Combined therapy with RAD001 e BEZ235 overcomes resistance of PET immortalized cell lines to mTOR inhibition

Abstract

Pancreatic endocrine tumors (PETs) are characterised by an indolent behaviour in terms of tumor growth. However, most patients display metastasis at diagnosis and no cure is currently available. Since the PI3K/AKT/mTOR axis is deregulated in PETs, the mTOR inhibitor RAD001 represents the first line treatment. Nevertheless, some patients do not respond to treatments and most acquire resistance. Inhibition of mTOR leads to feedback re-activation of PI3K activity, which may promote resistance to RAD001. Thus, PI3K represents a novel potential target for PETs. We tested the impact of three novel PI3K inhibitors (BEZ235, BKM120 and BYL719) on proliferation of PET cells that are responsive (BON-1) or unresponsive (QGP-1) to RAD001. BEZ235 was the most efficient in inhibiting proliferation in PET cells. Furthermore, combined treatment with BEZ235 and RAD001 exhibited synergic effects and was also effective in BON-1 that acquired resistance to RAD001 (BON-1 RR). Analysis of PI3K/AKT/mTOR pathway showed that RAD001 and BEZ235 only partially inhibited mTOR-dependent phosphorylation of 4EBP1. By contrast, combined therapy with the two inhibitors strongly inhibited phosphorylation of 4EBP1, assembly of the translational initiation complex and protein synthesis. Thus, combined treatment with BEZ235 may represent suitable therapy to counteract primary and acquired resistance to RAD001 in PETs.

Therapeutic Benefit of Selective Inhibition of p110α PI3-Kinase in Pancreatic Neuroendocrine Tumors

“…Therefore, it is tempting to speculate that a combination of p110α and mTOR inhibitors in the treatment of PanNETs may cooperate to enhance the effectiveness of each compound alone. In line with this, combined RAD001 (rapalogue) and BEZ235 (a dual mTOR/PI3K inhibitor) treatment of neuroendocrine tumor cells in vitro overcomes resistance to RAD001 (47). Sunitinib, a tyrosine kinase inhibitor, is another targeted therapy currently being used in the clinic in PanNET patients.…”

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

“…Several rapalogs and angiogenesis inhibitors were first evaluated in two-dimensional (2D) cell culture models, such as BON-1, QGP-1 and CM (Townsend et al 1993, Arany et al 1994, Zitzmann et al 2010, Vandamme et al 2016. In addition, these well-characterized in vitro models are used to investigate acquired therapy resistance (Passacantilli et al 2014, Vandamme et al 2016, Aristizabal Prada et al 2018, Benten et al 2018).…”

“…BEZ235 showed promise in multiple preclinical studies. High efficiency in inhibiting the PI3K-Akt-mTOR pathway and cell proliferation has been ascribed to its combined PI3K, mTORC1 and mTORC2 inhibition (Maira et al 2008, Passacantilli et al 2014. Vandamme et al demonstrated that BEZ235 is able to overcome in vitro acquired rapalog resistance (Vandamme et al 2016).…”

“…Vandamme et al demonstrated that BEZ235 is able to overcome in vitro acquired rapalog resistance (Vandamme et al 2016). In addition, Passacantilli et al showed by using in vitro pNET assays that mTORC1 activity was inhibited at 1-10 nM, while for PI3K and mTORC2 kinase activity inhibition higher doses of 100-250 nM were needed (Passacantilli et al 2014). The latter study evaluated the combination of everolimus alongside with BEZ235.…”

The synergistic inhibition of breast cancer proliferation by combined treatment with 4EGI-1 and MK2206

“…[43][44][45] Given that 4EGI-1 treatment induced the feedback activation of Akt, we speculated that preventing the activation of Akt may enhance the antitumor effect of 4EGI-1. Indeed, as expected, our results showed that MK2206 in combination with 4EGI-1 had a synergistic effect on the inhibition of breast cancer cell proliferation.…”