Metformin and Everolimus: A Promising Combination for Neuroendocrine Tumors Treatment

Abstract

Introduction: Treatment options for neuroendocrine tumors (NETs) are rarely curative, as NETs frequently show resistance to medical therapy. The use of everolimus, an mTOR inhibitor, is limited by the development of resistance, probably due to the activation of Akt signaling. In this context, the antidiabetic drug metformin is able to inhibit mTOR, providing a rationale for the use of metformin and everolimus in combination. Methods: We investigated the effects of the metformin and everolimus combination on NET cell proliferation, apoptosis, colony formation, cell viability, NET spheroids growth and the involvement of the Akt and mTOR pathways, and also developed everolimus-resistant NET cells to further study this combination. Results: Metformin and everolimus in combination are more effective than monotherapy in inhibiting pancreatic NET (PAN-NET) cell proliferation (−71% ± 13%, p < 0.0001 vs. basal), whereas no additive effects were observed on pulmonary neuroendocrine tumor (PNT) cell proliferation. The combinatorial treatment is more effective than monotherapy in inhibiting colony formation, cell viability, NET spheroids growth rate and mTOR phosphorylation in both NET cell lines. In a PAN-NET cell line, metformin did not affect Akt phosphorylation; conversely, it significantly decreased Akt phosphorylation in a PNT cell line. Using everolimus-resistant NET cells, we confirmed that metformin maintained its effects, acting by two different pathways: Akt-dependent or independent, depending on the cell type, with both leading to mTOR suppression. Conclusions: Considering the promising effects of the everolimus and metformin combination in NET cells, our results provide a rationale for its use in NET patients.

Lactate in the tumour microenvironment: From immune modulation to therapy

“…Water-soluble rapamycin analogues (temsirolimus and everolimus), ATP-competitive mTOR inhibitors (MLN0128, PP242, AZD2014 and AZD8055), and dual PI3K/mTOR inhibitors (NVP-BEZ235, LY3023414, SAR245409, XL765, PQR309, XH00230381967, SN20229799306, GSK2126458, and PKI-587) have been used to treat multiple cancers [101] . Although the antitumour effect of mTOR inhibitor monotherapy alone was limited, the combination of mTOR inhibition and other treatments, such as anti-PD-1 antibody or metformin, had synergistic antitumour activity [ 102 , 103 ]. These synergistic effects of targeting mTOR pathway and inhibiting glycolysis have also been reported in several cancers, including lymphoma, leukaemia, and colorectal cancer [ 104 , 105 ].…”

Impact of Diabetes and Metformin Use on Enteropancreatic Neuroendocrine Tumors: Post Hoc Analysis of the CLARINET Study

“…The first study (MetNet1, NCT02294006), is a prospective, open-label, single-arm trial in which patients with advanced panNETs will receive metformin in combination with first-line somatostatin analogs and everolimus, and the second (MetNet2, NCT02823691) is a pilot, single-arm, open-label, prospective study investigating the safety profile of upfront metformin in combination with lanreotide in patients with advanced well-differentiated gastrointestinal and lung NETs [ 24 ]. In both studies, patients without DM taking metformin are included, based on published preclinical data indicating that metformin also produces direct (cell-autonomous) antitumor effects, independent of glucose extracellular concentration [ 25 , 26 ].…”

Integrated or Independent Actions of Metformin in Target Tissues Underlying Its Current Use and New Possible Applications in the Endocrine and Metabolic Disorder Area

“…Metformin inhibited the cellular proliferation of neuroendocrine tumor cells of different origins and reduced cell viability in two pNET cell lines (BON-1 and QPG-1). Actually, the effective metformin concentrations in cell growth media exceeded the plasma metformin levels reached in patients treated with safe dosages, just as in studies with pituitary tumor cell cultures [ 13 , 187 , 246 , 247 , 248 , 249 ].…”

“…Finally, in QPG-1 cells, metformin was shown to upregulate the aryl hydrocarbon receptor-interacting protein (AIP). The outcome of AIP silencing in these cells, suggest the involvement of this factor in the antitumorigenic effect of metformin, which is again related to the mTOR pathway downregulation [ 248 , 249 ].…”

“…Indeed, Vitali and coworkers showed that the combined treatment was more effective than monotherapy in inhibiting pNET cells in vitro. Moreover, the authors also developed a model of everolimus-resistant cells and proved that metformin maintained its effects in these cells [ 248 ].…”