TRPS1 regulates oestrogen receptor binding and histone acetylation at enhancers

The chromatin state is finely tuned to regulate function and specificity for transcription factors such as oestrogen receptor alpha (ER), which contributes to cell growth in breast cancer. ER transcriptional potential is mediated, in large part, by the specific associated proteins and co-factors that interact with it. Despite the identification and characterisation of several ER coregulators, a complete and systematic view of ER-regulating chromatin modifiers is lacking. By exploiting a focused siRNA screen that investigated the requirement for a library of 330 chromatin regulators in ER-mediated cell growth, we find that the NuRD and coREST histone deacetylation complexes are critical for breast cancer cell proliferation. Further, by proteomic and genomics approaches, we discover the transcription factor TRPS1 to be a key interactor of the NuRD and coREST complexes. Interestingly, TRPS1 gene amplification occurs in 28% of human breast tumours and is associated with poor prognosis. We propose that TRPS1 is required to repress spurious binding of ER, where it contributes to the removal of histone acetylation. Our data suggest that TRPS1 is an important ER-associated transcriptional repressor that regulates cell proliferation, chromatin acetylation and ER binding at the chromatin of cis-regulatory elements.

A Phase II Study of Pembrolizumab in EGFR-Mutant, PD-L1+, Tyrosine Kinase Inhibitor Naïve Patients With Advanced NSCLC

BACKGROUND

Despite the significant antitumor activity of pembrolizumab in NSCLC, clinical benefit has been less frequently observed in patients whose tumors harbor EGFR mutations compared to EGFR wild-type patients. Our single-center experience on the KEYNOTE-001 trial suggested that pembrolizumab-treated EGFR-mutant patients, who were tyrosine kinase inhibitor (TKI) naïve, had superior clinical outcomes to those previously treated with a TKI. As TKI naïve EGFR-mutants have generally been excluded from pembrolizumab studies, data to guide treatment decisions in this patient population is lacking, particularly in patients with programmed death ligand 1 (PD-L1) expression ≥50%.

METHODS

We conducted a phase II trial (NCT02879994) of pembrolizumab in TKI naive patients with EGFR mutation-positive, advanced NSCLC and PD-L1-positive (≥1%, 22C3 antibody) tumors. Pembrolizumab was administered 200 mg every 3 weeks. The primary endpoint was objective response rate. Secondary endpoints included safety of pembrolizumab, additional pembrolizumab efficacy endpoints, and efficacy and safety of an EGFR TKI after pembrolizumab.

RESULTS

Enrollment was ceased due to lack of efficacy after 11 of 25 planned patients were treated. Eighty-two percent of trial patients were treatment naïve, 64% had sensitizing EGFR mutations, and 73% had PD-L1 expression ≥50%. Only 1 patient had an objective response (9%), but repeat analysis of this patient's tumor definitively showed the original report of an EGFR mutation to be erroneous. Observed treatment-related adverse events were similar to prior experience with pembrolizumab, but two deaths within 6 months of enrollment, including one attributed to pneumonitis, were of concern.

CONCLUSIONS

Pembrolizumab's lack of efficacy in TKI naïve, PD-L1+, EGFR-mutant patients with advanced NSCLC, including those with PD-L1 expression ≥50%, suggests that it is not an appropriate therapeutic choice in this setting.

Abstract PD4-04: Combined inhibition of mTOR and CDK4/6 is required for optimal blockade of E2F function and long term growth inhibition in estrogen receptor positive breast cancer

The cyclin dependent kinase (CDK) –retinoblastoma (RB) -E2F pathway plays a critical role in the control of cell cycle in estrogen receptor positive (ER+) breast cancer. Small molecule inhibitors of CDK4/6 have shown promise in this tumour type in combination with hormonal therapies, reflecting the particular dependence of this subtype of cancer on cyclin D1 and E2F transcription factors. mTOR inhibitors have also shown potential in clinical trials in this disease setting. Recent data has suggested cooperation between the phosphatidylinositol 3-kinase (PI3K) pathway and CDK4/6 inhibition in preventing early adaptation and eliciting growth arrest, but the mechanisms of the interplay between these pathways have not been fully elucidated. Here we show that profound and durable inhibition of ER+ breast cancer growth is likely to require multiple hits on E2F mediated transcription. We demonstrate that inhibition of mTOR using the mTORC1/2 inhibitor vistusertib at 300nM causes a >50% decrease in cyclin D1 protein levels and RB phosphorylation in three cell lines. At these concentrations, vistusertib treatment also elicits marked effects on E2F mediated transcription, causing changes in the mRNA levels of 28 out of 43 (65%) of a selected set of E2F target genes.Combined inhibition of mTOR, CDK4/6 and ER delivers profound and durable regressions in breast cancer cell lines and xenografts (110.2% tumour growth inhibition at day 48). In vivo data show, that over a period of 58 days, tumours failed to re-grow in the presence of the triplet combination compared to either agent alone, suggesting, that the triplet is necessary to maintain growth inhibition. Furthermore, we show that CDK4/6 inhibitor resistant cell lines re-activate the CDK-RB-E2F pathway, but remain sensitive to mTOR inhibition (EC50 52.7 nM in parental cells vs 39.6-73.3 nM in a number of palbociclib resistant cell populations), suggesting that mTORC1/2 inhibitors may represent an option for patients that have relapsed on CDK4/6 therapy. A Phase I study (PASTOR) combining the dual TOR kinase inhibitor Vistusertib with Palbociclib, and Fulvestrant is underway to explore safety and efficacy of the triplet combination in patients with metastatic breast cancer.

Citation Format: Oelmann E, Michaloglou C, Crafter C, Siersbaek R, Delpuech O, Curven J, Carnevalli L, Staniszweska A, Polanska U, Cheraghchi-Bashi A, Lawson M, Chernukhin I, McEwen R, Carroll J, Cosulich S. Combined inhibition of mTOR and CDK4/6 is required for optimal blockade of E2F function and long term growth inhibition in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD4-04.

Intracerebral Xenotransplantation of GFP Mouse Bone Marrow Stromal Cells in Intact and Stroke Rat Brain: Graft Survival and Immunologic Response

The present study characterized survival and immunologic response of bone marrow stromal cells (BMSCs) following transplantation into intact and stroke brains. In the first study, intrastriatal transplantation of BMSC (60,000 in 3 μl) or vehicle was performed in normal adult Sprague-Dawley male rats that subsequently received daily cyclosporin A (CsA, 10 mg/kg, IP in 3 ml) or vehicle (olive oil, similar volume) starting on day of surgery up to 3 days posttransplantation. Animals were euthanized at 3 or 30 days posttransplantation and brains were processed either for green fluorescent protein (GFP) microscopy or flow cytometry (FACS). Both GFP epifluorescence and FACS scanning revealed GFP+ BMSCs in both groups of transplanted rats with or without CsA, although significantly increased (1.6- to 3-fold more) survival of GFP+ BMSCs was observed in the immunosuppressed animals. Further histologic examination revealed widespread dispersal of BMSCs away from the graft core accompanied by many long outgrowth processes in non-CsA-transplanted animals, whereas a very dense graft core, with cells expressing only sporadic short outgrowth processes, was observed in CsA-transplanted animals. There were no detectable GFP+ BMSCs in nontrans-planted rats that received CsA or vehicle. Immunologic response via FACS analysis revealed a decreased presence of cytotoxic cells, characterized by near complete absence of CD8+ cells, and lack of activation depicted by low CD69 expression in CsA-treated transplanted animals. In contrast, elevated levels of CD8+ cells and increased activation of CD69 expression were observed in transplanted animals that received vehicle alone. CD4+ helper cells were almost nondetectable in transplanted rats that received CsA, but also only minimally elevated in transplanted rats that received vehicle. Nontransplanted rats that received either CsA or vehicle displayed very minimal detectable levels of all three lymphocyte markers. In the second study, a new set of male Sprague-Dawley rats initially received bilateral stereotaxic intrastriatal transplantation of BMSCs and 3 days after were subjected to unilateral transient occlusion of middle cerebral artery. The animals were allowed to survive for 3 days after stroke without CsA immunosuppression. Epifluorescence microscopy revealed significantly higher (5-fold more) survival of transplanted GFP+ BMSCs in the stroke striatum compared with the intact striatum. The majority of the grafts remained within the original dorsal striatal transplant site, characterized by no obvious migration in intact striatum, but with long-distance migration along the ischemic penumbra in the stroke striatum. Moreover, FACS scanning analyses revealed low levels of immunologic response of grafted BMSCs in both stroke and intact striata. These results, taken together, suggest that xenotransplantation of mouse BMSCs into adult rats is feasible. Immunosuppression therapy can enhance xenograft survival and reduce graft-induced immunologic response; however, in the acute phase posttransplantation, BMSCs can survive in intact and stroke brain, and may even exhibit long-distance migration and increased outgrowth processes without immunosuppression.

The role of family physicians in cancer care: perspectives of primary and specialty care providers

BACKGROUND

Currently, the specific role of family physicians (fps) in the care of people with cancer is not well defined. Our goal was to explore physician perspectives and contextual factors related to the coordination of cancer care and the role of fps.

METHODS

Using a constructivist grounded theory approach, we conducted telephone interviews with 58 primary and cancer specialist health care providers from across Canada.

RESULTS

The participants-21 fps, 15 surgeons, 12 medical oncologists, 6 radiation oncologists, and 4 general practitioners in oncology-were asked to describe both the role that fps currently play and the role that, in their opinion, fps should play in the future care of cancer patients across the cancer continuum. Participants identified 3 key roles: coordinating cancer care, managing comorbidities, and providing psychosocial care to patients and their families. However, fps and specialists discussed many challenges that prevent fps from fully performing those roles: ■ The fps described communication problems resulting from not being kept "in the loop" because they weren't copied on patient reports and also the lack of clearly defined roles for all the various health care providers involved in providing care to cancer patients.■ The specialists expressed concerns about a lack of patient access to fp care, leaving specialists to fill the care gaps. The fps and specialists both recommended additional training and education for fps in survivorship care, cancer screening, genetic testing, and new cancer treatments.

CONCLUSIONS

Better communication, more collaboration, and further education are needed to enhance the role of fps in the care of cancer patients.

Cell cycle-coupled expansion of AR activity promotes cancer progression

The androgen receptor (AR) is required for prostate cancer (PCa) survival and progression, and ablation of AR activity is the first line of therapeutic intervention for disseminated disease. While initially effective, recurrent tumors ultimately arise for which there is no durable cure. Despite the dependence of PCa on AR activity throughout the course of disease, delineation of the AR-dependent transcriptional network that governs disease progression remains elusive, and the function of AR in mitotically active cells is not well understood. Analyzing AR activity as a function of cell cycle revealed an unexpected and highly expanded repertoire of AR-regulated gene networks in actively cycling cells. New AR functions segregated into two major clusters: those that are specific to cycling cells and retained throughout the mitotic cell cycle ('Cell Cycle Common'), versus those that were specifically enriched in a subset of cell cycle phases ('Phase Restricted'). Further analyses identified previously unrecognized AR functions in major pathways associated with clinical PCa progression. Illustrating the impact of these unmasked AR-driven pathways, dihydroceramide desaturase 1 was identified as an AR-regulated gene in mitotically active cells that promoted pro-metastatic phenotypes, and in advanced PCa proved to be highly associated with development of metastases, recurrence after therapeutic intervention and reduced overall survival. Taken together, these findings delineate AR function in mitotically active tumor cells, thus providing critical insight into the molecular basis by which AR promotes development of lethal PCa and nominate new avenues for therapeutic intervention.

Abstract P3-07-20: Biological functions of ERβ in triple negative breast cancer and its utility as a novel therapeutic drug target

Background: Triple negative breast cancer (TNBC) accounts for approximately 20% of all breast cancer diagnoses. It is the most aggressive form of breast cancer and clinical management is problematic due to lack of available targeted therapies. We have shown that approximately 30% of all TNBCs express estrogen receptor beta (ERβ), a ligand binding transcription factor, and a potential drug target for patients with this form of the disease.

Methods: Using novel ERβ-expressing TN cell lines developed in our laboratory, we assessed the impacts of ERβ on proliferation, invasion, migration, and alterations in cell cycle progression following estrogen and ERβ-specific agonist treatment. We also characterized the ERβ transcriptome and cistrome in these models through microarray and ChIP-Seq, respectively. Finally, we determined the tumoral response of cell line xenografts and PDXs treated with 17β-estradiol.

Results: We found that both estrogen and multiple ERβ-specific agonists elicit significant anti-tumor effects in ERβ+ TNBC cell lines and tumor xenografts. Activation of ERβ with estrogen and ERβ-specific agonists resulted in inhibition of cell proliferation primarily through a G1/S phase cell cycle arrest. Substantial reductions in cell migration and invasion were also observed following treatment. Microarray studies revealed that ERβ differentially regulated the expression of approximately 1000 genes following estrogen treatment. Of these genes, the most striking effects were observed in a family of small secreted cysteine protease inhibitors known as cystatins, which were highly induced following ERβ activation. ChIP-Seq and ChIP-PCR identified ERβ binding sites in the promoter region of each cystatin and demonstrated ERβ-mediated alterations in chromatin marks and recruitment of PolII around these promoters. We found that cystatins directly interact with TGFβ receptor 2 (TGFβR2) and block downstream TGFβ ligand-mediated activation of the canonical signaling pathway. Depletion of cystatins from conditioned media or through siRNA-mediated silencing reduced the ability of ERβ to elicit these anti-tumor effects. In vivo, estrogen treatment of mice harboring ERβ+ TNBC cell line xenografts or PDXs resulted in increased tumoral expression and serum levels of cystatins, and suppressed tumor growth.

Conclusions: Our data demonstrated that estrogen and ERβ-specific agonists elicit anti-cancer effects in ERβ+ TNBC, both in vitro and in vivo. These effects are partially mediated by cystatins which can interact with, and inhibit, canonical TGFβ signaling, a pathway known to drive TNBC progression. Given the lack of targeted therapies for TNBC patients, the present data suggests that estrogen or ERβ-specific agonists offer a novel approach to manage this subset of patients.

Citation Format: Reese JM, Bruinsma ES, Suman VJ, Nelson AW, Chernukhin I, Carroll JS, Ingle JN, Goetz MP, Hawse JR. Biological functions of ERβ in triple negative breast cancer and its utility as a novel therapeutic drug target [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 P3-07-20.

Mechanisms of oestrogen receptor (ER) gene regulation in breast cancer

Most breast cancers are driven by a transcription factor called oestrogen receptor (ER). Understanding the mechanisms of ER activity in breast cancer has been a major research interest and recent genomic advances have revealed extraordinary insights into how ER mediates gene transcription and what occurs during endocrine resistance. This review discusses our current understanding on ER activity, with an emphasis on several evolving, but important areas of ER biology.

Family History-Taking in Paediatrics: It’s Much More Than Just A Checklist

BACKGROUND: Family history (FH) is a risk factor for many conditions in pediatric practice; interest has increased in supporting systematic FH taking in this area by identifying core conditions for enquiry and developing point of care tools. There is little published about current practice to inform implementing such changes.

OBJECTIVES: To inform future FH taking interventions by identifying pediatricians' perceptions, attitudes, beliefs, and current practices.

DESIGN/METHODS: The Theoretical Domains Framework (TDF) was used to develop a comprehensive interview scheme. Semi-structured interviews were conducted with community and hospital-based pediatricians Analysis was by the constant comparison method, using a thematic approach. This study was funded by the Canadian Institutes of Health Research.

RESULTS: The data revealed FH taking to be a firmly embedded, but complex aspect of pediatric practice. Participants described FH as part of regular, holistic care, extending to social and interpersonal, as well as clinical purposes; in addition to disease risk assessment, FH information helped clarify diagnosis, and select medication; tailor the overall patient management based on family circumstances; and provide psychosocial support for parents. It was also used as a method to build a relationship with parents/carers. FH and social history information were inextricably linked and often appeared to be the same concept in participants’ minds. Participating pediatricians generally expressed confidence in their FH skills and reported tailoring their approach according to experience, after initial training early in their career. While acknowledging some challenges in ensuring accuracy, they were attuned to nuances in their interactions with parents and children which would affect whether, and what, they were told about illness in the family. Most were not concerned about formal evidence, and would not change their practice except for “good reason”.

CONCLUSION: The use of the TDF helped ensure a comprehensive approach to FH taking in pediatric practice. The findings suggest that FH taking in this setting is a complex activity, embedded in routine care. Recommendations for systematic enquiry about specific conditions cannot be seen as a simple additional activity to current practice. Efforts to make FH taking more systematic may founder if they fail to take into account pediatricians’ attitudes, perspectives, and practices. Further studies should explore and seek to confirm and expand our observations.