NRAS-mutated melanoma cell lines are susceptible to G2/M blockage and cell death activation in response to estrogen treatment

Gender differences in melanoma incidence and mortality indirectly indicate melanoma as a hormone-related cancer. A protective role of estrogen has long been suggested but several conflicting results have been produced so far about the beneficial action of estradiol and its analogues. Estrogen plays its action by binding two receptors, ERα and ERβ, mainly exerting proliferative or antitumor activity, respectively. Accordingly ERβ expression inversely correlates with melanoma progression. In view of ERs opposite activities on cancer growth and progression, great relevance holds on their relative expression. Therefore we demonstrated that both ERα and ERβ receptors were localized mainly in the nuclei of all primary and metastatic melanoma cell lines analyzed, with different levels of expression. According to that, we treated some melanoma cell lines with 17β-estradiol, the most active form of circulating estrogen, and found a cell cycle block at G2/M boundary at high hormonal doses only in those melanoma cells with high level of ERβ respect to ERα. In order to discriminate between ER α and β activities, we used the ERβ selective agonist LY500307 (Erteberel), already described as a potential therapeutic agent for Glioblastoma. Our data showed a G2 consistent block in a dose and time-dependent manner, in melanoma cell lines either NRAS or BRAF mutated. This cell cycle block was associated with a pro-apoptotic signal, demonstrated by Annexin/PI positive cells and PARP cleavage. Erteberel dose dependent effect was more evident in NRAS mutated metastatic cell lines, thus suggesting that melanoma staging in combination with genetic background may underlie the Erteberel effectiveness. In conclusion, these preliminary results show the particular efficacy of Erteberel treatment in melanoma cell line carrying the NRAS mutation, suggesting its possible therapeutic use in the future. Ongoing studies will investigate the mechanism of G2/mitotic arrest and relative apoptosis program activation with particular attention to NRAS mutated melanoma cells, still lacking effective target therapies.