Resistance of prostate cancer cells to the next-generation antiandrogen enzalutamide may be mediated by a multitude of survival signaling pathways. In this study, we tested whether increased expression of NF-κB2/p52 induces prostate cancer cell resistance to enzalutamide and whether this response is mediated by aberrant androgen receptor (AR) activation and AR splice variant production. LNCaP cells stably expressing NF-κB2/p52 exhibited higher survival rates than controls when treated with enzalutamide. C4-2B and CWR22Rv1 cells chronically treated with enzalutamide were found to express higher levels of NF-κB2/p52. Downregulation of NF-κB2/p52 in CWR22Rv1 cells chronically treated with enzalutamide rendered them more sensitive to cell growth inhibition by enzalutamide. Analysis of the expression levels of AR splice variants by quantitative reverse transcription PCR and Western blotting revealed that LNCaP cells expressing p52 exhibit higher expression of AR splice variants. Downregulation of expression of NF-κB2/p52 in VCaP and CWR22Rv1 cells by short hairpin RNA abolished expression of splice variants. Downregulation of expression of either full-length AR or the splice variant AR-V7 led to an increase in sensitivity of prostate cancer cells to enzalutamide. These results collectively demonstrate that resistance to enzalutamide may be mediated by NF-κB2/p52 via activation of AR and its splice variants.

Docetaxel is the first-line standard treatment for castration resistant prostate cancer (CRPC). However, relapse eventually occurs due to the development of resistance to docetaxel. In order to unravel the mechanism of acquired docetaxel resistance, we established docetaxel-resistant prostate cancer cells, TaxR, from castration resistant C4-2B prostate cancer cells. The IC50 for docetaxel in TaxR cells was about 70-fold higher than parental C4-2B cells. Global gene expression analysis revealed alteration of expression of a total of 1604 genes with 52% being upregulated and 48% downregulated. ABCB1, which belongs to the ATP-binding cassette (ABC) transporter family, was identified among the top upregulated genes in TaxR cells. The role of ABCB1 in the development of docetaxel resistance was examined. Knockdown of ABCB1 expression by its specific shRNA or inhibitor resensitized docetaxel resistant TaxR cells to docetaxel treatment by enhancing apoptotic cell death. Furthermore, we identified that apigenin, a natural product of the flavone family, inhibits ABCB1 expression and resensitizes docetaxel resistant prostate cancer cells to docetaxel treatment. Collectively, these results suggest that overexpression of ABCB1 mediates acquired docetaxel resistance and targeting ABCB1 expression could be potential approach to resensitize docetaxel resistant prostate cancer cells to docetaxel treatment.

Castration resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signaling. Alternative splicing of the AR to generate constitutively active, ligand-independent variants is one of the principal mechanisms that promote the development of resistance to next-generation anti-androgens such as enzalutamide. Here, we demonstrate that the splicing factor heterogeneous nuclear RNA-binding protein A1 (hnRNPA1) plays a pivotal role in the generation of AR splice variants such as AR-V7. HnRNPA1 is overexpressed in prostate tumors compared to benign prostates and its expression is regulated by NF-kappaB2/p52 and c-Myc. CRPC cells resistant to enzalutamide exhibit higher levels of NF-kappaB2/p52, c-Myc, hnRNPA1, and AR-V7. Levels of hnRNPA1 and of AR-V7 are positively correlated with each other in PCa. The regulatory circuit involving NF-kappaB2/p52, c-Myc and hnRNPA1 plays a central role in the generation of AR splice variants. Downregulation of hnRNPA1 and consequently of AR-V7 resensitizes enzalutamide-resistant cells to enzalutamide, indicating that enhanced expression of hnRNPA1 may confer resistance to AR-targeted therapies by promoting the generation of splice variants. These findings may provide a rationale for co-targeting these pathways to achieve better efficacy through AR blockade.

In this article, we address the problem of how to extend the definition of functional dependencies (FDs) in incomplete relations to XML documents (called XFDs) using the well-known strong satisfaction approach.We propose a syntactic definition of strong XFD satisfaction in an XML document and then justify it by showing that, similar to the case in relational databases, for the case of simple paths, keys in XML are a special case of XFDs. We also propose a normal form for XML documents based on our definition of XFDs and provide a formal justification for it by proving that it is a necessary and sufficient condition for the elimination of redundancy in an XML document.

Purpose Use of enzalutamide has produced a revolutionary change in the treatment of advanced prostate cancer. However, clinical resistance to enzalutamide can develop swiftly in initial responders. This study aimed to test whether overexpression of IL-6 and constitutive activation of Stat3 in prostate cancer cells increase resistance to enzalutamide. Experimental design Sensitivity of prostate cancer cells to enzalutamide was tested using cell growth assays and clonogenic assays. Quantitative reverse transcription-PCR, ELISA and Western blotting were performed to detect expression levels of IL-6, c-Myc, survivin and AR. Expression of Stat3 was downregulated using siRNA specific to Stat3. ChIP assay was performed to examine recruitment of AR to the PSA promoter. Results Prostate cancer cells expressing autocrine IL-6 are resistant to enzalutamide and autocrine IL-6 leads to constitutive activation of Stat3 and its target genes. Down regulation of Stat3 led to an increase in sensitivity of prostate cancer cells to enzalutamide. Overexpression of constitutively active Stat3 in prostate cancer cells induced resistance to enzalutamide treatment. Constitutively active Stat3 also enhanced the recruitment of AR to PSA promoter which could not be disrupted by enzalutamide. The Stat3 inhibitor AG490 reversed enzalutamide resistance in prostate cancer cells, while combination treatment with enzalutamide and AG490 significantly inhibited cell growth and induced cell apoptosis. Conclusions This study demonstrates that the autocrine IL-6 pathway induces enzalutamide resistance in prostate cancer cells via the constitutive activation of Stat3. Co-targeting IL6-Stat3 pathway with enzalutamide may be utilized for treatment of advanced prostate cancer.