Conjugation of a Photosensitizer to an Oligoarginine-Based Cell-Penetrating Peptide Increases the Efficacy of Photodynamic Therapy

Emerging Approaches for Enabling RNAi Therapeutics

RNA interference (RNAi) is a primitive evolutionary mechanism developed to escape incorporation of foreign genetic material. siRNA has been instrumental in achieving the therapeutic potential of RNAi by theoretically silencing any gene of interest in a reversible and sequence-specific manner. Extrinsically administered siRNA generally needs a delivery vehicle to span across different physiological barriers and load into the RISC complex in the cytoplasm in its functional form to show its efficacy. This review discusses the designing principles and examples of different classes of delivery vehicles that have proved to be efficient in RNAi therapeutics. We also briefly discuss the role of RNAi therapeutics in genetic and rare diseases, epigenetic modifications, immunomodulation and combination modality to inch closer in creating a personalized therapy for metastatic cancer. At the end, we present, strategies and look into the opportunities to develop efficient delivery vehicles for RNAi which can be translated into clinics.

Conjugated Photosensitizers for Imaging and PDT in Cancer Research

Early cancer detection and perfect understanding of the disease are imperative toward efficient treatments. It is straightforward that, for choosing a specific cancer treatment methodology, diagnostic agents undertake a critical role. Imaging is an extremely intriguing tool since it assumes a follow up to treatments to survey the accomplishment of the treatment and to recognize any conceivable repeating injuries. It also permits analysis of the disease, as well as to pursue treatment and monitor the possible changes that happen on the tumor. Likewise, it allows screening the adequacy of treatment and visualizing the state of the tumor. Additionally, when the treatment is finished, observing the patient is imperative to evaluate the treatment methodology and adjust the treatment if necessary. The goal of this review is to present an overview of conjugated photosensitizers for imaging and therapy.

Endosomal Escape and Cytosolic Penetration of Macromolecules Mediated by Synthetic Delivery Agents

Cell delivery reagents often exploit the endocytic pathway as a route of cell entry. Once endocytosed, these reagents must overcome endosomal entrapment to ensure the release of their macromolecular cargo into the cytosol of cells. In this review, we describe several examples of prototypical synthetic reagents that are capable of endosomal escape and examine their mechanisms of action, their efficiencies, and their effects on cells. Although these delivery systems are chemically distinct, some commonalities in how they interact with cellular membranes can be inferred. This, in turn, sheds some light on the process of endosomal escape, and may help guide the development and optimization of next-generation delivery tools.

How Does the Encapsulation of Porphyrinic Photosensitizers into Polymer Matrices Affect Their Self-Association and Dynamic Properties?

Photodynamic therapy (PDT) with porphyrinic photosensitizers largely relies on efficient drug formulations to prevent porphyrin aggregation and to enhance water solubility and stability in physiologic environments. In this study, we compare two polymeric carrier systems, polyvinylpyrrolidone (PVP) and block copolymer micelles (BCMs) formed by the poloxamer Kolliphor P188 (KP), for their encapsulation efficiencies of porphyrin (xPP) and chlorin e6 (xCE) derivatives. Monomerization, loading efficiency, and dynamic properties were examined by ¹ H NMR spectroscopy chemical shift titration, DOSY, and T₂ relaxation time measurements. Binding affinity was determined by UV/Vis spectroscopy. Both PVP and KP-BCMs were well suited to disaggregate and encapsulate amphiphilic xCE, whereas they were less efficient for the xPP compounds. PVP exhibited higher monomerization efficiency than KP-BCMs. Significant differences were found in the dynamic behavior of the carriers. PVP formed rather stable complexes with the porphyrinic compounds, whereas a dynamic equilibrium between free and bound porphyrins was found to exist in the presence of KP-BCMs. This may have a considerable impact on the pharmacokinetic properties of the corresponding delivery systems.

Real-Time Visualization of Lysosome Destruction Using a Photosensitive Toluidine Blue Nanogel

Breaking the lysosome helps its sequestered payloads access their molecular targets in cells and thus enhances the intracellular drug delivery. Current strategies for lysosomal escape involve direct physical interactions with the lipid membrane. These interactions pose a systemic toxicity and uncontrolled membrane rupture risk. Here, we report a light-detonated lysosome disruption using a hyaluronan (HA) nanogel packed with toludine blue (TB). The HA/TB nanogel is concentrated within the lysosomes. The applied light assists TB in generating reactive oxygen species and destroying the lysosome in situ, both in cells and isolated lysosomes. Real time fluorescent tracking reveals that quenched TB fluorescence recovers along with lysosome explosion, relocates to the nucleus, and is presented as a fluorescent sparkling in cells. This HA/TB, composed of all clinically approved materials, represents a biocompatible and facile strategy to "bomb" lysosomes in a spatiotemporally controlled fashion.

Synthesis and coordination studies of 5-(4′-carboxyphenyl)-10,15,20-tris(pentafluorophenyl)porphyrin and its pyrrolidine-fused chlorin derivative

An efficient strategy was developed to obtain carboxyphenyl porphyrin, chlorins and metal complexes, with potential applications in photonics and biology.

Fluorescent and Photosensitizing Conjugates of Cell-Penetrating Peptide TAT(47-57): Design, Microwave-Assisted Synthesis at 60 °C, and Properties

Conjugates based on cell-penetrating peptides (CPPs) are scientifically relevant owing to their structural complexity; their ability to enter cells and deliver drugs, labels, antioxidants, bioactive compounds, or DNA fragments; and, consequently, their potential for application in research and biomedicine. In this study, carboxyamidated fluorescently labeled conjugates FAM-GG-TAT(47-57)-NH2 and FAM-PEG6-TAT(47-57)-NH2 and photosensitizer-labeled conjugate Chk-PEG6-TAT(47-57)-NH2 [where TAT(47-57) is the CPP, 5(6)-carboxyfluorescein is the (FAM) fluorophore, chlorin k (Chk) is the photosensitizer, and the dipeptide glycyl-glycine (GG) or hexaethylene glycol (PEG6) is the spacer] were originally designed, prepared, and fully characterized. Practically, all chemical reactions of the synthetic steps (peptide synthesis, spacer incorporation, and conjugation) were microwave-assisted at 60 °C using optimized protocols to give satisfying yields and high-quality products. Detailed analyses of the conjugates using spectrofluorimetry and singlet oxygen detection showed that they display photophysical properties typical of FAM or Chk. Anticandidal activity assays showed that not only this basic property of TAT(47-57) was preserved in the conjugates but also that the minimal inhibitory concentration was slightly reduced for cells incubated with PS-bearing conjugate Chk-PEG6-TAT(47-57)-NH2. Overall, these results indicated that the synthetic approach on-resin assisted by microwaves at 60 °C is simple, straightforward, selective, metal-free, sufficiently fast, cleaner, and more cost-effective than those previously used for preparing this type of macromolecule. Furthermore, such new data show that microwaves at 60 °C and/or conjugation did not harm the integrity of the conjugates' constituents. Therefore, FAM-GG-TAT(47-57)-NH2, FAM-PEG6-TAT(47-57)-NH2, and Chk-PEG6-TAT(47-57)-NH2 have high potential for practical applications in biochemistry, biophysics, and therapeutics.

Membrane Oxidation in Cell Delivery and Cell Killing Applications

Cell delivery or cell killing processes often involve the crossing or disruption of cellular membranes. We review how, by modifying the composition and properties of membranes, membrane oxidation can be exploited to enhance the delivery of macromolecular cargoes into live human cells. We also describe how membrane oxidation can be utilized to achieve efficient killing of bacteria by antimicrobial peptides. Finally, we present recent evidence highlighting how membrane oxidation is intimately engaged in natural biological processes such as antigen delivery in dendritic cells and in the killing of bacteria by antimicrobial peptides. Overall, the insights that have been recently gained in this area should facilitate the development of more effective delivery technologies and antimicrobial therapeutic approaches.

Multilayer photodynamic therapy for highly effective and safe cancer treatment

Recent efforts to develop tumor-targeted photodynamic therapy (PDT) photosensitizers (PSs) have greatly advanced the potential of PDT in cancer therapy, although complete eradication of tumor cells by PDT alone remains challenging. As a way to improve PDT efficacy, we report a new combinatory PDT therapy technique that specifically targets multilayers of cells. Simply mixing different PDT PSs, even those that target distinct receptors (this may still lead to similar cell-killing pathways), may not achieve ideal therapeutic outcomes. Instead, significantly improved outcomes likely require synergistic therapies that target various cellular pathways. In this study, we target two proteins upregulated in cancers: the cannabinoid CB2 receptor (CB₂R, a G-protein coupled receptor) and translocator protein (TSPO, a mitochondria membrane receptor). We found that the CB₂R-targeted PS, IR700DX-mbc94, triggered necrotic cell death upon light irradiation, whereas PDT with the TSPO-targeted IR700DX-6T agent led to apoptotic cell death. Both PSs significantly inhibited tumor growth in vivo in a target-specific manner. As expected, the combined CB₂R- and TSPO-PDT resulted in enhanced cell killing efficacy and tumor inhibition with lower drug dose. The median survival time of animals with multilayer PDT treatment was extended by as much as 2.8-fold over single PDT treatment. Overall, multilayer PDT provides new opportunities to treat cancers with high efficacy and low side effects.

STATEMENT OF SIGNIFICANCE

Photodynamic therapy (PDT) is increasingly used as a minimally invasive, controllable and effective therapeutic procedure for cancer treatment. However, complete eradication of tumor cells by PDT alone remains challenging. In this study, we investigate the potential of multilayer PDT in cancer treatment with high efficacy and low side effects. Through PDT targeting two cancer biomarkers located at distinct subcellular localizations, remarkable synergistic effects in cancer cell killing and tumor inhibition were observed in both in vitro and in vivo experiments. This strategy may be widely applied to treat various cancer types by using strategically designed PDT photosensitizers that target corresponding upregulated receptors at tactical subcellular localization.

Functional peptides for siRNA delivery

siRNA is considered as a potent therapeutic agent because of its high specificity and efficiency in suppressing genes that are overexpressed during disease development. For nearly two decades, a significant amount of efforts has been dedicated to bringing the siRNA technology into clinical uses. However, only limited success has been achieved to date, largely due to the lack of a cell type-specific, safe, and efficient delivery technology to carry siRNA into the target cells' cytosol where RNA interference takes place. Among the emerging candidate nanocarriers for siRNA delivery, peptides have gained popularity because of their structural and functional diversity. A variety of peptides have been discovered for their ability to translocate siRNA into living cells via different mechanisms such as direct penetration through the cellular membrane, endocytosis-mediated cell entry followed by endosomolysis, and receptor-mediated uptake. This review is focused on the multiple roles played by peptides in siRNA delivery, such as membrane penetration, endosome disruption, targeting, as well as the combination of these functionalities.

Targeted Nanomaterials for Phototherapy

Phototherapies involve the irradiation of target tissues with light. To further enhance selectivity and potency, numerous molecularly targeted photosensitizers and photoactive nanoparticles have been developed. Active targeting typically involves harnessing the affinity between a ligand and a cell surface receptor for improved accumulation in the targeted tissue. Targeting ligands including peptides, proteins, aptamers and small molecules have been explored for phototherapy. In this review, recent examples of targeted nanomaterials used in phototherapy are summarized.

Selective Photocatalytic Disinfection by Coupling StrepMiniSog to the Antibody Catalyzed Water Oxidation Pathway

For several decades reactive oxygen species have been applied to water quality engineering and efficient disinfection strategies; however, these methods are limited by disinfection byproduct and catalyst-derived toxicity concerns which could be improved by selectively targeting contaminants of interest. Here we present a targeted photocatalytic system based on the fusion protein StrepMiniSOG that uses light within the visible spectrum to produce reactive oxygen species at a greater efficiency than current photosensitizers, allowing for shorter irradiation times from a fully biodegradable photocatalyst. The StrepMiniSOG photodisinfection system is unable to cross cell membranes and like other consumed proteins, can be degraded by endogenous digestive enzymes in the human gut, thereby reducing the consumption risks typically associated with other disinfection agents. We demonstrate specific, multi-log removal of Listeria monocytogenes from a mixed population of bacteria, establishing the StrepMiniSOG disinfection system as a valuable tool for targeted pathogen removal, while maintaining existing microbial biodiversity.

Photoinduced apoptosis using a peptide carrying a photosensitizer

A novel molecule, TatBim-Alexa, consisting of the HIV1 Tat cell-penetrating peptide, the Bim apoptosis-inducing peptide, and Alexa Fluor 546 was synthesized for photoinducion of apoptosis. The Alexa Fluor 546 was used as a photosensitizer and covalently attached at the C-terminus of TatBim peptide by the thiol-maleimide reaction. Photo-dependent cytosolic internalization of TatBim-Alexa and photo-dependent apoptosis using TatBim-Alexa were demonstrated in several kinds of mammalian cells including human cancer cell lines.

Conjugation of photosensitisers to antimicrobial peptides increases the efficiency of photodynamic therapy in cancer cells

Some antimicrobial peptides (AMPs) have the ability to penetrate and kill not only pathogenic microorganisms but also cancer cells, while they are less active toward normal eukaryotic cells. Here we have investigated the potential of three AMPs, namely apidaecin 1b (Api), magainin 2 (Mag) and buforin II (Buf), as carriers of drugs for cancer cells by using the hydrophobic photosensitiser 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (cTPP) as the drug model, conjugated to the N-terminus of the peptides. Flow cytometry measurements demonstrated that conjugation of cTPP increased its rate and efficiency of uptake in A549 human lung adenocarcinoma cells in the order Mag > Buf > Api. In vitro photodynamic therapy (PDT) experiments showed that the increased uptake of the conjugated cTPP determined 100% cell killing at concentrations in the nanomolar range while micromolar concentrations were required for the same killing effect with unconjugated cTPP. Serum proteins interacted with cTPP conjugated to Buf and Api and slightly interfered with the cellular uptake of these conjugates but not with that of Mag. The data suggest electrostatic interactions of the conjugates with sialic acid and ganglioside rich domains, as lipid rafts of the plasma membrane, followed by cell internalization via non-caveolar dynamin-dependent endocytosis as indicated by the effects of inhibitors of specific endocytic pathways. Our study demonstrated that the three AMPs investigated, Mag in particular, have the ability to carry a hydrophobic cargo inside cancer cells and may therefore represent useful carriers of anticancer drugs, especially those with a poor capacity to penetrate inside the target cells.

Photosensitizer-loaded bubble-generating mineralized nanoparticles for ultrasound imaging and photodynamic therapy

In this work, we have developed photosensitizer-loaded bubble-generating calcium carbonate (CaCO₃)-mineralized nanoparticles that have potential for ultrasound imaging (US)-guided photodynamic therapy (PDT) of tumors. A photosensitizer, chlorin e6 (Ce6)-loaded CaCO₃-mineralized nanoparticles (Ce6-BMNs), was prepared using an anionic block copolymer-templated in situ mineralization method. Ce6-BMNs were composed of the Ce6-loaded CaCO₃ core and the hydrated poly(ethylene glycol) (PEG) shell. Ce6-BMNs exhibited excellent stability under serum conditions. Ce6-BMNs showed enhanced echogenic US signals at tumoral acid pH by generating carbon dioxide (CO₂) bubbles. Ce6-BMNs effectively inhibited Ce6 release at physiological pH (7.4). At a tumoral acidic pH (6.4), Ce6 release was accelerated with CO₂ bubble generation due to the dissolution of the CaCO₃ mineral core. Upon irradiation of Ce6-BMN-treated MCF-7 breast cancer cells, the cell viability dramatically decreased with increasing Ce6 concentration. The phototoxicity of the Ce6-BMNs was much higher than that of free Ce6. On the basis of tumoral pH-responsive CO₂ bubble-generation and simultaneous Ce6 release at the target tumor site, these CaCO₃ mineralized nanoparticles can be considered as promising theranostic nanoparticles for US imaging-guided PDT in the field of tumor therapy.

Selective aggregation of PAMAM dendrimer nanocarriers and PAMAM/ZnPc nanodrugs on human atheromatous carotid tissues: a photodynamic therapy for atherosclerosis

Photodynamic therapy (PDT) involves the action of photons on photosensitive molecules, where atomic oxygen or OH(-) molecular species are locally released on pathogenic human cells, which are mainly carcinogenic, thus causing cell necrosis. The efficacy of PDT depends on the local nanothermodynamic conditions near the cell/nanodrug system that control both the level of intracellular translocation of nanoparticles in the pathogenic cell and their agglomeration on the cell membrane. Dendrimers are considered one of the most effective and promising drug carriers because of their relatively low toxicity and negligible activation of complementary reactions. Polyamidoamine (PAMAM) dendrite delivery of PDT agents has been investigated in the last few years for tumour selectivity, retention, pharmacokinetics and water solubility. Nevertheless, their use as drug carriers of photosensitizing molecules in PDT for cardiovascular disease, targeting the selective necrosis of macrophage cells responsible for atheromatous plaque growth, has never been investigated. Furthermore, the level of aggregation, translocation and nanodrug delivery efficacy of PAMAM dendrimers or PAMAM/zinc phthalocyanine (ZnPc) conjugates on human atheromatous tissue and endothelial cells is still unknown. In this work, the aggregation of PAMAM zero generation dendrimers (G0) acting as drug delivery carriers, as well as conjugated G0 PAMAM dendrimers with a ZnPc photosensitizer, to symptomatic and asymptomatic human carotid tissues was investigated by using atomic force microscopy (AFM). For the evaluation of the texture characteristics of the AFM images, statistical surface morphological and fractal analytical methodologies and Minkowski functionals were used. All statistical quantities showed that the deposition of nanodrug carriers on healthy tissue has an inverse impact when comparing to the deposition on atheromatous tissue with different aggregation features between G0 and G0/ZnPc nanoparticles and with considerably larger G0/ZnPc aggregations on the atheromatous plaque. The results highlight the importance of using PAMAM dendrimer carriers as a novel and promising PDT platform for atherosclerosis therapies.

Supramolecular intracellular delivery of an anionic porphyrin by octaarginine-conjugated per-O-methyl-β-cyclodextrin

A convenient and efficient method for intracellular delivery of a water-soluble anionic porphyrin has been developed by utilizing its supramolecular interaction with per-O-methyl-β-cyclodextrin bearing an octaarginine chain as a cell-penetrating peptide.

Cannabinoid CB2 receptor as a new phototherapy target for the inhibition of tumor growth

The success of targeted cancer therapy largely relies upon the selection of target and the development of efficient therapeutic agents that specifically bind to the target. In the current study, we chose a cannabinoid CB2 receptor (CB2R) as a new target and used a CB2R-targeted photosensitizer, IR700DX-mbc94, for phototherapy treatment. IR700DX-mbc94 was prepared by conjugating a photosensitizer, IR700DX, to mbc94, whose binding specificity to CB2R has been previously demonstrated. We found that phototherapy treatment using IR700DX-mbc94 greatly inhibited the growth of CB2R positive tumors but not CB2R negative tumors. In addition, phototherapy treatment with nontargeted IR700DX did not show significant therapeutic effect. Similarly, treatment with IR700DX-mbc94 without light irradiation or light irradiation without the photosensitizer showed no tumor-inhibitory effect. Taken together, IR700DX-mbc94 is a promising phototherapy agent with high target-specificity. Moreover, CB2R appears to have great potential as a phototherapeutic target for cancer treatment.

Cellular uptake of octaarginine-conjugated tetraarylporphyrin included by per-O-methylated β-cyclodextrin

This paper describes the synthesis, structural characterization and cellular uptake of a supramolecular 1 : 2 inclusion complex of meso-tetraphenylporphyrin having an octaarginine peptide chain (R8-TPP) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TMe-β-CD). R8-TPP was synthesized by 2 approaches: (1) on-resin conjugation of the N-terminal of octaarginine with 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin, followed by cleavage from the resin, and (2) Michael addition reaction between 5-[4-(3-maleimidopropylamido)phenyl]-10,15,20-triphenylporphyrin and cysteine-octaarginine peptide (Cys-Arg8). The R8-TPP obtained from both the approaches formed stable inclusion complexes with TMe-β-CD by which non-substituted phenyl groups at the 10- and 20-positions were included to form trans-type 1 : 2 inclusion complexes. The complexation prevented the self-aggregation of R8-TPP, which resulted in the solubilisation of R8-TPP in aqueous media. A cellular uptake study using HeLa cells showed that R8-TPP complexed with TMe-β-CD in a serum-free medium was efficiently taken up by the cells and uniformly dispersed in the cytosol. In the serum-containing medium, the R8-TPP-TMe-β-CD complex dissociated, and the serum protein bound R8-TPP. The R8-TPP-protein complex was localized in the endosomes of the cells. The cytosol-dispersed R8-TPP showed a higher photo-induced cytotoxicity than its endosome-trapped counterpart.

Pancreatic cancer-associated Cathepsin E as a drug activator

Pancreatic ductal adenocarcinoma (PDAC) is challenging to treat, and better means to detect and/or treat pancreatic cancer are urgently needed to save lives. Cathepsin E (Cath E) is a proteolytic enzyme highly expressed in PDAC. In this study, a novel approach using Cath E activation of a Cath E-specific prodrug was demonstrated. Specific activation of the prodrug is expected to kill pancreatic cancer cells without harming normal pancreatic cells. A novel 5-aminolevulinic acid (5-ALA) prodrug was custom-designed to be activated selectively by endogenous Cath E within the PDAC cells. The 5-ALA prodrug was incubated with Cath E-positive and -negative tumor cells and illuminated with various doses of light. In addition, mice genetically engineered to develop PDAC were injected intravenously with the 5-ALA prodrug, and the pancreas was treated with light irradiation. One day after treatment, PDAC tissue was assessed for apoptosis. The 5-ALA prodrug was activated within the Cath E-positive tumor but not in the normal pancreatic tissue. When used in combination with light treatment, it allowed delivery of selective photodynamic therapy (PDT) to the cancerous tissues, with minimal harm to the adjacent normal tissues. With this novel Cath E activation approach, it is possible to detect pancreatic cancer cells accurately and specifically impair their viability, while sparing normal cells. This treatment could result in fewer side effects than the non-specific treatments currently in use. Cath E is a specific and effective drug activator for PDAC treatment.

Photoinactivation of Gram positive and Gram negative bacteria with the antimicrobial peptide (KLAKLAK)(2) conjugated to the hydrophilic photosensitizer eosin Y

We test the hypothesis that the antimicrobial peptide (KLAKLAK)(2) enhances the photodynamic activity of the photosensitizer eosin Y upon conjugation. The conjugate eosin-(KLAKLAK)(2) was obtained by solid-phase peptide synthesis. Photoinactivation assays were performed against the Gram-negative bacteria Escherichia coli , Pseudomonas aeruginosa , and multidrug resistant Acinetobacter baumannii AYE, as well as the Gram-positive bacteria Staphylococcus aureus , and Staphylococcus epidermidis . Partitioning assays were performed with E. coli and S. aureus . Photohemolysis and photokilling assays were also performed to assess the photodynamic activity of the conjugate toward mammalian cells. Eosin-(KLAKLAK)(2) photoinactivates 99.999% of 10(8) CFU/mL of most bacteria tested at a concentration of 1 μM or below. In contrast, neither eosin Y nor (KLAKLAK)(2) cause any significant photoinactivation under similar conditions. The increase in photodynamic activity of the photosensitizer conferred by the antimicrobial peptide is in part due to the fact that (KLAKLAK)(2) promotes the association of eosin Y to bacteria. Eosin-(KLAKLAK)(2) does not significantly associate with red blood cells or the cultured mammalian cell lines HaCaT, COS-7, and COLO 316. Consequently, little photodamage or photokilling is observed with these cells under conditions for which bacterial photoinactivation is achieved. The peptide (KLAKLAK)(2) therefore significantly enhances the photodynamic activity of eosin Y toward both Gram-positive and Gram-negative bacteria while interacting minimally with human cells. Overall, our results suggest that antimicrobial peptides such as (KLAKLAK)(2) might serve as attractive agents that can target photosensitizers to bacteria specifically.

Application of near-infrared dyes for tumor imaging, photothermal, and photodynamic therapies

Near-infrared (NIR) dyes, small organic molecules that function in the NIR region, have received increasing attention in recent years as diagnostic and therapeutic agents in the field of tumor research. They have been demonstrated great successes in imaging and treating tumors both in vitro and in vivo. And their different applications in clinical practices have made rapid gains. This review primarily focuses on the progress of the application of NIR dyes in tumor imaging and therapy. In particular, advances in the use of different NIR dyes in tumor-specific imaging, photothermal, and photodynamic therapies are discussed. Limitations and prospects associated with NIR dyes in diagnostic and therapeutic application are also reviewed.

Improving the endosomal escape of cell-penetrating peptides and their cargos: strategies and challenges

Cell penetrating peptides (CPPs) can deliver cell-impermeable therapeutic cargos into cells. In particular, CPP-cargo conjugates tend to accumulate inside cells by endocytosis. However, they often remain trapped inside endocytic organelles and fail to reach the cytosolic space of cells efficiently. In this review, the evidence for CPP-mediated endosomal escape is discussed. In addition, several strategies that have been utilized to enhance the endosomal escape of CPP-cargos are described. The recent development of branched systems that display multiple copies of a CPP is presented. The use of viral or synthetic peptides that can disrupt the endosomal membrane upon activation by the low pH of endosomes is also discussed. Finally, we survey how CPPs labeled with chromophores can be used in combination with light to stimulate endosomal lysis. The mechanisms and challenges associated with these intracellular delivery methodologies are discussed.

In vitro phototoxicity and dark-toxicity of a novel synthesized pyropheophorbide-a-paclitaxel conjugate against cancer cell lines

Synthesis of pyropheophorbide-a-paclitaxel (PPa-PTX) conjugate was performed in high yield with the aim of searching for an optimal agent for cancer treatment. After synthesis, the conjugate was confirmed to be linked through an ester bond at the 2′ position of the paclitaxel moiety using multi-nuclear magnetic resonance spectroscopy. Phototoxicity of PPa and PPa-PTX conjugate, as well as PTX, was evaluated with three human cancer cell lines (HeLa, CaSki and TC-1). The new conjugate at 0.01–0.06 μM displayed 20–40% higher phototoxicity in HeLa and CaSki cell lines than free PPa and PTX. Furthermore, cellular uptake of these bio-molecules was examined by confocal laser scanning microscopy. Although PPa-PTX showed a delayed uptake compared to PPa, it penetrated completely into cells within 24 h incubation.

New insights into the mechanisms for photodynamic therapy-induced cancer cell death

Photodynamic therapy (PDT) is a promising therapeutic modality for cancer treatment; however, a more detailed understanding is needed to improve the clinical use of this therapy. PDT induces cancer cell death by apoptosis, necrosis, and autophagy, and these mechanisms can be concurrently occurred. PDT destroys cancer cells by inducing apoptosis through diverse signaling pathways coupled with Bcl-2 family members, caspases, and apopotosis-inducing factor. When the apoptotic pathway is unavailable, PDT can cause cancer cell death through induction of a necrotic or autophagic mechanism. Autophagy is occurred in a Bax-independent manner and can be stimulated in parallel with apoptosis. PDT directly destroys cancer cells by inducing either apoptotic or necrotic death. PDT also can induce autophagy as a death or a survival mechanism. These mechanisms are dependent on a variety of parameters including the nature of the photosensitizer, PDT dose, and cell genotype. Understanding the complex cross talk between these pathways may improve the effectiveness of PDT. Here, we discuss the interplay between these mechanisms based on recent evidence and suggest prospects with regard to advances in PDT.

A cell penetrating peptide-integrated and enediyne-energized fusion protein shows potent antitumor activity

Arginine-rich peptides belong to a subclass of cell penetrating peptides that are taken up by living cells and can be detected freely diffusing inside the cytoplasm and nucleoplasm. This phenomenon has been attributed to either an endocytotic mode of uptake and a subsequent release from vesicles or a direct membrane penetration. Lidamycin is an antitumor antibiotic, which consists of an active enediyne chromophore (AE) and a noncovalently bound apoprotein (LDP). In the present study, a fusion protein (Arg)(9)-LDP composed of cell penetrating peptide (Arg)(9) and LDP was prepared by DNA recombination, and the enediyne-energized fusion protein (Arg)(9)-LDP-AE was prepared by molecular reconstitution. The data in fixed cells demonstrated that (Arg)(9)-LDP could rapidly enter cells, and the results based on fluorescence activated cell sorting indicated that the major route for (Arg)(9)-mediated cellular uptake of protein molecules was endocytosis. (Arg)(9)-LDP-AE demonstrated more potent cytotoxicity against different carcinoma cell lines than lidamycin in vitro. In the mouse hepatoma 22 model, (Arg)(9)-LDP-AE (0.3mg/kg) suppressed the tumor growth by 89.2%, whereas lidamycin (0.05 mg/kg) by 74.6%. Furthermore, in the glioma U87 xenograft model in nude mice, (Arg)(9)-LDP-AE at 0.2mg/kg suppressed tumor growth by 88.8%, compared with that of lidamycin by 62.9% at 0.05 mg/kg. No obvious toxic effects were observed in all groups during treatments. The results showed that energized fusion protein (Arg)(9)-LDP-AE was more effective than lidamycin and would be a promising candidate for glioma therapy. In addition, this approach to manufacturing fusion proteins might serve as a technology platform for the development of new cell penetrating peptides-based drugs.

meso-arylporpholactones and their reduction products

The rational syntheses of meso-tetraaryl-3-oxo-2-oxaporphyrins 5, known as porpholactones, via MnO(4)(-)-mediated oxidations of the corresponding meso-tetraaryl-2,3-dihydroxychlorins (7) is detailed. Since chlorin 7 is prepared from the parent porphyrin 1, this amounts to a 2-step replacement of a pyrrole moiety in 1 by an oxazolone moiety. The stepwise reduction of the porpholactone 5 results in the formation of chlorin analogues, meso-tetraaryl-3-hydroxy-2-oxachlorin (11) and meso-tetraaryl-2-oxachlorins (12). The reactivity of 11 with respect to nucleophilic substitution by O-, N-, and S-nucleophiles is described. The profound photophysical consequences of the formal replacement of a pyrrole with an oxazolone (porphyrin-like chromophore) or (substituted) oxazole moiety (chlorin-like chromophore with, for the parent oxazolochlorin 12, red-shifted Q(x) band with enhanced oscillator strengths) are detailed and rationalized on the basis of SAC-CI and MNDO-PSDCI molecular orbital theory calculations. The single crystal X-ray structures of the porpholactones point at a minor steric interaction between the carbonyl oxygen and the flanking phenyl group. The essentially planar structures of all chromophores in all oxidation states prove that the observed optical properties originate from the intrinsic electronic properties of the chromophores and are not subject to conformational modulation.

Receptor-targeting phthalocyanine photosensitizer for improving antitumor photocytotoxicity

Photodynamic therapy (PDT) is a promising therapeutic modality which uses a photosensitizer to capture visible light resulting in phototoxicity in the irradiated region. PDT has been used in a number of pathological indications, including tumor. A key desirable feature of the photosensitizer is the high phototoxicity on tumor cells but not on normal cells. In this study, we conjugate a gonadotropin-releasing hormone (GnRH) to a photosensitizer, Zinc phthalocyanine (ZnPc), in order to enhance its specificity to breast cancer, which over-expresses GnRH receptor. ZnPc has unique advantages over other photosensitizers, but is difficult to derivatize and purify as a single isomer. We previously developed a straight-forward way to synthesize mono-substituted β-carboxy-phthalocyanine zinc (ZnPc-COOH). Photophysical and photochemical parameters of this ZnPc-GnRH conjugate including fluorescence quantum yield (Ф_f), fluorescence decay time (τ_s) and singlet oxygen quantum yield (Ф_Δ) were evaluated and found comparable with that of ZnPc, indicating that addition of a GnRH peptide does not significantly alter the generation of singlet oxygen from ZnPc. Cellular uptakes and phototoxicities of this conjugate were tested and found significantly enhanced on human breast cancer cell lines overexpressing GnRH receptors (MDA-MB-231 and MCF-7 cells) compared to cells with low levels of GnRH receptors, such as human embryonic lung fibroblast (HELF) and human liver carcinoma (HepG2) cells. In addition, the cellular uptake of this conjugate toward MCF-7 cells were found clearly alleviated by a GnRH receptor blocker Cetrorelix, suggesting that the cellular uptake of this conjugate was GnRH receptor-mediated. Put together, these findings revealed that coupling ZnPc with GnRH analogue was an effective way to improve the selectivity of ZnPc towards tumors with over-expressed GnRH receptors.

Conjugation to the cell-penetrating peptide TAT potentiates the photodynamic effect of carboxytetramethylrhodamine

Background

Cell-penetrating peptides (CPPs) can transport macromolecular cargos into live cells. However, the cellular delivery efficiency of these reagents is often suboptimal because CPP-cargo conjugates typically remain trapped inside endosomes. Interestingly, irradiation of fluorescently labeled CPPs with light increases the release of the peptide and its cargos into the cytosol. However, the mechanism of this phenomenon is not clear. Here we investigate the molecular basis of the photo-induced endosomolytic activity of the prototypical CPPs TAT labeled to the fluorophore 5(6)-carboxytetramethylrhodamine (TMR).

Methodology/Principal Findings

We report that TMR-TAT acts as a photosensitizer that can destroy membranes. TMR-TAT escapes from endosomes after exposure to moderate light doses. However, this is also accompanied by loss of plasma membrane integrity, membrane blebbing, and cell-death. In addition, the peptide causes the destruction of cells when applied extracellularly and also triggers the photohemolysis of red blood cells. These photolytic and photocytotoxic effects were inhibited by hydrophobic singlet oxygen quenchers but not by hydrophilic quenchers.

Conclusions/Significance

Together, these results suggest that TAT can convert an innocuous fluorophore such as TMR into a potent photolytic agent. This effect involves the targeting of the fluorophore to cellular membranes and the production of singlet oxygen within the hydrophobic environment of the membranes. Our findings may be relevant for the design of reagents with photo-induced endosomolytic activity. The photocytotoxicity exhibited by TMR-TAT also suggests that CPP-chromophore conjugates could aid the development of novel Photodynamic Therapy agents.

Gold nanorod-photosensitizer complex for near-infrared fluorescence imaging and photodynamic/photothermal therapy in vivo

A gold nanorod (GNR)-photosensitizer complex was developed for noninvasive near-infrared fluorescence imaging and cancer therapy. We showed that (a) fluorescence emission and singlet oxygen generation by AlPcS(4) were quenched after complex formation with GNRs; (b) 4-fold greater intracellular uptake and better in vitro phototoxicity were observed in GNR-AlPcS(4)-treated cells than in free AlPcS(4)-treated cells; and (c) after intravenous injection of the GNR-AlPcS(4) complex, tumor sites were clearly identified on near-infrared fluorescence images as early as 1 h after injection. The tumor-to-background ratio increased over time and was 3.7 at 24 h; tumor growth reduced by 79% with photodynamic therapy (PDT) alone and by 95% with dual photothermal therapy (PTT) and PDT. This novel multifunctional nanomedicine may be useful for near-infrared fluorescence imaging and PTT/PDT in various cancers.

Synthesis and photophysical properties of sulfonamidophenyl porphyrins as models for activatable photosensitizers

The ability to localize agents to specific anatomic sites remains an important aspect in designing more efficient therapeutics. Light-activated therapies, in particular, allow for the focal ablation of target tissues and cells. In order to increase the specificity of these agents, stimuli-activated systems have been developed, which are nonphototoxic in the absence of activation. To this end, we propose a novel paradigm for excited state quenching and activation based upon the direct conjugation of quenching moieties to the porphyrinic macrocycle. Model compounds, based upon meso-(p-aminophenyl)porphyrins were synthesized bearing 1 to 4 sulfonamide-linked 2,4-dinitrobenzene. The singlet oxygen and fluorescence quantum yields of these compounds were obtained and compared, as well as the kinetics of activation with relevant activating agents. In addition, methods were developed to further modify the porphyrin in order to modulate the polarity and effect conjugation to biomolecules or nanoparticulate scaffolds. These systems may prove useful in the treatment of a number of disease states, such as cancer and bacterial infection.