast carcinoma tumours both variants were present. This study reveals two novel splice variants of HER2. Additionally, the potential biological activity for HER2-PI9 and HER2-I12 in breast cancer cells is also reported..

SRC-3, a Steroid Receptor Coactivator: Implication in Cancer

Steroid receptor coactivator-3 (SRC-3), also known as amplified in breast cancer 1 (AIB1), is a member of the SRC family. SRC-3 regulates not only the transcriptional activity of nuclear receptors but also many other transcription factors. Besides the essential role of SRC-3 in physiological functions, it also acts as an oncogene to promote multiple aspects of cancer. This review updates the important progress of SRC-3 in carcinogenesis and summarizes its mode of action, which provides clues for cancer therapy.

TBL1XR1 Ensures Balanced Neural Development Through NCOR Complex-Mediated Regulation of the MAPK Pathway

TBL1XR1 gene is associated with multiple developmental disorders presenting several neurological aspects. The relative protein is involved in the modulation of important cellular pathways and master regulators of transcriptional output, including nuclear receptor repressors, Wnt signaling, and MECP2 protein. However, TBL1XR1 mutations (including complete loss of its functions) have not been experimentally studied in a neurological context, leaving a knowledge gap in the mechanisms at the basis of the diseases. Here, we show that Tbl1xr1 knock-out mice exhibit behavioral and neuronal abnormalities. Either the absence of TBL1XR1 or its point mutations interfering with stability/regulation of NCOR complex induced decreased proliferation and increased differentiation in neural progenitors. We suggest that this developmental unbalance is due to a failure in the regulation of the MAPK cascade. Taken together, our results broaden the molecular and functional aftermath of TBL1XR1 deficiency associated with human disorders.

Steroid receptor coactivator 3 (SRC-3/AIB1) is enriched and functional in mouse and human Tregs

A subset of CD4 + lymphocytes, regulatory T cells (Tregs), are necessary for central tolerance and function as suppressors of autoimmunity against self-antigens. The SRC-3 coactivator is an oncogene in multiple cancers and is capable of potentiating numerous transcription factors in a wide variety of cell types. Src-3 knockout mice display broad lymphoproliferation and hypersensitivity to systemic inflammation. Using publicly available bioinformatics data and directed cellular approaches, we show that SRC-3 also is highly enriched in Tregs in mice and humans. Human Tregs lose phenotypic characteristics when SRC-3 is depleted or pharmacologically inhibited, including failure of induction from resting T cells and loss of the ability to suppress proliferation of stimulated T cells. These data support a model for SRC-3 as a coactivator that actively participates in protection from autoimmunity and may support immune evasion of cancers by contributing to the biology of Tregs.

An evaluation of palbociclib as a breast cancer treatment option: a current update

INTRODUCTION

Patients with hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer have benefitted from treatment with palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor capable of selectively targeting mechanisms of cell cycle progression that contribute to tumor cell proliferation. Palbociclib use in this setting demonstrates improved progression-free survival when given in combination with aromatase inhibitors or fulvestrant.

AREAS COVERED

The authors describe the current state of research surrounding palbociclib use in breast cancer, present evidence supporting a role for palbociclib in additional subtypes of metastatic breast cancer such as HER2-positive (HER2+) and triple-negative, report ongoing clinical trials aimed at expanding the scope of use for palbociclib, and discuss expected clinical results that will better inform decisions on including palbociclib as a part of breast cancer treatment strategies.

EXPERT OPINION

Preclinical and clinical studies have shown promising evidence for palbociclib use in metastatic HER2+ and androgen receptor-expressing triple-negative breast cancer but mixed results in the adjuvant/neoadjuvant setting, where differences may only be detectable in high-risk disease. Palbociclib combinations may constitute viable replacements for chemotherapy in the neoadjuvant setting as part of de-escalation strategies. Investigation into synergy of palbociclib with immunotherapies is also ongoing based on non-canonical effects of CDK4/6 inhibition on the tumor immune microenvironment.

Screening and Identification of Key Biomarkers in Acquired Lapatinib-Resistant Breast Cancer

Lapatinib, targeting the human epidermal growth factor receptor family members HER1 and HER2, has been approved by the US Food and Drug Administration for use in metastatic HER2-positive breast cancer. However, resistance to lapatinib remains a common challenge to HER2-positive metastatic breast cancer. Until now, the molecular mechanisms of acquired resistance to lapatinib (ALR) have remained unclear. With no definite biomarkers currently known, we aimed to screen for key biomarkers in ALR. In this research, we identified 55 differentially expressed genes (DEGs, 20 upregulated, 35 downregulated) through bioinformatic analysis using microarray datasets GSE16179, GSE38376, and GSE51889 from the Gene Expression Omnibus (GEO) database. The related gene function was explored using the Gene Ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. The protein-protein interaction (PPI) network was constructed with the Search Tool for the Retrieval of Interacting Genes (STRING) and Cytoscape. The functional enrichment of the DEGs was analyzed, including negative regulation of the B cell apoptotic process, DNA replication, solute:proton symporter activity, synthesis, and degradation of ketone bodies, and metal sequestration by antimicrobial proteins. Analysis of seven hub genes revealed their concentration mainly in DNA replication and cell cycle. Survival analysis revealed that MCM10 and SPC24 may be related with poor prognosis in patients with ALR. Meanwhile, the prediction model of lapatinib sensitivity was constructed, and emerging role of the model was further analyzed using several webtools. In conclusion, hub genes are involved in the complex mechanisms underlying ALR in breast cancer and provide favorable support for treatment of ALR in future.

ETS transcription factor ESE-1/Elf3 is an independent prognostic factor of survival in HR+HER2+ breast cancer patients

PURPOSE

The ETS transcription factor ESE-1 has been shown to be important in HER2⁺ breast cancer and ESE-1 mRNA expression has been shown to associate with prognostic outcomes in the HER2⁺ subtype, as well as in ER⁺, HER2⁺ luminal B patients. However, the clinical significance of ESE-1 protein expression remains unknown. The purpose of the current exploratory study is to evaluate the prognostic value of ESE-1 protein expression in molecular breast cancer subtypes with special emphasis on hormone receptor positive HER2⁺(HR⁺ HER2⁺) and the HER2 positive (HER2⁺-only) breast cancer patients.

METHODS

We developed a mouse monoclonal anti-ESE-1 antibody, verified its specificity, epitope, and used immunohistochemical staining to assess ESE-1 expression in an IBC approved archive of 957 breast tumor samples. Using Pearson product correlation, contingency analysis, and long rank P value testing, we analyzed the association of ESE-1 expression with clinicopathological features and survival outcomes in HR⁺HER2^-; HR⁺HER2⁺; HR^- HER2^- (Triple negative) and HR^-HER2⁺ (HER2 subtype) patients.

RESULTS

ESE-1, nuclear or cytoplasmic, was not significantly associated with survival outcomes in HR⁺HER2^-, triple-negative, or HER2⁺-only breast cancer patients. However, high nuclear ESE-1 was associated with poor survival outcomes in hormone receptor positive (ERα⁺, PR⁺) HER2⁺ patients and was an independent prognostic marker for that group.

CONCLUSIONS

This study provides evidence for prognostic significance of nuclear ESE-1 in ERalpha positive breast cancers patients also positive for HER2 indicating that crosstalk between ERalpha and ESE-1 in HER2⁺ tumors could be important for prognostic outcomes. Further studies regarding the nature of interaction between ESE-1 and ERalpha in these tumors are warranted.

Activation of Src mediates acquired cisplatin resistance in human lung carcinoma cells

Cisplatin (CDDP) is the most effective chemotherapeutic drug against lung carcinoma. However, the emergence of resistant clones has severely limited its clinical application. We found that the cisplatin-resistant lung carcinoma cell line A549/CDDP had increased levels of the phosphorylated gap junction protein Cx43 and SRC tyrosine kinase, and low levels of total Cx43 protein and reduced gap junction formation. The SRC kinase inhibitor PP2 increased the expression of total Cx43 protein and enhanced cisplatin sensitivity, indicating that activated SRC kinase induces chemoresistance by decrease total Cx43 level. Furthermore, Cx43 gene silencing in the drug-resistant cell lines abrogated the sensitizing effect of PP2. Taken together, targeting SRC kinase by PP2 reverses cisplatin resistance by upregulating Cx43 protein levels, indicating a novel pathway of cisplatin resistance that may be amenable to therapeutic intervention.

The emerging role of CDK4/6i in HER2-positive breast cancer

Prior to the advent of the monoclonal antibody trastuzumab, human epidermal growth-factor receptor 2 (HER2)-positive (HER2+) breast cancer (BC) was associated with an aggressive clinical course and poor survival outcomes. In the era of effective HER2-directed therapies, median survival rates for patients with metastatic HER2+ BC now approach 5 years. Despite these improvements, the majority of affected patients unfortunately die from disease. Therapies to overcome treatment resistance are being actively pursued. One strategy has been to target the cyclin-dependent kinases 4/6 (CDK4/6), as they are downstream of HER2 and many of the cellular pathways driving resistance to HER2-targeted therapies, and play a key role in proliferation by controlling transition through the G1 restriction point to the S phase of the cell cycle. In this article, we review the published literature with regard to the rationale for CDK4/6-directed therapies in HER2+ BC and discuss ongoing clinical research and new challenges in the field.

Metabolic Dysregulation Controls Endocrine Therapy-Resistant Cancer Recurrence and Metastasis

Cancer recurrence and metastasis involves many biological interactions, such as genetic, transcription, environmental, endocrine signaling, and metabolism. These interactions add a complex understanding of cancer recurrence and metastatic progression, delaying the advancement in therapeutic opportunities. We highlight the recent advances on the molecular complexities of endocrine-related cancers, focusing on breast and prostate cancer, and briefly review how endocrine signaling and metabolic programs can influence transcriptional complexes for metastasis competence. Nuclear receptors and transcriptional coregulators function as molecular nodes for the crosstalk between endocrine signaling and metabolism that alter downstream gene expression important for tumor progression and metastasis. This exciting regulatory axis may provide insights to the development of cancer therapeutics important for these desensitized endocrine-dependent cancers.

Metabolic Reprogramming in Breast Cancer and Its Therapeutic Implications

Current standard-of-care (SOC) therapy for breast cancer includes targeted therapies such as endocrine therapy for estrogen receptor-alpha (ERα) positive; anti-HER2 monoclonal antibodies for human epidermal growth factor receptor-2 (HER2)-enriched; and general chemotherapy for triple negative breast cancer (TNBC) subtypes. These therapies frequently fail due to acquired or inherent resistance. Altered metabolism has been recognized as one of the major mechanisms underlying therapeutic resistance. There are several cues that dictate metabolic reprogramming that also account for the tumors' metabolic plasticity. For metabolic therapy to be efficacious there is a need to understand the metabolic underpinnings of the different subtypes of breast cancer as well as the role the SOC treatments play in targeting the metabolic phenotype. Understanding the mechanism will allow us to identify potential therapeutic vulnerabilities. There are some very interesting questions being tackled by researchers today as they pertain to altered metabolism in breast cancer. What are the metabolic differences between the different subtypes of breast cancer? Do cancer cells have a metabolic pathway preference based on the site and stage of metastasis? How do the cell-intrinsic and -extrinsic cues dictate the metabolic phenotype? How do the nucleus and mitochondria coordinately regulate metabolism? How does sensitivity or resistance to SOC affect metabolic reprogramming and vice-versa? This review addresses these issues along with the latest updates in the field of breast cancer metabolism.

Cyclin E1 and Rb modulation as common events at time of resistance to palbociclib in hormone receptor-positive breast cancer

CDK4/6 inhibitors represent a new treatment standard for hormone receptor-positive (HR+), HER2-negative advanced breast cancer (BC) patients. Although efficacious, resistance to these agents is universal. Here, we profiled a large panel of HR+ BC cell lines with conditioned resistance to the CDK4/6 inhibitor palbociclib, and analyzed cell cycle-related markers by gene expression profiles (GEP) and western blot (WB). GEP showed high molecular heterogeneity among the models, with E2F targets being significantly enriched both during treatment and at the time of resistance. By both WB and GEP, a common molecular feature at the time of palbociclib resistance was the concomitant overexpression of cyclin E1 and down-regulation of Rb. CCNE1 was the only significantly up-regulated gene among E2F targets at resistance with CCNE1 genomic amplification being observed in two resistant models. Rb was downregulated in all resistant models; a reduction of RB1 copy number was observed in three resistant cell lines. In silico analyses showed that CCNE1/RB1 ratio correlated with palbociclib IC50 in different datasets of both breast and non-breast cancer cell lines, performing better than CCNE1 or RB1 taken separately. Finally, the CCNE1/RB1 ratio was shown to be an adverse prognostic factor in patients with ER+ BC and to be able to discriminate palbociclib-sensitive versus resistant among patients enrolled in the NeoPalAna trial, a neoadjuvant trial testing palbociclib, performing better than CCNE1 or RB1 alone. Our data suggest that the CCNE1/RB1 ratio may be a viable biomarker of palbociclib resistance, warranting further clinical validation.

The expression levels of two genes involved in controlling the cell cycle offers a promising predictive indicator of whether women with hormone receptor–positive breast cancer are likely to develop resistance to the drug palbociclib. A team led by Luca Malorni and Ilenia Migliaccio from the Hospital of Prato, Italy, analyzed gene and protein profiles in a panel of breast cancer cell lines with differential sensitivity to palbociclib. The researchers found that, compared to palbociclib-sensitive cell lines, those that were drug-resistant tended to have elevated expression of one cell-cycle–related gene, called CCNE1, and reduced expression of another, called Rb. The ratio of CCNE1:Rb expression proved to be an accurate prognostic factor among patients enrolled in a clinical trial of palbociclib, performing better than either CCNE1 or Rb levels on their own.

Valvular heart disease as a possible predictor of trastuzumab-induced cardiotoxicity in patients with breast cancer

Although the use of trastuzumab has been reported to improve overall survival in patients with HER2-positive breast cancer, there is increasing concern about the adverse effects of trastuzumab-induced cardiotoxicity (TIC). The aim of the present study was to investigate the predictor of TIC and to consider appropriate management for such patients. The present study breast cancer 119 patients with breast cancer who had been treated with trastuzumab. Patients were referred to our department for cardiac function screening. The patients' baseline characteristics, echocardiographic data, presence of trastuzumab-induced cardiotoxicity (TIC) and all-cause mortality were investigated. TIC was defined as a manifestation of overt heart failure or ≥10% reduction of left ventricular ejection fraction (LVEF) from baseline to an LVEF <55% in asymptomatic patients. During the follow-up period (mean, 1,410 days), symptomatic heart failure occurred in 2 out of 119 patients (1.6%), 11 patients (9.2%) had asymptomatic impairment of cardiac function that was ameliorated by discontinuing trastuzumab and 20 patients (16.8%) succumbed to cancer-associated fatality. In the logistic regression analysis, only the presence of valvular heart disease at the baseline was indicated to be a predictor of TIC. There was no other predictor for TIC, including baseline characteristics, other therapies and echocardiographic parameters. In addition, impairment of cardiac function was ameliorated by discontinuing trastuzumab. TIC occurred in ~10% of the patients treated with trastuzumab. Only the presence of valvular heart disease seems to be associated with occurrence of TIC, with no other specific predictor of TIC demonstrated in the present study. The present data suggests the importance of regular monitoring of cardiac function, and that presence of valvular heart disease may be a possible predictor of TIC.

Overcoming Therapeutic Resistance of Triple Positive Breast Cancer with CDK4/6 Inhibition

Triple positive breast cancers overexpress both the human epidermal growth factor receptor 2 (HER2) oncogene and the hormonal receptors (HR) to estrogen and progesterone. These cancers represent a unique therapeutic challenge because of a bidirectional cross-talk between the estrogen receptor alpha (ERα) and HER2 pathways leading to tumor progression and resistance to targeted therapy. Attempts to combine standard of care HER2-targeted drugs with antihormonal agents for the treatment of HR+/HER2+ breast cancer yielded encouraging results in preclinical experiments but did improve overall survival in clinical trial. In this review, we dissect multiple mechanisms of therapeutic resistance typical of HR+/HER2+ breast cancer, summarize prior clinical trials of targeted agents, and describe novel rational drug combinations that include antihormonal agents, HER2-targeted drugs, and CDK4/6 inhibitors for treatment of the HR+/HER2+ breast cancer subtype.

Metabolic enzyme PFKFB4 activates transcriptional coactivator SRC-3 to drive breast cancer

Alterations in both cell metabolism and transcriptional programs are hallmarks of cancer that sustain rapid proliferation and metastasis 1 . However, the mechanisms that control the interaction between metabolic reprogramming and transcriptional regulation remain unclear. Here we show that the metabolic enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4) regulates transcriptional reprogramming by activating the oncogenic steroid receptor coactivator-3 (SRC-3). We used a kinome-wide RNA interference-based screening method to identify potential kinases that modulate the intrinsic SRC-3 transcriptional response. PFKFB4, a regulatory enzyme that synthesizes a potent stimulator of glycolysis 2 , is found to be a robust stimulator of SRC-3 that coregulates oestrogen receptor. PFKFB4 phosphorylates SRC-3 at serine 857 and enhances its transcriptional activity, whereas either suppression of PFKFB4 or ectopic expression of a phosphorylation-deficient Ser857Ala mutant SRC-3 abolishes the SRC-3-mediated transcriptional output. Functionally, PFKFB4-driven SRC-3 activation drives glucose flux towards the pentose phosphate pathway and enables purine synthesis by transcriptionally upregulating the expression of the enzyme transketolase. In addition, the two enzymes adenosine monophosphate deaminase-1 (AMPD1) and xanthine dehydrogenase (XDH), which are involved in purine metabolism, were identified as SRC-3 targets that may or may not be directly involved in purine synthesis. Mechanistically, phosphorylation of SRC-3 at Ser857 increases its interaction with the transcription factor ATF4 by stabilizing the recruitment of SRC-3 and ATF4 to target gene promoters. Ablation of SRC-3 or PFKFB4 suppresses breast tumour growth in mice and prevents metastasis to the lung from an orthotopic setting, as does Ser857Ala-mutant SRC-3. PFKFB4 and phosphorylated SRC-3 levels are increased and correlate in oestrogen receptor-positive tumours, whereas, in patients with the basal subtype, PFKFB4 and SRC-3 drive a common protein signature that correlates with the poor survival of patients with breast cancer. These findings suggest that the Warburg pathway enzyme PFKFB4 acts as a molecular fulcrum that couples sugar metabolism to transcriptional activation by stimulating SRC-3 to promote aggressive metastatic tumours.

Therapeutic Challenge with a CDK 4/6 Inhibitor Induces an RB-Dependent SMAC-Mediated Apoptotic Response in Non-Small Cell Lung Cancer

Purpose: The retinoblastoma tumor suppressor (RB), a key regulator of cell-cycle progression and proliferation, is functionally suppressed in up to 50% of non-small cell lung cancer (NSCLC). RB function is exquisitely controlled by a series of proteins, including the CyclinD-CDK4/6 complex. In this study, we interrogated the capacity of a CDK4/6 inhibitor, palbociclib, to activate RB function.Experimental Design and Results: We employed multiple isogenic RB-proficient and -deficient NSCLC lines to interrogate the cytostatic and cytotoxic capacity of CDK 4/6 inhibition in vitro and in vivo We demonstrate that while short-term exposure to palbociclib induces cellular senescence, prolonged exposure results in inhibition of tumor growth. Mechanistically, CDK 4/6 inhibition induces a proapoptotic transcriptional program through suppression of IAPs FOXM1 and Survivin, while simultaneously augmenting expression of SMAC and caspase-3 in an RB-dependent manner.Conclusions: This study uncovers a novel function of RB activation to induce cellular apoptosis through therapeutic administration of a palbociclib and provides a rationale for the clinical evaluation of CDK 4/6 inhibitors in the treatment of patients with NSCLC. Clin Cancer Res; 24(6); 1402-14. ©2018 AACR.

mRNA methylation by NSUN2 in cell proliferation

Methylation is a prevalent post-transcriptional modification that occurs in almost all RNA species. NSUN2, a nucleolar RNA methyltransferase, has been shown to methylate mRNAs encoding factors that control cell division and growth arrest, thereby affecting their stability and/or translation. Here, the author summarizes the recent progress in understanding NSUN2-mediated mRNA methylation and its implications in cell proliferation and senescence. WIREs RNA 2016, 7:838-842. doi: 10.1002/wrna.1380 For further resources related to this article, please visit the WIREs website.