Design, development, and evaluation of novel polymer-drug conjugates and interpolymer complexes for the treatment of neurodegenerative disease.

Neurodegenerative diseases (NDs) pose a growing global healthcare challenge due to their complex aetiology. Alzheimer's disease (AD), the most prevalent form of dementia, is a progressive ND characterised by amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs), largely driven by oxidative stress (OS) and increased cholinesterase activity. Current treatments are mainly symptomatic and target single pathways, offering limited impact on disease progression. Increasingly, multi-target therapies are being considered more effective for addressing the multifactorial nature of AD. However, such compounds face challenges such as poor solubility, instability, and toxicity, leading to low bioavailability. Polymer-drug conjugates (PDCs) offer a promising strategy by covalently linking bioactive molecules to water-soluble polymer backbones, improving solubility and therapeutic efficacy. This study aimed to develop novel PDCs and their nano-polyplexes as multifunctional therapeutic agents for AD treatment. Vanillin, an antioxidant, was conjugated to polyallylamine hydrochloride (NM10 and NM15), while the cholinesterase inhibitor naphthalimidohexylamine (HEXNAP) was conjugated to polyacrylic acid (N5 and N10). These conjugates were thoroughly characterised, and their antioxidant and cholinesterase inhibitory activities were evaluated. Additionally, in silico molecular modelling was performed to determine cholinesterase inhibition mechanisms. NM15 (unadjusted and adjusted value) showed significantly enhanced antioxidant activity (p ≤ 0.0001) compared to vanillin. The adjusted value of N5 showed significantly greater AChE and BuChE inhibition (p ≤ 0.0001) compared to HEXNAP. Kinetic and modelling studies revealed that N5 acts as a competitive inhibitor of BuChE, interacting with key active sites of both human AChE and BuChE enzymes. NM15 and N5 were selected as lead PDCs based on their enhanced antioxidant and cholinesterase inhibitory activity. A nano-polyplex (N5NM15) was then formulated by mixing oppositely charged NM15 and N5 conjugates. Characterisation by Cryo-TEM revealed uniform nanoparticles with an average size of 30.5±7.9 nm. The nano-polyplex demonstrated significantly enhanced antioxidant (p ≤ 0.01) and cholinesterase inhibitory activity (p ≤ 0.01) compared to parent drugs. In cellular studies, the nano-polyplex was non-toxic to undifferentiated human SH-SY5Y cells (>90% viability) but showed moderate toxicity in BV-2 cells (75% viability, p ≤ 0.001). It also significantly protected SH-SY5Y cells against H₂O₂-induced OS (45% protection, p ≤ 0.0001), reduced BuChE activity in SH-SY5Y cells (p ≤ 0.01), reduced LPS-induced inflammation in BV-2 cells (>20%, p ≤ 0.01), and decreased Aβ aggregation (>10%, p ≤ 0.01). In okadaic acid-stressed SH-SY5Y cells, both N5NM15 and PAA reduced neurotoxicity (50%, p ≤ 0.0001) and total tau levels (p ≤ 0.01). Notably, PAA alone demonstrated significant neuroprotective (˃35%, p ≤ 0.0001) and anti-inflammatory effects (˃75%, p ≤ 0.0001) in both cell lines and inhibited Aβ aggregation (˃20%, p ≤ 0.001). In vivo Drosophila studies showed N5NM15 and PAA were toxic to GMR-GAL4 flies but well tolerated in ELAV-GAL4 flies. Behavioural and survival assays showed a potential mild protective effect at a lower N5NM15 dose (3.5:1 μg/mL) in the early disease stage, but a high dose (44:12.5 μg/mL) caused significant toxicity, particularly in both female wild-type (p ≤ 0.0001) and tauopathy models (p ≤ 0.05). Overall, this study highlights the potential of multifunctional PDC nano-polyplexes as therapeutic agents for AD.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

2025

Author dc:creator

• Mahadik, Nuruddin

Advisor dc:contributor.advisor

• Thompson, C., Kong Thoo Lin, P., and Barron, G.

• Polymer-drug conjugates
• Nano-polyplex
• Multi-target treatment
• Neurodegenerative diseases
• Alzheimer's disease
• Vanillin
• Naphthalimidohexylamine
• Antioxidant
• Anticholinesterase
• Drosophila melanogaster

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:3316026
https://doi.org/10.48526/rgu-wt-3316026

Author Identifier

0009-0004-3298-2587

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:3316026