Prevention of cutaneous phototoxicity in photodynamic therapy

Enhanced singlet oxygen production by photodynamic therapy and a novel method for its intracellular measurement

The generation of singlet oxygen (SO) in the presence of specific photosensitizers (PSs) or semiconductor quantum dots (QDs) and its application in photodynamic therapy (PDT) is of great interest to develop cancer therapies with no need of surgery, chemotherapy, and/or radiotherapy. This work was focused on the identification of the main factors leading to the enhancement of SO production using Rose Bengal (RB), and Methylene Blue (MB) as PS species in organic and aqueous mediums. Subsequently, the capacity of zinc oxide (ZnO), zinc sulfide (ZnS), and ZnO/ZnS core-shell QDs as well as manganese (Mn(+2)) doped ZnO and ZnS nanoparticles (NPs) as potential PS was also investigated. Many variable parameters such as type of quencher, PSs, NPs, as well as its different concentrations, light source, excitation wavelength, reaction time, distance from light source, and nature of solvent were used. The degradation kinetics of the quenchers generated by SO species and the corresponding quantum yields were determined by monitoring the photo-oxidation of the chemical quencher and measuring its disappearance by fluorometry and spectrophotometry in the presence of NPs. Small intracellular changes of SO induced by these metal Zn (zinc) NPs and PDT could execute and accelerate deadly programs in these leukemic cells, providing in this way an innovative modality of treatment. In order to perform further more specific in vitro cytotoxic studies on B-chronic lymphocytic leukemia cells exposed to Zn NPs and PDT, we needed first to measure and ascertain those possible intracellular SO variations generated by this type of treatment; for this purpose, we have also developed and tested a novel method first described by us.

Chlorin e6 derivative radachlorin mainly accumulates in mitochondria, lysosome and endoplasmic reticulum and shows high affinity toward tumors in nude mice in photodynamic therapy

The efficacy of photodynamic therapy (PDT) depends upon the amount of photosensitizer accumulated in the malignant tissues. Radachlorin is a popular photosensitizer used in photodynamic therapy to treat various types of cancer. In this study, we have studied the main organelles responsible for the accumulation of radachlorin in human anaplastic thyroid cancer in vitro and in vivo. The optimal time window for uptake and clearance of radachlorin also was studied. Confocal microscopic images confirmed that the radachlorin is mainly acquired by mitochondria and partially by lysosome and endoplasmic reticulum. Studies also showed that the maximum amount of radachlorin was accumulated within 3-6 h after the treatment. Radachlorin also showed a higher affinity toward malignant tumors compared to the other organs in mice xenograft model. Uptake of radachlorin reached an optimum amount within 6 h and most of the radachlorins were also cleared from the body in next 48 h. Therefore, detailed information regarding exact accumulation sites and a time window in which maximum amount of drug is accumulated and cleared were obtained by this study. Hence, not only the efficacy of the treatment can be increased but the phototoxicity after the treatment also can be controlled.

Skin protection for photosensitized patients

BACKGROUND AND OBJECTIVE

The goal of this study was to evaluate various creams for their capability to protect photosensitized skin from visible light.

STUDY DESIGN/MATERIALS AND METHODS

Two cover creams and creams containing various combinations of Vaseline with TiO(2), ZnO, and Fe(2)O(3) were used to measure the reduced light transmission and the light absorption spectrum. In vitro and in vivo tests were performed to assess the protection from light by above mentioned compounds.

RESULTS

The cover creams and the 50% TiO(2) cream showed similar efficacy in reducing light transmission, while the sunscreen was less efficient by a factor of 5. Cell protection by 25% TiO(2)+25% ZnO, TiO(2), or the cover creams was more efficient than protection by the sunscreen or other compounds. In vivo, the dark cover cream protected the skin by a factor of 3.4 better than the sunscreen.

CONCLUSION

The dark cover cream has acceptable properties to protect photosensitized skin.

Effect of N-acetylcysteïne on Photofrin-induced skin photosensitivity in patients

BACKGROUND AND OBJECTIVE

One of the major side effects of photodynamic therapy (PDT) employing Photofrin as the sensitizer is enhanced photosensitivity of the skin. The basic mechanism in PDT damage is believed to be the formation of singlet oxygen and radical species. N-acetylcysteïne (NAC) increases glutathione levels and is known to prevent pathology elicited by radicals and reactive species.

STUDY DESIGN/MATERIALS AND METHODS

NAC was tested in a randomized, open label study for its protective effect on skin photosensitivity. Twenty-seven patients treated with PDT for central obstructive lung cancer or esophageal cancer received either "early" or "delayed" NAC, starting 5 or 10 days after Photofrin, in a dose of 3 x 600 mg per day for 5 days. Light, obtained from a halogen lamp (fluence rate 200 mW.cm-2) was used to illuminate skin patches of 2.5 cm2 on the back (10, 25, and 50 J.cm-2). Skin response was measured by using a visual scoring system and by measuring the redness using a reflectance meter.

RESULTS

Skin responses varied from no changes at 10 J.cm-2 to redness with edema at energies of 50 J.cm-2. In the absence of edema, measurements with the reflectance meter appeared to be more sensitive than visual scoring.

CONCLUSION

In a limited number of patients, there was a trend for decreased sensitivity after NAC, but statistical analysis failed to show any significant protective effect of this short course of NAC.

Partial protection of photodynamic-induced skin reactions in mice by N-acetylcysteine: a preclinical study

The major side effect of photodynamic therapy (PDT) using Photofrin is enhanced skin sensitivity for sunlight, which persists for 3-8 weeks after injection. Formation of singlet oxygen and radicals is believed to be involved in the basic mechanism of inducing skin damage. Reducing this side effect would make PDT more widely acceptable, particularly for palliative use. Hairless dorsal skin patches of mice, injected with 10 mg kg-1 photofrin intraperitoneally (i.p.) 24 h before illumination, were used to evaluate the effect of increasing light doses. The light was obtained from a halogen lamp and transmitted via a fiber optic to illuminate a field of 2.5 cm2. After establishing a dose-response relationship for single or fractionated light dose illumination of the skin, drugs known to scavenge radicals, quench singlet oxygen or interfere with histamine release were tested for their protective effect. N-acetyl-cysteine (NAC), a radical scavenger, administered i.p. (1000 and 2000 mg kg-1) 1 h before illumination produced a significant decrease in skin damage at light doses > 50 J cm-2 (protection factor of 1.3-1.8). When NAC was administered in a dose of 500 mg kg-1, no protection was observed. Fractionated illumination experiments in combination with multiple injections of NAC (1000 mg kg-1) also failed to show any protection. The addition of Ranitidine, a histamine blocking agent (25-100 mg kg-1), given prior to illumination, resulted in a limited protection at higher light doses. From this study we conclude that NAC could be of value in amelioration of the photosensitivity in patients treated with PDT.

Spectroscopic properties of potential sensitizers for new photodynamic therapy start mechanisms via two-step excited electronic states

Three substituted tetraazaporphyrins, octa-(4-tert-butylphenyl)-tetrapyrazinoporphyrazine, tetra-(4-tert-butyl)phthalocyanine and tetra-(4-tert-butyl)phthalocyanatomagnesium(t4-PcMg), were spectroscopically checked in solutions and liposomes with respect to suitability as potential sensitizers of a possible new start mechanism for photodynamic therapy (PDT) from a stepwise excited higher singlet state. This PDT start mechanism was recently proposed to overcome the problem of O2 (1delta2)-caused cutaneous phototoxicity in PDT. By means of absorption and fluorescence measurements as well as nonlinear absorption investigation, transient spectroscopy and lasing experiments, compound t4-PcMg was found to have the most appropriate properties: Based on a high fluorescence quantum yield (phiF1 = 0.84) and a very low crossing to the triplet (phiISC = 0.05), two higher excited states can be effectively populated both by two stepwise absorption transitions at 674nm consecutive absorption transitions at 684 and and 710 nm. Moreover, t4-PcMg incorporates into liposomes very well with spectroscopic properties similar to those in solution.

Cutaneous photoprotection using a hydroxyl radical scavenger in photodynamic therapy

Photodynamic therapy (PDT) is emerging as an effective therapy for a variety of malignant diseases, including head and neck cancer. Prolonged cutaneous photosensitivity following therapy, however, remains the most significant side effect. The biochemical mechanism of this sensitivity, and indeed of the tumoricidal effect of PDT, is uncertain, but is believed to involve formation of singlet oxygen and possibly other oxygen-derived free radicals. This laboratory recently reported that a singlet oxygen scavenger, diphenylisobenzofuran (DPIBF), afforded cutaneous photoprotection to 67% of animals treated with PDT. Those results, the first from an in vivo study, supported the idea that singlet oxygen plays a significant role in PDT and its associated toxicity. They also, however, suggested that it is not the sole intermediate. The current study looks at the photoprotective effects of the hydroxyl radical scavenger dimethyl thiourea, alone and in conjunction with DPIBF. Our results strongly support a role for the hydroxyl radical in producing the cutaneous phototoxicity associated with PDT.

Dihematoporphyrin ether-induced photosensitivity in laryngeal papilloma patients

Twenty-six patients with recurrent laryngeal papillomatosis received 2.5 mg/kg of Dihematoporphyrin Ether (DHE) intravenously prior to photodynamic therapy. All patients experienced some degree of photosensitivity, the only known side effect of DHE. Reported reactions included mild erythema and inflammation (88%), swelling (58%), blistering (23%), ocular discomfort (61.5%), pruritus (38%), and skin hyperpigmentation (46%). Length of sensitivity ranged from 4-17 weeks, with an average duration of 9 weeks. No long-term debilitating sequelae were noted. Degree of skin reaction mainly depended on how compliant the patient was in following precaution instructions. Although restrictive precautions were often difficult to strictly adhere to, most patients felt the potential benefits of the therapy far outweighed any inconvenience.