Angiostatic kinase inhibitors to sustain photodynamic angio-occlusion

Hippo pathway in non-small cell lung cancer: mechanisms, potential targets, and biomarkers

Lung cancer is the primary contributor to cancer-related deaths globally, and non-small cell lung cancer (NSCLC) constitutes around 85% of all lung cancer cases. Recently, the emergence of targeted therapy and immunotherapy revolutionized the treatment of NSCLC and greatly improved patients' survival. However, drug resistance is inevitable, and extensive research has demonstrated that the Hippo pathway plays a crucial role in the development of drug resistance in NSCLC. The Hippo pathway is a highly conserved signaling pathway that is essential for various biological processes, including organ development, maintenance of epithelial balance, tissue regeneration, wound healing, and immune regulation. This pathway exerts its effects through two key transcription factors, namely Yes-associated protein (YAP) and transcriptional co-activator PDZ-binding motif (TAZ). They regulate gene expression by interacting with the transcriptional-enhanced associate domain (TEAD) family. In recent years, this pathway has been extensively studied in NSCLC. The review summarizes a comprehensive overview of the involvement of this pathway in NSCLC, and discusses the mechanisms of drug resistance, potential targets, and biomarkers associated with this pathway in NSCLC.

Synergic vascular photodynamic activity by methylene blue-curcumin supramolecular assembly

A supramolecular assembly was obtained by combining methylene blue (MB) with a natural plant extract, curcumin (Curc), in a stoichiometric ratio of 1:4 in aqueous solution (90% PBS + 10% ethanol) at room temperature. The MB-Curc supramolecular assembly was evidenced by absorption and fluorescence spectroscopies, and the stoichiometry and bonding constant were obtained using Cieleńs model. Its stability and photostability were evaluated by chromatographic analysis and UV-Vis absorption. The MB-Curc avoids the aggregation of both isolated compounds and efficiently produces singlet oxygen (ΦΔ= 0.52 ± 0.03). Its potential for photodynamic antiangiogenic treatments was evaluated through the vascular effect observed in chicken chorioallantoic membrane (CAM) assay. The results showed intense damage in CAM vascular network by MB-Curc after irradiation, which is higher than the effect of isolated compounds, indicating a synergistic vascular effect. This combination can be essential to prevent cancer revascularization after photodynamic application and improve the efficacy of this approach. The characteristics exhibited by MB-Curc make it a potential candidate for use in cancer treatments through photodynamic antiangiogenic therapy.

Photodynamic Therapy Combined with Ferroptosis Is a Synergistic Antitumor Therapy Strategy

Ferroptosis is a programmed death mode that regulates redox homeostasis in cells, and recent studies suggest that it is a promising mode of tumor cell death. Ferroptosis is regulated by iron metabolism, lipid metabolism, and intracellular reducing substances, which is the mechanism basis of its combination with photodynamic therapy (PDT). PDT generates reactive oxygen species (ROS) and 1O2 through type I and type II photochemical reactions, and subsequently induces ferroptosis through the Fenton reaction and the peroxidation of cell membrane lipids. PDT kills tumor cells by generating excessive cytotoxic ROS. Due to the limited laser depth and photosensitizer enrichment, the systemic treatment effect of PDT is not good. Combining PDT with ferroptosis can compensate for these shortcomings. Nanoparticles constructed by photosensitizers and ferroptosis agonists are widely used in the field of combination therapy, and their targeting and biological safety can be improved through modification. These nanoparticles not only directly kill tumor cells but also further exert the synergistic effect of PDT and ferroptosis by activating antitumor immunity, improving the hypoxia microenvironment, and inhibiting the tumor angiogenesis. Ferroptosis-agonist-induced chemotherapy and PDT-induced ablation also have good clinical application prospects. In this review, we summarize the current research progress on PDT and ferroptosis and how PDT and ferroptosis promote each other.

The Chicken Embryo Chorioallantoic Membrane as an In Vivo Model for Photodynamic Therapy

For many decades the chicken embryo chorioallantoic membrane (CAM) has been used for research as an in vivo model in a large number of different fields, including toxicology, bioengineering, and cancer research. More specifically, the CAM is also a suitable and convenient model system in the field of photodynamic therapy (PDT), mainly due to the easy access of its membrane and the possibility of grafting or growing tumors on the membrane and, interestingly, to study the PDT effects on its dense vascular network. In addition, the CAM is simple to handle and cheap. Since the CAM is not innervated until later stages of the embryo development, its use in research is simplified compared to other in vivo models as far as ethical and regulatory issues are concerned. In this review different incubation and drug administration protocols of relevance for PDT are presented. Moreover, data regarding the propagation of light at different wavelengths and CAM development stages are provided. Finally, the effects induced by photobiomodulation on the CAM angiogenesis and its impact on PDT treatment outcome are discussed.

Medication Trends for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is central vision loss with aging, was the fourth main cause of blindness in 2015, and has many risk factors, such as cataract surgery, cigarette smoking, family history, hypertension, obesity, long-term smart device usage, etc. AMD is classified into three categories: normal AMD, early AMD, and late AMD, based on angiogenesis in the retina, and can be determined by bis-retinoid N-retinyl-N-retinylidene ethanolamine (A2E)-epoxides from the reaction of A2E and blue light. During the reaction of A2E and blue light, reactive oxygen species (ROS) are synthesized, which gather inflammatory factors, induce carbonyl stress, and finally stimulate the death of retinal pigment epitheliums (RPEs). There are several medications for AMD, such as device-based therapy, anti-inflammatory drugs, anti-VEGFs, and natural products. For device-based therapy, two methods are used: prophylactic laser therapy (photocoagulation laser therapy) and photodynamic therapy. Anti-inflammatory drugs consist of corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs). Anti-VEGFs are classified antibodies for VEGF, aptamer, soluble receptor, VEGF receptor-1 and -2 antibody, and VEGF receptor tyrosine kinase inhibitor. Finally, additional AMD drug candidates are derived from natural products. For each medication, there are several and severe adverse effects, but natural products have a potency as AMD drugs, as they have been used as culinary materials and/or traditional medicines for a long time. Their major application route is oral administration, and they can be combined with device-based therapy, anti-inflammatory drugs, and anti-VEGFs. In general, AMD drug candidates from natural products are more effective at treating early and intermediate AMD. However, further study is needed to evaluate their efficacy and to investigate their therapeutic mechanisms.

Potentiality, Limitations, and Consequences of Different Experimental Models to Improve Photodynamic Therapy for Cancer Treatment in Relation to Antiangiogenic Mechanism

The relevance of experimentally gained information represents a long-term debating issue in the field of molecular biology research. The loss of original conditions in the in vitro environment affects various biological mechanisms and cellular interactions. Consequently, some biochemical mechanisms are lost or critically altered. Analyses in these modified conditions could, therefore, distort the relevancy of experimentally gained information. In some cases, the similarities with original conditions are so small that utilization of simpler in vitro models seems impossible, or could occur in a very limited way. To conclude, the study of more complex phenomena places higher demands on the complexity of the experimental model. The latest information highlights the fact that the tumor angiogenesis mechanism has very complex features. This complexity can be associated with a wide range of angiogenic factors expressed by a variety of malignant and non-malignant cells. Our article summarizes the results from various experimental models that were utilized to analyze a photodynamic therapy effect on tumor angiogenic mechanisms. Additionally, based on the latest information, we present the most important attributes and limitations of utilized experimental models. We also evaluate the essential problems associated with angiogenic mechanism induction after photodynamic therapy application.

The Crosstalk between Src and Hippo/YAP Signaling Pathways in Non-Small Cell Lung Cancer (NSCLC)

The advancement of new therapies, including targeted therapies and immunotherapies, has improved the survival of non-small-cell lung cancer (NSCLC) patients in the last decade. Some NSCLC patients still do not benefit from therapies or encounter progressive disease during the course of treatment because they have intrinsic resistance, acquired resistance, or lack a targetable driver mutation. More investigations on the molecular biology of NSCLC are needed to find useful biomarkers for current therapies and to develop novel therapeutic strategies. Src is a non-receptor tyrosine kinase protein that interacts with cell surface growth factor receptors and the intracellular signaling pathway to maintain cell survival tumorigenesis in NSCLC. The Yes-associated protein (YAP) is one of the main effectors of the Hippo pathway and has been identified as a promoter of drug resistance, cancer progression, and metastasis in NSCLC. Here, we review studies that have investigated the activation of YAP as mediated by Src kinases and demonstrate that Src regulates YAP through three main mechanisms: (1) direct phosphorylation; (2) the activation of pathways repressing Hippo kinases; and (3) Hippo-independent mechanisms. Further work should focus on the efficacy of Src inhibitors in inhibiting YAP activity in NSCLC. In addition, future efforts toward developing potentially reasonable combinations of therapy targeting the Src–YAP axis using other therapies, including targeted therapies and/or immunotherapies, are warranted.

Anti-angiogenic effects of crenolanib are mediated by mitotic modulation independently of PDGFR expression

Background

Crenolanib is a tyrosine kinase inhibitor targeting PDGFR-α, PDGFR-β and Fms related tyrosine kinase-3 (FLT3) that is currently evaluated in several clinical trials. Although platelet-derived growth factor receptor (PDGFR) signalling pathway is believed to play an important role in angiogenesis and maintenance of functional vasculature, we here demonstrate a direct angiostatic activity of crenolanib independently of PDGFR signalling.

Methods

The activity of crenolanib on cell viability, migration, sprouting, apoptosis and mitosis was assessed in endothelial cells, tumour cells and fibroblasts. Alterations in cell morphology were determined by immunofluorescence experiments. Flow-cytometry analysis and mRNA expression profiles were used to investigate cell differentiation. In vivo efficacy was investigated in human ovarian carcinoma implanted on the chicken chorioallantoic membrane (CAM).

Results

Crenolanib was found to inhibit endothelial cell viability, migration and sprout length, and induced apoptosis independently of PDGFR expression. Treated cells  showed altered actin arrangement and nuclear aberrations. Mitosis was affected at several levels including mitosis entry and centrosome clustering. Crenolanib suppressed human ovarian carcinoma tumour growth and angiogenesis in the CAM model.

Conclusions

The PDGFR/FLT3 inhibitor crenolanib targets angiogenesis and inhibits tumour growth in vivo unrelated to PDGFR expression. Based on our findings, we suggest a broad mechanism of action of crenolanib.

Biodegradable core-shell electrospun nanofibers containing bevacizumab to treat age-related macular degeneration

Age-related macular degeneration (AMD) is a degenerative ocular disease that affects the central retina. It is considered the main cause of blindness and loss of vision worldwide. Angiogenic factors are associated with AMD, which has led to the use of antiangiogenic drugs, such as bevacizumab, to treat the disease using frequent intravitreal injections. In the present study, biodegradable core shell nanofibers containing bevacizumab were prepared by the coaxial electrospinning technique. It is thought that the shell could control the release of the drug, while the core would protect and store the drug. Poly(caprolactone) (PCL) and gelatin were used to form the shell of the nanofibers, while poly(vinyl alcohol) (PVA) and bevacizumab comprised the core. The nanofibers were characterized using microscopy techniques, thermal analysis, and FTIR. The results showed that core-shell nanofibers were produced as designed. Bevacizumab activity was evaluated using a chicken embryo chorioallantoic membrane (CAM) assay. An enzyme-linked immunosorbent assay was used to quantify the amount of the drug released from the different nanofibers in vitro. The toxicity of the nanofibers was evaluated in human retinal pigment epithelial (ARPE) cells. The CAM results demonstrated that bevacizumab maintained its antiangiogenic activity when incorporated into the nanofibers. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests revealed that the nanofibers showed no cellular toxicity, even in the presence of bevacizumab. The core-shell structure of the nanofibers reduced the release rate of bevacizumab compared with PVA nanofibers. The bevacizumab-loaded biodegradable nanofibers presented interesting properties that would potentially constitute an alternative therapy to intravitreal injections to treat AMD.

A Tumor Vascular-Targeted Interlocking Trimodal Nanosystem That Induces and Exploits Hypoxia

Vascular-targeted photodynamic therapy (VTP) is a recently approved strategy for treating solid tumors. However, the exacerbated hypoxic stress makes tumor eradication challenging with such a single modality approach. Here, a new graphene oxide (GO)-based nanosystem for rationally designed, interlocking trimodal cancer therapy that enables VTP using photosensitizer verteporfin (VP) (1) with codelivery of banoxantrone dihydrochloride (AQ4N) (2), a hypoxia-activated prodrug (HAP), and HIF-1α siRNA (siHIF-1α) (3) is reported. The VTP-induced aggravated hypoxia is highly favorable for AQ4N activation into AQ4 (a topoisomerase II inhibitor) for chemotherapy. However, the hypoxia-induced HIF-1α acts as a "hidden brake," through downregulating CYP450 (the dominant HAP-activating reductases), to substantially hinder AQ4N activation. siHIF-1α is rationally adopted to suppress the HIF-1α expression upon hypoxia and further enhance AQ4N activation. This trimodal nanosystem significantly delays the growth of PC-3 tumors in vivo compared to the control nanoparticles carrying VP, AQ4N, or siHIF-1α alone or their pairwise combinations. This multimodal nanoparticle design presents, the first example exploiting VTP to actively induce hypoxia for enhanced HAP activation. It is also revealed that HAP activation is still insufficient under hypoxia due to the hidden downregulation of the HAP-activating reductases (CYP450), and this can be well overcome by GO nanoparticle-mediated siHIF-1α intervention.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

A genomic screen for angiosuppressor genes in the tumor endothelium identifies a multifaceted angiostatic role for bromodomain containing 7 (BRD7)

Tumor angiogenesis is characterized by deregulated gene expression in endothelial cells (EC). While studies until now have mainly focused on overexpressed genes in tumor endothelium, we here describe the identification of transcripts that are repressed in tumor endothelium and thus have potential suppressive effects on angiogenesis. We identified nineteen putative angiosuppressor genes, one of them being bromodomain containing 7 (BRD7), a gene that has been assigned tumor suppressor properties. BRD7 was studied in more detail, and we demonstrate that BRD7 expression is inversely related to EC activation. Ectopic expression of BRD7 resulted in a dramatic reduction of EC proliferation and viability. Furthermore, overexpression of BRD7 resulted in a bromodomain-dependent induction of NFκB-activity and NFκB-dependent gene expression, including ICAM1, enabling leukocyte–endothelial interactions. In silico functional annotation analysis of genome-wide expression data on BRD7 knockdown and overexpression revealed that the transcriptional signature of low BRD7 expressing cells is associated with increased angiogenesis (a.o. upregulation of angiopoietin-2, VEGF receptor-1 and neuropilin-1), cytokine activity (a.o. upregulation of CXCL1 and CXCL6), and a reduction of immune surveillance (TNF-α, NFκB, ICAM1). Thus, combining in silico and in vitro data reveals multiple pathways of angiosuppressor and anti-tumor activities of BRD7.

miRNAs: micro-managers of anticancer combination therapies

Angiogenesis is one of the hallmarks of cancer progression and as such has been considered a target of therapeutic interest. However, single targeted agents have not fully lived up to the initial promise of anti-angiogenic therapy. Therefore, it has been suggested that combining therapies and agents will be the way forward in the oncology field. In recent years, microRNAs (miRNAs) have received considerable attention as drivers of tumor development and progression, either acting as tumor suppressors or as oncogenes (so-called oncomiRs), as well as in the process of tumor angiogenesis (angiomiRs). Not only from a functional, but also from a therapeutic view, miRNAs are attractive tools. Thus far, several mimics and antagonists of miRNAs have entered clinical development. Here, we review the provenance and promise of miRNAs as targets as well as therapeutics to contribute to anti-angiogenesis-based (combination) treatment of cancer.

Improved Photodynamic Therapy Efficacy of Protoporphyrin IX-Loaded Polymeric Micelles Using Erlotinib Pretreatment

Photodynamic therapy (PDT) has attracted widespread attention in recent years as a noninvasive and highly selective approach for cancer treatment. We have previously reported a significant increase in the 90-day complete response rate when tumor-bearing mice are treated with the epidermal growth factor receptor (EGFR) inhibitor erlotinib prior to PDT with the photosensitizer benzoporphyrin-derivative monoacid ring A (BPD-MA) compared to treatment with PDT alone. To further explore this strategy for anticancer therapy and clinical practice, we tested whether pretreatment with erlotinib also exhibited a synergistic therapeutic effect with a nanocarrier containing the clinically relevant photosensitizer protoporphyrin IX (PpIX). The PpIX was encapsulated within biodegradable polymeric micelles formed from the amphiphilic block copolymer poly(ethylene glycol)-polycaprolactone (PEG-PCL). The obtained micelles were characterized systematically in vitro. Further, an in vitro cytotoxicity study showed that PDT with PpIX loaded micelles did exhibit a synergistic effect when combined with erlotinib pretreatment. Considering the distinct advantages of polymeric nanocarriers in vivo, this study offers a promising new approach for the improved treatment of localized tumors. The strategy developed here has the potential to be extended to other photosensitizers currently used in the clinic for photodynamic therapy.

The clinical application of angiostatic therapy in combination with radiotherapy: past, present, future

Although monotherapy with angiostatic drugs is still far from effective, there is abundant evidence that angiostatic therapy can improve the efficacy of conventional treatments like radiotherapy. This has instigated numerous efforts to optimize and clinically implement the combination of angiostatic drugs with radiation treatment. The results from past and present clinical trials that explored this combination therapy indeed show encouraging results. However, current findings also show that the combination has variable efficacy and is associated with increased toxicity. This indicates that combining radiotherapy with angiostatic drugs not only holds opportunities but also provides several challenges. In the current review, we provide an update of the most recent insights from clinical trials that evaluated the combination of angiostatic drugs with radiation treatment. In addition, we discuss the outstanding questions for future studies in order to improve the clinical benefit of combining angiostatic therapy with radiation therapy.

Combination of ruthenium(II)-arene complex [Ru(η6-p-cymene)Cl2(pta)] (RAPTA-C) and the epidermal growth factor receptor inhibitor erlotinib results in efficient angiostatic and antitumor activity

Ruthenium-based compounds show strong potential as anti-cancer drugs and are being investigated as alternatives to other well-established metal-based chemotherapeutics. The organometallic compound [Ru(η6-p-cymene)Cl2(pta)], where pta = 1,3,5-triaza-7-phosphaadamantane (RAPTA-C) exhibits broad acting anti-tumor efficacy with intrinsic angiostatic activity. In the search for an optimal anti-angiogenesis drug combination, we identified synergistic potential between RAPTA-C and the epidermal growth factor receptor (EGFR) inhibitor, erlotinib. This drug combination results in strong synergistic inhibition of cell viability in human endothelial (ECRF24 and HUVEC) and human ovarian carcinoma (A2780 and A2780cisR) cells. Additionally, erlotinib significantly enhances the cellular uptake of RAPTA-C relative to treatment with RAPTA-C alone in human ovarian carcinoma cells, but not endothelial cells. Drug combinations induce the formation of chromosome bridges that persist after mitotic exit and delay abscission in A2780 and A2780cisR, therefore suggesting initiation of cellular senescence. The therapeutic potential of these compounds and their combination is further validated in vivo on A2780 tumors grown on the chicken chorioallantoic membrane (CAM) model, and in a preclinical model in nude mice. Immunohistochemical analysis confirms effective anti-angiogenic and anti-proliferative activity in vivo, based on a significant reduction of microvascular density and a decrease in proliferating cells.

Beyond the Barriers of Light Penetration: Strategies, Perspectives and Possibilities for Photodynamic Therapy

Photodynamic therapy (PDT) is a photochemistry based treatment modality that involves the generation of cytotoxic species through the interactions of a photosensitizer molecule with light irradiation of an appropriate wavelength. PDT is an approved therapeutic modality for several cancers globally and in several cases has proved to be effective where traditional treatments have failed. The key parameters that determine PDT efficacy are 1. the photosensitizer (nature of the molecules, selectivity, and macroscopic and microscopic localization etc.), 2. light application (wavelength, fluence, fluence rate, irradiation regimes etc.) and 3. the microenvironment (vascularity, hypoxic regions, stromal tissue density, molecular heterogeneity etc.). Over the years, several groups aimed to monitor and manipulate the components of these critical parameters to improve the effectiveness of PDT treatments. However, PDT is still misconstrued to be a surface treatment primarily due to the limited depths of light penetration. In this review, we present the recent advances, strategies and perspectives in PDT approaches, particularly in cancer treatment, that focus on increasing the 'damage zone' beyond the reach of light in the body. This is enabled by a spectrum of approaches that range from innovative photosensitizer excitation strategies, increased specificity of phototoxicity, and biomodulatory approaches that amplify the biotherapeutic effects induced by photodynamic action. Along with the increasing depth of understanding of the underlying physical, chemical and physiological mechanisms, it is anticipated that with the convergence of these strategies, the clinical utility of PDT will be expanded to a powerful modality in the armamentarium for the management of cancer.

Pluronic® P123/F127 mixed micelles delivering sorafenib and its combination with verteporfin in cancer cells

Here, we developed Pluronic® P123/F127 (poloxamer) mixed micelles for the intravenous delivery of the anticancer drug sorafenib (SRB) or its combination with verteporfin (VP), a photosensitizer for photodynamic therapy that should complement well the cytotoxicity profile of the chemotherapeutic. SRB loading inside the core of micelles was governed by the drug:poloxamer weight ratio, while in the case of the SRB-VP combination, a mutual interference between the two drugs occurred and only specific ratios could ensure maximum loading efficiency. Coentrapment of SRB did not alter the photophysical properties of VP, confirming that SRB did not participate in any bimolecular process with the photosensitizer. Fluorescence resonance energy-transfer measurement of micelles in serum protein-containing cell-culture medium demonstrated the excellent stability of the system in physiologically relevant conditions. These results were in line with the results of the release study showing a release rate of both drugs in the presence of proteins slower than in phosphate buffer. SRB release was sustained, while VP remained substantially entrapped in the micelle core. Cytotoxicity studies in MDA-MB231 cells revealed that at 24 hours, SRB-loaded micelles were more active than free SRB only at very low SRB concentrations, while at 24+24 hours a prolonged cytotoxic effect of SRB-loaded micelles was observed, very likely mediated by the block in the S phase of the cell cycle. The combination of SRB with VP under light exposure was less cytotoxic than both the free combination and VP-loaded micelles + SRB-loaded micelles combination. This behavior was clearly explainable in terms of micelle uptake and intracellular localization. Besides the clear advantage of delivering SRB in poloxamer micelles, our results provide a clear example that each photochemotherapeutic combination needs detailed investigations on their particular interaction, and no generalization on enhanced cytotoxic effects should be derived a priori.

Quantification of cancer cell extravasation in vivo

Cancer cell 'invasiveness' is one of the main driving forces in cancer metastasis, and assays that quantify this key attribute of cancer cells are crucial in cancer metastasis research. The research goal of many laboratories is to elucidate the signaling pathways and effectors that are responsible for cancer cell invasion, but many of these experiments rely on in vitro methods that do not specifically simulate individual steps of the metastatic cascade. Cancer cell extravasation is arguably the most important example of invasion in the metastatic cascade, whereby a single cancer cell undergoes transendothelial migration, forming invasive processes known as invadopodia to mediate translocation of the tumor cell from the vessel lumen into tissue in vivo. We have developed a rapid, reproducible and economical technique to evaluate cancer cell invasiveness by quantifying in vivo rates of cancer cell extravasation in the chorioallantoic membrane (CAM) of chicken embryos. This technique enables the investigator to perform well-powered loss-of-function studies of cancer cell extravasation within 24 h, and it can be used to identify and validate drugs with potential antimetastatic effects that specifically target cancer cell extravasation. A key advantage of this technique over similar assays is that intravascular cancer cells within the capillary bed of the CAM are clearly distinct from extravasated cells, which makes cancer cell extravasation easy to detect. An intermediate level of experience in injections of the chorioallantoic membrane of avian embryos and cell culture techniques is required to carry out the protocol.

Anticancer Organometallic Osmium(II)-p-cymene Complexes

Osmium compounds are attracting increasing attention as potential anticancer drugs. In this context, a series of bifunctional organometallic osmium(II)-p-cymene complexes functionalized with alkyl or perfluoroalkyl groups were prepared and screened for their antiproliferative activity. Three compounds from the series display selectivity toward cancer cells, with moderate cytotoxicity observed against human ovarian carcinoma (A2780) cells, whereas no cytotoxicity was observed on non-cancerous human embryonic kidney (HEK-293) cells and human endothelial (ECRF24) cells. Two of these three cancer-cell-selective compounds induce cell death largely via apoptosis and were also found to disrupt vascularization in the chicken embryo chorioallantoic membrane (CAM) model. Based on these promising properties, these compounds have potential clinical applications.

The role of photodynamic therapy in overcoming cancer drug resistance

Many modalities of cancer therapy induce mechanisms of treatment resistance and escape pathways during chronic treatments, including photodynamic therapy (PDT). It is conceivable that resistance induced by one treatment might be overcome by another treatment. Emerging evidence suggests that the unique mechanisms of tumor cell and microenvironment damage produced by PDT could be utilized to overcome cancer drug resistance, to mitigate the compensatory induction of survival pathways and even to re-sensitize resistant cells to standard therapies. Approaches that capture the unique features of PDT, therefore, offer promising factors for increasing the efficacy of a broad range of therapeutic modalities. Here, we highlight key preclinical findings utilizing PDT to overcome classical drug resistance or escape pathways and thus enhance the efficacy of many pharmaceuticals, possibly explaining the clinical observations of the PDT response to otherwise treatment-resistant diseases. With the development of nanotechnology, it is possible that light activation may be used not only to damage and sensitize tumors but also to enable controlled drug release to inhibit escape pathways that may lead to resistance or cell proliferation.

Optical Imaging, Photodynamic Therapy and Optically Triggered Combination Treatments

Optical imaging is becoming increasingly promising for real-time image-guided resections, and combined with photodynamic therapy (PDT), a photochemistry-based treatment modality, optical approaches can be intrinsically "theranostic." Challenges in PDT include precise light delivery, dosimetry, and photosensitizer tumor localization to establish tumor selectivity, and like all other modalities, incomplete treatment and subsequent activation of molecular escape pathways are often attributable to tumor heterogeneity. Key advances in molecular imaging, target-activatable photosensitizers, and optically active nanoparticles that provide both cytotoxicity and a drug release mechanism have opened exciting avenues to meet these challenges. The focus of the review is optical imaging in the context of PDT, but the general principles presented are applicable to many of the conventional approaches to cancer management. We highlight the role of optical imaging in providing structural, functional, and molecular information regarding photodynamic mechanisms of action, thereby advancing PDT and PDT-based combination therapies of cancer. These advances represent a PDT renaissance with increasing applications of clinical PDT as a frontline cancer therapy working in concert with fluorescence-guided surgery, chemotherapy, and radiation.

Photoactivation of lysosomally sequestered sunitinib after angiostatic treatment causes vascular occlusion and enhances tumor growth inhibition

The angiogenesis inhibitor sunitinib is a tyrosine kinase inhibitor that acts mainly on the VEGF and PDGF pathways. We have previously shown that sunitinib is sequestered in the lysosomes of exposed tumor and endothelial cells. This phenomenon is part of the drug-induced resistance observed in the clinic. Here, we demonstrate that when exposed to light, sequestered sunitinib causes immediate destruction of the lysosomes, resulting in the release of sunitinib and cell death. We hypothesized that this photoactivation of sunitinib could be used as a vaso-occlusive vascular-targeting approach to treating cancer. Spectral properties of sunitinib and its lysosomal accumulation were measured in vitro. The human A2780 ovarian carcinoma transplanted onto the chicken chorioallantoic membrane (CAM) and the Colo-26 colorectal carcinoma model in Balb/c mice were used to test the effects of administrating sunitinib and subsequently exposing tumor tissue to light. Tumors were subsequently resected and subject to immunohistochemical analysis. In A2780 ovarian carcinoma tumors, treatment with sunitinib+light resulted in immediate specific angio-occlusion, leading to a necrotic tumor mass 24 h after treatment. Tumor growth was inhibited by 70% as compared with the control group (**P<0.0001). Similar observations were made in the Colo-26 colorectal carcinoma, where light exposure of the sunitinib-treated mice inhibited tumor growth by 50% as compared with the control and by 25% as compared with sunitinib-only-treated tumors (N≥4; P=0.0002). Histology revealed that photoactivation of sunitinib resulted in a change in tumor vessel architecture. The current results suggest that the spectral properties of sunitinib can be exploited for application against certain cancer indications.

Examination of the role of galectins during in vivo angiogenesis using the chick chorioallantoic membrane assay

Angiogenesis is a complex multi-process involving various activities of endothelial cells. These activities are influenced in vivo by environmental conditions like interactions with other cell types and the microenvironment. Galectins play a role in several of these interactions and are therefore required for proper execution of in vivo angiogenesis. In this chapter we describe a method to study galectins and galectin inhibitors during physiologic and pathophysiologic angiogenesis in vivo using the chicken chorioallantoic membrane (CAM) assay.

The emerging quest for the optimal angiostatic combination therapy

Angiostatic therapies are now routinely embedded in the daily clinical management of cancer. Although these agents clearly benefit patient survival rates, the effect is only moderate with sometimes considerable side effects. A major cause of failure in this respect is the induction of resistance and tolerability against these drugs. Most angiostatic drugs are tyrosine kinase inhibitors that aim to inhibit or neutralize the activity of tumour-produced growth factors. Frustrating the tumour cells in this way results in genetic adaptations in the cells, turning them into mutants that are dependent on other growth mechanisms. It may therefore be necessary to shift to another class of drugs that directly target the tumour vasculature. It is evident that improvement of future angiogenesis inhibitors can only arise from two efforts. First, through the identification of better targets, preferably specifically expressed in the tumour vasculature. Secondly, through the development of combination therapies. The present review highlights the current efforts and challenges in trying to develop effective angiostatic combination therapies.

The chicken chorioallantoic membrane model in biology, medicine and bioengineering

The chicken chorioallantoic membrane (CAM) is a simple, highly vascularized extraembryonic membrane, which performs multiple functions during embryonic development, including but not restricted to gas exchange. Over the last two decades, interest in the CAM as a robust experimental platform to study blood vessels has been shared by specialists working in bioengineering, development, morphology, biochemistry, transplant biology, cancer research and drug development. The tissue composition and accessibility of the CAM for experimental manipulation, makes it an attractive preclinical in vivo model for drug screening and/or for studies of vascular growth. In this article we provide a detailed review of the use of the CAM to study vascular biology and response of blood vessels to a variety of agonists. We also present distinct cultivation protocols discussing their advantages and limitations and provide a summarized update on the use of the CAM in vascular imaging, drug delivery, pharmacokinetics and toxicology.

Synthesis and characterization of a new class of anti-angiogenic agents based on ruthenium clusters

New triruthenium-carbonyl clusters derivatized with glucose-modified bicyclophosphite ligands have been synthesized. These compounds were found to have cytostatic and cytotoxic activity and depending on the number of bicyclophosphite ligands, and could be tuned for either anti-cancer or specific anti-angiogenic activity. While some compounds had a broad cellular toxicity profile in several cell types others showed endothelial cell specific dose-dependent anti-proliferative and anti-migratory efficacy. A profound inhibition of angiogenesis was also observed in the in vivo chicken chorioallantoic membrane (CAM) model, and consequently, these new compounds have considerable potential in drug design, e.g. for the treatment of cancer.

Optimization and regeneration kinetics of lymphatic-specific photodynamic therapy in the mouse dermis

Lymphatic vessels transport fluid, antigens, and immune cells to the lymph nodes to orchestrate adaptive immunity and maintain peripheral tolerance. Lymphangiogenesis has been associated with inflammation, cancer metastasis, autoimmunity, tolerance and transplant rejection, and thus, targeted lymphatic ablation is a potential therapeutic strategy for treating or preventing such events. Here we define conditions that lead to specific and local closure of the lymphatic vasculature using photodynamic therapy (PDT). Lymphatic-specific PDT was performed by irradiation of the photosensitizer verteporfin that effectively accumulates within collecting lymphatic vessels after local intradermal injection. We found that anti-lymphatic PDT induced necrosis of endothelial cells and pericytes, which preceded the functional occlusion of lymphatic collectors. This was specific to lymphatic vessels at low verteporfin dose, while higher doses also affected local blood vessels. In contrast, light dose (fluence) did not affect blood vessel perfusion, but did affect regeneration time of occluded lymphatic vessels. Lymphatic vessels eventually regenerated by recanalization of blocked collectors, with a characteristic hyperplasia of peri-lymphatic smooth muscle cells. The restoration of lymphatic function occurred with minimal remodeling of non-lymphatic tissue. Thus, anti-lymphatic PDT allows control of lymphatic ablation and regeneration by alteration of light fluence and photosensitizer dose.

Low-dose angiostatic tyrosine kinase inhibitors improve photodynamic therapy for cancer: lack of vascular normalization

Photodynamic therapy (PDT) is an effective clinical treatment for a number of different cancers. PDT can induce hypoxia and inflammation, pro-angiogenic side effects, which may counteract its angio-occlusive mechanism. The combination of PDT with anti-angiogenic drugs offers a possibility for improved anti-tumour outcome. We used two tumour models to test the effects of the clinically approved angiostatic tyrosine kinase inhibitors sunitinib, sorafenib and axitinib in combination with PDT, and compared these results with the effects of bevacizumab, the anti-VEGF antibody, for the improvement of PDT. Best results were obtained from the combination of PDT and low-dose axitinib or sorafenib. Molecular analysis by PCR revealed that PDT in combination with axitinib suppressed VEGFR-2 expression in tumour vasculature. Treatment with bevacizumab, although effective as monotherapy, did not improve PDT outcome. In order to test for tumour vessel normalization effects, axitinib was also applied prior to PDT. The absence of improved PDT outcome in these experiments, as well as the lack of increased oxygenation in axitinib-treated tumours, suggests that vascular normalization did not occur. The current data imply that there is a future for certain anti-angiogenic agents to further improve the efficacy of photodynamic anti-cancer therapy.

Vascular targeting to the SST2 receptor improves the therapeutic response to near-IR two-photon activated PDT for deep-tissue cancer treatment

BACKGROUND

Broader clinical acceptance of photodynamic therapy is currently hindered by (a) poor depth efficacy, and (b) predisposition towards establishment of an angiogenic environment during the treatment. Improved depth efficacy is being sought by exploiting the NIR tissue transparency window and by photo-activation using two-photon absorption (2PA). Here, we use two-photon activation of PDT sensitizers, untargeted and targeted to SST2 receptors or EGF receptors, to achieve deep tissue treatment.

METHODS

Human tumor lines, positive or negative for SST2r expression were used, as well as murine 3LL cells and bovine aortic endothelial cells. Expression of SST2 receptors on cancer cells and tumor vasculature was evaluated in vitro and frozen xenograft sections. PDT effects on tumor blood flow were followed using in vivo scanning after intravenous injection of FITC conjugated dextran 150K. Dependence of the PDT efficacy on the laser pulse duration was evaluated. Effectiveness of targeting to vascular SST2 receptors was compared to that of EGF receptors, or no targeting.

RESULTS

Tumor vasculature stained for SST2 receptors even in tumors from SST2 receptor negative cell lines, and SST2r targeted PDT led to tumor vascular shutdown. Stretching the pulse from ~120fs to ~3ps led to loss of the PDT efficacy especially at greater depth. PDT targeted to SST2 receptors was much more effective than untargeted PDT or PDT targeted to EGF receptors.

GENERAL SIGNIFICANCE

The use of octreotate to target SST2 receptors expressed on tumor vessels is an excellent approach to PDT with few recurrences and some long term cures.

Photoacoustic microscopy: a potential new tool for evaluation of angiogenesis inhibitor

The feasibility of photoacoustic microscopy (PAM) for evaluation of angiogenesis inhibitor was investigated on a chick embryo model in vivo. Different concentrations of the angiogenesis inhibitor, Sunitinib, were applied to the chorioallantoic membrane (CAM) of the chick embryos. Imaging of microvasculature in embryo CAMs was acquired using a laser-scanning PAM system; while the optical microscopy (OM) capturing the microvascular images of the same set of CAMs for comparison served as a gold standard for validating the results from PAM. The microvascular density as a function of applied Sunitinib concentration has been quantified in both PAM and OM images. The results from these two modalities have a good agreement, suggesting that PAM could provide an unbiased quantification of microvascular density for objective evaluation of anti-angiogenesis medication. In comparison with conventional OM which enables only two-dimensional enface imaging, PAM is capable of three-dimensional analysis of microvessels, including not only morphology but also functions, as demonstrated in part by the imaging result on a canine bladder model. The emerging PAM technique shows promise to be used in clinical and preclinical settings for comprehensive and objective evaluation of anti-angiogenesis medications.

Ecological photodynamic therapy: new trend to disrupt the intricate networks within tumor ecosystem

As with natural ecosystems, species within the tumor microenvironment are connected by pairwise interactions (e.g. mutualism, predation) leading to a strong interdependence of different populations on each other. In this review we have identified the ecological roles played by each non-neoplastic population (macrophages, endothelial cells, fibroblasts) and other abiotic components (oxygen, extracellular matrix) directly involved with neoplastic development. A way to alter an ecosystem is to affect other species within the environment that are supporting the growth and survival of the species of interest, here the tumor cells; thus, some features of ecological systems could be exploited for cancer therapy. We propose a well-known antitumor therapy called photodynamic therapy (PDT) as a novel modulator of ecological interactions. We refer to this as "ecological photodynamic therapy." The main goal of this new strategy is the improvement of therapeutic efficiency through the disruption of ecological networks with the aim of destroying the tumor ecosystem. It is therefore necessary to identify those interactions from which tumor cells get benefit and those by which it is impaired, and then design multitargeted combined photodynamic regimes in order to orchestrate non-neoplastic populations against their neoplastic counterpart. Thus, conceiving the tumor as an ecological system opens avenues for novel approaches on treatment strategies.

Rapid angiogenesis onset after discontinuation of sunitinib treatment of renal cell carcinoma patients

PURPOSE

To investigate the angiogenic changes in primary tumor tissue of renal cell carcinoma (RCC) patients treated with VEGF-targeted therapy.

EXPERIMENTAL DESIGN

Phase II trials of VEGF pathway-targeted therapy given before cytoreductive surgery were carried out with metastatic RCC patients with the primary tumor in situ to investigate the necessity of nephrectomy. Primary tumor tissues were obtained and assessed for angiogenesis parameters. Results were compared with similar analyses on untreated tumors.

RESULTS

Sunitinib or bevacizumab pretreatment resulted in a significant reduction of microvessel density in the primary tumor. Also, an increase in vascular pericyte coverage was found in sunitinib-pretreated tumors, consistent with efficient angiogenesis inhibition. Expression of several key regulators of angiogenesis was found to be suppressed in pretreated tissues, among which VEGFR-1 and VEGFR-2, angiopoietin-1 and angiopoietin-2 and platelet-derived growth factor-B. In addition, apoptosis in tumor and endothelial cells was induced. Interestingly, in sunitinib-pretreated tissues a dramatic increase of the number of proliferating endothelial cells was observed, which was not the case in bevacizumab-pretreated tumors. A positive correlation with the interval between halting the therapy and surgery was found, suggesting a compensatory angiogenic response caused by the discontinuation of sunitinib treatment.

CONCLUSION

This study describes, for the first time, the angiostatic response in human primary renal cancers at the tissue level upon treatment with VEGF-targeted therapy. Discontinuation of treatment with tyrosine kinase inhibitors leads to accelerated endothelial cell proliferation. The results of this study contribute important data to the ongoing discussion on the discontinuation of treatment with kinase inhibitors.

Tumor angiogenesis is enforced by autocrine regulation of high-mobility group box 1

The endothelium plays a pivotal role in the progression of solid tumors and is considered a highly relevant target for therapy. However, it emerges that current clinical angiogenesis inhibitors that act through inhibition of tumor-derived growth factors are prone to inducing drug resistance. Therefore, markers of tumor endothelial cells (ECs) themselves provide attractive novel therapeutic targets. In a screen for markers of tumor angiogenesis, we recently identified high-mobility group box 1 (HMGB1), known to act as proinflammatory cytokine and chromatin-binding molecule. Here we report on the role of HMGB1 in angiogenesis by showing that its overexpression is associated with an increased angiogenic potential of ECs. HMGB1 stimulates the expression of players in vascular endothelial growth factor and platelet-derived growth factor signaling, both in vitro and in vivo. Importantly, we show that HMGB1 triggers and helps to sustain this proangiogenic gene expression program in ECs, additionally characterized by increased activity of matrix metalloproteinases, integrins and nuclear factor-κB. Moreover, we found that HMGB1 is involved in several autocrine and/or paracrine feedback mechanisms resulting in positive enforcement of HMGB1 expression, and that of its receptors, RAGE (receptor for advanced glycation end products) and Toll-like receptor 4 (TLR4). Interference in HMGB1 expression and/or function using knockdown approaches and antibody-mediated targeting to break this vicious circle resulted in inhibited migration and sprouting of ECs. Using different in vivo models, therapeutic efficacy of HMGB1 targeting was confirmed. First, we demonstrated induction of HMGB1 expression in the chicken embryo chorioallantoic membrane (CAM) neovasculature following both photodynamic therapy and tumor challenge. We subsequently showed that anti-HMGB1 antibodies inhibited vessel density in both models, accompanied by a reduced vascular expression of angiogenic growth factor receptors. Collectively, these data identify HMGB1 as an important modulator of tumor angiogenesis and suggest the feasibility of targeting HMGB1 for multi-level cancer treatment.

Angiogenesis inhibition by the maleimide-based small molecule GNX-686

We investigated the anti-angiogenic properties of GNX-686, a newly identified maleimide-based small molecule. In vitro studies on HUVEC showed that GNX-686 inhibited cell growth with an ED(50) of 20-25 μM, while human HeLa tumor cells and non-transformed embryonic mouse fibroblasts were less sensitive for the drug. More importantly, at 4 μM, a concentration that was non-toxic to any cell in culture, GNX-686 showed a significant inhibitory effect on tube formation by HUVEC, indicating a profound anti-angiogenic activity. Angiogenesis inhibition was subsequenly tested in the chorioallantoic membrane (CAM) of the chicken embryo. A significant angiostatic activity was observed in the CAM model, and results were compared with the effect of bevacizumab, a well known and clinically used VEGF inhibitor. Under our experimental conditions, GNX-686 was found to be as effective as bevacizumab, significantly changing the morphology of the vascular network, as illustrated and quantified by the relative number of branching points and the relative mean mesh size of the vascular network. In another in vivo model of neovascularization, the mouse retinopathy of prematurity (ROP), the vascular network of GNX-686-treated mice was significantly altered, reducing the density of the retinal microvasculature, as compared to the control retinas. Immunohistochemical processing of the GNX-686 treated (4μM) eyes showed over 50% reduction of the number of cell nuclei associated with neovasculature, as compared to the control-treated eye. Taken together these results demonstrate that GNX-686 is a promising anti-angiogenic compound that could be developed for the treatment of diseases characterized by aberrant angiogenesis such as ocular pathologies and cancer.