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.