A potential oncogenic activity of platelet-derived growth factor d in prostate cancer progression

Exploring the impact of PDGFD in osteosarcoma metastasis through single-cell sequencing analysis

PURPOSE

The overall survival rate for metastatic osteosarcoma hovers around 20%. Responses to second-line chemotherapy, targeted therapies, and immunotherapies have demonstrated limited efficacy in metastatic osteosarcoma. Our objective is to validate differentially expressed genes and signaling pathways between non-metastatic and metastatic osteosarcoma, employing single-cell RNA sequencing (scRNA-seq) and additional functional investigations. We aim to enhance comprehension of metastatic mechanisms and potentially unveil a therapeutic target.

METHODS

scRNA-seq was performed on two primary osteosarcoma lesions (1 non-metastatic and 1 metastatic). Seurat package facilitated dimensionality reduction and cluster identification. Copy number variation (CNV) was predicted using InferCNV. CellChat characterized ligand-receptor-based intercellular communication networks. Differentially expressed genes underwent GO function enrichment analysis and GSEA. Validation was achieved through the GSE152048 dataset, which identified PDGFD-PDGFRB as a common ligand-receptor pair with significant contribution. Immunohistochemistry assessed PDGFD and PDGFRB expression, while multicolor immunofluorescence and flow cytometry provided insight into spatial relationships and the tumor immune microenvironment. Kaplan-Meier survival analysis compared metastasis-free survival and overall survival between high and low levels of PDGFD and PDGFRB. Manipulation of PDGFD expression in primary osteosarcoma cells examined invasion abilities and related markers.

RESULTS

Ten clusters encompassing osteoblasts, osteoclasts, osteocytes, fibroblasts, pericytes, endothelial cells, myeloid cells, T cells, B cells, and proliferating cells were identified. Osteoblasts, osteoclasts, and osteocytes exhibited heightened CNV levels. Ligand-receptor-based communication networks exposed significant fibroblast crosstalk with other cell types, and the PDGF signaling pathway was activated in non-metastatic osteosarcoma primary lesion. These results were corroborated by the GSE152048 dataset, confirming the prominence of PDGFD-PDGFRB as a common ligand-receptor pair. Immunohistochemistry demonstrated considerably greater PDGFD expression in non-metastatic osteosarcoma tissues and organoids, correlating with extended metastasis-free and overall survival. PDGFRB expression showed no significant variation between non-metastatic and metastatic osteosarcoma, nor strong correlations with survival times. Multicolor immunofluorescence suggested co-localization of PDGFD with PDGFRB. Flow cytometry unveiled a highly immunosuppressive microenvironment in metastatic osteosarcoma. Manipulating PDGFD expression demonstrated altered invasive abilities and marker expressions in primary osteosarcoma cells from both non-metastatic and metastatic lesions.

CONCLUSIONS

scRNA-seq illuminated the activation of the PDGF signaling pathway in primary lesion of non-metastatic osteosarcoma. PDGFD displayed an inhibitory effect on osteosarcoma metastasis, likely through the suppression of the EMT signaling pathway.

Cancer-Associated Fibroblast Heterogeneity, Activation and Function: Implications for Prostate Cancer

The continuous remodeling of the tumor microenvironment (TME) during prostate tumorigenesis is emerging as a critical event that facilitates cancer growth, progression and drug-resistance. Recent advances have identified extensive communication networks that enable tumor-stroma cross-talk, and emphasized the functional importance of diverse, heterogeneous stromal fibroblast populations during malignant growth. Cancer-associated fibroblasts (CAFs) are a vital component of the TME, which mediate key oncogenic events including angiogenesis, immunosuppression, metastatic progression and therapeutic resistance, thus presenting an attractive therapeutic target. Nevertheless, how fibroblast heterogeneity, recruitment, cell-of-origin and differential functions contribute to prostate cancer remains to be fully delineated. Developing our molecular understanding of these processes is fundamental to developing new therapies and biomarkers that can ultimately improve clinical outcomes. In this review, we explore the current challenges surrounding fibroblast identification, discuss new mechanistic insights into fibroblast functions during normal prostate tissue homeostasis and tumorigenesis, and illustrate the diverse nature of fibroblast recruitment and CAF generation. We also highlight the promise of CAF-targeted therapies for the treatment of prostate cancer.

E3 ligase HUWE1 promotes PDGF D-mediated osteoblastic differentiation of mesenchymal stem cells by effecting polyubiquitination of β-PDGFR

Mesenchymal stem cells (MSCs) are adult stem cell populations and exhibit great potential in regenerative medicine and oncology. Platelet-derived growth factors (PDGFs) are well known to regulate MSC biology through their chemotactic and mitogenic properties. However, their direct roles in the regulation of MSC lineage commitment are unclear. Here, we show that PDGF D promotes the differentiation of human bone marrow mesenchymal stem cells (hBMSCs) into osteoblasts and inhibits hBMSC differentiation into adipocytes. We demonstrate that PDGF D-induced β-actin expression and polymerization are essential for mediating this differential regulation of osteoblastogenesis and adipogenesis. Interestingly, we found that PDGF D induces massive upward molecular weight shifts of its cognate receptor, PDGF receptor beta (β-PDGFR) in hBMSCs, which was not observed in fibroblasts. Proteomic analysis indicated that the E3 ubiquitin ligase HECT, UBA, and WWE domain–containing protein 1 (HUWE1) associates with the PDGF D-activated β-PDGFR signaling complex in hBMSCs, resulting in β-PDGFR polyubiquitination. In contrast to the well-known role of ubiquitin in protein degradation, we provide evidence that HUWE1-mediated β-PDGFR polyubiquitination delays β-PDGFR internalization and degradation, thereby prolonging AKT signaling. Finally, we demonstrate that HUWE1-regulated β-PDGFR signaling is essential for osteoblastic differentiation of hBMSCs, while being dispensable for PDGF D-induced hBMSC migration and proliferation as well as PDGF D-mediated inhibition of hBMSC differentiation into adipocytes. Taken together, our findings provide novel insights into the molecular mechanism by which PDGF D regulates the commitment of hBMSCs into the osteoblastic lineage.

Potential Role of Diabetes Mellitus-Associated T Cell Senescence in Epithelial Ovarian Cancer Omental Metastasis

Epithelial ovarian cancer (EOC) is one of the most common causes of cancer-related deaths among women and is associated with age and age-related diseases. With increasing evidence of risks associated with metabolic inflammatory conditions, such as obesity and type 2 diabetes mellitus (T2DM), it is important to understand the complex pathophysiological mechanisms underlying cancer progression and metastasis. Age-related conditions can lead to both genotypic and phenotypic immune function alterations, such as induction of senescence, which can contribute to disease progression. Immune senescence is a common phenomenon in the ageing population, which is now known to play a role in multiple diseases, often detrimentally. EOC progression and metastasis, with the highest rates in the 75-79 age group in women, have been shown to be influenced by immune cells within the "milky spots" or immune clusters of the omentum. As T2DM has been reported to cause T cell senescence in both prediabetic and diabetic patients, there is a possibility that poor prognosis in EOC patients with T2DM is partly due to the accumulation of senescent T cells in the omentum. In this review, we explore this hypothesis with recent findings, potential therapeutic approaches, and future directions.

The Role of Cancer-Associated Fibroblasts in Prostate Cancer Tumorigenesis

Tumors strongly depend on their surrounding tumor microenvironment (TME) for growth and progression, since stromal elements are required to generate the optimal conditions for cancer cell proliferation, invasion, and possibly metastasis. Prostate cancer (PCa), though easily curable during primary stages, represents a clinical challenge in advanced stages because of the acquisition of resistance to anti-cancer treatments, especially androgen-deprivation therapies (ADT), which possibly lead to uncurable metastases such as those affecting the bone. An increasing number of studies is giving evidence that prostate TME components, especially cancer-associated fibroblasts (CAFs), which are the most abundant cell type, play a causal role in PCa since the very early disease stages, influencing therapy resistance and metastatic progression. This is highlighted by the prognostic value of the analysis of stromal markers, which may predict disease recurrence and metastasis. However, further investigations on the molecular mechanisms of tumor-stroma interactions are still needed to develop novel therapeutic approaches targeting stromal components. In this review, we report the current knowledge of the characteristics and functions of the stroma in prostate tumorigenesis, including relevant discussion of normal prostate homeostasis, chronic inflammatory conditions, pre-neoplastic lesions, and primary and metastatic tumors. Specifically, we focus on the role of CAFs, to point out their prognostic and therapeutic potential in PCa.

PDGFD induces ibrutinib resistance of diffuse large B‑cell lymphoma through activation of EGFR

Ibrutinib, an FDA approved, orally administered BTK inhibitor, has demonstrated high response rates to diffuse large B-cell lymphoma (DLBCL), however, complete responses are infrequent and acquired resistance to BTK inhibition can emerge. The present study investigated the role of the platelet-derived growth factor D (PDGFD) gene and the ibrutinib resistance of DLBCL in relation to epidermal growth factor receptor (EGFR). Bioinformatics was used to screen and analyze differentially expressed genes (DEGs) in complete response (CR), partial response (PR) and stable disease (SD) in DLBCL treatment with ibrutinib, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to analyze enriched the signaling pathways increasing DEGs. The Search Tool for Interactions of Chemicals database was used to analyze the target genes of ibrutinib. An interaction network of DEGs, disease-related genes and ibrutinib was constructed. The expression of PDGFD in tissues that were resistant or susceptible to DLBCL/ibrutinib was detected via immunohistochemistry (IHC), and the expression of PDGFD in DLBCL/ibrutinib-resistant strains and their parental counterparts were examined via reverse transcription-quantitative PCR and western blot analyses. Subsequently, a drug-resistant cell model of DLBCL/ibrutinib in which PDGFD was silenced was constructed. The apoptosis of the DLBCL/ibrutinib-resistant strains was examined using MTT and flow cytometry assays. EGFR gene expression was then assessed. At the same time, a PDGFD-interfering plasmid and an EGFR overexpression plasmid were transfected into the DLBCL drug-resistant cells (TMD8-ibrutinib, HBL1-ibrutinib) separately or together. MTT was used to measure cell proliferation and changes in the IC₅₀ of ibrutinib. A total of 86 DEGs that increased in the CR, PR and SD tissues were screened, and then evaluated with GO and KEGG. The interaction network diagram showed that there was a regulatory relationship between PDGFD and disease-related genes, and that PDGFD could indirectly target the ibrutinib target gene EGFR, indicating that PDGFD could regulate DLBCL via EGFR. IHC results showed high expression of PDGFD in diffuse large B-cell lymphoma tissues with ibrutinib tolerance. PDGFD expression in ibrutinib-resistant DLBCL cells was higher compared with in parental cells. Following interference with PDGFD expression in ibrutinib-resistant DLBCL cells, the IC₅₀ value of ibrutinib decreased, the rate of apoptosis increased and EGFR expression decreased. In brief, EGFR overexpression can reverse the resistance of DLBCL to ibrutinib via PDGFD interference, and PDGFD induces the resistance of DLBCL to ibrutinib via EGFR.

Elevated preoperative platelet distribution width predicts poor prognosis in Esophageal Squamous Cell Carcinoma

Activated platelets play a multifaceted role in tumorigenesis and progression. Platelet distribution width (PDW) is generally applied platelet parameters from routine blood test. Preoperative PDW has been considered a prognostic factor in many cancers. Nevertheless, the prognostic value of PDW in esophageal squamous cell carcinoma (ESCC) remains unknown. The study aimed to investigate whether preoperative PDW could serve as a prognostic factor in patients with ESCC. A total of 495 patients with ESCC undergoing curative surgery were enrolled. The relationship between PDW and clinical features in ESCC was analyzed using chi-square tests. Receiver operating characteristic (ROC) curve was used to determine the optimal cut-off value. Overall survival (OS) and disease-free survival (DFS) stratified by PDW were evaluated by Kaplan-Meier method and log-rank test. Univariate and multivariate Cox regression were used to evaluate the prognostic effect of PDW. Of the 495 patients, elevated PDW was observed in 241(48.7%) of the patients, respectively. An elevated PDW was correlated with depth of tumor (T stage, P = 0.031), nerve infiltration (P = 0.016), hospital time after operation (P = 0.020), platelet (P < 0.001), red cell distribution width (P < 0.001), and aspartate transaminase (P = 0.001). Moreover, elevated PDW (PDW ≥ 13.4 fL) predicted a worse OS and DFS in patients with ESCC (both P < 0.001). Multivariate analyses revealed that PDW was independently associated with OS (hazard ratios 1.194; 95% confidence interval 1.120-1.273; P < 0.001) and DFS (hazard ratios 2.562; 95% confidence interval 1.733-3.786; P < 0.001). Our findings indicated that elevated PDW could serve as an independent worse survival in ESCC.

An oncogenic activity of PDGF-C and its splice variant in human breast cancer

Despite strong evidence for the involvement of PDGF signaling in breast cancer, little is known about the PDGF ligand responsible for PDGFR activation during breast cancer progression. Here, we found PDGF-C to be highly expressed in breast carcinoma cell lines. Immunohistochemical analysis of invasive breast cancer revealed an association between increased PDGF-C expression and lymph node metastases, Ki-67 proliferation index, and poor disease-free survival. We also identified a PDGF-C splice variant encoding truncated PDGF-C (t-PDGF-C) isoform lacking the signal peptide and the N-terminal CUB domain. While t-PDGF C homodimer is retained intracellularly, it can be secreted as a heterodimer with full-length PDGF-C (FL-PDGF-C). PDGF-C downregulation reduced anchorage-independent growth and matrigel invasion of MDA-MB-231 cells. Conversely, ectopic expression of t-PDGF-C enhanced phenotypic transformation and invasion in BT-549 cells expressing endogenous FL-PDGF-C. The present study provides new insights into the functional significance of PDGF-C and its splice variant in human breast cancer.

Platelet-derived growth factor-D expression mediates the effect of differentiated degree on prognosis in epithelial ovarian cancer

Platelet-derived growth factor-D (PDGF-D) can enhance invasion and metastasis in several human malignancies. Although several studies have been performed to investigate the association between clinicopathological characteristics and prognosis in epithelial ovarian cancer (EOC), the mediation effect of PDGF-D on above-mentioned association have been seldom assessed. In this study, we detected the PDGF-D expression from the tissues of patients with EOC and further collected clinicopathological characteristics and prognostic information to identify whether PDGF-D mediated the effect of differentiated degree on prognosis in patients with EOC. A total of 190 paraffin-embedded tissue samples from patients with EOC between July 2005 and December 2010 were collected. We performed a Kaplan-Meier analysis for the association between differentiated degree and prognosis followed by a causal mediation analysis. The analysis results indicated that differentiated degree was associated with prognosis and PDGF-D mediated the effect of differentiated degree on prognosis in patients with EOC, which might be a potential target for ovarian cancer treatment.

Platelet-derived growth factor-D enables liver myofibroblasts to promote tumor lymphangiogenesis in cholangiocarcinoma

BACKGROUND & AIMS

In cholangiocarcinoma, early metastatic spread via lymphatic vessels often precludes curative therapies. Cholangiocarcinoma invasiveness is fostered by an extensive stromal reaction, enriched in cancer-associated fibroblasts (CAFs) and lymphatic endothelial cells (LECs). Cholangiocarcinoma cells recruit and activate CAFs by secreting PDGF-D. Herein, we investigated the role of PDGF-D and liver myofibroblasts in promoting lymphangiogenesis in cholangiocarcinoma.

METHODS

Human cholangiocarcinoma specimens were immunostained for podoplanin (LEC marker), α-SMA (CAF marker), VEGF-A, VEGF-C, and their cognate receptors (VEGFR2, VEGFR3). VEGF-A and VEGF-C secretion was evaluated in human fibroblasts obtained from primary sclerosing cholangitis explants. Using human LECs incubated with conditioned medium from PDGF-D-stimulated fibroblasts we assessed migration, 3D vascular assembly, transendothelial electric resistance and transendothelial migration of cholangiocarcinoma cells (EGI-1). We then studied the effects of selective CAF depletion induced by the BH3 mimetic navitoclax on LEC density and lymph node metastases in vivo.

RESULTS

In cholangiocarcinoma specimens, CAFs and LECs were closely adjacent. CAFs expressed VEGF-A and VEGF-C, while LECs expressed VEGFR2 and VEGFR3. Upon PDGF-D stimulation, fibroblasts secreted increased levels of VEGF-C and VEGF-A. Fibroblasts, stimulated by PDGF-D induced LEC recruitment and 3D assembly, increased LEC monolayer permeability, and promoted transendothelial EGI-1 migration. These effects were all suppressed by the PDGFRβ inhibitor, imatinib. In the rat model of cholangiocarcinoma, navitoclax-induced CAF depletion, markedly reduced lymphatic vascularization and reduced lymph node metastases.

CONCLUSION

PDGF-D stimulates VEGF-C and VEGF-A production by fibroblasts, resulting in expansion of the lymphatic vasculature and tumor cell intravasation. This critical process in the early metastasis of cholangiocarcinoma may be blocked by inducing CAF apoptosis or by inhibiting the PDGF-D-induced axis.

LAY SUMMARY

Cholangiocarcinoma is a highly malignant cancer affecting the biliary tree, which is characterized by a rich stromal reaction involving a dense population of cancer-associated fibroblasts that promote early metastatic spread. Herein, we show that cholangiocarcinoma-derived PDGF-D stimulates fibroblasts to secrete vascular growth factors. Thus, targeting fibroblasts or PDGF-D-induced signals may represent an effective tool to block tumor-associated lymphangiogenesis and reduce the invasiveness of cholangiocarcinoma.

Possible Role and Therapeutic Target of PDGF-D Signalling in Colorectal Cancer

Platelet-derived growth factor D (PDGF-D) has been shown to mediate cellular processes of importance in cancer progression. This study aimed to investigate the expression and putative involvement of PDGF-D signaling in colorectal carcinogenesis. PDGF-D was expressed in vascular endothelial cells in tumor and normal tissues. PDGF-D stimulation of cells altered genes of importance in carcinogenic processes. In addition, PDGF-D increased the proliferation rate while imatinib inhibited these effects. PDGF-D and its PDGF receptor beta (PDGFR-β) are expressed in colorectal cancer and blockage of PDGF-D/PDGFR-β signaling using tyrosine kinase inhibitors, such as imatinib, might be important in inhibiting tumor-promoting actions.

Prostate Specific Antigen, Mean Platelet Volume, and Platelet Distribution Width in Combination to Discriminate Prostate Cancer from Benign Prostate Hyperplasia

Background:

Prostate cancer (PCa) represents the second most commonly diagnosed malignancy and the sixth leading cause for cancer related death among men worldwide. Although use of the prostate specific antigen (PSA) as a diagnostic marker has improved the detection and management of PCa, low specificity and sensitivity has limited its clinical efficacy. Moreover, elevated PSA is frequently observed in benign prostate hyperplasia (BPH). Mean platelet volume (MPV) and platelet distribution width (PDW) are commonly used indicators of platelet activation. The purpose of current study was to investigate the ability of PSA, MPV, and PDW individually or in combination, to differentiate PCa from BPH.

Materials and Methods:

This study included 100 patients with PCa and 108 patients with BPH. We collected all participants’ clinical and laboratory characteristics. The benefit of adding MPV and PDW to a model with only PSA was evaluated as an increased in the area under the curve (AUC) obtained by receiver operating curve (ROC).

Results:

PCa patients had reduced MPV and elevated PSA and PDW levels compared to BPH patients. Single biomarkers had AUC values ranging from 0.683 for PDW to 0.865 for PSA. Moreover, the combination of PSA, MPV, and PDW increased the AUC to 0.935 (0.892-0.964) (p<0.0001), significantly higher than those of any single marker.

Conclusions:

The combined use of PSA, MPV, and PDW may be clinically useful in distinguishing between PCa and BPH.

PDGF-C and PDGF-D signaling in vascular diseases and animal models

Members of the platelet-derived growth factor (PDGF) family are well known to be involved in different pathological conditions. The cellular and molecular mechanisms induced by the PDGF signaling have been well studied. Nevertheless, there is much more to discover about their functions and some important questions to be answered. This review summarizes the known roles of two of the PDGFs, PDGF-C and PDGF-D, in vascular diseases. There are clear implications for these growth factors in several vascular diseases, such as atherosclerosis and stroke. The PDGF receptors are broadly expressed in the cardiovascular system in cells such as fibroblasts, smooth muscle cells and pericytes. Altered expression of the receptors and the ligands have been found in various cardiovascular diseases and current studies have shown important implications of PDGF-C and PDGF-D signaling in fibrosis, neovascularization, atherosclerosis and restenosis.

MLLT11/AF1q boosts oncogenic STAT3 activity through Src-PDGFR tyrosine kinase signaling

Constitutive STAT3 activation by tyrosine phosphorylation of mutated or amplified tyrosine kinases (pYSTAT3) is critical for cancer initiation, progression, invasion, and motility of carcinoma cells. We showed that AF1q is associated with STAT3 signaling in breast cancer cells. In xenograft models, enhanced AF1q expression activated STAT3 and promoted tumor growth and metastasis in immunodeficient NSG mice. The cytokine secretory phenotype of MDA-MB-231LN breast cancer cells with altered AF1q expression revealed changes in expression of platelet-derived growth factor subunit B (PDGF-B). AF1q-induced PDGF-B stimulated motility, migration, and invasion of MDA-MB-231LN cells, and AF1q up-regulated platelet-derived growth factor receptor (PDGFR) signaling. Further, AF1q-induced PDGFR signaling enhanced STAT3 activity through Src kinase activation, which could be blocked by the Src kinase inhibitor PP1. Moreover, AF1q up-regulated tyrosine kinase signaling through PDGFR signaling, which was blockable by imatinib. In conclusion, we demonstrated that enhanced AF1q expression contributes to persistent and oncogenic pYSTAT3 levels in invasive carcinoma cells by activating Src kinase through activation of the PDGF-B/PDGFR cascade. Therefore, AF1q plays an essential role as a cofactor in PDGF-B-driven STAT3 signaling.

Involvement of platelet-derived growth factor ligands and receptors in tumorigenesis

Platelet-derived growth factor (PDGF) isoforms and their receptors have important roles during embryogenesis, particularly in the development of various mesenchymal cell types in different organs. In the adult, PDGF stimulates wound healing and regulates tissue homeostasis. However, overactivity of PDGF signalling is associated with malignancies and other diseases characterized by excessive cell proliferation, such as fibrotic conditions and atherosclerosis. In certain tumours, genetic or epigenetic alterations of the genes for PDGF ligands and receptors drive tumour cell proliferation and survival. Examples include the rare skin tumour dermatofibrosarcoma protuberance, which is driven by autocrine PDGF stimulation due to translocation of a PDGF gene, and certain gastrointestinal stromal tumours and leukaemias, which are driven by constitute activation of PDGF receptors due to point mutations and formation of fusion proteins of the receptors, respectively. Moreover, PDGF stimulates cells in tumour stroma and promotes angiogenesis as well as the development of cancer-associated fibroblasts, both of which promote tumour progression. Inhibitors of PDGF signalling may thus be of clinical usefulness in the treatment of certain tumours.

Identification of zinc finger protein of the cerebellum 5 as a survival factor of prostate and colorectal cancer cells

Identification of specific drug targets is very important for cancer therapy. We recently identified zinc finger protein of the cerebellum 5 (ZIC5) as a factor that promotes melanoma aggressiveness by platelet-derived growth factor D (PDGFD) expression. However, its roles in other cancer types remain largely unknown. Here we determined the roles of ZIC5 in prostate cancer (PCa) and colorectal cancer (CRC) cells. Results showed that ZIC5 was highly expressed in CRC and dedifferentiated PCa tissues, whereas little expression was observed in relevant normal tissues. Knockdown of ZIC5 decreased proliferation of several PCa and CRC cell lines with induction of cell death. ZIC5 knockdown significantly suppressed PDGFD expression transcriptionally, and PDGFD suppression also decreased proliferation of PCa and CRC cell lines. In addition, suppression of ZIC5 or PDGFD expression decreased levels of phosphorylated focal adhesion kinase (FAK) and signal transducer and activator of transcription 3 (STAT3) which are associated with PCa and CRC aggressiveness. Furthermore, knockdown of ZIC5 or PDGFD enhanced death of PCa and CRC cells induced by the anti-cancer drugs docetaxel or oxaliplatin, respectively. These results suggest that ZIC5 and PDGFD promote survival of PCa and CRC cells by enhancing FAK and STAT3 activity, and that the roles of ZIC5 are consistent across several cancer types.

Genetic association analysis of the RTK/ERK pathway with aggressive prostate cancer highlights the potential role of CCND2 in disease progression

The RTK/ERK signaling pathway has been implicated in prostate cancer progression. However, the genetic relevance of this pathway to aggressive prostate cancer at the SNP level remains undefined. Here we performed a SNP and gene-based association analysis of the RTK/ERK pathway with aggressive prostate cancer in a cohort comprising 956 aggressive and 347 non-aggressive cases. We identified several loci including rs3217869/CCND2 within the pathway shown to be significantly associated with aggressive prostate cancer. Our functional analysis revealed a statistically significant relationship between rs3217869 risk genotype and decreased CCND2 expression levels in a collection of 119 prostate cancer patient samples. Reduced expression of CCND2 promoted cell proliferation and its overexpression inhibited cell growth of prostate cancer. Strikingly, CCND2 downregulation was consistently observed in the advanced prostate cancer in 18 available clinical data sets with a total amount of 1,095 prostate samples. Furthermore, the lower expression levels of CCND2 markedly correlated with prostate tumor progression to high Gleason score and elevated PSA levels, and served as an independent predictor of biochemical relapse and overall survival in a large cohort of prostate cancer patients. Together, we have identified an association of genetic variants and genes in the RTK/ERK pathway with prostate cancer aggressiveness, and highlighted the potential importance of CCND2 in prostate cancer susceptibility and tumor progression to metastasis.

Convergence of eicosanoid and integrin biology: Role of Src in 12-LOX activation

12-Lipoxygenase (12-LOX) metabolizes arachidonic acid to 12(S)-hydroxyeicosatetraenoic acid, or 12(S)-HETE, a proinflammatory bioactive lipid implicated in tumor angiogenesis, growth, and metastasis. The mechanisms underlying 12-LOX-mediated signaling in cancer progression are still ill-defined. In the present study we demonstrate that 12-LOX phosphorylation and subsequent enzymatic activity occurs after integrin β4 stimulation and Src kinase recruitment to the integrin subunit. Inhibition of Src activity by PP2 or Src dominant-negative mutants reduced 12-LOX tyrosine phosphorylation and 12(S)-HETE production in response to integrin β4 stimulation in A431 cells. The pertinent Src-targeted residues for 12-LOX activity were mapped to Y19 and Y614, where 12-LOX mutants Y19F and Y614F showed 70% less enzymatic activity. Furthermore, we have shown that the 12-LOX activity modulated by these residues impacts migration. To our knowledge, this is the first report that c-Src kinase activity is required for β4-integrin-mediated phosphorylation of 12-LOX.

PDGF-D/PDGFRβ promotes tongue squamous carcinoma cell (TSCC) progression via activating p38/AKT/ERK/EMT signal pathway

Platelet-derived growth factor D (PDGF-D) signaling plays significant roles during the development and progression of human malignancies via interacting with the receptor of PDGF-D (PDGFR). Meanwhile, the majority of human tumor metastasis is closely associated with epithelial-mesenchymal transition (EMT). However, the underlying mechanism between PDGF-D/PDGFR signaling and EMT which involved in tumor metastasis remain dismal. This study aimed to investigate the role of PDGF-D signaling during EMT process of tongue squamous cell carcinoma (TSCC). In our study, the expression of PDGF-D and PDGFR were examined in primary TSCC samples and the expression of PDGF-D was also determined in TSCC cell lines. In addition, the correlation between PDGF-D expression and TSCC aggressive histopathological features was analyzed. Our results implied that upregulation of PDGFRβ in UM1 cells induced with exogenous PDGF-D can remarkably promote tumor cells invasiveness; conversely, when using small interfering RNA (siRNA), the invasiveness can be severely prohibited. Furthermore, PDGF-D downstream signal molecules p38, AKT, ERK and EMT biomarkers (E-cadherin, N-cadherin, Vimentin and snail) were measured using Western blot. Our results showed that PDGF-D can induce p38, AKT and ERK phosphorylation; downregulate epithelial markers and upregulate mesenchymal markers. On the contrary, PDGFRβ siRNA significantly prohibited p38, AKT and ERK phosphorylation; inhibited EMT process. Function analysis revealed that PDGFRβ siRNA obviously interfered with UM1 cell migration and invasion, according to transwell and wound healing assay. In conclusion, this study suggested that EMT process can be triggered by the PDGF-D/PDGFRβ axis in TSCC, and then involved in the tumor cell invasion via activation of p38/AKT/ERK/EMT pathway.

The interaction between androgen receptor and PDGF-D in the radiation response of prostate carcinoma

PURPOSE

To determine the functional relationship between androgen receptor (AR) and PDGF D as it relates to the radiation response of PTEN-null prostate cancer (PCa) cells and the effect of enzalutamide on these interactions.

METHODS AND MATERIALS

Using murine PTEN-null prostate epithelial cell line and human prostate carcinoma LNCaP (PTEN-mutant) models, nuclear and cytosolic AR levels were determined by immunoblot analysis and the transcriptional activity of nuclear AR was assessed by RT-PCR analysis of its target genes with or without irradiation. Cell survival was evaluated by clonogenic assay or sulforhodamine B (SRB) assay upon irradiation in the absence or presence of the AR antagonist enzalutamide.

RESULTS

PTEN loss resulted in upregulation of AR expression in a PDGF-D dependent manner and irradiation selectively increased the nuclear AR protein level and its activity in a murine cell model. When the functional significance of AR in cell survival was tested, treatment with enzalutamide resulted in radiosensitization of human LNCaP cells. Similarly to the murine model, PDGF-D overexpression increased the nuclear AR level and its transcriptional activity in LNCaP cells. PDGF-D over-expression was associated with radioresistance and enzalutamide treatment effectively reversed PDGF-D-mediated radioresistance in LNCaP cells.

CONCLUSIONS

We have demonstrated that AR, a target of the PTEN and PDGF D-downstream signaling program, contributes to radiation resistance in human PCa cells. In addition, this study suggests that anti-androgens such as enzalutamide may serve as radiation sensitizers for the treatment of PCa patients, particularly so in patients with loss of PTEN or overexpression of PDGF-D.

Functional malignant cell heterogeneity in pancreatic neuroendocrine tumors revealed by targeting of PDGF-DD

Intratumoral heterogeneity is an inherent feature of most human cancers and has profound implications for cancer therapy. As a result, there is an emergent need to explore previously unmapped mechanisms regulating distinct subpopulations of tumor cells and to understand their contribution to tumor progression and treatment response. Aberrant platelet-derived growth factor receptor beta (PDGFRβ) signaling in cancer has motivated the development of several antagonists currently in clinical use, including imatinib, sunitinib, and sorafenib. The discovery of a novel ligand for PDGFRβ, platelet-derived growth factor (PDGF)-DD, opened the possibility of a previously unidentified signaling pathway involved in tumor development. However, the precise function of PDGF-DD in tumor growth and invasion remains elusive. Here, making use of a newly generated Pdgfd knockout mouse, we reveal a functionally important malignant cell heterogeneity modulated by PDGF-DD signaling in pancreatic neuroendocrine tumors (PanNET). Our analyses demonstrate that tumor growth was delayed in the absence of signaling by PDGF-DD. Surprisingly, ablation of PDGF-DD did not affect the vasculature or stroma of PanNET; instead, we found that PDGF-DD stimulated bulk tumor cell proliferation by induction of paracrine mitogenic signaling between heterogeneous malignant cell clones, some of which expressed PDGFRβ. The presence of a subclonal population of tumor cells characterized by PDGFRβ expression was further validated in a cohort of human PanNET. In conclusion, we demonstrate a previously unrecognized heterogeneity in PanNET characterized by signaling through the PDGF-DD/PDGFRβ axis.

Clinical significance of platelet derived growth factor-C and -D in gastric cancer

Platelet-derived growth factor (PDGF)-C and PDGF-D are frequently upregulated in human cancers and play important roles in tumor progression, angiogenesis and metastasis. However, the distribution, frequency and prognostic value of PDGF-C and PDGF-D expression in gastric cancer have not been clarified. The present study evaluated the association between expression of PDGF-C and PDGF-D, clinicopathological factors and outcomes, in patients with gastric cancer. Gastric adenocarcinoma tumor samples were obtained from 204 patients who underwent curative gastrectomy between 2003 and 2007. The expression of PDGF-C and PDGF-D was analyzed by immunohistochemical staining. High expression of PDGF-C and PDGF-D was detected in 114 (56%) and 151 (74%) tumors, respectively. PDGF-D expression was significantly associated with tumor depth (P=0.039), histopathology (P<0.01), tumor stage (P=0.01) and recurrence (P<0.01), whereas PDGF-C expression correlated only with histopathology (P=0.05). High PDGF-D expression was also associated with significantly shorter relapse-free survival (RFS) time (P<0.01), whilst high PDGF-C expression was associated with marginally, but not significantly, shorter RFS (P=0.10). On multivariate analysis, high PDGF-D expression was determined to be an independent prognostic factor (hazard ratio, 3.3; 95% confidence interval, 1.20–9.4; P=0.02). These findings indicate that high PDGF-D expression is strongly associated with tumor progression, recurrence, distant metastasis and poor outcomes in patients with gastric cancer. PDGF-D may therefore be an independent prognostic factor and a novel therapeutic target.

Matriptase activation and shedding through PDGF-D-mediated extracellular acidosis

Activation of β-platelet-derived growth factor receptor (β-PDGFR) is associated with prostate cancer (PCa) progression and recurrence after prostatectomy. Analysis of the β-PDGFR ligands in PCa revealed association between PDGF-D expression and Gleason score as well as tumor stage. During the course of studying the functional consequences of PDGF ligand-specific β-PDGFR signaling in PCa, we discovered a novel function of PDGF-D for activation/shedding of the serine protease matriptase leading to cell invasion, migration, and tumorigenesis. The present study showed that PDGF-D, not PDGF-B, induces extracellular acidification, which correlates with increased matriptase activation. A cDNA microarray analysis revealed that PDGF-D/β-PDGFR signaling upregulates expression of the acidosis regulator carbonic anhydrase IX (CAIX), a classic target of the transcriptional factor hypoxia-inducible factor-1α (HIF-1α). Cellular fractionation displayed a strong HIF-1α nuclear localization in PDGF-D-expressing cells. Treatment of vector control or PDGF-B-expressing cells with the HIF-1α activator CoCl2 led to increased CAIX expression accompanied by extracellular acidosis and matriptase activation. Furthermore, the analysis of the CAFTD cell lines, variants of the BPH-1 transformation model, showed that increased PDGF-D expression is associated with enhanced HIF-1α activity, CAIX induction, cellular acidosis, and matriptase shedding. Importantly, shRNA-mediated knockdown of CAIX expression effectively reversed extracellular acidosis and matriptase activation in PDGF-D-transfected BPH-1 cells and in CAFTD variants that express endogenous PDGF-D at a high level. Taken together, these novel findings reveal a new paradigm in matriptase activation involving PDGF-D-specific signal transduction leading to extracellular acidosis.

Dynamic regulation of platelet-derived growth factor D (PDGF-D) activity and extracellular spatial distribution by matriptase-mediated proteolysis

The oncogenic roles of PDGF-D and its proteolytic activator, matriptase, have been strongly implicated in human prostate cancer. Latent full-length PDGF-D (FL-D) consists of a CUB domain, a growth factor domain (GFD), and the hinge region in between. Matriptase processes the FL-D dimer into a GFD dimer (GFD-D) in a stepwise manner, involving generation of a hemidimer (HD), an intermediate product containing one FL-D subunit and one GFD subunit. Although the HD is a pro-growth factor that can be processed into the GFD-D by matriptase, the HD can also act as a dominant-negative ligand that prevents PDGF-B-mediated β-PDGF receptor activation in fibroblasts. The active GFD-D can be further cleaved into a smaller and yet inactive form if matriptase-mediated proteolysis persists. Through mutagenesis and functional analyses, we found that the R(340)R(341)GR(343)A (P4-P1/P1') motif within the GFD is the matriptase cleavage site through which matriptase can deactivate PDGF-D. Comparative sequence analysis based on the published crystal structure of PDGF-B predicted that the matriptase cleavage site R(340)R(341)GR(343)A is within loop III of the GFD, a critical structural element for its binding with the β-PDGF receptor. Interestingly, we also found that matriptase processing regulates the deposition of PDGF-D dimer species into the extracellular matrix (ECM) with increased binding from the FL-D dimer, to the HD, and to the GFD-D. Furthermore, we provide evidence that R(340)R(341)GR(343)A within the GFD is critical for PDGF-D deposition and binding to the ECM. In this study, we report a structural element crucial for the biological function and ECM deposition of PDGF-D and provide molecular insight into the dynamic functional interplay between the serine protease matriptase and PDGF-D.

Investigational therapies up to Phase II which target PDGF receptors: potential anti-cancer therapeutics

INTRODUCTION

The platelet-derived growth factor receptor (PDGFR) pathway has important functions in cell growth and, by overexpression or mutation, could also be a driver for tumor development. Moreover, PDGFR is expressed in a tumoral microenvironment and could promote tumorigenesis. With these biological considerations, the PDGFR pathway could be an interesting target for therapeutics. Currently, there are many molecules under development that target the PDGFR pathway in different types of cancer.

AREAS COVERED

In this review, the authors report the different molecules under development, as well as those approved albeit briefly, which inhibit the PDGFR pathway. Furthermore, the authors summarize their specificities, their toxicities, and their development.

EXPERT OPINION

Currently, most PDGFR kinase inhibitors are multikinase inhibitors and therefore do not simply target the PDGFR pathway. The development of more specific PDGFR inhibitors could improve drug efficacy. Moreover, selecting tumors harboring mutations or amplifications of PDGFR could improve outcomes associated with the use of these molecules. The authors believe that new technologies, such as kinome arrays or pharmacologic assays, could be of benefit to understanding resistance mechanisms and develop more selective PDGFR inhibitors.

The host microenvironment influences prostate cancer invasion, systemic spread, bone colonization, and osteoblastic metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in men worldwide. Most PCa deaths are due to osteoblastic bone metastases. What triggers PCa metastasis to the bone and what causes osteoblastic lesions remain unanswered. A major contributor to PCa metastasis is the host microenvironment. Here, we address how the primary tumor microenvironment influences PCa metastasis via integrins, extracellular proteases, and transient epithelia-mesenchymal transition (EMT) to promote PCa progression, invasion, and metastasis. We discuss how the bone-microenvironment influences metastasis; where chemotactic cytokines favor bone homing, adhesion molecules promote colonization, and bone-derived signals induce osteoblastic lesions. Animal models that fully recapitulate human PCa progression from primary tumor to bone metastasis are needed to understand the PCa pathophysiology that leads to bone metastasis. Better delineation of the specific processes involved in PCa bone metastasize is needed to prevent or treat metastatic PCa. Therapeutic regimens that focus on the tumor microenvironment could add to the PCa pharmacopeia.

Tyrosine kinase inhibitors in the treatment of prostate cancer: taking the next step in clinical development

INTRODUCTION

Prostate cancer (PCa) is the most frequently diagnosed, non-cutaneous malignancy in Western countries. Until recently, few therapeutic options were available for patients with advanced PCa. Although these treatments may delay progression of disease, none are curative. Therefore, research continues to investigate other treatments for advanced PCa. Tyrosine kinase inhibitors (TKIs) have been extensively studied as a treatment for multiple malignancies and may represent an additional strategy. In addition to limiting cellular proliferation and metastasis, there is also growing interest in using these treatments to impact the bone microenvironment and reduce associated morbidity from PCa.

AREAS COVERED

Several TKIs have been evaluated in the preclinical setting in advanced PCa. Targets reviewed include the epidermal growth factor family, VEGF receptor, c-Src family kinases, platelet-derived growth factor and c-Met.

EXPERT OPINION

Despite strong biological rationale for the use of TKIs therapy for the treatment of PCa, Phase III clinical trials have produced disappointing results. As TKI strategies move forward, the failures of past trials need to be better understood. New approaches with these treatments will also have to take into account modern anti-androgens and a treatment landscape that now includes immunotherapy.

A randomized phase II study of cediranib alone versus cediranib in combination with dasatinib in docetaxel resistant, castration resistant prostate cancer patients

BACKGROUND

Activation of the vascular endothelial growth factor receptor (VEGFR) and the oncogenic Src pathway has been implicated in the development of castration-resistant prostate cancer (CRPC) in preclinical models. Cediranib and dasatinib are multi-kinase inhibitors targeting VEGFR and Src respectively. Phase II studies of cediranib and dasatinib in CRPC have shown single agent activity.

METHODS

Docetaxel-pretreated CRPC patients were randomized to arm A: cediranib alone (20 mg/day) versus arm B: cediranib (20 mg/day) plus dasatinib (100 mg/day) given orally on 4-week cycles. Primary endpoint was 12-week progression-free survival (PFS) as per the Prostate Cancer Clinical Trials Working Group (PCWG2). Patient reported outcomes were evaluated using Functional Assessment of Cancer Therapy-Prostate (FACT-P) and Present Pain Intensity (PPI) scales. Correlative studies of bone turnover markers (BTM), including bone alkaline phosphate (BAP) and serum beta-C telopeptide (B-CTx) were serially assayed. Results A total of 22 patients, 11 per arm, were enrolled. Baseline demographics were similar in both arms. Median number of cycles =4 in arm A (range 1-12) and 2 in arm B (range 1-9). Twelve-week PFS was 73 % in arm A versus 18 % in arm B (p = 0.03). Median PFS in months (arm A versus B) was: 5.2 versus 2.6 (95 % CI: 1.9-6.5 versus 1.4-not reached). Most common grade 3 toxicities were hypertension, anemia and thrombocytopenia in arm A and hypertension, diarrhea and fatigue in arm B. One treatment-related death (retroperitoneal hemorrhage) was seen in arm A. FACT-P and PPI scores did not significantly change in either arm. No correlation between BTM and PFS was seen in either arm.

CONCLUSIONS

Although limited by small numbers, this randomized study showed that the combination of VEGFR and Src targeted therapy did not result in improved efficacy and may be associated with a worse outcome than VEGFR targeted therapy alone in patients with CRPC. ClinicalTrials.gov number: NCT01260688.

Gastric cancer-derived MSC-secreted PDGF-DD promotes gastric cancer progression

PURPOSE

This study was designed to investigate the role of PDGF-DD secreted by gastric cancer-derived mesenchymal stem cells (GC-MSCs) in human gastric cancer progression.

METHODS

Gastric cancer cells were indirectly co-cultured with GC-MSCs in a transwell system. The growth and migration of gastric cancer cells were evaluated by cell colony formation assay and transwell migration assay, respectively. The production of PDGF-DD in GC-MSCs was determined by using Luminex and ELISA. Neutralization of PDGFR-β by su16f and siRNA interference of PDGF-DD in GC-MSCs was used to demonstrate the role of PDGF-DD produced by GC-MSCs in gastric cancer progression.

RESULTS

GC-MSC conditioned medium promoted gastric cancer cell proliferation and migration in vitro and in vivo. Co-culture with GC-MSCs increased the phosphorylation of PDGFR-β in SGC-7901 cells. Neutralization of PDGFR-β by su16f blocked the promoting role of GC-MSC conditioned medium in gastric cancer cell proliferation and migration. Recombinant PDGF-DD duplicated the effects of GC-MSC conditioned medium on gastric cancer cells. Knockdown of PDGF-DD in GC-MSCs abolished its effects on gastric cancer cells in vitro and in vivo.

CONCLUSIONS

PDGF-DD secreted by GC-MSCs is capable of promoting gastric cancer cell progression in vitro and in vivo. Targeting the PDGF-DD/PDGFR-β interaction between MSCs and gastric cancer cells may represent a novel strategy for gastric cancer therapy.

A critical role of the PTEN/PDGF signaling network for the regulation of radiosensitivity in adenocarcinoma of the prostate

PURPOSE

Loss or mutation of the phosphate and tensin homologue (PTEN) is a common genetic abnormality in prostate cancer (PCa) and induces platelet-derived growth factor D (PDGF D) signaling. We examined the role of the PTEN/PDGF axis on radioresponse using a murine PTEN null prostate epithelial cell model.

METHODS AND MATERIALS

PTEN wild-type (PTEN+/+) and PTEN knockout (PTEN-/-) murine prostate epithelial cell lines were used to examine the relationship between the PTEN status and radiosensitivity and also to modulate the PDGF D expression levels. PTEN-/- cells were transduced with a small hairpin RNA (shRNA) lentiviral vector containing either scrambled nucleotides (SCRM) or sequences targeted to PDGF D (shPDGF D). Tumorigenesis and morphogenesis of these cell lines were evaluated in vivo via subcutaneous injection of male nude mice and in vitro using Matrigel 3-dimensional (3D) culture. Effects of irradiation on clonogenic survival, cell migration, and invasion were measured with respect to the PTEN status and the PDGF D expression level. In addition, apoptosis and cell cycle redistribution were examined as potential mechanisms for differences seen.

RESULTS

PTEN-/- cells were highly tumorigenic in animals and effectively formed foci in 3D culture. Importantly, loss of PDGF D in these cell lines drastically diminished these phenotypes. Furthermore, PTEN-/- cells demonstrated increased clonogenic survival in vitro compared to PTEN+/+, and attenuation of PDGF D significantly reversed this radioresistant phenotype. PTEN-/- cells displayed greater migratory and invasive potential at baseline as well as after irradiation. Both the basal and radiation-induced migratory and invasive phenotypes in PTEN-/- cells required PDGF D expression. Interestingly, these differences were independent of apoptosis and cell cycle redistribution, as they showed no significant difference.

CONCLUSIONS

We propose that PDGF D represents a potentially promising target for PCa treatment resistance in the absence of PTEN function, and warrants further laboratory evaluation and clinical study.

Targeting the PDGF signaling pathway in tumor treatment

Platelet-derived growth factor (PDGF) isoforms and PDGF receptors have important functions in the regulation of growth and survival of certain cell types during embryonal development and e.g. tissue repair in the adult. Overactivity of PDGF receptor signaling, by overexpression or mutational events, may drive tumor cell growth. In addition, pericytes of the vasculature and fibroblasts and myofibroblasts of the stroma of solid tumors express PDGF receptors, and PDGF stimulation of such cells promotes tumorigenesis. Inhibition of PDGF receptor signaling has proven to useful for the treatment of patients with certain rare tumors. Whether treatment with PDGF/PDGF receptor antagonists will be beneficial for more common malignancies is the subject for ongoing studies.

The osteoblastic and osteoclastic interactions in spinal metastases secondary to prostate cancer

Prostate cancer (PC) is one of the most common cancers arising in men and has a high propensity for bone metastasis, particularly to the spine. At this stage, it often causes severe morbidity due to pathological fracture and/or metastatic epidural spinal cord compression which, if untreated, inevitably leads to intractable pain, neurological deficit, and paralysis. Unfortunately, the underlying molecular mechanisms driving growth of secondary PC in the bony vertebral column remain largely unknown. Further investigation is warranted in order to identify therapeutic targets in the future. This review summarizes the current understanding of PC bone metastasis in the spine, highlighting interactions between key tumor and bone-derived factors which influence tumor progression, especially the functional roles of osteoblasts and osteoclasts in the bone microenvironment through their interactions with metastatic PC cells and the critical pathway RANK/RANKL/OPG in bone destruction.

Role of the EphB2 receptor in autophagy, apoptosis and invasion in human breast cancer cells

The Eph and Ephrin proteins, which constitute the largest family of receptor tyrosine kinases, are involved in normal tissue development and cancer progression. Here, we examined the expression and role of the B-type Eph receptor EphB2 in breast cancers. By immunohistochemistry using a progression tissue microarray of human clinical samples, we found EphB2 to be expressed in benign tissues, but strongly increased in cancers particularly in invasive and metastatic carcinomas. Subsequently, we found evidence that EphB2, whose expression varies in established cell breast lines, possesses multiple functions. First, the use of a DOX-inducible system to restore EphB2 function to low expressers resulted in decreased tumor growth in vitro and in vivo, while its siRNA-mediated silencing in high expressers increased growth. This function involves the onset of apoptotic death paralleled by caspases 3 and 9 activation. Second, EphB2 was also found to induce autophagy, as assessed by immunofluorescence and/or immunoblotting examination of the LC3, ATG5 and ATG12 markers. Third, EphB2 also has a pro-invasive function in breast cancer cells that involves the regulation of MMP2 and MMP9 metalloproteases and can be blocked by treatment with respective neutralizing antibodies. Furthermore, EphB2-induced invasion is kinase-dependent and is impeded in cells expressing a kinase-dead mutant EphB2. In summary, we identified a mechanism involving a triple role for EphB2 in breast cancer progression, whereby it regulates apoptosis, autophagy, and invasion.

Platelet-derived growth factor-D and Rho GTPases regulate recruitment of cancer-associated fibroblasts in cholangiocarcinoma

Cholangiocarcinoma (CCA) is characterized by an abundant stromal reaction. Cancer-associated fibroblasts (CAFs) are pivotal in tumor growth and invasiveness and represent a potential therapeutic target. To understand the mechanisms leading to CAF recruitment in CCA, we studied (1) expression of epithelial-mesenchymal transition (EMT) in surgical CCA specimens and CCA cells, (2) lineage tracking of an enhanced green fluorescent protein (EGFP)-expressing human male CCA cell line (EGI-1) after xenotransplantation into severe-combined-immunodeficient mice, (3) expression of platelet-derived growth factors (PDGFs) and their receptors in vivo and in vitro, (4) secretion of PDGFs by CCA cells, (5) the role of PDGF-D in fibroblast recruitment in vitro, and (6) downstream effectors of PDGF-D signaling. CCA cells expressed several EMT biomarkers, but not alpha smooth muscle actin (α-SMA). Xenotransplanted CCA masses were surrounded and infiltrated by α-SMA-expressing CAFs, which were negative for EGFP and the human Y-probe, but positive for the murine Y-probe. CCA cells were strongly immunoreactive for PDGF-A and -D, whereas CAFs expressed PDGF receptor (PDGFR)β. PDGF-D, a PDGFRβ agonist, was exclusively secreted by cultured CCA cells. Fibroblast migration was potently induced by PDGF-D and CCA conditioned medium and was significantly inhibited by PDGFRβ blockade with Imatinib and by silencing PDGF-D expression in CCA cells. In fibroblasts, PDGF-D activated the Rac1 and Cdc42 Rho GTPases and c-Jun N-terminal kinase (JNK). Selective inhibition of Rho GTPases (particularly Rac1) and of JNK strongly reduced PDGF-D-induced fibroblast migration.

CONCLUSION

CCA cells express several mesenchymal markers, but do not transdifferentiate into CAFs. Instead, CCA cells recruit CAFs by secreting PDGF-D, which stimulates fibroblast migration through PDGFRβ and Rho GTPase and JNK activation. Targeting tumor or stroma interactions with inhibitors of the PDGF-D pathway may offer a novel therapeutic approach.

Platelet-type 12-lipoxygenase induces MMP9 expression and cellular invasion via activation of PI3K/Akt/NF-κB

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of death in males in the United States. Using human prostate cancer specimens, the authors have previously shown that elevated expression levels of 12-lipoxygenase (12-LOX) occurred more frequently in advanced stage, high-grade prostate cancer, suggesting that 12-LOX expression is associated with carcinoma progression and invasion. Previous reports from their group and others have shown that 12-LOX is a positive modulator of invasion and metastasis; however, the mechanism remains unclear. In this work, a new link between 12-LOX and the matrix metalloproteinase 9 (MMP9) in prostate cancer angiogenesis is reported. This study demonstrated that overexpression of 12-LOX in prostate cancer PC-3 cells resulted in elevated expression of MMP9 mRNA, protein and secretion. Exogenous addition of 12(S)-hydroxy eicosatetraenoic acid, the sole and stable end product of arachidonic acid metabolism by 12-LOX, is able to increase MMP9 expression in wild-type PC-3 cells. Furthermore, using pharmacological and genetic inhibition approaches, it was found that 12-LOX activates phosphoinositol 3 kinase (PI3K)/Akt, which results in nuclear factor-kappa B (NF-κB)-driven MMP9 expression, ensuing in enhanced chemoattraction of endothelial cells. Specific inhibitors of 12-LOX, PI3K or NF-κB inhibited MMP9 expression in 12-LOX-expressing PC-3 cells and resulted in the blockade of the migratory ability of endothelial cells. In summary, the authors have identified a new pathway by which overexpression of 12-LOX in prostate cancer cells leads to augmented production of MMP9 via activation of PI3K/Akt/NF-κB signaling. The role of 12-LOX-mediated MMP9 secretion in endothelial cell migration may account for the proangiogenic function of 12-LOX in prostate cancer.

Emerging roles of PDGF-D in EMT progression during tumorigenesis

Platelet-derived growth factor-D (PDGF-D) signaling pathway has been reported to be involved in regulating various cellular processes, such as cell growth, apoptotic cell death, migration, invasion, angiogenesis and metastasis. Recently, multiple studies have shown that PDGF-D plays a critical role in governing epithelial-to-mesenchymal transition (EMT), although the underlying mechanism of PDGF-D-mediated acquisition of EMT is largely unclear. Therefore, this mini review will discuss recent advances in our understanding of the role of PDGF-D in the acquisition of EMT during tumorigenesis. Furthermore, we will summarize the function of chemical inhibitors and natural compounds that are known to inactivate PDGF-D signaling pathway, which leads to the reversal of EMT. In summary, inactivation of PDGF-D could be a novel strategy for achieving better treatment outcome of patients inflicted with cancers.

Down-regulation of platelet-derived growth factor-D expression blockades NF-κB pathway to inhibit cell proliferation and invasion as well as induce apoptosis in esophageal squamous cell carcinoma

Substantial evidence has demonstrated that platelet-derived growth factor-D (PDGF-D) is tightly associated with the development and progression of tumors. However, its biological functions in esophageal squamous cell carcinoma (ESCC) remain to be delineated. In this study, we found that expressions of PDGF-D mRNA and protein in ESCC tissues and cells were significantly higher than that in normal esophageal epithelial tissues (P < 0.05), further investigation showed that PDGF-D protein level in EC1 cells was obviously higher than those in EC9706 and Eca109 cells (P < 0.05). Elevated PDGF-D level was closely associated with TNM staging, tumor differentiation and lymph node metastasis (P < 0.05), but not related to the patients' age and gender (P > 0.05). In addition, down-regulation of PDGF-D expression markedly inhibited proliferation, reduced invasion and induced apoptosis in EC1 cells. More importantly, reduced PDGF-D level evoked the down-regulation of p65 and p-IκBα proteins and elevation of IκBα protein of NF-κB pathway, accompanied with the decreases of bcl-2 and MMP-9 protein expressions and increases of bax protein level and caspase-3 activities. Correctively, our data suggest that PDGF-D plays pivotal roles in the development and progression of ESCC, and combinations with PDGF-D and NF-κB pathway may be effective and feasible molecular targets for therapy of ESCC.

Maternal transmission effect of a PDGF-C SNP on nonsyndromic cleft lip with or without palate from a Chinese population

Cleft lip with or without palate (CL/P) is a common congenital anomaly with a high birth prevalence in China. Based on a previous linkage signal of nonsyndromic CL/P (NSCL/P) on the chromosomal region 4q31–q32 from the Chinese populations, we screened the 4q31–q32 region for susceptibility genes in 214 trios of Han Chinese. PDGF-C, an important developmental factor, resides in the region and has been implicated in NSCL/P. However, in our family-based association test (transmission disequilibrium test; TDT), we could not conclude an association between PDGF-C and NSCL/P as previously suggested. Instead, we found strong evidence for parent-of-origin effect at a PDGF-C SNP, rs17035464, by a likelihood ratio test (unadjusted p-value = 0.0018; I_m = 2.46). The location of rs17035464 is 13 kb downstream of a previously reported, NSCL/P-associated SNP, rs28999109. Furthermore, a patient from our sample trios was observed with a maternal segmental uniparental isodisomy (UPD) in a region containing rs17035464. Our findings support the involvement of PDGF-C in the development of oral clefts; moreover, the UPD case report contributes to the collective knowledge of rare variants in the human genome.

Cediranib inhibits both the intraosseous growth of PDGF D-positive prostate cancer cells and the associated bone reaction

BACKGROUND

The major cause of death in prostate cancer (PCa) cases is due to distant metastatic lesions, with the bone being the most prevalent site for secondary colonization. Utilization of small molecule inhibitors to treat bone metastatic PCa have had limited success either as monotherapies or in combination with other chemotherapeutics due to intolerable toxicities. In the current study, we developed a clinically relevant in vivo intraosseous tumor model overexpressing the platelet-derived growth factor D (PDGF D) to test the efficacy of a newly characterized vascular endothelial growth factor receptor (VEGFR)/PDGFR inhibitor, cediranib (also called AZD2171).

METHODS

An intratibial-injection model was established utilizing DU145 cells with or without increased PDGF D expression. Tumor-bearing mice were treated by daily gavage administration of cediranib and/or weekly i.p. injection of docetaxel for 7 weeks. Tibiae were monitored by in vivo/ex vivo X-rays and histomorphometry analysis was performed to estimate tumor volume and tumor-associated trabecular bone growth.

RESULTS

Cediranib reduced intraosseous growth of prostate tumors as well as tumor-associated bone responses. When compared to the standard chemotherapeutic agent docetaxel, cediranib exhibited a stronger inhibition of tumor-associated bone response. The efficacy of cediranib was further enhanced when the drug was co-administered with docetaxel. Importantly, the therapeutic benefits of cediranib and docetaxel are more prominent in intraosseous prostate tumors overexpressing PDGF D.

CONCLUSION

These novel findings support the utilization of cediranib, either alone or in combination with docetaxel, to treat bone metastatic PCa exhibiting PDGF D expression.

Differential tumorigenic potential and matriptase activation between PDGF B versus PDGF D in prostate cancer

The platelet-derived growth factors (PDGF A, B, C, and D) and their receptors (α-PDGFR and β-PDGFR) play an indispensible role in physiologic and pathologic conditions, including tumorigenesis. The transformative β-PDGFR is overexpressed and activated during prostate cancer progression, but the identification and functional significance of its complementary ligand have not been elucidated. This study examined potential oncogenic functions of β-PDGFR ligands PDGF B and PDGF D, using nonmalignant prostate epithelial cells engineered to overexpress these ligands. In our models, PDGF D induced cell migration and invasion more effectively than PDGF B in vitro. Importantly, PDGF D supported prostate epithelial cell tumorigenesis in vivo and showed increased tumor angiogenesis compared with PDGF B. Autocrine signaling analysis of the mitogen-activated protein kinase and phosphoinositide 3-kinase pathways found PDGF D-specific activation of the c-jun-NH2-kinase (JNK) signaling cascade. Using short hairpin RNA and pharmacologic inhibitors, we showed that PDGFD-mediated phenotypic transformation is β-PDGFR and JNK dependent. Importantly, we made a novel finding of PDGF D-specific increase in the shedding and activation of the serine protease matriptase in prostate epithelial cells. Our study, for the first time to our knowledge, showed ligand-specific β-PDGFR signaling as well as PDGF D-specific regulation of matriptase activity and its spatial distribution through shedding. Taken together with our previous finding that matriptase is a proteolytic activator of PDGF D, this study provides a molecular insight into signal amplification of the proteolytic network and PDGF signaling loop during cancer progression.

PDGF-D/PDGF-ββ receptor-regulated chemotaxis of malignant mesothelioma cells

BACKGROUND/AIMS

Our earlier study suggested that platelet-derived growth factor (PDGF)- ββ receptor regulates chemotaxis of human malignant mesothelioma cells such as MSTO-211H, NCIH-2052, NCIH-2452, and NCIH-28 cells, but not non-malignant Met5A cells. The present study was designed to gain further insight into the PDGF-ββ receptor signals underlying the chemotaxis.

METHODS

PDGF-D secreted from cells, activation of Akt and ERK, and cell migration were monitored for cells with and without knocking-down PDGF-ββ receptor.

RESULTS

FBS significantly stimulated PDGF-D secretion from malignant mesothelioma cells, but not Met5A cells. PDGF-D activated Akt and ERK in both the non-malignant and malignant cells. PDGF-D significantly facilitated migration of malignant mesothelioma cells, but not Met5A cells, with the extent varying among the cell types. The facilitatory action of PDGF-D was clearly prevented by knocking-down PDGF-ββ receptor or inhibitors of PI3 kinase, PDK1, Akt, Rac1, ROCK, and MEK.

CONCLUSION

The results of the present study indicate that PDGF-D promotes malignant mesothelioma cell chemotaxis through PDGF-ββ receptor signaling pathways along a PI3 kinase/PDK1/Akt/Rac1/ROCK axis and relevant to ERK activation.

Sunitinib in combination with docetaxel and prednisone in chemotherapy-naive patients with metastatic, castration-resistant prostate cancer: a phase 1/2 clinical trial

BACKGROUND

This phase 1/2 study assessed sunitinib combined with docetaxel (Taxotere) and prednisone in chemotherapy-naive metastatic, castration-resistant prostate cancer (mCRPC) patients.

PATIENTS AND METHODS

To determine the recommended phase 2 dose (RP2D), 25 patients in four dose escalation cohorts received 3-week cycles of sunitinib (2 weeks on, 1 week off), docetaxel and prednisone, preceded by a 4-week sunitinib 50 mg/day lead in. RP2D was evaluated in 55 additional patients. The primary end point was prostate-specific antigen (PSA) response rate.

RESULTS

One phase 1 dose-limiting toxicity occurred (grade 3 hyponatremia). The RP2D was sunitinib 37.5 mg/day, docetaxel 75 mg/m(2) and prednisone 5 mg b.i.d. During phase 2, confirmed PSA responses occurred in 31 patients [56.4% (95% confidence interval 42.3-69.7)]. Median time to PSA progression was 9.8 months. Forty-one patients (75%) were treated >3 months, 12 (22%) completed the study (16 cycles) and 43 (78%) discontinued (36% for disease progression and 27% adverse events). The most frequent treatment-related grade 3/4 adverse events were neutropenia (53%; 15% febrile) and fatigue/asthenia (16%). Among 33 assessable patients, 14 (42.4%) had confirmed partial response. Median progression-free and overall survivals were 12.6 and 21.7 months, respectively.

CONCLUSION

This combination was moderately well tolerated, with promising response rate and survival benefit, justifying further investigation in mCRPC.

Evidence for cell density affecting C2C12 myogenesis: possible regulation of myogenesis by cell-cell communication

INTRODUCTION

Community effect is a phenomenon caused by cell-cell communication during myogenesis. In myogenic C2C12 cells in vitro, the confluent phase is needed for myogenesis induction.

METHODS

To examine the cell-density effect, growth kinetics and myogenic differentiation were investigated in cells plated at four different cell densities.

RESULTS

We found that expression of a myogenic differentiation marker was high in a density-dependent manner. At high density, where cell-cell contact was obvious, contact inhibition after the proliferation stage was accompanied by microarray findings demonstrating upregulation of negative regulating cell-cycle markers, including CDKI p21 and the muscle differentiation markers MyoD and myogenin. Interestingly, developmentally regulated protein expression (drebrin) protein expression was also upregulated in a density-dependent manner.

CONCLUSIONS

These results suggest that contact inhibition after the proliferation stage may induce growth arrest via cell-cell communication through the expression of CDKI p21 and may be responsible for progressing cell fusion.

Small-molecule protein tyrosine kinase inhibitors for the treatment of metastatic prostate cancer

The microenvironment is critical to the growth of prostate cancer (PCa) in the bone. Thus, for clinical efficacy, therapies must target tumor-microenvironment interactions. Several protein tyrosine kinases have been implicated in the development and growth of PCa bone metastasis. In this review, specific protein tyrosine kinases that regulate these complex interactions, including PDGFR, the EGFR family, c-Src, VEGFR, IGF-1R, FGFR and c-Met will be discussed, with an emphasis on why these kinases are promising therapeutic targets for metastatic PCa treatment. For each of these kinases, small-molecule inhibitors have reached clinical trials. Current results of these trials and future prospects for the use of tyrosine kinase inhibitors for the treatment of PCa bone metastases are also discussed.

PTEN regulates PDGF ligand switch for β-PDGFR signaling in prostate cancer

Platelet-derived growth factor (PDGF) family members are potent growth factors that regulate cell proliferation, migration, and transformation. Clinical studies have shown that both PDGF receptor β (β-PDGFR) and its ligand PDGF D are up-regulated in primary prostate cancers and bone metastases, whereas PDGF B, a classic ligand for β-PDGFR, is not frequently detected in clinical samples. In this study, we examined the role of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in the regulation of PDGF expression levels using both a prostate-specific, conditional PTEN-knockout mouse model and mouse prostate epithelial cell lines established from these mice. We found an increase in PDGF D and β-PDGFR expression levels in PTEN-null tumor cells, accompanied by a decrease in PDGF B expression. Among Akt isoforms, increased Akt3 expression was most prominent in mouse PTEN-null cells, and phosphatidylinositol 3-kinase/Akt activity was essential for the maintenance of increased PDGF D and β-PDGFR expression. In vitro deletion of PTEN resulted in a PDGF ligand switch from PDGF B to PDGF D in normal mouse prostate epithelial cells, further demonstrating that PTEN regulates this ligand switch. Similar associations between PTEN status and PDGF isoforms were noted in human prostate cancer cell lines. Taken together, these results suggest a mechanism by which loss of PTEN may promote prostate cancer progression via PDGF D/β-PDGFR signal transduction.

A novel function for platelet-derived growth factor D: induction of osteoclastic differentiation for intraosseous tumor growth

Although increasing evidence suggests a critical role for platelet-derived growth factor (PDGF) receptor β (β-PDGFR) signaling in prostate cancer (PCa) progression, the precise roles of β-PDGFR and PDGF isoform-specific cell signaling have not been delineated. Recently, we identified the PDGF-D isoform as a ligand for β-PDGFR in PCa and showed that PDGF-D is activated by serine protease-mediated proteolytic removal of the CUB domain in a two-step process, yielding first a hemidimer (HD) and then a growth factor domain dimer. Herein, we demonstrate that the expression of PDGF-D in human PCa LNCaP cells leads to enhanced bone tumor growth and bone responses in immunodeficient mice. Histopathological analyses of bone tumors generated by PDGF-D-expressing LNCaP cells (LNCaP-PDGF-D) revealed osteolytic and osteoblastic responses similar to those observed in human PCa bone metastases. Importantly, we discovered a novel function of PDGF-D in the regulation of osteoclast differentiation, independent of the RANKL/RANK signaling axis. Although both PDGF-B and -D were able to activate β-PDGFR, only PDGF-D was able to induce osteoclastic differentiation in vitro, and upregulate the expression and nuclear translocation of nuclear factor of activated T cells 1, a master transcription factor for osteoclastogenesis. Taken together, these results reveal a new function of PDGF-D as a regulator of osteoclastic differentiation, an activity critical for the establishment of skeletal metastatic deposit in PCa patients.

Inhibitory effect of soluble platelet-derived growth factor receptor β on intraosseous growth of breast cancer cells in nude mice

Bone metastasis is a frequent complication of advanced breast cancer. On the basis of functional and molecular evidence, signaling mediated by the binding of platelet-derived growth factor (PDGF)-BB and -DD to PDGF receptor β (PDGFRβ) is critical for the survival and growth of metastatic breast cancer cells within the bone microenvironment. In this study, we propose a new approach to blocking PDGFRβ signaling using soluble PDGFRβ (sPDGFRβ) as a decoy receptor for PDGF-BB and -DD secreted from tumor cells and bone marrow stromal cells. A bone-seeking TNBCT/Bo cell line was established by in vivo selection from TNBCT human breast cancer cells, which are negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 protein expression. The TNBCT/Bo cells were transfected with a mammalian expression vector encoding the extracellular domain of PDGFRβ. A stable transfectant (TNBCT/Bo-sPDGFRβ) grew at a similar rate to that of control cells under normal culture conditions, although growth stimulation of human fibroblasts with PDGF-BB was neutralized by the culture medium from TNBCT/Bo-sPDGFRβ cells. Intratibial injection of TNBCT/Bo-sPDGFRβ cells into athymic nude mice resulted in a significant decrease in tumor incidence compared with control mice (P < 0.01). This attenuated growth correlated with decreased cancer cell proliferation, angiogenesis, and recruitment of stromal cells, and with an increase in the number of apoptotic cells. These findings suggest that sPDGFRβ is useful for the treatment of breast cancer bone metastasis.