Bortezomib-mediated proteasome inhibition as a potential strategy for the treatment of rhabdomyosarcoma

Bortezomib promotes the TRAIL-mediated killing of resistant rhabdomyosarcoma by ErbB2/Her2-targeted CAR-NK-92 cells via DR5 upregulation

Treatment resistance and immune escape are hallmarks of metastatic rhabdomyosarcoma (RMS), underscoring the urgent medical need for therapeutic agents against this disease entity as a key challenge in pediatric oncology. Chimeric antigen receptor (CAR)-based immunotherapies, such as the ErbB2 (Her2)-CAR-engineered natural killer (NK) cell line NK-92/5.28.z, provide antitumor cytotoxicity primarily through CAR-mediated cytotoxic granule release and thereafter-even in cases with low surface antigen expression or tumor escape-by triggering intrinsic NK cell-mediated apoptosis induction via additional ligand/receptors. In this study, we showed that bortezomib increased susceptibility toward apoptosis in clinically relevant RMS cell lines RH30 and RH41, and patient-derived RMS tumor organoid RMS335, by upregulation of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor DR5 in these metastatic, relapsed/refractory (r/r) RMS tumors. Subsequent administration of NK-92/5.28.z cells significantly enhanced antitumor activity in vitro. Applying recombinant TRAIL instead of NK-92/5.28.z cells confirmed that the synergistic antitumor effects of the combination treatment were mediated via TRAIL. Western blot analyses indicated that the combination treatment with bortezomib and NK-92/5.28.z cells increased apoptosis by interacting with the nuclear factor κB, JNK, and caspase pathways. Overall, bortezomib pretreatment can sensitize r/r RMS tumors to CAR- and, by upregulating DR5, TRAIL-mediated cytotoxicity of NK-92/5.28.z cells.

Molecular characterization of ANKRD1 in rhabdomyosarcoma cell lines: expression, localization, and proteasomal degradation

Rhabdomyosarcoma (RMS) is the most common soft tissue malignancy in children and adolescents. Respecting the age of the patients and the tumor aggressiveness, investigation of the molecular mechanisms of RMS tumorigenesis is directed toward the identification of novel therapeutic targets. To contribute to a better understanding of the molecular pathology of RMS, we investigated ankyrin repeat domain 1 (ANKRD1), designated as a potential marker for differential diagnostics. In this study, we used three RMS cell lines (SJRH30, RD, and HS-729) to assess its expression profile, intracellular localization, and turnover. They express wild-type ANKRD1, as judged by the sequencing of the open reading frame. Each cell line expressed a different amount of ANKRD1 protein, although the transcript level was similar. According to western blot analysis, ANKRD1 protein was expressed at detectable levels in the SJRH30 and RD cells (SJRH30 > RD), but not in the HS-729, even after immunoprecipitation. Immunocytochemistry revealed nuclear and cytoplasmic localization of ANKRD1 in all examined cell lines. Moreover, the punctate pattern of ANKRD1 staining in the nuclei of RD and HS-729 cells overlapped with coilin, indicating its association with Cajal bodies. We have shown that RMS cells are not able to overexpress ANKRD1 protein, which can be attributed to its proteasomal degradation. The unsuccessful attempt to overexpress ANKRD1 in RMS cells indicates the possibility that its overexpression may have detrimental effects for RMS cells and opens a window for further research into its role in RMS pathogenesis and for potential therapeutic targeting.

Mesenchymal tumor organoid models recapitulate rhabdomyosarcoma subtypes

Rhabdomyosarcomas (RMS) are mesenchyme-derived tumors and the most common childhood soft tissue sarcomas. Treatment is intense, with a nevertheless poor prognosis for high-risk patients. Discovery of new therapies would benefit from additional preclinical models. Here, we describe the generation of a collection of 19 pediatric RMS tumor organoid (tumoroid) models (success rate of 41%) comprising all major subtypes. For aggressive tumors, tumoroid models can often be established within 4-8 weeks, indicating the feasibility of personalized drug screening. Molecular, genetic, and histological characterization show that the models closely resemble the original tumors, with genetic stability over extended culture periods of up to 6 months. Importantly, drug screening reflects established sensitivities and the models can be modified by CRISPR/Cas9 with TP53 knockout in an embryonal RMS model resulting in replicative stress drug sensitivity. Tumors of mesenchymal origin can therefore be used to generate organoid models, relevant for a variety of preclinical and clinical research questions.

Comprehensive Profiling Reveals Prognostic and Immunogenic Characteristics of Necroptosis in Soft Tissue Sarcomas

Soft tissue sarcomas (STSs) are heterogeneous malignancies derived from mesenchymal cells. Due to its rarity, heterogeneity, and limited overall response to chemotherapy, STSs represent a therapeutic challenge. Necroptosis is a novel therapeutic strategy for enhancing immunotherapy of cancer. Nevertheless, no research has explored the relationship between necroptosis-related genes (NRGs) and STSs. In this study, differentially expressed NRGs were identified using The Cancer Genome Atlas (TCGA) and The Cancer Genotype-Tissue Expression (GTEx) project. The expression levels of 34 NRGs were significantly different. Several key NRGs were validated using RT-qPCR and our own sequencing data. Patients with STSs were divided into two clusters using consensus cluster analysis, and significant differences were observed in their survival (p=0.002). We found the differentially expressed genes (DEGs) between the two clusters and carried out subsequent analysis. The necroptosis-related gene signatures with 10 key DEGs were identified with a risk score constructed. The prognosis of TCGA-SARC cohort with low necroptosis-related risk score was better (p<0.001). Meanwhile, the low-risk group had a significantly increased immune infiltration. Using the data of GSE17118 and another immunotherapy cohort as external validations, we observed significant survival differences between the two risk groups (p=0.019). The necroptosis-related risk score proved to be an independent prognostic factor, and a nomogram was further established and integrated with other clinical features. Notably, the necroptosis-related gene signature could also act as the prognostic indicator in other malignancies based on pan-cancer analysis. In summary, the study outlines NRGs in STSs and their potential role in prognosis and will be one of the important directions for future research.

The Infectious Bronchitis Coronavirus Pneumonia Model Presenting a Novel Insight for the SARS-CoV-2 Dissemination Route

Infectious bronchitis (IB) of chickens is a highly contagious disease characterized by damage of the respiratory system and reproductive organs in young animals caused by a virus of the genus Gamma coronavirus. The condition of the respiratory system caused by the IB virus in chickens has many similarities with the pathology of the respiratory system caused by SARS-CoV-2 in humans. The effectiveness of virucidal drugs (Argovit, Triviron, Ecocid, and lauric acid monoglyceride) was tested on chickens inoculated with a tenfold dose of a vaccine strain based on the attenuated virus H120 against IB of chickens. On the 6th day after inoculation, inflammatory changes in the intestines, lungs, and thymus were observed in the control group. The experimental groups were characterized by less pronounced inflammatory reactions and a lower proportion of thymus and lung probes containing genomic IB virus RNA. Since the virucidal activity of four orally administrated formulations was possible only in the intestine, the experimental data indirectly confirmed the hypothesis of the possibility of the predominant accumulation of coronaviruses in the intestine and subsequent lung damage due to the hematogenous redistribution of viral particles and IBV antigens. It was suggested that other coronaviruses including SARS-CoV-2 can implement a similar mechanism.

Establishment and characterization of NCC-ssRMS2-C1: a novel patient-derived cell line of spindle cell/sclerosing rhabdomyosarcoma

Spindle cell/sclerosing rhabdomyosarcoma (ssRMS) is a rare subtype of rhabdomyosarcoma (RMS) that has fascicular spindle cell and/or sclerosing morphology. SsRMS has a diverse molecular background and is categorized into three groups: congenital/infantile ssRMS with a gene fusion involving the NCOA2 and VGLL2, ssRMS with the MYOD1 mutation, and ssRMS with no recurrent identifiable genetic alterations. Because ssRMS is a newly defined disease concept of RMS, the optimal treatment methods have not been determined. This results in unfavorable prognosis and consequently signals the urgent need for continuous research. Patient-derived cell lines are essential tools in basic and translational research. However, only two ssRMS cell lines with the MYOD1 mutation have been reported to date. Thus, we established a novel ssRMS cell line named NCC-ssRMS2-C1 using a surgically resected tumor tissue from an adult ssRMS patient. NCC-ssRMS2-C1 cells retained the copy number alterations corresponding to the original tumor and are categorized into the group with no recurrent identifiable genetic alterations. NCC-ssRMS2-C1 cells demonstrated constant proliferation, spheroid formation, and capability for invasion in vitro, reflecting the malignant features of the original tumor tissue. In a drug screening test, ssRMS demonstrated remarkable sensitivity to romidepsin, trabectedin, actinomycin D, and bortezomib. Hence, we conclude that the NCC-ssRMS2-C1 cell line is the first ssRMS cell line which belongs to the group with no recurrent identifiable genetic alterations, and it will be a useful resource in both basic and translational studies for ssRMS.

The Proteasome Inhibitor Ixazomib Inhibits the Formation and Growth of Pulmonary and Abdominal Osteosarcoma Metastases in Mice

Osteosarcoma is the most common form of primary bone cancer. Over 20% of osteosarcoma patients present with pulmonary metastases at diagnosis, and nearly 70% of these patients fail to respond to treatment. Previous work revealed that human and canine osteosarcoma cell lines are extremely sensitive to the therapeutic proteasome inhibitor bortezomib in vitro. However, bortezomib has proven disappointingly ineffective against solid tumors including sarcomas in animal experiments and clinical trials. Poor tumor penetration has been speculated to account for the inconsistency between in vitro and in vivo responses of solid tumors to bortezomib. Here we show that the second-generation proteasome inhibitor ixazomib, which reportedly has enhanced solid tumor penetration compared to bortezomib, is toxic to human and canine osteosarcoma cells in vitro. We used experimental osteosarcoma metastasis models to compare the efficacies of ixazomib and bortezomib against primary tumors and metastases derived from luciferase-expressing KRIB or 143B human osteosarcoma cell lines in athymic mice. Neither proteasome inhibitor reduced the growth of primary intramuscular KRIB tumors, however both drugs inhibited the growth of established pulmonary metastases created via intravenous inoculation with KRIB cells, which were significantly better vascularized than the primary tumors. Only ixazomib slowed metastases from KRIB primary tumors and inhibited the growth of 143B pulmonary and abdominal metastases, significantly enhancing the survival of mice intravenously injected with 143B cells. Taken together, these results suggest ixazomib exerts better single agent activity against osteosarcoma metastases than bortezomib. These data provide hope that incorporation of ixazomib, or other proteasome inhibitors that penetrate efficiently into solid tumors, into current regimens may improve outcomes for patients diagnosed with metastatic osteosarcoma.

Identification of clinically achievable combination therapies in childhood rhabdomyosarcoma

Purpose

Systemic therapy has improved rhabdomyosarcoma event-free and overall survival; however, approximately 40 % of patients will have progressive or recurrent disease which is difficult to cure and remains a considerable challenge. Minimal progress has been made in improving outcomes for metastatic or relapsed RMS due to a lack of effective therapeutic agents. Targeted therapies are likely to be incorporated into regimens which rely on conventional cytotoxic chemotherapy. A system to evaluate novel combinations of interest is needed.

Methods

In this study, we explored 8 agents, 5 that are routinely used or similar to agents used in the clinical management of RMS and 3 biologically targeted agents with novel mechanisms of action, the Wee1 inhibitor AZD1775, the tyrosine kinase inhibitor cabozantinib, and the proteasome inhibitor bortezomib. All were tested individually at clinically achievable concentrations for activity in 4 RMS cell lines and then for potential synergy in two-drug combinations.

Results

We found single-agent activity in five of the agents (or their active metabolites) that constitute the standard of care in RMS and for AZD1775 with mean IC50 values of 207 ng/ml, well below clinically achievable levels. In addition, the combination of individual cytotoxic chemotherapeutics currently used for RMS demonstrated largely synergistic activity with higher, but clinically achievable concentrations of AZD1775 in our assays.

Conclusions

Prioritization of chemotherapeutics in RMS is possible using an in vitro system that can define novel drug combinations worthy of future investigation. AZD1775 exhibits single-agent activity, as well as synergy with conventional cytotoxic chemotherapy, and is a novel targeted agent that warrants further study in RMS.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-016-3077-8) contains supplementary material, which is available to authorized users.

The importance of being dead: cell death mechanisms assessment in anti-sarcoma therapy

Cell death can occur through different mechanisms, defined by their nature and physiological implications. Correct assessment of cell death is crucial for cancer therapy success. Sarcomas are a large and diverse group of neoplasias from mesenchymal origin. Among cell death types, apoptosis is by far the most studied in sarcomas. Albeit very promising in other fields, regulated necrosis and other cell death circumstances (as so-called "autophagic cell death" or "mitotic catastrophe") have not been yet properly addressed in sarcomas. Cell death is usually quantified in sarcomas by unspecific assays and in most cases the precise sequence of events remains poorly characterized. In this review, our main objective is to put into context the most recent sarcoma cell death findings in the more general landscape of different cell death modalities.

Gene Expression Analysis of the 26S Proteasome Subunit PSMB4 Reveals Significant Upregulation, Different Expression and Association with Proliferation in Human Pulmonary Neuroendocrine Tumours

Background: Proteasomal subunit PSMB4 was suggested to be a survival gene in an animal model of hepatocellular carcinoma and in glioblastoma cell lines. In pulmonary adenocarcinoma, a high expression of these genes was found to be associated with poor differentiation and survival. This study investigates the gene expression levels of 26S proteasome subunits in human pulmonary neuroendocrine tumours including typical (TC) and atypical (AC) carcinoid tumours as well as small cell (SCLC) and large cell (LCNEC) neuroendocrine carcinomas.

Material and methods: Gene expression levels of proteasomal subunits (PSMA1, PSMA5, PSMB4, PSMB5 and PSMD1) were investigated in 80 neuroendocrine pulmonary tumours (each 20 TC, AC, LCNLC and SCLC) and compared to controls. mRNA levels were determined by using TaqMan assays. Immunohistochemistry on tissue microarrays (TMA) was performed to determine the expression of ki67, cleaved caspase 3 and PSMB4.

Results: All proteasomal subunit gene expressions were significantly upregulated in TC, AC, SCLC and LCNEC compared to controls. PSMB4 mRNA is differently expressed between all neuroendocrine tumour subtypes demonstrating the highest expression and greatest range in LCNEC (p=0.043), and is significantly associated with proliferative activity (p=0.039).

Conclusion: In line with other 26S proteasomal subunits PSMB4 is significantly increased, but differently expressed between pulmonary neuroendocrine tumours and is associated with the proliferative activity. Unlike in pulmonary adenocarcinomas, no association with biological behaviour was observed, suggesting that increased proteasomal subunit gene expression is a common and probably early event in the tumorigenesis of pulmonary neuroendocrine tumours regardless of their differentiation.

Linking the activity of bortezomib in multiple myeloma and autoimmune diseases

Since their introduction to the clinic 10 years ago, proteasome inhibitors have become the cornerstone of anti-multiple myeloma therapy. Despite significant progress in understanding the consequences of proteasome inhibition, the unique activity of bortezomib is still unclear. Disappointing results from clinical trials with bortezomib in other malignancies raise the question of what makes multiple myeloma so sensitive to proteasome inhibition. Successful administration of bortezomib in various immunological disorders that exhibit high antibody production suggests that the balance between protein synthesis and degradation is a key determinant of sensitivity to proteasome inhibition because a high rate of protein production is a shared characteristic in plasma and myeloma cells. Initial or acquired resistance to bortezomib remains a major obstacle in the clinic as in vitro data from cell lines suggest a key role for the β5 subunit mutation in resistance; however the mutation was not found in patient samples. Recent studies indicate the importance of selecting for a subpopulation of cells that produce lower amounts of paraprotein during bortezomib therapy.

PAX3-FOXO1 induces up-regulation of Noxa sensitizing alveolar rhabdomyosarcoma cells to apoptosis

Alveolar rhabdomyosarcoma (ARMS) has a much poorer prognosis than the more common embryonal subtype. Most ARMS tumors characteristically possess a specific genomic translocation between the genes of PAX3/7 and FOXO1 (FKHR), which forms fusion proteins possessing the DNA binding domains of PAX3/7 and the more transcriptionally potent transactivation domain of FOXO1. We have shown that the proapoptotic BH3-only family member Noxa is upregulated by the PAX3-FOXO1 fusion transcription factor in a p53-independent manner. The increased expression of Noxa renders PAX3-FOXO1-expressing cells more susceptible to apoptosis induced by a γ-secretase inhibitor (GSI1, Z-LLNle-CHO), the proteasome inhibitor bortezomib, and BH3 mimetic ABT-737. Apoptosis in response to bortezomib can be overcome by shRNA knockdown of Noxa. In vivo treatment with bortezomib reduced the growth of tumors derived from a PAX3-FOXO1-expressing primary myoblast tumor model and RH41 xenografts. We therefore demonstrate that PAX3-FOXO1 up-regulation of Noxa represents an unanticipated aspect of ARMS tumor biology that creates a therapeutic window to allow induction of apoptosis in ARMS cells.

The evolution of systemic therapy in sarcoma

Approximately 50% of patients with localized soft tissue sarcomas will develop recurrent disease after complete surgical resection, requiring alternative means of treatment. Conventional chemotherapy comprising of doxorubicin and ifosfamide has shown benefit in advanced disease, however, there remains a clear need for more effective, less toxic, therapies for the treatment of this heterogeneous group of mesenchymal malignancies. Recently, greater emphasis has been placed on the underlying biology of individual sarcoma subtypes, with the development and evaluation of novel therapies both in common and in rare subtypes. In addition, there is a greater specificity in the selection of chemotherapy agents based on activity in individual histological subtypes. Despite these advances the management of sarcoma, and in particular of rare subtypes, remains a major challenge. Some histological subtypes are resistant to conventional chemotherapy and patients with these diseases should be offered participation in early phase clinical trials of novel drugs.

BAG3 induction is required to mitigate proteotoxicity via selective autophagy following inhibition of constitutive protein degradation pathways

Simultaneous inhibition of the two major constitutive protein quality control (PQC) pathways, that is, the ubiquitin-proteasome system (UPS) and the aggresome-autophagy system, has been suggested as a promising strategy to trigger cell death in cancer cells. However, we observed that one third of rhabdomyosarcoma (RMS) cells survives parallel inhibition of the UPS by Bortezomib and the aggresome-autophagy pathway by the cytoplasmic histone deacetylase 6 inhibitor ST80, and is able to regrow upon drug removal, thus pointing to the induction of compensatory pathways. Here, we identify Bcl-2-associated athanogene 3 (BAG3) as a critical mediator of inducible resistance in surviving cells after concomitant blockage of constitutive PQC pathways by mitigating ST80/Bortezomib-triggered proteotoxicity via selective autophagy. ST80/Bortezomib cotreatment upregulates BAG3 mRNA and protein levels in surviving cells in addition to triggering the accumulation of insoluble protein aggregates. Intriguingly, knockdown of BAG3 by RNA interference severely impairs clearance of protein aggregates, significantly increases cell death and reduces long-term survival and clonogenic growth during recovery after ST80/Bortezomib cotreatment. Similarly, inhibition of autophagy by inducible autophagy-related protein 7 knockdown prevents removal of protein aggregates and cell regrowth during recovery after ST80/Bortezomib cotreatment. Also, the inhibition of lysosomal degradation using the V-ATPase pump inhibitor Bafilomycin A1 enhances accumulation of protein aggregates, and completely abolishes regrowth after Bortezomib/ST80-induced proteotoxic stress. By identifying BAG3 as a key mediator of inducible resistance by mitigating proteotoxicity via selective autophagy after inhibition of constitutive PQC systems, our study provides new insights into the regulation of PQC pathways in cancer cells and identifies new targets for therapeutic intervention.

In vitro expanded bone marrow-derived murine (C57Bl/KaLwRij) mesenchymal stem cells can acquire CD34 expression and induce sarcoma formation in vivo

Mesenchymal stem cells (MSCs) have currently generated numerous interests in pre-clinical and clinical applications due to their multiple lineages differentiation potential and immunomodulary effects. However, accumulating evidence indicates that MSCs, especially murine MSCs (mMSCs), can undergo spontaneous transformation after long-term in vitro culturing, which might reduce the therapeutic application possibilities of these stem cells. In the present study, we observed that in vitro expanded bone marrow (BM) derived mMSCs from the C57Bl/KaLwRij mouse strain can lose their specific stem cells markers (CD90 and CD105) and acquire CD34 expression, accompanied with an altered morphology and an impaired tri-lineages differentiation capacity. Compared to normal mMSCs, these transformed mMSCs exhibited an increased proliferation rate, an enhanced colony formation and migration ability as well as a higher sensitivity to anti-tumor drugs. Transformed mMSCs were highly tumorigenic in vivo, resulting in aggressive sarcoma formation when transplanted in non-immunocompromised mice. Furthermore, we found that Notch signaling downstream genes (hey1, hey2 and heyL) were significantly upregulated in transformed mMSCs, while Hedgehog signaling downstream genes Gli1 and Ptch1 and the Wnt signaling downstream gene beta-catenin were all decreased. Taken together, we observed that murine in vitro expanded BM-MSCs can transform into CD34 expressing cells that induce sarcoma formation in vivo. We assume that dysregulation of the Notch(+)/Hh(-)/Wnt(-) signaling pathway is associated with the malignant phenotype of the transformed mMSCs.

Effect of inhibition of the ubiquitin-proteasome system and Hsp90 on growth and survival of rhabdomyosarcoma cells in vitro

Background

The ubiquitin-proteasome system (UPS) and the heat shock response (HSR) are two critical regulators of cell homeostasis, as their inhibition affects growth and survival of normal cells, as well as stress response and invasiveness of cancer cells. We evaluated the effects of the proteasome inhibitor Bortezomib and of 17-DMAG, a competitive inhibitor of Hsp90, in rhabdomyosarcoma (RMS) cells, and analyzed the efficacy of single-agent exposures with combination treatments.

Methods

To assess cytotoxicity induced by Bortezomib and 17-DMAG in RMS cells, viability was measured by MTT assay after 24, 48 and 72 hours. Western blotting and immunofluorescence analyses were carried out to elucidate the mechanisms of action. Apoptosis was measured by FACS with Annexin-V-FITC and Propidium Iodide.

Results

Bortezomib and 17-DMAG, when combined at single low-toxic concentrations, enhanced growth inhibition of RMS cells, with signs of autophagy that included intensive cytoplasmic vacuolization and conversion of cytosolic LC3-I protein to its autophagosome-associated form. Treatment with lysosomal inhibitor chloroquine facilitates apoptosis, whereas stimulation of autophagy by rapamycin prevents LC3-I conversion and cell death, suggesting that autophagy is a resistance mechanism in RMS cells exposed to proteotoxic drugs. However, combination treatment also causes caspase-dependent apoptosis, PARP cleavage and Annexin V staining, as simultaneous inhibition of both UPS and HSR systems limits cytoprotective autophagy, exacerbating stress resulting from accumulation of misfolded proteins.

Conclusion

The combination of proteasome inhibitor Bortezomib with Hsp90 inhibitor 17-DMAG, appears to have important therapeutic advantages in the treatment of RMS cells compared with single-agent exposure, because compensatory survival mechanisms that occur as side effects of treatment may be prevented.

Characterization of the protein ubiquitination response induced by Doxorubicin

Doxorubicin is commonly considered to exert its anti-tumor activity by triggering apoptosis of cancer cells through DNA damage. Recent reports have shown that Doxorubicin elicits a marked heat shock response, and that either inhibition or silencing of heat shock proteins enhance the Doxorubicin apoptotic effect in neuroblastoma cells. In order to investigate whether Doxorubicin may also act through protein modification, we performed a proteomic analysis of ubiquitinated proteins. Here we show that nanomolar Doxorubicin treatment of neuroblastoma cells caused: (a) dose-dependent over-ubiquitination of a specific set of proteins in the absence of measurable inhibition of proteasome, (b) protein ubiquination patterns similar to those with Bortezomib, a proteasome inhibitor, (c) depletion and loss of activity of ubiquitinated enzymes such as lactate dehydrogenase and α-enolase, and (d) a decrease in HSP27 solubility, probably a consequence of its binding to denatured proteins. These data strongly reinforce the hypothesis that Doxorubicin may also exert its effect by damaging proteins.

Pediatric genitourinary tumors

PURPOSE OF REVIEW

To review the 2008-2009 literature on pediatric genitourinary tumors and highlight the most significant publications.

RECENT FINDINGS

New techniques such as gene expression profiling, PET, nephron-sparing surgery, and stem cell transplantation are being incorporated into contemporary treatments for pediatric patients with genitourinary tumors. The WTX gene is the most commonly mutated gene in Wilms tumor, and its product enhances Wilms tumor gene 1-mediated transcription. Germline WTX mutations cause an X-linked sclerosing bone dysplasia but do not appear to predispose to Wilms tumor formation. Protocadherin gene clusters on chromosome 5q31 may act as tumor suppressors. In rhabdomyosarcoma, ILK and platelet-derived growth factor receptor-A join the paired box gene 7 and 3-forkhead box O1 fusions as potential therapeutic targets, and muscle-specific microRNAs offer promise as adjuvant therapy. Despite the high cure rate of Wilms tumor, long-term survivors remain at risk of death from various causes.

SUMMARY

In general, the prognosis for patients with pediatric genitourinary tumors is favorable. The elucidation of the molecular abnormalities in these tumors is determining risk stratification, treatment strategies, and candidates for new drug development.

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.

Proteasome inhibition: a new therapeutic strategy to cancer treatment

The ubiquitin-proteasome system is a major pathway for protein degradation. Targeting this pathway using proteasome inhibitors represents a novel approach for the treatment of cancer. Proteasome inhibitors lower cell proliferation and induce apoptosis in solid and hematologic malignancies through multiple mechanisms, including stabilization of cell cycle regulators and pro-apoptotic factors, stimulation of bone morphogenetic protein signaling, inhibition of protein translation, and sensitization to ligand-induced apoptosis. In this connection, proteasome inhibition activates macroautophagy, a compensatory protein degradation system, as well as other pro-survival signaling pathways. Inhibition of these auto-protective responses sensitizes cancer cells to the anti-proliferative effects of proteasome inhibitors.

Initial response to treatment was highly associated with the prognosis of childhood rhabdomyosarcoma: a retrospective analysis of a single center experience in Korea

PURPOSE

Following the introduction of a multimodal approach to diagnosis and treatment, the prognosis of rhabdomyosarcoma (RMS) has markedly improved over the last three decades. However, there are few data on treatment outcomes in Korean patients.

MATERIALS AND METHODS

We performed a retrospective analysis of 77 patients with RMS diagnosed and treated at Seoul National University Children's Hospital between 1986 and 2005.

RESULTS

The overall 5-year survival and event-free survival rates for all patients were 77% and 59%, respectively. The Intergroup Rhabdomyosarcoma Study clinical grouping and initial response to treatment (20-week response) were important prognostic factors.

CONCLUSIONS

The outcome of childhood RMS was closely associated with the initial staging and the initial response to treatment. Modulating therapies according to initial responses and risk factors is critical, and new treatment strategies for high-risk patients are needed.

PAX3-FKHR sensitizes human alveolar rhabdomyosarcoma cells to camptothecin-mediated growth inhibition and apoptosis

Patients with alveolar rhabdomyosarcoma (ARMS) have poorer response to conventional chemotherapy and lower survival rates than those with embryonal RMS (ERMS). By high-throughput screening, we identified camptothecin as an ARMS-selective inhibitor. Camptothecin more efficiently inhibited proliferation and induced apoptosis in Rh30 (ARMS) than RD (ERMS) cells. Ectopic expression of the PAX3-FKHR (PF) fusion protein in RD cells significantly increased sensitivity, whereas siRNA knockdown of PF decreased sensitivity of Rh30 cells to camptothecin. The sensitization required a transcriptionally active PF, and camptothecin downregulated levels of PF protein. These findings suggest that it is feasible to develop agents that preferentially block the growth of ARMS.

Sorafenib inhibits tumor growth and vascularization of rhabdomyosarcoma cells by blocking IGF-1R-mediated signaling

The growth of many soft tissue sarcomas is dependent on aberrant growth factor signaling, which promotes their proliferation and motility. With this in mind, we evaluated the effect of sorafenib, a receptor tyrosine kinase inhibitor, on cell growth and apoptosis in sarcoma cell lines of various histological subtypes. We found that sorafenib effectively inhibited cell proliferation in rhabdomyosarcoma, synovial sarcoma and Ewing’s sarcoma with IC₅₀ values <5 μM. Sorafenib effectively induced growth arrest in rhabdomyosarcoma cells, which was concurrent with inhibition of Akt and Erk signaling. Studies of ligand-induced phosphorylation of Erk and Akt in rhabdomyosarcoma cells showed that insulin-like growth factor-1 is a potent activator, which can be blocked by treatment with sorafenib. In vivo sorafenib treatment of rhabdomyosarcoma xenografts had a significant inhibitory effect on tumor growth, which was associated with inhibited vascularization and enhanced necrosis in the adjacent tumor stroma. Our results demonstrate that in vitro and in vivo growth of rhabdomyosarcoma can be suppressed by treatment with sorafenib, and suggests the possibilities of using sorafenib as a potential adjuvant therapy for the treatment of rhabdomyosarcoma.