The vascular-targeting fusion toxin VEGF121/rGel inhibits the growth of orthotopic human bladder carcinoma tumors

Light-enhanced VEGF121/rGel: A tumor targeted modality with vascular and immune-mediated efficacy

Interactions between stromal cells and tumor cells pay a major role in cancer growth and progression. This is reflected in the composition of anticancer drugs which includes compounds directed towards the immune system and tumor-vasculature in addition to drugs aimed at the cancer cells themselves. Drug-based treatment regimens are currently designed to include compounds targeting the tumor stroma in addition to the cancer cells. Treatment limiting adverse effects remains, however, one of the major challenges for drug-based therapy and novel tolerable treatment modalities with diverse high efficacy on both tumor cells and stroma is therefore of high interest. It was hypothesized that the vascular targeted fusion toxin VEGF₁₂₁/rGel in combination with the intracellular drug delivery technology photochemical internalization (PCI) stimulate direct cancer parenchymal cell death in addition to inhibition of tumor perfusion, and that an immune mediated response is relevant for treatment outcome. The aim of the present study was therefore to elucidate the anticancer mechanisms of VEGF₁₂₁/rGel-PCI. In contrast to VEGF₁₂₁/rGel monotherapy, VEGF₁₂₁/rGel-PCI was found to mediate its effect through VEGFR1 and VEGFR2, and a targeted treatment effect was shown on two VEGFR1 expressing cancer cell lines. A cancer parenchymal treatment effect was further indicated on H&E stains of CT26-CL25 and 4 T1 tumors. VEGF₁₂₁/rGel-PCI was shown, by dynamic contrast enhanced MRI, to induce a sustained inhibition of tumor perfusion in both tumor models. A 50% complete remission (CR) of CT26.CL25 colon carcinoma allografts was found in immunocompetent mice while no CR was detected in CT26.CL25 bearing athymic mice. In conclusion, the present report indicate VEGF₁₂₁/rGel -PCI as a treatment modality with multimodal tumor targeted efficacy that should be further developed towards clinical utilization.

A critical review on ramucirumab in the treatment of advanced urothelial cancer

Advanced urothelial cancer (UC) is a lethal disease despite current advances in systemic therapy, including platinum chemotherapy combinations and immune checkpoint inhibition. Tumor angiogenesis is involved in UC growth and metastatic progression. Proangiogenic signaling through the VEGFR is a key process in UC with prognostic significance. Targeting of VEGFR2 with the monoclonal antibody ramucirumab has been tested in various different tumor types. In this review, we discuss the development of the drug in the context of its preclinical and clinical use with a focus on UC. Improvements in our ability to predict responses and resistance are key for maximizing its efficacy and selecting the most appropriate combinations with other active agents.

Targeting of Tumor Neovasculature with GrB/VEGF121, a Novel Cytotoxic Fusion Protein

Angiogenesis is a critical process in numerous diseases, and intervention in neovascularization has therapeutic value in several disease settings, including ocular diseases, arthritis, and in tumor progression and metastatic spread. Various vascular targeting agents have been developed, including those that inhibit growth factor receptor tyrosine kinases, blocking antibodies that interfere with receptor signal transduction, and strategies that trap growth factor ligands. Limited anti-tumor efficacy studies have suggested that the targeted delivery of the human pro-apoptotic molecule Granzyme B to tumor cells has significant potential for cancer treatment. Here, we review biological vascular targeting agents, and describe a unique vascular targeting agent composed of Granzyme B and the VEGF receptor ligand VEGF₁₂₁. The fusion protein GrB/VEGF₁₂₁ demonstrates cytotoxicity at nanomolar or sub-nanomolar levels, excellent pharmacokinetic and efficacy profiles, and has significant therapeutic potential targeting tumor vasculature.

Ultrasound Molecular Imaging of Angiogenesis Using Vascular Endothelial Growth Factor-Conjugated Microbubbles

Imaging of angiogenesis receptors could provide a sensitive and clinically useful method for detecting neovascularization such as occurs in malignant tumors, and responses to antiangiogenic therapies for such tumors. We tested the hypothesis that microbubbles (MB) tagged with human VEGF₁₂₁ (MB_VEGF) bind to the kinase insert domain receptor (KDR) in vitro and angiogenic endothelium in vivo, and that this specific binding can be imaged on a clinical ultrasound system. In this work, targeted adhesion of MB_VEGF was evaluated in vitro using a parallel plate flow system containing adsorbed recombinant human KDR. There was more adhesion of MB_VEGF to KDR-coated plates when the amount of VEGF₁₂₁ on each MB or KDR density on the plate was increased. MB_VEGF adhesion to KDR-coated plates decreased with increasing wall shear rate. On intravital microscopic imaging of bFGF-stimulated rat cremaster muscle, there was greater microvascular adhesion of MB_VEGF compared to that of isotype IgG-conjugated control MB (MB_CTL). To determine if MB_VEGF could be used to ultrasonically image angiogenesis, ultrasound imaging was performed in mice bearing squamous cell carcinoma after intravenous injection of MB_VEGF. Ultrasound videointensity enhancement in tumor was significantly higher for MB_VEGF (17.3 ± 9.7 dB) compared to MB_CTL (3.8 ± 4.4 dB, n = 6, p < 0.05). This work demonstrates the feasibility of targeted ultrasound imaging of an angiogenic marker using MB_VEGF. This approach offers a noninvasive bedside method for detecting tumor angiogenesis and could be extended to other applications such as molecular monitoring of therapeutic angiogenesis or antiangiogenic therapies in cardiovascular disease or cancer.

Translational aspects in targeting the stromal tumour microenvironment: from bench to bedside

Solid tumours comprise, not only malignant cells but also a variety of stromal cells and extracellular matrix proteins. These components interact via an array of signalling pathways to create an adaptable network that may act to promote or suppress cancer progression. To date, the majority of anti-tumour chemotherapeutic agents have principally sought to target the cancer cell. Consequently, resistance develops because of clonal evolution, as a result of selection pressure during tumour expansion. The concept of activating or inhibiting other cell types within the tumour microenvironment is relatively novel and has the advantage of targeting cells which are genetically stable and less likely to develop resistance. This review outlines key players in the stromal tumour microenvironment and discusses potential targeting strategies that may offer therapeutic benefit.

Sortase-catalyzed in vitro functionalization of a HER2-specific recombinant Fab for tumor targeting of the plant cytotoxin gelonin

We report on the preparation of a new type of immunotoxin via in vitro ligation of the αHer2 antigen binding fragment (Fab) of the clinically-validated antibody trastuzumab to the plant toxin gelonin, employing catalysis by the bacterial enzyme sortase A (SrtA). The αHer2 Fab was fused with the extended SrtA recognition motif LPET↓GLEH 6 at the C-terminus of its heavy chain, thereby preventing interference with antigen binding, while the toxin was equipped with a Gly 2 sequence at its N-terminus, distant to the catalytically active site in the C-terminal region. Site-specific in vitro transpeptidation led to a novel antibody-toxin conjugate wherein gelonin had effectively replaced the Fc region of a conventional (monomerized) immunoglobulin. After optimization of reaction conditions and incubation time, the resulting Fab-Gelonin ligation product was purified to homogeneity in a two-step procedure by means of Strep-Tactin affinity chromatography--utilizing the Strep-tag II appended to gelonin--and size exclusion chromatography. Binding activity of the immunotoxin for the Her2 ectodomain was indistinguishable from the unligated Fab as measured by real-time surface plasmon resonance spectroscopy. Specific cytotoxic potency of Fab-Gelonin was demonstrated against two Her2-positive cell lines, resulting in EC 50 values of ~1 nM or lower, indicating a 1000-fold enhanced cell-killing activity compared with gelonin itself. Thus, our strategy provides a convenient route to the modular construction of functional immunotoxins from Fabs of established tumor-specific antibodies with gelonin or related proteotoxins, also avoiding the elevated biosafety levels that would be mandatory for the direct biotechnological preparation of corresponding fusion proteins.

Pharmacodynamics, tissue distribution, toxicity studies and antitumor efficacy of the vascular targeting fusion toxin VEGF121/rGel

As a part of an ongoing assessment of its mechanism of action, we evaluated the in vivo pharmacokinetics, tissue distribution, toxicity and antitumor efficacy of VEGF(121)/rGel, a novel fusion protein. Pharmacokinetic studies showed that VEGF(121)/rGel cleared from the circulation in a biphasic manner with calculated half-lives of 0.3 and 6h for the alpha and beta phases, respectively. Pharmacokinetic evaluation of (64)Cu-DOTA-VEGF(121)/rGel showed relatively high blood retention 30 min after injection (26.6 ± 1.73% ID/g), dropping to 11.8 ± 2.83% and 0.82 ± 0.11% ID/g at 60 and 240 min post injection, respectively. Tissue uptake studies showed that kidneys, liver and tumor had the highest drug concentrations 48 h after administration. The maximum tolerated dose (MTD), based on a QOD×5 i.v. administration schedule, was found to be 18 mg/kg with an LD(50) of 25mg/kg. Treatment of BALB/c mice with VEGF(121)/rGel at doses up to the MTD caused no alterations in hematologic parameters. However, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) parameters increased in a dose-related manner. The no-observable-adverse-effect-level (NOAEL) was determined to be 20% of the MTD (3.6 mg/kg). VEGF(121)/rGel treatment of mice bearing orthotopically-placed MDA-MB-231 breast tumors caused increased vascular permeability of tumor tissue by 53% compared to saline-treated controls. Immunohistochemical analysis showed significant tumor hypoxia and necrosis as a consequence of vascular damage. In summary, VEGF(121)/rGel appears to be an effective therapeutic agent causing focused damage to tumor vasculature with minimal toxic effects to normal organs. This agent appears to be an excellent candidate for further clinical development.

In vitro and in vivo anti-tumor activities of anti-EGFR single-chain variable fragment fused with recombinant gelonin toxin

PURPOSE

Epidermal growth factor receptor (EGFR) plays an important role in the growth and metastasis of many solid tumors. Strategies that target EGFR hold promising therapeutic potential for the treatment for non-small cell lung cancer (NSCLC), as EGFR is normally overexpressed in these tumors. This study was designed to determine whether an anti-EGFR immunotoxin has anti-tumor activity against NSCLC, and if so, to further investigate the possible mechanisms of cytotoxicity.

METHODS

A fusion protein of anti-EGFR single-chain variable fragment (anti-EGFR scFv) and the plant toxin gelonin (rGel) was constructed, expressed in bacteria, and purified to homogeneity. Cytotoxicity of anti-EGFR scFv/rGel (E/rG) immunotoxin was assessed on A549, HCC827, and H1975 cells (EGFR-overexpressing NSCLC-derived cell lines) and A549 xenografts in nude mice.

RESULTS

Cytotoxicity experiments using E/rG on A549, HCC827, and H1975 cells demonstrated that E/rG can specifically inhibit proliferation of these cells, whereas it did not affect the proliferation of Raji cells that do not express EGFR. Treatment for A549 xenografts in nude mice with E/rG resulted in significant suppression of tumor growth compared to controls. Immunofluorescence in frozen tissue sections confirmed that E/rG could specifically bind to tumor tissues in nude mice bearing A549 tumor xenografts, while rGel alone showed no binding activity. Furthermore, E/rG inhibited the growth of A549 cells by cytotoxic effects that blocked tumor proliferation, and the immunotoxin-induced cell death may be mediated by autophagy.

CONCLUSIONS

These results showed that E/rG might have significant potential as a novel clinical therapeutic agent against human NSCLC.

Cytotoxicity of VEGF(121)/rGel on vascular endothelial cells resulting in inhibition of angiogenesis is mediated via VEGFR-2

Background

The fusion protein VEGF₁₂₁/rGel composed of the growth factor VEGF₁₂₁ and the plant toxin gelonin targets the tumor neovasculature and exerts impressive anti-vascular effects. We have previously shown that VEGF₁₂₁/rGel is cytotoxic to endothelial cells overexpressing VEGFR-2 but not to endothelial cells overexpressing VEGFR-1. In this study, we examined the basis for the specific toxicity of this construct and assessed its intracellular effects in vitro and in vivo.

Methods

We investigated the binding, cytotoxicity and internalization profile of VEGF₁₂₁/rGel on endothelial cells expressing VEGFR-1 or VEGFR-2, identified its effects on angiogenesis models in vitro and ex vivo, and explored its intracellular effects on a number of molecular pathways using microarray analysis.

Results

Incubation of PAE/VEGFR-2 and PAE/VEGFR-1 cells with ¹²⁵I-VEGF₁₂₁/rGel demonstrated binding specificity that was competed with unlabeled VEGF₁₂₁/rGel but not with unlabeled gelonin. Assessment of the effect of VEGF₁₂₁/rGel on blocking tube formation in vitro revealed a 100-fold difference in IC₅₀ levels between PAE/VEGFR-2 (1 nM) and PAE/VEGFR-1 (100 nM) cells. VEGF₁₂₁/rGel entered PAE/VEGFR-2 cells within one hour of treatment but was not detected in PAE/VEGFR-1 cells up to 24 hours after treatment. In vascularization studies using chicken chorioallantoic membranes, 1 nM VEGF₁₂₁/rGel completely inhibited bFGF-stimulated neovascular growth. The cytotoxic effects of VEGF₁₂₁/rGel were not apoptotic since treated cells were TUNEL-negative with no evidence of PARP cleavage or alteration in the protein levels of select apoptotic markers. Microarray analysis of VEGF₁₂₁/rGel-treated HUVECs revealed the upregulation of a unique "fingerprint" profile of 22 genes that control cell adhesion, apoptosis, transcription regulation, chemotaxis, and inflammatory response.

Conclusions

Taken together, these data confirm the selectivity of VEGF₁₂₁/rGel for VEGFR-2-overexpressing endothelial cells and represent the first analysis of genes governing intoxication of mammalian endothelial cells by a gelonin-based targeted therapeutic agent.

Mouse bladder wall injection

Mouse bladder wall injection is a useful technique to orthotopically study bladder phenomena, including stem cell, smooth muscle, and cancer biology. Before starting injections, the surgical area must be cleaned with soap and water and antiseptic solution. Surgical equipment must be sterilized before use and between each animal. Each mouse is placed under inhaled isoflurane anesthesia (2-5% for induction, 1-3% for maintenance) and its bladder exposed by making a midline abdominal incision with scissors. If the bladder is full, it is partially decompressed by gentle squeezing between two fingers. The cell suspension of interest is intramurally injected into the wall of the bladder dome using a 29 or 30 gauge needle and 1 cc or smaller syringe. The wound is then closed using wound clips and the mouse allowed to recover on a warming pad. Bladder wall injection is a delicate microsurgical technique that can be mastered with practice.

Novel targeted agents for the treatment of bladder cancer: translating laboratory advances into clinical application

Bladder cancer is a common and frequently lethal cancer. Natural history studies indicate two distinct clinical and molecular entities corresponding to invasive and non-muscle invasive disease. The high frequency of recurrence of noninvasive bladder cancer and poor survival rate of invasive bladder cancer emphasizes the need for novel therapeutic approaches. These mechanisms of tumor development and promotion in bladder cancer are strongly associated with several growth factor pathways including the fibroblast, epidermal, and the vascular endothelial growth factor pathways. In this review, efforts to translate the growing body of basic science research of novel treatments into clinical applications will be explored.

Inhibition of prostate cancer osteoblastic progression with VEGF121/rGel, a single agent targeting osteoblasts, osteoclasts, and tumor neovasculature

PURPOSE

A hallmark of prostate cancer (PCa) progression is the development of osteoblastic bone metastases, which respond poorly to available therapies. We previously reported that VEGF(121)/rGel targets osteoclast precursors and tumor neovasculature. Here we tested the hypothesis that targeting nontumor cells expressing these receptors can inhibit tumor progression in a clinically relevant model of osteoblastic PCa.

EXPERIMENTAL DESIGN

Cells from MDA PCa 118b, a PCa xenograft obtained from a bone metastasis in a patient with castrate-resistant PCa, were injected into the femurs of mice. Osteoblastic progression was monitored following systemic administration of VEGF(121)/rGel.

RESULTS

VEGF(121)/rGel was cytotoxic in vitro to osteoblast precursor cells. This cytotoxicity was specific as VEGF(121)/rGel internalization into osteoblasts was VEGF(121) receptor driven. Furthermore, VEGF(121)/rGel significantly inhibited PCa-induced bone formation in a mouse calvaria culture assay. In vivo, VEGF(121)/rGel significantly inhibited the osteoblastic progression of PCa cells in the femurs of nude mice. Microcomputed tomographic analysis revealed that VEGF(121)/rGel restored the bone volume fraction of tumor-bearing femurs to values similar to those of the contralateral (non-tumor-bearing) femurs. VEGF(121)/rGel significantly reduced the number of tumor-associated osteoclasts but did not change the numbers of peritumoral osteoblasts. Importantly, VEGF(121)/rGel-treated mice had significantly less tumor burden than control mice. Our results thus indicate that VEGF(121)/rGel inhibits osteoblastic tumor progression by targeting angiogenesis, osteoclastogenesis, and bone formation.

CONCLUSIONS

Targeting VEGF receptor (VEGFR)-1- or VEGFR-2-expressing cells is effective in controlling the osteoblastic progression of PCa in bone. These findings provide the basis for an effective multitargeted approach for metastatic PCa.

Multiplexed PET probes for imaging breast cancer early response to VEGF₁₂₁/rGel treatment

In this study, we applied multiplexed positron emission tomography (PET) probes to monitor glucose metabolism, cellular proliferation, tumor hypoxia and angiogenesis during VEGF₁₂₁/rGel therapy of breast cancer. Two doses of 12 mg/kg VEGF₁₂₁/rGel, administered intraperitoneally, resulted in initial delay of tumor growth, but the growth resumed 4 days after tumor treatment was stopped. The average tumor growth rate expressed as V/V(0), were 1.11 ± 0.07, 1.21 ± 0.10, 1.58 ± 0.36 and 2.64 ± 0.72 at days 1, 3, 7 and 14, respectively. Meanwhile, the VEGF₁₂₁/rGel treatment group showed V/V₀ ratios of 1.04 ± 0.06, 1.05 ± 0.11, 1.09 ± 0.17 and 1.86 ± 0.36 at days 1, 3, 7 and 14, respectively. VEGF₁₂₁/rGel treatment led to significantly decreased uptake of ¹⁸F-FPPRGD2 at day 1 (24.0 ± 8.8%, p < 0.05) and day 3 (36.3 ± 9.2%, p < 0.01), relative to the baseline, which slowly recovered to the baseline at day 14. ¹⁸F-FMISO uptake was increased in the treated tumors at day 1 (23.9 ± 15.7%, p < 0.05) and day 3 (51.4 ± 29.4%, p < 0.01), as compared to the control group. At days 7 and 14, ¹⁸F-FMISO uptake restored to the baseline level. The relative reductions in FLT uptake in treated tumors were approximately 13.0 ± 4.5% at day 1 and 25.0 ± 4.4% (p < 0.01) at day 3. No significant change of ¹⁸F-FDG uptake was observed in VEGF₁₂₁/rGel treated tumors, compared with the control group. The imaging findings were supported by ex vivo analysis of related biomarkers. Overall, longitudinal imaging studies with 4 PET tracers demonstrated the feasibility and usefulness of multiplexed probes for quantitative measurement of antitumor effects of VEGF₁₂₁/rGel at the early stage of treatment. This preclinical study should be helpful in accelerating anticancer drug development and promoting the clinical translation of molecular imaging.

Challenges associated with the targeted delivery of gelonin to claudin-expressing cancer cells with the use of activatable cell penetrating peptides to enhance potency

Background

Treatment of tumors with macromolecular toxins directed to cytoplasmic targets requires selective endocytosis followed by release of intact toxin from the endosomal/lysosomal compartment. The latter step remains a particular challenge. Claudins 3 and 4 are tight junction proteins that are over-expressed in many types of tumors. This study utilized the C-terminal 30 amino acid fragment of C. perfringens enterotoxin (CPE), which binds to claudins 3 and 4, to deliver a toxin in the form of recombinant gelonin (rGel) to the cytoplasm of the human ovarian carcinoma cell line 2008.

Results

CPE was fused to rGel at its N-terminal end via a flexible G₄S linker. This CPE-G₄S-rGel molecule was internalized into vesicles from which location it produced little cytotoxicity. To enhance release from the endosomal/lysosomal compartment a poly-arginine sequence (R₉) was introduced between the CPE and the rGel. CPE-R₉-rGel was 10-fold more cytotoxic but selectivity for claudin-expressing cells was lost. The addition of a poly-glutamic acid sequence (E₉) through a G₄S linker to R₉-rGel (E₉-G₄S-R₉-rGel) largely neutralized the non-selective cell membrane penetrating activity of the R₉ motif. However, introduction of CPE to the E₉-G₄S-R₉-rGel fusion protein (CPE-E₉-G₄S-R₉-rGel) further reduced its cytotoxic effect. Treatment with the endosomolytic reagent chloroquine increased the cytotoxicity of CPE-E₉-G₄S-R₉-rGel. Several types of linkers susceptible to cleavage by furin and endosomal cathepsin B were tested for their ability to enhance R₉-rGel release but none of these modifications further enhanced the cytotoxicity of CPE-E₉-G₄S-R₉-rGel.

Conclusion

We conclude that while a claudin-3 and -4 ligand serves to deliver rGel into 2008 cells the delivered molecules were entrapped in intracellular vesicles. Incorporation of R₉ non-specifically increased rGel cytotoxicity and this effect could be masked by inclusion of an E9 sequence. However, the putative protease cleavable sequences tested were inadequate for release of R₉-rGel from CPE-E₉-G₄S-R₉-rGel.

Antitumor activity of fibroblast growth factor receptor 3-specific immunotoxins in a xenograft mouse model of bladder carcinoma is mediated by apoptosis

Human single-chain Fv directed against fibroblast growth factor receptor 3 (FGFR3) have been shown to block proliferation of RT112 bladder carcinoma cells in vitro. Here, we examined the ability of the recombinant gelonin toxin (rGel) to enhance this inhibitory effect in vitro and in vivo on the bladder cancer cell line RT112 and the corresponding xenografts. Immunotoxins were genetically engineered by fusing FGFR3-specific Fv fragments (3C) to the NH(2) terminus of rGel and expressed as a soluble protein in Escherichia coli. The 3C/rGel fusion construct showed an IC(50) of 200 nmol/L against log-phase RT112 cells compared with 1,500 nmol/L for free rGel. Immunofluorescence studies showed that the 3C/rGel construct internalized rapidly into the cytoplasm of RT112 cells within 1 h of exposure. The mechanism of immunotoxin-induced cell death was found to be mediated by apoptosis. RT112 tumor xenografts in severe combined immunodeficient mice treated with 50 mg/kg 3C/rGel exhibited considerable growth delay relative to control tumors and a significant reduction of 55% to 70% in mean tumor size. Immunohistochemical analysis showed that tumors from mice treated with 3C/rGel displayed considerable apoptotic damage compared with control groups. Subcellular location of FGFR3 in immunotoxin-treated tumors indicated a translocation of FGFR3 to the nuclear membrane in contrast to tumors from saline-treated controls. These results show that FGFR3-driven immunotoxins may be an effective therapeutic agent against human bladder and other tumor types overexpressing FGFR3.

VEGF receptors and neuropilins are expressed in the urothelial and neuronal cells in normal mouse urinary bladder and are upregulated in inflammation

Recent evidence supports a role for vascular endothelium growth factor (VEGF) signaling in bladder inflammation. However, it is not clear what bladder cells are targeted by VEGF. Therefore, we determined the nature of cells responding to VEGF in normal and inflamed bladders by tagging such cells in vivo with a targeted fluorescent tracer, scVEGF/Cy, an engineered single-chain VEGF labeled with Cy5.5 dye, which identifies cells with accessible and functionally active VEGF receptors. Inflammation was induced by intravesical instillation of PAR-activating peptides or BCG. In vivo NIRF imaging with intravenously injected scVEGF/Cy revealed accumulation of the tracer in the control mouse bladder and established that inflammation increased the steady-state levels of tracer uptake. Ex vivo colocalization of Cy5.5 dye revealed that in normal and at a higher level in inflamed bladder, accumulation of scVEGF/Cy occurs in both urothelial and ganglial cells, expressing VEGF receptors VEGFR-1 and VEGFR-2, as well as VEGF coreceptors neuropilins (NRP) NRP1 and NRP2. PCR results indicate that the messages for VEGF-Rs and NRPs are present in the bladder mucosa and ChIP/QPCR analysis indicated that inflammation induced upregulation of genes encoding VEGFRs and NRPs. Our results strongly suggest new and blossoming VEGF-driven processes in bladder urothelial cells and ganglia in the course of inflammation. We expect that molecular imaging of the VEGF pathway in the urinary tract by receptor-mediated cell tagging in vivo will be useful for clinical diagnosis and therapeutic monitoring, and will help to accelerate the development of bladder-targeting drugs and treatments.

Bladder cancer angiogenesis and metastasis--translation from murine model to clinical trial

In the majority of cases, death from bladder cancer results from metastatic disease. Understanding the closely linked mechanisms of invasion, metastasis and angiogenesis in bladder cancer has allowed us to develop new therapeutic strategies that harbor the promise of decisive improvements in patient survival. The essential link between cell based experiments and the translation of novel agents into human patients with bladder cancer is the animal model. With emphasis on the orthotopic xenograft model, this review outlines some key mechanisms relevant to angiogenesis and the development of metastasis in bladder cancer. We highlight especially pathways related to MMP-9, IL-8, VEGF and EGFR. Most commonly, expression patterns of these markers in patients have correlated to disease progression and patient survival, which has led to laboratory investigations of these markers and eventually novel targeted therapies that are translated back into the clinic by means of clinical trials. Although imperfect in their translatability into clinical efficacy, animal models remain a critical tool in bladder cancer research.

SNS-032 prevents tumor cell-induced angiogenesis by inhibiting vascular endothelial growth factor

Cell proliferation, migration, and capillary network formation of endothelial cells are the fundamental steps for angiogenesis, which involves the formation of new blood vessels. The purpose of this study is to investigate the effect of a novel aminothiazole SNS-032 on these critical steps for in vitro angiogenesis using a coculture system consisting of human umbilical vein endothelial cells (HUVECs) and human glioblastoma cells (U87MG). SNS-032 is a potent selective inhibitor of cyclin-dependent kinases 2, 7, and 9, and inhibits both transcription and cell cycle. In this study, we examined the proliferation and viability of HUVECs and U87MG cells in the presence of SNS-032 and observed a dose-dependent inhibition of cellular proliferation in both cell lines. SNS-032 inhibited threedimensional capillary network formations of endothelial cells. In a coculture study, SNS-032 completely prevented U87MG cell-mediated capillary formation of HUVECs. This inhibitor also prevented the migration of HUVECs when cultured alone or cocultured with U87MG cells. In addition, SNS-032 significantly prevented the production of vascular endothelial growth factor (VEGF) in both cell lines, whereas SNS-032 was less effective in preventing capillary network formation and migration of endothelial cells when an active recombinant VEGF was added to the medium. In conclusion, SNS-032 prevents in vitro angiogenesis, and this action is attributable to blocking of VEGF.

Increased expression of VEGF121/VEGF165-189 ratio results in a significant enhancement of human prostate tumor angiogenesis

Vascular endothelial growth factor (VEGF) is a proangiogenic factor upregulated in many tumors. The alternative splicing of VEGF mRNA renders 3 major isoforms of 121, 165 and 189 amino-acids in humans (1 less amino-acid for each mouse VEGF isoform). We have designed isoform specific real time QRT-PCR assays to quantitate VEGF transcripts in mouse and human normal and malignant prostates. In the human normal prostate, VEGF(165) was the predominant isoform (62.8% +/- 5.2%), followed by VEGF(121) (22.5% +/- 6.3%) and VEGF(189) (p < 0.001) (14.6% +/- 2.1%). Prostate tumors showed a significant increase in the percentage of VEGF(121) and decreases in VEGF(165) (p < 0.01) and VEGF(189) (p < 0.05). However, the amount of total VEGF mRNA was similar between normal and malignant prostates. VEGF(164) was the transcript with the highest expression in the mouse normal prostate. Unlike human prostate cancer, tumors from TRAMP mice demonstrated a significant increase in total VEGF mRNA levels and in each of the VEGF isoforms, without changes in the relative isoform ratios. Morpholino phosphorodiamide antisense oligonucleotide technology was used to increase the relative amount of VEGF(121) while proportionally decreasing VEGF(165) and VEGF(189) levels in human prostate cell lines, through the modification of alternative splicing, without changing transcription levels and total amount of VEGF. The increase in the VEGF(121)/VEGF(165-189) ratio in PC3 cells resulted in a dramatic increase in prostate tumor angiogenesis in vivo. Our results underscore the importance of VEGF(121) in human prostate carcinoma and demonstrate that the relative expression of the different VEGF isoforms has an impact on prostate carcinogenesis.