The use of porphyrins and non-ionizing radiation for treatment of cancer

Clinical development of photodynamic agents and therapeutic applications

Background

Photodynamic therapy (PDT) is photo-treatment of malignant or benign diseases using photosensitizing agents, light, and oxygen which generates cytotoxic reactive oxygens and induces tumour regressions. Several photodynamic treatments have been extensively studied and the photosensitizers (PS) are key to their biological efficacy, while laser and oxygen allow to appropriate and flexible delivery for treatment of diseases.

Introduction

In presence of oxygen and the specific light triggering, PS is activated from its ground state into an excited singlet state, generates reactive oxygen species (ROS) and induces apoptosis of cancer tissues. Those PS can be divided by its specific efficiency of ROS generation, absorption wavelength and chemical structure.

Main body

Up to dates, several PS were approved for clinical applications or under clinical trials. Photofrin® is the first clinically approved photosensitizer for the treatment of cancer. The second generation of PS, Porfimer sodium (Photofrin®), Temoporfin (Foscan®), Motexafin lutetium, Palladium bacteriopheophorbide, Purlytin®, Verteporfin (Visudyne®), Talaporfin (Laserphyrin®) are clinically approved or under-clinical trials. Now, third generation of PS, which can dramatically improve cancer-targeting efficiency by chemical modification, nano-delivery system or antibody conjugation, are extensively studied for clinical development.

Conclusion

Here, we discuss up-to-date information on FDA-approved photodynamic agents, the clinical benefits of these agents. However, PDT is still dearth for the treatment of diseases in specifically deep tissue cancer. Next generation PS will be addressed in the future for PDT. We also provide clinical unmet need for the design of new photosensitizers.

Dye Sensitizers for Photodynamic Therapy

Photofrin^® was first approved in the 1990s as a sensitizer for use in treating cancer via photodynamic therapy (PDT). Since then a wide variety of dye sensitizers have been developed and a few have been approved for PDT treatment of skin and organ cancers and skin diseases such as acne vulgaris. Porphyrinoid derivatives and precursors have been the most successful in producing requisite singlet oxygen, with Photofrin^® still remaining the most efficient sensitizer (quantum yield = 0.89) and having broad food and drug administration (FDA) approval for treatment of multiple cancer types. Other porphyrinoid compounds that have received approval from US FDA and regulatory authorities in other countries include benzoporphyrin derivative monoacid ring A (BPD-MA), meta-tetra(hydroxyphenyl)chlorin (m-THPC), N-aspartyl chlorin e6 (NPe6), and precursors to endogenous protoporphyrin IX (PpIX): 1,5-aminolevulinic acid (ALA), methyl aminolevulinate (MAL), hexaminolevulinate (HAL). Although no non-porphyrin sensitizer has been approved for PDT applications, a small number of anthraquinone, phenothiazine, xanthene, cyanine, and curcuminoid sensitizers are under consideration and some are being evaluated in clinical trials. This review focuses on the nature of PDT, dye sensitizers that have been approved for use in PDT, and compounds that have entered or completed clinical trials as PDT sensitizers.

Uroporphyrinogen decarboxylase is a radiosensitizing target for head and neck cancer

Head and neck cancer (HNC) is the eighth most common malignancy worldwide, comprising a diverse group of cancers affecting the head and neck region. Despite advances in therapeutic options over the last few decades, treatment toxicities and overall clinical outcomes have remained disappointing, thereby underscoring a need to develop novel therapeutic approaches in HNC treatment. Uroporphyrinogen decarboxylase (UROD), a key regulator of heme biosynthesis, was identified from an RNA interference-based high-throughput screen as a tumor-selective radiosensitizing target for HNC. UROD knockdown plus radiation induced caspase-mediated apoptosis and cell cycle arrest in HNC cells in vitro and suppressed the in vivo tumor-forming capacity of HNC cells, as well as delayed the growth of established tumor xenografts in mice. This radiosensitization appeared to be mediated by alterations in iron homeostasis and increased production of reactive oxygen species, resulting in enhanced tumor oxidative stress. Moreover, UROD was significantly overexpressed in HNC patient biopsies. Lower preradiation UROD mRNA expression correlated with improved disease-free survival, suggesting that UROD could potentially be used to predict radiation response. UROD down-regulation also radiosensitized several different models of human cancer, as well as sensitized tumors to chemotherapeutic agents, including 5-fluorouracil, cisplatin, and paclitaxel. Thus, our study has revealed UROD as a potent tumor-selective sensitizer for both radiation and chemotherapy, with potential relevance to many human malignancies.

Identification of HL60 Proteins Affected by 5-Aminolevulinic Acid-Based Photodynamic Therapy Using Mass Spectrometric Approach

A combination of mass spectrometric techniques was used for identification of HL60 leukemia cell proteins affected by 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT). We compared two-dimensional electrophoresis (2-DE) protein maps of ALA-treated non-irradiated and irradiated cells and found extensive changes in the proteome of HL60 cells. The silver-stained 2-DE pattern of HL60 proteins contained more than 1 350 spots. Matrix-assisted laser desorption/ionisation mass spectrometry and microcapillary liquid chromatography/tandem mass spectrometry have identified twelve proteins differing in their intensity or position following ALA-PDT. Several endoplasmic reticulum, mitochondrial, ribosomal and cytoplasmic proteins were determined showing the impact of ALA-PDT-mediated cytotoxicity on some cellular pathways.

Protein changes in HL60 leukemia cells associated with 5-aminolevulinic acid-based photodynamic therapy. Early effects on endoplasmic reticulum chaperones

Using two-dimensional electrophoresis we investigated the effect of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT; induction with 1 mM ALA for 4 h followed by blue light dose of 18 J/cm2) on the protein expression in HL60 leukemia cells. ALA-PDT resulted in extensive qualitative and quantitative changes in the protein pattern of HL60 cell lysates. Of more than 1350 protein spots recognized on the protein maps of ALA-induced cells, seven proteins were enhanced and 17 suppressed following irradiation. Three of these, calreticulin precursor, p58 microsomal protein (ERp57) and protein disulfide isomerase (p55) have been identified by matrix-assisted laser desorption and ionization-mass spectrometry and the pI/molecular weight parameters of the affected proteins were estimated by computer analysis. The findings suggest participation of endoplasmic reticulum Ca(2+)-binding chaperones and/or Ca2+ signaling in ALA-PDT mediated cytotoxicity.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Selective destruction of leukaemic cells by photo-activation of 5-aminolaevulinic acid-induced protoporphyrin-IX

The effect of 5-aminolaevulinic acid-based photodynamic therapy (ALA-PDT) on the viability and proliferation of leukaemia/lymphoma cells as well as normal human lymphocytes has been investigated by flow cytometry-propidium iodide assay (FC-PI), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and bromodeoxyuridine (BrdU) incorporation and on clonogenic activity of normal human bone marrow progenitor cells by clonogenic methods. ALA-PDT (1 mM 5-ALA, 4 h, 18 J cm-2) reduces the number and/or suppressed proliferation of leukaemic cells of promyelocytic (HL60), B-cell-derived (DAUDI) and T-cell-derived (JURKAT) cell lines by 2 logs and that of the HEL erythroleukaemia cells by 77%. The effect of ALA-PDT on quiescent human lymphocytes is small (85% viable cells after ALA-PDT). The proliferation of lymphocytes subjected to ALA-PDT and induced with phytohaemagglutinin (PHA) decreases by 75% as compared to the untreated control. For normal human bone marrow progenitors, 58% of colony-forming units-granulocytes-macrophages (CFU-GM) and 55% burst-forming units-erythrocytes (BFU-E) activities are preserved.

An optical phantom with tissue-like properties in the visible for use in PDT and fluorescence spectroscopy

The design and characterization of optical phantoms which have the same absorption and scattering characteristics as biological tissues in a broad spectral window (between 400 and 650 nm) are presented. These low-cost phantoms use agarose dissolved in water as the transparent matrix. The latter is loaded with various amounts of silicon dioxide, Intralipid, ink, blood, azide, penicillin, bovine serum, and fluorochromes. The silicon dioxide and Intralipid particles are responsible for the light scattering whereas the ink and blood are the absorbers. The penicillin and the azide are used to ensure the conservation of such phantoms when stored at 4 degrees C. The serum and fluorochromes, such as Coumarin 30, produce an autofluorescence similar to human tissues. Various fluorochromes or photosensitizers can be added to these phantoms to simulate a cancer photodetection procedure. The absorption and fluorescence spectroscopy of the porphyrin-type fluorescent markers used clinically for such photodetection procedures is similar in these phantoms and in live tissues. The mechanical properties of these gelatinous phantoms are also of interest as they can easily be moulded and reshaped with a conventional cutter, so that complex structures and shapes, with different optical properties, can be designed. The optical properties of these phantoms were determined between 400 and 650 nm by measuring their effective attenuation coefficient (mu eff) and total reflectance (Rd). The microscopic absorption and reduced scattering coefficients (mu a, mu s') were deduced from mu eff and Rd using a Monte Carlo simulation.