S2-6: ErbB3 Expression Is Required for Maintenance of Normal and Transformed Luminal Breast Epithelial Cells

The ErbB receptor tyrosine kinase family regulates breast development and cancer. ErbB2/HER2 expression correlates with HER2-enriched breast cancers, while epidermal growth factor receptor (EGFR) expression often correlates with triple negative breast cancers. Less is known regarding ErbB3, which harbors only weak kinase activity, but strongly activates phosphatidylinositol-3 kinase (PI3K)/Akt signaling upon heterodimerization with EGFR or ErbB2. We report herein that ERBB3 mRNA expression strongly correlates with Luminal A/B breast cancers, which express lower levels of EGFR and ErbB2. Mammary-specific loss of ErbB3 in mice reduced Akt phosphorylation and caused cell death in the luminal epithelium. A decreased luminal population in ErbB3-deficient epithelium correlated with expansion of the mammary stem/progenitor fraction. In normal breast samples, ERBB3 mRNA expression was highest in mature/progenitor luminal populations, and lowest in the stem/basal population. Loss of ErbB3 shifted gene expression in mammary epithelial cells to resemble a mammary stem cell signature. The genes most greatly impacted by ErbB3 loss produced a signature that correlated with decreased overall survival in tamoxifen-treated patients. Knock-down of ErbB3 in human luminal breast cancer cells caused decreased cell growth under conditions of estrogen deprivation, decreased expression of the gene encoding aromatase, and impaired expression of estrogen receptor-induced genes, including those that encode progesterone receptor and TFF1. Treatment of MCF7 luminal breast cancer xenografts with AMG-888, a humanized monoclonal antibody directed against ErbB3, decreased tumor growth. Combination of AMG-888 with the estrogen receptor inhibitor fulvestrant caused MCF7 tumor regression. Taken together, these results suggest that ErbB3 is required to sustain normal and transformed luminal epithelial cells of the breast, and suggest that targeting ErbB3 may improve the clinical outcome of breast cancers treated with endocrine therapy.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S2-6.

Abstract P5-06-10: ErbB Signaling Is Required for Activation of Phosphatidylinositol-3 Kinase and Transformation of Mammary Epithelial Cells by Polyomavirus Middle T Antigen

Summary

Polyomavirus middle T (PyVmT) transforms cells through phosphatidylinositol 3-kinase (PI3K). Overexpression of ErbB2/ErbB3 heterodimers, potent activators of PI3K, occurs in PyVmT-driven mouse mammary tumors, but without known cause and consequence. Inhibition of ErbB2 with lapatinib, or genetically engineered loss of ErbB3, decreased PI3K signaling and tumor growth in mice, suggesting ErbB2/ErbB3 is required by PyVmT. ErbB2/ErbB3 formed signaling complexes containing PyVmT, p85 and Src. EZN-3920, a novel high-affinity oligonucleotide targeting ErbB3 transcripts, impaired ErbB3 expression in vivo, decreased PI3K signaling, cell survival, and growth of tumors, and improved response to lapatinib. Therefore, PyVmT utilizes ErbB2/ErbB3 overexpression to drive PI3K signaling. Furthermore, the challenge of ErbB3 as a kinase-inactive therapeutic target can be overcome by targeting ErbB3 mRNA transcripts in vivo. Significance

Given the widespread use of, and knowledge gained from the MMTV-PyVmT transgenic mouse breast cancer model, understanding how PyVmT utilizes existing cell signaling programs is necessary to interpret how results impact our understanding/treatment of human breast cancers. We found that ErbB2/ErbB3 heterodimers were a necessary part of PyVmT signaling complexes involving Src and PI3K, and that PyVmT depends on ErbB3 in the breast epithelium for PI3K activity and tumor growth. Because ErbB3 harbors a weak/inactive tyrosine kinase, therapeutic anti-ErbB3 interventions present with challenges. Further, anti-ErbB3 antibodies that block ligand interaction with ErbB3 do not alter ligand-independent ErbB3 signaling. However. these challenges were overcome using high-affinity oligonucleotides targeting ErbB3 mRNA. Use of the oligonucleotide EZN-3920 effectively reduced ErbB3 expression, inhibited PyVmT tumor growth, and improved the response of tumors to lapatinib. These results support oligonucleotide knock-down of targets as potential therapeutic strategy.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-06-10.

Transcriptional and Post-Translational Upregulation of HER3 (ErbB3) Counteracts Antitumor Effect of HER2 Tyrosine Kinase Inhibitors

We hypothesized that sustained inhibition of HER3 and its output to PI3K/Akt is required for the optimal antitumor effect of HER2 inhibitors. Therefore, we examined the temporal effect of the HER2 tyrosine kinase inhibitor (TKI) lapatinib (lap) on feedback upregulation of active HER3 in HER2-overexpressing breast cancer cells. A time course with lap-treated cells showed 3 to 5-fold upregulation of HER3 RNA and protein, beginning at 4 h and increasing through 48 h. P-Tyr immunoblot of HER3 immunoprecipitates revealed recovery of HER3 phosphorylation at and beyond 13 h of treatment. Site-specific antibodies revealed HER3 phosphorylation at Y1197 and Y1289, two of the six p85 binding sites in HER3. Recovery of P-HER3 correlated temporally with recovery of T308 P-Akt. The upregulation of HER3 RNA upon treatment with lap suggested that inhibition of active HER2 and PI3K/Akt derepresses the transcription factor FoxO3a. Putative FoxO3a binding sites were identified within the 5' flanking region upstream of the HER3 transcription start site. Transfection with FoxO3a siRNA reduced basal and lap-induced HER3 RNA levels 2 to 5-fold compared to control cells. Conversely, overexpression of FoxO3a increased HER3 RNA 2.5-fold, which could be further enhanced by lap treatment. In addition to these transcriptional mechanisms, the recovery of P-HER3 upon lap-induced inhibition of HER2 suggested engagement of another tyrosine kinase transactivating HER3 and/or that HER2 had been incompletely inhibited by the TKI. However, IGF-IR, Src, and MET TKIs did not inhibit the recovery of P-HER3. On the other hand, the addition of trastuzumab (tz) to lap-treated cells prevented recovery of P-HER3, suggesting that disruption of a ligand-independent HER2-HER3 interaction was involved in partial maintenance of HER3 phosphorylation.The upregulation of HER3 RNA and partial maintenance of P-HER3 and P-Akt suggested that combined inhibition of HER2 and HER3 will synergistically inhibit tumor cell viability. Transfection with HER3 siRNA sensitized HER2+ breast cancer cells to each lap and tz as assessed by Apo-BrdU (apoptosis) and 3D-Matrigel growth assays. Further, treatment with AMG-888, a HER3 monoclonal antibody (AMGEN-U3), sensitized cells to each lap and tz. Ongoing studies include the treatment of BT474 xenografts in athymic mice with lap ± AMG-888 using [18F]-FDG-PET as a non-invasive imaging biomarker to predict treatment outcome. Finally, we examined HER3 levels by immunohistochemistry in sections from tumor blocks of patients enrolled in a neoadjuvant trial where lap was given alone during the first 6 weeks of therapy. The percent and intensity of tumor cell staining was calculated as a histoscore (Human Pathol. 26:291, 1995). On week 2 of therapy, HER3 levels increased 135% above pre-therapy levels (n=8; p=0.03, Mann-Whitney). These data suggest that upon inhibition of the HER2 tyrosine kinase, HER2+ breast cancers 1) upregulate HER3 by transcriptional mechanisms and partially maintain HER3 function by post-translational mechanisms; 2) this compensatory phosphorylation of HER3 partially maintains PI3K/Akt; and 3) inhibition of HER3 sensitizes HER2-dependent breast cancer cells to HER2 inhibitors.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 63.

Exon 9 and exon 20 mutations in PIK3CA confer resistance to HER2 inhibitors in HER2-overexpressing breast cancer cells

Abstract #4054

The anti-tumor effect of HER2 antagonists in HER2-dependent breast cancer cells has been proposed to rely on inhibition of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. Mutations in the p110α catalytic subunit of PI3K occur in up to 40% of breast cancers and activation of this pathway has been implicated in resistance to the HER2 antibody trastuzumab (T). PIK3CA mutations cluster in two regions in the helical (E542K, E545K; exon 9) and catalytic (H1047R; exon 20) domains. We studied the role of these mutants in resistance to HER2 inhibitors in breast cancer cells with HER2 amplification. Two lines with endogenous H1047R p110 (PI3K), SUM190 and HCC1954, and SKBR3, SUM225, and BT474 cells stably transduced with retroviral vectors encoding HA-tagged wild-type, E545K, or H1047R p110, were studied for their response to the HER2 tyrosine kinase inhibitor lapatinib ditosylate (L; GW-572016) and T. In monolayer and 3D cell proliferation assays, partial resistance to L and T was conferred by either mutation compared to WT p110. After prolonged L treatment, Ser473 phosphorylation of Akt recovered in all cells with endogenous or ectopic p110 mutants in spite of continued inhibition of Y1248 P-HER2 and Y1289 P-HER3 by L. Further, BT474 cells with either p110 mutant could be passaged in the continued presence of L. Immunoprecipitation of p85, the regulatory subunit of PI3K, showed that PI3K association with HER3 was abrogated by T and L. RNAi of HER3 in MCF10A/HER2/PI3KE545K and MCF10A/HER2/PI3KH1047R cells markedly but not completely inhibited growth suggesting that the PI3K mutants may still depend on HER3 for full activation. We hypothesized that in cells with mutant PI3K, the mutants coexist in a pool with WT enzyme, and that mutant and WT p110α are bound to p85 in variable proportions. Experiments to measure whether the ratio of mutant to WT p110 bound to p85, assayed by mass spectrometry, will increase in the PI3K-mutant cells with acquired resistance to L are in progress. To test the role of these mutants on resistance to anti-HER2 therapies in vivo, athymic mice bearing BT474 xenografts with ectopic WT, E545K, or H1047R p110 are undergoing treatment with L and T. Finally, we analyzed mutations of PIK3CA in a cohort of 40 patients with locally advanced HER2+ breast cancer treated with weekly single-agent T for 3 weeks, followed by T with docetaxel for a total of 12 weeks before surgery (Mohsin et al. JCO 23:2460, 2005). Sequential core biopsies at weeks 1 and 3 after initiation of T were taken. Eight of 40 tumors (20%) expressed mutant PI3K, 2 in exon 9 and 6 in exon 20. PIK3CA mutations did not correlate with change in Ki67 (p=0.97) or cleaved caspase 3 (p=0.51) in weeks 1 or 3 of treatment nor with pathologic complete response (p=0.21). These data suggest that, if mutant PI3K confers relative resistance to T, a shorter time to recurrence may be a more robust endpoint as the initial cellular or clinical response may not be a good indicator of this resistance.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4054.

Patterns of HER-family receptor dimerization in trastuzumab susceptible and trastuzumab resistant cell lines

2533

Background: HER2 overexpression is associated with accelerated disease progression and poor prognosis in breast cancer. Trastuzumab, a monoclonal antibody targeting the extracellular domain of HER2, is effective in the treatment of metastatic breast cancer. However, most patients treated with trastuzumab eventually develop clinical resistance. To investigate the role of HER-family receptors in trastuzumab resistance, we measured HER-family receptor expression, dimerization, and phosphorylation in trastuzumab susceptible and resistant cell lines. Methods: Cell lysates from trastuzumab susceptible and resistant BT474 and SKBR3 cell lines were obtained from the Arteaga and Esteva laboratories. Proximity-based, multiplexed assays were used to detect and quantify HER1, HER2, and HER3 expression and phosphorylation levels, as well as HER1/HER1, HER1/HER2, HER1/HER3, HER2/HER2, and HER2/HER3 dimers. Samples were incubated with a mixture of HER specific antibodies conjugated either with fluorescent reporter tags (eTags), or biotin, which binds a reporter tag releasing agent (chemical scissor). Reporter molecules are released based on proximity to the scissor in a photochemical reaction and separated by capillary gel electrophoresis. Results: In comparison to trastuzumab susceptible parental cell lines, both SKBR3 and BT474 trastuzumab-resistant cell lines displayed upregulated HER1 expression. Resistant BT474 cell lines exhibited markedly increased levels of HER1/HER2 heterodimers. Increases in HER2 phosphorylation in the trastuzumab resistant SKBR3 cell line were observed, consistent with previous studies implicating trastuzumab in the induction of HER2 phosphorylation. Total HER2 and HER3 levels were similar in trastuzumab susceptible and resistant BT474 cell lines. Conclusions: The development of trastuzumab resistance in these cell line models correlated with HER1 expression and the appearance of HER1:HER2 dimers. Since signaling initiated by such heterodimers is ineffectively antagonized by trastuzumab, these data suggest that selection for proliferative signaling mediated by HER1:HER2 dimers may represent a mechanism of trastuzumab resistance in breast cancer.

No significant financial relationships to disclose.

Effects of adjuvants on safety and efficacy of an Escherichia coli J5 bacterin

The effects of using a water-soluble adjuvant or an emulsified oil-based adjuvant on the safety, antibody titer, and clinical responses of an Escherichia coli J5 bacterin were tested in an experimental infection trial. Fifty-one cows were assigned to 17 blocks of 3. Two cows within each block of 3 were vaccinated with a commercially prepared E. coli J5 bacterin containing either a water-soluble adjuvant or the same bacterin preparation emulsified in oil. One cow in each block was an unvaccinated control. Cows were immunized at drying off and 42 d later. The right or left front mammary quarter of each experimental cow was challenged by intramammary infusion of E. coli 727 between 14 and 35 DIM. Areas of inflammation at the primary injection site were greater 1, 2, and 3 d following primary vaccination for bacterin containing oil-in-water adjuvant compared with bacterin containing water-soluble adjuvant. Whey anti-E. coli J5 IgG titers were higher at calving for cows vaccinated with bacterin containing oil-in-water adjuvant than for cows either vaccinated with bacterin containing water-soluble adjuvant or unvaccinated controls. Serum x-E. coli J5 IgG titers were higher at calving for vaccinated cows than for unvaccinated controls. Peak bacterial counts in milk from challenged quarters were greater for unvaccinated controls than for cows vaccinated with bacterin containing water-in-oil adjuvant. Bacterial counts in milk from challenged quarters and clinical score both were greater in unvaccinated controls than cows vaccinated with bacterin containing water-in-oil adjuvant between 12 and 24 h postchallenge. Clinical responses were similar between unvaccinated controls and cows vaccinated with bacterin containing water-soluble adjuvant.

Identification of a mutant bovine herpesvirus-1 (BHV-1) in post-arrival outbreaks of IBR in feedlot calves and protection with conventional vaccination

Outbreaks of infectious bovine rhinotracheitis (IBR) have recently been observed in vaccinated feedlot calves in Alberta a few months post-arrival. To investigate the cause of these outbreaks, lung and tracheal tissues were collected from calves that died of IBR during a post-arrival outbreak of disease. Bovine herpesvirus-1 (BHV-1), the causative agent of IBR, was isolated from 6 out of 15 tissues. Of these 6 isolates, 5 failed to react with a monoclonal antibody specific for one of the epitopes on glycoprotein D, one of the most important antigens of BHV-1. The ability of one of these mutant BHV-1 isolates to cause disease in calves vaccinated with a modified-live IBR vaccine was assessed in an experimental challenge study. After one vaccination, the majority of the calves developed humoral and cellular immune responses. Secondary vaccination resulted in a substantially enhanced level of immunity in all animals. Three months after the second vaccination, calves were either challenged with one of the mutant isolates or with a conventional challenge strain of BHV-1. Regardless of the type of virus used for challenge, vaccinated calves experienced significantly (P < 0.05) less weight loss and temperature rises, had lower nasal scores, and shed less virus than non-vaccinated animals. The only statistically significant (P < 0.05) difference between the 2 challenge viruses was the amount of virus shed, which was higher in non-vaccinated calves challenged with the mutant virus than in those challenged with the conventional virus. These data show that calves vaccinated with a modified-live IBR vaccine are protected from challenge with either the mutant or the conventional virus.

Inactivation of Pasteurella (Mannheimia) haemolytica leukotoxin causes partial attenuation of virulence in a calf challenge model

The leukotoxin of Pasteurella (Mannheimia) haemolytica is believed to play a significant role in pathogenesis, causing cell lysis and apoptosis that lead to the lung pathology characteristic of bovine shipping fever. Using a system for Cre-lox recombination, a nonpolar mutation within the lktC transacylase gene of the leukotoxin operon was created. The lktC locus was insertionally inactivated using a loxP-aph3-loxP cassette, and then the aph3 marker was excised from the chromosome by Cre recombinase expressed from a P. haemolytica plasmid. The resulting lktC strain (SH2099) secretes inactive leukotoxin and carries no known antibiotic resistance genes. Strain SH2099 was tested for virulence in a calf challenge model. We inoculated 3 x 10(8) or 3 x 10(9) CFU of wild-type or mutant bacteria into the lungs of healthy, colostrum-deprived calves via transthoracic injection. Animals were observed for clinical signs and for nasal colonization for 4 days, after which they were euthanized and necropsied. The lower inoculum (3 x 10(8) CFU) caused significantly fewer deaths and allowed lung pathology to be scored and compared, while the 3 x 10(9) CFU dose of either the wild-type or mutant was lethal to >/=50% of the calves. The estimated 50% lethal dose of SH2099 was four times higher than that of the wild-type strain. Lung lesion scores were reduced twofold in animals inoculated with the mutant, while clinical scores were nearly equivalent for both strains. The wild-type and mutant strains were equally capable of colonizing the upper respiratory tracts of the calves. In this study, the P. haemolytica lktC mutant was shown to be less virulent than the parent strain.

Public and private health insurance of US foreign-born residents: implications of the 1996 welfare reform law

OBJECTIVE

US policy towards immigrants is undergoing considerable change, often in the absence of objective data. In this paper, the insurance status of the US foreign-born population is presented overall and disaggregated by race, ethnicity and length of residence in the USA.

DESIGN

Data from the National Health Interview Surveys, a cross-sectional household survey representing the non-institutionalized US population, was used to identify respondents as foreign- or native-born and to determine the type of health insurance coverage. The surveys also collected race and ethnicity information from all respondents based on self-reports, and, for the foreign-born population, the length of residence in the USA.

RESULTS

Compared to native-born residents, foreign-born residents are twice as likely to be uninsured (26.3% versus 13.0%), less likely to have private insurance (62.3% vs 78.8% and Medicare (88.6% vs 96.2%) and somewhat more likely to have Medicaid (6.5% vs 4.1%). A separate analysis of Hispanic and Asian foreign-born residents was conducted. Length of residence in the USA, race and ethnicity significantly impact the type and extent of health insurance coverage among the foreign-born population.

CONCLUSION

Recent legislative initiatives restricting immigrants' access to public services could lead to adverse public health consequences including further exacerbation of the high rates of uninsuredness found in this study.

NF-kappa B as a target for anti-inflammatory gene therapy: suppression of inflammatory responses in monocytic and stromal cells by stable gene transfer of I kappa B alpha cDNA

One of the most challenging issues of anti-inflammatory gene therapy is the complexity of inflammatory pathways. Transcription factor NF-kappa B plays a pivotal role in activation of multiple inflammatory molecules, and therefore represents the logical target for intervention. We evaluated the feasibility of suppressing the inflammatory responses in different cell lines through specific inhibition of NF-kappa B by gene transfer of I kappa B alpha, the naturally occurring intracellular inhibitor of NF-kappa B. The I kappa B alpha overexpressing cells were established using retroviral gene transfer or stable transfection with the wild-type (wt) I kappa B alpha cDNA. In all cell types, overexpression of wt I kappa B alpha resulted in a profound (> 100-fold) increase of the I kappa B alpha message and a moderate (two- to three-fold) increase of the I kappa B alpha protein. The effects of the I kappa B alpha overexpression on the NF-kappa B activation and the inflammatory responses varied significantly in different cell lines. In conditionally immortalized human endometrial stromal cells, overexpression of I kappa B alpha prevented both interleukin-1 (IL-1)-inducible degradation of endogenous I kappa B alpha protein and activation of NF-kappa B. Accordingly, induction of cytokines interleukin-8 (IL-8) and Gro gamma was markedly suppressed. In monocytic THP-1 cells, both lipopolysaccharide (LPS)-inducible degradation of I kappa B alpha and NF-kappa B activation were only partially inhibited by overexpression of exogenous I kappa B alpha cDNA. None the less, the LPS-induced transcription of IL-1 beta and secretion of cytokines interleukin-6 (IL-6) and IL-8 were virtually abolished. In epithelial HT-29 cells, no inflammatory responses were inhibited. These results demonstrate the range of responses in various cell lines to gene transfer of I kappa B alpha and indicate the feasibility of suppression of inflammatory responses in appropriate target cells and their progeny by suppression of NF-kappa B.

A restriction map of the ribosomal RNA genes and the short single-copy DNA sequence of the pearl millet chloroplast genome

The chloroplast rDNA genes of pearl millet (Pennisetum americanum) have been cloned and physically mapped. The chloroplast genome of the pearl millet contains two identical rRNA genes located on DNA sequences that are inverted with respect to one another and separated by 12 kb of single-copy DNA. The rRNA genes were positioned on a restriction endonuclease map by using as hybridization probes specific cloned rDNA sequences from the chloroplast DNA of the alga Euglena gracilis. The 16S and 23S rRNA genes were shown to be approx. 2 kb from one another, and the 5S RNA gene is immediately adjacent to the 23S tRNA gene.