Use of AD Informer Set compounds to explore validity of novel targets in Alzheimer's disease pathology

Abstract

Introduction A chemogenomic set of small molecules with annotated activities and implicated roles in Alzheimer's disease (AD) called the AD Informer Set was recently developed and made available to the AD research community: https://treatad.org/data-tools/ad-informer-set/. Methods Small subsets of AD Informer Set compounds were selected for AD‐relevant profiling. Nine compounds targeting proteins expressed by six AD‐implicated genes prioritized for study by Target Enablement to Accelerate Therapy Development for Alzheimer's Disease (TREAT‐AD) teams were selected for G‐protein coupled receptor (GPCR), amyloid beta (Aβ) and tau, and pharmacokinetic (PK) studies. Four non‐overlapping compounds were analyzed in microglial cytotoxicity and phagocytosis assays. Results The nine compounds targeting CAPN2, EPHX2, MDK, MerTK/FLT3, or SYK proteins were profiled in 46 to 47 primary GPCR binding assays. Human induced pluripotent stem cell (iPSC)‐derived neurons were treated with the same nine compounds and secretion of Aβ peptides (Aβ40 and Aβ42) as well as levels of phosphophorylated tau (p‐tau, Thr231) and total tau (t‐tau) peptides measured at two concentrations and two timepoints. Finally, CD1 mice were dosed intravenously to determine preliminary PK and/or brain‐specific penetrance values for these compounds. As a final cell‐based study, a non‐overlapping subset of four compounds was selected based on single‐concentration screening for analysis of both cytotoxicity and phagocytosis in murine and human microglia cells. Discussion We have demonstrated the utility of the AD Informer Set in the validation of novel AD hypotheses using biochemical, cellular (primary and immortalized), and in vivo studies. The selectivity for their primary targets versus essential GPCRs in the brain was established for our compounds. Statistical changes in tau, p‐tau, Aβ40, and/or Aβ42 and blood–brain barrier penetrance were observed, solidifying the utility of specific compounds for AD. Single‐concentration phagocytosis results were validated as predictive of dose–response findings. These studies established workflows, validated assays, and illuminated next steps for protein targets and compounds.

Microglial Phagocytosis/Cell Health High‐Content Assay

“…Based on the results of testing idelalisib (inhibition effect) and saracatinib (stimulation effect), we showed that microglial phagocytosis of pHrodo-myelin/membrane debris microglia, with results contributing to two papers (Potjewyd et al, 2022a(Potjewyd et al, , 2022b. Currently, the assay is being used in our AD drug discovery projects targeting the TREM2 pathway of microglia, specifically for the selection of INPP5D inhibitors and PLCG2 activators respectively.…”

“…We suggest that idelalisib and saracatinib can be used as references for the phagocytosis assay on microglia such as HMC3 cells. The assay was applied for the characterization of chemical probes targeting microglia, with results contributing to two papers (Potjewyd et al., 2022a, 2022b). Currently, the assay is being used in our AD drug discovery projects targeting the TREM2 pathway of microglia, specifically for the selection of INPP5D inhibitors and PLCG2 activators respectively.…”