NRF2 activation in BON‑1 neuroendocrine cancer cells reduces the cytotoxic effects of a novel Ruthenium(II)‑curcumin compound: A pilot study

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) are a group of rare tumors whose specific pathogenetic mechanisms of resistance to therapies have not been completely revealed yet. Chemotherapy is the main therapeutic approach in patients with GEP-NEN, however, novel combination regimens and targeted therapy are continuously explored. In the present study, the anticancer effect of a novel Ruthenium (Ru)(II)-Bisdemethoxycurcumin (Ru-bdcurc) compound was evaluated in BON-1 cell line, one of the few cell lines derived from GEP-NEN, largely used in experimental research of this type of tumors. The experimental data revealed that the Ru-bdcurc compound induced cell death in a dose-dependent manner, in vitro. Biochemical studies demonstrated that, in response to the lower dose of treatment, BON-1 cells activated the nuclear factor erythroid 2-related factor 2 (NRF2) pathway with induction of some of its targets including catalase and p62 as well as of the antiapoptotic marker Bcl2, all acting as chemoresistance mechanisms. NRF2 induction associated also with increased expression of endogenous p53 which is reported to be dysfunctional in BON-1 cells and to inhibit apoptosis. Genetic or pharmacologic targeting of NRF2 inhibited the activation of the NRF2 pathway, as well as of endogenous dysfunctional p53, in response to the lower dose of Ru-bdcurc, increasing the cell death. To assess the interplay between NRF2 and dysfunctional p53, genetic targeting of p53 showed reduced activation of the NRF2 pathway in response to the lower dose of Ru-bdcurc, increasing the cell death. These findings identified for the first time a possible dysfunctional p53/NRF2 interplay in BON-1 cell line that can be a novel key determinant in cell resistance to cytotoxic agents to be evaluated also in GEP-NEN.