Investigating aberrant signalling in enzalutamide-resistant prostate cancer

Abstract

Prostate cancer is usually androgen-dependent and consequently, initial therapy for many patients, particularly with advanced disease, is androgen withdrawal, via anti-androgen therapeutics. Most patients respond to anti-androgen therapy in the early stages of their disease but many will develop resistance, entering a “castrate-resistant” disease state. Enzalutamide and ARN-509 have shown promise in the treatment of castration resistant prostate cancer (CRPC) patients, however response rates are just 50% and there is the inevitable development of resistance and subsequent disease progression. The aims of this study are to investigate the role of HER2/HER3 in CRPC models (Casodex-, Enzalutamide- and ARN509-resistant cell lines) and the signalling pathway(s) that can be stimulated through HER2/HER3 activation in these models. In addition, the project focusses on drug-resistant disease models, investigating the genes upregulated in a cell-line model of enzalutamide-resistance. The data showed that HER2/HER3 has a crucial role in the CRPC model cell lines, seen in the activation of both MAP kinase and PI3K/Akt pathways, which are responsible for tumour growth and metastasis. This activity is more pronounced in enzalutamide resistant- LNCaP cells. For that reason, this study aimed to interrogate the global gene expression consequences in this enzalutamide resistant- LNCaP cell model. These aims were approached using Illumina Human HT-12 arrays to detect significantly up-regulated genes and therefore could have a vital role in proliferation, migration and cell cycle. SGK1 and TROP-2 were selected from this microarray to study in more details. The data showed an increase in the expression of SGK1 in Casodex-, enzalutamide- and ARN509-resistant cell lines, compared with parental LNCaP cells. AR regulates SGK1 in both LNCaP and enzalutamide resistant- LNCaP cells. However, GR regulates SGK1 and AR target genes in enzalutamide resistant- LNCaP cells. This study indicated that GR has no effect on the AR target genes in parental LNCaP cells. SGK1 has a vital role in the proliferation, migration and cell cycle of the enzalutamide resistant- LNCaP cell line. In addition, the data from this study showed an increase in the expression of TROP-2 in enzalutamide resistant- LNCaP cells, compared with LNCaP parental cells. The results obtained from this study suggested that TROP-2 might regulates pAkt, pERK1, c-MYC and p27 signalling that are important in proliferation and cell cycle of enzalutamide resistant- LNCaP cells. In addition, TROP-2 potentially regulates the migration of ii enzalutamide resistant- LNCaP cells by its effect on the EMT process that is important in metastases. SGK1 and TROP-2 demonstrated higher protein expression in patients’ tissue samples who had relapsed after androgen withdrawal, compared to naïve patients. In conclusion, SGK1 and TROP-2 could represent either potential biomarkers of enzalutamide-resistance, or potential therapeutic targets in advanced disease.