Her2/neu extracellular domain shedding in uterine serous carcinoma: implications for immunotherapy with trastuzumab

Narrative review on the evolving role of HER2/neu targeting in uterine serous cancers

Background and Objective

Serous endometrial cancers (ECs) are an aggressive histotype of ECs which are disproportionately responsible for 40% of cancer-specific mortality rates despite constituting only 5-10% of all uterine cancers in incidence. In recent times, it has become increasingly evident that about 20-40% of uterine serous cancers (USCs) have molecular alterations in ERBB2 pathway with human epidermal growth factor receptor 2 (HER2/neu) amplification or overexpression. We summarise the evidence on genetic and molecular alterations in HER2/neu pathway in USC with a focus on testing criteria, targeting agents and resistance mechanisms.

Methods

We conducted a database search of PubMed/Medline up to 28th February 2023 for articles published in the English language using pre-defined search terms. One hundred and seventy-one relevant articles were subsequently reviewed for eligibility and inclusion in the review.

Key Content and Findings

The Cancer Genome Atlas (TCGA) classification is a significant development in the molecular profiling of ECs with a positive impact on the treatment of these tumors including USCs. Testing criteria for HER2/neu in USC with immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) has evolved in more than a decade with progress made towards EC specific testing guidelines. The findings of a recent phase III study have led to the development of practice changing guidelines towards improving patient outcomes.

Conclusions

Molecular aberration in the HER2/neu pathway contributes to the aggressive behaviour of USC. Considering the clinical benefit conferred by HER2/neu targeted therapy, HER2/neu testing is recommended for all cases of serous EC in advanced and recurrent settings. Trastuzumab in combination with platinum and taxanes based chemotherapy is the recommended treatment option for patients with advanced or recurrent serous cancers who test positive to HER2/neu. Clinical trials on targeted therapy are ongoing and future research should focus on selection of patients who will derive the most benefit from such therapy.

In Vivo and In Vitro Efficacy of Trastuzumab Deruxtecan in Uterine Serous Carcinoma

Uterine serous carcinoma (USC) is a rare, biologically aggressive variant of endometrial cancer with a high recurrence rate and poor prognosis. HER2 overexpression (3+ positivity) by IHC and/or FISH ERBB2 gene amplification is detected in approximately one-third of patients with USC. Clinical trials incorporating trastuzumab with standard chemotherapy have recently demonstrated improved progression-free and overall survival in advanced-stage or recurrent USC that overexpresses HER2. However, a large number of patients with USC eventually developed resistance to trastuzumab. Trastuzumab deruxtecan (T-DXd) is a novel HER2-directed antibody-drug conjugate with a topoisomerase I inhibitor payload recently approved by the Food and Drug Administration (FDA) for multiple tumor indications. Here, we investigated the in vitro and in vivo efficacy of T-DXd in primary USC cell lines and xenografts with different HER2 expression. T-DXd-induced cell growth suppression in HER2-overexpressing cell lines in vitro, increased early and late apoptosis as assessed by annexin and propidium iodide staining, and, similarly to trastuzumab, T-DXd-induced significant antibody-dependent cellular cytotoxicity in the presence of peripheral blood lymphocytes. While negligible activity was detected against USC cell lines with low HER2 expression, T-DXd demonstrated significant bystander killing against USC tumors with low/negligible HER2 when such cells were admixed with HER2 3+ tumor cells in vitro. T-DXd showed tumor growth suppression in in vivo USC PDX models that overexpress HER2 at 3+ levels, prolonging survival when compared with controls, with minimal toxicity. Future clinical trials are warranted in patients with USC failing trastuzumab treatment.

HER2 Oncogene as Molecular Target in Uterine Serous Carcinoma and Uterine Carcinosarcoma

Uterine serous carcinoma (USC) and uterine carcinosarcoma (UCS) are two rare histologic variants of uterine carcinoma, with distinct molecular profiles and aggressive metastatic potential. As the effectivity of traditional platinum-based chemotherapy for USC and UCS is low, and there are high rates of resistance and recurrence, the development of novel targeted therapeutics is needed. Human epidermal growth factor receptor 2 (HER2) has proven to be an oncogene of increasing interest in these cancers, as HER2 protein overexpression and/or c-ERBB2 gene amplification ranges from ~30 to 35% in USC, and between ~15 and 20% in UCS. This review summarizes the existing clinical and preclinical evidence, as well as ongoing clinical trials of HER2-targeting therapeutics, and identifies potential areas of further development and inquiry.

Trastuzumab deruxtecan in recurrent uterine serous carcinoma resistant to trastuzmab based-chemotherapy

Background

Treatment of uterine serous carcinoma (USC) is challenging; effective treatment options for metastatic and recurrent disease are needed.

Case

A 68-year-old woman with recurrent, metastatic, USC overexpressing HER2/neu experienced durable response to the antibody drug conjugate (ADC) trastuzumab-deruxtecan (T-DXd), after failing multiple standard and experimental treatments targeting HER2/neu. She experienced a significant reduction in disease burden, disappearance of metastatic back bone pain as well as normalization of CA-125 quickly after starting treatment. Her disease continued to show response to treatment over 5 months and 7 cycles of T-DXd therapy. She did not experience any dose-limiting side effects and tolerated treatment with 5.4 mg/kg T-DXd without issue.

Conclusion

T-DXd may present a new treatment option for chemotherapy-resistant uterine serous carcinoma.

Inhibition of DPAGT1 suppresses HER2 shedding and trastuzumab resistance in human breast cancer

Human epidermal growth factor receptor 2-targeted (HER2-targeted) therapy is the mainstay of treatment for HER2+ breast cancer. However, the proteolytic cleavage of HER2, or HER2 shedding, induces the release of the target epitope at the ectodomain (ECD) and the generation of a constitutively active intracellular fragment (p95HER2), impeding the effectiveness of anti-HER2 therapy. Therefore, identifying key regulators in HER2 shedding might provide promising targetable vulnerabilities against resistance. In the current study, we found that upregulation of dolichyl-phosphate N-acetylglucosaminyltransferase (DPAGT1) sustained high-level HER2 shedding to confer trastuzumab resistance, which was associated with poor clinical outcomes. Upon trastuzumab treatment, the membrane-bound DPAGT1 protein was endocytosed via the caveolae pathway and retrogradely transported to the ER, where DPAGT1 induced N-glycosylation of the sheddase - ADAM metallopeptidase domain 10 (ADAM10) - to ensure its expression, maturation, and activation. N-glycosylation of ADAM10 at N267 protected itself from ER-associated protein degradation and was essential for DPAGT1-mediated HER2 shedding and trastuzumab resistance. Importantly, inhibition of DPAGT1 with tunicamycin acted synergistically with trastuzumab treatment to block HER2 signaling and reverse resistance. These findings reveal a prominent mechanism for HER2 shedding and suggest that targeting DPAGT1 might be a promising strategy against trastuzumab-resistant breast cancer.

HER2 Signaling in Breast Cancer

HER2 gene amplification occurs in many breast cancer patients and is associated with poor clinical prognosis. Trastuzumab is a therapeutic monoclonal antibody binding to HER2 and inhibits growth of HER2-positive breast cancer cells and used as a principal treatment for HER2-positive breast cancer. Unfortunately, some HER2-positive breast cancers eventually relapse after trastuzumab treatment. To investigate the molecular mechanism of trastuzumab resistance, we generated trastuzumab-resistant cells using a mouse model and found ECM1 protein is increased in trastuzumab-resistant cells. ECM1 was shown to increase EGFR signaling via upregulated matrix metalloproteinase 9/galectin-3/mucin pathway. To further find the novel mediators of HER2-driven signaling pathways in breast cancer, we investigated the upregulated proteins in HER2-overexpressing breast cancer cells using a proteomics approach and found that KRT19 is strongly upregulated in HER2-positive breast cancer cells and it activates HER2 signaling by binding to HER2 and stabilizes the receptor on the cell membrane. Moreover, we found that treatment of KRT19 antibody resulted in reduced cell viability of trastuzumab-resistant HER2-positive breast cancer cells as well as trastuzumab-sensitive cancer cells both in vitro and in vivo.

Overcoming trastuzumab resistance in HER2-positive breast cancer using combination therapy

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) comprises around 20-30% of all BC subtypes and is correlated with poor prognosis. For many years, trastuzumab, a monoclonal antibody, has been used to inhibit the HER2 activity. Though, the main resistance to trastuzumab has challenged the use of this drug in the management of HER2-positive BC. Therefore, the determination of resistance mechanisms and the incorporation of new agents may lead to the development of a better blockade of the HER family receptor signaling. During the last few years, some therapeutic drugs have been developed for treating patients with trastuzumab-resistant HER2-positive BC that have more effective influences in the management of this condition. In this regard, the present study aimed at reviewing the mechanisms of trastuzumab resistance and the innovative therapies that have been investigated in trastuzumab-resistant HER2-positive BC subjects.

Targeting human epidermal growth factor receptor 2 (HER2) in gynecologic malignancies

PURPOSE OF REVIEW

The purpose of this review is to describe the role of the human epidermal growth factor receptor 2 (HER2) as a biomarker and potential target in gynecologic malignancies and to describe contemporary updates in the use of anti-HER2 treatments for these cancers.

RECENT FINDINGS

Approximately 25-30% of all patients with uterine serous carcinoma overexpress tumoral HER2. The anti-HER2 antibody trastuzumab represents an effective, targeted therapy with significant efficacy in the treatment of HER2-positive breast and gastric cancer. Recently, trastuzumab efficacy has also been demonstrated in a randomized controlled trial of women with advanced or recurrent uterine serous carcinoma. Additionally, trastuzumab may be effective in women with HER2-positive uterine carcinosarcoma. The role of anti-HER2 therapy is unclear in women with other gynecologic malignancies but is being evaluated.

SUMMARY

HER2 amplification/overexpression is an effective therapeutic target in select gynecologic malignancies, and especially in the rare endometrial cancer subtype, uterine serous carcinoma. As anti-HER2-targeted therapies become increasingly available, more treatment options may become available for women with HER2-positive disease.

PI3K oncogenic mutations mediate resistance to afatinib in HER2/neu overexpressing gynecological cancers

OBJECTIVE

Aberrant expression of HER2/neu and PIK3CA gene products secondary to amplification/mutations are common in high-grade-serous-endometrial (USC) and ovarian-cancers (HGSOC). Because scant information is currently available in the literature on the potential negative effect of PIK3CA mutations on the activity of afatinib, in this study we evaluate for the first time the role of oncogenic PIK3CA mutations as a potential mechanism of resistance to afatinib in HGSOC and USC overexpressing HER2/neu.

METHODS

We used six whole-exome-sequenced primary HGSOC/USC cell-lines and three xenografts overexpressing HER2/neu and harboring mutated or wild-type PIK3CA/PIK3R1 genes to evaluate the role of PI3K-mutations as potential mechanism of resistance to afatinib, an FDA-approved pan-c-erb-inhibitor in clinical trials in USC. Primary-USC harboring wild-type-PIK3CA gene was transfected with plasmids encoding oncogenic PIK3CA-mutations (H1047R/E545K). The effect of afatinib on HER2/PI3K/AKT/mTOR pathway was evaluated by immunoblotting.

RESULTS

We found PI3K wild-type cell-lines to be significantly more sensitive (lower IC₅₀) than PI3K-mutated cell-lines p = 0.004). In vivo, xenografts of primary cell-line USC-ARK2, transfected with the PIK3CA-H1047R or E545K hotspot-mutations, exhibited significantly more rapid tumor growth when treated with afatinib, compared to mice harboring ARK2-tumors transfected with wild-type-PIK3CA (p = 0.041 and 0.001, respectively). By western-blot, afatinib effectively reduced total and phospho-HER2 proteins in all cell-lines. However, H1047R/E545K-PIK3CA-transfected-ARK2-cells demonstrated a greater compensatory increase in phosphorylated-AKT proteins after afatinib exposure when compared to controls ARK2.

CONCLUSIONS

Oncogenic PI3K mutations may represent a major mechanism of resistance to afatinib. Combinations of c-erb with PIK3CA, AKT or mTOR inhibitors may be necessary to more efficiently block the PIK3CA/AKT/mTOR pathway.

Moving forward with actionable therapeutic targets and opportunities in endometrial cancer: NCI clinical trials planning meeting report on identifying key genes and molecular pathways for targeted endometrial cancer trials

The incidence and mortality rates from endometrial cancer are increasing. There have been no new drugs approved for the treatment of endometrial cancer in decades. The National Cancer Institute, Gynecologic Cancer Steering Committee identified the integration of molecular and/or histologic stratification into endometrial cancer management as a top strategic priority. Based on this, they convened a group of experts to review the molecular data in this disease. Here we report on the actionable opportunities and therapeutic directions identified for incorporation into future clinical trials.

A Tri-part Protein Complementation System Using Antibody-Small Peptide Fusions Enables Homogeneous Immunoassays

Protein-fragment complementation is a valuable tool for monitoring protein interactions. In complementation assays, the reporter fragments are directly fused to the interacting proteins, eliminating the possibility of monitoring native interactions. In principle, complementation could be achieved by placing the reporter fragments on antibodies which bind to the proteins of interest, enabling the monitoring of endogenous protein interactions or detection of a single protein in a homogeneous immunoassay. Previous reports have demonstrated proof-of-concept of this approach; however, current complementation systems have not met the practical requirements as suitable fusion partners for antibodies while providing the sensitivity needed for immunoassays. To surmount these challenges, we created a first-in-class, tri-part split luciferase consisting of two 11-residue peptides that are used as the antibody appendages. As an initial proof-of-concept, we used antibody-peptide fusions and found them to be capable of quantifying pg/mL concentrations of soluble or cell-bound HER2, proving this unique complementation system overcomes previous limitations and transforms this approach from merely possible to practical and useful. As shown herein, this dual-peptide system provides a rapid, simple, and sensitive "add-and-read" homogeneous immunoassay platform that can be broadly adapted as an alternative to traditional immunoassays, and in the future should enable complementation to be expanded to monitoring endogenous protein interactions.

Objective, domain-specific HER2 measurement in uterine and ovarian serous carcinomas and its clinical significance

Introduction

HER2 overexpression/amplification is identified in up to 40% of uterine serous carcinomas (USC) and 10% of ovarian serous carcinomas (OSC). However, clinical trials using various HER2-targeted agents failed to show significant responses. FDA-approved HER2 assays target only the protein's intracellular domain (ICD) and not the extracellular domain (ECD). Previous quantitative studies in breast cancer by our group have shown that ICD of HER2 is expressed in some cases that do not express the HER2 ECD. We measured HER2 ICD and ECD in USC and OSC samples, and determined their relationship with clinico-pathologic characteristics and survival.

Methods

We measured HER2 ICD and ECD levels in 2 cohorts of USC and OSC comprising 102 and 175 patients, respectively. HER2 antibodies targeting ICD (CB11) and ECD (SP3) were validated and standardized using the AQUA® method of quantitative immunofluorescence (QIF) and a previously reported HER2 standardization tissue microarray (TMA). Objective, population-based cut-points were used to stratify patients according to HER2 ICD/ECD status.

Results

In USC, 8% of patients with high HER2 ICD had low ECD levels (6/75 patients). In OSC, 42% of patients with high HER2 ICD had low ECD levels (29/69 patients). HER2 ICD/ECD status in USC and OSC was not significantly associated with major clinico-pathological features or survival.

Conclusion

Using objective, domain-specific HER2 measurement, 8% of USC and 42% of OSC patients with high HER2 ICD levels do not show uniform overexpression of the ECD. This may be related to the presence of p95 HER2, an oncogenic fragment generated by full protein cleavage or alternative initiation of translation. These observations raise the possibility that USC/OSCs expressing low ECD despite being HER2-positive by ICD measurement, may benefit from therapies directed against the intracellular domain (e.g. lapatinib or afatinib) alone or in combination with extracellular domain-directed drugs (e.g. trastuzumab, pertuzumab, T-DM1).

Systematic assessment of HER2/neu in gynecologic neoplasms, an institutional experience

BACKGROUND

HER2/neu overexpression and/or amplification has been widely studied in a number of solid tumors, primarily in the breast. In gynecologic neoplasms, determination of HER2/neu status has not been well studied as a predictive biomarker in anti-HER2/neu treatment.

METHODS

We systematically evaluated the HER2/neu reactions by immunohistochemistry and fluorescent in situ hybridization in malignant gynecologic neoplasms as experienced in our institution.

RESULTS

The HER2/neu overexpression or amplification occurred in 8 % of the cancers of the gynecological organs in our series. Majority of the HER2/neu overexpression and/or amplification occurred in clear cell (27 %) and serous (11 %) carcinomas. HER2/neu positivity was also seen in undifferentiated as well as in mixed clear cell and serous carcinomas. Discordant IHC and FISH results (positive by FISH but not IHC) was seen in 2 cases. Majority of the HER2/neu overexpression and/or amplification occurs in the endometrium rather than the ovary. Heterogeneity of the HER2/neu by IHC staining was in < 2 % of the tumors in our series.

CONCLUSIONS

We recommend the HER2/neu studies on Müllerian carcinomas of clear cell, serous, and undifferentiated types, particularly when they arise in the endometrium. Since there are some discordant IHC/FISH results, we also propose performing the HER2/neu testing by FISH when the IHC score is less than 3 + .

Selecting Targets for Tumor Imaging: An Overview of Cancer-Associated Membrane Proteins

Tumor targeting is a booming business: The global therapeutic monoclonal antibody market accounted for more than $78 billion in 2012 and is expanding exponentially. Tumors can be targeted with an extensive arsenal of monoclonal antibodies, ligand proteins, peptides, RNAs, and small molecules. In addition to therapeutic targeting, some of these compounds can also be applied for tumor visualization before or during surgery, after conjugation with radionuclides and/or near-infrared fluorescent dyes. The majority of these tumor-targeting compounds are directed against cell membrane-bound proteins. Various categories of targetable membrane-bound proteins, such as anchoring proteins, receptors, enzymes, and transporter proteins, exist. The functions and biological characteristics of these proteins determine their location and distribution on the cell membrane, making them more, or less, accessible, and therefore, it is important to understand these features. In this review, we evaluate the characteristics of cancer-associated membrane proteins and discuss their overall usability for cancer targeting, especially focusing on imaging applications.

Ridaforolimus improves the anti-tumor activity of dual HER2 blockade in uterine serous carcinoma in vivo models with HER2 gene amplification and PIK3CA mutation

OBJECTIVE

Uterine serous carcinomas (USC) harbor simultaneous HER2 (ERBB2) over-expression and gain of function mutations in PIK3CA. These concurrent alterations may uncouple single agent anti-HER2 therapeutic efficacy making inhibition of the mammalian target of rapamycin (mTOR) a promising option to heighten anti-tumor response.

METHODS

Both in vitro and in vivo experiments were conducted to assess proliferation, cell death and anti-tumor activity of ridaforolimus, lapatinib and combination lapatinib, trastuzumab (L/T) and ridaforolimus. With institutional approval, NOD/SCID mice bearing xenografts of non-immortalized, HER2 gene amplified cell lines (ARK1, ARK2) with and without PIK3CA gene mutations were divided into four arm cohorts. Ridaforolimus was administered alone and in combination with L/T. Tumor volumes were assessed and posttreatment analysis was performed.

RESULTS

We observed dose dependent in vitro abrogation of downstream target proteins including phospho-AKT and phospho-S6. In both in vivo models, single agent ridaforolimus impaired xenograft tumor growth. Combination ridaforolimus and L/T, however, further improved the observed anti-tumor activity only in the ARK1 model with the PIK3CA gene mutation (E542K). The addition of mTOR inhibition to dual HER2 blockade added no additional anti-tumor effects in the ARK2 xenografts. Western blot and immunohistochemical analysis of downstream pathway alterations following in vivo treatment revealed dual HER2 blockade with ridaforolimus was necessary to induce apoptosis, decrease proliferation and abrogate phospho-S6 protein expression in the PIK3CA mutated model.

CONCLUSIONS

These pilot data suggest that PIK3CA gene mutation may be an effective biomarker for selecting those HER2 over-expressing USC tumors most likely to benefit from mTOR inhibition.

PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas

OBJECTIVES

We evaluated the role of PIK3CA-mutations as mechanism of resistance to trastuzumab in primary HER2/neu-amplified uterine-serous-carcinoma (USC) cell lines.

METHODS

Fifteen whole-exome-sequenced USC cell lines were tested for HER2/neu-amplification and PIK3CA-mutations. Four HER2/neu-amplified USC (2-harbouring wild-type-PIK3CA-genes and 2-harbouring oncogenic-PIK3CA-mutations) were evaluated in in vitro dose-titration-proliferation-assays, cell-viability and HER2 and S6-protein-phosphorylation after exposure to trastuzumab. USC harbouring wild-type-PIK3CA were transfected with plasmids encoding oncogenic PIK3CA-mutations (i.e., H1047R/R93Q) and exposed to trastuzumab. Finally, trastuzumab efficacy was tested by using two USC xenograft mouse models.

RESULTS

Seven out of fifteen (46%) of the USC cell lines were HER2/neu-amplified by fluorescence in situ hybridisation. Within these tumours four out of seven (57%) were found to harbour oncogenic PIK3CA-mutations vs two out of eight (25%) of the HER2/neu not amplified cell lines (P=0.01). HER2/neu-amplified/PIK3CA-mutated USC were highly resistant to trastuzumab when compared with HER2/neu-amplified/wild-type-PIK3CA cell lines (P=0.02). HER2/neu-amplified/PIK3CA wild-type cell lines transfected with oncogenic PIK3CA-mutations increased their resistance to trastuzumab (P<0.0001). Trastuzumab was effective in reducing tumour growth (P=0.001) and improved survival (P=0.0001) in mouse xenografts harbouring HER2-amplified/PIK3CA wild-type USC but not in HER2-amplified/PIK3CA-mutated tumours.

CONCLUSIONS

Oncogenic PIK3CA mutations are common in HER2/neu-amplified USC and may constitute a major mechanism of resistance to trastuzumab treatment.

The Therapeutic Challenge of Targeting HER2 in Endometrial Cancer

Endometrial cancer is the most common gynecologic cancer in the United States, diagnosed in more than 50,000 women annually. While the majority of women present with low-grade tumors that are cured with surgery and adjuvant radiotherapy, a significant subset of women experience recurrence and do not survive their disease. A disproportionate number of the more than 8,000 annual deaths attributed to endometrial cancer are due to high-grade uterine cancers, highlighting the need for new therapies that target molecular alterations specific to this subset of tumors. Numerous correlative scientific investigations have demonstrated that the HER2 (ERBB2) gene is amplified in 17%-33% of carcinosarcoma, uterine serous carcinoma, and a subset of high-grade endometrioid endometrial tumors. In breast cancer, this potent signature has directed women to anti-HER2-targeted therapies such as trastuzumab and lapatinib. In contrast to breast cancer, therapy with trastuzumab alone revealed no responses in women with recurrent HER2 overexpressing endometrial cancer, suggesting that these tumors may possess acquired or innate trastuzumab resistance mechanisms. This review explores the literature surrounding HER2 expression in endometrial cancer, focusing on trastuzumab and other anti-HER2 therapy and resistance mechanisms characterized in breast cancer but germane to endometrial tumors. Understanding resistance pathways will suggest combination therapies that target both HER2 and key oncogenic escape pathways in endometrial cancer.

IMPLICATIONS FOR PRACTICE

This review summarizes the role of HER2 in endometrial cancer, with a focus on uterine serous carcinoma. The limitations to date of anti-HER2 therapy in this disease site are examined, and mechanisms of drug resistance are outlined based on the experience in breast cancer. Potential opportunities to overcome inherent resistance to anti-HER2 therapy in endometrial cancer are detailed, offering opportunities for further clinical study with the goal to improve outcomes in this challenging disease.

Dacomitinib (PF-00299804), a second-generation irreversible pan-erbB receptor tyrosine kinase inhibitor, demonstrates remarkable activity against HER2-amplified uterine serous endometrial cancer in vitro

Uterine serous carcinoma (USC) is an aggressive subtype of endometrial cancer that carries an extremely poor prognosis. Up to 35 % of USC may overexpress the epidermal growth factor receptor-2 (HER2/neu) at strong (i.e., 3+) level by immunohistochemistry (IHC) or harbor HER2/neu gene amplification by fluorescence in situ hybridization (FISH). In this study, we assessed the sensitivity of a panel of USC cell lines with and without HER2/neu gene amplification to dacomitinib (PF-00299804), an irreversible pan-human epidermal growth factor receptor tyrosine kinase inhibitor. Eight primary cell lines (i.e., four harboring HER2/neu gene amplification by FISH and four FISH- cell lines), all demonstrating similar in vitro growth rates, were evaluated in viability/proliferation assays. The effect of dacomitinib on cell growth, cell cycle distribution, and signaling was determined using flow cytometry-based assays. Dacomitinib caused a significantly stronger growth inhibition in HER2/neu FISH+ USC cell lines when compared to FISH- USC (dacomitinib half maximal inhibitory concentration (IC50) mean ± SEM = 0.02803 ± 0.003355 μM in FISH+ versus 1.498 ± 0.2209 μM in FISH- tumors, P < 0.0001). Dacomitinib growth inhibition was associated with a significant and dose-dependent decline in phosphorylated HER2/neu and S6 transcription factor and a dose-dependent and time-dependent cell cycle arrest in G0/G1 in FISH+ USC. Dacomitinib is remarkably effective against chemotherapy-resistant HER2/neu gene-amplified USC. Clinical studies with dacomitinib in HER2/neu FISH+ USC patients resistant to standard salvage chemotherapy are warranted.

HER2 over-expressing high grade endometrial cancer expresses high levels of p95HER2 variant

BACKGROUND

Subsets of high grade endometrial cancer (EnCa) over-express HER2 (ERBB2), yet clinical trials have failed to demonstrate any anti-tumor activity utilizing trastuzumab, an approved platform for HER2 positive breast cancer (BrCa). A truncated p95HER2 variant lacking the trastuzumab binding site may confer resistance. The objective of this investigation was to characterize the expression of the p95HER2 truncated variant in EnCa.

MATERIALS AND METHODS

With institutional approval, 86 high grade EnCa tumors were identified with tumor specimens from surgeries performed between 2000 and 2011. Clinical data were collected and all specimens underwent tumor genotyping, HER2 immunohistochemistry (IHC, HercepTest®), HER2 fluorescent in situ hybridization (FISH), along with total HER2 (H2T) and p95HER2 assessment with VeraTag® testing. Regression models were used to compare a cohort of 86 breast tumors selected for equivalent HER2 protein expression.

RESULTS

We identified 44 high grade endometrioid and 42 uterine serous carcinomas (USC). IHC identified high HER2 expression (2+ or 3+) in 59% of the tumors. HER2 gene amplification was observed in 16 tumors (12 USC, 4 endometrioid). Both HER2 gene amplification and protein expression correlated with H2T values. High p95HER2 expression above 2.8RF/mm2 was observed in 53% (n=54) with significant correlation with H2T levels. When matched to a cohort of 107 breast tumors based on HercepTest HER2 expression, high grade EnCa presented with higher p95 levels (p<0.001).

CONCLUSIONS

These data demonstrate that compared to BrCa, high grade EnCa expresses higher levels of p95HER2 possibly providing rationale for the trastuzumab resistance observed in EnCa.

Extracellular matrix protein 1 regulates cell proliferation and trastuzumab resistance through activation of epidermal growth factor signaling

INTRODUCTION

Extracellular matrix protein 1 (ECM1) is a secreted glycoprotein with putative functions in cell proliferation, angiogenesis and differentiation. Expression of ECM1 in several types of carcinoma suggests that it may promote tumor development. In this study, we investigated the role of ECM1 in oncogenic cell signaling in breast cancer, and potential mechanisms for its effects.

METHODS

In order to find out the functional role of ECM1, we used the recombinant human ECM1 and viral transduction systems which stably regulated the expression level of ECM1. We examined the effect of ECM1 on cell proliferation and cell signaling in vitro and in vivo. Moreover, tissues and sera of patients with breast cancer were used to confirm the effect of ECM1.

RESULTS

ECM1 protein was increased in trastuzumab-resistant (TR) cells, in association with trastuzumab resistance and cell proliferation. Through physical interaction with epidermal growth factor receptor (EGFR), ECM1 potentiated the phosphorylation of EGFR and extracellular signal-regulated kinase upon EGF treatment. Moreover, ECM1-induced galectin-3 cleavage through upregulation of matrix metalloproteinase 9 not only improved mucin 1 expression, but also increased EGFR and human epidermal growth factor receptor 3 protein stability as a secondary signaling.

CONCLUSIONS

ECM1 has important roles in both cancer development and trastuzumab resistance in breast cancer through activation of EGFR signaling.

Dual HER2 targeting impedes growth of HER2 gene-amplified uterine serous carcinoma xenografts

PURPOSE

Uterine serous carcinoma (USC) is an aggressive subtype of endometrial cancer that commonly harbors HER2 gene amplification. We investigated the effectiveness of HER2 inhibition using lapatinib and trastuzumab in vitro and in xenografts derived from USC cell lines and USC patient-derived xenografts.

EXPERIMENTAL DESIGN

Immunohistochemistry and FISH were performed to assess HER2 expression in 42 primary USC specimens. ARK1, ARK2, and SPEC2 cell lines were treated with trastuzumab or lapatinib. Cohorts of mice harboring xenografts derived from ARK2 and SPEC2 cell lines and EnCa1 and EnCa2 primary human USC samples were treated with either vehicle, trastuzumab, lapatinib, or the combination of trastuzumab and lapatinib. Acute and chronic posttreatment tumor samples were assessed for downstream signaling alterations and examined for apoptosis and proliferation.

RESULTS

HER2 gene amplification (24%) correlated significantly with HER2 protein overexpression (55%). All models were impervious to single-agent trastuzumab treatment. Lapatinib decreased in vitro proliferation of all cell lines and in vivo growth of HER2-amplified xenografts (ARK2, EnCa1). In addition, dual therapy with trastuzumab and lapatinib resulted in significant antitumor activity only in ARK2 and EnCa1 tumors. Dual HER2 therapy induced on target alteration of downstream MAPK and PI3K pathway mediators only in HER2-amplified models, and was associated with increased apoptosis and decreased proliferation.

CONCLUSIONS

Although trastuzumab alone did not impact USC growth, dual anti-HER2 therapy with lapatinib led to improved inhibition of tumor growth in HER2-amplified USC and may be a promising avenue for future investigation.

Neratinib shows efficacy in the treatment of HER2/neu amplified uterine serous carcinoma in vitro and in vivo

OBJECTIVES

Uterine serous carcinoma (USC) represents an aggressive variant of endometrial cancer and accounts for a large proportion of deaths annually. HER2/neu amplification is associated with USC in approximately 30-35% of cases. The objective of this study was to determine the sensitivity of a panel of primary USC cell lines to the small tyrosine kinase inhibitor neratinib, an ErbB1 and HER2 inhibitor, both in vitro and in vivo.

METHODS

HER2/neu amplification was determined by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in 24 USC cell lines. Flow cytometry was used to determine the effects of neratinib on cell viability, cell cycle distribution and signaling in vitro. Mice harboring HER2/neu amplified xenografts were treated with neratinib to assess the efficacy of the drug in vivo.

RESULTS

HER2/neu amplification was noted in 8/24 primary cell lines. Data regarding the efficacy of neratinib was determined using 4 HER2 amplified cell lines and 4 non-amplified cell lines with similar growth rates. Data revealed that cell lines with HER2/neu amplification were exquisitely more sensitive to neratinib compared to non-amplified cell lines (mean ± SEM IC50: 0.011μM ± 0.0008 vs. 0.312μM ± 0.0456 p<0.0001). Neratinib caused arrest in the G0/G1 phase of the cell cycle and resulted in decreased autophosphorylation of HER2 and activation of S6. Neratinib treated mice harboring xenografts of HER2/neu amplified USC showed delayed tumor growth and improved overall survival compared to vehicle (p=0.0019).

CONCLUSIONS

Neratinib may be a potential treatment option for patients harboring HER2/neu amplified USC. Clinical trials for this subset of endometrial cancer patients are warranted.

Development of targeted therapy in uterine serous carcinoma, a biologically aggressive variant of endometrial cancer

Endometrial cancer (EC) is the most common female genital malignancy in the USA. Most carcinomas arising from the uterus are estrogen dependent and are associated with obesity and hypertension. They are designated type I ECs and typically, due to their early diagnosis secondary to postmenopausal bleeding, have a good prognosis. By contrast, type II ECs develop in older patients, are not hormone dependent and are responsible for most recurrences and deaths from EC. Uterine serous cancer constitutes up to 10% of all endometrial tumors, and represents the most biologically aggressive variant of type II EC. This article will describe the most salient molecular markers that have been identified in uterine serous cancer, thus far with emphasis on the use of erbB2 (HER2/neu) as the first of a series of therapeutic markers for the treatment of this highly-aggressive subset of ECs.

Challenges in the clinical utility of the serum test for HER2 ECD

Approximately 15-30% of breast cancers over-express the HER2/neu receptor. Historically, over-expression of HER2/neu has been identified using IHC or FISH, both of which are invasive approaches requiring tissue samples. Recent evidence has shown that some tumors identified as "negative" using these methods can respond to HER2/neu targeted therapy. Shedding of the extracellular domain (ECD) of the receptor into the circulation has led to the development of a serum test of HER2 ECD as an additional approach to probe HER2/neu overexpression. The serum test will be able to monitor the dynamic changes of HER2 status over the course of disease progression. Some studies further suggest that the serum HER2 ECD level and its change may serve as a biomarker to reflect patients' response to therapy. Yet more than 10years after the first serum HER2 ECD test was approved by the FDA, serum HER2 testing has yet to be widely used in clinical practice. In this article we will review the progress of the serum HER2 ECD test and discuss some obstacles impeding its incorporation into broad clinical practice. We will also discuss recent improvements in the sensitivity and specificity of the assay that offer some hope for the future of serum HER2 test.