[Show abstract][Hide abstract] ABSTRACT: Tuberculosis (TB) causes almost 2 million deaths annually, and an increasing number of patients are resistant to existing therapies. Patients who have TB require lengthy chemotherapy, possibly because of poor penetration of antibiotics into granulomas where the bacilli reside. Granulomas are morphologically similar to solid cancerous tumors in that they contain hypoxic microenvironments and can be highly fibrotic. Here, we show that TB-infected rabbits have impaired small molecule distribution into these disease sites due to a functionally abnormal vasculature, with a low-molecular-weight tracer accumulating only in peripheral regions of granulomatous lesions. Granuloma-associated vessels are morphologically and spatially heterogeneous, with poor vessel pericyte coverage in both human and experimental rabbit TB granulomas. Moreover, we found enhanced VEGF expression in both species. In tumors, antiangiogenic, specifically anti-VEGF, treatments can "normalize" their vasculature, reducing hypoxia and creating a window of opportunity for concurrent chemotherapy; thus, we investigated vessel normalization in rabbit TB granulomas. Treatment of TB-infected rabbits with the anti-VEGF antibody bevacizumab significantly decreased the total number of vessels while normalizing those vessels that remained. As a result, hypoxic fractions of these granulomas were reduced and small molecule tracer delivery was increased. These findings demonstrate that bevacizumab treatment promotes vascular normalization, improves small molecule delivery, and decreases hypoxia in TB granulomas, thereby providing a potential avenue to improve delivery and efficacy of current treatment regimens.
Proceedings of the National Academy of Sciences 01/2015; 112(6). DOI:10.1073/pnas.1424563112 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multiplexed, phenotypic, intravital cytometric imaging requires novel fluorophore conjugates that have an appropriate size for long circulation and diffusion and show virtually no nonspecific binding to cells/serum while binding to cells of interest with high specificity. In addition, these conjugates must be stable and maintain a high quantum yield in the in vivo environments. Here, we show that this can be achieved using compact (∼15 nm in hydrodynamic diameter) and biocompatible quantum dot (QD) -Ab conjugates. We developed these conjugates by coupling whole mAbs to QDs coated with norbornene-displaying polyimidazole ligands using tetrazine-norbornene cycloaddition. Our QD immunoconstructs were used for in vivo single-cell labeling in bone marrow. The intravital imaging studies using a chronic calvarial bone window showed that our QD-Ab conjugates diffuse into the entire bone marrow and efficiently label single cells belonging to rare populations of hematopoietic stem and progenitor cells (Sca1(+)c-Kit(+) cells). This in vivo cytometric technique may be useful in a wide range of structural and functional imaging to study the interactions between cells and between a cell and its environment in intact and diseased tissues.
Proceedings of the National Academy of Sciences 01/2014; DOI:10.1073/pnas.1421632111 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Efficient generation of competent vasculogenic cells is a critical challenge of human induced pluripotent stem (hiPS) cell-based regenerative medicine. Biologically relevant systems to assess functionality of the engineered vessels in vivo are equally important for such development. Here, we report a unique approach for the derivation of endothelial precursor cells from hiPS cells using a triple combination of selection markers-CD34, neuropilin 1, and human kinase insert domain-containing receptor-and an efficient 2D culture system for hiPS cell-derived endothelial precursor cell expansion. With these methods, we successfully generated endothelial cells (ECs) from hiPS cells obtained from healthy donors and formed stable functional blood vessels in vivo, lasting for 280 d in mice. In addition, we developed an approach to generate mesenchymal precursor cells (MPCs) from hiPS cells in parallel. Moreover, we successfully generated functional blood vessels in vivo using these ECs and MPCs derived from the same hiPS cell line. These data provide proof of the principle that autologous hiPS cell-derived vascular precursors can be used for in vivo applications, once safety and immunological issues of hiPS-based cellular therapy have been resolved. Additionally, the durability of hiPS-derived blood vessels in vivo demonstrates a potential translation of this approach in long-term vascularization for tissue engineering and treatment of vascular diseases. Of note, we have also successfully generated ECs and MPCs from type 1 diabetic patient-derived hiPS cell lines and use them to generate blood vessels in vivo, which is an important milestone toward clinical translation of this approach.
Proceedings of the National Academy of Sciences 07/2013; 110(31). DOI:10.1073/pnas.1310675110 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Medulloblastoma is the most common pediatric malignant brain tumor. Although current therapies improve survival, these regimens are highly toxic and are associated with significant morbidity. Here, we report that placental growth factor (PlGF) is expressed in the majority of medulloblastomas, independent of their subtype. Moreover, high expression of PlGF receptor neuropilin 1 (Nrp1) correlates with poor overall survival in patients. We demonstrate that PlGF and Nrp1 are required for the growth and spread of medulloblastoma: PlGF/Nrp1 blockade results in direct antitumor effects in vivo, resulting in medulloblastoma regression, decreased metastasis, and increased mouse survival. We reveal that PlGF is produced in the cerebellar stroma via tumor-derived Sonic hedgehog (Shh) and show that PlGF acts through Nrp1-and not vascular endothelial growth factor receptor 1-to promote tumor cell survival. This critical tumor-stroma interaction-mediated by Shh, PlGF, and Nrp1 across medulloblastoma subtypes-supports the development of therapies targeting PlGF/Nrp1 pathway.
[Show abstract][Hide abstract] ABSTRACT: The recent approval of a prostate cancer vaccine has renewed hope for anticancer immunotherapies. However, the immunosuppressive
tumor microenvironment may limit the effectiveness of current immunotherapies. Antiangiogenic agents have the potential to
modulate the tumor microenvironment and improve immunotherapy, but they often are used at high doses in the clinic to prune
tumor vessels and paradoxically may compromise various therapies. Here, we demonstrate that targeting tumor vasculature with
lower vascular-normalizing doses, but not high antivascular/antiangiogenic doses, of an anti-VEGF receptor 2 (VEGFR2) antibody
results in a more homogeneous distribution of functional tumor vessels. Furthermore, lower doses are superior to the high
doses in polarizing tumor-associated macrophages from an immune inhibitory M2-like phenotype toward an immune stimulatory
M1-like phenotype and in facilitating CD4+ and CD8+ T-cell tumor infiltration. Based on this mechanism, scheduling lower-dose anti-VEGFR2 therapy with T-cell activation induced
by a whole cancer cell vaccine therapy enhanced anticancer efficacy in a CD8+ T-cell–dependent manner in both immune-tolerant and immunogenic murine breast cancer models. These findings indicate that
vascular-normalizing lower doses of anti-VEGFR2 antibody can reprogram the tumor microenvironment away from immunosuppression
toward potentiation of cancer vaccine therapies. Given that the combinations of high doses of bevacizumab with chemotherapy
have not improved overall survival of breast cancer patients, our study suggests a strategy to use antiangiogenic agents in
breast cancer more effectively with active immunotherapy and potentially other anticancer therapies.
Proceedings of the National Academy of Sciences 10/2012; 109(43):17561-17566. DOI:10.1073/pnas.1215397109 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Brain metastases are a serious obstacle in the treatment of patients with human epidermal growth factor receptor-2 (HER2)-amplified breast cancer. Although extracranial disease is controlled with HER2 inhibitors in the majority of patients, brain metastases often develop. Because these brain metastases do not respond to therapy, they are frequently the reason for treatment failure. We developed a mouse model of HER2-amplified breast cancer brain metastasis using an orthotopic xenograft of BT474 cells. As seen in patients, the HER2 inhibitors trastuzumab and lapatinib controlled tumor progression in the breast but failed to contain tumor growth in the brain. We observed that the combination of a HER2 inhibitor with an anti-VEGF receptor-2 (VEGFR2) antibody significantly slows tumor growth in the brain, resulting in a striking survival benefit. This benefit appears largely due to an enhanced antiangiogenic effect: Combination therapy reduced both the total and functional microvascular density in the brain xenografts. In addition, the combination therapy led to a marked increase in necrosis of the brain lesions. Moreover, we observed even better antitumor activity after combining both trastuzumab and lapatinib with the anti-VEGFR2 antibody. This triple-drug combination prolonged the median overall survival fivefold compared with the control-treated group and twofold compared with either two-drug regimen. These findings support the clinical development of this three-drug regimen for the treatment of HER2-amplified breast cancer brain metastases.
Proceedings of the National Academy of Sciences 10/2012; 72(24 Supplement). DOI:10.1073/pnas.1216078109 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The blood vessels of cancerous tumours are leaky and poorly organized. This can increase the interstitial fluid pressure inside tumours and reduce blood supply to them, which impairs drug delivery. Anti-angiogenic therapies--which 'normalize' the abnormal blood vessels in tumours by making them less leaky--have been shown to improve the delivery and effectiveness of chemotherapeutics with low molecular weights, but it remains unclear whether normalizing tumour vessels can improve the delivery of nanomedicines. Here, we show that repairing the abnormal vessels in mammary tumours, by blocking vascular endothelial growth factor receptor-2, improves the delivery of smaller nanoparticles (diameter, 12 nm) while hindering the delivery of larger nanoparticles (diameter, 125 nm). Using a mathematical model, we show that reducing the sizes of pores in the walls of vessels through normalization decreases the interstitial fluid pressure in tumours, thus allowing small nanoparticles to enter them more rapidly. However, increased steric and hydrodynamic hindrances, also associated with smaller pores, make it more difficult for large nanoparticles to enter tumours. Our results further suggest that smaller (∼12 nm) nanomedicines are ideal for cancer therapy due to their superior tumour penetration.
[Show abstract][Hide abstract] ABSTRACT: Unlike platelet-derived growth factor-B (PDGF-B), the role of PDGF-D in tumor progression or treatment is largely unknown. To this end, we determined the role of PDGF-D in breast cancer progression, metastasis, and response to chemotherapy.
We first examined PDGF-D expression in human breast carcinomas by immunohistochemical (IHC) staining. To mimic high PDGF-D expressing tumors, we stably transfected the breast cancer cell lines MDA-MB-231 and 4T1 with pdgf-d cDNA, and implanted these tumor cells orthtopically into nude mice. We monitored tumor growth by caliper measurement and bioluminescence imaging. We also used short hairpin RNA interference (shRNAi) and imatinib to block PDGF-D/PDGFRβ signaling. Finally, we studied the effect of PDGF-D on doxorubicin delivery and efficacy.
Human breast cancers express high levels of PDGF-D. Overexpression of PDGF-D promoted tumor growth and lymph node metastasis through increased proliferation, decreased apoptosis, and induction of CXCR4 expression. Blockade of CXCR4 signaling abolished PDGF-D-induced lymph node metastasis. Furthermore, overexpression of PDGF-D increased perivascular cell coverage and normalized tumor blood vessels. As a result, PDGF-D overexpression facilitated tissue penetration of doxorubicin and enhanced its treatment efficacy.
PDGF-D is highly expressed in human breast cancer and facilitates tumor growth and lymph node metastasis, making it a potential target in breast cancer. At the same time, PDGF-D increases drug delivery and hence improves the efficacy of chemotherapy through vessel normalization. Therefore, judicious use of PDGF-D/PDGFRβ blockers would be necessary to minimize the adverse effects on concomitantly administered cytotoxic therapies.
Clinical Cancer Research 04/2011; 17(11):3638-48. DOI:10.1158/1078-0432.CCR-10-2456 · 8.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: MRI biomarkers of tumor edema, vascular permeability, blood volume, and average vessel caliber are increasingly being employed to assess the efficacy of tumor therapies. However, the dependence of these biomarkers on a number of physiological factors can compromise their sensitivity and complicate the assessment of therapeutic efficacy. Here we examine the response of these MRI tumor biomarkers to cediranib, a potent vascular endothelial growth factor receptor (VEGFR) inhibitor, in an orthotopic mouse glioma model. A significant increase in the tumor volume and relative vessel caliber index (rVCI) and a slight decrease in the water apparent diffusion coefficient (ADC) were observed for both control and cediranib treated animals. This contrasts with a clinical study that observed a significant decrease in tumor rVCI, ADC and volume with cediranib therapy. While the lack of a difference between control and cediranib treated animals in these biomarker responses might suggest that cediranib has no therapeutic benefit, cediranib treated mice had a significantly increased survival. The increased survival benefit of cediranib treated animals is consistent with the significant decrease observed for cediranib treated animals in the relative cerebral blood volume (rCBV), relative microvascular blood volume (rMBV), transverse relaxation time (T2), blood vessel permeability (K(trans)), and extravascular-extracellular space (ν(e)). The differential response of pre-clinical and clinical tumors to cediranib therapy, along with the lack of a positive response for some biomarkers, indicates the importance of evaluating the whole spectrum of different tumor biomarkers to properly assess the therapeutic response and identify and interpret the therapy-induced changes in the tumor physiology.
PLoS ONE 03/2011; 6(3):e17228. DOI:10.1371/journal.pone.0017228 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Primary tumors secrete factors that alter the microenvironment of distant organs, rendering those organs as fertile soil for subsequent metastatic cancer cell colonization. Although the lungs are exposed to these factors ubiquitously, lung metastases usually develop as a series of discrete lesions. The underlining molecular mechanisms of the formation of these discrete lesions are not understood. Here we show that primary tumors induce formation of discrete foci of vascular hyperpermeability in premetastatic lungs. This is mediated by endothelial cell-focal adhesion kinase (FAK), which up-regulates E-selectin, leading to preferential homing of metastatic cancer cells to these foci. Suppression of endothelial-FAK or E-selectin activity attenuates the number of cancer cells homing to these foci. Thus, localized activation of endothelial FAK and E-selectin in the lung vasculature mediates the initial homing of metastatic cancer cells to specific foci in the lungs.
Proceedings of the National Academy of Sciences 02/2011; 108(9):3725-30. DOI:10.1073/pnas.1100446108 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Delivery of blood-borne molecules and nanoparticles from the vasculature to cells in the tissue differs dramatically between tumor and normal tissues due to differences in their vascular architectures. Here we show that two simple measures of vascular geometry--δ(max) and λ--readily obtained from vascular images, capture these differences and link vascular structure to delivery in both tissue types. The longest time needed to bring materials to their destination scales with the square of δ(max), the maximum distance in the tissue from the nearest blood vessel, whereas λ, a measure of the shape of the spaces between vessels, determines the rate of delivery for shorter times. Our results are useful for evaluating how new therapeutic agents that inhibit or stimulate vascular growth alter the functional efficiency of the vasculature and more broadly for analysis of diffusion in irregularly shaped domains.
Proceedings of the National Academy of Sciences 02/2011; 108(5):1799-803. DOI:10.1073/pnas.1018154108 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recurrent glioblastomas (rGBM) invariably relapse after initial response to anti-VEGF therapy. There are 2 prevailing hypotheses on how these tumors escape antiangiogenic therapy: switch to VEGF-independent angiogenic pathways and vessel co-option. However, direct evidence in rGBM patients is lacking. Thus, we compared molecular, cellular, and vascular parameters in autopsy tissues from 5 rGBM patients who had been treated with the pan-VEGF receptor tyrosine kinase inhibitor cediranib versus 7 patients who received no therapy or chemoradiation but no antiangiogenic agents. After cediranib treatment, endothelial proliferation and glomeruloid vessels were decreased, and vessel diameters and perimeters were reduced to levels comparable to the unaffected contralateral brain hemisphere. In addition, tumor endothelial cells expressed molecular markers specific to the blood-brain barrier, indicative of a lack of revascularization despite the discontinuation of therapy. Surprisingly, in cediranib-treated GBM, cellular density in the central area of the tumor was lower than in control cases and gradually decreased toward the infiltrating edge, indicative of a change in growth pattern of rGBMs after cediranib treatment, unlike that after chemoradiation. Finally, cediranib-treated GBMs showed high levels of PDGF-C (platelet-derived growth factor C) and c-Met expression and infiltration by myeloid cells, which may potentially contribute to resistance to anti-VEGF therapy. In summary, we show that rGBMs switch their growth pattern after anti-VEGF therapy--characterized by lower tumor cellularity in the central area, decreased pseudopalisading necrosis, and blood vessels with normal molecular expression and morphology--without a second wave of angiogenesis.
Cancer Research 01/2011; 71(1):19-28. DOI:10.1158/0008-5472.CAN-10-2602 · 9.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Not all tumor vessels are equal. Tumor-associated vasculature includes immature vessels, regressing vessels, transport vessels undergoing arteriogenesis and peritumor vessels influenced by tumor growth factors. Current techniques for analyzing tumor blood flow do not discriminate between vessel subtypes and only measure average changes from a population of dissimilar vessels. We developed methodologies for simultaneously quantifying blood flow (velocity, flux, hematocrit and shear rate) in extended networks at single-capillary resolution in vivo. Our approach relies on deconvolution of signals produced by labeled red blood cells as they move relative to the scanning laser of a confocal or multiphoton microscope and provides fully resolved three-dimensional flow profiles within vessel networks. Using this methodology, we show that blood velocity profiles are asymmetric near intussusceptive tissue structures in tumors in mice. Furthermore, we show that subpopulations of vessels, classified by functional parameters, exist in and around a tumor and in normal brain tissue.
[Show abstract][Hide abstract] ABSTRACT: In brain tumors, cerebral edema is a significant source of morbidity and mortality. Recent studies have shown that inhibition of vascular endothelial growth factor (VEGF) signaling induces transient vascular normalization and reduces cerebral edema, resulting in a modest survival benefit in glioblastoma patients. During anti-VEGF treatment, circulating levels of angiopoietin (Ang)-2 remained high after an initial minor reduction. It is not known, however, whether Ang-2 can modulate anti-VEGF treatment of glioblastoma. Here, we used an orthotopic glioma model to test the hypothesis that Ang-2 is an additional target for improving the efficacy of current anti-VEGF therapies in glioma patients.
To recapitulate high levels of Ang-2 in glioblastoma patients during anti-VEGF treatment, Ang-2 was ectopically expressed in U87 glioma cells. Animal survival and tumor growth were assessed to determine the effects of Ang-2 and anti-VEGF receptor 2 (VEGFR2) treatment. We also monitored morphologic and functional vascular changes using multiphoton laser scanning microscopy and immunohistochemistry.
Ectopic expression of Ang-2 had no effect on vascular permeability, tumor growth, or survival, although it resulted in higher vascular density, with dilated vessels and reduced mural cell coverage. On the other hand, when combined with anti-VEGFR2 treatment, Ang-2 destabilized vessels without affecting vessel regression and compromised the survival benefit of VEGFR2 inhibition by increasing vascular permeability. VEGFR2 inhibition normalized tumor vasculature whereas ectopic expression of Ang-2 diminished the beneficial effects of VEGFR2 blockade by inhibiting vessel normalization.
Cancer treatment regimens combining anti-VEGF and anti-Ang-2 agents may be an effective strategy to improve the efficacy of current anti-VEGF therapies.
Clinical Cancer Research 07/2010; 16(14):3618-27. DOI:10.1158/1078-0432.CCR-09-3073 · 8.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tumor neovascularization and growth might be promoted by the recruitment of bone marrow-derived cells (BMDC), which include endothelial precursor cells and "vascular modulatory" myelomonocytic (CD11b+) cells. BMDCs may also drive tumor regrowth after certain chemotherapeutic and vascular disruption treatments. In this study, we evaluated the role of BMDC recruitment in breast and lung carcinoma xenograft models after local irradiation (LI). We depleted the bone marrow by including whole-body irradiation (WBI) of 6 Gy as part of a total tumor dose of 21 Gy, and compared the growth delay with the one achieved after LI of 21 Gy. In both models, the inclusion of WBI induced longer tumor growth delays. Moreover, WBI increased lung tumor control probability by LI. Exogenous delivery of BMDCs from radiation-naïve donors partially abrogated the WBI effect. Myeloid BMDCs, primarily macrophages, rapidly accumulated in tumors after LI. Intratumoral expression of stromal-derived factor 1alpha (SDF-1alpha), a chemokine that promotes tissue retention of BMDCs, was noted 2 days after LI. Conversely, treatment with an inhibitor of SDF-1alpha receptor CXCR4 (AMD3100) with LI significantly delayed tumor regrowth. However, when administered starting from 5 days post-LI, AMD3100 treatment was ineffective. Lastly, with restorative bone marrow transplantation of Tie2-GFP-labeled BMDC population, we observed an increased number of monocytes but not endothelial precursor cells in tumors that recurred following LI. Our results suggest that an increase in intratumoral SDF-1alpha triggered by LI recruits myelomonocytes/macrophages which promotes tumor regrowth.
Cancer Research 07/2010; 70(14):5679-85. DOI:10.1158/0008-5472.CAN-09-4446 · 9.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Patients with bilateral vestibular schwannomas associated with neurofibromatosis type 2 (NF2) experience significant morbidity such as complete hearing loss. We have recently shown that treatment with bevacizumab provided tumor stabilization and hearing recovery in a subset of NF2 patients with progressive disease. In the current study, we used two animal models to identify the mechanism of action of anti-vascular endothelial growth factor (VEGF) therapy in schwannomas. The human HEI193 and murine Nf2(-/-) cell lines were implanted between the pia and arachnoid meninges as well as in the sciatic nerve to mimic central and peripheral schwannomas. Mice were treated with bevacizumab (10 mg/kg/wk i.v.) or vandetanib (50 mg/kg/d orally) to block the VEGF pathway. Using intravital and confocal microscopy, together with whole-body imaging, we measured tumor growth delay, survival rate, as well as blood vessel structure and function at regular intervals. In both models, tumor vessel diameter, length/surface area density, and permeability were significantly reduced after treatment. After 2 weeks of treatment, necrosis in HEI193 tumors and apoptosis in Nf2(-/-) tumors were significantly increased, and the tumor growth rate decreased by an average of 50%. The survival of mice bearing intracranial schwannomas was extended by at least 50%. This study shows that anti-VEGF therapy normalizes the vasculature of schwannoma xenografts in nude mice and successfully controls the tumor growth, probably by reestablishing a natural balance between VEGF and semaphorin 3 signaling.
Cancer Research 05/2010; 70(9):3483-93. DOI:10.1158/0008-5472.CAN-09-3107 · 9.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The vessel caliber index (VCI), a magnetic resonance imaging biomarker of the average blood vessel diameter, is increasingly being used as a tool for assessing tumor angiogenesis and response to antiangiogenic therapy. However, although the VCI has been correlated with histological vessel diameters, good quantitative agreement with histology has been lacking. In addition, no VCI validation studies have been performed in vivo where the structural deformations frequently associated with histological tissue preparation are not present. This study employs intravital optical microscopy (IVM) measurements of cerebral blood vessel diameters in a mouse orthotopic glioma model to provide the first such in vivo validation. Two VCI correlation models, both a linear and a 3/2-power dependence on the DeltaR2*/DeltaR2 ratio, were compared with the IVM data. The linear VCI model, determined from steady-state susceptibility contrast (SSC) images, was found to be in excellent quantitative agreement with the intravitally determined VCI for separate tumor size matched groups of mice. In addition, preliminary data indicate that the VCI is independent of whether a dynamic susceptibility contrast or SSC measurement method is used.
[Show abstract][Hide abstract] ABSTRACT: The PI3K-AKT-FoxO pathway is integral to lifespan regulation in lower organisms and essential for the stability of long-lived cells in mammals. Here, we report the impact of combined FoxO1, 3, and 4 deficiencies on mammalian brain physiology with a particular emphasis on the study of the neural stem/progenitor cell (NSC) pool. We show that the FoxO family plays a prominent role in NSC proliferation and renewal. FoxO-deficient mice show initial increased brain size and proliferation of neural progenitor cells during early postnatal life, followed by precocious significant decline in the NSC pool and accompanying neurogenesis in adult brains. Mechanistically, integrated transcriptomic, promoter, and functional analyses of FoxO-deficient NSC cultures identified direct gene targets with known links to the regulation of human brain size and the control of cellular proliferation, differentiation, and oxidative defense. Thus, the FoxO family coordinately regulates diverse genes and pathways to govern key aspects of NSC homeostasis in the mammalian brain.
[Show abstract][Hide abstract] ABSTRACT: Recent clinical trials of antivascular endothelial growth factor (VEGF) agents for glioblastoma showed promising progression-free and overall survival rates. However, available clinical imaging does not separate antitumor effects from antipermeability effects of these agents. Thus although anti-VEGF agents may decrease tumor contrast-enhancement, vascularity, and edema, the mechanisms leading to improved survival in patients remain incompletely understood. Our goal was to determine whether alleviation of edema by anti-VEGF agents alone could increase survival in mice.
We treated mice bearing three different orthotopic models of glioblastoma with a VEGF-targeted kinase inhibitor, cediranib. Using intravital microscopy, molecular techniques, and magnetic resonance imaging (MRI), we measured survival, tumor growth, edema, vascular morphology and function, cancer cell apoptosis and proliferation, and circulating angiogenic biomarkers.
We show by intravital microscopy that cediranib significantly decreased tumor vessel permeability and diameter. Moreover, cediranib treatment induced normalization of perivascular cell coverage and thinning of the basement membrane, as mirrored by an increase in plasma collagen IV. These rapid changes in tumor vascular morphology and function led to edema alleviation -- as measured by MRI and by dry/wet weight measurement of water content -- but did not affect tumor growth. By immunohistochemistry, we found a transient decrease in macrophage infiltration and significant but minor changes in tumor cell proliferation and apoptosis. Systemically, cediranib increased plasma VEGF and placenta growth factor levels, and the number of circulating CXCR4(+)CD45(+) cells. However, by controlling edema, cediranib significantly increased survival of mice in the face of persistent tumor growth.
Anti-VEGF agents may be able to improve survival of patients with glioblastoma, even without inhibiting tumor growth.