The immunoconjugate "icon" targets aberrantly expressed endothelial tissue factor causing regression of endometriosis

Abstract

Endometriosis is a major cause of chronic pain, infertility, medical and surgical interventions, and health care expenditures. Tissue factor (TF), the primary initiator of coagulation and a modulator of angiogenesis, is not normally expressed by the endothelium; however, prior studies have demonstrated that both blood vessels in solid tumors and choroidal tissue in macular degeneration express endothelial TF. The present study describes the anomalous expression of TF by endothelial cells in endometriotic lesions. The immunoconjugate molecule (Icon), which binds with high affinity and specificity to this aberrant endothelial TF, has been shown to induce a cytolytic immune response that eradicates tumor and choroidal blood vessels. Using an athymic mouse model of endometriosis, we now report that Icon largely destroys endometriotic implants by vascular disruption without apparent toxicity, reduced fertility, or subsequent teratogenic effects. Unlike antiangiogenic treatments that can only target developing angiogenesis, Icon eliminates pre-existing pathological vessels. Thus, Icon could serve as a novel, nontoxic, fertility-preserving, and effective treatment for endometriosis.

Figure 1

Expression of TF in endothelial cells from human ectopic endometrium: Immunohistochemistry was performed as described in the Methods. Eutopic proliferative endometrium from patients with endometriosis showing low to no TF staining in glands or stromal cells; vessels walls and endothelial cells are unstained (arrows) (original magnification, ×100; A and C); ectopic endometriotic implants from the same patients, respectively, displaying strong TF immunostaining in endothelial cells (arrows) with moderate TF immunostaining of ectopic glands and stromal cells (original magnification, ×100; B and D). (n = 6).

Figure 2

Gross morphological analysis: Representative lesions from placebo (left) or 10-μg Icon-treated (right) ATN mice with established human endometriotic lesions displaying obvious differences in gross surface vascularization (n = 15). Arrows point to the lesions.

Figure 3

Microscopic endometriotic vessel analysis: Vessels in human peritoneal endometriotic implants present in ATN mice were visualized by immunohistochemical staining for vWF after treatment with vehicle control (A) or 10 μg Icon (B; n = 5, ×200). C: Morphometric analysis demonstrated that both 5 and 10 μg Icon resulted in a significant decrease in vessel size in mice with residual lesions. Vessel size is reported in arbitrary units. Statistical analysis was conducted by analysis of variance (n = 5, *P < 0.05).

Figure 4

Immunofluorescence for Icon: Human endometrium recovered from control treated mouse was immunostained consecutively for CD31 (detected with phycoerythrin) and DAPI (blue; left). Endometriotic lesion in an ATN mouse extracted four hours after injection with FITC-labeled Icon (green) were also stained with CD31 and DAPI (right). (×400, n = 3).

Figure 5

Fertility studies: ATN mice were treated with Icon or placebo once a week for four weeks. Two weeks after the last Icon treatment, mice were mated. All mice conceived. The average number of viable pups is shown in dark bars, whereas the number of nonviable pups is shown in light bars (n = 4 per group; *P < 0.05).