Promotion of Proapoptotic Signals by Lysosomal Photodamage

We previously reported that low-level lysosomal photodamage enhanced the efficacy of subsequent mitochondrial photodamage, resulting in a substantial promotion of apoptotic cell death. We now extend our analysis of the sequential PDT protocol to include two additional lysosomal-targeting photosensitizers. These agents, because of enhanced permeability, are more potent than the agent (N-aspartyl chlorin E6, NPe6) used in the initial study. Addition of the cell-permeable cysteine protease inhibitor E-64d and calcium chelator BAPTA-AM almost completely suppressed sequential PDT-induced loss of mitochondrial membrane potential and activation of procaspases-3 and -7. These inhibitors did not, however, suppress the proapoptotic effect of a BH3 mimetic or mitochondrial photodamage. Knockdowns of ATG7 or ATG5, proteins normally associated with autophagy, suppressed photodamage induced by the sequential PDT protocol. These effects appear to be independent of the autophagic process as pharmacological inhibition of autophagy offered no such protection. Effects of ATG7 and ATG5 knockdowns may reflect the role that ATG7 plays in regulating lysosome permeability, and the likelihood that a proteolytic fragment of ATG5 amplifies mitochondrial proapoptotic processes. Our results suggest that low-dose photodamage that sequentially targets lysosomes and mitochondria may offer significant advantages over the use of single photosensitizers.

Synthesis, spectroscopic, and in vitro investigations of 2,6-diiodo-BODIPYs with PDT and bioimaging applications

A series of five mono-styryl and their corresponding symmetric di-styryl-2,6-diiodo-BODIPYs containing indolyl, pyrrolyl, thienyl or tri(ethylene glycol)phenyl groups were synthesized using Knoevenagel condensations. The yields for the condensation reactions were improved up to 40% using microwave irradiation (90°C for 1h at 400W) due to lower decomposition of BODIPYs upon prolonged heating. The spectroscopic, structural (including the X-ray of a di-styryl-2,6-diiodo-BODIPY) and in vitro properties of the BODIPYs were investigated. The extension of π-conjugation through the 3,5-dimethyls of the known phototoxic 2,6-diiodo-BODIPY 1 produced bathochromic shifts in the absorption and emission spectra, in the order of 63-125nm for the mono-styryl- and 128-220nm for the di-styryl-BODIPYs in DMSO. The largest red-shifts were observed for the indolyl-containing BODIPYs while the largest fluorescence quantum yields were observed for the tri(ethyleneglycol)phenylstyryl-BODIPYs. Among this series, only the mono-styryl-BODIPYs were phototoxic (IC50=2-15μM at 1.5J/cm(2)), and were observed to localize preferentially in the cell ER and mitochondria. On the other hand, the di-styryl-BODIPYs were found to have low or no phototoxicity (IC50>100μM at 1.5J/cm(2)). Among this series of compounds BODIPY 2a shows the most promise for application as photosensitizer in PDT.

Apoptosis and associated phenomena as a determinants of the efficacy of photodynamic therapy

Failure of neoplastic cells to respond to conventional chemotherapy is usually associated with factors that limit access of drugs to subcellular sites, differences in cell-cycle kinetics or mutations leading to loss of drug-activation pathways or other processes that govern response factors. For PDT, efficacy depends mainly on selective uptake of photosensitizers by neoplastic cells, oxygenation levels, the suitable direction of irradiation and the availability of pathways to cell death that are highly conserved among mammalian cell types. While it is possible to engineer PDT-resistant cell types, current evidence suggests that the major obstacles to cancer control relate to drug, light and oxygen distribution. This review discusses some of the factors that can govern PDT-induced cell death.

Damage control radiology in the severely injured patient: what the anaesthetist needs to know

In the treatment of severely injured patients, the term 'damage control radiology' has been used to parallel the modern concept of damage control surgery and the allied development of continuous damage control resuscitation from patient retrieval, through all transfers, to appropriate primary treatment. The aims of damage control radiology are (i) rapid identification of life-threatening injuries including bleeding sites, (ii) identification or exclusion of head or spinal injury, and (iii) prompt and accurate triage of patients to the operating theatre for thoracic, abdominal, or both surgeries or the angiography suite for endovascular haemorrhage control. If we are to achieve these aims, patients must have immediate access to modern multidetector computed tomography (MDCT) which is without doubt the most potent weapon in the diagnostic armamentarium. The most severely injured patients are those who have the most to benefit from early diagnosis and life-saving therapies. The traditional teaching that these patients should go immediately to surgery is challenged by technological developments in MDCT and recent clinical evidence.

Reversible effects of photodamage directed toward mitochondria

When the initial effect of photodynamic therapy (PDT) involves mitochondrial photodamage, an early effect is loss of the mitochondrial membrane potential (ΔΨm ). Using murine hepatoma 1c1c7 cells and a photosensitizing agent known to target mitochondria, we examined loss of ΔΨm , initiation of apoptosis and loss of viability as a function of time and light dose. There was a correlation between loss of viability and the rapid disappearance of ΔΨm, as detected by the potential-sensitive probe Mitotracker Orange (MTO). Loss of ΔΨm was, however, reversible even with a substantial loss of viability. Unless there was a supralethal level of photodamage, 1c1c7 cells recovered their mitochondrial membrane potential, even if the cell population was on the pathway to apoptosis and cell death. These results indicate that when mitochondria are the initial PDT target, a qualitative estimate of photokilling can be provided by assessing the initial loss of ΔΨm.

Enhanced efficacy of photodynamic therapy via a sequential targeting protocol

This study was designed to examine determinants of the discovery that low-dose lysosomal photodamage (lyso-PDT) could potentiate the efficacy of subsequent low-dose mitochondrial photodamage (mito-PDT). The chlorin NPe6 and the benzoporphyrin derivative (BPD) were used to separately target lysosomes and mitochondria, respectively, in murine hepatoma cells. Lyso-PDT (LD(5) conditions) followed by mito-PDT (LD(15) conditions) enhanced the loss of the mitochondrial membrane potential, activation of procaspases-3/7 and photokilling. Reversing the sequence was less effective. The optimal sequence did not enhance reactive oxygen species formation above that obtained with low-dose mito-PDT. In contrast, alkalinization of lysosomes with bafilomycin also enhanced low-dose mito-PDT photokilling, but via a different pathway. This involves redistribution of iron from lysosomes to mitochondria leading to enhanced hydroxyl radical formation, effects not observed after the sequential procedure. Moreover, Ru360, an inhibitor of mitochondrial calcium and iron uptake, partially suppressed the ability of bafilomycin to enhance mito-PDT photokilling without affecting the enhanced efficacy of the sequential protocol. We conclude that sequential PDT protocol promotes PDT efficacy by a process not involving iron translocation, but via promotion of the pro-apoptotic signal that derives from mitochondrial photodamage.

ImaGiNe Seldinger: first simulator for Seldinger technique and angiography training

In vascular interventional radiology, procedures generally start with the Seldinger technique to access the vasculature, using a needle through which a guidewire is inserted, followed by navigation of catheters within the vessels. Visual and tactile skills are learnt in a patient apprenticeship which is expensive and risky for patients. We propose a training alternative through a new virtual simulator supporting the Seldinger technique: ImaGiNe (imaging guided interventional needle) Seldinger. It is composed of two workstations: (1) a simulated pulse is palpated, in an immersive environment, to guide needle puncture and (2) two haptic devices provide a novel interface where a needle can direct a guidewire and catheter within the vessel lumen, using virtual fluoroscopy. Different complexities are provided by 28 real patient datasets. The feel of the simulation is enhanced by replicating, with the haptics, real force and flexibility measurements. A preliminary validation study has demonstrated training effectiveness for skills transfer.

Effects of the oxygenation level on formation of different reactive oxygen species during photodynamic therapy

We examined the effect of the oxygenation level on efficacy of two photosensitizing agents, both of which target lysosomes for photodamage, but via different photochemical pathways. Upon irradiation, the chlorin termed NPe6 forms singlet oxygen in high yield while the bacteriopheophorbide WST11 forms only oxygen radicals (in an aqueous environment). Photokilling efficacy by WST11 in cell culture was impaired when the atmospheric oxygen concentration was reduced from 20% to 1%, while photokilling by NPe6 was unaffected. Studies in a cell-free system revealed that the rates of photobleaching of these agents, as a function of the oxygenation level, were correlated with results described above. Moreover, the rate of formation of oxygen radicals by either agent was more sensitive to the level of oxygenation than was singlet oxygen formation by NPe6. These data indicate that the photochemical process that leads to oxygen radical formation is more dependent on the oxygenation level than is the pathway leading to formation of singlet oxygen.

Compression of the dorsalis pedis artery: a novel cause of blue toe syndrome

Blue toe syndrome (BTS) is an important vascular condition characterized by painful blue discoloration of one or more digits. It is frequently due to emboli and is important because of the risk of progressive ischemia and tissue loss. A 53-year-old male presented with recurrent episodes of painful blue discoloration and blistering of the skin of the right hallux. On examination, the patient was found to have a cool, blue-purple great toe; all peripheral pulses were present. The patient was investigated for coagulopathy and potential sources of emboli, but the only abnormality was significant stenosis of the dorsalis pedis artery due to extrinsic compression by the extensor hallucis brevis tendon. In the absence of any other embolic source or abnormality, we believe that this case presents a novel and potentially remediable cause of BTS and indicates the need for a careful search for an underlying lesion when common causes of BTS have been excluded.

Light-Activated Pharmaceuticals: Mechanisms and Detection

Photodynamic therapy relies on the interaction between light, oxygen and a photosensitizing agent. Its medical significance relates to the ability of certain agents, usually based on porphyrin or phthalocyanine structures, to localize somewhat selectively in neoplastic cells and their vasculature. Subsequent irradiation, preferably at a sufficiently high wavelength to have a significant pathway through tissues, results in a photophysical reaction whereby the excited state of the photosensitizing agent transfers energy to molecular oxygen and results in the formation of reactive oxygen species. Analogous reactive nitrogen species are also formed. These contain both nitrogen and oxygen atoms. The net result is both direct tumor cell death and a shutdown of the tumor vasculature. Other processes may also occur that promote the anti-tumor response but these are outside the scope of this review.

Inhibition of endocytic processes by photodynamic therapy

BACKGROUND AND OBJECTIVES

Recent studies have demonstrated an effect of photodamage on the endocytic pathway involved in recycling of membrane components. Using a series of agents with known sub-cellular targets, we explored the determinants of photodynamic inhibition of endocytic processes in three cell lines: A murine leukemia, a murine hepatoma, and a non-malignant epithelial cell line of human origin.

STUDY DESIGN/MATERIALS AND METHODS

The PI-3 kinase antagonist wortmannin blocks endosomal processing pathway dependent on this enzyme, providing an indication of the "flux" of endocytosis. Microscopic observations were used to assess the effect of photodamage on this pathway. Photosensitizing agents specific for mitochondrial, endoplasmic reticulum (ER), lysosomal, and endosomal photodamage were employed.

RESULTS

Sub-lethal photodamage directed against endosomes or lysosomes interrupted early steps in this endocytic process in the hepatoma cell line. A mechanism for these effects is proposed. Mitochondrial photodamage could interrupt endocytosis, but at levels that also induced apoptosis. ER photodamage did not affect endocytosis even at lethal levels. Somewhat similar results were obtained with other cell lines, but there were sufficient differences to indicate that the cell phenotype is, in part, a determinant of the endocytic response to PDT.

CONCLUSIONS

PDT is therefore seen to have an effect on endocytic processes. Further work will be needed to delineate the role of these endocytic effects in the array of responses to photodynamic therapy.

Evaluation of diethyl-3-3'-(9,10-anthracenediyl)bis acrylate as a probe for singlet oxygen formation during photodynamic therapy

The cell-permeable anthracene analog diethyl-3-3'-(9,10-anthracenediyl)bis acrylate (DADB) was recently identified as a highly selective probe for singlet oxygen ((1)O(2)). Now, we show that DADB can be used to monitor (1)O(2) formation in cell culture during photodynamic therapy. An atypical property of DADB is that fluorescence emission is decreased upon oxidation. Using photosensitizers that target specific organelles, we determined that DADB could detect (1)O(2) whether formed in ER, mitochondria or lysosomes. DADB fluorescence was not, however, significantly altered when the photosensitizing agent was the palladium bacteriopheophorbide termed WST11, an agent reported to produce mainly oxygen radicals upon irradiation in an aqueous environment, whereas singlet oxygen was formed in organic solvents.

Correlation between subcellular localization and photodynamic efficacy

A variety of agents have now been identified that can selectively sensitize neoplastic cells and other tissues to light. This review classifies a group of photosensitizers according to their initial affinity for specific sub-cellular organelles in vitro, and describes the consequences of each major localization site with regard to direct tumor cell kill. Considerations pertinent to determinants of efficacy in animal models and in clinical applications are also pointed out. One consequence of photodynamic therapy leading to cell death involves photodamage to anti-apoptotic members of the Bcl-2. These proteins are located on the endoplasmic reticulum and mitochondrial membranes. Direct mitochondrial photodamage can also initiate apoptosis. Agents that target lysosomes can bring about apoptotic death via an indirect route, but this does not appear to limit their usefulness. Agents that target the plasma membrane can re-localize to the cytosol during irradiation and cause photodamage to elements of the apoptotic process, resulting in necrosis. Implications of these findings are discussed.

Patient experience, pain, and quality of life after lower limb angioplasty: a multisite prospective cohort study

PURPOSE

To explore the experience of patients undergoing endovascular lower limb angioplasty and evaluate the improvements in quality of life and disease-related symptoms after the procedure.

METHODS

Patients completed a questionnaire before treatment and three questionnaires after the procedure (immediately after the procedure, and again 4 weeks and 3 months later). Anxiety, patient understanding, procedure-related pain, and disease-related pain were assessed by a visual analog score (VAS). Complications, analgesic requirements, and satisfaction were recorded. Changes to quality of life were assessed by the validated SF36 questionnaire.

RESULTS

A total of 88 patients (41%) responded. Overall, disease-related pain decreased over 3 months after the procedure. Smokers had more pain both before and after the procedure (P < 0.05). Explanation was considered better if provided by radiologist (P < 0.05). Sixty-nine percent of patients found the procedures less painful (mean VAS 2.5) than they had anticipated (VAS 5.5). Fifty percent of patients experienced adverse effects related to their puncture site, but this was highest among patients who had undergone the procedure before and smokers. The greatest quality-of-life improvements were in emotional and general health. Higher levels of disease-related pain were associated with worse general, emotional, and physical health (P < 0.05).

CONCLUSION

Lower limb angioplasty provides symptomatic and quality-of-life improvements. Implementation of simple measures could improve patient satisfaction-for example, treatment should be explained by the radiologist in advance. Routine prescription of analgesics with particular attention to smokers and those undergoing repeat interventions is suggested.

Photodynamic therapy of cancer: an update

Photodynamic therapy (PDT) is a clinically approved, minimally invasive therapeutic procedure that can exert a selective cytotoxic activity toward malignant cells. The procedure involves administration of a photosensitizing agent followed by irradiation at a wavelength corresponding to an absorbance band of the sensitizer. In the presence of oxygen, a series of events lead to direct tumor cell death, damage to the microvasculature, and induction of a local inflammatory reaction. Clinical studies revealed that PDT can be curative, particularly in early stage tumors. It can prolong survival in patients with inoperable cancers and significantly improve quality of life. Minimal normal tissue toxicity, negligible systemic effects, greatly reduced long-term morbidity, lack of intrinsic or acquired resistance mechanisms, and excellent cosmetic as well as organ function-sparing effects of this treatment make it a valuable therapeutic option for combination treatments. With a number of recent technological improvements, PDT has the potential to become integrated into the mainstream of cancer treatment.

Effects of endosomal photodamage on membrane recycling and endocytosis

The flux of receptor-independent endocytosis can be estimated by addition of wortmannin to cell cultures. Membrane influx is unaffected but traffic out of late endosomes is impaired, resulting in a substantial enlargement of these organelles. Using the 1c1c7 murine hepatoma, we investigated the effect of endosomal photodamage on this endocytic pathway. We previously reported that photodamage catalyzed by the lysosomal photosensitizer NPe6 prevented wortmannin-induced endosomal swelling, indicating an earlier block in the process. In this study, we show that endosomal photodamage, initiated by photodamage from an asymmetrically substituted porphine or a phthalocyanine also prevents wortmannin-induced endosomal swelling, even when the photodynamic therapy (PDT) dose is insufficient to cause endosomal disruption. As the PDT dose is increased, endosomal breakage occurs, as does apoptosis and cell death. Very high PDT doses result in necrosis. We propose that photodamage to endosomes results in alterations in the endosomal structure such that influx of new material is inhibited and receptor-independent endocytosis is prevented. In an additional series of studies, we found that the swollen late endosomes induced by wortmannin are unable to retain previously accumulated fluorescent probes or photosensitizers.