Platelet-derived growth factor-AA and -alpha receptor expression suggests an autocrine and/or paracrine loop in osteosarcoma

Comprehensive analysis of secretome and transcriptome stability of Wharton jelly mesenchymal stromal cells during good manufacturing practice-compliant production

BACKGROUND

Mesenchymal stromal cells (MSCs) hold promise for cell-based therapies due to their ability to stimulate tissue repair and modulate immune responses. Umbilical cord-derived MSCs from Wharton jelly (WJ) offer advantages such as low immunogenicity and potent immune modulatory effects. However, ensuring consistent quality and safety throughout their manufacturing process remains critical. RNA sequencing (RNA-seq) emerges as a crucial tool for assessing genetic stability and expression dynamics in cell-based therapeutic products.

METHODS

We examined the secretome and transcriptome of WJ-MSC signatures throughout Good Manufacturing Practice (GMP) production, focusing on the performance of total RNA or Massive Analysis of cDNA Ends (MACE) sequencing.

RESULTS

Through extensive transcriptomic analysis, we demonstrated consistent stability of WJ-MSC expression signatures across different manufacturing stages. Notably, MACE-seq showed improved identification of key expression patterns related to senescence and immunomodulation.

CONCLUSIONS

These findings highlight the potential of MACE-seq as a quality assessment tool for WJ-MSC-based therapies, ensuring their efficacy and safety in clinical applications. Importantly, MACE-seq demonstrated its value in characterizing WJ-MSC-derived products, offering insights that traditional assays cannot provide.

Targeting PDGF-CC as a promising therapeutic strategy to inhibit cholangiocarcinoma progression

BACKGROUND

Cholangiocarcinoma (CCA) is an aggressive malignancy with limited treatment options and poor prognosis. Platelet-Derived Growth Factor CC (PDGF-CC) has been implicated in the progression of various tumors, but its specific role in CCA is not well understood. This study aims to investigate the expression and function of PDGF-CC in CCA and evaluate its potential as a therapeutic target.

METHODS

We conducted gene expression analysis using the GEPIA database to compare PDGF-CC mRNA levels in CCA tissues and normal tissues. Serum samples from CCA patients were analyzed for PDGF-CC protein levels, and immunohistochemistry was used to assess PDGF-CC expression in tissue samples. The impact of PDGF-CC on CCA cell behavior was examined by knocking out PDGF-CC in HuCCT1 and QBC939 cell lines, followed by assessments of cell proliferation, migration, invasion, and colony formation in vitro. Additionally, the effects of PDGF-CC knockout were evaluated in xenograft models. The therapeutic potential of PDGF-CC inhibition was further explored using pharmacological inhibitors and antibodies.

RESULTS

PDGF-CC mRNA and protein levels were significantly elevated in CCA tissues and patient sera compared to normal controls. Immunohistochemical analysis confirmed increased PDGF-CC expression in CCA tissues. High PDGF-CC expression correlated with poor overall survival in CCA patients, as shown by Kaplan-Meier analysis. Functional assays revealed that PDGF-CC knockout significantly reduced proliferation, migration, invasion, and colony formation in HuCCT1 and QBC939 cells, the lines with the highest PDGF-CC levels. In vivo, PDGF-CC knockout markedly decreased tumor growth in xenograft models. Pharmacological inhibition of PDGF-CC mirrored the effects of genetic knockout, suggesting it as a viable therapeutic strategy.

CONCLUSIONS

This study underscores the critical role of PDGF-CC in CCA progression and supports the potential of PDGF-CC inhibitors as a therapeutic approach. Given the association between high PDGF-CC expression and poor prognosis, targeting PDGF-CC may improve outcomes for CCA patients. Further clinical investigations are warranted to develop PDGF-CC-targeted therapies for CCA.

Amicis Omnia Sunt Communia: NF-κB Inhibition as an Alternative to Overcome Osteosarcoma Heterogeneity

Tumor heterogeneity poses a significant challenge in osteosarcoma (OS) treatment. In this regard, the "omics" era has constantly expanded our understanding of biomarkers and altered signaling pathways (i.e., PI3K/AKT/mTOR, WNT/β-catenin, NOTCH, SHH/GLI, among others) involved in OS pathophysiology. Despite different players and complexities, many commonalities have been described, among which the nuclear factor kappa B (NF-κB) stands out. Its altered activation is pervasive in cancer, with pleiotropic action on many disease-relevant traits. Thus, in the scope of this article, we highlight the evidence of NF-κB dysregulation in OS and its integration with other cancer-related pathways while we summarize the repertoire of compounds that have been described to interfere with its action. In silico strategies were used to demonstrate that NF-κB is closely coordinated with other commonly dysregulated signaling pathways not only by functionally interacting with several of their members but also by actively participating in the regulation of their transcription. While existing inhibitors lack selectivity or act indirectly, the therapeutic potential of targeting NF-κB is indisputable, first for its multifunctionality on most cancer hallmarks, and secondly, because, as a common downstream effector of the many dysregulated pathways influencing OS aggressiveness, it turns complex regulatory networks into a simpler picture underneath molecular heterogeneity.

Fibrous periosteum repairs bone fracture and maintains the healed bone throughout mouse adulthood

Bone is regarded as one of few tissues that heals without fibrous scar. The outer layer of the periosteum is covered with fibrous tissue, whose function in bone formation is unknown. We herein developed a system to distinguish the fate of fibrous-layer periosteal cells (FL-PCs) from the skeletal stem/progenitor cells (SSPCs) in the cambium-layer periosteum and bone marrow in mice. We showed that FL-PCs did not participate in steady-state osteogenesis, but formed the main body of fibrocartilaginous callus during fracture healing. Moreover, FL-PCs invaded the cambium-layer periosteum and bone marrow after fracture, forming neo-SSPCs that continued to maintain the healed bones throughout adulthood. The FL-PC-derived neo-SSPCs expressed lower levels of osteogenic signature genes and displayed lower osteogenic differentiation activity than the preexisting SSPCs. Consistent with this, healed bones were thinner and formed more slowly than normal bones. Thus, the fibrous periosteum becomes the cellular origin of bones after fracture and alters bone properties permanently.

Host-derived growth factors drive ERK phosphorylation and MCL1 expression to promote osteosarcoma cell survival during metastatic lung colonization

PURPOSE

For patients with osteosarcoma, disease-related mortality most often results from lung metastasis-a phenomenon shared with many solid tumors. While established metastatic lesions behave aggressively, very few of the tumor cells that reach the lung will survive. By identifying mechanisms that facilitate survival of disseminated tumor cells, we can develop therapeutic strategies that prevent and treat metastasis.

METHODS

We analyzed single cell RNA-sequencing (scRNAseq) data from murine metastasis-bearing lungs to interrogate changes in both host and tumor cells during colonization. We used these data to elucidate pathways that become activated in cells that survive dissemination and identify candidate host-derived signals that drive activation. We validated these findings through live cell reporter systems, immunocytochemistry, and fluorescent immunohistochemistry. We then validated the functional relevance of key candidates using pharmacologic inhibition in models of metastatic osteosarcoma.

RESULTS

Expression patterns suggest that the MAPK pathway is significantly elevated in early and established metastases. MAPK activity correlates with expression of anti-apoptotic genes, especially MCL1. Niche cells produce growth factors that increase ERK phosphorylation and MCL1 expression in tumor cells. Both early and established metastases are vulnerable to MCL1 inhibition, but not MEK inhibition in vivo. Combining MCL1 inhibition with chemotherapy both prevented colonization and eliminated established metastases in murine models of osteosarcoma.

CONCLUSION

Niche-derived growth factors drive MAPK activity and MCL1 expression in osteosarcoma, promoting metastatic colonization. Although later metastases produce less MCL1, they remain dependent on it. MCL1 is a promising target for clinical trials in both human and canine patients.

Altered regulation of mesenchymal cell senescence in adipose tissue promotes pathological changes associated with diabetic wound healing

Pathologic diabetic wound healing is caused by sequential and progressive deterioration of hemostasis, inflammation, proliferation, and resolution/remodeling. Cellular senescence promotes wound healing; however, diabetic wounds exhibit low levels of senescent factors and accumulate senescent cells, which impair the healing process. Here we show that the number of p15^INK4B + PDGFRα + senescent mesenchymal cells in adipose tissue increases transiently during early phases of wound healing in both non-diabetic mice and humans. Transplantation of adipose tissue from diabetic mice into non-diabetic mice results in impaired wound healing and an altered cellular senescence–associated secretory phenotype (SASP), suggesting that insufficient induction of adipose tissue senescence after injury is a pathological mechanism of diabetic wound healing. These results provide insight into how regulation of senescence in adipose tissue contributes to wound healing and could constitute a basis for developing therapeutic treatment for wound healing impairment in diabetes.

Type-2 diabetic adipose tissue impairs transient senescence during wound healing with expression of different components of the senescence-associated secretory phenotype (SASP), and this is associated with deteriorated wound healing.

Phase I/II study of single-agent lenvatinib in children and adolescents with refractory or relapsed solid malignancies and young adults with osteosarcoma (ITCC-050)☆

Background

We report results from the phase I dose-finding and phase II expansion part of a multicenter, open-label study of single-agent lenvatinib in pediatric and young adult patients with relapsed/refractory solid tumors, including osteosarcoma and radioiodine-refractory differentiated thyroid cancer (RR-DTC) (NCT02432274).

Patients and methods

The primary endpoint of phase I was to determine the recommended phase II dose (RP2D) of lenvatinib in children with relapsed/refractory solid malignant tumors. Phase II primary endpoints were progression-free survival rate at 4 months (PFS-4) for patients with relapsed/refractory osteosarcoma; and objective response rate/best overall response for patients with RR-DTC at the RP2D.

Results

In phase I, 23 patients (median age, 12 years) were enrolled. With lenvatinib 14 mg/m², three dose-limiting toxicities (hypertension, n = 2; increased alanine aminotransferase, n = 1) were reported, establishing 14 mg/m² as the RP2D. In phase II, 31 patients with osteosarcoma (median age, 15 years) and 1 patient with RR-DTC (age 17 years) were enrolled. For the osteosarcoma cohort, PFS-4 (binomial estimate) was 29.0% [95% confidence interval (CI) 14.2% to 48.0%; full analysis set: n = 31], PFS-4 by Kaplan–Meier estimate was 37.8% (95% CI 20.0% to 55.4%; full analysis set) and median PFS was 3.0 months (95% CI 1.8-5.4 months). The objective response rate was 6.7% (95% CI 0.8% to 22.1%). The patient with RR-DTC had a best overall response of partial response. Some 60.8% of patients in phase I and 22.6% of patients in phase II (with osteosarcoma) had treatment-related treatment-emergent adverse events of grade ≥3.

Conclusions

The lenvatinib RP2D was 14 mg/m². Single-agent lenvatinib showed activity in osteosarcoma; however, the null hypothesis could not be rejected. The safety profile was consistent with previous tyrosine kinase inhibitor studies. Lenvatinib is currently being investigated in osteosarcoma in combination with chemotherapy as part of a randomized, controlled trial (NCT04154189), in pediatric solid tumors in combination with everolimus (NCT03245151), and as a single agent in a basket study with enrollment ongoing (NCT04447755).

•

The recommended phase II dose of lenvatinib in children with relapsed/refractory solid malignant tumors is 14 mg/m².

•

This dose is equivalent to the recommended dose of 24 mg/day for single-agent lenvatinib in adults with DTC.

•

Single-agent lenvatinib showed activity of interest in children and young adults with osteosarcoma.

•

Based on this initial report, lenvatinib is currently being investigated in combination with chemotherapy in osteosarcoma.

Identification of secreted factors in dental pulp cell-conditioned medium optimized for neuronal growth

With their potent regenerative and protective capacities, stem cell-derived conditioned media emerged as an effective alternative to cell therapy, and have a prospect to be manufactured as pharmaceutical products for tissue regeneration applications. Our study investigates the neuroregenerative potential of human dental pulp cells (DPCs) conditioned medium (CM) and defines an optimization strategy of DPC-CM for enhanced neuronal outgrowth. Primary sensory neurons from mouse dorsal root ganglia were cultured with or without DPC-CM, and the lengths of βIII-tubulin positive neurites were measured. The impacts of several manufacturing features as the duration of cell conditioning, CM storage, and preconditioning of DPCs with some factors on CM functional activity were assessed on neurite length. We observed that DPC-CM significantly enhanced neurites outgrowth of sensory neurons in a concentration-dependent manner. The frozen storage of DPC-CM had no impact on experimental outcomes and 48 h of DPC conditioning is optimal for an effective activity of CM. To further understand the regenerative feature of DPC-CM, we studied DPC secretome by human growth factor antibody array analysis and revealed the presence of several factors involved in either neurogenesis, neuroprotection, angiogenesis, and osteogenesis. The conditioning of DPCs with the B-27 supplement enhanced significantly the neuroregenerative effect of their secretome by changing its composition in growth factors. Here, we show that DPC-CM significantly stimulate neurite outgrowth in primary sensory neurons. Moreover, we identified secreted protein candidates that can potentially promote this promising regenerative feature of DPC-CM.

Prognostic and Therapeutic Utility of Variably Expressed Cell Surface Receptors in Osteosarcoma

Background

Six cell surface receptors, human epidermal growth factor receptor-2 (Her-2), platelet-derived growth factor receptor-β (PDGFR-β), insulin-like growth factor-1 receptor (IGF-1R), insulin receptor (IR), c-Met, and vascular endothelial growth factor receptor-3 (VEGFR-3), previously demonstrated variable expression across varying patient-derived and standard osteosarcoma (OS) cell lines. The current study sought to validate previous expression patterns and evaluate whether these receptors offer prognostic and/or therapeutic value.

Methods

Patient-derived OS cell lines (n = 52) were labeled with antibodies to Her-2, PDGFR-β, IGF-1R, IR, c-Met, and VEGFR-3. Expression was characterized using flow cytometry. The difference in geometric mean fluorescent intensity (geoMFI_diff = geoMFI_positive - geoMFI_negative) was calculated for each receptor across all cell lines. Receptor expression was categorized as low (Q1), intermediate (Q2, Q3), or high (Q4). The event-free survival (EFS) and overall survival for the six cell surface receptors were estimated by the Kaplan-Meier method. Differences in hazard for EFS event and overall survival event for patients in each of the three expression levels in each of the six cell surface receptors were assessed using the log-rank test.

Results

All 6 receptors were variably expressed in the majority of cell lines. IR and PDGFR-β expressions were found to be significant predictors for EFS amongst patients with nonmetastatic disease (p=0.02 and 0.01, respectively). The hazard ratio for EFS was significantly higher between high IR and intermediate IR expression (HR = 2.66, p=0.02), as well as between high PDGFR-β and intermediate PDGFR-β expression (HR = 5.68, p=0.002). Her-2, c-Met, IGF-1R, and VEGFR-3 were not found to be significant predictors for either EFS or overall survival.

Conclusion

The six cell surface receptors demonstrated variable expression across the majority of patient-derived OS cell lines tested. Limited prognostic value was offered by IR and PDGFR-β expression within nonmetastatic patients. The remaining receptors do not provide clear prognostic utility. Nevertheless, their consistent, albeit variable, surface expression across a large panel of patient-derived OS cell lines maintains their potential use as future therapeutic targets.

Hypoxia in bone metastasis and osteolysis

Hypoxia is a common feature in tumors, driving pathways that promote epithelial-to-mesenchymal transition, invasion, and metastasis. Clinically, high levels of hypoxia-inducible factor (HIF) expression and stabilization at the primary site in many cancer types is associated with poor patient outcomes. Experimental evidence suggests that HIF signaling in the primary tumor promotes their dissemination to the bone, as well as the release of factors such as LOX that act distantly on the bone to stimulate osteolysis and form a pre-metastatic niche. Additionally, the bone itself is a generally hypoxic organ, fueling the activation of HIF signaling in bone resident cells, promoting tumor cell homing to the bone as well as osteoclastogenesis. The hypoxic microenvironment of the bone also stimulates the vicious cycle of tumor-induced bone destruction, further fueling tumor cell growth and osteolysis. Furthermore, hypoxia appears to regulate key tumor dormancy factors. Thus, hypoxia acts both on the tumor cells as well as the metastatic site to promote tumor cell metastasis.

Hypoxia promotes osteosarcoma cell proliferation and migration through enhancing platelet-derived growth factor-BB/platelet-derived growth factor receptor-β axis

Osteosarcoma is a primary malignant bone tumor, characterized by high therapeutic resistance and poor outcomes, due to unclear pathological mechanisms. It has been shown recently that the platelet-derived growth factor (PDGF)/platelet-derived growth factor receptor (PDGFR) pathway is closely associated with the pathogenesis of osteosarcoma. Hypoxia is a critical hallmark of tumor microenvironment that promotes the malignant phenotype in many solid tumors and a fundamental impediment to effective tumor therapy. In this study, we confirmed that hypoxia is an important feature of osteosarcoma, validated by the positive immunohistochemistry staining of hypoxia marker hypoxia-inducible factor-1α (HIF-1α) and carbonic anhydrase IX (CAIX) in osteosarcoma tissue samples. More importantly, we discovered that hypoxia could transcriptionally upregulate the expression of both PDGF-BB and PDGFR-β in osteosarcoma cells in vitro. Likewise, we also established that hypoxia-induced PDGF-BB is strongly related to the enhanced cell proliferation and migration, by activating AKT, ERK1/2, and STAT3 signaling pathways. Notably, when using an antibody to block the autocrine of PDGF-BB, cell proliferation and migration were partially aborted in hypoxia. Collectively, we demonstrated that the hypoxia-activated PDGF-BB/PDGFR-β axis plays essential roles in osteosarcoma progression. These findings may shed light on the molecular pathogenesis of osteosarcoma, and provide a novel strategy for osteosarcoma treatment by combinational targeting hypoxia and PDGF-BB/PDGFR signaling.

Prolonged response to sorafenib in a patient with refractory metastatic osteosarcoma and a somatic PDGFRA D846V mutation

Outcome for patients with metastatic or recurrent/refractory osteosarcoma remains poor. Responses to sorafenib, a multikinase inhibitor, have been seen in recurrent/refractory osteosarcoma, although specific biomarkers of response have not been described. We report a partial response in a 7-year-old with refractory osteosarcoma treated with sorafenib 200 mg twice daily. Toxicities included Common Terminology Criteria for Adverse Events Grade 2 skin toxicities and growth suppression. After 51 months of therapy, he suffered a recurrence. Tumor sequencing later revealed a PDGFRA D846V mutation that was not identified in the relapse specimen. This case demonstrates prolonged partial response to sorafenib and provides a potential biomarker for response.

Potential role of CSF cytokine profiles in discriminating infectious from non-infectious CNS disorders

Current laboratory testing of cerebrospinal fluid (CSF) does not consistently discriminate between different central nervous system (CNS) disease states. Rapidly distinguishing CNS infections from other brain and spinal cord disorders that share a similar clinical presentation is critical. New approaches focusing on aspects of disease biology, such as immune response profiles that can have stimulus-specific attributes, may be helpful. We undertook this preliminary proof-of-concept study using multiplex ELISA to measure CSF cytokine levels in various CNS disorders (infections, autoimmune/demyelinating diseases, lymphomas, and gliomas) to determine the potential utility of cytokine patterns in differentiating CNS infections from other CNS diseases. Both agglomerative hierarchical clustering and mixture discriminant analyses revealed grouping of CNS disease types based on cytokine expression. To further investigate the ability of CSF cytokine levels to distinguish various CNS disease states, non-parametric statistical analysis was performed. Mann-Whitney test analysis demonstrated that CNS infections are characterized by significantly higher CSF lP-10/CXCL10 levels than the pooled non-infectious CNS disorders (p = 0.0001). Within the infection group, elevated levels of MDC/CCL22 distinguished non-viral from viral infections (p = 0.0048). Each disease group of the non-infectious CNS disorders independently showed IP-10/CXCL10 levels that are significantly lower than the infection group [(autoimmune /demyelinating disorders (p = 0.0005), lymphomas (p = 0.0487), gliomas (p = 0.0294), and controls (p = 0.0001)]. Additionally, of the non-infectious diseases, gliomas can be distinguished from lymphomas by higher levels of GRO/CXCL1 (p = 0.0476), IL-7 (p = 0.0119), and IL-8 (p = 0.0460). Gliomas can also be distinguished from autoimmune/demyelinating disorders by higher levels of GRO/CXCL1 (p = 0.0044), IL-7 (p = 0.0035) and IL-8 (p = 0.0176). Elevated CSF levels of PDGF-AA distinguish lymphomas from autoimmune/demyelinating cases (p = 0.0130). Interrogation of the above comparisons using receiver operator characteristic analysis demonstrated area under the curve (AUC) values (ranging from 0.8636–1.0) that signify good to excellent utility as potential diagnostic discriminators. In conclusion, our work indicates that upon formal validation, measurement of CSF cytokine levels may have clinical utility in both identifying a CNS disorder as infectious in etiology and, furthermore, in distinguishing viral from non-viral CNS infections.

Role of Activator Protein-1 Complex on the Phenotype of Human Osteosarcomas Generated from Mesenchymal Stem Cells

Osteosarcoma (OS) is a highly aggressive bone tumor that usually arises intramedullary at the extremities of long bones. Due to the fact that the peak of incidence is in the growth spurt of adolescence, the specific anatomical location, and the heterogeneity of cells, it is believed that osteosarcomagenesis is a process associated with bone development. Different studies in murine models showed that the tumor-initiating cell in OS could be an uncommitted mesenchymal stem cell (MSC) developing in a specific bone microenvironment. However, only a few studies have reported transgene-induced human MSCs transformation and mostly obtained undifferentiated sarcomas. In our study, we demonstrate that activator protein 1 family members induce osteosarcomagenesis in immortalized hMSC. c-JUN or c-JUN/c-FOS overexpression act as tumorigenic factors generating OS with fibroblastic or pleomorphic osteoblastic phenotypes, respectively. Stem Cells 2018;36:1487-1500.

PDGF/PDGFR effects in osteosarcoma and the "add-on" strategy

New treatment options for advanced osteosarcoma have remained limited. The platelet-derived growth factor (PDGF)/platelet-derived growth factor receptor (PDGFR) pathway plays an important role in the development and metastasis of osteosarcoma, via either direct autocrine stimulation of tumor cells, or paracrine stimulation on tumor stromal cells. It promotes angiogenesis to overcome hypoxia in the tumor microenvironment, and modulates tumor interstitial fluid pressure to control the influx and efflux of other agents. Targeting the PDGF/PDGFR pathway is a promising therapeutic method to overcome drug resistance and improve patients' outcome in osteosarcoma. Further evidence is needed to define the detailed mechanism. Results from clinical trials using PDGF/PDGFR inhibitor as a single agent were disappointing, both in osteosarcoma and soft tissue sarcoma. However, when combined with other agents, named as "add-on" strategy, a synergistic antitumor effect has been confirmed in soft tissue sarcoma, and should be attempted in osteosarcoma.

Genetic variants of PDGF signaling pathway genes predict cutaneous melanoma survival

To investigate whether genetic variants of platelet-derived growth factor (PDGF) signaling pathway genes are associated with survival of cutaneous melanoma (CM) patients, we assessed associations of single-nucleotide polymorphisms in PDGF pathway with melanoma-specific survival in 858 CM patients of M.D. Anderson Cancer Center (MDACC). Additional data of 409 cases from Harvard University were also included for further analysis. We identified 13 SNPs in four genes (COL6A3, NCK2, COL5A1 and PRKCD) with a nominal P < 0.05 and false discovery rate (FDR) < 0.2 in MDACC dataset. Based on linkage disequilibrium, functional prediction and minor allele frequency, a representative SNP in each gene was selected. In the meta-analysis using MDACC and Harvard datasets, there were two SNPs associated with poor survival of CM patients: rs6707820 C>T in NCK2 (HR = 1.87, 95% CI = 1.35-2.59, P_meta= 1.53E-5); and rs2306574 T>C in PRKCD (HR = 1.73, 95% CI = 1.33-2.24, P_meta= 4.56E-6). Moreover, CM patients in MDACC with combined risk genotypes of these two loci had markedly poorer survival (HR = 2.47, 95% CI = 1.58-3.84, P < 0.001). Genetic variants of rs6707820 C>T in NCK2 and rs2306574 T>C in PRKCD of the PDGF signaling pathway may be biomarkers for melanoma survival.

Primary intracranial soft tissue sarcomas in children, adolescents, and young adults: single institution experience and review of the literature

There is a paucity of literature reporting the outcome of intracranial sarcomas (IS) in children, adolescents, and young adults (CAYA). A multimodal therapeutic approach is commonly used, with no well-established treatment consensus. We conducted a retrospective review of CAYA with IS, treated at our institution, to determine their clinical findings, treatments, and outcomes. Immunohistochemistry (PDGFRA and EGFR) and DNA sequencing were performed on 5 tumor samples. A literature review of IS was also conducted. We reviewed 13 patients (median age, 7 years) with a primary diagnosis of IS between 1990 and 2015. Diagnoses included unclassified sarcoma (n = 9), chondrosarcoma (n = 2), and rhabdomyosarcoma (n = 2). Five patients underwent upfront gross total resection (GTR) of the tumor. The 5-drug regimen (vincristine, doxorubicin, cyclophosphamide, etoposide, and ifosfamide) was the most common treatment used. Nine patients died due to progression or recurrence (n = 8) or secondary malignancy (n = 1). The median follow-up period of the 4 surviving patients was 1.69 years (range 1.44-5.17 years). The 5-year progression-free survival and overall survival rates were 21 and 44 %, respectively. BRAF, TP53, KRAS, KIT, ERBB2, MET, RET, ATM, and EGFR mutations were detected in 4 of the 5 tissue samples. All 5 samples were immunopositive for PDGFRA, and only 2 were positive for EGFR. IS remain a therapeutic challenge due to high progression and recurrence rates. Collaborative multi-institutional studies are warranted to delineate a treatment consensus and investigate tumor biology to improve the disease outcome.

Bone Sarcomas in Pediatrics: Progress in Our Understanding of Tumor Biology and Implications for Therapy

The pediatric bone sarcomas osteosarcoma and Ewing sarcoma represent a tremendous challenge for the clinician. Though less common than acute lymphoblastic leukemia or brain tumors, these aggressive cancers account for a disproportionate amount of the cancer morbidity and mortality in children, and have seen few advances in survival in the past decade, despite many large, complicated, and expensive trials of various chemotherapy combinations. To improve the outcomes of children with bone sarcomas, a better understanding of the biology of these cancers is needed, together with informed use of targeted therapies that exploit the unique biology of each disease. Here we summarize the current state of knowledge regarding the contribution of receptor tyrosine kinases, intracellular signaling pathways, bone biology and physiology, the immune system, and the tumor microenvironment in promoting and maintaining the malignant phenotype. These observations are coupled with a review of the therapies that target each of these mechanisms, focusing on recent or ongoing clinical trials if such information is available. It is our hope that, by better understanding the biology of osteosarcoma and Ewing sarcoma, rational combination therapies can be designed and systematically tested, leading to improved outcomes for a group of children who desperately need them.

Platelet derived growth factor (PDGF) contained in Platelet Rich Plasma (PRP) stimulates migration of osteoblasts by reorganizing actin cytoskeleton

Platelet-rich plasma (PRP) is a platelet concentrate in a small volume of plasma. It is highly enriched in growth factors able to stimulate the migration and growth of bone-forming cells. PRP is often used in clinical applications, as dental surgery and fracture healing. Platelet derived growth factor (PDGF), is highly concentrated in PRP and it was shown in our previous studies to provide the chemotactic stimulus to SaOS-2 osteoblasts to move in a microchemotaxis assay. Aim of the present studies is to analyze the effects of a PRP pretreatment (short time course: 30-150 min) of SaOS-2 cells with PRP on the organization of actin cytoskeleton, the main effector of cell mobility. The results indicate that a pretreatment with PRP increases chemokinesis and chemotaxis and concomitantly induces the organization of actin microfilaments, visualized by immunocytochemistry, in a directionally elongated phenotype, which is characteristic of the cells able to move. PRP also produces a transient increase in the expression of PGDF α receptor. This reorganization is blocked by the immunoneutralization of PDGF demonstrating the responsibility of this growth factor in triggering the mechanisms responsible for cellular movements.

Current therapeutic strategies and novel approaches in osteosarcoma

Osteosarcoma is the most frequent malignant primary bone tumor and a main cause of cancer-related death in children and adolescents. Although long-term survival in localized osteosarcoma has improved to about 60% during the 1960s and 1970s, long-term survival in both localized and metastatic osteosarcoma has stagnated in the past several decades. Thus, current conventional therapy consists of multi-agent chemotherapy, surgery and radiation, which is not fully adequate for osteosarcoma treatment. Innovative drugs and approaches are needed to further improve outcome in osteosarcoma patients. This review describes the current management of osteosarcoma as well as potential new therapies.

Imatinib mesylate inhibits cell growth of malignant peripheral nerve sheath tumors in vitro and in vivo through suppression of PDGFR-β

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive and associated with poor prognosis. Basic research to develop new treatment regimens is critically needed.

METHODS

The effects of imatinib mesylate on MPNSTs were examined in six human MPNST cell lines and in a xenograft mouse model.

RESULTS

The results showed expression of platelet-derived growth factor receptor-β and suppression of its phosphorylation by imatinib mesylate in all six cell lines. Imatinib mesylate effectively suppressed MPNST cell growth in vitro at concentrations similar to those used clinically (1.46 - 4.6 μM) in three of six cell lines. Knockdown of PDGFR-β by transfection with a specific siRNA also caused significant reduction in cell proliferation in the sensitive cell lines, but not in the resistant cell lines. Furthermore, imatinib mesylate also significantly suppressed colony formation within soft agar and tumor growth in xenograft models using two of the three sensitive MPNST cell lines. There was excellent agreement between in vitro and in vivo sensitivity to imatinib mesylate, suggesting possible selection of imatinib-sensitive tumors by in vitro analysis.

CONCLUSIONS

The results suggest that imatinib mesylate may be useful in the treatment of MPNST patients and in vitro studies may help select cells that are sensitive to imatinib mesylate in vivo.

PDGFs and PDGFRs in canine osteosarcoma: new targets for innovative therapeutic strategies in comparative oncology

Platelet derived growth factor receptor (PDGFR)α and PDGFRβ are tyrosine kinase receptors that are overexpressed in 70-80% of human osteosarcomas (OSAs) and may be suitable therapeutic targets for specific kinase inhibitors (TKIs). Canine OSA shows histopathological and clinical features similar to human OSA, and is considered an excellent model in comparative oncology. This study investigated PDGF-A, PDGF-B, PDGFRα and PDGFRβ expression in 33 canine OSA samples by immunohistochemistry and in seven primary canine OSA cell lines by Western blot and quantitative PCR analysis. Immunohistochemical data showed that PDGF-A and PDGF-B are expressed in 42% and 60% of the OSAs analysed, respectively, while PDGFRα and PDGFRβ were expressed in 78% and 81% of cases, respectively. Quantitative PCR data showed that all canine OSA cell lines overexpressed PDGFRα, while 6/7 overexpressed PDGFRβ and PDGF-A relative to a normal osteoblastic cell line. Moreover, in vitro treatment with a specific PDGFR inhibitor, AG1296, caused a dose- and time-dependent decrease in AKT phosphorylation. Collectively, these data show that PDGFRs/PDGFs are co-expressed in canine osteosarcomas, which suggests that an autocrine and/or paracrine loop is involved and that they play an important role in the aetiology of OSA. PDGFRs may be suitable targets for the treatment of canine OSA with a specific TKI.

Targeted therapy in bone and soft tissue sarcoma in children and adolescents

Pediatric soft-tissue and bone sarcomas are a heterogeneous group of tumors of mesenchymal origin which affect approximately 1,500 children in the United States each year. Using multimodal therapy (surgery, radiation, and chemotherapy),the overall 5-year survival rate for children with soft-tissue and bone sarcomas is approximately 60%–70%. However, the prognosis for children with metastatic or recurrent disease is poor; and, furthermore, the improvements in the overall cure rate have slowed. It is highly unlikely that further advances in the treatment of pediatric soft-tissue and bone sarcomas will come from traditional cytotoxic chemotherapy. Based on research advances in understanding the biology of pediatric soft-tissue and bone sarcomas, improved cure rates will likely be driven by new types of treatment which target the specific abnormalities within these tumors. These new targeted therapies may include small molecules, antibodies, or other immunotherapies. This review briefly describes the biology of the major types of pediatric sarcomas, discusses potential targets for new therapy, and highlights some recent and current clinical trials using targeted therapy.

Expression of platelet-derived growth factor-alpha receptor in human osteosarcoma is not a predictor of outcome

AIMS

The aims of this study were to examine the prognostic relevance of platelet-derived growth factor-α receptor (PDGFRA) expression in human osteosarcomas and to evaluate the mutation status of exon 12 and exon 18 of the PDGFRA gene.

METHODS

PDGFRA expression was examined in 100 human osteosarcomas by immunohistochemistry using paraffin embedded tumour tissues, and capillary sequencing of genomic DNA was performed to search for mutations in exons 12 and 18 of the PDGFRA gene.

RESULTS

Ninety-six osteosarcomas showed PDGFRA expression ranging from 4% to 90% (mean 40%, median 37.5%, SD 27.11%). Furthermore, DNA sequence of exon 12 and exon 18 of the PDGFRA gene were not altered in 40 tumours with high PDGFRA expression. Overall and disease-free survival analysis did not reveal any differences between osteosarcoma patients with high PDGFRA expression and patients with low PDGFRA expression.

CONCLUSIONS

The protein expression is not linked to mutations in exon 12 or exon 18 of PDGFRA gene. Therefore, treatment modalities based on the suppression of PDGFRA tyrosine kinase activity may need further investigation. PDGFRA expression is not a prognostic marker for osteosarcoma patients.

Multicenter phase II trial assessing effectiveness of imatinib mesylate on relapsed or refractory KIT-positive or PDGFR-positive sarcoma

BACKGROUND

Imatinib myselate is a molecularly targeted drug that inhibits Abl tyrosine kinase, as well as type III tyrosine kinase receptors such as platelet-derived growth factor receptor (PDGFR), KIT, colony-stimulating factor 1 receptor (CSF-1R), and discoidin domain receptor (DDR). Ph1 chromosome-positive chronic myeloid leukemias (CMLs), KIT-positive gastrointestinal stromal tumors (GISTs), and PDGFR-positive dermatofibrosarcoma protuberans (DFSP) have been reported to be responsive to imatinib treatment. We conducted a multicenter Phase II trial of imatinib in patients with relapsed or refractory KIT-positive (excluding GISTs) or PDGFR-positive sarcomas.

METHODS

Patient ages ranged from 12 and 75 years. Eligibility criteria included (1) metastatic sarcomas with a definitive diagnosis based on histopathology or that were completely unresectable and locally advanced; (2) relapsed or refractory cases that had completed standard treatment; and (3) a tumor confirmed by immunohistochemical staining to be KIT- or PDGFR-positive. A 600-mg dose of imatinib was administered to patients once a day, with each patient receiving six courses of the drug and each course lasting 4 weeks. In cases categorized as stable or progressive, the imatinib dose was increased to 800 mg/day administered twice daily.

RESULTS

A total of 25 patients who met the eligibility criteria were enrolled in the trial; 22 were evaluated for response. The response rate with a 600 mg/day dose of imatinib was 4.5% (0 complete response, 1 partial response). There were no other objective responses after increasing imatinib to 800 mg/day (0/10). We estimated 50% progression-free survival to be 61.0 days for an imatinib dose of 600 mg/day based on the Kaplan-Meier method. Side effects of imatinib were generally similar to those observed in previous clinical trials.

CONCLUSIONS

Our results did not indicate effectiveness of imatinib monotherapy at a dose of 600 or 800 mg/day in patients with relapsed or refractory KIT-positive (excluding GISTs) or PDGFR-positive sarcomas. Our findings suggest the need to evaluate the synergistic effect of combination therapy with other anticancer drugs.

Imatinib mesylate in children and adolescents with cancer

Imatinib is an inhibitor of the BCR-ABL fusion gene product that characterizes chronic myeloid leukemia (CML), and of the related tyrosine kinases c-KIT and platelet-derived growth factor (PDGF) receptor. The drug is now included as front-line therapy for CML and Philadelphia chromosome-positive acute lymphoblastic leukemia in children and adolescents, though valid concerns about serious late sequelae remain unresolved and are important issues for further study. European and North American consortia have conducted phase I and II clinical trials of imatinib in children and adolescents with brain and other solid tumors that have provided little evidence of efficacy.

Targets for cancer therapy in childhood sarcomas

Development of chemotherapeutic treatment modalities resulted in a dramatic increase in the survival of children with many types of cancer. Still, in case of some pediatric cancer entities including rhabdomyosarcoma, osteosarcoma and Ewing's sarcoma, survival of patients remains dismal and novel treatment approaches are urgently needed. Therefore, based on the concept of targeted therapy, numerous potential targets for the treatment of these cancers have been evaluated pre-clinically or in some cases even clinically during the last decade. This review gives an overview over many different potential therapeutic targets for treatment of these childhood sarcomas, including receptor tyrosine kinases, intracellular signaling molecules, cell cycle and apoptosis regulators, proteasome, hsp90, histone deacetylases, angiogenesis regulators and sarcoma specific fusion proteins. The large number of potential therapeutic targets suggests that improved comparability of pre-clinical models might be necessary to prioritize the most effective ones for future clinical trials.

Cytogenetic and molecular characterization of plutonium-induced rat osteosarcomas

The association between ionizing radiation and the subsequent development of osteosarcoma has been well described, but little is known about the cytogenetic and molecular events, which could be involved in the formation of radiation-induced osteosarcomas. Here, we performed comparative genomic hybridization (CGH) to detect chromosomal copy number changes in a series of 16 rat osteosarcomas induced by injection of plutonium-238. Recurrent gains/amplifications were observed at chromosomal regions 3p12-q12, 3q41-qter, 4q41-qter, 6q12-q16, 7q22-q34, 8q11-q23, 9q11-q22, 10q32.1-qter, and 12q, whereas recurrent losses were observed at 1p, 1q, 3q23-q35, 5q21-q33, 8q24-q31, 10q22-q25, 15p, 15q, and 18q. The gained region at 7q22-q34 was homologous to human chromosome bands 12q13-q15/8q24/22q11-q13, including the loci of Mdm2, Cdk4, c-Myc and Pdgf-b genes. The lost regions at 5q21-q33, 10q22-q25 and 15q contained tumor suppressor genes such as p16INK4a/p19ARF, Tp53 and Rb1. To identify potential target gene(s) for the chromosomal aberrations, we compared the expression levels of several candidate genes, located within the regions of frequent chromosomal aberrations, between the tumors and normal osteoblasts by using quantitative RT-PCR analysis. The Cdk4, c-Myc, Pdgf-b and p57KIP2 genes were thought to be possible target genes for the frequent chromosomal gain at 7q22-34 and loss at 1q in the tumors, respectively. In addition, mutations of the Tp53 gene were found in 27% (4 of 15) osteosarcomas. Our data may contribute to further understanding of the molecular mechanisms underlying osteosarcomas induced by ionizing radiation in human.

Novel therapeutic agents for osteosarcoma

Osteosarcoma is the most common malignant primary bone tumor in childhood. Despite multiagent chemotherapy and aggressive surgical resection, 30% of patients with localized disease and 80% of patients with metastatic disease at diagnosis will relapse. Survival for these patients has remained unchanged over the past 20 years. A number of novel agents in various stages of development hold promise for improving therapy for patients with osteosarcoma. This article will focus on novel therapeutic approaches, including agents targeting signal-transduction pathways, inhibitors of the tumor microenvironment and immunomodulatory agents, as well as overcoming resistance mechanisms and the use of novel delivery mechanisms.

PDGFRalpha: a new therapeutic target in the treatment of hepatocellular carcinoma?

BACKGROUND

Hepatocellular carcinoma (HCC) develops most often in a background of chronic inflammatory liver injury from viral infection or alcohol use. Most HCCs are diagnosed at a stage at which surgical resection is not feasible. Even in patients receiving surgery rates of recurrence and metastasis remain high. There are few effective HCC therapies and hence a need for novel, rational approaches to treatment. Platelet derived growth factor receptor-alpha (PDGFR-alpha) is involved in tumor angiogenesis and maintenance of the tumor microenvironment and has been implicated in development and metastasis of HCC.

OBJECTIVE

To examine PDGFR-alpha as a target for therapy of HCC and explore opportunities and strategies for PDGFR-alpha inhibition.

METHODS

A review of relevant literature.

RESULTS/CONCLUSIONS

Targeted inhibition of PDGFR-alpha is a rational strategy for prevention and therapy of HCC.

Ligand-dependent platelet-derived growth factor receptor (PDGFR)-alpha activation sensitizes rare lung cancer and sarcoma cells to PDGFR kinase inhibitors

Platelet-derived growth factor (PDGF) receptors (PDGFR) and their ligands play critical roles in several human malignancies. Sunitinib is a clinically approved multitargeted tyrosine kinase inhibitor that inhibits vascular endothelial growth factor receptor, c-KIT, and PDGFR, and has shown clinical activity in various solid tumors. Activation of PDGFR signaling has been described in gastrointestinal stromal tumors (PDGFRA mutations) as well as in chronic myeloid leukemia (BCR-PDGFRA translocation), and sunitinib can yield clinical benefit in both settings. However, the discovery of PDGFR activating mutations or gene rearrangements in other tumor types could reveal additional patient populations who might benefit from treatment with anti-PDGFR therapies, such as sunitinib. Using a high-throughput cancer cell line screening platform, we found that only 2 of 637 tested human tumor-derived cell lines show significant sensitivity to single-agent sunitinib exposure. These two cell lines [a non-small-cell lung cancer (NSCLC) and a rhabdomyosarcoma] showed expression of highly phosphorylated PDGFRA. In the sunitinib-sensitive adenosquamous NSCLC cell line, PDGFRA expression was associated with focal PFGRA gene amplification, which was similarly detected in a small fraction of squamous cell NSCLC primary tumor specimens. Moreover, in this NSCLC cell line, focal amplification of the gene encoding the PDGFR ligand PDGFC was also detected, and silencing PDGFRA or PDGFC expression by RNA interference inhibited proliferation. A similar codependency on PDGFRA and PDGFC was observed in the sunitinib-sensitive rhabdomyosarcoma cell line. These findings suggest that, in addition to gastrointestinal stromal tumors, rare tumors that show PDGFC-mediated PDGFRA activation may also be clinically responsive to pharmacologic PDGFRA or PDGFC inhibition.

Specific tyrosine kinase inhibitors regulate human osteosarcoma cells in vitro

Inhibitors of specific tyrosine kinases are attractive lead compounds for development of targeted chemotherapies for many tumors, including osteosarcoma. We asked whether inhibition of specific tyrosine kinases would decrease the motility, colony formation, and/or invasiveness by human osteosarcoma cell lines (TE85, MNNG, 143B, SAOS-2, LM-7). An EGF-R inhibitor reduced motility of all five cell lines by 50% to 80%. In contrast, an IGF-1R inhibitor preferentially reduced motility by 42% in LM-7 cells and a met inhibitor preferentially reduced motility by 80% in MNNG cells. The inhibitors of EGF-R, IGF-1R, and met reduced colony formation by more than 80% in all tested cell lines (TE85, MNNG, 143B). The EGF-R inhibitor reduced invasiveness by 62% in 143B cells. The JAK inhibitor increased motility of SAOS-2 and LM7 cells without affecting colony formation or invasiveness. Inhibitors of HER-2, NGF-R, and PDGF-Rs did not affect motility, invasiveness, or colony formation. These results support the hypothesis that specific tyrosine kinases regulate tumorigenesis and/or metastasis in osteosarcoma.

Platelet-derived growth factor receptor as a prognostic marker and a therapeutic target for imatinib mesylate therapy in osteosarcoma

The purpose of this review was to determine whether imatinib mesylate (STI571, Gleevec) has a role in the treatment of osteosarcoma. The expression of platelet-derived growth factor (PDGF) receptor and its ligand was examined in a panel of surgical specimens obtained from 54 osteosarcoma patients, and then the expression was compared with prognosis. The effects of imatinib mesylate on growth and molecular events in 10 patient-derived osteosarcoma cell cultures were investigated. Immunohistochemical studies demonstrated frequent expression of PDGF-AA (80.4%) and PDGF-alpha receptor (79.6%) and their correlation with inferior event-free survival (P < .05). PDGF-B-B and PDGF-beta-receptor expressions were also frequent (75.4% and 86%, respectively); however, statistically significant inferior event-free survival was not demonstrated (P = .15). In vitro studies demonstrated that imatinib mesylate had a variable cytotoxic effect on various osteosarcoma primary cultures, with an IC(50) of 5.6 microM to 9.5 microM, and blocked the PDGF-induced intracellular signal transduction as well as inhibition of downstream Akt phosphorylation. Mitogen-activated protein kinase (MAPK) was constitutively activated despite PDGF stimulation and imatinib mesylate treatment in 7 of 10 osteosarcoma cultures, perhaps explaining uncontrolled proliferation and relative unresponsiveness to imatinib. Imatinib mesylate could not be viewed as having a role as a single agent at current conventional doses for the treatment of osteosarcoma. These findings predicted activity in osteosarcoma clinical trials and suggested that in vitro model systems predict clinical behavior and that PDGF and its receptor expression could potentially be used for determining prognosis of osteosarcoma.

Expression of platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor in ameloblastomas

BACKGROUND

Platelet-derived growth factor (PDGF)-AA isoform and its receptor, PDGF-alpha receptor (PDGFRA) regulate tooth development and growth. We investigated the expression of both proteins in ameloblastomas, to contribute the understanding of the potential role of the PDGF/PDGFR system in this odontogenic neoplasm.

METHOD

Twenty-nine specimens of ameloblastoma were analyzed for PDGF-AA and PDGFRA expression using immunohistochemistry. The proliferation activity was investigated with the MIB-1 antibody. Additionally, capillary sequencing of genomic DNA was performed to search for mutations in therapeutically relevant exons 12 and 18 of the PDGFRA gene.

RESULTS

PDGF-AA and PDGFRA expression were detectable in all cases with the exception of one tumor. However, protein expression levels did neither correlate with each other nor with MIB-1 expression. Unicystic ameloblastomas did not differ from solid tumors with regard to PDGF-AA, PDGFRA, and MIB-1 expression. One tumor revealed a somatic mutation of exon 12 of the PDGFRA gene.

CONCLUSION

PDGF-AA and PDGFRA proteins are regularly expressed in variable levels in ameloblastomas, and somatic mutations of exon 12 and exon 18 of the PDGFRA gene are rare findings.

A phase II study of imatinib mesylate in children with refractory or relapsed solid tumors: a Children's Oncology Group study

BACKGROUND

Imatinib mesylate is a small molecule inhibitor of certain tyrosine kinases, most notably the chimeric bcr-abl fusion protein found in CML. It also inhibits KIT and PDGF receptor tyrosine kinases in vitro. Ewing sarcoma, osteosarcoma, neuroblastoma, desmoplastic small round cell, and synovial sarcomas often overexpress KIT or the PDGF receptor. A phase II study of imatinib in children and young adults with select solid tumors was performed.

PROCEDURE

Patients less than 30 years of age with refractory or recurrent Ewing sarcoma, osteosarcoma, neuroblastoma, desmoplastic small round cell, synovial sarcomas or GIST were eligible. Imatinib was administered daily for 28 day courses at a dose of 440 mg/m(2)/day. Responses were assessed according to Response Evaluation Criteria in Solid Tumor (RECIST).

RESULTS

Seventy eligible patients, 48 male and 22 female, were enrolled and 59 were evaluable for response. Only one partial response was seen among 24 patients with Ewing sarcoma. There were no other objective responses. Hemorrhagic pleural effusions occurred in seven patients with pulmonary lesions, four of whom had progressive disease at the time of the hemorrhage. Intratumoral bleeding was reported in three additional patients.

CONCLUSION

Imatinib as a single agent at a dose of 440 mg/m(2)/day demonstrated little or no activity as a single agent in children with relapsed or refractory Ewing sarcoma, osteosarcoma, neuroblastoma, or desmoplastic small round cell tumors.

Decorin-mediated effects in cancer cell biology

Decorin is a multifunctional molecule of the extracellular matrix. Among the multitude of assigned functions the most intriguing is the ability to inhibit the growth and the metastasis of a wide range of cancer cells in vitro. Decorin was established to directly interact with EGFR and erb2, inducing protracted receptor internalization, which results in attenuation of the receptor-mediated intacellular signaling and induction of apoptosis. Studies by our group of osteosarcoma cells described the first exception to the established decorin-mediated growth suppression model. Osteosarcoma cells constitutively produced decorin and they were not sensitive to decorin-induced growth arrest. On the contrary, decorin seemed to be beneficial to osteosarcoma cells, since it was necessary for cell migration and acted as mediator, counteracting the TGFbeta2-induced cytostatic function. Importantly, decorin did not induce p21 expression whereas EGFR appeared to be overexpressed and continuously phosphorylated in our osteosarcoma model. These data provide new insight on pathways that cancer cells might employ to overcome the established decorin-induced growth suppression.

Characterization of the G-quadruplexes in the duplex nuclease hypersensitive element of the PDGF-A promoter and modulation of PDGF-A promoter activity by TMPyP4

The proximal 5′-flanking region of the human platelet-derived growth factor A (PDGF-A) promoter contains one nuclease hypersensitive element (NHE) that is critical for PDGF-A gene transcription. On the basis of circular dichroism (CD) and electrophoretic mobility shift assay (EMSA), we have shown that the guanine-rich (G-rich) strand of the DNA in this region can form stable intramolecular parallel G-quadruplexes under physiological conditions. A Taq polymerase stop assay has shown that the G-rich strand of the NHE can form two major G-quadruplex structures, which are in dynamic equilibrium and differentially stabilized by three G-quadruplex-interactive drugs. One major parallel G-quadruplex structure of the G-rich strand DNA of NHE was identified by CD and dimethyl sulfate (DMS) footprinting. Surprisingly, CD spectroscopy shows a stable parallel G-quadruplex structure formed within the duplex DNA of the NHE at temperatures up to 100°C. This structure has been characterized by DMS footprinting in the double-stranded DNA of the NHE. In transfection experiments, 10 μM TMPyP4 reduced the activity of the basal promoter of PDGF-A ∼40%, relative to the control. On the basis of these results, we have established that ligand-mediated stabilization of G-quadruplex structures within the PDGF-A NHE can silence PDGF-A expression.

Expression of c-kit in human osteosarcoma and its relevance as a prognostic marker

AIMS

To examine the prognostic relevance of c-kit expression in human osteosarcomas and to evaluate the mutation status in exon 9 and exon 11 of the c-kit gene.

METHODS

c-kit expression was examined in 100 human osteosarcomas by immunohistochemistry using paraffin embedded tumour tissues, and capillary sequencing of genomic DNA was performed to search for mutations in exons 9 and 11 of the c-kit gene.

RESULTS

20 osteosarcomas showed c-kit expression ranging from 5% to 90% (mean 5.9%; SD 16.74%). Furthermore, DNA sequences of exon 9 and exon 11 of the c-kit gene were not altered in these tumours. Overall and disease free survival analysis did not reveal any differences between patients with osteosarcoma with c-kit expression and those with c-kit negative tumours.

CONCLUSIONS

C-kit expression is not a prognostic marker in patients with osteosarcoma. The protein expression is not linked to mutations in exon 9 or exon 11 of the c-kit gene. Therefore, these exons may not function as targets for treatment modalities based on the suppression of c-kit tyrosine kinase activity.

Transforming growth factor-beta as a key molecule triggering the expression of versican isoforms v0 and v1, hyaluronan synthase-2 and synthesis of hyaluronan in malignant osteosarcoma cells

Versican, a large sized chondroitin-sulphate proteoglycan (PG), and its binding partner, hyaluronan (HA), are extracellular matrix (ECM) components that play an essential role in transformed cell behavior. Expression of certain versican isoforms has been implicated in cell migration and proliferation of cancer cells and, on the other hand, disruption of HA synthesis by inhibiting hyaluronan synthase-2 (HAS2) expression in osteosarcoma cells by suppressing cell proliferation, invasiveness and motility. Considering that growth factors, such as TGF-beta, bFGF and PDGF-BB, are important regulators for the expression of the ECM macromolecules, in this study we examined the effect of these growth factors on the expression of the various versican isoforms, HA synthases as well as HA synthesis by MG-63 osteosarcoma cells and normal human osteoblastic periodontal ligament cells (hPDL). Real-time PCR and metabolic labelling followed by fine HPLC analysis coupled to radiochemical detection were the methods utilized. It was found that, contrary to normal hPDL cells, osteosarcoma MG-63 cells do not constitutively express the versican isoforms V0 and V1. Exogenous addition of TGF-beta2 stimulated the versican transcript levels mainly by forcing osteosarcoma cells to express V1 and V0 isoforms. PDGF-BB and bFGF had only minor effects in these cells. In hPDL cells a strong stimulation of the V3 transcript by all growth factors was observed. TGF-beta2 was also the major stimulator of HAS2 isoform expression as well as hyaluronan synthesis in osteosarcoma cells, while PDGF-BB exerted dominant influence on HAS2 isoform expression and hyaluronan biosynthesis by osteoblasts. The obtained results show for the first time that TGF-beta2 triggers the malignant phenotype pattern of versican and hyaluronan expression in human osteosarcoma cells and indicate that this growth factor may account for the metastatic potential of these cells.

Molecularly Targeted Therapy for Pediatric Brain Tumors

Treatment of pediatric brain tumors remains a challenge because of the toxicity associated with conventional treatment and the relative resistance of tumors at the time of recurrence. The traditional approach of administering cytotoxic agents at the maximum tolerated dose is being supplanted by the development of molecularly targeted agents aimed at critical cellular changes that are responsible for the growth and spread of cancer cells. These agents theoretically should be more specific for tumor cells and less toxic to normal cells. While the idea of targeted therapy has generated much excitement in the oncology community, the degree of benefit to patients with central nervous system (CNS) tumors remains unclear. Numerous challenges remain in the development of these agents, including identification of meaningful targets, delivery of agents in sufficient quantity at the target site, and determination of any biologic response to these agents. This article discusses the rationale behind several of these agents and their use in pediatric patients with brain tumors.

Structural and functional specificities of PDGF-C and PDGF-D, the novel members of the platelet-derived growth factors family

The platelet-derived growth factor (PDGF) family was for more than 25 years assumed to consist of only PDGF-A and -B. The discovery of the novel family members PDGF-C and PDGF-D triggered a search for novel activities and complementary fine tuning between the members of this family of growth factors. Since the expansion of the PDGF family, more than 60 publications on the novel PDGF-C and PDGF-D have been presented, highlighting similarities and differences to the classical PDGFs. In this paper we review the published data on the PDGF family covering structural (gene and protein) similarities and differences among all four family members, with special focus on PDGF-C and PDGF-D expression and functions. Little information on the protein structures of PDGF-C and -D is currently available, but the PDGF-C protein may be structurally more similar to VEGF-A than to PDGF-B. PDGF-C contributes to normal development of the heart, ear, central nervous system (CNS), and kidney, while PDGF-D is active in the development of the kidney, eye and brain. In adults, PDGF-C is active in the kidney and the central nervous system. PDGF-D also plays a role in the lung and in periodontal mineralization. PDGF-C is expressed in Ewing family sarcoma and PDGF-D is linked to lung, prostate and ovarian cancers. Both PDGF-C and -D play a role in progressive renal disease, glioblastoma/medulloblastoma and fibrosis in several organs.

Combined low-dose imatinib mesylate and paclitaxel lack synergy in an experimental model of extra-osseous hormone-refractory prostate cancer

OBJECTIVE

To determine the efficacy of low-dose imatinib mesylate (STI571) alone or combined with a taxane (paclitaxel) in inhibiting the growth of experimental extra-osseous hormone-refractory prostate cancer.

MATERIALS AND METHODS

Orthotopic PC3 prostate tumours were established in male severe combined-immunodeficient mice; on day 3 the mice were randomly assigned to one of four groups: paclitaxel 10 mg/kg intraperitoneally once a week; STI571 50 mg/kg once a day for 6/7 weekdays; combined paclitaxel and STI571; and vehicle-treated controls. On day 40, the primary prostate tumour and metastatic lymphadenopathy were removed and measured. Effects were correlated with tumour cell proliferation and microvessel density.

RESULTS

Paclitaxel reduced the mean tumour weight and volume by 21.3% (not significant) and 73.7% (P < 0.05), respectively, compared to controls, and reduced the number of lymph node metastases by 49.1% (P < 0.05) and mean lymph node size by 13.5% (not significant). Adding low-dose STI571 had a small additive effect on tumour weight and the incidence of lymph node metastases, but this was not significant compared to paclitaxel alone. STI571 alone did not inhibit tumour progression. Antitumour effects were associated with parallel changes in tumour cell proliferation with no significant changes in neo-angiogenesis.

CONCLUSION

Combined low-dose STI571 and paclitaxel had little synergy in this experimental model. Low-dose STI571 monotherapy was not effective in extra-osseous disease, apparently due to a site-specific failure to up-regulate beta-platelet-derived growth factor receptor expression in prostate cancer cells and associated tumour stroma.

Targeting the platelet-derived growth factor receptor alpha with a neutralizing human monoclonal antibody inhibits the growth of tumor xenografts: implications as a potential therapeutic target

Platelet-derived growth factor receptor alpha (PDGFRalpha) is a type III receptor tyrosine kinase that is expressed on a variety of tumor types. A neutralizing monoclonal antibody to human PDGFRalpha, which did not cross-react with the beta form of the receptor, was generated. The fully human antibody, termed 3G3, has a Kd of 40 pmol/L and blocks both PDGF-AA and PDGF-BB ligands from binding to PDGFRalpha. In addition to blocking ligand-induced cell mitogenesis and receptor autophosphorylation, 3G3 inhibited phosphorylation of the downstream signaling molecules Akt and mitogen-activated protein kinase. This inhibition was seen in both transfected and tumor cell lines expressing PDGFRalpha. The in vivo antitumor activity of 3G3 was tested in human glioblastoma (U118) and leiomyosarcoma (SKLMS-1) xenograft tumor models in athymic nude mice. Antibody 3G3 significantly inhibited the growth of U118 (P=0.0004) and SKLMS-1 (P <0.0001) tumors relative to control. These data suggest that 3G3 may be useful for the treatment of tumors that express PDGFRalpha.

Prognostic Significance of Allelic Imbalance at the c-kit Gene Locus and c-kit Overexpression by Immunohistochemistry in Pediatric Osteosarcomas

Purpose

Since the recent development of biologic agents targeting oncogenes, increasing attention has been focused on determining the role of tyrosine kinase receptors in the pathogenesis of tumors. Our study was designed to investigate the status of region 4q12, which contains the candidate gene c-kit, and the expression of c-kit by immunohistochemistry (IHC).

Patients and Methods

Paired blood and biopsy specimens of 68 children treated for high-grade primary osteosarcomas were collected. Microsatellite analysis at two genomic sites containing c-kit gene was performed on paired DNA using a sensible fluorescent polymerase chain reaction technology. To confirm the DNA data, we studied c-kit protein expression by IHC in 56 available paraffin-embedded tumor tissues.

Results

The frequency of allelic imbalance (AI) at locus 4q12 was 39% in the overall population. In agreement with previous studies, we did not detect microsatellite instability, allowing us to hypothesize that this pathway is not implicated. Furthermore, the normal status at locus 4q12 was associated with a significantly better survival in the whole osteosarcoma population (P = .05). IHC overexpression of c-kit was concordant in all cases presenting an AI. However, normal status at locus 4q12 was correlated to an absence of c-kit protein expression in 19 (65.5%) of 29 informative cases.

Conclusion

Allelotyping of locus 4q12, which contains the c-kit gene, could help pediatric osteosarcoma prognostic screening and showed a strong correlation with overexpression of c-kit protein. These results allowed us to hypothesize that, in some cases, a mutation of c-kit gene could lead to a protein overexpression.