Abstract
Photodynamic therapy (PDT) uses photosensitisers such as protoporphyrin IX (PpIX) to target tumours via the release of toxic singlet oxygen when irradiated. The effectivity of the treatment is limited by the innate properties of the photosensitizers; they typically exhibit inefficient accumulation in target tissue and high dark toxicity. Carbon dots (CDs) are biocompatible fluorescent nanoparticles which can improve PpIX cellular uptake and solubility. In this work, we present conjugates synthesised by host-guest encapsulation (PpIX@CD) and amide cross-linking (PpIX-CD). Characterization demonstrated conjugates have a loading efficiency of 34–48% and similar singlet oxygen production to PpIX. PpIX-containing CDs showed a 2.2 to 3.7-fold decrease in dark toxicity. PpIX-CD and PpIX@CD showed equivalent light-induced toxicity to PpIX in concentrations >1 μg/ml, leading to a 3.2 to 4.1-fold increase in photo-toxicity index (PI). The less soluble fraction of cross-linked conjugates (PpIX-CD)p did not show significant difference from PpIX. Confocal light scanning microscopy demonstrated rapid intracellular uptake and accumulation of conjugates. Our results demonstrate the variations between cross-linking strategies in CD-based conjugates, highlighting their potential as carriers in drug delivery and bioimaging applications.
Highlights
Photodynamic therapy (PDT) has seen advances in recent years as an alternative cancer treatment due to its non-invasive nature, specificity and selectivity [1]
protoporphyrin IX (PpIX)-Carbon dots (CDs) was fabricated with a modified cross-linking protocol which formed a covalent amide bond between the amine groups of CA-EDA CDs and carboxylic acid groups of PPIX
PpIX@CD was successfully synthesized by a one-pot reaction of sucrose, EDA and PpIX, and was recovered as a dark red liquid
Summary
Photodynamic therapy (PDT) has seen advances in recent years as an alternative cancer treatment due to its non-invasive nature, specificity and selectivity [1]. The term “PDT” describes a range of protocols based on the excitation of photosensitizers (PS) in the presence of oxygen to singlet oxygen (1O2) leading to tumour ablation [2]. PDT has been proven to be clinically effective presenting positive results in basal cell carcinoma, endobronchial lung cancer, and nonmuscle invasive bladder cancer [3,4,5]. Nanoparticle-photosensitizer conjugates have received increased interest due to several advantages such as; (i) large surface-volume ratios for increased loading efficiency, (ii) the formation of amphiphilic compounds to avoid aggregation, and (iii) the enhanced permeability and retention effect for increased accumulation in tumours due to “leaky” vasculature [7,8,9].
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