Translational/personalized medicine, pharmaco/surgico/radiogenomics, lymphatic spread of cancer, and medical ignoromes

In the elusive quest for "personalized" cancer treatments based on pharmacogenomics, diverse challenges must be overcome: questionable validity of "molecular models of life," obstacles to bidirectional translation of scientific advances from bench to bedside to community, and limitations of bioinformatics to recognize and deal with "ignoramics/ignoromes" (expanding unknowns in cancer biology, theranostics, and therapeutic choices). These considerations apply to lymphatic system functioning-lymphatic vessels, lymph, lymph nodes, and lymphocytes-in diseases like cancer.

Lymphangiogenesis and hemangiogenesis: potential targets for therapy

This review updates historical background from century-old observations on embryonic lymphatic system development through current understanding of the molecular basis of lymphvasculogenesis/lymphangiogenesis ("molecular lymphology"), highlighting similarities and differences with analogous blood vasculature processes. Topics covered include molecular mechanisms in lymphatic development, structural adaptations of the lymphatic vasculature to particulate and cellular transport and trafficking, lymphogenous route of clinical cancer spread, preservation of delineated lymphatic pathways during cancer operations, and anti-lymphangiogenesis in cancer therapy.

Establishment of primary cultures of human brain microvascular endothelial cells to provide an in vitro cellular model of the blood-brain barrier

We describe a method for generating primary cultures of human brain microvascular endothelial cells (HBMVECs). HBMVECs are derived from microvessels isolated from temporal tissue removed during operative treatment of epilepsy. The tissue is mechanically fragmented and size filtered using polyester meshes. The resulting microvessel fragments are placed onto type I collagen-coated flasks to allow HBMVECs to migrate and proliferate. The overall process takes less than 3 h and does not require specialized equipment or enzymatic processes. HBMVECs are typically cultured for approximately 1 month until confluent. Cultures are highly pure ( approximately 97% endothelial cells; approximately 3% pericytes), are reproducible, and show characteristic brain endothelial markers (von Willebrand factor, glucose transporter-1) and robust expression of tight and adherens junction proteins as well as caveolin-1 and efflux protein P-glycoprotein. Monolayers of HBMVECs show characteristically high transendothelial electric resistance and have proven useful in multiple functional studies for in vitro modeling of the human blood-brain barrier.

Radioprotection from radiation-induced lymphedema without tumor protection

Lymphedema or tissue swelling from impaired lymph drainage commonly occurs after regional nodal dissection and/or radiation therapy for cancer control. Treatment options for this disabling and life-altering complication involve long-term labor-intensive commitments. Sentinel node biopsy can forestall removal of negative regional nodes, offering some protection against lymphedema, however, most preventive measures are elusive, ineffective, or unproven. Our goal was to determine whether the radioprotectant amifostine could prevent or retard the development of lymphedema in a rodent radiation therapy-dependent model yet not offer tumor protection from the therapeutic effects of radiation therapy. We pre-treated rats after unilateral radical groin dissection with the organic thiophosphate radioprotectant amifostine or placebo prior to single dose post-operative groin radiation therapy and monitored hindlimb volumes, wound scores, and tissue lymphostasis. In addition, we determined whether amifostine protected human MCF7 breast cancer cells exposed to a range of radiation therapy doses in an in vitro clonogenic assay and an in vivo MCF7 tumor xenograft model. Our findings indicate that amifostine markedly reduced the volume of limb lymphedema and dramatically improved wound healing and tissue lymphostasis in the rodent lymphedema model. The in vivo and in vitro studies further demonstrated that amifostine offered no MCF7 tumor protection from radiation therapy. These pre-clinical findings provide proof-of-principle to further delineate specific mechanisms underlying amifostine's beneficial effects, determine optimal amifostine-radiation therapy dosing regimens, and thereby expedite translation into clinical trials to reduce lymphedema incidence and severity in cancer patients at high lymphedema risk in whom radiation therapy is the recommended therapy.

Lymphedema-distichiasis syndrome without FOXC2 mutation: evidence for chromosome 16 duplication upstream of FOXC2

A patient with the classical phenotype of Lymphedema-Distichiasis syndrome (OMIM 153400) is described who showed no mutations in the sequence of FOXC2. Accordingly, a Gene Chip 250k array analysis was undertaken with dense SNP genotyping of the genomic region surrounding the FOXC2 locus on Chromosome 16 followed by copy number evaluation by real time PCR. The latter assay showed evidence of a duplicated region 5' of FOXC2 that could be causative for the patient's striking phenotype, which included both distichiasis and a hyperplastic refluxing lymphatic vascular and lymph node phenotype associated with pubertal onset lymphedema, scoliosis and strabismus.

Congenital lymphatic dysplasias: genetics review and resources for the lymphologist

Diagnosing congenital lymphatic dysplasia and counseling the parents of babies with possible genetic conditions represents a difficult task. This article attempts to provide a guide to establishing genetic tools and a reference library for use in the diagnostic work-up of congenital lymphatic diseases. The tools that are outlined herein are not meant to replace genetic counseling; their role is merely to facilitate the interaction between lymphologist and geneticist. These tools are a way of identifying lymphatic dysplasias at a very early stage.

"Ignoramics" in medical and premedical education

As physician-essayist Lewis Thomas has urged, ignorance-based courses and curricula are urgently needed in medical education to prepare future generations of scientific physicians and physician-scientists for the uncertain, rapidly changing world ahead. This article reviews the evolving concept of ignorance in general and specifically in medicine and its relationship to knowledge. Issues about goals, content, and assessment of such ignorance-based courses are discussed along with the experience of the University of Arizona's National Institutes of Health-sponsored Summer Institute on Medical Ignorance for medical student researchers and disadvantaged high school students. Summer Institute on Medical Ignorance activities can be readily replicated or adopted in their entirety or partially in both live and Internet-based formats. These will serve to introduce medical ignoramics and questioning as a way to balance the information-overloaded medical curriculum.

Lymphology, medical ignorance/ignoramics and the Nobel connection: Howard Florey, Joshua Lederberg, and Françoise Barre-Sinoussi

Intriguing interludes with Nobel laureates have marked the history of Lymphology. Bounded (or rather unbounded) by a mutual fascination with ignorance and the unknown, their curiosity converged around microbes, infections, and host responses mediated by the lymphatic system. These studies transcended a simple "molecular model of life".

Novel FOXC2 missense mutation identified in patient with lymphedema-distichiasis syndrome and review

Lymphedema-distichiasis (OMIM 153400) is a dominantly inherited disorder typically presenting with lymphedema at puberty and distichiasis at birth. The condition has been decisively linked to mutations in the forkhead transcription factor FOXC2 which have been primarily frameshift mutations truncating the protein. We report here a novel missense mutation along with a literature review summarizing reported mutations.

Chy-3mice areVegfchaploinsufficient and exhibit defective dermal superficial to deep lymphatic transition and dermal lymphatic hypoplasia

Recent advances in molecular lymphology and lymphatic phenotyping techniques in small animals offer new opportunities to delineate mutant mouse models. Chy-3 mutant mice were originally named for their chylous ascites, but the underlying lymphatic disorder was not defined. We now re-examined these mice and applied advanced genotyping and lymphatic phenotyping techniques to pinpoint the specific lymphatic defect in this mouse model. We demonstrated that Chy-3 mice carry a large chromosomal deletion that includes Vegfc and narrowed this region by monitoring the heterozygosity of genetic markers. We found that Chy-3 mice not only exhibited chylous ascites but also lymphedema of the hind paws and, in approximately half of the males, lymphedema of the penis. Visual lymphangiography and immunofluorescence staining showed a hypoplastic dermal lymphatic network, whereas the blood vasculature appeared unaffected. This hypoplastic lymphatic network was functional, and all adult Chy-3 mice exhibited a lateral lymphatic pathway directly connecting the inguinal to the axillary lymph node. The dermal superficial to deep lymphatic connections in upper limbs and in all cervical regions were intact and functionally drained the upper body. Lymphatic tracer was not transported from the dermal to the deep truncal lymphatic system in the lower limbs, even though the deep lymphatic vessels and nodes were present and patent. These findings further delineate the lymphatic phenotype of Chy-3 mice, identify a collateral lymph drainage pathway previously undescribed in other genetic models of lymphedema, and demonstrate a predilection for lymphatic abnormalities of the lower limbs.

Schlemm??s Canal Endothelia, Lymphatic, or Blood Vasculature?

In the human eye, the final barrier for aqueous humor to cross before returning to systemic circulation is the inner wall of Schlemm's canal. Unfortunately, the specific contribution of the inner wall to total outflow resistance in the conventional pathway is unknown in both normal and glaucomatous eyes. To better understand inner wall physiology, we contrasted it with 2 specialized continuous endothelia, initial lymphatic, and blood capillary endothelia. Specifically, we compare their developmental origin, morphology, junctional complexes, microenvironment, and physiologic responses to different biomechanical factors. Our evaluation concludes that the inner wall of Schlemm's canal is unique, sharing extraordinary characteristics with both types of specialized endothelia in addition to having distinctive features of its own.

Abnormal recruitment of periendothelial cells to lymphatic capillaries in digestive organs of angiopoietin-2-deficient mice

The fine structure of lymphatic capillaries in the digestive organs of angiopoietin-2 (Ang2) knockout mice was studied by using both immunohistochemistry and electron microscopy. The genetic deletion of Ang2 yielded hypoplasia and disorganization of the lymphatic capillaries, with their shapes being irregular, and an aberrant recruitment of vascular periendothelial cells immunopositive for smooth muscle actin to the lymphatic capillaries. The abnormal lymphatic periendothelial cells were considered to be a type of pericyte for the lymphatic capillaries after the deletion of Ang2, because they were ultrastructurally characterized by abundant thin myofilaments in their cytoplasm and long cytoplasmic extensions similar to those shown by blood vascular pericytes. The genetic replacement of Ang2 with Ang1 rescued the defects, viz., the disorganization and disordered structure of the lymphatic capillaries. The present findings suggest that Ang2 serves the morphogenesis of lymphatic capillaries as an agonist for the receptor, Tie2, and that Ang1 can replace Ang2 in guiding lymphatic formation and development.

Massive localized lipolymphedema pseudotumor in a morbidly obese patient

We describe a 31 year old man with a massive localized tumor-like lipolymphedema, a puzzling entity that afflicts the morbidly obese. The 281 kg man presented with a growing ulcerated bleeding mass located on his proximal medial thigh and suspicious for sarcoma. After en bloc resection of the 28.2 kg edematous mass, no evidence of neoplasm was found, only prominent lymphatic vessel dilation and edema with large quantities of unremarkable adipose and connective tissue. The lesion conformed to the diagnostic criteria for massive localized lipolymphedema (MLL) pseudotumor.

Structure function relationships in the lymphatic system and implications for cancer biology

The lymphatic system, composed of lymphatic vessels, lymph, lymph nodes, and lymphocytes, is a distinctive vasculature (discontinuous basement membrane, open endothelial junctions, anchoring filaments, valves, and intrinsic contractility), different yet similar to the blood vasculature; an integral component of the plasma-tissue fluid-lymph circulation (the "blood-lymph loop"); and the center of the immunoregulatory network. Lymphatics are involved in diverse developmental, growth, repair, and pathologic processes both analogous to and distinct from those affecting the blood vasculature. Interference with the blood-lymph loop produces swelling [an imbalance between lymph formation (regulated by Starling's law of transcapillary fluid exchange) and lymph absorption], scarring, nutritional and immunodysregulatory disorders, as well as disturbances in lymph(hem)angiogenesis (lymphedema-angiodysplasia syndromes). The lymphatic system is also the stage on which key events during cancer development and progression are played out, and historically, also forms the basis for current evaluation, prognostication, and/or both operative and non-operative treatment of most cancers. Recent advances in molecular lymphology (e.g., discovery of lymphatic growth factors, endothelial receptors, transcription factors, genes, and highly specific immunohistochemical markers) and growing interest in lymphangiogenesis, combined with fresh insights and refined tools in clinical lymphology, including non-invasive lymphatic imaging, are opening up a window for translation to the clinical arena. Therefore, in cancer biology, attention to the multifaceted structure-function relationships within this vast, relatively unexplored system is long overdue.

Comparative lymphatic, ocular, and metabolic phenotypes of Foxc2 haploinsufficient and aP2-FOXC2 transgenic mice

FOXC2 mutations cause the lymphatic/ocular disorder Lymphedema-Distichiasis (LD), and Foxc2 haploinsufficient mice mimic this disorder. To determine if FOXC2 overexpression might also cause lymphatic and/or ocular abnormalities, we performed dynamic lymphatic imaging (Evans blue dye), ocular tissue examination, and metabolic profiles in mice: transgenic for FOXC2 with an adipocyte (aP2) promoter (aP2-FOXC2 Tg), heterozygous for targeted disruption of Foxc2 (Foxc2+/-), or compound heterozygous and transgenic (Foxc2+/-, Tg) compared to wild-type controls (WT). Foxc2+/-; aP2-FOXC2 Tg; and Foxc2+/-, Tg, exhibited LD's distinctive hyperplastic lymphatic phenotype characterized by increased number of lymphatic channels and lymph nodes as well as retrograde lymph reflux. Foxc2+/-, and Foxc2+/-, Tg but not aP2-FOXC2 Tg or WT showed an abnormal ocular phenotype. Previously described alterations in brown/ white fat distribution and lean phenotype in aP2-FOXC2 transgenics were confirmed. AP2-FOXC2 Tg immunohistochemistry disclosed aberrant FOXC2 expression in ectopic sites, especially embryonic heart. Lymphatic system links with fat metabolism are discussed.

Lymphatic vascular defects promoted by Prox1 haploinsufficiency cause adult-onset obesity

Multiple organs cooperate to regulate appetite, metabolism, and glucose and fatty acid homeostasis. Here, we identified and characterized lymphatic vasculature dysfunction as a cause of adult-onset obesity. We found that functional inactivation of a single allele of the homeobox gene Prox1 led to adult-onset obesity due to abnormal lymph leakage from mispatterned and ruptured lymphatic vessels. Prox1 heterozygous mice are a new model for adult-onset obesity and lymphatic vascular disease.

Foxc2 is expressed in developing lymphatic vessels and other tissues associated with lymphedema–distichiasis syndrome

The molecular events involved in lymphatic development are poorly understood. Hence, the genes responsible for hereditary lymphedema are of great interest due to the potential for providing insights into the mechanisms of lymphatic development, the diagnosis, prevention and treatment of lymphedema, and lymphangiogenesis during tumor growth. Mutations in the FOXC2 transcription factor cause a major form of hereditary lymphedema, the lymphedema-distichiasis syndrome. We have conducted a study of Foxc2 expression during mouse development using immunohistochemistry, and examined its expression in lymphatics compared to its paralog Foxc1 and to Vegfr-3, Prox1 and other lymphatic and blood vascular proteins. We have found that Foxc2 is expressed in lymphatic primordia, jugular lymph sacs, lymphatic collectors and capillaries, as well as in podocytes, developing eyelids and other tissues associated with abnormalities in lymphedema-distichiasis syndrome.

Syndromic classification of hereditary lymphedema

Since the late 1800's, the familial occurrence of peripheral lymphedema has been well-documented in Milroy and Meige syndromes. However, the presence of lymphedema in many other hereditary dysmorphic syndromes has not been fully appreciated. In order to establish more standardized and detailed clinical phenotypic criteria as the basis for rational classification and for greater precision in screening and genetic linkage studies, we conducted a comprehensive literature search and review of OMIM-identified and non-identified hereditary syndromes in which lymphedema was reported as a feature. Modes of inheritance, associated clinical features and images, and specific organ involvement were inventoried and suggested pathophysiologic mechanisms noted. The findings support the recommendation that when peripheral lymphedema of undetermined etiology is found, further careful, comprehensive clinical, including detailed dysmorphic, evaluation along with lymphatic imaging with subsequent syndromic classification is warranted. This information can provide clues to underlying pathogenesis and form the basis for genetic counseling and prognostication as well as offer guidance to the clinical investigator translating research at the molecular level into new approaches for evaluation and therapy.

FOXC2 haploinsufficient mice are a model for human autosomal dominant lymphedema-distichiasis syndrome

Lymphedema-distichiasis (LD) (OMIM 153400) is a rare autosomal-dominant condition characterized by pubertal onset of lower limb lymphedema and an aberrant second row of eyelashes arising from the meibomian glands. In some patients cardiac, skeletal and other defects coexist. We previously identified inactivating, nonsense and frameshift mutations in the forkhead transcription factor FOXC2 in affected members of LD families. To further delineate the relationship of FOXC2 deficiency to the clinical (and lymphangiodysplastic) phenotype in this syndrome, we performed dynamic lymphatic imaging and immunohistochemical examination of lymphatic tissues in mice heterozygous (+/-) for a targeted disruption of Foxc2. Adult heterozygote mice characteristically exhibited a generalized lymphatic vessel and lymph node hyper plasia and rarely exhibited hindlimb swelling. Retrograde lymph flow through apparently incompetent interlymphangion valves into the mesenteric nodes, intestinal wall and liver was also observed. In addition, Foxc2 +/- mice uniformly displayed distichiasis. We conclude that Foxc2 haploinsufficient mice mimic closely the distinctive lymphatic and ocular phenotype of LD patients. Furthermore, the craniofacial, cardiovascular and skeletal abnormalities sometimes associated with LD have previously been shown to be fully penetrant in homozygous Foxc2 null mice. This Foxc2 mutant mouse thus provides an ideal model for exploring molecular mechanisms and physiologic events in mesenchymal differentiation associated with lymphatic growth and development and the clinical abnormalities seen in human LD syndrome.

Angiopoietin-2 is required for postnatal angiogenesis and lymphatic patterning, and only the latter role is rescued by Angiopoietin-1

VEGF and Angiopoietin-1 requisitely collaborate during blood vessel development. While Angiopoietin-1 obligately activates its Tie2 receptor, Angiopoietin-2 can activate Tie2 on some cells, while it blocks Tie2 activation on others. Our analysis of mice lacking Angiopoietin-2 reveals that Angiopoietin-2 is dispensable for embryonic vascular development but is requisite for subsequent angiogenic remodeling. Unexpectedly, mice lacking Angiopoietin-2 also exhibit major lymphatic vessel defects. Genetic rescue with Angiopoietin-1 corrects the lymphatic, but not the angiogenesis, defects, suggesting that Angiopoietin-2 acts as a Tie2 agonist in the former setting, but as an antagonist in the latter setting. Our studies define a vascular growth factor whose primary role is in postnatal angiogenic remodeling and also demonstrate that members of the VEGF and Angiopoietin families collaborate during development of the lymphatic vasculature.