KRN951, a highly potent inhibitor of vascular endothelial growth factor receptor tyrosine kinases, has antitumor activities and affects functional vascular properties

Tivozanib in the treatment of renal cell carcinoma

Renal cell carcinoma (RCC) is an aggressive malignancy compared to other urological malignancies and has been associated with poor responses to conventional cytotoxic chemotherapy. Interferon-α and interleukin-2 were previously utilized in a limited number of patients with good performance status due to toxicity and safety issues. Over the last decade, through advances in the understanding of the biology and pathology of RCC, the important role of vascular endothelial growth factor (VEGF) in RCC has been identified. Data from randomized trials have led to the approval of first-generation tyrosine kinase inhibitors (TKIs) sorafenib, sunitinib, and pazopanib; however, these agents inhibit a wide variety of kinase targets and are associated with a range of adverse effects. More recently, a new generation TKI, axitinib, has been approved by the US Food and Drug Administration. Tivozanib is a novel TKI, which is a potent inhibitor of VEGF-1, VEGF-2, VEGF-3, c-kit, and PDGR kinases, with a more restricted target spectrum. Phase II and III studies have demonstrated significant activity and a favorable safety profile as an initial targeted treatment for advanced RCC. This review examines the emerging data with tivozanib for the treatment of advanced RCC. Preclinical investigations as well as Phase I, II, and III data are examined; data on the comparative benefits of tivozanib are reviewed. Finally, we discuss the future potential of tivozanib in combination, biomarkers associated with tivozanib response, and acquisition of resistance and nonkidney cancer indications.

Phase Ib study of tivozanib (AV-951) in combination with temsirolimus in patients with renal cell carcinoma

BACKGROUND

Tivozanib is a potent and selective tyrosine kinase inhibitor of vascular endothelial growth factor receptors (VEGFR)-1, -2 and -3, with a long half-life. Tivozanib has demonstrated clinical activity and acceptable tolerability in renal cell carcinoma (RCC). This phase Ib study determined the recommended phase II dose (RP2D) and evaluated the safety and clinical activity of tivozanib plus temsirolimus, a mammalian target of rapamycin inhibitor.

PATIENTS AND METHODS

Patients with advanced RCC were administered open-label tivozanib 0.5, 1.0 or 1.5mg/d orally (3 weeks on/1 week off) and temsirolimus 15 or 25 mg/week intravenously in a 3+3 dose-escalation design and subsequent expansion cohort.

RESULTS

Of 27 patients treated, 20 patients had received ≥ 1 prior VEGF-targeted therapy. No dose-limiting toxicities occurred; the RP2D was determined to be tivozanib 1.5mg/d plus temsirolimus 25mg/week. Combination of tivozanib plus temsirolimus demonstrated acceptable tolerability and suggested no synergistic toxicity. The most common grade ≤ 3 adverse events were fatigue and thrombocytopenia (15% each). One patient each required dose reduction of tivozanib or temsirolimus due to an adverse event. Confirmed partial responses and stable disease were achieved at 23% and 68%, respectively. Pharmacokinetic analyses may suggest lack of an interaction between tivozanib and temsirolimus.

CONCLUSIONS

In this small phase Ib study, tivozanib and temsirolimus were safely combined at the fully recommended dose and schedule of both agents. The observed clinical activity and manageable toxicity profile of this combination warrant further exploration in patients with RCC.

Recent advances in the treatment of metastatic renal cell carcinoma

In the past 5 years, the treatment of patients with metastatic renal cell carcinoma has changed dramatically from being largely cytokine-based with the emergence of targeted therapy. Following the elucidation of various molecular pathways in renal cell carcinoma, targeted agents (particularly vascular endothelial growth factor-targeting antiangiogenic agents) now form the backbone of most therapeutic strategies for patients with metastatic renal cell carcinoma and the outcome of treatment has improved. However, many tumors eventually develop resistance to targeted therapy due to secondary mutation of the target protein or compensatory changes within the target pathway that bypass the site of inhibition. On the other hand, there are new forms of immunotherapy that hold the promise of improving the outcome for patients with metastatic renal cell carcinoma. In this article, we describe some of these new therapies, including the anti-vascular endothelial growth factor monoclonal antibody bevacizumab, several receptor tyrosine kinase inhibitors (sorafenib, sunitinib, pazopanib, axitinib, and tivozanib), the mammalian target of rapamycin inhibitors temsirolimus and everolimus, and new immunotherapy modalities, such as anti-cytotoxic T-lymphocyte-associated antigen 4 antibody and anti-programmed cell death 1/programmed cell death-ligand 1 antibody. We also discuss their role in the current management of patients with metastatic renal cell carcinoma.

Anti-angiogenic and anti-tumor effects of TAK-593, a potent and selective inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptor tyrosine kinase

We recently reported that TAK-593, a novel imidazo[1,2-b]pyridazine derivative, is a highly potent and selective inhibitor of the vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) receptor tyrosine kinase families. Moreover, TAK-593 exhibits a uniquely long-acting inhibitory profile towards VEGF receptor 2 (VEGFR2) and PDGF receptor β (PDGFRβ). In this study, we demonstrated that TAK-593 potently inhibits VEGF- and PDGF-stimulated cellular phosphorylation and proliferation of human umbilical vein endothelial cells and human coronary artery smooth muscle cells. TAK-593 also potently inhibits VEGF-induced tube formation of endothelial cells co-cultured with fibroblasts. Oral administration of TAK-593 exhibited strong anti-tumor effects against various human cancer xenografts along with good tolerability despite a low level of plasma exposure. Even after the blood and tissue concentrations of TAK-593 decreased below the detectable limit, a pharmacodynamic marker (phospho VEGFR2) was almost completely suppressed, indicating that its long duration of enzyme inhibition might contribute to the potent activity of TAK-593. Immunohistochemical staining indicated that TAK-593 showed anti-proliferative and pro-apoptotic effects on tumors along with a decrease of vessel density and inhibition of pericyte recruitment to microvessels in vivo. Furthermore, dynamic contrast-enhanced magnetic resonance imaging revealed that TAK-593 reduced tumor vessel permeability prior to the onset of anti-tumor activity. In conclusion, TAK-593 is an extremely potent VEGFR/PDGFR kinase inhibitor whose potent anti-angiogenic activity suggests therapeutic potential for the treatment of solid tumors.

Tyrosine kinase inhibitor-induced thyroid disorders: a review and hypothesis

BACKGROUND

Thyroid dysfunction is a well-known adverse effect of sunitinib, a drug that targets multiple receptor tyrosine kinases, including vascular endothelial growth factor receptor (VEGFR). As several kinds of tyrosine kinase inhibitors (TKIs) are now available, this has been postulated to be a side effect of the TKIs that target the VEGFR (VEGF-TKIs). However, sunitinib, one of the first-generation TKIs, likely causes thyroid dysfunction more frequently than other TKI classes, leading not only to hypothyroidism, but also to thyrotoxicosis.

SUMMARY

Based on the reports published to date, including our own studies, we have hypothesized that sunitinib may exert these effects, because it targets a broad spectrum of tyrosine kinases. This not only includes VEGFR2, but also VEGFR1 and the platelet-derived growth factor receptor (PDGFR). This, in turn, may suggest that not only VEGFR2 but also the PDGFR and/or the VEGFR1 play an important role during angiogenesis in the thyroid.

CONCLUSIONS

Our current hypothesis may explain the mechanisms that underlie TKI-induced thyroid disorders. By learning how various kinds of TKIs affect thyroid function, we may elucidate how the angiogenesis in thyroid is regulated both physiologically and pathologically.

Structure, development, preclinical and clinical efficacy of tivozanib (KRN-951, AV-951)

Tivozanib hydrochloride monohydrate (tivozanib; formerly KRN-951, AV-951) is a potent pan-VEGF receptor tyrosine kinase inhibitor. The biological activity of tivozanib seems to outstand that of other VEGF tyrosine kinase inhibitors. In Phase I studies, observed side effects are generally mild, with hypertension being the most common adverse event. In single-agent Phase II and III studies in patients with advanced or metastatic renal cell carcinoma, tivozanib has demonstrated convincing clinical activity. Further clinical trials of tivozanib combined with various cytotoxic drug regimens as well as other classes of target-specific anticancer agents (e.g., mTOR inhibitors) for other indications are underway. Tivozanib has not yet been approved for regular use.

c-Myc enhances colon cancer cell-mediated angiogenesis through the regulation of HIF-1α

Angiogenesis plays a pivotal role in tumor growth. The hypoxia-inducible factor 1, α subunit (HIF-1α)/vascular endothelial growth factor pathway is the most important pathway for regulating angiogenesis in the tumor microenvironment. c-Myc is an important oncogene that has many biological functions. In this study, we investigated the role of c-Myc in tumor angiogenesis. We found that the overexpression of c-Myc in colon cancer cells could promote the expression of HIF-1α and that of vascular endothelial growth factor. Moreover, we found that c-Myc regulated HIF-1α at the post-transcriptional level. The results revealed c-Myc-dependent regulation of HIF-1α instead of HIF-1α-dependent c-Myc regulation for the first time. They also showed that c-Myc was essential to regulate colon cancer cell-mediated angiogenesis and contributed to tumor growth. This research provides the theoretical basis for clinical trials of new therapeutic targets of c-Myc and HIF-1α in colon cancer cells.

Tivozanib: current status and future directions in the treatment of solid tumors

INTRODUCTION

Tivozanib is a novel tyrosine kinase inhibitor (TKI) which inhibits vascular endothelial growth factor (VEGF) receptors-1, -2, and -3 at nanomolar concentrations.

AREAS COVERED

A comprehensive MEDLINE and American Society of Clinical Oncology abstract search was performed to gather all relevant clinical and translational data related to tivozanib. We discuss pre-clinical studies associated with tivozanib, and the results of a Phase I assessment in advanced solid tumors. We highlight combination studies with tivozanib, including pairings of tivozanib with cytotoxic therapy in patients with colorectal cancer and breast cancer. A randomized discontinuation Phase II study and a randomized Phase III study assessing the activity of tivozanib in metastatic renal cell carcinoma (mRCC) are described in detail.

EXPERT OPINION

Tivozanib will face the challenge of entering an already crowded therapeutic space in mRCC-emerging combination studies and biomarker assessments may distinguish this agent among other VEGF-TKIs. The current review will outline the development pathway of tivozanib to date, and offer lessons learned and future opportunities.

Vascular endothelial growth factor (VEGF) receptors: drugs and new inhibitors

The recent launch onto the market of five VEGFR inhibitors indicates the therapeutic value of these agents and the importance of the research in the field of angiogenesis inhibitors for future oncologic therapy. In this Perspective we briefly report the inhibitors that are in clinical use, while we dedicate two wider sections to the compounds that are in clinical trials and to the new derivatives appearing in the literature. We especially consider the medicinal chemistry aspect of the topic and report the structure-activity relationship studies and the binding mode of some inhibitors as well as the biological data of the compounds discovered in the past 5 years.

A guide to picking the most selective kinase inhibitor tool compounds for pharmacological validation of drug targets

To establish the druggability of a target, genetic validation needs to be supplemented with pharmacological validation. Pharmacological studies, especially in the kinase field, are hampered by the fact that many reference inhibitors are not fully selective for one target. Fortunately, the initial trickle of selective inhibitors released in the public domain has steadily swelled into a stream. However, rationally picking the most selective tool compound out of the increasing amounts of available inhibitors has become progressively difficult due to the lack of accurate quantitative descriptors of drug selectivity. A recently published approach, termed 'selectivity entropy', is an improved way of expressing selectivity as a single-value parameter and enables rank ordering of inhibitors. We provide a guide to select the best tool compounds for pharmacological validation experiments of candidate drug targets using selectivity entropy. In addition, we recommend which inhibitors to use for studying the biology of the 20 most investigated kinases that are clinically relevant: Abl (ABL1), AKT1, ALK, Aurora A/B, CDKs, MET, CSF1R (FMS), EGFR, FLT3, ERBB2 (HER2), IKBKB (IKK2), JAK2/3, JNK1/2/3 (MAPK8/9/10), MEK1/2, PLK1, PI3Ks, p38α (MAPK14), BRAF, SRC and VEGFR2 (KDR).

Pharmacological strategies to overcome HER2 cross-talk and Trastuzumab resistance

Approximately 20-30% of breast cancers show increased expression of the HER2 receptor tyrosine kinase. Trastuzumab (Herceptin) is a clinically approved anti-HER2 monoclonal antibody. Many patients with HER2-overexpressing metastatic breast cancer respond to trastuzumab; however, a subset display primary drug resistance. In addition, many patients who initially respond to trastuzumab ultimately develop disease progression. Multiple molecular mechanisms contributing to trastuzumab resistance have been proposed in the literature. These mechanisms include cross-signaling from related HER/erbB receptors and compensatory signaling from receptors outside of the HER/erbB family, including receptors for insulin-like growth factor-I, vascular endothelial growth factor, and transforming growth factor beta. The major downstream signaling pathway activated by HER2 cross-talk is PI3K/mTOR, and a potential integrator of receptor cross-talk is Src-focal adhesion kinase (FAK) signaling. PI3K, Src, and FAK have independently been implicated in trastuzumab resistance. In this review, we will discuss pharmacological inhibition of HER2 cross-talk as a strategy to treat trastuzumab-refractory HER2-overexpresssing breast cancer.

Miniaturized embryo array for automated trapping, immobilization and microperfusion of zebrafish embryos

Zebrafish (Danio rerio) has recently emerged as a powerful experimental model in drug discovery and environmental toxicology. Drug discovery screens performed on zebrafish embryos mirror with a high level of accuracy the tests usually performed on mammalian animal models, and fish embryo toxicity assay (FET) is one of the most promising alternative approaches to acute ecotoxicity testing with adult fish. Notwithstanding this, automated in-situ analysis of zebrafish embryos is still deeply in its infancy. This is mostly due to the inherent limitations of conventional techniques and the fact that metazoan organisms are not easily susceptible to laboratory automation. In this work, we describe the development of an innovative miniaturized chip-based device for the in-situ analysis of zebrafish embryos. We present evidence that automatic, hydrodynamic positioning, trapping and long-term immobilization of single embryos inside the microfluidic chips can be combined with time-lapse imaging to provide real-time developmental analysis. Our platform, fabricated using biocompatible polymer molding technology, enables rapid trapping of embryos in low shear stress zones, uniform drug microperfusion and high-resolution imaging without the need of manual embryo handling at various developmental stages. The device provides a highly controllable fluidic microenvironment and post-analysis eleuthero-embryo stage recovery. Throughout the incubation, the position of individual embryos is registered. Importantly, we also for first time show that microfluidic embryo array technology can be effectively used for the analysis of anti-angiogenic compounds using transgenic zebrafish line (fli1a:EGFP). The work provides a new rationale for rapid and automated manipulation and analysis of developing zebrafish embryos at a large scale.

Antitumor Activity and Safety of Tivozanib (AV-951) in a Phase II Randomized Discontinuation Trial in Patients With Renal Cell Carcinoma

Purpose

The antitumor activity and safety of tivozanib, which is a potent and selective vascular endothelial growth factor receptor-1, -2, and -3 inhibitor, was assessed in patients with advanced/metastatic renal cell carcinoma (RCC).

Patients and Methods

In this phase II, randomized discontinuation trial, 272 patients received open-label tivozanib 1.5 mg/d (one cycle equaled three treatment weeks followed by a 1-week break) orally for 16 weeks. Thereafter, 78 patients who demonstrated ≥ 25% tumor shrinkage continued to take tivozanib, and 118 patients with less than 25% tumor change were randomly assigned to receive tivozanib or a placebo in a double-blind manner; patients with ≥ 25% tumor growth were discontinued. Primary end points included safety, the objective response rate (ORR) at 16 weeks, and the percentage of randomly assigned patients who remained progression free after 12 weeks of double-blind treatment; secondary end points included progression-free survival (PFS).

Results

Of 272 patients enrolled onto the study, 83% of patients had clear-cell histology, 73% of patients had undergone nephrectomy, and 54% of patients were treatment naive. The ORR after 16 weeks of tivozanib treatment was 18% (95% CI, 14% to 23%). Of the 118 randomized patients, significantly more patients who were randomly assigned to receive double-blind tivozanib remained progression free after 12 weeks versus patients who received the placebo (49% v 21%; P = .001). Throughout the study, the ORR was 24% (95% CI, 19% to 30%), and the median PFS was 11.7 months (95% CI, 8.3 to 14.3 months) in the overall study population. The most common grade 3 and 4 treatment-related adverse event was hypertension (12%).

Conclusion

Tivozanib was active and well tolerated in patients with advanced RCC. These data support additional development of tivozanib in advanced RCC.

Progress and contrasts of the development of tivozanib for therapy of kidney cancer

INTRODUCTION

Targets for drug development for the treatment of kidney cancer (renal cell carcinoma; RCC) include vascular endothelial growth factor (VEGF) and its receptors and mammalian target of rapamycin. Currently available oral multitargeted VEGF tyrosine kinase inhibitors (TKIs) that have been approved by the US Food and Drug Administration for advanced RCC, include sunitinib, sorafenib and pazopanib. Off-target TKI inhibition can potentially preclude full-dose combination with other targeted and chemotherapeutic agents. There is a need to develop more potent and selective targeted agents for RCC therapy, which are more effective and have minimal off-target effects.

AREAS COVERED

This drug evaluation review addresses the ongoing development for the treatment of RCC with tivozanib: a potent, selective and long-half-life VEGF TKI. The testing for clinical efficacy alone or in combination with other therapies for RCC and for other tumor types, and the clinical and market relevance of introducing another RCC therapy are discussed.

EXPERT OPINION

Tivozanib is distinguished by its high potency, selectivity, long-half-life and its potential to be effectively combined with other agents in RCC. This may offer more effective, yet well-tolerated treatment options. The relative clinical and market relevance remain to be seen, both for RCC therapy and other tumor types.

Third generation tyrosine kinase inhibitors and their development in advanced renal cell carcinoma

Angiogenesis in general and the vascular endothelial growth factor (VEGF) signaling axis in particular is a validated target in renal cell carcinoma (RCC). Clear-cell carcinoma of the kidney is now recognized as a malignancy that is sensitive to inhibitors of the VEGF pathway. Treatment options for patients with metastatic renal cell carcinoma have evolved in dramatic fashion over the past 6 years, and a new paradigm has developed. The cytokines interferon-α and interleukin-2 were previously utilized for therapy, but since December 2005, six new agents have been approved in the United States for the treatment of advanced RCC. Two are tyrosine kinase inhibitors (TKI's) including sunitinib and recently pazopanib, and the multikinase inhibitor sorafenib. The current review examines the evolving data with the next generation of TKI's, axitinib and tivozanib being developed for the treatment of advanced RCC. These agents were synthesized to provide increased target specificity and enhanced target inhibition. The preclinical and clinical data are examined, an overview of the development of these TKI's is provided, and discussion plus speculation concerning their potential roles as RCC therapy is provided.

Intussusceptive microvascular growth in tumors

Intussusception is an alternative to the sprouting mode of angiogenesis. The advantage of this mechanism of vascular growth is that blood vessels are generated more rapidly and the capillaries thereby formed are less leaky. This review article summarizes our current knowledge concerning the role played by intussusceptive microvascular growth in tumor growth. Interestingly, an angiogenic switch from sprouting to intussusceptive angiogenesis occurs after treatment with angiogenesis inhibitors and may be considered as a tumor-protective adaptative response.

Assessment of peripheral tissue perfusion disorder in streptozotocin-induced diabetic rats using dynamic contrast-enhanced MRI

PURPOSE

To assess peripheral tissue perfusion disorder in streptozotocin (STZ)-induced diabetic rats by using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

MATERIALS AND METHODS

A rat diabetes model was produced by intravenous injection of STZ. Diabetic rats were sustainably treated with either saline or insulin using an Alzet osmotic pump. Hind paw tissue perfusion was measured by signal intensity (SI) enhancement after gadolinium diethylenetriaminepentaacetic acid injection in DCE-MRI study and quantified using the initial area under the SI-time curve (IAUC). Peripheral tissue uptake of [(14)C]iodoantipyrine (IAP) was also determined as a marker of tissue blood flow for comparison with the IAUC value indicating tissue perfusion.

RESULTS

STZ caused hyperglycemia at 1 and 2 weeks after injection. Treatment with insulin significantly alleviated hyperglycemia. At 2 weeks after STZ injection, peripheral tissue perfusion was clearly reduced in the diabetic rats and its reduction was significantly improved in the insulin-treated diabetic rats. Tissue perfusion evaluated by DCE-MRI was similar to the tissue blood flow measured by [(14)C]IAP uptake.

CONCLUSION

Our findings demonstrated that DCE-MRI can assess peripheral tissue perfusion disorder in diabetes. DCE-MRI could be suitable for noninvasive evaluation of peripheral tissue perfusion in both preclinical and clinical studies. It may also be useful for developing novel drugs to protect against diabetic vascular complications.

Vascular endothelial growth factor-targeted therapy for the treatment of renal cell carcinoma

Vascular endothelial growth factor (VEGF)-targeted agents have rapidly been adopted into standard-of-care treatment for renal cell carcinoma (RCC). However, a substantial proportion of patients fail to respond to these agents or experience considerable toxicity. This article reviews the benefits and limitations of currently approved anti-VEGF agents in advanced and metastatic RCC, and the role for newly approved and developmental agents. Sunitinib and bevacizumab plus interferon (IFN)-α have demonstrated significant improvements in progression-free survival (PFS) compared with IFNα in treatment-naïve patients. A PFS benefit has also been shown with sorafenib versus placebo second-line to cytokine therapy. However, no anti-VEGF agent has shown a significant overall survival benefit. Anti-VEGF therapy is generally well tolerated, but a number of key adverse events, including dermatological, mucosal and constitutional symptoms, may limit treatment compliance and success. Pazopanib is a recently approved, highly selective anti-VEGF agent that shows benefit in PFS over IFNα, with low rates of treatment-related adverse events and, therefore, may be better tolerated than other currently approved agents. The advent of VEGF-targeted therapy for RCC has greatly improved prospects for patients with advanced or metastatic disease, but more efficacious agents are required that demonstrate a clear survival advantage. Ongoing trials evaluating novel anti-VEGF therapies could establish whether the increased potency and selectivity of these agents results in improved efficacy and tolerability in RCC patients, further improving their prognosis.

Biologic and clinical activity of tivozanib (AV-951, KRN-951), a selective inhibitor of VEGF receptor-1, -2, and -3 tyrosine kinases, in a 4-week-on, 2-week-off schedule in patients with advanced solid tumors

PURPOSE

To assess the maximum tolerated dose (MTD)/dose-limiting toxicities (DLT), safety, pharmacokinetics, and pharmacodynamics of tivozanib, a potent and selective oral VEGF receptor (VEGFR) tyrosine kinase inhibitor.

EXPERIMENTAL DESIGN

Dose levels of 1.0, 1.5, and 2.0 mg/d tivozanib for 28 days followed by 14 days of medication were explored in patients with advanced solid tumors.

RESULTS

Forty-one patients were enrolled. Animal data incorrectly predicted toxicity, resulting in DLTs at the starting dose (2.0 mg) consisting of grade 3 proteinuria and hypertension and grade 3 ataxia. At 1.0 mg, no DLT was observed. At an intermediate dose (1.5 mg), 1 patient experienced DLT consisting of grade 3 hypertension. This dose was determined as the MTD. Of 10 additional patients treated at 1.5 mg, 1 patient each experienced grade 3 hypertension and grade 3 fatigue, and 2 patients experienced grade 3 and 4 transaminase elevation. In 12 additional patients treated at 1.0 mg, no DLT was observed. Pharmacokinetics displayed long absorption time, dose proportional exposure, and a half-life of 4.7 days. Plasma levels of VEGF-A and soluble VEGFR-2 showed dose-dependent increases and decreases, respectively. Dynamic contrast-enhanced MRI indicated reduction in tumor perfusion. Clinical activity was observed in renal cell cancer, colorectal cancer, and other tumors.

CONCLUSION

Tivozanib was well tolerated with manageable side effects. The pharmacokinetics profile revealed that tivozanib was suitable for once-daily dosing. Encouraging and durable clinical activity was observed. The recommended daily dose of tivozanib in a 4-week-on and 2-week-off dosing regimen is 1.5 mg.

Assessment of multiparametric MRI in a human glioma model to monitor cytotoxic and anti-angiogenic drug effects

Early imaging or blood biomarkers of tumor response is needed to customize anti-tumor therapy on an individual basis. This study evaluates the sensitivity and relevance of five potential MRI biomarkers. Sixty nude rats were implanted with human glioma cells (U-87 MG) and randomized into three groups: one group received an anti-angiogenic treatment (Sorafenib), a second a cytotoxic drug [1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU (Carmustine)] and a third no treatment. The tumor volume, apparent diffusion coefficient (ADC) of water, blood volume fraction (BVf), microvessel diameter (vessel size index, VSI) and vessel wall integrity (contrast enhancement, CE) were monitored before and during treatment. Sorafenib reduced tumor CE as early as 1 day after treatment onset. By 4 days after treatment onset, tumor BVf was reduced and tumor VSI was increased. By 14 days after treatment onset, ADC was increased and the tumor growth rate was reduced. With BCNU, ADC was increased and the tumor growth rate was reduced 14 days after treatment onset. Thus, the estimated MRI parameters were sensitive to treatment at different times after treatment onset and in a treatment-dependent manner. This study suggests that multiparametric MR monitoring could allow the assessment of new anti-tumor drugs and the optimization of combined therapies.

Development of second-generation VEGFR tyrosine kinase inhibitors: current status

The vascular endothelial growth factor (VEGF) signaling pathway appears to be the dominant pathway involved in tumor angiogenesis, providing a rationale for targeting the VEGF receptors (VEGFR-1, -2, and -3) in the treatment of cancers. In particular, VEGF signaling is thought to be important in renal cell carcinoma (RCC) because of the deregulation of the pathway through nearly uniform loss of the von Hippel Lindau protein. The tyrosine kinase inhibitors (TKIs) sorafenib, sunitinib, and pazopanib are approved by the US Food and Drug Administration for the treatment of advanced RCC; however, these multitargeted agents inhibit a wide range of kinase targets in addition to the VEGFRs, resulting in a range of adverse effects unrelated to efficient VEGF blockade. This article reviews recent advances in the development of the second-generation VEGFR TKIs, including the more selective VEGFR TKIs tivozanib and axitinib, and focuses on the potential benefits of novel inhibitors with improved potency and selectivity.

Current status of vascular endothelial growth factor inhibition in age-related macular degeneration

Angiogenesis, the process by which new vessels are created from pre-existing vasculature, has become the subject of intense research in recent years. Increased rates of angiogenesis are associated with several disease states, including cancer, age-related macular degeneration (AMD), psoriasis, rheumatoid arthritis, and diabetic retinopathy. Vascular endothelial growth factor (VEGF) is an important modulator of angiogenesis, and has been implicated in the pathology of a number of conditions, including AMD, diabetic retinopathy, and cancer. AMD is a progressive disease of the macula and the third major cause of blindness worldwide. If not treated appropriately, AMD can progress to involve both eyes. Until recently, the treatment options for AMD have been limited, with photodynamic therapy (PDT) the mainstay of treatment. Although PDT is effective at slowing disease progression, it rarely results in improved vision. Several therapies have been or are now being developed for neovascular AMD, with the goal of inhibiting VEGF. These VEGF inhibitors include the RNA aptamer pegaptanib, partial and full-length antibodies ranibizumab and bevacizumab, the VEGF receptor decoy aflibercept, small interfering RNA-based therapies bevasiranib and AGN 211745, sirolimus, and tyrosine kinase inhibitors, including vatalanib, pazopanib, TG 100801, TG 101095, AG 013958, and AL 39324. At present, established therapies have met with great success in reducing the vision loss associated with neovascular AMD, whereas those still under investigation offer the potential for further advances. In AMD patients, these therapies slow the rate of vision loss and in some cases increase visual acuity. Although VEGF-inhibitor therapies are a milestone in the treatment of these disease states, several concerns need to be addressed before their impact can be fully realized.

Significance of phospho-vascular endothelial growth factor receptor-2 expression in pancreatic cancer

Vascular endothelial growth factor receptors (VEGFRs) are mainly expressed by endothelial cells, but they are also expressed by some cancer cells, including pancreatic cancer. The objective of this study was to evaluate the significance of VEGFRs expression in pancreatic cancer cells. A total of 107 primary pancreatic tumors were stained with antibodies against VEGFR-1, VEGFR-2, phospho-VEGFR-2 (pVEGFR-2), VEGFR-3, VEGF-A, VEGF-C, and VEGF-D. VEGFR-2 and pVEGFR-2 expression were positive in 74 (69%) and 54 (50%) of 107 pancreatic cancers. There was a significant correlation (P < 0.001) between VEGFR-2 expression and pVEGFR-2 expression. pVEGFR-2 was significantly associated with invasion to the anterior capsule of pancreas (P = 0.032) and arterial invasion (P = 0.012). In contrast, VEGFR-1 and VEGFR-3 expression was only observed in 13 (12%) and 15 (14%) of 107 pancreatic cancers, and was not associated with any clinicopathological features. The prognosis of pVEGFR-2 positive patients with stage IIA tumors was significantly (P = 0.0441) poorer than that of pVEGFR-2-negative patients. VEGF-A, VEGF-C, and VEGF-D expression was positive in 42 (39%), 82 (77%), and 39 (36%) of 107 pancreatic cancers, respectively. The prognosis for VEGF-A-positive patients was significantly (P = 0.0425) poor, but not for VEGF-C-positive and VEGF-D-positive patients. A multivariate analysis indicated pVEGFR-2 expression to be an independent prognostic factor, but not VEGF-A. These findings suggested that VEGFR-2 signaling might therefore be associated with the prognosis of patients with pancreatic cancer. The expression of pVEGFR-2 might be a novel predictive prognostic marker for patients with pancreatic cancers, especially at clinical stage IIA.

E7050: a dual c-Met and VEGFR-2 tyrosine kinase inhibitor promotes tumor regression and prolongs survival in mouse xenograft models

c-Met is the cellular receptor for hepatocyte growth factor (HGF) and is known to be dysregulated in various types of human cancers. Activation of the HGF/c-Met pathway causes tumor progression, invasion, and metastasis. Vascular endothelial growth factor (VEGF) is also known as a key molecule in tumor progression through the induction of tumor angiogenesis. Because of their key roles in tumor progression, these pathways provide attractive targets for therapeutic intervention. We have generated a novel, orally active, small molecule compound, E7050, which inhibits both c-Met and vascular endothelial growth factor receptor (VEGFR)-2. In vitro studies indicate that E7050 potently inhibits phosphorylation of both c-Met and VEGFR-2. E7050 also potently represses the growth of both c-met amplified tumor cells and endothelial cells stimulated with either HGF or VEGF. In vivo studies using E7050 showed inhibition of the phosphorylation of c-Met and VEGFR-2 in tumors, and strong inhibition of tumor growth and tumor angiogenesis in xenograft models. Treatment of some tumor lines containing c-met amplifications with high doses of E7050 (50-200 mg/kg) induced tumor regression and disappearance. In a peritoneal dissemination model, E7050 showed an antitumor effect against peritoneal tumors as well as a significant prolongation of lifespan in treated mice. Our results indicate that E7050 is a potent inhibitor of c-Met and VEGFR-2 and has therapeutic potential for the treatment of cancer.

Increase in tumour permeability following TGF-beta type I receptor-inhibitor treatment observed by dynamic contrast-enhanced MRI

Background:

To enhance the success rate of nanocarrier-mediated chemotherapy combined with an anti-angiogenic agent, it is crucial to identify parameters for tumour vasculature that can predict a response to the treatment of the anti-angiogenic agent.

Methods:

To apply transforming growth factor (TGF)-β type I receptor (TβR-I) inhibitor, A-83-01, to combined therapy, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was carried out in mice bearing colon 26 cells using gadolinium (Gd)-DTPA and for its liposomal formulation to evaluate changes in tumour microvasculature following A-83-01. Tumour vascular parameters from DCE-MRI were compared with histological assessment and apparent diffusion coefficient of water in tumour generated by diffusion-weighted MRI.

Results:

Contrary to evaluations reported for anti-angiogenic agents, A-83-01 treatment increased the initial area under the Gd concentration–time curve (IAUGC₆₀), volume transfer constant (K^trans) and fractional plasma volume (v_p) significantly within 24 h, that was positively related to α-smooth muscle actin-positive pericyte coverage and tumour cell proliferation, and was correlated inversely with the apparent diffusion coefficient. The vascular function of the tumour improved by A-83-01 treatment was well assessed on post-liposomal Gd-DTPA-enhanced MR images, which predicted delivery of a liposomal drug to the tumour.

Conclusion:

These findings suggest that DCE-MRI and, in particular, K^trans and v_p quantitation, provide important additional information about tumour vasculature by A-83-01 treatment.

Antitumor effects of 2-oxoglutarate through inhibition of angiogenesis in a murine tumor model

Hypoxia-inducible factor 1 (HIF-1) plays essential roles in tumor angiogenesis and growth by regulating the transcription of several key genes in response to hypoxic stress and growth factors. HIF-1 is a heterodimeric transcriptional activator consisting of inducible alpha and constitutive beta subunits. In oxygenated cells, proteins containing the prolyl hydroxylase domain (PHD) directly sense intracellular oxygen concentrations. PHDs tag HIF-1alpha subunits for polyubiquitination and proteasomal degradation by prolyl hydroxylation using 2-oxoglutarate (2-OX) and dioxygen. Our recent studies showed that 2-OX reduces HIF-1alpha, erythropoietin, and vascular endothelial growth factor (VEGF) expression in the hepatoma cell line Hep3B when under hypoxic conditions in vitro. Here, we report that similar results were obtained in Lewis lung cancer (LLC) cells in in vitro studies. Furthermore, 2-OX showed potent antitumor effects in a mouse dorsal air sac assay and a murine tumor xenograft model. In the dorsal air sac assay, 2-OX reduced the numbers of newly formed vessels induced by LLC cells. In a murine tumor xenograft model, intraperitoneal injection of 2-OX significantly inhibited tumor growth and angiogenesis in tumor tissues. Moreover, 5-fluorouracil combined with 2-OX significantly inhibited tumor growth in this model, which was accompanied by reduction of Vegf gene expression and inhibited angiogenesis in tumor tissues. These results suggest that 2-OX is a promising anti-angiogenic therapeutic agent.

Broad antitumor activity in breast cancer xenografts by motesanib, a highly selective, oral inhibitor of vascular endothelial growth factor, platelet-derived growth factor, and Kit receptors

PURPOSE

Angiogenesis plays a critical role in breast cancer development and progression. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that regulates endothelial cell proliferation and survival. We investigated the effects of motesanib, a novel, oral inhibitor of VEGF receptors 1, 2, and 3; platelet-derived growth factor receptor; and Kit receptor, on the growth of xenografts representing various human breast cancer subtypes.

EXPERIMENTAL DESIGN

Athymic nude mice were implanted with MCF-7 (luminal) or MDA-MB-231 (mesenchymal) tumor fragments or Cal-51 (mixed/progenitor) tumor cells. Once tumors were established, animals were randomized to receive increasing doses of motesanib alone or motesanib plus cytotoxic chemotherapy (docetaxel, doxorubicin, or tamoxifen).

RESULTS

Across all three xenograft models, motesanib treatment resulted in significant dose-dependent reductions in tumor growth, compared with vehicle-treated controls, and in marked reductions in viable tumor fraction and blood vessel density. No significant effect on body weight was observed with compound treatment compared with control-treated animals. Motesanib did not affect the proliferation of tumor cells in vitro. There was a significantly greater reduction in xenograft tumor growth when motesanib was combined with docetaxel (MDA-MB-231 tumors) or with the estrogen receptor modulator tamoxifen (MCF-7 tumors), compared with either treatment alone, but not when combined with doxorubicin (Cal-51 tumors).

CONCLUSIONS

Treatment with motesanib alone or in combination with chemotherapy inhibits tumor growth in vivo in various models of human breast cancer. These data suggest that motesanib may have broad utility in the treatment of human breast cancer.

Combination of antiangiogenesis with chemotherapy for more effective cancer treatment

Angiogenesis is a hallmark of tumor development and metastasis and is now a validated target for cancer treatment. However, the survival benefits of antiangiogenic drugs have thus far been rather modest, stimulating interest in developing more effective ways to combine antiangiogenic drugs with established chemotherapies. This review discusses recent progress and emerging challenges in this field; interactions between antiangiogenic drugs and conventional chemotherapeutic agents are examined, and strategies for the optimization of combination therapies are discussed. Antiangiogenic drugs such as the anti-vascular endothelial growth factor antibody bevacizumab can induce a functional normalization of the tumor vasculature that is transient and can potentiate the activity of coadministered chemoradiotherapies. However, chronic angiogenesis inhibition typically reduces tumor uptake of coadministered chemotherapeutics, indicating a need to explore new approaches, including intermittent treatment schedules and provascular strategies to increase chemotherapeutic drug exposure. In cases where antiangiogenesis-induced tumor cell starvation augments the intrinsic cytotoxic effects of a conventional chemotherapeutic drug, combination therapy may increase antitumor activity despite a decrease in cytotoxic drug exposure. As new angiogenesis inhibitors enter the clinic, reliable surrogate markers are needed to monitor the progress of antiangiogenic therapies and to identify responsive patients. New targets for antiangiogenesis continue to be discovered, increasing the opportunities to interdict tumor angiogenesis and circumvent resistance mechanisms that may emerge with chronic use of these drugs.

Macromolecular dynamic contrast-enhanced (DCE)-MRI detects reduced vascular permeability in a prostate cancer bone metastasis model following anti-platelet-derived growth factor receptor (PDGFR) therapy, indicating a drop in vascular endothelial growth factor receptor (VEGFR) activation

The antivascular function of the platelet-derived growth factor receptor (PDGFR) inhibitor imatinib combined with paclitaxel has been demonstrated by invasive immunohistochemistry. The purpose of this study was to 1) noninvasively monitor the response to anti-PDGFR treatment, and 2) understand the underlying mechanism of this response. Thus, response to treatment was studied in a prostate cancer bone metastasis model using macromolecular (biotin-bovine serum albumin [BSA]-Gd-diethylene triamine pentaacetic acid [GdDTPA]) dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Human prostate cancer (PC-3MM2) bone metastases that caused osteolysis and grew in neighboring muscle showed a high blood-volume fraction (fBV) and vascular permeability (PS) at the tumor periphery compared to muscle tissue and intraosseous tumor. Imatinib alone or with paclitaxel significantly reduced PS by 35% (one-tailed paired t-test, P = 0.045) and 40% (P = 0.0003), respectively, whereas paclitaxel alone or no treatment had no effect. Based on changes in PS, we hypothesized that imatinib interferes with the signaling pathway of vascular endothelial growth factor (VEGF). This mechanism was verified by immunohistochemistry. It demonstrated reduced activation of both PDGFR-beta and VEGF receptor 2 (VEGFR2) in imatinib-treated mice. Our study therefore demonstrates that macromolecular DCE-MRI can be used to detect early vascular effects associated with response to therapy targeted to PDGFR, and provides insight into the role played by VEGF in anti-PDGFR therapy.

Tumor recovery by angiogenic switch from sprouting to intussusceptive angiogenesis after treatment with PTK787/ZK222584 or ionizing radiation

Inhibitors of angiogenesis and radiation induce compensatory changes in the tumor vasculature both during and after treatment cessation. To assess the responses to irradiation and vascular endothelial growth factor-receptor tyrosine kinase inhibition (by the vascular endothelial growth factor tyrosine kinase inhibitor PTK787/ZK222854), mammary carcinoma allografts were investigated by vascular casting; electron, light, and confocal microscopy; and immunoblotting. Irradiation and anti-angiogenic therapy had similar effects on the tumor vasculature. Both treatments reduced tumor vascularization, particularly in the tumor medulla. After cessation of therapy, the tumor vasculature expanded predominantly by intussusception with a plexus composed of enlarged sinusoidal-like vessels containing multiple transluminal tissue pillars. Tumor revascularization originated from preserved alpha-smooth muscle actin-positive vessels in the tumor cortex. Quantification revealed that recovery was characterized by an angiogenic switch from sprouting to intussusception. Up-regulated alpha-smooth muscle actin-expression during recovery reflected the recruitment of alpha-smooth muscle actin-positive cells for intussusception as part of the angio-adaptive mechanism. Tumor recovery was associated with a dramatic decrease (by 30% to 40%) in the intratumoral microvascular density, probably as a result of intussusceptive pruning and, surprisingly, with only a minimal reduction of the total microvascular (exchange) area. Therefore, the vascular supply to the tumor was not severely compromised, as demonstrated by hypoxia-inducible factor-1alpha expression. Both irradiation and anti-angiogenic therapy cause a switch from sprouting to intussusceptive angiogenesis, representing an escape mechanism and accounting for the development of resistance, as well as rapid recovery, after cessation of therapy.

Bioinformatics based Ligand-Docking and in-silico screening

We report a novel method, ChooseLD (CHOOse biological information Semi-Empirically on the Ligand Docking), which uses simulated annealing (SA) based on bioinformatics for protein-ligand flexible docking. The fingerprint alignment score (FPAScore) value is used to determine the docking conformation of the ligand. This method includes the matching of chemical descriptors such as fingerprints (FPs) and the root mean square deviation (rmsd) calculation of the coordinates of atoms of the chemical descriptors. Here, the FPAScore optimization for the translation and rotation of a rigid body is performed using the Metropolis Monte Carlo method. Our ChooseLD method will find wide application in the field of biochemistry and medicine to improve the search for new drugs targeting various proteins implicated in diseases.

Incorporating a vascular term into a reference region model for the analysis of DCE-MRI data: a simulation study

A vascular term was incorporated into a reference region (RR) model analysis of DCE-MRI data, and its effect on the accuracy of the model in estimating tissue kinetic parameters in a tissue of interest (TOI) was systematically investigated through computer simulations. Errors in the TOI volume transfer constant (K(trans,TOI)) and TOI extravascular extracellular volume (v(e,TOI)) that result when the fractional plasma volume (v(p)) was included in (1) neither region, (2) TOI only (3) both regions were investigated. For nominal values of tumor kinetic parameters (v(e,TOI) = 0.40 and K(trans,TOI) = 0.25 min(-1)), if the vascular term was included in neither region or the TOI only, K(trans,TOI) error was within 20% for 0.03 < v(p,TOI) < 0.10, and v(e,TOI) error was within 20% for the range of v(p,TOI) studied (0.01-0.10). The effects of temporal resolution were shown to be complex, and in some cases errors increased with increasing temporal resolution.

Evaluation of human brain tumor heterogeneity using multiple T1-based MRI signal weighting approaches

Vascular-space-occupancy (VASO) MRI without contrast injection was explored for imaging cerebral blood volume (CBV) and tissue heterogeneity in gliomas (n = 10). VASO contrast complemented contrast-enhanced T(1)-weighted (GAD-T(1)w), FLAIR and T(1)w magnetization-prepared-rapid-gradient-echo (MPRAGE) images. High-grade gliomas showed a VASO-outlined hyperintense zone corresponding to long-T(1) regions in MPRAGE and to nonenhancing regions in GAD-T(1)w images. FLAIR, MPRAGE, and VASO data were used to segment tumors into multiple zones of different T(1). After removal of known resection areas using pre- and postsurgical MRI, the volume of overlap between the hyperintense VASO-zone and the long-T(1) MPRAGE zone correlated with that of GAD-T(1)w enhancement (R(2) = 0.99) and tumor grade. Based on these correlations, this remaining long T(1) overlap area was tentatively assigned to necrosis. In one promising case the collective T(1)-weighted approach accurately identified a low-grade glioma despite the presence of contrast enhancement in GAD-T(1)w images consequential to chemoradiation-associated treatment effect. The results suggest that this collective T(1)-weighted approach may provide useful information for regional assessment of heterogeneous tumors and for guiding treatment-related decisions in patients with gliomas.

A cryptic vascular endothelial growth factor T-cell epitope: identification and characterization by mass spectrometry and T-cell assays

Vascular endothelial growth factor (VEGF) is involved in various physiologic processes, such as angiogenesis or wound healing, but is also crucial in pathologic events, such as tumor growth. Thus, clinical anti-VEGF treatments have been developed that could already show beneficial effects for cancer patients. In this article, we describe the first VEGF-derived CD8(+) T-cell epitope. The natural HLA ligand SRFGGAVVR was identified by differential mass spectrometry in two primary renal cell carcinomas (RCC) and was significantly overpresented on both tumor tissues. SRFGGAVVR is derived from a cryptic translated region of VEGF presumably by initiation of translation at the nonclassic start codon CUG(499). SRFGGAVVR-specific T cells were generated in vitro using peptide-loaded dendritic cells or artificial antigen-presenting cells. SRFGGAVVR-specific CD8(+) T cells, identified by HLA tetramer analysis after in vitro stimulation, were fully functional T effector cells, which were able to secrete IFN-gamma on stimulation and killed tumor cells in vitro. Additionally, we have quantitatively analyzed VEGF mRNA and protein levels in RCC tumor and normal tissue samples by gene chip analysis, quantitative reverse transcription-PCR, in situ hybridization, and bead-based immunoassay. In the future, T cells directed against VEGF as a tumor-associated antigen may represent a possible way of combining peptide-based anti-VEGF immunotherapy with already existent anti-VEGF cancer therapies.

Anti-tumor activity and tumor vessel normalization by the vascular endothelial growth factor receptor tyrosine kinase inhibitor KRN951 in a rat peritoneal disseminated tumor model

We assessed the antitumor efficacy of KRN951, a novel tyrosine kinase inhibitor of vascular endothelial growth factor receptors, using a rat colon cancer RCN-9 syngeneic model in which the tumor cells are transplanted into the peritoneal cavity of F344 rats. KRN951 treatments that commenced 4 days after tumor transplantation (day 4) significantly inhibited tumor-induced angiogenesis, the formation of tumor nodules in the mesenteric windows, and the accumulation of malignant ascites. Moreover, KRN951 treatments initiated on day 14, by which time angiogenesis and malignant ascites have already been well established, resulted in the regression of newly formed tumor vasculatures with aberrant structures and also in the apparent loss of malignant ascites by the end of the study period. Quantitative analysis of the vessel architecture on mesenteric windows revealed that KRN951 not only regressed, but also normalized the tumor-induced neovasculature. Continuous daily treatments with KRN951 significantly prolonged the survival of rats bearing both early stage and more advanced-stage tumors, compared with the vehicle-treated animals. The results of our current study thus show that KRN951 inhibits colon carcinoma progression in the peritoneal cavity by blocking tumor angiogenesis, ascites formation, and tumor spread, thereby prolonging survival. Moreover, these studies clearly demonstrate the therapeutic effects of KRN951 against established tumors in the peritoneal cavity, including the regression and normalization of the tumor neovasculature. Our findings therefore suggest that KRN951 has significant potential as a future therapeutic agent in the treatment of peritoneal cancers with ascites.

VEGF signaling inhibitors: more pro-apoptotic than anti-angiogenic

The vascular endothelial growth factor (VEGF) family of polypeptide growth factors regulates a family of VEGF receptor (VEGFR) tyrosine kinases with pleiotropic downstream effects. Angiogenesis is the best known of these effects, but additional VEGF-dependent actions include increased vascular permeability, paracrine/autocrine growth factor release, enhancement of cell motility, and inhibition of apoptosis. In theory, therapeutic inhibition of angiogenesis should reduce tumor perfusion and thus increase tumor hypoxia and chemoresistance, but in clinical practice the VEGF antibody bevacizumab acts as a broad-spectrum chemosensitizer. Since VEGFR expression occurs in many tumor types, such chemosensitization is more readily explained by direct inhibition of tumor cell survival signals than by indirect stromal/vascular effects. The emerging model of anti-VEGF drug action being mediated primarily by tumoral (as distinct from endothelial) VEGFRs has clinically important implications for optimizing the anti-metastatic efficacy of this expanding drug class.