Stretching the structural envelope of imatinib to reduce ß-amyloid production by modulating both ß- and γ-secretase cleavages of APP.

We previously showed that the anticancer drug imatinib mesylate (IMT, trade name: Gleevec) and a chemically distinct compound, DV2-103 (a kinase-inactive derivative of the potent Abl and Src kinase inhibitor, PD173955) lower Aß levels at low micromolar concentrations primarily through a lysosome-dependent mechanism that renders APP less susceptible to proteolysis by BACE1 without directly inhibiting BACE1 enzymatic activity, or broadly inhibiting the processing of other BACE1 substrates. Additionally, IMT indirectly inhibits γ-secretase and stimulates autophagy, and thus may decrease Aß levels through multiple pathways. In two recent studies we demonstrated similar effects on APP metabolism caused by derivatives of IMT and DV2-103. In the present study, we synthesized and tested radically altered IMT isomers (IMTi's) that possess medium structural similarity to IMT. Independent of structural similarity, these isomers manifest widely differing potencies in altering APP metabolism. These will enable us to choose the most potent isomers for further derivatization.

Reduced Kv3.1 Activity in Dentate Gyrus Parvalbumin Cells Induces Vulnerability to Depression.

BACKGROUND: Parvalbumin (PV)-expressing interneurons are important for cognitive and emotional behaviors. These neurons express high levels of p11, a protein associated with depression and action of antidepressants. METHODS: We characterized the behavioral response to subthreshold stress in mice with conditional deletion of p11 in PV cells. Using chemogenetics, viral-mediated gene delivery, and a specific ion channel agonist, we studied the role of dentate gyrus PV cells in regulating anxiety-like behavior and resilience to stress. We used electrophysiology, imaging, and biochemical studies in mice and cells to elucidate the function and mechanism of p11 in dentate gyrus PV cells. RESULTS: p11 regulates the subcellular localization and cellular level of the potassium channel Kv3.1 in cells. Deletion of p11 from PV cells resulted in reduced hippocampal level of Kv3.1, attenuated capacity of high-frequency firing in dentate gyrus PV cells, and altered short-term plasticity at synapses on granule cells, as well as anxiety-like behavior and a pattern separation deficit. Chemogenetic inhibition or deletion of p11 in these cells induced vulnerability to depressive behavior, whereas upregulation of Kv3.1 in dentate gyrus PV cells or acute activation of Kv3.1 using a specific agonist induced resilience to depression. CONCLUSIONS: The activity of dentate gyrus PV cells plays a major role in the behavioral response to novelty and stress. Activation of the Kv3.1 channel in dentate gyrus PV cells may represent a target for the development of cell-type specific, fast-acting antidepressants.

Brain Permeable Tafamidis Amide Analogs for Stabilizing TTR and Reducing APP Cleavage.

Tafamidis, 1, a potent transthyretin kinetic stabilizer, weakly inhibits the γ-secretase enzyme in vitro. We have synthesized four amide derivatives of 1. These compounds reduce production of the Aß peptide in N2a695 cells but do not inhibit the γ-secretase enzyme in cell-free assays. By performing fluorescence correlation spectroscopy, we have shown that TTR inhibits Aß oligomerization and that addition of tafamidis or its amide derivative does not affect TTR's ability to inhibit Aß oligomerization. The piperazine amide derivative of tafamidis (1a) efficiently penetrates and accumulates in mouse brain and undergoes proteolysis under physiological conditions in mice to produce tafamidis.

Development of Gleevec Analogues for Reducing Production of ß-Amyloid Peptides through Shifting ß-Cleavage of Amyloid Precursor Proteins.

Imatinib mesylate, 1a, inhibits production of ß-amyloid (Aß) peptides both in cells and in animal models. It reduces both the ß-secretase and γ-secretase cleavages of the amyloid precursor protein (APP) and mediates a synergistic effect, when combined with a ß-secretase inhibitor, BACE IV. Toward developing more potent brain-permeable leads, we have synthesized and evaluated over 75 1a-analogues. Several compounds, including 2a-b and 3a-c, inhibited production of Aß peptides with improved activity in cells. These compounds affected ß-secretase cleavage of APP similarly to 1a. Compound 2a significantly reduced production of the Aß42 peptide, when administered (100 mg/kg, twice daily by oral gavage) to 5 months old female mice for 5 days. A combination of compound 2a with BACE IV also reduced Aß levels in cells, more than the additive effect of the two compounds. These results open a new avenue for developing treatments for Alzheimer's disease using 1a-analogues.

Development of Kinase Inactive PD173955 Analogues for Reducing Production of Aß Peptides.

Compound 3a, DV2-103, is a kinase inactive analogue of a potent Abl1/Src kinase inhibitor, PD173955, 2. Both compounds, 2 and 3a, are known to reduce production of beta amyloid (Aß) peptide in cells and animal models. We have now prepared and evaluated a series of PD-173955 analogues, several of which reduced Aß production potently. This occurs in cells expressing human full-length amyloid precursor protein (APP) and not in cells expressing APP ß-C terminal fragment (APP-C99), suggesting that the kinase inactive analogues strongly affect ß-secretase (BACE1) cleavage of APP, similarly to Gleevec. A combination of the kinase inactive analogues of PD173955 with a BACE1 inhibitor (BACEi), namely, BACE IV, strongly reduced Aß levels in cells, as noted previously with Gleevec and analogues. Several potent compounds also penetrated and accumulated in mouse brain in high nanomolar to low micromolar concentration.