No abstract

The factors triggering pancreatic neuroendocrine tumor (PanNET) progression are largely unknown. Here we investigated the role and mechanisms of the sumoylation enhancing protein RSUME in PanNET tumorigenesis. Immunohistochemical studies showed that RSUME is strongly expressed in normal human pancreas, in particular in β-cells. RSUME expression is reduced in insulinomas and is nearly absent in other types of PanNETs suggesting a role in PanNET tumorigenesis. In human pancreatic neuroendocrine BON1 cells, RSUME stimulates hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor-A (VEGF-A), which are key components of tumor neovascularisation. In contrast, RSUME suppresses nuclear factor-κB (NF-κB) and its target interleukin-8 (IL-8). Correspondingly, PanNET cells with RSUME knockdown showed decreased HIF-1α activity and increased NF-κB and IL-8 production leading to a moderate reduction of VEGF-A release as reduced HIF-1α/VEGF-A production is partly compensated by NF-κB/IL-8-induced VEGF-A. Notably, RSUME stabilizes the tumor suppressor PTEN, which is frequently lost in PanNETs and whose absence is associated with metastasis formation. In vivo orthotopic transplantation of PanNET cells with or without RSUME expression into nude mice showed that PanNETs without RSUME have reduced PTEN expression, grow faster and form multiple liver metastases. In sum, RSUME differentially regulates key components of PanNET formation suggesting that the observed loss of RSUME in advanced PanNETs is critically involved in PanNET tumorigenesis, particularly in metastasis formation.

Aggressive pituitary tumors are rare but difficult to manage, as there is no effective chemotherapy to restrict their growth and cause their shrinkage. Within these tumors, growth-promoting cascades, like the PI3K/mTOR pathway, appear to be activated. We tested the efficacy of two inhibitors of this pathway, NVP-BKM120 (Buparlisib; pan-PI3K) and NVP-BEZ235 (dual PI3K/mTOR), both in vitro on immortalized pituitary tumor cells (GH3) and on primary cell cultures of human pituitary tumors and in vivo on a rat model of prolactin (PRL) tumors (SMtTW3). In vitro, NVP-BEZ235 had a potent apoptotic and cytostatic effect that was characterized by decreased cyclin D/E and Cdk4/2 protein levels and subsequent accumulation of cells in G 1 . In vivo, the effect was transient, with a decrease in mitotic index and increase in apoptosis; long-term treatment had no significant inhibitory effect on tumor growth. In contrast, while NVP-BKM120 had little effect in vitro, it dramatically limited tumor growth in vivo. Increased Akt phosphorylation observed only in the NVP-BEZ235-treated tumors may explain the differential response to the two inhibitors. Primary cell cultures of human PRL pituitary tumors responded to NVP-BEZ235 with reduced cell viability and decreased hormone secretion, whereas NVP-BKM120 had little effect. Altogether, these results show a potential for PI3K inhibitors in the management of aggressive pituitary tumors.

To determine the maximum tolerated dose of irinotecan administered every 2 weeks, in combination with a fixed and continuous administration of temozolomide, in patients with glioblastoma at first relapse. Patients received oral temozolomide at a fixed and continuous dose of 50 mg/m divided into three daily doses, except for a single 100 mg/m dose, administered before every irinotecan infusion. Irinotecan was given intravenously on days 8 and 22 of 28-day cycles. The starting dose of irinotecan was 100 mg/m, and this was escalated by increments of 15 mg/m in cohorts of 3-6 evaluable patients. Determination of the dose-limiting toxicity was based on toxicities recorded from day 1 of the first cycleto day 8 of the third cycle. Enzyme-inducing antiepileptic drugs were not allowed. Tumor response was assessed by MRI every 8 weeks. Twelve patients were enrolled in this phase I study. The three patients enrolled at dose level 1 and six of nine patients enrolled at dose level 2 were evaluable for toxicity. The maximum tolerated dose of irinotecan was 100 mg/m. The dose-limiting toxicities were hematologic and gastrointestinal. Nine patients were evaluable for response: one patient achieved a partial response, four patients remained stable, and four patients had disease progression. The combination of metronomic temozolomide and irinotecan every 2 weeks can be safely administered at the recommended doses; a phase II study with this combination was started and has completed accrual.