Incidence and outcomes of post-transplant lymphoproliferative disease after 5365 solid-organ transplants over a 20-year period at two UK transplant centres.

Post-transplant lymphoproliferative disease (PTLD) is a life-threatening complication of solid-organ transplantation (SOT). We present the incidence and outcomes of PTLD in a cohort of 5365 SOT recipients over a 20-year period at two UK transplant centres. With a median follow-up of 7.7 years, 142 of 5365 patients have developed PTLD. Cumulative incidence was 18% at five years after multivisceral transplant and 1%-3% at five years following the other SOT types. Twenty-year cumulative incidence was 2%-3% following liver and heart transplantation and 10% following kidney transplantation. Median overall survival (OS) following SOT was 16 years, which is significantly reduced compared with the age-adjusted UK population. There is relatively high early mortality following diagnosis of PTLD and only patients surviving two years regained a longer-term survival approaching the non-PTLD SOT cohort. Of 90 patients with monomorphic PTLD, diffuse large B-cell lymphoma, 66 were treated with first-line rituximab monotherapy and 24 received first-line rituximab plus chemotherapy. Up-front rituximab monotherapy does not appear to compromise OS, but the number of patients dying from non-lymphoma causes before and after treatment remains high with both treatment approaches. Multivariate analysis of all 90 monomorphic PTLD patients identified an International Prognostic Index (IPI) of 3+ as the strongest pretreatment variable associating with inferior one-year OS.

Textural equilibrium melt geometries around tetrakaidecahedral grains.

In textural equilibrium, partially molten materials minimize the total surface energy bound up in grain boundaries and grain-melt interfaces. Here, numerical calculations of such textural equilibrium geometries are presented for a space-filling tessellation of grains with a tetrakaidecahedral (truncated octahedral) unit cell. Two parameters determine the nature of the geometries: the porosity and the dihedral angle. A variety of distinct melt topologies occur for different combinations of these two parameters, and the boundaries between different topologies have been determined. For small dihedral angles, wetting of grain boundaries occurs once the porosity has exceeded 11%. An exhaustive account is given of the main properties of the geometries: their energy, pressure, mean curvature, contiguity and areas on cross sections and faces. Their effective permeabilities have been calculated, and demonstrate a transition between a quadratic variation with porosity at low porosities to a cubic variation at high porosities.

Antibody drug conjugates of cleavable amino-alkyl and aryl maytansinoids.

Natural products have been used for many medicinal purposes for centuries. Antibody drug conjugates (ADCs) have utilized this rich source of small molecule therapeutics to produce several clinically useful treatments. ADCs based on the natural product maytansine have been successful clinically. The authors further the utility of the anti-cancer natural product maytansine by developing efficacious payloads and linker-payloads for conjugating to antibodies. The success of our approach was realized in the EGFRvIII targeting ADC EGFRvIII-16. The ADC was able to regress tumors in 2 tumor models (U251/EGFRvIII and MMT/EGFRvIII). When compared to a positive control ADC, the efficacy observed was similar or improved while the isotype control ADCs had no effect.

Angiopoietins bind thrombomodulin and inhibit its function as a thrombin cofactor.

Angiopoietin-1 (Ang1) and Angiopoietin-2 (Ang2) are ligands for Tie2, an endothelial-specific receptor tyrosine kinase that is an essential regulator of angiogenesis. Here we report the identification, via expression cloning, of thrombomodulin (TM) as another receptor for Ang1 and Ang2. Thrombomodulin is an endothelial cell surface molecule that plays an essential role as a coagulation inhibitor via its function as a cofactor in the thrombin-mediated activation of protein C, an anticoagulant protein, as well as thrombin-activatable fibrinolysis inhibitor (TAFI). Ang1 and Ang2 inhibited the thrombin/TM-mediated generation of activated protein C and TAFI in cultured endothelial cells, and inhibited the binding of thrombin to TM in vitro. Ang2 appears to bind TM with higher affinity than Ang1 and is a more potent inhibitor of TM function. Consistent with a potential role for angiopoietins in coagulation, administration of thrombin to mice rapidly increased plasma Ang1 levels, presumably reflecting release from activated platelets (previously shown to contain high levels of Ang1). In addition, Ang1 levels were significantly elevated in plasma prepared from wound blood, suggesting that Ang1 is released from activated platelets at sites of vessel injury. Our results imply a previously undescribed role for angiopoietins in the regulation of hemostasis.

The Melting Column as a Filter of Mantle Trace-Element Heterogeneity.

The observed variability of trace-element concentration in basaltic lavas and melt inclusions carries information about heterogeneity in the mantle. The difficulty is to disentangle the contributions of source heterogeneity (i.e., spatial variability of mantle composition before melting) and process heterogeneity (i.e., spatial and temporal variability in melt transport). Here we investigate the end-member hypothesis that variability arises due to source heterogeneity alone. We model the attenuation of trace-element variability introduced into the bottom of a one-dimensional, steady-state melting column. Our results show that the melting column can be considered to be a filter that attenuates variability according to the wavelength of heterogeneity, the partition coefficient of the trace element, melt productivity, and the efficiency of melt segregation. We further show that while the model can be fit to the observations, this requires assumptions inconsistent with constraints on the timescales of magma assembly. Hence, we falsify the end-member hypothesis and, instead, conclude that observed variability requires heterogeneity of melt transport. This might take the form of channels or waves and would almost certainly interact with source heterogeneity.

Resistance to Anti-VEGF Therapy Mediated by Autocrine IL6/STAT3 Signaling and Overcome by IL6 Blockade.

Anti-VEGF therapies benefit several cancer types, but drug resistance that limits therapeutic response can emerge. We generated cell lines from anti-VEGF-resistant tumor xenografts to investigate the mechanisms by which resistance develops. Of all tumor cells tested, only A431 (A431-V) epidermoid carcinoma cells developed partial resistance to the VEGF inhibitor aflibercept. Compared with the parental tumors, A431-V tumors secreted greater amounts of IL6 and exhibited higher levels of phospho-STAT3. Notably, combined blockade of IL6 receptor (IL6R) and VEGF resulted in enhanced activity against A431-V tumors. Similarly, inhibition of IL6R enhanced the antitumor effects of aflibercept in DU145 prostate tumor cells that displays high endogenous IL6R activity. In addition, post hoc stratification of data obtained from a clinical trial investigating aflibercept efficacy in ovarian cancer showed poorer survival in patients with high levels of circulating IL6. These results suggest that the activation of the IL6/STAT3 pathway in tumor cells may provide a survival advantage during anti-VEGF treatment, suggesting its utility as a source of response biomarkers and as a therapeutic target to heighten efficacious results. Cancer Res; 76(8); 2327-39. ©2016 AACR.

ERBB3/HER2 signaling promotes resistance to EGFR blockade in head and neck and colorectal cancer models.

EGFR blocking antibodies are approved for the treatment of colorectal cancer and head and neck squamous cell carcinoma (HNSCC). Although ERBB3 signaling has been proposed to limit the effectiveness of EGFR inhibitors, the underlying molecular mechanisms are not fully understood. To gain insight into these mechanisms, we generated potent blocking antibodies against ERBB3 (REGN1400) and EGFR (REGN955). We show that EGFR and ERBB3 are coactivated in multiple HNSCC cell lines and that combined blockade of EGFR and ERBB3 inhibits growth of these cell lines more effectively than blockade of either receptor alone. Blockade of EGFR with REGN955 strongly inhibited activation of ERK in HNSCC cell lines, whereas blockade of ERBB3 with REGN1400 strongly inhibited activation of Akt; only the combination of the 2 antibodies blocked both of these essential downstream pathways. We used a HER2 blocking antibody to show that ERBB3 phosphorylation in HNSCC and colorectal cancer cells is strictly dependent on association with HER2, but not EGFR, and that neuregulin 1 activates ERBB3/HER2 signaling to reverse the effect of EGFR blockade on colorectal cancer cell growth. Finally, although REGN1400 and REGN955 as single agents slowed the growth of HNSCC and colorectal cancer xenografts, the combination of REGN1400 plus REGN955 caused significant tumor regression. Our results indicate that activation of the Akt survival pathway by ERBB3/HER2 limits the effectiveness of EGFR inhibition, suggesting that REGN1400, which is currently in a phase I clinical trial, could provide benefit when combined with EGFR blocking antibodies.

Inhibition of delta-like ligand 4 induces luteal hypervascularization followed by functional and structural luteolysis in the primate ovary.

Using specific inhibitors established that angiogenesis in the ovarian follicle and corpus luteum is driven by vascular endothelial growth factor. Recently, it has been demonstrated that the Notch ligand, delta-like ligand 4 (Dll4) negatively regulates vascular endothelial growth factor-mediated vessel sprouting and branching. To investigate the role of Dll4 in regulation of the ovarian vasculature, we administered a neutralizing antibody to Dll4 to marmosets at the periovulatory period. The vasculature was examined on luteal d 3 or d 10: angiogenesis was determined by incorporation of bromodeoxyuridine, staining for CD31 and cell death by staining for activated caspase-3. Ovulatory progesterone rises were monitored to determine effects of treatment on luteal function and time to recover normal cycles in a separate group of animals. Additionally, animals were treated in the follicular or midluteal phase to determine effects of Dll4 inhibition on follicular development and luteal function. Controls were treated with human IgG (Fc). Corpora lutea from marmosets treated during the periovulatory period exhibited increased angiogenesis and increased vascular density on luteal d 3, but plasma progesterone was significantly suppressed. By luteal d 10, corpora lutea in treated ovaries were significantly reduced in size, with involution of luteal cells, increased cell death, and suppressed plasma progesterone concentrations. In contrast, initiation of anti-Dll4 treatment during the midluteal phase produced only a slight suppression of progesterone for the remainder of the cycle. Moreover, Dll4 inhibition had no appreciable effect on follicular development. These results show that Dll4 has a specific and critical role in the development of the normal luteal vasculature.

DCE and DW-MRI monitoring of vascular disruption following VEGF-Trap treatment of a rat glioma model.

Vascular-targeted therapies have shown promise as adjuvant cancer treatment. As these agents undergo clinical evaluation, sensitive imaging biomarkers are needed to assess drug target interaction and treatment response. In this study, dynamic contrast enhanced MRI (DCE-MRI) and diffusion-weighted MRI (DW-MRI) were evaluated for detecting response of intracerebral 9 L gliosarcomas to the antivascular agent VEGF-Trap, a fusion protein designed to bind all forms of Vascular Endothelial Growth Factor-A (VEGF-A) and Placental Growth Factor (PGF). Rats with 9 L tumors were treated twice weekly for two weeks with vehicle or VEGF-Trap. DCE- and DW-MRI were performed one day prior to treatment initiation and one day following each administered dose. Kinetic parameters (K(trans), volume transfer constant; k(ep), efflux rate constant from extravascular/extracellular space to plasma; and v(p), blood plasma volume fraction) and the apparent diffusion coefficient (ADC) over the tumor volumes were compared between groups. A significant decrease in kinetic parameters was observed 24 hours following the first dose of VEGF-Trap in treated versus control animals (p < 0.05) and was accompanied by a decline in ADC values. In addition to the significant hemodynamic effect, VEGF-Trap treated animals exhibited significantly longer tumor doubling times (p < 0.05) compared to the controls. Histological findings were found to support imaging response metrics. In conclusion, kinetic MRI parameters and change in ADC have been found to serve as sensitive and early biomarkers of VEGF-Trap anti-vascular targeted therapy.

Angiopoietin-1/Tie-2 activation contributes to vascular survival and tumor growth during VEGF blockade.

Approval of the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab by the FDA in 2004 reflected the success of this vascular targeting strategy in extending survival in patients with advanced cancers. However, consistent with previous reports that experimental tumors can grow or recur during VEGF blockade, it has become clear that many patients treated with VEGF inhibitors will ultimately develop progressive disease. Previous studies have shown that disruption of VEGF signaling in tumors induces remodeling in surviving vessels, and link increased expression of angiopoietin-1 (Ang-1) with this process. However, overexpression of Ang-1 in different tumors has yielded divergent results, restricting angiogenesis in some systems while promoting it in others. These data raise the possibility that effects of Ang-1/Tie-2 may be context-dependent. Expression of an Ang-1 construct (Ang1*) did not significantly change tumor growth in our model prior to treatment, although vessels exhibited changes consistent with increased Tie-2 signaling. During inhibition of VEGF, however, both overexpression of Ang1* and administration of an engineered Ang-1 agonist (Bow-Ang1) strikingly protected tumors and vasculature from regression. In this context, Ang-1/Tie-2 activation limited tumor hypoxia, increased vessel caliber, and promoted recruitment of mural cells. Thus, these studies support a model in which activation of Tie-2 is important for tumor and vessel survival when VEGF-dependent vasculature is stressed. Understanding such mechanisms of adaptation to this validated form of therapy may be important in designing regimens that make the best use of this approach.

Angiopoietin-1 therapy enhances fibrosis and inflammation following folic acid-induced acute renal injury.

The loss of interstitial capillaries is a feature of several experimental models of renal disease and this contributes to secondary kidney injury. Angiopoietin-1 is a secreted growth factor which binds to Tie-2 present on endothelia to enhance cell survival thereby stabilizing capillary architecture in-vitro. Previous studies showed that angiopoietin-1 prevented renal capillary and interstitial lesions following experimental ureteric obstruction. We tested here the effect of angiopoietin-1 treatment on capillary loss and associated tubulointerstitial damage known to follow recovery from folic acid-induced tubular necrosis and acute renal injury. We found that delivery of angiopoietin-1 by adenoviral vectors stabilized peritubular capillaries in folic acid nephropathy but this was accompanied by profibrotic and inflammatory effects. These results suggest that the use of endothelial growth factor therapy for kidney disease may have varying outcomes that depend on the disease model tested.

Sustained VEGF blockade results in microenvironmental sequestration of VEGF by tumors and persistent VEGF receptor-2 activation.

Vascular endothelial growth factor (VEGF) blockade has been validated clinically as a treatment for human cancers, yet virtually all patients eventually develop progressive disease during therapy. In order to dissect this phenomenon, we examined the effect of sustained VEGF blockade in a model of advanced pediatric cancer. Treatment of late-stage hepatoblastoma xenografts resulted in the initial collapse of the vasculature and significant tumor regression. However, during sustained treatment, vessels recovered, concurrent with a striking increase in tumor expression of perlecan, a heparan sulfate proteoglycan. Whereas VEGF mRNA was expressed at the periphery of surviving clusters of tumor cells, both secreted VEGF and perlecan accumulated circumferential to central vessels. Vascular expression of heparanase, VEGF receptor-2 ligand binding, and receptor activation were concurrently maintained despite circulating unbound VEGF Trap. Endothelial survival signaling via Akt persisted. These findings provide a novel mechanism for vascular survival during sustained VEGF blockade and indicate a role for extracellular matrix molecules that sequester and release biologically active VEGF.

VEGF Trap complex formation measures production rates of VEGF, providing a biomarker for predicting efficacious angiogenic blockade.

VEGF is the best characterized mediator of tumor angiogenesis. Anti-VEGF agents have recently demonstrated impressive efficacy in human cancer trials, but the optimal dosing of such agents must still be determined empirically, because biomarkers to guide dosing have yet to be established. The widely accepted (but unverified) assumption that VEGF production is quite low in normal adults led to the notion that increased systemic VEGF levels might quantitatively reflect tumor mass and angiogenic activity. We describe an approach to determine host and tumor production of VEGF, using a high-affinity and long-lived VEGF antagonist now in clinical trials, the VEGF Trap. Unlike antibody complexes that are usually rapidly cleared, the VEGF Trap forms inert complexes with tissue- and tumor-derived VEGF that remain stably in the systemic circulation, where they are readily assayable, providing unprecedented capability to accurately measure VEGF production. We report that VEGF production is surprisingly high in non-tumor-bearing rodents and humans, challenging the notion that systemic VEGF levels can serve as a sensitive surrogate for tumor load; tumor VEGF contribution becomes significant only with very large tumor loads. These findings have the important corollary that anti-VEGF therapies must be sufficiently dosed to avoid diversion by host-derived VEGF. We further show that our assay can indicate when VEGF is optimally blocked; such biomarkers to guide dosing do not exist for other anti-VEGF agents. Based on this assay, VEGF Trap doses currently being assessed in clinical trials are in the efficacious range.

Dexamethasone treatment and ICAM-1 deficiency impair VEGF-induced angiogenesis in adult brain.

BACKGROUND: Infusion of exogenous vascular endothelial growth factor (VEGF) into adult brain at doses above 60 ng/day induces dramatic angiogenesis accompanied by vascular leak and inflammation. Blood vessels formed by this treatment are dilated and tortuous, exhibiting a pathological morphology. Pathological VEGF-induced angiogenesis is preceded by vascular leak and inflammation, which have been proposed to mediate subsequent angiogenesis. METHODS: To test this hypothesis, we infused VEGF into the brains of adult rats to induce pathological angiogenesis. Some of these rats were treated with dexamethasone, a potent anti-inflammatory glucocorticoid, to inhibit inflammation and edema. RESULTS: We demonstrate that inhibition of inflammation by treatment with dexamethasone significantly attenuated VEGF-induced pathological angiogenesis. To present converging evidence that inflammation may be important in this angiogenic process, we also demonstrate that mice genetically deficient in the inflammatory mediator intercellular adhesion molecule-1 have attenuated VEGF-induced angiogenesis. These same mice showed normal amounts of physiological angiogenesis in response to enriched environments, however, suggesting that a generalized reduction in vascular plasticity could not account for their poor angiogenic response to VEGF. CONCLUSIONS: Taken together, the data from these experiments suggest that the inflammation which occurs before or during VEGF-induced pathological brain angiogenesis plays a contributory role in the pathological angiogenic process.

Angiopoietin-2 functions as an autocrine protective factor in stressed endothelial cells.

Angiopoietin (Ang)-2, a context-dependent agonist/antagonist for the vascular-specific Tie2 receptor, is highly expressed by endothelial cells at sites of normal and pathologic angiogenesis. One prevailing model suggests that in these settings, Ang-2 acts as an autocrine Tie2 blocker, inhibiting the stabilizing influence of the Tie2 activator Ang-1, thereby promoting vascular remodeling. However, the effects of endogenous Ang-2 on cells that are actively producing it have not been studied in detail. Here, we demonstrate that Ang-2 expression is rapidly induced in endothelial cells by the transcription factor FOXO1 after inhibition of the phosphatidylinositol 3-kinase/Akt pathway. We employ RNAi and blocking antibodies to show that in this setting, Ang-2 unexpectedly functions as a Tie2 agonist, bolstering Akt activity so as to provide negative feedback on FOXO1-regulated transcription and apoptosis. In addition, we show that Ang-2, like Ang-1, activates Tie2/Akt signaling in vivo, thereby inhibiting the expression of FOXO1 target genes. Consistent with a role for Ang-2 as a Tie2 activator, we demonstrate that Ang-2 inhibits vascular leak. Our data suggests a model in which Ang-2 expression is induced in stressed endothelial cells, where it acts as an autocrine Tie2 agonist and protective factor.

Administration of vascular endothelial growth factor Trap during the 'post-angiogenic' period of the luteal phase causes rapid functional luteolysis and selective endothelial cell death in the marmoset.

The intense angiogenesis characteristic of early corpus luteum development is dependent upon vascular endothelial growth factor (VEGF) as inhibitors of VEGF administered at the peri-ovulatory period suppress endothelial cell proliferation and progesterone secretion. We now report that administration of VEGF Trap, a soluble decoy receptor-based inhibitor, at the mid- or the late luteal phase in the marmoset results in a rapid decline in plasma progesterone. Since vascularisation of the corpus luteum is largely complete by the mid-luteal phase, it suggested that this functional luteolysis involved mechanisms other than inhibition of angiogenesis. A second experiment investigated the role of VEGF in maintaining the integrity of the luteal vasculature and hormone-producing cells. VEGF Trap was administered to marmosets in the mid-luteal phase and ovaries were obtained 1, 2, 4 or 8 days later for localisation of activated caspase-3 staining in the corpus luteum and compared with those obtained 2, 4 and 8 days after administration of control protein. The number of cells with activated caspase-3 staining was significantly increased after administration of VEGF Trap. Dual staining of activated caspase-3 with the endothelial cell marker CD31 showed that at 1 day post-treatment, more than 90% caspase-3-stained cells were vascular endothelium, prior to detection of an increasing incidence in death of hormone-producing cells on days 2 and 4. Staining with CD31 showed that the endothelial cell area was decreased after treatment. By 8 days after treatment, corpora lutea had regressed to varying degrees, while all control corpora lutea remained healthy. These results show that VEGF inhibition in the mid- or the late luteal phase induces functional luteolysis in the marmoset that is associated with premature and selective death of endothelial cells.

VEGF trap abolishes shear stress- and overload-dependent angiogenesis in skeletal muscle.

OBJECTIVE: To determine which elements of the angiogenic process are controlled by VEGF under physiological conditions. METHODS: VEGF Trap was administered at 10 mg x kg(-1) by subcutaneous injection twice weekly to mice, which were subject to one of two established angiogenic stimuli: (1) increasing blood flow by administration of prazosin (50 mg L(-1)); (2) muscle overload by extirpation of a synergist. Angiogenesis was determined by calculating capillary to fiber ratio (C:F), and proliferating cell nuclear antigen (PCNA) staining localized to capillaries or the interstitium used to measure cell proliferation. Characteristic ultrastructural changes were quantified using electron microscopy. RESULTS: Administration of VEGF Trap abolished the increases in C:F seen in both models, and prevented growth of luminal filopodia and large vacuole formation. Overload-induced proliferation associated with capillaries was reduced, along with endothelial cell number abluminal sprouts and basement membrane breakage. However, interstitial proliferation remained high, along with the increased capillary association of pericytes and fibroblasts. CONCLUSIONS: VEGF is required for both models of angiogenesis, although some morphological changes lie upstream, or are independent of, VEGF involvement. The abolition of angiogenesis in a model unaffected by NO inhibition shows that NO is not required for all VEGF-dependent angiogenesis in vivo.

VEGF modulates erythropoiesis through regulation of adult hepatic erythropoietin synthesis.

Vascular endothelial growth factor (VEGF) exerts crucial functions during pathological angiogenesis and normal physiology. We observed increased hematocrit (60-75%) after high-grade inhibition of VEGF by diverse methods, including adenoviral expression of soluble VEGF receptor (VEGFR) ectodomains, recombinant VEGF Trap protein and the VEGFR2-selective antibody DC101. Increased production of red blood cells (erythrocytosis) occurred in both mouse and primate models, and was associated with near-complete neutralization of VEGF corneal micropocket angiogenesis. High-grade inhibition of VEGF induced hepatic synthesis of erythropoietin (Epo, encoded by Epo) >40-fold through a HIF-1alpha-independent mechanism, in parallel with suppression of renal Epo mRNA. Studies using hepatocyte-specific deletion of the Vegfa gene and hepatocyte-endothelial cell cocultures indicated that blockade of VEGF induced hepatic Epo by interfering with homeostatic VEGFR2-dependent paracrine signaling involving interactions between hepatocytes and endothelial cells. These data indicate that VEGF is a previously unsuspected negative regulator of hepatic Epo synthesis and erythropoiesis and suggest that levels of Epo and erythrocytosis could represent noninvasive surrogate markers for stringent blockade of VEGF in vivo.

Angiopoietin 1 causes vessel enlargement, without angiogenic sprouting, during a critical developmental period.

Early in development, endothelial cells proliferate, coalesce, and sprout to form a primitive plexus of undifferentiated microvessels. Subsequently, this plexus remodels into a hierarchical network of different-sized vessels. Although the processes of proliferation and sprouting are well studied and are dependent on the angiogenic growth factor VEGF, the factors involved in subsequent vessel remodeling are poorly understood. Here, we show that angiopoietin 1 can induce circumferential vessel enlargement, specifically on the venous side of the circulation. This action is due to the ability of angiopoietin 1 to promote endothelial cell proliferation in the absence of angiogenic sprouting; vessel growth without sprouting has not been ascribed to other vascular growth factors, nor has specificity for a particular segment of the vasculature. Moreover, angiopoietin 1 potently mediates widespread vessel enlargement only during a brief postnatal period, in particular, prior to the fourth postnatal week, corresponding to stages in which VEGF inhibition causes widespread vessel regression. These findings show that angiopoietin 1 has a potentially unique role among the vascular growth factors by acting to enlarge blood vessels without inducing sprouting, and also define a critical window of vascular plasticity in neonatal development. Finding the key molecular factors that regulate this plasticity may prove crucial to the further development of pro- and anti-angiogenic therapies.