Combined vascular endothelial growth factor receptor and epidermal growth factor receptor (EGFR) blockade inhibits tumor growth in xenograft models of EGFR inhibitor resistance

PURPOSE

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) gefitinib and erlotinib benefit some non-small cell lung cancer (NSCLC) patients, but most do not respond (primary resistance) and those who initially respond eventually progress (acquired resistance). EGFR TKI resistance is not completely understood and has been associated with certain EGFR and K-RAS mutations and MET amplification.

EXPERIMENTAL DESIGN

We hypothesized that dual inhibition of the vascular endothelial growth factor (VEGF) and EGFR pathways may overcome primary and acquired resistance. We investigated the VEGF receptor/EGFR TKI vandetanib, and the combination of bevacizumab and erlotinib in vivo using xenograft models of EGFR TKI sensitivity, primary resistance, and three models of acquired resistance, including models with mutated K-RAS and secondary EGFR T790M mutation.

RESULTS

Vandetanib, gefitinib, and erlotinib had similar profiles of in vitro activity and caused sustained tumor regressions in vivo in the sensitive HCC827 model. In all four resistant models, vandetanib and bevacizumab/erlotinib were significantly more effective than erlotinib or gefitinib alone. Erlotinib resistance was associated with a rise in both host and tumor-derived VEGF but not EGFR secondary mutations in the KRAS mutant-bearing A549 xenografts. Dual inhibition reduced tumor endothelial proliferation compared with VEGF or EGFR blockade alone, suggesting that the enhanced activity of dual inhibition is due at least in part to antiendothelial effects.

CONCLUSION

These studies suggest that erlotinib resistance may be associated with a rise in both tumor cell and host stromal VEGF and that combined blockade of the VEGFR and EGFR pathways can abrogate primary or acquired resistance to EGFR TKIs. This approach merits further evaluation in NSCLC patients.

Matrigel cytometry: a novel method for quantifying angiogenesis in vivo

Many of the current in vivo methods to evaluate angiogenesis are poorly quantifiable. Recently, the Matrigel plug assay has become the method of choice in many studies involving in vivo testing for angiogenesis. When known angiogenic factors are mixed with Matrigel and injected subcutaneously into mice, endothelial cells migrate into the gel plug. These endothelial cells form vessel-like structures, a process that mimics the formation of capillary networks. Here, we present a modification of the traditional Matrigel assay with improved method to quantify the amount of endothelial cells that incorporate into the plug. The removed plugs were subjected to a mild protease treatment, yielding intact cells. The liberated cells were then stained using an endothelial cell-specific markers, and counted by flow cytometry. This novel combination of FACS analysis with the traditional Matrigel assay improves the ability to quantify in vivo angiogenesis, and for the first time enables to determine the number of migrating and proliferating endothelial cells which reflects the angiogenesis rate.

Tumor-vascular interactions and tumor dormancy

Tumor progression is dependent on a number of sequential steps, including initial tumor-vascular interactions and recruitment of blood vessels (i.e., the angiogenic switch), as well as tumor cells interacting with the surrounding microenvironment and its different components. Failure of a microscopic tumor to complete one or more of these early stages may lead to delayed clinical manifestation of the cancer and a state of stable non-progressing disease (i.e., tumor dormancy). In this review, some of the clinical and experimental evidence is summarized, suggesting that microscopic human cancers, either primary, recurrent or metastatic, can remain in an asymptomatic, non-detectable, and occult state for a long period of time. We also review current experimental human tumor dormancy models which closely recapitulate clinically observed delay in tumor progress.

Doxycycline inhibits vascular leakage and prevents ovarian hyperstimulation syndrome in a murine model

OBJECTIVE

To determine whether doxycycline would inhibit the development of ovarian hyperstimulation syndrome (OHSS) in a murine model.

DESIGN

Testing the effect of oral doxycycline treatment on gonadotropin-induced peritoneal capillary leakage in mice.

SETTING

Animal research facility.

ANIMAL(S)

Four-week-old female C57Bl/6 mice.

INTERVENTION(S)

Ovarian hyperstimulation syndrome was induced in mice by administering gonadotropins for 3 days followed by human chorionic gonadotropin. Peritoneal vascular leakage was quantified using the Miles vascular permeability assay. Mice were treated with daily oral doxycycline or vehicle.

MAIN OUTCOME MEASURE(S)

The concentration of dye in abdominal fluid extracted by peritoneal lavage was measured spectrophotometrically. Ascites volume was determined using dye dilution.

RESULT(S)

Doxycycline inhibited peritoneal vascular leakage and ascites accumulation in the hormonally stimulated mice. Doxycycline treatment did not inhibit ovarian stimulation or ovulation when compared with controls, as indicated by similar ovarian morphology, ovarian weights, and corpora lutea counts. Importantly, vessel density within the corpora lutea was similar in the two groups.

CONCLUSION(S)

Doxycycline prevents OHSS in a murine model without compromising ovarian stimulation. This effect is caused by inhibition of vascular leakage. Doxycycline's potential in preventing human OHSS is promising and warrants further studies.

Doxycycline induces membrane expression of VE-cadherin on endothelial cells and prevents vascular hyperpermeability

The endothelium lining blood vessels serves as a barrier against vascular hyperpermeability, and its maintenance is critical to organ health. Inflammatory mediators evoke tissue edema by disrupting the expression of membrane junctional proteins, which mediate binding between endothelial cell membranes. Endothelial cell-cell junctions form a diffusion barrier between the intravascular and interstitial space. To prevent the morbidity and mortality caused by exaggerated vascular permeability associated with pathological states (e.g., inflammatory and hypersensitivity disorders, pulmonary edema, traumatic lung injury, cerebral edema resulting from stroke, and others), it is important to develop therapeutic approaches to stabilize these interendothelial junctions. Vascular endothelial growth factor (VEGF), a potent proangiogenic cytokine, was first described as vascular permeability factor (VPF). Doxycycline, a tetracycline derivative, has been shown to inhibit angiogenesis in both humans and animal models. We now report that oral doxycycline prevents VPF/VEGF-induced vascular permeability, interleukin-2-induced pulmonary edema, and delayed-type hypersensitivity (DTH) in mice. Remarkably, doxycycline also inhibits tumor growth and tumor-associated vascular hyperpermeability. Finally, we show that doxycycline targets the adherens junction in vascular endothelial cells by inducing the total amount of VE-cadherin expression while decreasing the degree of its phosphorylation. The potential of doxycyline as a therapeutic inhibitor of vascular hyperpermeability in human clinical conditions is promising and warrants further studies.

An orally delivered small-molecule formulation with antiangiogenic and anticancer activity

Targeting angiogenesis, the formation of blood vessels, is an important modality for cancer therapy. TNP-470, a fumagillin analog, is among the most potent and broad-spectrum angiogenesis inhibitors. However, a major clinical limitation is its poor oral availability and short half-life, necessitating frequent, continuous parenteral administration. We have addressed these issues and report an oral formulation of TNP-470, named Lodamin. TNP-470 was conjugated to monomethoxy-polyethylene glycol-polylactic acid to form nanopolymeric micelles. This conjugate can be absorbed by the intestine and selectively accumulates in tumors. Lodamin significantly inhibits tumor growth, without causing neurological impairment in tumor-bearing mice. Using the oral route of administration, it first reaches the liver, making it especially efficient in preventing the development of liver metastasis in mice. We show that Lodamin is an oral nontoxic antiangiogenic drug that can be chronically administered for cancer therapy or metastasis prevention.

Successful inhibition of intracranial human glioblastoma multiforme xenograft growth via systemic adenoviral delivery of soluble endostatin and soluble vascular endothelial growth factor receptor-2: laboratory investigation

OBJECT

Glioblastoma multiforme (GBM) is characterized by neovascularization, raising the question of whether angiogenic blockade may be a useful therapeutic strategy for this disease. It has been suggested, however, that, to be useful, angiogenic blockade must be persistent and at levels sufficient to overcome proangiogenic signals from tumor cells. In this report, the authors tested the hypothesis that sustained high concentrations of 2 different antiangiogenic proteins, delivered using a systemic gene therapy strategy, could inhibit the growth of established intracranial U87 human GBM xenografts in nude mice.

METHODS

Mice harboring established U87 intracranial tumors received intravenous injections of adenoviral vectors encoding either the extracellular domain of vascular endothelial growth factor receptor-2-Fc fusion protein (Ad-VEGFR2-Fc) alone, soluble endostatin (Ad-ES) alone, a combination of Ad-VEGFR2-Fc and Ad-ES, or immunoglobulin 1-Fc (Ad-Fc) as a control.

RESULTS

Three weeks after treatment, magnetic resonance imaging-based determination of tumor volume showed that treatment with Ad-VEGFR2-Fc, Ad-ES, or Ad-VEGFR2-Fc in combination with Ad-ES, produced 69, 59, and 74% growth inhibition, respectively. Bioluminescent monitoring of tumor growth revealed growth inhibition in the same treatment groups to be 62, 74, and 72%, respectively. Staining with proliferating cell nuclear antigen and with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling showed reduced tumor cell proliferation and increased apoptosis in all antiangiogenic treatment groups.

CONCLUSIONS

These results suggest that systemic delivery and sustained production of endostatin and soluble VEGFR2 can slow intracranial glial tumor growth by both reducing cell proliferation and increasing tumor apoptosis. This work adds further support to the concept of using antiangiogenesis therapy for intracranial GBM.

Rosiglitazone and delayed onset of proliferative diabetic retinopathy

OBJECTIVE

To evaluate whether rosiglitazone maleate, an oral peroxisome-proliferating activated receptor gamma agonist and oral insulin sensitizing agent with potential antiangiogenic activity, delays onset of proliferative diabetic retinopathy (PDR).

METHODS

Longitudinal medical record review of all patients treated with rosiglitazone receiving both medical and ophthalmic care at the Joslin Diabetes Center from May 1, 2002, to May 31, 2003 (N = 124), and matched control patients not taking a glitazone drug (N = 158). The mean duration of follow-up was 2.8 years (range, 0.3-9.0 years).

RESULTS

Baseline characteristics and final hemoglobin A(1c) values (7.6% and 7.8%, respectively) were similar in the rosiglitazone and control groups (P = .10). In eyes with severe nonproliferative diabetic retinopathy at baseline (rosiglitazone group, 14 eyes; control group, 24 eyes), progression to PDR over 3 years occurred in 19.2% in the rosiglitazone group and 47.4% in the control group, representing a 59% relative risk reduction (Wilcoxon, P = .045; log-rank, P = .059). Fewer eyes in the rosiglitazone group experienced 3 or more lines of visual acuity loss (P = .03). The incidence of diabetic macular edema was similar in both groups.

CONCLUSIONS

Rosiglitazone may delay the onset of PDR, possibly because of its antiangiogenic activity. Future clinical investigations should consider analysis of this potential benefit along with ongoing evaluation of potential cardiac risk in studies where the risk-benefit profiles are deemed appropriate.

The role of heparin in angiogenesis

A series of experiments is described in which: (i) mast cells were found to accumulate at a tumour site before the ingrowth of new capillaries; (ii) heparin released by mast cells increased the migration of capillary endothelial cells in vitro; and (iii) heparin enhanced tumour angiogenesis in vivo. These experiments led to the discovery that protamine and platelet factor 4 are angiogenesis inhibitors. This finding suggests a central role for heparin or related glycosaminoglycans in the growth regulation of capillary blood vessels.

Glycogen storage disease: new approaches to therapy

Detailed studies of the effect of 32 days of intravenous alimentation on the metabolic, hormonal and clinical status of a 4-year-old boy with Type I glycogenosis revealed that the biochemical abnormalities and growth failure in this disorder are a consequence of glucose lack after brief periods of fasting which results from the inborn enzyme deficiency. Long-term (1.5-5.7 years) observations of the therapeutic effects of portacaval shunt without and with continuous overnight intragastic glucose by gastrostomy in two brothers, and of continuous overnight intragastric glucose alone in five other patients with this disorder, on metabolic status and physical growth and development suggest that adequate glucose can be provided by the intragastric route without hepatic portal circulatory by-pass. The introduction of this therapy in the first year of life should prevent the serious risk to life and long-term failure in growth and development previously observed in patients with Types I and III glycogenosis.

The placenta theory and the origin of infantile hemangioma

The pathogenesis of infantile hemangioma is unknown. In recent years, much of the focus has been placed at identifying the cell type(s) responsible for tumor initiation. New discoveries in infantile hemangioma suggest an involvement of progenitor cells in the pathogenesis of this vascular tumor. Both embryonic and extra-embryonic tissues have been postulated as potential sources for these progenitor cells. This review focuses on the placental theory, which proposes that a fetal placental progenitor is the cell type of origin for infantile hemangioma. Special emphasis will be placed on placental vasculogenesis and the presence and transit of placental progenitor cells during gestation.

Dendritic cells augment choroidal neovascularization

PURPOSE

Dendritic cells (DCs) are innate immune cells that have recently been shown to support angiogenesis in tumors, endometriosis, and lymph nodes. A major cause of legal blindness is wet age-related macular degeneration (wet ARMD), wherein abnormal blood vessels grow under the retina, an abnormality also referred to as choroidal neovascularization (CNV). The purpose of the present study was to investigate the role of DCs in the development of CNV.

METHODS

Laser photocoagulation was used to induce CNV in C57BL/6J mice. The authors analyzed CNV lesions for the presence of DCs using flow cytometry and immunostaining at designated times. They also analyzed the effects of intravenous DC transplantation on CNV development by measuring the lesion area using confocal microscopy 1 week after laser injury.

RESULTS

The authors analyzed CNV lesions for the presence of DCs by flow cytometry and observed that CD11c(+) major histocompatibility complex (MHC) class II(+) DCs transiently infiltrated the CNV lesions, reaching a peak at 2 to 4 days after laser injury. These DCs were mostly immature (CD11c(+) MHCII(low)) and expressed vascular endothelial growth factor receptor 2. Immunostaining of laser-induced CNV lesions confirmed that DCs are located at the sites of newly formed blood vessels. Intravenously injected DCs incorporated into the CNV lesions. However, only immature DCs enhanced CNV size.

CONCLUSIONS

These results suggest a role for DCs in promoting angiogenesis and lesion growth in laser-induced CNV. The present data suggest that DCs may represent potential cellular targets for therapeutic intervention in wet ARMD.

Phase II study of temozolomide, thalidomide, and celecoxib for newly diagnosed glioblastoma in adults

We conducted a phase II study of the combination of temozolomide and angiogenesis inhibitors for treating adult patients with newly diagnosed glioblastoma. Patients who had stable disease following standard radiation therapy received temozolomide for 5 days in 28-day cycles, in combination with daily thalidomide and celecoxib. Patients were treated until tumor progression or development of unacceptable toxicity. Four-month progression-free survival (PFS) from study enrollment was the primary end point, and overall survival (OS) was the secondary end point. In addition, we sought to correlate response with O(6)-methylguanine-DNA methyltransferase promoter methylation status and serum levels of angiogenic peptides. Fifty patients with glioblastoma were enrolled (18 women, 32 men). Median age was 54 years (range, 29-78) and median KPS score was 90 (range, 70-100). From study enrollment, median PFS was 5.9 months (95% confidence interval [CI]: 4.2-8.0) and 4-month PFS was 63% (95% CI: 46%-75%). Median OS was 12.6 months (95% CI: 8.5-16.4) and 1-year OS was 47%. Of the 47 patients evaluable for best response, none had a complete response, five (11%) had partial response, four (9%) had minor response, 22 (47%) had stable disease, and 16 (34%) had progressive disease. Analysis of serial serum samples obtained from 47 patients for four angiogenic peptides failed to show a significant correlation with response or survival for three of the peptides; higher vascular endothelial growth factor levels showed a trend toward correlation with decreased OS (p=0.07) and PFS (p=0.09). The addition of celecoxib and thalidomide to adjuvant temozolomide was well tolerated but did not meet the primary end point of improvement of 4-month PFS from study enrollment.

Potent antitumor effects of ZD6474 on neuroblastoma via dual targeting of tumor cells and tumor endothelium

Among children with relapsed or refractory neuroblastoma, the prognosis is poor and novel therapeutic strategies are needed to improve long-term survival. As with other solid tumors, high vascular density within neuroblastoma is associated with advanced disease, and therapeutic regimens directed against the tumor vasculature may provide clinical benefit. The receptor tyrosine kinase RET is widely expressed in neuroblastoma and is known to activate key signal transduction pathways involved in tumor cell survival and progression including Ras/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt. We investigated the effect of dual targeting of tumor cells and tumor endothelium with ZD6474, a small-molecule tyrosine kinase inhibitor of vascular endothelial growth factor (VEGF) receptor 2, epidermal growth factor receptor, and RET. ZD6474 inhibited the phosphorylation of RET in neuroblastoma cells and had a direct effect on tumor cell viability in seven neuroblastoma cell lines. In a human neuroblastoma xenograft model, ZD6474 inhibited tumor growth by 85% compared with treatment with vehicle alone. In contrast, no significant inhibition of tumor growth was observed after treatment with bevacizumab, an antihuman VEGF monoclonal antibody, or the epidermal growth factor receptor inhibitor erlotinib, either alone or in combination. Immunohistochemical analysis showed that ZD6474 treatment led to an increase in endothelial cell apoptosis along with inhibition of VEGF receptor-2 activation on tumor endothelium. In conclusion, dual targeting of tumor cells, potentially through RET inhibition, and tumor vasculature with ZD6474 leads to potent antitumor effects. This approach merits further investigation for patients with neuroblastoma.

2-methoxyestradiol inhibits hypoxia-inducible factor-1{alpha} and suppresses growth of lesions in a mouse model of endometriosis

Endometriosis, the presence of ectopic endometrial tissue outside the uterine cavity, is a common disease affecting women during their reproductive years. Current therapeutic success is often unsatisfactory because of limited insight into disease mechanisms. Nevertheless, angiogenesis plays an essential role in the pathogenesis of the disease, making it a potential novel target for therapy. In the current study, we demonstrate in an established mouse model of endometriosis that transient hypoxia in transplanted endometriosis-like lesions results in the up-regulation of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to the expression of vascular endothelial growth factor (VEGF), a key player in endometriosis-associated angiogenesis. Systemic treatment with the angiogenesis inhibitor 2-methoxyestradiol suppressed HIF-1alpha expression in vivo, resulting in a decreased downstream expression of HIF-1alpha target genes, such as for VEGF, phosphoglycerate kinase, and glucose transporter-1. 2-Methoxyestradiol also suppressed VEGF-induced vascular permeability, as demonstrated in a modified Miles assay. Finally, systemic treatment with 2-methoxyestradiol significantly inhibited the growth of endometriosis-like lesions in a dose-dependent manner. In conclusion, hypoxia appears to play an important role in the pathogenesis of endometriosis and endometriosis-associated angiogenesis, and the angiogenesis inhibitor 2-methoxyestradiol may be a potential candidate for systemic treatment in the future.

Inhibition of p53 response in tumor stroma improves efficacy of anticancer treatment by increasing antiangiogenic effects of chemotherapy and radiotherapy in mice

Inactivation of p53 function, which frequently occurs in tumors, can significantly modulate tumor cell sensitivity to radiation and chemotherapeutic drugs. However, in addition to acting on malignant cells, anticancer agents act on the cells of tumor stroma, causing activation of a p53 response. The effect of this response on treatment outcome has been the subject of the present study. Tumors with p53-deficient stroma were generated using mouse tumorigenic packaging cells that produce a p53 inhibitory retrovirus, encoding a dominant-negative p53 mutant. Tumors maintaining wild-type p53 in their stroma were formed by cells of similar origin but deficient in retroviral production due to the deletion of the packaging signal in the retroviral vector. Comparison of these tumor models, differing only in p53 status of their stromas, showed that tumors with p53-deficient stroma were significantly more sensitive to experimental chemotherapy and radiotherapy. A similar effect was achieved when anticancer treatment was combined with pharmacologic suppression of p53 by the cyclic form of pifithrin alpha, a small-molecule inhibitor of p53. Potentiation of the anticancer effect of chemotherapy and radiotherapy by p53 suppression in the tumor stroma is likely to be due to the increased sensitivity of p53-deficient endothelium to genotoxic stress as shown both in cell culture and in experimental tumors. Thus, reversible pharmacologic suppression of p53 may be a viable approach to improving anticancer treatment via an enhanced antiangiogenic effect of chemotherapy and radiotherapy.

Malignant progression and blockade of angiogenesis in a murine transgenic model of neuroblastoma

Targeted expression of MYCN to the neural crest [under control of the rat tyrosine hydroxylase (TH) promoter] causes neuroblastoma in transgenic mice (TH-MYCN) and is a well-established model for this disease. Because high levels of MYCN are associated with enhanced tumor angiogenesis and poor clinical outcome in neuroblastoma, we serially characterized malignant progression, angiogenesis, and sensitivity to angiogenic blockade in tumors from these animals. Tumor cells were proliferative, secreted high levels of the angiogenic ligand vascular endothelial growth factor (VEGF), and recruited a complex vasculature expressing the angiogenic markers VEGF-R2, alpha-SMA, and matrix metalloproteinases MMP-2 and MMP-9, all of which are also expressed in human disease. Treatment of established murine tumors with the angiogenesis inhibitor TNP-470 caused near-complete ablation, with reduced proliferation, enhanced apoptosis, and vasculature disruption. Because TNP-470 has been associated with neurotoxicity, we tested the recently described water-soluble HPMA copolymer-TNP-470 conjugate (caplostatin), which showed comparable efficacy and was well tolerated without weight loss or neurotoxicity as measured by rotarod testing. This study highlights the importance of angiogenesis inhibition in a spontaneous murine tumor with native tumor-microenvironment interactions, validates the use of mice transgenic for TH-MYCN as a model for therapy in this common pediatric tumor, and supports further clinical development of caplostatin as an antiangiogenic therapy in childhood neuroblastoma.

Platelet-associated PF-4 as a biomarker of early tumor growth

Early tumor detection and intervention are important determinants of survival in patients with cancer. We have recently reported that the "platelet angiogenesis proteome" may be used to detect microscopic tumors in mice. We now present evidence that changes in platelet-associated platelet factor-4 (PF-4) detect malignant growth across a spectrum of human cancers in mice. A deregulated expression of an 8206-Da protein was observed by surfaceenhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-ToF MS) proteomic comparison of platelets from normal and tumor-bearing mice. The differentially expressed protein was identified as PF-4 by tandem mass spectrometry and ProteinChip immunoassay using anti-PF-4 antibody. The platelet-associated PF-4 appeared to be up-regulated in early growth of human liposarcoma, mammary adenocarcinoma, and osteosarcoma. A 120-day follow-up study of liposarcoma revealed a sustained 2-fold or higher increase of platelet-associated PF-4 at 19, 30, and 120 days. In contrast, only an insignificant change of PF-4 was observed in the plasma of mice bearing the different human tumor xenografts, and throughout the 120 days of the liposarcoma study. We conclude that platelet-associated PF-4, but not its plasma counterpart, may represent a potential biomarker of early tumor presence.