Intracellular delivery and activation of the genetically encoded photosensitizer Killer Red by quantum dots encapsulated in polymeric micelles

Methods for Intracellular Delivery of Quantum Dots

Quantum dots (QDs) have attracted considerable attention as fluorescent probes for life sciences. The advantages of using QDs in fluorescence-based studies include high brilliance, a narrow emission band allowing multicolor labeling, a chemically active surface for conjugation, and especially, high photostability. Despite these advantageous features, the size of the QDs prevents their free transport across the plasma membrane, limiting their use for specific labeling of intracellular structures. Over the years, various methods have been evaluated to overcome this issue to explore the full potential of the QDs. Thus, in this review, we focused our attention on physical and biochemical QD delivery methods-electroporation, microinjection, cell-penetrating peptides, molecular coatings, and liposomes-discussing the benefits and drawbacks of each strategy, as well as presenting recent studies in the field. We hope that this review can be a useful reference source for researches that already work or intend to work in this area. Strategies for the intracellular delivery of quantum dots discussed in this review (electroporation, microinjection, cell-penetrating peptides, molecular coatings, and liposomes).

Genetically Encoded Photosensitizer for Destruction of Protein or Cell Function

There are several paths when excited molecules return to the ground state. In the case of fluorescent molecules, the dominant path is fluorescence emission that is greatly contributing to bioimaging. Meanwhile, photosensitizers transfer electron or energy from chromophore to the surrounding molecules, including molecular oxygen. Generated reactive oxygen species has potency to attack other molecules by oxidation. In this chapter, we introduce the chromophore-assisted light inactivation (CALI) method using a photosensitizer to inactivate proteins in a spatiotemporal manner and development of CALI tools, which is useful for investigation of protein functions and dynamics, by inactivation of the target molecules. Moreover, photosensitizers with high efficiency make it possible optogenetic control of cell ablation in living organisms and photodynamic therapy. Further development of photosensitizers with different excitation wavelengths will contribute to the investigation of multiple proteins or cell functions through inactivation in the different positions and timings.

Functionalization of Cadmium Selenide Quantum Dots with Poly(ethylene glycol): Ligand Exchange, Surface Coverage, and Dispersion Stability

Semiconductor quantum dots synthesized using rapid mixing of precursors by injection into a hot solution of solvents and surfactants have surface ligands that sterically stabilize the dispersions in nonpolar solvents. Often, these ligands are exchanged to disperse the quantum dots in polar solvents, but quantitative studies of quantum dot surfaces before and after ligand exchange are scarce. We studied exchanging trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) ligands on as-synthesized CdSe quantum dots dispersed in hexane with a 2000 g/mol thiolated poly(ethylene glycol) (PEG) polymer. Using infrared spectroscopy we quantify the absolute surface concentration of TOP/TOPO and PEG ligands per unit area before and after ligand exchange. While 50-85% of the TOP/TOPO ligands are removed upon ligand exchange, only a few are replaced with PEG. Surprisingly, the remaining TOP/TOPO ligands outnumber the PEG ligands, but these few PEG ligands are sufficient to disperse the quantum dots in polar solvents such as chloroform, tetrahydrofuran, and water. Moreover, as-synthesized quantum dots once easily dispersed in hexane are no longer dispersible in nonpolar solvents after ligand exchange. A subtle coverage-dependent balance between attractive PEG-solvent interactions and repulsive TOP/TOPO-solvent interactions determines the dispersion stability.

Deep-penetrating photodynamic therapy with KillerRed mediated by upconversion nanoparticles

The fluorescent protein KillerRed, a new type of biological photosensitizer, is considered as a promising substitute for current synthetic photosensitizes used in photodynamic therapy (PDT). However, broad application of this photosensitiser in treating deep-seated lesions is challenging due to the limited tissue penetration of the excitation light with the wavelength falling in the visible spectral range. To overcome this challenge, we employ upconversion nanoparticles (UCNPs) that are able to convert deep-penetrating near infrared (NIR) light to green light to excite KillerRed locally, followed by the generation of reactive oxygen species (ROS) to kill tumour cells under centimetre-thick tissue. The photosensitizing bio-nanohybrids, KillerRed-UCNPs, are fabricated through covalent conjugation of KillerRed and UCNPs. The resulting KillerRed-UCNPs exhibit excellent colloidal stability in biological buffers and low cytotoxicity in the dark. Cross-comparison between the conventional KillerRed and UCNP-mediated KillerRed PDT demonstrated superiority of KillerRed-UCNPs photosensitizing by NIR irradiation, manifested by the fact that ∼70% PDT efficacy was achieved at 1-cm tissue depth, whereas that of the conventional KillerRed dropped to ∼7%.

STATEMENT OF SIGNIFICANCE

KillerRed is a protein photosensitizer that holds promise as an alternative for the existing hydrophobic photosensitizers that are widely used in clinical photodynamic therapy (PDT). However, applications of KillerRed to deep-seated tumours are limited by the insufficient penetration depth of the excitation light in highly scattering and absorbing biological tissues. Herein, we reported the deployment of upconversion nanoparticles (UCNPs) to enhance the treatment depth of KillerRed by converting the deep-penetrating near-infrared (NIR) light to upconversion photoluminescence and activating the PDT effect of KillerRed under deep tissues. This work demonstrated clear potential of UCNPs as the NIR-to-visible light converter to overcome the light penetration limit that has plagued PDT application for many years.

Towards PDT with Genetically Encoded Photosensitizer KillerRed: A Comparison of Continuous and Pulsed Laser Regimens in an Animal Tumor Model

The strong phototoxicity of the red fluorescent protein KillerRed allows it to be considered as a potential genetically encoded photosensitizer for the photodynamic therapy (PDT) of cancer. The advantages of KillerRed over chemical photosensitizers are its expression in tumor cells transduced with the appropriate gene and direct killing of cells through precise damage to any desired cell compartment. The ability of KillerRed to affect cell division and to induce cell death has already been demonstrated in cancer cell lines in vitro and HeLa tumor xenografts in vivo. However, the further development of this approach for PDT requires optimization of the method of treatment. In this study we tested the continuous wave (593 nm) and pulsed laser (584 nm, 10 Hz, 18 ns) modes to achieve an antitumor effect. The research was implemented on CT26 subcutaneous mouse tumors expressing KillerRed in fusion with histone H2B. The results showed that the pulsed mode provided a higher rate of photobleaching of KillerRed without any temperature increase on the tumor surface. PDT with the continuous wave laser was ineffective against CT26 tumors in mice, whereas the pulsed laser induced pronounced histopathological changes and inhibition of tumor growth. Therefore, we selected an effective regimen for PDT when using the genetically encoded photosensitizer KillerRed and pulsed laser irradiation.

Nanostructures of an amphiphilic zinc phthalocyanine polymer conjugate for photodynamic therapy of psoriasis

Psoriasis is a chronic inflammatory skin disease affecting 2-5% of the population worldwide and it severely affects patient quality of life. In this study, an amphiphilic zinc phthalocyanine polymer conjugate (ZPB) was synthesized, in which zinc phthalocyanine (ZnPc) was conjugated with the poly(ethylene glycol) (PEG) chain of Brij 58. ZPB showed two maximum UV-vis absorption wavelengths, 348 nm and 678 nm. A monomolecular micelle of ZPB formed in water with a mean size of 25 nm and zeta potential of -15 mV. The nanostructures aggregated into cloudy precipitates, which were easily dispersed. The nanostructure showed the shell-core structure with the ZnPc segments as the core and the PEG chains as the shell. The anti-psoriasis effect of the ZPB nanostructure was explored using a guinea pig psoriasis model. After comparing the anti-psoriasis effects of saline, light alone, ZPB alone, and the combination of light and ZPB, the combination of light and ZPB showed the best photodynamic therapy of psoriasis based on the light excitation of the photosensitizer ZPB and the psoriasis was nearly cured according to the histopathological investigation. The ZPB nanostructure is a promising anti-psoriasis nanomedicine based on photodynamic therapy.

Core/shell quantum dots encapsulated in biocompatible oil-core nanocarriers as two-photon fluorescent markers for bioimaging

Highly fluorescent quantum dots (QDs)-loaded nanocapsules, intended for fluorescent cell imaging, were prepared via an emulsification/solvent-evaporation method. CdSe/ZnS core/shell quantum dots were applied as cargo; Poloxamer 403 as the polymer component; Cremophor EL as the nonionic surfactant; and mineral oil, oleic acid, or silicone oil were applied as the oil phases. Transmission electron microscopy, atomic force microscopy, dynamic light scattering, and zeta potential measurements were used to characterize the novel QDs-labeled nanoparticles by particle size, distribution, and morphology, as well as by ζ-potential and physical stability. The fabricated long-lasting nanocapsules exhibit good luminescence properties upon both one-photon and two-photon excitation. The potential of the encapsulated QDs for fluorescent imaging was evaluated in cytotoxicity studies as well as in imaging of intracellular localization, accumulation, and distribution of QDs delivered to well-characterized human cancer cell lines--doxorubicin-sensitive breast (MCF-7/WT) and alveolar basal epithelial (A549)--as well as on normal human umbilical vein endothelial (HUVEC) cells, as investigated by confocal laser scanning microscopy (CLSM). The colloidal CdSe/ZnS-loaded nanocapsules are shown to exhibit strong two-photon-induced luminescence upon excitation in the NIR optical transmission window spectral range, making them ideal markers for bioimaging application. The total two-photon cross section of a single nanocapsule was determined to be about 4.1 × 10(6) GM at 800 nm.

Polymeric nanocarrier systems for photodynamic therapy

Photodynamic therapy (PDT) is an emerging treatment modality that involves the combined action of photosensitizers (PSs) and light for treatment of solid tumor and other diseases. Although this therapeutic method has been considered as an alternative to classical cancer treatments, clinical PDT requires further advances in selectivity and therapeutic efficacy to overcome numerous shortages related to conventional PDT. In this regard, great efforts have been devoted to the development of polymeric nanocarrier-encapsulated PSs for targeted PDT, aiming at improvement of water solubility and tumor-specificity of hydrophobic PSs. Here, we discuss the general concepts and considerations of polymeric nanocarriers for efficient delivery of PSs. In recent, the amphiphilic PS-polymer conjugate-based self-quenchable nanoparticles and PS-polymer-conjugate/quencher nanocomplexes have emerged as an attractive delivery platform for efficient and reliable PDT. They can incorporate and deliver the PS in a photodynamically inactive state but demonstrate cytotoxic effects by tumor environment-sensitive activation mechanisms, so that the photodynamic cancer treatment can achieve maximum target specificity. Here, we report the recent achievements on the development of activatable PS formulations based on PS-polymer conjugates.

MicroRNA delivery with osmotic polysorbitol-based transporter suppresses breast cancer cell proliferation

MicroRNAs (miRNA) are short oligonucleotides of endogenous origin involved in post-transcriptional regulation and are altered in disease, making them potential therapeutic targets. miRNA replacement is necessary in cells with downregulated miRNAs levels in response to disease. miRNA 145 is a novel tumor suppressor gene involved in cell suppression, invasion and migration of cancer cells; it is downregulated in most cancers. Delivery of therapeutic miRNA using nanoparticles enhances the chances of successful delivery and expression of genes at the target site. We evaluated polysorbitol-mediated transporter (PSMT) in the cellular delivery of miRNA 145. The polysorbitol backbone possesses osmotic properties and leads to enhanced cellular uptake. PSMT delivers genes into cells by a caveolae-mediated endocytic pathway. Caveolae expression is usually altered in transformed cancer cells. Physicochemical characterization, and the transfection efficiency and transgene expression capability of PSMT/reporter plasmid DNA nanoparticles, were determined. GFP-tagged miRNA 145 delivery with PSMT was confirmed by confocal microscopy and Western blotting. The functional effects of miRNA 145 delivered with PSMT were analyzed by confocal microscopy, as well as in apoptosis, proliferation and wound healing assays. Finally, the expression of an miRNA 145 target protein, c-myc, was determined by Western blotting after intracellular delivery of PSMT/miRNA 145 nanoparticle (NP).

The application of KillerRed for acute protein inactivation in living cells

Generating loss of protein function is a powerful investigatory tool particularly if carried out on a physiologically relevant timescale in a live-cell fluorescent imaging experiment. KillerRed mediated chromophore assisted light inactivation (CALI) uses genetic encoding for specificity and light for acute inactivation that can also be spatially restricted. This unit provides protocols for setting up and carrying out properly controlled KillerRed experiments during live-cell imaging of cultured cells.