Assessment of the "smart" polymer poly(acrylic acid) for drug delivery

Abstract

Anticancer drug delivery systems are currently in the spotlight of anticancer research in order to address the harmful side effects commonly associated with anticancer drug treatment. The unique ability of "smart" polymers to respond to external stimuli, including changes to pH, make them promising candidates for anticancer drug delivery and cell specific targeting. Tumour tissues have a higher acidity than non-cancerous surrounding tissues. In this study the potential of the pH-responsive "smart" polymer poly(acrylic acid) (PAA) was investigated. PAA has functional groups that become ionised in response to pH changes, resulting in the chemical nature of PAA becoming altered to form poly(sodium acrylate) (PNaA). Nuclear Magnetic Resonance (NMR) spectroscopy was used to assess the purity of PNaA analogues and the effectiveness of multiple purification processes. 1H NMR spectroscopy detected the presence of residual impurities (1,4-dioxane and acrylic acid/sodium acrylate monomers) from synthesis in polymers that were purified by the commonly used precipitation. Dialysis was used as the secondary purification method to remove residual impurities; their removal was confirmed by 1H NMR and free solution Capillary Electrophoresis (CE). Free solution CE analysis of the dialysed 3-arm star and hyperbranched PNaA samples determined through significant change in polymer peak intensity that a change in the polymer structure had potentially occurred. Novel UV irradiation studies were also conducted on the 3-arm star and hyperbranched PNaA architectures to assess if photodegradation had occurred to the polymer during dialysis as it was not conducted in a light controlled environment. Photodegradation studies were inconclusive without a definitive evidence of degradation. Cytotoxicity of dialysed PNaA analogues was assessed via the MTT assay with L6 myoblast cells and L1210 progenitor leukaemia cells used as noncancerous and cancerous models, respectively. While L1210 progenitor cell line studies resulted in an IC50 determination and a dose-dependent cytotoxicity, the L6 myoblast cell line studies displayed a significant increase in cellular proliferation to levels above that of the controls. This increase when compared to the controls suggests that the MTT assay may not be an appropriate cell based cytotoxicity assay for PNaA. As the MTT is based on mitochondrial activity it is possible that the polymer is affecting cellular mitochondrial production. Preliminary novel studies into the grafting of a fluorescent tag to linear PNaA using a model compound were conducted. CE was used to monitor the grafting efficiency for the first time in this study. Grafting was confirmed by peak area and electrophoretic mobility analysis and the grafting was characterised via novel dispersity studies. Previous results obtained into the interaction of PNaA and serum proteins was reanalysed as previously the absorbance was not corrected when converting migration times to electrophoretic mobility as stated in a more recently published work [1]. Studies conducted under simulated physiological conditions (pH 7.4, 37 °C) were unsuccessful due to adsorption onto the capillary wall in both coated and uncoated capillaries. Studies conducted at pH 9.2 indicated that there are weak interactions between PNaA analogues and serum proteins. The potential of isotachophoresis (ITP) for development of a new cell count method for mammalian cells was also investigated. Studies determined that poly(N-vinyl pyrrolidone) (PVP) was an insufficient capillary coating for migrations conducted in a 250 µm i.d. capillary, with stripping of the coating occurring at both coating concentrations (1 % and 3 % PVP) used. The preliminary work conducted in this study suggests that ITP has the potential to be used as a cell count method for mammalian cells, as cells were successfully injected and migrated in this study. This work opens the way to determine the potential of PAA/PNaA as a drug delivery system.

Date of Award	2015
Original language	English