1 Department of Pathology, Geneva University Hospital, Geneva, 2 Department of Obstetrics and Gynaecology, Geneva University Hospital, Geneva, 3 Department of Biology, Faculty of Sciences, University of Geneva, 4 Fondation pour Recherches Médicales, University of Geneva, 5 Department of Geriatrics, Geneva University Hospital and 6 Swiss Federal Institute of Technology, Lausanne, Switzerland
7 To whom correspondence should be addressed at: Department of Obstetrics and Gynaecology, Geneva University Hospital, 30 Boulevard de la Cluse, 1211 Geneva 14, Switzerland. e-mail: Attila.Major{at}hcuge.ch
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Abstract |
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Key words: BDP/endometrial ablation/PDT/rat model
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Introduction |
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PDT uses the light activation of a photosensitizer to generate highly reactive oxygen intermediates, leading to tissue destruction by apoptosis and/or necrosis (Sickenberg et al., 2000). Various photosensitizers, such as 5-aminolevulinic acid (ALA) and benzoporphyrin derivative (BPD), administered topically or systemically, have been used for endometrial ablation in animal models with good results (Wyss et al., 1994a
; b
; Gannon et al., 1995
; Fehr et al., 1996a
;b
; Steiner et al., 1996
). However, most of these studies targeted the endometrial glands directly by either topical or systemic application of a photosensitizer. In order to accumulate the photosensitizer in the endometrial glands, long intervals between drug administration and light application were needed.
BPD-monoacid ring A (BPD-MA), verteporfin (Visudyne)TM, is a second-generation photosensitizer injected in a liposomal formulation, which has been accepted by many health authorities as a new and effective treatment for macular degeneration. Despite the typical activation of the verteporfin at a wavelength of 690 nm, it can also be activated at 630 nm (Waterfield et al., 1994; Panjehpour et al., 2002
). In the present study, because of the thickness of the rat uterus, activation at a wavelength of 630 nm is desirable, since deeper penetration at 690 nm is not necessary. The drug becomes effective within minutes after injection and it is rapidly eliminated within 24 h from the tissues, resulting in a skin photosensitivity that lasts <2 days in general (Richter et al., 1993
). In a previous study, we showed that by using tin ethyl etiopurpurin as a photosensitizer we could target the vasculature using a short druglight interval, resulting in effective photodynamic therapy (Major et al., 1999a
;b
). In the present study, we decided to evaluate the structural effect of PDT with a second-generation dye BPD-MA (verteporfin) on the rat uterus by using it in an intravenous injection and with a short drug-light interval of 5 min. This short druglight interval was chosen based on animal studies showing the great specificity of BPD-MA in targeting the neovasculature when used at a short druglight interval (Fingar et al., 1999
; Major et al., 1999b
). In addition, we also planned to determine the optimal concentration of this drug required for selective endometrial tissue destruction.
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Materials and methods |
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Statistical analysis
Comparisons between the treated and the untreated sides were performed using Students paired t-test for continuous variables (number of glands and myometrium thickness, averaged over three measures for each data point) and Wilcoxon signed-rank test for the binary variable (inflammation status). When the overall differences of continuous response variables were statistically significant, we performed multiple comparisons for each verteporfin concentration while adjusting the appropriate significance levels according to Bonferronis correction (P threshold becomes 0.05/6 = 0.0083). As there were not enough observations to fulfil ANOVA assumptions, we checked for the equality of distribution of the response variables among the different levels of verteporfin concentrations using the KruskalWallis test. Possible trends in dose-effects were evaluated using linear regression with the continuous response measures as the dependent variables and the verteporfin concentration as the predictor. A non-parametric test for trend across ordered group was applied to evaluate the effect of verteporfin concentration on the inflammation status.
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Results |
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Discussion |
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Studies evaluating PDT in endometrial ablation have primarily used ALA as the photosensitizer, due to its rapid elimination from the tissue. These studies targeted mainly the cellular compartment (Wyss et al., 1994b; Gannon et al., 1995
; Fehr et al., 1996b
; Steiner et al., 1996
). A few studies have evaluated the effect of BPD-MA-mediated PDT on endometrial tissue using topical application (Wyss et al., 1994a
; Hornung et al., 1998
). To the best of our knowledge, the present study is the first in which a second-generation photosensitizer, BPD-MA, was administrated by i.v. injection followed by PDT only a few minutes after drug administration. We decided to give verteporfin by i.v. injection for two reasons, first to test its use and efficacy in this mode of administration and secondly to determine whether we can avoid intrauterine application, thus making it more practical in the clinical setting in future human application.
Verteporfin used by systemic injection proved to be very effective in endometrial glandular ablation at all concentrations. The optimal drug concentration, defined as that which causes total glandular destruction with minimal loss of the myometrial thickness and minimal inflammatory reaction, seemed to range from 0.25 to 0.125 mg/kg. The lowest dose (0.0625 mg/kg) used, despite the good conservation of the myometrial thickness, was not efficient for total glandular ablation. With the highest concentration (2 and 1 mg/kg), despite their efficacy on glandular destruction, a significant loss of myometrial thickness, severe inflammatory reaction and adherence of the adjacent organ to the uterus was recorded. Nevertheless, a total selectivity in terms of complete destruction of the endometrium without harm to the myometrium has not been observed in the rat model. However, this could have some advantage, as the destruction of a small proportion of the inner myometrium might avoid the possibility of endometrial regeneration. The long-term effect of verteporfin on endometrial ablation needs to be evaluated in further studies. In the human uterus, PDT provides a better chance of selective destruction of the endometrium while conserving the myometrium, due to its thickness. The rather thick myometrium will be protected from complete destruction, even in the absence of complete tissue PDT selectivity, by the penetration depth of the light being set at 630 or even at 690 nm.
In summary, using PDT shortly after verteporfin administration, thereby targeting the endometrial vasculature, results in endometrial ablation with high efficacy. Thus, this therapy may contribute to a new treatment modality for endometrial ablation. Further studies using different drug/light doses and intervals to increase the endometrial tissue selectivity are underway.
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Acknowledgements |
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References |
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Submitted on February 19, 2003; resubmitted on April 11, 2003; accepted on May 8, 2003.