Verteporfin: a milestone in opthalmology and photodynamic therapy

Next generation of porphysomes for improved photodynamic therapy applications

Porphysomes are a class of liposome-like nanoparticles that have demonstrated efficacy in photothermal therapy (PTT) and photodynamic therapy (PDT) against cancer. These nanoparticles results from the self-assembly of amphiphilic phospholipid-porphyrin (PL-Por) conjugates. Despite their potential, porphysomes exhibit a high photothermal effect and a weak photodynamic activity as long as they remain intact within the body. In this study, we present the design of a novel generation of smart porphysomes capable of undergoing active dissociation and releasing porphyrin moieties upon illumination, thereby enabling tunable photothermal properties with enhanced photodynamic efficiency. These new porphysomes are composed of smart PL-Por conjugates that exhibit one or two ROS-responsive linkers separating the polar head group from the porphyrin moiety. Among the designed molecules, we demonstrated that monosubstituted conjugates bearing either pyro-a or pheo-a porphyrinoids with one ROS-responsive bond and shorter linker showed the best performance in terms of stability, photothermal and photodynamic efficiencies in vitro. Moreover, these assemblies were found to achieve complete tumor ablation in 80 % of PC3 prostate subcutaneous tumor-bearing mice after 30 days post-PDT, compared to 0 % using conventional porphysomes. Consequently, our strategy enabled the development of a versatile platform for delivering porphyrin-based photosensitizers for enhanced photodynamic applications.

Unlocking the power of immune checkpoint inhibitors: Targeting YAP1 reduces anti-PD1 resistance in skin cutaneous melanoma

BACKGROUND AND PURPOSE

Immune checkpoint inhibitors, such as anti-PD1, revolutionized melanoma treatment. However, resistance and low response rates remain problems. Our goal was to pinpoint actionable biomarkers of resistance to anti-PD1 treatment and verify therapeutic effectiveness in vivo.

EXPERIMENTAL APPROACH

Using receiver operating characteristic (ROC) and survival analysis in a database of 1434 samples, we identified the strongest resistance-associated genes. Inhibitors were evaluated in C57BL/6J mice using wild-type B16-F10, and BRAF, -PTEN, -CDKN2A-mutant YUMM1.7 melanoma cell lines. We investigated the synergistic impact of anti-PD1 therapy and yes-associated protein 1 (YAP1) inhibition by non-photoactivated Verteporfin. Tumour volume was determined at fixed cutoff points, normalized to body weights.

KEY RESULTS

In the anti-PD1-treated melanoma cohort, YAP1 was the strongest druggable candidate overexpressed in non-responder patients (ROC AUC = 0.699, FC = 1.8, P=1.1E-8). The baseline YAP1 expression correlated with worse progression-free survival (HR = 2.51, P=1.2E-6, FDR = 1%), and overall survival (HR = 2.15, P = 1.2E-5, FDR = 1%). In YUMM1.7, combination of Verteporfin plus anti-PD1 reduced tumour size more than anti-PD1 monotherapy (P=0.008), or control (P=0.021). There was no difference between the cohorts in B16-F10 inoculated mice. We found increased expression of YAP1 in YUMM1.7 mice compared to B16-F10. The combination therapy induced a more-immune-inflamed phenotype characterized by increased expression of T cell and M1 macrophage markers.

CONCLUSIONS AND IMPLICATIONS

Verteporfin with anti-PD1 exhibited antitumor potential by promoting a pro-inflammatory tumour microenvironment in melanoma. We believe that YAP1 acts as a master regulator of anti-PD1 resistance.

M2 macrophages promote subconjunctival fibrosis through YAP/TAZ signalling

PURPOSE

To evaluate the role of M2 macrophages in subconjunctival fibrosis after silicone implantation (SI) and investigate the underlying mechanisms.

MATERIALS AND METHODS

A model of subconjunctival fibrosis was established by SI surgery in rabbit eyes. M2 distribution and collagen deposition were evaluated by histopathology. The effects of M2 cells on the migration (using wound-scratch assay) and activation (by immunofluorescence and western blotting) of human Tenon's fibroblasts (HTFs) were investigated.

RESULTS

There were more M2 macrophages (CD68+/CD206+ cells) occurring in tissue samples around silicone implant at 2 weeks postoperatively. Dense collagen deposition was observed at 8 weeks after SI. In vitro experiment showed M2 expressed high level of CD206 and transforming growth factor-β1 (TGF-β1). The M2-conditioned medium promoted HTFs migration and the synthesis of collagen I and fibronectin. Meanwhile, M2-conditioned medium increased the protein levels of TGF-β1, TGF-βR II, p-Smad2/3, yes-associated protein (YAP), and transcriptional coactivator with PDZ-binding motif (TAZ). Verteporfin, a YAP inhibitor, suppressedTGF-β1/Smad2/3-YAP/TAZ pathway and attenuated M2-induced extracellular matrix deposition by HTFs.

CONCLUSIONS

TGF-β1/Smad2/3-YAP/TAZ signalling may be involved in M2-induced fibrotic activities in HTFs. M2 plays a key role in promoting subconjunctival fibrosis and can serve as an attractive target for anti-fibrotic therapeutics.

A Physiochemical, In Vitro, and In Vivo Comparative Analysis of Verteporfin-Lipid Conjugate Formulations: Solid Lipid Nanoparticles and Liposomes

VisudyneⓇ, a liposomal formulation of verteporfin (benzoporphyrin derivative; BPD), is the only nanomedicine approved to date for photodynamic therapy (PDT). We have previously demonstrated that BPD conjugated to the lysophospholipid 1-arachidoyl-2-hydroxy-sn-glycero-3-phosphocholine (BPD-PC) exhibits the greatest physical stability in liposomes, while maintaining cancer cell phototoxicity, from a panel of BPD lipid conjugates evaluated. In this study, we prepared 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-based solid lipid nanoparticles (LNPs) that stably entrap BPD-PC, which resemble the composition of the SpikevaxⓇ Moderna COVID-19 vaccine, and compared them to a DPPC based liposomal formulation (Lipo BPD-PC). We evaluated the photochemical, optical, and phototherapeutic properties of both formulations. We also investigated the in vivo distribution and tumor microdistribution of both formulations. Our results demonstrated that Lipo BPD-PC is able to generate 17% more singlet oxygen than LNP BPD-PC, while interestingly, LNP BPD-PC is able to produce 76% more hydroxyl radicals and/or peroxynitrite anion. Importantly, only 28% of BPD-PC leaches out of the LNP BPD-PC formulation during 7 days of incubation in serum at 37 °C, while 100% of BPD-PC leaches out of the Lipo BPD-PC formulation under the same conditions. Despite these differences, there was no significant difference in cellular uptake of BPD-PC or phototoxicity in CT1BA5 murine pancreatic cancer cells (derived from a genetically engineered mouse model). Interestingly, PDT using LNP BPD-PC was more efficient at inducing immunogenic cell death (calreticulin membrane translocation) than Lipo BPD-PC when using IC25 and IC50 PDT doses. In vivo studies revealed that CT1BA5 tumor fluorescence signals from BPD-PC were 2.41-fold higher with Lipo BPD-PC than with LNP BPD-PC; however, no significant difference was observed in tumor tissue selectivity or tumor penetration. As such, we present LNP BPD-PC as a unique and more stable nanoplatform to carry BPD lipid conjugates, such as BPD-PC, with a potential for future photodynamic immune priming studies and multiagent drug delivery.

The Hippo signalling pathway and its impact on eye diseases

The Hippo signalling pathway, an evolutionarily conserved kinase cascade, has been shown to be crucial for cell fate determination, homeostasis and tissue regeneration. Recent experimental and clinical studies have demonstrated that the Hippo signalling pathway is involved in the pathophysiology of ocular diseases. This article provides the first systematic review of studies on the regulatory and functional roles of mammalian Hippo signalling systems in eye diseases. More comprehensive studies on this pathway are required for a better understanding of the pathophysiology of eye diseases and the development of effective therapies.

Tyrosine phosphorylation-mediated YAP1-TFAP2A interactions coordinate transcription and trastuzumab resistance in HER2+ breast cancer

Trastuzumab resistance in HER2+ breast cancer (BC) is the major reason leading to poor prognosis of BC patients. Oncogenic gene overexpression or aberrant activation of tyrosine kinase SRC is identified to be the key modulator of trastuzumab response. However, the detailed regulatory mechanisms underlying SRC activation-associated trastuzumab resistance remain poorly understood. In the present study, we discover that SRC-mediated YAP1 tyrosine phosphorylation facilitates its interaction with transcription factor AP-2 alpha (activating enhancer binding protein 2 alpha, TFAP2A), which in turn promotes YAP1/TEAD-TFAP2A (YTT) complex-associated transcriptional outputs, thereby conferring trastuzumab resistance in HER2+ BC. Inhibition of SRC kinase activity or disruption of YTT complex sensitizes cells to trastuzumab treatment in vitro and in vivo. Additionally, we also identify YTT complex co-occupies the regulatory regions of a series of genes related to trastuzumab resistance and directly regulates their transcriptions, including EGFR, HER2, H19 and CTGF. Moreover, YTT-mediated transcriptional regulation is coordinated by SRC kinase activity. Taken together, our study reveals that SRC-mediated YTT complex formation and transcriptions are responsible for multiple mechanisms associated with trastuzumab resistance. Therefore, targeting HER2 signaling in combination with the inhibition of YTT-associated transcriptional outputs could serve as the treatment strategy to overcome trastuzumab resistance caused by SRC activation.

Establishing a Robust and Reliable Response from a Potent Osmium-Based Photosensitizer Via Lipid Nanoformulation†

Osmium (Os) based photosensitizers (PSs) are a unique class of nontetrapyrrolic metal-containing PSs that absorb red light. We recently reported a highly potent Os(II) PS, rac-[Os(phen)2 (IP-4T)](Cl)2 , referred to as ML18J03 herein, with light EC50 values as low as 20 pm. ML18J03 also exhibits low dark toxicity and submicromolar light EC50 values in hypoxia in some cell lines. However, owing to its longer oligothiophene chain, ML18J03 is not completely water soluble and forms 1-2 μm sized aggregates in PBS containing 1% DMSO. This aggregation causes variability in PDT efficacy between assays and thus unreliable and irreproducible reports of in vitro activity. To that end, we utilized PEG-modified DPPC liposomes (138 nm diameter) and DSPE-mPEG2000 micelles (10.2 nm diameter) as lipid nanoformulation vehicles to mitigate aggregation of ML18J03 and found that the spectroscopic properties important to biological activity were maintained or improved. Importantly, the lipid formulations decreased the interassay variance between the EC50 values by almost 20-fold, with respect to the unformulated ML18J03 when using broadband visible light excitation (P = 0.0276). Herein, lipid formulations are presented as reliable platforms for more accurate in vitro photocytotoxicity quantification for PSs prone to aggregation (such as ML18J03) and will be useful for assessing their in vivo PDT effects.

Zinc-Substituted Pheophorbide A Is a Safe and Efficient Antivascular Photodynamic Agent

The present study focuses on the photodynamic activity of zinc-substituted pheophorbide a against human endothelial cells. Previously, zinc pheophorbide a has been shown to be a very potent photosensitizer but also a strong albumin binder. Binding to albumin significantly reduces its availability to cancer cells, which may necessitate the use of relatively high doses. Here we show that zinc pheophorbide a is very effective against vascular endothelial cells, even in its albumin-complexed form. Albumin complexation increases the lysosomal accumulation of the drug, thus enhancing its efficiency. Zinc pheophorbide a at nanomolar concentrations induces endothelial cell death via apoptosis, which in many cases is considered a desirable cell death mode because of its anti-inflammatory effect. Additionally, we demonstrate that in comparison to tumor cells, endothelial cells are much more susceptible to photodynamic treatment with the use of the investigated compound. Our findings demonstrate that zinc pheophorbide a is a very promising photosensitizer for use in vascular-targeted photodynamic therapy against solid tumors, acting as a vascular shutdown inducer. It can also possibly find application in the treatment of a range of vascular disorders. Numerous properties of zinc pheophorbide a are comparable or even more favorable than those of the well-known photosensitizer of a similar structure, palladium bacteriopheophorbide (TOOKAD^®).

Membrane composition is a functional determinant of NIR-activable liposomes in orthotopic head and neck cancer

Near-infrared (NIR)-activable liposomes containing photosensitizer (PS)-lipid conjugates are emerging as tunable, high-payload, and tumor-selective platforms for photodynamic therapy (PDT)-based theranostics. To date, the impact that the membrane composition of a NIR-activable liposome (the chemical nature and subsequent conformation of PS-lipid conjugates) has on their in vitro and in vivo functionality has not been fully investigated. While their chemical nature is critical, the resultant physical conformation dictates their interactions with the immediate biological environments. Here, we evaluate NIR-activable liposomes containing lipid conjugates of the clinically-used PSs benzoporphyrin derivative (BPD; hydrophobic, membrane-inserting conformation) or IRDye 700DX (hydrophilic, membrane-protruding conformation) and demonstrate that membrane composition is critical for their function as tumor-selective PDT-based platforms. The PS-lipid conformations were primarily dictated by the varying solubilities of the two PSs and assisted by their lipid conjugation sites. Conformation was further validated by photophysical analysis and computational predictions of PS membrane partitioning (topological polar surface area [tPSA], calculated octanol/water partition [cLogP], and apparent biomembrane permeability coefficient [P_app]). Results show that the membrane-protruding lipo-IRDye700DX exhibits 5-fold more efficient photodynamic generation of reactive molecular species (RMS), 12-fold expedited phototriggered burst release of entrap-ped agents, and 15-fold brighter fluorescence intensity as compared to the membrane-inserting lipo-BPD-PC (phosphatidylcholine conjugate). Although the membrane-inserting lipo-BPD-PC exhibits less efficient photo-dynamic generation of RMS, it allows for more sustained phototriggered release, 10-fold greater FaDu cancer cell phototoxicity, and 7.16-fold higher tumor-selective delivery in orthotopic mouse FaDu head and neck tumors. These critical insights pave the path for the rational design of emerging NIR-activable liposomes, whereby functional consequences of membrane composition can be tailored toward a specific therapeutic purpose.

Transpupillary collagen photocrosslinking for targeted modulation of ocular biomechanics

The central vision-threatening event in glaucoma is dysfunction and loss of retinal ganglion cells (RGCs), thought to be promoted by local tissue deformations. Here, we sought to reduce tissue deformation near the optic nerve head by selectively stiffening the peripapillary sclera, i.e. the scleral region immediately adjacent to the optic nerve head. Previous scleral stiffening studies to treat glaucoma or myopia have used either pan-scleral stiffening (not regionally selective) or regionally selective stiffening with limited access to the posterior globe. We present a method for selectively stiffening the peripapillary sclera using a transpupillary annular light beam to activate methylene blue administered by retrobulbar injection. Unlike prior approaches to photocrosslinking in the eye, this approach avoids the damaging effects of ultraviolet light by employing red light. This targeted photocrosslinking approach successfully stiffened the peripapillary sclera at 6 weeks post-treatment, as measured by whole globe inflation testing. Specifically, strain was reduced by 47% when comparing treated vs. untreated sclera within the same eye (n = 7, p=0.0064) and by 54% when comparing the peripapillary sclera of treated vs. untreated eyes (n = 7, p<0.0001). Post-treatment characterization of RGCs (optic nerve axon counts/density, and grading), retinal function (electroretinography), and retinal histology revealed that photocrosslinking was associated with some ocular toxicity. We conclude that a transpupillary photocrosslinking approach enables selective scleral stiffening targeted to the peripapillary region that may be useful in future treatments of glaucoma.

The Role of Photoactivated and Non-Photoactivated Verteporfin on Tumor

Verteporfin (VP) has long been clinically used to treat age-related macular degeneration (AMD) through photodynamic therapy (PDT). Recent studies have reported a significant anti-tumor effect of VP as well. Yes-associated protein (YAP) is a pro-tumorigenic factor that is aberrantly expressed in various cancers and is a central effector of the Hippo signaling pathway that regulates organ size and tumorigenesis. VP can inhibit YAP without photoactivation, along with suppressing autophagy, and downregulating germinal center kinase-like kinase (GLK) and STE20/SPS1-related proline/alanine-rich kinase (SPAK). In addition, VP can induce mitochondrial damage and increase the production of reactive oxygen species (ROS) upon photoactivation, and is an effective photosensitizer (PS) in anti-tumor PDT. We have reviewed the direct and adjuvant therapeutic action of VP as a PS, and its YAP/TEA domain (TEAD)-dependent and independent pharmacological effects in the absence of light activation against cancer cells and solid tumors. Based on the present evidence, VP may be repositioned as a promising anti-cancer chemotherapeutic and adjuvant drug.

Recent Emergence of Rhenium(I) Tricarbonyl Complexes as Photosensitisers for Cancer Therapy

Photodynamic therapy (PDT) is emerging as a significant complementary or alternative approach for cancer treatment. PDT drugs act as photosensitisers, which upon using appropriate wavelength light and in the presence of molecular oxygen, can lead to cell death. Herein, we reviewed the general characteristics of the different generation of photosensitisers. We also outlined the emergence of rhenium (Re) and more specifically, Re(I) tricarbonyl complexes as a new generation of metal-based photosensitisers for photodynamic therapy that are of great interest in multidisciplinary research. The photophysical properties and structures of Re(I) complexes discussed in this review are summarised to determine basic features and similarities among the structures that are important for their phototoxic activity and future investigations. We further examined the in vitro and in vivo efficacies of the Re(I) complexes that have been synthesised for anticancer purposes. We also discussed Re(I) complexes in conjunction with the advancement of two-photon PDT, drug combination study, nanomedicine, and photothermal therapy to overcome the limitation of such complexes, which generally absorb short wavelengths.

Targeted delivery of mitomycin C-loaded and LDL-conjugated mesoporous silica nanoparticles for inhibiting the proliferation of pterygium subconjunctival fibroblasts

Pterygium is a degenerative disease that characterized by excessive fibrovascular proliferation. To reduce the recurrence rate, surgery is the main strategy, in combination with adjacent procedures or adjunctive therapy. One of the most common adjunctive agents, mitomycin C (MMC), is known as an alkylating agent that inhibits fibroblast proliferation but is limitedly applied in pterygium due to various complications. A previous study demonstrated that activated pterygium subconjunctival fibroblasts overexpressed low-density lipoprotein (LDL) receptors. In this study, we designed and synthesized MMC-loaded mesoporous silica nanoparticles conjugated with LDL (MMC@MSNs-LDL) to deliver MMC into activated pterygium fibroblasts in a targeted manner. The MMC loading efficiency was approximately 6%. The cell viability test (CCK-8 assay) revealed no cytotoxicity for the empty carrier MSNs at a concentration of ≤1 mg/ml after administration for 48 h in subconjunctival fibroblasts. Primary pterygium and normal human subconjunctival fibroblasts with or without stimulation by vascular endothelial growth factor (VEGF) were treated as follows: 1) 10 μg/ml MMC@MSNs-LDL for 24 h (MMC concentration: 0.6 μg/ml); 2) 0.2 mg/ml MMC for 5 min then cultured for 24 h after MMC removal; and 3) normal culture without any drug treatment. At 24 h, the anti-proliferative effect of MMC@MSNs-LDL in activated pterygium fibroblasts was similar to that of MMC (cell viability: 46.2 ± 5.5% vs 40.5 ± 1.1%, respectively, P = 0.349). Furthermore, the cytotoxicity of MMC@MSNs-LDL to normal fibroblasts with or without VEGF stimulation was significantly lower than that of traditional MMC (cell viability: 75.6 ± 4.4% vs 36.0 ± 1.5%, respectively, P < 0.001; 84.7 ± 5.5% vs 35.7 ± 1.3%, P < 0.001). The binding of fluorescently labeled MMC@MSNs-LDL in fibroblasts was assessed using confocal fluorescence microscopy. The uptake of targeted nanoparticles in fibroblasts was time dependent and saturated at 6 h. VEGF-activated pterygium fibroblasts showed more uptake of MMC@MSNs-LDL than normal fibroblasts with or without VEGF activation (both P < 0.001). Our data strongly suggest that MMC@MSNs-LDL had an effective antiproliferative role in activated pterygium fibroblasts, with reduced toxicity to normal fibroblasts compared to traditional application of MMC. LDL-mediated drug delivery might have great potential in the management of pterygium recurrence.

Verteporfin-photodynamic therapy is effective on gastric cancer cells

Photodynamic therapy (PDT) induces photochemical reactions, resulting in the destruction of tumor cells via singlet (S1) oxygen production. This cellular destruction occurs specifically in tumor cells, following selective accumulation of a photosensitizer and its excitation by a specific wavelength. Verteporfin (VP) is a second-generation photosensitizer that is currently being used worldwide in PDT to treat age-related macular degeneration. In addition, clinical trials with VP-PDT demonstrated anti-tumor efficacy and overall safety when used to treat locally advanced pancreatic cancer. In the present study, we examined the anti-tumor effect of VP-PDT on gastric cancer (GC) cell lines in vitro to conduct an initial assessment of its potential clinical applicability to this specific type of cancer. We evaluated the viability of MKN45 and MKN74 cancer cell lines after VP-PDT exposure and calculated the half maximal effective concentration (EC₅₀) values for VP. Apoptosis in VP-PDT-exposed GC cells was observed. Furthermore, the EC₅₀ values for a 30-min treatment with VP (2.5 J/cm² of 660 nm LED light) were 0.61 and 1.21 µM for MKN45 and MKN74, respectively. When VP treatment times were increased, the EC₅₀ values decreased. In conclusion, VP-PDT may be developed as an effective treatment for GC.

Verteporfin inhibits oxidative phosphorylation and induces cell death specifically in glioma stem cells

Glioblastoma multiforme (GBM) is the most malignant primary brain tumour in adults. Since glioma stem cells (GSCs) are associated with therapeutic resistance as well as the initiation and recurrence in GBM, therapies targeting GSCs are considered to be effective for long-term survival in GBM. Several reports suggested that oxidative phosphorylation (OXPHOS) of cancer stem cells is important for their survival; however, the requirement of OXPHOS in GSCs remains unclear. Few effective and safe agents that target GSC mitochondria are available in clinical settings. In this study, we demonstrated that GSCs had high OXPHOS activity compared with isogenic differentiated GSCs and that GSC survival depended on their OXPHOS activity. Remarkably, we showed that complexes III and IV had broad therapeutic windows and that the expression levels of mitochondrial DNA-coded components of complexes III and IV were elevated in GSCs compared with differentiated GSCs. Moreover, our search of the Food and Drug Administration-approved drugs for those targeting GSC mitochondria revealed that verteporfin (Visudyne^® ), a drug approved for macular degeneration, was a novel GSC-specific cytotoxic compound that reduced OXPHOS activity. Importantly, the cytotoxic effect of verteporfin was specific to GSCs without any toxicity to normal cells, and the IC₅₀ of approximately 200 nm was ten times less than its maximum blood concentration in humans. Overall, these findings indicated that high mitochondrial OXPHOS of GSCs is a potential GSC-specific vulnerability and that clinically available drugs, such as verteporfin, might become novel GSC-specific cytotoxic agents.

Therapeutic Enhancement of Verteporfin-mediated Photodynamic Therapy by mTOR Inhibitors

Photodynamic therapy (PDT) with photosensitizer verteporfin is a clinically approved vascular disrupting modality that is currently in clinical trial for cancer treatment. In this study, we evaluated PDT in combination with either mTORC1 inhibitor rapamycin or mTORC1/C2 dual inhibitor AZD2014 for therapeutic enhancement in SVEC endothelial cells. Verteporfin-PDT alone induced cell apoptosis by activating the intrinsic apoptotic pathway. However, it increased the expression of anti-apoptotic protein MCL-1 and the phosphorylation of S6, a downstream molecule of mTOR signaling. In contrast, mTOR inhibitors rapamycin and AZD2014 did not induce apoptosis in SVEC cells. They suppressed MCL-1 expression and S6 phosphorylation and imposed a potent inhibition on cell proliferation. PDT in combination with mTOR inhibitors activated the intrinsic apoptotic pathway and resulted in increased apoptosis. Combination treatments also led to sustained inhibition of cell proliferation. Although AZD2014 was more effective for cell growth inhibition and PDT enhancement than rapamycin at the higher concentrations examined in the study, both inhibitors effectively enhanced PDT response, suggesting that inhibition of mTORC1 is crucial for PDT enhancement. Our results indicate that mTOR inhibitors mechanistically cooperate with PDT for enhanced cell death and sustained growth inhibition, supporting a combination approach for therapeutic enhancement.

Mechanistic research holds promise for bacterial vaccines and phage therapies for Pseudomonas aeruginosa

Vaccines for Pseudomonas aeruginosa have been of longstanding interest to immunologists, bacteriologists, and clinicians, due to the widespread prevalence of hospital-acquired infection. As P. aeruginosa becomes increasingly antibiotic resistant, there is a dire need for novel treatments and preventive vaccines. Despite intense efforts, there currently remains no vaccine on the market to combat this dangerous pathogen. This article summarizes current and past vaccines under development that target various constituents of P. aeruginosa. Targeting lipopolysaccharides and O-antigens have shown some promise in preventing infection. Recombinant flagella and pili that target TLR5 have been utilized to combat P. aeruginosa by blocking its motility and adhesion. The type 3 secretion system components, such as needle-like structure PcrV or exotoxin PopB, are also potential vaccine targets. Outer membrane proteins including OprF and OprI are newer representatives of vaccine candidates. Live attenuated vaccines are a focal point in this review, and are also considered for novel vaccines. In addition, phage therapy is revived as an effective option for treating refractory infections after failure with antibiotic treatment. Many of the aforementioned vaccines act on a single target, thus lacking a broad range of protection. Recent studies have shown that mixtures of vaccines and combination approaches may significantly augment immunogenicity, thereby increasing their preventive and therapeutic potential.

Anatomical Retinal Changes after Photodynamic Therapy in Chronic Central Serous Chorioretinopathy

Purpose

To evaluate anatomical retinal changes measured by spectral-domain optical coherence tomography (SD-OCT), after applying photodynamic therapy (PDT) for treatment of chronic central serous chorioretinopathy (CSC).

Methods

A retrospective analysis was conducted on 43 patients (48 eyes) with chronic CSC treated with PDT. Visual acuity (VA), central retinal thickness (CRT), outer nuclear layer (ONL) thickness, subretinal fluid (SRF), and photoreceptor ellipsoid zone (EZ) measured by SD-OCT were collected at baseline and at 3, 6, and 12 months after PDT. Differences between normally distributed variables were calculated by a paired-sample t-test; p < 0.05 was considered statistically significant.

Results

Mean age was 50 ± 9.8 years. Mean time from diagnosis to PDT was 12.5 months. Baseline VA was 0.51 ± 0.24 and significantly improved (p < 0.001) to 0.74 ± 0.26 one year after PDT. CRT and SRF significantly decreased (p < 0.001) at 3, 6, and 12 months after treatment. ONL thickness and EZ did not significantly change at any point during follow-up.

Conclusions

Not significant changes were found in the ONL or EZ 12 months after PDT.

Targeting Phosphatidylinositol 3-Kinase Signaling Pathway for Therapeutic Enhancement of Vascular-Targeted Photodynamic Therapy

Vascular-targeted photodynamic therapy (PDT) selectively disrupts vascular function by inducing oxidative damages to the vasculature, particularly endothelial cells. Although effective tumor eradication and excellent safety profile are well demonstrated in both preclinical and clinical studies, incomplete vascular shutdown and angiogenesis are known to cause tumor recurrence after vascular-targeted PDT. We have explored therapeutic enhancement of vascular-targeted PDT with PI3K signaling pathway inhibitors because the activation of PI3K pathway was involved in promoting endothelial cell survival and proliferation after PDT. Here, three clinically relevant small-molecule inhibitors (BYL719, BKM120, and BEZ235) of the PI3K pathway were evaluated in combination with verteporfin-PDT. Although all three inhibitors were able to synergistically enhance PDT response in endothelial cells, PDT combined with dual PI3K/mTOR inhibitor BEZ235 exhibited the strongest synergism, followed in order by combinations with pan-PI3K inhibitor BKM120 and p110α isoform-selective inhibitor BYL719. Combination treatments of PDT and BEZ235 exhibited a cooperative inhibition of antiapoptotic Bcl-2 family protein Mcl-1 and induced more cell apoptosis than each treatment alone. In addition to increasing treatment lethality, BEZ235 combined with PDT effectively inhibited PI3K pathway activation and consequent endothelial cell proliferation after PDT alone, leading to a sustained growth inhibition. In the PC-3 prostate tumor model, combination treatments improved treatment outcomes by turning a temporary tumor regrowth delay induced by PDT alone to a more long-lasting treatment response. Our study strongly supports the combination of vascular-targeted PDT and PI3K pathway inhibitors, particularly mTOR inhibitors, for therapeutic enhancement. Mol Cancer Ther; 16(11); 2422-31. ©2017 AACR.

Molecular Features of the YAP Inhibitor Verteporfin: Synthesis of Hexasubstituted Dipyrrins as Potential Inhibitors of YAP/TAZ, the Downstream Effectors of the Hippo Pathway

Porphyrin derivatives, in particular verteporfin (VP), a photosensitizer initially designed for cancer therapy, have been identified as inhibitors of the YAP-TEAD interaction and transcriptional activity. Herein we report the efficient convergent synthesis of the dipyrrin half of protoporphyrin IX dimethyl ester (PPIX-DME), in which the sensitive vinyl group was created at the final stage by a dehydroiodination reaction. Two other dipyrrin derivatives were synthesized, including dipyrrin 19 [(Z)-2-((3,5-dimethyl-4-vinyl-2H-pyrrol-2-ylidene)methyl)-3,5-dimethyl-4-vinyl-1H-pyrrole], containing two vinyl groups. We found that VP and dipyrrin 19 showed significant inhibitory effects on TEAD transcriptional activity in MDA-MB-231 human breast cancer cells, whereas other compounds did not show significant changes. In addition, we observed a marked decrease in both YAP and TAZ levels following VP treatment, whereas dipyrrin 19 treatment primarily decreased the levels of YAP and receptor kinase AXL, a downstream target of YAP. Together, our data suggest that, due to their chemical structures, porphyrin- and dipyrrin-related derivatives can directly target YAP and/or TAZ proteins and inhibit TEAD transcriptional activity.

PDT with TOOKAD(®) studied in the chorioallantoic membrane of fertilized eggs

BACKGROUND

The potential application of TOOKAD(®)-PDT for the treatment of blood vessels was investigated. TOOKAD(®) (WST09), a novel palladium-bacteriopheophorbide absorbs light in the near IR with a high quantum yield of intersystem crossing. Our study assessed the efficacy of this drug in inducing vascular damage with a view to its possible use in the treatment of age-related macular degeneration.

METHODS

Vascular damage of TOOKAD(®)-PDT was studied in neovessels of the chorioallantoic membrane of fertilized eggs. Pharmacokinetic investigations were done by video microscopy and laser scanning microscopy. To induce damage vessels were irradiated with 763nm light from a diode laser.

RESULTS

TOOKAD(®) was accumulated in the vessels in the first minutes following injection. TOOKAD(®) fluorescence was seen predominantly in the lumen and not in the vascular endothelial layer. Although fluorescence was very weak it could be attributed to TOOKAD(®) from the fluorescence spectrum in the circulation. Damage assessment was done 24h after application of 763nm light. No significant difference in the degree of damage was observed with different short drug-light intervals (1-10min), but damage increased with the light energy dose. Closure of smaller vessels and vanished capillaries could be achieved by irradiation with 5J/cm(2) and a TOOKAD(®) dose of 33μg/embryo, corresponding to a phototoxic efficacy of 0.0062.

CONCLUSIONS

From the results discussed in this work, TOOKAD(®) could be a potential drug for the PDT of age-related macular degeneration in which the growth of new vessels in the choroids can lead to loss of vision.

Photodynamic effect of 5-aminolevulinic acid-loaded nanoparticles on bladder cancer cells: a preliminary investigation

OBJECTIVE

The aim of this study was to assess the photodynamic effect of nanoparticles loaded with a photosensitizing nanomedicine, 5-aminolevulinic acid (5-ALA), on T24 bladder cancer cells in vitro.

MATERIAL AND METHODS

The nanoprecipitation technique was successfully used to prepare the drug-loaded polymeric nanoparticles. The drug loading rate and the drug loading efficiency were determined by ultraviolet spectrophotometry. The size and morphology of nanoparticles were detected using dynamic light scattering (DLS) and transmission electron microscopy. Cytotoxicity to T24 bladder cancer cells was assessed by coincubating 5-ALA-loaded nanoparticles of different concentrations with T24 bladder cancer cells. The cell growth inhibitory rate was measured after irradiation by a 650 nm wavelength diode laser.

RESULTS

The drug loading rate of 5-ALA-loaded nanoparticles was 7% with a loading efficiency of 85%. The T24 cell growth inhibitory rates after incubation with 5.0, 10.0, 25.0 and 50.0 μg/ml 5-ALA-loaded nanoparticles were 73.19%, 79.95%, 83.86% and 89.74%, respectively, which demonstrated significantly higher cytotoxicity than those in the empty nanoparticle groups and 5-ALA free drug groups (p < 0.05).

CONCLUSIONS

5-ALA-loaded nanoparticles were successfully prepared and had a significantly enhanced photodynamic tumoricidal effect on bladder cancer cells in vitro.

Verteporfin-based photodynamic therapy overcomes gemcitabine insensitivity in a panel of pancreatic cancer cell lines

BACKGROUND AND OBJECTIVE

Pancreatic cancer is notoriously difficult to treat and resistant to virtually all therapeutics including gemcitabine, the standard front line agent for palliative chemotherapy. Early clinical studies point to a potential role for photodynamic therapy (PDT) in the management of this deadly disease. Here we examine PDT with verteporfin for treatment of cells that are nonresponsive to gemcitabine and identify intracellular and extracellular factors that govern sensitivity to each modality.

STUDY DESIGN

Using MTS we assess cytotoxicity of verteporfin-PDT in gemcitabine-treated nonresponsive populations from a panel of five pancreatic cancer cell lines representing a range of tumor histopathology and origin. We conduct Western blots for pro-/anti-apoptotic proteins bax and Bcl-XL to identify factors relevant to PDT and gemcitabine sensitivity. To examine the role of extracellular matrix influences we compare response to each modality in traditional cell culture conditions and cells grown on a laminin-rich basement membrane.

RESULTS

All cell lines have gemcitabine nonresponsive populations (17-33%) at doses up to 1 mM while moderate total verteporfin PDT doses (1-6 µM J/cm2) produce nearly complete killing. Our data shows that cells that are nonresponsive to sustained gemcitabine incubation are sensitive to verteporfin PDT indicating that the latter is agnostic to gemcitabine sensitivity. Verteporfin-based PDT decreases Bcl-XL and increases the bax/Bcl-XL ratio toward a pro-apoptotic balance. Insensitivity to gemcitabine is increased in cells that are adherent to basement membrane relative to traditional tissue culture conditions.

CONCLUSIONS

Collectively these results indicate the ability of verteporfin-based PDT to bypass intracellular and extracellular cues leading to gemcitabine resistance and point to the emerging role of this therapy for treatment of pancreatic cancer.

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.

How were new medicines discovered?

Preclinical strategies that are used to identify potential drug candidates include target-based screening, phenotypic screening, modification of natural substances and biologic-based approaches. To investigate whether some strategies have been more successful than others in the discovery of new drugs, we analysed the discovery strategies and the molecular mechanism of action (MMOA) for new molecular entities and new biologics that were approved by the US Food and Drug Administration between 1999 and 2008. Out of the 259 agents that were approved, 75 were first-in-class drugs with new MMOAs, and out of these, 50 (67%) were small molecules and 25 (33%) were biologics. The results also show that the contribution of phenotypic screening to the discovery of first-in-class small-molecule drugs exceeded that of target-based approaches - with 28 and 17 of these drugs coming from the two approaches, respectively - in an era in which the major focus was on target-based approaches. We postulate that a target-centric approach for first-in-class drugs, without consideration of an optimal MMOA, may contribute to the current high attrition rates and low productivity in pharmaceutical research and development.

Estimation of blood microcirculation in integuments by non-invasive speckle-optical method under the photodynamic action

In studies on animals (rats, rabbits) an experimental technique for estimation of microhemocirculation parameters of tissue under treatment has been developed. This technique has been used to compare the changes of speckle-optical parameters of skin microhemodynamics in laser-irradiated and light-isolated areas in the course of photodynamic therapy. Strong correlation between efficiency of tissue response and injection-photoirradiation time interval has been established. The results obtained are confirmed by the data of microhemodynamics estimation in the course of photodynamic therapy by the method of intravital microscopy. The defined ways of modification of the speckle-optical module will make it possible to optimize the conditions of parameters registration taking into account the object features and to improve informativity and sensitivity of the method.

Disparity between prostate tumor interior versus peripheral vasculature in response to verteporfin-mediated vascular-targeting therapy

Photodynamic therapy (PDT) is a light-based cancer treatment modality. Here we employed both in vivo and ex vivo fluorescence imaging to visualize vascular response and tumor cell survival after verteporfin-mediated PDT designed to target tumor vasculature. EGFP-MatLyLu prostate tumor cells, transduced with EGFP using lentivirus vectors, were implanted in athymic nude mice. Immediately after PDT with different doses of verteporfin, tumor-bearing animals were injected with a fluorochrome-labeled albumin. The extravasation of fluorescent albumin along with tumor EGFP fluorescence was monitored noninvasively with a whole-body fluorescence imaging system. Ex vivo fluorescence microscopy was performed on frozen sections of tumor tissues taken at different times after treatment. Both in vivo and ex vivo imaging demonstrated that vascular-targeting PDT with verteporfin significantly increased the extravasation of fluorochrome-labeled albumin in the tumor tissue, especially in the tumor periphery. Although PDT induced substantial vascular shutdown in interior blood vessels, some peripheral tumor vessels were able to maintain perfusion function up to 24 hr after treatment. As a result, viable tumor cells were typically detected in the tumor periphery in spite of extensive tumor cell death. Our results demonstrate that vascular-targeting PDT with verteporfin causes a dose- and time-dependent increase in vascular permeability and decrease in blood perfusion. However, compared to the interior blood vessels, peripheral tumor blood vessels were found less sensitive to PDT-induced vascular shutdown, which was associated with subsequent tumor recurrence in the tumor periphery.

Photodynamic therapy of cancer. Basic principles and applications

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality approved for clinical treatment of several types of cancer and non-oncological disorders. In PDT, a compound with photosensitising properties (photosensitiser, PS) is selectively accumulated in malignant tissues. The subsequent activation of the PS by visible light, preferentially in the red region of the visible spectrum (lambda>or=600 nm), where tissues are more permeable to light, generates reactive oxygen species, mainly singlet oxygen ((1)O(2)), responsible for cytotoxicity of neoplastic cells and tumour regression. There are three main mechanisms described by which (1)O(2) contributes to the destruction of tumours by PDT: direct cellular damage, vascular shutdown and activation of immune response against tumour cells. The advantages of PDT over other conventional cancer treatments are its low systemic toxicity and its ability to selectively destroy tumours accessible to light. Therefore, PDT is being used for the treatment of endoscopically accessible tumours such as lung, bladder, gastrointestinal and gynaecological neoplasms, and also in dermatology for the treatment of non-melanoma skin cancers (basal cell carcinoma) and precancerous diseases (actinic keratosis). Photofrin, ALA and its ester derivatives are the main compounds used in clinical trials, though newer and more efficient PSs are being evaluated nowadays.

Video monitoring of neovessel occlusion induced by photodynamic therapy with verteporfin (Visudyne), in the CAM model

The aim of the present study was to monitor photodynamic angioocclusion with verteporfin in capillaries. Details of this process were recorded under a microscope in real-time using a high-sensitivity video camera. A procedure was developed based on intravenous (i.v.) injection of a light-activated drug, Visudyne^®, into the chorioallantoic membrane (CAM) of a 12-day-old chicken embryo. The effect of light activation was probed after 24 h by i.v. injection of a fluorescent dye (FITC dextran), and analysis of its fluorescence distribution. The angioocclusive effect was graded based on the size of the occluded vessels, and these results were compared with clinical observations. The time-resolved thrombus formation taking place in a fraction of the field of view was video recorded using a Peltier-cooled CCD camera. This vessel occlusion in the CAM model was reproducible and, in many ways, similar to that observed in the clinical use of verteporfin. The real-time video recording permitted the monitoring of platelet aggregation and revealed size-selective vascular closure as well as some degree of vasoconstriction. Platelets accumulated at intravascular junctions within seconds after verteporfin light activation, and capillaries were found to be closed 15 min later at the applied conditions. Larger-diameter vessels remained patent. Repetition of these data with a much more sensitive camera revealed occlusion of the treated area after 5 min with doses of verteporfin and light similar to those used clinically. Consequently, newly developed light-activated drugs can now be studied under clinically relevant conditions.

Strategies for enhanced photodynamic therapy effects

Photodynamic therapy (PDT) is a treatment modality for the selective destruction of cancerous and nonneoplastic pathologies that involves the simultaneous presence of light, oxygen and a light-activatable chemical called a photosensitizer (PS) to achieve a cytotoxic effect. The photophysics and mechanisms of cell killing by PDT have been extensively studied in recent years, and PDT has received regulatory approval for the treatment of a number of diseases worldwide. As the application of this treatment modality expands with regard to both anatomical sites and disease stages, it will be important to develop strategies for enhancing PDT outcomes. This article focuses on two broad approaches for PDT enhancement: (1) mechanism-based combination treatments in which PDT and a second modality can be designed to either increase the susceptibility of tumor cells to PDT or nullify the treatment outcome-mitigating molecular responses triggered by PDT of tumors, and (2) the more recent approaches of PS targeting, either by specific cellular function-sensitive linkages or via conjugation to macromolecules.

Polymeric photosensitizer prodrugs for photodynamic therapy

A targeting strategy based on the selective enzyme-mediated activation of polymeric photosensitizer prodrugs (PPP) within pathological tissue has led to the development of agents with the dual ability to detect and treat cancer. Herein, a detailed study of a simple model system for these prodrugs is described. We prepared "first-generation" PPP by directly tethering the photosensitizer (PS) pheophorbide a to poly-(L)-lysine via epsilon amide links and observed that by increasing the number of PS on a polymer chain, energy transfer between PS units improved leading to better quenching efficiency. Fragmentation of the PPP backbone by trypsin digestion gave rise to a pronounced fluorescence increase and to more efficient generation of reactive oxygen species upon light irradiation. In vitro tests using the T-24 bladder carcinoma cell line and ex vivo experiments using mouse intestines illustrated the remarkable and selective ability of these PPP to fluoresce and induce phototoxicity upon enzymatic activation. This work elucidated the basic physicochemical parameters, such as water solubility and quenching/activation behavior, required for the future elaboration of more adaptable "second-generation" PPP, in which the PS is tethered to a proteolytically stable polymer backbone via enzyme-specific peptide linkers. This polymer architecture offers great flexibility to tailor make the PPP to target any pathological tissue known to over-express a specific enzyme.

"Competitive Quenching": A Mechanism by Which Perihydroxylated Perylenequinone Photosensitizers Can Prevent Adverse Phototoxic Damage Caused by Verteporfin During Photodynamic Therapy

Incorporation of photodynamic therapy into clinical practice for induction of vascular photo-occlusion highlights the need to prevent adverse phototoxicity to sensitive juxtaposed tissues, particularly in the retina. We developed a system termed "competitive quenching" to prevent adverse phototoxic damage. It involves differential compartmentalization of a photoactivator to the intravascular compartment for photoexcitation and delivery of phototoxicity to targeted vessels. A different photodynamic agent is partitioned to the extravascular retinal space to quench reactive oxygen species generated by photosensitization, thereby protecting the adjacent retinal tissues from adverse phototoxicity. The absorption spectra of quenchers must span wavelengths that are shorter and excluded from the spectral range of photoexcitation light to prevent photoactivation of the quencher. Perihydroxylated perylenequinones were found to be suitable to function as "competitive quenchers" with the prototype hypericin identified as a potent quencher. Here we examined the mechanisms operative in competitive quenching and suggest that hypericin forms a complex with verteporfin, thereby quenching singlet oxygen formation. Furthermore, we show that hypericin, with six phenolic hydroxyls, protects retinal and endothelial hybridoma cells from phototoxicity more effectively than the dimethyl tetrahydroxy helianthrone structural analog with only four such phenolic hydroxyls. The findings suggest that hydroxyl numbers contribute to the efficacy of competitive quenching.

Functionalized fullerenes mediate photodynamic killing of cancer cells: Type I versus Type II photochemical mechanism

Photodynamic therapy (PDT) employs the combination of nontoxic photosensitizers (PS) and harmless visible light to generate reactive oxygen species (ROS) and kill cells. Most clinically studied PS are based on the tetrapyrrole structure of porphyrins, chlorines, and related molecules, but new nontetrapyrrole PS are being sought. Fullerenes are soccer-ball shaped molecules composed of 60 or 70 carbon atoms and have attracted interest in connection with the search for biomedical applications of nanotechnology. Fullerenes are biologically inert unless derivatized with functional groups, whereupon they become soluble and can act as PS. We have compared the photodynamic activity of six functionalized fullerenes with 1, 2, or 3 hydrophilic or 1, 2, or 3 cationic groups. The octanol-water partition coefficients were determined and the relative contributions of Type I photochemistry (photogeneration of superoxide in the presence of NADH) and Type II photochemistry (photogeneration of singlet oxygen) were studied by measurement of oxygen consumption, 1270-nm luminescence and EPR spin trapping of the superoxide product. We studied three mouse cancer cell lines: (J774, LLC, and CT26) incubated for 24 h with fullerenes and illuminated with white light. The order of effectiveness as PS was inversely proportional to the degree of substitution of the fullerene nucleus for both the neutral and the cationic series. The monopyrrolidinium fullerene was the most active PS against all cell lines and induced apoptosis 4-6 h after illumination. It produced diffuse intracellular fluorescence when dichlorodihydrofluorescein was added as an ROS probe, suggesting a Type I mechanism for phototoxicity. We conclude that certain functionalized fullerenes have potential as novel PDT agents and phototoxicity may be mediated both by superoxide and by singlet oxygen.

Susceptibility of Cryptococcus neoformans to photodynamic inactivation is associated with cell wall integrity

Photodynamic therapy is a rapidly developing antimicrobial technology which combines a nontoxic photoactivatable dye or photosensitizer with harmless visible light of the correct wavelength to excite the dye to its reactive triplet state to generate reactive oxygen species toxic to cells. In this report we present evidence that the fungal pathogen Cryptococcus neoformans is susceptible to photodynamic inactivation by use of a polycationic conjugate of polyethyleneimine and the photosensitizer chlorin(e6). A C. neoformans rom2 mutant, with a mutation involving a putative Rho1 guanyl nucleotide exchange factor that is part of the protein kinase C-cell wall integrity pathway, demonstrated a compromised cell wall and less (1,3)beta-d glucan than the wild-type strain and increased accumulation of PEI-ce6 as assessed by fluorescence uptake and confocal microscopy. Interestingly, C. neoformans rom2 was hypersusceptible to photodynamic inactivation and coincubation of wild-type C. neoformans strain KN99alpha with caspofungin-enhanced photoinactivation. These studies demonstrated that C. neoformans is sensitive to photodynamic therapy and illustrated the significance of cell wall integrity in microbial susceptibility to antimicrobial photodynamic inactivation.

HPLC study of chlorin e6 and its molecular complex with polyvinylpyrrolidone

Several HPLC methods with UV detection were developed for qualitative and quantitative analysis of chlorin e(6) and photosensitizer Photolon either in the free form or upon pre-derivatization (methylation) under reversed- and normal-phase conditions. Optimum analysis conditions providing the best resolution of analytes were found at acidic pH where polar groups are completely protonated. The separation was performed by gradient elution with mobile phases of 0.08% trifluoroacetic acid and acetonitrile on an XTerra RP(18) column. The method was specific, accurate and precise, allowing the analysis of chlorin e(6) in the presence of numerous degradation products useful in the manufacturing process and quality control of chlorin e(6) and Photolon.

Protease-stable polycationic photosensitizer conjugates between polyethyleneimine and chlorin(e6) for broad-spectrum antimicrobial photoinactivation

We previously showed that covalent conjugates between poly-L-lysine and chlorin(e6) were efficient photosensitizers (PS) of both gram-positive and gram-negative bacteria. The polycationic molecular constructs increased binding and penetration of the PS into impermeable gram-negative cells. We have now prepared a novel set of second-generation polycationic conjugates between chlorin(e6) and three molecular forms of polyethyleneimine (PEI): a small linear, a small cross-linked, and a large cross-linked molecule. The conjugates were characterized by high-pressure liquid chromatography and tested for their ability to kill a panel of pathogenic microorganisms, the gram-positive Staphylococcus aureus and Streptococcus pyogenes, the gram-negative Escherichia coli and Pseudomonas aeruginosa, and the yeast Candida albicans, after exposure to low levels of red light. The large cross-linked molecule efficiently killed all organisms, while the linear conjugate killed gram-positive bacteria and C. albicans. The small cross-linked conjugate was the least efficient antimicrobial PS and its remarkably low activity could not be explained by reduced photochemical quantum yield or reduced cellular uptake. In contrast to polylysine conjugates, the PEI conjugates were resistant to degradation by proteases such as trypsin that hydrolyze lysine-lysine peptide bonds, The advantage of protease stability combined with the ready availability of PEI suggests these molecules may be superior to polylysine-PS conjugates for photodynamic therapy of localized infections.

Tumor Vascular Permeabilization by Vascular-Targeting Photosensitization: Effects, Mechanism, and Therapeutic Implications

PURPOSE

Loss of vascular barrier function has been observed shortly following vascular-targeting photodynamic therapy. However, the mechanism involved in this event is still not clear, and the therapeutic implications associated with this pathophysiologic change have not been fully explored.

EXPERIMENTAL DESIGN

The effect of vascular-targeting photodynamic therapy on vascular barrier function was examined in both s.c. and orthotopic MatLyLu rat prostate tumor models and endothelial cells in vitro, using photosensitizer verteporfin. Vascular permeability to macromolecules (Evans blue-albumin and high molecular weight dextran) was assessed with dye extraction (ex vivo) and intravital microscopy (in vivo) methods. Intravital microscopy was also used to monitor tumor vascular functional changes after vascular-targeting photodynamic therapy. The effects of photosensitization on monolayer endothelial cell morphology and cytoskeleton structures were studied with immunofluorescence staining.

RESULTS

Vascular-targeting photodynamic therapy induced vascular barrier dysfunction in the MatLyLu tumors. Thus, tumor uptake of macromolecules was significantly increased following photodynamic therapy treatments. In addition to vascular permeability increase, blood cell adherence to vessel wall was observed shortly after treatment, further suggesting the loss of endothelial integrity. Blood cell adhesion led to the formation of thrombi that can occlude blood vessels, causing vascular shutdown. However, viable tumor cells were often detected at tumor periphery after vascular-targeting photodynamic therapy. Endothelial cell barrier dysfunction following photodynamic therapy treatment was also observed in vitro by culturing monolayer endothelial cells on Transwell inserts. Immunofluorescence study revealed microtubule depolymerization shortly after photosensitization treatment and stress actin fiber formation thereafter. Consequently, endothelial cells were found to retract, and this endothelial morphologic change led to the formation of intercellular gaps.

CONCLUSIONS

Vascular-targeting photodynamic therapy permeabilizes blood vessels through the formation of endothelial intercellular gaps, which are likely induced via endothelial cell microtubule depolymerization following vascular photosensitization. Loss of endothelial barrier function can ultimately lead to tumor vascular shutdown and has significant implications in drug transport and tumor cell metastasis.