ERBB3 Amplification Research Articles

Combination targeted treatment may enhance antitumor activity in ERBB3 amplified high-grade serous endometrial cancer cells resistant to single agent targeted therapy

Objectives: Up-regulation of ERBB pathways represent targetable alterations in many high grade endometrial cancers (EC); ERBB3 amplifications in particular may contribute to ineffective pathway targeting due to persistent co-activation of other ERBB binding partners, leading to tumor growth and survival. The efficacy of downstream dual-inhibition of MEK+AKT or MEK+PI3K in an ERBB3 amplified EC primary tumor was studied using a microcancer 3D ex-vivo tumor cell viability assay. Methods: Tumor was prospectively collected from a patient with stage II, FIGO grade 3, serous EC and genomic characterization was performed using multiple sequencing methods: whole exome, RNA, and MatePair analysis. Somatic mutations, structural variance, with transcriptomic profiling was used to identify potential driver pathways for subsequent pharmacologic inhibition. Primary tumor cells were grown in a three-dimensional environment and the formed microcancers were subjected to drug treatment. Cell viability was determined by the CellTiter-Glow Luminescent Assay. Data transformation and dose-response curves were generated using GraphPad PRISM using four parameter logistic regression. CompuSyn software with the Chou-Talalay method was used to analyze drug interactions and synergy. The Fractional response-Combination index (Fa-CI) plot was generated with Microsoft Excel. Capivasertib, GDC-0084, and cobimetinib were used to inhibit AKT, PI3K/mTOR, and MEK, respectively. Inhibitory effect was defined as percent reduction in ATP at clinically-defined predicted plasma maximum concentration (Cmax) values. Results: Genomic sequencing revealed overexpression of a mutated ERBB3 (c.889G>T; p.Asp297Tyr) transcript within a 6N focal amplification. Additional pertinent alterations included a MYC mid-level gain, and TP53 double hit (loss and exonic splicing silencer (ESS)). Inhibition of cell viability was moderate by single agents: capivasertib, cobimetanib, or GDC-0084, as shown by inhibitory effect values of 33.9%, 35.9% and 49.9%, respectively. Two combinations with cobimetinib demonstrated increasing inhibitory effect values of 76.2% for cobimetanib/capivasertib at the Cmax of capivasertib and 79.7% for cobimetanib/GDC-0084 at the Cmax of cobimetanib. Synergy was evidenced by a combination index <1 at all points with Fa>0.8 (Figure 1). Conclusions: Combined inhibition of MEK and PI3K-AKT-mTOR pathways synergistically suppress viability in a patient-derived high-grade serous EC harboring a ERBB3 amplification. Further ex-vivo testing should be performed in endometrial tumors with other ERBB3 aberrations to allow generalization of results. Up-regulation of ERBB pathways represent targetable alterations in many high grade endometrial cancers (EC); ERBB3 amplifications in particular may contribute to ineffective pathway targeting due to persistent co-activation of other ERBB binding partners, leading to tumor growth and survival. The efficacy of downstream dual-inhibition of MEK+AKT or MEK+PI3K in an ERBB3 amplified EC primary tumor was studied using a microcancer 3D ex-vivo tumor cell viability assay. Tumor was prospectively collected from a patient with stage II, FIGO grade 3, serous EC and genomic characterization was performed using multiple sequencing methods: whole exome, RNA, and MatePair analysis. Somatic mutations, structural variance, with transcriptomic profiling was used to identify potential driver pathways for subsequent pharmacologic inhibition. Primary tumor cells were grown in a three-dimensional environment and the formed microcancers were subjected to drug treatment. Cell viability was determined by the CellTiter-Glow Luminescent Assay. Data transformation and dose-response curves were generated using GraphPad PRISM using four parameter logistic regression. CompuSyn software with the Chou-Talalay method was used to analyze drug interactions and synergy. The Fractional response-Combination index (Fa-CI) plot was generated with Microsoft Excel. Capivasertib, GDC-0084, and cobimetinib were used to inhibit AKT, PI3K/mTOR, and MEK, respectively. Inhibitory effect was defined as percent reduction in ATP at clinically-defined predicted plasma maximum concentration (Cmax) values. Genomic sequencing revealed overexpression of a mutated ERBB3 (c.889G>T; p.Asp297Tyr) transcript within a 6N focal amplification. Additional pertinent alterations included a MYC mid-level gain, and TP53 double hit (loss and exonic splicing silencer (ESS)). Inhibition of cell viability was moderate by single agents: capivasertib, cobimetanib, or GDC-0084, as shown by inhibitory effect values of 33.9%, 35.9% and 49.9%, respectively. Two combinations with cobimetinib demonstrated increasing inhibitory effect values of 76.2% for cobimetanib/capivasertib at the Cmax of capivasertib and 79.7% for cobimetanib/GDC-0084 at the Cmax of cobimetanib. Synergy was evidenced by a combination index <1 at all points with Fa>0.8 (Figure 1). Combined inhibition of MEK and PI3K-AKT-mTOR pathways synergistically suppress viability in a patient-derived high-grade serous EC harboring a ERBB3 amplification. Further ex-vivo testing should be performed in endometrial tumors with other ERBB3 aberrations to allow generalization of results.

Pertuzumab plus trastuzumab (P+T) in patients (Pts) with uterine cancer (UC) with ERBB2 or ERBB3 amplification, overexpression or mutation: Results from the Targeted Agent and Profiling Utilization Registry (TAPUR) study.

5508 Background: TAPUR is a phase II basket study evaluating anti-tumor activity of commercially available targeted agents in pts with advanced cancers with genomic alterations. Results in a cohort of UC pts with ERBB2 or ERBB3 amplification , overexpression or mutation treated with P+T are reported. Methods: Eligible pts had advanced UC, no standard treatment options, measurable disease, ECOG PS 0-2, and adequate organ function. Genomic testing was performed in CLIA-certified, CAP-accredited site selected labs. Pts matched to P+T had UC with ERBB2 or ERBB3 amplification or overexpression or a pre-specified ERBB2 mutation. Recommended dosing was P at an initial dose of 840 mg intravenously (IV) over 60 minutes (m), then 420 mg IV over 30-60 m every 3 weeks (wks), and T at an initial dose of 8 mg/kg IV over 90 m, then 6 mg/kg IV over 30-60 m every 3 wks until disease progression. Simon 2-stage design tested the null disease control (DC) - defined as partial (PR), complete response (CR) or stable disease at 16+ weeks (SD 16+) - rate of 15% vs. 35% (power = 0.85; α = 0.10). If ≥2 of 10 pts in stage 1 have DC, 18 more pts are enrolled. If ≥7 of 28 pts have DC, the null DC rate is rejected. Secondary endpoints are progression-free survival (PFS), overall survival (OS) and safety. Results: Twenty-eight female pts were enrolled from August 2017 to November 2019; all pts were evaluable for efficacy and toxicity. Demographics and outcomes are summarized in Table. Twenty-two pts had tumors with ERBB2 amplification (21) or overexpression (1); 4 tumors had ERBB2 mutations; 1 tumor had ERBB3 amplification; 1 tumor had both an ERBB2 amplification and mutation. Two PR and 7 SD16+ were observed in pts with ERBB2 amplification, and 1 SD16+ was observed in a pt with ERBB2 V8421 mutation only (no amplification) for DC and objective response (OR) rates of 37% (95% CI, 21% to 50%) and 7.1% (95% CI, 0.8% to 24%), respectively. One pt experienced grade 3 muscle weakness at least possibly related to P+T. Conclusions: P+T demonstrated evidence of anti-tumor activity in heavily pre-treated UC pts with ERBB2 amplification or certain mutations. Additional study is warranted to confirm the efficacy of P+T in this pt population. Clinical trial information: NCT02693535. [Table: see text]

Genomic Profiling Aids Classification of Diagnostically Challenging Uterine Mesenchymal Tumors With Myomelanocytic Differentiation.

Although diagnosis of high-grade uterine mesenchymal tumors (UMTs) exhibiting classic morphologic features is straightforward, diagnosis is more challenging in tumors in which prototypical features are poorly developed, focal, and/or coexist with features seen in other neoplasms. Here, we sought to define the repertoire of somatic genetic alterations in diagnostically challenging UMTs with myomelanocytic differentiation, including some reported as perivascular epithelioid cell tumors (PEComas). In 17 samples from 15 women, the tumors were histologically heterogenous. Immunohistochemical expression of at least 1 melanocytic marker (HMB45, Melan-A, or MiTF) was identified in all tumors, and of myogenic markers (desmin or smooth muscle actin) in most tumors. Targeted massively parallel sequencing revealed several genetic alterations, most commonly in TP53 (41% mutation, 12% deletion), TSC2 (29% mutation, 6% deletion), RB1 (18% deletion), ATRX (24% mutation), MED12 (12% mutation), BRCA2 (12% deletion), CDKN2A (6% deletion) as well as FGFR3, NTRK1, and ERBB3 amplification (each 6%). Gene rearrangements (JAZF1-SUZ12; DNAJB6-PLAG1; and SFPQ-TFE3) were identified in 3 tumors. Integrating histopathologic, immunohistochemical, and genetic findings, tumors from 4 patients were consistent with malignant PEComa (1 TFE3-rearranged); 6 were classified as leiomyosarcomas; 3 showed overlapping features of PEComa and other sarcoma types (leiomyosarcoma or low-grade endometrial stromal sarcoma); and 2 were classified as sarcoma, not otherwise specified. Our findings suggest that diagnostically challenging UMTs with myomelanocytic differentiation represent a heterogenous group of neoplasms which harbor a diverse repertoire of somatic genetic alterations; these genetic alterations can aid classification.

Genomic Landscape and Targeted Treatment of Gallbladder Cancer: Results of a First Ongoing Prospective Study.

Background Prognosis of gallbladder cancer (GBC) has not changed in the past 20 years. Comprehensive genomic profiling (CGP) carries potential to determine the actionability for multiple targets, including ERBB2 , ERBB3 , MET , ROSI , FGFR , and PIK3 . This study evaluates the role of CGP and targeted therapies. Methods This is a multicenter, prospective, single-arm study. All consecutive patients of unresectable and/or metastatic GBC of age ≥18 years were enrolled. Hybrid capture-based CGP was performed by Foundation Medicine CDx. All patients received first-line chemotherapy with gemcitabine–cisplatin regimen. Patients with ERBB2/3 amplification received trastuzumab with capecitabine or nab-paclitaxel, and patients with MET amplification were treated with crizotinib. For ERBB2/3 mutations, lapatinib plus capecitabine regimen was used. Results Fifty patients were studied with a median age of 56 years (range 26–83) and a male-to-female ratio of 1:1.6. ERBB2 and ERBB3 amplification was seen in 9 (18%) and 2 (4%) patients, respectively. Four patients with ERBB2 amplification received trastuzumab and/or lapatinib, showed partial response, and maintained response beyond 12 weeks. One patient had mixed response, whereas two patients progressed on trastuzumab and lapatinib. Three patients with ERBB3 mutations showed response to lapatinib–capecitabine. One patient with MET amplification responded to crizotinib for 4 weeks. PIK3 mutations were present in 14% of cases and were independent of ERBB aberrations. Conclusion GBC is enriched in 28% of patients with ERBB2 and ERBB3 amplifications and/or mutations. Responses are seen with lapatinib in concurrent ERBB2 mutation and amplification. ERBB3 mutation showed response to lapatinib. MET and PIK3 are new findings in GBC, which may be targeted.

Genomic architecture of gallbladder cancer: Results of a first prospective study.

e16628 Background: Rarity in western countries precluded Gallbladder cancer (GBC) from prospective research. Comprehensive Genomic profiling carries potential to determine oncogenic pathways, driver mutations and possible resistance mechanisms. This study is evaluating the role of comprehensive genomic profiling and role of targeted therapies therein. Methods: This is a single center, prospective, study conducted from Aug2018-Dec2019. All consecutive patients of unresectable and/or metastatic GBC of age ≥18 years were enrolled. Hybrid capture based comprehensive genomic profiling was performed by Foundation Medicine CDx. Microsatellite instability and PDL1 expression were studied. Results: Median age was 56 years (range:26-83) with male to female ratio of 1:1.6. NGS information was available for 50 patients. ERBB pathway was aberrated in 44% of patients. ERBB2 &amp; ERBB3 amplification was seen in 9(18%) and 2(4%) patients respectively. ERBB2 mutations were present concurrently with amplification in 3 patients. MET amplification was present in 3 (6%) PIK3CA mutations were seen in 14% of cases. PIK3CA mutations were independent of ERBB aberrations. FGFR2 mutation, FGFR2 and FGFR3 amplification was present in one patient each. NF1 and NF2 mutations were seen in three and two patients respectively. Median TMB (n = 39) was 5 mut/Mb with range of 1-14 mut/Mb. PDL1 (n = 31) of ≥ 1% was present in 32% of cases and it ranged from 1-100%. MSI (n = 39) was stable in all cases. Other somatic mutations and/or amplifications are shown in Table. Conclusions: GBC is enriched in 28% of patients with ERBB2 &amp; ERBB3 amplifications and/or mutations. FGFR2 mutation is rare in GBC. PIK3CA aberrations are common. Phase 2 trial of frontline Trastuzumab combined with chemotherapy is ongoing. [Table: see text]

The characterization of ERBB family mutations in Chinese biliary tract cancers.

e15595 Background: Next generation sequencing has been applied to identify actionable mutations in biliary tract cancers (BTCs). ERBB family genes, especially ERBB2 and ERBB3, serve as effective biomarkers for BTCs targeted therapy as shown in MyPathway and SUMMIT clinical trials. However, the distribution and major mutation types of ERBB family genes were not clear in Chinese BTC patients. Methods: Deep sequencing targeting 450 cancer genes was performed on FFPE and matching blood samples collected from a cohort of 716 Chinese BTC patients. Genomic alterations including single nucleotide variations (SNV), short and long insertions/deletions (Indels), copy number variations, gene rearrangements and fusions were analyzed. Results: A total of 14% (101/716) of patients with a median age of 62 years old, including 45 males and 56 females, were identified harboring ERBB family mutations. Somatic ERBB family mutations occurred with a rate of 29% in gallbladder carcinoma (GBCA), 13% in extrahepatic cholangiocarcinoma (EHCCA), 12% in hilar cholangiocarcinoma (HCCA) and 8% in intrahepatic cholangiocarcinoma (IHCCA). No germline mutation was detected. A high rate of ERBB2 gene amplification was observed in GBCA (17%). In IHCCA and EHCCA, SNV/Indel accounted for 3% and 5%, respectively, and was the major variation in ERBB2. In HCCA, SNV/Indel was the most common mutation in ERBB3 (8%). In BTC patients, TP53 (81%) and CDK12 (36%) were the top-ranked co-mutant genes with ERBB2. The mutant frequency of CDK12 was significantly different between patients with or without an ERBB2 mutation ( p&lt; 0.001). ERBB2 S310F/Y, ERBB3 V104L/M were hotspot mutations within the ERBB family in BTCs. Conclusions: ERBB family mutations were detected in 14% of Chinese BTC patients. Similar to Western populations (PMID: 27622582), ERBB2 gene amplification was the most common mutation in GBCA in Chinese patients. Unlike ERBB2/ ERBB3 amplification which has been reported as the major mutation in previous studies, our study of other BTC types revealed ERBB2/ ERBB3 SNV/Indel as the major mutation. BTC patients harboring ERBB family mutations have the potential to benefit from pan-HER inhibitors.

Abstract P3-01-08: HER2-negative metastatic breast cancer with HER2-positive circulating tumor cells (CTCs): A new CTC-defined HER2-positive subgroup

Abstract Introduction: CTCs can overexpress HER2 discordant from tumor HER2 expression. We aimed to describe characteristics of a CTC-defined group of pts with metastatic breast cancer (MBC) that is tumor HER2- and CTC HER2+ (HER2 tumor- CTC+). Methods: We retrospectively analyzed data from pts treated at Northwestern University who had serial evaluation of CTCs and circulating tumor DNA (ctDNA). We included pts with pathologically confirmed HER2- MBC and HER2+ CTCs. CTCs were enumerated with the CellSearch immunomagnetic kit (Menarini Silicon Biosystems), HER2 expression on CTCs was determined using the CellSearch CXC Kit in 7.5 cc whole blood, and ctDNA was analyzed using the Guardant360 NGS assay (Guardant Health). Results: Among 98 pts with HER2- MBC and CTC analysis, 46 (47%) had at least 1 HER2+ CTC. In this cohort the median age was 53. At initial BC diagnosis, 80% had early stage or locally advanced BC and 20% had de-novo metastatic disease. Baseline histology was 65% ductal, 20% lobular, 2% mixed ductal and lobular, and 13% unknown. Pathology of metastatic tumor was hormone receptor positive (HR+)/HER2- in 78% and triple negative in 22%. Detailed HER2 immunohistochemistry (IHC) and FISH results from metastases were available from 63% of pts of whom 72% had an IHC score of 0 or 1 and 28% had an IHC score of 2 with negative FISH testing. The median time from the most recent pathologic metastatic tumor assessment to the detection of a HER2+ CTC was 6.5 mo. Twenty-two pts had simultaneous (within 8 weeks) HER2- tumor confirmation and HER2+ CTC detection. The median lines of endocrine therapy (ET) for MBC prior to detection of HER2+ CTCs was 1 (range 0-5, 41% no ET, 17% 1 line, 41% &amp;gt;2 lines). Pts received a median of 2 (range 0-10) prior systemic therapies for MBC prior to detection of HER2+ CTCs, (20% 0 lines, 41% 1-3 lines, and 39% &amp;gt;4 lines). Among these 46 pts, CTCs were analyzed longitudinally in 104 samples, with HER2+ CTCs detected in 77 samples. Number of HER2+ CTCs at initial detection ranged from &amp;lt;5 in 24%, 5-50 in 43%, and &amp;gt;50 in 33%, with a median of 11.5 HER2+ CTCs. CTC clusters were noted in 37% of pts. At initial detection the proportion of CTCs that were HER2+ was 0-25% in 13% of pts, 26-50% in 46% of pts, and 51-100% in 41% of pts. Seven pts had ERBB2 aberrations in ctDNA. Of 12 pts with tumor sequencing, 2 had ERBB2 mutations, 1 had ERBB3 amplification, and 1 had overexpression of ERBB3 RNA. After detection of HER2+ CTCs, 18 pts received HER2 directed therapy (with chemotherapy in 13 pts, with endocrine therapy in 4 pts, and as monotherapy in 1 pt). Imaging demonstrated a partial response or stable disease in 9 pts (clinical benefit rate 50%), including in 1 pt with trastuzumab monotherapy, progressive disease in 8 pts, and not evaluated in 1 pt. Conclusions: HER2+ CTCs are frequently detected simultaneously or soon after HER2- tumor assessment in MBC. Within this newly defined subgroup, the several responses seen with HER2 targeted therapy serve as a proof of concept that HER2 tumor- CTC+ patients can benefit from HER2 targeted therapy. Future studies are needed to determine a clinically relevant threshold for HER2+ CTCs to guide further study of HER2 therapy combinations in HER2 tumor- CTC+ pts. Citation Format: Shah AN, Gerratana L, Zhang Q, Davis AA, Zhang Y, Flaum L, Behdad A, Platanias L, Gradishar WJ, Cristofanilli M. HER2-negative metastatic breast cancer with HER2-positive circulating tumor cells (CTCs): A new CTC-defined HER2-positive subgroup [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-01-08.

Abstract 1346: Pan-ERBB inhibitor blocks tumor growth and metastasis

Abstract The Epidermal Growth Factor Receptor family of transmembrane tyrosine kinases (ErbB) is over-expressed, correlates with poor prognosis and negatively correlates with disease free survival in many cancer types. EGFR, HER2 and ErbB3 are known to be highly expressed and active, and have been targeted by both kinase inhibitors and monoclonal antibodies, both with disappointing results. Importantly, though, these therapeutics only target either a single receptor or the kinase domain alone. It is well known that these receptors function as heterodimers, and blocking of a single receptor will only promote the hetero-dimerization of the remaining family members. Furthermore, while the tyrosine kinase activity of these receptors is well known, less appreciated are the kinase-independent mechanisms by which they drive cancer progression. These include the modulation of calcium signaling and mitochondrial and nuclear translocation and activity as transcriptional co-factors. The highly conserved juxta-membrane domain (JD) of the ErbB receptors regulates these kinase-independent functions, as well as receptor homo- and hetero-dimerization. Upon ligand binding, the JD forms anti-parallel dimers between the receptors, resulting in receptor dimerization and intracellular trafficking. These protein-protein interactions result in cell growth, survival, migration and invasion. We have previously shown that peptides mimicking this JD can act in a dominant-negative fashion, promoting the formation of non-functional ErbB dimers (consisting of EGFR, HER2 and ErbB3) that induce rapid, ErbB-dependent cell death. Using Cell Penetrating Peptides synthesized in tandem with the JD, these peptides (called EJ1) rapidly cross the plasma membrane, bind the ErbB receptors, and induce cell death in cell lines and PDX lines grown in culture. Death results from a combination of apoptotic and necrotic mechanisms, due to inactivation of mitochondrial function and calcium signaling (as well as kinase inhibition). Although EJ1 peptides display rapid ErbB-dependent cell death in vitro, they are rapidly cleared in vivo, limiting their efficacy. To stabilize in vivo activity, the active peptide (which is an alpha-helix) was stabilized with hydrocarbon staples. Based on this, we hypothesized that SAH-EJ1 would be an effective targeted therapeutic for the treatment of ErbB-dependent cancer. We therefore tested SAH-EJ1 in 3 different ErbB-dependent models of cancer, including EGFRvIII-driven glioblastoma, a PDX model of basal-like breast cancer with EGFR and ErbB3 amplification, and a PDX model of lung cancer with EGFR kinase domain mutations driven by Erlotinib treatment. In each of these models, substantial inhibition of tumor growth was observed, as well as extended survival. Citation Format: Joyce A. Schroeder, Sabrina Maisel, Derrick Broka. Pan-ERBB inhibitor blocks tumor growth and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1346. doi:10.1158/1538-7445.AM2017-1346

Abstract 3897: High-throughput profiling of actionable mutations in salivary duct carcinoma

Abstract Salivary duct carcinoma (SDC) is a highly aggressive subtype of salivary gland cancers and there is no established standard therapy for this disease. Thus, development of molecular markers for SDC will be important to guide the diagnosis and therapy of this aggressive tumor. We performed next-generation sequencing using the Ion Torrent AmpliSeq cancer panel, which explores the mutational status of hotspot regions in 50 cancer-associated genes, and we analyzed copy number variations (CNVs) of 21 genes by NanoString nCounter for 37 patients with SDC. Fluorescent in situ hybridization was also conducted to confirm ERBB2 gene amplification. Clinical records and tumor histopathology of the patients were retrospectively reviewed. Genetic alterations were detected in 29 of 37 (78.3%) tumors, including mutations in PIK3CA (N = 9, 24.3%), ERBB2 (N = 4, 10.8%), and EGFR (N = 4, 10.8%). To our knowledge, this is the first time that ERBB2 mutations have been reported in this tumor type. Both PIK3CA and ERBB2 mutation status were associated with poor overall survival, but without statistical significance. ERBB2 amplification was strong and common in SDC and almost all cases also exhibited EGFR and ERBB3 amplifications. This study reports the largest and most comprehensive analysis of DNA aberrations in SDC. Our results show that PIK3CA and/or ERBB2 alterations in the development of SDC might be a useful diagnostic tool and could serve as a potential therapeutic target. Key words: Salivary duct carcinoma, next-generation sequencing, molecular markers, PIK3CA, ERBB2, EGFR Citation Format: Bo Mi Ku, Yeon-Hee Bae, Hyun Ae Jung, Jong-Mu Sun, Young Hyeh Ko, Han-Sin Jeong, Young-Ik Son, Chung-Hwan Baek, Keunchil Park, Myung-Ju Ahn. High-throughput profiling of actionable mutations in salivary duct carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3897. doi:10.1158/1538-7445.AM2015-3897

Oligomerization of the Nrdp1 E3 Ubiquitin Ligase Is Necessary for Efficient Autoubiquitination but Not ErbB3 Ubiquitination

Overexpression of the ErbB3 receptor tyrosine kinase protein in breast and other cancers contributes to tumor malignancy and therapeutic resistance. The RBCC/TRIM family RING finger E3 ubiquitin ligase Nrdp1 mediates the ubiquitination of ErbB3 in normal mammary epithelial cells to facilitate receptor degradation and suppress steady-state receptor levels. Post-transcriptional loss of Nrdp1 in patient breast tumors allows ErbB3 overexpression and receptor contribution to tumor progression, and elevated lability through autoubiquitination contributes to the observed loss of Nrdp1 in tumors relative to normal tissue. To begin to understand the mechanisms underlying Nrdp1 protein self-regulation through lability, we investigated the structural determinants required for efficient autoubiquitination and ErbB3 ubiquitination. Using mutagenesis, chemical cross-linking, size exclusion chromatography, and native polyacrylamide gel electrophoresis, we demonstrate that Nrdp1 self-associates into a stable oligomeric complex in cells. Deletion of its coiled-coil domain abrogates oligomerization but does not affect Nrdp1-mediated ErbB3 ubiquitination or degradation. On the other hand, the presence of the coiled-coil domain is necessary for efficient Nrdp1 autoubiquitination via a trans mechanism, indicating that Nrdp1 ubiquitination of its various targets is functionally separable. Finally, a GFP fusion of the coiled-coil domain stabilizes Nrdp1 and potentiates ErbB3 ubiquitination and degradation. These observations point to a model whereby the coiled-coil domain plays a key role in regulating Nrdp1 lability by promoting its assembly into an oligomeric complex, and raise the possibility that inhibition of ligase oligomerization via its coiled-coil domain could be of therapeutic benefit to breast cancer patients by restoring Nrdp1 protein.

Competitive-differential polymerase chain reaction for gene dosage estimation of erbB-1 (egfr), erbB-2, and erbB-3 oncogenes.

Increases in the average gene copy number (AGCN) of the erbB oncogenes, especially the erbB-2 gene, have been found in a variety of human cancers. Such information is useful with respect to prognosis of the disease. Poor reproducibility and DNA damage complicate quantitative polymerase chain reaction (PCR)-based methods. Therefore, we describe a quantitative PCR method for the estimation of AGCN in the oncogenes erbB-1 (egfr), erbB-2, and erbB-3. The method comprises a competitive and differential PCR in a one-tube reaction (competitive-differential PCR, or cdPCR). Genomic sequences of the oncogene and the human beta-globin (HBB) reference gene and two competitors for the oncogene and reference gene were amplified with two primer pairs simultaneously. The competitors were chosen to be amplified with the same efficiency as the genomic sequences. Using this method, we confirmed egfr and erbB-2 amplification in cancer cell lines and tumor tissue, and we also detected erbB-3 amplifications. Furthermore, gene dosage decreases were detectable, e.g., an erbB-2 hemizygosity in MCF-7 cells. Thus, cdPCR facilitates the detection of both increases and decreases in AGCN with high reproducibility, sensitivity, and accuracy. This method is therefore suitable for clinical studies on erbB oncogene dosage deviations.