Potential of phenothiazines to synergistically block calmodulin and reactivate PP2A in cancer cells

Phenothiazines (PTZ) are well known as inhibitors of monoamine neurotransmitter receptors, notably dopamine receptors. Because of this activity they are used for decades as antipsychotic drugs. In addition, significant anti-cancer properties have been ascribed to them. Several attempts for their repurposing were made, however, their incompletely understood polypharmacology is challenging. Here we examined the potential of PTZ to synergistically act on two cancer associated targets, calmodulin (CaM) and the tumor suppressor protein phosphatase 2A (PP2A). Both proteins are known to modulate the Ras-MAPK pathway activity. Consistently, combinations of a CaM inhibitor and a PP2A activator synergistically inhibited cancer cells with KRAS or BRAF mutations. We identified the covalently reactive PTZ derivative fluphenazine mustard as an inhibitor of Ras driven proliferation and Ras membrane organization. We confirmed its anti-CaM activity in vitro and through a cellular CaM target engagement bioluminescence resonance energy transfer (BRET) assay. Our results suggest that improved PTZ derivatives retaining their synergistic CaM inhibitory and PP2A activating properties, but without neurological side-effects, may be interesting to pursue further as anti-cancer agents.

A High-Throughput BRET Cellular Target Engagement Assay Links Biochemical to Cellular Activity for Bruton’s Tyrosine Kinase

Protein kinases are intensely studied mediators of cellular signaling. While traditional biochemical screens are capable of identifying compounds that modulate kinase activity, these assays are limited in their capability of predicting compound behavior in a cellular environment. Here, we aim to bridge target engagement and compound-cellular phenotypic behavior by utilizing a bioluminescence resonance energy transfer (BRET) assay to characterize target occupancy within living cells for Bruton’s tyrosine kinase (BTK). Using a diverse chemical set of BTK inhibitors, we determine intracellular engagement affinity profiles and successfully correlate these measurements with BTK cellular functional readouts. In addition, we leveraged the kinetic capability of this technology to gain insight into in-cell target residence time and the duration of target engagement, and to explore a structural hypothesis.

262Circulating muscle-derived mir-206 links skeletal muscle dysfunction to cardiac autonomic denervation

Purpose Recent studies and our preliminary data demonstrate that muscle-specific ablation of the autophagy-related protein Atg7, leads to block of autophagy, sarcopenia and destabilization of the neuro-muscular junction (NMJ). In addition, Atg7 knock-out (Atg7 KO) muscle fibers release exosomes containing the muscle specific, miR-206, which is consistently elevated in the plasma. Interestingly, we found that miR-206 content was elevated in the heart, suggesting cardiac uptake of the miR-carrying circulating exosomes. We thus aimed at defining the effects of miR-206 on heart homeostasis. Methods Here, we analyzed the cardiac phenotype of adult (12mo.) and aged (24mo.) Atg7 KO mice, as well as of adult C57BL/6J mice injected, via tail vein, with scramble- or miR-206-loaded exosomes. Exosomes were isolated from EDL muscle of control and Atg7 KO mice, as well as from HEK293 cells. Heart function was assessed by echocardiography and ECG-telemetry. Confocal IF, whole-mount IF on heart blocks and multiphoton imaging were used to assess heart structure and sympathetic innervation. Bioinformatics, molecular and biochemical analyses were performed to identify novel targets of miR-206. IF, BRET assay and imaging of TrKA translocation were performed in cultured sympathetic neurons (SNs). Results We demonstrate that circulating exosomes, containing miR-206, are taken up by the heart leading to sympathetic dysinnervation, accompanied to reduction in the neurogenic control of cardiac rhythm and increased arrhythmogenesis. In vitro assays demonstrated that exosome-carried miR-206 targets cardiac SNs (cSNs), compromising cell structure and function. Indeed, increased miR-206 expression is accompanied by cSN atrophy, irregular axonal distribution of the active neurotransmitter release sites, and reduction in axonal sprouting. These effects are likely attributed to the miR-206-mediated down-regulation of the NGF receptor p75, as demonstrated by bioinformatics, luciferase assay, molecular and biochemical analyses in vitro and ex vivo. BRET assay, performed in cultured SNs treated with exosomes carrying miR-206, showed reduced formation of p75/TrkA complexes, which generate high-affinity binding sites for NGF and enhance neurotrophin responsiveness. Consistent with impaired NGF retrograde transport, miR-206 over-expressing SNs displayed reduced NGF protein content and decreased phosphorylation of Akt, which is an NGF downstream target, regulating neuronal survival. Interestingly, these latter results were confirmed in the stellate ganglia from Atg KO and miR-206 treated mice. miR-206 causes heart dysinnervation Conclusions We identify miR-206 as a key molecular player in the “muscle-to-heart” communication. miR-206 may participate to the pathogenesis of secondary cardiac dysfunction in skeletal muscle diseases associated to increased circulating levels of miR-206, ranging from ageing to neurodegenerative disorders (i.e. ALS, DMD).

A Dual GLP-1/GIP Receptor Agonist Does Not Antagonize Glucagon at Its Receptor but May Act as a Biased Agonist at the GLP-1 Receptor

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are important regulators of metabolism, making their receptors (GLP-1R and GIPR) attractive targets in the treatment of type 2 diabetes mellitus (T2DM). GLP-1R agonists are used clinically to treat T2DM but the use of GIPR agonists remains controversial. Recent studies suggest that simultaneous activation of GLP-1R and GIPR with a single peptide provides superior glycemic control with fewer adverse effects than activation of GLP-1R alone. We investigated the signaling properties of a recently reported dual-incretin receptor agonist (P18). GLP-1R, GIPR, and the closely related glucagon receptor (GCGR) were expressed in HEK-293 cells. Activation of adenylate cyclase via Gαs was monitored using a luciferase-linked reporter gene (CRE-Luc) assay. Arrestin recruitment was monitored using a bioluminescence resonance energy transfer (BRET) assay. GLP-1, GIP, and glucagon displayed exquisite selectivity for their receptors in the CRE-Luc assay. P18 activated GLP-1R with similar potency to GLP-1 and GIPR with higher potency than GIP. Interestingly, P18 was less effective than GLP-1 at recruiting arrestin to GLP-1R and was inactive at GCGR. These data suggest that P18 can act as both a dual-incretin receptor agonist, and as a G protein-biased agonist at GLP-1R.

Variable G protein determinants of GPCR coupling selectivity

G protein-coupled receptors (GPCRs) activate four families of heterotrimeric G proteins, and individual receptors must select a subset of G proteins to produce appropriate cellular responses. Although the precise mechanisms of coupling selectivity are uncertain, the Gα subunit C terminus is widely believed to be the primary determinant recognized by cognate receptors. Here, we directly assess coupling between 14 representative GPCRs and 16 Gα subunits, including one wild-type Gα subunit from each of the four families and 12 chimeras with exchanged C termini. We use a sensitive bioluminescence resonance energy transfer (BRET) assay that provides control over both ligand and nucleotide binding, and allows direct comparison across G protein families. We find that the Gs- and Gq-coupled receptors we studied are relatively promiscuous and always couple to some extent to Gi1 heterotrimers. In contrast, Gi-coupled receptors are more selective. Our results with Gα subunit chimeras show that the Gα C terminus is important for coupling selectivity, but no more so than the Gα subunit core. The relative importance of the Gα subunit core and C terminus is highly variable and, for some receptors, the Gα core is more important for selective coupling than the C terminus. Our results suggest general rules for GPCR-G protein coupling and demonstrate that the critical G protein determinants of selectivity vary widely, even for different receptors that couple to the same G protein.

AlphaScreen HTS and Live-Cell Bioluminescence Resonance Energy Transfer (BRET) Assays for Identification of Tau–Fyn SH3 Interaction Inhibitors for Alzheimer Disease

Alzheimer disease (AD) is the most common neurodegenerative disease, and with Americans’ increasing longevity, it is becoming an epidemic. There are currently no effective treatments for this disorder. Abnormalities of Tau track more closely with cognitive decline than the most studied therapeutic target in AD, amyloid-β, but the optimal strategy for targeting Tau has not yet been identified. On the basis of considerable preclinical data from AD models, we hypothesize that interactions between Tau and the Src-family tyrosine kinase, Fyn, are pathogenic in AD. Genetically reducing either Tau or Fyn is protective in AD mouse models, and a dominant negative fragment of Tau that alters Fyn localization is also protective. Here, we describe a new AlphaScreen assay and a live-cell bioluminescence resonance energy transfer (BRET) assay using a novel BRET pair for quantifying the Tau–Fyn interaction. We used these assays to map the binding site on Tau for Fyn to the fifth and sixth PXXP motifs to show that AD-associated phosphorylation at microtubule affinity regulating kinase sites increases the affinity of the Tau–Fyn interaction and to identify Tau–Fyn interaction inhibitors by high-throughput screening. This screen has identified a variety of chemically tractable hits, suggesting that the Tau–Fyn interaction may represent a good drug target for AD.