Modelling stromal-cancer cell interactions in prostate tumours

Prostate cancer is a disease with high incidence and mortality rates. A recent research focus has been on identifying cells of origin which initiate tumourigenesis and cancer repopulating cells responsible for tumour growth and resistance to therapies, as they are an important novel therapeutic target. Our ability to identify these cells in the prostate has been hampered by a lack of human models to study disease progression. Whilst the use of primary human prostate cancer specimens is preferable over commonly used cell and xenograft lines, they display low survival and growth in in vivo assays. It is well established that the stroma plays an important role in prostate biology, however is rarely considered in the use of cancer cell focused approaches. As such this thesis aimed to create models of prostate cancer that are biologically accurate, in order to identify cells of origin and cancer repopulating cells, by providing an enriching stromal environment to primary tissues. Chapter 3 aimed to define potential cells of origin in prostate cancer. Stem cells and transient-amplifying/progenitors from the basal compartment were subjected to in vivo tumour initiation models where the stroma drives malignant transformation. The results confirmed that basal cells were able to initiate tumours, however the tumourigenic potential resided within the transient-amplifying cells, rather than the stem cells. Chapter 4 then examined prostate cancer repopulating cells. Due to observations that the stroma plays an important role in prostate biology, a bioassay was developed where primary localised prostate cancer tissues and cells were combined with inductive mouse mesenchyme to enhance survival and growth in vivo. Mouse mesenchyme did confer a survival and growth advantage of prostate cancer tissues and was essential for the survival and growth of subfractionated cancer cells, thus creating the first assay to study cancer repopulating cells in vivo using primary tissue. Chapter 5 utlised this chimeric xenografting approach to examine cancer repopulating cells in the context of systemic and paracrine androgen signalling, in attempt to identify the cancer repopulating cells which are resistant to current therapies. While androgen deprivation therapy is usually the treatment modality for advanced disease, this model demonstrated castrate-resistant cancer repopulating cells are also present in localised tumours. Furthermore, this study also showed that low stromal androgen receptor levels dampened the response to castration, demonstrating the complex relationship between cancer repopulating cells and the surrounding microenvironment. Overall, this thesis reports the development of models which can be utilised to study cells of origin and cancer repopulating cells in prostate malignancy, using human clinical specimens. This body of work demonstrates the important role that the stroma plays in prostate cancer and maintaining a supportive microenvironment in in vivo models. Future efforts can use these models to further dissect the biology of prostate cancer progression, in particular determine how cancer repopulating cells can be therapeutically targeted to provide better outcomes for patients

Modelling stromal-cancer cell interactions in prostate tumours

Prostate cancer is a disease with high incidence and mortality rates. A recent research focus has been on identifying cells of origin which initiate tumourigenesis and cancer repopulating cells responsible for tumour growth and resistance to therapies, as they are an important novel therapeutic target. Our ability to identify these cells in the prostate has been hampered by a lack of human models to study disease progression. Whilst the use of primary human prostate cancer specimens is preferable over commonly used cell and xenograft lines, they display low survival and growth in in vivo assays. It is well established that the stroma plays an important role in prostate biology, however is rarely considered in the use of cancer cell focused approaches. As such this thesis aimed to create models of prostate cancer that are biologically accurate, in order to identify cells of origin and cancer repopulating cells, by providing an enriching stromal environment to primary tissues. Chapter 3 aimed to define potential cells of origin in prostate cancer. Stem cells and transient-amplifying/progenitors from the basal compartment were subjected to in vivo tumour initiation models where the stroma drives malignant transformation. The results confirmed that basal cells were able to initiate tumours, however the tumourigenic potential resided within the transient-amplifying cells, rather than the stem cells. Chapter 4 then examined prostate cancer repopulating cells. Due to observations that the stroma plays an important role in prostate biology, a bioassay was developed where primary localised prostate cancer tissues and cells were combined with inductive mouse mesenchyme to enhance survival and growth in vivo. Mouse mesenchyme did confer a survival and growth advantage of prostate cancer tissues and was essential for the survival and growth of subfractionated cancer cells, thus creating the first assay to study cancer repopulating cells in vivo using primary tissue. Chapter 5 utlised this chimeric xenografting approach to examine cancer repopulating cells in the context of systemic and paracrine androgen signalling, in attempt to identify the cancer repopulating cells which are resistant to current therapies. While androgen deprivation therapy is usually the treatment modality for advanced disease, this model demonstrated castrate-resistant cancer repopulating cells are also present in localised tumours. Furthermore, this study also showed that low stromal androgen receptor levels dampened the response to castration, demonstrating the complex relationship between cancer repopulating cells and the surrounding microenvironment. Overall, this thesis reports the development of models which can be utilised to study cells of origin and cancer repopulating cells in prostate malignancy, using human clinical specimens. This body of work demonstrates the important role that the stroma plays in prostate cancer and maintaining a supportive microenvironment in in vivo models. Future efforts can use these models to further dissect the biology of prostate cancer progression, in particular determine how cancer repopulating cells can be therapeutically targeted to provide better outcomes for patients

Basal Progenitors Contribute to Repair of the Prostate Epithelium Following Induced Luminal Anoikis

Contact with the extracellular matrix is essential for maintenance of epithelial cells in many tissues, while in its absence epithelial cells can detach and undergo anoikis. Here, we show that anoikis of luminal cells in the prostate epithelium is followed by a program of tissue repair that is mediated in part by differentiation of basal epithelial cells to luminal cells. We describe a mouse model in which inducible deletion of E-cadherin in prostate luminal cells results in their apoptotic cell death by anoikis, in the absence of phenotypic effects in the surrounding stroma. Quantitative assessments of proliferation and cell death in the luminal and basal compartments indicate that basal cells can rapidly generate luminal cells. Thus, our findings identify a role for basal-to-luminal differentiation in prostate epithelial repair, and provide a normal context to analogous processes that may occur during prostate cancer initiation

Luminal Cells Are Favored as the Cell of Origin for Prostate Cancer

The identification of cell types of origin for cancer has important implications for tumor stratification and personalized treatment. For prostate cancer, the cell of origin has been intensively studied, but it has remained unclear whether basal or luminal epithelial cells, or both, represent cells of origin under physiological conditions in vivo. Here, we use a novel lineage-tracing strategy to assess the cell of origin in a diverse range of mouse models, including Nkx3.1+/−; Pten+/−, Pten+/−, Hi-Myc, and TRAMP mice, as well as a hormonal carcinogenesis model. Our results show that luminal cells are consistently the observed cell of origin for each model in situ; however, explanted basal cells from these mice can generate tumors in grafts. Consequently, we propose that luminal cells are favored as cells of origin in many contexts, whereas basal cells only give rise to tumors after differentiation into luminal cells

Luminal cells are favored as the cell of origin for prostate cancer.

The identification of cell types of origin for cancer has important implications for tumor stratification and personalized treatment. For prostate cancer, the cell of origin has been intensively studied, but it has remained unclear whether basal or luminal epithelial cells, or both, represent cells of origin under physiological conditions in vivo. Here, we use a novel lineage-tracing strategy to assess the cell of origin in a diverse range of mouse models, including Nkx3.1(+/-); Pten(+/-), Pten(+/-), Hi-Myc, and TRAMP mice, as well as a hormonal carcinogenesis model. Our results show that luminal cells are consistently the observed cell of origin for each model in situ; however, explanted basal cells from these mice can generate tumors in grafts. Consequently, we propose that luminal cells are favored as cells of origin in many contexts, whereas basal cells only give rise to tumors after differentiation into luminal cells

Transdifferentiation as a Mechanism of Treatment Resistance in a Mouse Model of Castration-Resistant Prostate Cancer.

Current treatments for castration-resistant prostate cancer (CRPC) that target androgen receptor (AR) signaling improve patient survival, yet ultimately fail. Here, we provide novel insights into treatment response for the antiandrogen abiraterone by analyses of a genetically engineered mouse (GEM) model with combined inactivation of Trp53 and Pten, which are frequently comutated in human CRPC. These NPp53 mice fail to respond to abiraterone and display accelerated progression to tumors resembling treatment-related CRPC with neuroendocrine differentiation (CRPC-NE) in humans. Cross-species computational analyses identify master regulators of adverse response that are conserved with human CRPC-NE, including the neural differentiation factor SOX11, which promotes neuroendocrine differentiation in cells derived from NPp53 tumors. Furthermore, abiraterone-treated NPp53 prostate tumors contain regions of focal and/or overt neuroendocrine differentiation, distinguished by their proliferative potential. Notably, lineage tracing in vivo provides definitive and quantitative evidence that focal and overt neuroendocrine regions arise by transdifferentiation of luminal adenocarcinoma cells. These findings underscore principal roles for TP53 and PTEN inactivation in abiraterone resistance and progression from adenocarcinoma to CRPC-NE by transdifferentiation.Significance: Understanding adverse treatment response and identifying patients likely to fail treatment represent fundamental clinical challenges. By integrating analyses of GEM models and human clinical data, we provide direct genetic evidence for transdifferentiation as a mechanism of drug resistance as well as for stratifying patients for treatment with antiandrogens. Cancer Discov; 7(7); 736-49. ©2017 AACR.See related commentary by Sinha and Nelson, p. 673This article is highlighted in the In This Issue feature, p. 653