Selective Gamma-secretase Inhibitors Research Articles

Efficacy and safety of nirogacestat in patients with desmoid tumor and adenomatous polyposis coli (APC) mutation: Phase 3 DeFi analyses.

11558 Background: Nirogacestat (niro) is a targeted and selective gamma secretase inhibitor approved in the US for adults with progressing desmoid tumors (DT). In the phase 3 DeFi study, niro demonstrated significant improvement vs placebo (pbo) in progression-free survival (PFS: HR, 0.29 [95% CI: 0.15-0.55]; P<.001), objective response rate (ORR: 41% vs 8%; P<.001); and patient-reported outcomes (PROs) of pain, DT-specific symptom burden, physical and role functioning, and overall quality of life ( P≤.01, all). DT are driven by Wnt/β-catenin signaling pathway alterations and about 10-20% of DT are associated with mutations in the APC tumor suppressor gene, which may confer more aggressive DT behavior. Because patients with APC mutations may do worse, regardless of specific therapy, a post hoc analysis was conducted to assess effects of niro in patients with progressing DT and APC mutations. Methods: DeFi was a global, double-blind study that evaluated the efficacy, safety, and tolerability of niro in adults with progressing DT. Patients were randomized to oral niro (150 mg) or pbo twice-daily in continuous 28-day cycles. Descriptive post hoc analyses were conducted to assess effects of niro in patients with somatic and/or germline APC mutations. Results: Among 29 patients in DeFi with APC mutations (niro=13; pbo=16), 19 (66%) were female, 16 (55%) were aged ≤30 years, and 22 (76%) were refractory to prior treatment (with a median of 3 prior lines of treatment). In patients with APC mutation, PFS was improved with niro vs pbo (HR, 0.21 [95% CI: 0.05-1.00], P=.016). Confirmed ORR was 38% (5/13) for niro vs 13% (2/16) for pbo. Niro-treated patients also had greater reduction in median best percent change from baseline compared with pbo-treated patients in target tumor size (-29.5 vs +2.2), volumetric MRI (-71.0 vs +5.4), and T2 hyperintensity (-74.1 vs -21.0). Across all PROs assessed — Brief Pain Inventory, GODDESS DT Symptom Scale and DT Impact Scale, and European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 — patients treated with niro had numerically greater improvement from baseline at cycle 10 than pbo. Analyses were limited due to the small sample size. Adverse events in >50% of niro-treated patients with APC mutation were diarrhea, nausea, rash maculopapular, and fatigue; ovarian toxicity occurred in 9 of 10 of females of reproductive potential (6 resolved, 2 lost to follow-up, 1 ongoing and receiving niro). Conclusions: Improvement in PFS, ORR, tumor imaging characteristics and PROs was observed with niro compared to pbo in patients with DT harboring APC mutations. Efficacy and safety of niro in patients with APC mutations were generally consistent with findings for the overall DeFi population, suggesting that niro can provide clinically meaningful benefit to patients with progressing DT and APCmutations. Clinical trial information: NCT03785964 .

RINGSIDE phase 2/3 trial of AL102 for treatment of desmoid tumors (DT): Phase 2 results.

11515 Background: For patients with desmoid tumors (DT, aggressive fibromatosis), systemic therapy that results in tumor regression, symptom improvement and durable tolerability is needed. Gamma secretase inhibitors (GSIs) have demonstrated antitumor activity against DT. AL102 is a potent, orally available, selective GSI under investigation for treatment of DT. Methods: RINGSIDE (AL-DES-01) is a Phase 2/3 study for patients with progressing DT. In the open-label Phase 2 study (Part A), adults with progressing DT (≥10% unidimensional growth within 18 months or DT-related pain requiring non-opioid medication) were randomized to three dosing regimens: 1.2 mg QD, 2 mg intermittent BIW (2 days on 5 days off), or 4 mg intermittent BIW. Patients who complete Phase 2 roll over into an open-label extension (OLE). RINGSIDE Phase 3 (Part B) is a double-blind, placebo-controlled study evaluating the chosen dose regimen from Phase 2 (1.2 mg once daily) utilizing PFS as the primary endpoint. We report updated efficacy and safety results from RINGSIDE Phase 2. Results: Enrollment of all 42 patients into Phase 2 was completed as of March 2022. As of January 3, 2023, median time on study was 10.5 months (range 0.8 – 14.7) and 30 patients (71.4%) were still on study, 10 (23.8%) of whom rolled over to the OLE. Mean age was 39.9 years, 73.8% were women and 69% had received prior desmoid cancer therapy. The best response in the evaluable population as assessed by blinded independent central review (BICR) was partial response (PR) in 6/12 patients (50%) for 1.2 mg QD, 3/13 patients (23.1%) for 4 mg BIW, and 5/11 patients (45.5%) for 2 mg BIW. Disease control rate was 100%, 91%, and 97% in these groups, respectively. A consistent pattern of deeper, more rapid and maintained response was observed with 1.2 mg QD. Median volume change (BICR) from baseline was -51.9% for 1.2 mg QD, -9.5% for 4 mg BIW, and -15.2% for 2 mg BIW at Week 16 and -76.4%, -35.5%, and -51.2%, respectively, at Week 28. Similar patterns were observed for % changes from baseline in T2 signal intensity, suggesting reduction of tumor cellularity. Consistent with the mechanism of action of GSIs, the five most common Grade 1-2 treatment-emergent adverse events (TEAEs) were diarrhea, nausea, fatigue, alopecia, and dry skin. Grade 3 drug-related TEAEs were reported in 26.2% of patients across all tested doses. There were no Grade 4, Grade 5, or serious TEAEs related to AL102 per investigator assessment. There were no new safety signals. Conclusions: In this Phase 2 study, AL102 was safe and generally well tolerated across all tested doses. The safety profile was consistent with the GSI class of drugs. Tumor response, volume reduction and T2 signal reduction were observed earlier in the 1.2 mg QD group, with deeper and maintained treatment responses. This dose was selected for study in RINGSIDE Phase 3, which is currently enrolling in multiple countries. Clinical trial information: NCT04871282 .

Abstract CT070: Double-blind placebo-controlled trial of AL102 for treatment of progressing desmoid tumors: the RINGSIDE phase 3 study design

Abstract Background: There is an unmet need for effective systemic therapy for desmoid tumors (DT, aggressive fibromatosis) that provides durable tolerability, symptom improvement, and tumor regression. Gamma secretase inhibitors (GSIs) demonstrate antitumor activity against DT. AL102 is a potent, orally available, selective GSI under investigation as an antineoplastic agent. Methods: RINGSIDE (AL-DES-01) is a 2-part Phase 2/3 study. In the open-label Phase 2 study (Part A), adults with progressing DT (≥10% unidimensional growth within 18 months or DT-related pain requiring non-opioid medication) were randomized to three dosing regimens: 1.2 mg once daily, 2 mg intermittent BIW (2 days on 5 days off), or 4 mg intermittent BIW. RINGSIDE Phase 3 (Part B) is a double-blind, placebo-controlled study evaluating the chosen dose regimen from Phase 2 (1.2 mg once daily) in adults and adolescents (≥12 years of age) with recurrent or treatment-naïve histologically confirmed progressing DT per investigator. For eligibility, progression is defined as ≥20% measured by MRI or CT scan according to RECIST v1.1 within 12 months of the screening visit. Planned enrollment is for ≈156 subjects globally to be randomized 1:1 to either AL102 1.2 mg once daily or placebo. Randomization will be stratified according to tumor location: intra-abdominal vs. extra-abdominal (including abdominal wall). Subjects will undergo MRI or CT scans (using the same modality throughout the study) every 12 weeks to assess tumor response according to RECIST v1.1 by blinded independent central review (BICR). The primary endpoint is progression-free survival (PFS) by BICR based on RECIST v1.1. Primary and secondary endpoints are summarized in Table 1. The trial is currently enrolling. Table 1. RINGSIDE Phase 3 Study Endpoints Objectives Endpoints Primary Evaluate effects of AL102 on disease progression PFS defined as time from randomization until date of assessment of progression (assessed by BICR based on RECIST v1.1) or death by any cause Secondary Evaluate additional effects of AL102 on tumor response • ORR (CR and PR) by BICR based on RECIST v1.1 • DOR defined by time from CR or PR (by BICR based on RECIST v1.1) until first documentation of disease progression or death from any cause Evaluate effects of AL102 on quality of life • Change from baseline in quality of life as determined by: • GOunder/Desmoid Tumor Research Foundation (DTRF) DEsmoid Symptom Scale and Impact Scale (GODDESS) • Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function • EuroQol 5-Dimensional (EQ-5D-3L) questionnaire • Patient’s Global Impression of Change (PGI-C) • Change from baseline in pain assessment using Brief Pain Inventory (BPI) short form Evaluate safety and tolerability of AL102 • Frequency, duration and severity of treatment-emergent adverse events (TEAEs) and serious AEs • Time to treatment discontinuation due to TEAE BICR: blinded independent central review; CR: complete response; DOR: duration of response; ORR: objective response rate; PR: partial response; PFS: progression-free survival; RECIST: Response Evaluation Criteria in Solid Tumors Citation Format: Mrinal Gounder, Robin L. Jones, Jonathan Yovell, Gary Gordon, Bernd Kasper. Double-blind placebo-controlled trial of AL102 for treatment of progressing desmoid tumors: the RINGSIDE phase 3 study design [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT070.

1488MO Initial results of phase II/III trial of AL102 for treatment of desmoid tumors (DT)

AL102 is a potent, orally available, selective gamma secretase inhibitor (GSI) under investigation as an antineoplastic agent. GSIs have antitumor activity against DT, including AL101 (2 confirmed PRs >3.5 years and >1 year; 1 stable disease for 1 year). There remains an unmet need for effective systemic therapy in DT, associated with durable tolerability, tumor regression, and symptom improvement.

904P ACCURACY: A phase II trial of AL101, a selective gamma secretase inhibitor, in subjects with recurrent/metastatic (R/M) adenoid cystic carcinoma (ACC) harboring Notch activating mutations (Notchmut): Results of 6-mg cohort

Notch signaling plays a key role in ACC tumorigenesis. Notchmut are found in ∼20% of ACC tumors, which are aggressive with a poor prognosis (Ferrarotto 2016, Ho 2019). No therapies are approved for R/M ACC. AL101, an investigational γ-secretase inhibitor, blocks Notch signaling and inhibits tumors in ACC patient-derived xenograft models with Notchmut (AACR ‘19, Abstr 4885). AL101 has clinical activity at 4 mg once weekly (QW) with a disease control rate of 68% (15% partial response) and appears to be well tolerated (Ferrarotto ESMO ‘20, #919MO).

919MO ACCURACY a phase II trial of AL101, a selective gamma secretase inhibitor, in subjects with recurrent/metastatic (R/M) adenoid cystic carcinoma (ACC) harboring Notch activating mutations (Notchmut)

919MO ACCURACY a phase II trial of AL101, a selective gamma secretase inhibitor, in subjects with recurrent/metastatic (R/M) adenoid cystic carcinoma (ACC) harboring Notch activating mutations (Notchmut)

Decreased axonal transport rates in the Tg2576 APP transgenic mouse: improvement with the gamma‐secretase inhibitor MRK‐560 as detected by manganese‐enhanced MRI

Neuropil deposition of beta-amyloid (Aβ) peptides is believed to be a key event in the neurodegenerative process of Alzheimer's disease (AD). An early and consistent clinical finding in AD is olfactory dysfunction with associated pathology. Interestingly, transgenic amyloid precursor protein (Tg2576) mice also show early amyloid pathology in olfactory regions. Moreover, a recent study indicates that axonal transport is compromised in the olfactory system of Tg2576 mice, as measured by manganese-enhanced magnetic resonance imaging (MEMRI). Here we tested whether the putative axonal transport deficit in the Tg2576 mouse model improves in response to a selective gamma-secretase inhibitor, N-[cis-4-[(4-chlorophenyl)-sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560). Tg2576 mice or wild-type (WT) littermates were treated daily with MRK-560 (30 μmol/kg) or vehicle for 4 (acute) or 29 days (chronic). The subsequent MEMRI analysis revealed a distinct axonal transport dysfunction in the Tg2576 mice compared with its littermate controls. Interestingly, the impairment of axonal transport could be fully reversed by chronic administration of MRK-560, in line with the significantly lowered levels of both soluble and insoluble forms of Aβ found in the brain and olfactory bulbs (OBs) following treatment. However, no improvement of axonal transport was observed after acute treatment with MRK-560, where soluble but not insoluble forms of Aβ were reduced in the brain and OBs. The present results show that axonal transport is impaired in Tg2576 mice compared with WT controls, as measured by MEMRI. Chronic treatment in vivo with a gamma-secretase inhibitor, MRK-560, significantly reduces soluble and insoluble forms of Aβ, and fully reverses the axonal transport dysfunction.

450PD - A Phase IB Combination Study of RO4929097 (RO), A Gamma-Secretase Inhibitor, and Temsirolimus (TEM) in Patients (PTS) with Advanced Solid Tumors

ABSTRACT Background The notch signalling pathway has a critical role in regulating cellular differentiation, proliferation, and apoptosis. RO is a potent and selective gamma-secretase inhibitor with antitumor activity in animal models. Pre-clinical experiments indicate that the PI3K/AKT/mTOR pathway may mediate resistance to gamma secretase inhibitors, providing a rationale for combination therapy with RO and TEM. Methods A phase Ib dose-escalation study with a 3 + 3 design was conducted. Three dose levels (DLs) were planned. Objectives were to determine the recommended phase II dose (RP2D), safety, pharmacokinetics (PK) and pharmacodynamics (PD) of the combination. Eligible pts received once daily oral RO on a 3 day on/4 day off schedule every week (QW), and intravenous QW TEM. Initial doses were 10 mg RO and 25 mg TEM. Cycles were every 21 days, except for cycle 1, which was 28 days. Treatment-related dose-limiting toxicities (DLTs) were evaluated during cycle 1. Results 17 pts (data cut-off 26-Apr-2012) have been treated on three DLs. Number of pts, DLTs and schedule are shown in Table 1. Demographics: M:F 6:11; median age: 60 yrs (range 28-84); ECOG 0/1:4/13. Pts received a median of 3 cycles (range 1-12). The most common adverse events (AEs) related to the study drug combination included: fatigue (82%; G3 6%), mucositis, (71%; G3 6%), neutropenia (59%; G3 12%), anemia (59%; G3 0%), and hypertriglyceridemia (59%, G3 0%).Two DLTs (G3 rash, G3 mucositis) were observed in the same patient in DL1 prompting dose expansion. No additional DLTs were observed. Of 15 patients evaluable for response, no objective responses were observed. 11 pts (73%) had stable disease (SD) as their best response; with 3 pts (sarcoma, neuroendocrine, non-small cell lung cancer) on therapy for ≥6 cycles. Conclusions RO can be safely combined with TEM. The RP2D was established as RO at 20 mg combined with 37.5 mg of TEM. PK and circulating angiogenic factors analyses will be presented. Dose Level RO Dose (mg) TEM Dose (mg) No. of pts treated No. of pts with DLT DLT 1 † 10 25 8 1 G3 rash, G3 mucositis 2 20 25 3 0 3 ∧ 20 37.5 6 0 † 2 pts were not evaluable for DLT ∧ DL3 (RP2D) was expanded to 6 pts Disclosure All authors have declared no conflicts of interest.

Amyloid precursor protein selective gamma-secretase inhibitors for treatment of Alzheimer's disease

IntroductionInhibition of gamma-secretase presents a direct target for lowering Aβ production in the brain as a therapy for Alzheimer's disease (AD). However, gamma-secretase is known to process multiple substrates in addition to amyloid precursor protein (APP), most notably Notch, which has limited clinical development of inhibitors targeting this enzyme. It has been postulated that APP substrate selective inhibitors of gamma-secretase would be preferable to non-selective inhibitors from a safety perspective for AD therapy.MethodsIn vitro assays monitoring inhibitor potencies at APP γ-site cleavage (equivalent to Aβ40), and Notch ε-site cleavage, in conjunction with a single cell assay to simultaneously monitor selectivity for inhibition of Aβ production vs. Notch signaling were developed to discover APP selective gamma-secretase inhibitors. In vivo efficacy for acute reduction of brain Aβ was determined in the PDAPP transgene model of AD, as well as in wild-type FVB strain mice. In vivo selectivity was determined following seven days x twice per day (b.i.d.) treatment with 15 mg/kg/dose to 1,000 mg/kg/dose ELN475516, and monitoring brain Aβ reduction vs. Notch signaling endpoints in periphery.ResultsThe APP selective gamma-secretase inhibitors ELN318463 and ELN475516 reported here behave as classic gamma-secretase inhibitors, demonstrate 75- to 120-fold selectivity for inhibiting Aβ production compared with Notch signaling in cells, and displace an active site directed inhibitor at very high concentrations only in the presence of substrate. ELN318463 demonstrated discordant efficacy for reduction of brain Aβ in the PDAPP compared with wild-type FVB, not observed with ELN475516. Improved in vivo safety of ELN475516 was demonstrated in the 7d repeat dose study in wild-type mice, where a 33% reduction of brain Aβ was observed in mice terminated three hours post last dose at the lowest dose of inhibitor tested. No overt in-life or post-mortem indications of systemic toxicity, nor RNA and histological end-points indicative of toxicity attributable to inhibition of Notch signaling were observed at any dose tested.ConclusionsThe discordant in vivo activity of ELN318463 suggests that the potency of gamma-secretase inhibitors in AD transgenic mice should be corroborated in wild-type mice. The discovery of ELN475516 demonstrates that it is possible to develop APP selective gamma-secretase inhibitors with potential for treatment for AD.

Contribution of γ-secretase to calcium-mediated cell death

Presenilins are the catalytic subunit of the large gamma-secretase complex, that promotes intramembranous proteolysis of the beta-amyloid precursor protein (APP), resulting in the production of beta-amyloid (A beta). Mutant presenilin causes early-onset familial Alzheimer's disease (FAD), is related to abnormal Ca(2+) signaling, and render cells vulnerable to cell death. In the present study, we demonstrated that Ca(2+)-mediated cell death is functionally associated with gamma-secretase activity. We found that gamma-secretase activity was elevated during Ca(2+)-mediated cell death. Using selective gamma-secretase inhibitors, we examined the role of gamma-secretase in cell death triggered by increased intracellular Ca(2+). Indeed, treatment with the selective gamma-secretase inhibitors, compound E, DAPT, or L-685.458 significantly decreased Ca(2+)-triggered cell death with that of the controls, but did not affect staurosporin or tunicamycin-mediated cell death. These results implicate the role of gamma-secretase activity in Ca(2+)-mediated cell death.

P3-101: GSI-953, a potent and selective gamma-secretase inhibitor, modulates Abeta peptides in mice and humans: Translating the PK/PD biomarker relationships in different biological compartments between rodent and human

P3-101: GSI-953, a potent and selective gamma-secretase inhibitor, modulates Abeta peptides in mice and humans: Translating the PK/PD biomarker relationships in different biological compartments between rodent and human

P4-366: GSI-953, a potent and selective gamma-secretase inhibitor: Modulation of beta-amyloid peptides and plasma and cerebrospinal fluid pharmacokinetic/pharmacodynamic relationships in humans

P4-366: GSI-953, a potent and selective gamma-secretase inhibitor: Modulation of beta-amyloid peptides and plasma and cerebrospinal fluid pharmacokinetic/pharmacodynamic relationships in humans

Contribution of Presenilin Transmembrane Domains 6 and 7 to a Water-containing Cavity in the γ-Secretase Complex

Gamma-secretase is a multiprotein complex responsible for the intramembranous cleavage of the amyloid precursor protein and other type I transmembrane proteins. Mutations in Presenilin, the catalytic core of this complex, cause Alzheimer disease. Little is known about the structure of the protein and even less about the catalytic mechanism, which involves proteolytic cleavage in the hydrophobic environment of the cell membrane. It is basically unclear how water, needed to perform hydrolysis, is provided to this reaction. Presenilin transmembrane domains 6 and 7 seem critical in this regard, as each bears a critical aspartate contributing to catalytic activity. Current models imply that both aspartyl groups should closely oppose each other and have access to water. This is, however, still to be experimentally verified. Here, we have performed cysteine-scanning mutagenesis of both domains and have demonstrated that several of the introduced residues are exposed to water, providing experimental evidence for the existence of a water-filled cavity in the catalytic core of Presenilin. In addition, we have demonstrated that the two aspartates reside within this cavity and are opposed to each other in the native complex. We have also identified the conserved tyrosine 389 as a critical partner in the catalytic mechanism. Several additional amino acid substitutions affect differentially the processing of gamma-secretase substrates, implying that they contribute to enzyme specificity. Our data suggest the possibility that more selective gamma-secretase inhibitors could be designed.

Characterization of the reconstituted gamma-secretase complex from Sf9 cells co-expressing presenilin 1, nicastrin [correction of nacastrin], aph-1a, and pen-2.

Gamma-secretase catalyzes the proteolytic processing of a number of integral membrane proteins, including amyloid precursor protein (APP) and Notch. The native gamma-secretase is a heterogeneous population of large membrane protein complexes containing presenilin 1 (PS1) or presenilin 2 (PS2), aph-1a or aph-1b, nicastrin, and pen-2. Here we report the reconstitution of a gamma-secretase complex in Sf9 cells by co-infection with baculoviruses carrying the PS1, nicastrin, pen-2, and aph-1a genes. The reconstituted enzyme processes C99 and the Notch-like substrate N160 and displays the characteristic features of gamma-secretase in terms of sensitivity to a gamma-secretase inhibitor, upregulation of Abeta42 production by a familial Alzheimer's disease (FAD) mutation in the APP gene, and downregulation of Notch processing by PS1 FAD mutations. However, the ratio of Abeta42:Abeta40 production by the reconstituted gamma-secretase is significantly higher than that of the native enzyme from 293 cells. Unlike in mammalian cells where PS1 FAD mutations cause an increase in Abeta42 production, PS1 FAD missense mutations in the reconstitution system alter the cleavage sites in the C99 substrate without changing the Abeta42:Abeta40 ratio. In addition, PS1DeltaE9 is a loss-of-function mutation in both C99 and N160 processing. Reconstitution of gamma-secretase provides a homogeneous system for studying the individual gamma-secretase complexes and their roles in Abeta production, Notch processing and AD pathogenesis. These studies may provide important insight into the development of a new generation of selective gamma-secretase inhibitors with an improved side effect profile.

Presenilins and γ-Secretase Inhibitors Affect Intracellular Trafficking and Cell Surface Localization of the γ-Secretase Complex Components

The intramembranous cleavage of Alzheimer beta-amyloid precursor protein and the signaling receptor Notch is mediated by the presenilin (PS, PS1/PS2)-gamma-secretase complex, the components of which also include nicastrin, APH-1, and PEN-2. In addition to its essential role in gamma-secretase activity, we and others have reported that PS1 plays a role in intracellular trafficking of select membrane proteins including nicastrin. Here we examined the fate of PEN-2 in the absence of PS expression or gamma-secretase activity. We found that PEN-2 is retained in the endoplasmic reticulum and has a much shorter half-life in PS-deficient cells than in wild type cells, suggesting that PSs are required for maintaining the stability and proper subcellular trafficking of PEN-2. However, the function of PS in PEN-2 trafficking is distinct from its contribution to gamma-secretase activity because inhibition of gamma-secretase activity by gamma-secretase inhibitors did not affect the PEN-2 level or its egress from the endoplasmic reticulum. Instead, membrane-permeable gamma-secretase inhibitors, but not a membrane-impermeable derivative, markedly increased the cell surface levels of PS1 and PEN-2 without affecting that of nicastrin. In support of its role in PEN-2 trafficking, PS1 was also required for the gamma-secretase inhibitor-induced plasma membrane accumulation of PEN-2. We further showed that gamma-secretase inhibitors specifically accelerated the Golgi to the cell surface transport of PS1 and PEN-2. Taken together, we demonstrate an essential role for PSs in intracellular trafficking of the gamma-secretase components, and that selective gamma-secretase inhibitors differentially affect the trafficking of the gamma-secretase components, which may contribute to an inactivation of gamma-secretase.

The inhibition of gamma-secretase as a therapeutic approach to Alzheimer's disease.

Alzheimer's disease is a dementing neurodegenerative disorder for which there is no effective treatment at present. Genetic and biological studies provide evidence that the production and deposition of amyloid-beta peptides (Abeta contribute to the etiology of Alzheimer's disease. gamma-Secretase is the pivotal enzyme in generating the C terminus of Abeta which determines its aggregability and speed of deposition. Drugs that regulate the production of Abeta by inhibiting gamma-secretase activity could provide an effective therapy for Alzheimer's disease, although recent studies suggest that gamma-secretase plays important roles in cellular signaling. This review focuses on studies of the gamma-secretase biology and provides the direction for developing effective and selective gamma-secretase inhibitors as drugs for the treatment of Alzheimer's disease.

Presenilin-dependent “γ-Secretase” Processing of Deleted in Colorectal Cancer (DCC)

The presenilin-gamma-secretase complex plays a critical role in mediating intramembranous proteolysis of several type I membrane proteins, including beta-amyloid precursor protein (APP) and Notch. We now show that deleted in colorectal cancer (DCC) is subject to proteolysis within the ectodomain segment both in cultured cells and in vivo and that the residual membrane-tethered DCC "stub" is subsequently processed by gamma-secretase to generate a derivative termed DCC-intracellular domain (ICD). The production of DCC-ICD is inhibited by selective gamma-secretase inhibitors, and by the expression of the dominant negative PS1 D385A variant. Moreover, the membrane-tethered DCC "stubs" accumulate to high levels in PS1-deficient embryos. We also demonstrate that expression of a DCC-Gal4 chimera is capable of activating transcription in a luciferase-based reporter assay and this activity is dependent on gamma-secretase activity. Our findings offer the proposal that DCC performs dual roles both as a cell surface receptor that modulates intracellular signaling pathways and as a transcriptional coactivator that relies on gamma-secretase-dependent production and nuclear translocation of the cytoplasmic domain.

Presenilin-1 and -2 Are Molecular Targets for γ-Secretase Inhibitors

Presenilins are integral membrane protein involved in the production of amyloid beta-protein. Mutations of the presenilin-1 and -2 gene are associated with familial Alzheimer's disease and are thought to alter gamma-secretase cleavage of the beta-amyloid precursor protein, leading to increased production of longer and more amyloidogenic forms of A beta, the 4-kDa beta-peptide. Here, we show that radiolabeled gamma-secretase inhibitors bind to mammalian cell membranes, and a benzophenone analog specifically photocross-links three major membrane polypeptides. A positive correlation is observed among these compounds for inhibition of cellular A beta formation, inhibition of membrane binding and cross-linking. Immunological techniques establish N- and C-terminal fragments of presenilin-1 as specifically cross-linked polypeptides. Furthermore, binding of gamma-secretase inhibitors to embryonic membranes derived from presenilin-1 knockout embryos is reduced in a gene dose-dependent manner. In addition, C-terminal fragments of presenilin-2 are specifically cross-linked. Taken together, these results indicate that potent and selective gamma-secretase inhibitors block A beta formation by binding to presenilin-1 and -2.