Abstract
The long wavelength absorbing photosensitizer (PS) is important in allowing deeper penetration of near-infrared light into tumor tissue for photodynamic therapy (PDT). A suitable drug delivery vehicle is important to attain a sufficient concentration of PS at the tumor site. Presently, we developed graphene oxide (GO) nanoparticles containing long wavelength absorbing PS in the form of the chlorin derivative purpurin-18-N-ethylamine (maximum absorption wavelength [λmax] 707 nm). The GO–PS complexes comprised a delivery system in which PS was loaded by covalent and noncovalent bonding on the GO nanosheet. The two GO–PS complexes were fully characterized and compared concerning their synthesis, stability, cell viability, and dark toxicity. The GO–PS complexes produced significantly-enhanced PDT activity based on excellent drug delivery effect of GO compared with PS alone. In addition, the noncovalent GO–PS complex displayed higher photoactivity, corresponding with the pH-induced release of noncovalently-bound PS from the GO complex in the acidic environment of the cells. Furthermore, the noncovalently bound GO‒PS complex had no dark toxicity, as their highly organized structure prevented GO toxicity. We describe an excellent GO complex-based delivery system with significantly enhanced PDT with long wavelength absorbing PS, as well as reduced dark toxicity as a promising cancer treatment.
Highlights
Graphene, an sp2-bonded two-dimensional carbon nanosheet in the form of a honeycomb lattice, is a nanomaterial that has received much attention for diverse applications, such as nanoelectronics, energy storage and conversion, nanocomposite materials, and biomedicine, on the basis of its extraordinary physicochemical properties [1,2,3,4,5]
Methyl pheophorbide-a (MPa) was converted to purpurin-18 (P18), and esterification of P18 afforded purpurin-18 methyl ester (P18ME)
Cell viability determinations demonstrated that both graphene oxide (GO)–PS complexes 2 and 3 had significantly enhanced Photodynamic therapy (PDT) activity compared to that of free PS
Summary
An sp2-bonded two-dimensional carbon nanosheet in the form of a honeycomb lattice, is a nanomaterial that has received much attention for diverse applications, such as nanoelectronics, energy storage and conversion, nanocomposite materials, and biomedicine, on the basis of its extraordinary physicochemical properties [1,2,3,4,5]. Photodynamic therapy (PDT), which is a non-invasive and patient-specific cancer treatment, uses a photosensitizer (PS) to absorb light of an appropriate wavelength and transfer photon energy to the surrounding oxygen, which generates highly toxic singlet oxygen (1O2) [29,30,31,32,33,34,35]. GO has been studied for use as a PDT, as well as a combination PDT/PTT [29,36,37,38] These studies typically used only commercially available PSs that do not absorb at long wavelengths; these include chlorin e6 (Ce6, λmax 660 nm) [29,30], zinc (II) phthalocyanine (λmax 670 nm) [37], porphyrin derivative [38], and 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH, Photochlor; λmax 665 nm) [39]. The toxicity of GO is important as a potential delivery vehicle
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