ErbB3 Antibodies Research Articles

Cisplatin-induced increase in heregulin 1 and its attenuation by the monoclonal ErbB3 antibody seribantumab in bladder cancer

Cisplatin-based combination chemotherapy is the foundation for treatment of advanced bladder cancer (BlCa), but many patients develop chemoresistance mediated by increased Akt and ERK phosphorylation. However, the mechanism by which cisplatin induces this increase has not been elucidated. Among six patient-derived xenograft (PDX) models of BlCa, we observed that the cisplatin-resistant BL0269 express high epidermal growth factor receptor, ErbB2/HER2 and ErbB3/HER3. Cisplatin treatment transiently increased phospho-ErbB3 (Y1328), phospho-ERK (T202/Y204) and phospho-Akt (S473), and analysis of radical cystectomy tissues from patients with BlCa showed correlation between ErbB3 and ERK phosphorylation, likely due to the activation of ERK via the ErbB3 pathway. In vitro analysis revealed a role for the ErbB3 ligand heregulin1-β1 (HRG1/NRG1), which is higher in chemoresistant lines compared to cisplatin-sensitive cells. Additionally, cisplatin treatment, both in PDX and cell models, increased HRG1 levels. The monoclonal antibody seribantumab, that obstructs ErbB3 ligand-binding, suppressed HRG1-induced ErbB3, Akt and ERK phosphorylation. Seribantumab also prevented tumor growth in both the chemosensitive BL0440 and chemoresistant BL0269 models. Our data demonstrate that cisplatin-associated increases in Akt and ERK phosphorylation is mediated by an elevation in HRG1, suggesting that inhibition of ErbB3 phosphorylation may be a useful therapeutic strategy in BlCa with high phospho-ErbB3 and HRG1 levels.

Neuregulin Signaling Is a Mechanism of Therapeutic Resistance in Head and Neck Squamous Cell Carcinoma.

EGFR signaling confers resistance to radiotherapy and is a validated target in head and neck squamous cell carcinoma (HNSCC). The inhibition of EGFR in combination with radiotherapy improves local control and overall survival in these patients; however, therapeutic resistance limits the efficacy of this approach. We therefore sought to identify cellular mechanisms that cause resistance to EGFR inhibition and radiotherapy in HNSCC. Though clonal isolation of carcinoma cells exposed to increasing concentrations of cetuximab, we found that resistant cells upregulate prosurvival ErbB3 and AKT signaling. Using EFM-19 cells and confirmatory analysis of protein levels, we demonstrate that cetuximab resistance is characterized by enhanced neuregulin expression identifying a novel adaptive mechanism of therapeutic resistance. Inhibition of this autocrine loop with CDX-3379 (an ErbB3 specific antibody) was sufficient to block ErbB3/AKT signaling in cetuximab resistant cells. The combination of CDX-3379 and cetuximab reduced proliferation and survival after radiotherapy in several HNSCC cell lines. These in vitro findings were confirmed in xenograft tumor growth experiments including an approach using growth factor-supplemented Matrigel. In vivo, the delivery of EGFR and ErbB3 antibodies significantly reduced tumor growth in cetuximab-resistant FaDu and CAL27 xenografts. In summary, this work demonstrates that autocrine NRG ligand secretion is a mechanism for therapeutic resistance to cetuximab and radiotherapy. This cross-resistance to both therapeutic modalities identifies NRG as an actionable therapeutic target for improving treatment regimens in HNSCC.

ErbB3 Targeting Enhances the Effects of MEK Inhibitor in Wild-Type BRAF/NRAS Melanoma.

MEK-ERK1/2 signaling is elevated in melanomas that are wild-type for both BRAF and NRAS (WT/WT), but patients are insensitive to MEK inhibitors. Stromal-derived growth factors may mediate resistance to targeted inhibitors, and optimizing the use of targeted inhibitors for patients with WT/WT melanoma is a clinical unmet need. Here, we studied adaptive responses to MEK inhibition in WT/WT cutaneous melanoma. The Cancer Genome Atlas data set and tumor microarray studies of WT/WT melanomas showed that high levels of neuregulin-1 (NRG1) were associated with stromal content and ErbB3 signaling. Of growth factors implicated in resistance to targeted inhibitors, NRG1 was effective at mediating resistance to MEK inhibitors in patient-derived WT/WT melanoma cells. Furthermore, ErbB3/ErbB2 signaling was adaptively upregulated following MEK inhibition. Patient-derived cancer-associated fibroblast studies demonstrated that stromal-derived NRG1 activated ErbB3/ErbB2 signaling and enhanced resistance to a MEK inhibitor. ErbB3- and ErbB2-neutralizing antibodies blocked the protective effects of NRG1 in vitro and cooperated with the MEK inhibitor to delay tumor growth in both cell line and patient-derived xenograft models. These results highlight tumor microenvironment regulation of targeted inhibitor resistance in WT/WT melanoma and provide a rationale for combining MEK inhibitors with anti-ErbB3/ErbB2 antibodies in patients with WT/WT cutaneous melanoma, for whom there are no effective targeted therapy options.Significance: This work suggests a mechanism by which NRG1 regulates the sensitivity of WT NRAS/BRAF melanomas to MEK inhibitors and provides a rationale for combining MEK inhibitors with anti-ErbB2/ErbB3 antibodies in these tumors. Cancer Res; 78(19); 5680-93. ©2018 AACR.

Anti-Trop2 blockade enhances the therapeutic efficacy of ErbB3 inhibition in head and neck squamous cell carcinoma

ErbB3 has been widely implicated in treatment resistance, but its role as a primary treatment target is less clear. Canonically ErbB3 requires EGFR or ErbB2 for activation, whereas these two established treatment targets are thought to signal independently of ErbB3. In this study, we show that ErbB3 is essential for tumor growth of treatment-naive HNSCC patient-derived xenografts. This ErbB3 dependency occurs via ErbB3-mediated control of EGFR activation and HIF1α stabilization, which require ErbB3 and its ligand neuregulin-1. Here, we show that ErbB3 antibody treatment selects for a population of ErbB3-persister cells that express high levels of the transmembrane protein Trop2 that we previously identified as an inhibitor of ErbB3. Co-treatment with anti-ErbB3 and anti-Trop2 antibodies is synergistic and produces a greater anti-tumor response than either antibody alone. Collectively, these data both compel a revision of ErbB-family signaling and delineate a strategy for its effective inhibition in HNSCC.

Abstract POSTER-THER-1411: MM-141, an IGF-1R and ErbB3 directed tetravalent bispecific antibody, inhibits ovarian cancer cell growth in vitro

Abstract PURPOSE OF STUDY: Insulin-like growth factor receptor 1 (IGF-1R) signaling has been implicated in the pathogenesis of ovarian cancer. However, IGF-1R inhibitors have had limited efficacy in clinical trials to date. ErbB3, a member of the ErbB receptor tyrosine kinase family, can activate AKT survival signaling through binding of its ligand heregulin (HRG) in a majority of IGF-1 sensitive human cancer cell lines. ErbB3 and pAKT expression are upregulated following IGF-1R blockade and thus activated ErbB3 signaling may represent a potential escape route in the development of resistance to therapy. MM-141, an IGF-1R and ErbB3 directed bispecific antibody, blocks and degrades IGF-1R and ErbB3 containing receptor complexes leading to inhibition of downstream tumor pro-survival signaling to a greater extent as compared to anti-IGF-1R and ErbB3 antibodies. Here we explore the activity of MM-141 in ovarian cancer cell lines in vitro. EXPERIMENTAL PROCEDURES: Growth inhibitory activity of MM-141 was tested on a panel of established ovarian cancer cell lines in vitro. The ability of MM-141 to inhibit basal and IGF-1- and HRG-induced signaling was explored by ELISA and western blotting analyses. DATA SUMMARY: Inhibition of cell proliferation mediated by MM-141 varied among the ovarian cancer cell lines profiled in vitro. Furthermore, MM-141 treatment inhibited basal and ligand-activated IGF-1R, ErbB3 and downstream signaling in a selection of these ovarian cell lines. CONCLUSIONS: Our findings suggest that co-inhibition of IGF-1R and ErbB3 signaling with MM-141 has the potential to be an effective therapy for ovarian cancer patients by blocking redundant survival pathway activation. Citation Format: Michael Curley, Akos Czibere, Alexey Lugovskoy. MM-141, an IGF-1R and ErbB3 directed tetravalent bispecific antibody, inhibits ovarian cancer cell growth in vitro [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1411.

A phase 1, open-label study to evaluate the safety and pharmacokinetics of the anti ErbB3 antibody, KTN3379, alone or in combination with targeted therapies in patients with advanced tumors.

2598 Background: KTN3379 is a human monoclonal antibody against a unique epitope of human epidermal growth factor receptor-3 (ErbB3) blocking ligand (neuregulin (NRG)) dependent and independent act...

Effect of MM-141 on gemcitabine and nab-paclitaxel potentiation in preclinical models of pancreatic cancer through induction of IGF-1R and ErbB3 degradation.

289 Background: Gemcitabine, the first-line treatment for pancreatic cancer, has been improved by addition of nab-paclitaxel. However, patient response to this regimen is limited. Oncogenic insulin-like growth factor 1 (IGF-1) and heregulin (HRG) signaling are associated with increased cancer risk and decreased response to anti-metabolites and taxanes. Therefore, we explored MM-141, a novel bispecific antibody that blocks ErbB3 and IGF-1 receptor (IGF-1R) signaling, in combination with nab-paclitaxel and gemcitabine in preclinical models of pancreatic cancer. Methods: Combinations with MM-141, gemcitabine, and nab-paclitaxel were investigated in pancreatic cancer cell lines, in vitro and in vivo. The effects of MM-141, gemcitabine, and nab-paclitaxel on tumor growth and signaling were measured by 3D spheroid growth, ELISA, Western, and mouse xenograft experiments. Results: In vitro studies show that IGF-1 and HRG are potent activators of AKT signaling, leading to increased pancreatic tumor cell proliferation and decreased sensitivity to gemcitabine and nab-paclitaxel. MM-141 inhibits ligand-induced AKT activation, induces IGF-1R and ErbB3 degradation better than a mixture of IGF-1R and ErbB3 antibodies, and sensitizes cells to gemcitabine and nab-paclitaxel, in vitro. In vivo, MM-141 combines favorably with a nab-paclitaxel/gemcitabine regimen, leading to curative outcomes in a subset of treated mice. Conclusions: ErbB3 and IGF-1R co-inhibition is required to inhibit AKT signaling in pancreatic adenocarcinoma cell lines. These receptors are associated with chemoresistance to gemcitabine and nab-paclitaxel, which is abrogated by co-administration with MM-141. MM-141-induced degradation of oncogenic receptor complexes is likely essential to reverse chemoresistance and enhance effects of the nab-paclitaxel/gemcitabine regimen. These data, taken together with wide-spread expression of IGF-1R and ErbB3 in Stage IV pancreatic adenocarcinoma tissue, support clinical exploration of a MM-141/nab-paclitaxel/gemcitabine regimen in frontline metastatic pancreatic cancer. Preparations for a randomized Phase 2 study are underway.

Abstract 2611: Function blocking ERBB3 antibody inhibits adaptive response to RAF inhibitor

Abstract ERBB3/HER3 is a member of the EGFR family of receptor tyrosine kinase. Our lab recently showed that treating melanoma cells with the FDAapproved small molecule BRAF inhibitor vemurafenib leads to an increase in ERBB3 signaling when grown in the presence of its ligand neuregulin (NRG1). Here, we show that targeting ERBB3 with a monoclonal antibody inhibits its activation and downstream signaling in the presence of vemurafenib and NRG1. This inhibition of ERBB3 led to a decrease in proliferation and increase in apoptosis in vitro as measured by EdU and AnnexinV/PI staining. Targeting ERBB3 in combination with mutant BRAF in vivo resulted in a delay of tumor re-growth in immune deficient mice compared to targeting mutant BRAF alone. Taken together, these results indicate that targeting ERBB3 in combination with mutant BRAF in melanoma may help enhance the initial effects of vemurafenib in the clinic. Citation Format: Curtis Harrison Kugel, Edward J. Hartsough, Michael A. Davies, Andrew E. Aplin. Function blocking ERBB3 antibody inhibits adaptive response to RAF inhibitor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2611. doi:10.1158/1538-7445.AM2014-2611

Abstract 5437: Dual targeting of ErbB-2 and ErbB-3: A new potential strategy for the treatment of pancreatic cancer

Abstract Background: Pancreatic cancer (PC) is one of the most lethal cancers and there is an urgent need to find out new therapeutic approaches. Deregulated signaling through ErbB-1 and ErbB-2, members of the epidermal growth factor receptor family, frequently occurs in PC. However, attempts aiming at inhibiting ErbB-1 and ErbB-2 have revealed only a modest impact on disease outcome. A growing body of evidence suggests that ErbB-3 and its ligand NRG-1β are key players in driving oncogenic signaling and resistance to targeted therapy in PC. We have recently developed a novel humanized ErbB-3 antibody, named EV20, which displayed a potent antitumor activity by promoting receptor downregulation in vitro and in vivo. Here we hypothesized that targeting of ErbB-3 with EV20 would enhance the therapeutic effect of ErbB-2 inhibitors in PC. Materials and Methods: Three different PC cell lines (BxPC-3, HPAF II and SW1990) were chosen based on their metastatic origin, genetic background (KRAS status) and responsiveness to erlotinib. The expression of ErbB-1, ErbB-2 and ErbB-3 was analyzed by FACS and WB. The effects of trastuzumab, cetuximab, EV20 and their combinations on NRG-1β-induced activation of the ErbB3/PI3K/Akt axis, cell proliferation, and in vivo tumor growth were evaluated by standard procedures. Results: ErbB-1 was overexpressed by all the cell lines, whereas the expression levels of ErbB-2 and ErbB-3 were moderate in HPAFII cells and low in BxPC-3 and SW1990 cells. NRG-1β was more effective than EGF (an ErbB-1 ligand) in activating ErbB-3 downstream signaling, which was not inhibited by cetuximab, despite a high ErbB-1 expression in the cells. Conversely, inhibition of ErbB-2 and/or ErbB-3 resulted in a marked suppression of NRG-1β-driven Akt activation. Finally, EV20 in combination with trastuzumab exerted a superior antitumor activity compared to single agent alone in terms of cell proliferation and growth of PC xenografts in nude mice. Conclusions: Dual targeting of ErbB-2 and ErbB-3 could represent a newer therapeutic approach in PC. Note: This abstract was not presented at the meeting. Citation Format: Gianluca Sala, Reza Ghasemi, Emily Capone, Ilario Giovanni Rapposelli, Sara Traini, Cosmo Rossi, Pier Giorgio Natali, Stefano Iacobelli. Dual targeting of ErbB-2 and ErbB-3: A new potential strategy for the treatment of pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5437. doi:10.1158/1538-7445.AM2014-5437

Abstract 2718: REGN1400, a fully-human ERBB3 antibody, potently inhibits tumor growth in preclinical models, both as a monotherapy and in combination with EGFR or HER2 blockers

Abstract ERBB3 is a member of the ERBB family of receptor tyrosine kinases, that includes EGFR and HER2, well-established drivers of tumorigenesis. Recent preclinical studies indicate that both EGFR and HER2 cooperate with ERBB3 to activate the phosphatidylinositol-3 kinase/Akt survival pathway and to promote tumor cell survival. Furthermore, ERBB3 activation has been demonstrated to mediate resistance to EGFR inhibitors in non-small cell lung cancer cell lines and to HER2 inhibitors in breast cancer cell lines. Consistent with these findings, anti-ERBB3 monoclonal antibodies have been shown to inhibit the growth of human tumor xenografts, demonstrating the importance of ERBB3 for tumor growth in vivo. REGN1400 is a fully-human anti-ERBB3 monoclonal antibody that binds human ERBB3 with high affinity (KD ∼50pM) and potently inhibits binding of the ERBB3 ligand neuregulin 1 (IC50 ∼30pM). REGN1400 inhibited phosphorylation of ERBB3 and Akt in multiple human tumor cell lines in vitro, including A431 (epidermoid carcinoma), MDA-MB-175-VII (breast cancer) and FaDu (head and neck cancer). In addition, REGN1400 strongly inhibited the growth of these cell lines in vitro. Consistent with its potent effects on tumor cell growth in vitro, REGN1400 strongly inhibited the growth of A431 and FaDu tumor xenografts in a dose-dependent manner, providing 70% and 97% tumor growth inhibition, respectively. Inhibition of FaDu tumor growth by REGN1400 was accompanied by a significant decrease in tumor ERBB3 phosphorylation, as assessed by both western blot and immunohistochemistry, confirming target inhibition in vivo. While treatment of FaDu tumors with single agent REGN1400 provided almost complete tumor growth inhibition, but not regression, the combination of REGN1400 plus anti-EGFR antibody caused significant tumor regression. Furthermore, combination treatment with REGN1400 plus the anti-HER2 antibody trastuzumab inhibited the growth of BT474 breast tumor xenografts more potently than either single agent. These findings indicate that ERBB3-directed therapies might be more effective when combined with agents that inhibit other ERBB family members. Finally, gene profiling studies in REGN1400-treated tumor cells revealed upregulation of several genes that could promote resistance to REGN1400, e.g., ERBB3 itself and ERBB4. Further analysis of tumor gene expression changes induced by REGN1400 could provide insight into potentially useful combination regimens. In summary, REGN1400, a novel anti-ERBB3 antibody, exhibits significant antitumor activity in preclinical models, suggesting the possibility that it could provide benefit to patients with multiple types of cancer, either as a single agent or when combined with therapies targeting other ERBB family members. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2718. doi:1538-7445.AM2012-2718

A Two-in-One Antibody against HER3 and EGFR Has Superior Inhibitory Activity Compared with Monospecific Antibodies

Extensive crosstalk among ErbB/HER receptors suggests that blocking signaling from more than one family member may be essential to effectively treat cancer and limit drug resistance. We generated a conventional IgG molecule MEHD7945A with dual HER3/EGFR specificity by phage display engineering and used structural and mutational studies to understand how a single antigen recognition surface binds two epitopes with high affinity. As a human IgG1, MEHD7945A exhibited dual action by inhibiting EGFR- and HER3-mediated signaling invitro and invivo and the ability to engage immune effector functions. Compared with monospecific anti-HER antibodies, MEHD7945A was more broadly efficacious in multiple tumor models, showing that combined inhibition of EGFR and HER3 with a single antibody is beneficial.

An ErbB-3 antibody, MP-RM-1, inhibits tumor growth by blocking ligand-dependent and independent activation of ErbB-3/Akt signaling

The ErbB receptors, such as ErbB-1 and ErbB-2, have been intensely pursued as targets for cancer therapeutics. Although initially efficacious in a subset of patients, drugs targeting these receptors led invariably to resistance, which is often associated with reactivation of the ErbB-3-PI3K-Akt signaling. This may be overcome by an ErbB-3 ligand that abrogates receptor-mediated signaling. Toward this end, we have generated a mouse monoclonal antibody, MP-RM-1, against the extracellular domain (ECD) of ErbB-3 receptor. Assessment of human tumor cell lines, as well as early passage tumor cells revealed that MP-RM-1 effectively inhibited both NRG-1β-dependent and -independent ErbB-3 activation. The antagonizing effect of MP-RM-1 was of non-competitive type, as binding of [(125)I]-labeled NRG-1β to ErbB-3 was not influenced by the antibody. MP-RM-1 treatment led, in most instances, to decreased ErbB-3 expression. In addition, MP-RM-1 was able to inhibit the colony formation ability of tumor cells and tumor growth in two human tumor xenograft nude mouse models. Treatment with the antibody was associated with a decreased ErbB-3 and Akt phosphorylation and ErbB-3 expression in the excised tumor tissue. Collectively, these results indicate that MP-RM-1 has the potential to interfere with signaling by ErbB-3 and reinforce the notion that ErbB-3 could be a key target in cancer-drug design.

Targeting ErbB3-mediated stromal–epithelial interactions in pancreatic ductal adenocarcinoma

Background:We sought to investigate the role of ErbB3-mediated signalling on the interaction between pancreatic cancer-associated fibroblasts (CAF) and carcinoma cells in an effort to disrupt tumourigenic pancreatic ductal adenocarcinoma (PDAC) stromal–epithelial cross-communication.Methods:Primary CAF cultures were established from human PDAC surgical specimens. AsPC-1 pancreatic cancer cell murine subcutaneous xenografts were developed in the presence and absence of CAF and were subsequently treated with epidermal growth factor receptor (EGFR) inhibitors (erlotinib) and ErbB3 inhibitors (MM-121, monoclonal ErbB3 antibody).Results:Cancer-associated fibroblasts were found to secrete neuregulin-1 (NRG-1), which promoted proliferation via phosphorylation of ErbB3 and AKT in AsPC-1 PDAC cells. This signalling cascade was effectively inhibited both in vitro and in vivo by specific ErbB3 blockade with MM-121, with greater degree of tumourigenesis inhibition when combined with erlotinib. The CAF–AsPC-1 pancreatic cancer xenografts reached significantly greater tumour volume than those xenografts lacking CAF and were resistant to the anti-tumour effects of EGFR inhibition with erlotinib.Conclusion:Cancer-associated fibroblasts-derived NRG-1 promote PDAC tumourigenesis via ErbB3-AKT signalling and overcomes single-agent EGFR inhibition. Disruption of this stromally mediated tumourigenic mechanism is best obtained through combined EGFR-ErbB3 inhibition with both erlotinib and MM-121. We have identified the NRG-1/ErbB3 axis as an attractive molecular target for the interruption of tumourigenic stromal–epithelial interactions within the PDAC microenvironment.

ErbB protein modifications are secondary to severe cell membrane alterations induced by elisidepsin treatment

Elisidepsin is a marine-derived anti-tumor agent with unique mechanism of action. It has been suggested to induce necrosis associated with severe membrane damage. Since indirect evidence points to the involvement of ErbB receptor tyrosine kinases and lipid rafts in the mechanism of action of elisidepsin, we investigated the effect of the drug on the distribution of ErbB proteins and systematically compared the elisidepsin sensitivity of cell lines overexpressing ErbB receptors. Stable expression of a single member of the ErbB family (ErbB1-3) or co-transfection of ErbB2 and ErbB3 did not modify the elisidepsin sensitivity of CHO and A431 cells. However, elisidepsin induced the redistribution of ErbB3 and two GPI-anchored proteins (transfected GPI-anchored eGFP and placental alkaline phosphatase) from the plasma membrane to intracellular vesicles without comparable effects on ErbB1 and ErbB2. Elisidepsin increased the binding of a conformational sensitive anti-ErbB3 antibody without modifying the binding of other ErbB2 or ErbB3 antibodies, and it decreased the homoassociation of both ErbB2 and ErbB3. We also found that elisidepsin decreased the fluorescence anisotropy of a membrane specific fluorescent probe and induced a blue shift in the emission spectrum of Laurdan pointing to significant changes in the order of the plasma membrane possibly associated with the formation of liquid ordered domains. Although the distribution of ErbB proteins is preferentially altered by elisidepsin, our data question their role in determining sensitivity to the drug. We assume that induction of liquid ordered domains is the primary action of elisidepsin leading to all the other observed changes.

Effects of an ErbB-3 antibody, MP-RM-1, on tumor growth and ligand-dependent and -independent activation of ErbB-3/akt signaling.

e13538 Background: The ErbB receptors, such as ErbB-1 and ErbB-2, have been intensely pursued as targets for cancer therapeutics. Although initially efficacious in a subset of patients, drugs targeting these receptors led invariably to resistance which is often associated with reactivation of the ErbB-3-PI3K-Akt signaling. This may be overcome by an ErbB-3 ligand binding molecule that abrogates ErbB-3 mediated signaling. Methods: we have generated a mouse monoclonal antibody, MP-RM-1, against the extracellular domain (ECD) of ErbB-3 receptor. The ability of the antibody to suppress NRG-1b-dependent and independent ErbB-3 signaling was evaluated in vitro by western blotting using a panel of human tumor cell lines (breast, melanoma, stomach and prostate) as well as early passage tumor cells obtained from patients. The effect on tumor growth in vitro was evaluated with clonogenic assay and in vivo using human tumor xenograft nude mouse models. Results: MP-RM-1 effectively inhibited NRG-1b stimulated and basal ErbB-3/Akt activation. Treatment with the antibody led, in most instances, to a decreased ErbB-3 expression. In addition, MP-RM-1 was able to inhibit the colony formation ability of tumor cells and tumor growth in human melanoma and prostate carcinoma xenografts. Tumors from animals treated with the antibody displayed a lower ErbB-3/Akt phosphorylation that was accompanied by a decreased ErbB-3 expression. Conclusions: MP-RM-1 has the potential to interfere with signaling by ErbB-3/Akt signaling and can be regarded as a potential candidate for clinical development.

Abstract 4464: C-erbB3 protein modifications are secondary to severe cell membrane alterations induced by Irvalec treatment in CHO cells

Abstract Irvalec® is a marine-derived antitumor agent that is currently undergoing phase II clinical trials. The compound induces a necrotic cell death associated with the appearance of membrane blebs and severe cell swelling reflecting a serious membrane damage caused by the drug. Indirect evidence has also suggested a possible role of ErbB proteins, in particular ErbB3, and lipid rafts in conferring sensitivity to Irvalec treatment. In order to assess the role of ErbB protein expression in the mechanism of action of Irvalec, and to measure the effect of drug treatment on the clustering properties of these proteins, we generated CHO cell lines stably transfected with ErbB2 (CHO-ErbB2) or with ErbB2 and ErbB3 (CHO-ErbB2-3). The IC50 values of the three cell lines for Irvalec did not differ significantly from each other. On the other hand treatment with Irvalec induced a significant increase in the binding of a conformational sensitive antibody to ErbB3 (ErbB3.105.5) without modifying the binding of other ErbB3 antibodies or antibodies against ErbB2. In addition, Irvalec treatment decreased the homoassociation of ErbB2 and ErbB3 measured by flow cytometric FRET. A431 cells transfected with GPI-anchored GFP or ErbB3-citrine showed significant Irvalec-induced patching of the GPI-anchor and ErbB3, whereas the distribution of ErbB1 and ErbB2 were not affected in cells transfected with ErbB1-GFP or ErbB2-mYFP. In conclusion, our data do not support a role for ErbB proteins in determining sensitivity to Irvalec, but show that these receptors are indirectly affected by exposing cells to the compound. These alterations should be ascribed to cell membrane modifications induced by Irvalec treatment Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4464.

An ErbB3 antibody, MM-121, is active in cancers with ligand-dependent activation.

ErbB3 is a critical activator of phosphoinositide 3-kinase (PI3K) signaling in epidermal growth factor receptor (EGFR; ErbB1), ErbB2 [human epidermal growth factor receptor 2 (HER2)], and [hepatocyte growth factor receptor (MET)] addicted cancers, and reactivation of ErbB3 is a prominent method for cancers to become resistant to ErbB inhibitors. In this study, we evaluated the in vivo efficacy of a therapeutic anti-ErbB3 antibody, MM-121. We found that MM-121 effectively blocked ligand-dependent activation of ErbB3 induced by either EGFR, HER2, or MET. Assessment of several cancer cell lines revealed that MM-121 reduced basal ErbB3 phosphorylation most effectively in cancers possessing ligand-dependent activation of ErbB3. In those cancers, MM-121 treatment led to decreased ErbB3 phosphorylation and, in some instances, decreased ErbB3 expression. The efficacy of single-agent MM-121 was also examined in xenograft models. A machine learning algorithm found that MM-121 was most effective against xenografts with evidence of ligand-dependent activation of ErbB3. We subsequently investigated whether MM-121 treatment could abrogate resistance to anti-EGFR therapies by preventing reactivation of ErbB3. We observed that an EGFR mutant lung cancer cell line (HCC827), made resistant to gefitinib by exogenous heregulin, was resensitized by MM-121. In addition, we found that a de novo lung cancer mouse model induced by EGFR T790M-L858R rapidly became resistant to cetuximab. Resistance was associated with an increase in heregulin expression and ErbB3 activation. However, concomitant cetuximab treatment with MM-121 blocked reactivation of ErbB3 and resulted in a sustained and durable response. Thus, these results suggest that targeting ErbB3 with MM-121 can be an effective therapeutic strategy for cancers with ligand-dependent activation of ErbB3.

Protein Kinase A-mediated Gating of Neuregulin-dependent ErbB2-ErbB3 Activation Underlies the Synergistic Action of cAMP on Schwann Cell Proliferation

In Schwann cells (SCs), cyclic adenosine monophosphate (cAMP) enhances the action of neuregulin, the most potent known mitogen for SCs, by synergistically increasing the activation of two crucial signaling pathways: ERK and Akt. However, the underlying mechanism of cross-talk between neuregulin and cAMP signaling remains mostly undefined. Here, we report that the activation of protein kinase A (PKA), but not that of exchange protein activated by cAMP (EPAC), enhances S-phase entry of SCs by synergistically enhancing the ligand-dependent tyrosine phosphorylation/activation of the neuregulin co-receptor, ErbB2-ErbB3. The role of PKA in neuregulin-ErbB signaling was confirmed using PKA inhibitors, pathway-selective cAMP analogs, and natural ligands stimulating PKA activity in SCs, such as adenosine and epinephrine. Two basic observations defined the synergistic action of PKA as "gating" for neuregulin-ErbB signaling: 1) the activation of PKA was not sufficient to induce S-phase entry or the activation of either ErbB2 or ErbB3; and 2) the presence of neuregulin was strictly required to ignite ErbB activation and thereby ERK and Akt signaling. However, PKA directly phosphorylated ErbB2 on Thr-686, a highly conserved intracellular regulatory site that was required for the PKA-mediated synergistic enhancement of neuregulin-induced ErbB2-ErbB3 activation and proliferation in SCs. The gating action of PKA on neuregulin-induced ErbB2-ErbB3 activation has important biological significance, because it insures signal amplification into the ERK and Akt pathways without compromising either the neuregulin dependence or the high specificity of ErbB signaling pathways.

ErbB transmembrane tyrosine kinase receptors are expressed by sensory and motor neurons projecting into sciatic nerve.

Adult spinal cord motor and dorsal root ganglion (DRG) sensory neurons express multiple neuregulin-1 (NRG-1) isoforms that act as axon-associated factors promoting neuromuscular junction formation and Schwann cell proliferation and differentiation. NRG-1 isoforms are also expressed by muscle and Schwann cells, suggesting that motor and sensory neurons are themselves acted on by NRG-1 isoforms produced by their peripheral targets. To test this hypothesis, we examined the expression of the NRG-1 receptor subunits erbB2, erbB3, and erbB4 in rat lumbar DRG and spinal cord. All three erbB receptors are expressed in these tissues. Sciatic nerve transection, an injury that induces Schwann cell expression of NRG-1, alters erbB expression in DRG and cord. Virtually all DRG neurons are erbB2- and erbB3-immunoreactive, with erbB4 also detectable in many neurons. In spinal cord white matter, erbB2 and erbB4 antibodies produce dense punctate staining, whereas the erbB3 antibody primarily labels glial cell bodies. Spinal cord dorsal and ventral horn neurons, including alpha-motor neurons, exhibit erbB2, erbB3, and erbB4 immunoreactivity. Spinal cord ventral horn also contains a population of small erbB3+/S100beta+/GFAP- cells (GFAP-negative astrocytes or oligodendrocytes). We conclude that sensory and motor neurons projecting into sciatic nerve express multiple erbB receptors and are potentially NRG-1 responsive.

Heregulin-dependent activation of phosphoinositide 3-kinase and Akt via the ErbB2/ErbB3 co-receptor.

The ErbB2/ErbB3 heregulin co-receptor has been shown to couple to phosphoinositide (PI) 3-kinase in a heregulin-dependent manner. The recruitment and activation of PI 3-kinase by this co-receptor is presumed to occur via its interaction with phosphorylated Tyr-Xaa-Xaa-Met (YXXM) motifs occurring in the ErbB3 C terminus. In this study, mutant ErbB3 receptor proteins expressed in COS7 cells were used to investigate PI 3-kinase-dependent signaling pathways activated by the ErbB2/ErbB3 co-receptor. We observed that a mutant ErbB3 protein with each of its six YXXM motifs containing a Tyr --> Phe substitution was unable to bind either the p85 regulatory or p110 catalytic subunit of PI 3-kinase. However, restoration of a single YXXM motif was sufficient to mediate association with the PI 3-kinase holoenzyme, although at a lower level than wild-type ErbB3. When ErbB3 YXXM motifs were restored in pairs, evidence for cooperativity between two, those incorporating Tyr-1273 and Tyr-1286, was observed. Interestingly, we have shown that an apparent association of PI 3-kinase activity with ErbB2/Neu was due to the residual presence of ErbB3 in ErbB2 immunoprecipitates. The necessity of ErbB3 association with PI 3-kinase for downstream signaling to the effector kinase Akt was also investigated. Here, the heregulin-dependent translocation of Akt to the plasma membrane and its subsequent activation was observed in intact NIH-3T3 fibroblasts. Recruitment of PI 3-kinase to ErbB3 was required for both activities, and it appeared that ErbB2 activation alone was not sufficient to activate PI 3-kinase signaling in these cells.