Högskolan i Skövde

Objective: Digitoxin is a kind of plant-derived cardiac glycoside that is used to treat heart diseases, especially in congestive heart failure or arrhythmia. However, its potentiality presented as an anti-tumour drug remains unexplored. Pembrolizumab, a monoclonal IgG4 antibody, designed to block the PD‒1 receptor have demonstrated anti-tumour effect in patients with melanoma and a wide range of other cancers including renal cell carcinoma, ovarian cancer and Hodgkin lymphoma. The aim of this study was designed to investigate the pharmacological benefits of a digitoxin and pembrolizumab treatment of prostate cancer cell line.

Materials and methods: LNCaP (prostate cancer) cells were seeded and treated with digitoxin, pembrolizumab and a combination of both. The MTS assay was utilized to determine the number of viable cells. PD‒1, PD‒L1 and PD‒L2 genes expression was determined by qPCR (quantitative Polymerase Chain Reaction). Amplex-Red assay was used to measure ROS levels in LNCaP cells.

Results: Cell viability in LNCaP cells was significantly inhibited by digitoxin 10-100 nM and pembrolizumab 0,5-100 mg/l.  A combination treatment with digitoxin 10 nM + pembrolizumab 50 mg/l was statistically significant with decreased cell viability compared to untreated control in LNCaP after 72h of treatment and showed a synergistic effect. The ROS levels was decreased by 25 nM digitoxin + 50 mg/l pembrolizumab and 100 nM digitoxin + 50 mg/l pembrolizumab. qPCR study indicated that digitoxin and pembrolizumab intervention caused an increase in the gene expression of the PD‒1 and PD‒L1/L2 genes.

Conclusions: These findings suggest that digitoxin and pembrolizumab plays a potential anti-tumour role in LNCaP cells in vitro, thus could be used as a new therapy to treat prostate cancer.