Abstract P3-11-05: RANK ligand is a target for breast cancer prevention in BRCA1 mutation carriers

Background: BRCA1 mutation carriers often undergo prophylactic mastectomy to minimize their risk of breast cancer. The value of targeting ovarian hormones to prevent breast tumorigenesis remains contentious and the identification of an effective and acceptable chemoprevention strategy remains a 'holy grail' for the field. Recently, luminal progenitor cells have been identified as the likely cell-of-origin for BRCA1-associated breast tumors1. In addition, deregulated progesterone signaling has been implicated as a potential mechanism underlying tumor development in Brca1-deficient mammary glands2, although its role in luminal progenitor activation in BRCA1 mutation carriers is unknown. RANKL (Receptor Activator of Nuclear Factor-kappa B Ligand) has been identified as a key paracrine effector of progesterone-induced mammary epithelial proliferation in both mouse and human tissue3-5. Notably, RANKL and its receptor RANK play a critical role in the development of breast cancer, with inhibition of RANKL resulting in attenuation of tumorigenesis in mouse models of hormone-driven mammary carcinogenesis6,7.

Methods: We explored a role for the RANK/RANKL pathway during the preneoplastic phase in freshly isolated, histologically normal specimens from BRCA1 mutation carriers using a combination of strategies. RANK and RANKL expression in breast cancer was also evaluated in formalin fixed paraffin embedded (FFPE) archival sections by IHC. All samples were obtained with relevant IRB approval. A role for RANKL inhibition in attenuating tumor onset was studied using models that recapitulate human basal-like cancer.

Results: A RANK+ subset of luminal progenitor cells was identified in histologically normal breast tissue from BRCA1-mutation carriers. The RANK+ luminal progenitors exhibited higher proliferative activity compared to RANK- progenitors. RNA profiling revealed a distinctive molecular signature, consistent with the RANK+ subset being a possible target for neoplastic transformation. In established BRCA1-associated breast tumors, a four-fold higher incidence of RANK expression was observed, compared to tumors from non-carriers. In ongoing work, histologically normal pre-neoplastic BRCA1mut/+ tissue is being studied using ex vivo breast organoid assays to determine whether RANKL inhibition can attenuate breast epithelial proliferation.

Conclusions: Our data raise the possibility that RANK signaling is implicated in the initiation of tumorigenesis in BRCA1 mutation carriers (and possibly other high risk women) and that RANKL is a promising chemoprevention target. The findings are of sufficient interest to have led to a clinical trial, BRCA-D (Registered as ACTRN12614000694617). A finalized abstract will be submitted in early September, during the Late-Breaking Abstract submission period.

References:

1. Lim et al Nature Med 2009: 15, 907-13.

2. Poole et al Science 2006: 314, 1467-70.

3. Asselin-Labat et al Nature 2010: 465, 798-802.

4. Joshi et al Nature 2010: 465, 803-7.

5. Tanos et al Sci Transl Med 2013: 5, 182ra55.

6. Schramek et al Nature 2010: 468, 98-102.

7. Gonzales-Suarez et al Nature 2010: 468, 103-7.

Citation Format: Lindeman GJ, Nolan E, Pal B, Vaillant F, Giner G, Whitehead L, Mann GB, Lok SW, Shackleton K, Kathleen Cuningham Foundation Consortium (kConFab), Smyth GK, Visvader JE. RANK ligand is a target for breast cancer prevention in BRCA1 mutation carriers. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-11-05.

Akathisia: prevalence and risk factors in a community-dwelling sample of patients with schizophrenia. Results from the FACE-SZ dataset

The main objective of this study was to determine the prevalence of akathisia in a community-dwelling sample of patients with schizophrenia, and to determine the effects of treatments and the clinical variables associated with akathisia. 372 patients with schizophrenia or schizoaffective disorder were systematically included in the network of FondaMental Expert Center for Schizophrenia and assessed with validated scales. Akathisia was measured with the Barnes Akathisia Scale (BAS). Ongoing psychotropic treatment was recorded. The global prevalence of akathisia (as defined by a score of 2 or more on the global akathisia subscale of the BAS) in our sample was 18.5%. Patients who received antipsychotic polytherapy were at higher risk of akathisia and this result remained significant (adjusted odd ratio=2.04, p=.025) after controlling the influence of age, gender, level of education, level of psychotic symptoms, substance use comorbidities, current administration of antidepressant, anticholinergic drugs, benzodiazepines, and daily-administered antipsychotic dose. The combination of second-generation antipsychotics was associated with a 3-fold risk of akathisia compared to second-generation antipsychotics used in monotherapy. Our results indicate that antipsychotic polytherapy should be at best avoided and suggest that monotherapy should be recommended in cases of akathisia. Long-term administration of benzodiazepines or anticholinergic drugs does not seem to be advisable in cases of akathisia, given the potential side effects of these medications.

Metabolic syndrome, abdominal obesity and hyperuricemia in schizophrenia: Results from the FACE-SZ cohort

OBJECTIVE

Abdominal obesity was suggested to be a better predictor than Metabolic Syndrome (MetS) for cardiovascular mortality, however this is has not been extensively studied in schizophrenia. Hyperuricemia (HU) was also suggested to be both an independent risk factor for greater somatic comorbidity and a global metabolic stress marker in patients with schizophrenia. The aim of this study was to estimate the prevalence of MetS, abdominal obesity and HU, to examine the association between metabolic parameters with HU in a cohort of French patients with schizophrenia or schizo-affective disorder (SZ), and to estimate the prevalence rates of treatment of cardio-vascular risk factors.

METHOD

240 SZ patients (age=31.4years, male gender 74.3%) were systematically included. Metabolic syndrome was defined according to the International Diabetes Federation and HU if serum uric acid level was above 360μmol/L.

RESULTS

MetS, abdominal obesity and HU were found respectively in 24.2%, 21.3% and 19.6% of patients. In terms of risk factors, multiple logistic regression showed that after taking into account the potential confounders, the risk for HU was higher in males (OR=5.9, IC95 [1.7-21.4]) and in subjects with high waist circumference (OR=3.1, IC95 [1.1-8.3]) or hypertriglyceridemia (OR=4.9, IC95 [1.9-13]). No association with hypertension, low HDL cholesterol or high fasting glucose was observed. Only 10% of patients with hypertension received a specific treatment, 18% for high fasting glucose and 8% for dyslipidemia.

CONCLUSIONS

The prevalence of MetS, abdominal obesity and hyperuricemia is elevated in French patients with schizophrenia, all of which are considerably under-diagnosed and undertreated. HU is strongly associated with abdominal obesity but not with psychiatric symptomatology.

Orthostatic hypotension and associated conditions in geriatric inpatients

Screening of orthostatic hypotension (OH) was performed in 285 patients aged 75  years. Current drugs, reasons for admission, geriatric syndromes, and confounding medical conditions were collected. Patients with OH (n = 116, 41%) as compared to those without OH (n = 169) more frequently (P < 0.01) presented falls in the last 6  months (62 vs. 40%, P < 0.001), a fall as the reason for the current admission (49 vs. 26%, P < 0.001), feeling of fainting (20 vs. 6%, P = 0.002), syncope (29 vs. 4%, P < 0.001) or functional decline (71 vs. 47%, P = 0.012). No difference was observed between the two groups in terms of age (85  ±  5 vs. 84  ±  4  years), gender (59 vs. 50% female), common geriatric conditions (e.g. malnutrition 46 vs. 58%, dementia 22 vs. 26%), comorbidity or confounding conditions (dehydration 28 vs. 30%, sepsis 2 vs. 6%). No difference was detected in the use of drugs with psychotropic cardiovascular or diuretic effect, or in their associations. Orthostatic hypotension is frequent upon hospital admission and should be screened, particularly in geriatric fallers. This absence of relation between OH and drugs use suggests that non-pharmacological interventions should be first attempted in older inpatients with OH before deciding to reduce or withdraw useful drugs.

Abstract P5-03-02: Expression of RANK and RANK ligand (RANKL) in breast carcinoma and distinct breast epithelial cells from BRCA1 mutation carriers

Background: Breast tumors in BRCA1 mutation carriers likely arise from luminal progenitor (LP) cells, previously shown to exhibit aberrant growth properties. Oophorectomy, and possibly tamoxifen, reduce breast cancer risk in BRCA1 carriers, potentially via inhibition of paracrine mediated signaling to stem/progenitor cells. RANKL is a major paracrine effector of progesterone's mitogenic action in mammary epithelium via its receptor RANK, and has a role in ovarian hormone-dependent activation of stem cells. Here we assessed RANK and RANKL expression in breast tumors and normal breast epithelial subtypes from women with mutations of BRCA1 (mBRCA1) or BRCA2 (mBRCA2).

Methods: RANK and RANKL expression in breast cancer or normal breast tissue samples with mBRCA1, mBRCA2 or wildtype (WT) BRCA1/2 were analyzed in formalin fixed paraffin embedded (FFPE) sections by IHC. kConFab and The Royal Melbourne Hospital Tissue Bank provided the samples used in this analysis; these samples were obtained with relevant IRB approval. RANK expression on normal breast epithelial cells was measured by flow cytometry. Antibodies against human RANK (N-1H8, N-2B10; Amgen) and RANKL (M366; Amgen) were used in both assays. Incidence of IHC staining was scored as a positive IHC signal of any intensity. The overall expression was generated using the H scoring method which is calculated as the staining intensity of the tumor (0-3) multiplied by the percentage of positively staining cells.

Results: Breast tumors from women with mBRCA1 had a higher incidence of RANK expression (68/162; 42%) compared with mBRCA2 (17/113; 15%) or WT (34/314; 11%) and higher overall H score (21.3) compared with mBRCA2 (8.0) or WT (3.4); RANKL expression did not vary greatly between groups: mBRCA1 (13/135; 10%), mBRCA2 (5/114; 4%), WT (23/212; 11%). In normal breast tissue, LP (Lin−EpCAM+CD49f+) and basal/stem cells (Lin−EpCAM−CD49fhi) expressed RANK on their surface. Similar expression patterns were seen in these epithelial subtypes from each BRCA1/2 genotype. Stromal cells (Lin−EpCAM−CD49f−) had minimal RANK expression.

Conclusions: RANK expression intensity and incidence scores are both enriched approximately 4-fold in breast tumors from BRCA1 carriers compared with other genotypes. Also, RANK is normally expressed in breast LP cells as well as the basal/stem cell containing population. Ongoing studies will assess functional regulation of LP or mammary stem cell activity by RANKL and determine if the RANKL/RANK signaling pathway affects the aberrant growth characteristics of these cells from BRCA1 mutation carriers.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-03-02.

Abstract P2-09-01: Targeting BCL-2 with the BH3 mimetic ABT-199 in ER-positive breast cancer

Background: Impairment of apoptosis is a hallmark of cancer and can result in resistance to therapy. Over-expression of the pro-survival protein BCL-2 is common in breast cancer, with elevated levels found in approximately 85% of luminal tumors. Although BCL-2 has been shown to be an important prognostic marker, its role as a therapeutic target has yet to be fully explored. Small molecule inhibitors termed ‘BH3 mimetics’ that mimic the action of pro-apoptotic BH3-only proteins have recently been developed. These bind and neutralize BCL-2 pro-survival proteins. We have previously shown that the BH3 mimetic ABT-737 (which neutralizes BCL-2, BCL-XL and BCL-W) synergizes with docetaxel in BCL-2-positive patient-derived xenograft (PDX) models. Recently, a potent BCL-2-specific inhibitor, ABT-199, has been developed that is showing considerable promise in early phase studies of lymphoid malignancies. Since BCL-2 expression is prominent in the luminal B tumors, we sought to determine whether it might be feasible to target luminal B tumors with combination therapy comprising endocrine therapy (tamoxifen) and a BH3 mimetic (ABT-737 or ABT-199), using novel PDX models of luminal B breast cancer.

Methods and Results: A panel of 36 primary breast tumor xenografts (including 15 luminal tumors) was generated in immunocompromised (NOG) mice. Three BCL-2-positive luminal B models (23T, 315T, 50T), as determined by Ki-67 immunostaining and gene expression profiling, and a control BCL-2-positive, ER-negative model (838T) were selected for further study. Cohorts of mice bearing tumor xenografts were treated with either ABT-737 (50 mg/kg i.p. d1-10), tamoxifen or both agents in q21d cycles. Tumor response and overall survival were significantly improved by combination therapy in all three ER-positive xenograft models, when compared to tamoxifen alone (p&lt;0.005). Despite abundant BCL-XL expression in tumors, similar efficacy was observed with the selective BCL-2 inhibitor ABT-199 (50 mg/kg o.g. d1-5 and 8-12 q21d) and tamoxifen (p&lt;0.005), revealing that BCL-2 is a crucial target. Unexpectedly, both BH3 mimetics were found to counteract the side effect of tamoxifen-induced endometrial hyperplasia. In addition, we observed that BH3 mimetics synergized with dual PI3K/mTOR inhibitors in the induction of apoptosis. In the 315T model, where AKT was found to be activated, triple therapy with ABT-737, a PI3K/mTOR inhibitor (PKI-587) and tamoxifen further augmented tumor response in vivo, when compared to ABT-737 and tamoxifen (p&lt;0.004).

Discussion: Patient derived xenograft models of luminal B breast cancer have been derived that recapitulate the phenotype of the primary tumor. Here we have demonstrated that concomitant targeting of BCL-2 confers marked benefit above tamoxifen alone. Moreover, synergy between BH3 mimetics and PI3K/mTOR inhibitors could be exploited by targeting of both survival pathways, a strategy that appeared both safe and effective. Collectively, our findings provide a rationale for clinical evaluation of BH3 mimetics in early phase studies in breast cancer. Here, BCL-2 protein or mRNA expression (as determined by immunohistochemistry or RT-PCR, respectively) could provide a suitable companion biomarker for patient selection.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-09-01.

Abstract A035: Role of the transcription factor Id4 in the developing mammary gland

Transcription factors are essential for controlling cell fate decisions and differentiation during embryonic and adult development. Although transcription factors have been implicated in regulating development of the mammary gland, most of these have not been defined at a cellular level. Recent studies in the laboratory have identified the transcriptional regulator Inhibitor of Differentiation 4 (Id4) as a highly expressed gene in the mammary stem cell (MaSC)-enriched population of both mouse and human mammary glands. This population also contains progenitors and mature myoepithelial cells. Germ-line deletion of Id4 in mice has previously revealed a role for this gene in neuronal differentiation1, and more recently, as a regulator of mammary gland development through its suppression of p38MAPK2. Id4 has been identified as differentially regulated in breast cancers and plays a role in the negative regulation of BRCA13,4. We have developed a conditional knockout mouse model to investigate the function of Id4 specifically in the mammary epithelium. Id4 is expressed in myoepithelial cells of the terminal end buds and ducts, with expression reducing after puberty. Consistent with previous findings2, Id4-deficient mammary glands displayed a prominent reduction in ductal elongation and branching. We found that Id4-deficient mammary epithelial cells also have a diminished capacity to maintain the balance of luminal to myoepithelial cells, and that the MaSC/basal subset had significantly reduced repopulating capacity when assayed by transplantation. Understanding the mechanism and role of Id4 in the developing mammary gland may reveal important parallels with the role of Id4 in breast cancer.

1. Yun et al. Development, 2004. 131(21):5441-8

2. Dong et al. Development, 2011. 138(23):5247-56

3. Beger et al. PNAS, 2001. 98(1):130-5

4. Roldan et al. Cancer Biology and Therapy, 2006. 5(5):505-10

Citation Format: Sarah A. Best, NaiYang Fu, Francois Vaillant, Geoff J. Lindeman, Jane E. Visvader. Role of the transcription factor Id4 in the developing mammary gland. [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 A035.

Trimetazidine demonstrated cardioprotective effects through mitochondrial pathway in a model of acute coronary ischemia

Myocardial ischemia affects mitochondrial function leading to ionic imbalance and susceptibility to ventricular fibrillation. Trimetazidine (TMZ), a metabolic agent, is clinically used as an anti-anginal therapy. This study was conducted to compare the effect of TMZ 20 mg immediate release (IR) and TMZ 35 mg modified release (MR), two bioequivalent marketed formulations of TMZ, on cardioprotection during acute ischemia in pigs. A 4-day oral treatment with TMZ 20 mg IR (800 mg, tid) or TMZ 35 mg MR (1,400 mg, bid) had no effect on ventricular fibrillation threshold (VFT) prior to ischemia but significantly prevented the decrease in VFT observed in placebo-treated groups after a 1-min left anterior descending coronary artery occlusion. This effect occurred without modifying cardiac hemodynamic and conduction parameters. In both TMZ-treated groups, a significant reduction of the ischemic area as well as a protection of cardiomyocytes were observed. Cardiac enzymatic activity (phosphorylase, succinate dehydrogenase, ATPase) was increased in TMZ-treated groups. Both formulations preserved mitochondrial structure and improved mitochondrial function as demonstrated by a twofold increase of oxidative phosphorylation, by a reduction of reactive oxygen species (ROS) production (>30 %) and by a trend to increase the mitochondrial calcium retention capacity. In this model of ischemia, both TMZ formulations, leading to equivalent TMZ plasma exposures, demonstrated similar cardioprotective effects. This protection could be attributed to a preservation of mitochondrial structure and function, which plays a central role in ATP and ROS production and consequently could be considered as a target of cardioprotection.

PD08-02: Targeting BCL-2 Expressing Breast Tumors with BH3-Mimetics – A New Class of Drugs in Breast Cancer?

Background: Impairment of apoptosis is a hallmark of cancer and can result in resistance to chemotherapy. Tumor resistance to apoptosis is frequently acquired through deregulated expression of BCL-2 family members or inactivation of the p53 tumor suppressor pathway. Over-expression of the pro-survival protein BCL-2 is common in breast cancer (where it is readily detected by immunostaining), and has been shown to be an important prognostic marker. A potential role for BCL-2 as a therapeutic target in breast cancer, however, has not been explored. Recently, small molecules termed ‘BH3-mimetics’ have been developed that mimic the action of pro-apoptotic BH3-only proteins. These bind and neutralize pro-survival proteins including BCL-2. Here we have derived a panel of primary breast tumor xenografts (that include basal-like breast tumors) to study the efficacy of the BH3-mimetic ABT-737 combined with docetaxel in targeting BCL-2-positive breast cancer.

Methods and Results: We first studied the expression of BCL-2, pro-survival family members BCL-XL and MCL-1, and the pro-apoptotic protein BIM in tissue microarrays of 197 primary breast tumors, which were subtyped on the basis of ER, PR, HER2, CK5/6 and EGFR expression. BCL-2 was overexpressed in luminal (83.3%), HER2−positive (50.0%), basal-like (18.5%) and ‘marker-null’ (41.4%) breast cancers. BCL-2-positive tumors generally co-expressed BCL-XL (96.2%), MCL-1 (94.7%) and BIM (93.5%). To determine whether the BH3-mimetic ABT-737 (which neutralizes BCL-2, BCL-XL and BCL-W) was effective in targeting BCL-2-expressing breast tumors, we generated a panel of 28 primary breast tumor xenografts in immunocompromised NOG mice. Five xenograft lines (838T, 24T, 315T, 13T and 806T) were selected for further analysis. Four were basal-like, and one (315T) was a luminal B tumor, as determined by gene profiling. Mice bearing tumor xenografts were treated with ABT-737 (50 mg/kg i.p. d1-10), docetaxel (10 mg/kg i.p. d1) or a combination in q21d cycles. Tumor response and overall survival were significantly improved by combination therapy, but only for tumors that expressed elevated levels of BCL-2. Treatment with ABT-737 alone was ineffective, suggesting that ABT-737 sensitized tumors to docetaxel. Combination therapy was accompanied by a marked increase in apoptosis and dissociation of BIM from BCL-2, indicating that a perturbation of BIM complexes may contribute to the activation of the apoptotic cascade. Notably, ABT-737 appeared effective in targeting BCL-2-expressing basal-like tumor xenografts (838T and 24T) harboring p53 mutations.

Discussion: Primary breast tumor xenograft models that recapitulate the phenotype of the primary tumor have been developed as useful ‘proof-of-principle', pre-clinical models. Here we provide the first in vivo evidence that BH3-mimetics can be used to sensitize primary BCL-2-expressing breast tumors to taxane chemotherapy. Our results suggest that elevated BCL-2 expression constitutes a predictive response marker in breast cancer. These findings provide a rationale for the development of clinical protocols using the oral analogue ABT-263 (navitoclax) as an adjunct to taxane chemotherapy in BCL-2-expressing basal-like and luminal breast cancer.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD08-02.

Abstract S5-6: Steroid Hormone Regulation of Mammary Stem Cell Function

Background: The ovarian hormones estrogen and progesterone profoundly influence breast cancer risk, underpinning the benefit of endocrine therapies in the treatment of breast cancer. Modulation of their effects through ovarian ablation or chemoprevention strategies also significantly decreases breast cancer incidence. Conversely, there is an increased risk of breast cancer associated with pregnancy in the short-term. The cellular mechanisms underlying these observations, however, are poorly defined. We and others recently isolated mammary epithelial populations enriched for mammary stem cells (MaSCs), committed luminal progenitor and mature luminal cells from both mouse and human mammary glands. Unexpectedly, MaSCs exhibited a receptor-negative phenotype for ERα , PR and ErbB2. Given the central important of estrogen and progesterone signaling to mammary gland development and cancer, we sought to determine whether these hormones could indirectly modulate MaSC function. Methods and Results: We utilized mouse models to directly study the effects of steroid hormones on the in vivo repopulating ability of MaSCs. Ovariectomy markedly diminished MaSC number and the extent of ductal outgrowth in vivo. The relative contribution of estrogen and progesterone to the regulation of MaSC activity was next examined using hormone pellets or antagonists. MaSC activity increased in animals treated with both estrogen and progesterone. Remarkably, even three weeks of treatment with the aromatase inhibitor letrozole was sufficient to reduce the MaSC pool. The outgrowth potential of these cells was again affected, suggesting that MaSCs retain a ‘memory’ of estrogen deprivation, perhaps through perturbation of their cycling status. Indeed, cell cycle analysis revealed an increase in the percentage of MaSC-enriched cells in G0/G1 in ovariectomized glands compared to controls. This was accompanied by a profound reduction in the expression of cell cycle genes including Cyclin D1.

We further evaluated the effect of the hormonal environment on MaSC function during pregnancy, where progesterone (and prolactin) have prominent roles. Pregnancy led to a transient 11-fold increase in MaSC numbers. This was accompanied by marked elevation in the expression of the progesterone target gene RANK ligand in luminal cells, together with its receptor RANK in the MaSC-containing population. To determine whether MaSC activity is in part mediated through paracrine signals from RANK ligand, inhibitors of RANK signaling were evaluated. Treatment of virgin or pregnant mice with an anti-RANK ligand monoclonal antibody in vivo significantly impaired the clonogenic activity of the MaSC-enriched but not luminal subpopulation.

Discussion: Despite lacking the steroid hormone receptors ERα and PR, MaSCs appear to be exquisitely sensitive to hormone signaling, presumably via paracrine signaling that includes the RANK signaling pathway. The augmented MaSC pool during pregnancy suggests a cellular basis for the short-term increase in breast cancer incidence following pregnancy. Our findings further indicate that breast cancer chemoprevention may in part be achieved through suppression of MaSC function. We speculate that inhibitors of RANK and other stem cell signaling pathways could represent potential chemoprevention agents.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S5-6.

Abstract P4-04-03: Transcriptome Analyses of Mouse and Human Mammary Cell Subpopulations Reveals Multiple Conserved Genes and Pathways

INTRODUCTION: Molecular characterization of the normal epithelial cell types that reside in the mammary gland is an important step toward understanding pathways that regulate self-renewal, lineage commitment, and differentiation along the hierarchy. We previously reported distinct stages in human mammary epithelial cell development and linked them to breast tumor subtypes previously defined by gene expression profiling. Here we determined the gene expression signatures of four distinct subpopulations isolated from the mouse mammary gland. The epithelial cell signatures were used to interrogate mouse models of mammary tumorigenesis and to compare with their normal human counterpart subsets to identify conserved genes and networks.

METHODS: RNA was prepared from freshly sorted mouse mammary cell subpopulations (mammary stem cell (MaSC)-enriched, committed luminal progenitor, mature luminal and stromal cell) and used for gene expression profiling analysis on the Illumina platform. Gene signatures were derived and compared with those previously reported for the analogous normal human mammary cell subpopulations. The mouse and human epithelial subset signatures were then subjected to Ingenuity Pathway Analysis (IPA) to identify conserved pathways.

RESULTS: The four mouse mammary cell subpopulations exhibited distinct gene signatures. Comparison of these signatures with the molecular profiles of different mouse models of mammary tumorigenesis revealed that tumors arising in MMTV-Wnt-1 and p53-/- mice were enriched for MaSC-subset genes, whereas the gene profiles of MMTV-Neu and MMTV-PyMT tumors were most concordant with the luminal progenitor cell signature. Comparison of the mouse mammary epithelial cell signatures with their human counterparts revealed substantial conservation of genes, whereas IPA highlighted a number of conserved pathways in the three epithelial subsets.

CONCLUSIONS: The conservation of genes and pathways across species further validates the use of the mouse as a model to study mammary gland development and highlights pathways that are likely to govern cell-fate decisions and differentiation. It is noteworthy that many of the conserved genes in the MaSC population have been considered as epithelialmesenchymal transition (EMT) signature genes. Therefore, the expression of these genes in tumor cells may reflect basal epithelial cell characteristics and not necessarily cells that have undergone an EMT. Comparative analyses of normal mouse epithelial subsets with murine tumor models have implicated distinct cell types in contributing to tumorigenesis in the different models.

Figures available in online version.

Protective role of selenium supplementation against cardiac lesions induced by the combination of levomepromazine and risperidone in the rabbit

Neuroleptics are a suspected cause of sudden death in psychiatric patients, especially in those with pre-existing cardiac lesions. As these lesions were previously shown to be associated with selenium (Se) deficiency, the aim of the present study was to evidence the possible protective effect of Se supplementation against cardiac lesions induced by the combination of the neuroleptic drugs levomepromazine and risperidone in the rabbit. Two groups of 6 rabbits were treated with 3 mg/kg of levomepromazine daily intramuscularly combined with 1 mg/kg of risperidone intramuscularly every other week for 3 consecutive months, and one group additionally received a solution of sodium selenite (2 μg/kg/day) intramuscularly during the whole treatment period. Furthermore, one group of six untreated animals was given the Se supplementation and another group of six control animals received saline daily. Blood samples were drawn before and at the end of the treatment period for the measurement of serum Se levels. At the end of the study, all animals were sacrificed and their hearts were removed for the measurement of tissue Se concentrations. In addition, the hearts were prepared for histopathological examination. A variety of cardiac lesions was found in the neuroleptics-treated animals without supplementation and to a lesser extent in the control and Se-supplemented untreated animals. Importantly, only rare cardiac lesions were observed in neuroleptics-Se-treated animals. The most striking differences in Se concentrations were noted in the myocardium: as compared to controls, there was a 43% reduction in neuroleptics-treated, but non-Se-supplemented animals (p < .01), at the end of the treatment period, whereas only a 14% reduction (p < .05) was noted in the neuroleptics-Se-treated animals. These results confirm that neuroleptics induce cardiac lesions associated with Se deficiency. Selenium supplementation markedly decreased the incidence and severity of neuroleptics-induced cardiac lesions and these findings may serve as a basis for further evaluation of the protective role of Se supplementation in neuroleptics-treated patients. However, Se supplementation in normal animals without Se deficiency was also shown to be cardiotoxic.

Investigation of human mammary stem and progenitor subpopulations from BRCA1 mutation carriers and noncarriers

504

Background: We have previously isolated discrete populations of mouse mammary epithelial cells (MECs) and defined a population that expresses ‘basal’ markers and is highly enriched for mammary stem cells. This subset was ‘triple negative’ for ER, PR and ErbB2 expression and is reminiscent of the basal subtype of breast cancer, suggesting that the mammary stem cell may be the ‘cell of origin’ for this poor prognosis group. Since tumors arising in BRCA1 mutation carriers often exhibit a ‘basal’ phenotype, we hypothesized that the mammary stem cell pool is aberrant in these women. Our objective was to define the human MEC hierarchy and evaluate the functional characteristics of MECs from BRCA1± and normal breast tissue. Methods: Single cell suspensions prepared from fresh human BRCA1± and normal breast tissue were sorted by flow cytometry. Hematopoietic (CD45+, CD235a+) and endothelial (CD31+) cells were removed, and the remaining viable ‘lineage minus’ (Lin-) MECs fractionated based on cell surface markers. These subpopulations were evaluated by immunostaining, RNA profiling, in vitro culture in Matrigel and in vivo xenotransplantation into ‘humanised’ mammary fat pads of immunocompromised mice. Results: Lin- cells fractionated with α6-integrin (CD49f) and epithelial cell adhesion molecule (EpCAM) revealed three discrete MEC subpopulations. A stem/progenitor population that preferentially yields breast outgrowths in vivo has been identified. These subpopulations gave rise in vitro to colonies that were either large and heterogenous or small and homogenous. Only the latter differentiated into milk-producing cells when exposed to lactogenic stimuli. Immunostaining confirmed their origins from myoepithelial and luminal progenitor cells respectively. Intriguingly, BRCA1± MECs exhibited perturbed in vitro growth properties when compared to normal controls. Conclusions: Our studies provide evidence for a human MEC hierarchy, a model to interrogate the perturbation noted in pre-neoplastic tissue derived from BRCA1 mutation carriers and the identification of the cell of transformation in BRCA1 associated breast cancer. These findings may have implications on developing prevention strategies for hereditary breast cancer.

No significant financial relationships to disclose.

Delineating the epithelial hierarchy in the mouse mammary gland

Reconstitution assays have shown that mouse mammary stem cells reside within the mature mammary gland in vivo. Single cells could be prospectively isolated and shown to regenerate an entire mammary gland that exhibited full developmental capacity. The more recent identification of luminal progenitor populations has indicated that the mammary epithelium is organized in a hierarchical manner. Further definition of epithelial cell types in both mouse and human mammary glands will provide insight into the "cells of origin" in the different subtypes of breast cancer, as well as the nature of cancer-propagating cells. Here, we review the known characteristics of mammary stem and progenitor cells, their steroid receptor status, and the pathways that have thus far been implicated in regulating their self-renewal and differentiation.

Role of selenium in heart lesions produced by neuroleptics in the rabbit

Organic and/or functional heart lesions sometimes resulting in sudden death have been described in psychiatric patients treated with neuroleptics. As selenium has been suggested previously to play a role in the development of such lesions, the present study was undertaken to determine whether a correlation could be found between heart lesions induced by neuroleptics and changes in blood selenium as well as myocardial tissue concentrations in the rabbit. Twelve NZW adult rabbits were treated intramuscularly with both levomepromazine (3 mg kg(-1) day(-1)) and risperidone (1 mg kg(-1) once every other week) for 3 months, and compared with 12 saline-treated controls. Blood samples were drawn before and at the end of the study. Tissue samples from the heart, liver and kidneys were obtained at the end of treatment, and the hearts were examined histologically. Heart lesions including disorganization of cardiac fibers, myolysis, interstitial and endocardial fibrosis, and necrosis were noted in treated animals, but not in controls. There was a 20% decrease in selenium blood levels and a 50% decrease in selenium myocardial tissue levels in treated animals compared with controls (P < 0.001). In contrast, no differences in selenium levels in liver and kidneys were found across the experimental groups. These results suggest a possible correlation between selenium depletion and neuroleptics-induced heart lesions.

The Runx genes as dominant oncogenes

We have shown previously that Runx2 is a frequent target (approximately equal to 30%) for proviral insertion in murine leukemia virus (MLV) induced T cell tumors in CD2-MYC transgenic mice. Further investigation of a large panel of these tumors revealed that a small number also contain insertions at either Runx3 or Runx1. None of the tumors contained insertions at more than one family member, but in each case proviral insertion was associated with a high level of expression from the upstream (P1) promoter of the respective target gene. Moreover, we confirmed that transcriptional activation of Runx1 does not affect the integrity of the coding sequence, as previously observed for Runx2. These observations suggest that the three Runx genes act as functionally redundant oncogenes in T-cell lymphoma development. To explore the oncogenic potential of Runx2 further we created transgenic mice that over-express this gene in the T cell compartment. These CD2-Runx2 animals show a preneoplastic enlargement of the CD8 immature single positive (ISP) thymocyte pool and develop lymphomas at a low incidence. Although the CD8 ISP population is greatly increased, unlike their wild type counterparts these cells are largely non-cycling. Co-expression of c-MYC in this lineage accentuates the CD8 ISP skew and induces rapid tumor development, confirming the potent synergy that exists between these two oncogenes. Experiments designed to understand the nature of the observed synergy are ongoing and are based on the hypothesis that Runx2 may exert a survival effect in c-MYC expressing tumors in vivo while c-MYC may rescue cells from the antiproliferative effects of Runx2. The oncogenic potential of Runx1 is also being assessed using primary murine embryonic fibroblasts (MEFs). These studies have revealed that while Runx1 exerts a growth suppressive effect in wild type cells a growth promoting effect is seen in the absence of p53, suggesting that the Runx genes may harbor latent oncogene-like properties.

Proviral insertion indicates a dominant oncogenic role for Runx1/AML-1 in T-cell lymphoma

The RUNX1/AML1 gene is a frequent target for chromosomal translocations in human leukemia. The biological properties of the resulting fusion products and the finding that haploinsufficiency increases the risk of developing leukemia (W-J. Song et al., Nat. Genet., 23: 166-175, 1999; M. Osata et al., Blood, 93: 1817-1824, 1999) have led to the widely held view that RUNX1 loss-of-function is a key event. However, we now report that the gene is a target for insertional mutagenesis in T-cell lymphomas of mice carrying a MYC oncogene, where promoter insertion results in overexpression without affecting the integrity of the coding sequence. Moreover, Runx1 haploinsufficiency does not accelerate lymphoma development in MYC/Runx2 transgenic or murine leukemia virus-infected mice. These findings reveal that the Runx1 gene can also act as a dominant oncogene and suggest that the involvement of the Runx gene family in human leukemia may be more widespread and complex than previously realized.

Mitochondrial cytochrome c release is caspase-dependent and does not involve mitochondrial permeability transition in didemnin B-induced apoptosis

Permeability transition, and a subsequent drop in mitochondrial membrane potential (DeltaPsi(m)), have been suggested to be mechanisms by which cytochrome c is released from the mitochondria into the cytosol during apoptosis. Furthermore, a drop in DeltaPsi(m) has been suggested to be an obligate early step in the apoptotic pathway. Didemnin B, a branched cyclic peptolide described to have immunosuppressive, anti-tumour, and anti-viral properties, induces rapid apoptosis in a range of mammalian cell lines. Induction of apoptosis by didemnin B in cultured human pro-myeloid HL-60 cells is the fastest and most complete ever described with all cells being apoptotic after 3 h of treatment. By utilizing the system of didemnin B-induced apoptosis in HL-60 cells, and the potent inhibitors of mitochondrial permeability transition, cyclosporin A and bongkrekic acid, we show that permeability transition as determined by changes in DeltaPsi(m) and mitochondrial Ca2+ fluxing, is not a requirement for apoptosis or cytochrome c release. In this system, changes in mitochondrial membrane potential and cytochrome c release are shown to be dependent on caspase activation, and to occur concurrently with the release of caspase-9 from mitochondria, genomic DNA fragmentation and apoptotic body formation.