Endocrine Abstracts

Adrenocortical carcinoma (ACC) is a rare, heterogeneous malignancy with a poor prognosis, particularly when metastatic at diagnosis. To date, radical surgery, possibly associated to mitotane adjuvant therapy, is the only available treatment. However, the mean 5-year survival rate drops under 10% in metastatic ACC and chemo-resistance often develops. Thus, more specific and effective drugs for ACC treatment are urgently required. The antidiabetic drug metformin, used in type 2 diabetes treatment, has been associated with decreased cancer incidence and mortality in several human cancers, suggesting us the possibility to test its potential efficacy on ACC too. Our study wants to evaluate the potential anti-cancer effects of metformin in vitro on H295R adrenocortical tumour cell line. Treating cells with increasing doses of metformin (0.5–250 mM) affects cell viability and proliferation in a dose- and time-dependent manner, as we observed by MTS and cell count assay (IC₅₀ after 7days: 23.8±0.9 and 10.1±0.3 mM respectively). This inhibitory effect was also confirmed by [³H]thymidine incorporation assay. Moreover, combining metformin and mitotane leads to a synergistic effect which reduces cell viability more than metformin alone (IC₅₀ after 7days: 16.7±1.1 mM). To further investigate the molecular mechanisms by which metformin inhibits cell growth, we performed western blot analysis after 6 and 24 h treatment with different doses of metformin (20, 50, and 100 mM), and we analysed some of the signalling pathways related to cell proliferation and survival. We observed a dose-dependent decrease of ERK1/2 phosphorylation and an increase of AMPK activation, associated with a decreased mTOR phosphorylation. In conclusion, our data suggest that metformin interferes in vitro with H295R proliferation, showing a synergistic effect when combined with mitotane. Further studies have to be performed in vivo by using animal models to prove the potential anti-cancer effect of metformin in adrenocortical carcinoma.

Disclosure: ENS@T CANCER – FP7/2007-2013 (grant number 259735). MIUR-FIRB 2010 (grant number RBAP1153LS).