Anti-brolucizumab immune response as one prerequisite for rare retinal vasculitis/retinal vascular occlusion adverse events.

In October 2019, Novartis launched brolucizumab, a single-chain variable fragment molecule targeting vascular endothelial growth factor A, for the treatment of neovascular age-related macular degeneration. In 2020, rare cases of retinal vasculitis and/or retinal vascular occlusion (RV/RO) were reported, often during the first few months after treatment initiation, consistent with a possible immunologic pathobiology. This finding was inconsistent with preclinical studies in cynomolgus monkeys that demonstrated no drug-related intraocular inflammation, or RV/RO, despite the presence of preexisting and treatment-emergent antidrug antibodies (ADAs) in some animals. In this study, the immune response against brolucizumab in humans was assessed using samples from clinical trials and clinical practice. In the brolucizumab-naïve population, anti-brolucizumab ADA responses were detected before any treatment, which was supported by the finding that healthy donors can harbor brolucizumab-specific B cells. This suggested prior exposure of the immune system to proteins with structural similarity. Experiments on samples showed that naïve and brolucizumab-treated ADA-positive patients developed a class-switched, high-affinity immune response, with several linear epitopes being recognized by ADAs. Only patients with RV/RO showed a meaningful T cell response upon recall with brolucizumab. Further studies in cynomolgus monkeys preimmunized against brolucizumab with adjuvant followed by intravitreal brolucizumab challenge demonstrated that high ADA titers were required to generate ocular inflammation and vasculitis/vascular thrombosis, comparable to RV/RO in humans. Immunogenicity therefore seems to be a prerequisite to develop RV/RO. However, because only 2.1% of patients with ADA develop RV/RO, additional factors must play a role in the development of RV/RO.

A root cause analysis to identify the mechanistic drivers of immunogenicity against the anti-VEGF biotherapeutic brolucizumab.

Immunogenicity against intravitreally administered brolucizumab has been previously described and associated with cases of severe intraocular inflammation, including retinal vasculitis/retinal vascular occlusion (RV/RO). The presence of antidrug antibodies (ADAs) in these patients led to the initial hypothesis that immune complexes could be key mediators. Although the formation of ADAs and immune complexes may be a prerequisite, other factors likely contribute to some patients having RV/RO, whereas the vast majority do not. To identify and characterize the mechanistic drivers underlying the immunogenicity of brolucizumab and the consequence of subsequent ADA-induced immune complex formation, a translational approach was performed to bridge physicochemical characterization, structural modeling, sequence analysis, immunological assays, and a quantitative systems pharmacology model that mimics physiological conditions within the eye. This approach revealed that multiple factors contributed to the increased immunogenic potential of brolucizumab, including a linear epitope shared with bacteria, non-natural surfaces due to the single-chain variable fragment format, and non-native drug species that may form over prolonged time in the eye. Consideration of intraocular drug pharmacology and disease state in a quantitative systems pharmacology model suggested that immune complexes could form at immunologically relevant concentrations modulated by dose intensity. Assays using circulating immune cells from treated patients or treatment-naïve healthy volunteers revealed the capacity of immune complexes to trigger cellular responses such as enhanced antigen presentation, platelet aggregation, endothelial cell activation, and cytokine release. Together, these studies informed a mechanistic understanding of the clinically observed immunogenicity of brolucizumab and associated cases of RV/RO.

TNF leads to mtDNA release and cGAS/STING-dependent interferon responses that support inflammatory arthritis.

Tumor necrosis factor (TNF) is a key driver of several inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease, and psoriasis, in which affected tissues show an interferon-stimulated gene signature. Here, we demonstrate that TNF triggers a type-I interferon response that is dependent on the cyclic guanosine monophosphate-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. We show that TNF inhibits PINK1-mediated mitophagy and leads to altered mitochondrial function and to an increase in cytosolic mtDNA levels. Using cGAS-chromatin immunoprecipitation (ChIP), we demonstrate that cytosolic mtDNA binds to cGAS after TNF treatment. Furthermore, TNF induces a cGAS-STING-dependent transcriptional response that mimics that of macrophages from rheumatoid arthritis patients. Finally, in an inflammatory arthritis mouse model, cGAS deficiency blocked interferon responses and reduced inflammatory cell infiltration and joint swelling. These findings elucidate a molecular mechanism linking TNF to type-I interferon signaling and suggest a potential benefit for therapeutic targeting of cGAS/STING in TNF-driven diseases.

Pharmacological Inhibition of MALT1 Protease Leads to a Progressive IPEX-Like Pathology.

Genetic disruption or short-term pharmacological inhibition of MALT1 protease is effective in several preclinical models of autoimmunity and B cell malignancies. Despite these protective effects, the severe reduction in regulatory T cells (Tregs) and the associated IPEX-like pathology occurring upon congenital disruption of the MALT1 protease in mice has raised concerns about the long-term safety of MALT1 inhibition. Here we describe the results of a series of toxicology studies in rat and dog species using MLT-943, a novel potent and selective MALT1 protease inhibitor. While MLT-943 effectively prevented T cell-dependent B cell immune responses and reduced joint inflammation in the collagen-induced arthritis rat pharmacology model, in both preclinical species, pharmacological inhibition of MALT1 was associated with a rapid and dose-dependent reduction in Tregs and resulted in the progressive appearance of immune abnormalities and clinical signs of an IPEX-like pathology. At the 13-week time point, rats displayed severe intestinal inflammation associated with mast cell activation, high serum IgE levels, systemic T cell activation and mononuclear cell infiltration in multiple tissues. Importantly, using thymectomized rats we demonstrated that MALT1 protease inhibition affects peripheral Treg frequency independently of effects on thymic Treg output and development. Our data confirm the therapeutic potential of MALT1 protease inhibitors but highlight the safety risks and challenges to consider before potential application of such inhibitors into the clinic.

Discovery of LOU064 (Remibrutinib), a Potent and Highly Selective Covalent Inhibitor of Bruton's Tyrosine Kinase.

Bruton's tyrosine kinase (BTK), a cytoplasmic tyrosine kinase, plays a central role in immunity and is considered an attractive target for treating autoimmune diseases. The use of currently marketed covalent BTK inhibitors is limited to oncology indications based on their suboptimal kinase selectivity. We describe the discovery and preclinical profile of LOU064 (remibrutinib, 25), a potent, highly selective covalent BTK inhibitor. LOU064 exhibits an exquisite kinase selectivity due to binding to an inactive conformation of BTK and has the potential for a best-in-class covalent BTK inhibitor for the treatment of autoimmune diseases. It demonstrates potent in vivo target occupancy with an EC90 of 1.6 mg/kg and dose-dependent efficacy in rat collagen-induced arthritis. LOU064 is currently being tested in phase 2 clinical studies for chronic spontaneous urticaria and Sjoegren's syndrome.

The NLRP3 inflammasome pathway is activated in sarcoidosis and involved in granuloma formation.

Sarcoidosis is a disease characterised by granuloma formation. There is an unmet need for new treatment strategies beyond corticosteroids. The NLRP3 inflammasome pathway is expressed in innate immune cells and senses danger signals to elicit inflammatory interleukin (IL)-1ß; it has recently become a druggable target. This prompted us to test the role of the NLRP3 inflammasome and IL-1ß pathway in granuloma formation and sarcoidosis.19 sarcoid patients and 19 healthy volunteers were recruited into this pilot study. NLRP3 inflammasome activity was measured in bronchoalveolar lavage (BAL) cells and lung and skin biopsies using immunohistochemistry, Western blot, reverse-transcriptase PCR and ELISA. For in vivo experiments we used the trehalose 6,6'-dimycolate-granuloma mouse model and evaluated lung granuloma burden in miR-223 knockout and NLRP3 knockout mice, as well as the treatment effects of MCC950 and anti-IL-1ß antibody therapy.We found strong upregulation of the NLRP3 inflammasome pathway, evidenced by expression of activated NLRP3 inflammasome components, including cleaved caspase-1 and IL-1ß in lung granuloma, and increased IL-1ß release of BAL cells from sarcoid patients compared to healthy volunteers (p=0.006). mRNA levels of miR-223, a micro-RNA downregulating NLRP3, were decreased and NLRP3 mRNA correspondingly increased in alveolar macrophages from sarcoid patients (p<0.005). NLRP3 knockout mice showed decreased and miR-223 knockout mice increased granuloma formation compared to wild-type mice. Pharmacological interference using NLRP3 pathway inhibitor MCC950 or an anti-IL-1ß antibody resulted in reduced granuloma formation (p<0.02).In conclusion, our data provide evidence of upregulated inflammasome and IL-1ß pathway activation in sarcoidosis and suggest both as valid therapeutic targets.

Requirement of Mucosa-Associated Lymphoid Tissue Lymphoma Translocation Protein 1 Protease Activity for Fcγ Receptor-Induced Arthritis, but Not Fcγ Receptor-Mediated Platelet Elimination, in Mice.

OBJECTIVE: Fcγ receptors (FcγR) play important roles in both protective and pathogenic immune responses. The assembly of the CBM signalosome encompassing caspase recruitment domain-containing protein 9, B cell CLL/lymphoma 10, and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT-1) is required for optimal FcγR-induced canonical NF-κB activation and proinflammatory cytokine release. This study was undertaken to clarify the relevance of MALT-1 protease activity in FcγR-driven events and evaluate the therapeutic potential of selective MALT-1 protease inhibitors in FcγR-mediated diseases. METHODS: Using genetic and pharmacologic disruption of MALT-1 scaffolding and enzymatic activity, we assessed the relevance of MALT-1 function in murine and human primary myeloid cells upon stimulation with immune complexes (ICs) and in murine models of autoantibody-driven arthritis and immune thrombocytopenic purpura (ITP). RESULTS: MALT-1 protease function is essential for optimal FcγR-induced production of proinflammatory cytokines by various murine and human myeloid cells stimulated with ICs. In contrast, MALT-1 protease inhibition did not affect the Syk-dependent, FcγR-mediated production of reactive oxygen species or leukotriene B4 . Notably, pharmacologic MALT-1 protease inhibition in vivo reduced joint inflammation in the murine K/BxN serum-induced arthritis model (mean area under the curve for paw swelling of 45.42% versus 100% in control mice; P = 0.0007) but did not affect platelet depletion in a passive model of ITP. CONCLUSION: Our findings indicate a specific contribution of MALT-1 protease activity to FcγR-mediated events and suggest that MALT-1 protease inhibitors have therapeutic potential in a subset of FcγR-driven inflammatory disorders.

GPR91 senses extracellular succinate released from inflammatory macrophages and exacerbates rheumatoid arthritis.

When SUCNR1/GPR91-expressing macrophages are activated by inflammatory signals, they change their metabolism and accumulate succinate. In this study, we show that during this activation, macrophages release succinate into the extracellular milieu. They simultaneously up-regulate GPR91, which functions as an autocrine and paracrine sensor for extracellular succinate to enhance IL-1ß production. GPR91-deficient mice lack this metabolic sensor and show reduced macrophage activation and production of IL-1ß during antigen-induced arthritis. Succinate is abundant in synovial fluids from rheumatoid arthritis (RA) patients, and these fluids elicit IL-1ß release from macrophages in a GPR91-dependent manner. Together, we reveal a GPR91/succinate-dependent feed-forward loop of macrophage activation and propose GPR91 antagonists as novel therapeutic principles to treat RA.

A Novel Potent Oral Series of VEGFR2 Inhibitors Abrogate Tumor Growth by Inhibiting Angiogenesis.

This paper describes the identification of 6-(pyrimidin-4-yloxy)-naphthalene-1-carboxamides as a new class of potent and selective human vascular endothelial growth factor receptor 2 (VEGFR2) tyrosine kinase inhibitors. In biochemical and cellular assays, the compounds exhibit single-digit nanomolar potency toward VEGFR2. Compounds of this series show good exposure in rodents when dosed orally. They potently inhibit VEGF-driven angiogenesis in a chamber model and rodent tumor models at daily doses of less than 3 mg/kg by targeting the tumor vasculature as demonstrated by ELISA for TIE-2 in lysates or by immunohistochemical analysis. This novel series of compounds shows a potential for the treatment of solid tumors and other diseases where angiogenesis plays an important role.

Contextual compound screening for improved therapeutic discovery.

Cellular behaviors are governed by combinations of systemic and microenvironmental factors; together, these regulate cell signaling responses to growth factors. This contextual microenvironmental influence also determines drug sensitivity. Hence using in vitro systems that model contextual cellular behavior is highly beneficial for effective therapeutic development. Angiogenesis (formation of blood vessels) is driven by a series of dynamic endothelial cell signaling responses to growth factors under the influence of the vascular extracellular matrix and adjacent pericytes. In vitro primary human vascular cell co-cultures self-assemble into capillary-like structures through reciprocal heterotypic interactions that mimic angiogenic context dynamics. By using temporal live-cell imaging-based analysis, unique angiogenic microenvironments can be delineated to quantify the contextual activity of compound inhibitors. We used this in vitro organotypic contextual screening approach to conduct structure-activity relationship analysis on a combretastatin A-4 analogue series to identify novel compounds with potent vascular disrupting activity in vivo.

The tyrosine kinase BMX is an essential mediator of inflammatory arthritis in a kinase-independent manner.

Inflammatory cytokines like TNF play a central role in autoimmune disorders such as rheumatoid arthritis. We identified the tyrosine kinase bone marrow kinase on chromosome X (BMX) as an essential component of a shared inflammatory signaling pathway. Transient depletion of BMX strongly reduced secretion of IL-8 in cell lines and primary human cells stimulated by TNF, IL-1ß, or TLR agonists. BMX was required for phosphorylation of p38 MAPK and JNK, as well as activation of NF-κB. The following epistasis analysis indicated that BMX acts downstream of or at the same level as the complex TGF-ß activated kinase 1 (TAK1)-TAK1 binding protein. At the cellular level, regulation of the IL-8 promoter required the pleckstrin homology domain of BMX, which could be replaced by an ectopic myristylation signal, indicating a requirement for BMX membrane association. In addition, activation of the IL-8 promoter by in vitro BMX overexpression required its catalytic activity. Genetic ablation of BMX conferred protection in the mouse arthritis model of passive K/BxN serum transfer, confirming that BMX is an essential mediator of inflammation in vivo. However, genetic replacement with a catalytically inactive BMX allele was not protective in the same arthritis animal model. We conclude that BMX is an essential component of inflammatory cytokine signaling and that catalytic, as well as noncatalytic functions of BMX are involved.

Everolimus and PTK/ZK show synergistic growth inhibition in the orthotopic BL16/BL6 murine melanoma model.

PURPOSE: Everolimus (RAD001, Afinitor) is an mTORC1 pathway inhibitor, and vatalanib (PTK/ZK) is a pan VEGF-R tyrosine kinase inhibitor (TKI). These two drugs have been shown to have overlapping but also distinct anti-angiogenic effects. Consequently, we investigated the pharmacokinetics (PK) and pharmacodynamics (PD) of their combination in vivo. METHODS: Murine melanoma B16/BL6 cells were grown orthotopically in BL6/C57 mice by injection into the derma of both ears to create a primary tumour which metastasized rapidly to the cervical lymph nodes. Mice were treated daily p.o. with PTK/ZK (100 mg/kg) or everolimus (1 mg/kg) or their combination, and anti-tumour efficacy (PD) assessed. In the same model, plasma PK of everolimus was measured following single doses of the monotherapy or combination schedules. RESULTS: Two independent experiments showed that combination of everolimus and PTK/ZK caused at least additive increases in anti-tumour activity compared to either monotherapy, without increases in toxicity. Pooling the data to improve the statistical power demonstrated the interactions to be synergistic. PK modelling showed that although PTK/ZK increased everolimus plasma concentrations by about twofold, this PK drug-drug interaction could not account for the increased anti-tumour effect of the combination. Modelling of the PTK/ZK dose-response curve in this model suggested that any effect of everolimus on the PK of PTK/ZK was unlikely to affect efficacy. Measurement of changes in tumour and plasma VEGF levels at the endpoint of therapy confirmed earlier observations of differential effects of these two agents. CONCLUSIONS: The combination of everolimus and PTK/ZK hold promise for the treatment of human cancers.

Angiogenesis is present in experimental autoimmune encephalomyelitis and pro-angiogenic factors are increased in multiple sclerosis lesions.

BACKGROUND: Angiogenesis is a common finding in chronic inflammatory diseases; however, its role in multiple sclerosis (MS) is unclear. Central nervous system lesions from both MS and experimental autoimmune encephalomyelitis (EAE), the animal model of MS, contain T cells, macrophages and activated glia, which can produce pro-angiogenic factors. Previous EAE studies have demonstrated an increase in blood vessels, but differences between the different phases of disease have not been reported. Therefore we examined angiogenic promoting factors in MS and EAE lesions to determine if there were changes in blood vessel density at different stages of EAE. METHODS: In this series of experiments we used a combination of vascular casting, VEGF ELISA and immunohistochemistry to examine angiogenesis in experimental autoimmune encephalomyelitis (EAE). Using immunohistochemistry we also examined chronic active MS lesions for angiogenic factors. RESULTS: Vascular casting and histological examination of the spinal cord and brain of rats with EAE demonstrated that the density of patent blood vessels increased in the lumbar spinal cord during the relapse phase of the disease (p < 0.05). We found an increased expression of VEGF by inflammatory cells and a decrease in the recently described angiogenesis inhibitor meteorin. Examination of chronic active human MS tissues demonstrated glial expression of VEGF and glial and blood vessel expression of the pro-angiogenic receptor VEGFR2. There was a decreased expression of VEGFR1 in the lesions compared to normal white matter. CONCLUSIONS: These findings reveal that angiogenesis is intimately involved in the progression of EAE and may have a role in MS.

Biological evidence for dual antiangiogenic-antiaromatase activity of the VEGFR inhibitor PTK787/ZK222584 in vivo.

PURPOSE: Targeting vascular endothelial growth factor (VEGF) and estrogen receptor signaling pathways concomitantly may enhance benefit in estrogen receptor-positive breast cancer. We had shown previously that the VEGF receptor tyrosine kinase inhibitor PTK787/ZK222584 (PTK/ZK) is a competitive aromatase inhibitor in vitro. Here we investigated (a) whether PTK/ZK shows both antiangiogenic and antiaromatase inhibitory properties in vivo, and (b) whether the combination of PTK/ZK and letrozole is superior to letrozole alone. EXPERIMENTAL DESIGN: Estrogen-dependent human breast cancer cells engineered to express aromatase (MCF7 AROM 1 and BT474 AROM) were used. Mice were treated with vehicle, PTK/ZK (25, 50, or 100 mg/kg), letrozole, or PTK/ZK in combination with letrozole. RESULTS: In MCF7 AROM 1 tumors, all treatments induced growth suppression and were associated with a reduction in cell turnover index, a composite measurement of both proliferation and apoptosis. PTK/ZK significantly reduced vessel density. Whereas letrozole caused tumor regression, PTK/ZK stabilized tumor volumes. The growth suppressive and antiangiogenic effects of PTK/ZK were confirmed in BT474 AROM xenografts. The addition of PTK/ZK did not enhance the growth-suppressive effects of letrozole. However, PTK/ZK decreased progesterone receptor (PgR) and TFF1 expression and uterine weight, indicating that PTK/ZK decreases 17beta-estradiol (E2) signaling in vivo. CONCLUSION: The VEGF receptor inhibitor PTK/ZK showed effects on E2-dependent gene expression consistent with aromatase inhibition as well as antiangiogenesis in xenograft models of breast cancer. The combination with letrozole was not superior to letrozole alone. Overall, these results provide further support for a potential therapeutic approach of dual inhibition of VEGF and E2 signaling using a single agent.

In vivo and in vitro SAR of tetracyclic MAPKAP-K2 (MK2) inhibitors. Part II.

Spirocyclopropane- and spiroazetidine-substituted tetracycles 13D-E and 16A are described as orally active MK2 inhibitors. The spiroazetidine derivatives are potent MK2 inhibitors with IC(50)<3 nM and inhibit the release of TNFalpha (IC(50)<0.3 microM) from hPBMCs and hsp27 phosphorylation in anisomycin stimulated THP-1 cells. The spirocyclopropane analogues are less potent against MK2 (IC(50)=0.05-0.23 microM), less potent in cells (IC(50)<1.1 microM), but show good oral absorption. Compound 13E (100mg/kg po; bid) showed oral activity in rAIA and mCIA, with significant reduction of swelling and histological score.

Mural cell associated VEGF is required for organotypic vessel formation.

BACKGROUND: Blood vessels comprise endothelial cells, mural cells (pericytes/vascular smooth muscle cells) and basement membrane. During angiogenesis, mural cells are recruited to sprouting endothelial cells and define a stabilizing context, comprising cell-cell contacts, secreted growth factors and extracellular matrix components, that drives vessel maturation and resistance to anti-angiogenic therapeutics. METHODS AND FINDINGS: To better understand the basis for mural cell regulation of angiogenesis, we conducted high content imaging analysis on a microtiter plate format in vitro organotypic blood vessel system comprising primary human endothelial cells co-cultured with primary human mural cells. We show that endothelial cells co-cultured with mural cells undergo an extensive series of phenotypic changes reflective of several facets of blood vessel formation and maturation: Loss of cell proliferation, pathfinding-like cell migration, branching morphogenesis, basement membrane extracellular matrix protein deposition, lumen formation, anastamosis and development of a stabilized capillary-like network. This phenotypic sequence required endothelial-mural cell-cell contact, mural cell-derived VEGF and endothelial VEGFR2 signaling. Inhibiting formation of adherens junctions or basement membrane structures abrogated network formation. Notably, inhibition of mural cell VEGF expression could not be rescued by exogenous VEGF. CONCLUSIONS: These results suggest a unique role for mural cell-associated VEGF in driving vessel formation and maturation.

mTOR inhibitor RAD001 (everolimus) has antiangiogenic/vascular properties distinct from a VEGFR tyrosine kinase inhibitor.

PURPOSE: Comparison of the antiangiogenic/vascular properties of the oral mammalian target of rapamycin (mTOR) inhibitor RAD001 (everolimus) and the vascular endothelial growth factor receptor (VEGFR) inhibitor vatalanib (PTK/ZK). EXPERIMENTAL DESIGN: Antiproliferative activity against various tumor histotypes and downstream effects on the mTOR pathway were measured in vitro. In vivo, antitumor activity, plasma, and tumor RAD001 levels were measured. Activity in several different angiogenic/vascular assays in vitro and in vivo was assessed and compared with PTK/ZK. RESULTS: RAD001 inhibited proliferation in vitro (IC50 values<1 nmol/L to >1 micromol/L), and in sensitive and insensitive tumor cells, pS6 kinase and 4E-BP1 were inhibited. Activity in vitro did not correlate with activity in vivo and significant responses were seen in tumors with IC50 values>10-fold higher than tumor RAD001 concentrations. In vitro, RAD001 inhibited the proliferation of VEGF-stimulated and fibroblast growth factor-stimulated human endothelial cells but not dermal fibroblasts and impaired VEGF release from both sensitive and insensitive tumor cells but did not inhibit migration of human endothelial cells. In vivo, in tumor models derived from either sensitive or insensitive cells, RAD001 reduced Tie-2 levels, the amount of mature and immature vessels, total plasma, and tumor VEGF. RAD001 did not affect blood vessel leakiness in normal vasculature acutely exposed to VEGF nor did it affect tumor vascular permeability (Ktrans) as measured by dynamic contrast-enhanced magnetic resonance imaging. However, the pan-VEGFR inhibitor PTK/ZK inhibited endothelial cell migration and vascular permeability but had less effect on mature vessels compared with RAD001. CONCLUSIONS: VEGFR and mTOR inhibitors show similar but also distinct effects on tumor vascular biology, which has implications for their clinical activity alone or in combination.

Differential effects of the vascular endothelial growth factor receptor inhibitor PTK787/ZK222584 on tumor angiogenesis and tumor lymphangiogenesis.

Halting tumor growth by interfering with tumor-induced angiogenesis is an attractive therapeutic approach. Such treatments include humanized antibodies blocking the activity of vascular endothelial growth factor (VEGF)-A (bevacizumab), soluble VEGF receptor (VEGFR) constructs (VEGF-Trap), or small-molecule inhibitors of VEGFR signaling, including PTK787/ZK222584 (PTK/ZK), sorafenib, and sunitinib. PTK/ZK has been shown previously to specifically block VEGF-induced phosphorylation of VEGFR-1, -2 and -3 and thereby to inhibit endothelial cell proliferation, differentiation, and tumor angiogenesis. We have investigated the effect of PTK/ZK on tumor angiogenesis and tumor lymphangiogenesis using the Rip1Tag2 transgenic mouse model of pancreatic beta cell carcinogenesis. In Rip1Tag2 mice, tumor angiogenesis is predominantly mediated by VEGF-A, and as expected, PTK/ZK efficiently impaired tumor blood vessel angiogenesis and tumor growth. Double-transgenic Rip1Tag2;Rip1VEGF-C and Rip1Tag2;Rip1VEGF-D mice not only exhibit VEGF-A-dependent blood vessel angiogenesis but also tumor lymphangiogenesis induced by the transgenic expression of VEGF-C or -D. In these mouse models, PTK/ZK also repressed tumor blood vessel angiogenesis and tumor growth yet failed to affect tumor lymphangiogenesis and lymphogenic metastasis. Adenoviral delivery of soluble VEGFR-3 also did not prevent tumor lymphangiogenesis in these mice. In contrast, spontaneous tumor lymphangiogenesis, as observed by the stochastic expression of VEGF-C and -D in tumors of neural cell adhesion molecule-deficient Rip1Tag2 mice, was repressed by PTK/ZK and soluble VEGFR-3. The results indicate that the time of onset and the levels of VEGF-C/D expression may be critical variables in efficiently repressing tumor lymphangiogenesis and that pathways other than VEGFR signaling may be involved in tumor lymphangiogenesis.

Effects of the dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 on the tumor vasculature: implications for clinical imaging.

Dysregulated angiogenesis and high tumor vasculature permeability, two vascular endothelial growth factor (VEGF)-mediated processes and hallmarks of human tumors, are in part phosphatidylinositol 3-kinase (PI3K) dependent. NVP-BEZ235, a dual PI3K/mammalian target of rapamycin (mTOR) inhibitor, was found to potently inhibit VEGF-induced cell proliferation and survival in vitro and VEGF-induced angiogenesis in vivo as shown with s.c. VEGF-impregnated agar chambers. Moreover, the compound strongly inhibited microvessel permeability both in normal tissue and in BN472 mammary carcinoma grown orthotopically in syngeneic rats. Similarly, tumor interstitial fluid pressure, a phenomenon that is also dependent of tumor permeability, was significantly reduced by NVP-BEZ235 in a dose-dependent manner on p.o. administration. Because RAD001, a specific mTOR allosteric inhibitor, was ineffective in the preceding experiments, we concluded that the effects observed for NVP-BEZ235 are in part driven by PI3K target modulation. Hence, tumor vasculature reduction was correlated with full blockade of endothelial nitric oxide (NO) synthase, a PI3K/Akt-dependent but mTORC1-independent effector involved in tumor permeability through NO production. In the BN472 tumor model, early reduction of permeability, as detected by K(trans) quantification using the dynamic contrast-enhanced magnetic resonance imaging contrasting agent P792 (Vistarem), was found to be a predictive marker for late-stage antitumor activity by NVP-BEZ235.

Inhibition of multiple vascular endothelial growth factor receptors (VEGFR) blocks lymph node metastases but inhibition of VEGFR-2 is sufficient to sensitize tumor cells to platinum-based chemotherapeutics.

Vascular endothelial growth factor receptors (VEGFR) have important roles in cancer, affecting blood and lymphatic vessel functionality as well as tumor cells themselves. We compared the efficacy of a VEGFR tyrosine kinase inhibitor, PTK787/ZK222584 (PTK/ZK), which targets the three VEGFRs, with blocking antibodies directed against VEGFR-2 (DC101) or VEGF-A (Pab85618) in a metastatic melanoma model. Although all inhibitors exerted comparable effects on primary tumor growth, only PTK/ZK significantly reduced lymph node metastasis formation. A comparable decrease in lymphatic vessel density following blockade of VEGFR-2 (DC101) or the three VEGFRs (PTK/ZK) was observed in the metastases. However, the functionality of lymphatics surrounding the primary tumor was more significantly disrupted by PTK/ZK, indicating the importance of multiple VEGFRs in the metastatic process. The antimetastatic properties of PTK/ZK were confirmed in a breast carcinoma model. B16/BL6 tumor cells express VEGF ligands and their receptors. Blockade of a VEGFR-1 autocrine loop with PTK/ZK inhibited tumor cell migration. Furthermore, the tumor cells also showed enhanced sensitivity to platinum-based chemotherapy in combination with PTK/ZK, indicating that autocrine VEGFRs are promoting tumor cell migration and survival. In summary, our results suggest that, in addition to blocking angiogenesis, combined inhibition of the three VEGFRs may more efficiently target other aspects of tumor pathophysiology, including lymphatic vessel functionality, tumor cell dissemination, survival pathways, and response to chemotherapeutic compounds.