Abstract B09: Targeting the anti-apoptotic protein Mcl-1 with the mTOR inhibitor RAD001 sensitizes luminal breast cancers to the Bcl-2/Bcl-xL inhibitor ABT-263

In an effort to enhance therapeutic tumor cell killing in luminal breast cancers, we investigated the inhibition of the anti-apoptotic Bcl-2 family proteins Bcl-2, Bcl-xL and Mcl-1. Anti-apoptotic Bcl-2 proteins are inhibitors of the intrinsic apoptotic pathway that sequester and inhibit pro-apoptotic Bcl-2 family members. Sustained overexpression of anti-apoptotic Bcl-2 family members frequently occurs in cancers and supports tumor initiation, tumor progression, therapeutic resistance and poor patient survival. While only 2/324 and 1/324 luminal breast cancers curated by The Cancer Genome Atlas (TCGA) had gene amplification of BCL2 and BCL2L1 (encoding Bcl-xL) respectively, 21/324 (<8%) displayed MCL1 amplification. Wap-Myc transgenic mouse mammary tumors, which are highly enriched for the luminal A transcription signature, displayed profoundly increased Mcl-1 levels as compared to normal mammary tissue, suggesting a role for Mcl-1 in luminal breast cancer biology. Using a panel of four MCL1-amplified breast cancer cell lines, we found that two were marginally sensitive to treatment with ABT-263, a BH3-mimetic that targets Bcl-2 and Bcl-xL. Conversely, ectopic overexpression of Mcl-1 decreased sensitivity to ABT-263. ABT-263 induced minimal cell killing in MCF7 xenografts and had no effect on tumor growth. Similarly, ABT-263 did not affect tumor growth in luminal-like Wap-Myc mouse mammary tumors. Thus, luminal breast cancer cells expressing increased Mcl-1 are poorly responsive to Bcl-2/Bcl-xL inhibition.

Upregulation of Mcl-1 expression and activity, an established ABT-263-resistance mechanism in leukemias and lymphomas, was observed in MCL1-amplified luminal breast cancer cell lines treated with ABT-263 in culture and in vivo. ABT-263 also increased the anti-apoptotic activity of Mcl-1 towards the pro-apoptotic Bcl-2 family member BIM, suggesting that Mcl-1 upregulation compensates for inhibition of Bcl-2 and Bcl-xL by ABT-263. There are currently no Mcl-1 specific inhibitors. However, Mcl-1 undergoes cap-dependent translation, and thus inhibition of cap-dependent translation has been proposed as a method to inhibit the protein expression of Mcl-1. Importantly, the mTOR pathway is required for efficient cap-dependent translation in many cancer cells. We found that the rapalogue RAD001/everolimus, an mTOR inhibitor, decreased Mcl-1 protein levels in MCL1-amplified luminal breast cancer cell lines. Furthermore, RAD001 blocked Mcl-1 protein upregulation in response to ABT-263, producing increased cell killing and decreased cell growth in all MCL1-amplified luminal breast cancer cell lines. Treatment of luminal Wap-Myc mammary tumors with RAD001 decreased tumor volume by 40%, while treatment with ABT-263 had no effect on tumor volume. These data suggest that Mcl-1 targeting may be superior to Bcl-2/Bcl-xL targeting in luminal breast cancers, particularly in luminal breast cancers with MCL1-amplification. Furthermore, we have identified the mTOR pathway as a potential therapeutic target for blocking Mcl-1 expression in luminal breast cancers.

Citation Format: Michelle M. Williams, Linus Lee, Meghan M. Morrison, Andrew J. Williams, Violeta Sanchez, Donna Hicks, Rebecca Cook. Targeting the anti-apoptotic protein Mcl-1 with the mTOR inhibitor RAD001 sensitizes luminal breast cancers to the Bcl-2/Bcl-xL inhibitor ABT-263. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B09.

Abstract B28: Rictor/mTORC2 drives formation, progression, and therapeutic resistance of HER2-amplified breast cancers

Although HER2-targeted therapies substantially improve the outcome for patients with HER2-amplified breast cancer, resistance to HER2 targeting is frequently observed. HER2-amplified tumors depend on the HER2-mediated activation of the phosphatidylinositol-3kinase (PI3K)/Akt pathway, which becomes reactivated in many therapeutically resistant HER2-amplified tumors. We investigated the mTOR complexes mTORC1 and mTORC2 as potential therapeutic targets in HER2-amplified breast cancers, based on their roles as activators (mTORC2) or effectors (mTORC1) of Akt. We found that genomic gains in Rictor, encoding a necessary mTORC2 cofactor, correlated with poor survival in breast cancer patients, while genomic gains in Raptor, an mTORC1 cofactor, did not. Rictor protein levels were increased in invasive breast cancers as compared to ductal carcinoma in situ (DCIS). Conditional Rictor gene ablation decreased growth, cell survival and invasion of human HER2-amplified breast cancer cells by blocking Akt signaling. Treatment of HER2 positive cells with the HER2/EGFR inhibitor Lapatinib caused Rictor upregulation. However, Rictor knockdown improved cell killing in Lapatinib-treated cells and impaired Akt signaling and cell survival in Lapatinib-resistant HER2 positive breast cancer cells. Together, these results demonstrate the pivotal role of mTORC2 in HER2-amplified breast cancers and support efforts to develop mTORC2-targeted therapies.

Citation Format: Meghan M. Morrison, Bayley A. Jones, Donna J. Hicks, Violeta Sanchez, Valeria M. Estrada, Michelle M. Williams, Dana Brantley-Sieders, Rebecca S. Cook. Rictor/mTORC2 drives formation, progression, and therapeutic resistance of HER2-amplified breast cancers. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B28.

Abstract B048: The role of mTORC2 in mammary morphogenesis and HER2-mediated tumorigenesis

Breast cancer is the most common malignancy among western women. Approximately 20% of breast cancers exhibit overexpression of human epithelial growth factor receptor 2 (HER2), a marker of aggressive disease. While HER2-targeted therapies have improved patient survival in this subset, resistance to these molecularly-targeted therapies often occurs, underscoring the need for increased understanding of the signaling pathways required for HER2-mediated transformation and tumor malignancy. As such, transformation by HER2 requires signaling through the phosphoinositide 3-kinase (PI3K)/Akt signaling cascade, that regulates cell growth/survival, metabolism and motility. While targeting PI3K/Akt in HER2-positive breast cancers has been met with some clinical success, it is also associated with extreme toxicity. Understanding factors both upstream and downstream of PI3K is necessary to improve patient morbidity and mortality and will allow us to understand the earliest events driving HER2-related tumorigenesis.

The serine/threonine kinase mammalian target of rapamycin (mTOR) controls key cellular processes, including growth, survival and metabolism. mTOR operates downstream and within the PI3K/Akt pathway within two structurally and functionally distinct complexes known as mTORC1 and mTORC2, whose activity and substrate specificity are regulated by complex-specific cofactors. Specifically, the protein Raptor is a required cofactor for the rapamycin-sensitive mTORC1 complex, which is activated downstream of PI3K/Akt and mediates cell growth and metabolism. The protein Rictor is a required cofactor for mTORC2, which controls cell survival, polarity, and cytoskeletal dynamics. mTORC2 supports Akt activation through direct phosphorylation on S473, which is necessary for maximal PI3K/Akt signaling. The clinical efficacy of rapamycin in luminal breast cancers underscores the importance of mTOR signaling in breast cancers and supports its role as an effector of PI3K. However, little is known about the distinct role of mTORC2 in breast cancer. Interestingly, emerging evidence from prostate and glioblastoma models suggest a direct link between mTORC2 and PI3K-driven cancer progression.

Our preliminary data shows that loss of Rictor/mTORC2, but not Raptor/mTORC1, in primary mammary epithelial cells (PMECs) impairs branching morphogenesis, proliferation, survival and phosphorylation of Akt (S473), leading us to hypothesize that mTORC2 drives PI3K/Akt-mediated cell survival of normal and HER2-transformed breast epithelial cells. We show that loss of Rictor/mTORC2 decreases three-dimensional growth, survival, migration and phosphorylation of Akt (S473) in HER2-positive breast cancer cells and HER2-transformed MCF10A mammary epithelial cells. Additionally, Rictor loss sensitizes HER2-positive breast cancer cells to the HER2 inhibitor, lapatinib. These and additional results from in vivo studies would support investigations into novel treatment combinations to improve the outcome for patients with HER2-amplified breast cancers.

Impact: mTORC2 remains understudied in breast cancers. This study will be the first to examine the role of mTORC2 in mammary morphogenesis and in HER2-transformed breast cancers, providing unprecedented knowledge and mechanistic understanding of mTORC2 in breast cancers. Because HER2 is overexpressed in nearly 20% of all breast cancers, these findings will impact a significant number of patients.

Citation Format: Meghan M. Morrison, Dana Brantley-Sieders, Donna Hicks, Violeta Sanchez, Rebecca Cook. The role of mTORC2 in mammary morphogenesis and HER2-mediated tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B048.

Abstract A007: Mutant PIK3CA accelerates HER2-driven transgenic mammary tumor progression, enhances cancer stem cell features, and induces resistance to combinations of anti-HER2 therapies

The HER2 (ERBB2) oncogene is amplified in 20-25% of breast cancers and is associated with poor patient outcome. Mutational activation of PIK3CA, the gene encoding the p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K), occurs in ~30% of breast cancers. HER2 amplification and PIK3CA mutations often co-occur in breast cancer. Aberrant activation of the PI3K pathway has been shown to correlate with a diminished response to HER2-directed therapies. We sought to directly determine whether mutant PI3K enhances HER2-induced tumor progression and promotes resistance to HER2 inhibition in vivo. For this purpose, we generated a conditional transgenic mouse model of HER2-overexpressing (HER2+), PIK3CAH1047R-mutant breast cancer. Mice expressing both human HER2 and mutant PIK3CA in the mammary epithelium developed tumors with shorter latencies compared to mice expressing PIK3CA alone (p=0.0012) or HER2 alone (p<0.0001). HER2 and mutant PIK3CA also strongly cooperated to promote lung metastases following tail vein injection of cells derived from transgenic tumors (p<0.01). PIK3CA and HER2+/PIK3CA tumors were histologically diverse (i.e., adenocarcinoma, adenomyoepithelioma, adenocarcinoma with squamous metaplasia, and metaplastic carcinoma), expressed luminal and basal cytokeratins by IHC, and were associated with the claudin-low subtype of human breast cancers by microarray analysis. Accordingly, HER2+/PIK3CA tumors expressed elevated transcripts encoding EMT and stem cell markers, such as Snail, Slug, Twist, Bmi1, ITGB1 (CD29), and Procr. Further, single cells from HER2+/PIK3CA tumors formed more and larger mammospheres compared to cells from HER2-driven tumors. HER2+/PIK3CA mammospheres and tumors were completely resistant to the HER2 monocolonal antibody trastuzumab, alone and in combination with the HER2 tyrosine kinase inhibitor lapatinib or with pertuzumab, an antibody that inhibits ligand-induced HER2 dimerization. Both drug resistance and enhanced mammosphere formation were reversed by treatment with the pan-PI3K inhibitor BKM120. BKM120 treatment strongly inhibited T308 and S473 pAKT, whereas pAKT levels were unaffected by trastuzumab in combination with lapatinib or with pertuzumab. We further generated a model of resistance to the combination of trastuzumab, pertuzumab, and BKM120 by long-term treatment of HER2+/PIK3CA tumor transplants. Tumors initially responded, but a subset (3/11) resumed growth in the presence of drugs within 2 weeks of treatment initiation. Resistance was maintained following passaging in mice. We are currently performing whole-exome sequencing on resistant vs. untreated tumors in order to determine the mechanism(s) of resistance. In sum, PIK3CAH1047R accelerates HER2-mediated breast epithelial transformation and metastatic progression, alters the intrinsic phenotype of HER2-overexpressing cancers and generates resistance to FDA-approved combinations of anti-HER2 therapies. We propose the mouse model presented herein will be a valuable tool to investigate the underlying biology of HER2+/PI3K-mutant tumors and for the preclinical testing of therapeutic strategies against this subtype of breast cancer.

Citation Format: Ariella B. Hanker, Adam Pfefferle, Justin M. Balko, Maria Gabriela Kuba, Christian D. Young, Violeta Sanchez, Cammie R. Sutton, Hailing Cheng, Charles M. Perou, Jean J. Zhao, Rebecca S. Cook, Carlos L. Arteaga. Mutant PIK3CA accelerates HER2-driven transgenic mammary tumor progression, enhances cancer stem cell features, and induces resistance to combinations of anti-HER2 therapies. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A007.

UVB irradiation as a tool to assess ROS-induced damage in human spermatozoa

One of the consequences of oxygen metabolism is the production of reactive oxygen species (ROS) which in a situation of imbalance with antioxidants can damage several biomolecules, compromise cell function and even lead to cellular death. The particularities of the sperm cell make it particularly vulnerable to ROS attack compromising its functionality, mirrored in terms of fertility outcome and making the study of the origin of sperm ROS, as well as the alterations they cause very important. In the present work, we used UVB irradiation, an easy experimental approach known as a potent inducer of ROS formation, to better understand the origin of ROS damage without any confounding effects that usually exist in disease models in which ROS are reported to play a role. To address these issues we evaluated sperm mitochondrial ROS production using the Mitosox Red Probe, mitochondrial membrane potential using the JC-1 probe, lipid peroxidation through BODIPY probe and vitality using PI. We observed that UVB irradiation leads to an increase in sperm mitochondrial ROS production and lipid peroxidation that occur previously to an observable mitochondrial dysfunction. We concluded that sperm UVB irradiation appears to be a good and easily manipulated in vitro model system to study mitochondria-induced oxidative stress in spermatozoa and its consequences, which may be relevant in terms of dissecting the action pathways of many other pathologies, drugs and contaminants, including endocrine disruptors.

Development of multi-physics code systems based on the reactor dynamics code DYN3D

The reactor dynamics code DYN3D has been coupled with the CFD code ANSYS CFX and the 3D thermal hydraulic core model FLICA4. In the coupling with ANSYS CFX, DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the coupling with FLICA4 only the neutron kinetics module of DYN3D is used. Fluid dynamics and related transport phenomena in the reactor's coolant and fuel behavior is calculated by FLICA4.

The correctness of the coupling of DYN3D with both thermal hydraulic codes was verified by the calculation of different test problems. These test problems were set-up in such a way that comparison with the DYN3D stand-alone code was possible. This included steady-state and transient calculations of a mini-core consisting of nine real-size PWR fuel assemblies with ANSYS CFX/DYN3D as well as mini-core and a full core steady-state calculation using FLICA4/DYN3D.

Abstract 4698: Gene expression profiles of triple negative breast cancer epithelial and stromal cells are predictive of treatment response

Lacking human epithelial growth factor receptor 2 (HER2) amplification as well as estrogen and progesterone receptors, TNBC is a heterogeneous collection of biologically diverse cancers that likely contributes to variable clinical outcomes for patients suffering from this disease. Since TNBC lacks well-defined molecular targets, we recently performed gene expression (GE) analyses and identified six distinct molecular TNBC subtypes with unique biologies. To further decipher the contribution of tumor epithelium and its adjacent stroma to the biology of TNBC and clinical response to treatments, we performed GE analysis on biopsy material from 20 TNBC patients enrolled in a phase II clinical trial [VICC-BRE0904; a neoadjuvant study of cisplatin and paclitaxel±RAD001 (mTOR inhibitor)]. We isolated RNA from both tumor epithelial and stromal cells using laser capture microdissection. Our goal is to determine if GE from tumor epithelial and/or stromal cells is predictive of response to treatment. Our preliminary results indicate that there is differential GE in both tumor epithelial as well as stromal cells in pretreatment biopsies of responders versus non-responders. Patients with higher expression of proliferation genes such as MKI67, KIFCI, AURKB, E2F3, and DNA damage response genes TP53BP2, CHEK1, RPA1, BLM were more responsive to treatment compared to non-responders. Upon completion of the phase II clinical trial and correlative molecular analyses, we anticipate identifying biomarkers of drug sensitivity that will provide insight to novel combination therapies for the different subtypes of TNBC.

Citation Format: Bojana Jovanovic, Steven X. Chen, Brian D. Lehmann, Kimberly N. Johnson, Violeta Sanchez, Maria G. Kuba, Melinda E. Sanders, Ingrid A. Mayer, Harold L. Moses, Jennifer A. Pietenpol. Gene expression profiles of triple negative breast cancer epithelial and stromal cells are predictive of treatment response. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4698. doi:10.1158/1538-7445.AM2013-4698

Oxidative stress in immunocompetent patients with severe community-acquired pneumonia. A pilot study

OBJECTIVE

A comparison was made of the oxidative stress (OS) levels of patients with either viral or bacterial severe community-acquired pneumonia (sCAP) and of patients without infection (healthy volunteers (HV) and patients with acute myocardial infarction (AMI)).

DESIGN

A prospective observational study was made.

PATIENTS

Critically ill patients with sCAP.

VARIABLES

The TBARS level was measured as an index of oxidative injury. SOD, CAT and redox glutathione system (GSH, GSSG, GR, GPx) activities were measured as reflecting antioxidant capacity. Severity of illness was assessed by the APACHE II, SOFA and SIRS scores.

RESULTS

Thirty-seven subjects were included: 15 patients with CAP (12 of bacterial origin [BCAP] and 3 due to 2009 A/H1N1 virus [VCAP]), 10 HV and 12 AMI patients. Intensive care CAP mortality was 26.7% (n=4). Plasmatic TBARS levels were higher in CAP patients than in HV, but similar to those recorded in AMI patients. In contrast, VCAP was associated with lower TBARS levels, and some components of the glutathione redox system were higher in BCAP patients and HV. The OS levels did not differ between survivors and non-survivors.

CONCLUSION

Our results suggest the occurrence of higher OS in sCAP patients compared with HV. In contrast, lower TBARS levels were observed in VCAP patients, suggesting an increase of antioxidant activity related to the redox glutathione system. However, further research involving a larger cohort is needed in order to confirm these findings.

Joint source/channel coding for prioritized wireless transmission of multiple 3-D regions of interest in 3-D medical imaging data

This paper presents a 3-D medical image coding method featuring two major improvements to previous work on 3-D region of interest (RoI) coding for telemedicine applications. Namely, 1) a data prioritization scheme that allows coding of multiple 3-D-RoIs; and 2) a joint/source channel coding scheme that allows prioritized transmission of multiple 3-D-RoIs over wireless channels. The method, which is based on the 3-D integer wavelet transform and embedded block coding with optimized truncation with 3-D context modeling, generates scalable and error-resilient bit streams with 3-D-RoI decoding capabilities. Coding of multiple 3-D-RoIs is attained by prioritizing the wavelet-transformed data according to a Gaussian mixed distribution, whereas error resiliency is attained by employing the error correction capabilities of rate-compatible punctured turbo codes. The robustness of the proposed method is evaluated for transmission of real 3-D medical images over Rayleigh-fading channels with a priori knowledge of the channel condition. Evaluation results show that the proposed coding method provides a superior performance compared to equal error protection and unequal error protection techniques.

Anesthesia-induced developmental neurodegeneration: the role of neuronal organelles

Exposure to general anesthetics (GAs) and antiepileptics during critical stages of brain development causes significant neurotoxicity to immature neurons. Many animal, and emerging human studies have shown long-term functional sequelae manifested as behavioral deficits and cognitive impairments. Since GAs and antiepileptic drugs are a necessity, current research is focused on deciphering the mechanisms responsible for anesthesia-induced developmental neurotoxicity so that protective strategies can be devised. These agents promote massive and wide-spread neuroapoptosis that is caused by the impairment of integrity and function of neuronal organelles. Mitochondria and endoplasmic reticulum are particularly vulnerable. By promoting significant release of intracellular calcium from the endoplasmic reticulum, anesthetics cause an increase in mitochondrial calcium load resulting in the loss of their integrity, release of pro-apoptotic factors, functional impairment of ATP synthesis, and enhanced accumulation of reactive oxygen species. The possibility that GAs may have direct damaging effects on mitochondria, resulting in the impairment of their morphogenesis, also has been proposed. This review will present evidence that neuronal organelles are critical and early targets of anesthesia-induced developmental neurotoxicity.

Human cytomegalovirus infection of THP-1 derived macrophages reveals strain-specific regulation of actin dynamics

Human cytomegalovirus (HCMV) remains latent in cells of the myeloid lineage after primary infection. The THP-1 monocytic cell line is conditionally permissive for infection and has been used primarily to study the process of HCMV reactivation when the cells are induced to differentiate. In the present report, we characterized lytic infection in THP-1 derived macrophages using two strains of HCMV, Towne and BAC-derived TR. Our findings indicate that these cells express viral genes of all three kinetic classes and produce extracellular virus, but that there is a delay in these processes relative to productively infected fibroblasts. Importantly, our studies in THP-1 derived macrophages revealed strain-specific differences in pp65 trafficking and actin dynamics. Based on these observations, our studies indicate that differentiated THP-1 cells can serve as a valuable model for lytic infection.

Abstract LB-103: Conditional loss of ErbB3 delays mammary gland hyperplasias induced by mutant PIK3CA in transgenic mice, but does not affect mammary tumor latency, gene expression or signaling

The phosphatidylinositol-3-kinase (PI3K) pathway is the most frequently mutated pathway in breast cancer. Signaling through the ErbB family of receptor tyrosine kinases (RTKs) strongly activates PI3K. Six YXXM PI3K binding motifs in ErbB3 make this RTK a strong upstream activator of PI3K. Mutations in PIK3CA, the gene encoding the p110α catalytic subunit of PI3K, are associated with increased PI3K activity, enhanced transformation, and drug resistance. We hypothesized that upstream receptors, such as ErbB3, are still required to localize PI3K to the plasma membrane and maximally drive tumor formation induced by mutant PI3K. To test this hypothesis, we generated a doxycycline (Dox)-inducible system in triple transgenic mice (MMTV-rtTA, Tet-Op-HA-PIK3CAH1047R-IRES-Luc and Tet-Op-Cre) which are homozygous or heterozygous for floxed ErbB3 alleles. In this model, referred to as iPI3K.iCre.ErbB3FL/FL, Dox induces the expression of PIK3CAH1047R and Cre recombinase. This results in Cre-mediated deletion of floxed ErbB3 alleles in mammary cells expressing PIK3CAH1047R. Loss of ErbB3 delayed mammary hyperplasias induced by PIK3CAH1047R in 12-week old animals. The mean mammary tumor latency of iPI3K.iCre.ErbB3FL/+ animals was 398 days compared to 419 days in iPI3K.iCre.ErbB3FL/FL animals (p=0.93). Both ErbB3FL/Fl and ErbB3+ tumors showed mixed pathologies of solid, papillary or cribiform adenocarcinomas (with and without squamous metaplasia). The heterogeneity of PI3K mutant tumors was also shown by the mixed expression of cytokeratin 8-positive (luminal-like) and cytokeratin 5-positive (basal-like) epithelial cells, which was not altered by loss of ErbB3. Microarray analysis of tumors revealed similar gene expression patterns in tumors with or without ErbB3. Immunoblot analysis of tumor lysates confirmed the absence of ErbB3 protein in iPI3K.iCre.ErbB3FL/FL tumors. However, downstream effectors of PI3K such as Akt, PDK1, SGK1, GSK3, 4EBP1 and S6 were similarly phosphorylated in tumors with and without ErbB3 expression. RTKs other than ErbB3, such as ErbB2, PDGFR, EGFR and MSPR, were phosphorylated in both tumor types. In ErbB3+ tumors, P-ErbB3 associated with p85, the regulatory subunit of PI3K, and coprecipitated with p85 antibodies. In ErbB3-deficient tumors and in breast cancer cell lines where ErbB3 was knocked down with RNAi, several P-Tyr proteins remained bound to p85, including the adaptor molecules IRS-1 and Gab2. We speculate these molecules circumvent a potential requirement for ErbB3 in cancers induced and driven by mutant PIK3CA. However, ErbB3 is required for the early mouse mammary hyperplasias induced by mutant PI3K.

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 LB-103. doi:1538-7445.AM2012-LB-103

P1-07-19: Analysis of HER2−Status in Breast Cancer by Mass Spectrometry in Archival, Formalin-Fixed Tissues

HER2 (ERBB2) is overexpressed in about 25% of breast cancers and predicts clinical benefit from trastuzumab, as well as response to anthracycline-based chemotherapy. Fluorescence in situ hybridization (FISH) to detect HER2 gene copy number and immunohistochemistry (IHC) to detect HER2 protein levels are approved by the FDA to identify HER2−positive (H2) tumors. However, the 2007 ASCO/CAP report concluded that approximately 20% of HER2 testing may be inaccurate. Further, the available data did not clearly demonstrate clear superiority of either IHC or FISH as a predictor of benefit from anti-HER2 therapy. Discordance between these methods is as high as 5%. Thus, novel complementary quantitative methods for interrogating HER2 expression in tumors are needed.

Targeted protein analysis by multiple reaction monitoring mass spectrometry (MRM-MS) offers a powerful approach to configure assays for specific proteins without using antibodies. Our studies using this platform have demonstrated applicability to formalin-fixed, paraffin-embedded (FFPE) specimens. In the current studies, we used this approach to measure signals from two tryptic peptides specific to HER2, one each from the extracellular and intracellular domains, selected from among 28 candidates based on their signal intensity and sharpness of their chromatographic profiles. Preliminary studies with a HER2−overexpressing BT474 xenograft in mice demonstrated quantitation and detected previously reported HER2 ectodomain shedding. Subsequent analysis of FFPE tissue from five H2 and five triple-negative (TN) tumors yielded measurement of at least 1 femptomole of receptor for H2 tumors and less than 0.2 femptomole of receptor for TN tumors per microgram of digest analyzed. If we assume 200 picograms of protein per cell, the results suggest 110,00 to 468,000 receptors per cell in the H2 tumors and only 2,000 to 14,000 receptors per cell in the TN tumors. Despite significant biological variability in receptor levels measured among the specimens of each type, a clear separation of the H2 and TN tumors was achieved based on the peptide quantitation. This preliminary study demonstrates the potential of MRM-MS in FFPE tissue to provide an alternate approach to IHC-based protein analysis. MRM-MS offers the potential for more, accurate and robust HER2 quantification in clinical breast cancer tissues. The next phase of this work will encompass a larger sample set, including tumors with equivocal and negative FISH and/or IHC test results. Correlation with response to anti-Her2 therapy will be performed in samples with available follow-up data.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-07-19.