Concentration-Dependent Modulation of Amyloid-␤ in Vivo and in Vitro Using the ␥-Secretase Inhibitor, LY-450139

ABSTRACT LY-450139 is a ␥-secretase inhibitor shown to have efficacy in multiple cellular and animal models. Paradoxically, robust elevations of plasma amyloid-␤ (A␤) have been reported in dogs and humans after administration of subefficacious doses. The present study sought to further evaluate A␤ responses to LY-450139 in the guinea pig, a nontransgenic model that has an A␤ sequence identical to that of human. Male guinea pigs were treated with LY-450139 (0.2-60 mg/kg), and brain, cerebrospinal fluid, and plasma A␤ levels were characterized at 1, 3, 6, 9, and 14 h postdose. Low doses significantly elevated plasma A␤ levels at early time points, with return to baseline within hours. Higher doses inhibited A␤ levels in all compartments at early time points, but elevated plasma A␤ levels at later time points. To determine whether this phenomenon occurs under steadystate drug exposure, guinea pigs were implanted with subcutaneous minipumps delivering LY-450139 (0.3-30 mg/kg/day) for 5 days. Plasma A␤ was significantly inhibited at 10 -30 mg/kg/day, but significantly elevated at 1 mg/kg/day. To further understand the mechanism of A␤ elevation by LY-450139, H4 cells overexpressing the Swedish mutant of amyloid-precursor protein and a mouse embryonic stem cell-derived neuronal cell line were studied. In both cellular models, elevated levels of secreted A␤ were observed at subefficacious concentrations, whereas dose-responsive inhibition was observed at higher concentrations. These results suggest that LY-450139 modulates the ␥-secretase complex, eliciting A␤ lowering at high concentrations but A␤ elevation at low concentrations. The pathological accumulation of amyloid-␤ peptide into dense core plaques in the brains of Alzheimer's disease patients is the ultimate target of multiple disease-modifying drug discovery efforts. One strategy that has entered the clinic is the use of a ␥-secretase inhibitor to reduce central A␤ production. Preclinically, multiple ␥-secretase inhibitors have demonstrated central and peripheral A␤-lowering activity in transgenic mouse lines overexpressing human mutant amyloid precursor protein The ability of plasma and CSF A␤ to track pharmacological changes in brain A␤ provides a useful method for tracking the efficacy of ␥-secretase inhibitors in the clinic. Because each compartment may have varying degrees of drug exposure and different clearance rates for both drug and A␤, it is important to understand the dynamics of A␤ in each compartment. Dose-response and time course studies with ␥-secretase inhibitors in transgenic mice have revealed difArticle, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.106.110700. ABBREVIATIONS

SynGAP: a Synaptic RasGAP that Associates with the PSD-95/SAP90 Protein Family

AbstractThe PSD-95/SAP90 family of proteins has recently been implicated in the organization of synaptic structure. Here, we describe the isolation of a novel Ras-GTPase activating protein, SynGAP, that interacts with the PDZ domains of PSD-95 and SAP102 in vitro and in vivo. SynGAP is selectively expressed in brain and is highly enriched at excitatory synapses, where it is present in a large macromolecular complex with PSD-95 and the NMDA receptor. SynGAP stimulates the GTPase activity of Ras, suggesting that it negatively regulates Ras activity at excitatory synapses. Ras signaling at the postsynaptic membrane may be involved in the modulation of excitatory synaptic transmission by NMDA receptors and neurotrophins. These results indicate that SynGAP may play an important role in the modulation of synaptic plasticity

Treatment with 24 hour istaroxime infusion in patients hospitalised for acute heart failure: a randomised, placebo-controlled trial

Istaroxime is a first-in-class agent which acts through inhibition of the sarcolemmal Na+ /K+ pump and activation of the SERCA2a pump. This study assessed the effects of a 24 h infusion of istaroxime in patients hospitalised for acute heart failure (AHF)

Treatment with 24 hour istaroxime infusion in patients hospitalised for acute heart failure: a randomised, placebo‐controlled trial

Istaroxime is a first-in-class agent which acts through inhibition of the sarcolemmal Na+ /K+ pump and activation of the SERCA2a pump. This study assessed the effects of a 24 h infusion of istaroxime in patients hospitalised for acute heart failure (AHF)

Concentration-dependent modulation of Aβ in vivo and in vitro using the γ-secretase inhibitor, LY-450139 Running Title: γ-secretase inhibitor modulates Aβ production Corresponding Author

Abstract LY-450139 is a γ-secretase inhibitor shown to have efficacy in multiple cellular and animal models. Paradoxically, robust elevations of plasma Aβ have been reported in dogs and humans following administration of sub-efficacious doses. The present study sought to further evaluate Aβ responses to LY-450139 in the guinea pig, a non-transgenic model that has an Aβ sequence identical to that of human. Male guinea pigs were treated with LY-450139 (0.2-60 mg/kg), and brain, CSF, and plasma Aβ levels were characterized at 1, 3, 6, 9, and 14h post-dose. Low doses significantly elevated plasma Aβ levels at early time points, with return to baseline within hours. Higher doses inhibited Aβ levels in all compartments at early time points, but elevated plasma Aβ levels at later time points. To determine whether this phenomenon occurs under steadystate drug exposure, guinea pigs were implanted with subcutaneous minipumps delivering LY-450139 (0.3-30 mg/kg/day) for 5 days. Plasma Aβ was significantly inhibited at 10-30 mg/kg/day, but significantly elevated at 1 mg/kg/day. To further understand the mechanism of Aβ elevation by LY-450139, H4 cells over-expressing APP Sw and a mouse embryonic stem cell-derived neuronal cell line were studied. In both cellular models, elevated levels of secreted Aβ was observed at sub-efficacious concentrations, while dose-responsive inhibition was observed at higher concentrations. These results suggest that LY-450139 modulates the γ-secretase complex, eliciting Aβ lowering at high concentrations, but Aβ elevation at low concentrations. JPET # 110700 (4