Background/Objectives: Metastatic prostate cancer (PCa) is the leading cause of cancer-related deaths and a major contributor to cancer mortality in men. Most patients with metastatic PCa eventually develop metastatic castration-resistant prostate cancer (mCRPC), characterized by resistance to treatment with androgen-deprivation therapy, and often later the development of resistance to other types of agents. MAGMAS, a 13.8 kDa mitochondrial-associated protein, facilitates the import of nuclear-encoded proteins into the mitochondrial matrix. Overexpression of MAGMAS has been observed in several aggressive cancers, including breast, glioblastoma, and prostate cancer. When overexpressed, MAGMAS acts as a cytoprotective protein by scavenging reactive oxygen species (ROS), maintaining ROS levels that support cell proliferation while avoiding the induction of apoptosis. This study investigates the role of MAGMAS in therapy resistance in PCa cells. Methods/Results: Quantitative immunoblotting revealed that MAGMAS is endogenously upregulated in docetaxel-resistant (DR) PCa cell lines compared to their docetaxel-sensitive parental counterparts. While MAGMAS depletion alone did not affect the survival of DR cells, it significantly sensitized them to docetaxel (DTX), as indicated by a marked reduction in clonogenic potential. Additionally, transient knockdown of MAGMAS in these resistant cells significantly decreased the levels of ABCB1 protein. Consistent with these findings, sub-therapeutic inhibition of MAGMAS using the novel BT#9 inhibitor, in combination with increasing concentrations of DTX, enhanced the sensitivity of DR cells to DTX, as demonstrated by proliferation and clonogenic assays. Lastly, RNA tumor expression predicts overall survival (OS). Conclusions: These results implicate MAGMAS in PCa chemoresistance and suggest that targeting this protein could provide a novel therapeutic strategy for treating DR tumors.

Metastatic castration-resistant prostate cancer (mCRPC) remains lethal, and lineage plasticity drives a subset of tumors to neuroendocrine prostate cancer (NEPC), most often treatment-emergent (t-NEPC). Prostate-specific membrane antigen (PSMA), the target of radioligand therapies for advanced prostate cancer (PCa), is heterogeneously expressed across metastatic sites but lost during neuroendocrine differentiation, excluding many patients from these therapies. The glycolytic enzyme Enolase 1 (ENO1) is a promising alternative target because it localizes to the surface of human tumors and promotes cancer growth and metastasis. However, it remains understudied in advanced PCa compared with ENO2 (neuron-specific enolase), a canonical neuroendocrine marker. We report here that total and cell surface ENO1 are more abundant than ENO2 in PSMA-negative mCRPC and NEPC cells. ENO1 silencing reduced cell proliferation and clonogenic growth even when triggering ENO2 upregulation. Targeting cell surface ENO1 with a monoclonal antibody decreased proliferation, clonogenicity, and tumorsphere formation in mCRPC cells, including docetaxel-resistant cells. This was associated with S-phase accumulation, elevated phospho histone p-H2A.X, and increased apoptosis. Significantly higher transcript expression of ENO1 than ENO2 was observed in clinical prostate tumors, including high-Gleason and neuroendocrine tumors, concomitant with elevated expression of their transcriptional regulator MYC. These findings position cell-surface ENO1 as a therapeutic and theranostic target for PSMA-low, treatment-refractory PCa.