Targeting The Treatment-Induced Developmental Reprogramming Process That Facilitates Progression Of Prostate Cancer

Abstract Metastatic prostate cancer (PCa) develops resistance to hormone therapies through androgen receptor (AR) dependent and independent mechanisms. Previously we described a remarkable and reversible adaptive cellular plasticity that permits adherent AR+ PCa cells (LNCaP, VCaP, LAPC4 and CWR22rv1) to efficiently reprogram to non-adherent AR-/lo cells by exposure to an androgen-free, custom-formulated stem cell medium (STM). STM-reprogrammed cells grew as rosettes/spheroids on conventional tissue culture treated dishes, were resistant to enzalutamide compared to parental cells and had high tumor forming efficiency when xenografted into castrated and intact male mice. Reprogrammed cells overexpressed genes associated with the stem cell state, expressed cell surface antigens characteristic of neural crest stem cells (NRCAM, HNK-1, CD271 and CD29) and showed increased in vitro invasive behaviour through a matrix-coated membrane and increased invasion in vivo into zebrafish following yolk-sac xenografting. When re-exposed to serum-containing mediums, reprogrammed cells could be re-differentiated back to AR+ prostate-like cancer cells or to other differentiated cell lineages derived from neural/neural crest stem cells (neural-, oligodendrocyte-, glia- or osteoblast-like). Gene expression profiling data from reprogrammed cells was analyzed to identify activation of key signalling pathways associated with this transition and outcomes were confirmed by qPCR (for mRNAs) and Western blotting (for protein levels). Inhibitors of Bmi1 (PTC-209), PI-3-kinase (LY294002), Akt (MK2206) or NF-κB (Copper-DDC) were employed to determine whether they interfered with acquired non-adherent (spheroidal) colony formation in the LNCaP model system exposed to STM. Results indicated that key molecules in the non-classical NF-κB pathway (RelB and p100) were upregulated in the transition to AR-/lo stem-like cells and that Bmi1 and phospho-Akt proteins were also consistently overexpressed in all cell models in response to reprogramming. Inhibitors of Bmi1, PI-3-kinase, and Akt significantly suppressed the ability of LNCaP cells to form non-adherent spheroids in the STM, while an inhibitor of NF-κB was able to reduce the number and size of spheroids. The results support the idea that this adaptive and reversible tumor cell plasticity that generates resistance to androgen deprivation is targetable by agents directed at key genes associated with the developmental reprogramming process described previously. Citation Format: Mannan Nouri, Amy Anne Lubik, Josselin Caradec, Na Li, Sarah Truong, Brett G. Hollier, Ralph Buttyan. Targeting the treatment-induced developmental reprogramming process that facilitates progression of prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3344.