Abstract BL1: Deciphering stem and progenitor cells to understand breast cancer

Breast cancer is a highly heterogeneous disease at the molecular and pathological levels. To understand heterogeneity and potential ‘cells of origin’ of breast cancer, it is important to dissect the normal mammary epithelial differentiation hierarchy as well as the cellular composition of breast tumors. Discrete populations of mouse and human mammary epithelial cells have been isolated on the basis of cell surface marker expression, yielding three primary populations including a stem cell-enriched population and two luminal populations. Their responsiveness to female steroid hormones was investigated, revealing the importance of paracrine regulation of ER/PR– stem/progenitor cells by ER/PR+ luminal ‘hormone sensor’ cells. RANKL was found to be a key paracrine effector of progesterone signaling, underscoring the central role that female hormones play in normal mammary gland homeostasis and cancer. Consistent with this observation, a RANK+ luminal progenitor cell was found to be the likely target cell that gives rise to breast cancer in BRCA1 mutation carriers. Pre-clinical studies further indicate that it may be possible to target this ‘culprit’ cell with the RANKL inhibitor denosumab. This finding is now being tested in a randomized phase III prevention study, ‘BRCA-P’.

In further studies, a quiescent stem cell that remains hormone responsive has been identified. Lineage tracing, combined with high resolution 3D imaging (visualizing large regions of intact tissue), was carried out to track stem and progenitor cells in situ. These studies have revealed the presence of long-lived stem cells that replenish mammary epithelium, while unipotent progenitors appear to play an essential role in sustaining the independent lineages on a day-to-day basis. In order to generate a comprehensive single cell expression resource and explore molecular heterogeneity in the mouse mammary gland, single cell profiling at key developmental stages was performed. This has revealed novel intermediates and unexpected changes in the transcriptional landscape that could inform a role for distinct cell types during mammary oncogenesis.

To gain insight into cancer heterogeneity and clonal dynamics at cellular resolution, 3D imaging was combined with lineage tracing to track specific cells during cancer development. Through the application of a novel pipeline, the epithelial-to-mesenchymal transition (EMT) was found to be a frequent event, thus highlighting the inherent plasticity of mammary tumors. These findings are currently being extended to human tumors to further understand inter- and intra-tumoral heterogeneity.

In parallel, our group has established a bank of patient-derived xenograft (PDX) and patient derived organoid (PDO) models to facilitate the transfer of laboratory findings to the clinic. These serve as useful pre-clinical models to test promising agents. Initial efforts have focused on BH3 mimetics, a new class of drug that targets the BCL-2 family of pro-survival proteins. This work is leading to early phase clinical trials, currently focused on patients with metastatic ER+ breast cancer.

Citation Format: JE Visvader, GJ Lindeman. Deciphering stem and progenitor cells to understand breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr BL1.

Abstract PD7-07: Synergistic targeting of CDK4/6 and BCL-2 pathways in estrogen receptor positive breast cancer

Background: Despite incremental advances in chemotherapy and endocrine therapy, survival outcomes for patients with ER-positive (ER+) metastatic breast cancer (MBC) remain poor. The majority of relapsing tumors exhibit deregulation of the cyclin-dependent kinase 4 and 6 (CDK4/6)/cyclin D1 (CCND1)/Rb signaling pathway. CDK4/6 inhibitors (such as palbociclib) in combination with endocrine therapy have been shown to significantly improve progression free survival in patients who are in 1st or 2nd line relapse, although overall survival benefit has yet to be demonstrated. This may reflect their largely cytostatic mechanism of action, with minimal induction of tumor cell death. Thus, combinatorial strategies that also induce apoptosis could be beneficial. Notably, the pro-survival protein BCL-2 is overexpressed in the majority of ER+ tumors and the potent and specific BCL-2 inhibitor venetoclax (ABT-199) has been found to synergize with endocrine therapy in patient derived xenograft (PDX) models. Promising activity has also been observed in an early phase clinical trial. We therefore investigated dual targeting of the CDK4/6 and BCL-2 pathways in pre-clinical models of ER+ and BCL-2+ breast cancer.

Results: We first examined endocrine sensitive or resistant cell-lines and found that pro-survival BCL-2 proteins were upregulated in resistant cells. BCL-2 family protein levels were also found to be elevated in palbociclib resistant cells, suggesting that BCL-2 could represent a therapeutic target. We next determined whether venetoclax improved response to dual therapy comprising the selective estrogen receptor degrader fulvestrant and palbociclib. In clonogenic assays of endocrine sensitive breast cancer cell lines, triple therapy containing venetoclax significantly reduced the number and size of colonies, when compared to double therapy. The addition of venetoclax to fulvestrant/palbociclib also augmented cell death in tumor organoid models derived from either ER+ BCL-2+ primary tumors or PDX models. Moreover, triple therapy improved tumor response and overall survival in mice bearing ER+ BCL-2+ PDX tumors. Mechanistically, this was accompanied by increased apoptosis and reduced cellular proliferation (as determined by cleaved caspase-3 and Ki67 levels, respectively). As CDK4/6 inhibitors have recently been shown to promote anti-tumor immunity, we evaluated immune modulation using the ER+ 67NR cell line in a syngeneic (BALB/c) mouse mammary tumor model. Similar to the PDX models, triple therapy comprising fulvestrant, palbociclib and venetoclax was more effective than double therapy comprising either fulvestrant/palbociclib or fulvestrant/venetoclax. Flow cytometric analysis of tumors revealed that this was accompanied by a reduced intratumoral FOXP3+:cytotoxic CD8 T-cell ratio.

Conclusions: The addition of the BCL-2 inhibitor venetoclax to conventional therapy comprising endocrine therapy and a CDK4/6 inhibitor augments tumor response and elicits a favorable intratumoral immune profile. Collectively, these findings support investigation of combination therapy in the clinic for patients with ER+ BCL-2+ MBC.

Citation Format: Whittle JR, Vaillant F, Policheni AN, Liu K, Pal B, Giner G, Fernandez K, Gray DH, Caldon CE, Smyth GK, Visvader JE, Lindeman GJ. Synergistic targeting of CDK4/6 and BCL-2 pathways in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD7-07.

Abstract PD1-06: A phase 1b dose-escalation and expansion study of the BCL-2 inhibitor venetoclax combined with tamoxifen in ER and BCL-2–positive metastatic breast cancer (MBC)

Background: Venetoclax, a potent and selective inhibitor of the survival protein BCL-2 (recently approved in CLL and in development in other hematopoietic malignancies), has yet to be evaluated in pts with solid tumors. BCL-2 is overexpressed in ˜85% of ER+ breast cancer. Pre-clinical findings using patient-derived xenograft breast tumor models suggest that venetoclax synergizes with endocrine therapy by increasing apoptosis. Here we report mBEP, an investigator-initiated phase 1b study of venetoclax with tamoxifen in 33 pts with ER+ (>1%), BCL-2+ (>10%, 2-3+ intensity) and HER2– MBC.

Methods: We conducted a 3+3 dose escalation study comprising cohorts receiving venetoclax 200, 400, 600 or 800 mg/d with tamoxifen 20 mg/d (continued until progression). The primary endpoint was to determine the maximum tolerated dose (MTD), define dose-limiting toxicities (DLTs) and identify the recommended phase 2 dose (RP2D). In a dose expansion phase (at the RP2D), secondary endpoints including safety and tolerability, response at 24 wks (RECIST v1.1), clinical benefit rate (CBR) and progression-free survival (PFS) were studied.

Results: In the escalation phase (n=15 pts), treatment was well tolerated with no DLTs or high-grade (Gd 3/4) adverse events observed, apart from asymptomatic on-target lymphopenia (Gd 3, 2/15 pts). MTD was not reached. The 800 mg/d dose was selected as the RP2D and the cohort expanded to include 24 pts with ≥24 wks follow up (range 24-105 wks). Fifteen pts had received prior regimens for MBC (median 3, range 1-9) that included tamoxifen in 5/15.

For the RP2D cohort (n=24), overall responses (OR) included 1 CR (4%) and 12 PR (50%), with 5 SD (21%), corresponding to a CBR of 75%. The 9 pts treated in the first line setting experienced a 78% OR (7/9 pts) and 11% SD (1/9 pts), equating to an 89% CBR. The data are immature for determining median PFS for the RP2D cohort (currently 40+ wks).

Treatment responses were pre-empted by metabolic responses (FDG-PET) at 4 wks (seen in 13/16 (81%) pts studied), and correlated with serial changes in circulating tumor DNA (ctDNA). Intriguingly, responses and clinical benefit were observed in pts with plasma-detected ESR1 mutations (4/10 and 7/10, respectively).

The most common treatment-related AEs (CTCAE v4.0) for all pts were lymphopenia in 29/33 (88%; 57% Gd 1-2, 30% Gd 3-4), neutropenia in 24/33 (73%; 67% Gd 1-2, 6% Gd 3), nausea in 22/33 (67%; all ≤Gd 2), anemia in 13/33 (39%; 33% Gd 1-2, 6% G3), thrombocytopenia in 11/33 (33%; all ≤Gd 2), vomiting in 11/33 (33%, all ≤Gd 2), diarrhea in 10/33 (30%; 24% Gd 1-2, 6% Gd 3), infection in 9/33 (27%; 18% Gd 2, 9% Gd 3) and fatigue in 7/33 (21%; all ≤Gd 2). There was one possible treatment-related SAE (infection).

Conclusions: In the first clinical study to evaluate venetoclax in a solid tumor, we demonstrate that combining venetoclax with endocrine therapy has a tolerable safety profile and elicits remarkable activity in ER+ and BCL-2+ MBC. These findings support further investigation of combination therapy for patients with BCL-2-positive breast cancer.

Sponsor: The Royal Melbourne Hospital (ACTRN12615000702516)

Citation Format: Lindeman GJ, Lok SW, Whittle JR, Siow ZR, Bergin AR, Dawson S-J, Desai J, Gray DH, Liew D, Mann GB, Murugasu A, Roberts AW, Rosenthal MA, Shackleton K, Sherman P, Silva MJ, Teh C, Travers A, Vaillant F, Visvader JE. A phase 1b dose-escalation and expansion study of the BCL-2 inhibitor venetoclax combined with tamoxifen in ER and BCL-2–positive metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD1-06.

Abstract S2-04: RANK ligand as a target for breast cancer prevention in BRCA1 mutation carriers

Background: BRCA1 mutation carriers commonly undergo prophylactic mastectomy to reduce their risk of breast cancer. The precise role of chemoprevention with tamoxifen, which reduces the incidence of ER-positive breast cancer in the general population, is uncertain for BRCA1 mutation carriers, where uptake has been modest. The identification of an effective and acceptable prevention therapy therefore remains a 'holy grail' for the field. Precancerous BRCA1mut/+ tissue harbors an aberrant population of luminal progenitor cells and deregulated progesterone signaling has been implicated in BRCA1-associated oncogenesis. Since Receptor Activator of Nuclear Factor-kappa B ligand (RANKL) is a key paracrine effector of progesterone signaling, and RANKL and its receptor RANK contribute to mammary tumorigenesis, we investigated a role for this pathway in the preneoplastic phase of BRCA1 mutation carriers.

Methods: We explored a role for the RANK/RANKL pathway during the preneoplastic phase in freshly isolated (histologically normal) patient specimens from BRCA1 mutation carriers using several approaches. RANK and RANKL expression in breast cancer was evaluated in formalin fixed paraffin embedded (FFPE) archival sections by IHC from the kConFab and the Amgen Tissue Banks. All samples were obtained with patient consent and relevant IRB approval. A role for RANKL inhibition in attenuating tumor onset was studied using the MMTV-cre/Brca1fl/fl/p53+/– mouse model that recapitulates human basal-like breast cancer.

Results: We identified two subsets of luminal progenitors (RANK+ and RANK–) in histologically normal tissue of BRCA1 mutation carriers and found that RANK+ cells are highly proliferative, exhibit grossly aberrant DNA repair and bear a molecular signature similar to that of basal-like breast cancer. Moreover, high levels of RANK expression prevailed in established BRCA1-associated tumors. These data suggest that RANK+ and not RANK– progenitors are a key target population in these women. Notably, inhibition of RANKL signaling by denosumab in 3D breast organoids derived from pre-neoplastic BRCA1mut/+ tissue attenuated progesterone-induced proliferation. Furthermore, inhibition of RANKL with either the RANKL inhibitor OPG-Fc or a RANKL monoclonal antibody in a Brca1-deficient mouse model significantly curtailed mammary tumorigenesis, when compared to controls (p<0.001).

Conclusions: Together these findings identify a targetable pathway in a putative cell of origin population in BRCA1 mutation carriers and implicate RANKL blockade as a promising breast cancer prevention strategy.

Citation Format: Lindeman GJ, Nolan E, Vaillant F, Branstetter D, Pal B, Giner G, Whitehead L, Lok SW, Mann GB, kConFab Consortium, Rohrbach K, Huang L-Y, Soriano R, Smyth GK, Dougall WC, Visvader JE. RANK ligand as a target for breast cancer prevention in BRCA1 mutation carriers [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S2-04.

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.

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<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<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<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.

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 BSF1-2: Understanding Stem Cells To Get Abreast of Breast Cancer

Gene profiling studies have provided a basis for classifying breast cancer into at least six molecular subtypes and stimulated interest in identifying the cell type in which these distinct subtypes arise. Elucidating the normal cellular hierarchy within breast tissue is essential for identifying the ‘cell of origin’ that is targeted for neoplastic transformation. Stem cells, which lie at the apex of the normal tissue hierarchy, represent strong candidates, given that they are long-lived and capable of self-renewal. Alternatively, committed progenitor cells (stem cell descendants) or even mature progeny could also serve as cells of origin in breast cancer. Under these circumstances, cells would need to acquire certain stem cell-like properties (such as self-renewal) during tumorigenesis.

Our group (and others) have isolated discrete subpopulations of mouse and human mammary epithelial cells on the basis of cell-surface markers and defined subsets that are highly enriched for basal/mammary stem cells, committed luminal progenitor cells and mature luminal cells. Gene profiling revealed remarkable similarities between their molecular signatures and certain subtypes of breast cancer. Notably, the luminal progenitor signature (and not the basal/stem cell signature) was most similar to basal-like breast cancer. Moreover, breast tissue from breast cancer prone BRCA1 mutation carriers was found to contain increased numbers of luminal progenitors, which had aberrant growth and differentiation properties. Taken together, these findings suggest that luminal progenitors (and not basal/stem cells) are the likely target that give rise to basal-like breast cancer. Key markers (such as KIT) expressed by luminal progenitor cells could serve as therapeutic targets for breast cancer prevention or therapy. The cancer stem cell (CSC) hypothesis is in many ways distinct from the ‘cell of origin’ concept. This model proposes that established tumors are hierarchically organised (like normal tissue) and contain a subpopulation of cells with tumor propagating ability. CSCs are not necessarily derived from transformed stem cells. However, CSCs do need to acquire key stem cell properties (such as self-renewal capability). Breast CSCs have now been identified by several groups using xenograft models. Our laboratory has studied syngeneic mouse models of mammary tumorigenesis and found that a subset (but not all) appear to conform to the CSC hypothesis. The luminal progenitor marker (CD61/≥3-integrin) was found to identify a CSC population in mammary tumor-prone MMTV-wnt-1 and BALB/c-p53+/−, but not in MMTV-neu/erbB2 mice. We speculate that the CSC model may not necessarily apply to all breast tumors. Rather, the conventional ‘clonal evolution’ model (or perhaps a hybrid model) may also be relevant in some cases of breast cancer.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr BSF1-2.

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.

Targeted prostate cancer screening in men with mutations in BRCA1 and BRCA2 detects aggressive prostate cancer: preliminary analysis of the results of the IMPACT study

OBJECTIVE

To evaluate the role of targeted prostate cancer screening in men with BRCA1 or BRCA2 mutations, an international study, IMPACT (Identification of Men with a genetic predisposition to ProstAte Cancer: Targeted screening in BRCA1/2 mutation carriers and controls), was established. This is the first multicentre screening study targeted at men with a known genetic predisposition to prostate cancer. A preliminary analysis of the data is reported.

PATIENTS AND METHODS

Men aged 40-69 years from families with BRCA1 or BRCA2 mutations were offered annual prostate specific antigen (PSA) testing, and those with PSA > 3 ng/mL, were offered a prostate biopsy. Controls were men age-matched (± 5 years) who were negative for the familial mutation.

RESULTS

In total, 300 men were recruited (205 mutation carriers; 89 BRCA1, 116 BRCA2 and 95 controls) over 33 months. At the baseline screen (year 1), 7.0% (21/300) underwent a prostate biopsy. Prostate cancer was diagnosed in ten individuals, a prevalence of 3.3%. The positive predictive value of PSA screening in this cohort was 47·6% (10/21). One prostate cancer was diagnosed at year 2. Of the 11 prostate cancers diagnosed, nine were in mutation carriers, two in controls, and eight were clinically significant.

CONCLUSIONS

The present study shows that the positive predictive value of PSA screening in BRCA mutation carriers is high and that screening detects clinically significant prostate cancer. These results support the rationale for continued screening in such men.

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.

Expression of LMO4 and outcome in pancreatic ductal adenocarcinoma

Identification of a biomarker of prognosis and response to therapy that can be assessed preoperatively would significantly improve overall outcomes for patients with pancreatic cancer. In this study, patients whose tumours exhibited high LMO4 expression had a significant survival advantage following operative resection, whereas the survival of those patients whose tumours had low or no LMO4 expression was not significantly different when resection was compared with operative biopsy alone.

Risk-reducing surgery, screening and chemoprevention practices of BRCA1 and BRCA2 mutation carriers: a prospective cohort study

This study prospectively evaluated the utilization of cancer risk management strategies in a multi-institutional cohort of BRCA1 and BRCA2 mutation carriers using a self-report questionnaire. Of 142 unaffected female mutation carriers, 70 (49%) had elected to receive their mutation result. Of those who knew their mutation result, 11% underwent bilateral mastectomy (BM), 29% had bilateral oophorectomy (BO), 78% performed regular breast self-examination (BSE), and 80%, 89%, 67%, and 0% had at least annual clinical breast examination (CBE), mammography, transvaginal ultrasound (TVU), and CA125, respectively. A further 20%, 7%, 0%, 21%, and 75%, respectively, reported never having had these tests. For women who elected not to receive their mutation result, 0% underwent BM, 6% underwent BO, and 77%, 42%, 56%, 7%, and 0% had regular BSE, CBE, mammography, TVU, and CA125, respectively. Only one woman used chemoprevention outside a clinical trial. Uptake of prophylactic surgery and screening was associated with knowing one's mutation status (for all behaviors except BSE), age (for BO and CBE) and residence (for mammography). In this cohort, the minority of mutation carriers utilized risk-reducing surgery or chemoprevention and a substantial minority were not undergoing regular cancer-screening tests.

Genetic, functional, and histopathological evaluation of two C-terminal BRCA1 missense variants

BACKGROUND

The vast majority of BRCA1 missense sequence variants remain uncharacterized for their possible effect on protein expression and function, and therefore are unclassified in terms of their pathogenicity. BRCA1 plays diverse cellular roles and it is unlikely that any single functional assay will accurately reflect the total cellular implications of missense mutations in this gene.

OBJECTIVE

To elucidate the effect of two BRCA1 variants, 5236G>C (G1706A) and 5242C>A (A1708E) on BRCA1 function, and to survey the relative usefulness of several assays to direct the characterisation of other unclassified variants in BRCA genes.

METHODS AND RESULTS

Data from a range of bioinformatic, genetic, and histopathological analyses, and in vitro functional assays indicated that the 1708E variant was associated with the disruption of different cellular functions of BRCA1. In transient transfection experiments in T47D and 293T cells, the 1708E product was mislocalised to the cytoplasm and induced centrosome amplification in 293T cells. The 1708E variant also failed to transactivate transcription of reporter constructs in mammalian transcriptional transactivation assays. In contrast, the 1706A variant displayed a phenotype comparable to wildtype BRCA1 in these assays. Consistent with functional data, tumours from 1708E carriers showed typical BRCA1 pathology, while tumour material from 1706A carriers displayed few histopathological features associated with BRCA1 related tumours.

CONCLUSIONS

A comprehensive range of genetic, bioinformatic, and functional analyses have been combined for the characterisation of BRCA1 unclassified sequence variants. Consistent with the functional analyses, the combined odds of causality calculated for the 1706A variant after multifactorial likelihood analysis (1:142) indicates a definitive classification of this variant as "benign". In contrast, functional assays of the 1708E variant indicate that it is pathogenic, possibly through subcellular mislocalisation. However, the combined odds of 262:1 in favour of causality of this variant does not meet the minimal ratio of 1000:1 for classification as pathogenic, and A1708E remains formally designated as unclassified. Our findings highlight the importance of comprehensive genetic information, together with detailed functional analysis for the definitive categorisation of unclassified sequence variants. This combination of analyses may have direct application to the characterisation of other unclassified variants in BRCA1 and BRCA2.

Bfk: a novel weakly proapoptotic member of the Bcl-2 protein family with a BH3 and a BH2 region

Proteins of the Bcl-2 family are critical regulators of apoptosis. Proapoptotic members, like Bax, contain three of the four Bcl-2 homology regions (BH1-3), while BH3-only proteins, like Bim, possess only the short BH3 motif. Database searches revealed Bfk, an unusual novel member of the Bcl-2 family that contains a BH2 and BH3 region but not BH1 or BH4. Bfk is thus most closely related to Bcl-G(L). It lacks a C-terminal membrane anchor and is cytosolic. Enforced expression of Bfk weakly promoted apoptosis and antagonized Bcl-2's prosurvival function. Like Bcl-G(L), Bfk did not bind to any Bcl-2 family members, even though its BH3 motif can mediate association with prosurvival proteins. Low amounts of Bfk were found in stomach, ovary, bone marrow and spleen, but its level in the mammary gland rose markedly during pregnancy, suggesting that Bfk may play a role in mammary development.

The LIM domain gene LMO4 inhibits differentiation of mammary epithelial cells in vitro and is overexpressed in breast cancer

LMO4 belongs to a family of LIM-only transcriptional regulators, the first two members of which are oncoproteins in acute T cell leukemia. We have explored a role for LMO4, initially described as a human breast tumor autoantigen, in developing mammary epithelium and breast oncogenesis. Lmo4 was expressed predominantly in the lobuloalveoli of the mammary gland during pregnancy. Consistent with a role in proliferation, forced expression of this gene inhibited differentiation of mammary epithelial cells. Overexpression of LMO4 mRNA was observed in 5 of 10 human breast cancer cell lines. Moreover, in situ hybridization analysis of 177 primary invasive breast carcinomas revealed overexpression of LMO4 in 56% of specimens. Immunohistochemistry confirmed overexpression in a high percentage (62%) of tumors. These studies imply a role for LMO4 in maintaining proliferation of mammary epithelium and suggest that deregulation of this gene may contribute to breast tumorigenesis.

SOCS1 deficiency results in accelerated mammary gland development and rescues lactation in prolactin receptor-deficient mice

Prolactin is essential for proliferation and differentiation of the developing mammary gland. We have explored a role for Suppressor of Cytokine Signaling 1 (SOCS1) as a modulator of the prolactin response using mice deficient in SOCS1, which were rescued from neonatal death by deletion of the Interferon gamma (IFN gamma) gene. SOCS1(-/-)/IFN gamma(-/-) mice exhibited accelerated lobuloalveolar development in the mammary gland during late pregnancy and precocious lactation. Significantly, the lactogenic defect in prolactin receptor heterozygous females could be rescued by deletion of a single SOCS1 allele. These findings establish a role for SOCS1 as a negative regulator of prolactin signaling and suggest that SOCS1 is required for the prevention of lactation prior to parturition.

Design, production and characterization of FLIN2 and FLIN4: the engineering of intramolecular ldb1:LMO complexes

The nuclear LIM-only (LMO) transcription factors LMO2 and LMO4 play important roles in both normal and leukemic T-cell development. LIM domains are cysteine/histidine-rich domains that contain two structural zinc ions and that function as protein-protein adaptors; members of the LMO family each contain two closely spaced LIM domains. These LMO proteins all bind with high affinity to the nuclear protein LIM domain binding protein 1 (ldb1). The LMO-ldb1 interaction is mediated through the N-terminal LIM domain (LIM1) of LMO proteins and a 38-residue region towards the C-terminus of ldb1 [ldb1(LID)]. Unfortunately, recombinant forms of LMO2 and LMO4 have limited solubility and stability, effectively preventing structural analysis. Therefore, we have designed and constructed a fusion protein in which ldb1(LID) and LIM1 of LMO2 can form an intramolecular complex. The engineered protein, FLIN2 (fusion of the LIM interacting domain of ldb1 and the N-terminal LIM domain of LMO2) has been expressed and purified in milligram quantities. FLIN2 is monomeric, contains significant levels of secondary structure and yields a sharp and well-dispersed one-dimensional (1)H NMR spectrum. The analogous LMO4 protein, FLIN4, has almost identical properties. These data suggest that we will be able to obtain high-resolution structural information about the LMO-ldb1 interactions.

E2F4 is exported from the nucleus in a CRM1-dependent manner

E2F is a family of transcription factors required for normal cell cycle control and for cell cycle arrest in G1. E2F4 is the most abundant E2F protein in many cell types. In quiescent cells, it is localized to the nucleus, where it is bound to the retinoblastoma-related protein p130. During entry into the cell cycle, the protein disappears from the nucleus and appears in the cytoplasm. The mechanism by which this change occurs has, in the past, been unclear. We have found that E2F4 is actively exported from the nucleus and that leptomycin B, a specific inhibitor of nuclear export, inhibits this process. E2F4 export is mediated by two hydrophobic export sequences, mutations in either of which result in export failure. Individual export mutants of E2F4, but not a mutant with inactivation of both export signals, can be efficiently excluded from the nucleus by forced coexpression of the nuclear export receptor CRM1. Similarly, CRM1 overexpression can prevent cell cycle arrest induced by the cyclin kinase inhibitor p16(INK4a), an E2F4-dependent process. Taken together, these data suggest that nuclear export contributes to the regulation of E2F4 function, including its ability to regulate exit from G1 in association with a suitable pocket protein.

E2F4 and E2F5 play an essential role in pocket protein-mediated G1 control

E2F transcription factors are major regulators of cell proliferation. The diversity of the E2F family suggests that individual members perform distinct functions in cell cycle control. E2F4 and E2F5 constitute a defined subset of the family. Until now, there has been little understanding of their individual biochemical and biological functions. Here, we report that simultaneous inactivation of E2F4 and E2F5 in mice results in neonatal lethality, suggesting that they perform overlapping functions during mouse development. Embryonic fibroblasts isolated from these mice proliferated normally and reentered from Go with normal kinetics compared to wild-type cells. However, they failed to arrest in G1 in response to p16INK4a. Thus, E2F4 and E2F5 are dispensable for cell cycle progression but necessary for pocket protein-mediated G1 arrest of cycling cells.

The proapoptotic BH3-only protein bim is expressed in hematopoietic, epithelial, neuronal, and germ cells

Proapoptotic Bcl-2 family members activate cell death by neutralizing their anti-apoptotic relatives, which in turn maintain cell viability by regulating the activation of the cell death effectors, the caspases. Bim belongs to a distinct subgroup of proapoptotic proteins that only resemble other Bcl-2 family members within the short BH3 domain. Gene targeting experiments in mice have shown that Bim is essential for the execution of some but not all apoptotic stimuli, for hematopoietic cell homeostasis, and as a barrier against autoimmunity. There are three Bim isoforms, Bim(S), Bim(L), and Bim(EL), which have different proapoptotic potencies due at least in part to differences in interaction with the dynein motor complex. The expression pattern of Bim was investigated by immunohistochemical staining, immunoprecipitation followed by Western blotting, and in situ hybridization. Bim was found in hematopoietic, epithelial, neuronal, and germ cells. Bim(L) and Bim(EL) were coexpressed at similar levels in many cell types, but Bim(S) was not detected. Microscopic examination revealed a punctate pattern of Bim(L) and Bim(EL) immunostaining, indicating association with cytoplasmic structures. These results are discussed in the context of the phenotype of Bim-deficient mice and the post-translational regulation of Bim's pro-apoptotic activity.

A specific, nonproliferative role for E2F-5 in choroid plexus function revealed by gene targeting

Homozygous E2F-5 knockout embryos and mice have been generated. Although embryonic development appeared normal, newborn mice developed nonobstructive hydrocephalus, suggesting excessive cerebrospinal fluid (CSF) production. Although the CSF-producing choroid plexus displayed normal cellular organization, it contained abundant electron-lucent epithelial cells, consistent with excessive CSF secretory activity. Moreover, E2F-5 CNS expression in normal animals was largely confined to the choroid plexus. Cell cycle kinetics were not perturbed in homozygous knockout embryo fibroblasts. Thus, E2F-5 is not essential for cell proliferation. Rather, it affects the secretory behavior of a differentiated neural tissue.

The subcellular localization of E2F-4 is cell-cycle dependent

The E2F family of transcription factors plays a crucial role in cell cycle progression. E2F activity is tightly regulated by a number of mechanisms, which include the timely synthesis and degradation of E2F, interaction with retinoblastoma protein family members ("pocket proteins"), association with DP heterodimeric partner proteins, and phosphorylation of the E2F/DP complex. Here we report that another mechanism, subcellular localization, is important for the regulation of E2F activity. Unlike E2F-1, -2, or -3, which are constitutively nuclear, ectopic E2F-4 and -5 were predominantly cytoplasmic. Cotransfection of expression vectors encoding p107, p130, or DP-2, but not DP-1, resulted in the nuclear localization of E2F-4 and -5. Moreover, the transcriptional activity of E2F-4 was markedly enhanced when it was invariably nuclear. Conversely, it was reduced when the protein was excluded from the nucleus, implying that E2F-4 transcription function depends upon its cytological location. In keeping with this, the nuclear/cytoplasmic ratios of endogenous E2F-4 changed as cells exited G0, with high ratios in G0 and early G1 and a progressive increase in cytoplasmic E2F-4 as cells approached S phase. Thus, the subcellular location of E2F-4 is regulated in a cell cycle-dependent manner, providing another potential mechanism for its functional regulation.

Analysis of hematopoiesis in max 41 transgenic mice that exhibit sustained elevations of blood granulocytes and monocytes

An unusual mouse line (max 41) that carries an inserted transgene encoding the nuclear transcription factor, Max, exhibits a 50- to 60-fold elevation of blood neutrophils and a 10-fold elevation of blood monocytes. Analysis showed that these elevated levels of blood cells were sustained incrementally by a sevenfold increase in mature neutrophils in the bone marrow and spleen and a fourfold increase in granulocyte-committed progenitor cells with normal turnover times for mature neutrophils and monocytes in the marrow and blood. the progenitor cells were not autonomous and exhibited a normal quantitative responsiveness to stimulation in vitro by the four colony-stimulating factors. A consistent anomaly noted was that, when stimulated by macrophage colon-stimulating factor, max 41 progenitor cells formed mainly granulocyte-containing colonies, rather than the usual macrophage colonies. The blast colony-forming cells from max 41 mice did not generate abnormal numbers or types of progenitor cells. The transgenic max 41 model requires further analysis to establish the regulatory anomaly responsible for the excessive production of granulocytes and monocytes, but has emphasized that most neutrophils generated in the marrow normally never leave the organ.

Overexpressed max is not oncogenic and attenuates myc-induced lymphoproliferation and lymphomagenesis in transgenic mice

The cellular growth promoting function of the Myc oncoprotein requires its heterodimerization with the Max protein, but Max can also form complexes that inhibit Myc action. To determine whether max overexpression in vivo is oncogenic and whether it can modulate the action of Myc, we generated transgenic mice in which the max gene was directed to express in lymphoid cells by a linked immunoglobulin heavy chain enhancer (E mu). Expression of the transgene at substantially higher levels than the endogenous max gene did not perturb lymphoid homeostasis in adult animals nor predispose to lymphomagenesis. The numbers of B-lymphoid cells in very young animals were reduced. Moreover, analysis of bi-transgenic E mu-myc/E mu-max mice revealed that max overexpression attenuated the premalignant B-lymphoproliferative state induced by an E mu-myc transgene and reduced the rate of lymphoma onset. These results suggest that elevation of Max expression in vivo inhibits the function of Myc.

B-lymphoid to granulocytic switch during hematopoiesis in a transgenic mouse strain

B-lymphoid and myeloid development are markedly perturbed in a unique transgenic mouse strain, max 41. Pro-B, pre-B, and B lymphocytes were severely reduced but granulocytes were greatly elevated. This phenotype could be adoptively transferred with bone marrow cells. It was not alleviated by bcl-2 or myc transgenes that promote lymphocyte survival or proliferation. Bitransgenic myc/max 41 mice developed pre-B cell lymphoma. An accompanying massive granulocytosis unexpectedly proved to be clonally derived from the pre-B lymphoma cells. These observations suggest that B lymphopoiesis in max 41 mice has been diverted to granulocyte production. Since neither cell type expressed the transgene, this novel lymphomyeloid deviation probably reflects insertional alteration of a hematopoietic regulatory gene.

Cyclin D1 transgene impedes lymphocyte maturation and collaborates in lymphomagenesis with the myc gene

Cyclin D1 is the regulatory subunit of certain protein kinases thought to advance the G1 phase of the cell cycle. Deregulated cyclin D1 expression has been implicated in several human neoplasms, most consistently in centrocytic B lymphoma, where the cyclin D1 gene usually has been translocated to an immunoglobulin locus. To determine directly whether constitutive cyclin D1 expression is lymphomagenic, transgenic mice were generated having the cyclin D1 gene linked to an immunoglobulin enhancer. Despite abundant transgene expression, their lymphocytes were normal in cell cycle activity, size and mitogen responsiveness, but young transgenic animals contained fewer mature B- and T-cells. Although spontaneous tumours were infrequent, lymphomagenesis was much more rapid in mice that co-expressed the cyclin D1 transgene and a myc transgene than in mice expressing either transgene alone. Moreover, the spontaneous lymphomas of myc transgenic animals often ectopically expressed the endogenous cyclin D1 gene. These findings indicate that this G1 cyclin can modulate differentiation and collaborate with myc-like genes in oncogenesis.

Intravenous or oral adjuvant CMF for node-positive breast cancer

To assess the optimal duration and method of administration of adjuvant cyclophosphamide, methotrexate and 5-fluorouracil (CMF) chemotherapy, 116 patients with positive axillary nodes after total mastectomy and axillary dissection were reviewed retrospectively. CMF was administered in three progressively shorter regimens, which consisted of oral CMF for either 12 or six cycles and intravenous (i.v.) CMF for six cycles. Median follow-up for surviving patients was 62 months. The three groups were matched for major prognostic factors. There was no advantage in using more than six cycles of adjuvant CMF. There was an improved crude 3 year disease-free survival (84 vs 65%, P = 0.05) and a trend towards improved overall survival (92 vs 85%, P = NS) in patients treated with six cycles of oral CMF compared with i.v. CMF. Survival rates were not significantly different beyond 3 years. Leucopenia and alopecia were more severe with oral CMF (P less than 0.01), and compliance worse with oral CMF x 12 (P = 0.01). Since the data suggest that i.v. CMF is at least as equal as oral CMF a randomized controlled trial should be undertaken.

Management of testicular seminoma at Westmead Hospital from 1980 to 87

Testicular seminoma comprises fewer than 1% of male cancers but is a relatively common malignancy in young men. The management and outcome of 73 consecutive patients with testicular seminoma were reviewed. Median follow-up was 51 months (range: 15-109 months). Their median age was 37 years (range: 21-67 years). There was a history of testicular maldescent in 5.5% of patients. Beta-human chorionic gonadotropin was elevated in 22% of patients prior to orchidectomy and in 5% post-surgery. The majority of patients had stage I (78%) or stage II (19%) seminoma after clinical staging. One patient (2%) with stage I seminoma relapsed, while two patients (14%) with stage II seminoma relapsed. The latter two were salvaged with further therapy. One of two patients treated for stage III seminoma died. A residual mass after radiotherapy was commonly observed in patients with stage II seminoma, but did not represent viable tumour. These results reflect the high cure rates that are achievable in seminoma with radiotherapy for early stage and non-bulky abdominal disease and, more recently, with cisplatin-based chemotherapy for bulky abdominal or disseminated disease.

The role of bipedal lymphangiography in testicular seminoma

Determining the extent of intra-abdominal spread of testicular seminoma by radiographic studies is an essential step in planning rational treatment following orchidectomy. CT scanning is generally accepted as being superior to lymphangiography in assessing the retroperitoneal space. We reviewed the relative contribution of these two procedures in a retrospective analysis of 73 consecutive patients with testicular seminoma managed at Westmead Hospital between January 1980 and September 1987. Abdominal CT scans and bipedal lymphangiography (LAG) were carried out in 72 and 51 patients respectively, 50 patients undergoing both procedures. We found concordance between the two techniques to be 88%. Upstaging occurred in 5 patients using CT (10%), 7 patients using LAG (14%), and in 8 patients (16%) when both tests were utilised. Four patients were upstaged by both techniques while the remaining 4 patients were upstaged using one technique alone. Serum beta-HCG was not a reliable screen for residual disease. Residual disease in the few patients with an elevated serum beta-HCG was easily detected by CT scanning. We conclude that there is a continuing role for LAG in assessing patients with clinical Stage I seminoma when the abdominal CT scan is equivocal or normal.