Effect of Selective Serotonin (5-HT)2B Receptor Agonist BW723C86 on Epidermal Growth Factor/Transforming Growth Factor-α Receptor Tyrosine Kinase and Ribosomal p70 S6 Kinase Activities in Primary Cultures of Adult Rat Hepatocytes.

Serotonin (5-hydroxytryptamine; 5-HT) can induce hepatocyte DNA synthesis and proliferation by autocrine secretion of transforming growth factor (TGF)-α through 5-HT2B receptor/phospholipase C (PLC)/Ca2+ and a signaling pathway involving epidermal growth factor (EGF)/TGF-α receptor tyrosine kinase (RTK)/extracellular signal-regulated kinase 2 (ERK2)/mammalian target of rapamycin (mTOR). In the present study, we investigated whether 5-HT or a selective 5-HT2B receptor agonist BW723C86, would stimulate phosphorylation of TGF-α RTK and ribosomal p70 S6 kinase (p70S6K) in primary cultures of adult rat hepatocytes. Western blotting analysis was used to detect 5-HT- or BW723C86 (10-6 M)-induced phosphorylation of EGF/TGF-α RTK and p70S6K. Our results showed that 5-HT- or BW723C86 (10-6 M)-induced phosphorylation of EGF/TGF-α RTK peaked at between 5 and 10 min. On the other hand, 5-HT- or BW723C86 (10-6 M)-induced phosphorylation of p70S6K peaked at about 30 min. Furthermore, a selective 5-HT2B receptor antagonist LY272015, a specific PLC inhibitor U-73122, a membrane-permeable Ca2+ chelator BAPTA/AM, an L-type Ca2+ channel blocker verapamil, somatostatin, and a specific p70S6K inhibitor LY2584702 completely abolished the phosphorylation of p70S6K induced by both 5-HT and BW723C86. These results indicate that phosphorylation of p70S6K is dependent on the 5-HT2B-receptor-mediated autocrine secretion of TGF-α. In addition, these results demonstrate that the hepatocyte proliferating action of 5-HT and BW723C86 are mediated by phosphorylation of p70S6K, a downstream element of the EGF/TGF-α RTK signaling pathway.

Interferon regulatory factor 1 eliminates mycobacteria by suppressing p70 S6 kinase via mechanistic target of rapamycin signaling.

OBJECTIVES: Although it has been reported that Interferon regulatory factor 1 (IRF1) inhibits Mycobacterium tuberculosis (Mtb) infection via inducible nitric oxide synthase (iNOS) in mice, how it counteracts with mycobacterial infection in human remains largely obscure. This study was conducted to investigated the effect of IRF1 on Mtb infection in human macrophages (Mϕs). METHODS: We thus investigated the IRF1 expression by using PBMC and monocytes of pulmonary tuberculosis (TB) patients and human monocyte-derived macrophages (hMDMs) and THP-1-derived macrophages (THP-1-Mϕ). We used gain-of-function and loss-of-function approaches to explore the role of IRF1 on Mtb infection. RESULTS: IRF1 was significantly induced in PBMC and monocytes of pulmonary TB patients in vivo and in human Mϕs in vitro. We demonstrated that IRF1 protects Mϕs from Mtb infection. Concurrently, IRF1 promotes the expression of several pro-inflammatory cytokines including IL-6, TNF-α and IL-8, indicating IRF1-mediated activation of innate immunity upon Mtb infection. Gain-of-function and loss-of-function approaches have demonstrated that IRF1 suppresses the mechanistic target of rapamycin (mTOR)/p70 S6 kinase (p70 S6K) cascade to exert its anti-Mtb effect. CONCLUSIONS: The discovery of a novel function of IRF1 in facilitating anti-mycobacterial effect through suppressing mTOR/p70 S6K signaling in Mϕs may provide a promoting therapeutic target for tuberculosis.

A phase I trial of LY2584702 tosylate, a p70 S6 kinase inhibitor, in patients with advanced solid tumours.

BACKGROUND: LY2584702 tosylate (hereafter referred to as LY2584702) is a potent, highly selective adenosine triphosphate (ATP) competitive inhibitor against p70 S6 kinase, a downstream component of the phosphatidylinositol-3-kinase signalling pathway which regulates cell proliferation and survival. LY2584702 exhibited anti-tumour activity in preclinical analysis. METHODS: Patients with advanced solid tumours were treated with LY2584702 orally on a 28-day cycle until the criteria for maximum tolerated dose (MTD) were met. Skin biopsies were collected for pharmacodynamic analysis, and levels of phospho-S6 protein were examined. The primary objective was to determine a phase II dose and schedule with secondary objectives of observing safety and tolerability. Dose escalation was based upon Common Terminology Criteria for Adverse Events Version 3.0. RESULTS: Thirty-four patients were enrolled onto this phase I study and treated with LY2584702 on a QD (once-daily) or BID (twice-daily) dosing schedule. Part A dose escalation (n=22) began with 300 mg BID (n=2). Due to toxicity, this was scaled back to doses of 25mg (n=3), 50 mg (n=8), 100mg (n=3), and 200 mg (n=6) QD. Part B dose escalation (n=12) included 50 mg (n=3), 75 mg (n=3), and 100 mg (n=6) BID. Seven patients experienced dose-limiting toxicity (DLT). All DLTs were Grade 3 and included vomiting, increased lipase, nausea, hypophosphataemia, fatigue and pancreatitis. CONCLUSION: The MTD was determined to be 75 mg BID or 100mg QD. No responses were observed at these levels. Pharmacokinetic analysis revealed substantial variability in exposure and determined that LY2584702 treatment was not dose proportional with increasing dose.