Photodynamic therapy (PDT) has been used traditionally for oncologic and ophthalmic indications. In addition, the enormous potential for the use of PDT agents in cardiovascular diseases is currently being translated into reality. Preclinical studies with various photosensitizers have demonstrated reduction in atheromatous plaque and prevention of intimal hyperplasia. With recent advances in light-based vascular devices and laser diode technology, the clinical use of cardiovascular photodynamic therapy is even more likely. Two photosensitizers, 5-aminolevulinic acid (ALA) and AntrinR (motexafin lutetium) Injection, are under clinical evaluation with many other agents in preclinical testing. Here, preclinical studies are reviewed and the clinical viability of cardiovascular photodynamic therapy is discussed.
Graft coronary artery disease (GCAD) is the chief complication following cardiac transplantation. Presently, there are limited treatment options. Insights into more expedient diagnosis and amelioration, if only partially, of GCAD are fervently sought. The selectivity of Antrin Injection (Lu-Tex) with subsequent photoactivation has been evaluated in several preclinical atherosclerosis models. The inhibitory effect of Lu-Tex induced photosensitization was demonstrated with human bypass coronary smooth muscle cells. The biodistribution of Lu-Tex was evaluated in a rat model of heterotopic cardiac allografts 60 days following transplantation. Lu-Tex was retained in the cardiac allograft, exhibiting a five-fold increase in retention between the allograft and native heart. These findings lead us to suggest that further studies are warranted to ascertain the merits of Lu-Tex for the diagnosis and possible attenuation of chronic graft vascular disease.
Markus Renschler, Alan Yuen, Timothy Panella, Thomas Wieman, Shona Dougherty, Laura Esserman, Masoud Panjehpour, Scott Taber, Victor Fingar, Elizabeth Lowe, Julie Engel, Bert Lum, Kathryn Woodburn, Wai-Fung Cheong, Richard Miller
Photodynamic therapy (PDT) of locally recurrent breast cancer has been limited to treatment of small lesions because of non- selective necrosis of adjacent normal tissues in the treatment field. Lutetium Texaphyrin (PCI-0123, Lu-Tex) is a photosensitizer with improved tumor localization that is activated by 732 nm light, which can penetrate through larger tumors. We have evaluated Lu-Tex in a Phase I trial and in an ongoing Phase II trial in women with locally recurrent breast cancer with large tumors who have failed radiation therapy. Patients received Lu-Tex intravenously by rapid infusion 3 hours before illumination of cutaneous or subcutaneous lesions. In Phase I, Lu-Tex doses were escalated from 0.6 to 7.2 mg/kg in 7 cohorts. Sixteen patients with locally recurrent breast cancer lesions were treated. Dose limiting toxicities above 5.5 mg/kg were pain in the treatment field during therapy, and dysesthesias in light exposed areas. No necrosis of normal tissues in the treated field was noticed. Responses were observed in 60% of evaluable patients [n equals 15, 27% complete remission (CR), 33% partial remission (PR)], with 63% of lesions responding (n equals 73: 45% CR, 18% PR). In Phase II, 25 patients have been studied to date, receiving two treatments ranging from 1.0 to 3.0 mg/kg at a 21 day interval. Treatment fields up to 480 cm2 in size were treated successfully and activity has been observed. Patients have experienced pain at the treatment site but no tissue necrosis. These studies demonstrate the feasibility of Lu-Tex PDT to large chest wall areas in women who have failed radiation therapy for the treatment of locally recurrent breast cancer. Treatment conditions are currently being optimized in the ongoing Phase II trials.
Lutetium texaphyrin (Lu-Tex) photodynamic therapy (PDT) relies on the presence of the water-soluble Lu-Tex, oxygen, and light (activation around 730 nm). Cytotoxic oxygen species are produced that cause irreversible damage to biological substrates. Damage may be inflicted via direct cell kill mechanisms or through vasculature effects that cause hypoxia. The addition of hypoxia enhanced drugs, such as Mitomycin C (MMC), can potentially increase the anti-tumor response. RIF-1 bearing C3H mice received 10 micrometers ol Lu-Tex/kg and were illuminated with 100 J/cm2 3 hours postinjection. Mice received MMC (2.5 or 5 mg/kg, before and after light) in conjunction with PDT and were compared to subsets of drug alone controls. A significant improvement in PDT response was observed when MMC was added to the dosing regimen; the effect was more pronounced at the highest MMC dose of 5 mg/kg: MMC prior to PDT gave a median tumor regrowth time (10X original volume) of 28 days compared to MMC and PDT alone, 16.3 and 14.9 days, respectively. The anti-tumor activity of lutetium texaphyrin induced PDT was improved by the addition of the bioreductive alkylating agent mitomycin C.
Cardiovascular disease is the chief cause of death in the western world. Lutetium texaphyrin (PCI-0123) is a pure, synthetic, aqueous-soluble macrocycle that localizes in both cancerous lesions and atheromatous plaque. The lutetium texaphyrin complex is a potent photosensitizer in vivo, where it is activated by tissue-penetrating far red light (720 - 760 nm). Patient diagnosis and treatment planning are possible with PCI-0123 fluorescence imaging. In this study the localization and selective eradication of atheromatous plaque using PCI-0123 and photoangioplasty are discussed.
Lutetium texaphyrin (PCI-0123) is currently in clinical trials as a PDT agent for the treatment of cancer patients. The drug is cleared rapidly from the plasma, and photoirradiation can be performed shortly after drug administration.T He photosensitizer as yet does not appear to elicit any significant skin photosensitivity. These characteristics favor frequent multiple PDT treatments with PCI-0123. In order to support repeated PDT treatments in the clinic, the safety of multiple drug dosing was studied in rats and mice. In rats, each group received 5 consecutive daily intravenous administrations of 5, 15, 30, or 60 mg/kg/day of PCI-0123. There were no deaths in any of the groups, and no drug-related effects were detected in the 5 mg/kg/day group. In mice, there were no observable signs of toxicity after consecutive daily administration of 10 micrometers ol/kg/day of PCI-0123 for 13 days. The feasibility and efficacy of repeated PDT treatments were assessed in C3H mice bearing RIF-1 tumors. Repeated PDT proved to be superior to a single PDT treatment. Repeated PDT treatments were well tolerated. Seven PDT treatments were administered over a nine day period without significant toxicity while achieving good therapeutic responses. All six groups receiving repeated PDT treatments showed an improved response compared to groups receiving a single PDT cycle, and the improvement was statistically significant for five of these groups. Sixty-two percent of mice receiving four sequential daily treatments were cured, and daily treatments were superior to regimens with longer intervals between PDT cycles.
We compared sites of photodamage with modes of PDT-induced cell death, using murine leukemia tumor cells in vitro. Photodamage to mitochondrial or mitochondrial/lysosomal sites, but not tot he outer membrane, evoked a rapid apoptotic response: DNA changes were observed within 10 min, chromatin fragmentation within 1 hr after PDT. When limited photodamage to the cell membrane also occurred, we observed a delayed apoptotic response; fragmented nuclei were not detected until 24 hr after PDT. More drastic membrane damage, resulting in impaired amino acid transport, prevented an apoptotic response to PDT. A hypothesis accounting for these observations is proposed. Results of in vivo studies suggest that the more efficacious sensitizes generally produce an apoptotic response to PDT, but this question is not yet fully resolved.
Lutetium texaphyrin (PCI-0123) is presently in clinical trials for the treatment of neoplasms. An argon-pumped dye laser has mostly been used to generate light for PCI-0123 photoactivation. However, lasers are expensive and produce a limited area of illumination, so the efficacy of light emitting diodes (LEDs) was investigated. An LED array was developed so that the spectral emission matched the far red absorption spectrum of PCI-0123. A preclinical PDT efficacy study comparing the laser and the LED was undertaken using EMT6-bearing animals. The LED and laser light sources were statistically comparable in eradicating the murine mammary sarcomas using PCI-0123 as the photosensitizer.
Texaphyrins are water soluble porphyrinoids which selectively localize in atheromatous plaque. The paramagnetic gadolinium texaphyrin is an excellent contrast agent which enables plaque detection by MRI. The diamagnetic lutetium texaphyrin, using fluorescence methods, was also shown to label atheromatous plaque. The chemical environment of bound lutetium texaphyrin within plaque was determined by fluorescence emission spectra to be predominantly lipophilic. The texaphyrin was found to bind to the lower density lipoproteins in the atherosclerotic-induced animals. Lutetium texaphyrin is an excellent candidate for photoatherolytic therapy.
Lutetium texaphyrin (PCI-0123) is a pure, stabile, water-soluble photosensitizer with a broad absorption band centered at 732 nm. Lutetium texaphyrin has shown considerable promise in the treatment of murine mammary tumors. PDT requires the coexistence of a photosensitizer, oxygen and light. Light fluences, rates and delivery methods have a profound influence on oxygen depletion and re-equilibration and therefore tumor responsiveness. The effect of different photoirradiation and sensitizer dose in eradicating/retarding EMT6 tumors in BALB/c mice using lutetium texaphyrin was evaluated. An increase in light fluences increased efficacy. No difference was observed between a continuous versus a fractionated light protocol. A reduction in time between sensitizer injection and laser treatment enhanced tumor treatment.
The porphycenes represent a new class of photosensitizing agent with enhanced absorbance in the red. We examined the photodynamic effects of two porphycenes, a monomer and a pyrazine-linked dimer, using the P388 murine leukemia and P388/ADR, a subline that expresses the multidrug-resistance phenotype. The monomer localized at mitochondrial loci while the dimer photosensitized lysosomes and the cell membrane. the dimer was more phototoxic in terms of cells killed and photons absorbed, perhaps because of the difference in localization sites. Phototoxic effects of both porphycenes could be abolished by the addition of the oxygen scavenger trolox (a vitamin E analog) during irradiation. Both porphycenes were recognized by the multidrug transporter, an outward transport process associated with multidrug resistance. Photodynamic actio of the porphycenes in cell culture was associated with apoptosis, resulting in DNA fragmentation. Inhibition of phospholipase C activity prevented initiation of apoptosis after irradiation without protecting cells from photodamage at sites of sensitizer localization. At high concentrations, the porphycenes exhibit a 'dark toxicity' that also was associated with apoptosis, but subsequent irradiation abolished apoptosis, perhaps via destruction of endonucleases, and only necrotic cell death was observed.
We characterized sites of photodamage catalyzed by two cationic photosensitizers tetrabromo- rhodamine 123 (TBR), which is recognized by the multidrug transporter, and a monocationic porphyrin (MCP), which is not. The transporter is an outward transport system associated with examples of drug resistance. Irradiation of multidrug-resistant cells treated with TBR resulted in highly selective photodamage to the transporter site, while MCP catalyzed non- specific membrane damage to cells regardless of transporter expression.
The photobiology of a group of iminium salts was examined. The nonfluorescent copper derivative (CDS1) had an almost undetectable triplet yield, but could catalyze phototoxic effects in cell culture and experimental animal tumors, apparently without the involvement of singlet oxygen. The Zn analog and the metal-free iminium salt both exhibited fluorescence, and were somewhat more efficacious that CDS1, perhaps because both type I and type II processes were available. The nonfluorescent Ni analog was inactive as a photosensitizer. Fluorescent probes indicated that CDS1 and its zinc analog catalyzed photodamage at mitochondrial loci, the metal-free derivative at membrane loci. Because of its very low fluorescence yield, the metal-free iminium salt showed only faint intracellular fluorescence, but the Zn analog was unusual in this regard, with irradiation leading to a photoproduct with very intense intracellular fluorescence which was not readily photobleached.
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