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1.  The anti-erbB3 antibody MM-121/SAR256212 in combination with trastuzumab exerts potent antitumor activity against trastuzumab-resistant breast cancer cells 
Molecular Cancer  2013;12:134.
Background
Elevated expression of erbB3 receptor has been reported to induce resistance to therapeutic agents, including trastuzumab in erbB2-overexpressing breast cancer. Our recent studies indicate that erbB3 interacts with both erbB2 and IGF-1 receptor to form a heterotrimeric complex in trastuzumab-resistant breast cancer cells. Herein, we investigate the antitumor activity of MM-121/SAR256212, a fully human anti-erbB3 antibody (Ab), against two erbB2-overexpressing breast cancer cell lines resistant to trastuzumab.
Methods
MTS-based proliferation assays were used to determine cell viability upon treatment of trastuzumab and/or MM-121/SAR256212. Cell cycle progression was examined by flow cytometric analysis. Western blot analyses were performed to determine the expression and activation of proteins. Tumor xenografts were established by inoculation of the trastuzumab-resistant BT474-HR20 cells into nude mice. The tumor-bearing mice were treated with trastuzumab and/or MM-121/SAR256212 via i.p injection to determine the Abs’ antitumor activity. Immunohistochemical analyses were carried out to study the Abs’ inhibitory effects on tumor cell proliferation and induction of apoptosis in vivo.
Results
MM-121 significantly enhanced trastuzumab-induced growth inhibition in two sensitive and two resistant breast cancer cell lines. MM-121 in combination with trastuzumab resulted in a dramatic reduction of phosphorylated erbB3 (P-erbB3) and Akt (P-Akt) in the in vitro studies. MM-121 combined with trastuzumab did not induce apoptosis in the trastuzumab-resistant cell lines under our cell culture condition, rather induced cell cycle G1 arrest mainly associated with the upregulation of p27kip1. Interestingly, in the tumor xenograft model established from the trastuzumab-resistant cells, MM-121 in combination with trastuzumab as compared to either agent alone dramatically inhibited tumor growth correlated with a significant reduction of Ki67 staining and increase of cleaved caspase-3 in the tumor tissues.
Conclusions
The combination of MM-121 and trastuzumab not only inhibits erbB2-overexpressing breast cancer cell proliferation, but also promotes the otherwise trastuzumab-resistant cells undergoing apoptosis in an in vivo xenografts model. Thus, MM-121 exhibits potent antitumor activity when combined with trastuzumab under the studied conditions. Our data suggest that further studies regarding the suitability of MM-121 for treatment of breast cancer patients whose tumors overexpress erbB2 and become resistant to trastuzumab may be warranted.
doi:10.1186/1476-4598-12-134
PMCID: PMC3829386  PMID: 24215614
MM-121; SAR256212; erbB3; erbB2; Trastuzumab resistance; Breast cancer
2.  Inhibition of Notch Signaling in Combination with Paclitaxel Reduces Platinum-Resistant Ovarian Tumor Growth 
Frontiers in Oncology  2014;4:171.
Introduction: Ovarian cancer (OvCa) is the most lethal gynecologic malignancy in the United States because of chemoresistant recurrent disease. Our objective was to investigate the efficacy of inhibiting the Notch pathway with a γ-secretase inhibitor (GSI) in an OvCa patient-derived xenograft model as a single agent therapy and in combination with standard chemotherapy.
Methods: Immunocompromised mice bearing xenografts derived from clinically platinum-sensitive human ovarian serous carcinomas were treated with vehicle, GSI (MRK-003) alone, paclitaxel and carboplatin (P/C) alone, or the combination of GSI and P/C. Mice bearing platinum-resistant xenografts were given GSI with or without paclitaxel. Gene transcript levels of the Notch pathway target Hes1 were analyzed using RT-PCR. Notch1 and Notch3 protein levels were evaluated. The Wilcoxon rank-sum test was used to assess significance between the different treatment groups.
Results: Expression of Notch1 and 3 was variable. GSI alone decreased tumor growth in two of three platinum-sensitive ovarian tumors (p < 0.05), as well as in one of three platinum-sensitive tumors (p = 0.04). The combination of GSI and paclitaxel was significantly more effective than GSI alone and paclitaxel alone in all platinum-resistant ovarian tumors (all p < 0.05). The addition of GSI did not alter the effect of P/C in platinum-sensitive tumors. Interestingly, although the response of each tumor to chronic GSI exposure did not correlate with its endogenous level of Notch expression, GSI did negatively affect Notch signaling in an acute setting.
Conclusion: Inhibiting the Notch signaling cascade with a GSI reduces primary human xenograft growth in vivo. GSI synergized with conventional cytotoxic chemotherapy only in the platinum-resistant OvCa models with single agent paclitaxel. These findings suggest inhibition of the Notch pathway in concert with taxane therapy may hold promise for treatment of platinum-resistant OvCa.
doi:10.3389/fonc.2014.00171
PMCID: PMC4083224  PMID: 25072022
ovarian cancer; Notch; γ-secretase inhibitor; chemoresistance; patient-derived xenograft
3.  Overcoming Trastuzumab Resistance in Breast Cancer by Targeting Dysregulated Glucose Metabolism 
Cancer research  2011;71(13):4585-4597.
Trastuzumab shows remarkable efficacy in treatment of ErbB2-positive breast cancers when used alone or in combination with other chemotherapeutics. However, acquired resistance develops in most treated patients, necessitating alternate treatment strategies. Increased aerobic glycolysis is a hallmark of cancer and inhibition of glycolysis may offer a promising strategy to preferentially kill cancer cells. In this study, we investigated the antitumor effects of trastuzumab in combination with glycolysis inhibitors in ErbB2-positive breast cancer. We found that trastuzumab inhibits glycolysis via downregulation of heat shock factor 1 (HSF1) and lactate dehydrogenase A (LDH-A) in ErbB2-positive cancer cells, resulting in tumor growth inhibition. Moreover, increased glycolysis via HSF1 and LDH-A contributes to trastuzumab resistance. Importantly, we found that combining trastuzumab with glycolysis inhibition synergistically inhibited trastuzumab-sensitive and -resistant breast cancers in vitro and in vivo, due to more efficient inhibition of glycolysis. Taken together, our findings show how glycolysis inhibition can dramatically enhance the therapeutic efficacy of trastuzumab in ErbB2-positive breast cancers, potentially useful as a strategy to overcome trastuzumab resistance.
doi:10.1158/0008-5472.CAN-11-0127
PMCID: PMC3129363  PMID: 21498634
Warburg effect; glycolysis; HSF1; LDH-A; trastuzumab; ErbB2; resistance
4.  Management of ErbB2-positive Breast Cancer: Insights from Preclinical and Clinical Studies with Lapatinib 
The management of human epidermal growth factor receptor 2-positive (ErbB2+) breast cancer is challenging; patients with ErbB2+ breast tumors have more aggressive disease and a poor prognosis. The increasing incidence of breast cancer in Asia and the limitations of existing treatments pose additional challenges. In this review, we summarize the preclinical and clinical evidence that indicates how lapatinib, a novel inhibitor that targets the human epidermal growth factor receptor (ErbB1) and ErbB2 may help clinicians address four particularly challenging issues in the management of ErbB2+ breast cancer. These issues are: (i) trastuzumab therapy failure, (ii) development of central nervous system metastases, (iii) minimizing toxicity and (iv) selecting the most appropriate partners (chemotherapy and non-chemotherapy) for combination therapy with lapatinib. Lapatinib, in combination with chemotherapeutic agents, such as capecitabine, provides clinical benefits to patients with ErbB2+ breast cancer, including patients who develop progressive disease on trastuzumab. Lapatinib, in combination with non-chemotherapeutic agents, such as letrozole, may also provide a chemotherapy-free treatment option for postmenopausal patients with estrogen receptor-positive/ErbB2+ metastatic breast cancer. Encouraging results have also emerged regarding the synergistic effects of lapatinib in combination with other agents for the treatment of ErbB2+ breast cancer. Promising findings have also been reported for the use of lapatinib to prevent and treat central nervous system metastases. Collectively, these results indicate that the judicious use of lapatinib, an effective oral therapy with a manageable toxicity profile, can enhance the management of patients with ErbB2+ breast cancer.
doi:10.1093/jjco/hyq084
PMCID: PMC2964177  PMID: 20542996
breast cancer; ErbB1; ErbB2; lapatinib; tyrosine kinase inhibitor; review
5.  Therapeutic targeting of erbB3 with MM-121/SAR256212 enhances antitumor activity of paclitaxel against erbB2-overexpressing breast cancer 
Breast Cancer Research : BCR  2013;15(5):R101.
Introduction
Elevated expression of erbB3 rendered erbB2-overexpressing breast cancer cells resistant to paclitaxel via PI-3 K/Akt-dependent upregulation of Survivin. It is unclear whether an erbB3-targeted therapy may abrogate erbB2-mediated paclitaxel resistance in breast cancer. Here, we study the antitumor activity of an anti-erbB3 antibody MM-121/SAR256212 in combination with paclitaxel against erbB2-overexpressing breast cancer.
Methods
Cell growth assays were used to determine cell viability. Cells undergoing apoptosis were quantified by a specific apoptotic ELISA. Western blot analyses were performed to assess the protein expression and activation. Lentiviral vector containing shRNA was used to specifically knockdown Survivin. Tumor xenografts were established by inoculation of BT474-HR20 cells into nude mice. The tumor-bearing mice were treated with paclitaxel and/or MM-121/SAR256212 to determine whether the antibody (Ab) enhances paclitaxel’s antitumor activity. Immunohistochemistry was carried out to study the combinatorial effects on tumor cell proliferation and induction of apoptosis in vivo.
Results
MM-121 significantly facilitated paclitaxel-mediated anti-proliferative/anti-survival effects on SKBR3 cells transfected with a control vector or erbB3 cDNA. It specifically downregulated Survivin associated with inactivation of erbB2, erbB3, and Akt. MM-121 enhances paclitaxel-induced poly(ADP-ribose) polymerase (PARP) cleavage, activation of caspase-8 and -3, and apoptosis in both paclitaxel-sensitive and -resistant cells. Specific knockdown of Survivin in the trastuzumab-resistant BT474-HR20 cells dramatically enhanced paclitaxel-induced apoptosis, suggesting that increased Survivin caused a cross-resistance to paclitaxel. Furthermore, the studies using a tumor xenograft model-established from BT474-HR20 cells revealed that either MM-121 (10 mg/kg) or low-dose (7.5 mg/kg) paclitaxel had no effect on tumor growth, their combinations significantly inhibited tumor growth in vivo. Immunohistochemical analysis showed that the combinations of MM-121 and paclitaxel significantly reduced the cells with positive staining for Ki-67 and Survivin, and increased the cells with cleaved caspase-3.
Conclusions
The combinations of MM-121 and paclitaxel not only inhibit tumor cell proliferation, but also promote erbB2-overexpressing breast cancer cells to undergo apoptosis via downregulation of Survivin in vitro and in vivo, suggesting that inactivation of erbB3 with MM-121 enhances paclitaxel-mediated antitumor activity against erbB2-overexpressing breast cancers. Our data supports further exploration of the combinatorial regimens consisting of MM-121 and paclitaxel in breast cancer patients with erbB2-overexpressing tumors, particularly those resistant to paclitaxel.
doi:10.1186/bcr3563
PMCID: PMC3978722  PMID: 24168763
6.  Boolean ErbB network reconstructions and perturbation simulations reveal individual drug response in different breast cancer cell lines 
BMC Systems Biology  2014;8:75.
Background
Despite promising progress in targeted breast cancer therapy, drug resistance remains challenging. The monoclonal antibody drugs trastuzumab and pertuzumab as well as the small molecule inhibitor erlotinib were designed to prevent ErbB-2 and ErbB-1 receptor induced deregulated protein signalling, contributing to tumour progression. The oncogenic potential of ErbB receptors unfolds in case of overexpression or mutations. Dimerisation with other receptors allows to bypass pathway blockades. Our intention is to reconstruct the ErbB network to reveal resistance mechanisms. We used longitudinal proteomic data of ErbB receptors and downstream targets in the ErbB-2 amplified breast cancer cell lines BT474, SKBR3 and HCC1954 treated with erlotinib, trastuzumab or pertuzumab, alone or combined, up to 60 minutes and 30 hours, respectively. In a Boolean modelling approach, signalling networks were reconstructed based on these data in a cell line and time course specific manner, including prior literature knowledge. Finally, we simulated network response to inhibitor combinations to detect signalling nodes reflecting growth inhibition.
Results
The networks pointed to cell line specific activation patterns of the MAPK and PI3K pathway. In BT474, the PI3K signal route was favoured, while in SKBR3, novel edges highlighted MAPK signalling. In HCC1954, the inferred edges stimulated both pathways. For example, we uncovered feedback loops amplifying PI3K signalling, in line with the known trastuzumab resistance of this cell line. In the perturbation simulations on the short-term networks, we analysed ERK1/2, AKT and p70S6K. The results indicated a pathway specific drug response, driven by the type of growth factor stimulus. HCC1954 revealed an edgetic type of PIK3CA-mutation, contributing to trastuzumab inefficacy. Drug impact on the AKT and ERK1/2 signalling axes is mirrored by effects on RB and RPS6, relating to phenotypic events like cell growth or proliferation. Therefore, we additionally analysed RB and RPS6 in the long-term networks.
Conclusions
We derived protein interaction models for three breast cancer cell lines. Changes compared to the common reference network hint towards individual characteristics and potential drug resistance mechanisms. Simulation of perturbations were consistent with the experimental data, confirming our combined reverse and forward engineering approach as valuable for drug discovery and personalised medicine.
doi:10.1186/1752-0509-8-75
PMCID: PMC4087127  PMID: 24970389
ErbB; RPPA; Network reconstruction; Boolean model; Breast cancer cell line; Drug resistance
7.  Targeting inhibitor of apoptosis proteins in combination with ErbB antagonists in breast cancer 
Introduction
Inhibitor of apoptosis (IAPs) proteins are a family of proteins that can block apoptosis in normal cells and have been suggested to cause resistance to apoptosis in cancer. Overexpression of oncogenic receptor tyrosine kinases is common in breast cancer; in particular 20% of all cases show elevated Her2. Despite clinical success with the use of targeted therapies, such as Trastuzumab, only up to 35% of Her2-positive patients initially respond. We reasoned that IAP-mediated apoptosis resistance might contribute to this insensitivity to receptor tyrosine kinase therapy, in particular ErbB antagonists. Here we examine the levels of IAPs in breast cancer and evaluate whether targeting IAPs can enhance apoptosis in response to growth factor receptor antagonists and TRAIL.
Methods
IAP levels were examined in a breast cancer cell line panel and in patient samples. IAPs were inhibited using siRNA or cell permeable mimetics of endogenous inhibitors. Cells were then exposed to TRAIL, Trastuzumab, Lapatinib, or Gefitinib for 48 hours. Examining nuclear morphology and staining for cleaved caspase 3 was used to score apoptosis. Proliferation was examined by Ki67 staining.
Results
Four members of the IAP family, Survivin, XIAP, cIAP1 and cIAP2, were all expressed to varying extents in breast cancer cell lines or tumours. MDAMB468, BT474 and BT20 cells all expressed XIAP to varying extents. Depleting the cells of XIAP overcame the intrinsic resistance of BT20 and MDAMB468 cells to TRAIL. Moreover, siRNA-based depletion of XIAP or use of a Smac mimetic to target multiple IAPs increased apoptosis in response to the ErbB antagonists, Trastuzumab, Lapatinib or Gefitinib in Her2-overexpressing BT474 cells, or Gefitinib in EGFR-overexpressing MDAMB468 cells.
Conclusions
The novel findings of this study are that multiple IAPs are concomitantly expressed in breast cancers, and that, in combination with clinically relevant Her2 treatments, IAP antagonists promote apoptosis and reduce the cell turnover index of breast cancers. We also show that combination therapy of IAP antagonists with some pro-apoptotic agents (for example, TRAIL) enhances apoptosis of breast cancer cells. In some cases (for example, MDAMB468 cells), the enhanced apoptosis is profound.
doi:10.1186/bcr2328
PMCID: PMC2716510  PMID: 19563669
8.  Heregulin β1 drives gefitinib-resistant growth and invasion in tamoxifen-resistant MCF-7 breast cancer cells 
Introduction
Resistance to anti-epidermal growth factor receptor (anti-EGFR) therapies is an emerging clinical problem. The efficacy of anti-EGFR therapies can be influenced by the presence of heregulins (HRGs), which can bind erbB3/4 receptors and can activate alternative signalling pathways. In the present study we have examined whether HRG signalling can circumvent EGFR blockade in an EGFR-positive tamoxifen-resistant MCF-7 (Tam-R) breast cancer cell line.
Methods
Tam-R cells, incubated with the selective EGFR tyrosine kinase inhibitor gefitinib ('Iressa', ZD1839), were exposed to HRGβ1 and the effects on erbB receptor dimerization profiles and on activation of associated downstream signalling components were assessed by immunoprecipitation, western blotting and immunocytochemistry. The effects of HRGβ1 on gefitinib-treated Tam-R cell growth and invasion were also examined, and HRGβ1 expression levels were assessed in breast cancer tissue by immunohistochemistry to address the potential clinical relevance of such a resistance mechanism.
Results
In Tam-R cells, HRGβ1 promoted erbB3/erbB2 and erbB3/EGFR heterodimerization, promoted ERK1/2 and AKT pathway activation and increased cell proliferation and invasion. Gefitinib prevented HRGβ1-driven erbB3/EGFR heterodimerization, ERK1/2 activation and Tam-R cell proliferation, but HRGβ1-driven erbB3/erbB2 heterodimerization, AKT activation and Tam-R cell invasion were maintained. A combination of gefitinib and the phosphatidylinositol 3-kinase inhibitor LY294002 effectively blocked HRGβ1-mediated intracellular signalling activity, growth and invasion in Tam-R cells. Similarly, targeting erbB2 with trastuzumab in combination with gefitinib in Tam-R cells reduced HRGβ1-induced erbB2 and ERK1/2 activity; however, HRGβ1-driven AKT activity and cell growth were maintained while cell invasion was significantly enhanced with this combination. In clinical tissue all samples demonstrated cytoplasmic tumour epithelial HRGβ1 protein staining, with expression correlating with EGFR positivity and activation of both AKT and ERK1/2.
Conclusion
HRGβ1 can overcome the inhibitory effects of gefitinib on cell growth and invasion in Tam-R cells through promotion of erbB3/erbB2 heterodimerization and activation of the phosphatidylinositol 3-kinase/AKT signalling pathway. This may have implications for the effectiveness of anti-EGFR therapies in breast cancer as HRGβ1 is enriched in many EGFR-positive breast tumours.
doi:10.1186/bcr1754
PMCID: PMC2206726  PMID: 17686159
9.  A novel fully human antitumour immunoRNase targeting ErbB2-positive tumours 
British Journal of Cancer  2011;104(11):1716-1723.
Background:
ErbB2 is an attractive target for immunotherapy, as it is a tyrosine kinase receptor overexpressed on tumour cells of different origin, with a key role in the development of malignancy. Trastuzumab, the only humanised anti-ErbB2 antibody currently used in breast cancer with success, can engender cardiotoxicity and a high fraction of patients is resistant to Trastuzumab treatment.
Methods:
A novel human immunoRNase, called anti-ErbB2 human compact antibody-RNase (Erb-hcAb-RNase), made up of the compact anti-ErbB2 antibody Erbicin-human-compact Antibody (Erb-hcAb) and human pancreatic RNase (HP-RNase), has been designed, expressed in mammalian cell cultures and purified. The immunoRNase was then characterised as an enzymatic protein, and tested for its biological actions in vitro and in vivo on ErbB2-positive tumour cells.
Results:
Erb-hcAb-RNase retains the enzymatic activity of HP-RNase and specifically binds to ErbB2-positive cells with an affinity comparable with that of the parental Erb-hcAb. Moreover, this novel immunoRNase is endowed with an effective and selective antiproliferative action for ErbB2-positive tumour cells both in vitro and in vivo. Its antitumour activity is more potent than that of the parental Erb-hcAb as the novel immunoconjugate has acquired RNase-based cytotoxicity in addition to the inhibitory growth effects, antibody-dependent and complement-dependent cytotoxicity of Erb-hcAb.
Conclusion:
Erb-hcAb-RNase could be a promising candidate for the immunotherapy of ErbB2-positive tumours.
doi:10.1038/bjc.2011.146
PMCID: PMC3111160  PMID: 21559015
immunotherapy; ErbB2/HER2; immunoRNase; breast cancer; Trastuzumab
10.  Two novel human anti-ErbB2 immunoagents are active on trastuzumab-resistant tumours 
British Journal of Cancer  2010;102(3):513-519.
Background:
Overexpression of ErbB2 receptor in breast cancer is associated with disease progression and poor prognosis. Trastuzumab, the only humanised anti-ErbB2 antibody currently used in breast cancer, has proven to be effective; however, a relevant problem for clinical practice is that a high fraction of breast cancer patients shows primary or acquired resistance to trastuzumab treatment.
Methods:
We tested on trastuzumab-resistant cells two novel human anti-tumour immunoconjugates engineered in our laboratory by fusion of a human anti-ErbB2 scFv, termed Erbicin, with either a human RNase or the Fc region of a human IgG1. Both Erbicin-derived immunoagents (EDIAs) are selectively cytotoxic for ErbB2-positive cancer cells in vitro and vivo, target an ErbB2 epitope different from that recognised by trastuzumab and do not show cardiotoxic effects.
Results:
We report that EDIAs are active also on trastuzumab-resistant tumour cells both in vitro and in vivo, most likely because of the different epitope recognised, as EDIAs, unlike trastuzumab, were found to be able to inhibit the signalling pathway downstream of ErbB2.
Conclusion:
These results suggest that EDIAs are immunoagents that could not only fulfil the therapeutic need of patients ineligible to trastuzumab treatment due to cardiac dysfunction but also prove to be useful for breast cancer patients unresponsive to trastuzumab treatment.
doi:10.1038/sj.bjc.6605499
PMCID: PMC2822937  PMID: 20051960
ErbB2/Her2; immunotherapy; ImmunoRNase; trastuzumab; resistance
11.  HER2 Phosphorylation Is Maintained by a PKB Negative Feedback Loop in Response to Anti-HER2 Herceptin in Breast Cancer 
PLoS Biology  2010;8(12):e1000563.
A feedback loop maintains HER2 receptor signalling and cell survival in response to Herceptin treatment in HER2-positive breast cancers, but this Herceptin resistance may be bypassed by pan-HER inhibitors.
Herceptin (trastuzumab) is used in patients with breast cancer who have HER2 (ErbB2)–positive tumours. However, its mechanisms of action and how acquired resistance to Herceptin occurs are still poorly understood. It was previously thought that the anti-HER2 monoclonal antibody Herceptin inhibits HER2 signalling, but recent studies have shown that Herceptin does not decrease HER2 phosphorylation. Its failure to abolish HER2 phosphorylation may be a key to why acquired resistance inevitably occurs for all responders if Herceptin is given as monotherapy. To date, no studies have explained why Herceptin does not abolish HER2 phosphorylation. The objective of this study was to investigate why Herceptin did not decrease HER2 phosphorylation despite being an anti-HER2 monoclonal antibody. We also investigated the effects of acute and chronic Herceptin treatment on HER3 and PKB phosphorylation in HER2-positive breast cancer cells. Using both Förster resonance energy transfer (FRET) methodology and conventional Western blot, we have found the molecular mechanisms whereby Herceptin fails to abolish HER2 phosphorylation. HER2 phosphorylation is maintained by ligand-mediated activation of EGFR, HER3, and HER4 receptors, resulting in their dimerisation with HER2. The release of HER ligands was mediated by ADAM17 through a PKB negative feedback loop. The feedback loop was activated because of the inhibition of PKB by Herceptin treatment since up-regulation of HER ligands and ADAM17 also occurred when PKB phosphorylation was inhibited by a PKB inhibitor (Akt inhibitor VIII, Akti-1/2). The combination of Herceptin with ADAM17 inhibitors or the panHER inhibitor JNJ-26483327 was able to abrogate the feedback loop and decrease HER2 phosphorylation. Furthermore, the combination of Herceptin with JNJ-26483327 was synergistic in tumour inhibition in a BT474 xenograft model. We have determined that a PKB negative feedback loop links ADAM17 and HER ligands in maintaining HER2 phosphorylation during Herceptin treatment. The activation of other HER receptors via ADAM17 may mediate acquired resistance to Herceptin in HER2-overexpressing breast cancer. This finding offers treatment opportunities for overcoming resistance in these patients. We propose that Herceptin should be combined with a panHER inhibitor or an ADAM inhibitor to overcome the acquired drug resistance for patients with HER2-positive breast cancer. Our results may also have implications for resistance to other therapies targeting HER receptors.
Author Summary
HER2 (ErbB2) is a surface protein and member of the epidermal growth factor receptor (EGFR) family that is overexpressed in approximately one-fifth of breast cancers. HER2-positive breast tumours tend to be very aggressive, and patients with this type of tumour have a poor prognosis. A therapeutic monoclonal antibody called trastuzumab (Herceptin) has been designed to block HER2 signalling and is used as a treatment for patients with HER2-positive breast cancer. However, recent studies have shown that Herceptin does not decrease HER2 activation. This may be why patients invariably develop resistance if treated with Herceptin monotherapy. To date, no study has explained why Herceptin cannot abolish HER2 signalling despite being an anti-HER2 monoclonal antibody. We have found that Herceptin switches on a feedback loop that increases the production of the ADAM17 protein, a protease that in turn releases the growth factors that activate HER (ErbB) receptors. These growth factors activate HER2 and also the other members of the HER receptor family—EGFR, HER3 and HER4—in such a way as to maintain HER2 activation and cell survival in HER2-positive breast cancer cells. We have found that when Herceptin is provided in combination with ADAM17 inhibitors, the feedback loop is abrogated in cells. Furthermore, a pan-HER inhibitor that decreases the activation of other HER receptors can also inhibit the feedback loop and decrease HER2 activation when used in combination with Herceptin. We further demonstrated that the combination therapy of Herceptin with a pan-HER inhibitor is more effective than Herceptin alone in an animal model of breast cancer. We believe our results offer treatment strategies that may help overcome acquired Herceptin resistance in patients with HER2-positive breast cancer.
doi:10.1371/journal.pbio.1000563
PMCID: PMC3006345  PMID: 21203579
12.  Combination of antibody that inhibits ligand-independent HER3 dimerization and a p110α inhibitor potently blocks PI3K signaling and growth of HER2+ breast cancers 
Cancer research  2013;73(19):6013-6023.
We examined the effects of LJM716, a HER3 (ERBB3) neutralizing antibody that inhibits ligand-induced and ligand-independent HER3 dimerization, as a single agent and in combination with BYL719, an ATP competitive, p110α-specific inhibitor against HER2-overexpressing breast and gastric cancers. Treatment with LJM716 reduced HER2-HER3 and HER3-p85 dimers, P-HER3 and P-AKT both in vitro and in vivo. Treatment with LJM716 alone markedly reduced growth of BT474 xenografts. The combination of LJM716/lapatinib/trastuzumab significantly improved survival of mice with BT474 xenografts compared to lapatinib/trastuzumab (p=0.0012). LJM716 and BYL719 synergistically inhibited growth in a panel of HER2+ and PIK3CA mutant cell lines. The combination also inhibited P-AKT in HER2-overexpressing breast cancer cells and growth of HER2+ NCI-N87 gastric cancer xenografts more potently than LJM716 or BYL719 alone. Trastuzumab-resistant, HER2+/PIK3CA mutant MDA453 xenografts regressed completely after three weeks of therapy with LJM716 and BYL719 whereas either single agent inhibited growth only partially. Finally, mice with BT474 xenografts treated with trastuzumab/LJM716, trastuzumab/BYL719, LJM716/BYL719 or trastuzumab/LJM716/BYL719 exhibited similar rates of tumor regression after three weeks of treatment. Thirty weeks after treatment discontinuation, 14% of mice treated with trastuzumab/LJM716/BYL719 whereas >80% in all other treatment groups were sacrificed due to a recurrent large tumor burden (p=0.0066). These data suggest that dual blockade of the HER2 signaling network with a HER3 antibody that inhibits HER2-HER3 dimers in combination with a p110α-specific inhibitor in the absence of a direct HER2 antagonist is an effective treatment approach against HER2-overexpressing cancers.
doi:10.1158/0008-5472.CAN-13-1191
PMCID: PMC3790862  PMID: 23918797
PI3K; HER2; HER3; breast cancer
13.  A combination of Trastuzumab and 17-AAG induces enhanced ubiquitinylation and lysosomal pathwaydependent ErbB2 degradation and cytotoxicity in ErbB2-overexpressing breast cancer cells 
Cancer biology & therapy  2008;7(10):1630-1640.
ErbB2 (or Her2/Neu) overexpression in breast cancer signifies poorer prognosis, yet it has provided an avenue for targeted therapy as demonstrated by the success of humanized monoclonal antibody Trastuzumab (Herceptin™). Resistance to Trastuzumab and eventual failure in most cases, however, necessitate alternate ErbB2-targeted therapies. HSP90 inhibitors such as 17-allylaminodemethoxygeldanamycin (17-AAG), potently downregulate the cell surface ErbB2. While the precise mechanisms of Trastuzumab or 17-AAG action remain unclear, ubiquitinylation-dependent proteasomal or lysosomal degradation of ErbB2 appears to play a substantial role. As Trastuzumab and 17-AAG induce the recruitment of distinct E3 ubiquitin ligases, Cbl and CHIP respectively, to ErbB2, we hypothesized that 17-AAG and Trastuzumab combination could induce a higher level of ubiquitinylation and downregulation of ErbB2 as compared to single drug treatments. We present biochemical and cell biological evidence that combined 17-AAG and Trastuzumab treatment of ErbB2-overexpressing breast cancer cell lines leads to enhanced ubiquitinylation, downregulation from the cell surface and lysosomal degradation of ErbB2. Importantly, combined 17-AAG and Trastuzumab treatment induced synergistic growth arrest and cell death specifically in ErbB2-overexpressing but not in ErbB2-low breast cancer cells. Our results suggest the 17-AAG and Trastuzumab combination as a mechanism-based combinatorial targeted therapy for ErbB2-overexpressing breast cancer patients.
PMCID: PMC2727620  PMID: 18769124
ErbB2; 17-AAG; Trastuzumab; synergy; ubiquitin ligase
14.  NOTCH-1 and NOTCH-4 are novel gene targets of PEA3 in breast cancer: novel therapeutic implications 
Introduction
Women with triple-negative breast cancer have the worst prognosis, frequently present with metastatic tumors and have few targeted therapy options. Notch-1 and Notch-4 are potent breast oncogenes that are overexpressed in triple-negative and other subtypes of breast cancer. PEA3, an ETS transcription factor, is also overexpressed in triple-negative and other breast cancer subtypes. We investigated whether PEA3 could be the critical transcriptional activator of Notch receptors in MDA-MB-231 and other breast cancer cells.
Methods
Real-time PCR and Western blot analysis were performed to detect Notch-1, Notch-2, Notch-3 and Notch-4 receptor expression in breast cancer cells when PEA3 was knocked down by siRNA. Chromatin immunoprecipitation was performed to identify promoter regions for Notch genes that recruited PEA3. TAM-67 and c-Jun siRNA were used to identify that c-Jun was necessary for PEA3 enrichment on the Notch-4 promoter. A Notch-4 luciferase reporter was used to confirm that endogenous PEA3 or AP-1 activated the Notch-4 promoter region. Cell cycle analysis, trypan blue exclusion, annexin V flow cytometry, colony formation assay and an in vivo xenograft study were performed to determine the biological significance of targeting PEA3 via siRNA, Notch signaling via a γ-secretase inhibitor, or both.
Results
Herein we provide new evidence for transcriptional regulation of Notch by PEA3 in breast cancer. PEA3 activates Notch-1 transcription in MCF-7, MDA-MB-231 and SKBr3 breast cancer cells. PEA3 activates Notch-4 transcription in MDA-MB-231 cells where PEA3 levels are endogenously high. In SKBr3 and BT474 breast cancer cells where PEA3 levels are low, overexpression of PEA3 increases Notch-4 transcripts. Chromatin immunoprecipitation confirmed the enrichment of PEA3 on Notch-1 and Notch-4 promoters in MDA-MB-231 cells. PEA3 recruitment to Notch-1 was AP-1-independent, whereas PEA3 recruitment to Notch-4 was c-JUN-dependent. Importantly, the combined inhibition of Notch signaling via a γ-secretase inhibitor (MRK-003 GSI) and knockdown of PEA3 arrested growth in the G1 phase, decreased both anchorage-dependent and anchorage-independent growth and significantly increased apoptotic cells in vitro. Moreover, either PEA3 knockdown or MRK-003 GSI treatment significantly reduced tumor growth of MDA-MB-231 xenografts in vivo.
Conclusions
Taken together, the results from this study demonstrate for the first time that Notch-1 and Notch-4 are novel transcriptional targets of PEA3 in breast cancer cells. Targeting of PEA3 and/or Notch pathways might provide a new therapeutic strategy for triple-negative and possibly other breast cancer subtypes.
doi:10.1186/bcr2900
PMCID: PMC3218952  PMID: 21679465
15.  Nuclear HER4 mediates acquired resistance to trastuzumab and is associated with poor outcome in HER2 positive breast cancer 
Oncotarget  2014;5(15):5934-5949.
The role of HER4 in breast cancer is controversial and its role in relation to trastuzumab resistance remains unclear. We showed that trastuzumab treatment and its acquired resistance induced HER4 upregulation, cleavage and nuclear translocation. However, knockdown of HER4 by specific siRNAs increased trastuzumab sensitivity and reversed its resistance in HER2 positive breast cancer cells. Preventing HER4 cleavage by a γ-secretase inhibitor and inhibiting HER4 tyrosine kinase activity by neratinib decreased trastuzumab-induced HER4 nuclear translocation and enhanced trastuzumab response. There was also increased nuclear HER4 staining in the tumours from BT474 xenograft mice and human patients treated with trastuzumab. Furthermore, nuclear HER4 predicted poor clinical response to trastuzumab monotherapy in patients undergoing a window study and was shown to be an independent poor prognostic factor in HER2 positive breast cancer. Our data suggest that HER4 plays a key role in relation to trastuzumab resistance in HER2 positive breast cancer. Therefore, our study provides novel findings that HER4 activation, cleavage and nuclear translocation influence trastuzumab sensitivity and resistance in HER2 positive breast cancer. Nuclear HER4 could be a potential prognostic and predictive biomarker and understanding the role of HER4 may provide strategies to overcome trastuzumab resistance in HER2 positive breast cancer.
PMCID: PMC4171603  PMID: 25153719
breast cancer; HER4; HER2; trastuzumab; resistance
16.  Prediction of signaling cross-talks contributing to acquired drug resistance in breast cancer cells by Bayesian statistical modeling 
Background
Initial success of inhibitors targeting oncogenes is often followed by tumor relapse due to acquired resistance. In addition to mutations in targeted oncogenes, signaling cross-talks among pathways play a vital role in such drug inefficacy. These include activation of compensatory pathways and altered activities of key effectors in other cell survival and growth-associated pathways.
Results
We propose a computational framework using Bayesian modeling to systematically characterize potential cross-talks among breast cancer signaling pathways. We employed a fully Bayesian approach known as the p1-model to infer posterior probabilities of gene-pairs in networks derived from the gene expression datasets of ErbB2-positive breast cancer cell-lines (parental, lapatinib-sensitive cell-line SKBR3 and the lapatinib-resistant cell-line SKBR3-R, derived from SKBR3). Using this computational framework, we searched for cross-talks between EGFR/ErbB and other signaling pathways from Reactome, KEGG and WikiPathway databases that contribute to lapatinib resistance. We identified 104, 188 and 299 gene-pairs as putative drug-resistant cross-talks, respectively, each comprised of a gene in the EGFR/ErbB signaling pathway and a gene from another signaling pathway, that appear to be interacting in resistant cells but not in parental cells. In 168 of these (distinct) gene-pairs, both of the interacting partners are up-regulated in resistant conditions relative to parental conditions. These gene-pairs are prime candidates for novel cross-talks contributing to lapatinib resistance. They associate EGFR/ErbB signaling with six other signaling pathways: Notch, Wnt, GPCR, hedgehog, insulin receptor/IGF1R and TGF- β receptor signaling. We conducted a literature survey to validate these cross-talks, and found evidence supporting a role for many of them in contributing to drug resistance. We also analyzed an independent study of lapatinib resistance in the BT474 breast cancer cell-line and found the same signaling pathways making cross-talks with the EGFR/ErbB signaling pathway as in the primary dataset.
Conclusions
Our results indicate that the activation of compensatory pathways can potentially cause up-regulation of EGFR/ErbB pathway genes (counteracting the inhibiting effect of lapatinib) via signaling cross-talk. Thus, the up-regulated members of these compensatory pathways along with the members of the EGFR/ErbB signaling pathway are interesting as potential targets for designing novel anti-cancer therapeutics.
Electronic supplementary material
The online version of this article (doi:10.1186/s12918-014-0135-x) contains supplementary material, which is available to authorized users.
doi:10.1186/s12918-014-0135-x
PMCID: PMC4307189  PMID: 25599599
Drug resisance; Signaling cross-talk; Bayesian statistical modeling; p1-model; EGFR signaling; Breast cancer; Lapatinib
17.  Neratinib overcomes trastuzumab resistance in HER2 amplified breast cancer 
Oncotarget  2013;4(10):1592-1605.
Trastuzumab has been shown to improve the survival outcomes of HER2 positive breast cancer patients. However, a significant proportion of HER2-positive patients are either inherently resistant or develop resistance to trastuzumab. We assessed the effects of neratinib, an irreversible panHER inhibitor, in a panel of 36 breast cancer cell lines. We further assessed its effects with or without trastuzumab in several sensitive and resistant breast cancer cells as well as a BT474 xenograft model. We confirmed that neratinib was significantly more active in HER2-amplified than HER2 non-amplified cell lines. Neratinib decreased the activation of the 4 HER receptors and inhibited downstream pathways. However, HER3 and Akt were reactivated at 24 hours, which was prevented by the combination of trastuzumab and neratinib. Neratinib also decreased pHER2 and pHER3 in acquired trastuzumab resistant cells. Neratinib in combination with trastuzumab had a greater growth inhibitory effect than either drug alone in 4 HER2 positive cell lines. Furthermore, trastuzumab in combination with neratinib was growth inhibitory in SKBR3 and BT474 cells which had acquired resistance to trastuzumab as well as in a BT474 xenograft model. Innately trastuzumab resistant cell lines showed sensitivity to neratinib, but the combination did not enhance response compared to neratinib alone. Levels of HER2 and phospho-HER2 showed a direct correlation with sensitivity to neratinib. Our data indicate that neratinib is an effective anti-HER2 therapy and counteracted both innate and acquired trastuzumab resistance in HER2 positive breast cancer. Our results suggest that combined treatment with trastuzumab and neratinib is likely to be more effective than either treatment alone for both trastuzumab-sensitive breast cancer as well as HER2-positive tumors with acquired resistance to trastuzumab.
PMCID: PMC3858548  PMID: 24009064
breast cancer; HER2/ErbB2; trastuzumab (Herceptin); neratinib; panHER inhibitor
18.  γ-Secretase inhibitor enhances antitumour effect of radiation in Notch-expressing lung cancer 
British Journal of Cancer  2012;106(12):1953-1959.
Background:
Notch receptor has an important role in both development and cancer. We previously reported that inhibition of the Notch3 by γ-secretase inhibitor (GSI) induces apoptosis and suppresses tumour proliferation in non-small-cell lung cancer. Although radiation is reported to induce Notch activation, little is known about the relationship between radiation and Notch pathway.
Methods:
We examined the effect of combining GSI and radiation at different dosing in three Notch expressing lung cancer cell lines. The cytotoxic effect of GSI and radiation was evaluated using MTT assay and clonogenic assay in vitro and xenograft models. Expressions of Notch pathway, mitogen-activated protein kinase (MAPK) pathway and Bcl-2 family proteins were investigated using western blot analysis.
Results:
We discovered that the antitumour effect of combining GSI and radiation was dependent on treatment schedule. γ-Secretase inhibitor administration after radiation had the greatest growth inhibition of lung cancer in vitro and in vivo. We showed that the combination induced apoptosis of lung cancer cell lines through the regulation of MAPK and Bcl-2 family proteins. Furthermore, activation of Notch after radiation was ameliorated by GSI administration, suggesting that treatment with GSI prevents Notch-induced radiation resistance.
Conclusion:
Notch has an important role in lung cancer. Treatment with GSI after radiation can significantly enhance radiation-mediated tumour cytotoxicity.
doi:10.1038/bjc.2012.178
PMCID: PMC3388558  PMID: 22596234
Notch; γ-secretase inhibitor; radiation; apoptosis; non-small-cell lung cancer
19.  Trastuzumab Sensitizes Ovarian Cancer Cells to EGFR-targeted Therapeutics 
Background
Early studies have demonstrated comparable levels of HER2/ErbB2 expression in both breast and ovarian cancer. Trastuzumab (Herceptin), a therapeutic monoclonal antibody directed against HER2, is FDA-approved for the treatment of both early and late stage breast cancer. However, clinical studies of trastuzumab in epithelial ovarian cancer (EOC) patients have not met the same level of success. Surprisingly, however, no reports have examined either the basis for primary trastuzumab resistance in ovarian cancer or potential ways of salvaging trastuzumab as a potential ovarian cancer therapeutic.
Methods
An in vitro model of primary trastuzumab-resistant ovarian cancer was created by long-term culture of HER2-positive ovarian carcinoma-derived cell lines with trastuzumab. Trastuzumab treated vs. untreated parental cells were compared for HER receptor expression, trastuzumab sensitivity, and sensitivity to other HER-targeted therapeutics.
Results
In contrast to widely held assumptions, here we show that ovarian cancer cells that are not growth inhibited by trastuzumab are still responsive to trastuzumab. Specifically, we show that responsiveness to alternative HER-targeted inhibitors, such as gefitinib and cetuximab, is dramatically potentiated by long-term trastuzumab treatment of ovarian cancer cells. HER2-positive ovarian carcinoma-derived cells are, therefore, not "unresponsive" to trastuzumab as previously assumed, even when they not growth inhibited by this drug.
Conclusions
Given the recent success of EGFR-targeted therapeutics for the treatment of other solid tumors, and the well-established safety profile of trastuzumab, results presented here provide a rationale for re-evaluation of trastuzumab as an experimental ovarian cancer therapeutic, either in concert with, or perhaps as a "primer" for EGFR-targeted therapeutics.
doi:10.1186/1757-2215-3-7
PMCID: PMC2861058  PMID: 20346177
20.  Trastuzumab-resistant cells rely on a HER2-PI3K-FoxO-survivin axis and are sensitive to PI3K inhibitors 
Cancer research  2012;73(3):1190-1200.
The antibody trastuzumab is approved for treatment of patients with HER2 (ERBB2)-overexpressing breast cancer. A significant fraction of these tumors are either intrinsically resistant or acquire resistance rendering the drug ineffective. The development of resistance has been attributed to failure of the antibody to inhibit phosphatidylinositol-3 kinase (PI3K), which is activated by the HER2 network. Herein, we examined the effects of PI3K blockade in trastuzumab-resistant breast cancer cell lines. Treatment with the pan-PI3K inhibitor XL147 and trastuzumab reduced proliferation and pAKT levels, triggering apoptosis of trastuzumab-resistant cells. Compared to XL147 alone, the combination exhibited a superior antitumor effect against trastuzumab-resistant tumor xenografts. Further, treatment with XL147 and trastuzumab reduced the cancer stem cell (CSC) fraction within trastuzumab-resistant cells both in vitro and in vivo. These effects were associated with FoxO-mediated inhibition of transcription of the anti-apoptosis gene survivin (BIRC5) and the CSC-associated cytokine IL-8. RNAi-mediated or pharmacological inhibition of survivin restored sensitivity to trastuzumab in resistant cells. In a cohort of patients with HER2-overexpressing breast cancer treated with trastuzumab, higher pre-treatment tumor levels of survivin RNA correlated with poor response to therapy. Together, our results suggest that survivin blockade is required for therapeutic responses to trastuzumab and that by combining trastuzumab and PI3K inhibitors CSCs can be reduced within HER2+ tumors, potentially preventing acquired resistance to anti-HER2 therapy.
doi:10.1158/0008-5472.CAN-12-2440
PMCID: PMC3563941  PMID: 23204226
21.  Epigenetic silencing of miR-375 induces trastuzumab resistance in HER2-positive breast cancer by targeting IGF1R 
BMC Cancer  2014;14:134.
Background
Resistance to humanized monoclonal erbB2/HER2 antibody, trastuzumab (Herceptin), has become a pivotal obstacle for targeted therapy of HER2-positive breast cancers. The activation of alternative growth factor receptors, in particular, the insulin-like growth factor 1 receptor (IGF1R), represents a common feature of trastuzumab-refractory cells; however, the underlying mechanism remains elusive.
Methods
Trastuzumab-resistant breast cancer SKBr-3 cells were generated by long-term in vitro culture of SKBr-3 cells in the presence of trastuzumab. Among the differentially expressed microRNAs (miRNAs) screened by microarray analysis, candidate miRNA(s) predicted to target IGF1R was studied for its role in conferring trastuzumab resistance. The mechanism underlying decreased expression of IGF1R-targeted miRNA in refractory cells was also addressed.
Results
miR-375, which was downregulated and predicted to target IGF1R in trastuzumab-resistant HER2-positive breast cancer cells, could indeed inhibit the cellular luciferase activity in a reporter construct containing the 3′-UTR of IGF1R. Overexpression of miR-375 restored the sensitivity of cells to trastuzumab, while inhibition of miR-375 conferred trastuzumab resistance on HER2-positive breast cancer cells. Blockade of DNA methylation and histone deacetylation restored the expression of miR-375 in trastuzumab-resistant cells. A reverse correlation between the levels of miR-375 and IGF1R was validated in clinical breast cancers.
Conclusions
Epigenetic silencing of miR-375 causes the upregulation of IGF1R, which at least partially underlies trastuzumab resistance of breast cancer cells. Our study has implications for miR-375 as a potential target in combination with trastuzumab for treating HER2-positive breast cancers.
doi:10.1186/1471-2407-14-134
PMCID: PMC3974046  PMID: 24571711
miR-375; Insulin-like growth factor 1 receptor; Trastuzumab resistance; erbB2/HER2; Breast cancer
22.  X-Linked Inhibitor of Apoptosis Protein Inhibits Apoptosis in Inflammatory Breast Cancer Cells with Acquired Resistance to an ErbB1/2 Tyrosine Kinase Inhibitor 
Molecular cancer therapeutics  2010;9(5):1432-1442.
Inflammatory breast cancer (IBC) is a highly aggressive subtype of breast cancer that is often characterized by ErbB2 overexpression. ErbB2 targeting is clinically relevant using trastuzumab (anti-ErbB2 antibody) and lapatinib (small molecule ErbB1/2 inhibitor). However, acquired resistance is a common outcome even in IBC patients who show an initial clinical response, which limits the efficacy of these agents. In the present study, using a clonal population of GW583340 (lapatinib analog, ErbB1/2 inhibitor)-resistant IBC cells, we identified overexpression of an anti-apoptotic protein, XIAP, in acquired resistance to GW583340 in both ErbB2 overexpressing SUM190 and ErbB1 activated SUM149 cell lines derived from primary IBC tumors. A marked decrease in p-ErbB2, p-ErbB1, and downstream signaling was evident in the GW583340-resistant cells (rSUM190 and rSUM149) similar to parental counterparts treated with the drug, suggesting the primary mechanism of action of GW583340 was not compromised in resistant cells. However, rSUM190 and rSUM149 cells growing in GW583340 had significant XIAP overexpression and resistance to GW583340-mediated apoptosis. Additionally, stable XIAP overexpression using a lentiviral system reversed sensitivity to GW583340 in parental cells. The observed overexpression was identified to be caused by IRES-mediated XIAP translation. XIAP downregulation in rSUM190 and rSUM149 cells using a small molecule inhibitor (embelin), which abrogates the XIAP/procaspase 9 interaction, resulted in decreased viability, demonstrating that XIAP is required for survival of cells with acquired resistance to GW583340. These studies establish the feasibility of development of an XIAP inhibitor that potentiates apoptosis for use in IBC patients with resistance to ErbB2-targeting agents.
doi:10.1158/1535-7163.MCT-10-0160
PMCID: PMC2957814  PMID: 20406946
IRES; embelin; survivin; FOXO3a; p-AKT
23.  Human breast cancer cells harboring a gatekeeper T798M mutation in HER2 overexpress EGFR ligands and are sensitive to dual inhibition of EGFR and HER2 
Purpose
Mutations in receptor tyrosine kinase (RTK) genes can confer resistance to receptor-targeted therapies. A T798M mutation in the HER2 oncogene has been shown to confer resistance to the tyrosine kinase inhibitor (TKI) lapatinib. We studied the mechanisms of HER2-T798M-induced resistance to identify potential strategies to overcome that resistance.
Experimental Design
HER2-T798M was stably expressed in BT474 and MCF10A cells. Mutant cells and xenografts were evaluated for effects of the mutation on proliferation, signaling, and tumor growth after treatment with combinations of inhibitors targeting the EGFR-HER2-HER3-PI3K axis.
Results
A low 3% allelic frequency of the T798M mutant shifted10-fold the IC50 of lapatinib. In mutant-expressing cells, lapatinib did not block basal phosphorylation of HER2, HER3, AKT and ERK1/2. In vitro kinase assays showed increased autocatalytic activity of HER2-T798M. HER3 association with PI3K p85 was increased in mutant-expressing cells. BT474-T798M cells were also resistant to the HER2 antibody trastuzumab. These cells were sensitive to the pan-PI3K inhibitors BKM120 and XL147 and the irreversible HER2/EGFR TKI afatinib but not the MEK1/2 inhibitor CI-1040, suggesting continued dependence of the mutant cells on ErbB receptors and downstream PI3K signaling. BT474-T798M cells showed increased expression of the EGFR ligands EGF, TGFα, amphiregulin and HB-EGF. Addition of the EGFR neutralizing antibody cetuximab or lapatinib restored trastuzumab sensitivity of BT474-T798M cells and xenografts, suggesting increased EGFR ligand production was causally associated with drug resistance.
Conclusions
Simultaneous blockade of HER2 and EGFR should be an effective treatment strategy against HER2 gene-amplified breast cancer cells harboring T798M mutant alleles.
doi:10.1158/1078-0432.CCR-13-1038
PMCID: PMC3809918  PMID: 23948973
HER2; kinase domain mutations; EGFR; lapatinib; trastuzumab; cetuximab; breast cancer
24.  Multimodality Approaches to Treat Hypoxic Non–Small Cell Lung Cancer (NSCLC) Microenvironment 
Genes & Cancer  2012;3(2):141-151.
We found both in vitro and in vivo that survival of NSCLC cells in a hypoxic microenvironment requires Notch-1 signaling. A hypoxic tumor environment represents a problem for NSCLC treatment because it plays a critical role in cancer resistance to chemotherapy, tumor recurrence, and metastasis. Here we targeted hypoxic tumor tissue in an orthotopic NSCLC model. We inhibited the Notch-1/IGF-1R/Akt-1 axis using 3 agents: a γ-secretase inhibitor or GSI (MRK-003), a fully humanized antibody against the human IGF-1R (MK-0646), and a pan-Akt inhibitor (MK-2206), alone or in various combinations including therapeutics currently in clinical use. All treatments but Akt inhibition significantly prolonged the median survival of mice compared with controls. GSI treatment caused specific cell death of hypoxic tumors. Tumors excised from mice displayed a significant reduction of markers of hypoxia. Moreover, GSI treatment caused reduced metastasis to the liver and brain. MK-0646 was not specific to a hypoxic tumor environment but substantially increased the median survival of treated mice compared with controls. NSCLC cells evaded MK-0646 treatment by specifically overactivating EGF-R both in vivo and in 5 cell lines in vitro. This phenomenon is achieved at the level of protein stability. MK-0646 treatment caused increased erlotinib sensitivity in NSCLC cells poorly responsive to it. Sequential treatment with MK-0646 followed by erlotinib prolonged median survival of mice significantly. When the 2 drugs were administered simultaneously, no survival benefit was observed, and this combination therapy proved less effective than MK-0646 used as single agent. Our data offer novel information that may provide insights for the planning of clinical trials in humans, likely for maintenance therapy of NSCLC patients.
doi:10.1177/1947601912457025
PMCID: PMC3463922  PMID: 23050046
notch signaling; insulin-like growth factor 1 receptor signaling; tumor hypoxia
25.  Dual blockade of HER2 in HER2-overexpressing tumor cells does not completely eliminate HER3 function 
Purpose
Dual blockade of HER2 with trastuzumab with lapatinib or with pertuzumab is a superior treatment approach compared to single agent HER2 inhibitors. However, many HER2-overexpressing breast cancers still escape from this combinatorial approach. Inhibition of HER2 and downstream phosphatidylinositol-3 kinase (PI3K)/AKT causes a transcriptional and post-translational upregulation of HER3 which, in turn, counteracts the antitumor action of the HER2-directed therapies. We hypothesized that suppression of HER3 would synergize with dual blockade of HER2 in breast cancer cells sensitive and refractory to HER2 antagonists.
Experimental Design
Inhibition of HER2/HER3 in HER2+ breast cancer cell lines was evaluated by western blot. We analyzed drug-induced apoptosis and 2- and 3-dimensional growth in vitro. Growth inhibition of PI3K was examined in vivo in xenografts treated with combinations of trastuzumab, lapatinib, and the HER3 neutralizing monoclonal antibody U3-1287.
Results
Treatment with U3-1287 blocked the upregulation of total and phosphorylated HER3 that followed treatment with lapatinib and trastuzumab and, in turn, enhanced the anti-tumor action of the combination against trastuzumab-sensitive and -resistant cells. Mice bearing HER2+ xenografts treated with lapatinib, trastuzumab, and U3-1287 exhibited fewer recurrences and better survival compared to mice treated with lapatinib and trastuzumab.
Conclusions
Dual blockade of HER2 with trastuzumab and lapatinib does not eliminate the compensatory upregulation of HER3. Therapeutic inhibitors of HER3 should be considered as part of multi-drug combinations aimed at completely and rapidly disabling the HER2 network in HER2-overexpressing breast cancers.
doi:10.1158/1078-0432.CCR-12-2024
PMCID: PMC3563762  PMID: 23224399
HER2; HER3; lapatinib; trastuzumab; breast cancer

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