drug release. The ATP aptamer was hybridized with a complementary DNA, and the
drug doxorubicin was intercalated in this DNA duplex. At high concentrations of
ATP, the ATP aptamer binds ATP and therefore dissociates from the duplex
structure resulting in drug release. This system ensures that drugs are only released
within the mitochondria, where the ATP level is high. Using these multifunctional
nanoparticles, Chen et al. could show that this drug delivery system is even effective
in multidrug-resistant cancer cells (MCF-7/ADR cells) [106].
Virus Capsid
Virus capsids are protein-based nanoparticles that can be used to encapsulate
different molecules; the surface can also be modified with different molecules,
such as aptamers [85]. Cohen et al. developed a virus capsid based on the MS2
bacteriophage and loaded it with cationic porphyrins, which can be used for photodynamic therapy. The surface was modified with an aptamer that binds to MCF-7
cancer cells. This system showed cytotoxicity to MCF-7 cells, but no cytotoxicity to
non-targeted cells; furthermore no cytotoxicity was observed when a non MCF-7
binding aptamer was used [107].
3.2 Photothermal and Photodynamic Therapy
with Aptamer-Modified Nanoparticles
Apart from nanoparticles as delivery vehicles for drugs, nanoparticles themselves
can be the therapeutic part of an aptamer-modified nanoparticle system. Some
materials have the properties to cause photothermal or photodynamic effects [110].
In photodynamic therapy (PDT) usually a nontoxic photosensitizer is activated by
irradiation of the targeted tissue. Thereby, singlet oxygen (
1 O 2 ) is generated by the
photosensitizer using the energy from the radiation. Singlet oxygen is highly reactive
and causes severe reactions with cellular molecules which finally lead to cell death.
In PDT it is possible that the nanoparticle itself is the photosensitizer or the
photosensitizers are conjugated to nanoparticles via aptamers. In the latter case,
the nanoparticles quench the cytotoxic effects if the photosensitizers are close to the
nanoparticles in the absence of the target. By conformational changes upon target
binding of the aptamer, the photosensitizer is not quenched any longer, and cytotoxic
effects can occur after illumination (see Fig. 7) [8].
In photothermal therapy (PTT) nanoparticles prepared of a suitable material (e.g.,
gold) are irradiated. The resulting photon energy is transformed into heat which then
causes cell damage and finally cell death (see Fig. 8a) [7]. Table 5 shows the
components of aptamer-modified nanoparticles for PTT and PDT.
Aptamer-Modified Nanoparticles in Medical Applications
181
drug doxorubicin was intercalated in this DNA duplex. At high concentrations of
ATP, the ATP aptamer binds ATP and therefore dissociates from the duplex
structure resulting in drug release. This system ensures that drugs are only released
within the mitochondria, where the ATP level is high. Using these multifunctional
nanoparticles, Chen et al. could show that this drug delivery system is even effective
in multidrug-resistant cancer cells (MCF-7/ADR cells) [106].
Virus Capsid
Virus capsids are protein-based nanoparticles that can be used to encapsulate
different molecules; the surface can also be modified with different molecules,
such as aptamers [85]. Cohen et al. developed a virus capsid based on the MS2
bacteriophage and loaded it with cationic porphyrins, which can be used for photodynamic therapy. The surface was modified with an aptamer that binds to MCF-7
cancer cells. This system showed cytotoxicity to MCF-7 cells, but no cytotoxicity to
non-targeted cells; furthermore no cytotoxicity was observed when a non MCF-7
binding aptamer was used [107].
3.2 Photothermal and Photodynamic Therapy
with Aptamer-Modified Nanoparticles
Apart from nanoparticles as delivery vehicles for drugs, nanoparticles themselves
can be the therapeutic part of an aptamer-modified nanoparticle system. Some
materials have the properties to cause photothermal or photodynamic effects [110].
In photodynamic therapy (PDT) usually a nontoxic photosensitizer is activated by
irradiation of the targeted tissue. Thereby, singlet oxygen (
1 O 2 ) is generated by the
photosensitizer using the energy from the radiation. Singlet oxygen is highly reactive
and causes severe reactions with cellular molecules which finally lead to cell death.
In PDT it is possible that the nanoparticle itself is the photosensitizer or the
photosensitizers are conjugated to nanoparticles via aptamers. In the latter case,
the nanoparticles quench the cytotoxic effects if the photosensitizers are close to the
nanoparticles in the absence of the target. By conformational changes upon target
binding of the aptamer, the photosensitizer is not quenched any longer, and cytotoxic
effects can occur after illumination (see Fig. 7) [8].
In photothermal therapy (PTT) nanoparticles prepared of a suitable material (e.g.,
gold) are irradiated. The resulting photon energy is transformed into heat which then
causes cell damage and finally cell death (see Fig. 8a) [7]. Table 5 shows the
components of aptamer-modified nanoparticles for PTT and PDT.
Aptamer-Modified Nanoparticles in Medical Applications
181