Microtubule-Stabilizing 1,2,4-Triazolo[1,5-a]pyrimidines as Candidate Therapeutics for Neurodegenerative Disease: Matched Molecular Pair Analyses and Computational Studies Reveal New Structure-Activity Insights

A small-molecule microtubule-stabilizing agent safely reduces Aβ plaque and tau pathology in transgenic mouse models of Alzheimer's disease

INTRODUCTION

Intraneuronal inclusions composed of tau protein are found in Alzheimer's disease (AD) and other tauopathies. Tau normally binds microtubules (MTs), and its disengagement from MTs and misfolding in AD is thought to result in MT abnormalities. We previously identified triazolopyrimidine-containing MT-stabilizing compounds that provided benefit in AD mouse models and herein describe the characterization and efficacy testing of an optimized candidate, CNDR-51997.

METHODS

CNDR-51997 underwent pharmacokinetic, pharmacodynamic, safety pharmacology, and mouse tolerability testing. In addition, the compound was examined for efficacy in 5XFAD amyloid beta (Aβ) plaque mice and PS19 tauopathy mice.

RESULTS

CNDR-51997 significantly reduced Aβ plaques in 5XFAD mice and tau pathology in PS19 mice, with the latter also showing attenuated axonal dystrophy and gliosis. CNDR-51997 was well tolerated at doses that exceeded efficacy doses, with a good safety pharmacology profile.

DISCUSSION

CNDR-51997 may be a candidate for advancement as a potential therapeutic agent for AD and/or other tauopathies. Highlights There is evidence of microtubule alterations (MT) in Alzheimer's disease (AD) brain and in mouse models of AD pathology. Intermittent dosing with an optimized, brain-penetrant MT-stabilizing small-molecule, CNDR-51997, reduced both Aβ plaque and tau inclusion pathology in established mouse models of AD. CNDR-51997 attenuated axonal dystrophy and gliosis in a tauopathy mouse model, with a strong trend toward reduced hippocampal neuron loss. CNDR-51997 is well tolerated in mice at doses that are meaningfully greater than required for efficacy in AD mouse models, and the compound has a good safety pharmacology profile.

Design, Synthesis, and Evaluation of An Anti-trypanosomal [1,2,4]Triazolo[1,5-a]pyrimidine Probe for Photoaffinity Labeling Studies

Studies have shown that depending on the substitution pattern, microtubule (MT)-targeting 1,2,4-triazolo[1,5-a]pyrimidines (TPDs) can produce different cellular responses in mammalian cells that may be due to these compounds interacting with distinct binding sites within the MT structure. Selected TPDs are also potently bioactive against the causative agent of human African trypanosomiasis, Trypanosoma brucei, both in vitro and in vivo. So far, however, there has been no direct evidence of tubulin engagement by these TPDs in T. brucei. Therefore, to enable further investigation of anti-trypanosomal TPDs, a TPD derivative amenable to photoaffinity labeling (PAL) was designed, synthesized, and evaluated in PAL experiments using HEK293 cells and T. brucei. The data arising confirmed specific labeling of T. brucei tubulin. In addition, proteomic data revealed differences in the labeling profiles of tubulin between HEK293 and T. brucei, suggesting structural differences between the TPD binding site(s) in mammalian and trypanosomal tubulin.

Structure-based design and synthesis of BML284 derivatives: A novel class of colchicine-site noncovalent tubulin degradation agents

Our previous studies have demonstrated that BML284 is a colchicine-site tubulin degradation agent. To improve its antiproliferative properties, 45 derivatives or analogs of BML284 were designed and synthesized based on the cocrystal structure of BML284 and tubulin. Among them, 5i was the most potent derivative, with IC50 values ranging from 0.02 to 0.05 μM against the five tested tumor cell lines. Structure-activity relationship studies verified that the N1 atom of the pyrimidine ring was the key functional group for its tubulin degradation ability. The 5i-tubulin cocrystal complex revealed that the binding pattern of 5i to tubulin is similar to that of BML284. However, replacing the benzodioxole ring with an indole ring strengthened the hydrogen bond formed by the 2-amino group with E198, which improved the antiproliferative activity of 5i. Compound 5i effectively suppressed tumor growth at an intravenous dose of 40 mg/kg (every 2 days) in paclitaxel sensitive A2780S and paclitaxel resistant A2780T ovarian xenograft models, with tumor growth inhibition values of 79.4% and 82.0%, respectively, without apparent side effects, showing its potential to overcome multidrug resistance. This study provided a successful example of crystal structure-guided discovery of 5i as a colchicine-targeted tubulin degradation agent, expanding the scope of targeted protein degradation.

Design, synthesis, and biological investigation of selective human carbonic anhydrase II, IX, and XII inhibitors using 7-aryl/heteroaryl triazolopyrimidines bearing a sulfanilamide scaffold

A novel library of human carbonic anhydrase (hCA) inhibitors based on the 2-sulfanilamido[1,2,4]triazolo[1,5-a]pyrimidine skeleton modified at its 7-position was prepared by an efficient convergent procedure. These derivatives were evaluated in vitro for their inhibition properties against a representative panel of hCA isoforms (hCA I, II, IV, IX, and XII). The target tumour-associated isoforms hCA IX and XII were potently inhibited with KIs in the low nanomolar range of 5-96 nM and 4-72 nM, respectively. Compounds 1d, 1j, 1v, and 1x were the most potent hCA IX inhibitors with KIs of 5.1, 8.6, 4.7, and 5.1 nM, respectively. Along with derivatives 1d and 1j, compounds 1r and 1ab potently inhibited hCA XII isoform with KIs in a single-digit nanomolar range of 8.8, 5.4, 4.3, and 9.0 nM, respectively. Compounds 1e, 1m, and 1p exhibited the best selectivity against hCA IX and hCA XII isoforms over off-target hCA II, with selectivity indexes ranging from 5 to 14.

Structure-Activity Relationships, Tolerability and Efficacy of Microtubule-Active 1,2,4-Triazolo[1,5-a]pyrimidines as Potential Candidates to Treat Human African Trypanosomiasis

Tubulin and microtubules (MTs) are potential protein targets to treat parasitic infections and our previous studies have shown that the triazolopyrimidine (TPD) class of MT-active compounds hold promise as antitrypanosomal agents. MT-targeting TPDs include structurally related but functionally diverse congeners that interact with mammalian tubulin at either one or two distinct interfacial binding sites; namely, the seventh and vinca sites, which are found within or between α,β-tubulin heterodimers, respectively. Evaluation of the activity of 123 TPD congeners against cultured Trypanosoma brucei enabled a robust quantitative structure-activity relationship (QSAR) model and the prioritization of two congeners for in vivo pharmacokinetics (PK), tolerability and efficacy studies. Treatment of T. brucei-infected mice with tolerable doses of TPDs significantly decreased blood parasitemia within 24 h. Further, two once-weekly doses at 10 mg/kg of a candidate TPD significantly extended the survival of infected mice relative to infected animals treated with vehicle. Further optimization of dosing and/or the dosing schedule of these CNS-active TPDs may provide alternative treatments for human African trypanosomiasis.

Recent Progress on Microtubule Degradation Agents

Targeted protein degradation (TPD) has emerged as the most promising approach for the specific knockdown of disease-associated proteins and is achieved by exploiting the cellular quality control machinery. TPD technologies are highly advantageous in overcoming drug resistance as they degrade the whole target protein. Microtubules play important roles in many cellular processes and are among the oldest and most well-established targets for tumor chemotherapy. However, the development of drug resistance, risk of hypersensitivity reactions, and intolerable toxicities severely restrict the clinical applications of microtubule-targeting agents (MTAs). Microtubule degradation agents (MDgAs) operate via completely different mechanisms compared with traditional MTAs and are capable of overcoming drug resistance. The emergence of MDgAs has expanded the scope of TPD and provided new avenues for the discovery of tubulin-targeted drugs. Herein, we summarized the development of MDgAs, and discussed their degradation mechanisms, mechanisms of action on the binding sites, potential opportunities, and challenges.

How neurons maintain their axons long-term: an integrated view of axon biology and pathology

Axons are processes of neurons, up to a metre long, that form the essential biological cables wiring nervous systems. They must survive, often far away from their cell bodies and up to a century in humans. This requires self-sufficient cell biology including structural proteins, organelles, and membrane trafficking, metabolic, signalling, translational, chaperone, and degradation machinery-all maintaining the homeostasis of energy, lipids, proteins, and signalling networks including reactive oxygen species and calcium. Axon maintenance also involves specialised cytoskeleton including the cortical actin-spectrin corset, and bundles of microtubules that provide the highways for motor-driven transport of components and organelles for virtually all the above-mentioned processes. Here, we aim to provide a conceptual overview of key aspects of axon biology and physiology, and the homeostatic networks they form. This homeostasis can be derailed, causing axonopathies through processes of ageing, trauma, poisoning, inflammation or genetic mutations. To illustrate which malfunctions of organelles or cell biological processes can lead to axonopathies, we focus on axonopathy-linked subcellular defects caused by genetic mutations. Based on these descriptions and backed up by our comprehensive data mining of genes linked to neural disorders, we describe the 'dependency cycle of local axon homeostasis' as an integrative model to explain why very different causes can trigger very similar axonopathies, providing new ideas that can drive the quest for strategies able to battle these devastating diseases.

Structure-Activity Relationships, Tolerability and Efficacy of Microtubule-Active 1,2,4-Triazolo[1,5- a ]pyrimidines as Potential Candidates to Treat Human African Trypanosomiasis

Tubulin and microtubules (MTs) are potential protein targets to treat parasitic infections and our previous studies have shown that the triazolopyrimidine (TPD) class of MT- active compounds hold promise as antitrypanosomal agents. MT-targeting TPDs include structurally related but functionally diverse congeners that interact with mammalian tubulin at either one or two distinct interfacial binding sites; namely, the seventh and vinca sites, which are found within or between α,β-tubulin heterodimers, respectively. Evaluation of the activity of 123 TPD congeners against cultured Trypanosoma brucei enabled a robust quantitative structure-activity relationship (QSAR) model and the prioritization of two congeners for in vivo pharmacokinetics (PK), tolerability and efficacy studies. Treatment of T. brucei -infected mice with tolerable doses of TPDs 3 and 4 significantly decreased blood parasitemia within 24 h. Further, two once-weekly doses of 4 at 10 mg/kg significantly extended the survival of infected mice relative to infected animals treated with vehicle. Further optimization of dosing and/or the dosing schedule of these CNS-active TPDs may provide alternative treatments for human African trypanosomiasis.