0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial.

We determined the efficacy and safety of 0.1% RGN-259 ophthalmic solution (containing the regenerative protein thymosin ß4) in promoting the healing of persistent epithelial defects in patients with Stages 2 and 3 neurotrophic keratopathy. Complete healing occurred after 4 weeks in 6 of the 10 RGN-259-treated subjects and in 1 of the 8 placebo-treated subjects (p = 0.0656), indicating a strong efficacy trend. Additional efficacy was seen in the significant healing (p = 0.0359) with no recurrent defects observed at day 43, two weeks after cessation of treatment, while the one healed placebo-treated subject at day 28 suffered a recurrence at day 43. The Mackie classification disease stage improved in the RGN-259-treated group at Days 29, 36, and 43 (p = 0.0818, 0.0625, and 0.0467, respectively). Time to complete healing also showed a trend towards efficacy (p = 0.0829, Kaplan-Meier) with 0.1% RGN-259. RGN-259-treated subjects had significant improvements at multiple time points in ocular discomfort, foreign body sensation, and dryness which were not seen in the placebo group. No significant adverse effects were observed. In summary, the use of 0.1% RGN-259 promotes rapid healing of epithelial defects in neurotrophic keratopathy, improves ocular comfort, and is safe for treating this challenging population of patients.

Angiotropism, pericytic mimicry and extravascular migratory metastasis: an embryogenesis-derived program of tumor spread.

Intravascular dissemination of tumor cells is the accepted mechanism of cancer metastasis. However, the phenomenon of angiotropism, pericyte mimicry (PM), and extravascular migratory metastasis (EVMM) has questioned the concept that tumor cells metastasize exclusively via circulation within vascular channels. This new paradigm of cancer spread and metastasis suggests that metastatic cells employ embryonic mechanisms for attachment to the abluminal surfaces of blood vessels (angiotropism) and spread via continuous migration, competing with and replacing pericytes, i.e., pericyte mimicry (PM). This is an entirely extravascular phenomenon (i.e., extravascular migratory metastasis or EVMM) without entry (intravasation) into vascular channels. PM and EVMM have mainly been studied in melanoma but also occur in other cancer types. PM and EVMM appear to be a reversion to an embryogenesis-derived program. There are many analogies between embryogenesis and cancer progression, including the important role of laminins, epithelial-mesenchymal transition, and the re-activation of embryonic signals by cancer cells. Furthermore, there is no circulation of blood during the first trimester of embryogenesis, despite the fact that there is extensive migration of cells to distant sites and formation of organs and tissues during this period. Embryonic migration therefore is a continuous extravascular migration as are PM and EVMM, supporting the concept that these embryonic migratory events appear to recur abnormally during the metastatic process. Finally, the perivascular location of tumor cells intrinsically links PM to vascular co-option. Taken together, these two new paradigms may greatly influence the development of new effective therapeutics for metastasis. In particular, targeting embryonic factors linked to migration that are detected during cancer metastasis may be particularly relevant to PM/EVMM.

Monitoring Angiotropic Extravascular Migratory Metastasis In Vitro.

The mechanism of cancer cell migration from the primary tumor toward secondary sites is not fully understood. In addition to intravascular cellular migration, angiotropic extravascular migratory metastasis (EVMM) has been recognized as a metastatic pathway involving tumor cells crawling along the abluminal vascular surface to distant sites. A very simple in vitro 3D assay is described here, which is based on a previous in vitro angiogenesis assay. The assay involves monitoring single fluorescence-tagged migrating cancer cells in the presence of vascular structures in real time. This coculture assay represents a quantitative approach for monitoring the migration processes of cancer cells along vessels, demonstrating phenotypic switching and migration dynamics. This protocol can be used for molecular analyses and can also be adapted for screening of therapeutic agents to block cancer metastasis.

Thymosin ß4 and the anti-fibrotic switch

Wound healing involves a rapid response to the injury by circulating cells, followed by inflammation with an influx of inflammatory cells that release various factors. Soon after, cellular proliferation begins to replace the damaged cells and extracellular matrix, and then tissue remodeling restores normal tissue function. Various factors can lead to pathological wound healing when excessive and irreversible connective tissue/extracellular matrix deposition occurs, resulting in fibrosis. The process is initiated when immune cells, such as macrophages, release soluble factors that stimulate fibroblasts. TGFß is the most well-characterized macrophage derived pro-fibrotic mediator. Other soluble mediators of fibrosis include connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF), and interleukin 10 (IL-10). Thymosin ß4 (Tß4) has shown therapeutic benefit in preventing fibrosis/scarring in various animal models of fibrosis/scarring. The mechanism of action of Tß4 appears related, in part, to a reduction in the inflammatory response, including a reduction in macrophage infiltration, decreased levels of TGFß and IL-10, and reduced CTGF activation, resulting in both prevention of fibroblast conversion to myofibroblasts and production of normally aligned collagen fibers. The amino N-terminal end of Tß4, SDKP (serine-aspartate-lysine-proline), appears to contain the majority of anti-fibrotic activity and has shown excellent efficacy in many animal models of fibrosis, including liver, lung, heart, and kidney fibrosis. Ac-SDKP not only prevents fibrosis but can reverse fibrosis. Unanswered questions and future directions will be presented with regard to therapeutic uses alone and in combination with already approved drugs for fibrosis.

Matrigel: history/background, uses, and future applications.

Basement membranes are thin sheets of extracellular matrix with many diverse roles in the body. Those in normal tissue are also highly insoluble and resist attempts to extract and characterize their components. A mouse tumor, the EHS tumor, has provided large amounts of basement membrane material, which has facilitated the structural and functional characterization of its components. An extract of the tumor, known as Matrigel, contains components which reconstitute into a solid gel at 37°. This solid basement membrane matrix has been used in both cell culture and in vivo. Matrigel has been utilized in some 12,000-plus publications for a variety of studies with embryonic, normal, and stem or malignant cells. Evidence presented in this Commentary suggests that Matrigel isolated from tumors grown in diverse hosts could exert unique effects that could be helpful in analyzing the causes of various pathologies and for screening possible therapeutic agents.

Hematogenous metastasis and tumor dormancy as concepts or dogma? The continuum of vessel co-option and angiotropic extravascular migratory metastasis as an alternative.

It has been accepted for many years that tumor cells spread via the circulation to distant sites. The latency period between treatment and tumor recurrence has been attributed to dormant cells in distant organs that emerge and grow as metastatic tumors. These processes are accepted with an incomplete demonstration of their existence. Challenging such a well-established accepted paradigm is not easy as history as shown. An alternative or co-existing mechanism involving tumor cell migration along the outside of the vessels and co-option of the blood vessel has been studied for over 25 years and is presented. Several lines of data support this new mechanism of tumor spread and metastatic growth and is termed angiotropic extravascular migratory metastasis or EVMM. This slow migration along the outside of the vessel wall may explain the latency period between treatment and metastatic tumor growth. The reader is asked to be open to this possible new concept in how tumors spread and grow and the reason for this latency period. A full understanding of how tumors spread and grow is fundamental for the targeting of new therapeutics.

Thymosin ß4 induces the expression of vascular endothelial growth factor (VEGF) in a hypoxia-inducible factor (HIF)-1α-dependent manner.

Thymosin ß4 has multi-functional roles in cell physiology, but little is known about its mechanism(s) of action. We previously reported that thymosin ß4 stimulated angiogenesis through the induction of vascular endothelial growth factor (VEGF). To identify the mechanism of VEGF induction by thymosin ß4, we have used a luciferase assay system with VEGF in the 5' promoter region. We also analyzed the effect of thymosin ß4 on VEGF mRNA stability and on the expression and stability of hypoxia-inducible factor (HIF)-1α. We found that thymosin ß4 induces VEGF expression by an increase in the stability of HIF-1α protein. Analysis of the expression patterns of thymosin ß4 and HIF-1α in colon cancer tissue microarray showed that thymosin ß4 and HIF-1α co-localized in these biopsies. These data show that thymosin ß4 induces the expression of VEGF indirectly by increasing the protein stability of HIF-1α.

Multiple uses of basement membrane-like matrix (BME/Matrigel) in vitro and in vivo with cancer cells.

Significant advances in our understanding of cancer cell behavior, growth, and metastasis have been facilitated by studies using a basement membrane-like extracellular matrix extract, also known as Matrigel. The basement membrane is a thin extracellular matrix that is found in normal tissues and contacts epithelial and endothelial cells, smooth muscle, fat, Schwann cells, etc. It is composed of mainly laminin-111, collagen IV, heparan sulfate proteoglycan, entactin/nidogen, and various growth factors (fibroblast growth factor, transforming growth factor beta, epidermal growth factor, etc.). Most tumors of epithelial origin produce significant amounts of basement membrane matrix and interact with it particularly during metastasis. Cancer cells metastasize via degradation of the vessel basement membrane matrix to extravasate into the blood stream and colonize distant sites. This review will focus on the interaction of cancer cells and cancer stem cells with the basement membrane-like matrix and the various uses of this interaction to accelerate tumor growth in vivo and to develop in vitro assays for invasion, morphology, and dormancy. Such assays and methods have advanced our understanding of the process of cancer progression, the genes and pathways that are involved, the potential of various therapeutic agents, the effects of neighboring cells, and the role of stem cells.

The endothelial cell tube formation assay on basement membrane turns 20: state of the science and the art.

It has been more than 20 years since it was first demonstrated that endothelial cells will rapidly form capillary-like structures in vitro when plated on top of a reconstituted basement membrane extracellular matrix (BME, Matrigel, EHS matrix, etc.). Subsequently, this morphological differentiation has been demonstrated with a variety of endothelial cells; with endothelial progenitor cells; and with transformed/immortalized endothelial cells. The differentiation process involves several steps in blood vessel formation, including cell adhesion, migration, alignment, protease secretion, and tubule formation. Because the formation of vessel structures is rapid and quantifiable, endothelial cell differentiation on basement membrane has found numerous applications in assays. Such differentiation has been used (1) to study angiogenic and antiangiogenic factors, (2) to define mechanisms and pathways involved in angiogenesis, and (3) to define endothelial cell populations. Further, the endothelial cell differentiation assay has been successfully used to study processes ranging from wound repair and reproduction to development and tumor growth. The assay is easy to perform and is the most widely used in vitro angiogenesis assay.

Overexpression of malignancy-associated laminins and laminin receptors by angiotropic human melanoma cells in a chick chorioallantoic membrane model.

BACKGROUND: As distinct from intravascular/lymphatic dissemination, extravascular migratory metastasis (EVMM) has been described as a potential additional mechanism of melanoma spread in which tumor cells migrate along the external surfaces of vessels. Angiotropic melanoma cells are linked to the endothelium by a matrix containing laminin. In addition, it has been shown that C16 laminin-derived peptide increases extravascular migration of human green fluorescent protein (GFP) melanoma cells along vessels in a chicken chorioallantoic membrane model (CAM). In this study, we have tested the hypothesis that expression levels of some genes related to lamimin and metastasis are differentially expressed in vascularized angiotropic melanoma areas vs. avascular melanoma areas from the same tumor. DESIGN: C8161 human melanoma cells in a shell-less chick CAM assay were used to study EVMM associated with the presence of vascularized angiotropic melanoma areas. For both high-quality histomorphology and RNA preservation in paraffin-embedded tissue, we used a methanol-based fixative coupled with microwave-assisted rapid tissue processing as previously described. Using laser capture microdissection, angiotropic melanoma areas as well as avascular areas were microdissected. Using quantitative real time polymerase chain reaction (QRT-PCR), six genes have been studied: LAMC2 (laminin gamma2 chain), LAMA4 (laminin alpha4 chain), ITGB1 (integrin beta1), ITGB3 (integrin beta3), RSPA (ribosomal protein), and MMP2 (matrix metallopeptidase 2). QRT-PCR data were normalized to human GAPDH housekeeping gene and values were compared against Human Total RNA. Final results were expressed as percentage of expression. RESULTS: All tumors demonstrated a similar pattern, i.e. EVMM of angiotropic melanoma cells. The microdissected histopathological sections presented both angiotropic areas and avascular areas. All genes were overexpressed in angiotropic melanoma areas vs. avascular melanoma areas, especially LAMC2, LAMA4 and ITGB3 (respectively, 165.18, 208.86, and 483.69%). CONCLUSION: This study shows that several genes related to laminin are overexpressed in angiotropic melanoma areas vs. avascular melanoma areas. Since extravascular migration of melanoma cells along vessels has been demonstrated in the CAM model, taken together these results suggests that some laminins and laminin receptors may play a role in extravascular migratory metastasis. This model may represent a promising strategy to analyze differential gene expression in EVMM.

Thymosin ß4: potential to treat epidermolysis bullosa and other severe dermal injuries.

Thymosin ß4 is a naturally-occurring regenerative protein present in almost all cells and body fluids, including wound fluid. In multiple preclinical injury models, it promotes dermal repair and tissue regeneration. Thymosin ß4 acts by increasing keratinocyte/epithelial cell migration, angiogenesis, and cell survival, and by decreasing inflammation, apoptosis, and scarring. It also modulates cytokines, including those that cause itching. Thymosin ß4 promotes faster repair in various chronic human wounds, including pressure ulcers, stasis ulcers, and epidermolysis bullosa lesions. The faster healing time with increased keratinocyte migration and angiogenesis and reduction in both inflammation and scarring are especially important for epidermolysis bullosa patients who suffer from slow healing and inflammation that leads to itching, infections, pain, fluid loss, scarring, and tissue damage. These multiple mechanisms of action support thymosin ß4's role in accelerating dermal repair and suggest the potential to treat various types of severe wounds, including epidermolysis bullosa patients who suffer from frequent blistering wounds that can be life threatening. There is an urgent need at this time to develop a therapeutic, such as thymosin ß4, for epidermolysis bullosa. Despite progress in gene/stem cell therapy, there is no cure for this disease and careful wound management is the standard of care.

Angiogenic laminin-derived peptides stimulate wound healing.

Acceleration of the wound healing process by using angiogenic peptides has been demonstrated previously. Here we used select laminin-111 peptides, A13 and C16, from the laminin alpha1 and gamma1 chain, respectively, to test whether they are able to stimulate wound healing in a rat full thickness wound model. The 12-mer peptides C16 and A13 are highly angiogenic and bind to integrins alphavbeta3 and alpha5beta1. We show that A13 increases wound re-epithelialization as much as 17% over controls by day 4 and C16 increases coverage by 11%. Contraction of the treated wounds was increased as much as 11% for A13 and 8% for C16 at day 4. No differences were observed at day 7 with either peptide. The peptides also stimulated fibroblast migration in Boyden chamber assays. A13 increased cell migration as much as 2.4-fold on uncoated filters and as much as 16-fold on collagen type IV-coated filters over negative controls. Similarly, C16 also stimulated migration 1.8-fold on uncoated filters and as much as 12-fold on collagen-coated filters. A13 and C16 significantly decreased expression of the pro and active forms of matrix metalloproteinase 2 in foreskin fibroblasts indicating their role in collagen accumulation. We conclude that small bioactive angiogenic peptides can promote dermal wound healing and may offer a new class of stable and chemically manipulable therapeutics for wound healing.

Laminin-1-derived scrambled peptide AG73T disaggregates laminin-1-induced ovarian cancer cell spheroids and improves the efficacy of cisplatin.

We found previously that the laminin-1-derived synthetic peptide AG73 (LQVQLSIR) promoted ovarian cancer cell metastasis in vivo. We have now studied the role of this metastasis-promoting peptide in vitro using TAC3 ovarian cancer cells, which display anchorage-independent growth and form multicellular spheroids. Our goal is to better understand how this peptide can regulate metastasis in vivo. We found that the exogenous addition of either laminin-1 or peptide AG73 stimulated the formation and growth of the spheroids. Western blot analysis indicated that laminin-1 enhanced the expression of integrin beta1, and that AG73 peptide enhanced expression of syndecan-1 and downstream effectors, including mitogen-activated protein kinase (MAPK) and extracellular signal-related kinase (ERK), and also phosphatidylinositol (PI)-3 kinase/AKT activity signaling. The soluble peptide AG73T, which is a scramble peptide of AG73, was able to disaggregate the laminin-1-induced spheroids. Furthermore, the disaggregated cells were twice as sensitive to cisplatin as the intact spheroids. The AG73T peptide in the presence of laminin-1 suppressed expression of integrin beta1 and its downstream effectors, including MAPK/ERK and PI3/AKT activity signaling. The MEK inhibitor U0126 reduced TAC3 cell growth more effectively in the presence of both laminin-1 and AG73T than in the presence of laminin-1 alone. Inhibition of the PI3-K cascade with LY294002 was also more effective in the presence of laminin-1 and AG73T. The increased sensitivity to cisplatin in the presence of AG73T may be due to the greater bioavailability of the drug to the free-floating cells over the spheroids. These findings suggest a novel function of AG73T in ovarian cancer and help to define mechanisms important in ovarian cancer spheroid formation and spread.

RGN-259 (thymosin ß4) improves clinically important dry eye efficacies in comparison with prescription drugs in a dry eye model.

This study evaluated the clinical activity of RGN-259 (thymosin ß4) in comparison with cyclosporine A (CsA), diquafosol (DQS), and lifitegrast (LFA) in a murine model of dry eye. The model was NOD.B10-H2b mice in a 30-40% humidified environment together with daily scopolamine hydrobromide injections for 10 days. After desiccation stress, all drugs were evaluated after 10 treatment days. RGN-259 increased tear production similar to that in the DQS- and LFA-treated mice while CsA was inactive. RGN-259 improved corneal smoothness and decreased fluorescein staining similar to that of LFA group while CsA and DQS were inactive. Corneal epithelial detachment was reduced by RGN-259, and DQS and LFA showed similar activity but the CsA was inactive. RGN-259 increased conjunctival goblet cells and mucin production comparable to that seen with CsA, while DQS and LFA were inactive. RGN-259 reduced the over-expression of inflammatory factors comparable to that with CsA and LFA, while DQS was inactive. RGN-259 increased mucin production comparable to that observed with CsA, while DQS and LFA were inactive. In conclusion, RGN-259 promoted recovery of mucins and goblet cells, improved corneal integrity, and reduced inflammation in a dry eye mouse model and was equal to or more effective than prescription treatments.

Neuropeptide Y induces migration, proliferation, and tube formation of endothelial cells bimodally via Y1, Y2, and Y5 receptors.

Previously we discovered that NPY induces ischemic angiogenesis by activating Y2 and Y5 receptors. The receptors that mediate specific steps of the complex process of angiogenesis are unknown. Here, we studied in vitro NPY receptors subtypes involved in migration, proliferation, and differentiation of human endothelial cells. In cells that expressed Y1, Y2, and Y5 receptors, NPY bimodally stimulated migration and proliferation with a 2-fold increase at 10(-12) M and 10(-8) M (high- and low-affinity peaks, respectively). Preincubation of cells with NPY up-regulated the Y5 receptor and markedly enhanced endothelial cell migration and proliferation. NPY-induced endothelial cell migration was mimicked by agonists and fully blocked by antagonists for any specific NPY receptors (Y1, Y2, or Y5), while proliferation was blocked by any two antagonists (Y1+Y2, Y1+Y5, or Y2+Y5), and capillary tube formation on Matrigel was blocked by all three (Y1+Y2+Y5). Thus, NPY-induced angiogenesis requires participation of Y1, Y2, and Y5 receptor subtypes, with the Y5 receptor acting as an enhancer. We propose that these receptors form heteromeric complexes, and the Y1/Y2/Y5 receptor oligomer may be the uncloned Y3 receptor.

Thymosin beta 4 induces hair growth via stem cell migration and differentiation.

Thymosin beta 4 is a small 43-amino-acid molecule that has multiple biological activities, including promotion of cell migration angiogenesis, cell survival, protease production, and wound healing. We have found that thymosin beta 4 promotes hair growth in various rat and mice models including a transgenic thymosin beta 4 overexpressing mouse. We have also determined the mechanism by which thymosin beta 4 acts to promote hair growth by examining its effects on follicle stem cell growth, migration, differentiation, and protease production.

Laminin alpha5 chain metastasis- and angiogenesis-inhibiting peptide blocks fibroblast growth factor 2 activity by binding to the heparan sulfate chains of CD44.

Recently, we reported that the laminin alpha5 synthetic peptide A5G27 (RLVSYNGIIFFLK, residues 2,892-2,904) binds to the CD44 receptor of B16-F10 melanoma cells via the glycosaminoglycans on CD44 and inhibits tumor cell migration, invasion, and angiogenesis in a dominant-negative manner. Here, we have identified the potential mechanism of A5G27 activity using WiDr human colorectal carcinoma cells. WiDr cells bound to the laminin A5G27 peptide via the heparin-like and chondroitin sulfate B glycosaminoglycan side chains of CD44. Cell binding to fibroblast growth factor (FGF2) was blocked by laminin peptide A5G27 but not by either a scrambled version of this peptide or by another laminin peptide known to bind cell surface proteoglycans. FGF2 signaling involving tyrosine phosphorylation was also blocked by laminin peptide A5G27 but was not affected by peptide controls. Finally, we have shown that peptide A5G27 directly blocks FGF2 binding to heparin. Peptide A5G27 has sequence homology to a region on FGF2 that binds heparin and the FGF receptor and is important in FGF2 central cavity formation. We conclude that peptide A5G27 inhibits metastasis and angiogenesis by blocking FGF2 binding to the heparan sulfate side chains of CD44 variant 3, thus decreasing FGF2 bioactivity.

Endogenous osteonectin/SPARC/BM-40 expression inhibits MDA-MB-231 breast cancer cell metastasis.

Skeletal metastases occur with high incidence in patients with breast cancer and cause long-term skeletal morbidity. Osteonectin (SPARC, BM-40) is a bone matrix factor that is an in vitro chemoattractant for breast and prostate cancer cells. Increased expression of osteonectin is found in malignant breast tumors. We infected MDA-231 breast cancer cells with an adenovirus expressing osteonectin to examine the role of osteonectin expression in breast cancer cells and its effect on metastasis, in particular to bone. Expression of osteonectin did not affect MDA-231 cell proliferation, apoptosis, migration, cell aggregation, or protease cleavage of collagen IV. However, in vitro invasion of these osteonectin-infected cells through Matrigel and colony formation on Matrigel was decreased. Interestingly, high osteonectin expression in MDA-231 cells inhibited metastasis in a dose-dependent manner to many different organs including bone. The reduction in metastasis may be due to decreased platelet-tumor cell aggregation, because exogenous osteonectin inhibited platelet aggregation in vitro and the high osteonectin expression in MDA-231 cells reduced tumor cell-induced thrombocytopenia in vivo compared with control-infected cells. These studies suggest that high endogenous expression of osteonectin in breast cancer cells may reduce metastasis via reduced invasive activity and reduced tumor cell-platelet aggregation.

Safety and potential efficacy of gemfibrozil as a supportive treatment for children with late infantile neuronal ceroid lipofuscinosis and other lipid storage disorders.

Neuronal Ceroid Lipofuscinosis (NCL), also known as Batten disease, is a group of genetically distinct lysosomal disorders that mainly affect the central nervous system, resulting in progressive motor and cognitive decline primarily in children. Multiple distinct genes involved in the metabolism of lipids have been identified to date with various mutations in this family of diseases. There is no cure for these diseases but some new therapeutic approaches have been tested that offer more hope than the standard palliative care. Many of the therapeutic advances require invasive procedures but some progress in slowing the disease has been found and more options can be expected in the future. We also review the literature on children with disease/conditions other than NCL for the non-invasive use, safety, and tolerability of a lipid-lowering drug, gemfibrozil, as a potential treatment for NCLs. Gemfibrozil has shown efficacy in an animal model of NCL known as CLN2 (late infantile classic juvenile) and has been shown to be safe for lowering lipids in children. Among the 200 non-NCL children found in the published literature who were treated with gemfibrozil for NCL-related problems, only 3 experienced adverse events, including 2 with muscle pain and 1 with localized linear IgA bullous dermatitis. We conclude that gemfibrozil is safe for long-term use in children, causes minimal adverse events, is well tolerated, and may delay the progression of NCLs. Gemfibrozil may potentially be an alternative to more invasive therapeutic approaches currently under investigation and has the potential to be used in combination with other therapeutic approaches.

Inhibition of VEGF receptors significantly impairs mammary cancer growth in C3(1)/Tag transgenic mice through antiangiogenic and non-antiangiogenic mechanisms.

Cancer growth and progression is often critically influenced by the production of vascular endothelial growth factor (VEGF), a key mediator of angiogenesis. VEGF produced by tumor cells stimulates endothelial cell growth through the binding and activation of the KDR/Flk-1 receptor (VEGFR-2) on endothelial cells. Recently, some human breast cancer epithelial cells have been shown to express VEGF receptors, suggesting a potential autocrine-mediated growth stimulation of a subset of cancers by VEGF. We demonstrate that mammary tumors in the C3(1)/Tag transgenic model express VEGF and VEGF receptors and tumor growth is stimulated by this autocrine mechanism. GW654652, an indazolylpyrimidine, is a VEGFRs tyrosine kinase inhibitor that dramatically reduces both angiogenesis and tumor cell growth in this model, as demonstrated using both in vitro and in vivo assays. GW654652 significantly decreased cell proliferation and induced apoptosis in human umbilical vein endothelial cells and M6 mammary tumor cells derived from C3(1)/Tag (Tag: simian virus 40 T-antigen) transgenic mice. A 75% reduction in VEGF-induced angiogenesis was observed with GW654652 using the chick chorioallantoic membrane assay, whereas GW654652 produced an approximately 85% reduction in angiogenesis as assessed by the Matrigel plug assay. A profound inhibitory effect on tumor growth in the C3(1)/Tag transgenic model of human breast cancer was observed with oral administration of GW654652 as measured by delayed tumor onset, decreased multiplicity, reduced tumor volume, and extended animal survival. The antitumor effects of GW654652 were associated with reduced tumor vascularization and no apparent toxicity. Tumor growth, however, rapidly advanced following cessation of treatment. This is the first demonstration that a VEGF receptor inhibitor, GW654652, has a strong inhibitory effect on angiogenesis and tumor progression in a transgenic model of mammary cancer, suggesting that this is a useful approach for preclinical testing of such agents.