Taxane-Resistant Prostate Cancer: Restoring Anticancer Efficacy by Inhibiting NNMT
1. The Major Barrier in Prostate Cancer Therapy: Taxane Resistance
When prostate cancer progresses to the castration‑resistant prostate cancer (CRPC) stage, standard chemotherapeutics from the taxane class are primarily employed. However, many patients develop resistance that renders these agents ineffective, leading to treatment discontinuation. Determining how cancer cells evade these potent drugs was the top priority for the research team.
2. Omics Identifies the Master Regulator: NNMT
The team generated taxane‑resistant cell lines and performed an integrated omics analysis that interrogated the entire genome and proteome. They discovered that the enzyme nicotinamide N‑methyltransferase (NNMT) is abnormally overexpressed in resistant cells, functioning as a “resistance engine” that facilitates metastatic potential and phenotypic plasticity.
3. Inactivating NNMT Disrupts Cancer Cell Defense
Using CRISPR‑Cas9 gene editing and siRNA, the researchers silenced NNMT. Remarkably, previously drug‑refractory cancer cells regained sensitivity and underwent cell death. The study also demonstrated that this sensitization is mediated by suppression of TGF‑β signaling and epithelial‑mesenchymal transition (EMT), key pathways that drive metastasis.
4. Future Implications
The work goes beyond identifying the resistance mechanism; it also demonstrates therapeutic potential using NNMT inhibitors such as 1‑MNA. If NNMT‑targeted combination regimens are translated into the clinic, they could restore efficacy of existing taxanes and offer a new avenue for patients with previously untreatable prostate cancer to regain a healthier quality of life.
Drug resistance in patients remains a significant obstacle to successful treatment, even with improvements in cancer treatment strategies. Resistance to taxanes, such as docetaxel (Dtx) and cabazitaxel (Cbz), frequently emerges in castration resistant prostate cancer (CRPC). Through pulse selection of the parental cells (DU145), we established Dtx- and Cbz-resistant CRPC cell models and integrated different omic approaches, including transcriptomics and proteomics, to determine the molecular signatures underlying taxane resistance. Interestingly, several genes were regulated in the same direction (up- or down-regulation) at both the gene and protein expression levels in resistant cells compared to parental cells, suggesting that alterations primarily occur at the transcriptional level and manifest at the protein level. Among the differentially regulated genes, Cysteine Rich Protein 2 (CRIP2), a gene associated with tumor suppressor function, has been found to be the most downregulated in taxane-resistant cells. Conversely, Nicotinamide N-Methyltransferase (NNMT) exhibited a significant upregulation and has been validated in the context of taxane resistance. Its overexpression was shown to promote taxane resistance in two different CRPC cell lines, whereas depletion via siRNA or gRNA, as well as treatment with 1-methylnicotinamide (1-MNA, used as a feedback inhibitor)resensitized the resistant cells. RNA-sequencing of NNMT-knockout (CRISPR-Cas9) cells has indicated involvement of TGFβ signaling, and suppressing this pathway has further increased the taxane sensitivity. Epithelial Mesenchymal Transition (EMT) was another pathway depleted upon knockout, and subsequent analysis revealed a significant correlation between NNMT and EMT-related genes (VIM, CDH2, FN1, TGFB1, and ZEB2) in both the Cancer Cell Line Encyclopedia (CCLE) panel and patient data. Additionally, in cancers other than PC, NNMT has been observed to predict treatment outcomes, and notably, among the pat
It offers an innovative solution that restores drug responsiveness in end‑stage prostate cancer patients who have exhausted all available chemotherapies due to resistance. By targeting a novel driver of metastasis and disease progression, this approach could accelerate a future in which patients enjoy longer, less painful lives.