Endocrine Abstracts

Background: Pheochromocytomas (PHEO) are rare neuroendocrine tumors derived from chromaffin cells of the adrenal medulla. Catecholamins’ secretion is associated with a high risk of cardiovascular complications. Malignancy is rare, but still demands effective treatment. Metformin has been shown to have antiproliferative properties in several cancer cell lines, possibly related to its ability to inhibit cell proliferation pathways. Accordingly, we aimed to evaluate the effects of metformin in the survival and proliferation of PHEO cells.

Methods: Cell viability was evaluated by MTT and TRIPAN assays using the PC12-Adh PHEO cell line treated with metformin in increasing concentrations (0–30 mM). A lipid peroxidation assay and determination of O₂ consumption using a respirometer were performed to evaluate cellular stress. The effects of metformin on cell proliferation markers were analyzed by western blot.

Results and Discussion: Metformin at 20 mM induced an inhibition of 60% of cell viability after 48 h treatment, as compared to untreated controls, and increased cellular lipid peroxidation, while decreased O₂ consumption in PC12-Adh PHEO cells. Moreover, metformin treatment reduced the activation of proteins of the AMPK/PTEN/AKT/mTOR pathway, which suggests growth and cell proliferation impairment. We then performed a primary culture of a PHEO from a 10-year-old boy with VHL disease to test wheter metformin exerts its antiproliferative effects ex vivo. Our results suggest that metformin has a moderate inhibitory effect on the viability of PC12-Adh PHEO cells. This effect is associated with enhanced lipid peroxidation and decreased O₂ consumption by those cells, which are both suggestive of increased cellular stress. Moreover, metformin treatment induced a positive modulation of the AMPK/PTEN/AKT/mTOR signaling pathway. Altogether our results corroborate the hypothesis of an inhibitory effect of metformin on PHEO cellular proliferation in vitro.