Limitations in small intestinal neuroendocrine tumor therapy by mTor kinase inhibition reflect growth factor-mediated PI3K feedback loop activation via ERK1/2 and AKT.

Treatment of small intestinal neuroendocrine tumors (SINETs) with mammalian target of rapamycin (mTOR) inhibitors alone or with somatostatin analogs has been proposed as effective therapy, because both agents have been reported to exhibit antiproliferative activity. Because adenocarcinomas escape mTOR inhibition, we examined whether the escape phenomenon occurred in SINETs and whether usage of somatostatin analogs with mTOR inhibitors surmounted loss of inhibition. The effects of the somatostatin analog octreotide (OCT), the mTOR inhibitor RAD001 (RAD), or the combination were evaluated in SINET cell lines (KRJ-I, H-STS) using cell viability assays, western blotting, enzyme-linked immunosorbent assay, and reverse-transcription polymerase chain reaction to assess antiproliferative signaling pathways and feedback regulation. RAD (10(-9) M) incompletely decreased cell viability (-40% to +15%); growth escape (P < .001) was noted at 72 hours in both cell lines. Phosphorylated (p)mTOR/mTOR and pp70S6K/p70S6K ratios were decreased but were associated with increases in phosphorylated extracellular signal-regulated kinase (pERK)/ERK and pAKT/AKT in both cell lines, whereas phosphorylated insulin-like growth factor 1 receptor (pIGF-1R)/IGF-1R levels were elevated only in H-STS cells. Increased (P < .05) transcript levels for AKT1, MAPK, mTOR, IGF-1R, IGF-1, and TGFβ1 were evident. OCT (10(-6) M) itself had no significant effect on growth signaling in either cell line. An antiproliferative effect (66 ± 5%) using OCT+RAD was only noted in the KRJ-I cells (P < .05). SINET treatment with the mTOR inhibitor RAD had no antiproliferative effect based on activation of pAKT and pERK1/2. A combinatorial approach using OCT and RAD failed to overcome this escape phenomenon. However, differences in RAD response rates in individual NET cell lines suggested that pretreatment identification of different tumor sensitivity to mTOR inhibitors could provide the basis for individualized treatment.

Svejda B ，Kidd M ，Kazberouk A ，Lawrence B ，Pfragner R ，Modlin IM ... -  《-》

Oncogenic tyrosine kinase NPM/ALK induces activation of the rapamycin-sensitive mTOR signaling pathway.

Marzec M ，Kasprzycka M ，Liu X ，El-Salem M ，Halasa K ，Raghunath PN ，Bucki R ，Wlodarski P ，Wasik MA ... -  《ONCOGENE》

Compensatory activation of Akt in response to mTOR and Raf inhibitors - a rationale for dual-targeted therapy approaches in neuroendocrine tumor disease.

Several studies have established a link between aberrant PI(3)K-Akt-mTOR- and Ras-Raf-MEK-Erk1/2 signaling and neuroendocrine tumor disease. In this study, we comparatively investigate the antitumor potential of novel small-molecule inhibitors targeting mTOR (RAD001), mTOR/PI(3)K (NVP-BEZ235) and Raf (Raf265) on human NET cell lines of heterogeneous origin. All inhibitors induced potent antitumor effects which involved the induction of apoptosis and G0/G1 arrest. However, the dual mTOR/PI(3)K inhibitor NVP-BEZ235 was more efficient compared to the single mTOR inhibitor RAD001. Consistently, NVP-BEZ235 prevented the negative feedback activation of Akt as observed after treatment with RAD001. Raf265 inhibited Erk1/2 phosphorylation but strongly induced Akt phosphorylation and VEGF secretion, suggesting the existence of a compensatory feedback loop on PI3K-Akt signaling. Finally, combined treatment with RAD001 or NVP-BEZ235 and Raf265 was more efficient than single treatment with either kinase inhibitor. Together, our data provide a rationale for dual targeting of PI(3)K-Akt-mTOR- and Ras-Raf-MEK-Erk1/2 signaling in NET disease.

Zitzmann K ，Rüden Jv ，Brand S ，Göke B ，Lichtl J ，Spöttl G ，Auernhammer CJ ... -  《-》

Octreotide and the mTOR inhibitor RAD001 (everolimus) block proliferation and interact with the Akt-mTOR-p70S6K pathway in a neuro-endocrine tumour cell Line.

The mode of action of the somatostatin analog octreotide on neuro-endocrine tumour proliferation is largely unknown. Overexpression of the proto-oncogene Akt/PKB (protein kinase B) has been demonstrated in certain neuro-endocrine tumours: Akt activates downstream proteins including mTOR and p70S6K, which play an important role in cell proliferation. RAD001 (everolimus) is a novel agent that is being trialled in the treatment of neuro-endocrine tumours, and is known to interact with mTOR. We explored the mechanism of action of octreotide, RAD001, and their combination on cell proliferation and kinase activation in a neuro-endocrine tumour cell line (rat insulinoma cell line, INS1). Proliferation assays were used to determine the effects of octreotide, RAD001, and their combination on cell proliferation. Western blotting was used to characterize the expression of phosphorylated Akt, phosphorylated TSC2, phosphorylated mTOR, and phosphorylated 70S6K. Treatment with octreotide and RAD001 inhibited proliferation and attenuated phosphorylation of all downstream targets of Akt: TSC2, mTOR, and p70S6K. In this cell model, octreotide and RAD001 appear to act through a similar pathway and inhibit the Akt-mTOR-p70S6 kinase pathway downstream of Akt. There may be some overlapping effects of the two inhibitors on the mTOR pathway, although it is likely that other additional effects may differentiate the two agents.

Grozinsky-Glasberg S ，Franchi G ，Teng M ，Leontiou CA ，Ribeiro de Oliveira A Jr ，Dalino P ，Salahuddin N ，Korbonits M ，Grossman AB ... -  《-》

The PI3K/Akt and mTOR/P70S6K signaling pathways in human uveal melanoma cells: interaction with B-Raf/ERK.

Babchia N ，Calipel A ，Mouriaux F ，Faussat AM ，Mascarelli F ... -  《-》