Second Generation γ-Secretase Modulators Exhibit Different Modulation of Notch β and Aβ Production

The gamma-secretase complex is an appealing drug target when the therapeutic strategy is to alter amyloid-beta peptide (A beta) aggregation in Alzheimer disease. gamma-Secretase is directly involved in A beta formation and determines the pathogenic potential of A beta by generating the aggregation-prone A beta 42 peptide. Because gamma-secretase mediates cleavage of many substrates involved in cell signaling, such as the Notch receptor, it is crucial to sustain these pathways while altering the A beta secretion. A way of avoiding interference with the physiological function of gamma-secretase is to use gamma-secretase modulators (GSMs) instead of inhibitors of the enzyme. GSMs modify the A beta formation from producing the amyloid-prone A beta 42 variant to shorter and less amyloidogenic A beta species. The modes of action of GSMs are not fully understood, and even though the pharmacology of GSMs has been thoroughly studied regarding A beta generation, knowledge is lacking about their effects on other substrates, such as Notch. Here, using immunoprecipitation followed by MALDI-TOF MS analysis, we found that two novel, second generation GSMs modulate both Notch beta and A beta production. Moreover, by correlating S3-specific Val-1744 cleavage of Notch intracellular domain (Notch intracellular domain) to total Notch intracellular domain levels using immunocytochemistry, we also demonstrated that Notch intracellular domain is not modulated by the compounds. Interestingly, two well characterized, nonsteroidal anti-inflammatory drugs (nonsteroidal anti-inflammatory drug), R-flurbiprofen and sulindac sulfide, affect only A beta and not Notch beta formation, indicating that second generation GSMs and nonsteroidal anti-inflammatory drug-based GSMs have different modes of action regarding Notch processing.