Differential binding patterns of monoclonal antibody 2C4 to the ErbB3-p185her2/neu and the EGFR-p185her2/neu complexes

Molecular Pathways and Mechanisms of HER2 in Cancer Therapy

The oncogene ERBB2 encoding the receptor tyrosine-protein kinase erbB-2 (HER2) is frequently overexpressed or amplified and occasionally mutated in a variety of human cancers. The early discovery of this oncogene, its established oncogenic relevance in diverse cancers, its substantial expression on the surface of cancer cells, and its druggable catalytic activity have made it one of the most pursued targets in the history of cancer drug development. Initiatives targeting HER2 provided the early stimulus for several transformational pharmaceutical technologies, including mAbs, tyrosine kinase inhibitors, antibody-drug conjugates, and others. The seismic impact of these efforts has been felt in treatment of many cancers, including breast, gastroesophageal, lung, colorectal, and others. This impact continues to broaden with increasing indications on the horizon and a plethora of novel agents in development. However, implementation of these therapeutic strategies has been complex. The clinical translation of every one of these classes of agents has been notable for underperformance or overperformance characteristics that have informed new lines of research providing deeper insights into the mechanistic complexities and unrealized opportunities provided by this molecular target. Despite all the successes to date, the preponderance of scientific evidence indicates that the full potential of HER2 as a target for cancer therapeutics is far greater than currently realized, and numerous lines of investigation are ongoing to deepen and broaden the scope of impact of HER2 as a signaling, homing, or immunologic target. In this review, we explore the existing data and evolving paradigms surrounding this remarkable target for cancer therapy.

Using quantitative single molecule localization microscopy to optimize multivalent HER2-targeting ligands

Introduction

The progression-free survival of patients with HER2-positive metastatic breast cancer is significantly extended by a combination of two monoclonal antibodies, trastuzumab and pertuzumab, which target independent epitopes of the extracellular domain of HER2. The improved efficacy of the combination over individual antibody therapies targeting HER2 is still being investigated, and several molecular mechanisms may be in play: the combination downregulates HER2, improves antibody-dependent cell mediated cytotoxicity, and/or affects the organization of surface-expressed antigens, which may attenuate downstream signaling.

Methods

By combining protein engineering and quantitative single molecule localization microscopy (qSMLM), here we both assessed and optimized clustering of HER2 in cultured breast cancer cells.

Results

We detected marked changes to the cellular membrane organization of HER2 when cells were treated with therapeutic antibodies. When we compared untreated samples to four treatment scenarios, we observed the following HER2 membrane features: (1) the monovalent Fab domain of trastuzumab did not significantly affect HER2 clustering; (2) individual therapy with either trastuzumab or (3) pertuzumab produced significantly higher levels of HER2 clustering; (4) a combination of trastuzumab plus pertuzumab produced the highest level of HER2 clustering. To further enhance this last effect, we created multivalent ligands using meditope technology. Treatment with a tetravalent meditope ligand combined with meditope-enabled trastuzumab resulted in pronounced HER2 clustering. Moreover, compared to pertuzumab plus trastuzumab, at early time points this meditope-based combination was more effective at inhibiting epidermal growth factor (EGF) dependent activation of several downstream protein kinases.

Discussion

Collectively, mAbs and multivalent ligands can efficiently alter the organization and activation of the HER2 receptors. We expect this approach could be used in the future to develop new therapeutics.

Enhancement of photodynamic bactericidal activity of curcumin against Pseudomonas Aeruginosa using polymyxin B

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa) is an emerging opportunistic pathogen, which can cause bacterial skin diseases such as green nail syndrome, interdigital infections and folliculitis. Curcumin-mediated antimicrobial photodynamic therapy (aPDT) has been demonstrated as a promising therapeutic option for the treatment of skin infection though its inactivation of gram-negative bacteria such as P. aeruginosa.

MATERIALS AND METHODS

In the present study, we examined the adjuvant effect of polymyxin B on the antibacterial activity of curcumin-mediated aPDT against P. aeruginosa. P. aeruginosa was treated with curcumin in the presence of 0.1-0.5 mg/L polymyxin B and irradiated by blue LED light (10 J/cm²). Bacterial cultures treated with curcumin alone served as controls. Colony forming units (CFU) were counted and the viability of P. aeruginosa was calculated after aPDT treatment. The possible underlying mechanisms for the enhanced killing effects were also explored.

RESULTS

The killing effects of curcumin-mediated aPDT against P. aeruginosa was significantly enhanced by polymyxin B (over 2-log reductions). Moreover, it was also observed that addition of polymyxin B in the curcumin-mediated aPDT led to the apparent bacterial membrane damage with increased leakage of cytoplasmic contents and extensive DNA and protein degradation.

DISCUSSION

The photodynamic action of curcumin against P. aeruginosa could be significantly enhanced by the FDA-approved drug polymyxin B. Our results highlight the potential of introducing polymyxin B to enhance the effects of aPDT treatment against gram-negative skin infections, in particular, P. aeruginosa.

Peptide Ligands Specifically Targeting HER2 Receptor and the Role Played by a Synthetic Model System of the Receptor Extracellular Domain: Hypothesized Future Perspectives

A short (Fab)trastuzumab-derived peptide specific for HER2 receptor was identified. Its affinity for the model system HER2-DIVMP was found in a nanomolar range. The structural determinants responsible for the interaction between this ligand (A9) and HER2-DIVMP were investigated by both computational and NMR analysis. Next, the possibility of using A9 as HER2- specific probe for the nuclear medicine imaging was evaluated by conjugating A9 with the DTPA chelator and radiolabeling it with ¹¹¹In. The developed probe retained a nanomolar affinity to HER2-overexpressing cancer cells, however, some unspecific binding also occurred. The peptide internalization into cells by receptor-mediated endocytosis was also studied. Future perspectives are aimed at using A9 as a probe for molecular imaging diagnostics as well as active targeting of anticancer drugs. Lead structure optimization is needed to minimize the percentage of A9 unspecific binding and to increase the binding affinity to the receptor.

Efficacy and safety of HER2 inhibitors in combination with or without pertuzumab for HER2-positive breast cancer: a systematic review and meta-analysis

BACKGROUND

Although the dual anti-HER2 therapy, namely, pertuzumab plus trastuzumab and docetaxel, has shown promising results in HER2+ breast cancer patients, whether the dose, efficacy and safety of this treatment differs from those of other pertuzumab-based dual anti-HER2 therapies remain controversial. This systematic review evaluates the efficacy and safety of H (trastuzumab or trastuzumab emtansine ± chemotherapy) + P (pertuzumab) compared with those of H in HER2+ breast cancer patients.

METHODS

A comprehensive search was performed to identify eligible studies comparing the efficacy and safety of H + P versus H. The pathologic complete response (pCR), median progression-free survival (PFS) and overall survival (OS) were the primary outcomes, and safety was the secondary outcome. A subgroup analysis of pCR according to hormone receptor (HR) status was performed. All analyses were conducted using STATA 11.0.

RESULTS

Twenty-six studies (9872 patients) were identified. In the neoadjuvant setting, H + P significantly improved the pCR [odds ratio (OR) = 1.33; 95% confidence interval (CI), 1.08-1.63; p = 0.006]. In the metastatic setting, H + P significantly improved PFS [hazard ratios (HRs) = 0.75; 95% CI, 0.68-0.84; p < 0.001]. There was a trend towards better OS but that it did not reach statistical significance (HRs = 0.81; 95% CI, 0.64-1.03; p = 0.082). A subgroup analysis revealed that the HER2+/HR- patients who received H + P showed the highest increase in the pCR. Rash, diarrhea, epistaxis, mucosal inflammation, and anemia were significantly more frequently observed with H + P than with H, whereas myalgia was less frequent (OR = 0.91; 95% CI, 0.82-1.01; p = 0.072), and no significant difference in cardiac toxicity was observed between these therapies (OR = 1.26; 95% CI, 0.81-1.95; P = 0.309).

CONCLUSIONS

Our study confirms that H + P is superior to H in the (neo)adjuvant treatment of HER2+ breast cancer, and increase the risk of acceptable and tolerable toxicity (rash, diarrhea, epistaxis, mucosal inflammation, and anemia).

TRIAL REGISTRATION

A systematic review protocol was registered with PROSPERO (identification number: CRD42018110415 ).

Pan-HER-targeted approach for cancer therapy: Mechanisms, recent advances and clinical prospect

The Human Epidermal Growth Factor Receptor family is composed of 4 structurally related receptor tyrosine kinases that are involved in many human cancers. The efficacy and safety of HER inhibitors have been compared in a wide range of clinical trials, suggesting the superior inhibitory ability of multiple- HER-targeting blockade compared with single receptor antagonists. However, many patients are currently resistant to current therapeutic treatment and novel strategies are warranted to conquer the resistance. Thus, we performed a critical review to summarize the molecular involvement of HER family receptors in tumour progression, recent anti-HER drug development based on clinical trials, and the potential resistance mechanisms of anti-HER therapy.

Polyfunctional anti-human epidermal growth factor receptor 3 (anti-HER3) antibodies induced by HER3 vaccines have multiple mechanisms of antitumor activity against therapy resistant and triple negative breast cancers

BACKGROUND

Upregulation of human epidermal growth factor receptor 3 (HER3) is a major mechanism of acquired resistance to therapies targeting its heterodimerization partners epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2), but also exposes HER3 as a target for immune attack. We generated an adenovirus encoding full length human HER3 (Ad-HER3) to serve as a cancer vaccine. Previously we reported the anti-tumor efficacy and function of the T cell response to this vaccine. We now provide a detailed assessment of the antitumor efficacy and functional mechanisms of the HER3 vaccine-induced antibodies (HER3-VIAs) in serum from mice immunized with Ad-HER3.

METHODS

Serum containing HER3-VIA was tested in complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) assays and for its effect on HER3 internalization and degradation, downstream signaling of HER3 heterodimers and growth of metastatic HER2+ (BT474M1), HER2 therapy-resistant (rBT474), and triple negative (MDA-MB-468) breast cancers.

RESULTS

HER3-VIAs mediated CDC and ADCC, HER3 internalization, interruption of HER3 heterodimer-driven tumor signaling pathways, and anti-proliferative effects against HER2+ tumor cells in vitro and significant antitumor effects against metastatic HER2+ BT474M1, treatment refractory HER2+ rBT474 and triple negative MDA-MB-468 in vivo.

CONCLUSIONS

In addition to the T cell anti-tumor response induced by Ad-HER3, the HER3-VIAs provide additional functions to eliminate tumors in which HER3 signaling mediates aggressive behavior or acquired resistance to HER2-targeted therapy. These data support clinical studies of vaccination against HER3 prior to or concomitantly with other therapies to prevent outgrowth of therapy-resistant HER2+ and triple negative clones.

A semi high-throughput method for screening small bispecific antibodies with high cytotoxicity

Small bispecific antibodies that induce T-cell-mediated cytotoxicity have the potential to damage late-stage tumor masses to a clinically relevant degree, but their cytotoxicity is critically dependent on their structural and functional properties. Here, we constructed an optimized procedure for identifying highly cytotoxic antibodies from a variety of the T-cell-recruiting antibodies engineered from a series of antibodies against cancer antigens of epidermal growth factor receptor family and T-cell receptors. By developing and applying a set of rapid operations for expression vector construction and protein preparation, we screened the cytotoxicity of 104 small antibodies with diabody format and identified some with 103-times higher cytotoxicity than that of previously reported active diabody. The results demonstrate that cytotoxicity is enhanced by synergistic effects between the target, epitope, binding affinity, and the order of heavy-chain and light-chain variable domains. We demonstrate the importance of screening to determine the critical rules for highly cytotoxic antibodies.

Vaccination targeting human HER3 alters the phenotype of infiltrating T cells and responses to immune checkpoint inhibition

Expression of human epidermal growth factor family member 3 (HER3), a critical heterodimerization partner with EGFR and HER2, promotes more aggressive biology in breast and other epithelial malignancies. As such, inhibiting HER3 could have broad applicability to the treatment of EGFR- and HER2-driven tumors. Although lack of a functional kinase domain limits the use of receptor tyrosine kinase inhibitors, HER3 contains antigenic targets for T cells and antibodies. Using novel human HER3 transgenic mouse models of breast cancer, we demonstrate that immunization with recombinant adenoviral vectors encoding full length human HER3 (Ad-HER3-FL) induces HER3-specific T cells and antibodies, alters the T cell infiltrate in tumors, and influences responses to immune checkpoint inhibitions. Both preventative and therapeutic Ad-HER3-FL immunization delayed tumor growth but were associated with both intratumoral PD-1 expressing CD8⁺ T cells and regulatory CD4⁺ T cell infiltrates. Immune checkpoint inhibition with either anti-PD-1 or anti-PD-L1 antibodies increased intratumoral CD8⁺ T cell infiltration and eliminated tumor following preventive vaccination with Ad-HER3-FL vaccine. The combination of dual PD-1/PD-L1 and CTLA4 blockade slowed the growth of tumor in response to Ad-HER3-FL in the therapeutic model. We conclude that HER3-targeting vaccines activate HER3-specific T cells and induce anti-HER3 specific antibodies, which alters the intratumoral T cell infiltrate and responses to immune checkpoint inhibition.

WASF3 provides the conduit to facilitate invasion and metastasis in breast cancer cells through HER2/HER3 signaling

The WASF3 gene is overexpressed in high-grade breast cancer and promotes invasion and metastasis but does not affect proliferation. The HER2/ERBB2/NEU gene is also frequently overexpressed in breast cancer and has been shown to promote invasion and metastasis in these tumors. Here we show that WASF3 in present in the HER2 immunocomplex and suppression of WASF3 function leads to suppression of invasion even in the presence of HER2 expression. Overexpression of both HER2 and WASF3 in non-metastatic MCF7 breast cancer cells promotes invasion and metastasis more significantly than either gene alone. HER2 forms homodimers as well as heterodimers with other HER family members and we now show that the ability of WASF3 to promote invasion is highly dependent on the HER2/HER3 heterodimer. The engagement of WASF3 with the HER2/HER3 complex facilitates its phospho-activation and transcriptional upregulation, which is facilitated by HER2/HER3 activation of JAK/STAT signaling. In breast cancer cells overexpressing HER2, therefore, WASF3 is specifically required to facilitate the invasion/metastasis response. Targeting WASF3, therefore, could be a potential therapeutic approach to suppress metastasis of HER2-overexpressing breast tumors.

"Vertical" Inhibition of HER2 Yields Horizontal Gains in the Clinic

HER2-targeted therapy has moved beyond trastuzumab to include other monoclonals targeting the cell surface, receptor tyrosine kinase inhibitors of HER2, and antibody-drug conjugates. Afatinib, a small molecule receptor tyrosine kinase inhibitor, now joins the ranks of HER2-targeting agents in combination with trastuzumab. The combination brings new opportunities and challenges.

Monitoring serum HER2 levels in breast cancer patients

Background

We have developed a new approach to reduce the serum interference for ELISA. The purpose of this study is to investigate if we can use the optimized ELISA (MBB-ELISA) to detect serum soluble HER2/neu (sHER2) in early stage primary breast cancer and monitor its change during treatments.

Findings

We collected sera preoperatively from 118 primary breast cancer patients. Serum samples were also collected sequentially from a subset of patients during and after adjuvant treatment. sHER2 in these samples was measured by the MBB-ELISA. Only 16.7 % of tissue HER2 (tHER2) positive patients had significantly elevated sHER2 levels in serum. Interestingly, sera of some patients with tHER2 negative tumors, including those that were 2+ by IHC but negative by FISH, demonstrated slightly elevated sHER2 levels. Multivariate analysis demonstrated that patients with elevated sHER2 (> = 7 ng/ml) had significantly worse disease free survival. During treatments, sHER2 levels consistently fell in response to adjuvant therapies. Nevertheless, in all 4 patients who developed metastases, a steady rise in sHER2 levels was noted before metastatic disease became clinically evident.

Conclusions

For early stage breast cancers, sHER2 is a poor biomarker to predict tHER2 status, but may have value to supplement tissue tests to identify patients with HER2 tumors. Our results also suggest that sHER2 is worth further study as a biomarker to monitor breast cancer patients during treatments.

Combination of novel HER2-targeting antibody 1E11 with trastuzumab shows synergistic antitumor activity in HER2-positive gastric cancer

The synergistic interaction of two antibodies targeting the same protein could be developed as an effective anti-cancer therapy. Human epidermal growth factor receptor 2 (HER2) is overexpressed in 20-25% of breast and gastric cancer patients, and HER2-targeted antibody therapy using trastuzumab is effective in many of these patients. Nonetheless, improving therapeutic efficacy and patient survival is important, particularly in patients with HER2-positive gastric cancer. Here, we describe the development of 1E11, a HER2-targeted humanized monoclonal antibody showing increased efficacy in a highly synergistic manner in combination with trastuzumab in the HER2-overexpressing gastric cancer cell lines NCI-N87 and OE-19. The two antibodies bind to sub-domain IV of the receptor, but have non-overlapping epitopes, allowing them to simultaneously bind HER2. Treatment with 1E11 alone induced apoptosis in HER2-positive cancer cells, and this effect was enhanced by combination treatment with trastuzumab. Combination treatment with 1E11 and trastuzumab reduced the levels of total HER2 protein and those of aberrant HER2 signaling molecules including phosphorylated HER3 and EGFR. The synergistic antitumor activity of 1E11 in combination with trastuzumab indicates that it could be a novel potent therapeutic antibody for the treatment of HER2-overexpressing gastric cancers.

IgE-based Immunotherapy of Cancer -A Comparative Oncology Approach

Antibody-based immunotherapies are important therapy options in human oncology. Although human humoral specific immunity is constituted of five different immunoglobulin classes, currently only IgG-based immunotherapies have proceeded to clinical application.

This review, however, discusses the benefits and difficulties of IgE-based immunotherapy of cancer, with special emphasis on how to translate promising preclinical results into clinical studies. Pursuing the “Comparative Oncology” approach, novel drug candidates are investigated in clinical trials with veterinary cancer patients, most often dogs. By this strategy drug development could be speeded up, animal experiments could be reduced and novel therapy options could be introduced benefitting humans as well as man’s best friend.

Model-based analysis of HER activation in cells co-expressing EGFR, HER2 and HER3

The HER/ErbB family of receptor tyrosine kinases drives critical responses in normal physiology and cancer, and the expression levels of the various HER receptors are critical determinants of clinical outcomes. HER activation is driven by the formation of various dimer complexes between members of this receptor family. The HER dimer types can have differential effects on downstream signaling and phenotypic outcomes. We constructed an integrated mathematical model of HER activation, and trafficking to quantitatively link receptor expression levels to dimerization and activation. We parameterized the model with a comprehensive set of HER phosphorylation and abundance data collected in a panel of human mammary epithelial cells expressing varying levels of EGFR/HER1, HER2 and HER3. Although parameter estimation yielded multiple solutions, predictions for dimer phosphorylation were in agreement with each other. We validated the model using experiments where pertuzumab was used to block HER2 dimerization. We used the model to predict HER dimerization and activation patterns in a panel of human mammary epithelial cells lines with known HER expression levels in response to stimulations with ligands EGF and HRG. Simulations over the range of expression levels seen in various cell lines indicate that: i) EGFR phosphorylation is driven by HER1-HER1 and HER1-HER2 dimers, and not HER1-HER3 dimers, ii) HER1-HER2 and HER2-HER3 dimers both contribute significantly to HER2 activation with the EGFR expression level determining the relative importance of these species, and iii) the HER2-HER3 dimer is largely responsible for HER3 activation. The model can be used to predict phosphorylated dimer levels for any given HER expression profile. This information in turn can be used to quantify the potencies of the various HER dimers, and can potentially inform personalized therapeutic approaches.

A family of cell surface molecules called the HER receptor family plays important roles in normal physiology and cancer. This family has four members, HER1-4. These receptors convert signals received from the extracellular environment into cell decisions such as growth and survival – a process termed signal transduction. In particular, HER2 and HER3 are over-expressed in a number of tumors, and their expression levels are associated with abnormal growth and poor clinical prognosis. A key step in HER-mediated signal transduction is the formation of dimer complexes between members of this family. Different dimer types have different potencies for activating normal and aberrant responses. Prediction of the dimerization pattern for a given HER expression level may pave the way for personalized therapeutic approaches targeting specific dimers. Towards this end, we constructed a mathematical model for HER dimerization and activation. We determined unknown model parameters by analyzing HER activation data collected in a panel of human mammary epithelial cells that express different levels of the HER molecules. The model enables us to quantitatively link HER expression levels to receptor dimerization and activation. Further, the model can be used to support additional quantitative investigations into the basic biology of HER-mediated signal transduction.

Pertuzumab counteracts the inhibitory effect of ErbB2 on degradation of ErbB3

Overexpression of ErbB2 and ErbB3 is found in several human cancers, and ErbB2-ErbB3 heterodimers are known as the most potent signaling units among ErbB dimers. While ErbB2 probably undergoes weak endocytosis, ErbB3 is readily internalized even in the absence of added ligand and without requirement for kinase activity. Overexpression of ErbB2 has been demonstrated to inhibit epidermal growth factor-induced internalization and degradation of epidermal growth factor receptor. This happens due to epidermal growth factor receptor-ErbB2 dimerization and can be counteracted by the anti-ErbB2 antibody pertuzumab, which binds the dimerization arm of ErbB2. Pertuzumab does also inhibit ErbB2-ErbB3 dimerization, but to what extent this has effect on constitutive and/or ligand-induced downregulation of ErbB3 is not known. In this study, we demonstrate that expression of ErbB2 as such did not block constitutive internalization of ErbB3, but that heregulin-induced degradation of ErbB3 was significantly slowed in cells expressing high levels of ErbB2. Incubation with pertuzumab did, however, counteract this effect. This indicates that the formation of ErbB2-ErbB3 heterodimers inhibits downregulation of ErbB3 and supports the notion that pertuzumab inhibits ErbB2 dimerization. The inhibitory effect of pertuzumab on ligand-induced ErbB2-ErbB3 heterodimerization was confirmed by the observation that pertuzumab inhibited heregulin-induced phosphorylation of ErbB3 in cells expressing ErbB2 and efficiently reduced heregulin-induced downstream signaling in cells expressing low levels of ErbB2. Altogether the results indicate that pertuzumab can be a valuable therapeutic agent not only in cancers overexpressing ErbB2 but also in cancers co-expressing ErbB2 and ErbB3.

scFv-based "Grababody" as a general strategy to improve recruitment of immune effector cells to antibody-targeted tumors

Recruitment of immune cells to tumor cells targeted by a therapeutic antibody can heighten the antitumor efficacy of the antibody. For example, p185(her2/neu)-targeting antibodies not only downregulate the p185(her2/neu) kinase (ERBB2) but also trigger complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) through the antibody Fc region. Here, we describe a generalized strategy to improve immune cell recruitment to targeted cancer cells, using a modified scFv antibody we call a "Grababody" that binds the target protein and endogenous immunoglobulins. The model system we used to illustrate the use of this platform recognizes p185(her2/neu) and includes an IgG binding domain. The recombinant scFv Grababody that was created recruited circulating human IgGs and attracted immune cells carrying Fc receptors to tumor cells that expressed p185(her2/neu). The presence of the IgG binding domain significantly enhanced CDC and ADCC activity and improved antitumor activity in vivo. Our results illustrate a novel general approach to improve antibody-like proteins for therapeutic applications.

Interference-Free HER2 ECD as a Serum Biomarker in Breast Cancer

Over-expression of the HER2/neu receptor occurs in 20 to 30 percent of breast tumors and is linked to poorer prognosis. The HER2/neu expression status determines whether or not patient will receive trastuzumab-based treatment. In clinical practice, over-expression of HER2/neu is routinely identified using Immunohistochemistry (IHC) or Fluorescence in Situ Hybridization (FISH), both of which are invasive approaches requiring tissue samples. Serum assays for the Extra Cellular Domain of HER2/neu receptor (HER2 ECD) have been reported but the use is very limited due to serum interference factors (e.g. human anti-animal immunoglobulin antibodies) that lead to false test results and inconsistency with tissue Her2 status. We have developed an ELISA based approach using an MBB buffer to eliminate false results and to obtain more accurate assessment of HER2 ECD levels. Using this refined assay we retroactively measured HER2/neu levels from breast cancer patients and controls. Abnormal HER2 ECD levels were detected in about 32% of invasive breast cancer patients but not in controls or patients with benign diseases. In addition, we also showed that patients with elevated serum HER2 levels appeared to have worse survival regardless of treatments. In a small group of 12 Ductal Carcinoma in situ (DCIS) patients who received HER2/neu peptide vaccination and surgery, only one patient showed constantly rising HER2 levels after treatment and this patient had recurrence of HER2 positive tumor within 5 years. Our studies indicate that once the serum interference issue is resolved, serum HER2 ECD can have potential clinical utility to supplement the tissue based tests.

ERBB3 (HER3) is a key sensor in the regulation of ERBB-mediated signaling in both low and high ERBB2 (HER2) expressing cancer cells

Aberrant expression and activation of EGFR and ERBB2 (HER2) have been successfully targeted for cancer therapeutics. Recent evidence from both basic and clinical studies suggests that ERBB3 (HER3) serves as a key activator of downstream signaling through dimerization with other ERBB proteins and plays a critical role in the widespread clinical resistance to EGFR and HER2 targeting cancer therapies. As a result, HER3 is actively pursued as an antibody therapeutic target for cancer. Ligand binding is thought to be a prerequisite for dimerization of HER3 with other ERBB proteins, which results in phosphorylation of its c-terminal tyrosine residues and activation of downstream AKT and MAPK signaling pathways. In this study, we report that an anti-HER2 monoclonal antibody (HER2Mab), which blocks HER2 dimerization with HER3, induces HER3 dimerization with EGFR in both low and high HER2 expressing cancer cells. Treatment of the low HER2 expressing MCF7 cancer cells with HER2Mab promoted cell proliferation and migration in the absence of HER3 ligand stimulation. Follow-up studies revealed that HER2Mab-induced HER3 signaling via EGFR/HER3 dimerization and activation of downstream AKT signaling pathways. These results suggest that equilibrium of dimerization among the ERBB proteins can be perturbed by HER2Mab and HER3 plays a key role in sensing the perturbation.

Risk of rash with the anti-HER2 dimerization antibody pertuzumab: a meta-analysis

Pertuzumab is a novel humanized monoclonal antibody that blocks human epidermal growth factor receptor 2 (HER2) dimerization. It was recently approved by the US FDA for use in combination with trastuzumab and docetaxel for patients with HER2-positive metastatic breast cancer who have not received prior anti-HER2 therapy or chemotherapy for metastatic disease. Rash is inconsistently reported as a common adverse event in most clinical trials of pertuzumab, at varying incidences. In this study, we have investigated the overall incidence and risk of rash with pertuzumab. Relevant studies were identified from the PubMed database (1966-2012), abstracts presented at the American Society of Clinical Oncology annual conference (2004-2011), and Web of Science database (1998-2012). Eligible studies were prospective phase II-III clinical trials using pertuzumab in cancer patients. Incidence, relative risk (RR), and 95 % confidence intervals (CIs) were calculated using random-effects or fixed-effects models based on the heterogeneity of included studies. Data from a total of 1,726 patients (pertuzumab, n = 1,157; controls, n = 569) with breast, ovarian, and prostate cancers from eight clinical trials were included for analysis. The incidence of all-grade and high-grade rash with pertuzumab were 24.6 % (95 % CI 19.3-30.8 %) and 1.1 % (95 % CI 0.5-2.2 %), respectively. The risk varied with tumor types, as patients with prostate cancer had a lower incidence of rash (13.2 %; 95 % CI 8.0-21.1 %) than those with breast, ovarian, fallopian tube, and peritoneal cancer (P = 0.001). Overall, pertuzumab significantly increased the risk of rash in comparison with controls (RR 1.53; 95 % CI 1.12-2.09; P = 0.007). Pertuzumab is associated with a significant risk of rash, and the incidence varies among different tumor types. Prevention, early recognition, and appropriate treatment of this rash may lead to improvement in patient quality of life, adherence to therapy, and possibly optimize clinical outcomes.

A mathematical model for the effects of HER2 over-expression on cell cycle progression in breast cancer

In this paper, we present a mathematical model predicting the fraction of proliferating cells in G1, S, and G2/M phases of the cell cycle as a function of EGFR and HER2. We show that it is possible to find parameters for the mathematical model so that its predictions agree with the experimental observations that HER2 over-expression results in: (1) a shorter G1-phase and early S-phase entry; (2) and that with a 1-to-1 ration between EGFR and HER2, the growth advantage in HER2 over-expressing cells is indeed associated with the increase of the HER2 expression level.

Structural insights into the down-regulation of overexpressed p185(her2/neu) protein of transformed cells by the antibody chA21

p185(her2/neu) belongs to the ErbB receptor tyrosine kinase family, which has been associated with human breast, ovarian, and lung cancers. Targeted therapies employing ectodomain-specific p185(her2/neu) monoclonal antibodies (mAbs) have demonstrated clinical efficacy for breast cancer. Our previous studies have shown that p185(her2/neu) mAbs are able to disable the kinase activity of homomeric and heteromeric kinase complexes and induce the conversion of the malignant to normal phenotype. We previously developed a chimeric antibody chA21 that specifically inhibits the growth of p185(her2/neu)-overexpressing cancer cells in vitro and in vivo. Herein, we report the crystal structure of the single-chain Fv of chA21 in complex with an N-terminal fragment of p185(her2/neu), which reveals that chA21 binds a region opposite to the dimerization interface, indicating that chA21 does not directly disrupt the dimerization. In contrast, the bivalent chA21 leads to internalization and down-regulation of p185(her2/neu). We propose a structure-based model in which chA21 cross-links two p185(her2/neu) molecules on separate homo- or heterodimers to form a large oligomer in the cell membrane. This model reveals a mechanism for mAbs to drive the receptors into the internalization/degradation path from the inactive hypophosphorylated tetramers formed dynamically by active dimers during a "physiologic process."

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Time-resolved fluorescence resonance energy transfer (TR-FRET) to analyze the disruption of EGFR/HER2 dimers: a new method to evaluate the efficiency of targeted therapy using monoclonal antibodies

In oncology, simultaneous inhibition of epidermal growth factor receptor (EGFR) and HER2 by monoclonal antibodies (mAbs) is an efficient therapeutic strategy but the underlying mechanisms are not fully understood. Here, we describe a time-resolved fluorescence resonance energy transfer (TR-FRET) method to quantify EGFR/HER2 heterodimers on cell surface to shed some light on the mechanism of such therapies. First, we tested this antibody-based TR-FRET assay in NIH/3T3 cell lines that express EGFR and/or HER2 and in various tumor cell lines. Then, we used the antibody-based TR-FRET assay to evaluate in vitro the effect of different targeted therapies on EGFR/HER2 heterodimers in the ovarian carcinoma cell line SKOV-3. A simultaneous incubation with Cetuximab (anti-EGFR) and Trastuzumab (anti-HER2) disturbed EGFR/HER2 heterodimers resulting in a 72% reduction. Cetuximab, Trastuzumab or Pertuzumab (anti-HER2) alone induced a 48, 44, or 24% reduction, respectively. In contrast, the tyrosine kinase inhibitors Erlotinib and Lapatinib had very little effect on EGFR/HER2 dimers concentration. In vivo, the combination of Cetuximab and Trastuzumab showed a better therapeutic effect (median survival and percentage of tumor-free mice) than the single mAbs. These results suggest a correlation between the extent of the mAb-induced EGFR/HER2 heterodimer reduction and the efficacy of such mAbs in targeted therapies. In conclusion, quantifying EGFR/HER2 heterodimers using our antibody-based TR-FRET assay may represent a useful method to predict the efficacy and explain the mechanisms of action of therapeutic mAbs, in addition to other commonly used techniques that focus on antibody-dependent cellular cytotoxicity, phosphorylation, and cell proliferation.

Time-resolved fluorescence resonance energy transfer (TR-FRET) to analyze the disruption of EGFR/HER2 dimers: a new method to evaluate the efficiency of targeted therapy using monoclonal antibodies

In oncology, simultaneous inhibition of epidermal growth factor receptor (EGFR) and HER2 by monoclonal antibodies (mAbs) is an efficient therapeutic strategy but the underlying mechanisms are not fully understood. Here, we describe a time-resolved fluorescence resonance energy transfer (TR-FRET) method to quantify EGFR/HER2 heterodimers on cell surface to shed some light on the mechanism of such therapies. First, we tested this antibody-based TR-FRET assay in NIH/3T3 cell lines that express EGFR and/or HER2 and in various tumor cell lines. Then, we used the antibody-based TR-FRET assay to evaluate in vitro the effect of different targeted therapies on EGFR/HER2 heterodimers in the ovarian carcinoma cell line SKOV-3. A simultaneous incubation with Cetuximab (anti-EGFR) and Trastuzumab (anti-HER2) disturbed EGFR/HER2 heterodimers resulting in a 72% reduction. Cetuximab, Trastuzumab or Pertuzumab (anti-HER2) alone induced a 48, 44, or 24% reduction, respectively. In contrast, the tyrosine kinase inhibitors Erlotinib and Lapatinib had very little effect on EGFR/HER2 dimers concentration. In vivo, the combination of Cetuximab and Trastuzumab showed a better therapeutic effect (median survival and percentage of tumor-free mice) than the single mAbs. These results suggest a correlation between the extent of the mAb-induced EGFR/HER2 heterodimer reduction and the efficacy of such mAbs in targeted therapies. In conclusion, quantifying EGFR/HER2 heterodimers using our antibody-based TR-FRET assay may represent a useful method to predict the efficacy and explain the mechanisms of action of therapeutic mAbs, in addition to other commonly used techniques that focus on antibody-dependent cellular cytotoxicity, phosphorylation, and cell proliferation.

The role of HER3, the unpretentious member of the HER family, in cancer biology and cancer therapeutics

Many types of human cancer are characterized by deregulation of the human epidermal growth factor receptor (HER) family of tyrosine kinase receptors. In some cancers, genomic events causing overactivity of individual HER family members are etiologically linked with the pathogenesis of these cancers, and constitute the driving signaling function underlying their tumorigenic behavior. HER3 stands out among this family as the only member lacking catalytic kinase function. Cancers with driving HER3 amplifications or mutations have not been found, and studies of its expression in tumors have been only weakly provocative. However, substantial evidence, predominantly from experimental models, now suggest that its non-catalytic functions are critically important in many cancers driven by its' HER family partners. Furthermore, new insights into the mechanism of activation in the HER family has provided clear evidence of functionality in the HER3 kinase domain. The convergence of structural, mechanistic, and experimental evidence highlighting HER3 functions that may be critical in tumorigenesis have now led to renewed efforts towards identification of cancers or subtypes of cancers wherein HER3 function may be important in tumor progression or drug resistance. It appears now that its failure to earn the traditional definition of an oncogene has allowed the tumor promoting functions of HER3 to elude the effects of cancer therapeutics. But experimental science has now unmasked the unpretentious role of HER3 in cancer biology, and the next generation of cancer therapies will undoubtedly perform much better because of it.

HER3 comes of age: new insights into its functions and role in signaling, tumor biology, and cancer therapy

The human epidermal growth family (HER) of tyrosine kinase receptors underlies the pathogenesis of many types of human cancer. The oncogenic functions of three of the HER proteins can be unleashed through amplification, overexpression, or mutational activation. This has formed the basis for the development of clinically active targeted therapies. However, the third member HER3 is catalytically inactive, not found to be mutated or amplified in cancers, and its role and functions have remained shrouded in mystery. Recent evidence derived primarily from experimental models now seems to implicate HER3 in the pathogenesis of several types of cancer. Furthermore, the failure to recognize the central role of HER3 seems to underlie resistance to epidermal growth factor receptor (EGFR)- or HER2-targeted therapies in some cancers. Structural and biochemical studies have now greatly enhanced our understanding of signaling in the HER family and revealed the previously unrecognized activating functions embodied in the catalytically impaired kinase domain of HER3. This renewed interest and mechanistic basis has fueled the development of new classes of HER3-targeting agents for cancer therapy. However, identifying HER3-dependent tumors presents a formidable challenge and the success of HER3-targeting approaches depends entirely on the development and power of predictive tools.

HER/ErbB receptor interactions and signaling patterns in human mammary epithelial cells

BACKGROUND

Knowledge about signaling pathways is typically compiled based on data gathered using different cell lines. This approach implicitly assumes that the cell line dependence is not important. However, different cell lines do not always respond to a particular stimulus in the same way, and lack of coherent data collected from closely related cellular systems can be detrimental to the efforts to understand the regulation of biological processes. To address this issue, we created a clone library of human mammary epithelial (HME) cells that expresses different levels of HER2 and HER3 receptors in combination with endogenous EGFR/HER1. Using our clone library, we have quantified the receptor activation patterns and systematically tested the validity of the existing hypotheses about the interaction patterns between HER1-3 receptors.

RESULTS

Our study identified HER2 as the dominant dimerization partner for both EGFR and HER3. Contrary to earlier suggestions, we find that lateral interactions with HER2 do not lead to strong transactivation between EGFR and HER3, i.e., EGFR activation and HER3 activation are only weakly linked in HME cells. We also find that observed weak transactivation is uni-directional where stimulation of EGFR leads to HER3 activation whereas HER3 stimulation does not activate the EGFR. Repeating our experiments at lower cell confluency established that cell confluency is not a major factor in the observed interaction patterns. We have also quantified the dependence of the kinetics of Erk and Akt activation on different HER receptors. We found that HER3 signaling makes the strongest contribution to Akt activation and that, stimulation of either EGFR or HER3 leads to significant Erk activation.

CONCLUSION

Our study shows that clone cell libraries can be a powerful resource in systems biology research by making it possible to differentiate between various hypotheses in a consistent cellular background. Using our constructed clone library we profiled the cell signaling patterns to establish the role of HER2 in the crosstalk between EGFR and HER3 receptors in HME cells. Our results for HME cells show that the weak linkage between EGFR and HER3 pathways can lead to distinct downstream cellular signaling patterns in response to the ligands of these two receptors.

Pertuzumab increases epidermal growth factor receptor down-regulation by counteracting epidermal growth factor receptor-ErbB2 heterodimerization

Epidermal growth factor receptor (EGFR) and ErbB2 readily form heterodimers when both are expressed in the same cell and the EGFR is activated by one of its ligands. Our data show that such heterodimers are constitutively formed also in a ligand-independent manner on overexpression of EGFR and ErbB2 in porcine aortic endothelial cells. Interestingly, cross-linking experiments showed that incubation with the antibody pertuzumab, which has been shown to bind the dimerization arm of ErbB2, resulted in dissolution of EGFR-ErbB2 heterodimers. Incubation with pertuzumab also increased the amount of EGF-induced EGFR homodimers, and under these conditions, endocytosis of radiolabeled EGF was increased. This increase was significant, although slightly more EGF was internalized in cells expressing EGFR only compared with pertuzumab-treated cells expressing both EGFR and ErbB2. By confocal microscopy analysis, more EGF was observed in endosomes on incubation with pertuzumab, and under similar conditions, immunoblotting experiments showed increased EGFR degradation on incubation with both EGF and pertuzumab. These results show that pertuzumab enhanced the endocytic down-regulation of EGFR by counteracting EGFR-ErbB2 heterodimerization. Our previous results showing that ErbB2 counteracts EGFR endocytosis can therefore be explained by tethering of EGFR to ErbB2 at the plasma membrane.

Signal integration: a framework for understanding the efficacy of therapeutics targeting the human EGFR family

The human EGFR (HER) family is essential for communication between many epithelial cancer cell types and the tumor microenvironment. Therapeutics targeting the HER family have demonstrated clinical success in the treatment of diverse epithelial cancers. Here we propose that the success of HER family-targeted monoclonal antibodies in cancer results from their ability to interfere with HER family consolidation of signals initiated by a multitude of other receptor systems. Ligand/receptor systems that initiate these signals include cytokine receptors, chemokine receptors, TLRs, GPCRs, and integrins. We further extrapolate that improvements in cancer therapeutics targeting the HER family are likely to incorporate mechanisms that block or reverse stromal support of malignant progression by isolating the HER family from autocrine and stromal influences.