Efficacy and tolerability of exenatide once weekly versus sitagliptin in patients with type 2 diabetes mellitus: a retrospective analysis of pooled clinical trial data.

AIM: Therapies for type 2 diabetes mellitus that leverage the glucagon-like peptide-1 (GLP-1) receptor signaling pathway have been shown to reduce rates of hyperglycemia and have beneficial effects on body weight. This post hoc analysis compared the effects of 2 GLP-1 receptor- based therapies, exenatide once weekly (EQW), a GLP-1 receptor agonist, and sitagliptin (sita), a dipeptidyl peptidase-4 inhibitor, on glucose control across the range of baseline glycated hemoglobin (HbA1c) levels specified in the American Association of Clinical Endocrinologists and American College of Endocrinology treatment algorithm. MATERIALS AND METHODS: Data from patients treated with either EQW or sita for 26 weeks in 2 randomized, double-blind, comparator-controlled clinical trials were pooled and analyzed. Glycemic endpoints and cardiovascular risk factors were evaluated in subgroups and the overall population. RESULTS: Analysis included 737 patients on background therapies of diet and exercise and/or metformin. While both agents reduced HbA1c and fasting blood glucose (FBG) levels from baseline, significantly greater reductions in HbA1c and FBG levels occurred with EQW compared with sita across all baseline HbA1c level strata, and significantly more patients in the EQW group achieved goal HbA1c levels compared with the sita group. Patients treated with EQW also experienced significantly greater reductions in body weight and cholesterol levels compared with patients treated with sita. The incidences of the most common adverse events of nausea and diarrhea were higher in the EQW group compared with the sita group, and incidences of these adverse events decreased over time. Both groups experienced a low incidence of minor hypoglycemic events. CONCLUSION: Significantly greater improvements in HbA1c and FBG levels were observed in EQW- compared with sita-treated patients across all baseline HbA1c level strata. Additionally, greater reductions in body weight and some cardiovascular risk factors were observed with EQW treatment compared with sita treatment. Both EQW and sita were generally well tolerated; sita-treated patients experienced fewer adverse events than EQW-treated patients. TRIAL REGISTRATION: www.ClinicalTrials.gov identifiers: NCT00637273, NCT00676338.

Treatment of patients with type 2 diabetes with exenatide once weekly versus oral glucose-lowering medications or insulin glargine: achievement of glycemic and cardiovascular goals.

BACKGROUND: Diabetes is associated with a higher risk for adverse cardiovascular outcomes. To improve the health outcomes of patients with type 2 diabetes (T2DM), the American Diabetes Association (ADA) recommended target goals for the improvement of glycemic control and the reduction of cardiovascular risk factors associated with the disease. This retrospective analysis calculated the absolute benefit increase (ABI) of using exenatide once weekly (QW), a glucagon-like peptide-1 (GLP-1) receptor agonist, vs an oral glucose-lowering medication or insulin glargine to achieve ADA-recommended goals. The number needed to treat (NNT) to achieve these goals was also calculated and provides a useful clinical metric for comparing potential therapies from different drug classes. METHODS: Patient data from three double-blind or open label, 26-week, randomized, controlled trials were retrospectively analyzed separately. ABI and NNT were calculated by comparing the percentage of patients treated with exenatide QW (N = 641) vs metformin (N = 246), sitagliptin (N = 329), pioglitazone (N = 328), or insulin glargine (N = 223), who achieved a single glycemic, weight, blood pressure, or lipid goal or a composite of these recommended goals, during the DURATION-2, -3, and -4 clinical trials. RESULTS: Significant ABIs favoring exenatide QW over all four glucose-lowering medications were observed for at least one HbA1c glycemic goal. NNTs of 4 and 5 were calculated when exenatide QW was compared to sitagliptin for attaining HbA1c goals of <7.0% and ≤6.5%, respectively. Additionally, significantly more patients using exenatide QW compared to sitagliptin, pioglitazone, or insulin glargine attained the composite goal of HbA1c <7% or ≤6.5%, without weight gain or hypoglycemia. Exenatide QW was also favored over sitagliptin and insulin glargine for the achievement of the composite goals of HbA1c <7% (or ≤6.5%), systolic blood pressure <130 mm Hg, and low-density lipoprotein <2.59 mmol/L. For most goals, exenatide QW and metformin had similar effects in treatment naïve patients. CONCLUSIONS: This analysis assessed the between-therapy differences in achieving therapeutic goals with therapies commonly used for glycemic control in patients with T2DM. In clinical trials, exenatide QW assisted more patients in reaching the majority of ADA-recommended therapeutic goals than treatment with sitagliptin, pioglitazone, or insulin glargine. TRIAL REGISTRATION: NCT00637273, NCT00641056, NCT00676338.

Growth Arrest Specific 8 (Gas8) and G protein-coupled receptor kinase 2 (GRK2) cooperate in the control of Smoothened signaling.

The G protein-coupled receptor (GPCR)-like molecule Smoothened (Smo) undergoes dynamic intracellular trafficking modulated by the microtubule associated kinase GRK2 and recruitment of ß-arrestin. Of this trafficking, especially the translocation of Smo into primary cilia and back to the cytoplasm is essential for the activation of Hedgehog (Hh) signaling in vertebrates. The complete mechanism of this bidirectional transport, however, is not completely understood. Here we demonstrate that Growth Arrest Specific 8 (Gas8), a microtubule associated subunit of the Dynein Regulatory Complex (DRC), interacts with Smo to modulate this process. Gas8 knockdown in ciliated cells reduces Smo signaling activity and ciliary localization whereas overexpression stimulates Smo activity in a GRK2-dependent manner. The C terminus of Gas8 is important for both Gas8 interaction with Smo and facilitating Smo signaling. In zebrafish, knocking down Gas8 results in attenuated Hh transcriptional responses and impaired early muscle development. These effects can be reversed by the co-injection of Gas8 mRNA or by constitutive activation of the downstream Gli transcription factors. Furthermore, Gas8 and GRK2 display a synergistic effect on zebrafish early muscle development and some effects of GRK2 knockdown can be rescued by Gas8 mRNA. Interestingly, Gas8 does not interfere with cilia assembly, as the primary cilia architecture is unchanged upon Gas8 knock down or heterologous expression. This is in contrast to cells stably expressing both GRK2 and Smo, in which cilia are significantly elongated. These results identify Gas8 as a positive regulator of Hh signaling that cooperates with GRK2 to control Smo signaling.

Smoothened signaling in vertebrates is facilitated by a G protein-coupled receptor kinase.

Smoothened, a heptahelical membrane protein, functions as the transducer of Hedgehog signaling. The kinases that modulate Smoothened have been thoroughly analyzed in flies. However, little is known about how phosphorylation affects Smoothened in vertebrates, mainly, because the residues, where Smoothened is phosphorylated are not conserved from Drosophila to vertebrates. Given its molecular architecture, Smoothened signaling is likely to be regulated in a manner analogous to G protein-coupled receptors (GPCRs). Previously, it has been shown, that arrestins and GPCR kinases, (GRKs) not only desensitize G protein-dependent receptor signaling but also function as triggers for GPCR trafficking and formation of signaling complexes. Here we describe that a GRK contributes to Smoothened-mediated signaling in vertebrates. Knockdown of the zebrafish homolog of mammalian GRK2/3 results in lowered Hedgehog transcriptional responses, impaired muscle development, and neural patterning. Results obtained in zebrafish are corroborated both in cell culture, where zGRK2/3 phosphorylates Smoothened and promotes Smoothened signal transduction and in mice where deletion of GRK2 interferes with neural tube patterning. Together, these data suggest that a GRK functions as a vertebrate kinase for Smoothened, promoting Hedgehog signal transduction during early development.

Smoothened signal transduction is promoted by G protein-coupled receptor kinase 2.

Deregulation of the Sonic hedgehog pathway has been implicated in an increasing number of human cancers. In this pathway, the seven-transmembrane (7TM) signaling protein Smoothened regulates cellular proliferation and differentiation through activation of the transcription factor Gli. The activity of mammalian Smoothened is controlled by three different hedgehog proteins, Indian, Desert, and Sonic hedgehog, through their interaction with the Smoothened inhibitor Patched. However, the mechanisms of signal transduction from Smoothened are poorly understood. We show that a kinase which regulates signaling by many "conventional" 7TM G-protein-coupled receptors, G protein-coupled receptor kinase 2 (GRK2), participates in Smoothened signaling. Expression of GRK2, but not catalytically inactive GRK2, synergizes with active Smoothened to mediate Gli-dependent transcription. Moreover, knockdown of endogenous GRK2 by short hairpin RNA (shRNA) significantly reduces signaling in response to the Smoothened agonist SAG and also inhibits signaling induced by an oncogenic Smoothened mutant, Smo M2. We find that GRK2 promotes the association between active Smoothened and beta-arrestin 2. Indeed, Gli-dependent signaling, mediated by coexpression of Smoothened and GRK2, is diminished by beta-arrestin 2 knockdown with shRNA. Together, these data suggest that GRK2 plays a positive role in Smoothened signaling, at least in part, through the promotion of an association between beta-arrestin 2 and Smoothened.

The Rb-related p130 protein controls telomere lengthening through an interaction with a Rad50-interacting protein, RINT-1.

The oncogenic process often leads to a loss of normal telomere length control, usually as a result of activation of telomerase. Nevertheless, there are also telomerase-independent events that involve a Rad50-dependent recombination mechanism to maintain telomere length. Previous work has implicated the Rb family of proteins in the control of telomere length, and we now demonstrate that the p130 member of the Rb family is critical for telomere length control. p130 interacts specifically with the RINT-1 protein, previously identified as a Rad50-interacting protein. We further show that RINT-1 is essential for telomere length control. We propose that p130, forming a complex with Rad50 through RINT-1, blocks telomerase-independent telomere lengthening in normal cells. Given previous work implicating E2F in the control of telomerase gene expression, these results thus point to complementary roles for the Rb/E2F pathway in the control of telomere length.

A mechanism of COOH-terminal binding protein-mediated repression.

The E2F4 and E2F5 proteins specifically associate with the Rb-related p130 protein in quiescent cells to repress transcription of various genes encoding proteins important for cell growth. A series of reports has provided evidence that Rb-mediated repression involves both histone deacetylase (HDAC)-dependent and HDAC-independent events. Our previous results suggest that one such mechanism for Rb-mediated repression, independent of recruitment of HDAC, involves the recruitment of the COOH-terminal binding protein (CtBP) corepressor, a protein now recognized to play a widespread role in transcriptional repression. We now find that CtBP can interact with the histone acetyltransferase, cyclic AMP--responsive element--binding protein (CREB) binding protein, and inhibit its ability to acetylate histone. This inhibition is dependent on a NH2-terminal region of CtBP that is also required for transcription repression. These results thus suggest two complementary mechanisms for E2F/p130-mediated repression that have in common the control of histone acetylation at target promoters.

Huntingtin is present in the nucleus, interacts with the transcriptional corepressor C-terminal binding protein, and represses transcription.

Huntingtin is a protein of unknown function that contains a polyglutamine tract, which is expanded in patients with Huntington's disease (HD). We investigated the localization and a potential function for huntingtin in the nucleus. In human fibroblasts from normal and HD patients, huntingtin localized diffusely in the nucleus and in subnuclear compartments identified as speckles, promyelocytic leukemia protein bodies, and nucleoli. Huntingtin-positive nuclear bodies redistributed after treatment with sodium butyrate. By Western blot, purified nuclei had low levels of full-length huntingtin compared with the cytoplasm but contained high levels of N- and C-terminal huntingtin fragments, which tightly bound the nuclear matrix. Full-length huntingtin co-immunoprecipitated with the transcriptional corepressor C-terminal binding protein, and polyglutamine expansion in huntingtin reduced this interaction. Full-length wild-type and mutant huntingtin repressed transcription when targeted to DNA. Truncated N-terminal mutant huntingtin repressed transcription, whereas the corresponding wild-type fragment did not repress transcription. We speculate that wild-type huntingtin may function in the nucleus in the assembly of nuclear matrix-bound protein complexes involved with transcriptional repression and RNA processing. Proteolysis of mutant huntingtin may alter nuclear functions by disrupting protein complexes and inappropriately repressing transcription in HD.