In vitro photosensitization of tumour cell enzymes by photofrin II administered in vivo

Formation and Reactivity of New Isoporphyrins: Implications for Understanding the Tyr-His Cross-Link Cofactor Biogenesis in Cytochrome c Oxidase

Cytochrome c oxidase (CcO) catalyzes the reduction of dioxygen to water utilizing a heterobinuclear active site composed of a heme moiety and a mononuclear copper center coordinated to three histidine residues, one of which is covalently cross-linked to a tyrosine residue via a post-translational modification (PTM). Although this tyrosine-histidine moiety has functional and structural importance, the pathway behind this net oxidative C-N bond coupling is still unknown. A novel route employing an iron(III) meso-substituted isoporphyrin derivative, isoelectronic with Cmpd-I ((Por^•+)Fe^IV═O), is for the first time proposed to be a key intermediate in the Tyr-His cofactor biogenesis. Newly synthesized iron(III) meso-substituted isoporphyrins were prepared with azide, cyanide, and substituted imidazole functionalities, by adding nucleophiles to an iron(III) π-dication species formed via addition of trifluoroacetic acid to F₈Cmpd-I (F₈ = (tetrakis(2,6-difluorophenyl)porphyrinate)). Isoporphyrin derivatives were characterized at cryogenic temperatures via ESI-MS and UV-vis, ²H NMR, and EPR spectroscopies. Addition of 1,3,5-trimethoxybenzene or 4-methoxyphenol to the imidazole-substituted isoporphyrin led to formation of the organic product containing the imidazole coupled to aromatic substrate via a new C-N bond, as detected via cryo-ESI-MS. Experimental evidence for the formation of an imidazole-substituted isoporphyrin and its promising reactivity to form the imidazole-phenol coupled product yields viability to the herein proposed pathway behind the PTM (i.e., biogenesis) leading to the key covalent Tyr-His cross-link in CcO.

Metalloisoporphyrins: from synthesis to applications

An overview of the chemistry of isoporphyrin, the tautomer of porphyrin, whose existence was predicated by the Noble laureate Woodward, is presented with emphasis on hydroxy-isoporphyrins of tetra-aryl derivatives.

Tumor delivery of Photofrin® by PLL-g-PEG for photodynamic therapy

Photofrin® (porfimer sodium) is a photosensitive reagent used for photodynamic therapy (PDT) of tumors and dysplasias. Because only photo-irradiated sites are damaged, PDT is less invasive than systemic treatments. However, a photosensitive reaction is a major side effect of systemically delivered Photofrin. To enhance localization of Photofrin to tumors, we have formulated Photofrin with the tumor-localizing graft copolymer poly(ethylene glycol)-grafted poly(l-lysine), PLL-g-PEG. We demonstrate that Photofrin preferentially interacts with PLL-g-PEG through both ionic and hydrophobic interactions. The serum competitive study showed that the highly PEG-grafted PLL is better for preventing serum binding to the Photofrin/PLL-g-PEG complex. In tumor-bearing mice, formulation of Photofrin with PLL-g-PEG enhanced tumor localization of Photofrin as twice as Photofrin alone and concomitantly suppressed the photosensitivity reaction drastically.

Mitochondria are targets of photodynamic therapy

Photodynamic Therapy (PDT) is an evolving cancer treatment that depends on three known and variable components: photosensitizer, light and oxygen. Optimization of these variables yields reactive oxygen species, mainly singlet oxygen, that damage cellular components leading to cytotoxicity. Our research has demonstrated that porphyrin sensitizers, in particular, significantly inhibit the inner mitochondrial membrane enzymes cytochrome c oxidase and F(0)F(1) ATP synthase. These results were obtained from an in vivo-in vitro experimental protocol that exposes sensitizers to metabolic and pharmacokinetic events. The resulting inhibition of oxidative phosphorylation was expected to reduce ATP levels, which were quantitated in cells and were confirmed by (31)P-NMR spectroscopy of tumors in situ in animals treated with PDT. Based on these findings, and more recent investigations of apoptosis, there is little doubt that mitochondria are critical targets in the actions of PDT.

Mitochondria-based photodynamic anti-cancer therapy

As photodynamic therapy (PDT) becomes established as a treatment for cancer, there is increasing interest in identifying critical mechanisms of cell killing and understanding the bases for effective photosensitizers. The existence of multiple cellular targets makes it difficult to distinguish the critical events leading to cell death from PDT. However, with more sensitive techniques to detect photosensitizer localization, the isolation of PDT-resistant and -sensitive mutants and the use of innovative molecular and biochemical strategies to map cellular events occurring during and after photosensitization, some order is emerging from the chaos. The subcellular localization of many photosensitizers and the early responses to light activation indicate that mitochondria play a major role in photodynamic cell death. PDT with many agents which damage or inhibit different or multiple mitochondrial targets has many of the desirable characteristics for an effective anti-cancer therapy.

Photosensitization of the sunscreen octyl p-dimethylaminobenzoate by UVA in human melanocytes but not in keratinocytes

Sunscreens penetrate human epidermis and modify the biology of proliferating cells. This study addressed the question whether the UV response of cultured human cells is affected by direct treatment with nontoxic levels of sunscreens. Cell survival following exposure to UVC or unfiltered UBV was not altered by preincubation with 25 micrograms/mL of octyl p-dimethylaminobenzoate (o-PABA), 2-ethylhexyl p-methoxycinnamate (EHMC) or oxybenzone. However, UVA or UVB filtered to reproduce the solar UV spectrum penetrating to the basal layer of the epidermis, highly sensitized cells to killing by o-PABA but not by its hydrolysis product, 4-dimethylaminobenzoic acid. Sensitization was found in all cell types tested, except normal keratinocytes, and could be prevented by certain antioxidants particularly pyruvate and the hydroxyl radical scavenger mannitol. o-PABA and EHMC applied without UV reduced the adherence of cells. The results indicate that sunscreens may increase cell mobility and the combination of o-PABA with solar UV may selectively damage melanocytes in the skin.

Photodynamically induced effects in colon carcinoma cells (WiDr) by endogenous photosensitizers generated by incubation with 5-aminolaevulinic acid

Human adenocarcinoma cells of the line WiDr have been treated with 2 mM 5-aminolaevulinic acid (5-ALA) in the presence of 10% foetal calf serum. The treatment induces a linear accumulation of protoporphyrin IX (PpIX) for at least 7.5 h. After 7.5 h of incubation about 45% of the PpIX accumulated is cell-bound, while the rest is found in the medium (25%) or lost from the cells during washing with phosphate-buffered saline (30%). Exposure to white light at an intensity of 30 W/m2 for 18 min results in 95% reduction of clonogenicity in cells treated with 2 mM 5-ALA for 3.5 h. The enzymatic activities of enzymes located in cytosol (glyceraldehyde 3-phosphate dehydrogenase and lactate dehydrogenase) and lysosomes (acid phosphatase and beta-glucuronidase) are not influenced by a 5-ALA and light treatment inactivating about 35% of the cells. The MTT assay, which reflects mitochondrial dehydrogenase activity, but not succinate dehydrogenase, is partly inhibited by the same treatment. Treatment with 5-ALA in the absence of light increases O2 consumption by a factor of two, while the O2 consumption is inhibited when 5-ALA treatment is combined with exposure to light. In addition, 5-ALA and light exposure enhance accumulation of rhodamine 123 by 40% and reduce the intracellular ATP level by 25%. Confocal laser scanning microscopical analysis indicates granular perinuclear localization of the PpIX formed by 5-ALA treatment. In conclusion, photodynamic treatment using 5-ALA as a prodrug induces damage to mitochondrial function without inhibiting lysosomal and cytosolic marker enzymes.

Ultrastructural changes in PAM cells after photodynamic treatment with delta-aminolevulinic acid-induced porphyrins or photosan

Photodynamic therapy (PDT) is the combination of a photosensitizing drug (Ps) with light in the presence of oxygen leading to the generation of reactive molecular species and destruction of cancer cells. In this study we compared PDT with two Ps, the hematoporphyrin derivative Photosan (Ph) and delta-aminolevulinic acid (ALA)-induced endogenous protoporphyrin IX, with respect to mitochondrial function and ultrastructural alterations. The effects of PDT were investigated in PAM 212 cells after different Ps incubation times, light doses, and post-treatment periods. Both Ps induced a light dose-dependent impairment of the mitochondrial function with the dose-response curve being steep for ALA and flat for Ph. The prolongation of the incubation time from 4 to 20 h resulted in an increased reduction of mitochondrial activity after ALA PDT but not after Ph PDT. Treatment with an irradiation dose that decreased mitochondrial activity by 50% (IC50) led to early and profound changes of mitochondrial morphology in ALA photosensitized cells, whereas photosensitization with Ph resulted in more pronounced alterations of lysosomes. We conclude that at bioequivalent sublethal PDT exposures of PAM 212 cells, ALA-induced damage is primarily restricted to mitochondria, whereas Ph-induced cytotoxicity is mediated by damage of the lysosomal system.

Enhancement of the efficiency of photodynamic therapy of tumours by t-butyl-4-hydroxyanisole

The effects of photodynamic therapy (PDT) alone and in combination with 3(2)-t-butyl-4-hydroxyanisole (BHA) on Ehrlich ascites carcinoma (EAC) cells have been investigated. BHA, a widely used food antioxidant, administered to the cells prior to light exposure is found to cause concentration-dependent alterations of the haematoporphyrin derivative (HpD)-based PDT. BHA (0.15 mM) causes a small (about 10%) inhibition in the rate of HpD-photosensitized injury of EAC cells. In contrast, upon increasing the concentration of BHA from 0.15 to 0.5 mM, a 1.3-fold enhancement in HpD-PDT efficiency is achieved. The cytotoxic effect on the cells treated with HpD-PDT and a higher concentration of BHA (0.5 mM) is additive. When BHA (0.5 mM) is given immediately after HpD-PDT, the combination is found to be three to four times more effective than when BHA is added to EAC cells before phototherapy. In this treatment regimen BHA acts synergistically with HpD-PDT. Such a difference in the action of BHA on the efficiency of HpD-PDT might be explained by the ability of BHA to inhibit the HpD-photosensitized destruction of some biomolecules. An enhancing action of BHA on the intensity of HpD-photosensitized death of tumour cells is also observed in vivo. Even a single dose of BHA (0.6 mM kg-1, 15 min after irradiation) causes (in an additive manner) an approximately two-fold increase in the efficiency of HpD-PDT of mice bearing Ehrlich ascites tumour (intraperitoneal transplantation). The results obtained indicate that the potentiating effect of BHA on the HpD-PDT could be caused by the impairment of the mitochondrial respiration, since there is a good correspondence between the concentration of BHA that increases the efficiency of PDT and the concentration that inhibits the oxygen consumption and dehydrogenase activity of EAC cells. The influence of BHA on the efficiency of PDT does not depend on the nature of the photosensitizer used; the effects with chlorin-e6 trimethyl ester are similar to that seen for HpD.

Photodynamic therapy in the management of metastatic cutaneous adenocarcinomas: case reports from phase 1/2 studies using tin ethyl etiopurpurin (SnET2)

BACKGROUND AND OBJECTIVES

Photodynamic therapy (PDT) using a photoreactive purpurin, tin ethyl etiopurpurin (SnET2, Purlytin, Miravant Medical Technologies, Santa Barbara, CA), was investigated as a treatment for cutaneous metastatic disease that had failed other treatment options.

STUDY DESIGN/MATERIALS AND METHODS

Three patients with biopsy-proven metastatic adenocarcinoma of the skin were treated with a single dose of the study drug. Twenty-four hours later, the patients were exposed to a laser light at 664 nm in multiple light fields. Patients were followed for 6 months for safety, efficacy, recurrence, and palliative response.

RESULTS

After PDT with SnET2, complete response was observed in all 13 treated lesions in three patients, with no evidence of recurrence at any treated site at the 6-month follow-up. Two patients subsequently died of distant metastatic disease. One patient with local chest wall recurrence after mastectomy was disease-free 24 months after PDT.

CONCLUSIONS

PDT with SnET2 could be an effective treatment in locally advanced metastatic carcinoma of the skin.

Subcellular localization of Photofrin and aminolevulinic acid and photodynamic cross-resistance in vitro in radiation-induced fibrosarcoma cells sensitive or resistant to photofrin-mediated photodynamic therapy

The subcellular and, specifically, mitochondrial localization of the photodynamic sensitizers Photofrin and aminolevulinic acid (ALA)-induced protoporphyrin-IX (PpIX) has been investigated in vitro in radiation-induced fibrosarcoma (RIF) tumor cells. Comparisons were made of parental RIF-1 cells and cells (RIF-8A) in which resistance to Photofrin-mediated photodynamic therapy (PDT) had been induced. The effect on the uptake kinetics of Photofrin of coincubation with one of the mitochondria-specific probes 10N-Nonyl acridine orange (NAO) or rhodamine-123 (Rh-123) and vice versa was examined. The subcellular colocalization of Photofrin and PpIX with Rh-123 was determined by double-label confocal fluorescence microscopy. Clonogenic cell survival after ALA-mediated PDT was determined in RIF-1 and RIF-8A cells to investigate cross-resistance with Photofrin-mediated PDT. At long (18 h) Photofrin incubation times, stronger colocalization of Photofrin and Rh-123 was seen in RIF-1 than in RIF-8A cells. Differences between RIF-1 and RIF-8A in the competitive mitochondrial binding of NAO or Rh-123 with Photofrin suggest that the inner mitochondrial membrane is a significant Photofrin binding site. The differences in this binding may account for the PDT resistance in RIF-8A cells. With ALA, the peak accumulations of PpIX occurred at 5 h for both cells, and followed a diffuse cytoplasmic distribution compared to mitochondrial localization at 1 h ALA incubation. There was rapid efflux of PpIX from both RIF-1 and RIF-8A. As with Photofrin, ALA-induced PpIX exhibited weaker mitochondrial localization in RIF-8A than in RIF-1 cells. Clonogenic survival demonstrated cross-resistance to incubation in PpIX but not to ALA-induced PpIX, implying differences in mitochondrial localization and/or binding, depending on the source of the PpIX within the cells.

Vascular effects of photodynamic therapy

Vascular damage and blood flow stasis are consequences of photodynamic therapy (PDT) of solid tumors using many photosensitizers. Microvascular stasis and resulting hypoxia are effective means to produce cytotoxicity and tumor regression. The observation of blood flow stasis after photodynamic therapy results from a combination of damage to sensitive sites within the microvasculature and the resulting physiological responses to this damage. A generalized hypothesis for the mechanisms leading to vessel stasis begins with perturbation and damage to endothelial cells during light treatment of photosensitized tissues. Endothelial cell damage leads to the establishment of thrombogenic sites within the vessel lumen and this initiates a physiological cascade of responses including platelet aggregation, the release of vasoactive molecules, leukocyte adhesion, increases in vascular permeability, and vessel constriction. These effects from damage combine to produce blood flow stasis.

Effects of the inhibitors of energy metabolism, lonidamine and levamisole, on 5-aminolevulinic-acid-induced photochemotherapy

The ability of endogenously synthesized protoporphyrin IX (PpIX) to damage Chinese hamster lung fibroblasts of the line V79 by exposure to light was examined. This treatment induced reduction of cellular ATP, GTP, of the NADH/NAD+ ratio and of oxygen consumption. The present results indicate a close relationship between inhibition of respiration of irradiated cells and their ability to survive, e.g. 1 min of light exposure induced 90% inhibition of oxygen consumption and inactivation of approximately 95% of the cells, while the cellular content of ATP was reduced by only 15%. This indicates that the mitochondria are one of the primary targets of 5-aminolevulinic acid (ALA)-mediated photochemotherapy (PCT). In the present study, ALA-PCT was combined with the modulators of the glycolysis and the respiration chain, levamisole (LEV) and lonidamine (LND). A synergistic effect of combining ALA-PCT with non-toxic concentrations of LND was observed when LND was given prior to light exposure. This synergism was observed despite a substantial LND-induced inhibition of PpIX formation. At increasing doses of LND (>0.15 mM) the combination treatment becomes less efficient. This is due to the inhibition of PpIX synthesis induced by LND. A synergistic effect of ALA-PDT and LEV was found when LEV was given prior to light exposure. This was at least partly due to an LEV-stimulated effect on ALA-induced PpIX formation. However, it is not clear from the present results whether LEV may perturb energy metabolism in V79 cells since LEV alone did not reduce the energy charge or the NADH/NAD+ ratio. When LEV or LND were given after ALA-PCT, these 2 treatment modalities acted in an additive or slightly synergistic manner.

Photodynamic therapy of oral cancer. A review of basic mechanisms and clinical applications

Photodynamic therapy (PDT) is an experimental cancer treatment modality. PDT is based on the accumulation of a photosensitive dye in premalignant and malignant lesions. A certain period of time after the dye has been administered, tumor tissue may contain more of the sensitizer then the surrounding normal tissues. When tissue containing the sensitizer is exposed to light of a proper wavelength and dose, a photochemical reaction between sensitizer and light will occur. The activated photosensitizer reacts with available oxygen which subsequently damages cells and eventually may cause necrosis of the tumor. Photosensitizers can also be used for fluorescence detection. If a tumor contains more of the photosensitizer than the surrounding normal tissue, its fluorescence can potentially be utilized to detect tumors. Analogous to PDT, this can therefore be referred to as photodynamic detection (PDD). This paper reviews the basic mechanisms and clinical applications of PDT and PDD. Emphasis is placed on PDD and PDT with the photosensitizer Photofrin for detection and treatment of premalignant epithelial lesions and squamous cell carcinomas of the oral mucosa.

Inhibition of the ATPase activity of P-glycoprotein by porphyrin photosensitization of multidrug-resistant cells in vitro

The effectiveness of photodynamic therapy against P-glycoprotein ATPase activity in multidrug-resistant cells was studied. Chinese hamster ovary AUXB1 (drug-sensitive) and CR1R12 (multidrug-resistant) cell lines were compared with respect to uptake of 14C-polyhematoporphyrin and porphyrin photosensitization. Phototoxicity of Photofrin was similar in both cell lines, and no major differences in uptake or efflux of 14C-polyhematoporphyrin were observed. Porphyrin photosensitization in vitro of CR1R12 cells or isolated plasma membranes from these cells caused inhibition of P-glycoprotein ATPase activity. Application of porphyrin photosensitization at a sublethal level to CR1R12 cells resulted in a small but significant increase in adriamycin-induced cytotoxicity. The hydrophobic "picket-fence" porphyrin, meso-tetrakis-(o-propionamidophenyl)porphyrin, alpha,alpha,alpha,beta-isomer, was more inhibitory toward P-glycoprotein ATPase activity than the two less hydrophobic porphyrins tetraphenylporphine tetrasulfonate and Photofrin.

The effects of photodynamic therapy using differently substituted zinc phthalocyanines on vessel constriction, vessel leakage and tumor response

The effects of four different zinc phthalocyanines were studied during and after photodynamic therapy (PDT). Measurements of vessel constriction, vessel leakage, tumor interstitial pressure, eicosanoid release, and tumor response of chondrosarcoma were made in Sprague-Dawley rats. Animals were injected intravenously with 1 mumol/kg of mono-, di-, or tetrasulfonated zinc phthalocyanine, or 1 mumol/kg of a zinc phthalocyanine substituted with four tertiary butyl groups. Tissues were exposed to 400 J/cm2 670 nm light 24 h after photosensitizer injection. An additional group of animals was given indomethacin before treatment. The use of the monosulfonated and tertiary butyl substituted zinc phthalocyanines in PDT caused the release of specific eicosanoids, caused vessel constriction, and induced venule leakage and increases in tumor interstitial pressure. Tumor cures of 27% and 7% were observed. Photodynamic therapy using the disulfonated zinc phthalocyanine did not induce vessel constriction or the release of eicosanoids, however, tumor cure was 43%. The use of the tetrasulfonated zinc phthalocyanine caused intermediate effects between the mono- and disulfonated compounds. The administration of indomethacin to animals completely inhibited the effects of PDT using the monosulfonated compound but had minimal effects on treatment using the disulfonated compound. This suggests that the monosulfonated and disulfonated compounds act by different mechanisms of destruction.

Photodynamic therapy

Photodynamic therapy (PDT) has been developed over the past decade into a useful treatment for several types of solid cancers in man. This unique therapy requires a photosensitiser accumulated in tumours and local activation by visible light generally delivered from lasers and delivered to the patient through various types of fibers and endoscopes. PDT appears to be most effective in treating certain superficial, difficult to treat cancers such as carcinoma in situ of the urinary bladder (here complete control is the intent), but also is effectively used in bulkier tumours obstructing bronchi or the oesophagus where palliation can be achieved. The primary mechanism of action is the in situ generation of an active form of molecular oxygen (singlet oxygen) which causes the rapid, local onset of vascular stasis and eventual vascular haemorrhage and tumour wall destruction. This process appears to be mediated through various cytokines such as prostaglandin, lymphokines and thromboxanes. The ultimate clinical value of PDT will be seen over the next few years following health agency approval worldwide.

Preclinical examination of first and second generation photosensitizers used in photodynamic therapy

Numerous photosensitizers with absorption peaks spanning the 600-800 nm "therapeutic window" have been and continue to be synthesized. Structural modifications of the dyes can then be made in order to improve tumor deliverability and retention. Chemical alterations can also enhance the yields of light generated reactive oxygen species. Utilization of lipoproteins, emulsions and antibody conjugates can enhance the selectivity of drug localization. Most cell types and subcellular structures are highly photosensitive and biochemical analysis indicates that cellular target sites associated with PDT correlate with photosensitizer location. In vivo data suggest that vascular and direct tumor cell damage as well as systemic and local immunological reactions are involved in PDT responsiveness. Additional mechanistic, synthetic and developmental studies are required in order to fully appreciate the potentials of PDT. However, continued enthusiasm and support for basic PDT research (as observed during the past 8 years) will depend to a large extent on the outcome of the current clinical trials.

Increased efficacy of photodynamic therapy of R3230AC mammary adenocarcinoma by intratumoral injection of Photofrin II

Photodynamic therapy consists of the systemic administration of a derivative of haematoporphyrin (Photofrin II) followed 24-72 h later by exposure of malignant lesions to photoradiation. We investigated the efficacy of this treatment after direct intratumoral injection of Photofrin II. This direct treatment regimen resulted in higher rates of inhibition of mitochondrial cytochrome c oxidase (5.13% J-1 cm-2 x 10(-1) and succinate dehydrogenase (3.14% J-1 cm-2 x 10(-1] in vitro at 2 h after intratumoral injection compared to rates of inhibition obtained after intraperitoneal drug administration: 0.51 and 0.42% J-1 cm-2 x 10(-1), respectively. A significant delay in tumour growth in vivo was observed in animals that received intratumoral injections 2 h before photoradiation compared to animals injected intraperitoneally at either 2 or 24 h before photoradiation. The treatment protocols were compared with control groups, consisting of Photofrin II administration intratumorally or intraperitoneally without photoradiation, or photoradiation in the absence of Photofrin II. These data indicate that the intratumoral injection regimen with Photofrin II enhanced the efficacy of photodynamic therapy. The greater delay in tumour growth observed after intratumoral administration of Photofrin II suggests a mechanism favouring direct cell damage.