Highways and Detours in the Realm of Photodynamic Therapy.

Photodynamic therapy (PDT) has been a topic of interest since the first report in 1900 but has yet to become a 'mainstream' treatment protocol in the medical field. There are clear indications for which PDT might be the 'method of choice', but it is unlikely that there will be protocols for the treatment of systemic disease. This report discusses recent developments for promoting PDT efficacy, in the context of what is already known. Factors that can limit the scope of these applications are also indicated. Among the more interesting of these developments is the use of formulation techniques to target specific organelles for photodamage. This can enhance responses to PDT and circumvent situations where an impaired death pathway interferes with PDT efficacy.

Critical PDT Theory III: Events at the Molecular and Cellular Level.

Photodynamic therapy (PDT) is capable of eradicating neoplastic cells that are accessible to sufficient light and oxygen. There is adequate information now available for assessing conditions where PDT might be the therapy of choice, but limited access to clinical facilities and impediments to regulatory approval of new agents have limited clinical usage. Early reports mainly involved clinical data with few thoughts towards finding death pathways. In 2022, there is a clear understanding of the determinants of successful tumor eradication. While PDT may be the optimal method for many clinical indications, support for this approach has lagged. This report provides a commentary on some elements of recent progress in PDT at the molecular and cellular levels, along with a discussion of some of the limitations in current research efforts.

Photodynamic therapy: apoptosis, paraptosis and beyond.

Photodynamic therapy (PDT) is a light-catalyzed process that can initiate cellular death pathways from the formation of cytotoxic reactive oxygen species at sub-cellular sites. Apoptosis was the first such pathway to be identified. Autophagy can also occur and is often found to be cytoprotective. Another process termed paraptosis can also have lethal consequences, even in cells with an impaired apoptotic pathway. PDT in vivo can evoke other potentially cytotoxic processes including vascular shutdown and enhanced immunologic recognition of neoplastic cells. Using appropriate photosensitizing agents, sub-cellular PDT targeting can be directed so that the resulting interplay among assorted death and survival pathways will result in an enhanced level of photokilling.

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.

Surgery versus thrombolysis for initial management of acute limb ischaemia.

BACKGROUND: Both peripheral arterial thrombolysis and surgery can be used in the management of peripheral arterial ischaemia. Much is known about the indications, risks, and benefits of thrombolysis. However, whether thrombolysis works better than surgery for initial management of acute limb ischaemia remains unknown. This is the second update of the review first published in 2002. OBJECTIVES: To determine whether thrombolysis or surgery is the more effective technique in the initial management of acute limb ischaemia due to thromboembolism. SEARCH METHODS: For this update, the Cochrane Vascular Information Specialist (CIS) searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE Ovid, Embase Ovid, CINAHL, AMED, and clinical trials registries up to 7 May 2018. SELECTION CRITERIA: All randomised controlled studies comparing thrombolysis and surgery for initial treatment of acute limb ischaemia. DATA COLLECTION AND ANALYSIS: We independently assessed trial quality and extracted data. Agreement was reached by consensus. We performed analyses using odds ratios (ORs) and 95% confidence intervals (CIs). MAIN RESULTS: We identified no new studies for this update. We included five trials with a total of 1292 participants; agents used for thrombolysis were recombinant tissue plasminogen activator and urokinase. Trials were generally of moderate methodological quality. The quality of evidence according to GRADE was generally low owing to risk of bias (lack of blinding), imprecision in estimates, and heterogeneity.Trial results showed no clear differences in limb salvage, amputation, or death at 30 days (odds ratio (OR) 1.02, 95% confidence interval (CI) 0.41 to 2.55, 4 studies, 636 participants; OR 0.97, 95% CI 0.51 to 1.85, 3 studies, 616 participants; OR 0.59, 95% CI 0.31 to 1.14, 4 studies, 636 participants, respectively), and we rated the evidence as low, low, and moderate quality, respectively. Trial results show no clear differences for any of the three outcomes at six months or one year between initial surgery and initial thrombolysis. A single study evaluated vessel patency, so no overall association could be determined (OR 0.46, 95% CI 0.08 to 2.76, 20 participants; very low-quality evidence). Evidence of increased risk of major haemorrhage (OR 3.22, 95% CI 1.79 to 5.78, 4 studies, 1070 participants; low-quality evidence) and distal embolisation (OR 31.68, 95% CI 6.23 to 161.07, 3 studies, 678 participants; very low-quality evidence) was associated with thrombolysis treatment at 30 days, and there was no clear difference in stroke (OR 5.33, 95% CI 0.95 to 30.11, 5 studies, 1180 participants; low-quality evidence). Participants treated by initial thrombolysis had a greater reduction in the level of intervention required, compared with a pre-intervention prediction, at 30 days (OR 9.06, 95% CI 4.95 to 16.56, 2 studies, 502 participants). None of the included studies evaluated time to thrombolysis as an outcome. AUTHORS' CONCLUSIONS: There is currently no evidence in favour of either initial thrombolysis or initial surgery as the preferred option in terms of limb salvage, amputation, or death at 30 days, six months, or one year. Low-quality evidence suggests that thrombolysis may be associated with higher risk of haemorrhagic complications and ongoing limb ischaemia (distal embolisation). The higher risk of complications must be balanced against risks of surgery in each individual case. Trial results show no statistical difference in stroke, but the confidence interval is very wide, making it difficult to interpret whether this finding is clinically important. We used GRADE criteria to assess the quality of the evidence as generally low. We downgraded quality owing to risk of bias, imprecision, and heterogeneity between included studies.

Photodynamic therapy: Promoting in vitro efficacy of photodynamic therapy by liposomal formulations of a photosensitizing agent.

OBJECTIVE: A relatively low level of lysosomal photodamage has been shown capable of promoting the efficacy of photodamage simultaneously or subsequently directed to mitochondrial/ER sites. The procedure has hitherto involved the use of two photosensitizing agents that require irradiation at two different wavelengths and different formulation techniques. This, together with different pharmacokinetic profiles of the photosensitizers, adds a layer of complexity to a protocol that we have sought to circumvent. In this study, liposomal formulations were used to direct photodamage created by benzoporphyrin derivative (BPD, Verteporfin) to lysosomes, mitochondria and the ER. This resulted in the development of an optimal targeting profile using a single agent and a single wavelength of activating irradiation. MATERIALS/METHODS: These studies were carried out in monolayer cultures of OVCAR5 tumor cells. BPD localization was modified by lipid anchoring and formulation in liposomes, and was assessed by fluorescence microscopy. Irradiation was carried out at 690 ± 10 nm with photodamage assessed also using fluorescent probes and microscopy. RESULTS: BPD normally localizes in a wide variety of sub-cellular loci that include both mitochondria and the ER, but lysosomes are spared from photodamage. Using a liposomal formulation containing BPD anchored to a lipid resulted in the targeting of lysosomes. A mixture of liposomes containing "free" and "anchored" BPD was shown to significantly promote photokilling. Eliminating cholesterol from the formulation of the anchored product enhanced lysosomal photodamage; prior studies had revealed that excess cholesterol can have a cytoprotective effect when lysosomes are the PDT target. DISCUSSION: The ability of a liposomal formulation to change localization patterns permits directing photodynamic therapy toward specific sub-cellular loci, thereby promoting photokilling. Incorporating chemotherapeutic agents into such formulations could represent a logical next step in assessing the ability of directed photodamage to enhance tumor eradication. Lasers Surg. Med. 50:499-505, 2018. © 2018 Wiley Periodicals, Inc.

Photodynamic therapy as an effective therapeutic approach in MAME models of inflammatory breast cancer.

Photodynamic therapy (PDT) is a minimally invasive, FDA-approved therapy for treatment of endobronchial and esophageal cancers that are accessible to light. Inflammatory breast cancer (IBC) is an aggressive and highly metastatic form of breast cancer that spreads to dermal lymphatics, a site that would be accessible to light. IBC patients have a relatively poor survival rate due to lack of targeted therapies. The use of PDT is underexplored for breast cancers but has been proposed for treatment of subtypes for which a targeted therapy is unavailable. We optimized and used a 3D mammary architecture and microenvironment engineering (MAME) model of IBC to examine the effects of PDT using two treatment protocols. The first protocol used benzoporphyrin derivative monoacid A (BPD) activated at doses ranging from 45 to 540 mJ/cm(2). The second PDT protocol used two photosensitizers: mono-L-aspartyl chlorin e6 (NPe6) and BPD that were sequentially activated. Photokilling by PDT was assessed by live-dead assays. Using a MAME model of IBC, we have shown a significant dose-response in photokilling by BPD-PDT. Sequential activation of NPe6 followed by BPD is more effective in photokilling of tumor cells than BPD alone. Sequential activation at light doses of 45 mJ/cm(2) for each agent resulted in >90 % cell death, a response only achieved by BPD-PDT at a dose of 360 mJ/cm(2). Our data also show that effects of PDT on a volumetric measurement of 3D MAME structures reflect efficacy of PDT treatment. Our study is the first to demonstrate the potential of PDT for treating IBC.

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.

More Adventures in Photodynamic Therapy.

Photodynamic therapy is a procedure that can provide a selective eradication of neoplastic disease if sufficient drug, light, and oxygen are available. As this description suggests, it involves the photosensitization of malignant tissues to irradiation with photons in the visible range. While not suitable for tumors at unknown loci, it can be of use for eradication of cancer at surgical margins and therapy at sites where substantial surgery might otherwise be involved. Drug development has been delayed by several factors including the reluctance of major pharmaceutical firms in the United States to invest in this technology along with some unwise approaches in the past.

Sites of sub-cellular photodamage: Apoptotic and autophagic responses.

Log dose-response curves relating to the effect of mitochondrial photodamage on clonogenic survival using benzoporphyrin derivative. With wild-type cells, autophagy produces a "shoulder" on the curve which is absent when an ATG5 knockdown is examined. Loss of ATG5 prevents the process of autophagy, which is seen to be cytoprotective.

Critical PDT theory: Viability, cytotoxicity, proliferation and clonogenicity-Is there a difference?

Comparison of MTT versus clonogenic effects of photodynamic therapy in MCF-7c3 breast cancer cells in culture. Left: MTT data; right clonogenic data. A collection of photosensitizers was used to produce these results.

Annals of photodynamic therapy: Publish and/or Perish?

The current situation with regard to journal publishing is markedly different from the days when everything was done by mail and subscriptions paid the costs. In even earlier times, i.e., the era of Darwin, scientists tended to publish their findings in book form only after prolonged investigations. Now, publishing is Big Business, scavengers troll the internet for evidence of questionable data to report, significant numbers of CHF can be exchanged for access to journals and reviewing can be hazardous. In the era of the internet, appearance of a report with significant errors missed by reviewers can lead to 'publish AND perish'.

Annals of photodynamic therapy: Publish and/or perish?

The current situation with regard to journal publishing is markedly different from the days when everything was done by mail and subscriptions paid the costs. In even earlier times, i.e., the era of Darwin, scientists tended to publish their findings in book form only after prolonged investigations. Now, publishing is Big Business, scavengers troll the internet for evidence of questionable data to report, significant numbers of CHF can be exchanged for access to journals and reviewing can be hazardous. In the era of the internet, the appearance of a report with significant errors missed by reviewers can lead to 'publish AND perish'.

Highways and detours in the realm of photodynamic therapy for cancer control.

Critical elements of photodynamic therapy are a photosensitizing agent, light at a wavelength corresponding to an absorbance band of the agent, and sufficient oxygenation to create a cytotoxic concentration of reactive oxygen species. Other factors may promote efficacy, but these are critical.

Surgery versus thrombolysis for initial management of acute limb ischaemia.

BACKGROUND: Peripheral arterial thrombolysis is technique used in the management of peripheral arterial ischaemia. Much is known about the indications, risks and benefits of thrombolysis. However, it is not known whether thrombolysis works better than surgery in the initial treatment of acute limb ischaemia. OBJECTIVES: To determine the preferred initial treatment, surgery or thrombolysis, for acute limb ischaemia. SEARCH METHODS: For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched March 2013) and CENTRAL (2013, Issue 2). SELECTION CRITERIA: All randomised studies comparing thrombolysis and surgery for the initial treatment of acute limb ischaemia. DATA COLLECTION AND ANALYSIS: Each author independently assessed trial quality and extracted data. Agreement was reached by consensus. MAIN RESULTS: Five trials with a total of 1283 participants were included. There was no significant difference in limb salvage or death at 30 days, six months or one year between initial surgery and initial thrombolysis. However, stroke was significantly more frequent at 30 days in thrombolysis participants (1.3%) compared to surgery participants (0%) (Odds ratio (OR) 6.41; 95% confidence interval (CI) 1.57 to 26.22). Major haemorrhage was more likely at 30 days in thrombolysis participants (8.8%) compared to surgery participants (3.3%) (OR 2.80; 95% CI 1.70 to 4.60); and distal embolization was more likely at 30 days in thrombolysis participants (12.4%) compared to surgery participants (0%) (OR 8.35; 95% CI 4.47 to 15.58).Participants treated by initial thrombolysis underwent a less severe degree of intervention (OR 5.37; 95% CI 3.99 to 7.22) and displayed equivalent overall survival compared to initial surgery (OR 0.87; 95% CI 0.61 to 1.25). AUTHORS' CONCLUSIONS: Universal initial treatment with either surgery or thrombolysis cannot be advocated on the available evidence. There is no overall difference in limb salvage or death at one year between initial surgery and initial thrombolysis. Thrombolysis may be associated with a higher risk of ongoing limb ischaemia and haemorrhagic complications including stroke. The higher risk of complications must be balanced against risks of surgery in each person.

Fibrinolytic agents for peripheral arterial occlusion.

BACKGROUND: Peripheral arterial thrombolysis is used in the management of peripheral arterial ischaemia. Streptokinase was originally used but safety concerns led to a search for other agents. Urokinase and recombinant tissue plasminogen activator (rt-PA) have increasingly become established as first line agents for peripheral arterial thrombolysis. Potential advantages of these agents include improved safety, greater efficacy and a more rapid response. Recently drugs such as pro-urokinase, recombinant staphylokinase and alfimperase have been introduced. This is an update of a review first published in 2010. OBJECTIVES: To determine which fibrinolytic agents are most effective in peripheral arterial ischaemia. SEARCH METHODS: For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator (TSC) searched the Specialised Register (last searched March 2013) and CENTRAL (2013, Issue 3) for randomised controlled trials (RCTs) comparing fibrinolytic agents to treat peripheral arterial ischaemia. SELECTION CRITERIA: RCTs comparing fibrinolytic agents to treat peripheral arterial occlusion. DATA COLLECTION AND ANALYSIS: Data were analysed for the outcomes vessel patency, time to lysis, limb salvage, amputation, death, complications including major haemorrhage, stroke, and distal embolization. MAIN RESULTS: Five RCTs involving a total of 687 participants with a range of clinical indications were included. No new studies were included in this update. In one three-pronged study, vessel patency was greater with intra-arterial recombinant tissue plasminogen activator (rt-PA) than with intra-arterial streptokinase (P < 0.04) or intravenous rt-PA (P < 0.01). In participants with peripheral arterial occlusion there was no statistically significant difference in limb salvage at 30 days with either urokinase or rt-PA, though this may reflect the small numbers in the studies. Incidences of haemorrhagic complications varied with fibrinolytic regime but there was no statistically significant difference between intra-arterial urokinase and intra-arterial rt-PA. In the three-pronged study intravenous rt-PA and intra-arterial streptokinase were associated with a significantly higher risk of haemorrhagic complications than with intra-arterial rt-PA (P < 0.05). AUTHORS' CONCLUSIONS: There is some evidence to suggest that intra-arterial rt-PA is more effective than intra-arterial streptokinase or intravenous rt-PA in improving vessel patency in people with peripheral arterial occlusion. There was no evidence that rt-PA was more effective than urokinase for patients with peripheral arterial occlusion and some evidence that initial lysis may be more rapid with rt-PA, depending on the regime. Incidences of haemorrhagic complications were not statistically significantly greater with rt-PA than with other regimes. However, all of the findings come from small studies and a general paucity of results means that it is not possible to draw clear conclusions.

Photodynamic Therapy: Critical PDT Theory.

Photodynamic therapy can be useful for the eradication of malignant cells at sites that are accessible to light delivery. There are few adverse effects, with many clinical reports indicating that PDT has curative potential. Patients with minimal disease, where success is more likely, are also sought by those promoting other protocols. New photosensitizing agents that initiate light-catalyzed reactions continue to be discovered. Reports describing advances in understanding fundamental aspects of photobiology are always of interest. But, implications for treatment of neoplasia and other diseases are not always justified, especially when poorly penetrating wavelengths of light are employed, often at very high light doses. Efficacy is sometimes estimated by protocols that may not accurately measure photokilling. Many reports claiming potential clinical relevance for in vitro observations are based on a limited understanding of the determinants of clinical efficacy. The future of photodynamic therapy depends on an appreciation of what can be accomplished, especially when used with other modalities, but will also depend on the goals and interests of granting agencies, pharmaceutical groups, and clinical personnel. This commentary is intended to provide some thoughts on current research efforts, especially where clinical implications are suggested, hinted at or otherwise implied.

Critical PDT Theory VII: Preclinical Translation.

The translation of photodynamic effects into clinical practice is a complex process that involves the pharmacokinetics of photosensitizing agents, light dosimetry and oxygenation levels. But even the 'translation' of basic photobiology into meaningful preclinical information can be challenging. Some thoughts on directions for progress in clinical trials are suggested.

Critical PDT Theory V: What it Takes.

First evidence for an apoptotic response to photodamage provided by Oleinick's group in 1991.