Her2 cross talk and therapeutic resistance in breast cancer

Deciphering the Role of BCAR3 in Cancer Progression: Gene Regulation, Signal Transduction, and Therapeutic Implications

This review comprehensively explores the gene BCAR3, detailing its regulation at the gene, mRNA, and protein structure levels, and delineating its multifunctional roles in cellular signaling within cancer contexts. The discussion covers BCAR3's involvement in integrin signaling and its impact on cancer cell migration, its capability to induce anti-estrogen resistance, and its significant functions in cell cycle regulation. Further highlighted is BCAR3's modulation of immune responses within the tumor microenvironment, a novel area of interest that holds potential for innovative cancer therapies. Looking forward, this review outlines essential future research directions focusing on transcription factor binding studies, isoform-specific expression profiling, therapeutic targeting of BCAR3, and its role in immune cell function. Each segment builds towards a holistic understanding of BCAR3's operational mechanisms, presenting a critical evaluation of its therapeutic potential in oncology. This synthesis aims to not only extend current knowledge but also catalyze further research that could pivotally influence the development of targeted cancer treatments.

Unraveling Vulnerabilities in Endocrine Therapy-Resistant HER2+/ER+ Breast Cancer

Breast tumors overexpressing human epidermal growth factor receptor (HER2) confer intrinsic resistance to endocrine therapy (ET), and patients with HER2/estrogen receptor-positive (HER2+/ER+) breast cancer (BCa) are less responsive to ET than HER2-/ER+. However, real-world evidence reveals that a large subset of patients with HER2+/ER+ receive ET as monotherapy, positioning this treatment pattern as a clinical challenge. In the present study, we developed and characterized 2 in vitro models of ET-resistant (ETR) HER2+/ER+ BCa to identify possible therapeutic vulnerabilities. To mimic ETR to aromatase inhibitors (AIs), we developed 2 long-term estrogen deprivation (LTED) cell lines from BT-474 (BT474) and MDA-MB-361 (MM361). Growth assays, PAM50 subtyping, and genomic and transcriptomic analyses, followed by validation and functional studies, were used to identify targetable differences between ET-responsive parental and ETR-LTED HER2+/ER+ cells. Compared to their parental cells, MM361 LTEDs grew faster, lost ER, and increased HER2 expression, whereas BT474 LTEDs grew slower and maintained ER and HER2 expression. Both LTED variants had reduced responsiveness to fulvestrant. Whole-genome sequencing of aggressive MM361 LTEDs identified mutations in genes encoding transcription factors and chromatin modifiers. Single-cell RNA sequencing demonstrated a shift towards non-luminal phenotypes, and revealed metabolic remodeling of MM361 LTEDs, with upregulated lipid metabolism and ferroptosis-associated antioxidant genes, including GPX4. Combining a GPX4 inhibitor with anti-HER2 agents induced significant cell death in both MM361 and BT474 LTEDs. The BT474 and MM361 AI-resistant models capture distinct phenotypes of HER2+/ER+ BCa and identify altered lipid metabolism and ferroptosis remodeling as vulnerabilities of this type of ETR BCa.

Development and validation of a prognostic 15-gene signature for stratifying HER2+/ER+ breast cancer

Background

Human epidermal growth receptor 2-positive (HER2+) breast cancer (BC) is a heterogeneous subgroup. Estrogen receptor (ER) status is emerging as a predictive marker within HER2+ BCs, with the HER2+/ER+ cases usually having better survival in the first 5 years after diagnosis but have higher recurrence risk after 5 years compared to HER2+/ER-. This is possibly because sustained ER signaling in HER2+ BCs helps escape the HER2 blockade. Currently HER2+/ER+ BC is understudied and lacks biomarkers. Thus, a better understanding of the underlying molecular diversity is important to find new therapy targets for HER2+/ER+ BCs.

Methods

In this study, we performed unsupervised consensus clustering together with genome-wide Cox regression analyses on the gene expression data of 123 HER2+/ER+ BC from The Cancer Genome Atlas Breast Invasive Carcinoma (TCGA-BRCA) cohort to identify distinct HER2+/ER+ subgroups. A supervised eXtreme Gradient Boosting (XGBoost) classifier was then built in TCGA using the identified subgroups and validated in another two independent datasets (Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) and Gene Expression Omnibus (GEO) (accession number GSE149283)). Computational characterization analyses were also performed on the predicted subgroups in different HER2+/ER+ BC cohorts.

Results

We identified two distinct HER2+/ER+ subgroups with different survival outcomes using the expression profiles of 549 survival-associated genes from the Cox regression analyses. Genome-wide gene expression differential analyses found 197 differentially expressed genes between the two identified subgroups, with 15 genes overlapping the 549 survival-associated genes.XGBoost classifier, using the expression values of the 15 genes, achieved a strong cross-validated performance (Area under the curve (AUC) = 0.85, Sensitivity = 0.76, specificity = 0.77) in predicting the subgroup labels. Further investigation partially confirmed the differences in survival, drug response, tumor-infiltrating lymphocytes, published gene signatures, and CRISPR-Cas9 knockout screened gene dependency scores between the two identified subgroups.

Conclusion

This is the first study to stratify HER2+/ER+ tumors. Overall, the initial results from different cohorts showed there exist two distinct subgroups in HER2+/ER+ tumors, which can be distinguished by a 15-gene signature. Our findings could potentially guide the development of future precision therapies targeted on HER2+/ER+ BC.

Effects of siRNA-mediated Silencing of ERBB2, IGF-1R, and ITGB1 in HER2-positive Breast Cancer Cells

BACKGROUND/AIM

One of the hallmarks of cancer is deregulation of multiple signaling pathways, which can lead to uncontrolled proliferation and migration of cells. Over-expression and mutations in human epidermal growth factor receptor 2 (HER2) can lead to overactivation of these pathways, potentially developing cancer in different tissues, including breast tissue. IGF-1R and ITGB-1 are two receptors that have been linked to cancer development. Therefore, the aim of this study was to investigate the effects of silencing of the corresponding genes using specific siRNAs.

MATERIALS AND METHODS

Transient silencing of HER2, ITGB-1, and IGF-1R was conducted using siRNAs and expression was quantified by reverse transcription-quantitative polymerase chain reaction. Viability in human breast cancer cells SKBR3, MCF-7, and HCC1954 and cytotoxicity in HeLa cells were tested using WST-1 assay.

RESULTS

The use of anti-HER2 siRNAs in a breast cancer cell line over-expressing HER2 (SKBR3) led to a decrease in cell viability. However, silencing of ITGB-1 and IGF-1R in the same cell line had no significant effects. Silencing of any of the genes encoding any of the three receptors in MCF-7, HCC1954, and HeLa had no significant effects.

CONCLUSION

Our results provide evidence towards using siRNAs against HER2-positive breast cancer. Silencing of ITGB-1 and IGF-R1 did not significantly inhibit the growth of SKBR3 cells. Therefore, there is need for testing the effect of silencing ITGB-1 and IGF-R1 in other cancer cell lines over-expressing these biomarkers and explore their potential use in cancer therapy.

Privileged Scaffolds in Drug Discovery against Human Epidermal Growth Factor Receptor 2 for Cancer Treatment

HER2 is the membrane receptor tyrosine kinase showing overexpression in several human malignancies, particularly breast cancer. HER2 overexpression causes the activation of Ras- MAPK and PI3K/Akt/ NF-κB cellular signal transduction pathways that lead to cancer development and progression. HER2 is, therefore, presumed as one of the key targets for the development of tumor-specific therapies. Several preclinical have been developed that function by inhibiting the HER2 tyrosine kinase activity through the prevention of the dimerization process. Most HER2 inhibitors act as ATP competitors and prevent the process of phosphorylation, and abort the cell cycle progression and proliferation. In this review, the clinical drug candidates and potent pre-clinical newly developed molecules are described, and the core chemical scaffolds typically responsible for anti-HER2 activity are deciphered. In addition, the monoclonal antibodies that are either used in monotherapy or in combination therapy against HER2-positive cancer are briefly described. The identified key moieties in this study could result in the discovery of more effective HER2-targeted anticancer drug molecules and circumvent the development of resistance by HER2-specific chemotherapeutics in the future.

Challenges and emerging strategies for next generation liposomal based drug delivery: An account of the breast cancer conundrum

The global cancer burden is witnessing an upsurge with breast cancer surpassing other cancers worldwide. Furthermore, an escalation in the breast cancer caseload is also expected in the coming years. The conventional therapeutic regimens practiced routinely are associated with many drawbacks to which nanotechnological interventions offer a great advantage. But how eminent could liposomes and their advantages be in superseding these existing therapeutic modalities? A solution is reflected in this review that draws attention to a decade-long journey embarked upon by researchers in this wake. This text is a comprehensive discussion of liposomes, the front runners of the drug delivery systems, and their active and passive targeting approaches for breast cancer management. Active targeting has been studied over the decade by many receptors overexpressed on the breast cancer cells and passive targeting with many drug combinations. The results converge on the fact that the actively targeted formulations exhibit a superior efficacy over their non-targeted counterparts and the all liposomal formulations are efficacious over the free drugs. This undoubtedly underlines the dominion of liposomal formulations over conventional chemotherapy. These investigations have led to the development of different liposomal formulations with active and passive targeting capacities that could be explored in depth. Acknowledging and getting a deeper insight into the liposomal evolution through time also unveiled many imperfections and unchartered territories that can be explored to deliver dexterous liposomal formulations against breast cancer and more in the clinical trial pipeline.

The integrative bioinformatics approaches to predict the xanthohumol as anti-breast cancer molecule: Targeting cancer cells signaling PI3K and AKT kinase pathway

Background

Breast cancer is the most common type of cancer in women, and vast research is being conducted throughout the world for the treatment of this malignancy by natural products using various computational approaches. Xanthohumol, a prenylated flavonoid, is known for its anticancer activity; however, the mechanism behind its action is still in the preliminary stage.

Methods

The current study aimed to analyze the efficacy of xanthohumol compared to the currently available anticancer drugs targeting phosphoinositide-3-kinase (PI3K), serine/threonine kinase (AKT) receptors, and human epidermal growth factor receptor 2 (HER2) for breast cancer treatment through in silico analysis.

Results

The result revealed that the target compound showed significant binding affinity to targets within the PI3K, AKT, and HER2 signaling pathways with a binding energy of -7.5, -7.9, and -7.9 kcal/mol, respectively. Further prediction studies were then made concerning this compound's absorption, distribution, metabolism, and excretion (ADME) as well as drug-likeness properties, resulting in its oral bioavailability with only a single violation of Lipinski's rule of five.

Conclusions

The finding revealed the ability of xanthohumol to bind with multiple cancer cell signaling molecules including PI3K, AKT kinase, and HER2. The current novel study opened the door to advancing research into the management and treatment of breast cancer.

Comparison of a histone deacetylase inhibitor plus exemestane with exemestane alone in hormone receptor‑positive advanced breast cancer that progressed on prior endocrine therapy: A meta‑analysis

Currently, endocrine therapy is the standard treatment for hormone receptor-positive advanced breast cancer (ABC). Despite the high sensitivity of anti-estrogen therapy, many breast cancer patients still experience disease progression, relapse, and reduced overall survival (OS) because of endocrine resistance. Several underlying mechanisms of this phenomenon include a change in hormone receptor expression, mutations in ESR1 and modification of important signaling pathways, but thus far none of these can be defined as the complete explanation. Additionally, it has been shown that in some breast cancers, expression of the estrogen receptor (ER) can be repressed by epigenetic modifications such as DNA methylation and histone deacetylation, and this could be a mechanism for endocrine resistance. Interestingly, although the efficacy of the combination of histone deacetylase (HADC) inhibitors and exemestane in hormone receptor-positive ABC that progressed on prior endocrine therapy has been investigated in several studies, whether pharmacologic blocking of HDAC activity acts as a therapeutic strategy remains highly controversial. Herein, we conducted a meta-analysis to evaluate the efficacy and safety of an HDAC inhibitor plus exemestane vs. exemestane alone in this setting. Our meta-analysis demonstrated that the combination group exhibited significantly prolonged progression-free survival (PFS) [hazard ratio (HR)=0.776, 95% confidence interval (CI)=0.675-0.892, P=0.000] and an improved objective response rate (ORR) (RR=1.612, 95% CI=1.085-2.396, P=0.018) compared to those treated with exemestane alone. Additionally, in terms of OS, the combination group failed to achieve a significant clinical OS benefit (HR=0.811, 95% CI=0.596-1.104, P=0.183). Although grade 3/4 toxicities were more common in the combination group, those toxicities were mostly asymptomatic and manageable. In conclusion, the addition of an HDAC inhibitor to exemestane significantly improves PFS over exemestane alone in hormone receptor-positive ABC patients who progressed on previous endocrine therapy. Identification of novel biomarkers to select patients who will benefit from this combination strategy is a high priority.

Comparing Biomarkers for Predicting Pathological Responses to Neoadjuvant Therapy in HER2-Positive Breast Cancer: A Systematic Review and Meta-Analysis

INTRODUCTION

The predictive strength and accuracy of some biomarkers for the pathological complete response (pCR) to neoadjuvant therapy for HER2-positive breast cancer remain unclear. This study aimed to compare the accuracy of the HER2-enriched subtype and the presence of PIK3CA mutations, namely, TILs, HRs, and Ki-67, in predicting the pCR to HER2-positive breast cancer therapy.

METHODS

We screened studies that included pCR predicted by one of the following biomarkers: the HER2-enriched subtype and the presence of PIK3CA mutations, TILs, HRs, or Ki-67. We then calculated the pooled sensitivity, specificity, positive and negative predictive values (PPVs and NPVs, respectively), and positive and negative likelihood ratios (LRs). Summary receiver operating characteristic (SROC) curves and areas under the curve (AUCs) were used to estimate the diagnostic accuracy.

RESULTS

The pooled estimates of sensitivity and specificity for the HER2-enriched subtype and the presence of PIK3CA mutations, namely, TILs, HRs, and Ki-67, were 0.66 and 0.62, 0.85 and 0.27, 0.49 and 0.61, 0.54 and 0.64, and 0.68 and 0.51, respectively. The AUC of the HER2-enriched subtype was significantly higher (0.71) than those for the presence of TILs (0.59, p = 0.003), HRs (0.65, p = 0.003), and Ki-67 (0.62, p = 0.005). The AUC of the HER2-enriched subtype had a tendency to be higher than that of the presence of PIK3CA mutations (0.58, p = 0.220). Moreover, it had relatively high PPV (0.58) and LR+ (1.77), similar NPV (0.73), and low LR- (0.54) compared with the other four biomarkers.

CONCLUSIONS

The HER2-enriched subtype has a moderate breast cancer diagnostic accuracy, which is better than those of the presence of PIK3CA mutations, TILs, HRs, and Ki-67.

HER2-targeted therapies in gastric cancer

Molecular targeted therapy of cancer has always been the focus of clinicians. Among those therapeutic targets, the human epidermal growth factor receptor-2 (HER-2) signaling pathway is one of the most popular targets for translational research in cancer. However, unlike prospect in breast cancer, HER-2 inhibitor trastuzumab is the only molecular targeted drug approved by US Food and Drug Administration (FDA) for the first-line treatment of HER-2 positive advanced gastric cancer. On this basis, a variety of novel HER2- targeted drugs for gastric cancer are under development, and related clinical researches are in full swing, including small molecular kinase inhibitors (e.g., afatinib, neratinib, pyrotinib), antibody-drug conjugates (e.g., DS-8201a, RC48-ADC) and other novel therapies (e.g., ZW25, CAR-T, BVAC-B). In this study, we will summarize the recent advances in anti-HER-2 agents, potential mechanisms of resistance to HER2-targeted therapy in HER2-positive gastric cancer. We will also discuss the future prospects of potential strategies to overcome anti-HER-2 resistance and development of novel anti-HER-2 approaches for the treatment of HER2-positive gastric cancer patients.

Adjuvant endocrine therapy in HER2-positive breast cancer patients: systematic review and meta-analysis

Background

Approximately 50% of human epidermal growth factor receptor 2 (HER2)-positive breast cancer lesions express hormone receptors. These tumors present a unique therapeutic challenge, and the optimal endocrine therapeutic approach remains controversial. We aimed to study the optimal adjuvant endocrine therapy in this setting, to better establish the basis for clinical recommendations in HER2-positive disease.

Methods

We conducted a literature search up to May 2020, in which we identified randomized controlled trials (RCTs) that investigated the efficacy of various adjuvant hormonal therapies among premenopausal and postmenopausal patients with hormone receptor (HR)-positive, HER2-positive early breast cancer. Disease-free survival (DFS) was calculated with the random effect model and hazard ratios (HRs) with 95% confidence intervals (CI).

Results

Six RCTs (N = 5390 patients) were included in the final analysis. There was no significant difference in DFS between adjuvant treatment with aromatase inhibitors and tamoxifen (HR 0.99, 95% CI 0.68-1.44, P = 0.96). Furthermore, after omitting the ALTTO trial, as it did not randomize patients to hormonal therapy, no significant difference was observed between the two protocols (HR 1.06, 95% CI 0.65-1.73, P = 0.81).

Conclusion

Our study demonstrates similar DFS with tamoxifen and aromatase inhibitors as adjuvant endocrine treatment in HER2-positive HR-positive early-stage breast cancer patients. Future larger prospective studies focusing on the various contemporary endocrine regimens are warranted to validate our findings.

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Optimal adjuvant endocrine therapy for early-stage breast cancer with co-expression of HER2 and hr is unclear.

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Our analysis demonstrated no difference in disease-free survival between selected endocrine regimens among these patients.

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Study strength includes longer follow-up, premenopausal patients and current HER2 regimens and combinations.

Combination treatment with a PI3K/Akt/mTOR pathway inhibitor overcomes resistance to anti-HER2 therapy in PIK3CA-mutant HER2-positive breast cancer cells

Amplification and/or overexpression of human epidermal growth factor receptor 2 (HER2) are observed in 15–20% of breast cancers (HER2+ breast cancers), and anti-HER2 therapies have significantly improved prognosis of patients with HER2+ breast cancer. One resistance mechanism to anti-HER2 therapies is constitutive activation of the phosphoinositide 3-kinase (PI3K) pathway. Combination therapy with small-molecule inhibitors of AKT and HER2 was conducted in HER2+ breast cancer cell lines with or without PIK3CA mutations, which lead to constitutive activation of the PI3K pathway. PIK3CA mutations played important roles in resistance to single-agent anti-HER2 therapy in breast cancer cell lines. Combination therapy of a HER2 inhibitor and an AKT inhibitor, as well as other PI3K pathway inhibitors, could overcome the therapeutic limitations associated with single-agent anti-HER2 treatment in PIK3CA-mutant HER2+ breast cancer cell lines. Furthermore, expression of phosphorylated 4E-binding protein 1 (p4EBP1) following the treatment correlated with the antiproliferative activities of the combination, suggesting that p4EBP1 may have potential as a prognostic and/or efficacy-linking biomarkers for these combination therapies in patients with HER2+ breast cancer. These findings highlight potential clinical strategies using combination therapy to overcome the limitations associated with single-agent anti-HER2 therapies in patients with HER2+ breast cancer.

Targeting Rac and Cdc42 GEFs in Metastatic Cancer

The Rho family GTPases Rho, Rac, and Cdc42 have emerged as key players in cancer metastasis, due to their essential roles in regulating cell division and actin cytoskeletal rearrangements; and thus, cell growth, migration/invasion, polarity, and adhesion. This review will focus on the close homologs Rac and Cdc42, which have been established as drivers of metastasis and therapy resistance in multiple cancer types. Rac and Cdc42 are often dysregulated in cancer due to hyperactivation by guanine nucleotide exchange factors (GEFs), belonging to both the diffuse B-cell lymphoma (Dbl) and dedicator of cytokinesis (DOCK) families. Rac/Cdc42 GEFs are activated by a myriad of oncogenic cell surface receptors, such as growth factor receptors, G-protein coupled receptors, cytokine receptors, and integrins; consequently, a number of Rac/Cdc42 GEFs have been implicated in metastatic cancer. Hence, inhibiting GEF-mediated Rac/Cdc42 activation represents a promising strategy for targeted metastatic cancer therapy. Herein, we focus on the role of oncogenic Rac/Cdc42 GEFs and discuss the recent advancements in the development of Rac and Cdc42 GEF-interacting inhibitors as targeted therapy for metastatic cancer, as well as their potential for overcoming cancer therapy resistance.

Towards personalized treatment for early stage HER2-positive breast cancer

Advances in HER2-targeted therapies have improved the survival of patients with HER2-positive breast cancer. The standard-of-care treatment for localized disease has been chemotherapy and 1 year of adjuvant HER2-targeted therapy, typically with the anti-HER2 antibody trastuzumab. Despite the effectiveness of this treatment, disease relapse occurs in a subset of patients; thus, focus has been placed on escalating treatment by either combining different HER2-targeted agents or extending the duration of HER2-targeted therapy. Indeed, dual HER2-targeted therapies and extended-duration anti-HER2 therapy, as well as adjuvant therapy with the anti-HER2 antibody-drug conjugate T-DM1, have all been approved for clinical use. Emerging evidence suggests, however, that some patients do not derive sufficient benefit from these additional therapies to offset the associated toxicities and/or costs. Similarly, the universal use of chemotherapy might not benefit all patients, and treatment de-escalation through omission of chemotherapy has shown promise in clinical trials and is currently being explored further. The future of precision medicine should therefore involve tailoring of therapy based on the genetics and biology of each tumour and the clinical characteristics of each patient. Predictive biomarkers that enable the identification of patients who will benefit from either escalated or de-escalated treatment will be crucial to this approach. In this Review, we summarize the available HER2-targeted agents and associated mechanisms of resistance, and describe the current therapeutic landscape of early stage HER2-positive breast cancer, focusing on strategies for treatment escalation or de-escalation.

Targeted therapeutic options and future perspectives for HER2-positive breast cancer

Over the past 2 decades, there has been an extraordinary progress in the regimens developed for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Trastuzumab, pertuzumab, lapatinib, and ado-trastuzumab emtansine (T-DM1) are commonly recommended anti-HER2 target agents by the U.S. Food and Drug Administration. This review summarizes the most significant and updated research on clinical scenarios related to HER2-positive breast cancer management in order to revise the guidelines of everyday clinical practices. In this article, we present the data on anti-HER2 clinical research of neoadjuvant, adjuvant, and metastatic studies from the past 2 decades. We also highlight some of the promising strategies that should be critically considered. Lastly, this review lists some of the ongoing clinical trials, findings of which may soon be available.

BCAS2 Enhances Carcinogenic Effects of Estrogen Receptor Alpha in Breast Cancer Cells

Estrogen receptor alpha (ERα) has an established role in breast cancer biology. Transcriptional activation by ERα is a multistep process modulated by coactivator and corepressor proteins. Breast Cancer Amplified Sequence 2 (BCAS2), is a poorly studied ERα coactivator. In this work, we characterize some of the mechanisms through which this protein increases ERα activity and how this promotes carcinogenic processes in breast cancer cells. Using protein-protein interaction and luciferase assays we show that BCAS2 interacts with ERα both in vitro and in vivo and upregulates transcriptional activation of ERα directly through its N-terminal region (AF-1) and indirectly through its C-terminal (AF-2) region, acting in concert with AF-2 interacting coactivators. Elevated expression of BCAS2 positively affects proliferation, clonogenicity and migration of breast cancer cells and directly activates ERα regulated genes which have been shown to play a role in tumor growth and progression. Finally, we used signal transduction pathway inhibitors to elucidate how BCAS2 is regulated in these cells and observed that BCAS2 is preferentially regulated by the PI3K/AKT signaling pathway. BCAS2 is an AF-1 coactivator of ERα whose overexpression promotes carcinogenic processes, suggesting an important role in the development of estrogen-receptor positive breast cancer.

Extended Adjuvant Therapy with Neratinib Plus Fulvestrant Blocks ER/HER2 Crosstalk and Maintains Complete Responses of ER+/HER2+ Breast Cancers: Implications to the ExteNET Trial

PURPOSE

The phase III ExteNET trial showed improved invasive disease-free survival in patients with HER2⁺ breast cancer treated with neratinib versus placebo after trastuzumab-based adjuvant therapy. The benefit from neratinib appeared to be greater in patients with ER⁺/HER2⁺ tumors. We thus sought to discover mechanisms that may explain the benefit from extended adjuvant therapy with neratinib.Experimental Design: Mice with established ER⁺/HER2⁺ MDA-MB-361 tumors were treated with paclitaxel plus trastuzumab ± pertuzumab for 4 weeks, and then randomized to fulvestrant ± neratinib treatment. The benefit from neratinib was evaluated by performing gene expression analysis for 196 ER targets, ER transcriptional reporter assays, and cell-cycle analyses.

RESULTS

Mice receiving "extended adjuvant" therapy with fulvestrant/neratinib maintained a complete response, whereas those treated with fulvestrant relapsed rapidly. In three ER⁺/HER2⁺ cell lines (MDA-MB-361, BT-474, UACC-893) but not in ER⁺/HER2^- MCF7 cells, treatment with neratinib induced ER reporter transcriptional activity, whereas treatment with fulvestrant resulted in increased HER2 and EGFR phosphorylation, suggesting compensatory reciprocal crosstalk between the ER and ERBB RTK pathways. ER transcriptional reporter assays, gene expression, and immunoblot analyses showed that treatment with neratinib/fulvestrant, but not fulvestrant, potently inhibited growth and downregulated ER reporter activity, P-AKT, P-ERK, and cyclin D1 levels. Finally, similar to neratinib, genetic and pharmacologic inactivation of cyclin D1 enhanced fulvestrant action against ER⁺/HER2⁺ breast cancer cells.

CONCLUSIONS

These data suggest that ER blockade leads to reactivation of ERBB RTKs and thus extended ERBB blockade is necessary to achieve durable clinical outcomes in patients with ER⁺/HER2⁺ breast cancer.

Esophageal cancer cells resistant to T-DM1 display alterations in cell adhesion and the prostaglandin pathway

Trastuzumab-emtansine (T-DM1) is an antibody-drug conjugate that specifically targets HER2 thanks to its antibody component trastuzumab. In spite of responses to this novel agent, acquired resistance to treatment remains a major obstacle. Prolonged in vitro exposure of the gastroesophageal junction cancer cell line OE-19 to T-DM1, in the absence or presence of ciclosporin A resulted in the selection of two resistant cell lines to T-DM1. T-DM1-resistant cells presented an increased expression of adhesion genes, altered spreading and higher sensitivity to anoikis than parental cells. A resistant cell line showed decreased adhesion strength, increased migration speed and increased sensitivity to RhoA inhibition. Genes involved in the prostaglandin pathway were deregulated in resistant models. Addition of prostaglandin E₂ to T-DM1 partially restored its cytotoxic activity in resistant models. This work demonstrates that T-DM1-resistance may be associated with alterations of cell adhesion and the prostaglandin pathway, which might constitute novel therapeutic targets.

PI3K inhibition to overcome endocrine resistance in breast cancer

INTRODUCTION

Activation of the phosphatidylinositol-3 kinase (PI3K) pathway is a critical step in oncogenesis and plays a role in the development of treatment resistance for both estrogen receptor (ER) positive and human epidermal growth factor receptor 2 (HER2) positive breast cancers. Hence, there have been efforts to therapeutically inhibit this pathway.

AREAS COVERED

Several inhibitors of PI3K are now progressing through clinical trials with varying degrees of efficacy and toxicity to date. Numerous unresolved questions remain concerning the optimal isoform selectivity of PI3K inhibitors and use of predictive biomarkers. This review examines the most important PI3K inhibitors in ER positive breast cancer to date, with a particular focus on their role in overcoming endocrine therapy resistance and the possible use of PIK3CA mutations as a predictive biomarker.

EXPERT OPINION

We discuss some of the emerging challenges and questions encountered during the development of PI3K inhibitors from preclinical to phase III studies, including other novel biomarkers and future combinations to overcome endocrine resistance.

Aiming for the Insulin-like Growth Factor-1 system in breast cancer therapeutics

Despite the major discoveries occurred in oncology the recent years, breast malignancies remain one of the most common causes of cancer-related deaths for women in developed countries. Development of HER2-targeting drugs has been considered a breakthrough in anti-cancer approaches and alluded to the potential of targeting growth factors in breast cancer (BrCa) therapeutics. More than twenty-five years have passed since the Insulin-like Growth Factor-1 (IGF-1) system was initially recognized as a potential target candidate in BrCa therapy. To date, a growing body of studies have implicated the IGF-1 signaling with the BrCa biology. Despite the promising experimental evidence, the impression from clinical trials is rather disappointing. Several reasons may account for this and the last word regarding the efficacy of this system as a target candidate in BrCa therapeutics is probably not written yet. Herein, we provide the theoretical basis, as well as, a comprehensive overview of the current literature, regarding the different strategies targeting the various components of the IGF-1/IGF-1R axis in several pathophysiological aspects of BrCa, including the tumor micro-environment and cancer stemness. In addition, we review the rationale for targeting the IGF-1 system in the different BrCa molecular subtypes and in treatment resistant breast tumors with a focus on both the molecular mechanisms and on the clinical perspectives of such approaches in specific population subgroups. We also discuss the future challenges, as well as, the development of novel molecules and strategies targeting the system and suggest potential improvements in the field.

HER2-positive breast cancer is lost in translation: time for patient-centered research

No biomarker beyond HER2 itself, which suffers from a low positive predictive value, has demonstrated clinical utility in breast cancer, despite numerous attempts to improve treatment tailoring for the growing number of anti-HER2 targeted therapies. This prompted us to examine the body of evidence, using a systematic approach, to identify putative predictive biomarkers in HER2-positive breast cancer, and discuss the hitherto failure to address the needs of patients. In the future, it is hoped immune-based biomarkers will predict benefit from anti-HER2 treatments in the neoadjuvant and adjuvant settings. In advanced-stage disease, the quantification of tumour heterogeneity using molecular-imaging technology has generated informative data on the success or failure of the antibody-drug conjugate T-DM1. Treatment tailoring remains a high priority, in cost-constrained health-care systems, but such tailoring will require a dramatic shift in the way translational research is being conducted, with the establishment of large, easily accessible, and well-annotated databases of candidate predictive biomarkers. Single-centre biomarker research should become a thing of the past.

AMP-activated kinase (AMPK) regulates activity of HER2 and EGFR in breast cancer

AMP-activated Protein Kinase (AMPK) activity retards growth of many types of cancers. Investigating effects of AMPK activation on breast cancer cell signaling and survival, we found that breast cancer cell lines with amplification and over-expression of HER2 or EGFR are 2- to 5-fold more sensitive to cytotoxic effects of AICAR, a canonical pharmacological activator of AMPK, than breast cancer cell lines lacking HER2 or EGFR overexpression. Paralleling effects on cell survival, AICAR leads to dose- and time-dependent inhibition of HER2 and EGFR in HER2-amplified breast cancer cells, with activation of AMPK and suppression of HER2/EGFR activity preceding commitment to cell death. Transfection of constitutively active AMPKα also leads to decreased HER2 and EGFR phosphorylation, reduced downstream signaling associated with these receptor tyrosine kinases (RTKs), and reduced breast cancer cell growth, confirming effects of AMPK activity on HER2/EGFR. Ensuing co-immunoprecipitation experiments demonstrated an interaction of HER2 with AMPK and an in vitro phosphorylation assay found that HER2 and EGFR contain sequences that are potential substrates for AMPK. Our results lead us to postulate that AMPK regulates HER2 and EGFR activity in HER2-amplified breast cancer cells and thus activation of AMPK might provide therapeutic benefit in such cancers.

Clinical Implications of Mutations in the PI3K Pathway in HER2+ Breast Cancer: Prognostic or Predictive?

Recent advances in tumor genetics and drug development have led to the generation of a wealth of anti-cancer-targeted therapies. These drugs aim at targeting a particular vulnerability in the tumor generated in most cases as a result of dependence on an oncogene and/or loss of a tumor suppressor. Genes in the phosphoinositide 3-kinase (PI3K)/AKT pathway are the most frequently altered in human cancers. Aberrant activation of the PI3K/AKT pathway has been shown to confer resistance to HER2-targeted therapies. Several drugs targeting PI3K/ATK have been developed and are currently in clinical trials in different phases of clinical development, alone or in combination. The impact of mutations in the phosphoinositide 3-kinase (PI3K)/AKT pathway in HER2-amplified breast cancers will be the focus of this review.

Potential of overcoming resistance to HER2-targeted therapies through the PI3K/Akt/mTOR pathway

Human epidermal growth factor receptor 2 (HER2) overexpression occurs in up to 30% of breast cancers and is a marker of aggressive disease. While HER2-targeted therapies have improved outcomes in these tumors, resistance to these agents develops in a large proportion of patients. Determining molecular mechanisms underlying resistance might help improve outcomes for patients with HER2-positive disease by allowing development of strategies to overcome resistance. Activation of signaling pathways involving the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway might contribute to the development of resistance to HER2-targeted therapies. Several inhibitors of this pathway are under investigation in this disease setting and phase 3 data for everolimus in combination with trastuzumab and chemotherapy in trastuzumab-refractory, advanced disease are promising. In this review, molecular mechanisms underlying resistance to HER2-targeted therapies are considered and evidence for strategies to manage resistance is evaluated, including the use of inhibitors of the PI3K/Akt/mTOR pathway.

Biopsy confirmation of metastatic sites in breast cancer patients: clinical impact and future perspectives

Determination of hormone receptor (estrogen receptor and progesterone receptor) and human epidermal growth factor receptor 2 status in the primary tumor is clinically relevant to define breast cancer subtypes, clinical outcome, and the choice of therapy. Retrospective and prospective studies suggest that there is substantial discordance in receptor status between primary and recurrent breast cancer. Despite this evidence and current recommendations, the acquisition of tissue from metastatic deposits is not routine practice. As a consequence, therapeutic decisions for treatment in the metastatic setting are based on the features of the primary tumor. Reasons for this attitude include the invasiveness of the procedure and the unreliable outcome of biopsy, in particular for biopsies of lesions at complex visceral sites. Improvements in interventional radiology techniques mean that most metastatic sites are now accessible by minimally invasive methods, including surgery. In our opinion, since biopsies are diagnostic and changes in biological features between the primary and secondary tumors can occur, the routine biopsy of metastatic disease needs to be performed. In this review, we discuss the rationale for biopsy of suspected breast cancer metastases, review issues and caveats surrounding discordance of biomarker status between primary and metastatic tumors, and provide insights for deciding when to perform biopsy of suspected metastases and which one (s) to biopsy. We also speculate on the future translational implications for biopsy of suspected metastatic lesions in the context of clinical trials and the establishment of bio-banks of biopsy material taken from metastatic sites. We believe that such bio-banks will be important for exploring mechanisms of metastasis. In the future, advances in targeted therapy will depend on the availability of metastatic tissue.

HER2 expression and PI3K-Akt pathway alterations in gastric cancer

The anti-HER2 antibody trastuzumab has led to an era of personalized therapy in gastric cancer (GC). As a result, HER2 expression has become a major concern in GC. HER2 overexpression is seen in 7-34% of GC cases. Trastuzumab is an antibody that targets the HER2 extracellular domain and induces antibody-dependent cellular cytotoxicity and inhibition of the HER2 downstream signals. Mechanisms of resistance to trastuzumab have been reported in breast cancer. There are various mechanisms underlying trastuzumab resistance, such as alterations of HER2 structure or surroundings, dysregulation of HER2 downstream signal effectors and interaction of HER2 with other membrane receptors. The PI3K-Akt pathway is one of the main downstream signaling pathways of HER2. It is well known that PIK3CA mutations and phosphate and tensin homolog (PTEN) inactivation cause over-activation of the downstream signal without an upstream signal activation. Frequencies of PIK3CA mutations and PTEN inactivation have been reported to be 4-25 and 16-77%, respectively. However, little is known about the association between HER2 expression and PI3K-Akt pathway alterations in GC. We have found that HER2 over-expression was significantly correlated with pAkt expression in GC tissues. Furthermore, pAkt expression was correlated with poor prognosis. These results suggest that the PI3K-Akt pathway plays an important role in HER2-positive GC. Moreover, PIK3CA mutations and/or PTEN inactivation might affect the effectiveness of HER2-targeting therapy. Hence, it is necessary to clarify not only HER2 alterations but also PI3K-Akt pathway alterations for HER2-targeting therapy in GC. This review will introduce recent investigations and consider the current status of HER2-targeted therapy for treatment of GC.

Evolution of breast cancer therapeutics: Breast tumour kinase’s role in breast cancer and hope for breast tumour kinase targeted therapy

There have been significant improvements in the detection and treatment of breast cancer in recent decades. However, there is still a need to develop more effective therapeutic techniques that are patient specific with reduced toxicity leading to further increases in patients’ overall survival; the ongoing progress in understanding recurrence, resistant and spread also needs to be maintained. Better understanding of breast cancer pathology, molecular biology and progression as well as identification of some of the underlying factors involved in breast cancer tumourgenesis and metastasis has led to the identification of novel therapeutic targets. Over a number of years interest has risen in breast tumour kinase (Brk) also known as protein tyrosine kinase 6; the research field has grown and Brk has been described as a desirable therapeutic target in relation to tyrosine kinase inhibition as well as disruption of its kinase independent activity. This review will outline the current “state of play” with respect to targeted therapy for breast cancer, as well as discussing Brk’s role in the processes underlying tumour development and metastasis and its potential as a therapeutic target in breast cancer.

Current Approaches and Emerging Directions in HER2-resistant Breast Cancer

Human epidermal growth factor receptor-2 (HER2) is overexpressed in up to 30% of breast cancers; HER2 overexpression is indicative of poor prognosis. Trastuzumab, an anti-HER2 monoclonal antibody, has led to improved outcomes in patients with HER2-positive breast cancer, including improved overall survival in adjuvant and first-line settings. However, a large proportion of patients with breast cancer have intrinsic resistance to HER2-targeted therapies, and nearly all become resistant to therapy after initial response. Elucidation of underlying mechanisms contributing to HER2 resistance has led to development of novel therapeutic strategies, including those targeting HER2 and downstream pathways, heat shock protein 90, telomerase, and vascular endothelial growth factor inhibitors. Numerous clinical trials are ongoing or completed, including phase 3 data for the mammalian target of rapamycin inhibitor everolimus in patients with HER2-resistant breast cancer. This review considers the molecular mechanisms associated with HER2 resistance and evaluates the evidence for use of evolving strategies in patients with HER2-resistant breast cancer.

What is the potential of using PI3K inhibitors in the management of breast cancer in the clinic?

SUMMARY 

Even with hormone- and HER2-targeted anticancer agents, intrinsic and acquired resistance is a common occurrence in estrogen receptor-positive and HER2-positive breast cancers, respectively. As for triple-negative breast cancer, its relative uncommonness, aggressiveness and impressive heterogeneity have been only a few of the challenges researchers and clinicians face in making strides against this disease. This article reviews the involvement of the PI3K pathway in these resistance mechanisms. It also summarizes preclinical and clinical data suggesting the potential of combination therapy with PI3K inhibitors in preventing resistance and restoring sensitivity to hormone-targeted, HER2-targeted agents and chemotherapy.

The mTOR inhibitor rapamycin synergizes with a fatty acid synthase inhibitor to induce cytotoxicity in ER/HER2-positive breast cancer cells

Patients with ER/HER2-positive breast cancer have a poor prognosis and are less responsive to selective estrogen receptor modulators; this is presumably due to the crosstalk between ER and HER2. Fatty acid synthase (FASN) is essential for the survival and maintenance of the malignant phenotype of breast cancer cells. An intimate relationship exists between FASN, ER and HER2. We hypothesized that FASN may be the downstream effector underlying ER/HER2 crosstalk through the PI3K/AKT/mTOR pathway in ER/HER2-positive breast cancer. The present study implicated the PI3K/AKT/mTOR pathway in the regulation of FASN expression in ER/HER2-positive breast cancer cells and demonstrated that rapamycin, an mTOR inhibitor, inhibited FASN expression. Cerulenin, a FASN inhibitor, synergized with rapamycin to induce apoptosis and inhibit cell migration and tumorigenesis in ER/HER2-positive breast cancer cells. Our findings suggest that inhibiting the mTOR-FASN axis is a promising new strategy for treating ER/HER2-positive breast cancer.

Development of EHop-016: a small molecule inhibitor of Rac

The Rac inhibitor EHop-016 was developed as a compound with the potential to inhibit cancer metastasis. Inhibition of the first step of metastasis, migration, is an important strategy for metastasis prevention. The small GTPase Rac acts as a pivotal binary switch that is turned "on" by guanine nucleotide exchange factors (GEFs) via a myriad of cell surface receptors, to regulate cancer cell migration, survival, and proliferation. Unlike the related GTPase Ras, Racs are not usually mutated, but overexpressed or overactivated in cancer. Therefore, a rational Rac inhibitor should block the activation of Rac by its upstream effectors, GEFs, and the Rac inhibitor NSC23766 was developed using this rationale. However, this compound is ineffective at inhibiting the elevated Rac activity of metastatic breast cancer cells. Therefore, a panel of small molecule compounds were derived from NSC23766 and screened for Rac activity inhibition in metastatic cancer cells. EHop-016 was identified as a compound that blocks the interaction of Rac with the GEF Vav in metastatic human breast cancer cells with an IC50 of ~1μM. At higher concentrations (10μM), EHop-016 inhibits the related Rho GTPase Cdc42, but not Rho, and also reduces cell viability. Moreover, EHop-016 inhibits the activation of the Rac downstream effector p21-activated kinase, extension of motile actin-based structures, and cell migration. Future goals are to develop EHop-016 as a therapeutic to inhibit cancer metastasis, either individually or in combination with current anticancer compounds. The next generation of EHop-016-based Rac inhibitors is also being developed.

Current approaches and future directions in the treatment of HER2-positive breast cancer

Human epidermal growth factor receptor 2 (HER2), a member of the ErbB family of transmembrane receptor tyrosine kinases, is amplified in 20-30% of invasive breast cancers. HER2 amplification is associated with metastasis and reduced survival. Two HER2-directed therapies have been approved by the United States Food and Drug Administration for the treatment of HER2-overexpressing breast cancer: trastuzumab, a humanized monoclonal antibody against the extracellular portion of HER2; and lapatinib, a dual HER2- and epidermal growth factor receptor-specific tyrosine kinase inhibitor. Despite the improvement in overall survival with the addition of HER2-targeted agents to chemotherapy, many patients do not benefit from these agents because of inherent resistance. In addition, many patients who achieve an initial response eventually acquire drug resistance. Currently, several mechanisms of resistance have been described, including mutations in other signaling pathways, expression of a truncated form of HER2, receptor crosstalk, and autophagy. There are several approaches under study to target these pathways of resistance, including blocking PI3 kinase and mammalian target of rapamycin signaling, blocking neoangiogenesis and the vascular endothelial growth factor axis, using monoclonal antibody targeting of the HER2 dimerization site, and using HER2 monoclonal antibody-drug conjugates. Here we will review the current scientific rationale for these agents and how combinations of these agents may yield additive or synergistic effects and lead to improved outcomes for patients with HER2-amplified breast cancer.

Role of mTOR inhibition in preventing resistance and restoring sensitivity to hormone-targeted and HER2-targeted therapies in breast cancer

Even with hormone-targeted and human epidermal growth factor receptor 2 (HER2)-targeted anticancer agents, intrinsic resistance or acquired resistance are common occurrences in estrogen receptor-positive and HER2-positive breast cancers, respectively. Potential mechanisms for resistance to targeted agents include steric inhibition imposed by other cellular elements, molecular changes in the target receptor, alterations in the regulation of downstream signaling components, compensatory cross-talk with other signaling pathways, and pharmacogenetic alterations in the host. Evidence suggests that both hormone receptor-positive tumors and HER2-overexpressing tumors use the phosphoinositide 3-kinase/Akt/ mammalian target of rapamycin (mTOR) pathway to escape control of antihormone and anti-HER2 therapies. The combination of mTOR inhibitors with hormone-targeted or HER2-targeted therapies appears to be a promising strategy for overcoming resistant disease and preventing the development of resistance.

Advanced HER2-positive gastric cancer: current and future targeted therapies

The prognostic value of human epidermal growth factor receptor 2 (HER2) in gastric cancer is controversial. Consensus guidelines have standardized the testing of HER2 status in gastric cancer. Overexpression of this receptor occurs in approximately 20% of gastric and gastro-esophageal junction adenocarcinomas, predominantly those of the intestinal type. Recently, trastuzumab has emerged as the first targeted drug to improve overall survival when combined with chemotherapy in advanced HER2-positive gastric cancer. Primary and secondary resistance to trastuzumab has become a major problem and new strategies to overcome this resistance are needed. A high percentage of advanced HER2-positive gastric cancer patients who progress on trastuzumab therapy are candidates for second-line therapy. New families of targeted drugs, including tyrosine kinase inhibitors (TKIs) such as lapatinib and PF-00299804, mammalian target of rapamycin (mTOR) pathway inhibitors such as everolimus, heat-shock protein 90 (HSP90) inhibitors such as AUY922, HER dimerization inhibitors such as pertuzumab, and antibody-chemotherapy conjugates such as trastuzumab-emtansine (T-DM1), could offer alternative second-line treatments when trastuzumab-based first-line therapy fails.

Pharmacological strategies to overcome HER2 cross-talk and Trastuzumab resistance

Approximately 20-30% of breast cancers show increased expression of the HER2 receptor tyrosine kinase. Trastuzumab (Herceptin) is a clinically approved anti-HER2 monoclonal antibody. Many patients with HER2-overexpressing metastatic breast cancer respond to trastuzumab; however, a subset display primary drug resistance. In addition, many patients who initially respond to trastuzumab ultimately develop disease progression. Multiple molecular mechanisms contributing to trastuzumab resistance have been proposed in the literature. These mechanisms include cross-signaling from related HER/erbB receptors and compensatory signaling from receptors outside of the HER/erbB family, including receptors for insulin-like growth factor-I, vascular endothelial growth factor, and transforming growth factor beta. The major downstream signaling pathway activated by HER2 cross-talk is PI3K/mTOR, and a potential integrator of receptor cross-talk is Src-focal adhesion kinase (FAK) signaling. PI3K, Src, and FAK have independently been implicated in trastuzumab resistance. In this review, we will discuss pharmacological inhibition of HER2 cross-talk as a strategy to treat trastuzumab-refractory HER2-overexpresssing breast cancer.

Mechanisms of resistance to HER2 target therapy

In the past years, several agents targeting signaling proteins critical for breast cancer growth and dissemination entered clinical evaluation. They include drugs directed against the HER/ErbB family of receptor tyrosine kinases, especially HER2; several downstream signal transducers; and proteins involved in tumor angiogenesis and dissemination. Unfortunately, resistance to targeted agents is a quite common feature, and understanding of the molecular mechanisms predicting response or failure has become a crucial issue to optimize treatment and select patients who are the best candidates to respond. The neoadjuvant setting offers unique opportunities allowing tumor sampling and search for molecular determinants of response. A variety of tumor and host factors may account for the onset of resistance. Major progress has been made in the understanding of the mechanisms involved in the primary and acquired resistance to targeted agents, especially the anti-HER2 drugs, which play a pivotal role in the weaponry against breast cancer.

Simultaneous Inhibition of Estrogen Receptor and the HER2 Pathway in Breast Cancer: Effects of HER2 Abundance

The estrogen receptor (ER) pathway and the epidermal growth factor receptor (EGFR) pathway play pivotal roles in breast cancer progression. Targeted therapies able to intercept ER or signaling downstream to EGFR and its kin, HER2, are routinely used to treat distinct groups of breast cancer patients. However, patient responses are limited by resistance to endocrine therapy, which may be due to compensatory HER2/EGFR signaling. This raises the possibility that simultaneous interception of HER2 and ER may enhance therapeutic efficacy. To address the question, we treated breast cancer cells with both fulvestrant (ICI 182780), an ER antagonist with no agonist effects, and lapatinib, an orally available tyrosine kinase inhibitor specific to EGFR and HER2. Our results indicate that the combination of drugs is especially effective when applied to HER2-overexpressing, ER-positive cancer cells. Interestingly, fulvestrant activated the mitogen-activated protein kinase (MAPK) pathway of these cells, but complete inhibition of MAPK signaling was observed on cotreatment with lapatinib. Taken together, our observations reinforce the possibility that the effectiveness of combining anti-ER and anti-HER2/EGFR drugs may be especially effective on a relatively small subtype of HER2-overexpressing, ER-positive tumors of the breast.

Molecular Mechanisms of Trastuzumab Resistance in HER2 Overexpressing Breast Cancer

The epidermal growth factor receptor 2 (HER2) is a tyrosine kinase overexpressed in nearly 20% to 25% of invasive breast cancers. Trastuzumab is a humanized monoclonal antibody that targets HER2. The majority of patients with metastatic breast cancer initially respond to trastuzumab, however, within 1 year of treatment disease progresses. Several molecular mechanisms have been described as contributing to the development of trastuzumab resistance. They could be grouped as impaired access of trastuzumab to HER2, upregulation of HER2 downstream signaling pathways, signaling of alternative pathways, and impaired immune antitumor mechanisms. However, since many of them have overlapping effects, it would be of great clinical impact to identify the principal signaling pathways involved in drug resistance. Significant efforts are being applied to find other therapeutic modalities besides trastuzumab treatment to be used alone or in combination with current modalities.

Elevated insulin-like growth factor 1 receptor signaling induces antiestrogen resistance through the MAPK/ERK and PI3K/Akt signaling routes

INTRODUCTION

Insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) is phosphorylated in all breast cancer subtypes. Past findings have shown that IGF-1R mediates antiestrogen resistance through cross-talk with estrogen receptor (ER) signaling and via its action upstream of the epidermal growth factor receptor and human epidermal growth factor receptor 2. Yet, the direct role of IGF-1R signaling itself in antiestrogen resistance remains obscure. In the present study, we sought to elucidate whether antiestrogen resistance is induced directly by IGF-1R signaling in response to its ligand IGF-1 stimulation.

METHODS

A breast cancer cell line ectopically expressing human wild-type IGF-1R, MCF7/IGF-1R, was established by retroviral transduction and colony selection. Cellular antiestrogen sensitivity was evaluated under estrogen-depleted two-dimensional (2D) and 3D culture conditions. Functional activities of the key IGF-1R signaling components in antiestrogen resistance were assessed by specific kinase inhibitor compounds and small interfering RNA.

RESULTS

Ectopic expression of IGF-1R in ER-positive MCF7 human breast cancer cells enhanced IGF-1R tyrosine kinase signaling in response to IGF-1 ligand stimulation. The elevated IGF-1R signaling rendered MCF7/IGF-1R cells highly resistant to the antiestrogens tamoxifen and fulvestrant. This antiestrogen-resistant phenotype involved mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase/protein kinase B pathways downstream of the IGF-1R signaling hub and was independent of ER signaling. Intriguingly, a MAPK/ERK-dependent agonistic behavior of tamoxifen at low doses was triggered in the presence of IGF-1, showing a mild promitogenic effect and increasing ER transcriptional activity.

CONCLUSIONS

Our data provide evidence that the IGF-1/IGF-1R signaling axis may play a causal role in antiestrogen resistance of breast cancer cells, despite continuous suppression of ER transcriptional function by antiestrogens.

Target therapy in HER2-overexpressing breast cancer patients

The development of new therapeutic strategies, such as monoclonal antibodies directed against human epidermal growth factor receptor-2 (HER2), has offered new hopes for women with early breast cancer whose tumors overexpress HER2. We retrospectively analyzed the population-based data of Breast Cancer Registry of Palermo in 2004-2006, and selected 1401 invasive breast cancer cases, nonmetastatic at diagnosis, having HER2/neu oncogene expression determined. We have correlated this information to age, tumor stage at diagnosis (TNM), nodal involvement, and receptor status (ER and PgR). Survival analysis was conducted dividing the patients in two different groups according to date of diagnosis: one group diagnosed in 2004 and a second group in 2005-2006. In the 460 cases of 2004, nodal involvement, receptor status, age at diagnosis and TNM maintained a strong predictive value (p < 0.0001). In this group of patients, overall survival was significantly different according to the HER2 expression levels (p = 0.001). In the second group of patients (941 incident cases in 2005-2006) there was a statistically significant survival difference comparing patients with high levels of HER2 expression treated with trastuzumab versus those untreated (p = 0.006). Our data show that elevated levels of HER2 are a negative prognostic factor. In addition, patients overexpressing HER2 show a significant increase of overall survival when treated with trastuzumab.

Trastuzumab regulates IGFBP-2 and IGFBP-3 to mediate growth inhibition: implications for the development of predictive biomarkers for trastuzumab resistance

Activation of insulin-like growth factor-I receptor (IGF-IR) signaling is an important mechanism for trastuzumab resistance. IGF-binding proteins (IGFBP) modulate IGF-IR signaling and play important roles in the control of breast cancer progression. In this article, we report that trastuzumab treatment enhances the expression and secretion of IGFBP-3 in SKBR3 cells, a trastuzumab-sensitive breast cancer cell line, and that this upregulation of IGFBP-3 induced by trastuzumab correlates with trastuzumab-mediated growth inhibition. We describe a new role for IGFBP-3 in the regulation of IGF-I-mediated cross-talk between IGF-IR and ErbB2 signaling pathways. In particular, treatment of SKBR3 cells with recombinant IGFBP-3 blocks IGF-I-induced activation of IGF-IR and ErbB2, and stable expression of IGFBP-3 inhibits SKBR3 cell growth. We find an inverse relationship in the levels of secreted IGFBP-3 such that high levels of IGFBP-3 are associated with trastuzumab-sensitive breast cancer cells (SKBR3 and BT-474), whereas low levels of IGFBP-3 are found in trastuzumab-resistant cells (clone 3 and JIMT-1). In contrast to IGFBP-3, the secretion and expression of IGFBP-2 are upregulated in trastuzumab-resistant SKBR3 cells. Furthermore, we show that IGFBP-2 stimulates activation of ErbB2 and that trastuzumab reduces IGFBP-2-stimulated ErbB2 activation. Based on our data, we propose a novel mechanism of action whereby trastuzumab enhances the expression and secretion of IGFBP-3, which interferes with IGF-I-mediated mitogenic signaling via autocrine and paracrine mechanisms and reduces IGFBP-2-induced ErbB2 activation to mediate growth inhibition. Changes in secretion profiles of IGFBP-2 and IGFBP-3 in trastuzumab-sensitive and trastuzumab-resistant cells may promote the development of IGFBP-2 and IGFBP-3 as predictive biomarkers for trastuzumab resistance.

Role of trastuzumab in the management of HER2-positive metastatic breast cancer

Breast cancer is a major health issue in developed countries. Overexpression of HER2, a member of epidermal growth factor receptor family, occurs in 20%-30% of breast cancers. HER2 drives the cancer cells to develop a more aggressive phenotype, to metastasize to viscera and central nervous system, and to be less sensitive to chemotherapeutic agents. Trastuzumab (Herceptin®) is a monoclonal antibody directed against the extracellular domain of HER2. As single agent or with chemotherapy, trastuzumab improves survival of HER2-positive breast cancers. In the past years, trastuzumab has completely revolutionized the scenario of the treatment of HER2-positive breast cancer, representing one of the most remarkable examples of targeted therapy in oncology. However, issues such as the best chemotherapeutic companion to associate with trastuzumab, cardiac toxicities, and clinical resistance still require tremendous efforts by researchers. Here, we review pharmacology, efficacy studies, and toxicities of trastuzumab in metastatic breast cancer. Moreover, we provide some insights on resistance to therapy. Finally, we briefly discuss trastuzumab's place in the clinical setting.

Small is beautiful: insulin-like growth factors and their role in growth, development, and cancer

Insulin-like growth factors were discovered more than 50 years ago as mediators of growth hormone that effect growth and differentiation of bone and skeletal muscle. Interest of the role of insulin-like growth factors in cancer reached a peak in the 1990s, and then waned until the availability in the past 5 years of monoclonal antibodies and small molecules that block the insulin-like growth factor 1 receptor. In this article, we review the history of insulin-like growth factors and their role in growth, development, organism survival, and in cancer, both epithelial cancers and sarcomas. Recent developments regarding phase I to II clinical trials of such agents are discussed, as well as potential studies to consider in the future, given the lack of efficacy of one such monoclonal antibody in combination with cytotoxic chemotherapy in a first-line study in metastatic non-small-cell lung adenocarcinoma. Greater success with these agents clinically is expected when combining the agents with inhibitors of other cell signaling pathways in which cross-resistance has been observed.

Current standards in the treatment of metastatic breast cancer with focus on Lapatinib: a review by a Central European Consensus Panel

In breast cancer, early detection as well as new developments in therapeutic options has resulted in less patients presenting with metastatic disease. However, about one-third of women with early stage breast cancer will eventually develop metastatic disease. Furthermore, approximately 20-30% of patients with breast cancer have tumors that overexpress human epidermal growth factor receptor (HER-2), which is associated with an aggressive tumor phenotype and poor prognosis. The identification of the HER-2 protein led to the development of highly effective therapeutics directed at this receptor. Trastuzumab, a recombinant, humanized, monoclonal antibody that binds to the extracellular domain of the HER-2 protein, has shown significant clinical benefit in metastatic and early-stage HER-2-positive breast cancer. Since the cancer recurs after adjuvant therapy in some women, and metastatic breast cancer eventually develops resistance to trastuzumab, there is a need for alternative treatment modalities to block HER-2 signaling. One of these treatment options is lapatinib, an orally active small molecule that inhibits the tyrosine kinases of HER-2 and the epidermal growth factor receptor type 1 (EGFR). In this consensus statement current treatment options in metastatic and locally advanced disease are discussed with a special focus on lapatinib.

High-resolution genomic and expression analyses of copy number alterations in HER2-amplified breast cancer

INTRODUCTION

HER2 gene amplification and protein overexpression (HER2+) define a clinically challenging subgroup of breast cancer with variable prognosis and response to therapy. Although gene expression profiling has identified an ERBB2 molecular subtype of breast cancer, it is clear that HER2+ tumors reside in all molecular subtypes and represent a genomically and biologically heterogeneous group, needed to be further characterized in large sample sets.

METHODS

Genome-wide DNA copy number profiling, using bacterial artificial chromosome (BAC) array comparative genomic hybridization (aCGH), and global gene expression profiling were performed on 200 and 87 HER2+ tumors, respectively. Genomic Identification of Significant Targets in Cancer (GISTIC) was used to identify significant copy number alterations (CNAs) in HER2+ tumors, which were related to a set of 554 non-HER2 amplified (HER2-) breast tumors. High-resolution oligonucleotide aCGH was used to delineate the 17q12-q21 region in high detail.

RESULTS

The HER2-amplicon was narrowed to an 85.92 kbp region including the TCAP, PNMT, PERLD1, HER2, C17orf37 and GRB7 genes, and higher HER2 copy numbers indicated worse prognosis. In 31% of HER2+ tumors the amplicon extended to TOP2A, defining a subgroup of HER2+ breast cancer associated with estrogen receptor-positive status and with a trend of better survival than HER2+ breast cancers with deleted (18%) or neutral TOP2A (51%). HER2+ tumors were clearly distinguished from HER2- tumors by the presence of recurrent high-level amplifications and firestorm patterns on chromosome 17q. While there was no significant difference between HER2+ and HER2- tumors regarding the incidence of other recurrent high-level amplifications, differences in the co-amplification pattern were observed, as shown by the almost mutually exclusive occurrence of 8p12, 11q13 and 20q13 amplification in HER2+ tumors. GISTIC analysis identified 117 significant CNAs across all autosomes. Supervised analyses revealed: (1) significant CNAs separating HER2+ tumors stratified by clinical variables, and (2) CNAs separating HER2+ from HER2- tumors.

CONCLUSIONS

We have performed a comprehensive survey of CNAs in HER2+ breast tumors, pinpointing significant genomic alterations including both known and potentially novel therapeutic targets. Our analysis sheds further light on the genomically complex and heterogeneous nature of HER2+ tumors in relation to other subgroups of breast cancer.

Targeting signal transduction pathways in metastatic breast cancer: a comprehensive review

Greater understanding of the underlying etiology and biology of breast cancer is enabling the clinical development of targeted therapies for metastatic breast cancer (MBC). Following the successful introduction of trastuzumab, the first human epidermal growth factor receptor (HER) biologically targeted therapy to become widely used in MBC patients, other agents have been developed. Novel agents include monoclonal antibodies such as pertuzumab, which bind to receptors on the cell surface, and tyrosine kinase inhibitors (TKIs) such as lapatinib, which target intracellular pathways such as that of the epidermal growth factor receptor. There is also growing clinical experience with antiangiogenic agents, particularly in combination with chemotherapy. These include the monoclonal antibody bevacizumab, which targets vascular endothelial growth factor receptor, and multitargeted TKIs with antiangiogenic and antiproliferative activities, such as sunitinib. Combination treatment with multiple agents targeting both the HER family and angiogenic pathways (e.g., trastuzumab plus bevacizumab) is also showing activity in the clinical setting. Despite recent advances, there are unanswered questions regarding the management of MBC with targeted agents. Future studies are necessary to determine the optimal combinations, doses, and schedules required to maximize clinical activity while minimizing toxicity. Despite the temptation to use a targeted agent in all patients, identification of patient subgroups most likely to benefit must be a key goal and will be critical to the successful future use of these treatments. The aim of this review is to summarize some of the key signaling pathways involved in tumor progression and some of the novel therapies that are in development for MBC.