Exploring drug delivery systems tailored for [Pt(phen)(acylthiourea)]+ complexes
Date
2022
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Abstract
Three [Pt(phen)(Ln -O,S)]Cl complexes (PtLn), where phen represents 1,10-phenanthroline and L n -O,S various N,N-di(alkyl)-N`-acylthiourea ligands were successfully synthesized and characterized with yields ranging from 66% to 75%. Generation 4 (G4), acetamide functionalized generation 4 (G4-Ac) and generation 5 (G5-Ac) PAMAM and folic acid functionalized generation 4 (G4-FA) PAMAM dendrimers were successfully synthesized with yields ranging from 80% to 94% and characterized using 1H NMR, 13C NMR, FT-IR and mass spectrometry (ESI and MALDI-TOF) where applicable.
Host-guest adduct formation between G4 and PtLn complexes were challenging since G4 was found to exist as a polycation even near-neutral pH. The positively charged amine surface resulted in a small amount of complex degradation and inhibition of encapsulation due to electrostatic repulsion between the dendrimer and the cationic complex. To mitigate this, we acetylated the amine surface of the dendrimer and studied the host-guest interaction of this variant. The solvent was found to play an important role in the encapsulation process with DMSO-d6 showing the most promising results. Host-guest interactions of G4-Ac and PtL1 in DMSO-d6 were investigated in detail. Upon addition to G4-Ac, shifting of the aliphatic and aromatic peaks that belong to PtL1 were observed in the 1H NMR spectrum with a significant shift of 0.25 ppm and 0.26 ppm for Hd and Hd` of PtL1. At 300K, DOSY data showed the association between the complex and dendrimer with significant slower diffusion in the mixture (PtL1: 0.3 x10-10 m2 /s, G4-Ac: 0.2 x10-10 m2 /s) as compared to the free species (PtL1: 1.0 x10-10 m2 /s, G4-Ac: 0.4 x10-10 m2 /s). The observed 1H NMR chemical shifts and diffusion coefficient was a molar fraction-weighted average between the “bound” and “free” state of PtL1 which indicated that the dendrimer-complex interaction was in fast-exchange relative to the NMR time-scale. In efforts to further ascertain the extent of the interaction, viscosity measurements were conducted in order to calculate each respective hydrodynamic radii (RH) and volumes (VH) which will give a clear indication of host-guest association. The increase in viscosity for the mixture was attributed to an increase in concentration and increase in ionic strength since the complex is cationic. An 84% and 49% increase in VH was observed in PtL1 and G4-Ac respectively which indicates the formation of the host-guest complex. Dendrimer cavity size played an important role in encapsulation as NOE crosspeaks were observed between the aromatic protons of PtL3 and internal G5-Ac protons whereas none were observed between the complexes and G4-Ac. The mixture of [TBA]Cl and G4-Ac was briefly studied to investigate the effect of ionic strength on the dendrimers diffusion behaviour. An increase in viscosity was observed as a result of increased concentration and ionic strength. A 31% increase in G4-Ac VH was observed while a 40% decrease in [TBA]Cl VH was observed which provided evidence of dendrimer aggregation in the presence of a salt. We iv also investigated the host-guest interaction of well-known 5-Fluorouracil (5FU) as a positive control. Host-guest interactions of G5-5 Fluorouracil (5FU) indicated an electrostatic interaction as seen by the shifting of surface G5 protons (g` and f`) upon addition of 5FU as a result of proton abstraction from the weakly acidic 5FU by the basic surface amine groups of G5. The free complexes, 5FU (positive control), free dendrimers and dendrimer-drug mixtures were screened against A549 lunger cell line to evaluate their cytotoxic activity at 50 μM and 5 μM in DMSO-d6/D2O (6:1). The solvent displayed minimal cytotoxic activity which was attributed to the presence of deuterium as deuterated solvents were found to be more cytotoxic compared to their non-deuterated counterparts in literature.
The free complexes and dendrimer-complex mixtures were highly active with less than 1% cell viability at 50 μM. Free 5FU displayed less activity with a cell viability of 62.3% while G5+5FU displayed improved activity with a cell viability of 19.2% at 50 μM. G4-Ac +PtL1 and G4-Ac +PtL2 displayed higher cytotoxicity compared to their free counterparts at 5 μM which could be indicative of effective drug delivery although the results are preliminary. PAMAM dendrimers were found to be biocompatible with a cell viability of 53.30%, 58.78% and 64.53% for G4-Ac, G5 and G5-Ac respectively at 50 μM and acetamide functionalized dendrimers displayed less cytotoxicity compared to the amine terminated dendrimers.
Description
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Chemistry, University of the Witwatersrand, Johannesburg, 2022
Keywords
Drug delivery systems, [Pt(phen)(acylthiourea)]+ complexes