Long-term taxane exposure and transdifferentiation of prostate cancer in vitro.

254 Background: Development of aggressive variants of metastatic castration-resistant prostate cancer (AVPC) is a major challenge in the course of therapy but the underlying mechanisms of aggressive transdifferentiation are not completely understood and appropriate tumor models are missing. Here, we investigated the consequences of long-term taxane exposure on hormone-independent, BRCA2-mutated, AR-V7-positive 22Rv1 cells. Methods: 22Rv1 cells were treated with stepwise increased taxane concentrations for 10 months. Individual clones were picked and further cultured in media containing either docetaxel (Doce) or cabazitaxel (Caba). Passage-matched cells were maintained in culture without treatment. Further characterization was carried out using proliferation, migration, metabolic, and colony formation assays as well as proteomics, RNAseq analyses and xenotransplantation in immunodeficient mice. Results: In total, three single cell 22Rv1-DR clones (50-100-fold resistance to Doce) and three 22Rv1-CR clones (80-150-fold resistance to Caba) were successfully established. All clones showed cross-resistance to either drug. Expectedly, treatment-induced overexpression of ABCB1 was detected and validated. Moreover, alteration of drug resistance related SLC7A5, SLC3A2, and SLC25A24 genes was observed. Additionally, an enrichment analyses identified, among others, neuroendocrine transdifferentiation (GO-term “Neuroendocrine tumors”, p=4.46e-5) to be stimulated in prostate 22Rv1 cells under long-term treatment with Doce or Caba. In line with this, the neuroendocrine features were validated in vitro as well as in xenotransplanted tumors in vivo with upregulation of synaptophysin, chromogranin and neuron specific enolase accompanied by downregulation of the androgen receptor (AR) and upregulation of AR spice variants. Additionally, neuritic morphology, shift to higher nuclear-plasma ratio, partial loss of adherent properties and growth slowdown, along with higher migratory activity were detected. Conclusions: Long-term taxane exposure of 22Rv1 cells resulted in the development of neuroendocrine traits in individual cell clones that have successfully been translated into stable cell lines. Thus, we provide a new cell line model for secondary therapy-induced neuroendocrine transdifferentiation. Further in-depth analysis to identify individual alterations in the course of therapy is currently ongoing.