Teratogenicity induced by targeting a placental immunoglobulin transporter

Abstract

Approximately 3% of children in developed countries are born with nongenetic birth defects. However, the nature and mechanisms of teratogenesis are poorly understood. We investigated mechanisms of teratogen-mediated blockade of maternofetal transport by screening a combinatorial library for peptides that bind nonendothelial placental vasculature in pregnant mice. Here, we identified a peptide motif, TPKTSVT, that homes to the yolk sac, induces placental necrosis, and disrupts embryo development. We show that TPKTSVT promotes transcytosis of phage into the embryo and blocks the transplacental transport of immunoglobulins. Based on these data, we propose a model in which TPKTSVT targets a placental Fc receptor. Absence of TPKTSVT placental homing in mice lacking ␤2-microglobulin (␤2m) suggests FcRn͞␤2m as a target for the TPKTSVT, which is unexpected, given the normal development of FcRn͞␤2m-deficient progeny. High-throughput screening for embryotoxins that target placental receptors could be developed to systematically identify and avoid exposure to teratogenic drugs. T eratogens, substances that cause nongenetic fetal morbidity and mortality while being negligibly toxic to the mother, fall into two classes. The first class includes compounds that are actively or passively transferred through the maternofetal barrier and target fetal development by altering cell-signaling pathways controlling essential processes, such as angiogenesis, in the developing embryo (1, 2). Teratogens of the second class interfere with fetal development by affecting the delivery of nutrients to the embryo executed by the placenta (3, 4). In mammals, maternofetal molecule exchange occurs by filtration of blood from the maternal to the fetal side of the placenta through several distinct cell layers (4). Teratogens that target the placenta are thought to function by blocking receptors required for transport of nutrients to the fetus (3, 5). However, although many amino acid, fatty acid, nucleoside, and carbohydrate transporters are expressed in the placenta (6), the roles of specific receptors in the maintenance of maternofetal exchange and normal embryo development have not yet been established.In vivo phage display, a method for studying interactions between receptors expressed preferentially in an organ of interest and their ligands (7,8), is a prospective tool for molecular analysis of placental transport. Screenings of phage-displayed random peptide libraries in mice (9-12) and humans (13) have resulted in the isolation of ligands that selectively home to specific tissues when administered systemically. Homing ligands subsequently have been used to identify corresponding receptors differentially expressed in normal and tumor blood vessels (14-16). Here, we adapted this technology to select teratogenic ligands that bind nonendothelial receptors expressed on the villous placental epithelium, the site of maternofetal molecule exchange. Experimental ProceduresAnimals. Staged pregnant, 18 days postconception (dpc) C57BL͞6 female mice were ...

Ligand-Directed Surface Profiling of Human Cancer Cells with Combinatorial Peptide Libraries

“…To determine if the cell-binding peptides may target these tyrosine kinases, we employed the notion that receptor-binding peptide motifs often mimic natural ligands for these receptors (16,17,19). Thus, we tested whether the selected motifs mimic ligands for the candidate tyrosine kinases by determining whether tripeptides listed in Table 1 are embedded into longer peptides that may be responsible for cell surface binding.…”

“…Similarity of peptides to the corresponding receptor-binding ligands has already been used for validation of the IL-11Ra receptor as a target of an interleukin-11 mimic peptide homing to blood vessels in the prostate (17,24). We and others have modeled the usage of peptides homing to receptors expressed by tumors (18) or nonmalignant tissues (19,20) for directing the delivery of cytotoxics, proapoptotic peptides, metalloprotease inhibitors, cytokines, fluorophores, and genes (13,14). Thus, our approach provides a straightforward way to identify drugaccessible tumor cell surface receptors and to discover peptide ligands that can serve as mimetic prototype drugs.…”

“…In fact, combinatorial peptide libraries displayed from pIII protein of an M13-derived phage have now been successfully screened on intact cells and in vivo (13)(14)(15). Peptide ligands selected from unbiased screens without any predetermined notions about the nature of the cellular receptor repertoire have been used for the subsequent identification of the corresponding target cell surface receptors (16)(17)(18)(19)(20)(21). In addition, novel techniques, such as the biopanning and rapid analysis of selective interactive ligands (BRASIL), have enabled high-throughput phage library screening on cells (16).…”

Antiangiogenic Therapy Decreases Integrin Expression in Normalized Tumor Blood Vessels

“…Compared with quiescent established blood vessels, endothelial cells in angiogenic blood vessels express additional proteins, such as the a v h 3 , a v h 5 (6)(7)(8) and the a 5 h 1 integrins (9). Peptides that bind specifically to distinct vascular beds in normal mice and in a human subject, as identified by in vivo phage display, show the inherent molecular heterogeneity within the microvasculature (1,10,11). Intraorgan vascular heterogeneity has also been shown by two peptide phage that are ephrin A-type ligand mimetics that bind solely to the vasculature of normal murine pancreatic islets with increased localization to islet tumor blood vessels (12).…”

Leukemia targeting ligands isolated from phage display peptide libraries

“…A number of peptides binding specific cell surface markers were recovered from a variety of tissues in vivo and cell types in vitro. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Peptide ligands selectively binding to certain cell types can be linked to therapeutic compounds to target them to the site of interest. [22][23][24]29,31,32 Thus, the use of phage display may lead to the identification of novel ligands that can be used for targeted therapies even without prior knowledge about the identity of the target receptor.…”