Endocrine Abstracts

Introduction: Bronchial Carcinoids are rare neoplasms originating from the diffuse neuroendrocrine system. Surgery is the only effective therapy but may not be feasible due to metastases. Available therapy may control symptoms but not tumor bulk. Everolimus has shown promising results, however patients may develop resistance. Previous studies demonstrated that Everolimus reduces viability of NCI-H720 (Atypical Carcinoid) but not of NCI-H727 cells (Typical Carcinoid). In order to find molecular targets different from mTOR, we previously assessed CDKs and cyclins protein levels in both NCI-H720 and NCI-H727 cells and found a differential expression pattern.

Aim: This study is aimed to test the efficacy of a CDK inhibitor, Dinaciclib, alone and in combination with Everolimus on NCI-H720 and NCI-H727 cells. We also investigated the involvement of autophagy in mediating the effects of Dinaciclib on cell viability and LC3B expression (autophagosome protein) by using a well-established autophagy inhibitor, Chloroquine.

Methods: Cell viability was tested by a luminescent assay and protein levels by Western blot analysis.

Results: Treatment with Everolimus (100 nM) reduced viability in NCI-H720 (−26% vs control; P<0.01) and in NCI-H727 cells (−19% vs control; P<0.01). Dinaciclib (100 nM) significantly reduced viability in both NCI-H720 (−39% vs control; P<0.01) and NCI-H727 cells (−62% vs control; P<0.01). Dinaciclib potentiated the inhibitory affects of Everolimus on NCI-H720 viability (−24% vs Everolimus; P<0.01), while in NCI-H727 cells the combination did not modify the inhibitory effects of Dinaciclib. Co-treatment with Chloroquine 1 mM did not modify these results. In addition, we assessed autophagosome protein LC3B by Western blot analysis. We found that LC3B levels were not influenced by the employed drugs in NCI-H727 cells. In NCI-H720 Dinaciclib reduced LC3B levels independently of the combination with Everolimus (−37% and −48% respectively vs. control); Everolimus alone did not influence LC3B levels. Chloroquine determined a reduction in LC3B levels (−40% vs control), and this effect was not influenced by Everolimus. On the contrary, Dinaciclib potentiated Chloroquine effects on LC3B reduction (−44.5% vs Chloroquine) independently of the combination with Everolimus.

Conclusions: Our results indicate that Everolimus effects are not mediated by autophagy. On the contrary, Dinaciclib inhibits autophagy in NCI-H720 but not in NCI-H727, indicating that in the latter cells the antiproliferative effects of Dinaciclib are mediated by mechanisms different from autophagy. At the same time, Dinaciclib could represent a good candidate for medical treatment of Bronchial Carcinoids, especially for those patients resistant to Everolimus.