Hyperthermia potentiates the effects of aluminum phthalocyanine tetrasulfonate-mediated photodynamic toxicity in human malignant and normal cell lines

Melanoma resistance to photodynamic therapy: new insights

Melanoma is the most dangerous form of skin cancer, with a steeply rising incidence and a poor prognosis in its advanced stages. Melanoma is highly resistant to traditional chemotherapy and radiotherapy, although modern targeted therapies such as BRAF inhibitors are showing some promise. Photodynamic therapy (PDT, the combination of photosensitizing dyes and visible light) has been tested in the treatment of melanoma with some promising results, but melanoma is generally considered to be resistant to it. Optical interference by the highly-pigmented melanin, the antioxidant effect of melanin, the sequestration of photosensitizers inside melanosomes, defects in apoptotic pathways, and the efflux of photosensitizers by ATP-binding cassette transporters have all been implicated in melanoma resistance to PDT. Approaches to overcoming melanoma resistance to PDT include: the discovery of highly active photosensitizers absorbing in the 700-800-nm near infrared spectral region; interventions that can temporarily reduce the amount or pigmentation of the melanin; compounds that can reverse apoptotic defects or inhibit drug-efflux of photosensitizers; and immunotherapy approaches that can take advantage of the ability of PDT to activate the host immune system against the tumor being treated.

Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity

The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, tau(fluo), was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78 degrees C) and oxygen concentrations (0-190 microM). The analysis of tau(fluo) revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in liposomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous tau(fluo) increase for all PSs in free solution, while the opposite, a tau(fluo) decrease, occurred in all liposomal PSs.

Enhancing the antitumoral effect of hypericin-mediated photodynamic therapy by hyperthermia

BACKGROUND AND OBJECTIVES

In the previous study, we have found a synergistic effect on the RIF-1 tumor cell killing when hypericin-mediated photodynamic therapy (PDT) was combined with hyperthermia. The purpose of the present study was to investigate the antitumoral effect of hypericin-PDT in combination with hyperthermia in the RIF-1 mouse tumor model.

STUDY DESIGN/MATERIALS AND METHODS

Tumor response to PDT in combination with hyperthermia was compared to the response to PDT or hyperthermia alone. To explore the possible mechanism involved in the interaction of PDT and hyperthermia, we determined the tumor cell survival by in vivo/in vitro cell survival assay and analyzed the functional blood vessels by Hoechst 33342 staining. The mode of cell death was examined by TUNEL assay.

RESULTS

Enhanced tumor response was obtained by PDT immediately followed by hyperthermia. Tumor cell survival assay revealed that indirect vascular effect contributed greatly to the overall tumor cell death induced by PDT with hypericin, whereas direct tumor cytotoxicity played a major role in hyperthermia-induced tumor cell killing. Combining PDT with hyperthermia brought about a synergistic interaction on direct tumor cell killing. Even though PDT or hyperthermia alone induced severe blood vessel shutdown and the combined treatments led to significant potentiation of the vascular damage as examined by Hoechst staining, the gain in tumor cell death as a result of this secondary vascular effect was limited after the combined treatments. Following the cellular damage by PDT in combination with hyperthermia, tumor cells were triggered to undergo apoptosis.

CONCLUSIONS

Our study demonstrated the possibility of using hyperthermia to potentiate the antitumoral effect of hypericin-mediated PDT.

Postirradiation hyperthermia selectively potentiates the merocyanine 540-sensitized photoinactivation of small cell lung cancer cells

Lung cancer has long been considered a disease that might benefit from the dose escalation of radio/chemotherapy afforded by a stem cell transplant. However, the clinical experience with high-dose chemotherapy and autologous bone marrow transplantation in lung cancer has been disappointing, with most trials showing little or no improvement in long-term survival. Unfortunately, lung cancer has a tendency to metastasize to the bone marrow, and lung cancer cells are known to circulate in the peripheral blood. Therefore, there is concern that autologous stem cell grafts from lung cancer patients may reinoculate recipients with live tumor cells. Photochemical purging of stem cell grafts with Merocyanine 540 (MC540) is highly effective against a wide range of leukemia and lymphoma cells and is well tolerated by normal hematopoietic stem and progenitor cells. Most solid tumor cells (including lung cancer cells), however, are only moderately sensitive or refractory to MC540-mediated photodynamic therapy (PDT). We report here that postirradiation hyperthermia (< or = 42 degrees C, 3 h) potentiates the MC540-mediated photoinactivation of both wild-type (H69) and cisplatin-resistant mutant (H69/CDDP) small cell lung cancer cells by several orders of magnitude, while only minimally enhancing the depletion of normal human granulocyte/macrophage progenitor cells. Our data suggest that postirradiation hyperthermia provides a simple and effective means of extending the utility of MC540-PDT to the purging of stem cell grafts contaminated with lung cancer and possibly other solid tumor cells.

Photodynamic therapy and hyperthermia as an adjuvant modality in preventing tumor recurrence

BACKGROUND AND OBJECTIVE

The objective of this study was to determine the relative efficacy in preventing tumor recurrence by photodynamic therapy (PDT), and by ablative CO2 laser surgery followed by PDT, compared to ablative surgery alone (negative control) or ablative surgery followed by a course of hyperthermia (positive control).

STUDY DESIGN/MATERIALS AND METHODS

The cheek pouches of 36 hamsters were treated with 0.5% 9,10 dimethyl-1,2-benzanthracene in acetone three times a week. After 12 weeks all animals showed tumors of their cheek pouches and were divided into four groups. In groups number I, II, and III, all visible tumors were removed by aid of a CO2 laser. Animals of group I did not receive any further treatment. After tumor resection, the cheek pouches in group II were treated with hyperthermia by aid of a Nd:YAG laser and a temperature of 43 degrees C for 30 minutes. In group III after resection of the tumors, the cheek pouches were treated with PDT (75mW/cm2 175J/cm2--3mg/kg Photofrin i.p./24h). In group IV, the tumors were not excised, instead they were only treated with PDT (as above). All animals were observed for 50 days for any signs of tumor recurrence.

RESULTS

In group I (CO2) all tumors (100%) recurred within 50 days. In group II (CO2 + hyperthermia) 61%, in group III (CO2 + PDT) 27.7%, and in group IV (PDT) 50% of all tumors recurred. The first signs of recurrence could be seen in group I, followed by groups II and IV. Group III was the last one presenting tumor recurrence.

CONCLUSIONS

The combination of CO2 surgery and PDT produced significantly better results than CO2 surgery or PDT alone, and better than the combination of CO2 surgery and hyperthermia.

In vitro and in vivo effects of photodynamic therapy on murine malignant melanoma

BACKGROUND

The role of photodynamic therapy (PDT) in the treatment of malignant melanoma is not well defined, nor is it known whether the dark melanoma cells absorb the light used in PDT.

METHODS

IN VITRO STUDIES

2 x 10(5) B16 murine melanoma cells were incubated with aluminum phthalocyanine (AlpcS4, 2.5 mg/kg) and were then subjected to photoradiation (50, 100 or 200 J/cm2). Viability was then assessed. In vivo studies:

HISTOLOGY

C57/B1 mice received 2 x 10(5) B16 cells subcutaneously and were randomized into study (PDT) and three control groups. AlpcS4 2.5 mg/kg was injected intraperitoneally and the mice were exposed to light (100 J/cm2). After 24 hours they were sacrificed and underwent autopsies. Survival: 40 mice were randomized into PDT (40 J/cm2) and control groups and were monitored for 50 days. Tumor growth: 40 mice were randomized into one control and three treatment groups (PDT on day 3, 6, or 12 after injection with B16 cells), and were monitored for 50 days. Temperature: Tumor temperatures before and at the end of PDT were recorded.

RESULTS

IN VITRO STUDIES

PDT caused a decrease in cell viability to 15.5 +/- 0.7%, 11.5 +/- 2.1%, and 1.5 +/- 0.7% (at 50, 100, and 200 J/cm2, respectively; P < .001). A significant reduction in thymidine incorporation was noted at all energy levels. In vivo studies:

HISTOLOGY

PDT caused massive tumor necrosis. Survival: PDT prolonged the survival of mice (41 +/- 13.4 days) compared to controls (15.8 +/- 3.8 days, P < .001). Tumor growth: 31 days after injection with B16 cells, the tumor size was 2.6 +/- 0.3 cm in the control group and 1.6 +/- 0.2, 0.9 +/- 0.3, and 1.0 +/- 0.4 cm in the PDT groups (days 3, 6 and 12, respectively; P < .01). Temperature: PDT increased skin temperature to 42.8 degrees C +/- 1.3 degrees C, 45.3 degrees C +/- 3.5 degrees C, and 51.7 degrees C +/- 2.7 degrees C at 40, 60, and 100 J/cm2, respectively (P < .01).

CONCLUSIONS

Photodynamic therapy was found to have significant effects in experimental melanoma in mice. The role of PDT in human melanoma remains to be studied.

Photophysical and photobiological processes in the photodynamic therapy of tumours

Photodynamic therapy (PDT) is an innovative and attractive modality for the treatment of small and superficial tumours. PDT, as a multimodality treatment procedure, requires both a selective photosensitizer and a powerful light source which matches the absorption spectrum of the photosensitizer. Quadra Logic's Photofrin, a purified haematoporphyrin derivative, is so far the only sensitizer approved for phase III and IV clinical trials. The major drawbacks of this product are the lack of chemical homogeneity and stability, skin phototoxicity, unfavourable physicochemical properties and low selectivity with regard to uptake and retention by tumour vs. normal cells. Second-generation photosensitizers, including the phthalocyanines, show an increased photodynamic efficiency in the treatment of animal tumours and reduced phototoxic side effects. At the time of writing of this article, there were more than half a dozen new sensitizers in or about to start clinical trials. Most available data suggest a common mechanism of action. Following excitation of photosensitizers to long-lived excited singlet and/ or triplet states, the tumour is destroyed either by reactive singlet oxygen species (type II mechanism) and/or radical products (type I mechanism) generated in an energy transfer reaction. The major biological targets of the radicals produced and of singlet oxygen are well known today. Nucleic acids, enzymes and cellular membranes are rapidly attacked and cause the release of a wide variety of pathophysiologically highly reactive products, such as prostaglandins, thromboxanes and leukotrienes. Activation of the complement system and infiltration of immunologically active blood cells into the tumorous region enhance the damaging effect of these aggressive intermediates and ultimately initiate tumour necrosis. The purpose of this review article is to summarize the up-to-date knowledge on the mechanisms responsible for the induction of tumour necrotic reactions.