Combination therapy using verteporfin and ranibizumab; optimizing the timing in the CAM model

Engineering photodynamics for treatment, priming and imaging

Photodynamic therapy (PDT) is a photochemistry-based treatment approach that relies on the activation of photosensitizers by light to locally generate reactive oxygen species that induce cellular cytotoxicity, in particular for the treatment of tumours. The cytotoxic effects of PDT are depth-limited owing to light penetration limits in tissue. However, photodynamic priming (PDP), which inherently occurs during PDT, can prime the tissue microenvironment to adjuvant therapies beyond the direct PDT ablative zone. In this Review, we discuss the underlying mechanisms of PDT and PDP, and their application to the treatment of cancer, outlining how PDP can permeabilize the tumour vasculature, overcome biological barriers, modulate multidrug resistance, enhance immune responses, increase tumour permeability and enable the photochemical release of drugs. We further examine the molecular engineering of photosensitizers to improve their pharmacodynamic and pharmacokinetic properties, increase their molecular specificity and allow image guidance of PDT, and investigate engineered cellular models for the design and optimization of PDT and PDP. Finally, we discuss alternative activation sources, including ultrasound, X-rays and self-illuminating compounds, and outline key barriers to the clinical translation of PDT and PDP.

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.

Photodynamic Priming Improves the Anti-Migratory Activity of Prostaglandin E Receptor 4 Antagonist in Cancer Cells In Vitro

The combination of photodynamic agents and biological inhibitors is rapidly gaining attention for its promise and approval in treating advanced cancer. The activity of photodynamic treatment is mainly governed by the formation of reactive oxygen species upon light activation of photosensitizers. Exposure to reactive oxygen species above a threshold dose can induce cellular damage and cancer cell death, while the surviving cancer cells are "photodynamically primed", or sensitized, to respond better to other drugs and biological treatments. Here, we report a new combination regimen of photodynamic priming (PDP) and prostaglandin E2 receptor 4 (EP4) inhibition that reduces the migration and invasion of two human ovarian cancer cell lines (OVCAR-5 and CAOV3) in vitro. PDP is achieved by red light activation of the FDA-approved photosensitizer, benzoporphyrin derivative (BPD), or a chemical conjugate composed of the BPD linked to cetuximab, an anti-epithelial growth factor receptor (EGFR) antibody. Immunoblotting data identify co-inhibition of EGFR, cAMP-response element binding protein (CREB), and extracellular signal-regulated kinase 1/2 (ERK1/2) as key in the signaling cascades modulated by the combination of EGFR-targeted PDP and EP4 inhibition. This study provides valuable insights into the development of a molecular-targeted photochemical strategy to improve the anti-metastatic effects of EP4 receptor antagonists.

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.

Photodynamic therapy in combination with ranibizumab versus ranibizumab monotherapy for wet age-related macular degeneration: A systematic review and meta-analysis

OBJECTIVE

To evaluate the efficacy and safety between photodynamic therapy (PDT) combined with intravitreal ranibizumab (IVR) and ranibizumab monotherapy in treating wet age-related macular degeneration (AMD).

METHODS

A systematic search was performed in the PubMed, Embase, Web of Science and the Cochrane Library databases through December 31, 2017. The methodological quality of the references was evaluated according to the Cochrane quality assessment. RevMan 5.3 software was used to perform the meta-analysis.

RESULTS

Eight RCTs involving 817 participants were included. Wet AMD eyes in the mono-group achieved better best-corrected vision acuity (BCVA) than the combination group in month 12 (WMD = -0.19, 95% CI = -0.32 to -0.06, P = 0.004, I² = 18%). The proportion of patients gaining more than 15 letters from baseline in the mono-group was larger than that in the combination group (RR = 0.70, 95% CI: 0.56 to 0.87, P = 0.001). However, the number of ranibizumab injections with combination therapy was smaller than that with mono-therapy (MD = -1.13, 95% CI: -2.11 to -0.15, P = 0.02, I² = 85%). No significant differences were observed in the proportions of patients losing more than 15 letters, central retinal thickness (CRT), lesion size of choroidal neovascularization (CNV) and adverse events.

CONCLUSIONS

Combination therapy decreased the number of injections of ranibizumab, although its BCVA improvement was inferior to that of monotherapy over 12 months of follow-up. Given the inherent limitations of the included trials, more studies are needed to further validate and update the findings in this area.

Methods for Analyzing Tumor Angiogenesis in the Chick Chorioallantoic Membrane Model

Models of tumor angiogenesis have played a critical role in understanding the mechanisms involved in the recruitment of vasculature to the tumor mass, and have also provided a platform for testing antiangiogenic potential of new therapeutics that combat the development of malignant growth. In this regard, the chorioallantoic membrane (CAM) of the developing chick embryo has proven to be an elegant model for investigation of angiogenic processes. Here, we describe methods for effectively utilizing the preestablished vascular network of the chick CAM to investigate and quantify tumor-associated angiogenesis in a breast tumor model.

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.

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.

Angiostatic kinase inhibitors to sustain photodynamic angio-occlusion

Targeted angiostatic therapy receives major attention for the treatment of cancer and exudative age-related macular degeneration (AMD). Photodynamic therapy (PDT) has been used as an effective clinical approach for these diseases. As PDT can cause an angiogenic response in the treated tissue, combination of PDT with anti-angiogenic compounds should lead to improved therapy. This study was undertaken to test the clinically used small molecule kinase inhibitors Nexavar® (sorafenib), Tarceva® (erlotinib) and Sutent® (sunitinib) for this purpose, and to compare the results to the combination of Visudyne®-PDT with Avastin® (bevacizumab) treatment. When topically applied to the chicken chorioallantoic membrane at embryo development day (EDD) 7, a clear inhibition of blood vessel development was observed, with sorafenib being most efficient. To investigate the combination with phototherapy, Visudyne®-PDT was first applied on EDD11 to close all <100 μm vessels. Application of angiostatics after PDT resulted in a significant decrease in vessel regrowth in terms of reduced vessel density and number of branching points/mm(2) . As the 50% effective dose (ED50) for all compounds was approximately 10-fold lower, Sorafenib outperformed the other compounds. In vitro, all kinase inhibitors decreased the viability of human umbilical vein endothelial cells. Sunitinib convincingly inhibited the in vitro migration of endothelial cells. These results suggest the therapeutic potential of these compounds for application in combination with PDT in anti-cancer approaches, and possibly also in the treatment of other diseases where angiogenesis plays an important role.

Effect of photodynamic therapy (PDT), posterior subtenon injection of triamcinolone acetonide with PDT, and intravitreal injection of ranibizumab with PDT for retinal angiomatous proliferation

BACKGROUND

The purpose of this work was to compare the efficacy of photodynamic therapy (PDT) with or without posterior subtenon injections of triamcinolone acetonide (STA) or intravitreal injections of ranibizumab (IVR) for retinal angiomatous proliferation (RAP).

METHODS

Thirty-seven eyes from 33 consecutive patients with RAP were treated by PDT monotherapy (Group 1), PDT combined with STA (Group 2), or PDT combined with IVR (Group 3). The best-corrected visual acuity, greatest linear dimension, central retinal thickness, and number of treatments were compared among the three groups.

RESULTS

The change in mean best-corrected visual acuity (logMAR) at month 3, 6, and 12 after the initial treatment was better in Group 2 (-0.13, -0.23, and -0.21, respectively) and Group 3 (-0.018, 0.0028, and -0.0067, respectively) than in Group 1 (0.13, 0.19, and 0.23, respectively); Group 1 versus Group 2 was statistically significant (P = 0.018). The mean central retinal thickness was reduced from baseline in all groups, but the reduction amplitude was significantly greater in Group 2 than in Group 1 and Group 3. The mean number of treatments was significantly lower in Group 2 (1.1 ± 0.4) and Group 3 (1.5 ± 0.5) than in Group 1 (2.9 ± 0.9) in the 12 months after the initial treatment.

CONCLUSION

Treatment with STA + PDT may be an effective therapy for RAP lesions over 12 months of follow-up.

Combined intravitreal ranibizumab and verteporfin photodynamic therapy versus ranibizumab alone for the treatment of age-related macular degeneration

PURPOSE

To compare same-day combined therapy of photodynamic therapy with verteporfin (PDT-V) and intravitreal ranibizumab versus monotherapy with ranibizumab for the treatment of choroidal neovascularization.

METHODS

IN THIS PROSPECTIVE STUDY, THE TOTAL NUMBER OF EYES WAS RANDOMIZED INTO TWO GROUPS: in the first, treatment consisted of a combined therapy of PDT-V and ranibizumab 0.5 mg on the same day; in the second, ranibizumab 0.5 mg in 3 monthly injections. Best-corrected visual acuity (BCVA) and central macular thickness (CMT) on optical coherence tomography (OCT) were recorded before and 6 months after treatment.

RESULTS

A total of 47 eyes of 47 subjects were enrolled in the study. In the combined-therapy group (group 1), the mean baseline BCVA ± standard deviation (SD) was 32.65 ± 11.09 letters (Snellen equivalent, 20/59); in the ranibizumab-alone group (group 2), 29.13 ± 9.03 letters (20/70). At 6 months' follow-up, in group 1 the mean baseline BCVA was 39.06 ± 10.12 letters (20/42); in group 2, 33.87 ± 12.06 letters (20/57). Improvement was significant in both group 1 (P = 0.03) and group 2 (P = 0.002). In group 1, the mean CMT at baseline ± SD was 315 ± 95.49 μm; in group 2, 306.33 ± 71.61 μm. At 6 months' follow-up, in group 1 it was 202 ± 52.02 μm; in group 2, 226 ± 65.58 μm. Reduction was significant in both group 1 (P = 0.0007) and group 2 (P = 0.00001). After 6-months, the rate of retreated eyes was 29.4% in group 1 and 43.3% in group 2. The need for retreatment did not depend on the treatment protocol (P = 0.34).

CONCLUSIONS

From a functional and anatomic point of view, the two treatments showed equivalent efficacy, with fewer retreatments in group 1. No serious adverse events, such as retinal detachment, endophthalmitis, or ocular hypertension occurred in either group.

Vascular regrowth following photodynamic therapy in the chicken embryo chorioallantoic membrane

Photodynamic therapy (PDT) induces damage to the endothelium, which can lead to increased vascular permeability and, under intensive PDT conditions, even to platelet aggregation, vasoconstriction, and blood flow stasis. Eventually, ischemia, hypoxia, and inflammation can occur, resulting in angiogenesis. We studied the sequence of the vascular events after Visudyne^®-PDT in the chicken chorioallantoic membrane (CAM) at day 11 of development. Using epi-fluorescence microscopy, we monitored the regrowth of capillaries in the PDT treated area. Immediately after irradiation, the treatment resulted in blood flow arrest. And 24 h post PDT, sprouting of new blood vessels was observed at the edge of the PDT zone. Neovessels looping out from the edge of the PDT zone gave rise to specialized endothelial tip structures guiding the vessels towards the center of the treated area. At 48 h almost all of the treated area was repopulated with functional but morphologically altered vasculature. These observations also showed reperfusion of some of the vessels that had been closed by the PDT treatment. CAM samples were immunohistochemically stained for Ki-67 showing proliferation of endothelial cells in the PDT area. Also, several markers of immature and angiogenic blood vessels, such as αVβ3-integrin, vimentin and galectin-1, were found to be enhanced in the PDT area, while the endothelial maturation marker intercellular adhesion molecule (ICAM)-1 was found to be suppressed. These results demonstrate that the new vascular bed is formed by both neo-angiogenesis and reperfusion of existing vessels. Both the quantitative real-time RT–PCR profile and the response to pharmacological treatment with Avastin^®, an inhibitor of angiogenesis, suggest that angiogenesis occurs after PDT. The observed molecular profiling results and the kinetics of gene regulation may enable optimizing combination therapies involving PDT for treatment of cancer and other diseases.