Can trastuzumab be effective against tumors with low HER2/Neu (ErbB2) receptors?

EGFR trafficking: effect of dimerization, dynamics, and mutation

Spontaneous dimerization of EGF receptors (EGFR) and dysregulation of EGFR signaling has been associated with the development of different cancers. Under normal physiological conditions and to maintain homeostatic cell growth, once EGFR signaling occurs, it needs to be attenuated. Activated EGFRs are rapidly internalized, sorted through early endosomes, and ultimately degraded in lysosomes by a process generally known as receptor down-regulation. Through alterations to EGFR trafficking, tumors develop resistance to current treatment strategies, thus highlighting the necessity for combination treatment strategies that target EGFR trafficking. This review covers EGFR structure, trafficking, and altered surface expression of EGFR receptors in cancer, with a focus on how therapy targeting EGFR trafficking may aid tyrosine kinase inhibitor treatment of cancer.

A new anti-HER2 antibody that enhances the anti-tumor efficacy of trastuzumab and pertuzumab with a distinct mechanism of action

The majority of patients with metastatic breast cancer who are treated with the anti-HER2 monoclonal antibody, trastuzumab, generally develop resistance to the drug within a year after initiation of the treatment. Here we describe a new anti-HER2 humanized monoclonal antibody, 19H6-Hu, which binds to HER2 extracellular domain (ECD) with high affinity and inhibits proliferation of multiple HER2-overexpressing cancer cell lines as a single agent or in combination with trastuzumab. 19H6-Hu binds to the domain III in proximity to the domain IV of HER2 ECD, which differs from trastuzumab and pertuzumab. 19H6-Hu in combination with trastuzumab was more effective at blocking phosphorylation of ERK1/2, AKT(S473)and HER2 (Y1248) in HER2-positive cancer cells compared to trastuzumab alone or in combination with pertuzumab. Combination of three antibodies, 19H6-Hu, inetetamab (a trastuzumab analog) and pertuzumab exhibited much stronger inhibition of large NCI-N87 tumor xenografts (>400mm³) than the current standard of care, inetetamab (trastuzumab) plus Docetaxel (DTX), as well as the combination of 19H6-Hu, inetetamab and DTX. Our results highlight the functional variability of HER2 domains and provide a new insight into the design of HER2-targeting agents.

Change in Pattern of HER2 Fluorescent in Situ Hybridization (FISH) Results in Breast Cancers Submitted for FISH Testing: Experience of a Reference Laboratory Using US Food and Drug Administration Criteria and American Society of Clinical Oncology and College of American Pathologists Guidelines

Purpose

In 1998, the US Food and Drug Administration (FDA) approved human epidermal growth factor receptor 2 (HER2) testing guidelines to determine eligibility for HER2-directed therapy (HDT) in breast cancer. ASCO and the College of American Pathologists published immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH) HER2 testing guidelines in 2007 (AC2007) and updated these guidelines in 2013 (AC2013). We compared the HER2 FISH amplification frequency using these three guidelines.

Methods

Patient samples that were sent to the Mayo Clinic cytogenetics laboratory for FISH testing (n = 2,851; from November 2013 to October 2014) were analyzed. Frequency of HER2 FISH amplification was examined and impact of AC2013 assessed.

Results

IHC results were available for 1,922 patient samples (67.4%), 137 of which were from Mayo Clinic. Distribution was 2.4% IHC 0, 7.9% IHC 1+, 84.8% IHC 2+, and 2.5% IHC 3+. Among IHC 2+ patients, HER2 FISH positivity was 11.8% (FDA), 9.4% (AC2007), and 24.1% (AC2013). Overall, 11.8% (n = 339) were positive with a FISH ratio ≥ 2.0, 1.3% (n = 35) with a FISH ratio ≥ 2.0 despite a HER2 signal < 4.0, and 3.0% (n = 86) with HER2 signal ≥ 6.0 despite FISH ratio < 2.0. Among 405 patients (14.2%) who were initially considered FISH-equivocal (ratio < 2.0 with HER2 signal ≥ 4.0, but < 6.0; AC2013), use of an alternative chromosome 17 probe reassigned 212 (7.4% overall) patients to FISH-positive and 36 (1.3% overall) patients to FISH-negative, whereas 157 (5.5% overall) patients remained equivocal. Final HER2 positivity with AC2013 (23.6%) was increased (P < .001) compared with FDA (13.1%) and AC2007 (11%) guidelines.

Conclusion

In a reference laboratory cohort that was highly enriched for IHC 2+ patient samples, AC2013 guidelines led to a larger number of FISH-equivocal patients. Approximately one half of these FISH-equivocal patients (7.4% overall) became HER2-positive upon alternative FISH probe testing. However, these patients would not have participated in the pivotal HDT trials. Clinical utility data on HDT benefit in these patients and other special subsets are needed.

Marriage of antibody–drug conjugate with gold nanorods to achieve multi-modal ablation of breast cancer cells and enhanced photoacoustic performance

A multifunctional nano platform against cancer using SiO₂-coated gold nanorods and antibody–drug conjugate is constructed. It incorporates active targeting, antibody therapy, drug therapy, photothermal therapy, and enhanced photoacoustic performance.

The level of HER2 expression is a predictor of antibody-HER2 trafficking behavior in cancer cells

The receptor tyrosine kinase HER2 is known to play a central role in mitogenic signaling, motivating the development of targeted, HER2-specific therapies. However, despite the longstanding use of antibodies to target HER2, controversies remain concerning antibody/HER2 trafficking behavior in cancer cells. Understanding this behavior has direct relevance to the mechanism of action and effective design of such antibodies. In the current study, we analyzed the intracellular dynamics of trastuzumab, a marketed HER2-targeting antibody, in a panel of breast and prostate cancer cell lines that have a wide range of HER2 expression levels. Our results reveal distinct post-endocytic trafficking behavior of antibody-HER2 complexes in cells with different HER2 expression levels. In particular, HER2-overexpressing cells exhibit efficient HER2 recycling and limited reductions in HER2 levels upon antibody treatment, and consequently display a high level of antibody persistence on their plasma membrane. By contrast, in cells with low HER2 expression, trastuzumab treatment results in rapid antibody clearance from the plasma membrane combined with substantial decreases in HER2 levels and undetectable levels of recycling. A cell line with intermediate levels of HER2 expression exhibits both antibody recycling and clearance from the cell surface. Significantly, these analyses demonstrate that HER2 expression levels, rather than cell origin (breast or prostate), is a determinant of subcellular trafficking properties. Such studies have relevance to optimizing the design of antibodies to target HER2.

Blockade of a key region in the extracellular domain inhibits HER2 dimerization and signaling

BACKGROUND

Several treatment strategies target the human epidermal growth factor receptor 2 (HER2) in breast carcinomas, including monoclonal antibodies directed against HER2's extracellular domain (ECD) and small molecule inhibitors of its tyrosine kinase activity. Yet, novel therapies are needed that prevent HER2 dimerization with other HER family members, because current treatments are only partially effective.

METHODS

To test the hypothesis that HER2 activation requires a protein sequence in the HER2-ECD that mediates HER2 homo- and heterodimerization, we introduced a series of deletion mutations in the third subdomain of HER2-ECD. These deletion mutants were retrovirally expressed in breast cancer (BC) cells that naturally overexpress HER2 and in noncancerous, HER2-negative breast epithelial cells. One-factor analysis of variance or Student's t test were used to analyze differences. All statistical tests were two-sided.

RESULTS

The smallest deletion in the ECD domain of HER2, which removed only 16 amino acids (HER2-ECDΔ451-466), completely disrupted the oncogenic potential of HER2. In contrast to wild-type HER2, the mutant-inhibited anchorage-independent growth (mean number of colonies: mutant, 70, 95% confidence interval [CI] = 55 to 85; wild-type, 400, 95% CI = 320 to 480, P < .001) increased sensitivity to paclitaxel treatment in both transformed and nontransformed cells. Overexpression of HER2Δ451-466 efficiently inhibited activation of HER1, HER2, and HER3 in all cell lines tested.

CONCLUSIONS

These findings reveal that an essential "activating" sequence exists in the extracellular domain of HER2. Disruption of this sequence disables the HER2 dimerization loop, blocks subsequent activation of HER2-driven oncogenic signaling, and generates a dominant-negative form of HER2. Reagents specifically against this molecular activation switch may represent a novel targeted approach for the management of HER2-overexpressing carcinomas.

Impact of c-MYC protein expression on outcome of patients with early-stage HER2+ breast cancer treated with adjuvant trastuzumab NCCTG (alliance) N9831

PURPOSE

This study investigated the association between tumor MYC protein expression and disease-free survival (DFS) of patients randomized to receive chemotherapy alone (Arm A) or chemotherapy with sequential (Arm B) or concurrent trastuzumab (Arm C) in the N9831 (Alliance) adjuvant HER2(+) trastuzumab breast cancer trial.

EXPERIMENTAL DESIGN

This analysis included 1,736 patients randomized to Arms A, B, and C on N9831. Nuclear MYC protein expression was determined in tissue microarray sections containing three biopsies per patient or whole tissue sections using standard immunohistochemistry (clone 9E10). A tumor was considered positive for MYC protein overexpression (MYC(+)) if the nuclear 3+ staining percentage was more than 30%.

RESULTS

Five hundred and seventy-four (33%) tumors were MYC(+). MYC(+) was associated with hormone receptor positivity (χ(2), P = 0.006), tumors 2 cm or more (χ(2), P = 0.02), and a higher rate of nodal positivity (χ(2), P < 0.001). HRs for DFS (median follow-up: 6.1 years) for Arm C versus A were 0.52 (P = 0.006) and 0.65 (P = 0.006) for patients with MYC(+) and MYC(-) tumors, respectively (P(interaction) = 0.40). For Arm B versus A, HRs for patients with MYC(+) and MYC(-) tumors were 0.79 (P = 0.21) and 0.74 (P = 0.04), respectively (P(interaction) = 0.71). For Arm C versus B, HRs for patients with MYC(+) and MYC(-) tumors were 0.56 (P = 0.02) and 0.89 (P = 0.49), respectively (P(interaction) = 0.17).

CONCLUSIONS

Our data do not support an impact of tumor MYC protein expression on differential benefit from adjuvant 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.

C-MYC alterations and association with patient outcome in early-stage HER2-positive breast cancer from the north central cancer treatment group N9831 adjuvant trastuzumab trial

PURPOSE

Findings from the human epidermal growth factor receptor 2 (HER2) -positive National Surgical Adjuvant Breast and Bowel Project (NSABP) B31 trial suggested that MYC/HER2 coamplification (> 5.0 copies/nucleus) was associated with additional benefit from adjuvant trastuzumab in patients with early-stage breast cancer. To further explore this relationship, we investigated associations between MYC amplification and disease-free survival (DFS) in a similar adjuvant trastuzumab HER2-positive breast cancer trial-North Central Cancer Treatment Group (NCCTG) N9831.

PATIENTS AND METHODS

This analysis included 799 patients randomly assigned to receive chemotherapy alone or with concurrent trastuzumab on N9831. Fluorescence in situ hybridization (FISH) was performed by using a dual-probe mixture for MYC and centromere 8 (MYC:CEP8) on tissue microarrays. MYC amplification was prespecified as MYC:CEP8 ratio > 2.2 or average MYC copies/nucleus > 5.0. Exploratory variables included polysomy 8.

RESULTS

In comparing DFS (median follow-up, 4.0 years) between treatments, patients with MYC:CEP8 ratio ≤ 2.2 (n = 618; 77%) and > 2.2 (n = 181; 23%) had hazard ratios (HRs) of 0.46 (P < .001) and 0.67 (P = .33), respectively (interaction P = .38). Patients with MYC copies/nucleus ≤ 5.0 (n = 534; 67%) and > 5.0 (n = 265; 33%) had HRs of 0.52 (P = .002) and 0.48 (P = .02), respectively (interaction P = .94). Patients with MYC:CEP8 ratio < 1.3 with normal chromosome 8 copy number (n = 141; 18%) and ≥ 1.3 or < 1.3 with polysomy 8 (n = 658; 82%) had HRs of 0.66 (P = .28) and 0.44 (P < .001), respectively (interaction P = .23). Patients with MYC copies/nucleus < 2.5 (n = 130; 16%) and ≥ 2.5 (n = 669; 84%) had HRs of 1.07 (P = .87) and 0.42 (P < .001), respectively (interaction P = .05).

CONCLUSION

We did not confirm the B31 association between MYC amplification and additional trastuzumab benefit. Exploratory analyses revealed potential associations between alternative MYC/chromosome 8 copy number alterations and differential benefit of adjuvant trastuzumab.

HER2 and chromosome 17 effect on patient outcome in the N9831 adjuvant trastuzumab trial

PURPOSE

We examined associations between tumor characteristics (human epidermal growth factor receptor 2 [HER2] protein expression, HER2 gene and chromosome 17 copy number, hormone receptor status) and disease-free survival (DFS) of patients in the N9831 adjuvant trastuzumab trial.

PATIENTS AND METHODS

All patients (N = 1,888) underwent chemotherapy with doxorubicin and cyclophosphamide, followed by weekly paclitaxel with or without concurrent trastuzumab. HER2 status was determined by immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH) at a central laboratory, Mayo Clinic, Rochester, MN. Patients with conflicting local positive HER2 expression results but normal central laboratory testing were included in the analyses (n = 103).

RESULTS

Patients with HER2-positive tumors (IHC 3+, FISH HER2/centromere 17 ratio ≥ 2.0, or both) benefited from trastuzumab, with hazard ratios (HRs) of 0.46, 0.49, and 0.45, respectively (all P < .0001). Patients with HER2-amplified tumors with polysomic (p17) or normal (n17) chromosome 17 copy number also benefited from trastuzumab, with HRs of 0.52 and 0.37, respectively (P < .006). Patients who received chemotherapy alone and had HER2-amplified and p17 tumors had a longer DFS than those who had n17 (78% v 68%; P = .04), irrespective of hormone receptor status or tumor grade. Patients with HER2-normal tumors by central testing (n = 103) seemed to benefit from trastuzumab, but the difference was not statistically significant (HR, 0.51; P = .14). Patients with hormone receptor-positive or -negative tumors benefited from the addition of trastuzumab, with HRs of 0.42 (P = .005) and 0.60 (P = .0001), respectively.

CONCLUSION

These results confirm that IHC or FISH HER2 testing is appropriate for patient selection for adjuvant trastuzumab therapy. Trastuzumab benefit seemed independent of HER2/centromere 17 ratio and chromosome 17 copy number.

The role of ErbB3 and its binding partners in breast cancer progression and resistance to hormone and tyrosine kinase directed therapies

An increasingly important role for the ErbB3 receptor in the genesis and progression of breast cancer is emerging. ErbB3 is frequently overexpressed in breast cancer and coexpression of ErbB2/3 is a poor prognostic indicator. ErbB3 has also been implicated in the development of resistance to antiestrogens such as tamoxifen and ErbB tyrosine kinase inhibitors such as gefitinib. Persistent activation of the AKT pathway has been postulated to contribute to ErbB3-mediated resistance to these therapies. This activation may be due in part to the inappropriate production of the ErbB3 ligand heregulin. ErbB3 binding proteins, which negatively regulate ErbB3 protein levels and the ability of ErbB3 to transmit proliferative signals, also contribute to breast cancer progression and treatment resistance. These proteins include the intracellular RING finger E3 ubiquitin ligase Nrdp1 and the leucine-rich protein LRIG-1 that mediate receptor degradation. Ebp1, another ErbB3 binding protein, suppresses HRG driven breast cancer cell growth and contributes to tamoxifen sensitivity. These studies point to the importance of the evaluation of protein levels and functional activity of ErbB3 and its binding proteins in breast cancer prognosis and prediction of clinical response to treatment.

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

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

CD4+CD25+ regulatory T-cell frequency in HER-2/neu (HER)-positive and HER-negative advanced-stage breast cancer patients

PURPOSE

CD4(+)CD25(bright) regulatory T cells (Tregs) are increased in patients with several malignancies and correlate with disease stage and prognosis. Breast cancer patients represent a heterogeneous population with unpredictable disease progression even at advanced stages. Circulating Tregs in correlation with HER-2/neu (HER) status and treatment with chemotherapy, either alone or in combination with trastuzumab therapy, were monitored in advanced-stage breast cancer patients.

EXPERIMENTAL DESIGN

Circulating Treg frequency and absolute counts of 46 HER(+) and 28 HER(-), stage III and IV, breast cancer patients before therapy and during trastuzumab therapy and/or chemotherapy have been compared with 24 healthy donors and correlated with plasma HER extracellular domain concentration and clinical outcome.

RESULTS

Treg frequency in HER(+) patients was significantly increased compared with both HER(-) patients and healthy donors. Trastuzumab therapy, with or without combined chemotherapy, resulted in a progressive decrease of circulating Tregs. Percentage change in Tregs statistically correlated with percentage change in plasma HER extracellular domain. Furthermore, decrease in Tregs correlated with either objective clinical response or stable disease, whereas increased Treg frequency during trastuzumab therapy coincided with disease progression. No statistically significant change in Treg frequency following chemotherapy was observed in HER(-) patients.

CONCLUSIONS

Treg cell frequency does not directly correlate with clinical stage in breast cancer, as stage III and IV HER(+) and HER(-) patients exhibit significantly different Treg profiles. Trastuzumab therapy, either alone or combined with chemotherapy, results in decreased Treg frequency in HER(+) advanced patients with an objective clinical response.

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

Purpose

Human epidermal growth factor receptor 2 (HER-2) overexpression has been associated with the genesis and progression of a subset of breast cancers. The function of HER-2 may be upregulated by overexpression or by the availability of neuregulins (NRGs), a group of transmembrane growth factors. Transmembrane NRGs strongly activated HER-2 and cell proliferation in breast cancer cells that did not overexpress HER-2, and treatment with trastuzumab prevented the proliferative action of transmembrane NRG. This raised the relevant clinical question of whether patients considered as HER-2 negative, but expressing transmembrane NRG, may benefit from treatment with trastuzumab.

Patients and Methods

MCF7 cells expressing transmembrane NRG (MCF7-NRGα2c) were injected into mice, and their sensitivity to trastuzumab was assessed. A retrospective study of 124 patients with early-stage or metastatic breast cancer was conducted. Expression of transmembrane NRG was evaluated by immunohistochemistry. In 11 patients, Western blot for NRGs was also carried out. Statistics were performed to analyze possible correlations between NRG expression and response to trastuzumab-based therapies, event-free survival, and overall survival (OS).

Results

Trastuzumab inhibited tumor growth in mice injected with MCF7-NRGα2c cells. Transmembrane NRG was frequently expressed in breast cancer patients. Overexpression of transmembrane NRG significantly correlated with a longer event-free survival and OS in patients with low or normal HER-2 expression who were treated with trastuzumab-based therapies but not in patients with HER-2 overexpression.

Conclusion

We suggest that the spectrum of patients who may benefit from trastuzumab-based therapies may be widened to include patients with metastatic breast cancer without HER-2 amplification but who express transmembrane NRGs.