Vascular disrupting effects of combretastatin A4 phosphate on murine endometriotic lesions

Protein kinase CK2 participates in estrogen-mediated endothelial progenitor cell homing to endometriotic lesions through stromal cells in a stromal cell-derived factor-1- CXCR4-dependent manner

OBJECTIVE

To explore the possible mechanism of protein kinase CK2, which participates in estrogen recruitment of endothelial progenitor cells (EPCs), and its role in the angiogenesis of endometriosis lesions.

DESIGN

Laboratory study.

SETTING

University.

ANIMAL(S)

BALB/c mice.

INTERVENTION(S)

Exposure of human endometrial stromal cells (HESCs) to estrogen and CK2 inhibitor CX-4945 and endometrial stromal cells transfected with the protein kinase CK2 vector (HESC-CK2). Endometriosis models were induced by allogeneic mice transplantation of the endometrium into dorsal skinfold chambers. The mice received an IP injection of 50 mg/kg emodin per day or were treated with 100 μg/kg estrogen by SC injection once a week.

MAIN OUTCOME MEASURE(S)

The concentration of cytokines in cells was measured with ELISA. The migration of EPCs was examined using the scratch assay method and Transwell, a capillary tube-formation assay to determine EPC tube-forming capacity, and protein and mRNA expression with Western blot and polymerase chain reaction analyses, respectively.

RESULT(S)

Protein kinase CK2 participates in estrogen-mediated EPC homing to endometriotic lesions through stromal cells in a stromal cell-derived factor-1 (SDF-1)-CXCR4-dependent manner. Conditioned medium from endometrial stromal cells that were stably transfected with the protein kinase CK2 vector (HESC-CK2) or pretreated with estrogen significantly enhanced the migration and recruitment of EPCs. In contrast, conditioned medium from HESCs that were treated with CX-4945, a selective inhibitor of CK2, inhibited the mobility and viability of EPCs. Furthermore, CK2 overexpression significantly upregulated SDF-1 expression and secretion in endometrial stromal cells by activating the AKT/mTOR pathway. Moreover, treatment with the SDF-1 receptor CXCR4-specific inhibitor AMD3100 completely reversed the CK2-enhanced migration of EPCs.

CONCLUSION(S)

This study demonstrates that CK2 participates in estrogen-mediated EPC homing to endometriotic lesions through stromal cells in an SDF-1-CXCR4-dependent manner and may be a therapeutic target.

Combretastatins: An Overview of Structure, Probable Mechanisms of Action and Potential Applications

Combretastatins are a class of closely related stilbenes (combretastatins A), dihydrostilbenes (combretastatins B), phenanthrenes (combretastatins C) and macrocyclic lactones (combretastatins D) found in the bark of Combretum caffrum (Eckl. & Zeyh.) Kuntze, commonly known as the South African bush willow. Some of the compounds in this series have been shown to be among the most potent antitubulin agents known. Due to their structural simplicity many analogs have also been synthesized. Combretastatin A4 phosphate is the most frequently tested compounds in preclinical and clinical trials. It is a water-soluble prodrug that the body can rapidly metabolize to combretastatin A4, which exhibits anti-tumor properties. In addition, in vitro and in vivo studies on combretastatins have determined that these compounds also have antioxidant, anti-inflammatory and antimicrobial effects. Nano-based formulations of natural or synthetic active agents such as combretastatin A4 phosphate exhibit several clear advantages, including improved low water solubility, prolonged circulation, drug targeting properties, enhanced efficiency, as well as fewer side effects. In this review, a synopsis of the recent literature exploring the combretastatins, their potential effects and nanoformulations as lead compounds in clinical applications is provided.

Inhibition of erythropoietin-producing hepatoma receptor B4 (EphB4) signalling suppresses the vascularisation and growth of endometriotic lesions

BACKGROUND AND PURPOSE

The development of endometriotic lesions is crucially dependent on the formation of new blood vessels. In the present study, we analysed whether this process is regulated by erythropoietin-producing hepatoma receptor B4 (EphB4) signalling.

EXPERIMENTAL APPROACH

We first assessed the anti-angiogenic action of the EphB4 inhibitor NVP-BHG712 in different in vitro angiogenesis assays. Then, endometriotic lesions were surgically induced in the dorsal skinfold chamber and peritoneal cavity of NVP-BHG712- or vehicle-treated BALB/c mice. This allowed to study the effect of EphB4 inhibition on their vascularisation and growth by means of intravital fluorescence microscopy, high-resolution ultrasound imaging, histology and immunohistochemistry.

KEY RESULTS

Non-cytotoxic doses of NVP-BHG712 suppressed the migration, tube formation and sprouting activity of both human dermal microvascular endothelial cells (HDMEC) and mouse aortic rings. Accordingly, we also detected a lower blood vessel density in NVP-BHG712-treated endometriotic lesions. This was associated with a reduced lesion growth due to a significantly lower number of proliferating stromal cells when compared to vehicle-treated controls.

CONCLUSIONS AND IMPLICATIONS

Inhibition of EphB4 signalling suppresses the vascularisation and growth of endometriotic lesions. Hence, EphB4 represents a promising pharmacological target for the treatment of endometriosis.

Basic mechanisms of vascularization in endometriosis and their clinical implications

BACKGROUND

Vascularization is a major hallmark in the pathogenesis of endometriosis. An increasing number of studies suggests that multiple mechanisms contribute to the vascularization of endometriotic lesions, including angiogenesis, vasculogenesis and inosculation.

OBJECTIVE AND RATIONALE

In this review, we provide an overview of the basic mechanisms of vascularization in endometriosis and give special emphasis on their future clinical implications in the diagnosis and therapy of the disease.

SEARCH METHODS

Literature searches were performed in PubMed for English articles with the key words 'endometriosis', 'endometriotic lesions', 'angiogenesis', 'vascularization', 'vasculogenesis', 'endothelial progenitor cells' and 'inosculation'. The searches included both animal and human studies. No restriction was set for the publication date.

OUTCOMES

The engraftment of endometriotic lesions is typically associated with angiogenesis, i.e. the formation of new blood vessels from pre-existing ones. This angiogenic process underlies the complex regulation by angiogenic growth factors and hormones, which activate intracellular pathways and associated signaling molecules. In addition, circulating endothelial progenitor cells (EPCs) are mobilized from the bone marrow and recruited into endometriotic lesions, where they are incorporated into the endothelium of newly developing microvessels, referred to as vasculogenesis. Finally, preformed microvessels in shed endometrial fragments inosculate with the surrounding host microvasculature, resulting in a rapid blood supply to the ectopic tissue. These vascularization modes offer different possibilities for the establishment of novel diagnostic and therapeutic approaches. Angiogenic growth factors and EPCs may serve as biomarkers for the diagnosis and classification of endometriosis. Blood vessel formation and mature microvessels in endometriotic lesions may be targeted by means of anti-angiogenic compounds and vascular-disrupting agents.

WIDER IMPLICATIONS

The establishment of vascularization-based approaches in the management of endometriosis still represents a major challenge. For diagnostic purposes, reliable angiogenic and vasculogenic biomarker panels exhibiting a high sensitivity and specificity must be identified. For therapeutic purposes, novel compounds selectively targeting the vascularization of endometriotic lesions without inducing severe side effects are required. Recent progress in the field of endometriosis research indicates that these goals may be achieved in the near future.

Notch signaling controls sprouting angiogenesis of endometriotic lesions

Angiogenesis is essential for the engraftment and growth of endometriotic lesions. In this study, we analyzed whether this process is regulated by Notch signaling. Endometriotic lesions were induced by endometrial tissue transplantation into dorsal skinfold chambers of C57BL/6 mice, which were treated with the γ-secretase inhibitor DAPT or vehicle. Vascularization, morphology, and proliferation of the newly developing lesions were analyzed using intravital fluorescence microscopy, histology, and immunohistochemistry over 14 days. Inhibition of Notch signaling by DAPT significantly increased the number of angiogenic sprouts within the endometrial grafts during the first days after transplantation when compared to vehicle-treated controls. This was associated with an accelerated vascularization, as indicated by a higher functional microvessel density of DAPT-treated lesions on day 6. However, inhibition of Notch signaling did not affect the morphology and proliferating activity of the lesions, as previously described for tumors. Both DAPT- and vehicle-treated lesions finally consisted of cyst-like dilated glands, which were surrounded by a well-vascularized stroma and contained comparable numbers of proliferating cell nuclear antigen-positive cells. These findings demonstrate that sprouting angiogenesis in endometriotic lesions is controlled by Notch signaling. However, inhibition of Notch signaling does not have beneficial therapeutic effects on lesion development.

Evaluation of the antiproliferative, proapoptotic, and antiangiogenic effects of a double-stranded RNA mimic complexed with polycations in an experimental mouse model of leiomyoma

OBJECTIVE

To assess the antiproliferative, proapoptotic, and antiangiogenic effects of the double-stranded RNA mimic polyinosine-polycytidylic acid (pIC) complexed with polyethylenimine [pIC(PEI)] in xenografted human leiomyomas.

DESIGN

Heterologous leiomyoma mouse model.

SETTING

University-affiliated infertility center.

ANIMAL(S)

Ovariectomized and hormone-replaced nude mice (n = 16) who received human leiomyoma fragment transplantation.

INTERVENTION(S)

Leiomyoma fragments placed in the peritoneum of 5-week-old nude female mice and treated with the vehicle (n = 8) or 0.6 mg/kg [pIC(PEI)] (n = 8) for 4 weeks.

MAIN OUTCOME MEASURE(S)

The size of the leiomyoma implants, and cellular proliferation (Ki67), vascularization (PECAM), and apoptosis (OH-ends) assessed by quantitative immunohistochemical/immunofluorescent analysis of the recovered implants.

RESULT(S)

No significant differences were observed in the size of the leiomyoma implants between groups. Vascularization and proliferation were significantly decreased, and apoptosis was increased in the [pIC(PEI)]-treated group versus control.

CONCLUSION(S)

We hypothesize that the antiangiogenic and apoptotic effects exerted by [pIC(PEI)] might lead to a decrease in lesion size in this animal model if the compound is administered for longer periods of time. This study provides promising data on [pIC(PEI)] as a potential novel therapeutic agent against human leiomyoma.

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.

Combretastatins: more than just vascular targeting agents?

Several prodrugs of the naturally occurring combretastatins have undergone extensive clinical evaluation as vascular targeting agents (VTAs). Their increased selectivity toward endothelial cells together with their innate ability to rapidly induce vascular shutdown and inhibit tumor growth at doses up to 10-fold less than the maximum tolerated dose led to the clinical evaluation of combretastatins as VTAs. Tubulin is well established as the molecular target of the combretastatins and the vast majority of its synthetic derivatives. Furthermore, tubulin is a highly validated molecular target of many direct anticancer agents routinely used as front-line chemotherapeutics. The unique vascular targeting properties of the combretastatins have somewhat overshadowed their development as direct anticancer agents and the delineation of the various cell death pathways and anticancer properties associated with such chemotherapeutics. Moreover, the ongoing clinical trial of OXi4503 (combretastatin-A1 diphosphate) together with preliminary preclinical evaluation for the treatment of refractory acute myelogenous leukemia has successfully highlighted both the indirect and direct anticancer properties of combretastatins. In this review, we discuss the development of the combretastatins from nature to the clinic. The various mechanisms underlying combretastatin-induced cell cycle arrest, mitotic catastrophe, cell death, and survival are also reviewed in an attempt to further enhance the clinical prospects of this unique class of VTAs.