Discovery of Darovasertib (NVP-LXS196), a Pan-PKC Inhibitor for the Treatment of Metastatic Uveal Melanoma.

Uveal melanoma (UM) is the most common primary intraocular malignancy in the adult eye. Despite the aggressive local management of primary UM, the development of metastases is common with no effective treatment options for metastatic disease. Genetic analysis of UM samples reveals the presence of mutually exclusive activating mutations in the Gq alpha subunits GNAQ and GNA11. One of the key downstream targets of the constitutively active Gq alpha subunits is the protein kinase C (PKC) signaling pathway. Herein, we describe the discovery of darovasertib (NVP-LXS196), a potent pan-PKC inhibitor with high whole kinome selectivity. The lead series was optimized for kinase and off target selectivity to afford a compound that is rapidly absorbed and well tolerated in preclinical species. LXS196 is being investigated in the clinic as a monotherapy and in combination with other agents for the treatment of uveal melanoma (UM), including primary UM and metastatic uveal melanoma (MUM).

First-in-human study of naporafenib (LXH254) with or without spartalizumab in adult patients with advanced solid tumors harboring MAPK signaling pathway alterations.

BACKGROUND: We investigated naporafenib (LXH254), a pan-RAF kinase inhibitor, with or without spartalizumab, in patients with advanced solid tumors harboring MAPK pathway alterations. METHODS: This first-in-human phase 1 study had two dose-escalation arms: single-agent naporafenib (starting at 100 mg once-daily [QD]) and naporafenib (starting at the recommended dose/regimen)/spartalizumab (400 mg every 4 weeks). The naporafenib/spartalizumab dose-expansion part enrolled patients with KRAS-mutated non-small cell lung cancer (NSCLC) and NRAS-mutated melanoma. The primary objectives were to establish the maximum tolerated doses (MTD)/recommended doses for expansion (RDE) and evaluate tolerability and safety. RESULTS: A total of 142 patients were included in the naporafenib dose-escalation (n = 87), naporafenib/spartalizumab dose-escalation (n = 12) and naporafenib/spartalizumab dose-expansion (n = 43) arms. The MTD/RDE of naporafenib was 600 mg twice-daily (BID). In naporafenib escalation, five patients experienced 7 dose-limiting toxicities: decreased platelet count (1200 mg QD); neuralgia, maculopapular rash, pruritus (600 mg BID); increased blood bilirubin, hyponatremia, peripheral sensory neuropathy (800 mg BID). No DLTs occurred in the naporafenib/spartalizumab arm: the RDE was established at 400 mg BID. The most common treatment-related adverse events were rash and dermatitis acneiform (each 24.1%; naporafenib), nausea and pruritus (each 33.3%; naporafenib/spartalizumab; escalation) and rash (39.5%; naporafenib/spartalizumab; expansion). Naporafenib reduced DUSP6 expression in tumors. Two partial responses (PRs) occurred in naporafenib escalation, and 1 complete response and 3 PRs in the naporafenib/spartalizumab NRAS-mutated melanoma and KRAS-mutated NSCLC arms, respectively. CONCLUSIONS: Naporafenib, with or without spartalizumab, showed an acceptable safety profile, pharmacodynamic activity and limited antitumor activity. Additional naporafenib combination therapies are currently under investigation.

Initial Evidence for the Efficacy of Naporafenib in Combination With Trametinib in NRAS-Mutant Melanoma: Results From the Expansion Arm of a Phase Ib, Open-Label Study.

PURPOSE: No approved targeted therapy for the treatment of patients with neuroblastoma RAS viral (v-ras) oncogene homolog (NRAS)-mutant melanoma is currently available. PATIENTS AND METHODS: In this phase Ib escalation/expansion study (ClinicalTrials.gov identifier: NCT02974725), the safety, tolerability, and preliminary antitumor activity of naporafenib (LXH254), a BRAF/CRAF protein kinases inhibitor, were explored in combination with trametinib in patients with advanced/metastatic KRAS- or BRAF-mutant non-small-cell lung cancer (escalation arm) or NRAS-mutant melanoma (escalation and expansion arms). RESULTS: Thirty-six and 30 patients were enrolled in escalation and expansion, respectively. During escalation, six patients reported grade ≥3 dose-limiting toxicities, including dermatitis acneiform (n = 2), maculopapular rash (n = 2), increased lipase (n = 1), and Stevens-Johnson syndrome (n = 1). The recommended doses for expansion were naporafenib 200 mg twice a day plus trametinib 1 mg once daily and naporafenib 400 mg twice a day plus trametinib 0.5 mg once daily. During expansion, all 30 patients experienced a treatment-related adverse event, the most common being rash (80%, n = 24), blood creatine phosphokinase increased, diarrhea, and nausea (30%, n = 9 each). In expansion, the objective response rate, median duration of response, and median progression-free survival were 46.7% (95% CI, 21.3 to 73.4; 7 of 15 patients), 3.75 (95% CI, 1.97 to not estimable [NE]) months, and 5.52 months, respectively, in patients treated with naporafenib 200 mg twice a day plus trametinib 1 mg once daily, and 13.3% (95% CI, 1.7 to 40.5; 2 of 15 patients), 3.75 (95% CI, 2.04 to NE) months, and 4.21 months, respectively, in patients treated with naporafenib 400 mg twice a day plus trametinib 0.5 mg once daily. CONCLUSION: Naporafenib plus trametinib showed promising preliminary antitumor activity in patients with NRAS-mutant melanoma. Prophylactic strategies aimed to lower the incidence of skin-related events are under investigation.

LXH254, a Potent and Selective ARAF-Sparing Inhibitor of BRAF and CRAF for the Treatment of MAPK-Driven Tumors.

PURPOSE: Targeting RAF for antitumor therapy in RAS-mutant tumors holds promise. Herein, we describe in detail novel properties of the type II RAF inhibitor, LXH254. EXPERIMENTAL DESIGN: LXH254 was profiled in biochemical, in vitro, and in vivo assays, including examining the activities of the drug in a large panel of cancer-derived cell lines and a comprehensive set of in vivo models. In addition, activity of LXH254 was assessed in cells where different sets of RAF paralogs were ablated, or that expressed kinase-impaired and dimer-deficient variants of ARAF. RESULTS: We describe an unexpected paralog selectivity of LXH254, which is able to potently inhibit BRAF and CRAF, but has less activity against ARAF. LXH254 was active in models harboring BRAF alterations, including atypical BRAF alterations coexpressed with mutant K/NRAS, and NRAS mutants, but had only modest activity in KRAS mutants. In RAS-mutant lines, loss of ARAF, but not BRAF or CRAF, sensitized cells to LXH254. ARAF-mediated resistance to LXH254 required both kinase function and dimerization. Higher concentrations of LXH254 were required to inhibit signaling in RAS-mutant cells expressing only ARAF relative to BRAF or CRAF. Moreover, specifically in cells expressing only ARAF, LXH254 caused paradoxical activation of MAPK signaling in a manner similar to dabrafenib. Finally, in vivo, LXH254 drove complete regressions of isogenic variants of RAS-mutant cells lacking ARAF expression, while parental lines were only modestly sensitive. CONCLUSIONS: LXH254 is a novel RAF inhibitor, which is able to inhibit dimerized BRAF and CRAF, as well as monomeric BRAF, while largely sparing ARAF.

Design and Discovery of N-(3-(2-(2-Hydroxyethoxy)-6-morpholinopyridin-4-yl)-4-methylphenyl)-2-(trifluoromethyl)isonicotinamide, a Selective, Efficacious, and Well-Tolerated RAF Inhibitor Targeting RAS Mutant Cancers: The Path to the Clinic.

Direct pharmacological inhibition of RAS has remained elusive, and efforts to target CRAF have been challenging due to the complex nature of RAF signaling, downstream of activated RAS, and the poor overall kinase selectivity of putative RAF inhibitors. Herein, we describe 15 (LXH254, Aversa, R.; et al. Int. Patent WO2014151616A1, 2014), a selective B/C RAF inhibitor, which was developed by focusing on drug-like properties and selectivity. Our previous tool compound, 3 (RAF709; Nishiguchi, G. A.; et al. J. Med. Chem. 2017, 60, 4969), was potent, selective, efficacious, and well tolerated in preclinical models, but the high human intrinsic clearance precluded further development and prompted further investigation of close analogues. A structure-based approach led to a pyridine series with an alcohol side chain that could interact with the DFG loop and significantly improved cell potency. Further mitigation of human intrinsic clearance and time-dependent inhibition led to the discovery of 15. Due to its excellent properties, it was progressed through toxicology studies and is being tested in phase 1 clinical trials.

PARP Inhibition Increases the Response to Chemotherapy in Uveal Melanoma.

Uveal melanoma (UM) remains without effective therapy at the metastatic stage, which is associated with BAP-1 (BRCA1 associated protein) mutations. However, no data on DNA repair capacities in UM are available. Here, we use UM patient-derived xenografts (PDXs) to study the therapeutic activity of the PARP inhibitor olaparib, alone or in combination. First, we show that the expression and the activity of PARP proteins is similar between the PDXs and the corresponding patient's tumors. In vivo experiments in the PDX models showed that olaparib was not efficient alone, but significantly increased the efficacy of dacarbazine. Finally, using reverse phase protein arrays and immunohistochemistry, we identified proteins involved in DNA repair and apoptosis as potential biomarkers predicting response to the combination of olaparib and dacarbazine. We also observed a high increase of phosphorylated YAP and TAZ proteins after dacarbazine + olaparib treatment. Our results suggest that PARP inhibition in combination with the alkylating agent dacarbazine could be of clinical interest for UM treatment. We also observe an interesting effect of dacarbazine on the Hippo pathway, confirming the importance of this pathway in UM.

Antitumor Properties of RAF709, a Highly Selective and Potent Inhibitor of RAF Kinase Dimers, in Tumors Driven by Mutant RAS or BRAF.

Resistance to the RAF inhibitor vemurafenib arises commonly in melanomas driven by the activated BRAF oncogene. Here, we report antitumor properties of RAF709, a novel ATP-competitive kinase inhibitor with high potency and selectivity against RAF kinases. RAF709 exhibited a mode of RAF inhibition distinct from RAF monomer inhibitors such as vemurafenib, showing equal activity against both RAF monomers and dimers. As a result, RAF709 inhibited MAPK signaling activity in tumor models harboring either BRAFV600 alterations or mutant N- and KRAS-driven signaling, with minimal paradoxical activation of wild-type RAF. In cell lines and murine xenograft models, RAF709 demonstrated selective antitumor activity in tumor cells harboring BRAF or RAS mutations compared with cells with wild-type BRAF and RAS genes. RAF709 demonstrated a direct pharmacokinetic/pharmacodynamic relationship in in vivo tumor models harboring KRAS mutation. Furthermore, RAF709 elicited regression of primary human tumor-derived xenograft models with BRAF, NRAS, or KRAS mutations with excellent tolerability. Our results support further development of inhibitors like RAF709, which represents a next-generation RAF inhibitor with unique biochemical and cellular properties that enables antitumor activities in RAS-mutant tumors.Significance: In an effort to develop RAF inhibitors with the appropriate pharmacological properties to treat RAS mutant tumors, RAF709, a compound with potency, selectivity, and in vivo properties, was developed that will allow preclinical therapeutic hypothesis testing, but also provide an excellent probe to further unravel the complexities of RAF kinase signaling. Cancer Res; 78(6); 1537-48. ©2018 AACR.

Design and Discovery of N-(2-Methyl-5'-morpholino-6'-((tetrahydro-2H-pyran-4-yl)oxy)-[3,3'-bipyridin]-5-yl)-3-(trifluoromethyl)benzamide (RAF709): A Potent, Selective, and Efficacious RAF Inhibitor Targeting RAS Mutant Cancers.

RAS oncogenes have been implicated in >30% of human cancers, all representing high unmet medical need. The exquisite dependency on CRAF kinase in KRAS mutant tumors has been established in genetically engineered mouse models and human tumor cells. To date, many small molecule approaches are under investigation to target CRAF, yet kinase-selective and cellular potent inhibitors remain challenging to identify. Herein, we describe 14 (RAF709) [ Aversa , Biaryl amide compounds as kinase inhibitors and their preparation . WO 2014151616, 2014 ], a selective B/C RAF inhibitor, which was developed through a hypothesis-driven approach focusing on drug-like properties. A key challenge encountered in the medicinal chemistry campaign was maintaining a balance between good solubility and potent cellular activity (suppression of pMEK and proliferation) in KRAS mutant tumor cell lines. We investigated the small molecule crystal structure of lead molecule 7 and hypothesized that disruption of the crystal packing would improve solubility, which led to a change from N-methylpyridone to a tetrahydropyranyl oxy-pyridine derivative. 14 proved to be soluble, kinase selective, and efficacious in a KRAS mutant xenograft model.

Allosteric inhibition of SHP2 phosphatase inhibits cancers driven by receptor tyrosine kinases.

The non-receptor protein tyrosine phosphatase SHP2, encoded by PTPN11, has an important role in signal transduction downstream of growth factor receptor signalling and was the first reported oncogenic tyrosine phosphatase. Activating mutations of SHP2 have been associated with developmental pathologies such as Noonan syndrome and are found in multiple cancer types, including leukaemia, lung and breast cancer and neuroblastoma. SHP2 is ubiquitously expressed and regulates cell survival and proliferation primarily through activation of the RAS­ERK signalling pathway. It is also a key mediator of the programmed cell death 1 (PD-1) and B- and T-lymphocyte attenuator (BTLA) immune checkpoint pathways. Reduction of SHP2 activity suppresses tumour cell growth and is a potential target of cancer therapy. Here we report the discovery of a highly potent (IC50 = 0.071 µM), selective and orally bioavailable small-molecule SHP2 inhibitor, SHP099, that stabilizes SHP2 in an auto-inhibited conformation. SHP099 concurrently binds to the interface of the N-terminal SH2, C-terminal SH2, and protein tyrosine phosphatase domains, thus inhibiting SHP2 activity through an allosteric mechanism. SHP099 suppresses RAS­ERK signalling to inhibit the proliferation of receptor-tyrosine-kinase-driven human cancer cells in vitro and is efficacious in mouse tumour xenograft models. Together, these data demonstrate that pharmacological inhibition of SHP2 is a valid therapeutic approach for the treatment of cancers.

The Public Repository of Xenografts Enables Discovery and Randomized Phase II-like Trials in Mice.

More than 90% of drugs with preclinical activity fail in human trials, largely due to insufficient efficacy. We hypothesized that adequately powered trials of patient-derived xenografts (PDX) in mice could efficiently define therapeutic activity across heterogeneous tumors. To address this hypothesis, we established a large, publicly available repository of well-characterized leukemia and lymphoma PDXs that undergo orthotopic engraftment, called the Public Repository of Xenografts (PRoXe). PRoXe includes all de-identified information relevant to the primary specimens and the PDXs derived from them. Using this repository, we demonstrate that large studies of acute leukemia PDXs that mimic human randomized clinical trials can characterize drug efficacy and generate transcriptional, functional, and proteomic biomarkers in both treatment-naive and relapsed/refractory disease.

Inhibition of Wild-Type p53-Expressing AML by the Novel Small Molecule HDM2 Inhibitor CGM097.

The tumor suppressor p53 is a key regulator of apoptosis and functions upstream in the apoptotic cascade by both indirectly and directly regulating Bcl-2 family proteins. In cells expressing wild-type (WT) p53, the HDM2 protein binds to p53 and blocks its activity. Inhibition of HDM2:p53 interaction activates p53 and causes apoptosis or cell-cycle arrest. Here, we investigated the ability of the novel HDM2 inhibitor CGM097 to potently and selectively kill WT p53-expressing AML cells. The antileukemic effects of CGM097 were studied using cell-based proliferation assays (human AML cell lines, primary AML patient cells, and normal bone marrow samples), apoptosis, and cell-cycle assays, ELISA, immunoblotting, and an AML patient-derived in vivo mouse model. CGM097 potently and selectively inhibited the proliferation of human AML cell lines and the majority of primary AML cells expressing WT p53, but not mutant p53, in a target-specific manner. Several patient samples that harbored mutant p53 were comparatively unresponsive to CGM097. Synergy was observed when CGM097 was combined with FLT3 inhibition against oncogenic FLT3-expressing cells cultured both in the absence as well as the presence of cytoprotective stromal-secreted cytokines, as well as when combined with MEK inhibition in cells with activated MAPK signaling. Finally, CGM097 was effective in reducing leukemia burden in vivo. These data suggest that CGM097 is a promising treatment for AML characterized as harboring WT p53 as a single agent, as well as in combination with other therapies targeting oncogene-activated pathways that drive AML.

Studying clonal dynamics in response to cancer therapy using high-complexity barcoding.

Resistance to cancer therapies presents a significant clinical challenge. Recent studies have revealed intratumoral heterogeneity as a source of therapeutic resistance. However, it is unclear whether resistance is driven predominantly by pre-existing or de novo alterations, in part because of the resolution limits of next-generation sequencing. To address this, we developed a high-complexity barcode library, ClonTracer, which enables the high-resolution tracking of more than 1 million cancer cells under drug treatment. In two clinically relevant models, ClonTracer studies showed that the majority of resistant clones were part of small, pre-existing subpopulations that selectively escaped under therapeutic challenge. Moreover, the ClonTracer approach enabled quantitative assessment of the ability of combination treatments to suppress resistant clones. These findings suggest that resistant clones are present before treatment, which would make up-front therapeutic combinations that target non-overlapping resistance a preferred approach. Thus, ClonTracer barcoding may be a valuable tool for optimizing therapeutic regimens with the goal of curative combination therapies for cancer.

Targeting vascular pericytes in hypoxic tumors increases lung metastasis via angiopoietin-2.

Strategies to target angiogenesis include inhibition of the vessel-stabilizing properties of vascular pericytes. Pericyte depletion in early-stage non-hypoxic tumors suppressed nascent angiogenesis, tumor growth, and lung metastasis. In contrast, pericyte depletion in advanced-stage hypoxic tumors with pre-established vasculature resulted in enhanced intra-tumoral hypoxia, decreased tumor growth, and increased lung metastasis. Furthermore, depletion of pericytes in post-natal retinal blood vessels resulted in abnormal and leaky vasculature. Tumor transcriptome profiling and biological validation revealed that angiopoietin signaling is a key regulatory pathway associated with pericyte targeting. Indeed, pericyte targeting in established mouse tumors increased angiopoietin-2 (ANG2/Angpt2) expression. Depletion of pericytes, coupled with targeting of ANG2 signaling, restored vascular stability in multiple model systems and decreased tumor growth and metastasis. Importantly, ANGPT2 expression correlated with poor outcome in patients with breast cancer. These results emphasize the potential utility of therapeutic regimens that target pericytes and ANG2 signaling in metastatic breast cancer.

Inhibiting Tankyrases sensitizes KRAS-mutant cancer cells to MEK inhibitors via FGFR2 feedback signaling.

Tankyrases (TNKS) play roles in Wnt signaling, telomere homeostasis, and mitosis, offering attractive targets for anticancer treatment. Using unbiased combination screening in a large panel of cancer cell lines, we have identified a strong synergy between TNKS and MEK inhibitors (MEKi) in KRAS-mutant cancer cells. Our study uncovers a novel function of TNKS in the relief of a feedback loop induced by MEK inhibition on FGFR2 signaling pathway. Moreover, dual inhibition of TNKS and MEK leads to more robust apoptosis and antitumor activity both in vitro and in vivo than effects observed by previously reported MEKi combinations. Altogether, our results show how a novel combination of TNKS and MEK inhibitors can be highly effective in targeting KRAS-mutant cancers by suppressing a newly discovered resistance mechanism.

Pharmacological and genomic profiling identifies NF-κB-targeted treatment strategies for mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive malignancy that is characterized by poor prognosis. Large-scale pharmacological profiling across more than 100 hematological cell line models identified a subset of MCL cell lines that are highly sensitive to the B cell receptor (BCR) signaling inhibitors ibrutinib and sotrastaurin. Sensitive MCL models exhibited chronic activation of the BCR-driven classical nuclear factor-κB (NF-κB) pathway, whereas insensitive cell lines displayed activation of the alternative NF-κB pathway. Transcriptome sequencing revealed genetic lesions in alternative NF-κB pathway signaling components in ibrutinib-insensitive cell lines, and sequencing of 165 samples from patients with MCL identified recurrent mutations in TRAF2 or BIRC3 in 15% of these individuals. Although they are associated with insensitivity to ibrutinib, lesions in the alternative NF-κB pathway conferred dependence on the protein kinase NIK (also called mitogen-activated protein 3 kinase 14 or MAP3K14) both in vitro and in vivo. Thus, NIK is a new therapeutic target for MCL treatment, particularly for lymphomas that are refractory to BCR pathway inhibitors. Our findings reveal a pattern of mutually exclusive activation of the BCR-NF-κB or NIK-NF-κB pathways in MCL and provide critical insights into patient stratification strategies for NF-κB pathway-targeted agents.

Global chromatin profiling reveals NSD2 mutations in pediatric acute lymphoblastic leukemia.

Epigenetic dysregulation is an emerging hallmark of cancers. We developed a high-information-content mass spectrometry approach to profile global histone modifications in human cancers. When applied to 115 lines from the Cancer Cell Line Encyclopedia, this approach identified distinct molecular chromatin signatures. One signature was characterized by increased histone 3 lysine 36 (H3K36) dimethylation, exhibited by several lines harboring translocations in NSD2, which encodes a methyltransferase. A previously unknown NSD2 p.Glu1099Lys (p.E1099K) variant was identified in nontranslocated acute lymphoblastic leukemia (ALL) cell lines sharing this signature. Ectopic expression of the variant induced a chromatin signature characteristic of NSD2 hyperactivation and promoted transformation. NSD2 knockdown selectively inhibited the proliferation of NSD2-mutant lines and impaired the in vivo growth of an NSD2-mutant ALL xenograft. Sequencing analysis of >1,000 pediatric cancer genomes identified the NSD2 p.E1099K alteration in 14% of t(12;21) ETV6-RUNX1-containing ALLs. These findings identify NSD2 as a potential therapeutic target for pediatric ALL and provide a general framework for the functional annotation of cancer epigenomes.

Origin and function of myofibroblasts in kidney fibrosis.

Myofibroblasts are associated with organ fibrosis, but their precise origin and functional role remain unknown. We used multiple genetically engineered mice to track, fate map and ablate cells to determine the source and function of myofibroblasts in kidney fibrosis. Through this comprehensive analysis, we identified that the total pool of myofibroblasts is split, with 50% arising from local resident fibroblasts through proliferation. The nonproliferating myofibroblasts derive through differentiation from bone marrow (35%), the endothelial-to-mesenchymal transition program (10%) and the epithelial-to-mesenchymal transition program (5%). Specific deletion of Tgfbr2 in α-smooth muscle actin (αSMA)(+) cells revealed the importance of this pathway in the recruitment of myofibroblasts through differentiation. Using genetic mouse models and a fate-mapping strategy, we determined that vascular pericytes probably do not contribute to the emergence of myofibroblasts or fibrosis. Our data suggest that targeting diverse pathways is required to substantially inhibit the composite accumulation of myofibroblasts in kidney fibrosis.

An F876L mutation in androgen receptor confers genetic and phenotypic resistance to MDV3100 (enzalutamide).

UNLABELLED: Castration-resistant prostate cancer (CRPC) is the most aggressive, incurable form of prostate cancer. MDV3100 (enzalutamide), an antagonist of the androgen receptor (AR), was approved for clinical use in men with metastatic CRPC. Although this compound showed clinical efficacy, many initial responders later developed resistance. To uncover relevant resistant mechanisms, we developed a model of spontaneous resistance to MDV3100 in LNCaP prostate cancer cells. Detailed characterization revealed that emergence of an F876L mutation in AR correlated with blunted AR response to MDV3100 and sustained proliferation during treatment. Functional studies confirmed that AR(F876L) confers an antagonist-to-agonist switch that drives phenotypic resistance. Finally, treatment with distinct antiandrogens or cyclin-dependent kinase (CDK)4/6 inhibitors effectively antagonized AR(F876L) function. Together, these findings suggest that emergence of F876L may (i) serve as a novel biomarker for prediction of drug sensitivity, (ii) predict a "withdrawal" response to MDV3100, and (iii) be suitably targeted with other antiandrogens or CDK4/6 inhibitors. SIGNIFICANCE: We uncovered an F876L agonist-switch mutation in AR that confers genetic and phenotypic resistance to the antiandrogen drug MDV3100. On the basis of this fi nding, we propose new therapeutic strategies to treat patients with prostate cancer presenting with this AR mutation.

Pericyte depletion results in hypoxia-associated epithelial-to-mesenchymal transition and metastasis mediated by met signaling pathway.

The functional role of pericytes in cancer progression remains unknown. Clinical studies suggest that low numbers of vessel-associated pericytes correlated with a drop in overall survival of patients with invasive breast cancer. Using genetic mouse models or pharmacological inhibitors, pericyte depletion suppressed tumor growth but enhanced metastasis. Pericyte depletion was further associated with increased hypoxia, epithelial-to-mesenchymal transition (EMT), and Met receptor activation. Silencing of Twist or use of a Met inhibitor suppressed hypoxia and EMT/Met-driven metastasis. In addition, poor pericyte coverage coupled with high Met expression in cancer cells speculates the worst prognosis for patients with invasive breast cancer. Collectively, our study suggests that pericytes within the primary tumor microenvironment likely serve as important gatekeepers against cancer progression and metastasis.