An improved mouse model for endometriosis allows noninvasive assessment of lesion implantation and development

Tracing location by applying Emerald luciferase in an early phase of murine endometriotic lesion formation

The pathogenesis of endometriosis has not been fully elucidated. We focused on the behavior of the ectopic endometrium, that is, the origin of the endometriotic lesion, before adhering to the peritoneal cavity. To observe lesion formation in the very early phase, we developed a novel endometriosis animal model using bioluminescence technology. We established a new transgenic mouse that expressed Emerald luciferase (ELuc) under the control of the CAG promoter. This transgenic mouse, called the CAG-ELuc mouse, showed strong bioluminescence emission; we succeeded in tracing the lesion location by the emission of ELuc. The accuracy of tracing by ELuc was high (57.7-100% of correspondence) and depended on the dosage of E2 administration. In the very early phase after transplantation, the process of lesion formation can be observed non-invasively and chronologically. We have verified that the preferred location of the uterus (transplanted grafts) was fixed immediately after the transplantation of the grafts.

Bioluminescent imaging in induced mouse models of endometriosis reveals differences in four model variations

Our understanding of the aetiology and pathophysiology of endometriosis remains limited. Disease modelling in the field is problematic as many versions of induced mouse models of endometriosis exist. We integrated bioluminescent imaging of ‘lesions’ generated using luciferase-expressing donor mice. We compared longitudinal bioluminescence and histology of lesions, sensory behaviour of mice with induced endometriosis and the impact of the gonadotropin-releasing hormone antagonist Cetrorelix on lesion regression and sensory behaviour. Four models of endometriosis were tested. We found that the nature of the donor uterine material was a key determinant of how chronic the lesions were, as well as their cellular composition. The severity of pain-like behaviour also varied across models. Although Cetrorelix significantly reduced lesion bioluminescence in all models, it had varying impacts on pain-like behaviour. Collectively, our results demonstrate key differences in the progression of the ‘disease’ across different mouse models of endometriosis. We propose that validation and testing in multiple models, each of which may be representative of the different subtypes/heterogeneity observed in women, should become a standard approach to discovery science in the field of endometriosis.

Summary: Different versions of syngeneic mouse models of induced endometriosis exhibit disparities in chronicity and cellular composition of lesions, as well as endometriosis-associated hyperalgesia.

IL-37 affects the occurrence and development of endometriosis by regulating the biological behavior of endometrial stromal cells through multiple signaling pathways

Endometriosis (EMs) is a chronic inflammatory condition. Interleukin (IL)-37 is a member of the IL-1 family and an anti-inflammatory cytokine. This study aimed to evaluate the possible role of IL-37 in the EMs pathogenesis. We investigated the in vivo effect of IL-37 on EMs by injection with recombinant human IL-37 (rhIL-37) into EMs mice. Furthermore, we evaluated the in vitro effects of IL-37 on proliferation, adhesion, migration and invasiveness of endometrial stromal cells (ESCs), and explored whether Wnt/β-catenin and mitogen-activated protein kinase (MAPK) pathways were involved in this process. In cultured ESCs, IL-37 overexpression significantly suppressed both protein and mRNA expression of the inflammation-associated cytokines, including IL-1β, IL-6, IL-10 and tumor necrosis factor (TNF-α). Furthermore, IL-37 overexpression significantly inhibited ESCs proliferation, adhesion, migration, invasion and the activity of matrix metalloproteinase (MMP)-2 and MMP-9. In contrast, knockdown of IL-37 exerted the opposite effects. Importantly, the IL-37-mediated action in ESCs was through inactivation of Wnt/β-catenin, p38 MAPK, extracellular signal-related kinases MAPK and c-Jun N-terminal kinase MAPK pathways. Moreover, EMs mice treated with rhIL-37 showed the decreased endometriotic-like lesion size and lesion weight, lower expression of IL-1β, IL-6, IL-10, TNF-α, vascular endothelial growth factor (VEGF), soluble intercellular adhesion molecule-I (ICAM-I) and MMP-2/9 activity in peritoneal fluid compared with the wide type (WT) EMs mice. These findings suggest that IL-37 suppresses cell proliferation, adhesion, migration and invasion of human ESCs through multiple signaling pathways, thereby affecting the occurrence and development of EMs.

Progressive Fibrosis: A Progesterone- and KLF11-Mediated Sexually Dimorphic Female Response

Progressive scarring is ubiquitous postoperatively and in an array of chronic systemic diseases. Recent studies indicate that such scarring has a high female propensity; females are also almost exclusively affected by endometriosis, a common sex steroid-dependent fibrotic disease. Endometriosis-related fibrosis is regulated epigenetically through transcription factor Krüppel-like factor 11 (KLF11). In response to surgical induction of endometriosis, Klf11-/- female mice develop significant fibrosis in contrast to wild-type mice. We therefore hypothesized that female fibrotic predilection was mediated by differential sex steroid regulation of KLF11/collagen 1a1 signaling and investigated the fibrotic response in wild-type and Klf11-/- male and female animals using a sterile peritonitis model. Fibrosis selectively developed in Klf11-/- females. Fibrosis in these animals was almost completely abrogated by ovariectomy. Ovariectomized animals were selectively supplemented with estradiol, medroxyprogesterone acetate (MPA), or dihydrotestosterone; fibrosis was only observed in mice exposed to MPA. Fibrosis therefore selectively developed in Klf11-/- female mice in response to physiological or pharmacological progesterone. The fibrotic response in these animals was also mitigated in response to antiprogestin therapy. Profibrotic gene expression was activated in a primary human peritoneal cell line in response to KLF11 short hairpin RNA and MPA but not estradiol. KLF11/collagen 1a1 signaling previously shown to be linked to fibrosis was thus selectively dysregulated in MPA-treated cells. Our in vivo and in vitro findings in an animal model and human cells, respectively, suggest that progressive fibrotic scarring is a sexually dimorphic response irrespective of etiology; moreover, it is responsive to novel, individualized therapeutic intervention.

Relevant human tissue resources and laboratory models for use in endometriosis research

Endometriosis is characterized by the growth of endometrium‐like tissue outside the uterus, most commonly on the pelvic peritoneum and ovaries. Although it may be asymptomatic in some women, in others it can cause debilitating pain, infertility or other symptoms including fatigue. Current research is directed both at understanding the complex etiology and pathophysiology of the disorder and at the development of new nonsurgical approaches to therapy that lack the unwanted side effects of current medical management. Tools for endometriosis research fall into two broad categories; patient‐derived tissues, and fluids (and cells isolated from these sources) or models based on the use of cells or animals. In this review, we discuss the literature that has reported data from the use of these tools in endometriosis research and we highlight the strengths and weaknesses of each. Although many different models are reported in the literature, hypothesis‐driven research will only be facilitated with careful experimental design and selection of the most appropriate human tissue from patients with and without endometriosis and combinations of physiologically relevant in vitro and in vivo laboratory models.

Evaluation of the potential therapeutic effects of a double-stranded RNA mimic complexed with polycations in an experimental mouse model of endometriosis

OBJECTIVE

To assess the therapeutic potential of polyinosine-polycytidylic acid, a double-stranded RNA molecule with selective proapoptotic and antiangiogenic activity, complexed with polyethyleneimine (pIC(PEI)) in treating endometriosis.

DESIGN

A heterologous mouse model of endometriosis was created by injecting human endometrial fragments into the peritoneum. Endometrial fragments were engineered to express the fluorescent protein mCherry as a reporter to monitor status over the course of the 4-week study.

SETTING

University-affiliated infertility center.

ANIMAL(S)

Ovariectomized and hormone-replaced nude mice (n = 30) injected with fluorescent-labeled human endometrial fragments at 4-6 weeks of age.

INTERVENTION(S)

Animals (n = 10 per group) were injected with vehicle (control), the anti-VEGF compound CBO-P11 (0.6 mg/kg), or pIC(PEI) (0.6 mg/kg) twice weekly over the course of 4 weeks.

MAIN OUTCOME MEASURE(S)

Variations in the size of endometriotic implants were estimated by quantifying the expression of mCherry throughout the course of the experiment. Neovascularization, cellular proliferation, and apoptosis were estimated by quantitative immunofluorescence detection of PECAM, α-SMA, Ki67, and TUNEL.

RESULT(S)

pIC(PEI) promoted a significant increase in apoptosis and a decrease in neovascularization in human fragments, but did not reduce the size of endometriotic implants.

CONCLUSION(S)

While pIC(PEI) treatment had significant antiangiogenic and pro-apoptotic effects in this setting, longer periods of exposure than the ones supported by our heterologous model and/or assays in homologous mouse models of endometriosis may be necessary to detect an effect of this compound on lesion size.

Animal Models in Endometriosis Research

The initiation of endometriosis in women is difficult to investigate, because there is usually a delay of several years from the onset of lesion development to the clinical diagnosis. Animal models of endometriosis, on the other hand, provide an important contribution to the investigation of the disease pathogenesis and the efficacy of therapeutic intervention strategies.

ENMD-1068, a protease-activated receptor 2 antagonist, inhibits the development of endometriosis in a mouse model

OBJECTIVE

Protease-activated receptor 2 plays an important role in the pathogenesis of endometriosis. We studied the effect of ENMD-1068, a protease-activated receptor 2 antagonist, on the development of endometriosis in a noninvasive fluorescent mouse model.

STUDY DESIGN

A red fluorescent protein-expressing xenograft model of human endometriosis was created in nude mice. After endometriosis induction, the mice were injected intraperitoneally with either 25 mg/kg or 50 mg/kg ENMD-1068 or with 200 μL of the vehicle control daily for 5 days. The endometriotic lesions that developed in the mice were then counted, measured, and collected. The lesions were assessed for the production of interleukin 6 and monocyte chemotactic protein-1 by enzyme-linked immunosorbent assays and evaluated for the activation of nuclear factor-κB and the expression of vascular endothelial growth factor by immunohistochemical analyses. Cell proliferation and apoptosis were assessed by immunohistochemistry for Ki-67 and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, respectively.

RESULTS

ENMD-1068 dose-dependently inhibited the development of endometriotic lesions (P < .05) without apparent toxicity to various organs of the treated mice. Consistently, ENMD-1068 dose-dependently inhibited the expression of interleukin 6 and nuclear factor-κB (P < .05) and cell proliferation (P < .05) in the lesions, as well as increased the percentage of apoptotic cells (P < .05). ENMD-1068 reduced the levels of monocyte chemotactic protein-1 and vascular endothelial growth factor in the lesions (P < .05), but not in a dose-dependent manner.

CONCLUSION

Our study suggests that ENMD-1068 is effective in suppressing the growth of endometriosis, which might be attributed to the drug's antiangiogenic and antiinflammatory activities.

A red fluorescent nude mouse model of human endometriosis: advantages of a non-invasive imaging method

OBJECTIVES

To establish red fluorescent human endometriosis lesions in a nude mouse model and dynamically and non-invasively to compare intraperitoneal and subcutaneous injection models.

STUDY DESIGN

Primary cultures of endometrial stromal cells (ESCs) and epithelial cells (EECs) isolated from 24 patients with a normal uterine cavity were transfected with 2.5×10(8) (Group 1) and 1.25×10(8) (Group 2) plaque-forming units (PFU) of adenovirus encoding red fluorescent protein (Ad-RFP). Transfection efficiencies, fluorescence intensity and apoptosis rate of the two types of cells were compared in vitro. A mixture of 2.5×10(8) PFU Ad-RFP-infected approximately 400 EECs cell mass and 2×10(6) ESCs for 36h was injected individually into 24 female nude mice subcutaneously (Group A) or intraperitoneally (Group B). From Day 5 after injection, an in vivo imaging system (IVIS) was used to non-invasively observe and compare the lesions of the two groups every week until Day 33. Specifically, the fluorescent intensity, positive rates, persistence time and lesion weight in the implanted human endometriosis lesions were compared. A parametric Student's t-test and two-way analysis of variance were used for statistical analysis.

RESULTS

Compared with 1.25×10(8) PFU RFP, a titre of 2.5×10(8) PFU RFP ESCs and EECs incubated for 36h exhibited higher transfection efficiencies and higher fluorescence intensities in vitro. In vivo imaging of the fluorescent human endometriosis lesions originating from an RFP titre of 2.5×10(8) PFU showed that the intensity and lesion weight in Group A were significantly higher than in Group B. However, the two groups had the same RFP-positive rates and fluorescence persistence. The structure of each lesion was evaluated by immunohistochemistry to confirm its human endometrial origin.

CONCLUSIONS

The red fluorescent human endometriosis model established by subcutaneously injecting 2.5×10(8) PFU RFP-transfected stromal cells and epithelial cells into nude mice had a higher fluorescent positive rate from Day 5, higher intensity and weight but the same persistence as the intraperitoneal injection model.

A novel role of the Sp/KLF transcription factor KLF11 in arresting progression of endometriosis

Endometriosis affects approximately 10% of young, reproductive-aged women. Disease associated pelvic pain; infertility and sexual dysfunction have a significant adverse clinical, social and financial impact. As precise disease etiology has remained elusive, current therapeutic strategies are empiric, unfocused and often unsatisfactory. Lack of a suitable genetic model has impaired further translational research in the field. In this study, we evaluated the role of the Sp/KLF transcription factor KLF11/Klf11 in the pathogenesis of endometriosis. KLF11, a human disease-associated gene is etiologically implicated in diabetes, uterine fibroids and cancer. We found that KLF11 expression was diminished in human endometriosis implants and further investigated its pathogenic role in Klf11-/- knockout mice with surgically induced endometriotic lesions. Lesions in Klf11-/- animals were large and associated with prolific fibrotic adhesions resembling advanced human disease in contrast to wildtype controls. To determine phenotype-specificity, endometriosis was also generated in Klf9-/- animals. Unlike in Klf11-/- mice, lesions in Klf9-/- animals were neither large, nor associated with a significant fibrotic response. KLF11 also bound to specific elements located in the promoter regions of key fibrosis-related genes from the Collagen, MMP and TGF-β families in endometrial stromal cells. KLF11 binding resulted in transcriptional repression of these genes. In summary, we identify a novel pathogenic role for KLF11 in preventing de novo disease-associated fibrosis in endometriosis. Our model validates in vivo the phenotypic consequences of dysregulated Klf11 signaling. Additionally, it provides a robust means not only for further detailed mechanistic investigation but also the ability to test any emergent translational ramifications thereof, so as to expand the scope and capability for treatment of endometriosis.

Baboon model for the study of endometriosis

Endometriosis is a benign, estrogen-dependent disease and is now recognized as an enigmatic disease owing to its various clinical manifestations and locations. The lack of a reliable and specific method for the early detection of endometriosis often results in delayed diagnosis. So far, research has born inadequate findings regarding understanding the basic etiology or pathophysiology of endometriosis. Animal models that accurately represent the cellular and molecular changes associated with the initiation and progression of human endometriosis have significant potential to facilitate the development of better methods for the early detection and treatment of endometriosis. A number of animal model systems have been developed for the study of this disease. These models replicate many of the known salient features of human endometriosis. This review provides an insight into the use of the baboon model for studies focused on understanding human endometriosis.

Activation of mutated K-ras in donor endometrial epithelium and stroma promotes lesion growth in an intact immunocompetent murine model of endometriosis

Endometriosis is a common chronic gynaecological condition, affecting 5-10% of women of child-bearing age. Its study has been hampered by lack of genetically tractable models. We transplanted steroid-manipulated, menstrual-like endometrium from K-ras(G12V/+) /Ah-Cre(+/+) /ROSA26R-LacZ(+/+) mice into gonad-intact immunocompetent wild-type mice. This led to endometriosis-like lesion development. Long-term lesion survival depended on the presence of the activated K-ras in the small proportion of the cells in the mature lesion that had undergone Cre-mediated K-ras activation. LacZ activity demonstrated Cre-mediated recombination in both endometrial epithelial cells and stromal cells, and transgenic K-ras expression was confirmed by RT-PCR. The endometriosis lesions developed without exogenous oestradiol supplementation and anti-oestrogen (fulvestrant, ICI 182780) treatment greatly suppressed their growth. Immunohistochemistry confirmed that as in human endometriosis, there was invasion and activation of fibroblasts, endothelial cells, and macrophages, with marked collagen deposition in the lesions. This model provides an opportunity to investigate endometriosis lesion establishment, growth, and regression in genetically tractable, immunocompetent, and hormonally intact mice. Furthermore, for the first time it provides a suitable model to test clinically validated driver genes in a faithful mouse model of the predisposing endometriotic lesion, thus providing the correct cellular context and microenvironment for ovarian clear cell carcinogenesis.

Evaluation of the macroscopic growth degree of experimental endometriosis in rats

PURPOSE

To evaluate macroscopically the growth degree of self-transplantation of endometriosis in rats.

METHODS

Forty female rats, after a 7-day period for adpating and evaluating of the estrous cycle regularity, underwent tail abdominal midline laparotomy with 3-cm cuts. The average third of the left uterine horn was removed, 4mm x 4mm patches in liquid environment were made, and self-transplanted in the rat mesenterium with a single stitch, and the endometrial surface of the endometriotic implant facing the lumen of the peritoneal cavity. The rats were programmed to die after three weeks. The abdominal cavity displaying was held and self-transplants were identified and classified.

RESULTS

The results achieved were: one case for degree 0 (2,5%), three cases for degree 1 (7,5%), eleven cases for degree II (27,5%) and twenty-five cases for degree III (62,5%).

CONCLUSION

The experimental endometriosis development, through the self-transplantation technique, showed to be most common in degrees 3 and 2 of development.

Neuroendocrine-immune disequilibrium and endometriosis: an interdisciplinary approach

Endometriosis, a chronic disease characterized by endometrial tissue located outside the uterine cavity, affects one fourth of young women and is associated with chronic pelvic pain and infertility. However, an in-depth understanding of the pathophysiology and effective treatment strategies of endometriosis is still largely elusive. Inadequate immune and neuroendocrine responses are significantly involved in the pathophysiology of endometriosis, and key findings are summarized in the present review. We discuss here the role of different immune mechanisms particularly adhesion molecules, proteinglycan interactions, and pro-angiogenic mediators in the development and progression of the disease. Finally, we introduce the concept of endometrial dissemination as result of a neuroendocrine-immune disequilibrium in response to high levels of perceived stress caused by cardinal clinical symptoms of endometriosis.

Noninvasive assessment of ectopic uterine tissue development in rats using magnetic resonance imaging

OBJECTIVE

To non-invasively characterize ectopic uterine tissue (EUT) development in a modified autologous rat surgical model of endometriosis using magnetic resonance imaging (MRI).

DESIGN

Investigational MRI study.

SETTING

A pharmaceutical company.

ANIMAL(S)

Female Sprague Dawley rats.

INTERVENTION(S)

Uterine tissue was autotransplanted on the right peritoneal wall of rats. Rats were serially imaged after surgery and after endogenous hormone suppression, hormone supplementation, or ovariectomy. In addition, an MRI contrast agent was administered to examine EUT perfusion characteristics.

MAIN OUTCOME MEASURE(S)

Changes in transplanted EUT volume and perfusion were monitored using MRI.

RESULT(S)

The EUT growth could be readily monitored non-invasively by MRI. Although EUT growth was rapid during the initial 4 days after surgery, volume stabilized by the third week and maintained for at least 9 weeks after transplantation. The EUT volumes varied with the estrous cycle and were hormonally sensitive to ovariectomy, to Antide (GnRH antagonist), and to Antide followed by 17beta-E(2) supplementation. The use of an MRI contrast agent facilitated visualization of EUT wall perfusion.

CONCLUSION(S)

MRI allows for noninvasive, dynamic evaluation of transplanted EUT growth in the rat. This reproducible model will allow for performing quantifiable pharmacologic studies in pre-clinical drug discovery for therapies targeting endometriosis.

Animal models in endometriosis research

Endometriosis is a common gynaecological disease, defined as the presence of endometrial tissue outside the uterus, causing pelvic pain and subfertility in approximately 10% of women of reproductive age. Current therapies lead to pain relief, however, do not address the causes and entail severe side effects. Still little is known about the pathogenic processes leading to the development and maintenance of endometriosis. Because endometriosis occurs spontaneously only in humans and some non-human primates, animal models of induced endometriosis have been developed and are of high value for the evaluation of pathophysiological mechanisms underlying the development of this disease. These experimental models include the autotransplantation of uterine fragments into the peritoneal cavity of rodents and non-human primates or the heterotransplantation of human endometrial or endometriotic tissue to immunodeficient mice or onto the chicken chorioallantoic membrane (CAM). This review describes the animal models for endometriosis and assesses their different potentials and limitations in regard to endometriosis research, with the aim of developing novel non-invasive diagnostic tools and improved strategies for the treatment of endometriosis in women.

A novel noninvasive model of endometriosis for monitoring the efficacy of antiangiogenic therapy

Endometriosis, the presence of ectopic endometrial tissue, is a common disease associated with high morbidity and socioeconomic problems. Angiogenesis, the formation of new blood vessels, plays an important role in the formation and growth of endometriotic lesions. We have created a novel, noninvasive model to monitor the growth of these lesions and the associated angiogenesis in vivo. First, we generated luciferase-expressing transgenic mice by inserting the human ubiquitin C promoter coupled to the firefly luciferase reporter. Injection of luciferin in these mice causes full-body bioluminescence, which can be detected using a low-light CCD camera. Endometrial tissue from these transgenic mice was surgically implanted into nonluminescent recipients. Bioluminescence of lesions was noninvasively imaged after intravenous or intraperitoneal injection of luciferin. Transabdominal luminescence compared well with the location of the transgenic endometriotic lesions, and lesion size correlated with the intensity of luminescence. Systemic treatment with the angiogenesis inhibitors caplostatin and endostatin peptide mP-1 delayed and suppressed the onset and intensity of the luminescent signal. Caplostatin suppressed the growth of endometriotic lesions by 59% compared with controls. This novel, noninvasive model of endometriosis provides a means to study early angiogenesis in vivo and to monitor endometriotic growth and the efficacy of systemic antiangiogenic therapy.

Quantification of endometriotic lesions in a murine model by fluorimetric and morphometric analyses

BACKGROUND

In animal models of endometriosis, the identification and quantification of lesions originating from human endometrium is often hampered by the small size of the implants and their embedding in murine tissue. The purpose of the present study was to develop two new methods of quantifying endometriosis-like lesions in a nude mouse model: fluorimetry and morphometry.

METHODS

Human menstrual endometrium was labelled using a fluorescent tracker, carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE), and transplanted into the pelvic cavity of mice by injection through the peritoneum after performing a cutaneous incision. After 5 days, lesions were recovered by laparotomy. The fluorescence of the recovered endometriotic lesions was measured. Endometrial stroma and glands were immunostained in lesion sections with anti-CD10 and anti-CK22 antibodies, and their surface area was evaluated by morphometric analysis.

RESULTS

Fluorescent labelling allows identification of lesions not visible macroscopically. A good correlation was observed between fluorimetry and morphometry (r=0.88) applied for lesion quantification.

CONCLUSIONS

Fluorimetric evaluation combined with morphometric analysis of endometriosis-like lesions allows objective and reliable recording of endometriosis development in a nude mouse model. This quantification method could therefore be useful for future pharmacological and toxicological studies.

Development of an experimental model of endometriosis using mice that ubiquitously express green fluorescent protein

BACKGROUND

Aiming at improving an animal model of endometriosis, we developed a homologous mouse model using 'green mice' that ubiquitously express green fluorescent protein.

METHODS

Endometrial fragment obtained from estradiol (E2)-supplemented ovariectomized 'green mice' was minced and injected into the peritoneal cavity of ovariectomized wild-type mice. The recipient wild mice were raised with or without E2 supplementation for 2 weeks, and then were euthanized. Endometriotic lesions that developed in the abdomen were examined both macroscopically and microscopically under fluorescence, and weight of the lesions was measured.

RESULTS

The endometriotic lesions were more clearly detected under fluorescence imaging than by conventional macroscopic examination. Histologically, endometriotic lesions deriving from 'green mice' were sharply distinguished from surrounding host tissues under fluorescence microscopy. More lesions developed in E2-supplemented than control recipient mice. The measured fluorescence intensity of endometriotic lesions showed significant positive correlation with their weight (R=0.844, P<0.0001), and was significantly higher in E2-supplemented mice than in vehicle-supplemented mice (P=0.0062).

CONCLUSION

The present endometriosis model using 'green mice' would be useful for expeditious identification and quantitative evaluation of endometriotic lesions.

Quantitative assessment of human endometriotic tissue maintenance and regression in a noninvasive mouse model of endometriosis

Endometriosis is a prevalent disease characterized by the estrogen-dependent ectopic growth of endometrial tissue. Most of the current medical therapies consist in inducing a hypoestrogenic state in patients, but these treatments are associated with severe side effects and high recurrence rates. The development of convenient and reliable endometriosis animal models would be instrumental to accelerate the emergence of new therapeutic alternatives. Recently, we developed an improved experimental model for endometriosis, relying on the infection of human endometrial fragments by an adenovirus carrying the green fluorescent protein. Following injection of fluorescent fragments into nude mice, the implantation and growth of endometriotic-like lesions could be followed noninvasively. In the present work, we demonstrate that this model can be used to quantify the size of fluorescent endometriotic lesions by in vivo imaging. To this end, we repeatedly measured lesion size over a 4-week period in mice supplemented or not with estradiol. The model was adequate to confirm previous results showing that estrogen is dispensable for the implantation phase of endometrial tissue, whereas it is required for lesion maintenance. As a proof of concept for inducing regression of established lesions, ganciclovir was used to treat animals implanted with human fluorescent endometrial fragments expressing thymidine kinase. A significant decrease in lesion size was observed by in vivo imaging in ganciclovir-treated mice. Together, the data indicate that the noninvasive animal model described here provides a tool for drug testing and/or gene target validation in endometriosis.