In Vitro: LDN-57444 is a reversible, competitive inhibitor of UCH-L1, with an IC50 of 0.88 μM, and also suppresses UCH-L3 activity, with an IC50 of 25 μM. LDN-57444 (LDN, 5 μM for 1 hr) inhibits 70% of Uch activity in hippocampal slices of the mouse brain. LDN-57444 (5 μM for 2 hr) does not reduce potentiation further in APP/PS1 slices or in wt slices exposed to 200 nM Aβ. LDN-57444 (25-100 μM) inhibits ubiquitin-proteasome activity dose-dependently in SK-N-SH cells. LDN-57444 (50 μM) also induces apoptotic cell death, causes the endoplasmic reticulum stress and results in expression of spliced XBP-1(XBP-1s, 48KD) in SK-N-SH cells.
In Vivo: LDN-57444 (0.4 mg/kg, i.p.) blocks the beneficial effect of V-Uch-L1, and worsens contextual conditioning performance as the mice are exposed to the context at 1, 7, 14, and 21 days after training.