Development of proneurogenic, neuroprotective small molecules

Abstract

Degeneration of the hippocampus is associated with Alzheimer's disease and occurs very early in the progression of the disease. Current options for treating the cognitive symptoms associated with Alzheimer's are inadequate, giving urgency to the search for novel therapeutic strategies. Pharmacologic agents that safely enhance hippocampal neurogenesis may provide new therapeutic approaches. We discovered the first synthetic molecule, named P7C3, which protects newborn neurons from apoptotic cell death, and thus promotes neurogenesis in mice and rats in the subgranular zone of the hippocampal dentate gyrus, the site of normal neurogenesis in adult mammals. We describe the results of a medicinal chemistry campaign to optimize the potency, toxicity profile, and stability of P7C3. Systematic variation of nearly every position of the lead compound revealed elements conducive toward increases in activity and regions subject to modification. We have discovered compounds that are orally available, nontoxic, stable in mice, rats, and cell culture, and capable of penetrating the blood-brain barrier. The most potent compounds are active at nanomolar concentrations. Finally, we have identified derivatives that may facilitate mode-of-action studies through affinity chromatography or photo-cross-linking.

Fig 1

In vivo screen for pro-neurogenic compounds. Drugs were infused directly into the brain of ive mice over 7 days. Subsequent sectioning and immunohisochemical staining revealed newly formed neurons (black cells on right section).

Fig 2. Analysis of commercial analogs

In vivo analysis of commercially available analogs of P7C3. Data are expressed as mean ± SEM, 4 mice/compound. Compounds were infused ICV as a 10 μM solution introduced at a constant rate (12 μL/day) over 7 days.

Fig 3. Analysis of synthetic analogs

In vivo analysis of synthetic analogs of P7C3. Data are expressed as mean ± SEM, 4 mice/compound except compound 56 (1 mouse). Compounds were infused ICV as a 10 μM solution introduced at a constant rate (12 μL/day) over 7 days. Brackets indicate portion of analog that differs from P7C3.

Fig 4. Dose-Response of selected analogs

In vivo analysis of synthetic analogs of P7C3. Data are expressed as mean ± SEM, 4 mice/compound. Compounds were infused ICV at a constant rate (12 μL/day) over 7 days as a solution of the indicated concentration.

Scheme 1

P7C3 and commercially available analogs.

Scheme 2

Synthesis of deriviatives of P7C3.

Scheme 3

Modification of analog 7.

Scheme 4

a) 2,4-pentanedione, EtOH, 70 °C (45%). b) 4-pentynol, Cu(SO₄), NaAscorbate, H₂O/^tBuOH (54%)

Scheme 5

Synthesis of analogs with modified linkers.

Scheme 6

Synthesis of a coumarin-tagged derivative

Scheme 7

Regions of P7C3 subject to modification as labeled in Fig 3.