Abstract C58: The identification and characterization of prostate adenocarcinoma tumor-initiating cells
Authors: Hynes Paul G. , Abou-Kheir Wassim G. , Casey Orla M. , Fang Lei , Liu Yen-Nien , Sheppard-Tillman Heather , Martin Philip , Kelly Kathleen 
Published: May 2013

Abstract
The phenotype of prostate adenocarcinoma tumor initiating cells, also called cancer stem cells, has not been determined for primary prostate tumors. Both multipotent progenitors and luminal progenitor cells, residing in the basal or luminal compartments respectively, can act as prostate cancer cells of origin. The phenotype of tumor initiating cells may be similar to the cancer cell of origin or to its differentiated progeny. We have analyzed the phenotype of tumor initiating cells in a mouse model of aggressive prostate cancer initiated by Probasin promoter-driven Cre (Pb-Cre) dependent deletion of Pten and TP53. Pten deletion results in the development of PIN/adenocarcinoma, while combined Pten/TP53 deletion results in more aggressive progression, associated with significant tumor heterogeneity. The heterogeneity associated with the Pb-Cre4 Pten−/−TP53−/− mouse model is manifested in tumors consisting primarily of adenocarcinoma with foci of basal squamous carcinoma. The cellular source of this heterogeneity is unknown but may result from transformation of multipotent progenitors, or alternatively, from independent transformations of committed progenitors to the basal and luminal lineages.
The aim of this study was to interrogate the tumor initiating activity of the basal and luminal compartments in Pten−/−TP53−/− prostate tissue. In order to separate the basal and luminal lineages, we devised a fractionation scheme using markers preferentially expressed by either lineage. Lin−, EpCAM+ primary prostate tumor cells were labeled with CD49f and Prominin-1 (Prom-1) in order to differentiate basal and luminal populations respectively. Three distinct populations were identified: CD49fhi, Prom-1+ and CD49flo/− Prom-1−. The CD49fhi fraction was enriched for KRT5+ cells, while both the Prom-1+ and CD49flo/− Prom-1− fractions contained a mixture of KRT8+ and KRT5/KRT8 double positive cells. CD49fhi and Prom-1+ fractions possessed tumor initiating activity and generated serially transplantable primary tumors with distinct phenotypes. Tumors established from CD49fhi cells formed basal squamous tumors, while Prom-1+ derived tumors recapitulated the original prostate adenocarcinoma. No tumor initiation was observed from the CD49flo/−Prom-1− cells.
Each cell fraction also exhibited distinct in vitro characteristics. Long term self renewal potential of each fraction was monitored in vitro using the sphere formation assay over six generations. CD49fhi cells demonstrated the highest level of SFU activity at Generation 1. However, the Prom-1+ fraction consistently demonstrated higher SFU activity over the long term (Gen 2 – Gen 6). Following castration, populations of CD49fhi, Prom-1+ and CD49flo/− Prom-1− cells were identified in Pten−/−TP53−/− prostate tissue. Interestingly, castration resistant Prom-1+ cells demonstrated tumor initiating activity and the highest relative level of SFU activity over six generations. Prom-1+ cells expressed known progenitor cell markers such as Bmi1 and Krt19. Transcriptome analyses of cell fractions isolated from tumors of untreated or castrated mice are ongoing.
Our findings demonstrate that prostate adenocarcinoma tumor initiating cells reside in a population of self-renewing progenitors expressing a luminal and not a basal phenotype. In addition, Pten−/−TP53−/− adenocarcinoma tumor initiating cells survive as castration-resistant luminal progenitors.
Citation Format: Paul G. Hynes, Wassim G. Abou-Kheir, Orla M. Casey, Lei Fang, Yen-Nien Liu, Heather Sheppard-Tillman, Philip Martin, Kathleen Kelly. The identification and characterization of prostate adenocarcinoma tumor-initiating cells [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C58.