Dipeptidyl Peptidase-4 Inhibitor Enhances the Efficacy of Docetaxel via Adenosine Triphosphate Depletion and Modulation of Mitochondrial Fusion-Fission in Castration-Resistant Prostate Cancer.

Purpose

Dipeptidyl peptidase-4 (DPP4) inhibitors may influence prostate cancer (PCa) progression and clinical outcomes. Therefore, here we investigated whether the DPP4 inhibitor sitagliptin could enhance the cytotoxic effect of docetaxel (DOC) in castrationresistant prostate cancer cells and the underlying metabolic and mitochondrial mechanism.

Materials And Methods

We analyzed DPP4 expression using TCGA datasets and Western blot. The combined effects of sitagliptin and DOC were evaluated using cell viability assays, Annexin V-propidium iodide flow cytometry, and a PC3-derived xenograft mouse model. Intracellular adenosine triphosphate (ATP), NAD⁺/NADH ratios, and mitochondrial membrane potential were measured to assess metabolic stress. Mitochondrial dynamics were visualized via TOM20 immunofluorescence and Western blot analysis of MFN1, OPA1, and Drp1.

Results

DPP4 was significantly overexpressed in PCa tissues compared to normal controls. While sitagliptin alone had minimal effect on viability, its combination with DOC produced a greater inhibitory effect on PCa cell growth, most in PC3 cells. Mechanistically, sitagliptin initially triggered a transient ATP depletion that PC3 cells attempted to overcome through mitochondrial fusion (upregulation of MFN1/OPA1 and Drp1 S637 phosphorylation). However, the addition of DOC thwarted this metabolic adaptation, leading to a sustained energy depletion characterized by exhaustive NAD⁺ depletion and a significant drop in the NAD⁺/NADH ratio. This metabolic disruption was associated with loss of mitochondrial membrane potential, increased reactive oxygen species generation, and activation of the intrinsic apoptotic pathway, including cytochrome c release and caspase-3 cleavage. Finally, the combination therapy significantly suppressed tumor growth in vivo without significant changes in body weight. Additionally, quantitative analysis revealed a reduction in IC₅₀ values and CI values below 1, supporting a synergistic interaction between DOC and sitagliptin.

Conclusions

Sitagliptin enhances the cytotoxic effect of DOC in PCa cells and is associated with metabolic and mitochondrial dysfunction. This combination strategy may represent a promising therapeutic approach to improve therapeutic efficacy in advanced PCa.