Molecular Characterization Of Cancer Stem Cells From Patient-Derived Xenografts Of Advanced Prostate Cancer.

Introduction: Androgen-deprivation therapy is the standard treatment for prostate cancer. Despite the initial response, a fraction of cases manifest progression to castration-resistant prostate cancer. The paradigm of PCa recurrence is the existence of androgen-independent cancer stem cells, which differentiate into androgen-dependent cancer cells that reinitiate tumor growth. The phenotypic properties of cancer stem cells versus highly proliferative progenitor cells/facultative stem cells remain to be further characterized in terms of androgen receptor signaling, quiescence/proliferation, tumorigenicity, and therapy resistance. Methods: To address the molecular basis of CSC switch from androgen-dependency to independency we have employed two patient-derived xenograft models (LAPC-9 and BM-18) that have different androgen sensitivity properties. We have performed microarray and proteomic analysis of BM-18 tumor tissues prior to and following castration as well as androgen replacement. To characterize the cancer stem cells in these models we have isolated different subpopulations based on combination of selected markers and assessed the transcriptomic changes, proteomic profile, and in vivo self-renewal. Results: Castration induces a rapid tumor volume decrease in the BM-18 and a stabilization of tumor burden in the LAPC-9, reflecting different androgen-dependent cell states. Proteomic analysis of bulk BM-18 tumors (intact, 14 days post castration, 50 days post androgen replacement) indicates an enrichment of stem cell markers upon castration; CD44, NKX3.1, and ALDH1 isoforms. Microarray analysis has confirmed upregulation of CD44 and ALDH1A1 at castrated state, and downregulation of expression upon androgen replacement at early time points (24 hours). We have isolated CD44+/-ALDHhigh/low subpopulation by flow cytometry and analyzed their transcriptome and proteomic changes. Castration in the BM-18 model induces an increase in the subpopulations of CD44+/ALDHlow (from 0.44% to 2.3%) and CD44+/ALDHhigh (from 0.06% to 0.38%). However, the same subpopulations are decreased in the LAPC-9 model upon castration, while only the CD44-/ALDHhigh subset is enriched (from 3.5% to 7.1%). Conclusions: Different androgen-independent cancer stem cell subpopulations may be distinguished by the ALDH activity status in combination with CD44. The androgen-independent cells in the BM-18 androgen-dependent model are reflected by enrichment of CD44 expression, as well as a rare double positive population. In the androgen-independent LAPC-9 model, CD44 expression is contrastingly decreased, potentially reflecting androgen-dependent CD44+ cells, and ALDH activity increased in CD44- cells. Ongoing analysis may elucidate the molecular mechanisms controlling the different cancer stem cell fates and their androgen sensitivity. Cancer stem cell potential of the different cell populations will have to be elucidated by transplantation experiments. Citation Format: Sofia Karkampouna, Marta de Menna, Markus Germann, Joel Grosjean, Peter C. Gray, George N. Thalmann, Marianna Kruithof-de Julio. Molecular characterization of cancer stem cells from patient-derived xenografts of advanced prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B060.