Brain-penetrant, orally bioavailable microtubule-stabilizing small molecules are potential candidate therapeutics for Alzheimer's disease and related tauopathies

Abstract

Microtubule (MT) stabilizing drugs hold promise as potential treatments for Alzheimer's disease (AD) and related tauopathies. However, thus far epothilone D has been the only brain-penetrant MT-stabilizer to be evaluated in tau transgenic mice and in AD patients. Furthermore, this natural product exhibits potential deficiencies as a drug candidate, including an intravenous route of administration and the inhibition of the P-glycoprotein (Pgp) transporter. Thus, the identification of alternative CNS-active MT-stabilizing agents that lack these potential limitations is of interest. Toward this objective, we have evaluated representative compounds from known classes of non-naturally occurring MT-stabilizing small molecules. This led to the identification of selected triazolopyrimidines and phenylpyrimidines that are orally bioavailable and brain-penetrant without disruption of Pgp function. Pharmacodynamic studies confirmed that representative compounds from these series enhance MT-stabilization in the brains of wild-type mice. Thus, these classes of MT-stabilizers hold promise for the development of orally active, CNS-directed MT-stabilizing therapies.

Figure 1

Structures of epothilone D (1) and representative examples from different classes of non-naturally occurring compounds with reported MT-stabilizing activity.

Scheme 1

Scheme 2

Scheme 3

Figure 2

Comparison of activity of representative compounds in the QBI293 cell MT-stabilization (AcTub) assay.

Figure 3

AcTub immunofluorescence of QBI293 cells after 4 h of incubation with no test compound, colchicine (1 μM), 2 (100 nM), or 1 (100 nM).

Figure 4

Pgp-interaction assay (calcein-AM). Cyclosporin A is a known Pgp substrate, whereas verapamil and 1 are known Pgp inhibitors.

Figure 5

Brain and plasma pharmacokinetics of 9 and 20 after 5 mg/kg ip dosing to CD1 mice.

Figure 6

Brain and plasma levels of 9 and 20, 2 h after oral administration of 10 mg/kg.

Figure 7

Relative increase in AcTub level in the brain of WT mice that received 9 or 20, 1 mg/kg daily ip for 4 or 6 days: ∗, p < 0.05; ∗∗, p < 0.01, as determined by ANOVA with a Dunnett’s multiple comparison test.