Targeting Platelet-derived Growth Factor Receptor Research Articles

PDGF receptor mutations in human diseases.

PDGFRA and PDGFRB are classical proto-oncogenes that encode receptor tyrosine kinases responding to platelet-derived growth factor (PDGF). PDGFRA mutations are found in gastrointestinal stromal tumors (GISTs), inflammatory fibroid polyps and gliomas, and PDGFRB mutations drive myofibroma development. In addition, chromosomal rearrangement of either gene causes myeloid neoplasms associated with hypereosinophilia. Recently, mutations in PDGFRB were linked to several noncancerous diseases. Germline heterozygous variants that reduce receptor activity have been identified in primary familial brain calcification, whereas gain-of-function mutants are present in patients with fusiform aneurysms, Kosaki overgrowth syndrome or Penttinen premature aging syndrome. Functional analysis of these variants has led to the preclinical validation of tyrosine kinase inhibitors targeting PDGF receptors, such as imatinib, as a treatment for some of these conditions. This review summarizes the rapidly expanding knowledge in this field.

Combination therapy with Olaratumab/doxorubicin in advanced or metastatic soft tissue sarcoma -a single-Centre experience

BackgroundThe antibody targeting platelet-derived growth factor receptor alpha (PDGFRA), olaratumab, was approved in 2016 for metastatic soft tissue sarcoma (STS) in combination with doxorubicin based on promising results of a phase Ib/II trial by the Food and Drug Administration (FDA). However, recently the phase III ANNOUNCE trial could not confirm the additional value of olaratumab in this context.MethodsHere, in a retrospective analysis we share our single-centre experience with olaratumab/doxorubicin in STS by including n = 32 patients treated with olaratumab/doxorubicin between 2016 and 2019.ResultsMedian progression-free survival (PFS) in the overall cohort was 3.1 months (range 0.6–16.2). A response [complete remission (CR), partial remission (PR) or stable disease (SD)] was seen in n = 11 (34%) cases, whereas n = 21 (66%) patients showed progressive disease (PD). In n = 9 patients surgery was performed subsequently in an individual therapeutic approach. Out of n = 5 patients receiving additional regional hyperthermia, n = 3 achieved PR or SD.ConclusionsThis single-centre experience does also not support the promising phase Ib/II results for olaratumab/doxorubicin in STS. However, our findings do not preclude that olaratumab combination therapy could be valuable in a neoadjuvant setting. This warrants further exploration also taking into account the heterogeneous nature of STS.

Targeting platelet-derived growth factor receptor β inhibits the proliferation and motility of human pterygial fibroblasts

ABSTRACTBackground: Pterygium, a common eye disease with high postoperative recurrence, lacks effective therapeutic strategies. Therefore, it’s urgent to identify specific targets to develop rationally targeted molecular drugs for the pterygial therapy.Methods: The cell proliferation and motility were studied in both the primary human pterygial fibroblasts (hPFs) and an ex vivo pterygium model. hPFs transfected with the pCMV3-PDGFRB plasmid, PDGFRB siRNA and CRISPR/Cas9 system were used to determine the role of PDGFR-β in pterygial fibroblasts functions. Western blotting, immunohistochemistry and immunofluorescence were performed to evaluate the expression of the key proteins.Results: PDGFR-β expression in the pterygial stroma and primary hPFs was significantly higher than that in the conjunctiva and human conjunctival fibroblasts. PDGF-BB promoted the proliferation, migration and invasion of hPFs, which can be significantly suppressed by sunitinib via inhibition of the PDGFR-β/extracellular signal-regulated kinase (ERK) pathway. In the ex vivo model, the knockout of PDGFRB and sunitinib treatment blocked the proliferation and motility of fibroblasts in the pterygial stroma via the suppression of PDGFR-β/ERK pathway.Conclusion: This study demonstrates that PDGFR-β may be a potential therapeutic target for pterygium, and inhibition of PDGFR-β by sunitinib is a promising and effective approach for pterygium treatment.

Anti-angiogenic effects of crenolanib are mediated by mitotic modulation independently of PDGFR expression

BackgroundCrenolanib is a tyrosine kinase inhibitor targeting PDGFR-α, PDGFR-β and Fms related tyrosine kinase-3 (FLT3) that is currently evaluated in several clinical trials. Although platelet-derived growth factor receptor (PDGFR) signalling pathway is believed to play an important role in angiogenesis and maintenance of functional vasculature, we here demonstrate a direct angiostatic activity of crenolanib independently of PDGFR signalling.MethodsThe activity of crenolanib on cell viability, migration, sprouting, apoptosis and mitosis was assessed in endothelial cells, tumour cells and fibroblasts. Alterations in cell morphology were determined by immunofluorescence experiments. Flow-cytometry analysis and mRNA expression profiles were used to investigate cell differentiation. In vivo efficacy was investigated in human ovarian carcinoma implanted on the chicken chorioallantoic membrane (CAM).ResultsCrenolanib was found to inhibit endothelial cell viability, migration and sprout length, and induced apoptosis independently of PDGFR expression. Treated cells showed altered actin arrangement and nuclear aberrations. Mitosis was affected at several levels including mitosis entry and centrosome clustering. Crenolanib suppressed human ovarian carcinoma tumour growth and angiogenesis in the CAM model.ConclusionsThe PDGFR/FLT3 inhibitor crenolanib targets angiogenesis and inhibits tumour growth in vivo unrelated to PDGFR expression. Based on our findings, we suggest a broad mechanism of action of crenolanib.

Genetic Polymorphism on the Pharmacokinetics and Pharmacodynamics of Platelet-derived Growth Factor Receptor (PDGFR) Kinase Inhibitors.

Platelet-derived Growth Factor Receptor (PDGFR) is a kind of Receptor Tyrosine Kinases (RTKs). PDGFR Tyrosine Kinase Inhibitors (TKIs) which are small molecule inhibitors targeting PDGFR prevent and block cell proliferation signal transduction pathways. Recently, there have been 11 TKIs (including imatinib, sunitinib, regorafenib, sorafenib, pazopanib, axitinib, dasatinib, nilotinib, lenvatinib, cabozantinib and ponatinib) targeting PDGFR approved by FDA for the treatment of chronic myelogenous leukemia, gastrointestinal stromal tumors, renal cell carcinoma et al. Pharmacokinetics (PK) reflects the processes of drugs in body, while pharmacodynamics (PD) reflects the efficacy. Genetic polymorphisms of metabolizers and transporters contribute to highly inter-individual variability in PK and PD. This review aims to introduce the clinical applications, instruction and usage, PK, PD and pharmacogenetics of these PDGFR TKIs. In vivo and in vitro studies about PDGFR TKIs were searched from PubMed. Data and information were analyzed and summarized. The overview of (1) general information on PDGFR kinase inhibitors; (2) PK parameters of PDGFR kinase inhibitors; (3) metabolic enzymes and transporters of PDGFR kinase inhibitors; (4) main drug interactions of PDGFR kinase inhibitors; (5) adverse events of PDGFR kinase inhibitors; and (6) genetic polymorphism on PK and PD of PDGFR kinase inhibitors, was exhibited and discussed in this review. This review summarized the general information, PK, metabolic enzymes and transporters, main drug interactions, adverse events and pharmacogenetics of FDA approved PDGFR TKIs. Studies showed that Single nucleotide polymorphisms of metabolic enzymes and transporters had influence on the PK and PD of PDGFR TKIs.

Phase 1b/2 Randomized Study of MEDI-575 in Combination With Carboplatin Plus Paclitaxel Versus Carboplatin Plus Paclitaxel Alone in Adult Patients With Previously Untreated Advanced Non–Small-Cell Lung Cancer

IntroductionPlatinum doublet chemotherapy has represented the standard of care in advanced non–small-cell lung cancer for decades. Targeting platelet-derived growth factor receptors (PDGFR) is a potential mechanism to improve the efficacy of first-line therapy. This randomized phase 1b/2 trial investigated the addition of the anti-PDGFRα monoclonal antibody MEDI-575 to first-line carboplatin/paclitaxel (CP) chemotherapy. Patients and MethodsThe phase 1b component was a dose-escalation study combining MEDI-575 with carboplatin area under the plasma concentration versus time curve 6 and paclitaxel 200 mg/m2 (CPM), with the end point of identifying a recommended phase 2 dose. The phase 2 component randomized patients to CPM or CP, with primary end point of progression-free survival. Secondary end points included overall survival, overall response rate, and adverse event rates. ResultsOverall, 99 patients were enrolled and received either CPM (n = 53; 4 phase 1b, 49 phase 2) or CP (n = 46). Demographics were as follows: 63/36 male/female, 78/21 aged ≤ 70/> 70 years; 37/62 squamous/nonsquamous, 42/53 Eastern Cooperative Oncology Group performance status 0/1. The phase 2 portion of the trial did not meet its primary end point: progression-free survival was shorter with CPM (4.6 vs. 5.5 months) than CP. No significant difference was seen in overall response rate (31.7% vs. 22.5%) or median overall survival (10.0 vs. 11.8 months). More serious adverse events were observed in patients receiving CPM (47% vs. 40%); in particular, 9 patients in the CPM group had significant gastrointestinal or respiratory adverse events (including abscess, perforation, and pneumothorax). ConclusionThe addition of MEDI-575 to CP chemotherapy as first-line treatment of advanced non–small-cell lung cancer did not improve efficacy and resulted in increased toxicity.

Nintedanib inhibits macrophage activation and ameliorates vascular and fibrotic manifestations in the Fra2 mouse model of systemic sclerosis

BackgroundNintedanib is an inhibitor targeting platelet-derived growth factor receptor, fibroblast growth factor receptor and vascular endothelial growth factor receptor tyrosine kinases that has recently been approved for the treatment of...

Imatinib treatment of poor prognosis mesenchymal-type primary colon cancer: a proof-of-concept study in the preoperative window period (ImPACCT)

BackgroundThe identification of four Consensus Molecular Subtypes (CMS1–4) of colorectal cancer forms a new paradigm for the design and evaluation of subtype-directed therapeutic strategies. The most aggressive subtype - CMS4 - has the highest chance of disease recurrence. Novel adjuvant therapies for patients with CMS4 tumours are therefore urgently needed. CMS4 tumours are characterized by expression of mesenchymal and stem-like genes. Previous pre-clinical work has shown that targeting Platelet-Derived Growth Factor Receptors (PDGFRs) and the related KIT receptor with imatinib is potentially effective against mesenchymal-type colon cancer. In the present study we aim to provide proof for the concept that imatinib can reduce the aggressive phenotype of primary CMS4 colon cancer.MethodsTumour biopsies from patients with newly diagnosed stage I-III colon cancer will be analysed with a novel RT-qPCR test to pre-select patients with CMS4 tumours. Selected patients (n = 27) will receive treatment with imatinib (400 mg per day) starting two weeks prior to planned tumour resection. To assess treatment-induced changes in the aggressive CMS4 phenotype, RNA sequencing will be performed on pre- and post-treatment tissue samples.DiscussionThe development of effective adjuvant therapy for primary colon cancer is hindered by multiple factors. First, new drugs that may have value in the prevention of (early) distant recurrence are almost always first tested in patients with heavily pre-treated metastatic disease. Second, measuring on-target drug effects and biological consequences in tumour tissue is not commonly a part of the study design. Third, due to the lack of patient selection tools, clinical trials in the adjuvant setting require large patient populations. Finally, the evaluation of recurrence-prevention requires a long-term follow-up. In the ImPACCT trial these issues are addressed by including newly diagnosed pre-selected patients with CMS4 tumours prior to primary tumour resection, rather than non-selected patients with late-stage disease. By making use of the pre-operative window period, the biological effect of imatinib treatment on CMS4 tumours can be rapidly assessed. Delivering proof-of-concept for drug action in early stage disease should form the basis for the design of future trials with subtype-targeted therapies in colon cancer patients.Trial registrationClinicalTrials.gov: NCT02685046. Registration date: February 9, 2016.

Targeting Platelet-Derived Growth Factor Receptor β+ Scaffold Formation Inhibits Choroidal Neovascularization

Neovascular age-related macular degeneration is among the most common causes of irreversible blindness and manifests with choroidal neovascularization (CNV). Anti-vascular endothelial growth factor-A therapies are only partially effective and their chronic administration may impair functions of the choriocapillaris and retina. Thus, novel therapeutic targets are needed urgently. We have observed in a laser-induced model of CNV that a platelet-derived growth factor receptor β positive (PDGFRβ(+)) scaffold is formed before infiltration of neovessels into this scaffold to form CNV lesions, and that this scaffold limits the extent of neovascularization. Based on these observations we hypothesized that ablation of proliferating PDGFRβ(+) cells to prevent the formation of this scaffold might inhibit CNV growth and present a novel therapeutic approach for neovascular age-related macular degeneration. To test this hypothesis we targeted proliferating PDGFRβ(+) cells through independent distinct approaches after laser injury: i) by using an inducible genetic model to inhibit specifically proliferating PDGFRβ(+) cells, ii) by treating mice with a neutralizing anti-PDGFRβ antibody, iii) by administering an anti-PDGF-AB/BB aptamer, and iv) by using small chemical inhibitor approaches. The results show that therapeutic targeting of proliferating PDGFRβ(+) cells potently inhibits the formation of the pericyte-like scaffold, with concomitant attenuation of CNV. Moreover, we show that early inhibition of PDGFRβ(+) cell proliferation before neovessel formation is sufficient to inhibit scaffold formation and neovascularization.

MP92-09 COMBINATION THERAPY USING MOLECULAR-TARGETED DRUGS INHIBITING PLATELET-DERIVED GROWTH FACTOR RECEPTORS IN THE TUMOR MICROENVIRONMENT OF RENAL CELL CARCINOMA

You have accessJournal of UrologyKidney Cancer: Basic Research & Pathophysiology III1 Apr 2016MP92-09 COMBINATION THERAPY USING MOLECULAR-TARGETED DRUGS INHIBITING PLATELET-DERIVED GROWTH FACTOR RECEPTORS IN THE TUMOR MICROENVIRONMENT OF RENAL CELL CARCINOMA Hiroyuki Kitano, Jun Teishima, Ryo Yuge, Syunsuke Shinmei, Hirotaka Nagamatsu, Keisuke Goto, Kouichi Shoji, Syogo Inoue, Tetsutaro Hayashi, Kazuhiro Sentani, Yasuhiko Kitadai, Wataru Yasui, and Akio Matsubara Hiroyuki KitanoHiroyuki Kitano More articles by this author , Jun TeishimaJun Teishima More articles by this author , Ryo YugeRyo Yuge More articles by this author , Syunsuke ShinmeiSyunsuke Shinmei More articles by this author , Hirotaka NagamatsuHirotaka Nagamatsu More articles by this author , Keisuke GotoKeisuke Goto More articles by this author , Kouichi ShojiKouichi Shoji More articles by this author , Syogo InoueSyogo Inoue More articles by this author , Tetsutaro HayashiTetsutaro Hayashi More articles by this author , Kazuhiro SentaniKazuhiro Sentani More articles by this author , Yasuhiko KitadaiYasuhiko Kitadai More articles by this author , Wataru YasuiWataru Yasui More articles by this author , and Akio MatsubaraAkio Matsubara More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2016.02.2642AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Recent studies have shown that the tumor microenvironment, which is comprised of cancer cells and stroma, is involved in cancer progression and platelet-derived growth factor (PDGF) plays a major role in stromal activation. However, the impacts of molecular-targeted drugs on the stroma of renal cell carcinoma (RCC) remain unclear. Therefore, in this study, we used a tyrosine kinase inhibitor (TKI) and a mammalian target of rapamycin inhibitor (mTORI) targeting PDGF receptors with the aim of elucidating their effects on the RCC stroma and analyzing the treatment outcomes obtained with TKI/mTORI combination therapy. METHODS Orthotopic mouse models, created using Caki-1, a luciferase-expressing human RCC cell line, were divided into four groups: control (C), everolimus (E), sunitinib (S) and everolimus/sunitinib (ES). After four-week everolimus at 1 mg/kg/day and sunitinib at 10 mg/kg/day, tumors were removed. Cell viability was measured every 2 weeks by in vivo imaging. Cell proliferation was analyzed in extracted tissues by the Ki67 labeling index (Ki67-LI). Recruitment of cancer-associated fibroblasts (CAFs) and extracellular matrix growth were analyzed by immunostaining for a-smooth muscle actin and type 1 collagen, respectively, angiogenesis and lymphangiogenesis by immunofluorescence staining for CD31 and LYVE-1, respectively, and pericyte recruitment by double-immunofluorescence staining with antibodies against endothelial cell (CD31) and pericyte (desmin) markers. RESULTS Cell viability and Ki67-LI were significantly decreased in the E and ES groups as compared to the S group. We first confirmed expressions of PDGF receptors on CAFs and pericytes by double-immunofluorescence staining. Neither recruitment of CAFs nor growth of type 1 collagen was inhibited in the E group but both were significantly inhibited in the S and ES groups. Compared to the E group, angiogenesis and lymphangiogenesis were significantly inhibited in the S and ES groups. The C and E groups showed pericyte recruitment around blood vessels, but these cells were relatively sparse in the S and ES groups. CONCLUSIONS The comparison between TKI and mTORI revealed mTORI to have significantly greater inhibitory effects on cancer cells, while TKI exerted inhibitory effects on the stroma. Our findings suggest that combining these two molecular-targeted drugs, with the aim of targeting the tumor microenvironment, would be an effective treatment for RCC. © 2016FiguresReferencesRelatedDetails Volume 195Issue 4SApril 2016Page: e1165 Advertisement Copyright & Permissions© 2016MetricsAuthor Information Hiroyuki Kitano More articles by this author Jun Teishima More articles by this author Ryo Yuge More articles by this author Syunsuke Shinmei More articles by this author Hirotaka Nagamatsu More articles by this author Keisuke Goto More articles by this author Kouichi Shoji More articles by this author Syogo Inoue More articles by this author Tetsutaro Hayashi More articles by this author Kazuhiro Sentani More articles by this author Yasuhiko Kitadai More articles by this author Wataru Yasui More articles by this author Akio Matsubara More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

The Regulatory Roles of MicroRNA-146b-5p and Its Target Platelet-derived Growth Factor Receptor α (PDGFRA) in Erythropoiesis and Megakaryocytopoiesis

Emerging evidence has shown that microRNAs have key roles in regulating various normal physiological processes, whereas their deregulated expression is correlated with various diseases. The miR-146 family includes miR-146a and miR-146b, with a distinct expression spectrum in different hematopoietic cells. Recent work indicated that miR-146a has a close relationship with inflammation and autoimmune diseases. miR-146-deficient mice have developed some abnormal hematopoietic phenotypes, suggesting the potential functions of miR-146 in hematopoietic development. In this study, we found that miR-146b was consistently up-regulated in both K562 and CD34(+) hematopoietic stem/progenitor cells (HSPCs) undergoing either erythroid or megakaryocytic differentiation. Remarkably, erythroid and megakaryocytic maturation of K562 cells was induced by excess miR-146b but inhibited by decreased miR-146b levels. More importantly, an mRNA encoding receptor tyrosine kinase, namely platelet-derived growth factor receptor α (PDGFRA), was identified and validated as a direct target of miR-146b in hematopoietic cells. Gain-of-function and loss-of-function assays showed that PDGFRA functioned as a negative regulator in erythroid and megakaryocytic differentiation. miR-146b could ultimately affect the expression of the GATA-1 gene, which is regulated by HEY1 (Hairy/enhancer-of-split related with YRPW motif protein 1), a transcriptional repressor, via inhibition of the PDGFRA/JNK/JUN/HEY1 pathway. Lentivirus-mediated gene transfer also demonstrated that the overexpression of miR-146b promoted erythropoiesis and megakaryocytopoiesis of HSPCs via its regulation on the PDGFRA gene and effects on GATA-1 expression. Moreover, we confirmed that the binding of GATA-1 to the miR-146b promoter and induction of miR-146b during hematopoietic maturation were dependent on GATA-1. Therefore, miR-146b, PDGFRA, and GATA-1 formed a regulatory circuit to promote erythroid and megakaryocytic differentiation.

MiR-34a/c-Dependent PDGFR-α/β Downregulation Inhibits Tumorigenesis and Enhances TRAIL-Induced Apoptosis in Lung Cancer

Lung cancer is the leading cause of cancer mortality in the world today. Although some advances in lung cancer therapy have been made, patient survival is still poor. MicroRNAs (miRNAs) can act as oncogenes or tumor-suppressor genes in human malignancy. The miR-34 family consists of tumor-suppressive miRNAs, and its reduced expression has been reported in various cancers, including non-small cell lung cancer (NSCLC). In this study, we found that miR-34a and miR-34c target platelet-derived growth factor receptor alpha and beta (PDGFR-α and PDGFR-β), cell surface tyrosine kinase receptors that induce proliferation, migration and invasion in cancer. MiR-34a and miR-34c were downregulated in lung tumors compared to normal tissues. Moreover, we identified an inverse correlation between PDGFR-α/β and miR-34a/c expression in lung tumor samples. Finally, miR-34a/c overexpression or downregulation of PDGFR-α/β by siRNAs, strongly augmented the response to TNF-related apoptosis inducing ligand (TRAIL) while reducing migratory and invasive capacity of NSCLC cells.

Hypoxic Pulmonary Hypertension in Mice with Constitutively Active Platelet‐Derived Growth Factor Receptor‐β

Platelet-derived growth factor (PDGF) has been implicated in the pathobiology of vascular remodeling. The multikinase inhibitor imatinib that targets PDGF receptor (PDGFR), c-kit and Abl kinases, shows therapeutic efficacy against experimental pulmonary hypertension (PH); however, the role of PDGFR-b in experimental PH has not been examined by genetic approach. We investigated the chronic hypoxia-induced PH in mice carrying an activating point mutation of PDGFR-β (D849N) and evaluated the therapeutic efficacy of imatinib. In addition, we studied pulmonary global gene expression and confirmed the expression of identified genes by immunohistochemistry. Chronically hypoxic D849N mice developed PH and strong pulmonary vascular remodeling that was improved by imatinib (100 mg/kg/day) as evident from the significantly reduced right ventricular systolic pressure, right ventricular hypertrophy and muscularization of peripheral pulmonary arteries. Global gene expression analysis revealed that stromal cell derived factor SDF)-1α was significantly upregulated, which was confirmed by immunohistochemistry. Moreover, an enhanced immunoreactivity for SDF-1α, PDGFR-β and CXCR4, the receptor for SDF-1α was localized to the α-smooth muscle cell (SMC) actin positive pulmonary vascular cells in hypoxic mice and patients with idiopathic pulmonary arterial hypertension (IPAH). In conclusion, our findings substantiate the major role of PDGFR activation in pulmonary vascular remodeling by a genetic approach. Immunohistochemistry findings suggest a role for SDF-1α/CXCR4 axis in pulmonary vascular remodeling and point to a potential interaction between the chemokine SDF-1 and the growth factor PDGF signaling. Future studies designed to elucidate an interaction between the chemokine SDF-1 and the PDGF system may uncover novel therapeutic targets.

Engineered High-Affinity Affibody Molecules Targeting Platelet-Derived Growth Factor Receptor β In Vivo

Platelet-derived growth factor receptor (PDGFR) β is a marker of stromal pericytes and fibroblasts and represents an interesting target for both diagnosis and therapy of solid tumors. A receptor-specific imaging agent would be a useful tool for further understanding the prognostic role of this receptor in vivo. Affibody molecules constitute a class of very small binding proteins that are highly suited for in vivo imaging applications and that can be selected to specifically recognize a desired target protein. Here we describe the isolation of PDGFRβ-specific Affibody molecules with subnanomolar affinity. First-generation Affibody molecules were generated from a large naive library using phage display selection. Subsequently, sequences from binders having a desired selectivity profile and competing with the natural ligand for binding were used in the design of an affinity maturation library, which was created using a single partially randomized oligonucleotide. From this second-generation library, Affibody molecules with a 10-fold improvement in affinity (Kd=0.4–0.5 nM) for human PDGFRβ and a 4-fold improvement in affinity (Kd=6–7 nM) for murine PDGFRβ were isolated and characterized. Complete reversible folding after heating to 90 °C, as demonstrated by circular dichroism analysis, supports tolerance to labeling conditions for molecular imaging. The binders were highly specific, as verified by dot blot showing staining reactivity only with human and murine PDGFRβ, but not with human PDGFRα, or a panel of control proteins including 16 abundant human serum proteins. The final binder recognized the native conformation of PDGFRβ expressed in murine NIH-3T3 fibroblasts and human AU565 cells, and inhibited ligand-induced receptor phosphorylation in PDGFRβ-transfected porcine aortic endothelial cells. The PDGFRβ-specific Affibody molecule also accumulated around tumoral blood vessels in a model of spontaneous insulinoma, confirming a potential for in vivo targeting.

Expression of hedgehog signaling molecules in lung cancer

Abnormal hyperactivation of the hedgehog (Hh) pathway has been reported in many types of human cancers, including lung cancer. However, most reports are based on studies of fewer than three Hh target genes and the data vary between different studies. In the present report, we have determined the expression levels of several important components of the Hh pathway in lung cancers by using RT-PCR, in situ hybridization and immunohistochemistry. These molecules include Smoothened (SMO), Rab23, the downstream target platelet-derived growth factor receptor alpha (PDGFRα), hedgehog interacting protein (HIP ) and hepatocyte nuclear factor 3-beta (HNF3β). Our data show that some components of the hedgehog pathway, such as SMO, Rab23 and PDGFRα are expressed in many lung cancer specimens, although other hedgehog target genes are infrequently detected in lung cancer. Loss of HIP expression was found in several cases of lung cancers. Our study indicates that there might be some additional mechanisms involved in the hyperactivation of the Hh pathway. Thus, we suggest that lung cancer with heterogeneous tumor type harboring Hh signaling activation may have some novel and different regulatory mechanisms.

Platelet-derived growth factor receptor tyrosine kinase inhibitors: a review of the recent patent literature

Importance of the field: Platelet-derived growth factor receptor (PDGFR) is a compelling target for developing therapeutic agents to treat diseases associated with overactivated platelet-derived growth factor (PDGF) signaling and has proved to be particularly encouraging for cancer treatment. The efforts in this area have been greatly enhanced by the approval of tyrosine kinase inhibitors with PDGFR inhibitory activity such as imatinib, sunitinib and sorafenib.Areas covered in this review: This review surveys the small molecule PDGFR inhibitors reported in patent literature over the past 5 years (2005 – 2009).What the reader will gain: The reader will gain an overview of the chemical scaffolds and the activity/selectivity of the newly discovered PDGFR inhibitors.Take home message: Targeting PDGFR kinase with small molecule inhibitors has remained a very active area. Many new and novel PDGFR inhibitors with different selectivity profiles are being discovered and evaluated. In cancer therapy, the identification of novel and potent PDGFR inhibitors with preferred kinase inhibitory profiles that deliver superior antitumor efficacy, yet have manageable side effects and toxicities, will continue to be the key for success. Additionally, interest in targeting PDGF signaling for intervention of various vascular diseases and fibrotic conditions is expected to continue to grow.

Abstract 288: PDGFR alpha and PDGFR beta differentially regulate cell proliferation and migration/invasion in medulloblastoma cells

Abstract Medulloblastoma (MB) is the most common brain tumor in children and often spread to the spinal cord though the cerebrospinal fluid. Understanding the biological mechanism of this disease would provide a better care for these patients. Recently, overexpression of platelet derived growth factor receptor (PDGFR) alpha and beta has been linked to a metastatic stage of the disease. To comprehensively analyze the functions of PDGFRs and find their potential downstream targets in MB, we utilized Daoy cells, a metastatic MB cell line, as a MB model to assess the roles of PDGFR alpha and beta in this disease. The expression levels of PDGFR alpha and beta were determined by real time PCR and immunobloting. It was shown that Daoy cells express both PDGFR alpha and PDGFR beta. By using siRNAs to knockdown PDGFR alpha or beta specifically, and neutralizing antibody specific to PDGFR alpha and PDGFR beta respectively, it was demonstrated that PDGFR alpha signaling hinders cell proliferation and cell migration/invasion while PDGFR beta signaling promotes cell proliferation and migration/invasion. To elucidate the mechanism and find their potential downstream targets, total RNAs from the PDGFR knockdown cells were further analyzed by real time PCR and our results showed that PDGFR alpha and PDGFR beta signaling differentially modulate a set of genes which are important for cell death/surviving and proliferation such as NF kappa B, ATF3, Txnip and cMYC. To elucidate which pathway might govern the different roles of PDGFR alpha and beta in tumor cell proliferation/surviving, an NF kappa B report plasmid was co-transfected with siRNAs of PDGFRs into the MB cells and then the NF kappa B activities in the co-transfected cells were determined using a luciferase assay system. It was demonstrated that the NF kappa B activity was largely reduced in PDGFR beta knockdown cells, which suggested that PDGFR alpha and PDGFR beta may balance the cell proliferation/surviving signaling via cMYC and NF kappa B pathway. Furthermore, by analyzing the expression of cell surface protein on the PDGFR knockdown cells using immunohistochemistry staining, we demonstrated that CD44, a hall marker for cell migration/invasion was down regulated by PDGFR beta knockdown but not by PDGFR alpha knockdown, which implicated PDGFRs balance their migration/invasion signaling via CD44. Taken together, these data suggest that PDGFR alpha and PDGFR beta play different roles in cell proliferation and migration/invasion in MB brain tumor cells and these studies also highlight the potential of targeting PDGFRs signaling therapy in MB. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 288.

Efficacy and Safety of Pazopanib in Patients With Metastatic Renal Cell Carcinoma

Inactivation of the von Hippel-Lindau gene in clear-cell renal cell carcinomas (RCC) leads to overexpression of hypoxia inducible factor, a transcription factor regulating vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) gene expression. Pazopanib, an angiogenesis inhibitor targeting VEGF receptor, PDGF receptor, and c-KIT, was evaluated in patients with RCC. This phase II study was designed as a randomized discontinuation study but was revised to an open-label study on the recommendation of the data monitoring committee (based on week 12 response rate [RR] of 38% in the first 60 patients). The primary end point was changed from progressive disease rate at 16 weeks postrandomization to RR. Pazopanib 800 mg was administered orally once daily. Pazopanib 800 mg was administered orally once daily. The study enrolled 225 patients with metastatic RCC; 155 patients (69%) were treatment naïve, and 70 patients (31%) had received one prior cytokine- or bevacizumab-containing regimen. Overall RR was 35%; median duration of response was 68 weeks. Median progression-free survival (PFS) was 52 weeks. Eastern Cooperative Oncology Group performance status of 0 and time from diagnosis to treatment of more than 1 year were correlated with prolonged PFS. Pazopanib was generally well tolerated. The most common adverse events were diarrhea, fatigue, and hair depigmentation. The most common laboratory abnormalities were elevated AST and ALT. Pazopanib demonstrated durable activity in patients with advanced RCC and was generally well tolerated in this population. These findings support the further development of pazopanib in advanced RCC.

Combined Anti-Angiogenic Therapy Targeting PDGF and VEGF Receptors Lowers the Interstitial Fluid Pressure in a Murine Experimental Carcinoma

Elevation of the interstitial fluid pressure (IFP) of carcinoma is an obstacle in treatment of tumors by chemotherapy and correlates with poor drug uptake. Previous studies have shown that treatment with inhibitors of platelet-derived growth factor (PDGF) or vascular endothelial growth factor (VEGF) signaling lowers the IFP of tumors and improve chemotherapy. In this study, we investigated whether the combination of PDGFR and VEGFR inhibitors could further reduce the IFP of KAT-4 human carcinoma tumors. The tumor IFP was measured using the wick-in-needle technique. The combination of STI571 and PTK/ZK gave an additive effect on the lowering of the IFP of KAT-4 tumors, but the timing of the treatment was crucial. The lowering of IFP following combination therapy was accompanied by vascular remodeling and decreased vascular leakiness. The effects of the inhibitors on the therapeutic efficiency of Taxol were investigated. Whereas the anti-PDGF and anti-VEGF treatment did not significantly inhibit tumor growth, the inhibitors enhanced the effect of chemotherapy. Despite having an additive effect in decreasing tumor IFP, the combination therapy did not further enhance the effect of chemotherapy. Simultaneous targeting of VEGFR and PDGFR kinase activity may be a useful strategy to decrease tumor IFP, but the timing of the inhibitors should be carefully determined.

In Vivo Antitumor and Antimetastatic Activity of Sunitinib in Preclinical Neuroblastoma Mouse Model

Neuroblastoma (NB) is one of the most common pediatric solid tumors originating from the neural crest lineage. Despite intensive treatment protocols including megatherapy with hematopoietic stem cell transplantation, the prognosis of NB patients remains poor. More effective therapeutics are required. High vascularity has been described as a feature of aggressive, widely disseminated NB. Our previous work demonstrated the overexpression of vascular endothelial growth factor (VEGF) in NB, and we showed that an anti-VEGF receptor (VEGFR-2) antibody could induce sustained NB tumor suppression and regression. Sunitinib is a kinase inhibitor targeting platelet-derived growth factor receptors and VEGFRs and, therefore, a promising antiangiogenic agent. In this study, we investigated the antitumor activity of sunitinib and its synergistic cytotoxicity with conventional (cyclophosphamide) and novel (rapamycin) therapies. Both NB cell lines and tumor-initiating cells from patient tumor samples were used in our in vitro and in vivo models for these drug testing. We show that sunitinib inhibits tumor cell proliferation and phosphorylation of VEGFRs. It also inhibits tumor growth, angiogenesis, and metastasis in tumor xenograft models. Low-dose sunitinib (20 mg/kg) demonstrates synergistic cytotoxicity with an mTOR inhibitor, rapamycin, which is more effective than the traditional chemotherapeutic drug, cyclophosphamide. These preclinical studies provide the evidence of antitumor activity of sunitinib both in the early stage of tumor formation and in the progressive metastatic disease. These studies also provide the framework for clinical trial of sunitinib, alone and in combination with conventional and novel therapies to increase efficacy and improve patient outcome in NB.