Photocytotoxicity of mTHPC (temoporfin) loaded polymeric micelles mediated by lipase catalyzed degradation

Nanobody-mediated targeting of zinc phthalocyanine with polymer micelles as nanocarriers

Photodynamic therapy (PDT) is a suitable alternative to currently employed cancer treatments. However, the hydrophobicity of most photosensitizers (e.g., zinc phthalocyanine (ZnPC)) leads to their aggregation in blood. Moreover, non-specific accumulation in skin and low clearance rate of ZnPC leads to long-lasting skin photosensitization, forcing patients with a short life expectancy to remain indoors. Consequently, the clinical implementation of these photosensitizers is limited. Here, benzyl-poly(ε-caprolactone)-b-poly(ethylene glycol) micelles encapsulating ZnPC (ZnPC-M) were investigated to increase the solubility of ZnPC and its specificity towards cancers cells. Asymmetric flow field-flow fractionation was used to characterize micelles with different ZnPC-to-polymer ratios and their stability in human plasma. The ZnPC-M with the lowest payload (0.2 and 0.4% ZnPC w/w) were the most stable in plasma, exhibiting minimal ZnPC transfer to lipoproteins, and induced the highest phototoxicity in three cancer cell lines. Nanobodies (Nbs) with binding specificity towards hepatocyte growth factor receptor (MET) or epidermal growth factor receptor (EGFR) were conjugated to ZnPC-M to facilitate cell targeting and internalization. MET- and EGFR-targeting micelles enhanced the association and the phototoxicity in cells expressing the target receptor. Altogether, these results indicate that ZnPC-M decorated with Nbs targeting overexpressed proteins on cancer cells may provide a better alternative to currently approved formulations.

Nanocatalysts for modulating antitumor immunity: fabrication, mechanisms and applications

Immunotherapy harnesses the inherent immune system in the body to generate systemic antitumor immunity, offering a promising modality for defending against cancer. However, tumor immunosuppression and evasion seriously restrict the immune response rates in clinical settings. Catalytic nanomedicines can transform tumoral substances/metabolites into therapeutic products in situ, offering unique advantages in antitumor immunotherapy. Through catalytic reactions, both tumor eradication and immune regulation can be simultaneously achieved, favoring the development of systemic antitumor immunity. In recent years, with advancements in catalytic chemistry and nanotechnology, catalytic nanomedicines based on nanozymes, photocatalysts, sonocatalysts, Fenton catalysts, electrocatalysts, piezocatalysts, thermocatalysts and radiocatalysts have been rapidly developed with vast applications in cancer immunotherapy. This review provides an introduction to the fabrication of catalytic nanomedicines with an emphasis on their structures and engineering strategies. Furthermore, the catalytic substrates and state-of-the-art applications of nanocatalysts in cancer immunotherapy have also been outlined and discussed. The relationships between nanostructures and immune regulating performance of catalytic nanomedicines are highlighted to provide a deep understanding of their working mechanisms in the tumor microenvironment. Finally, the challenges and development trends are revealed, aiming to provide new insights for the future development of nanocatalysts in catalytic immunotherapy.

Ru(II) CONTAINING PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CRITIQUE ON REPORTING AND AN ATTEMPT TO COMPARE EFFICACY

Ruthenium(II)-based coordination complexes have emerged as photosensitizers (PSs) for photodynamic therapy (PDT) in oncology as well as antimicrobial indications and have great potential. Their modular architectures that integrate multiple ligands can be exploited to tune cellular uptake and subcellular targeting, solubility, light absorption, and other photophysical properties. A wide range of Ru(II) containing compounds have been reported as PSs for PDT or as photochemotherapy (PCT) agents. Many studies employ a common scaffold that is subject to systematic variation in one or two ligands to elucidate the impact of these modifications on the photophysical and photobiological performance. Studies that probe the excited state energies and dynamics within these molecules are of fundamental interest and are used to design next-generation systems. However, a comparison of the PDT efficacy between Ru(II) containing PSs and 1st or 2nd generation PSs, already in clinical use or preclinical/clinical studies, is rare. Even comparisons between Ru(II) containing molecular structures are difficult, given the wide range of excitation wavelengths, power densities, and cell lines utilized. Despite this gap, PDT dose metrics quantifying a PS's efficacy are available to perform qualitative comparisons. Such models are independent of excitation wavelength and are based on common outcome parameters, such as the photon density absorbed by the Ru(II) compound to cause 50% cell kill (LD50) based on the previously established threshold model. In this focused photophysical review, we identified all published studies on Ru(II) containing PSs since 2005 that reported the required photophysical, light treatment, and in vitro outcome data to permit the application of the Photodynamic Threshold Model to quantify their potential efficacy. The resulting LD50 values range from less than 1013 to above 1020 [hν cm-3], indicating a wide range in PDT efficacy and required optical energy density for ultimate clinical translation.

Nanoformulation of Tetrapyrroles Derivatives in Photodynamic Therapy: A Focus on Bacteriochlorin

Photodynamic therapy (PDT) is a well-known remedial treatment for cancer, infections, and various other diseases. PDT uses nontoxic dyes called photosensitizers (PS) that are activated in visible light at the proper wavelength to generate ROS (reactive oxygen species) that aid in killing tumor cells and destroying pathogenic microbes. Deciding a suitable photosensitizer is essential for enhancing the effectiveness of photodynamic therapy. It is challenging to choose the photosensitizer that is appropriate for specific pathological circumstances, such as different cancer species. Porphyrin, chlorin, and bacteriochlorin are tetrapyrroles used with proper functionalization in PDT, among which some compound has been clinically approved. Most photosensitizers are hydrophobic, have minimum solubility, and exhibit cytotoxicity due to the dispersion in biological fluid. This paper reviewed some nanotechnology-based strategies to overcome these drawbacks. In PDT, metal nanoparticles are widely used due to their enhanced surface plasmon resonance. The self-assembled nano-drug carriers like polymeric micelles, liposomes, and metal-based nanoparticles play a significant role in solubilizing the photosensitizer to make them biocompatible.

In Vitro Assessment of Binding Affinity, Selectivity, Uptake, Intracellular Degradation, and Toxicity of Nanobody-Photosensitizer Conjugates

Photosensitizers have recently been conjugated to nanobodies for targeted photodynamic therapy (PDT) to selectively kill cancer cells. The success of this approach relies on nanobody-photosensitizer conjugates that bind specifically to their targets with very high affinities (k_D in low nM range). Subsequently, upon illumination, these conjugates are very toxic and selective to cells overexpressing the target of interest (EC₅₀ in low nM range). In this chapter, protocols are described to determine the binding affinity of the nanobody-photosensitizer conjugates and assess the toxicity and selectivity of the conjugates when performing in vitro PDT studies. In addition, and because the efficacy of PDT also depends on the (subcellular) localization of the conjugates at the time of illumination, assays are described to investigate the uptake and the intracellular degradation of the nanobody-photosensitizer conjugates.

Immune Reprogramming Precision Photodynamic Therapy of Peritoneal Metastasis by Scalable Stem-Cell-Derived Extracellular Vesicles

The dissemination of tumor metastasis in the peritoneal cavity, also called peritoneal metastasis (PM) or carcinomatosis, represents a late stage of gastrointestinal and gynecological cancer with very poor prognosis, even when cytoreductive surgery is effective, due to residual microscopic disease. Photodynamic therapy (PDT) in the management of peritoneal metastasis has been clinically limited by the low tumor selectivity of photosensitizers (PS) and important adverse effects. Here, we propose extracellular nanovesicles (EVs) derived from mesenchymal stem/stromal cells (MSCs) as the fourth generation of immune active PS vectors that are able to target peritoneal metastasis with superior selectivity, potentiate PDT cytotoxicity at the tumor site without affecting healthy tissues, modulate the tumor microenvironment of immunocompetent colorectal and ovarian carcinomatosis models, and promote an antitumor immune response. A pioneering strategy was developed for high yield, large-scale production of MSC-EVs encapsulating the drug meta(tetrahydroxyphenyl)chlorin (mTHPC) (EVs-mTHPC) that is compatible with requirements of clinical translation and also preserves the topology and integrity of naturally produced EVs. Intraperitoneal injection of EVs-mTHPC showed an impressive enhancement of tumoral selectivity in comparison to the free drug and to the liposomal formulation Foslip (mean ratio of PS in tumors/organs of 40 for EVs-mTHPC versus 1.5 for the free PS and 5.5 for Foslip). PDT mediated by EVs-mTHPC permitted an important tumoral necrosis (55% of necrotic tumoral nodules versus 18% for Foslip (p < 0.0001)) and promoted antitumor immune cell infiltration, mainly proinflammatory M1-like CD80+ and CD8+ T cell effector. Intratumor proliferation was significantly decreased after PDT with EVs-mTHPC. Overall EVs vectorization of mTHPC afforded important tumoral selectivity while overcoming the PDT toxicity of the free drug and prolonged mice survival in the colorectal carcinomatosis model. MSC-EVs produced by our scalable manufacturing method appears like the clinically relevant fourth-generation PDT vehicle to overcome current limitations of PDT in the treatment of peritoneal metastasis and promote a hot tumor immune environment in PM.

Optical properties of photodynamic therapy drugs in different environments: the paradigmatic case of temoporfin

Computational tools have been used to study the photophysical and photochemical features of photosensitizers in photodynamic therapy (PDT) - a minimally invasive, less aggressive alternative for cancer treatment. PDT is mainly based on the activation of molecular oxygen through the action of a photoexcited sensitizer (photosensitizer). Temoporfin, widely known as mTHPC, is a second-generation photosensitizer, which produces the cytotoxic singlet oxygen when irradiated with visible light and hence destroys tumor cells. However, the bioavailability of the mostly hydrophobic photosensitizer, and hence its incorporation into cells, is fundamental to achieve the desired effect on malignant tissues via PDT. In this study, we focus on the optical properties of the temoporfin chromophore in different environments -in vacuo, in solution, encapsulated in drug delivery agents, namely cyclodextrin, and interacting with a lipid bilayer.

π-π-Stacked Poly(ε-caprolactone)-b-poly(ethylene glycol) Micelles Loaded with a Photosensitizer for Photodynamic Therapy

To improve the in vivo stability of poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL-PEG)-based micelles and cargo retention by π-π stacking interactions, pendant aromatic rings were introduced by copolymerization of ε-caprolactone with benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (TMC-Bz). It was shown that the incorporation of aromatic rings yielded smaller micelles (18–30 nm) with better colloidal stability in PBS than micelles without aromatic groups. The circulation time of i.v. injected micelles containing multiple pendant aromatic groups was longer (t½-α: ~0.7 h; t½-β: 2.9 h) than that of micelles with a single terminal aromatic group (t½ < 0.3 h). In addition, the in vitro partitioning of the encapsulated photosensitizer (meta-tetra(hydroxyphenyl)chlorin, mTHPC) between micelles and human plasma was favored towards micelles for those that contained the pendant aromatic groups. However, this was not sufficient to fully retain mTHPC in the micelles in vivo, as indicated by similar biodistribution patterns of micellar mTHPC compared to free mTHPC, and unequal biodistribution patterns of mTHPC and the host micelles. Our study points out that more detailed in vitro methods are necessary to more reliably predict in vivo outcomes. Furthermore, additional measures beyond π-π stacking are needed to stably incorporate mTHPC in micelles in order to benefit from the use of micelles as targeted delivery systems.

Amphiphilic phthalocyanines in polymeric micelles: a supramolecular approach toward efficient third-generation photosensitizers

In this paper we describe a straightforward supramolecular strategy to encapsulate silicon phthalocyanine (SiPc) photosensitizers (PS) in polymeric micelles made of poly(ε-caprolactone)-b-methoxypoly(ethylene glycol) (PCL-PEG) block copolymers. While PCL-PEG micelles are promising nanocarriers based on their biocompatibility and biodegradability, the design of our new PS favors their encapsulation. In particular, they combine two axial benzoyl substituents, each of them carrying either three hydrophilic methoxy(triethylenoxy) chains (1), three hydrophobic dodecyloxy chains (3), or both kinds of chains (2). The SiPc derivatives 1 and 2 are therefore amphiphilic, with the SiPc unit contributing to the hydrophobic core, while lipophilicity increases along the series, making it possible to correlate the loading efficacy in PCL-PEG micelles with the hydrophobic/hydrophilic balance of the PS structure. This has led to a new kind of third-generation nano-PS that efficiently photogenerates ¹O₂, while preliminary in vitro experiments demonstrate an excellent cellular uptake and a promising PDT activity.

Current state of the nanoscale delivery systems for temoporfin-based photodynamic therapy: Advanced delivery strategies

Enthusiasm for photodynamic therapy (PDT) as a promising technique to eradicate various cancers has increased exponentially in recent decades. The majority of clinically approved photosensitizers are hydrophobic in nature, thus, the effective delivery of photosensitizers at the targeted site is the main hurdle associated with PDT. Temoporfin (mTHPC, medicinal product name: Foscan®), is one of the most potent clinically approved photosensitizers, is not an exception. Successful temoporfin-PDT requires nanoscale delivery systems for selective delivery of photosensitizer. Over the last 25 years, the number of papers on nanoplatforms developed for mTHPC delivery such as conjugates, host-guest inclusion complexes, lipid-and polymer-based nanoparticles and carbon nanotubes is burgeoning. However, none of them appeared to be "ultimate". The present review offers the description of different challenges and achievements in nanoparticle-based mTHPC delivery focusing on the synergetic combination of various nano-platforms to improve temoporfin delivery at all stages of biodistribution. Furthermore, the association of different nanoparticles in one nanoplatform might be considered as an advanced strategy allowing the combination of several treatment modalities.

Evaluation of mTHPC-loaded PLGA nanoparticles for in vitro photodynamic therapy on C6 glioma cell line

Photodynamic therapy (PDT) is a very attractive strategy to complement or replace common cancer treatments such as radiotherapy, surgery, and chemotherapy. Some molecules have shown their efficiency as photosensitizers (PS), still many issues have to be solved such as the inherent cytotoxicity of the PS or its hydrophobic properties causing limitation in their solubility, leading to side effects. In this study, the encapsulation of an approved PS, the meso-tetra hydroxyphenylchlorine (mTHPC, Foscan®) within biocompatible and biodegradable poly(D, l-lactide-co-glycolide) acid (PLGA) NPs prepared by the nanoprecipitation method was studied. The mTHPC-loaded NPs (mTHPC ⊂ PLGA NPs) were analyzed by UV-vis spectroscopy to determine the efficiency of mTHPC encapsulation, and by dynamic light scattering (DLS) and atomic force microscopy (AFM) to determine mTHPC ⊂ PLGA NPs sizes, morphologies and surface charges. The longitudinal follow-up of mTHPC release from the NPs indicated that 50% of the encapsulated PS was retained within the NP matrix after a period of five days. Finally, the cytotoxicity and the phototoxicity of the mTHPC ⊂ PLGA NPs were determined in murine C6 glioma cell lines and compared to the ones of mTHPC alone. The studies showed a strong decrease of mTHPC cytotoxicity and an increase of mTHPC photo-cytotoxicity when mTHPC was encapsulated. In order to have a better insight of the underlying cellular mechanisms that governed cell death after mTHPC ⊂ PLGA NPs incubation and irradiation, annexin V staining tests were performed. The results indicated that apoptosis was the main cell death mechanism.

Molecular bionics - engineering biomaterials at the molecular level using biological principles

Life and biological units are the result of the supramolecular arrangement of many different types of molecules, all of them combined with exquisite precision to achieve specific functions. Taking inspiration from the design principles of nature allows engineering more efficient and compatible biomaterials. Indeed, bionic (from bion-, unit of life and -ic, like) materials have gained increasing attention in the last decades due to their ability to mimic some of the characteristics of nature systems, such as dynamism, selectivity, or signalling. However, there are still many challenges when it comes to their interaction with the human body, which hinder their further clinical development. Here we review some of the recent progress in the field of molecular bionics with the final aim of providing with design rules to ensure their stability in biological media as well as to engineer novel functionalities which enable navigating the human body.

Epidermal growth factor receptor (EGFR) density may not be the only determinant for the efficacy of EGFR-targeted photoimmunotherapy in human head and neck cancer cell lines

OBJECTIVE

The aim of this study was to investigate the effects of targeted photoimmunotherapy (PIT) in vitro on cell lines with various expression levels of epidermal growth factor receptor (EGFR) using an anti-EGFR targeted conjugate composed of Cetuximab and IR700DX, phthalocyanine dye.

MATERIALS AND METHODS

Relative EGFR density and cell binding assay was conducted in three human head & neck cancer cell lines (scc-U2, scc-U8, and OSC19) and one reference cell line A431. After incubation with the conjugate for 1 or 24 hours, cellular uptake and localization were investigated by confocal laser scanning microscopy and quantified by image analysis. Cell survival was determined using the MTS assay and alamarBlue assay after PIT with a 690 nm laser to a dose of 7 J.cm^-2 (at 5 mW.cm^-2 ). The mode of cell death was examined with flow cytometry using apoptosis/necrosis staining by Annexin V/propidium iodide, together with immunoblots of anti-apoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL.

RESULTS

A431 cells had the highest EGFR density followed by OSC19, and then scc-U2 and scc-U8. The conjugates were localized both on the surface and in the cytosol of the cells after 1- and 24-hour incubation. After 24-hour incubation the granular pattern was more pronounced and in a similar pattern of a lysosomal probe, suggesting that the uptake of conjugates by cells was via receptor-mediated endocytosis. The results obtained from the quantitative imaging analysis correlate with the level of EGFR expression. Targeted PIT killed scc-U8 and A431 cells efficiently; while scc-U2 and OSC19 were less sensitive to this treatment, despite having similar EGFR density, uptake and localization pattern. Scc-U2 cells showed less apoptotic cell dealth than in A431 after 24-hour targeted PIT. Immunoblots showed significantly higher expression of anti-apoptotic Bcl-2 and Bcl-xL proteins in scc-U2 cell lines compared to scc-U8.

CONCLUSION

Our study suggests that the effectiveness of EGFR targeted PIT is not only dependent upon EGFR density. Intrinsic biological properties of tumor cell lines also play a role in determining the efficacy of targeted PIT. We have shown that in scc-U2 cells this difference may be caused by differences in the apoptopic pathway. Lasers Surg. Med. 50:513-522, 2018. © 2018 Wiley Periodicals, Inc.

The alteration of temoporfin distribution in multicellular tumor spheroids by β-cyclodextrins

To be effective anticancer drugs must penetrate tissue efficiently, reaching all target population of cancer cells in a concentration sufficient to exert a therapeutic effect. This study aimed to investigate the ability of methyl-β-cyclodextrin (Me-β-CD) and 2-hydroxypropyl-β-cyclodextrin (Hp-β-CD) to alter the penetration and diffusion of temoporfin (mTHPC) in HT29 multicellular tumor spheroids. mTHPC had а nonhomogenous distribution only on the periphery of spheroids. The presence of β-CDs significantly altered the distribution of mTHPC consisting in the increase of both the depth of photosensitizer penetration and accumulation in HT29 spheroids. We suggest that this improvement is related to the nanoshuttle mechanism of β-CD action, when β-CDs facilitate mTHPC transportation to the cells in the inner layers of spheroids. As a result of mTHPC distribution improvement, β-CDs enhance mTHPC photosensitizing activity towards HT29 multicellular tumor spheroids. The observed effects strongly depend on the type of β-CD. Thus, varying the type of β-CD we can finely tune the possibility of using mTHPC for diagnostic (delimitation of tumor margins) or therapeutic purposes.

Legomedicine-A Versatile Chemo-Enzymatic Approach for the Preparation of Targeted Dual-Labeled Llama Antibody-Nanoparticle Conjugates

Conjugation of llama single domain antibody fragments (Variable Heavy chain domains of Heavy chain antibodies, VHHs) to diagnostic or therapeutic nanoparticles, peptides, proteins, or drugs offers many opportunities for optimized targeted cancer treatment. Currently, mostly nonspecific conjugation strategies or genetic fusions are used that may compromise VHH functionality. In this paper we present a versatile modular approach for bioorthogonal VHH modification and conjugation. First, sortase A mediated transPEGylation is used for introduction of a chemical click moiety. The resulting clickable VHHs are then used for conjugation to other groups employing the Cu⁺-independent strain-promoted alkyne–azide cycloadition (SPAAC) reaction. Using this approach, tail-to-tail bispecific VHHs and VHH-targeted nanoparticles are generated without affecting VHH functionality. Furthermore, this approach allows the bioconjugation of multiple moieties to VHHs for simple and convenient production of VHH-based theranostics.

EGFR targeted nanobody-photosensitizer conjugates for photodynamic therapy in a pre-clinical model of head and neck cancer

Photodynamic therapy (PDT) induces cell death through local light activation of a photosensitizer (PS) and has been used to treat head and neck cancers. Yet, common PS lack tumor specificity, which leads to collateral damage to normal tissues. Targeted delivery of PS via antibodies has pre-clinically improved tumor selectivity. However, antibodies have long half-lives and relatively poor tissue penetration, which could limit therapeutic efficacy and lead to long photosensitivity. Here, in this feasibility study, we evaluate at the pre-clinical level a recently introduced format of targeted PDT, which employs nanobodies as targeting agents and a water-soluble PS (IRDye700DX) that is traceable through optical imaging. In vitro, the PS solely binds to cells and induces phototoxicity on cells overexpressing the epidermal growth factor receptor (EGFR), when conjugated to the EGFR targeted nanobodies. To investigate whether this new format of targeted PDT is capable of inducing selective tumor cell death in vivo, PDT was applied on an orthotopic mouse tumor model with illumination at 1h post-injection of the nanobody-PS conjugates, as selected from quantitative fluorescence spectroscopy measurements. In parallel, and as a reference, PDT was applied with an antibody-PS conjugate, with illumination performed 24h post-injection. Importantly, EGFR targeted nanobody-PS conjugates led to extensive tumor necrosis (approx. 90%) and almost no toxicity in healthy tissues, as observed through histology 24h after PDT. Overall, results show that these EGFR targeted nanobody-PS conjugates are selective and able to induce tumor cell death in vivo. Additional studies are now needed to assess the full potential of this approach to improving PDT.

Overcoming the Achilles' heel of photodynamic therapy

This review summarizes the latest progress in deep photodynamic therapy (PDT), which overcomes the Achilles' heel of PDT.

Developments in PDT Sensitizers for Increased Selectivity and Singlet Oxygen Production

Photodynamic therapy (PDT) is a minimally-invasive procedure that has been clinically approved for treating certain types of cancers. This procedure takes advantage of the cytotoxic activity of singlet oxygen (¹O₂) and other reactive oxygen species (ROS) produced by visible and NIR light irradiation of dye sensitizers following their accumulation in malignant cells. The main two concerns associated with certain clinically-used PDT sensitizers that have been influencing research in this arena are low selectivity toward malignant cells and low levels of ¹O₂ production in aqueous media. Solving the selectivity issue would compensate for photosensitizer concerns such as dark toxicity and aggregation in aqueous media. One main approach to enhancing dye selectivity involves taking advantage of key methods used in pharmaceutical drug delivery. This approach lies at the heart of the recent developments in PDT research and is a point of emphasis in the present review. Of particular interest has been the development of polymeric micelles as nanoparticles for delivering hydrophobic (lipophilic) and amphiphilic photosensitizers to the target cells. This review also covers methods employed to increase ¹O₂ production efficiency, including the design of two-photon absorbing sensitizers and triplet forming cyclometalated Ir(III) complexes.

Targeted photodynamic therapy in head and neck squamous cell carcinoma: heading into the future

The aim of this article is to give an insight into the future of photodynamic therapy (PDT) in head and neck squamous cell carcinoma (HNSCC). Through the combination of a photosensitizing agent with light and oxygen, PDT produces highly cytotoxic reactive oxygen species leading to selective tumor eradication. PDT is an attractive treatment for focal therapy of localized tumors, especially in the case of unresectable tumors. In HNSCC, over 1500 patients have been treated by PDT, and the majority of them responded quite favorably to this treatment. However, the non-negligible photosensitization of healthy tissue is a major limitation for the clinical application of PDT. Improvement in tumor selectivity is the main challenge that can be taken up by the use of a new generation of photosensitizing nanoparticles. Passive targeting, by using functionalised nanocarriers to target to overexpressed transmembrane receptors afford attractive solutions. To this day, epidermal growth factor receptor (EGFR) remains the only validated molecular target for HNSCC, and photosensitizer immunoconjugates to EGFR have been developed for the intracellular delivery of photosensitizing agents. Depending on coordinated research between biomarkers, specific ligands, and photosensitizers, similar approaches could be rapidly developed. In addition, some photosensitizers hold high fluorescence yield and therefore could emerge as theranostic agents.

Quantum chemistry studies of meta-tetra(hydroxyphenyl)chlorin (mTHPC) and its isomers

Quantum chemistry methods were used to study the meta-tetra(hydroxyphenyl)chlorin (mTHPC) and its isomers. The mTHPC (Foscan®) is a commercial chlorin, used in photodynamic therapy (PDT) and is classified as a second-generation drug in PDT. The present work is to obtain quantum chemistry properties which can explain the high efficiency of the mTHPC compared with its isomers (ortho and para) and other chlorins. Based in the chemical hardness and ionization potential obtained from HOMO and LUMO orbitals energy, our results show that all chlorins have similar reactivity. Moreover, all chlorins have approximately the same capacity to storage energy in the triplet excited state, with energy differences between the ground state and the triplet excited state of 1.38, 1.39 and 1.36 eV for oTHPC, mTHPC and pTHPC, respectively. The calculated UV spectra (a very important quantity which can be correlated with the photosensitizer (PS) efficiency property), shows that the present chlorins all have a peak at 622 nm. Finally, after analysis of the dipole moment differences, between the three isomers, an explanation about the greater mTHPC efficiency in PDT, was possible. Due to its greater lipophilic character, mTHPC is absorbed by tumor cells to a greater degree than oTHPC and pTHPC. Our findings are consistent with literature and can be used to help new drug design for use in PDT.

Nanobody-photosensitizer conjugates for targeted photodynamic therapy

Photodynamic therapy (PDT) induces cell death through light activation of a photosensitizer (PS). Targeted delivery of PS via monoclonal antibodies has improved tumor selectivity. However, these conjugates have long half-lives, leading to relatively long photosensitivity in patients. In an attempt to target PS specifically to tumors and to accelerate PS clearance, we have developed new conjugates consisting of nanobodies (NB) targeting the epidermal growth factor receptor (EGFR) and a traceable PS (IRDye700DX). These fluorescent conjugates allow the distinction of cell lines with different expression levels of EGFR. Results show that these conjugates specifically induce cell death of EGFR overexpressing cells in low nanomolar concentrations, while PS alone or the NB-PS conjugates in the absence of light induce no toxicity. Delivery of PS using internalizing biparatopic NB-PS conjugates results in even more pronounced phototoxicities. Altogether, EGFR-targeted NB-PS conjugates are specific and potent, enabling the combination of molecular imaging with cancer therapy. From the clinical editor: This study investigates the role of EGFR targeting nanobodies to deliver traceable photosensitizers to cancer molecules for therapeutic exploitation and concomitant imaging. Altogether, EGFR-targeted NB-PS conjugates combine molecular imaging with cancer therapy, the method is specific and potent, paving the way to clinical application of this technology.

Complexes of Chlorin e6 with Pluronics and Polyvinylpyrrolidone: Structure and Photodynamic Activity in Cell Culture

Polymeric carriers are extensively used in photodynamic therapy (PDT) for increase of efficacy of photosensitizers. Here, we report the influence of nine Pluronic copolymers on phototoxicity of chlorin e6 (Ce6), in particular 5- to 7-fold rise in the phototoxicity caused by hydrophilic Pluronics F127, F108, F68 and F87 and practically no influence on Ce6 of more hydrophobic polymers. The revealed value of 0.2 mg mL(-1) of Pluronic F127 concentration sufficient for half-of-maximal increase of Ce6 photodynamic activity proved to be close to 0.16 mg mL(-1) inherent in well-documented carrier poly(N-vinylpyrrolidone) (PVP). The dissociation constants of Ce6 complexes with Pluronic F127 and PVP that were estimated from UV spectra were 0.252 and 0.036 mg mL(-1) , respectively, indicating higher stability of Ce6 complex with PVP. According to the results of (1) H-NMR studies of Ce6 complexes, the porphyrin interacts not only with hydrophobic regions but also with hydrophilic sides of both polymers.

Nanotechnology-based photodynamic therapy

According to recent advances in nanotechnology, various nano-sized formulations have been designed for the application in biomedical fields, including diagnosis, drug delivery, and therapeutics. The nanotechnology-based formulations have a great merit in the design of multifunctional platform for the biomedical applications. Therefore, recent trends in nanotechnology are moving onto the combination of nanotechnology and conventional therapeutic. Typically, photodynamic therapy (PDT) is one of promising techniques for the combination with nanotechnology owing to its less invasiveness. In this paper, we are going to briefly review recent advances in nanotechnology-based PDT, including selective delivery and excitation of photosensitizers, combination therapy, and multifunctional PDT.

Cellular and vascular effects of the photodynamic agent temocene are modulated by the delivery vehicle

The effects of the drug delivery system on the PDT activity, localization, and tumor accumulation of the novel photosensitizer temocene (the porphycene analogue of temoporfin or m-tetrahydroxyphenyl chlorin) were investigated against the P815 tumor, both in vitro and in DBA/2 tumor bearing mice. Temocene was administered either free (dissolved in PEG(400)/EtOH mixture), or encapsulated in Cremophor EL micelles or in DPPC/DMPG liposomes, chosen as model delivery vehicles. The maximum cell accumulation and photodynamic activity in vitro was achieved with the free photosensitizer, while temocene in Cremophor micelles hardly entered the cells. Notwithstanding, the micellar formulation showed the best in vivo response when used in a vascular regimen (short drug light interval), whereas liposomes were found to be an efficient drug delivery system for a tumor cell targeting strategy (long drug-light interval). PEG/EtOH formulation was discarded for further in vivo experiments as it provoked lethal toxic effects caused by photosensitizer aggregation. These results demonstrate that drug delivery systems modulate the vascular and cellular outcomes of photodynamic treatments with temocene.

Functional characterization of Fospeg, and its impact on cell cycle upon PDT of Huh7 hepatocellular carcinoma cell model

BACKGROUND

Although several treatment options are available for hepatocellular carcinoma (HCC), their application is mostly restricted to early diagnosed cases or includes liver transplantation, which is rarely available due to donor scarcity. The attractiveness of PDT as a cancer treatment does not only come from its minimal invasiveness, but also from the high selectivity due to tumor localization that can be applied. Precise focusing of light on tumor lesions will result in tumor-specific PDT activation. Novel photosensitizers can be applied in such low concentrations that cells not subjected to irradiation remain healthy. The lethal effect and mechanism of death induction of the photosensitizer Fospeg has never been studied on hepatocellular carcinoma. The aim of the present study is to functionally analyze the impact of PDT on Huh-7 HCC cell line, as well as to analyze its impact on cell cycle protein expression.

METHODS

Cellular viability, and proliferation assays were conducted via MTT and BrdU assay, respectively. Transfected cell models of Huh7 with different constructs harboring cell cycle genes and downstream reporter luciferase gene were generated.

RESULTS

Our results show a statistically significant decrease in both viability and proliferation of Huh-7 cells following PDT, while maintaining Fospeg and laser concentrations far below toxic levels. Proliferative cell cycle genes show a tendency of inhibition, while p53 levels show a significant increase following PDT.

CONCLUSION

Fospeg-mediated PDT is a promising strategy for treatment of hepatocellular carcinoma and needs to be further explored in vivo.

Fluorescence localization and kinetics of mTHPC and liposomal formulations of mTHPC in the window-chamber tumor model

BACKGROUND AND OBJECTIVE

Foslip® and Fospeg® are liposomal formulations of the photosensitizer mTHPC, intended for use in Photodynamic Therapy (PDT) of malignancies. Foslip consists of mTHPC encapsulated in conventional liposomes, Fospeg consists of mTHPC encapsulated in pegylated liposomes. Possible differences in tumor fluorescence and vasculature kinetics between Foslip, Fospeg, and Foscan® were studied using the rat window-chamber model.

MATERIAL AND METHODS

In 18 rats a dorsal skin fold window chamber was installed and a mammary carcinoma was transplanted in the subcutaneous tissue. The dosage used for intravenous injection was 0.15 mg/kg mTHPC for each formulation. At seven time-points after injection (5 minutes to 96 hours) fluorescence images were made with a CCD. The achieved mTHPC fluorescence images were corrected for tissue optical properties and autofluorescence by the ratio fluorescence imaging technique of Kascakova et al. Fluorescence intensities of three different regions of interest (ROI) were assessed; tumor tissue, vasculature, and surrounding connective tissue.

RESULTS

The three mTHPC formulations showed marked differences in their fluorescence kinetic profile. After injection, vascular mTHPC fluorescence increased for Foslip and Fospeg but decreased for Foscan. Maximum tumor fluorescence is reached at 8 hours for Fospeg and at 24 hours for Foscan and Foslip with overall higher fluorescence for both liposomal formulations. Foscan showed no significant difference in fluorescence intensity between surrounding tissue and tumor tissue (selectivity). However, Fospeg showed a trend toward tumor selectivity at early time points, while Foslip reached a significant difference (P < 0.05) at these time points.

CONCLUSIONS

Our results showed marked differences in fluorescence intensities of Fospeg, Foslip, and Foscan, which suggest overall higher bioavailability for the liposomal formulations. Pegylated liposomes seemed most promising for future application; as Fospeg showed highest tumor fluorescence at the earlier time points.

Can nanotechnology potentiate photodynamic therapy?

Photodynamic therapy (PDT) uses the combination of non-toxic dyes and harmless visible light to produce reactive oxygen species that can kill cancer cells and infectious microorganisms. Due to the tendency of most photosensitizers (PS) to be poorly soluble and to form nonphotoactive aggregates, drug-delivery vehicles have become of high importance. The nanotechnology revolution has provided many examples of nanoscale drug-delivery platforms that have been applied to PDT. These include liposomes, lipoplexes, nanoemulsions, micelles, polymer nanoparticles (degradable and nondegradable), and silica nanoparticles. In some cases (fullerenes and quantum dots), the actual nanoparticle itself is the PS. Targeting ligands such as antibodies and peptides can be used to increase specificity. Gold and silver nanoparticles can provide plasmonic enhancement of PDT. Two-photon excitation or optical upconversion can be used instead of one-photon excitation to increase tissue penetration at longer wavelengths. Finally, after sections on in vivo studies and nanotoxicology, we attempt to answer the title question, "can nano-technology potentiate PDT?"

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Spray-dried microparticles containing polymeric micelles encapsulating hematoporphyrin

The purpose of this study was to examine the properties of a new pulmonary delivery platform of microparticles containing micelles in which a therapeutic photosensitizing drug, hematoporphyrin (Hp), was encapsulated. Different poloxamers were used to form micellar Hp, and one of these, Pluronic L122-Hp, was subsequently incorporated into lactose microparticles by spray-drying. Spectral and morphological analyses were performed on both micellar Hp, and lactose microparticles containing micellar Hp (lactose-micellar Hp) before and after dissolution of the microparticles in water. Photodynamic activity of the various Hp samples were evaluated in human lung epithelial carcinoma A549 cells using a light-emitting diode (LED) device at a wavelength of 630 +/- 5 nm. No significant difference was observed between micellar Hp and lactose-micellar Hp regarding the generation of singlet oxygen. The mean particle size of the microparticles was 2.3 +/- 0.7 microm which is within the size range for potential lung delivery. The cellular uptake of micellar Hp and lactose-micellar Hp measured on A549 cells was at least twofold higher than those obtained with the Hp at equivalent concentrations. Micellar Hp exhibited higher cytotoxicity than Hp due to reduced formation of Hp aggregates and increased cellar uptake. The spectral properties as well as the photodynamic activity of the micellar Hp was retained when formulated into microparticles by spray-drying. Microparticles containing micelles have the potential for delivering micelle-encapsulated hydrophobic drugs in targeted therapy of pulmonary diseases.

Design and development of dendrimer photosensitizer-incorporated polymeric micelles for enhanced photodynamic therapy

Photodynamic therapy (PDT), which involves systemic administration of photosensitizers (PSs) followed by local photoillumination, is a promising method for the treatment of solid tumors and other diseases. Recently, considerable efforts have been devoted to the development of nanocarriers for the PS delivery with the aim of avoiding non-specific phototoxicity to normal tissues such as the skin. Here, we discuss the biological significance of the use of nanocarrier-encapsulated PSs in PDT. Also, we report our recent achievements on the development of dendrimer photosensitizer-loaded micelles as nanocarriers for PS delivery. We found that our nanocarriers greatly enhanced the PDT efficacy in vitro and in vivo, and also significantly reduced the skin phototoxicity. These results indicate the importance of a development strategy for nanocarriers and their great potential for clinical use. In addition, this review discusses the development of nanocarriers for emerging PDT-related technologies such as photodynamic diagnosis (PDD) and photochemical internalization (PCI).