Protein acetylation, which is central to transcriptional control as well as other cellular processes, is disrupted in Huntington's disease (HD). Treatments that restore global acetylation levels, such as inhibiting histone deacetylases (HDACs), are effective in suppressing HD pathology in model organisms. However, agents that selectively target the disease-relevant HDACs have not been available. SirT1 (Sir2 in Drosophila melanogaster) deacetylates histones and other proteins including transcription factors. Genetically reducing, but not eliminating, Sir2 has been shown to suppress HD pathology in model organisms. To date, small molecule inhibitors of sirtuins have exhibited low potency and unattractive pharmacological and biopharmaceutical properties. Here, we show that highly selective pharmacological inhibition of Drosophila Sir2 and mammalian SirT1 using the novel inhibitor selisistat (selisistat; 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide) can suppress HD pathology caused by mutant huntingtin exon 1 fragments in Drosophila, mammalian cells and mice. We have validated Sir2 as the in vivo target of selisistat by showing that genetic elimination of Sir2 eradicates the effect of this inhibitor in Drosophila. The specificity of selisistat is shown by its effect on recombinant sirtuins in mammalian cells. Reduction of HD pathology by selisistat in Drosophila, mammalian cells and mouse models of HD suggests that this inhibitor has potential as an effective therapeutic treatment for human disease and may also serve as a tool to better understand the downstream pathways of SirT1/Sir2 that may be critical for HD.
OBJECTIVE: To evaluate safety and tolerability of selisistat over 12 weeks in patients with Huntington's Disease (HD). BACKGROUND: Selisistat is a first-in-class SirT1 inhibitor shown to be safe and well tolerated in healthy volunteers and HD patients in short-term studies. DESIGN/METHODS: This was a double-blind, placebo-controlled, international multi-centre study of selisistat in individuals with Stage I-III HD. Participants (30-70 yrs) with genetically confirmed HD, a Unified Huntington Disease Rating Scale (UHDRS) Total Motor Score of >=5 and a Total Functional Capacity >=5 were randomized (1:1:1) to selisistat 50 or 200 mg or placebo once daily for 12 weeks. Safety and tolerability were evaluated by monitoring adverse events, vital signs, ECG and laboratory safety data throughout the study. Blood sampling for pharmacokinetics and soluble mutant huntingtin levels were collected throughout. RESULTS: A total of 144 patients were randomized and 125 patients (87%) completed the study. There were 9 serious adverse events, three in each treatment group, including one death in the placebo group. The most common adverse events were reversible increases in liver function tests without accompanying increases in bilirubin. All of these occurred in the selisistat groups; while most of these increases were <3×ULN, three events were classified as serious. No clinically relevant changes in the UHDRS readouts were observed during the relatively short treatment period. Levels of soluble mutant huntingtin in peripheral blood mononuclear cells showed borderline statistically significant (p=0.058, p=0.075) increases of similar magnitude at 12 weeks compared to placebo in the 50mg and 200mg groups respectively, that reverted to levels consistent with the placebo group at follow-up. CONCLUSIONS: Apart from increases in liver function tests in a subset of patients, selisistat was safe and well tolerated, and a trend for modulation of the levels of soluble mutant huntingtin was observed. Study supported by: Siena Biotech SpA.
Abstract Background. Complex feedback loops and crosstalk between the MEK/ERK and PI3K/mTOR pathways, thus molecular predictors of sensitivity/resistance and synergistic/antagonistic interactions are urgently needed for the effective clinical development of combination strategies. Here we hypothesize that PTEN status critically modulates the growth inhibitory activity of single and combined MEK and PI3K/mTOR inhibition. Methods. Molecular and functional effects of single and combined MEK (trametinib, T) and mTOR (everolimus, E) blockade were assessed in a panel of 29 cancer cell lines with different molecular ‘drivers’. Pharmacologic interactions were analyzed by conservative isobologram analysis. PTEN role was mechanistically assessed by either silencing PTEN expression by shRNA or overexpressing a functional PTEN protein by stable transfection. Specific proteins and their phosphorylation states were analyzed using Kinexus Antibody Microarrays. Results. In the cell line panel analyzed, the presence of a wt-PTEN was the only significant predictor of sensitivity to T (p=0.001), while BRAF mutations were significantly related to E resistance (p=0.015). PTEN silencing slightly increased resistance to T in the wt-PTEN melanoma cell line M14; conversely, wt-PTEN overexpression in the PTEN-del WM115 cell line, dramatically increased sensitivity to T. E-induced growth inhibition was not significantly affected. Combined MEK and mTOR inhibition resulted in a striking growth inhibitory synergism in cells lacking PTEN expression (CI: 0.4-0.0005), but not in those with an intact PTEN (CI: 1.2-107; p=0.001). However, PTEN silencing restored growth inhibitory synergism of combined T and E in M14 cells (CI:0.36); similarly, the slope of the CI/fraction affected curve was dramatically altered in PTEN-overexpressing WM115 cells, as compared to their control-transfected counterpart, again indicating that PTEN expression/function causally influences functional response to combined MEK and mTOR inhibition. Similar results in terms of synergistic/antagonistic pharmacologic interactions were obtained when either double PI3K/mTOR kinase inhibitors (PF-5212384) or AKT allosteric inhibitors (MK-2206) were used to block the PI3K/mTOR pathway in combination with T. Proteomic analysis indicated that a greater modification of protein expression/phosphorylation profiles in response to MEK or combined MEK/mTOR inhibition occurs in cells lacking a functional PTEN, as compared to the wt-PTEN-expressing ones; preliminary analysis suggests that AKT phosphorylation and NF-κB activation maybe be crucial mediators of synergistic growth-inhibitory interactions occurring with combined treatment. Conclusions. PTEN loss may constitute a suitable genetic/molecular marker of synergistic activity interactions between MEK/ERK and PI3K/mTOR pathway inhibitors. Citation Format: Ludovica Ciuffreda, Italia Falcone, Silvia Matteoni, Andrea Sacconi, Federico Malusa, Teresa De Luca, Ursula Cesta Incani, Anais Del Curatolo, Marina Konopleva, Michael Andreeff, Adriana Eramo, Ruggero De Maria, Donatella Del Bufalo, Francesco Cognetti, Michele Milella. PTEN loss as a putative biomarker of synergistic growth inhibitory activity of combined MEK/ERK and PI3K/mTOR pathway blockade. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2618. doi:10.1158/1538-7445.AM2014-2618
The prediction of pairing between microRNAs (miRNAs) and the miRNA recognition elements (MREs) on mRNAs is expected to be an important tool for understanding gene regulation. Here, we show that mRNAs that contain Pumilio recognition elements (PRE) in the proximity of predicted miRNA-binding sites are more likely to form stable secondary structures within their 3'-UTR, and we demonstrated using a PUM1 and PUM2 double knockdown that Pumilio proteins are general regulators of miRNA accessibility. On the basis of these findings, we developed a computational method for predicting miRNA targets that accounts for the presence of PRE in the proximity of seed-match sequences within poorly accessible structures. Moreover, we implement the miRNA-MRE duplex pairing as a two-step model, which better fits the available structural data. This algorithm, called MREdictor, allows for the identification of miRNA targets in poorly accessible regions and is not restricted to a perfect seed-match; these features are not present in other computational prediction methods.
Background Evidence suggests simultaneous dysfunction of CNS and peripheral inflammatory pathways in Huntington's disease (HD). A pattern of pro-inflammatory cytokine elevation has been observed in plasma in HD, with IL-6 significantly elevated in a group of subjects predicted to be, on average, 16 years from disease, with a parallel post-mortem cytokine expression profile seen in HD striatum. Furthermore, LPS stimulation of HD monocytes reveals an inherent hyper-reactivity that is similar to that seen in microglia, suggesting a cell-autonomous effect of mutant huntingtin in peripheral myeloid cells as well as in the CNS. Sirtuins, which are deacetylating enzymes, have been implicated as potential targets in ageing, metabolism and neurodegeneration. Selisistat, a member of the sirtuin deacetylase family and an inhibitor of SirT1 (Silencing information regulator T1), has a novel mode of action that may be pathologically relevant for HD. A Phase 1B study encompassing six EU sites (Germany, Poland and the UK) was carried out in 55 early-stage HD patients over 14 days at two dose levels (10 and 100 mg OD), with a randomised, double-blind, placebo-controlled, parallel group design. Aim To determine if the innate immune system is a potential target for Selisistat. Methods Cytokine assays were carried out using the MesoScale Discovery (MSD) multiplex platform, as per the manufacturer's recommendations, and analysed on a SECTOR 2400 instrument. The cytokines of interest included IL-1b, IL-6, IL-8 and TNF-α. The operator was blinded to the disease state of each sample during processing and statistical analysis was performed independently. Results and Conclusions Here we will present comparative analysis of the plasma cytokine profile of Huntington's disease patients at four time points, screening, baseline, day 14 and day 28, in each of the three treatment arms of the study.
