Aristotle: the first student of angiogenesis

Historical Overview of In Vivo and In Vitro Angiogenesis Assays

Most of angiogenesis assays were designed and developed during Folkman's era. But the growth of new blood vessels in several pathologic conditions as tumor development or inflammation were observed long time ago.The development of new blood vessels was early observed by ancient Egyptians who tried to destroy them by applying empirical methods. From the first observations regarding angiogenesis to a personalized therapy targeting newly formed blood vessels a lot of experimental in vitro and in vivo angiogenesis assays have been developed. The present work will overview the oldest and less known part of angiogenesis assays development, and in addition, it will present the newest data in the experimental field of angiogenesis which is rapidly improved by the needs of new antiangiogenic and antivascular therapy development.

Looking for the Word "Angiogenesis" in the History of Health Sciences: From Ancient Times to the First Decades of the Twentieth Century

This review deals with the origin of the term "angiogenesis", with an attention to John Hunter who is credited with this neologism. A part of the literature refers to a Hunter's work dating 1787, and the other part claims the first use of the term "angiogenesis" in the Hunter's masterpiece published in 1794. Since we were unable to find the term "angiogenesis" in Hunter's works, this review attempts to bring a new contribution to the historical research of this important concept, moving from ancient times to the first decades of the twentieth century, when "angiogenesis" begun to appear on titles of scientific articles. The development of the knowledge on the cardiocirculatory system and the principal steps of this fascinating subject were examined, with particular regard to microvascular bed and vessel sprouting, and to the intriguing observations on blood vessel neoformation that have been also made in the premicroscopic era. In Hunter's works, the concept of angiogenesis indeed emerges, but not the term "angiogenesis". The scientific language occurring during Hunter's time was still old-fashioned, and the term "angiogenesis" was not one of those he used, rather a much later neologism that sounds too modern to appear in that context. Would the first appearance of the term "angiogenesis" occur in late nineteenth century in studies dealing with embryogenesis and organ vascularization? The present study aims to explore the scientific literature and to open a debate to better define this matter.

Mechanisms of resistance to vascular endothelial growth factor blockade

Angiogenesis is essential for the growth of primary tumors and for their metastasis. This process is induced by factors, such as vascular endothelial growth factors (VEGFs), that bind to transmembrane VEGF receptors (VEGFRs). VEGF-A is the primary factor involved with angiogenesis; it binds to both VEGFR-1 and VEGFR-2. The inhibition of angiogenesis by obstructing VEGF-A signaling has been investigated as a method to treat solid tumors, but the development of resistance to this blockade has complicated treatment. The major mechanisms of this resistance to VEGF-A blockade include signaling by redundant receptors, such as the fibroblast growth factors, angiopoietin-1, ephrins, and other forms of VEGF. Other major mechanisms of resistance are increased metastasis of hypoxia-resistant tumor cells, recruitment of cell types capable of promoting VEGF-independent angiogenesis, and increased circulation of nontumor proangiogenic factors. Additional mechanisms of resistance to VEGF-A blockade include heterogeneity of responsiveness among tumor cells, use of anti-VEGF-A agents at insufficient doses or for insufficient duration, altered sensitivity to anti-VEGF-A agents by mutations in endothelial cells or vascular remodeling, maintenance of vascular sleeves that allow for easy regrowth of tumor vasculature upon discontinuation of therapy, vascular cooption, and intussusceptive angiogenesis. An understanding of these mechanisms may lead to the development of targeted therapies that overcome this resistance. Some of these approaches include the combined inhibition of redundant angiogenic pathways, proper patient selection for various therapies based on gene expression profiles, blockade of cellular migration by inhibition of colony-stimulating factor, or the use of agents to disrupt vascular architecture.

A history of the discovery of random x chromosome inactivation in the human female and its significance

Genetic determinants of sex in placental mammals developed by the evolution of primordial autosomes into the male and female sex chromosomes. The Y chromosome determines maleness by the action of the gene SRY, which encodes a protein that initiates a sequence of events prompting the embryonic gonads to develop into testes. The X chromosome in the absence of a Y chromosome results in a female by permitting the conversion of the embryonic gonads into ovaries. We trace the historical progress that resulted in the discovery that one X chromosome in the female is randomly inactivated in early embryogenesis, accomplishing approximate equivalency of X chromosome gene dosage in both sexes. This event results in half of the somatic cells in a tissue containing proteins encoded by the genes of the maternal X chromosome and half having proteins encoded by the genes of the paternal X chromosome, on average, accounting for the phenotype of a female heterozygote with an X chromosome mutation. The hypothesis of X chromosome inactivation as a random event early in embryogenesis was first described as a result of studies of variegated coat color in female mice. Similar results were found in women using the X chromosome-linked gene, glucose-6-phosphate dehydrogenase, studied in red cells. The random inactivation of the X chromosome-bearing genes for isoenzyme types A and B of glucose-6-phosphate dehydrogenase was used to establish the clonal origin of neoplasms in informative women with leiomyomas. Behind these discoveries are the stories of the men and women scientists whose research enlightened these aspects of X chromosome function and their implication for medicine.