Neuregulin Expression Modulates Clinical Response to Trastuzumab in Patients With Metastatic Breast Cancer

Neuregulin modulates hormone receptor levels in breast cancer through concerted action on multiple signaling pathways

The Neuregulins (NRGs) are growth factors that bind and activate ErbB/HER receptor tyrosine kinases. Some reports have described an interplay between this ligand-receptor system and hormonal receptors in breast cancer. However, the mechanisms by which NRGs regulate hormonal receptor signaling have not been sufficiently described. Here, we show that in breast cancer cells the activation of NRG receptors down-regulated ERα through a double mechanism that included post-transcriptional and transcriptional effects. This regulation required the concerted participation of three signaling routes: the PI3K/AKT/mTOR, ERK1/2, and ERK5 pathways. Moreover, these three routes were also involved in the phosphorylation of ERα at serines 118 and 167, two residues implicated in resistance to endocrine therapies. On the other hand, NRGs conferred resistance to fulvestrant in breast cancer cells and this resistance could be reversed when the three pathways activated by NRGs were simultaneously inhibited. Our results indicate that estrogen receptor-positive (ER+) breast tumors that can have access to NRGs may be resistant to fulvestrant. This resistance could be overcome if strategies to target the three main pathways involved in the interplay between NRG receptors and ERα could be developed.

PDCD4 limits prooncogenic neuregulin-ErbB signaling

The neuregulins and their ErbB/HER receptors play essential roles in mammalian development and tissue homeostasis. In addition, deregulation of their function has been linked to the pathogenesis of diseases such as cancer or schizophrenia. These circumstances have stimulated research into the biology of this ligand-receptor system. Here we show the identification of programmed cell death protein-4 (PDCD4) as a novel neuregulin-ErbB signaling mediator. Phosphoproteomic analyses identified PDCD4 as protein whose phosphorylation increased in cells treated with neuregulin. Mutagenesis experiments defined serine 67 of PDCD4 as a site whose phosphorylation increased upon activation of neuregulin receptors. Phosphorylation of that site promoted degradation of PDCD4 by the proteasome, which depended on exit of PDCD4 from the nucleus to the cytosol. Mechanistic studies defined mTORC1 and ERK1/2 as routes implicated in neuregulin-induced serine 67 phosphorylation and PDCD4 degradation. Functionally, PDCD4 regulated several important biological functions of neuregulin, such as proliferation, migration, or invasion.

Considerations for feature selection using gene pairs and applications in large-scale dataset integration, novel oncogene discovery, and interpretable cancer screening

Background

Advancements in transcriptomic profiling have led to the emergence of new challenges regarding data integration and interpretability. Variability between measurement platforms makes it difficult to compare between cohorts, and large numbers of gene features have encouraged the use black box methods that are not easily translated into biologically and clinically meaningful findings. We propose that gene rankings and algorithms that rely on relative expression within gene pairs can address such obstacles.

Methods

We implemented an innovative process to evaluate the performance of five feature selection methods on simulated gene-pair data. Along with TSP, we consider other methods that retain more information in their score calculations, including the magnitude of gene expression change as well as within-class variation. Tree-based rule extraction was also applied to serum microRNA (miRNA) pairs in order to devise a noninvasive screening tool for pancreatic and ovarian cancer.

Results

Gene pair data were simulated using different types of signal and noise. Pairs were filtered using feature selection approaches, including top-scoring pairs (TSP), absolute differences between gene ranks, and Fisher scores. Methods that retain more information, such as the magnitude of expression change and within-class variance, yielded higher classification accuracy using a random forest model. We then demonstrate two powerful applications of gene pairs by first performing large-scale integration of 52 breast cancer datasets consisting of 10,350 patients. Not only did we confirm known oncogenes, but we also propose novel tumorigenic genes, such as BSDC1 and U2AF1, that could distinguish between tumor subtypes. Finally, circulating miRNA pairs were filtered and salient rules were extracted to build simplified tree ensemble learners (STELs) for four types of cancer. These accessible clinical frameworks detected pancreatic and ovarian cancer with 84.8 and 93.6% accuracy, respectively.

Conclusion

Rank-based gene pair classification benefits from careful feature selection methods that preserve maximal information. Gene pairs enable dataset integration for greater statistical power and discovery of robust biomarkers as well as facilitate construction of user-friendly clinical screening tools.

Diabetes as a prognostic factor in HER-2 positive breast cancer patients treated with targeted therapy

PURPOSE

Recent studies revealed that metabolic stress influences the outcomes of breast cancer treatment. We sought to evaluate the prognostic effect of type 2 diabetes and find the molecular mechanism of relapses in postoperative HER-2+ breast cancer patients treated with HER-2 targeted therapy.

MATERIALS AND METHODS

We evaluated 190 HER-2+ breast cancer patients (pT1-4N0-2M0) who were treated with surgical resection and trastuzumab (HER-2 targeted therapy) between 2006 and 2015. Survival outcomes and failure patterns were compared between such patients with (n = 12) and without (n = 178) type 2 diabetes.

RESULTS

The median follow-up period was 42.4 months (range 12.0-124.7 months). Twenty-one patients (11.1%) showed relapse (including nine patients with locoregional failure), and three patients (1.6%) died as a result of cancer relapse. One-third of the patients with diabetes experienced relapse (4/12, 33.3%). The 3-year disease-free survival (DFS) and overall survival (OS) rates were 90.7% and 98.6%, respectively. Diabetic patients showed shorter DFS compared with non-diabetic patients (p = 0.006, 74.1% vs. 91.9%). OS was also shorter in diabetic patients compared with non-diabetic patients (p = 0.017, 91.7% vs. 99.1%). Of our interest, the levels of HER-3 and its ligand neuregulin-1 were significantly increased in the tumor specimen in HER-2+ breast cancer patients suffering with type 2 diabetes than that in the euglycemic control group.

CONCLUSIONS

Type 2 diabetes was associated with detrimental effects on survival in postoperative HER-2+ breast cancer patients who were treated with trastuzumab. The poor prognostic effect of diabetes in HER-2+ breast cancer patients could be associated with the high levels of HER-3 and neuregulin 1, thus it should be considered and evaluated more.

The immunoglobulin-like domain of neuregulins potentiates ErbB3/HER3 activation and cellular proliferation

The neuregulins (NRGs) represent a large family of membrane‐anchored growth factors, whose deregulation may contribute to the pathogenesis of several tumors. In fact, targeting of NRG‐activated pathways has demonstrated clinical benefit. To improve the efficacy of anti‐NRG therapies, it is essential to gain insights into the regions of NRGs that favor their pro‐oncogenic properties. Here, we have addressed the protumorigenic impact of different NRG domains. To do this, deletion mutants affecting different NRG domains were expressed in 293 and MCF7 cells. Of the five forms studied, only the wild‐type and a mutant lacking the Ig‐like domain (NRG^ΔIg) were properly sorted to the plasma membrane. Both forms were released as soluble forms to the culture media. However, the mutant NRG^ΔIg failed to efficiently activate HER2 and HER3 receptors, signaling pathways, and cell proliferation when compared to wild‐type NRG. Treatment with trastuzumab, a humanized antibody used in the breast cancer clinic, inhibited the constitutive activation of HER2, HER3, and downstream signaling in MCF7 cells constitutively expressing wild‐type NRG. In contrast, this treatment had a marginal effect on MCF7‐NRG^ΔIg cells. This study demonstrates that the Ig‐like region of NRGs exerts an important role in their capability to activate ErbB/HER receptors and mitogenic responses. Strategies aimed at targeting NRGs should consider that fact to improve neutralization of the pro‐oncogenic properties of NRGs.

Tumor-infiltrating lymphocytes predict prognosis of breast cancer patients treated with anti-Her-2 therapy

PURPOSE

Infiltration of tumor associated lymphocytes and count of its different phenotypes are potentially new independent predictor of prognosis in breast cancer. However, research related to it is less reported in breast cancer patients treated with anti-Her-2 therapy. Thus, we evaluated the relationship between survival and tumor infiltrating lymphocytes including its different phenotypes in tumors of such patients.

METHODS

Between 1999 and 2010, 98 patients diagnosed with primary breast cancer and treated with anti-Her-2 therapy at Sun-Yat-Sen University Cancer Center were included in the study. Biopsy specimens were collected post-operation but before chemotherapy. Tumor infiltrating lymphocytes as well as its FOXP3+, CD68+, IL-17+ phenotypes in both intratumoral and stromal sites and expression of FOXP3 in cancer cells were assessed.

RESULTS

Median follow-up time of 98 patients was 83.3 months (range 7.4-201 months). It suggested that patients with high stromal infiltration of TILs, lower count of FOXP3+ Tregs and CD68+ Mφ in stromal site, and high expression of FOXP3 in cancer cells had longer survival of OS. In multivariate Cox regression analysis, high count of intratumoral CD68+ Mφ [HR: 2.70 (1.00-7.31); p=0.050] and high expression of FOXP3 in cancer cells [HR: 0.29 (0.09-0.91); p=0.034] were independent prognostic factors for overall survival.

CONCLUSIONS

Tumor infiltrating lymphocytes as well as its FOXP3+, CD68+ phenotypes in stromal site, and expression of FOXP3 in cancer cells were significantly associated with OS, suggesting that they can be used as important pathological factor predicting prognosis of breast cancer patients treated with anti-Her-2 therapy.

Neuregulin expression in solid tumors: prognostic value and predictive role to anti-HER3 therapies

BACKGROUND

Neuregulins (NRG) are a family of epidermal growth factor ligands which act through binding to HER3 and HER4 receptors. NRGs are widely expressed in solid tumors. Their prognostic significance or their role as predictors of benefit from anti-HER3 therapy is not known.

RESULTS

Of 29 included studies, 7 studies reported the association between NRG and outcome. NRG was most commonly expressed in breast, prostate, colon and bladder cancers. NRG expression was not associated with either OS or PFS (HR: 3.47, 95% CI 0.78-15.47, p = 0.10 and HR: 1.64, 95% CI 0.94-2.86, p = 0.08, respectively). In 4 placebo controlled trials of anti-HER3 therapy, the addition of anti-HER3 antibodies to control therapy in unselected patients was not associated with improved PFS (HR: 0.88, 95% CI 0.75-1.04. p = 0.14). However, in patients with high NRG expression, there was significantly delayed progression (HR: 0.35, 95% CI 0.23-0.52, p < 0.001). Anti-HER3 antibodies were associated with increased risk of diarrhea, nausea and rash.

METHODS

A search of electronically available databases identified studies exploring clinical outcomes based on NRG expression, as well as placebo-controlled trials of HER3-directed therapy reporting results based on NRG expression status. Data were combined in a meta-analysis using generic inverse variance and random effects modeling for studies reporting the hazard ratio (HR) for overall (OS) or progression-free survival (PFS). Mantel-Haenszel random-effect modeling was used for odds ratio (OR) for 3-year and 5-year OS and PFS.

CONCLUSIONS

NRG expression is not associated with either OS or PFS, but is a predictor of benefit from anti-HER3 antibodies.

Five-weekly S-1 plus cisplatin therapy combined with trastuzumab therapy in HER2-positive gastric cancer: a phase II trial and biomarker study (WJOG7212G)

BACKGROUND

Five-weekly S-1 plus cisplatin (SP) therapy is the standard care for advanced gastric or esophagogastric junction cancer (GC/EGJC) in East Asia. However, its efficacy and safety when combined with trastuzumab therapy for human epidermal growth factor receptor 2 (HER2)-positive advanced GC/EGJC remains unclear.

METHODS

Patients received 5-weekly SP therapy (S-1 at 40-60 mg twice daily for 21 days plus cisplatin at 60 mg/m² on day 8, every 5 weeks) plus trastuzumab therapy (first dose of 8 mg/kg, then 6 mg/kg every 3 weeks). The primary end point was the response rate, and the secondary end points included progression-free survival, overall survival, safety, and serum biomarker levels.

RESULTS

Forty-four patients were enrolled. The response rate, progression-free survival, and overall survival were 61% (95% confidence interval 46-76%), 5.9 months, and 16.5 months respectively. The commonest grade 3 or grade 4 adverse events were neutropenia (30%) and anorexia (25%). A significantly higher response rate (92% vs 43%; P = 0.008) and longer progression-free survival (median 14.5 months vs 4.2 months; P = 0.028) were observed in patients with high (n = 14) compared with low (n = 17) pretreatment serum neuregulin 1 levels.

CONCLUSIONS

Five-weekly SP therapy combined with trastuzumab therapy showed a good antitumor response and acceptable toxicity in HER2-positive advanced GC/EGJC. Serum neuregulin 1 might be associated with the efficacy of this treatment regimen.

Recent Advances in ADAM17 Research: A Promising Target for Cancer and Inflammation

Since its discovery, ADAM17, also known as TNFα converting enzyme or TACE, is now known to process over 80 different substrates. Many of these substrates are mediators of cancer and inflammation. The field of ADAM metalloproteinases is at a crossroad with many of the new potential therapeutic agents for ADAM17 advancing into the clinic. Researchers have now developed potential drugs for ADAM17 that are selective and do not have the side effects which were seen in earlier chemical entities that targeted this enzyme. ADAM17 inhibitors have broad therapeutic potential, with properties ranging from tumor immunosurveillance and overcoming drug and radiation resistance in cancer, as treatments for cardiac hypertrophy and inflammatory conditions such as inflammatory bowel disease and rheumatoid arthritis. This review focuses on substrates and inhibitors identified more recently for ADAM17 and their role in cancer and inflammation.

Regulation of the prometastatic neuregulin-MMP13 axis by SRC family kinases: therapeutic implications

Metastatic dissemination of tumor cells is responsible for the fatal outcome of breast cancer. Therefore, understanding the mechanisms involved in dissemination is essential for the development of new therapeutic strategies to prevent metastasis. One mechanism involved in metastatic dissemination of breast cancer cells is dependent on control of the production of matrix metalloproteinases by the neuregulins (NRGs). The NRGs are polypeptide factors that act by binding to the ErbB/HER subfamily of receptor tyrosine kinases. NRG‐mediated activation of HER receptors causes an increase in the production of metalloprotease 13 (MMP13, also termed collagenase‐3), which facilitates metastatic dissemination of breast tumors. In this context, we aimed to explore whether the clinically approved tyrosine kinase inhibitor dasatinib was able to neutralize this mechanism of metastatic dissemination. Here, we show that dasatinib restricted NRG‐induced MMP13 upregulation, both in vitro and in vivo, and in vivo metastatic dissemination of breast cancer cells. Chemical proteomics studies showed that the main cellular targets of dasatinib were SRC family kinases (SFKs). Moreover, genetic studies showed that knockdown of SRC or YES strongly inhibited NRG‐induced MMP13 upregulation in vitro. Mechanistically, dasatinib treatment or knockdown of SRC also inhibited ERK1/2 kinases in vitro, which were required for NRG‐induced MMP13 upregulation. These results open the possibility of clinically exploring the antitumoral action of dasatinib in those tumors in which the NRG–MMP13 signaling axis may play a relevant role in the control of tumor cell dissemination.

A comprehensive review of heregulins, HER3, and HER4 as potential therapeutic targets in cancer

Heregulins (HRGs) bind to the receptors HER3 or HER4, induce receptor dimerization, and trigger downstream signaling that leads to tumor progression and resistance to targeted therapies. Increased expression of HRGs has been associated with worse clinical prognosis; therefore, attempts to block HRG-dependent tumor growth have been pursued. This manuscript summarizes the function and signaling of HRGs and review the preclinical evidence of its involvement in carcinogenesis, prognosis, and treatment resistance in several malignancies such as colorectal cancer, non-small cell lung cancer, ovarian cancer, and breast cancer. Agents in preclinical development and clinical trials of novel therapeutics targeting HRG-dependent signaling are also discussed, including anti-HER3 and -HER4 antibodies, anti-metalloproteinase agents, and HRG fusion proteins. Although several trials have indicated an acceptable safety profile, translating preclinical findings into clinical practice remains a challenge in this field, possibly due to the complexity of downstream signaling and patterns of HRG, HER3 and HER4 expression in different cancer subtypes. Improving patient selection through biomarkers and understanding the resistance mechanisms may translate into significant clinical benefits in the near future.

Antitumoral effect of Ocoxin in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is becoming one of the most prevalent types of cancer worldwide. The most efficient types of treatment at present include surgical resection and liver transplantation, but these treatments may only be used in a small percentage of patients. In order to identify novel therapeutic strategies for this disease, the present study explored the potential antitumoral effect of Ocoxin® oral solution (OOS) in HCC. OOS inhibited the proliferation of HCC cell lines in a time- and dose-dependent manner, being more efficient when used in combination with sorafenib, a standard of care treatment for patients diagnosed with advanced-stage disease. Mechanistic studies indicated that the effect of OOS was due to the induction of cell cycle arrest rather than the stimulation of apoptotic cell death. The cell cycle was slowed down in all phases in the HCC cell lines treated with OOS. Finally, when tested in animal models of HCC, OOS reduced tumor progression through the induction of necrosis in xenograft tumor models. Considering the poor prognosis and high resistance to antitumor treatments of HCC, the antiproliferative action of OOS, particularly in combination with sorafenib, provides the opportunity to investigate the effect of combined therapy in a clinical setting.

Antitumoral effect of Ocoxin on acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy whose incidence is growing in developed countries. In the relapse setting, very limited therapeutic options are available and in most cases only palliative care can be offered to patients. The effect of a composite formulation that contains several antioxidants, Ocoxin Oral solution (OOS), was tested in this condition. When analyzed in vitro, OOS exhibited anti-AML action that was both time and dose dependent. In vivo OOS induced a ralentization of tumor growth that was due to a decrease in cell proliferation. Such effect could, at least partially, be due to an increase in the cell cycle inhibitor p27, although other cell cycle proteins seemed to be altered. Besides, OOS induced an immunomodulatory effect through the induction of IL6. When tested in combination with other therapeutic agents normally used in the treatment of AML patients, OOS demonstrated a higher antiproliferative action, suggesting that it may be used in combination with those standard of care treatments to potentiate their antiproliferative action in the AML clinic.

Heregulin/ErbB3 Signaling Enhances CXCR4-Driven Rac1 Activation and Breast Cancer Cell Motility via Hypoxia-Inducible Factor 1α

The growth factor heregulin (HRG), a ligand of ErbB3 and ErbB4 receptors, contributes to breast cancer development and the promotion of metastatic disease, and its expression in breast tumors has been associated with poor clinical outcome and resistance to therapy. In this study, we found that breast cancer cells exposed to sustained HRG treatment show markedly enhanced Rac1 activation and migratory activity in response to the CXCR4 ligand SDF-1/CXCL12, effects mediated by P-Rex1, a Rac-guanine nucleotide exchange factor (GEF) aberrantly expressed in breast cancer. Notably, HRG treatment upregulates surface expression levels of CXCR4, a G protein-coupled receptor (GPCR) implicated in breast cancer metastasis and an indicator of poor prognosis in breast cancer patients. A detailed mechanistic analysis revealed that CXCR4 upregulation and sensitization of the Rac response/motility by HRG are mediated by the transcription factor hypoxia-inducible factor 1α (HIF-1α) via ErbB3 and independently of ErbB4. HRG caused prominent induction in the nuclear expression of HIF-1α, which transcriptionally activates the CXCR4 gene via binding to a responsive element located in positions -1376 to -1372 in the CXCR4 promoter, as revealed by mutagenesis analysis and chromatin immunoprecipitation (ChIP). Our results uncovered a novel function for ErbB3 in enhancing breast cancer cell motility and sensitization of the P-Rex1/Rac1 pathway through HIF-1α-mediated transcriptional induction of CXCR4.

HER-3 targeting alters the dimerization pattern of ErbB protein family members in breast carcinomas

Breast carcinogenesis is a multi-step process in which membrane receptor tyrosine kinases are crucial participants. Lots of research has been done on epidermal growth factor receptor (EGFR) and HER-2 with important clinical results. However, breast cancer patients present intrinsic or acquired resistance to available HER-2-directed therapies, mainly due to HER-3. Using new techniques, such as proximity ligation assay, herein we evaluate the dimerization pattern of HER-3 and the importance of context-dependent dimer formation between HER-3 and other HER protein family members. Additionally, we show that the efficacy of novel HER-3 targeting agents can be better predicted in certain breast cancer patient sub-groups based on the dimerization pattern of HER protein family members. Moreover, this model was also evaluated and reproduced in human paraffin-embedded breast cancer tissues.

Breast cancer dissemination promoted by a neuregulin-collagenase 3 signalling node

Advances in the treatment of breast cancer have resulted in increased survival. However, in the metastatic setting, the disease remains incurable. Therefore, understanding of the mechanisms that promote dissemination of breast cancer cells may favor the development of novel therapeutic strategies to fight those tumors. Here, we show that the ErbB ligands, Neuregulins (NRGs), promote metastatic dissemination of breast cancer cells by switching on a kinase-metalloproteinase network. Clinicopathological analyses demonstrated that NRG expression in breast tumors associated to lymph node invasion and poor patient outcome. Preclinical in vivo analyses showed that NRG expression favored in situ tumor growth, local spreading and metastatic dissemination. Genomic, biochemical and functional studies identified matrix metalloproteinases, particularly stromelysin 2 and collagenase 3, as key mediators of the NRG-induced dissemination properties of breast cancer cells. Mechanistic analyses demonstrated that NRG augmented metalloproteinase expression through a route controlled by ERK1/2 kinases. ERK1/2 increased collagenase 3 expression by controlling the activity of an SBF1-related transcription factor. In conclusion, we describe a pathway linked to breast cancer dissemination. The clinical availability of agents that target some of the components of this signalling pathway suggests that patients with tumors fed by NRGs or other factors able to activate the ERK-Collagenase 3 route may benefit from agents that act on that signalling axis.

Effect of Oncoxin Oral Solution in HER2-Overexpressing Breast Cancer

One of the most aggressive breast cancer subtypes includes tumors with high expression of HER2. Gene expression and functional studies have shown a link between HER2 overexpression and oxidative stress. Because of this, we hypothesized that Oncoxin Oral Solution (OOS), a composite product that contains several antioxidants, could have an antitumoral effect against HER2+ tumors. Dose-response studies, biochemical and cytometric assessment of the effect of OOS on cell cycle and apoptosis, and drug combination analyses were performed on BT474 and SKBR3 cells, 2 HER2-overexpressing breast cancer cell lines. OOS reduced the proliferation of these cells, and augmented the action of lapatinib, a HER2 inhibitor used in the breast cancer clinic. Moreover, OOS decreased growth of HER2+ tumors in mice. Mechanistically, OOS provoked cell cycle blockade through upregulation of p27 expression and downregulation of cyclin D levels. OOS also caused apoptotic cell death in HER2+ breast cancer cells, as indicated by increases in PARP cleavage as well as upregulation of caspase 8 and caspase 3 activities. These results demonstrate an antitumoral action of OOS in preclinical models of HER2+ breast cancer and suggest that it can be used with anti-HER2 therapies currently adopted as standard of care in the oncology clinic.

Advances in the Molecular Analysis of Breast Cancer: Pathway toward Personalized Medicine

Background

Breast cancer is a heterogeneous disease that encompasses a wide range of clinical behaviors and histological and molecular variants. It is the most common type of cancer affecting women worldwide and is the second leading cause of cancer death.

Methods

A comprehensive literature search was performed to explore the advances in molecular medicine related to the diagnosis and treatment of breast cancer.

Results

During the last few decades, advances in molecular medicine have changed the landscape of cancer treatment as new molecular tests complement and, in many instances, exceed traditional methods for determining patient prognosis and response to treatment options. Personalized medicine is becoming the standard of care around the world. Developments in molecular profiling, genomic analysis, and the discovery of targeted drug therapies have significantly improved patient survival rates and quality of life.

Conclusions

This review highlights what pathologists need to know about current molecular tests for classification and prognostic/predictive assessment of breast carcinoma as well as their role as part of the medical team.

Clinical Translation and Validation of a Predictive Biomarker for Patritumab, an Anti-human Epidermal Growth Factor Receptor 3 (HER3) Monoclonal Antibody, in Patients With Advanced Non-small Cell Lung Cancer

Background

During early clinical development, prospective identification of a predictive biomarker and validation of an assay method may not always be feasible. Dichotomizing a continuous biomarker measure to classify responders also leads to challenges. We present a case study of a prospective–retrospective approach for a continuous biomarker identified after patient enrollment but defined prospectively before the unblinding of data. An analysis of the strengths and weaknesses of this approach and the challenges encountered in its practical application are also provided.

Methods

HERALD (NCT02134015) was a double-blind, phase 2 study in patients with non-small cell lung cancer (NSCLC) randomized to erlotinib with placebo or with high or low doses of patritumab, a monoclonal antibody targeted against human epidermal growth factor receptor 3 (HER3). While the primary objective was to assess safety and progression-free survival (PFS), a secondary objective was to determine a single predictive biomarker hypothesis to identify subjects most likely to benefit from the addition of patritumab. Although not identified as the primary biomarker in the study protocol, on the basis of preclinical results from 2 independent laboratories, expression levels of the HER3 ligand heregulin (HRG) were prospectively declared the predictive biomarker before data unblinding but after subject enrollment. An assay to measure HRG mRNA was developed and validated. Other biomarkers, such as epidermal growth factor receptor (EGFR) mutation status, were also evaluated in an exploratory fashion. The cutoff value for high vs. low HRG mRNA levels was set at the median delta threshold cycle. A maximum likelihood analysis was performed to evaluate the provisional cutoff. The relationship of HRG values to PFS hazard ratios (HRs) was assessed as a measure of internal validation. Additional NSCLC samples were analyzed to characterize HRG mRNA distribution.

Results

The subgroup of patients with high HRG mRNA levels (“HRG-high”) demonstrated clinical benefit from patritumab treatment with HRs of 0.37 (P = 0.0283) and 0.29 (P = 0.0027) in the high- and low-dose patritumab arms, respectively. However, only 102 of the 215 randomized patients (47.4%) had sufficient tumor samples for HRG mRNA measurement. Maximum likelihood analysis showed that the provisional cutoff was within the optimal range. In the placebo arm, the HRG-high subgroup demonstrated worse prognosis compared with HRG-low. A continuous relationship was observed between increased HRG mRNA levels and lower HR. Additional NSCLC samples (N = 300) demonstrated a similar unimodal distribution to that observed in this study, suggesting that the defined cutoff may be applicable to future NSCLC studies.

Conclusions

The prospective–retrospective approach was successful in clinically validating a probable predictive biomarker. Post hoc in vitro studies and statistical analyses permitted further testing of the underlying assumptions. However, limitations of this analysis include the incomplete collection of adequate tumor tissue and a lack of stratification. In a phase 3 study, findings are being confirmed, and the HRG cutoff value is being further refined.

ClinicalTrials.gov Number

NCT02134015.

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High heregulin levels predict benefit from patritumab treatment in patients with NSCLC.

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A prospective–retrospective approach provisionally validated a predictive biomarker.

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Post hoc analyses can be used to test underlying assumptions in biomarker validation.

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The median may be a reasonable initial cutoff for a unimodal continuous biomarker.

Neuregulin autocrine signaling promotes self-renewal of breast tumor-initiating cells by triggering HER2/HER3 activation

Currently, only patients with HER2-positive tumors are candidates for HER2-targeted therapies. However, recent clinical observations suggest that the survival of patients with HER2-low breast cancers, who lack HER2 amplification, may benefit from adjuvant therapy that targets HER2. In this study, we explored a mechanism through which these benefits may be obtained. Prompted by the hypothesis that HER2/HER3 signaling in breast tumor-initiating cells (TIC) promotes self-renewal and survival, we obtained evidence that neuregulin 1 (NRG1) produced by TICs promotes their proliferation and self-renewal in HER2-low tumors, including in triple-negative breast tumors. Pharmacologic inhibition of EGFR, HER2, or both receptors reduced breast TIC survival and self-renewal in vitro and in vivo and increased TIC sensitivity to ionizing radiation. Through a tissue microarray analysis, we found that NRG1 expression and associated HER2 activation occurred in a subset of HER2-low breast cancers. Our results offer an explanation for why HER2 inhibition blocks the growth of HER2-low breast tumors. Moreover, they argue that dual inhibition of EGFR and HER2 may offer a useful therapeutic strategy to target TICs in these tumors. In generating a mechanistic rationale to apply HER2-targeting therapies in patients with HER2-low tumors, this work shows why these therapies could benefit a considerably larger number of patients with breast cancer than they currently reach.

Endometrial stromal tumors: immunohistochemical and molecular analysis of potential targets of tyrosine kinase inhibitors

BACKGROUND

The systemic treatment of malignant endometrial stromal tumors (EST) is not well established. A few reports describe objective responses to imatinib, which suggest a novel therapeutic strategy for these tumors. Due to these facts, we aimed to perform a retrospective analysis of possible molecular targets of tyrosine kinase inhibitors (TKI) in EST: KIT, PDGFRA and EGFR.

METHODS

52 endometrial stromal sarcomas and 13 undifferentiated endometrial sarcomas were examined and reviewed. Mutational analysis were performed for exons 9, 11, 13, and 17 of the KIT gene, exons 12 and 18 of the PDGFRA gene and exons 18, 19, 20 and 21 of the EGFR gene. The incidence and distribution of the KIT, PDGFRA, and EGFR expression were examined by immunohistochemistry, and EGFR amplification was assessed by fluorescence in situ hybridization.

RESULTS

No mutations in KIT, PDGFRA and EGFR genes were detected. Overexpression of KIT, PDGFRA, EGFR, was detected in 2 (3%), 23 (35.4%), 7 (10.8%) cases respectively, whereas amplification of EGFR gene was not found.

CONCLUSIONS

Absence of significant expression, amplification and activating mutations on these tyrosine kinase receptors suggest that it is unlikely that EST can benefit from therapies such as TKI on the systemic setting.

Neuregulin 1-HER axis as a key mediator of hyperglycemic memory effects in breast cancer

Poor outcomes in diabetic patients are observed across a range of human tumors, suggesting that cancer cells develop unique characteristics under diabetic conditions. Cancer cells exposed to hyperglycemic insults acquire permanent aggressive traits of tumor growth, even after a return to euglycemic conditions. Comparative genome-wide mapping of hyperglycemia-specific open chromatin regions and concomitant mRNA expression profiling revealed that the neuregulin-1 gene, encoding an established endogenous ligand for the HER3 receptor, is activated through a putative distal enhancer. Our findings highlight the targeted inhibition of NRG1-HER3 pathways as a potential target for the treatment breast cancer patients with associated diabetes.

Active kinase profiling, genetic and pharmacological data define mTOR as an important common target in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer. Despite response to chemotherapy, relapses are frequent and resistance to available treatments is often seen in the metastatic setting. Therefore, identification of new therapeutic targets is required. With this aim, we have profiled the activation status of 44 receptor tyrosine kinases (RTKs) and their major signaling pathways in patient-derived TNBC tumors. Frequent co-activation of several RTKs as well as the extracellular signal-regulated protein kinases 1 and 2 (Erk1/2) and mammalian target of rapamycin (mTOR) routes was found. Pharmacologic targeting of the activated kinases indicated that agents that attack the mTOR route are more potent and efficient antitumoral treatments than agents targeting RTKs. mTOR signals through two multiprotein complexes, mTORC1 and mTORC2. We used a genetic approach to explore the contribution of each of the two mTOR branches to the regulation of cell number of TNBC cells. RNA interference experiments indicated that mTORC1 predominated over mTORC2 in the control of TNBC cell proliferation. Moreover, RNA interference of mTOR had a superior antiproliferative action than separately acting on mTORC1 or mTORC2. To analyze the relevance of mTOR targeting in vivo, we used mice with TNBC. Treatment of these mice with BEZ235, a drug that targets mTOR, slowed tumor growth. Mechanistically, BEZ235 delayed cell cycle progression without affecting cell viability. Our results show that TNBCs are particularly sensitive to inhibition of the mTOR pathway, and indicate that mTOR targeting may be a more efficient anti-TNBC therapy than exclusively acting on the mTORC1 branch of the pathway. This is relevant as most mTOR inhibitors used in the clinic act on mTORC1. Collectively with the fact that BEZ235 synergized with drugs commonly used in the treatment of TNBC, our data support the clinical development of agents that act on mTOR as a therapy for this disease.

Androgen-independent prostate cancer cells circumvent EGFR inhibition by overexpression of alternative HER receptors and ligands

The deregulation of the epidermal growth factor receptor (EGFR) pathway plays a major role in the pathogenesis of prostate cancer (PCa). However, therapies targeting EGFR have demonstrated limited effectiveness in PCa. A potential mechanism to overcome EGFR blockade in cancer cells is the autocrine activation of alternative receptors of the human EGFR (HER) family through the overexpression of the HER receptors and ligands. In the present study, we were interested in analyzing if this intrinsic resistance mechanism might contribute to the inefficacy of EGFR inhibitors in PCa. To this end, we selected two androgen-independent human prostate carcinoma cell lines (DU145 and PC3) and established DU145 erlotinib-resistant cells (DUErR). Cells were treated with three EGFR inhibitors (cetuximab, gefinitib and erlotinib) and the sensitivity to each treatment was assessed. The gene expression of the four EGFR/HER receptors and seven ligands of the HER family was analyzed by real-time PCR prior to and after each treatment. The receptors expression and activation were further characterized by flow cytometry and western blot analysis. EGFR inhibition rapidly induced enhanced gene expression of the EGF, betacellulin and neuregulin-1 ligands along with HER2, HER3 and HER4 receptors in the DU145 cells. In contrast, slight changes were observed in the PC3 cells, which are defective in the phosphatase and tensin homolog (PTEN) tumor suppressor gene. In the erlotinib-resistant DUErR cells, the expression of HER2 and HER3 was increased at mRNA and protein levels together with neuregulin-1, leading to enhanced HER3 phosphorylation and the activation of the downstream PI3K/Akt survival pathway. HER3 blockage by a monoclonal antibody restored the cytostatic activity of erlotinib in DUErR cells. Our results confirm that the overexpression and autocrine activation of HER3 play a key role in mediating the resistance to EGFR inhibitors in androgen-independent PCa cells.

Basal/HER2 breast carcinomas: integrating molecular taxonomy with cancer stem cell dynamics to predict primary resistance to trastuzumab (Herceptin)

High rates of inherent primary resistance to the humanized monoclonal antibody trastuzumab (Herceptin) are frequent among HER2 gene-amplified breast carcinomas in both metastatic and adjuvant settings. The clinical efficacy of trastuzumab is highly correlated with its ability to specifically and efficiently target HER2-driven populations of breast cancer stem cells (CSCs). Intriguingly, many of the possible mechanisms by which cancer cells escape trastuzumab involve many of the same biomarkers that have been implicated in the biology of CS-like tumor-initiating cells. In the traditional, one-way hierarchy of CSCs in which all cancer cells descend from special self-renewing CSCs, HER2-positive CSCs can occur solely by self-renewal. Therefore, by targeting CSC self-renewal and resistance, trastuzumab is expected to induce tumor shrinkage and further reduce breast cancer recurrence rates when used alongside traditional therapies. In a new, alternate model, more differentiated non-stem cancer cells can revert to trastuzumab-refractory, CS-like cells via the activation of intrinsic or microenvironmental paths-to-stemness, such as the epithelial-to-mesenchymal transition (EMT). Alternatively, stochastic transitions of trastuzumab-responsive CSCs might also give rise to non-CSC cellular states that lack major attributes of CSCs and, therefore, can remain "hidden" from trastuzumab activity. Here, we hypothesize that a better understanding of the CSC/non-CSC social structure within HER2-overexpressing breast carcinomas is critical for trastuzumab-based treatment decisions in the clinic. First, we decipher the biological significance of CSC features and the EMT on the molecular effects and efficacy of trastuzumab in HER2-positive breast cancer cells. Second, we reinterpret the genetic heterogeneity that differentiates trastuzumab-responders from non-responders in terms of CSC cellular states. Finally, we propose that novel predictive approaches aimed at better forecasting early tumor responses to trastuzumab should identify biological determinants that causally underlie the intrinsic flexibility of HER2-positive CSCs to "enter" into or "exit" from trastuzumab-sensitive states. An accurate integration of CSC cellular states and EMT-related biomarkers with the currently available breast cancer molecular taxonomy may significantly improve our ability to make a priori decisions about whether patients belonging to HER2 subtypes differentially enriched with a "mesenchymal transition signature" (e.g., luminal/HER2 vs. basal/HER2) would distinctly benefit from trastuzumab-based therapy ab initio.

Study of compliance with prescription information sheet of trastuzumab prescriptions in a tertiary level hospital

INTRODUCTION

This study compares trastuzumab's actual conditions of use in clinical practice with those officially described on its summary of product characteristics. We also measure the cost associated with its use.

METHODS

Observational study of the prescription/indication of trastuzumab in a tertiary hospital from January 2006 to 31 December 2007. We analysed whether trastuzumab use in clinical practice complied with its summary of product characteristics, concerning the following: HER2 over expression, indication (breast cancer), treatment plan, line of treatment, dosage, frequency and number of cycles. To measure cost, we calculated the total number of milligrams used and then multiplied it by the laboratory's sale price per milligram plus VAT.

RESULTS

All patients (n=77) used trastuzumab for breast cancer. Sixty-two point two percent of patients presented with HER2+++ over expression. Twenty-nine treatment plans were used, that were not authorised on the summary of product characteristics. The total trastuzumab cost during the study period was €1537 622.73.

CONCLUSIONS

Although trastuzumab is always used for breast cancer, it is used in conditions other than those described on its summary of product characteristics, both for HER2 over expression and treatment plans.

Differential action of small molecule HER kinase inhibitors on receptor heterodimerization: therapeutic implications

Deregulation of ErbB/HER receptor tyrosine kinases has been linked to several types of cancer. The mechanism of activation of these receptors includes establishment of receptor dimers. Here, we have analyzed the action of different small molecule HER tyrosine kinase inhibitors (TKIs) on HER receptor dimerization. Breast cancer cell lines were treated with distinct TKIs and the formation of HER2-HER3 dimers was analyzed by coimmunoprecipitation and western blot or by Förster resonance energy transfer assays. Antibody-dependent cellular cytotoxicity was analyzed by measuring the release of lactate dehydrogenase and cell viability. Lapatinib and neratinib interfered with ligand-induced dimerization of HER receptors; while pelitinib, gefitinib, canertinib or erlotinib did not. Moreover, lapatinib and neratinib were able to disrupt previously formed receptor dimers. Structural analyses allowed the elucidation of the mechanism by which some TKIs prevent the formation of HER receptor dimers, while others do not. Experiments aimed at defining the functional importance of dimerization indicated that TKIs that impeded dimerization prevented down-regulation of HER2 receptors, and favored the action of trastuzumab. We postulate that TKIs that prevent dimerization and down-regulation of HER2 may augment the antitumoral action of trastuzumab, and this mechanism of action should be considered in the treatment of HER2 positive tumors which combine TKIs with antireceptor antibodies.

Transautocrine signaling by membrane neuregulins requires cell surface targeting, which is controlled by multiple domains

The neuregulins (NRGs) play important roles in animal development and homeostasis, and their deregulation has been linked to diseases such as cancer and schizophrenia. The NRGs belong to the epidermal growth factor (EGF) family of transmembrane growth factors. Although NRGs may be synthesized as transmembrane proteins (the pro-NRGs), some of them lack an N-terminal signal sequence, raising the question of how these pro-NRGs are directed to the plasma membrane. Here we have explored the domains of pro-NRGs that are required for their membrane anchoring, cell surface exposure, and biological activity. We show that an internal hydrophobic region acts as a membrane-anchoring domain, but other regions of pro-NRG are required for proper sorting to the plasma membrane. Using mutants that are located in different subcellular compartments, we show that only plasma membrane-exposed pro-NRG is biologically active. At this location, the pro-NRGs may act as transautocrine molecules (i.e. as membrane factors able to activate receptors present in cells that are in physical contact with the pro-NRG-producing cells (in trans) or capable of activating receptors present in the pro-NRG-producing cells (in cis)).

Quantitative assays for the measurement of HER1-HER2 heterodimerization and phosphorylation in cell lines and breast tumors: applications for diagnostics and targeted drug mechanism of action

Introduction

Ligand-bound and phosphorylated ErbB/HER heterodimers are potent signaling forms of this receptor family, and quantitative measurements of these active receptors may be predictive of patient response to targeted therapies. Using VeraTag™ technology, we developed and characterized quantitative assays measuring epidermal growth factor (EGF)-dependent increases in activated HER receptors in tumor cell line lysates and formalin-fixed, paraffin-embedded (FFPE) tumor sections. We demonstrated the ability of the assays to quantitatively measure changes in activated HER1 and HER2 receptor levels in cell lines following treatment with 2C4, erlotinib, and lapatinib. We utilized these assays to determine the prevalence and distribution of activated HER1, HER2, and HER1-HER2 heterodimers in 43 HER2-positive breast tumors.

Methods

Assays for activated HER1 and HER2 receptors in FFPE and cell lysate formats were developed using VeraTag™ technology, which requires the proximity of an antibody pair for light-dependent release of a fluorescently labeled tag, followed by capillary electrophoresis-based quantitation.

Results

Ligand-dependent and independent HER1-HER2 heterodimer levels measured by lysate and FFPE VeraTag™ assays trended with HER1 and HER2 expression levels in tumor cell lines, which was confirmed by co-immunoprecipitation. The formation of EGF-dependent HER1-HER2 heterodimers were inhibited by the HER2-targeted monoclonal antibody 2C4 and stabilized by the HER1 tyrosine kinase inhibitor (TKI) erlotinib. EGF-dependent HER1 and HER2 phosphorylation was inhibited by lapatinib and erlotinib. Further, we observed that dominant receptor signaling patterns may switch between HER1-HER1 and HER1-HER2, depending on drug mechanism of action and relative levels of HER receptors. In FFPE breast tumors that expressed both HER1 and HER2, HER1-HER2 heterodimers were detected in 25 to 50% of tumors, depending on detection method. The levels of activated phospho-HER1-HER2 heterodimers correlated with HER1 or HER2 levels in an analysis of 43 HER2-positive breast tumors.

Conclusions

VeraTag™ lysate assays can be used as a tool for understanding the mechanism of action of targeted HER-family inhibitors in the preclinical setting, while VeraTag™ FFPE assays of activated HER receptors combined with total HER2 measurements (HERmark^®) in tumor samples may provide a more accurate prediction of clinical response to both HER1 and HER2 targeted therapies.

P-Rex1 participates in Neuregulin-ErbB signal transduction and its expression correlates with patient outcome in breast cancer

The Neuregulins and their receptors, the ErbB/HER subfamily of receptor tyrosine kinases, have critical roles in animal physiology, and their deregulation is frequent in cancer. Here we report the identification of the guanine nucleotide exchange factor, phosphatidylinositol 3,4,5-triphosphate-dependent Rac exchanger 1 (P-Rex1), as a novel mediator in signalling by ErbB/HER receptors. P-Rex1 was formerly described as a phosphoinositide 3-kinase and Gβγ activated protein that regulates Rac function. We define how ErbB/HER receptors regulate P-Rex1 function, which involves dephosphorylation of inhibitory residues, and phosphorylation of activating residues of P-Rex. The net balance resulting from activation of this phosphorylation/dephosphorylation cycle of P-Rex1 favours Rac activation. Molecular and biological studies indicated that P-Rex1 phosphorylation regulated the proliferation of breast cancer cells, and P-Rex1 knockdown affected their migration or invasiveness, as well as their in vivo tumourigenic potential. Moreover, as we found correlation between high P-Rex1 expression and poor patient outcome in breast cancer, P-Rex1 targeting may be therapeutically relevant in cancer.

HER3 and downstream pathways are involved in colonization of brain metastases from breast cancer

INTRODUCTION

Metastases to the brain from breast cancer have a high mortality, and basal-like breast cancers have a propensity for brain metastases. However, the mechanisms that allow cells to colonize the brain are unclear.

METHODS

We used morphology, immunohistochemistry, gene expression and somatic mutation profiling to analyze 39 matched pairs of primary breast cancers and brain metastases, 22 unmatched brain metastases of breast cancer, 11 non-breast brain metastases and 6 autopsy cases of patients with breast cancer metastases to multiple sites, including the brain.

RESULTS

Most brain metastases were triple negative and basal-like. The brain metastases over-expressed one or more members of the HER family and in particular HER3 was significantly over-expressed relative to matched primary tumors. Brain metastases from breast and other primary sites, and metastases to multiple organs in the autopsied cases, also contained somatic mutations in EGFR, HRAS, KRAS, NRAS or PIK3CA. This paralleled the frequent activation of AKT and MAPK pathways. In particular, activation of the MAPK pathway was increased in the brain metastases compared to the primary tumors.

CONCLUSIONS

Deregulated HER family receptors, particularly HER3, and their downstream pathways are implicated in colonization of brain metastasis. The need for HER family receptors to dimerize for activation suggests that tumors may be susceptible to combinations of anti-HER family inhibitors, and may even be effective in the absence of HER2 amplification (that is, in triple negative/basal cancers). However, the presence of activating mutations in PIK3CA, HRAS, KRAS and NRAS suggests the necessity for also specifically targeting downstream molecules.

Analytical Validation of a Highly Quantitative, Sensitive, Accurate, and Reproducible Assay (HERmark) for the Measurement of HER2 Total Protein and HER2 Homodimers in FFPE Breast Cancer Tumor Specimens

We report here the results of the analytical validation of assays that measure HER2 total protein (H2T) and HER2 homodimer (H2D) expression in Formalin Fixed Paraffin Embedded (FFPE) breast cancer tumors as well as cell line controls. The assays are based on the VeraTag technology platform and are commercially available through a central CAP-accredited clinical reference laboratory. The accuracy of H2T measurements spans a broad dynamic range (2-3 logs) as evaluated by comparison with cross-validating technologies. The measurement of H2T expression demonstrates a sensitivity that is approximately 7–10 times greater than conventional immunohistochemistry (IHC) (HercepTest). The HERmark assay is a quantitative assay that sensitively and reproducibly measures continuous H2T and H2D protein expression levels and therefore may have the potential to stratify patients more accurately with respect to response to HER2-targeted therapies than current methods which rely on semiquantitative protein measurements (IHC) or on indirect assessments of gene amplification (FISH).

Irreversible pan-ErbB tyrosine kinase inhibitors and breast cancer: current status and future directions

Aberrant activation of HER2 through overexpression has been shown to play an important role in some breast cancers. Therapies against this receptor including the monoclonal antibody, trastuzumab, or the small tyrosine kinase inhibitor, lapatinib have shown to improve the prognosis of such patients. Despite overexpressing HER2, some patients do not respond to these targeted treatments or progress after a short period of time. Irreversible tyrosine kinase inhibitors have been developed to bypass several pathways that could be involved in this resistance. In vitro, these agents have been shown to be more potent and to prolong target inhibition. Clinical development of these agents is ongoing and early results are promising. This review will describe the biologic rationale that justifies the development of these agents in breast cancer focusing on the current status and future directions.

HER family receptor abnormalities in lung cancer brain metastases and corresponding primary tumors

PURPOSE

To compare the characteristics of deregulation of HER receptors and their ligands between primary tumor and corresponding brain metastases of non-small cell lung carcinoma (NSCLC).

EXPERIMENTAL DESIGN

Fifty-five NSCLC primary tumors and corresponding brain metastases specimens were examined for the immunohistochemical expression of epidermal growth factor receptor (EGFR), phosphorylated EGFR, Her2, Her3, and phosphorylated Her3, and their ligands EGF, transforming growth factor-alpha, amphiregulin, epiregulin, betacellulin, heparin-binding EGFR-like growth factor, neuregulin (NRG) 1, and NRG2. Analysis of EGFR copy number using fluorescence in situ hybridization and mutation by PCR-based sequencing was also done.

RESULTS

Metastases showed significantly higher immunohistochemical expression of EGF (membrane: brain metastases 66.0 versus primary tumors 48.5; P = 0.027; nucleus: brain metastases 92.2 versus 67.4; P = 0.008), amphiregulin (nucleus: brain metastases 53.7 versus primary tumors 33.7; P = 0.019), phosphorylated EGFR (membrane: brain metastases 161.5 versus primary tumors 76.0; P < 0.0001; cytoplasm: brain metastases 101.5 versus primary tumors 55.9; P = 0.014), and phosphorylated Her3 (membrane: brain metastases 25.0 versus primary tumors 3.7; P = 0.001) than primary tumors did. Primary tumors showed significantly higher expression of cytoplasmic transforming growth factor-alpha(primary tumors 149.8 versus brain metastases 111.3; P = 0.008) and NRG1 (primary tumors 158.5 versus brain metastases 122.8; P = 0.006). In adenocarcinomas, a similar high frequency of EGFR copy number gain (high polysomy and amplification) was detected in primary (65%) and brain metastasis (63%) sites. However, adenocarcinoma metastases (30%) showed higher frequency of EGFR amplification than corresponding primary tumors (10%). Patients whose primary tumors showed EGFR amplification tended to develop brain metastases at an earlier time point.

CONCLUSIONS

Our findings suggest that NSCLC brain metastases have some significant differences in HER family receptor-related abnormalities from primary lung tumors.

Targeting MET as a strategy to overcome crosstalk-related resistance to EGFR inhibitors

The hepatocyte growth factor (HGF)-mesenchymal-epithelial transition factor (MET) pathway has a key role in carcinogenesis; it is implicated in proliferation, inhibition of apoptosis, angiogenesis, migration, invasiveness, and metastasis. All of these molecular events are driven through membrane and intracellular coplayers and several downstream effector proteins. MET has been shown to cross react with epithelial growth factor receptor (EGFR) proteins and possibly substitutes their activity, thus conferring resistance to EGFR-targeting drugs. Therefore, identification of MET inhibitors might lead to new treatments for MET-triggered neoplasia and improve the sensitivity of molecularly targeted antineoplastic compounds that are currently in use. In this Review, we outline current data regarding the HGF-MET pathway during carcinogenesis and the strategies for therapeutic targeting of this pathway. We also discuss the rationale and future perspectives of the combinatorial blockade of HGF-MET and EGFR signalling cascades in cancer treatment.

Expression of Erk5 in early stage breast cancer and association with disease free survival identifies this kinase as a potential therapeutic target

Background

Breast cancer is the most common neoplasia in women. Even though advances in its treatment have improved disease outcome, some patients relapse. Therefore, attempts to better define the molecular determinants that drive breast cancer cell proliferation may help in defining potential therapeutic targets. Mitogen-activated protein kinases (MAPK) play important roles in tumorigenesis. One of them, Erk5, has been linked to the proliferation of breast cancer cells in vitro. Here we have investigated the expression and prognostic value of Erk5 in human breast cancer.

Methodology/Principal Findings

Animal and cellular models were used to study Erk5 expression and function in breast cancer. In 84 human breast tumours the expression of Erk5 was analyzed by immunohistochemistry. Active Erk5 (pErk5) was studied by Western blotting. Correlation of Erk5 with clinicopathological parameters and with disease-free survival in early stage breast cancer patients was analyzed. Expression of Erk5 was detected in most patients, and overexpression was found in 20%. Active Erk5 was present in a substantial number of samples, as well as in tumours from an animal breast cancer model. Overexpression of Erk5 was associated with a decrease in disease-free survival time, which was independent of other clinicopathological parameters of prognosis. Transient transfection of a short hairpin RNA (shRNA) targeting Erk5, and a stable cell line expressing a dominant negative form of Erk5 (Erk5^AEF), were used to investigate the influence of Erk5 on drugs used in the clinic to treat breast tumours. We found that inhibition of Erk5 decreased cancer cell proliferation and also sensitized these cells to the action of anti-HER2 therapies.

Conclusions/Significance

Overexpression of Erk5 is an independent predictor of disease-free survival in breast cancer, and may represent a future therapeutic target.

The HER-2 receptor and breast cancer: ten years of targeted anti-HER-2 therapy and personalized medicine

The human epidermal growth factor receptor (HER-2) oncogene encodes a transmembrane tyrosine kinase receptor that has evolved as a major classifier of invasive breast cancer and target of therapy for the disease. The validation of the general prognostic significance of HER-2 gene amplification and protein overexpression in the absence of anti-HER-2 targeted therapy is discussed in a study of 107 published studies involving 39,730 patients, which produced an overall HER-2-positive rate of 22.2% and a mean relative risk for overall survival (OS) of 2.74. The issue of HER-2 status in primary versus metastatic breast cancer is considered along with a section on the features of metastatic HER-2-positive disease. The major marketed slide-based HER-2 testing approaches, immunohistochemistry, fluorescence in situ hybridization, and chromogenic in situ hybridization, are presented and contrasted in detail against the background of the published American Society of Clinical Oncology-College of American Pathologists guidelines for HER-2 testing. Testing issues, such as the impact of chromosome 17 polysomy and local versus central HER-2 testing, are also discussed. Emerging novel HER-2 testing techniques, including mRNA-based testing by real-time polymerase chain reaction and DNA microarray methods, HER-2 receptor dimerization, phosphorylated HER-2 receptors, and HER-2 status in circulating tumor cells, are also considered. A series of biomarkers potentially associated with resistance to trastuzumab is discussed with emphasis on the phosphatase and tensin homologue deleted on chromosome ten/Akt and insulin-like growth factor receptor pathways. The efficacy results for the more recently approved small molecule HER-1/HER-2 kinase inhibitor lapatinib are also presented along with a more limited review of markers of resistance for this agent. Additional topics in this section include combinations of both anti-HER-2 targeted therapies together as well as with novel agents including bevacizumab, everolimus, and tenespimycin. A series of novel HER-2-targeting agents is also presented, including pertuzumab, ertumaxomab, HER-2 vaccines, and recently discovered tyrosine kinase inhibitors. Biomarkers predictive of HER-2 targeted therapy toxicity are included, and the review concludes with a consideration of HER-2 status in the prediction of response to non-HER-2 targeted treatments including hormonal therapy, anthracyclines, and taxanes.

Neuregulins and cancer

The neuregulins represent the largest subclass of polypeptide factors of the epidermal growth factor family of ligands. These molecules are synthesized as membrane-bound, biologically active growth factors that act by binding to the HER/ErbB receptor tyrosine kinases. Preclinical data have indicated that increased expression and function of neuregulins may provoke cancer. Furthermore, neuregulin expression has been detected in several neoplasias, and their presence may correlate with response to treatments that target the HER receptors such as trastuzumab. In addition, the neuregulins have also been implicated in resistance to anti-HER therapies. Therefore, targeting of the neuregulins may be helpful in neoplastic diseases in which these polypeptide factors contribute to tumor generation and/or maintenance.

The role of NRG3 in mammary development

The Neuregulin gene family encodes EGF-containing ligands which mediate their effects by binding to the ERBB receptor tyrosine kinases, a signalling network with important roles in both mammary gland development and breast cancer. Neuregulin3 (NRG3), a ligand for ERBB4, promotes early mammary morphogenesis and acts during specification of the mammary placode, an aggregate of epithelial cells that forms during mid-embryogenesis. Recent studies have shown that NRG3 can alter the cell fate of other epidermal progenitor populations when NRG3 is mis-expressed throughout the basal layer of the developing epidermis with the K14 promoter. Here evidence for a key function for NRG3 in promoting early mammary morphogenesis and the implication for the role of NRG3 in breast cancer and establishment of the mammary lineage are discussed.

The neuregulin family of genes and their multiple splice variants in breast cancer

The neuregulin family consists of four genes, NRG1-4 which can each encode products containing a domain related to the epidermal growth factor family of ligands. Each gene is subject to complex control of transcription and to splicing of their mRNA product to give many variant proteins. These do not contain secretory sequences but some, through their transmembrane sequence, are routed via the Golgi where they are glycosylated, to the cell surface. Here they may be released by regulated proteolysis to act as soluble proteins which can interact and activate members of the EGF receptor family of receptor tyrosine kinases. Other splice variants do not encode transmembrane sequences and these are found either in the cytoplasm or, if they encode a nuclear localisation sequence, in distinct compartments in the nucleoplasm. It has been shown that the variants containing a full EGF domain can act as receptor agonists but the function of the cytoplasmic and nuclear products is unknown as yet. All four neuregulin genes are expressed and play an important role in mammary gland development. They are also expressed at elevated levels in some cases of ductal carcinoma in situ of the breast and breast cancer. They seem to be active in this setting and their presence may affect the efficacy of treatment with endocrine agents or with signal transduction inhibitors directed at the EGF receptor family members. Much remains to be learned however of their normal function and their influence on breast cancer development, progression and response to therapy.

Dynamic expression of Erbb pathway members during early mammary gland morphogenesis

Similar to other epithelial appendages, mammary anlagen progress from stratified epithelium through placode and bud stages. Embryonic mammary morphogenesis is elicited by a combination of local cell migration, adhesion changes and proliferation, and these same developmental processes impact breast cancer etiology. The Erbb signaling network plays important roles in postnatal mammary gland morphogenesis and carcinogenesis. Neuregulin3 (Nrg3), an Erbb family ligand, has recently been shown to be involved in the specification of mammary glands in mice. To further examine the possible involvement of other Erbb family members and their ligands in early mammary morphogenesis, we have characterized their expression patterns during this process. We used whole mount in situ hybridization to analyze the expression patterns of these genes at stages prior to and during mammary placode formation. Immunohistochemistry was used to examine expression patterns at later bud stages. The Neuregulin ligands, Nrg1, Nrg2, Nrg3, Nrg4 and the receptors, Erbb1, Erbb2, Erbb3, Erbb4, were expressed either at stages prior to morphological appearance of the mammary placode or from the time that the placode is first morphologically distinct through to later bud stages. The expression patterns presented here suggest that multiple members of this signaling network are potential mediators of early mammary morphogenesis.

Transphosphorylation of kinase-dead HER3 and breast cancer progression: a new standpoint or an old concept revisited?

Although neither kinase-dead human epidermal growth factor receptor (HER)3 nor orphan HER2 can be activated by HER-related ligands on their own, the formation of HER2/HER3 heterodimers creates the most mitogenic and transforming receptor complex within the HER (erbB) family of transmembrane receptor tyrosine kinases. The incorporation of markers such as HER3 transactivation, HER2/HER3 dimer, or others that may provide information regarding the level of HER pathway engagement has been demonstrated to allow identification of patients who respond to or escape HER-targeted therapies. Pioneering studies showed that high expression of kinase-dead HER3 can predict early escape from the anti-HER2 monoclonal antibody trastuzumab. Also, the growth-inhibitory effects of HER1/2 tyrosine kinase inhibitors (TKIs) were previously found to be attenuated in the presence of heregulin, which is a high-affinity combinatorial ligand for HER3. All of these concepts are being revisited with respect to the efficacy of HER family TKI therapies; in particular, HER3 signalling buffered against incomplete inhibition of HER2 kinase activity has been suggested to be the mechanism that allows HER2 over-expressing breast cancer cells to escape HER TKIs. It remains to be elucidated whether reactivation of HER3 signalling can also account for the poor efficacy of HER TKIs in treating breast carcinomas that contain low overall levels of HER2 receptors. However, it appears that regardless of the mechanism that triggers the formation of oncogenic HER2/HER3 heterodimers (HER2 over-expression or overall low HER2 but high levels of the HER3 ligand heregulin), HER3 transphosphorylation is a common response of breast cancer cells upon treatment with current inhibitors of the HER receptor tyrosine kinase network. Because kinase-inactive HER3 is not presently an amenable target for forthcoming HER TKIs, molecular approaches that can efficiently block heregulin-triggered HER3 transactivation or nucleocytoplasmic trafficking of heregulin might offer novel strategies with which to manage HER-driven breast cancer disease.