There is considerable interest in identifying effective and safe drugs for
neurodegenerative disorders. Cell culture and animal model work have demonstrated that modulating gene expression through RXR-mediated pathways may mitigate or reverse
cognitive decline. However, because RXR is a dimeric partner for several
transcription factors, activating off-target transcription is a concern with RXR
ligands (rexinoids). This off-target gene modulation leads to unwanted side effects that can include low thyroid function and significant
hyperlipidemia. There is a need to develop rexinoids that have binding specificity for subsets of RXR heterodimers, to drive desired gene modulation, but that do not induce spurious effects. Herein, we describe experiments in which we analyze a series of novel and previously reported rexinoids for their ability to modulate specific gene pathways implicated in
neurodegenerative disorders employing a U87 cell culture model. We demonstrate that, compared to the FDA-approved rexinoid
bexarotene (1), several of these compounds are equally or more effective at stimulating gene expression via LXREs or Nurr1/NBREs and are superior at inducing
ApoE and/or
tyrosine hydroxylase (TH) gene and
protein expression, including analogs 8, 9, 13, 14, 20, 23, and 24, suggesting a possible therapeutic role for these compounds in Alzheimer's or
Parkinson's disease (PD). A subset of these potent RXR agonists can synergize with a presumed Nurr1
ligand and
antimalarial drug (
amodiaquine) to further enhance Nurr1/NBREs-directed transcription. This novel discovery has potential clinical implications for treatment of PD since it suggests that the combination of an RXR agonist and a Nurr1
ligand can significantly enhance RXR-Nurr1 heterodimer activity and drive enhanced therapeutic expression of the TH gene to increase endogenous synthesis of
dopamine. These data indicate that is it possible and prudent to develop novel rexinoids for testing of gene expression and side effect profiles for use in potential treatment of
neurodegenerative disorders, as individual rexinoids can have markedly different gene expression profiles but similar structures.