Selective Allosteric Inhibition of Phosphodiesterase 4B (PDE4B) as a Potential Anti-seizure Treatment for Dravet Syndrome
Abstract number :
2.349
Submission category :
7. Anti-seizure Medications / 7A. Animal Studies
Year :
2024
Submission ID :
1213
Source :
www.aesnet.org
Presentation date :
12/8/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Cassandra Kinch, PhD – Stream Neuroscience
Jong Rho, MD – University of California San Diego
Mitchell Kessler, MSc – University of Calgary
Kingsley Ibhazehiebo, PhD – Path Therapeutics
Cezar Gavrilovici, PhD – University of Calgary
Deepika Dogra, PhD – University of Calgary
Deborah Kurrasch, PhD – Path Therapeutics
Rationale: A growing body of evidence points to neurometabolic derangements as a source for seizure genesis1. phosphodiesterase 4 (PDE4) inhibition causes an accumulation of cyclic adenosine monophosphatase (cAMP), which results in seizure termination2 likely due to improved metabolism within neurons and neural support cells. Allosteric inhibition of PDE4 isoforms have shown improved tolerability compared to pan-PDE4 inhibitors.3 Here, we report findings from our lead discovery program supporting allosteric PDE4B inhibition as an anti-seizure treatment for Dravet Syndrome.
Methods: Zebrafish (scn1lab-/-), mouse (Scn1a+/-), and patient-derived brain organoid (SCN1A-/-) Dravet models were used to validate PDE4 as an anti-seizure target using the MitoREAD machine-learning derived screening platform. PT-3900 series, allosteric PDE4B inhibitors, were synthesized de novo to target a new allosteric binding pocket within the PDE4 active site. In vitro binding assays evaluated inhibitory potency and selectivity at PDE4B (Viva Biotech, Shanghai, China). In vivo assays included hyperthermia-induction and video-EEG recordings of spontaneous seizures in mice exposed to PDE4 inhibitors or placebo. Brain organoids grown from induced Pluripotent Stem Cells (iPSCs) derived from Dravet individuals were cultured in PDE4 inhibitors or placebo for 6 hours and evaluated using bioenergetic and hyperexcitability assays.
Results: Knockdown of pde4 isoforms in scn1lab-/- zebrafish decreased EEG hyperexcitability. Using in vitro binding assays, PT-3902 inhibited PDE4B with an IC50 of 27 nM, and shows 200-fold increased selectivity for PDE4B over PDE4D, with confirmed allostericity. Exposure to a proof-of-concept (POC) molecule results in seizure freedom in all treated Scn1a+/- mice (n=20-28), and a marked reduction in spike amplitude and frequency in video-EEG (n=8-10), compared to placebo-treated models (n=8, ~4-8 seizures/day). Additionally, mice exposed to PDE4 POC compounds live beyond postnatal day (P) 45, whereas control mice die by P30. Dravet brain organoids (n=10) exposed to PDE4 POC inhibitors showed restored bioenergetic profiles with reduced hyperexcitability vs placebo, with increased inhibitory and decreased excitatory signalling.
Conclusions: These findings indicate selective allosteric PDE4B inhibition as a potential anti-seizure treatment for Dravet Syndrome, with improved tolerability over pan-PDE4 inhibitors.
Funding: Brain Canada (PSG 2016), Dravet Canada, Alberta Children's Hospital Research Institute, Hotchkiss Brain Institute
Anti-seizure Medications