Prostate Cancer Cells With the AR-Low and EMT-High Phenotype Are Vulnerable to NAD+ Synthesis Inhibitors.

BACKGROUND: Metastatic prostate cancers are primarily treated by therapies targeting the androgen/androgen receptor (AR) signaling pathways. Despite the initial success, treatment resistance is almost universal, leading to disease progression and patient mortality. Currently, the molecular mechanism and vulnerability of treatment-resistant prostate cancers are poorly understood. These knowledge gaps are major obstacles in improving treatment and patient survival. Recently, we used the single-cell approach to establish a new anti-androgen/AR resistant cell model, in which tumor cells had an AR-low phenotype, expressing low levels of AR and AR-target genes, and were resistant to androgen-deprivation (ADT) and enzalutamide in vitro and in vivo.

METHODS: We determined the transcriptome of the treatment-resistant AR-low cells with bulk RNA-Seq, qRT-PCR, and chromatin immunoprecipitation (ChIP)-qPCR. We identified a metabolic vulnerability of the resistant cells with siRNA, plasmid-based overexpression and metabolic assays. We next determined whether the vulnerability can be exploited by small molecule inhibitors to enhance enzalutamide with proliferation and colony formation assays and Incucyte-based live cell imaging. We also determined the clinical relevance of the vulnerability with the prostate cancer TCGA data set.

RESULTS: The AR-low treatment resistant tumor cells had significantly different transcriptomes from the treatment-sensitive counterparts, notably represented by the EMT-high expression phenotype. The resistant cells were deficient in the expression of NAPRT, a rate determining enzyme in nicotinamide adenine dinucleotide (NAD+) biosynthesis, causing the resistant cells to be vulnerable to NAD+ biosynthesis inhibitors. Importantly, this vulnerability can be exploited to enhance enzalutamide efficacy in the castration sensitive setting as NAPRT-low was phenotypically associated with EMT-high and AR-low in subpopulations of tumor cells and patient samples.

CONCLUSION: Our newly established treatment-resistant cell model has the AR-low/EMT-high phenotype, which is clinically associated with enzalutamide resistance in patients. NAPRT-deficiency (NAPRT-low) can be a novel vulnerability associated with the AR-low/EMT-high phenotype and thus can be targeted by NAD+ inhibitors to improve enzalutamide efficacy.