The mevalonate precursor enzyme HMGCS1 is a novel marker and key mediator of cancer stem cell enrichment in luminal and basal models of breast cancer

The definitive characterization of common cancer stem cell (CSCs) subpopulations in breast cancer subtypes with distinct genotypic and phenotypic features remains an ongoing challenge. In this study, we have used a non-biased genome wide screening approach to identify transcriptional networks that may be specific to the CSC subpopulations in both luminal and basal breast cancer subtypes. In depth studies of three CSC-enriched breast cancer cell lines representing various subtypes of breast cancer revealed a striking hyperactivation of the mevalonate metabolic pathway in comparison to control cells. The upregulation of metabolic networks is a key feature of tumour cells securing growth and proliferative capabilities and dysregulated mevalonate metabolism has been associated with tumour malignancy and cellular transformation in breast cancer. Furthermore, accumulating evidence suggests that Simvastatin therapy, a mevalonate pathway inhibitor, could affect breast cancer progression and reduce breast cancer recurrence. When detailing the mevalonate pathway in breast cancer using a single-cell qPCR, we identified the mevalonate precursor enzyme, HMGCS1, as a specific marker of CSC-enriched subpopulations within both luminal and basal tumour subtypes. Down-regulation of HMGCS1 also decreased the CSC fraction and function in various model systems, suggesting that HMGCS1 is essential for CSC-activities in breast cancer in general. These data was supported by strong associations between HMGCS1 expression and aggressive features, such as high tumour grade, p53 mutations as well as ER-negativity in lymph node positive breast cancer. Importantly, loss of HMGCS1 also had a much more pronounced effect on CSC-activities compared to treatment with standard doses of Simvastatin. Taken together, this study highlights HMGCS1 as a potential gatekeeper for dysregulated mevalonate metabolism important for CSC-features in both luminal and basal breast cancer subtypes. Pharmacological inhibition of HMGCS1 could therefore be a superior novel treatment approach for breast cancer patients via additional CSC blocking functions.

Characterization of cell-free breast cancer patient-derived scaffolds using liquid chromatography-mass spectrometry/mass spectrometry data and RNA sequencing data

Patient-derived scaffolds (PDSs) generated from primary breast cancer tumors can be used to model the tumor microenvironment in vitro. Patient-derived scaffolds are generated by repeated detergent washing, removing all cells. Here, we analyzed the protein composition of 15 decellularized PDSs using liquid chromatography-mass spectrometry/mass spectrometry. One hundred forty-three proteins were detected and their relative abundance was calculated using a reference sample generated from all PDSs. We performed heatmap analysis of all the detected proteins to display their expression patterns across different PDSs together with pathway enrichment analysis to reveal which processes that were connected to PDS protein composition. This protein dataset together with clinical information is useful to investigators studying the microenvironment of breast cancers. Further, after repopulating PDSs with either MCF7 or MDA-MB-231 cells, we quantified their gene expression profiles using RNA sequencing. These data were also compared to cells cultured in conventional 2D conditions, as well as to cells cultured as xenografts in immune-deficient mice. We investigated the overlap of genes regulated between these different culture conditions and performed pathway enrichment analysis of genes regulated by both PDS and xenograft cultures compared to 2D in both cell lines to describe common processes associated with both culture conditions. Apart from our described analyses of these systems, these data are useful when comparing different experimental model systems. Downstream data analyses and interpretations can be found in the research article “Patient-derived scaffolds uncover breast cancer promoting properties of the microenvironment” [1].

Patient-derived scaffolds uncover breast cancer promoting properties of the microenvironment

Tumor cells interact with the microenvironment that specifically supports and promotes tumor development. Key components in the tumor environment have been linked to various aggressive cancer features and can further influence the presence of subpopulations of cancer cells with specific functions, including cancer stem cells and migratory cells. To model and further understand the influence of specific microenvironments we have developed an experimental platform using cell-free patient-derived scaffolds (PDSs) from primary breast cancers infiltrated with standardized breast cancer cell lines. This PDS culture system induced a series of orchestrated changes in differentiation, epithelial-mesenchymal transition, stemness and proliferation of the cancer cell population, where an increased cancer stem cell pool was confirmed using functional assays. Furthermore, global gene expression profiling showed that PDS cultures were similar to xenograft cultures. Mass spectrometry analyses of cell-free PDSs identified subgroups based on their protein composition that were linked to clinical properties, including tumor grade. Finally, we observed that an induction of epithelial-mesenchymal transition-related genes in cancer cells growing on the PDSs were significantly associated with clinical disease recurrences in breast cancer patients. Patient-derived scaffolds thus mimics in vivo-like growth conditions and uncovers unique information about the malignancy-inducing properties of tumor microenvironment.

Abstract P2-06-11: Sortilin targeted therapy in breast cancer with elevated progranulin expression

Background: A major challenge concerning breast cancer therapy is the occasional lack of effects using drugs that target cancer cells unspecifically. One possible explanation for this treatment failure is the existence of the small subpopulation of breast cancer stem cells that are believed to be more resistant towards conventional therapy and possesses the ability to drive tumor formation and disease progression. Cytokines secreted by nearby cells and other factors in the surrounding tumor microenvironment further stimulate the cancer cells, contributing to a heterogeneous and potentially more treatment resistant tumor. Thus, a more specific treatment approach targeting the breast cancer stem cell niche is crucial in preventing disease recurrences. In a cytokine screen, we identified progranulin as one of the main compounds secreted from cells exposed to hypoxia, leading to cancer stem cell propagation. Progranulin is involved in biological processes such as wound healing, inflammation and cancer progression. Progranulin and its receptor sortilin are known to be highly expressed in subgroups of breast cancer and are further associated with a clinically aggressive phenotype.

Methods/Results: By carrying out a number of in vitro and in vivo like screening assays, we demonstrate that progranulin influences the stem cell population in breast cancer and is responsible for spreading a cancer stem cell promoting signal to normoxic tumor areas. In breast cancer, progranulin induces a dedifferentiation process in the receiving cancer cells and expression of cancer stem cell markers together with an EMT-associated gene expression profile, leading to cancer stem cell expansion. By using siRNA and pharmacological inhibition of sortilin, we show that sortilin is a functional receptor of progranulin and is responsible for driving progranulin induced breast cancer stem cell propagation. Supporting the role of progranulin in cancer progression, administration of progranulin in immunocompromised mice induce lung metastasis in our breast cancer xenograft models. The use of different approaches for blocking sortilin, such as sortilin inhibitors, down-modulators or sortilin-targeted antibodies can prevent this dedifferentiation process, both in vitro and in vivo, making the tumor cells less aggressive and metastatic.

Conclusion: Targeting progranulin through its associated receptors is a potential therapeutic strategy for the treatment of patients with breast tumors having elevated progranulin or sortilin expression. By inhibiting the secretion based breast cancer progression, we could possibly block the formation of metastasis and cancer cell infiltration.

Citation Format: Berger K, Rhost S, Hughes E, Harrison H, Rafnsdottir S, Jacobsson H, Gregersson P, Magnusson Y, Fitzpatrick P, Andersson D, Ståhlberg A, Landberg G. Sortilin targeted therapy in breast cancer with elevated progranulin expression [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 P2-06-11.

Sortilin inhibition limits secretion-induced progranulin-dependent breast cancer progression and cancer stem cell expansion

Background

Cancer progression is influenced by genetic aberrations in the cancer cell population as well as by other factors including the microenvironment present within a tumour. Direct interactions between various cell types as well as cellular signalling via secreted cytokines can drive key tumourigenic properties associated with disease progression and treatment resistance. Also, cancer stem cell functions are influenced by the microenvironment. This challenging subset of cells has been linked to malignant properties. Within a screen, using in vivo like growth conditions, we identified progranulin as a highly secreted cytokine affecting cancer stem cells in breast cancer. This cytokine is known to play a role in numerous biological and tumour-related processes including therapy resistance in a range of cancer types.

Methods

Different in vitro and in vivo relevant conditions were used to validate breast cancer stem cell expansion mediated by progranulin and its receptor sortilin. Small interfering ribonucleic acid (siRNA) and pharmacological inhibition of sortilin were used to elucidate the role of sortilin as a functional receptor during progranulin-induced breast cancer stem cell propagation, both in vitro and in vivo, using breast cancer xenograft models. In addition, single-cell gene expression profiling as well as a Sox2 reporter breast cancer cell line were used to validate the role of dedifferentiation mediated by progranulin.

Results

In various in vivo-like screening assays, progranulin was identified as a potent cancer stem cell activator, highly secreted in ERα-negative breast cancer as well as in ERα-positive breast cancer under hypoxic adaptation. Progranulin exposure caused dedifferentiation as well as increased proliferation of the cancer stem cell pool, a process that was shown to be dependent on its receptor sortilin. Subcutaneous injections of progranulin or its active domain (GRN A) induced lung metastases in breast cancer xenograft models, supporting a major role for progranulin in cancer progression. Importantly, an orally bioavailable small molecule (AF38469) targeting sortilin, blocked GRN A-induced lung metastases and prevented cancer cell infiltration of the skin.

Conclusion

The collective results suggest that sortilin targeting represents a potential novel breast cancer therapy approach inhibiting tumour progression driven by secretion and microenvironmental influences.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1060-5) contains supplementary material, which is available to authorized users.

Benefits and risks with acellular dermal matrix (ADM) and mesh support in immediate breast reconstruction: a systematic review and meta-analysis

In modern implant-based immediate breast reconstruction, it has become common to use biological acellular dermal and synthetic matrices in combination with a tissue expander or an implant. The aim of this systematic review was to examine differences in recurrence of cancer, impact on oncological treatment, health related quality of life, complications and aesthetic outcome between matrix and no matrix in immediate breast reconstruction. Systematic searches, data extraction and assessment of methodological quality were performed according to predetermined criteria. Fifty-one studies were eligible and included in the review. The certainty of evidence for overall complication rate and implant loss is low (GRADE ⊕⊕□ □). The certainty of evidence for delay of adjuvant treatment, implant loss, infection, capsular contraction and aesthetic outcome is very low (GRADE ⊕□ □ □). No study reported data on recurrence of cancer or health related quality of life. In conclusion, there is a lack of high quality studies that compare the use of matrix with no matrix in immediate breast reconstruction. Specifically, there are no data on risk of recurrence of cancer, delay of adjuvant treatment and Health related quality of life (HRQoL). In addition, there is a risk of bias in many studies. It is often unclear what complications have been included and how they have been diagnosed, and how and when capsular contracture and aesthetic outcome have been evaluated. Controlled trials that further analyse the impact of radiotherapy, type of matrix and type of procedure (one or two stages) are necessary.