HER2 therapy: molecular mechanisms of trastuzumab resistance

Epithelial-to-mesenchymal transition (EMT) confers primary resistance to trastuzumab (Herceptin)

The rate of inherent resistance to single-agent trastuzumab in HER2-overexpressing metastatic breast carcinomas is impressive at above 70%. Unfortunately, little is known regarding the distinctive genetic signatures that could predict trastuzumab refractoriness ab initio. The epithelial-to-mesenchymal transition (EMT) molecular features, HER2 expression status and primary responses to trastuzumab were explored in the public Lawrence Berkeley Laboratory (LBL) Breast Cancer Collection. Lentivirus-delivered small hairpin RNAs were employed to reduce specifically and stably the expression of EMT transcription factors in trastuzumab-refractory basal/HER2+ cells. Cell proliferation assays and pre-clinical nude mice xenograft-based studies were performed to assess the contribution of specific EMT transcription factors to inherent trastuzumab resistance. Primary sensitivity to trastuzumab was restricted to the SLUG/SNAIL2-negative subset of luminal/HER2+ cell lines, whereas all of the SLUG/SNAIL2-positive basal/HER2+ cell lines exhibited an inherent resistance to trastuzumab. The specific knockdown of SLUG/SNAIL2 suppressed the stem-related CD44+CD24(-/low) mesenchymal immunophenotype by transcriptionally upregulating the luminal epithelial marker CD24 in basal/HER2+ cells. Basal/HER2+ cells gained sensitivity to the growth-inhibitory effects of trastuzumab following SLUG/SNAIL2 gene depletion, which induced the expression of the mesenchymal-to-epithelial transition (MET) genes involved in promoting an epithelial phenotype. The isolation of CD44+CD24(-/low) mesenchymal cells by magnetic-activated cell sorting (MACS) confirmed their intrinsic unresponsiveness to trastuzumab. A reduction in tumor growth and dramatic gain in sensitivity to trastuzumab in vivo were confirmed when the SLUG/SNAIL2 knockdown basal/HER2+ cells were injected into nude mice. HER2 overexpression in a basal, rather than in a luminal molecular background, results in a basal/HER2+ breast cancer subtype that is intrinsically resistant to trastuzumab. EMT transcription factors might induce an enhanced phenotypic plasticity that would allow basal/HER2+ breast cancer cells to "enter" into and "exit" dynamically from trastuzumab-responsive stem cell-like states. The systematic determination of SLUG/SNAIL2 as a stem/CD44+CD24(-/low) cell-associated protein may improve the therapeutic management of HER2+ breast carcinomas.

Semi-mechanistic population pharmacokinetic model of multivalent trastuzumab emtansine in patients with metastatic breast cancer

Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate (ADC) composed of multiple molecules of the antimicrotubule agent DM1 linked to trastuzumab, a humanized anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody. Pharmacokinetics data from phase I (n = 52) and phase II (n = 111) studies in HER2-positive metastatic breast cancer patients show a shorter terminal half-life for T-DM1 than for total trastuzumab (TTmAb). In this work, we translated prior preclinical modeling in monkeys to develop a semi-mechanistic population pharmacokinetics model to characterize T-DM1 and TTmAb concentration profiles. A series of transit compartments with the same disposition parameters was used to describe the deconjugation process from higher to lower drug-to-antibody ratios (DARs). The structure could explain the shorter terminal half-life of T-DM1 relative to TTmab. The final model integrates prior knowledge of T-DM1 DARs from preclinical studies and could provide a platform for understanding and characterizing the pharmacokinetics of other ADC systems.

Temporal profiling of lapatinib-suppressed phosphorylation signals in EGFR/HER2 pathways

Lapatinib is a clinically potent kinase inhibitor for breast cancer patients because of its outstanding selectivity for epidermal growth factor receptor (EGFR) and EGFR2 (also known as HER2). However, there is only limited information about the in vivo effects of lapatinib on EGFR/HER2 and downstream signaling targets. Here, we profiled the lapatinib-induced time- and dose-dependent phosphorylation dynamics in SKBR3 breast cancer cells by means of quantitative phosphoproteomics. Among 4953 identified phosphopeptides from 1548 proteins, a small proportion (5-7%) was regulated at least twofold by 1-10 μm lapatinib. We obtained a comprehensive phosphorylation map of 21 sites on EGFR/HER2, including nine novel sites on HER2. Among them, serine/threonine phosphosites located in a small region of HER2 (amino acid residues 1049-1083) were up-regulated by the drug, whereas all other sites were down-regulated. We show that cAMP-dependent protein kinase is involved in phosphorylation of this particular region of HER2 and regulates HER2 tyrosine kinase activity. Computational analyses of quantitative phosphoproteome data indicated for the first time that protein-protein networks related to cytoskeletal organization and transcriptional/translational regulation, such as RNP complexes (i.e. hnRNP, snRNP, telomerase, ribosome), are linked to EGFR/HER2 signaling networks. To our knowledge, this is the first report to profile the temporal response of phosphorylation dynamics to a kinase inhibitor. The results provide new insights into EGFR/HER2 regulation through region-specific phosphorylation, as well as a global view of the cellular signaling networks associated with the anti-breast cancer action of lapatinib.

mTOR inhibitors in breast cancer: a systematic review

PI3K/AKT/mTOR pathway is a crucial mediator of tumor progression. As the PI3K/Akt pathway is heavily deregulated in breast cancer, the application of mTOR inhibitors in breast cancer patients seems warranted. This is the first systematic review according to PRISMA guidelines to synthesize all available data of mTOR inhibitors in all subcategories of breast cancer. The search strategy retrieved 16 studies evaluating everolimus (1492 patients), seven studies examining temsirolimus (1245 patients), one study evaluating sirolimus (400 patients) and two studies evaluating MKC-1 (60 patients). The Breast Cancer Trials of Oral Everolimus-2 (BOLERO-2) study has marked a turning point in the evaluation of everolimus in the treatment of estrogen receptor positive breast cancer. Given the positive results, everolimus has entered NCCN 2012 guidelines, and its approval of its combination with exemestane by FDA and EMA is imminent. In addition, the promising antitumor activity and long-term disease control further suggest that mTOR inhibition with everolimus may provide an avenue for achieving long-lasting benefit from trastuzumab-based therapy in HER2-positive patients. Regarding temsirolimus, it seems that the agent may play, in the future, a role in the treatment of metastatic breast cancer; importantly, however, there is an unmet need to find its optimal target subpopulation.

Lapatinib plus capecitabine in treating HER2-positive advanced breast cancer: efficacy, safety, and biomarker results from Chinese patients

Overexpression of human epidermal growth factor receptor-2 (HER2) in metastatic breast cancer (MBC) is associated with poor prognosis. This single-arm open-label trial (EGF109491; NCT00508274) was designed to confirm the efficacy and safety of lapatinib in combination with capecitabine in 52 heavily pretreated Chinese patients with HER2-positive MBC. The primary endpoint was clinical benefit rate (CBR). Secondary endpoints included progression-free survival (PFS), time to response (TTR), duration of response (DoR), central nervous system (CNS) as first site of relapse, and safety. The results showed that there were 23 patients with partial responses and 7 patients with stable disease, resulting in a CBR of 57.7%. The median PFS was 6.34 months (95% confidence interval, 4.93–9.82 months). The median TTR and DoR were 4.07 months (range, 0.03–14.78 months) and 6.93 months (range, 1.45–9.72 months), respectively. Thirteen (25.0%) patients had new lesions as disease progression. Among them, 2 (3.8%) patients had CNS disease reported as the first relapse. The most common toxicities were palmar-plantar erythrodysesthesia (59.6%), diarrhea (48.1%), rash (48.1%), hyperbilirubinemia (34.6%), and fatigue (30.8%). Exploratory analyses of oncogenic mutations of PIK3CA suggested that of 38 patients providing a tumor sample, baseline PIK3CA mutation status was not associated with CBR (P = 0.639) or PFS (P = 0.989). These data confirm that the lapatinib plus capecitabine combination is an effective and well-tolerated treatment option for Chinese women with heavily pretreated MBC, irrespective of PIK3CA status.

Modulation of MicroRNA-194 and cell migration by HER2-targeting trastuzumab in breast cancer

Trastuzumab, a humanized monoclonal antibody directed against the extracellular domain of the HER2 oncoprotein, can effectively target HER2-positive breast cancer through several mechanisms. Although the effects of trastuzumab on cancer cell proliferation, angiogenesis and apoptosis have been investigated in depth, the effect of trastuzumab on microRNA (miRNA) has not been extensively studied. We have performed miRNA microarray profiling before and after trastuzumab treatment in SKBr3 and BT474 human breast cancer cells that overexpress HER2. We found that trastuzumab treatment of SKBr3 cells significantly decreased five miRNAs and increased three others, whereas treatment of BT474 cells significantly decreased two miRNAs and increased nine. The only change in miRNA expression observed in both cell lines following trastuzumab treatment was upregulation of miRNA-194 (miR-194) that was further validated in vitro and in vivo. Forced expression of miR-194 in breast cancer cells that overexpress HER2 produced no effect on apoptosis, modest inhibition of proliferation, significant inhibition of cell migration/invasion in vitro and significant inhibition of xenograft growth in vivo. Conversely, knockdown of miR-194 promoted cell migration. Increased miR-194 expression markedly reduced levels of the cytoskeletal protein talin2 and specifically inhibited luciferase reporter activity of a talin2 wild-type 3'-untranslated region, but not that of a mutant reporter, indicating that talin2 is a direct downstream target of miR-194. Trastuzumab treatment inhibited breast cancer cell migration and reduced talin2 expression in vitro and in vivo. Knockdown of talin2 inhibited cell migration/invasion. Knockdown of trastuzumab-induced miR-194 expression with a miR-194 inhibitor compromised trastuzumab-inhibited cell migration in HER2-overexpressing breast cancer cells. Consequently, trastuzumab treatment upregulates miR-194 expression and may exert its cell migration-inhibitory effect through miR-194-mediated downregulation of cytoskeleton protein talin2 in HER2-overexpressing human breast cancer cells.

Breast cancer chemoprevention: old and new approaches

In 1976, Sporn has defined chemoprevention as “the use of pharmacologic or natural agents that inhibit the development of invasive breast cancer either by blocking the DNA damage that initiates carcinogenesis, or by arresting or reversing the progression of premalignant cells in which such damage has already occurred.” Although the precise mechanism or mechanisms that promote a breast cancer are not completely established, the success of several recent clinical trials in preventive settings in selected high-risk populations suggests that chemoprevention is a rational and an appealing strategy. Breast cancer chemoprevention has focused heavily on endocrine intervention using selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs). Achieving much success in this particular setting and new approaches as low-dose administration are actually under investigations in several topics. Unfortunately, these drugs are active in prevention of endocrine responsive lesions only and have no effect in reducing the risk of estrogen-negative breast cancer. Thus, recently new pathways, biomarkers, and agents likely are to be effective in this subgroup of cancers and were put under investigation. Moreover, the identification of new potential molecular targets and the development of agents aimed at these targets within cancer have already had a significant impact on advanced cancer therapy and provide a wealth of opportunities for chemoprevention. This paper will highlight current clinical research in both ER-positive and ER-negative breast cancer chemoprevention, explaining the biologic effect of the various agents on carcinogenesis and precancerous lesions, and finally presenting an excursus on the state-of-the-art about new molecular targets under investigations in breast cancer settings.

Exosome removal as a therapeutic adjuvant in cancer

Exosome secretion is a notable feature of malignancy owing to the roles of these nanoparticles in cancer growth, immune suppression, tumor angiogenesis and therapeutic resistance. Exosomes are 30-100 nm membrane vesicles released by many cells types during normal physiological processes. Tumors aberrantly secrete large quantities of exosomes that transport oncoproteins and immune suppressive molecules to support tumor growth and metastasis. The role of exosomes in intercellular signaling is exemplified by human epidermal growth factor receptor type 2 (HER2) over-expressing breast cancer, where exosomes with the HER2 oncoprotein stimulate tumor growth and interfere with the activity of the therapeutic antibody Herceptin®. Since numerous observations from experimental model systems point toward an important clinical impact of exosomes in cancer, several pharmacological strategies have been proposed for targeting their malignant activities. We also propose a novel device strategy involving extracorporeal hemofiltration of exosomes from the entire circulatory system using an affinity plasmapheresis platform known as the Aethlon ADAPT™ (adaptive dialysis-like affinity platform technology) system, which would overcome the risks of toxicity and drug interactions posed by pharmacological approaches. This technology allows affinity agents, including exosome-binding lectins and antibodies, to be immobilized in the outer-capillary space of plasma filtration membranes that integrate into existing kidney dialysis systems. Device therapies that evolve from this platform allow rapid extracorporeal capture and selective retention of target particles < 200 nm from the entire circulatory system. This strategy is supported by clinical experience in hepatitis C virus-infected patients using an ADAPT™ device, the Hemopurifier®, to reduce the systemic load of virions having similar sizes and glycosylated surfaces as cancer exosomes. This review discusses the possible therapeutic approaches for targeting immune suppressive exosomes in cancer patients, and the anticipated significance of these strategies for reversing immune dysfunction and improving responses to standard of care treatments.

Preoperative Chemotherapy Plus Trastuzumab, Lapatinib, or Both in Human Epidermal Growth Factor Receptor 2–Positive Operable Breast Cancer: Results of the Randomized Phase II CHER-LOB Study

Purpose

This is a noncomparative, randomized, phase II trial of preoperative taxane-anthracycline in combination with trastuzumab, lapatinib, or combined trastuzumab plus lapatinib in patients with human epidermal growth factor receptor 2 (HER2) –positive, stage II to IIIA operable breast cancer. The primary aim was to estimate the percentage of pathologic complete response (pCR; no invasive tumor in breast and axillary nodes).

Patients and Methods

In the three arms, chemotherapy consisted of weekly paclitaxel (80 mg/m2) for 12 weeks followed by fluorouracil, epirubicin, and cyclophosphamide for four courses every 3 weeks. The patients randomly assigned to arm A received a 4-mg loading dose of trastuzumab followed by 2 mg weekly; in arm B patients received lapatinib 1,500 mg orally (PO) daily; and in arm C, patients received trastuzumab and lapatinib 1,000 mg PO daily.

Results

A total of 121 patients were randomly assigned. Diarrhea and dermatologic and hepatic toxicities were observed more frequently in patients receiving lapatinib. No episodes of congestive heart failure were observed. The rates of breast-conserving surgery were 66.7%, 57.9%, and 68.9% in arms A, B and C, respectively. The pCR rates were 25% (90% CI, 13.1% to 36.9%) in arm A, 26.3% (90% CI, 14.5% to 38.1%) in arm B, and 46.7% (90% CI, 34.4% to 58.9%) in arm C (exploratory P = .019).

Conclusion

The primary end point of the study was met, with a relative increase of 80% in the pCR rate achieved with chemotherapy plus trastuzumab and lapatinib compared with chemotherapy plus either trastuzumab or lapatinib. These data add further evidence supporting the superiority of a dual-HER2 inhibition for the treatment of HER2-positive breast cancer.

New developments in the treatment of HER2-positive breast cancer

Approximately 20%-30% of metastatic breast cancers show increased expression of the human epidermal growth factor receptor-2 (HER2) tyrosine kinase. Two HER2-specific therapies are currently approved for clinical treatment of patients with HER2-overexpressing metastatic breast cancer. Trastuzumab is a monoclonal antibody against HER2 and is approved for first-line treatment of HER2-positive metastatic breast cancer. Lapatinib is a small molecule dual inhibitor of epidermal growth factor receptor and HER2 tyrosine kinases, and is approved for trastuzumab-refractory disease. Although trastuzumab is a highly effective therapy for patients with HER2-overexpressing metastatic breast cancer, a significant number of patients in the initial clinical trials of trastuzumab monotherapy showed resistance to trastuzumab-based therapy. Further, among those who did respond, the initial trials indicated that the median time to progression was less than 1 year. Similarly, lapatinib is effective in a subset of trastuzumab-refractory cases, but the majority of patients display resistance. This review discusses the multiple molecular mechanisms of resistance that have been proposed in the literature. In addition, novel agents that are being tested for efficacy against HER2-positive breast cancer, including the antibodies pertuzumab and trastuzumab-DM1 and the immunotoxin affitoxin, are reviewed. The introduction of trastuzumab has revolutionized the clinical care of patients with HER2-positive metastatic breast cancer and has resulted in dramatic reductions in recurrences of early-stage HER2-positive breast cancer. The development and implementation of gene- and protein-based assays that measure potential molecular predictors of trastuzumab resistance will allow individualization of HER2-targeted therapeutic approaches, and may ultimately improve treatment of HER2-positive breast cancer.

Therapeutic implications of estrogen receptor signaling in HER2-positive breast cancers

There is considerable pre-clinical and clinical evidence demonstrating that HER2-positive breast cancers that express estrogen receptor (ER) exhibit intrinsic resistance to endocrine therapy. Therefore, in general, chemotherapy in combination with HER2-directed agents is recommended for all but the smallest HER2-positive early stage breast cancers regardless of ER status. This paradigm has recently come into question when responses to neo-adjuvant HER2-directed regimens were noted to vary based on ER expression, and pathologic complete response was noted not to be prognostic for ER-positive, HER2-positive breast cancers. These and other data suggest the possibility that a subset of HER2-positive, ER-positive breast cancers are driven primarily by ER, and biologically behave more like HER2-negative, ER-positive breast cancers. Identification of this subset of HER2-positive breast cancers is essential to avoid over-treatment of patients with small HER2-positive, ER-positive breast cancers, who may be optimally treated with endocrine therapy alone, or in combination with a HER2-directed agent, thereby avoiding the use of chemotherapy. Crosstalk between the ER and HER2 pathways has been established as playing a role in both intrinsic and acquired resistance to endocrine agents. Emerging data suggests that crosstalk between these pathways is also involved in resistance to HER2-directed agents. Unraveling the role of the ER pathway in resistance to HER2-directed agents could potentially result in therapeutic approaches that can improve outcome for patients with ER-positive, HER2-positive breast cancer.

HER2+ Breast Cancer Therapy: By CPP-ZFN Mediated Targeting of mTOR?

A significant fraction of HER2+ patients develop resistance to available therapies such as trastuzumab. The acquired resistance is primarily due to hyper activation of HER2 downstream PI3K/Akt/mTOR signalling pathway. Hence, identification of inhibitors of components of this pathway, particularly mTOR, is an area of intense investigation. Interestingly, mTOR specific inhibitors (rapamycin/rapalogs) have been tested and shown to potentiate the effect of HER2 inhibitors. However, the use of mTOR inhibitors will also be associated with the limitations inherently linked with extensive use of anticancer drugs e.g., toxicity and acquired drug resistance. Hereby, we hypothesize development of an alternative novel molecular therapeutic intervention based on cell penetrating peptide (CPP), a highly efficient carrier, conjugated to zinc finger nuclease (ZFN), a precise molecular scissor. The use of HER2 specific CPP conjugated to mTOR specific ZFN, will make the mTOR locus non-functional and inhibit the PI3K/Akt/mTOR pathway, essential for growth and proliferation of cancerous cells. With the availability of HER2+ cancerous cell specific CPP and proved applications of ZFN in targeted genome engineering of over 11 species, the prospects of success of CPP-ZFN anti-cancer therapy are very high.

Delivery of chemo-sensitizing siRNAs to HER2+-breast cancer cells using RNA aptamers

Human epidermal growth factor receptor 2 (HER2) expression in breast cancer is associated with an aggressive phenotype and poor prognosis, making it an appealing therapeutic target. Trastuzumab, an HER2 antibody-based inhibitor, is currently the leading targeted treatment for HER2(+)-breast cancers. Unfortunately, many patients inevitably develop resistance to the therapy, highlighting the need for alternative targeted therapeutic options. In this study, we used a novel, cell-based selection approach for isolating 'cell-type specific', 'cell-internalizing RNA ligands (aptamers)' capable of delivering therapeutic small interfering RNAs (siRNAs) to HER2-expressing breast cancer cells. RNA aptamers with the greatest specificity and internalization potential were covalently linked to siRNAs targeting the anti-apoptotic gene, Bcl-2. We demonstrate that, when applied to cells, the HER2 aptamer-Bcl-2 siRNA conjugates selectively internalize into HER2(+)-cells and silence Bcl-2 gene expression. Importantly, Bcl-2 silencing sensitizes these cells to chemotherapy (cisplatin) suggesting a potential new therapeutic approach for treating breast cancers with HER2(+)-status. In summary, we describe a novel cell-based selection methodology that enables the identification of cell-internalizing RNA aptamers for targeting therapeutic siRNAs to HER2-expressing breast cancer cells. The future refinement of this technology may promote the widespread use of RNA-based reagents for targeted therapeutic applications.

Drug repositioning for personalized medicine

Human diseases can be caused by complex mechanisms involving aberrations in numerous proteins and pathways. With recent advances in genomics, elucidating the molecular basis of disease on a personalized level has become an attainable goal. In many cases, relevant molecular targets will be identified for which approved drugs already exist, and the potential repositioning of these drugs to a new indication can be investigated. Repositioning is an accelerated route for drug discovery because existing drugs have established clinical and pharmacokinetic data. Personalized medicine and repositioning both aim to improve the productivity of current drug discovery pipelines, which expend enormous time and cost to develop new drugs, only to have them fail in clinical trials because of lack of efficacy or toxicity. Here, we discuss the current state of research in these two fields, focusing on recent large-scale efforts to systematically find repositioning candidates and elucidate individual disease mechanisms in cancer. We also discuss scenarios in which personalized drug repositioning could be particularly rewarding, such as for diseases that are rare or have specific mutations, as well as current challenges in this field. With an increasing number of drugs being approved for rare cancer subtypes, personalized medicine and repositioning approaches are poised to significantly alter the way we diagnose diseases, infer treatments and develop new drugs.

Efficacy and tolerability of lapatinib in the management of breast cancer

Approximately 20%–25% of all breast cancers over express a key cell surface growth factor receptor known as HER2. HER2 plays a key role in cell growth and proliferation and is linked to worse clinical outcomes, making it a logical therapeutic target. The first HER2 targeted drug to be approved by the FDA, was the humanized monoclonal antibody trastuzumab, after it showed improvements in survival in the adjuvant setting, and delayed time to progression in the metastatic setting. Although highly effective, for reasons that are not clear, some patients display resistance to trastuzumab. Lapatinib is an oral, small molecule tyrosine kinase inhibitor, that inhibits both the HER1 ahd HER2 receptors and may be able to overcome trastuzumab resistance. Lapatinib is approved in the second line setting for use in combination with capecitabine or with letrozole. In this review, we will discuss the indications, concerns or any issues with regards to the drug.

The HSP90 inhibitor XL888 overcomes BRAF inhibitor resistance mediated through diverse mechanisms

PURPOSE

The clinical use of BRAF inhibitors is being hampered by the acquisition of drug resistance. This study shows the potential therapeutic use of the HSP90 inhibitor (XL888) in six different models of vemurafenib resistance.

EXPERIMENTAL DESIGN

The ability of XL888 to inhibit growth and to induce apoptosis and tumor regression of vemurafenib-resistant melanoma cell lines was shown in vitro and in vivo. A novel mass spectrometry-based pharmacodynamic assay was developed to measure intratumoral HSP70 levels following HSP90 inhibition in melanoma cell lines, xenografts, and melanoma biopsies. Mechanistic studies were carried out to determine the mechanism of XL888-induced apoptosis.

RESULTS

XL888 potently inhibited cell growth, induced apoptosis, and prevented the growth of vemurafenib-resistant melanoma cell lines in 3-dimensional cell culture, long-term colony formation assays, and human melanoma mouse xenografts. The reversal of the resistance phenotype was associated with the degradation of PDGFRβ, COT, IGFR1, CRAF, ARAF, S6, cyclin D1, and AKT, which in turn led to the nuclear accumulation of FOXO3a, an increase in BIM (Bcl-2 interacting mediator of cell death) expression, and the downregulation of Mcl-1. In most resistance models, XL888 treatment increased BIM expression, decreased Mcl-1 expression, and induced apoptosis more effectively than dual mitogen-activated protein-extracellular signal-regulated kinase/phosphoinositide 3-kinase (MEK/PI3K) inhibition.

CONCLUSIONS

HSP90 inhibition may be a highly effective strategy at managing the diverse array of resistance mechanisms being reported to BRAF inhibitors and appears to be more effective at restoring BIM expression and downregulating Mcl-1 expression than combined MEK/PI3K inhibitor therapy.

Contribution of CXCL12 secretion to invasion of breast cancer cells

INTRODUCTION

Neu (HER2/ErbB2) is overexpressed in 25% to 30% of human breast cancer, correlating with a poor prognosis. Researchers in previous studies who used the mouse mammary tumor virus Neu-transgenic mouse model (MMTV-Neu) demonstrated that the Neu-YB line had increased production of CXCL12 and increased metastasis, whereas the Neu-YD line had decreased metastasis. In this study, we examined the role of increased production of CXCL12 in tumor cell invasion and malignancy.

METHODS

We studied invasion in the tumor microenvironment using multiphoton intravital imaging, in vivo invasion and intravasation assays. CXCL12 signaling was altered by using the CXCR4 inhibitor AMD3100 or by increasing CXCL12 expression. The role of macrophage signaling in vivo was determined using a colony-stimulating factor 1 receptor (CSF-1R) blocking antibody.

RESULTS

The Neu-YD strain was reduced in invasion, intravasation and metastasis compared to the Neu-YB and Neu deletion mutant (activated receptor) strains. Remarkably, in the Neu-YB strain, in vivo invasion to epidermal growth factor was dependent on both CXCL12-CXCR4 and CSF1-CSF-1R signaling. Neu-YB tumors had increased macrophage and microvessel density. Overexpression of CXCL12 in rat mammary adenocarcinoma cells increased in vivo invasion as well as microvessel and macrophage density.

CONCLUSIONS

Expression of CXCL12 by tumor cells results in increased macrophage and microvessel density and in vivo invasiveness.

MKNK1 is a YB-1 target gene responsible for imparting trastuzumab resistance and can be blocked by RSK inhibition

Trastuzumab (Herceptin) resistance is a major obstacle in the treatment of patients with HER2-positive breast cancers. We recently reported that the transcription factor Y-box binding protein-1 (YB-1) leads to acquisition of resistance to trastuzumab in a phosphorylation-dependent manner that relies on p90 ribosomal S6 kinase (RSK). To explore how this may occur we compared YB-1 target genes between trastuzumab-sensitive cells (BT474) and those with acquired resistance (HR5 and HR6) using genome-wide chromatin immunoprecipitation sequencing (ChIP-sequencing), which identified 1391 genes uniquely bound by YB-1 in the resistant cell lines. We then examined differences in protein expression and phosphorylation between these cell lines using the Kinexus Kinex antibody microarrays. Cross-referencing these two data sets identified the mitogen-activated protein kinase-interacting kinase (MNK) family as potentially being involved in acquired resistance downstream from YB-1. MNK1 and MNK2 were subsequently shown to be overexpressed in the resistant cell lines; however, only the former was a YB-1 target based on ChIP-PCR and small interfering RNA (siRNA) studies. Importantly, loss of MNK1 expression using siRNA enhanced sensitivity to trastuzumab. Further, MNK1 overexpression was sufficient to confer resistance to trastuzumab in cells that were previously sensitive. We then developed a de novo model of acquired resistance by exposing BT474 cells to trastuzumab for 60 days (BT474LT). Similar to the HR5/HR6 cells, the BT474LT cells had elevated MNK1 levels and were dependent on it for survival. In addition, we demonstrated that RSK phosphorylated MNK1, and that this phosphorylation was required for ability of MNK1 to mediate resistance to trastuzumab. Furthermore, inhibition of RSK with the small molecule BI-D1870 repressed the MNK1-mediated trastuzumab resistance. In conclusion, this unbiased integrated approach identified MNK1 as a player in mediating trastuzumab resistance as a consequence of YB-1 activation, and demonstrated RSK inhibition as a means to overcome recalcitrance to trastuzumab.

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.

Phase I study of lapatinib plus vinorelbine in patients with locally advanced or metastatic breast cancer overexpressing HER2

Background:

To determine the recommended doses of lapatinib (LPT) combined with vinorelbine (VNR) in women with human epidermal growth factor receptor 2-overexpressing advanced breast cancer pretreated with trastuzumab.

Methods:

In this phase I study, women were treated with oral daily LPT and i.v. VNR infused on days 1 and 8 every 3 weeks. Dose levels (DL) of LPT (mg)/VNR (mg m⁻²) ranged from 750/20 to 1250/30. The primary end point was feasibility based on maximal tolerated dose (MTD) and maximum administered dose (MAD). Pharmacokinetic interactions were investigated.

Results:

Of 33 patients included, 29 were evaluable. Two DLT occurred at DL4 (1000/25) meeting the MAD criteria. Despite an additional intermediate DL3′ (1250/22.5), MTD was reached at DL3 (1000/22.5). Grade 3–4 neutropenia was the most common toxicity (34% and 38% of patients, respectively). Other significant toxicities included grade 3–4 diarrhoea (3% each), and grade 3 asthenia (10%). Although not statistically significant, LPT (at 1000 or 1250 mg) decreased the VNR clearance by 30–40% compared with DL1.

Conclusion:

The MTD LPT 1000 mg/VNR 22.5 mg m⁻² (DL3) is recommended for additional development. Pharmacokinetic interactions might increase the exposure to VNR and consequently alter the hematological tolerance.

Highly sensitive proximity mediated immunoassay reveals HER2 status conversion in the circulating tumor cells of metastatic breast cancer patients

Background

The clinical benefits associated with targeted oncology agents are generally limited to subsets of patients. Even with favorable biomarker profiles, many patients do not respond or acquire resistance. Existing technologies are ineffective for treatment monitoring as they provide only static and limited information and require substantial amounts of tissue. Therefore, there is an urgent need to develop methods that can profile potential therapeutic targets with limited clinical specimens during the course of treatment.

Methods

We have developed a novel proteomics-based assay, Collaborative Enzyme Enhanced Reactive-immunoassay (CEER) that can be used for analyzing clinical samples. CEER utilizes the formation of unique immuno-complex between capture-antibodies and two additional detector-Abs on a microarray surface. One of the detector-Abs is conjugated to glucose oxidase (GO), and the other is conjugated to Horse Radish Peroxidase (HRP). Target detection requires the presence of both detector-Abs because the enzyme channeling event between GO and HRP will not occur unless both Abs are in close proximity.

Results

CEER was able to detect single-cell level expression and phosphorylation of human epidermal growth factor receptor 2 (HER2) and human epidermal growth factor receptor 1 (HER1) in breast cancer (BCa) systems. The shift in phosphorylation profiles of receptor tyrosine kinases (RTKs) and other signal transduction proteins upon differential ligand stimulation further demonstrated extreme assay specificity in a multiplexed array format. HER2 analysis by CEER in 227 BCa tissues showed superior accuracy when compared to the outcome from immunohistochemistry (IHC) (83% vs. 96%). A significant incidence of HER2 status alteration with recurrent disease was observed via circulating tumor cell (CTC) analysis, suggesting an evolving and dynamic disease progression. HER2-positive CTCs were found in 41% (7/17) while CTCs with significant HER2-activation without apparent over-expression were found in 18% (3/17) of relapsed BCa patients with HER2-negative primary tumors. The apparent 'HER2 status conversion' observed in recurrent BCa may have significant implications on understanding breast cancer metastasis and associated therapeutic development.

Conclusion

CEER can be multiplexed to analyze pathway proteins in a comprehensive manner with extreme specificity and sensitivity. This format is ideal for analyzing clinical samples with limited availability.

Mechanisms of Trastuzumab resistance in ErbB2-driven breast cancer and newer opportunities to overcome therapy resistance

The Human Epidermal Growth Factor Receptor 2 (Her2, ErbB2 or Neu) is overexpressed in about 20 – 25% of breast cancers and is causally linked to oncogenesis, providing opportunities for targeted therapy. Trastuzumab (Herceptin^™, Genentech Inc, San Francisco, CA), a humanized monoclonal antibody against ErbB2, is a successful example of this concept and has vastly improved the response to treatment and overall survival in a majority of ErbB2+ breast cancer patients. However, lack of response in some patients as well as relapse during the course of therapy in others, continue to challenge researchers and clinicians alike towards a better understanding of the fundamental mechanisms of Trastuzumab action and resistance to treatment. The exact in vivo mechanism of action of Trastuzumab remains enigmatic, given its direct effects on the ErbB2 signaling pathway as well as indirect contributions from the immune system, by virtue of the ability of Trastuzumab to elicit Antibody-Dependent Cellular Cytotoxicity. Consequently, multiple mechanisms of resistance have been proposed. We present here a comprehensive review of our current understanding of the mechanisms, both of Trastuzumab action and clinical resistance to Trastuzumab-based therapies. We also review newer strategies (based on ErbB2 receptor biology) that are being explored to overcome resistance to Trastuzumab therapy.

Continuous requirement of ErbB2 kinase activity for loss of cell polarity and lumen formation in a novel ErbB2/Neu-driven murine cell line model of metastatic breast cancer

Background:

Well over a quarter of human breast cancers are ErbB2-driven and constitute a distinct subtype with substantially poorer prognosis. Yet, there are substantial gaps in our understanding of how ErbB2 tyrosine kinase activity unleashes a coordinated program of cellular and extracellular alterations that culminate in aggressive breast cancers. Cellular models that exhibit ErbB2 kinase dependency and can induce metastatic breast cancer in immune competent hosts are likely to help bridge this gap.

Materials and Methods:

Here, we derived and characterized a cell line model obtained from a transgenic ErbB2/Neu-driven mouse mammary adenocarcinoma.

Results:

The MPPS1 cell line produces metastatic breast cancers when implanted in the mammary fat pads of immune-compromised as well as syngeneic immune-competent hosts. MPPS1 cells maintain high ErbB2 overexpression when propagated in DFCI-1 or related media, and their growth is ErbB2-dependent, as demonstrated by concentration-dependent inhibition of proliferation with the ErbB kinase inhibitor Lapatinib. When grown in 3-dimensional (3-D) culture on Matrigel, MPPS1 cells predominantly form large irregular cystic and solid structures. Remarkably, low concentrations of Lapatinib led to a switch to regular acinar growth on Matrigel. Immunofluorescence staining of control vs. Lapatinib-treated acini for markers of epithelial polarity revealed that inhibition of ErbB2 signaling led to rapid resumption of normal mammary epithelium-like cell polarity.

Conclusions:

The strict dependence of the MPPS1 cell system on ErbB2 signals for proliferation and alterations in cell polarity should allow its use to dissect ErbB2 kinase-dependent signaling pathways that promote loss of cell polarity, a key component of the epithelial mesenchymal transition and aggressiveness of ErbB2-driven breast cancers.

Treatment of HER2-positive breast cancer: current status and future perspectives

The advent of HER2-directed therapies has significantly improved the outlook for patients with HER2-positive early stage breast cancer. However, a significant proportion of these patients still relapse and die of breast cancer. Trials to define, refine and optimize the use of the two approved HER2-targeted agents (trastuzumab and lapatinib) in patients with HER2-positive early stage breast cancer are ongoing. In addition, promising new approaches are being developed including monoclonal antibodies and small-molecule tyrosine kinase inhibitors targeting HER2 or other HER family members, antibodies linked to cytotoxic moieties or modified to improve their immunological function, immunostimulatory peptides, and targeting the PI3K and IGF-1R pathways. Improved understanding of the HER2 signaling pathway, its relationship with other signaling pathways and mechanisms of resistance has also led to the development of rational combination therapies and to a greater insight into treatment response in patients with HER2-positive breast cancer. Based on promising results with new agents in HER2-positive advanced-stage disease, a series of large trials in the adjuvant and neoadjuvant settings are planned or ongoing. This Review focuses on current treatment for patients with HER2-positive breast cancer and aims to update practicing clinicians on likely future developments in the treatment for this disease according to ongoing clinical trials and translational research.

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.

The emerging importance of α-L-fucose in human breast cancer: a review

Breast cancer cells incorporate the simple sugar alpha-L-fucose (fucose) into glycoproteins and glycolipids which, in turn, are expressed as part of the malignant phenotype. We have noted that fucose is not simply a bystander molecule, but, in fact, contributes to many of the fundamental oncologic properties of breast cancer cells. Here, we summarize the evidence from us and others that fucose is necessary for key functions of neoplastic progression including hematogenous metastasis, tumor invasion through extracellular matrices including basement membranes and up-regulation of the Notch signaling system, with implications for epithelial-to-mesenchymal transition and activation of breast cancer stem cells. Additionally, certain breast cancer biomarkers are fucose-rich while a well-known marker of breast cancer progression, soluble E-selectin, is a known counter-receptor of fucosylated selectin ligands. We provide illustrative examples and supportive evidence drawn from work with human breast cancer cell lines in vitro as well as clinical studies with human pathologic material. And finally, we discuss evidence that fucose (or its absence) is central to the mechanisms of action of several experimental targeted therapies which may prove useful in breast cancer treatment. We propose that alpha-L-fucose is essential in order to construct first, the malignant and then the metastatic phenotype of many human breast cancers. This knowledge may inform the search for novel treatment approaches in breast cancer.

Herceptin conjugates linked by EDC boost direct tumor cell death via programmed tumor cell necrosis

Tumor-targeted antibody therapy is one of the safest biological therapeutics for cancer patients, but it is often ineffective at inducing direct tumor cell death and is ineffective against resistant tumor cells. Currently, the antitumor efficacy of antibody therapy is primarily achieved by inducing indirect tumor cell death, such as antibody-dependent cell cytotoxicity. Our study reveals that Herceptin conjugates, if generated via the crosslinker EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride), are capable of engendering human epidermal growth factor receptor 2 (Her2) positive tumor cells death. Using a high-performance liquid chromatography (HPLC) system, three peaks with estimated molecular weights of antibody monomer, dimer, and trimer were isolated. Both Herceptin trimer and dimer separated by HPLC induced significant levels of necrotic tumor cell death, although the trimer was more effective than the dimer. Notably, the Herceptin trimer also induced Herceptin-resistant tumor cell death. Surprisingly different from the known cell death mechanism that often results from antibody treatment, the Herceptin trimer elicited effective and direct tumor cell death via a novel mechanism: programmed cell necrosis. In Her2-positive cells, inhibition of necrosis pathways significantly reversed Herceptin trimer-induced cell death. In summary, the Herceptin trimer reported herein harbors great potential for overcoming tumor cell resistance to Herceptin treatment.

IQGAP1 protein binds human epidermal growth factor receptor 2 (HER2) and modulates trastuzumab resistance

Human epidermal growth factor receptor 2 (HER2) is overexpressed in 20-25% of breast cancers. Increased HER2 expression is an adverse prognostic factor and correlates with decreased patient survival. HER2-positive (HER2(+)) breast cancer is treated with trastuzumab. Unfortunately, some patients are intrinsically refractory to therapy, and many who do respond initially become resistant within 1 year. Understanding the molecular mechanisms underlying HER2 signaling and trastuzumab resistance is essential to reduce breast cancer mortality. IQGAP1 is a ubiquitously expressed scaffold protein that contains multiple protein interaction domains. By regulating its binding partners IQGAP1 integrates signaling pathways, several of which contribute to breast tumorigenesis. We show here that IQGAP1 is overexpressed in HER2(+) breast cancer tissue and binds directly to HER2. Knockdown of IQGAP1 decreases HER2 expression, phosphorylation, signaling, and HER2-stimulated cell proliferation, effects that are all reversed by reconstituting cells with IQGAP1. Reducing IQGAP1 up-regulates p27, and blocking this increase attenuates the growth inhibitory effects of IQGAP1 knockdown. Importantly, IQGAP1 is overexpressed in trastuzumab-resistant breast epithelial cells, and reducing IQGAP1 both augments the inhibitory effects of trastuzumab and restores trastuzumab sensitivity to trastuzumab-resistant SkBR3 cells. These data suggest that inhibiting IQGAP1 function may represent a rational strategy for treating HER2(+) breast carcinoma.

Adjuvant effect of HER-2/neu-specific adenoviral vector stimulating CD8⁺ T and natural killer cell responses on anti-HER-2/neu antibody therapy for well-established breast tumors in HER-2/neu transgenic mice

Approximately one third of patients with advanced human epidermal growth factor receptor 2 (HER-2)/neu-positive breast cancer respond to trastuzumab monotherapy, a humanized anti-HER-2/neu antibody. However, de novo and acquired antibody resistance is one of the major limitations of trastuzumab therapy warranting the search for other therapeutic strategies. One of the most remarkable features of adenovirus (AdV)-based vaccine is its ability to induce exceptionally high and sustained frequencies of transgene product-specific CD8(+) T-cell responses. In this study, we constructed two recombinant AdVs (AdV(OVA) and AdV(HER-2)) expressing ovalbumin (OVA) and HER-2/neu, and assessed AdV-induced antigen-specific cellular immune responses and preventive/therapeutic antitumor immunity. We demonstrate that AdV(OVA) stimulates efficient OVA-specific CD8(+) cytotoxic T lymphocyte (CTL) and natural killer responses, leading to preventive long-term immunity against OVA-expressing BL6-10ova melanoma in wild-type C56BL/6 mice. We further demonstrate that AdV(HER-2) stimulates HER-2/neu-specific CD8(+) CTL responses, leading to a significant reduction in breast carcinogenesis in transgenic FVBneuN mice (P<0.05), but has little therapeutic effect on pre-existing Tg1-1 tumor even at early stage (15 mm(3)). In contrast, the anti-HER-2/neu antibody therapy is capable of completely inhibiting Tg1-1 tumor growth at early stage, but fails to eradicate well-established Tg1-1 breast tumor (100 mm(3)). Interestingly, a combinatorial immunotherapy of anti-HER-2/neu antibody with AdV(HER-2) vaccine was capable of curing 4 of 10 studied mice bearing well-established Tg1-1 breast tumors and significantly delaying in death of the remaining six tumor-bearing mice (P<0.05). Taken together, our results suggest an adjuvant effect of AdV(HER-2) on anti-HER-2/neu antibody therapy for well-established breast tumor in transgenic FVBneuN mice, and this combinatorial immunotherapy of trastuzumab with AdV(HER-2) vaccine may be used as a new therapeutic strategy for treatment of advanced HER-2/neu-positive breast cancer.

Prognostic impact of phosphorylated HER-2 in HER-2+ primary breast cancer

PURPOSE

Tyrosine 1248 is one of the autophosphorylation sites of human epidermal growth factor receptor (HER)-2. We determined the prognostic value of the expression level of tyrosine 1248-phosphorylated HER-2 (pHER-2) in patients with HER-2(+) primary breast cancer using a reverse-phase protein array.

PATIENTS AND METHODS

The optimal cutoff value of pHER-2 for segregating disease-free survival (DFS) was determined by receiver operating characteristic (ROC) curve analysis. Five-year DFS for pHER-2 expression level was estimated with the Kaplan-Meier method using both derivation (n = 162) and validation (n = 227) cohorts.

RESULTS

Of the 162 patients in the derivation cohort, 26 had high HER-2 expression levels. The area under the ROC curve for pHER-2 level and DFS was 0.662. Nineteen of the 162 patients (11.7%) had high pHER-2 expression levels (pHER-2(high)); 143 patients (88.3%) had low pHER-2 expression levels (pHER-2(low)). Among the 26 patients with high HER-2 expression levels, the 17 pHER-2(high) patients had a significantly lower 5-year DFS rate than the nine pHER-2(low) patients (23.5% versus 77.8%). On multivariate analysis, only pHER-2(high) independently predicted DFS in the Cox proportional hazards model. In the validation cohort, among 61 patients with high HER-2 expression, the difference in 5-year DFS rates between pHER-2(high) (n = 7) and pHER-2(low) (n = 54) patients was marginal (57.1% versus 81.5%).

CONCLUSION

In patients with HER-2(+) primary breast cancer, pHER-2(high) patients had a lower 5-year DFS rate than pHER-2(low) patients. Quantification of pHER-2 expression level may provide prognostic information beyond the current standard HER-2 status.

Effects of an Engineered Anti-HER2 Antibody chA21 on Invasion of Human Ovarian Carcinoma Cell In Vitro

OBJECTIVE

HER-2 plays an important role in the development and progression of ovarian carcinoma. A number of monoclonal antibodies (MAbs) and engineered antibody fragments (such as scFvs) against the subdomain II or IV of HER-2 extracellular domain (ECD) have been developed. We investigated the effect of chA21, an engineered anti-HER-2 antibody that bind primarily to subdomain I, on ovarian carcinoma cell invasion in vitro, and explored its possible mechanisms.

METHODS

Growth inhibition of SK-OV-3 cells was assessed using a Methyl thiazolyl tetrazolium (MTT) assay. The invasion ability of SK-OV-3 was determined by a Transwell invasion assay. The expression of matrix metalloproteinase-2 (MMP-2) and its tissue inhibitors (TIMP-2) was detected by immunocytochemical staining, and the expression of p38 and the phosphorylation of p38 were assayed by both immunocytochemistry and Western blot.

RESULTS

After treatment with chA21, the invasion of human ovarian cancer SK-OV-3 cells was inhibited in dose- and time-dependent manners. Simultaneously the expression of p38, phospho-p38, MMP-2 and the MMP-2/TIMP-2 ratio decreased, while TIMP-2 expression increased. Additionally, the decrease in phospho-p38 was much greater than that of p38.

CONCLUSION

chA21 may inhibit SK-OV-3 cell invasion via the signal transduction pathway involving MMP-2, TIMP-2, p38 and the activation of p38MAPK.

HSP90 inhibition is effective in breast cancer: a phase II trial of tanespimycin (17-AAG) plus trastuzumab in patients with HER2-positive metastatic breast cancer progressing on trastuzumab

PURPOSE

HSP90 is a chaperone protein required for the stability of a variety of client proteins. 17-Demethoxygeldanamycin (17-AAG) is a natural product that binds to HSP90 and inhibits its activity, thereby inducing the degradation of these clients. In preclinical studies, HER2 is one of the most sensitive known client proteins of 17-AAG. On the basis of these data and activity in a phase I study, we conducted a phase II study of 17-AAG (tanespimycin) with trastuzumab in advanced trastuzumab-refractory HER2-positive breast cancer.

EXPERIMENTAL DESIGN

We enrolled patients with metastatic HER2(+) breast cancer whose disease had previously progressed on trastuzumab. All patients received weekly treatment with tanespimycin at 450 mg/m(2) intravenously and trastuzumab at a conventional dose. Therapy was continued until disease progression. The primary endpoint was response rate by Response Evaluation Criteria in Solid Tumors (RECIST) criteria.

RESULTS

Thirty-one patients were enrolled with a median age of 53 years and a median Karnofsky performance status (KPS) of 90%. The most common toxicities, largely grade 1, were diarrhea, fatigue, nausea, and headache. The overall response rate was 22%, the clinical benefit rate [complete response + partial response + stable disease] was 59%, the median progression-free survival was 6 months (95% CI: 4-9), and the median overall survival was 17 months (95% CI: 16-28).

CONCLUSIONS

This is the first phase II study to definitively show RECIST-defined responses for 17-AAG in solid tumors. Tanespimycin plus trastuzumab has significant anticancer activity in patients with HER2-positive, metastatic breast cancer previously progressing on trastuzumab. Further research exploring this therapeutic interaction and the activity of HSP90 inhibitors is clearly warranted.

Combining emerging agents in advanced breast cancer

Newer treatments have improved survival for patients with metastatic breast cancer over the last two decades, and a battery of new cytotoxic and targeted therapies is continuing to enhance this trend. This review outlines recent data and ongoing research in this area, by highlighting new developments (regarding approved but relatively new classes of cytotoxic and targeted agents) and also new classes of targeted therapy that are undergoing clinical evaluation. Mechanisms for synergy between agents are discussed where data are available, as is information on the rationale behind the development of agents that inhibit angiogenesis, DNA repair, histone deacetylases, heat shock proteins, or various signaling pathways in tumor proliferation. The abundance of clinical research surrounding anticancer agents, together with ongoing cancer biology research, is expected to further increase the available pool of therapeutic options for metastatic breast cancer. Concomitantly, in the absence of an effective targeted monotherapy, a better understanding of the interplay between biologic and cytotoxic anticancer agents will improve our ability to rationally design combination regimens with better efficacy and tolerability.

Synergy between inhibitors of androgen receptor and MEK has therapeutic implications in estrogen receptor-negative breast cancer

INTRODUCTION

Estrogen receptor-negative (ER-) breast cancer is a heterogeneous disease with limited therapeutic options. The molecular apocrine subtype constitutes 50% of ER-tumors and is characterized by overexpression of steroid response genes including androgen receptor (AR). We have recently identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in the molecular apocrine subtype. In this feedback loop, AR regulates ERK phosphorylation through the mediation of ErbB2 and, in turn, ERK-CREB1 signaling regulates the transcription of AR in molecular apocrine cells. In this study, we investigated the therapeutic implications of the AR-ERK feedback loop in molecular apocrine breast cancer.

METHODS

We examined a synergy between the AR inhibitor flutamide and the MEK inhibitor CI-1040 in the molecular apocrine cell lines MDA-MB-453, HCC-1954 and HCC-202 using MTT cell viability and annexin V apoptosis assays. Synergy was measured using the combination index (CI) method. Furthermore, we examined in vivo synergy between flutamide and the MEK inhibitor PD0325901 in a xenograft model of the molecular apocrine subtype. The effects of in vivo therapies on tumor growth, cell proliferation and angiogenesis were assessed.

RESULTS

We demonstrate synergistic CI values for combination therapy with flutamide and CI-1040 across three molecular apocrine cell lines at four dose combinations using both cell viability and apoptosis assays. Furthermore, we show in vivo that combination therapy with flutamide and MEK inhibitor PD0325901 has a significantly higher therapeutic efficacy in reducing tumor growth, cellular proliferation and angiogenesis than monotherapy with these agents. Moreover, our data suggested that flutamide and CI-1040 have synergy in trastuzumab resistance models of the molecular apocrine subtype. Notably, the therapeutic effect of combination therapy in trastuzumab-resistant cells was associated with the abrogation of an increased level of ERK phosphorylation that was developed in the process of trastuzumab resistance.

CONCLUSIONS

In this study, we demonstrate in vitro and in vivo synergies between AR and MEK inhibitors in molecular apocrine breast cancer. Furthermore, we show that combination therapy with these inhibitors can overcome trastuzumab resistance in molecular apocrine cells. Therefore, a combination therapy strategy with AR and MEK inhibitors may provide an attractive therapeutic option for the ER-/AR+ subtype of breast cancer.

Evasion mechanisms to Igf1r inhibition in rhabdomyosarcoma

Inhibition of the insulin-like growth factor 1 receptor (Igf1r) is an approach being taken in clinical trials to overcome the dismal outcome for metastatic alveolar rhabdomyosarcoma (ARMS), an aggressive muscle cancer of children and young adults. In our study, we address the potential mechanism(s) of Igf1r inhibitor resistance that might be anticipated for patients. Using a genetically engineered mouse model of ARMS, validated for active Igf1r signaling, we show that the prototypic Igf1r inhibitor NVP-AEW541 can inhibit cell growth and induce apoptosis in vitro in association with decreased Akt and Mapk phosphorylation. However, drug resistance in vivo is more common and is accompanied by Igf1r overexpression, Mapk reactivation, and Her2 overexpression. Her2 is found to form heterodimers with Igf1r in resistant primary tumor cell cultures, and stimulation with Igf2 leads to Her2 phosphorylation. The Her2 inhibitor lapatinib cooperates with NVP-AEW541 to reduce Igf1r phosphorylation and to inhibit cell growth even though lapatinib alone has little effect on growth. These results point to the potential therapeutic importance of simultaneous targeting of Igf1r and Her2 to abrogate resistance.

Combination of epitope-optimized DNA vaccination and passive infusion of monoclonal antibody against HER2/neu leads to breast tumor regression in mice

HER2/neu is an oncogene amplified and over-expressed in 20-30% of breast adenocarcinomas. Treatment with the humanized monoclonal antibody trastuzumab has shown efficacy in combination with cytotoxic agents, although resistance occurs over time. Novel approaches are needed to further increase antibody efficacy. In this study, we provide evidence in a mouse breast cancer therapeutic tumor model that the combination of active immunization with a modified HER2/neu DNA vaccine and passive infusion of an anti-HER2/neu monoclonal antibody leads to significant regression of established tumors. Our data indicate that combination therapy with a HER2/neu DNA vaccine and trastuzumab may have clinical activity in breast cancer patients.

Epidermal growth factor regulates Mcl-1 expression through the MAPK-Elk-1 signalling pathway contributing to cell survival in breast cancer

Myeloid cell leukaemia-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family that is elevated in a variety of tumour types including breast cancer. In breast tumours, increased Mcl-1 expression correlates with high tumour grade and poor patient survival. We have previously demonstrated that Her-2 levels correspond to increased Mcl-1 expression in breast tumours. Epidermal growth factor (EGF) receptor signalling is frequently deregulated in breast cancer and leads to increased proliferation and survival. Herein, we determined the critical downstream signals responsible for the EGF mediated increase of Mcl-1 and their role in cell survival. We found that both Mcl-1 mRNA and protein levels are rapidly induced upon stimulation with EGF. Promoter analysis revealed that an Elk-1 transcription factor-binding site is critical for EGF activation of the Mcl-1 promoter. Furthermore, we found that knockdown of Elk-1or inhibition of the Erk signalling pathway was sufficient to block EGF upregulation of Mcl-1 and EGF mediated cell survival. Using chromatin immunoprecipitation and biotin labelled probes of the Mcl-1 promoter, we found that Elk-1 and serum response factor are bound to the promoter after EGF stimulation. To determine whether Mcl-1 confers a survival advantage, we found that knockdown of Mcl-1 expression increased apoptosis whereas overexpression of Mcl-1 inhibited drug induced cell death. In human breast tumours, we found a correlation between phosphorylated Elk-1 and Mcl-1 protein levels. These results indicate that the EGF induced activation of Elk-1 is an important mediator of Mcl-1 expression and cell survival and therefore a potential therapeutic target in breast cancer.

Anticancer activity of Celastrol in combination with ErbB2-targeted therapeutics for treatment of ErbB2-overexpressing breast cancers

The receptor tyrosine kinase ErbB2 is overexpressed in up to a third of breast cancers, allowing targeted therapy with ErbB2-directed humanized antibodies such as Trastuzumab. Concurrent targeting of ErbB2 stability with HSP90 inhibitors is synergistic with Trastuzumab, suggesting that pharmacological agents that can inhibit HSP90 as well as signaling pathways activated by ErbB2 could be useful against ErbB2-overexpressing breast cancers. The triterpene natural product Celastrol inhibits HSP90 and several pathways relevant to ErbB2-dependent oncogenesis including the NFκB pathway and the proteasome, and has shown promising activity in other cancer models. Here, we demonstrate that Celastrol exhibits in vitro antitumor activity against a panel of human breast cancer cell lines with selectivity towards those overexpressing ErbB2. Celastrol strongly synergized with ErbB2-targeted therapeutics Trastuzumab and Lapatinib, producing higher cytotoxicity with substantially lower doses of Celastrol. Celastrol significantly retarded the rate of growth of ErbB2-overexpressing human breast cancer cells in a mouse xenograft model with only minor systemic toxicity. Mechanistically, Celastrol not only induced the expected ubiquitinylation and degradation of ErbB2 and other HSP90 client proteins, but it also increased the levels of reactive oxygen species (ROS). Our studies show that the Michael Acceptor functionality in Celastrol is important for its ability to destabilize ErbB2 and exert its bioactivity against ErbB2-overexpressing breast cancer cells. These studies suggest the potential use of Michael acceptor-containing molecules as novel therapeutic modalities against ErbB2-driven breast cancer by targeting multiple biological attributes of the driver oncogene.

Shift in cytotoxic target from estrogen receptor-positive to estrogen receptor-negative breast cancer cells by trastuzumab in combination with taxane-based chemotherapy

Trastuzumab has shown significant clinical benefits in patients with operable and metastatic HER2-positive breast cancer. However, the biological mechanism of the additional effect of trastuzumab administered in combination with conventional chemotherapy is poorly understood. We performed a retrospective analysis of 55 patients with HER2-positive breast cancer treated with anthracycline and taxane (chemotherapy alone; CT), or trastuzumab in combination with taxane-based chemotherapy (CT+T) for neoadjuvant chemotherapy. We determined the therapeutic efficacies [clinical (CR) and pathological complete responses (pCR)] and changes in the proportion of positive cells for each biomarker pre- to post-neoadjuvant chemotherapy for each treatment regimen. Clinical-CR and quasi-pCR rates defined as the absence of invasive tumors or only a few remaining invasive tumor cells were 6.9 and 31.0% in the CT group and 46.2 and 65.4% in the CT+T group, respectively. In the CT group, the proportion of estrogen receptor (ER)-/progesterone receptor (PgR)-positive cells decreased significantly following treatment (ER, 73.5 vs. 50.9%; P=0.02). Changes in the proportion of ER-/PgR-positive cells were not noted in the CT+T group (ER, 81.9 vs. 80.3%; P=0.61), although a relatively greater decrease in the proportion of Ki-67-positive cells was found in the CT+T group than that in the CT group (-26.5 vs. -13.7%). These findings indicate that CT+T inhibits ER-negative and Ki-67-positive breast cancer cells. In conclusion, trastuzumab sensitized ER-negative proliferative cells to cytotoxic chemotherapy. This finding may indicate an additional clinical effect of trastuzumab when administered in combination with conventional chemotherapy as neoadjuvant chemotherapy for HER2-positive breast cancer.

Her2-targeted therapies for gastric cancer

Gastric cancer is one of the most common malignancies and represents a major cause of cancer-related death in China. Her2 plays an important role in the activation of Her/ErbB family receptors and post-receptor signal transduction events. The rates of Her2 expression in gastric cancer range from 11.9% to 23.7%. Her2 expression correlates with Laruen's classification, location of primary tumor, and poor outcome in gastric cancer. Her2-targeted therapeutic strategies include the use of monoclonal antibodies and small molecule tyrosine kinase inhibitors. ToGA study is the first phase III randomized clinical trial to evaluate the efficacy and safety of trastuzumab, an anti-Her2 monoclonal antibody, in the first-line treatment of advanced and metastatic gastric cancer. Interestingly, trastuzumab could remarkably prolong the median overall survival of patients with gastric cancer to 13.8 mo. However, this trial also triggers much controversy over Her2-targeted therapies for gastric cancer.