Combinatorial Treatment with mTOR Inhibitors and Streptozotocin Leads to Synergistic In Vitro and In Vivo Antitumor Effects in Insulinoma Cells

Abstract

Streptozotocin-based chemotherapy is the first-line chemotherapy recommended for advanced pancreatic neuroendocrine tumors (pNETs), whereas targeted therapies, including mTOR inhibitors, are available in second-line treatment. Unfortunately, objective response rates to both treatments are limited. Because mTOR pathway activation, commonly observed in pNETs, has been reported as one of the major mechanisms accounting for chemoresistance, we investigated the potential benefit of mTOR inhibition combined with streptozotocin treatment in a subset of pNETs, namely insulinomas. To evaluate the potential of mTOR inhibition in combination with streptozotocin, we selected four different inhibitors acting at various levels of the pathway (everolimus: inhibition of mTORC1; MK-2206: inhibition of AKT; BKM120: inhibition of PI3K, mTORC1, and mTORC2; and BEZ235: inhibition of mTORC1 and mTORC2). Effects on cell viability and apoptosis were assessed in insulinoma cell lines INS-1E (rat) and MIN6 (mouse) and were confirmed by using a mouse model of hepatic tumor dissemination after intrasplenic xenograft. , all four combinations display synergistic effects. These combinations lead to heterogeneous mTOR pathway inhibition, in agreement with their respective target, and increased apoptosis., tumor growth in the liver was significantly inhibited by combining streptozotocin with everolimus ( = 0.0014), BKM120 ( = 0.0092), or BEZ235 ( = 0.008) as compared to each agent alone. These results suggest that targeting the mTOR pathway in combination with streptozotocin could be of potential benefit for insulinomas and pNET patients and thus support further clinical investigations. .

Lower threshold to NFκB activity sensitizes murine β-cells to streptozotocin

“…Having demonstrated that MIN6 express key NFκB signaling proteins, we next sought to determine whether STZ exposure directly induced NFκB signaling and activation. We used a dose of STZ (2 mM) known to induce a response in MIN6 cells without causing overwhelming cell death (Bollard et al 2018). MIN6 cells demonstrated no evidence of STZ-induced degradation of the NFκB inhibitory proteins IκBα or IκBβ at short (0.25-4 h; Fig.…”

Combined Targeting of Pathogenetic Mechanisms in Pancreatic Neuroendocrine Tumors Elicits Synergistic Antitumor Effects

“…Specifically, we used the INS-1E cell line (from a rat insulinoma), and the recently established human NT-3 cell line (from a human G2 PanNET) as models of well-differentiated tumors. Indeed, they express markers of NET cells, secrete insulin upon glucose stimulation, and show intermediate (INS-1E) or low (NT-3) proliferation rates [ 16 , 21 , 26 ]. In our studies, we also included human BON-1 cells, characterized by high proliferation rates, genetic alterations compatible with an aggressive behavior, and partial loss of typical markers of neuroendocrine differentiation [ 27 , 28 ].…”

“…Given the relevance of an overactivation of the PI3K pathway in several cancers, agents that can block this signaling cascade at various levels have been generated and several are already in clinics. Buparlisib, a PI3K inhibitor, has been evaluated for its anti-tumor efficacy in human and rodent PanNET cell lines in vitro, and was found to inhibit cell proliferation and induce apoptosis as a single agent [ 16 , 17 , 18 ]. Buparlisib in combination with streptozotocin also showed antitumor effects in vivo in a xenograft model of liver dissemination obtained upon intrasplenic INS-1E cells injection [ 16 ].…”

“…Buparlisib, a PI3K inhibitor, has been evaluated for its anti-tumor efficacy in human and rodent PanNET cell lines in vitro, and was found to inhibit cell proliferation and induce apoptosis as a single agent [ 16 , 17 , 18 ]. Buparlisib in combination with streptozotocin also showed antitumor effects in vivo in a xenograft model of liver dissemination obtained upon intrasplenic INS-1E cells injection [ 16 ].…”

Interplay Between Diabetes and Pancreatic Ductal Adenocarcinoma and Insulinoma: The Role of Aging, Genetic Factors, and Obesity

“…Anti-cancer drugs are used to treat insulinoma. Recently, a combination of mTOR inhibitors and streptozotocin was shown to have synergistic antitumor effects in insulinoma cells, both in vitro and in vivo ( 119 ). Everolimus, an mTOR inhibitor, was successfully used to treat advanced pancreatic neuroendocrine tumors in a phase 3 clinical trial ( 120 ) (RADIANT-3 ClinicalTrials.gov number, NCT00510068).…”