Preclinical Antitumor Activity of a Novel Anti-c-KIT Antibody-Drug Conjugate against Mutant and Wild-type c-KIT-Positive Solid Tumors.

Purpose: c-KIT overexpression is well recognized in cancers such as gastrointestinal stromal tumors (GIST), small cell lung cancer (SCLC), melanoma, non-small cell lung cancer (NSCLC), and acute myelogenous leukemia (AML). Treatment with the small-molecule inhibitors imatinib, sunitinib, and regorafenib resulted in resistance (c-KIT mutant tumors) or limited activity (c-KIT wild-type tumors). We selected an anti-c-KIT ADC approach to evaluate the anticancer activity in multiple disease models.Experimental Design: A humanized anti-c-KIT antibody LMJ729 was conjugated to the microtubule destabilizing maytansinoid, DM1, via a noncleavable linker (SMCC). The activity of the resulting ADC, LOP628, was evaluated in vitro against GIST, SCLC, and AML models and in vivo against GIST and SCLC models.Results: LOP628 exhibited potent antiproliferative activity on c-KIT-positive cell lines, whereas LMJ729 displayed little to no effect. At exposures predicted to be clinically achievable, LOP628 demonstrated single administration regressions or stasis in GIST and SCLC xenograft models in mice. LOP628 also displayed superior efficacy in an imatinib-resistant GIST model. Further, LOP628 was well tolerated in monkeys with an adequate therapeutic index several fold above efficacious exposures. Safety findings were consistent with the pharmacodynamic effect of neutropenia due to c-KIT-directed targeting. Additional toxicities were considered off-target and were consistent with DM1, such as effects in the liver and hematopoietic/lymphatic system.Conclusions: The preclinical findings suggest that the c-KIT-directed ADC may be a promising therapeutic for the treatment of mutant and wild-type c-KIT-positive cancers and supported the clinical evaluation of LOP628 in GIST, AML, and SCLC patients. Clin Cancer Res; 24(17); 4297-308. ©2018 AACR.

Identification of N-(4-((1R,3S,5S)-3-Amino-5-methylcyclohexyl)pyridin-3-yl)-6-(2,6-difluorophenyl)-5-fluoropicolinamide (PIM447), a Potent and Selective Proviral Insertion Site of Moloney Murine Leukemia (PIM) 1, 2, and 3 Kinase Inhibitor in Clinical Trials for Hematological Malignancies.

Pan proviral insertion site of Moloney murine leukemia (PIM) 1, 2, and 3 kinase inhibitors have recently begun to be tested in humans to assess whether pan PIM kinase inhibition may provide benefit to cancer patients. Herein, the synthesis, in vitro activity, in vivo activity in an acute myeloid leukemia xenograft model, and preclinical profile of the potent and selective pan PIM kinase inhibitor compound 8 (PIM447) are described. Starting from the reported aminopiperidyl pan PIM kinase inhibitor compound 3, a strategy to improve the microsomal stability was pursued resulting in the identification of potent aminocyclohexyl pan PIM inhibitors with high metabolic stability. From this aminocyclohexyl series, compound 8 entered the clinic in 2012 in multiple myeloma patients and is currently in several phase 1 trials of cancer patients with hematological malignancies.

A synthetic lethal screen reveals enhanced sensitivity to ATR inhibitor treatment in mantle cell lymphoma with ATM loss-of-function.

UNLABELLED: Mechanisms to maintain genomic integrity are essential for cells to remain viable. Not surprisingly, disruption of key DNA damage response pathway factors, such as ataxia telangiectasia-mutated (ATM)/ataxia telangiectasia and RAD3-related (ATR) results in loss of genomic integrity. Here, a synthetic lethal siRNA-screening approach not only confirmed ATM but identified additional replication checkpoint proteins, when ablated, enhanced ATR inhibitor (ATRi) response in a high-content γ-H2AX assay. Cancers with inactivating ATM mutations exhibit impaired DNA double-stranded break (DSB) repair and rely on compensatory repair pathways for survival. Therefore, impairing ATR activity may selectively sensitize cancer cells to killing. ATR inhibition in an ATM-deficient context results in phosphorylation of DNA-dependent protein kinase catalytic subunits (DNA-PKcs) and leads to induction of γ-H2AX. Using both in vitro and in vivo models, ATR inhibition enhanced efficacy in ATM loss-of-function mantle cell lymphoma (MCL) compared with ATM wild-type cancer cells. In summary, single-agent ATR inhibitors have therapeutic utility in the treatment of cancers, like MCL, in which ATM function has been lost. IMPLICATIONS: These data suggest that single-agent ATR inhibitors have therapeutic utility and that ATR uses a complex and coordinated set of proteins to maintain genomic stability that could be further exploited.

The identification and characterization of a STAT5 gene signature in hematologic malignancies.

BACKGROUND: The JAK-STAT pathway is an important signaling pathway downstream of multiple cytokine and growth factor receptors. Dysregulated JAK-STAT signaling has been implicated in the pathogenesis of multiple human malignancies. OBJECTIVE: Given this pivotal role of JAK-STAT dysregulation, it is important to identify patients with an overactive JAK-STAT pathway for possible treatment with JAK inhibitors. METHODS: We developed a gene signature assay to detect overactive JAK-STAT signaling. The cancer cell line encyclopedia and associated gene-expression data were used to correlate the activation status of STAT5 with the induction of a set of STAT5 target genes. RESULTS: Four target genes were identified (PIM1, CISH, SOCS2, and ID1), the expression of which correlated significantly with pSTAT5 status in 40 hematologic tumor cell lines. In pSTAT5-positive models, the expression of the gene signature genes decreased following ruxolitinib treatment, which corresponded to pSTAT5 downmodulation. In pSTAT5-negative cell lines, neither pSTAT5 modulation nor a change in signature gene expression was observed following ruxolitinib treatment. CONCLUSIONS: The gene signature can potentially be used to stratify or enrich for patient populations with activated JAK-STAT5 signaling that might benefit from treatments targeting JAK-STAT signaling. Furthermore, the 4-gene signature is a predictor of the pharmacodynamic effects of ruxolitinib.

Pan-PIM kinase inhibition provides a novel therapy for treating hematologic cancers.

PURPOSE: PIM kinases have been shown to act as oncogenes in mice, with each family member being able to drive progression of hematologic cancers. Consistent with this, we found that PIMs are highly expressed in human hematologic cancers and show that each isoform has a distinct expression pattern among disease subtypes. This suggests that inhibitors of all three PIMs would be effective in treating multiple hematologic malignancies. EXPERIMENTAL DESIGN: Pan-PIM inhibitors have proven difficult to develop because PIM2 has a low Km for ATP and, thus, requires a very potent inhibitor to effectively block the kinase activity at the ATP levels in cells. We developed a potent and specific pan-PIM inhibitor, LGB321, which is active on PIM2 in the cellular context. RESULTS: LGB321 is active on PIM2-dependent multiple myeloma cell lines, where it inhibits proliferation, mTOR-C1 signaling and phosphorylation of BAD. Broad cancer cell line profiling of LGB321 demonstrates limited activity in cell lines derived from solid tumors. In contrast, significant activity in cell lines derived from diverse hematological lineages was observed, including acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), multiple myeloma and non-Hodgkin lymphoma (NHL). Furthermore, we demonstrate LGB321 activity in the KG-1 AML xenograft model, in which modulation of pharmacodynamics markers is predictive of efficacy. Finally, we demonstrate that LGB321 synergizes with cytarabine in this model. CONCLUSIONS: We have developed a potent and selective pan-PIM inhibitor with single-agent antiproliferative activity and show that it synergizes with cytarabine in an AML xenograft model. Our results strongly support the development of Pan-PIM inhibitors to treat hematologic malignancies.

Pim2 is required for maintaining multiple myeloma cell growth through modulating TSC2 phosphorylation.

Multiple myeloma (MM) is the second most common hematologic malignancy. Despite recent treatment advances, it remains incurable. Here, we report that Pim2 kinase expression is highly elevated in MM cells and demonstrate that it is required for MM cell proliferation. Functional interference of Pim2 activity either by short hairpin RNAs or by a potent and selective small-molecule inhibitor leads to significant inhibition of MM cell proliferation. Pim inhibition results in a significant decrease of mammalian target of rapamycin C1 (mTOR-C1) activity, which is critical for cell proliferation. We identify TSC2, a negative regulator of mTOR-C1, as a novel Pim2 substrate and show that Pim2 directly phosphorylates TSC2 on Ser-1798 and relieves the suppression of TSC2 on mTOR-C1. These findings support Pim2 as a promising therapeutic target for MM and define a novel Pim2-TSC2-mTOR-C1 pathway that drives MM proliferation.

Neutralization of prolactin receptor function by monoclonal antibody LFA102, a novel potential therapeutic for the treatment of breast cancer.

Numerous lines of evidence suggest that the polypeptide hormone prolactin (PRL) may contribute to breast and prostate tumorigenesis through its interactions with the prolactin receptor (PRLR). Here, we describe the biologic properties of LFA102, a humanized neutralizing monoclonal antibody directed against the extracellular domain of PRLR. This antibody was found to effectively antagonize PRL-induced signaling in breast cancer cells in vitro and in vivo and to block PRL-induced proliferation in numerous cell line models, including examples of autocrine/paracrine PRL activity. A single administration of LFA102 resulted in regression of PRL-dependent Nb2-11 tumor xenografts and significantly prolonged time to progression. Finally, LFA102 treatment significantly inhibited PRLR signaling as well as tumor growth in a carcinogen-induced, estrogen receptor-positive rat mammary cancer model as a monotherapy and enhanced the efficacy of the aromatase inhibitor letrozole when administered in combination. The biologic properties of LFA102, elucidated by the preclinical studies presented here, suggest that this antibody has the potential to be a first-in-class, effective therapeutic for the treatment of PRL-dependent cancers.

Structure Guided Optimization, in Vitro Activity, and in Vivo Activity of Pan-PIM Kinase Inhibitors.

Proviral insertion of Moloney virus (PIM) 1, 2, and 3 kinases are serine/threonine kinases that normally function in survival and proliferation of hematopoietic cells. As high expression of PIM1, 2, and 3 is frequently observed in many human malignancies, including multiple myeloma, non-Hodgkins lymphoma, and myeloid leukemias, there is interest in determining whether selective PIM inhibition can improve outcomes of these human cancers. Herein, we describe our efforts toward this goal. The structure guided optimization of a singleton high throughput screening hit in which the potency against all three PIM isoforms was increased >10,000-fold to yield compounds with pan PIM K is < 10 pM, nanomolar cellular potency, and in vivo activity in an acute myeloid leukemia Pim-dependent tumor model is described.

Angiopoietin-1/Tie-2 activation contributes to vascular survival and tumor growth during VEGF blockade.

Approval of the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab by the FDA in 2004 reflected the success of this vascular targeting strategy in extending survival in patients with advanced cancers. However, consistent with previous reports that experimental tumors can grow or recur during VEGF blockade, it has become clear that many patients treated with VEGF inhibitors will ultimately develop progressive disease. Previous studies have shown that disruption of VEGF signaling in tumors induces remodeling in surviving vessels, and link increased expression of angiopoietin-1 (Ang-1) with this process. However, overexpression of Ang-1 in different tumors has yielded divergent results, restricting angiogenesis in some systems while promoting it in others. These data raise the possibility that effects of Ang-1/Tie-2 may be context-dependent. Expression of an Ang-1 construct (Ang1*) did not significantly change tumor growth in our model prior to treatment, although vessels exhibited changes consistent with increased Tie-2 signaling. During inhibition of VEGF, however, both overexpression of Ang1* and administration of an engineered Ang-1 agonist (Bow-Ang1) strikingly protected tumors and vasculature from regression. In this context, Ang-1/Tie-2 activation limited tumor hypoxia, increased vessel caliber, and promoted recruitment of mural cells. Thus, these studies support a model in which activation of Tie-2 is important for tumor and vessel survival when VEGF-dependent vasculature is stressed. Understanding such mechanisms of adaptation to this validated form of therapy may be important in designing regimens that make the best use of this approach.

VEGF Trap induces antiglioma effect at different stages of disease.

Pathological angiogenesis is a hallmark of cancer, specifically of glioblastomas, the most malignant and common primary brain tumor. Vascular endothelial growth factor (VEGF) is the key protein in the regulation of the hypervascular phenotype of primary malignant brain tumors. In this study, we tested VEGF Trap, a soluble decoy receptor for VEGF, in an intracranial glioma model. VEGF Trap was administered in short or prolonged schedules to animals bearing human gliomas at different stages of disease. Of importance, VEGF Trap treatment was efficacious in both initial and advanced phases of tumor development by significantly increasing overall survival. Furthermore, this effect was enhanced in animals treated with more prolonged regimens. In addition, we observed the emergence of a VEGF Trap-resistant phenotype characterized by tumor growth and increased invasiveness. Our results suggest that VEGF Trap will be effective in treating both patients with recurrent or progressive resectable glioblastoma and patients that have undergone extensive initial surgery. Finally, our results indicate that the clinical success of VEGF Trap may depend on a prolonged treatment in combined therapy aiming to simultaneously inhibit angiogenesis and tumor invasion.

The antileukemia activity of a human anti-CD40 antagonist antibody, HCD122, on human chronic lymphocytic leukemia cells.

B-cell chronic lymphocytic leukemia (B-CLL) is a lymphoproliferative disorder characterized by the surface expression of CD20, CD5 antigens, as well as the receptor CD40. Activation of CD40 by its ligand (CD40L) induces proliferation and rescues the cells from spontaneous and chemotherapy-induced apoptosis. CD40 activation also induces secretion of cytokines, such as IL-6, IL-10, TNF-alpha, IL-8, and GM-CSF, which are involved in tumor cell survival, migration, and interaction with cells in the tumor microenvironment. Here we demonstrate that in primary B-CLL tumor cells, the novel antagonist anti-CD40 monoclonal antibody, HCD122, inhibits CD40L-induced activation of signaling pathways, proliferation and survival, and secretion of cytokines. Furthermore, HCD122 is also a potent mediator of antibody-dependent cellular cytotoxicity (ADCC), lysing B-CLL cells more efficiently than rituximab in vitro, despite a significantly higher number of cell surface CD20 binding sites compared with CD40. Unlike rituximab, however, HCD122 (formerly CHIR-12.12) does not internalize upon binding to the cells. Our data suggest that HCD122 may inhibit B-CLL growth by blocking CD40 signaling and by ADCC-mediated cell lysis.

Sustained VEGF blockade results in microenvironmental sequestration of VEGF by tumors and persistent VEGF receptor-2 activation.

Vascular endothelial growth factor (VEGF) blockade has been validated clinically as a treatment for human cancers, yet virtually all patients eventually develop progressive disease during therapy. In order to dissect this phenomenon, we examined the effect of sustained VEGF blockade in a model of advanced pediatric cancer. Treatment of late-stage hepatoblastoma xenografts resulted in the initial collapse of the vasculature and significant tumor regression. However, during sustained treatment, vessels recovered, concurrent with a striking increase in tumor expression of perlecan, a heparan sulfate proteoglycan. Whereas VEGF mRNA was expressed at the periphery of surviving clusters of tumor cells, both secreted VEGF and perlecan accumulated circumferential to central vessels. Vascular expression of heparanase, VEGF receptor-2 ligand binding, and receptor activation were concurrently maintained despite circulating unbound VEGF Trap. Endothelial survival signaling via Akt persisted. These findings provide a novel mechanism for vascular survival during sustained VEGF blockade and indicate a role for extracellular matrix molecules that sequester and release biologically active VEGF.

VEGF Trap complex formation measures production rates of VEGF, providing a biomarker for predicting efficacious angiogenic blockade.

VEGF is the best characterized mediator of tumor angiogenesis. Anti-VEGF agents have recently demonstrated impressive efficacy in human cancer trials, but the optimal dosing of such agents must still be determined empirically, because biomarkers to guide dosing have yet to be established. The widely accepted (but unverified) assumption that VEGF production is quite low in normal adults led to the notion that increased systemic VEGF levels might quantitatively reflect tumor mass and angiogenic activity. We describe an approach to determine host and tumor production of VEGF, using a high-affinity and long-lived VEGF antagonist now in clinical trials, the VEGF Trap. Unlike antibody complexes that are usually rapidly cleared, the VEGF Trap forms inert complexes with tissue- and tumor-derived VEGF that remain stably in the systemic circulation, where they are readily assayable, providing unprecedented capability to accurately measure VEGF production. We report that VEGF production is surprisingly high in non-tumor-bearing rodents and humans, challenging the notion that systemic VEGF levels can serve as a sensitive surrogate for tumor load; tumor VEGF contribution becomes significant only with very large tumor loads. These findings have the important corollary that anti-VEGF therapies must be sufficiently dosed to avoid diversion by host-derived VEGF. We further show that our assay can indicate when VEGF is optimally blocked; such biomarkers to guide dosing do not exist for other anti-VEGF agents. Based on this assay, VEGF Trap doses currently being assessed in clinical trials are in the efficacious range.

VEGF trap in combination with radiotherapy improves tumor control in u87 glioblastoma.

PURPOSE: To determine the effect of vascular endothelial growth factor VEGF Trap (Regeneron Pharmaceuticals, Tarrytown, NY), a humanized soluble vascular endothelial growth factor (VEGF) receptor protein, and radiation (RT) on tumor growth in U87 glioblastoma xenografts in nude mice. METHODS AND MATERIALS: U87 cell suspensions were implanted subcutaneously into hind limbs of nude mice. VEGF Trap (2.5-25 mg/kg) was administered every 3 days for 3 weeks alone or in combination with a single dose of 10 Gy or fractionated RT (3 x 5 Gy). In addition, three scheduling protocols for VEGF Trap plus fractionated RT were examined. RESULTS: Improved tumor control was seen when RT (either single dose or fractionated doses) was combined with the lowest dose of VEGF Trap (2.5 mg/kg). Scheduling did not significantly affect the efficacy of combined therapy. Although high-dose VEGF Trap (10 mg/kg or 25 mg/kg) significantly reduced tumor growth over that of RT alone, there was no additional benefit to combining high-dose VEGF Trap with RT. CONCLUSIONS: Vascular endothelial growth factor Trap plus radiation is clearly better than radiation alone in a U87 subcutaneous xenograft model. Although high doses of VEGF Trap alone are highly efficacious, it is unclear whether such high doses can be used clinically without incurring normal tissue toxicities. Thus, information on lower doses of VEGF Trap and ionizing radiation is of clinical relevance.

Vascular endothelial growth factor trap combined with paclitaxel strikingly inhibits tumor and ascites, prolonging survival in a human ovarian cancer model.

Ovarian cancer is characterized by i.p. carcinomatosis and massive ascites. Vascular endothelial growth factor (VEGF) plays a pivotal role in tumor angiogenesis and vascular leakage leading to ascites. We assessed the efficacy of a soluble decoy receptor (VEGF Trap) combined with paclitaxel, in a mouse model of human ovarian cancer. Tumor burden after VEGF Trap plus paclitaxel was reduced by approximately 98% versus controls. No measurable ascites developed in the treated group. Morphologic studies showed that most residual tumor had degenerative changes. Diaphragmatic and hepatic tumors were not found in the VEGF Trap plus paclitaxel group in contrast to controls, indicating lack of metastasis. In vivo FITC-lectin tumor vessel imaging showed sparse, short, straight vessels in treated mice as compared to controls, in which vessels were numerous, irregular, tortuous, and leaky. In a survival study, all controls underwent euthanasia between 29 and 58 days after tumor cell inoculation (cachexia, extensive ascites, and tumor masses). In the VEGF Trap plus paclitaxel group, mice were ambulating and eating normally with no signs of disease for at least 81 days after tumor cell inoculation, and survival occurred for 129.9 +/- 38.88 days with no further treatment. We conclude that combination therapy with VEGF Trap plus paclitaxel may provide a novel, long-lasting therapeutic strategy for treatment of patients with ovarian cancer associated with ascites.

Haploinsufficiency of delta-like 4 ligand results in embryonic lethality due to major defects in arterial and vascular development.

Vascular development depends on the highly coordinated actions of a variety of angiogenic regulators, most of which apparently act downstream of vascular endothelial growth factor (VEGF). One potential such regulator is delta-like 4 ligand (Dll4), a recently identified partner for the Notch receptors. We generated mice in which the Dll4 gene was replaced with a reporter gene, and found that Dll4 expression is initially restricted to large arteries in the embryo, whereas in adult mice and tumor models, Dll4 is specifically expressed in smaller arteries and microvessels, with a striking break in expression just as capillaries merge into venules. Consistent with these arterial-specific expression patterns, heterozygous deletion of Dll4 resulted in prominent albeit variable defects in arterial development (reminiscent of those in Notch knockouts), including abnormal stenosis and atresia of the aorta, defective arterial branching from the aorta, and even arterial regression, with occasional extension of the defects to the venous circulation; also noted was gross enlargement of the pericardial sac and failure to remodel the yolk sac vasculature. These striking phenotypes resulting from heterozygous deletion of Dll4 indicate that vascular development may be as sensitive to subtle changes in Dll4 dosage as it is to subtle changes in VEGF dosage, because VEGF accounts for the only other example of haploid insufficiency, resulting in obvious vascular abnormalities. In summary, Dll4 appears to be a major trigger of Notch receptor activities previously implicated in arterial and vascular development, and it may represent a new opportunity for pro- and anti-angiogenic therapies.

Effects of potent VEGF blockade on experimental Wilms tumor and its persisting vasculature.

We characterized the effect of potent vascular endothelial growth factor (VEGF) blockade on early-stage Wilms tumor xenograft growth, vasculature and metastasis. VEGF is a key mediator of both physiologic and tumor angiogenesis. We recently described that potent VEGF blockade induces regression of established Wilms tumor xenografts and vessels, also reducing the size but not the incidence of pre-existing metastases. In these studies, we examined the effects of potent VEGF blockade on earlier stages of experimental Wilms tumors, focusing on tumor growth, vasculature and metastasis. Athymic mice received intrarenal human Wilms tumor cell implants. Biweekly treatment with vehicle or the VEGF-Trap, a high-affinity soluble decoy receptor incorporating regions of VEGFR1 and VEGFR2, was begun 1 week later (100 or 500 micrograms/dose, n=20 in each group). Mice were euthanized at week 6 to examine tumor weight, incidence of lung metastases, vascularity and expression of angiogenic factors. A cohort of mice was examined 2 weeks after cessation of treatment. Compared to controls, VEGF-Trap treated tumors were significantly smaller (100 micrograms/dose: 92.7% smaller, p=0.0017; 500 micro g/dose: 99.0% smaller, p=0.0009). The incidence of lung metastasis also decreased significantly (p<0.0055). VEGF-Trap nearly eradicated tumor vasculature. Rare persisting vessels were characterized by large caliber, quiescence (lacking proliferation/apoptosis) and arterialization (both phenotypic and molecular). Potent VEGF blockade caused near-arrest of experimental Wilms tumor growth, resulted in nearly avascular tumors, and also decreased the incidence and size of metastases. Persistent vessels in tumors treated with VEGF-Trap displayed specific morphologic and molecular features, suggestive of arterialization. Future strategies that target these persisting vessels may enhance the efficacy of VEGF blockade therapy.

TNP-470 promotes initial vascular sprouting in xenograft tumors.

TNP-470 (AGM-1470), an analogue of fumagillin, was one of the first molecules proposed to have antiangiogenic properties. This concept was based on its ability to inhibit both endothelial proliferation in vitro and tumor growth in vivo in a number of xenograft models. Yet, subsequent investigations indicated that the biochemical activities associated with TNP-470 are not selective for endothelial cells. Moreover, recent evidence suggests that this agent inhibits tumor growth in vivo, but without a corresponding decrease in angiogenesis. Therefore, we performed a detailed comparison of TNP-470 to a validated antiangiogenic agent, a VEGF inhibitor termed VEGF-Trap, using a xenograft model of Wilms tumor. Treatment with TNP-470 for 5 weeks significantly suppressed xenograft growth (83%). Surprisingly, this inhibition was not associated with a decrease in angiogenesis, but instead with an increase in tiny neovessels. To determine whether this was a direct effect of TNP-470 on tumor vessels, we examined its effect in a short-term assay using large tumors with established vasculature. In contrast to treatment with VEGF-Trap, which led to rapid vessel regression and tumor hypoxia, tumors exposed to TNP-470 for 1 day displayed increased capillary sprouting, with significantly increased microvessel density, vessel length, and branch points. TNP-470 did not induce tumor hypoxia as demonstrated by minimal pimonidazole staining and VEGF expression. TNP-470 did, however, cause a marked increase in apoptosis of tumor cells. Our results indicate that the antitumor effects of TNP-470 cannot be attributed to prevention of neoangiogenesis, but instead to its direct action on tumor cells.

The Shc adaptor protein is critical for VEGF induction by Met/HGF and ErbB2 receptors and for early onset of tumor angiogenesis.

The etiology and progression of a variety of human malignancies are linked to the deregulation of receptor tyrosine kinases (RTKs). To define the role of RTK-dependent signals in various oncogenic processes, we have previously engineered RTK oncoproteins that recruit either the Shc or Grb2 adaptor proteins. Although these RTK oncoproteins transform cells with similar efficiencies, fibroblasts expressing the Shc-binding RTK oncoproteins induced tumors with short latency (approximately 7 days), whereas cells expressing the Grb2-binding RTK oncoproteins induced tumors with delayed latency (approximately 24 days). The early onset of tumor formation correlated with the ability of cells expressing the Shc-binding RTK oncoproteins to produce vascular endothelial growth factor (VEGF) in culture and an angiogenic response in vivo. Consistent with this, treatment with a VEGF inhibitor, VEGF-Trap, blocked the in vivo angiogenic and tumorigenic properties of these cells. The importance of Shc recruitment to RTKs for the induction of VEGF was further demonstrated by using mutants of the Neu/ErbB2 RTK, where the Shc, but not Grb2, binding mutant induced VEGF. Moreover, the use of fibroblasts derived from ShcA-deficient mouse embryos, demonstrated that Shc was essential for the induction of VEGF by the Met/hepatocyte growth factor RTK oncoprotein and by serum-derived growth factors. Together, our findings identify Shc as a critical angiogenic switch for VEGF production downstream from the Met and ErbB2 RTKs.