The Amyloid-β Rise and γ-Secretase Inhibitor Potency Depend on the Level of Substrate Expression

153

124

The presenilin containing ␥-secretase complex is responsible for the regulated intramembraneous proteolysis of the amyloid precursor protein (APP), the Notch receptor, and a multitude of other substrates. ␥-Secretase catalyzes the final step in the generation of A␤ 40 and A␤ 42 peptides from APP. Amyloid ␤-peptides (A␤ peptides) aggregate to form neurotoxic oligomers, senile plaques, and congophilic angiopathy, some of the cardinal pathologies associated with Alzheimer's disease. Although inhibition of this protease acting on APP may result in potentially therapeutic reductions of neurotoxic A␤ peptides, nonselective inhibition of the enzyme may cause severe adverse events as a result of impaired Notch receptor processing. Here, we report the preclinical pharmacological profile of GSI-953 (begacestat), a novel thiophene sulfonamide ␥-secretase inhibitor (GSI) that selectively inhibits cleavage of APP over Notch. This GSI inhibits A␤ production with low nanomolar potency in cellular and cell-free assays of ␥-secretase function, and displaces a tritiated analog of GSI-953 from enriched ␥-secretase enzyme complexes with similar potency. Cellular assays of Notch cleavage reveal that this compound is approximately 16-fold selective for the inhibition of APP cleavage. In the human APP-overexpressing Tg2576 transgenic mouse, treatment with this orally active compound results in a robust reduction in brain, plasma, and cerebral spinal fluid A␤ levels, and a reversal of contextual fear-conditioning deficits that are correlated with A␤ load. In healthy human volunteers, oral administration of a single dose of GSI-953 produces dosedependent changes in plasma A␤ levels, confirming pharmacodynamic activity of GSI-953 in humans.This research was supported by Wyeth Research. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.

Section: Discussionsupporting

confidence: 66%

Begacestat (GSI-953): A Novel, Selective Thiophene Sulfonamide Inhibitor of Amyloid Precursor Protein γ-Secretase for the Treatment of Alzheimer's Disease

Martone

Zhou²,

Atchison³

et al. 2009

153

124

“…PF-3084014 similarly exhibited an elevation of A␤1-43 at doses that reduced levels of multiple other A␤ peptides, a finding previously reported in guinea pig brain after LY-411575 treatment (Du et al, 2007). DAPT, LY-411575, and LY-450139 all have been shown to preferentially inhibit A␤1-40 over A␤1-42 and elevate A␤ levels at low concentrations (Lanz et al, 2003(Lanz et al, , 2004Burton et al, 2008). PF-3084014 shares at least the former feature of these ␥-secretase inhibitors.…”

Section: Pharmacodynamics and Pharmacokinetics Of Pf-3084014 275mentioning

confidence: 53%

“…Modest increases in plasma A␤ were observed at low doses of PF-3084014, but they failed to achieve statistical significance, and the magnitude of potentiation paled in comparison with other ␥-secretase inhibitors Burton et al, 2008). As doses escalated, a period of A␤ inhibition would be expected to be followed by plasma A␤ potentiation (when drug levels are waning), as has also observed in human subjects (Siemers et al, 2005(Siemers et al, , 2007Martone et al, 2009).…”

Section: Pharmacodynamics and Pharmacokinetics Of Pf-3084014 275mentioning

confidence: 78%

“…These in vitro assays demonstrating effects on A␤ production and Notch cleavage will be presented, followed by in vivo pharmacokinetics and pharmacodynamics in guinea pigs and Tg2576 mice. As treatment with various ␥-secretase inhibitors have produced paradoxical increases in plasma A␤ at low concentrations in both preclinical species and humans (Lanz et al, 2004Siemers et al, 2005Siemers et al, , 2007Martone et al, 2009), and one compound has demonstrated elevations in rat brain A␤ (Burton et al, 2008), in vivo studies in guinea pigs were carefully designed to enable observation of all compartments in the presence of a wide range of drug concentrations both acutely and at steady state. The potentiation phenomenon is much more limited with PF-3084014, although the compound does show some forms of ␥-secretase modulation as revealed in the A␤ peptide profiles in multiple preclinical models.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Pharmacodynamics and Pharmacokinetics of the γ-Secretase Inhibitor PF-3084014

Lanz

Wood²,

Richter³

et al. 2010

PF-3084014 [(S)-2-((S)-5,7-difluoro-1,2,3,4-tetrahydronaphthalen-3-ylamino)-N-(1-(2-methyl-1-(neopentylamino)propan-2-yl)-1H-imidazol-4-yl)pentanamide] is a novel ␥-secretase inhibitor that reduces amyloid-␤ (A␤) production with an in vitro IC 50 of 1.2 nM (whole-cell assay) to 6.2 nM (cell-free assay). This compound inhibits Notch-related T-and B-cell maturation in an in vitro thymocyte assay with an EC 50 of 2.1 M. A single acute dose showed dose-dependent reduction in brain, cerebrospinal fluid (CSF), and plasma A␤ in Tg2576 mice as measured by enzyme-linked immunosorbent assay and immunoprecipitation (IP)/mass spectrometry (MS). Guinea pigs were dosed with PF-3084014 for 5 days via osmotic minipump at 0.03 to 3 mg/kg/day and exhibited dose-dependent reduction in brain, CSF, and plasma A␤. To further characterize A␤ dynamics in brain, CSF, and plasma in relation to drug exposure and Notchrelated toxicities, guinea pigs were dosed with 0.03 to 10 mg/kg PF-3084014, and tissues were collected at regular intervals from 0.75 to 30 h after dose. Brain, CSF, and plasma all exhibited dose-dependent reductions in A␤, and the magnitude and duration of A␤ lowering exceeded those of the reductions in B-cell endpoints. Other ␥-secretase inhibitors have shown high potency at elevating A␤ in the conditioned media of whole cells and the plasma of multiple animal models and humans. Such potentiation was not observed with PF-3084014. IP/MS analysis, however, revealed dose-dependent increases in A␤11-40 and A␤1-43 at doses that potently inhibited A␤1-40 and A␤1-42. PF-3084014, like previously described ␥-secretase inhibitors, preferentially reduced A␤1-40 relative to A␤1-42. Potency at A␤ relative to Notch-related endpoints in vitro and in vivo suggests that a therapeutic index can be achieved with this compound.Amyloid-␤ (A␤) peptide is the primary component of senile plaques (Glenner and Wong, 1984) and is the protein product of a gene [amyloid precursor protein (APP)] whose mutation can result in early-onset Alzheimer's disease. The intersection of this genetic and pathologic evidence has led to a strong focus on A␤ as a major culprit in the etiology of Alzheimer's disease. A number of compounds have advanced to the clinic with the goal of either reducing production of this peptide (e.g., ␤-or ␥-secretase inhibitors) or increasing its clearance from the brain (e.g., A␤ vaccines or monoclonal antibodies). Of these approaches, ␥-secretase has yielded the greatest diversity of chemical tools that enable the study of A␤ pharmacodynamics in animal models and humans. Bioavailable small-molecule inhibitors of ␥-secretase from various chemical series have been shown to rapidly reduce A␤ levels in brain, cerebrospinal fluid (CSF), and plasma from wild-type mice (Yohrling et al., 2007), rats (Best et al., 2005;El Mouedden et al., 2006;Lanz and Schachter, 2006), guinea pigs (Anderson et al., 2005;, and multiple muArticle, publication date, and citation information can be found at

“…First, in Tg2576 mice and neuronal cultures containing the Swedish mutation, the ␤-cleavage kinetics and compartmentalization of APP processing are probably different from those in the background systems (Hook et al, 2008;Yamakawa et al, 2010). Potency shift of ␤-secretase inhibitors and GSIs in the Tg2576 and background systems have been observed (Burton et al, 2008;Yamakawa et al, 2010). These observations imply that the pharmacokinetic(PK)/pharmacodynamic (PD) relationship of a therapeutic agent obtained from experiments using Tg2576 mice may not translate to nontransgenic animals and humans.…”

Section: Introductionmentioning

confidence: 94%

Quantitative Pharmacokinetic/Pharmacodynamic Analyses Suggest That the 129/SVE Mouse Is a Suitable Preclinical Pharmacology Model for Identifying Small-Molecule γ-Secretase Inhibitors

Lu¹,

Zhang²,

Nolan³

et al. 2011

Alzheimer's disease (AD) poses a serious public health threat to the United States. Disease-modifying drugs slowing AD progression are in urgent need, but they are still unavailable. According to the amyloid cascade hypothesis, inhibition of ␤-or ␥-secretase, key enzymes for the production of amyloid ␤ (A␤), may be viable mechanisms for the treatment of AD. For the discovery of ␥-secretase inhibitors (GSIs), the APP-overexpressing Tg2576 mouse has been the preclinical model of choice, in part because of the ease of detection of A␤ species in its brain, plasma, and cerebrospinal fluid (CSF). Some biological observations and practical considerations, however, argue against the use of the Tg2576 mouse. We reasoned that an animal model would be suitable for GSI discovery if the pharmacokinetic (PK)/pharmacodynamic (PD) relationship of a compound for A␤ lowering in this model is predictive of that in human. In this study, we assessed whether the background 129/SVE strain is a suitable preclinical pharmacology model for identifying new GSIs by evaluating the translatability of the intrinsic PK/PD relationships for brain and CSF A␤ across the Tg2576 and 129/SVE mouse and human. Using semimechanistically based PK/PD modeling, our analyses indicated that the intrinsic PK/PD relationship for brain A␤x-42 and CSF A␤x-40 in the 129/SVE mouse is indicative of that for human CSF A␤. This result, in conjunction with practical considerations, strongly suggests that the 129/SVE mouse is a suitable model for GSI discovery. Concurrently, the necessity and utilities of PK/PD modeling for rational interpretation of A␤ data are established.