Introduction: Type 5 phosphodiesterase (PDE5) inhibitors (PDE5i) lead to intracellular cyclic-guanosine monophosphate (cGMP) increase and are used for clinical treatment of erectile dysfunction. Studies found that cGMP may up/downregulate the growth of certain endocrine tumor cells, suggesting that the use of PDE5i could impact the risk of certain tumors, such as colorectal cancer.
Aim: We evaluated if PDE5i may impact thyroid cancer cell growth in vitro.
Materials and methods: We investigated caspase 3 activation by bioluminescence resonance energy transfer (BRET), in malignant (K1) and benign (Nthy-ori 3-1) thyroid cell lines, expressing a specific biosensor. Cells were treated with the PDE5i vardenafil or the cGMP analog 8-br-cGMP (nM-μM range) and reactions stopped at different time-points (0-24 h). The efficacy of vardenafil and 8-br-cGMP in inducing intracellular cGMP increase was evaluated by BRET, using a specific biosensor. The COS7 cell line served as a reference. Cleavage of caspase 3 was further evaluated by Western blotting, as well as phosphorylation of the proliferation-associated extracellularly regulated kinases 1 and 2 (ERK1/2), while nuclear fragmentation was evaluated by DAPI staining. Cell viability was investigated using 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) assay. Positive controls for cell death were set by treating cells with thapsigargin. Experiments were performed in triplicates and results analyzed by Kruskal-Wallis test (P<0.05 significance level).
Results: BRET experiments revealed that both vardenafil and 8-br-cGMP effectively induced dose-dependent intracellular cGMP increase (P<0.05) in both the K1 and Nthy-ori 3-1 cell lines, as well as in reference COS7 cells. However, no caspase 3 activation occurred between PDE5i-treated vs -untreated cells, at all concentrations and time-points tested (P≥0.05), in contrast to the results obtained using thapsigargin (P<0.05). These results match those obtained upon cell treatment with 8-br-cGMP, which failed in inducing caspase 3 clevage in all the cell lines (P≥0.05). Moreover, they reflect the lack of caspase 3 cleavage, evaluated by Western blotting, as well as missing nuclear fragmentation. Interestingly, the modulation of intracellular cGMP levels with vardenafil or the analog did not impact cell viability of both malignant and benign thyroid tumor cell lines, nor the phosphorylation of ERK1/2 (P≥0.05).
Conclusions: This study demonstrated that cGMP-mediated signals are not linked to cell viability and death in K1 and Nthy-ori 3-1 cell lines, suggesting that the use of PDE5i could not impact the growth of thyroid cancer cells.
21 May 2022 - 24 May 2022