mTOR inhibitors activate PERK signaling and favor viability of gastrointestinal neuroendocrine cell lines.

mTOR and Unfolded Protein Response (UPR) are two signaling pathways frequently activated in cancer cells. The mTOR pathway has been shown to be up-regulated in most gastroenteropancreatic neuroendocrine tumors. In contrast, little is known about the UPR status in neoplastic neuroendocrine cells. However, these hormone-producing cells are likely to present distinctive adaptations of this pathway, as other secretory cells. We therefore analyzed the status of the three axes of UPR and their relation to mTOR pathway in two gastrointestinal neuroendocrine tumors (GI-NET) cell lines STC-1 and GluTag. At baseline, pharmacological inducers activate the three arms of UPR: PERK, ATF6 and IRE1. Although hypoxia stimulates the PERK, ATF6 and IRE-1 pathways in both cell lines, glucose depletion activates UPR only in STC-1 cell line. Strikingly, P-p70S6K1 increases concomitantly to P-PERK and BiP in response to thapsigargin treatment, glucose depletion or hypoxia. We found that different mTOR inhibitors activate the PERK signaling pathway. To confirm that mTOR inhibition modulates PERK activation, we inhibited PERK and showed that it decreased cell viability when associated to mTOR inhibition, indicating that mTOR drives a PERK-dependent survival pathway. In conclusion, in GI-NET cell lines, UPR signaling is functional and PERK arm is induced by mTOR inhibition. These observations open up new perspectives for therapeutic strategies: the crosstalk between mTOR and UPR might contribute to the resistance to mTOR inhibitors and could be targeted by mTOR and PERK inhibitors in combination therapy.

Prognostic factors in neuroendocrine carcinoma: biological markers are more useful than histomorphological markers.

Gastroenteropancreatic neuroendocrine carcinomas (GEP-NEC) are a very aggressive type of cancer, for which prognostic factors are lacking. We analysed clinical and histomorphological prognostic markers of overall survival (OS), completed with a record of biological and haematological data of patients diagnosed between December 2002 and December 2015. The median OS was 16 months (95% CI 13.9-18.1). After univariate analysis, performance status (PS) ≥ 2 and stage IV were associated with a worse outcome (9 months and 14 months, respectively), as well as patients with lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) levels ≥ 2 ULN (9 months and 8 months, respectively). After multivariate analysis, LDH and AST levels were the only factors that remained significantly associated with better survival: HR 0.36 (p = 0.04) and 0.31 (p = 0.03), respectively. When patients had elevated LDH and AST levels, OS was 20 months, when they had high LDH or AST levels, 13 months and 8 months in the group with low LDH and AST levels (p < 0.001). Therefore, biological data appeared to be more relevant prognostic factors than usual factors described in other studies (PS, stage, and Ki-67). Considering LDH and AST levels at diagnosis could help physicians to predict survival and to stratify patients for clinical trials.

Design and Validation of the GI-NEC Score to Prognosticate Overall Survival in Patients With High-Grade Gastrointestinal Neuroendocrine Carcinomas.

Background: Prognostic markers for risk stratification of patients with gastrointestinal high-grade neuroendocrine carcinomas (GI-NECs) are lacking; we designed and validated a prognostic score for overall survival (OS). Methods: Consecutive patients diagnosed in five neuroendocrine specialist European centers were included. Patients were divided into three cohorts: a training cohort (TC), an external validation cohort (EVC), and a prospective validation cohort (PVC). Prognostic factors were identified by log-rank test, Cox-regression, and logistic regression analyses. The derived score was internally and externally validated. All statistical tests were two-sided. Results: Of 395 patients screened, 313 were eligible (TC = 109 patients, EVC = 184 patients, and PVC = 20 patients). The derived prognostic score included five variables: presence of liver metastases, alkaline phosphatase (ALK), lactate dehydrogenase (LDH), Eastern Cooperative Oncology Group performance status (ECOG PS), and Ki67. In multivariable analysis, the score was prognostic for OS (hazard ratio [HR] = 1.86, 95% confidence interval [CI] = 1.47 to 2.35, P < .001) and had good discrimination (C-index = 0.76) and calibration (mean error = 0.021, 90th percentile = 0.037) in the TC. These results were validated in the EVC and PVC, in which our score was able to prognosticate for OS when adjusted for other prognostic variables in the multivariable analysis (HR = 1.85, 95% CI = 1.27 to 2.71, P = .001; and HR = 4.51, 95% CI = 1.87 to 10.87, P = .001, respectively). The score classified patients into two groups with incremental risk of death: group A (0-2 points, 181 patients [63.9%], median OS = 19.4 months, 95% CI = 16.1 to 25.1) and group B (3-6 points, 102 patients [36.1%], median OS = 5.2 months, 95% CI = 3.6 to 6.9). Conclusions: The GI-NEC score identifies two distinct patient cohorts; it provides a tool for clinicians when making treatment decisions and may be used as a stratification factor in future clinical trials.