Characterization of cancer stem cell subpopulations from patient-derived xenografts of advanced prostate cancer

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. PCa recurrence is possibly due to androgen-independent cancer stem cells that reinitiate tumor growth. The properties of cancer stem cells versus highly proliferative progenitor cells remain to be further characterized at the cellular and gene expression level. To address the molecular basis of CSC switch from androgen dependency to independence, we have employed 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 by FACS cytometry, based on combination of selected markers (CD44 and ALDH activity measured by ALDELFUOR assay) aiming to assess the transcriptomic profile of these different populations. To assess response of these CD44+/-/ALDH+/- cells to androgen targeting compounds we have established an androgen-sensitive xenograft model (PNPCa) and tested it by ex vivo tissue culture and organoid viability assays. Proteomic and microarray analysis of bulk BM-18 tumors indicates enrichment of stem cell markers upon castration: CD44, NKX3.1 and ALDH1 isoforms. Readministration of testosterone induces decrease of these markers. Castration induces a rapid tumor volume decrease in the BM-18 as opposed to LAPC-9, reflecting different androgen-dependent cell states. CD44+/-/ALDHhigh/low subpopulations were isolated by flow cytometry and for transcriptomic analysis. Castration in the BM18 model induces an increase in the subpopulations of CD44+/ALDHlow and CD44+/ALDHhigh, while ALDHsingle and ALDHhigh total populations are decreased. Both CD44 expression and ALDH activity is increased in the LAPC-9 model upon castration. Treatment of PNPCa tumor parts ex vivo with enzalutamide inhibited expression of androgen receptor and keratin 8 expression. CD44+ organoids derived from the same tissue did not show altered viability after enzalutamide treatment. Different androgen-independent cancer stem cell populations may be distinguished by ALDH activity status and CD44. Androgen-independent cells in the BM-18 androgen-dependent model are reflected by enrichment of CD44 expression. The least abundant subpopulation CD44+/ALDHhigh is present in the LAPC-9 and expanded upon castration, while in the BM-18 model it is exclusively present after castration, reflecting different androgen sensitivity. Ongoing analysis may elucidate the molecular mechanisms controlling cancer stem cell fates, androgen sensitivity and drug resistance.