Rhabdomyosarcoma: An Overview

Case report: a diagnostically challenging conjunctival mass caused by the Epstein-Barr virus

We present a paediatric case of infectious mononucleosis in a 13-year old, manifesting with follicular conjunctivitis and a conjunctival mass in one eye with no evidence of leucocytosis on the blood count. The diagnosis was confirmed following surgical excision and biopsy. The case represented a diagnostic challenge due to its atypism and given the steady increase in the prevalence of EBV-related ocular diseases in the last years, this report can serve as an example to prompt earlier serological tests to identify the aetiology in similar cases. This is important because EBV can be treated with acyclovir early in the active viral phase.

GLI inhibitor GANT-61 diminishes embryonal and alveolar rhabdomyosarcoma growth by inhibiting Shh/AKT-mTOR axis

Rhabdomyosarcoma (RMS) typically arises from skeletal muscle. Currently, RMS in patients with recurrent and metastatic disease have no successful treatment. The molecular pathogenesis of RMS varies based on cancer sub-types. Some embryonal RMS but not other sub-types are driven by sonic hedgehog (Shh) signaling pathway. However, Shh pathway inhibitors particularly smoothened inhibitors are not highly effective in animals. Here, we show that Shh pathway effectors GLI1 and/or GLI2 are over-expressed in the majority of RMS cells and that GANT-61, a specific GLI1/2 inhibitor dampens the proliferation of both embryonal and alveolar RMS cells-derived xenograft tumors thereby blocking their growth. As compared to vehicle-treated control, about 50% tumor growth inhibition occurs in mice receiving GANT-61 treatment. The proliferation inhibition was associated with slowing of cell cycle progression which was mediated by the reduced expression of cyclins D1/2/3 & E and the concomitant induction of p21. GANT-61 not only reduced expression of GLI1/2 in these RMS but also significantly diminished AKT/mTOR signaling. The therapeutic action of GANT-61 was significantly augmented when combined with chemotherapeutic agents employed for RMS therapy such as temsirolimus or vincristine. Finally, reduced expression of proteins driving epithelial mesenchymal transition (EMT) characterized the residual tumors.

Eribulin synergizes with Polo-like kinase 1 inhibitors to induce apoptosis in rhabdomyosarcoma

Eribulin, a novel microtubule-interfering drug, was recently shown to exhibit high antitumor activity in vivo against various pediatric cancers. Here, we identify a novel synthetic lethal interaction of Eribulin together with Polo-like kinase 1 (PLK1) inhibitors against rhabdomyosarcoma (RMS) in vitro and in vivo. Eribulin and the PLK1 inhibitor BI 2536 at subtoxic concentrations synergize to induce apoptosis in RMS cells as confirmed by calculation of combination index (CI). Also, Eribulin/BI 2536 co-treatment is significantly more effective than monotherapy to reduce cell viability and inhibit colony formation of RMS cells. Similarly, Eribulin and BI 2536 act in concert to trigger apoptosis in a primary, patient-derived ARMS culture, underscoring the clinical relevance of this combination. Importantly, Eribulin and BI 2536 cooperate to suppress tumor growth in an in vivo model of RMS. On molecular grounds, Eribulin/BI 2536 co-treatment causes profound mitotic arrest, which is critically required for synergism, since inhibition of mitotic arrest by CDK1 inhibitor RO-3306 abolishes Eribulin/BI 2536-mediated apoptosis. Eribulin and BI 2536 cooperate to activate caspase-9, -3 and -8, which is necessary for apoptosis induction, since the broad-range caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk) reduces Eribulin/BI 2536-induced apoptosis significantly, yet partially. Intriguingly, knockdown of endonuclease G (ENDOG) also significantly inhibits Eribulin/BI 2536-triggered apoptosis, demonstrating the involvement of both caspase-dependent and -independent effector pathways. Synergistic induction of apoptosis is similarly found for Eribulin/BI 2536 co-treatment in neuroblastoma cells and for the combination of vincristine (another antimicrotubule chemotherapeutic) with Poloxin (another PLK1 inhibitor), thus pointing to a broader significance of this concomitant microtubule- and PLK1-targeting strategy for pediatric oncology. In conclusion, the identification of a novel synthetic lethality by dual targeting of mitosis using microtubule-interfering and PLK1-targeted drugs, i.e. Eribulin and BI 2536, has important implications for the development of more effective treatment strategies for RMS.

Preclinical evaluation of perifosine as a potential promising anti-rhabdomyosarcoma agent

Rhabdomyosarcoma (RMS) is a highly malignant and metastatic pediatric cancer that arises from the skeletal muscle. Recent studies have identified an important role of AKT signaling in RMS progression. In the current study, we investigated the activity of perifosine, an oral alkylphospholipid AKT inhibitor, against human RMS cells (RD and Rh-30 lines) both in vivo and in vitro, and studied the underlying mechanisms. We showed that perifosine significantly inhibited RMS cell growth in concentration- and time-dependent manners. Meanwhile, perifosine induced dramatic apoptosis in RMS cells. At the signaling level, perifosine blocked AKT activation, while inducing reactive oxygen species (ROS) production as well as JNK and P38 phosphorylations in RMS cells. Restoring AKT activation by introducing a constitutively active-AKT (CA-AKT) only alleviated (not abolished) perifosine-induced cytotoxicity in RD cells. Yet, the ROS scavenger N-acetyl cysteine (NAC) as well as pharmacological inhibitors against JNK (SP-600125) or P38 (SB-203580) suppressed perifosine-induced cytotoxicity in RMS cells. Thus, perifosine induces growth inhibition and apoptosis in RMS cells through mechanisms more than just blocking AKT. In vivo, oral administration of perifosine significantly inhibited growth of Rh-30 xenografts in severe combined immunodeficient (SCID) mice. Our data indicate that perifosine might be further investigated as a promising anti-RMS agent.

The novel tubulin polymerization inhibitor MHPT exhibits selective anti-tumor activity against rhabdomyosarcoma in vitro and in vivo

The dose-limiting toxicity caused by standard chemotherapy has become a major roadblock to successful rhabdomyosarcoma chemotherapy. By screening a thiazolidinone library including 372 compounds, a novel synthetic compound, 2-((4-hydroxyphenyl)imino)-5-(3-methoxybenzylidene)thiazolidin-4-one (MHPT), was identified as a potent and selective anti-rhabdomyosarcoma agent. MHPT inhibited 50% of the growth of the rhabdomyosarcoma cell lines RD and SJ-RH30 at 0.44 μM and 1.35 μM, respectively, while displaying no obvious toxicity against normal human fibroblast cells at 100 μM. Further investigation revealed that MHPT suppressed the polymerization of tubulin, leading to rhabdomyosarcoma cell growth arrest at the G2/M phase followed by apoptosis. In vivo, MHPT inhibited tumor growth by 48.6% relative to the vehicle control after 5 intraperitoneal injections of 40 mg/kg without appreciable toxicity to normal tissues and systems in an RD xenograft mouse model, while vincristine caused lethal toxicity when similar growth inhibition was achieved. As a moderate tubulin polymerization inhibitor compared with vincristine, MHPT requires a more dynamic tubulin to exert its cytotoxicity, which is a situation that only exists in cancer cells. This attribute may account for the low toxicity of MHPT in normal cells. Our data suggest that MHPT has the potential to be further developed into a selective anti-rhabdomyosarcoma drug with low toxicity.

Respiratory Distress Secondary to Rhabdomyosarcoma of the Tongue and Co-existent Choanal Atresia

Whilst rhabdomyosarcoma (RMS) is the third most common solid tumour in children, congenital RMS of the tongue is extremely rare and usually present as painless progressive mass since birth (Dagher and Helman in Oncologist 4:34-44, 1999; Childs and Goudy in Int J Pediatr Otorhinolaryngol 5:126-128, 2010). In neonates, presentation with respiratory distress is unexpected as neonates are preferential nasal breathers and restricted oral breathing due to tumour usually poses no problem. We herein report a case of rhabdomyosarcoma of the tongue with co-existent unilateral choanal atresia, presenting with respiratory distress. The baby developed upper respiratory tract infection following which developed severe respiratory distress. Airway symptoms were precipitated as there was combined obstruction of both the nostrils due to infection or adenoid enlargement and unilateral chonal atresia. Treatment of respiratory distress in the presence of RMS and bilateral nasal pathology must first prioritise the security of the airway, before taking a multi-factorial approach to the therapy of the lingual mass (Childs and Goudy in Int J Pediatr Otorhinolaryngol 5:126-128, 2010). This case illustrates the importance of vigilance with respect to co-existent nasal pathology, in order to avoid the occurrence of complete airway obstruction. We therefore feel that any diagnosis of lingual RMS should warrant a formal examination of both nasal cavities.

Decoding the ‘embryonic’ nature of embryonal rhabdomyosarcoma

Embryonal rhabdomyosarcoma is one of the major defined histologic variants of rhabdomyosarcoma that is mainly reported in children. The histologic appearance of this neoplastic entity recapitulates normal myogenesis. The tumor cells variably exhibit the different cellular phases of myogenesis ranging from undifferentiated mesenchymal cells to elongated myoblasts, multinucleated myotubes and differentiated muscle fibers. The carefully orchestrated embryonic signaling pathways that are involved in myogenesis, conceivably also result in the genesis of rhabdomyosarcoma; albeit as a corollary to an imbalance. We have attempted to review the pathogenesis of embryonal rhabdomyosarcoma in an endeavor to understand better, how closely it is linked to normal myogenesis in terms of its molecular dynamics and histologic presentation.

Ovarian embryonal rhabdomyosarcoma is a rare manifestation of the DICER1 syndrome

Embryonal rhabdomyosarcoma (ERMS), a soft tissue sarcoma, is one of the most common pediatric cancers. Certain ERMSs are associated with the DICER1 syndrome, a tumor predisposition syndrome caused by germ-line DICER1 mutations. Characteristic somatic mutations have also been identified in DICER1-associated tumor types. These "hotspot" mutations affect the catalytic activity of the DICER1 ribonuclease IIIb domain. Primary ovarian ERMS (oERMS) is extremely rare. We present a case of a 6-year-old girl with an oERMS harboring 2 DICER1 mutations. The girl also exhibited other DICER1 phenotypes: cystic nephroma (CN) and multinodular goiter. Somatic investigations of the CN identified a hotspot DICER1 mutation different from that in the oERMS. Significantly, the CN presented at 12 years of age, which is much older than the previously reported age range of susceptibility. This report documents the occurrence of DICER1 mutations in a case of oERMS, expanding the spectrum of DICER1-associated tumors.

Dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 synergizes with chloroquine to induce apoptosis in embryonal rhabdomyosarcoma

Aberrant activation of the phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway has been reported for rhabdomyosarcoma (RMS) and is implicated in survival of tumor cells as well as therapeutic resistance. In the present study, we searched for combination therapies with the dual PI3K/mTOR inhibitor NVP-BEZ235 (BEZ235) in RMS. Here, we identify a synthetic lethal interaction of BEZ235 together with the lysosomotropic agent chloroquine (CQ), which is effective against embryonal rhabdomyosarcoma (ERMS). BEZ235 and CQ at subtoxic concentrations synergize to induce apoptosis in ERMS cells, as confirmed by calculation of combination index (CI). BEZ235 and CQ cooperate to activate caspase-9, -3 and -8, which is crucial for apoptosis induction given that the broad-range caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk) blocks BEZ235/CQ-induced apoptosis. Additionally, pharmacological inhibition of lysosomal enzymes significantly reduces BEZ235/CQ-induced apoptosis, indicating concomitant activation of the lysosomal compartment. Importantly, BEZ235/CQ-induced apoptosis is significantly inhibited by antioxidants, implying that increased oxidative stress contributes to BEZ235/CQ-induced cell death. Importantly, our molecular studies reveal that BEZ235/CQ-induced apoptosis is mediated by cooperative downregulation of the antiapoptotic BCL-2 family protein MCL-1, since stabilization of MCL-1 by expression of a non-degradable MCL-1 phospho-defective mutant significantly decreases BEZ235/CQ-induced apoptosis. Also, overexpression of antiapoptotic BCL-2 leads to a significant reduction of BEZ235/CQ-induced apoptosis, emphasizing that an intact mitochondrial pathway of apoptosis is required for BEZ235/CQ-induced cell death. This identification of a synthetic lethality of BEZ235 and CQ has important implications for the development of molecular targeted therapies for RMS.

John M. Head and neck sarcomas: the UCLA experience

PURPOSE

To profile the clinical presentation, subtype distribution, and treatment results of sarcomas of the head and neck at a single tertiary academic center over an 11-year period.

MATERIALS AND METHODS

A retrospective review was performed by examining the records and reviewing the pathology of 186 patients with head and neck sarcomas treated at UCLA Medical Center from 2000 to 2011.

RESULTS

The mean age of the study population was 49 ± 22 years. 58% of the patients were male and 42% were female. Median duration of follow-up for the entire group was 18.5 months. The most common presenting symptom was a mass lesion in 59.9% of patients. The nasal cavity/sinus was the most common presenting site seen in 22% of patients. Solitary fibrous tumor/hemangiopericytoma was the most common subtype. 15% of patients had evidence of prior radiation exposure. 26.3% of tumors were greater than 5 cm and 35.5% were high-grade. Margins were positive in 31.2% of patients. Lymph node metastasis was rare at 6.5%. Perineural invasion was identified in 6.5%. Among all subtypes, 5-year recurrence-free survival and overall survival were 50% and 49%, respectively. Multivariate analysis demonstrated that grade and margin status were predictors of recurrence-free survival while grade and age affected overall survival.

CONCLUSIONS

Head and neck sarcomas are a rare entity frequently presenting as a mass lesion. In our series, lesions tended to be high-grade with a significant portion of surgical specimens having positive margins. Grade and margin status were the most important predictors of survival.

Brachytherapy in children with rhabdomyosarcomas of the nasolabial fold

BACKGROUND

Rhabdomyosarcomas (RMS) of the nasolabial fold can be difficult to manage surgically due to functional and cosmetic limitations. Therefore, brachytherapy (BT) has been proposed to improve local control while limiting the volume of irradiation as well as the extent of the surgical excision.

MATERIALS AND METHODS

Sixteen pediatric cases with RMS of the nasolabial fold treated from 1971 to 2005 were retrospectively reviewed.

RESULTS

Median follow-up was 4.4 years (1.7-33). Half of the patients were male and their age at diagnosis ranged from 4 months to 13.5 years. Histological subtypes included 10 embryonal and 6 alveolar RMS. Initial treatment consisted of induction multi-agent chemotherapy in all cases. In 12 patients, BT was combined with local excision (4 complete resections, 1 with macroscopic residual disease, and 7 with microscopic disease). Low dose-rate brachytherapy was performed in all cases according to the Paris system, using plastic catheters implanted per-operatively. The doses delivered ranged from 50 to 70 Gy, depending on chemotherapy response, and surgical margin status. 10 patients relapsed: 4 local, 6 regional, and 2 metastatic failures were reported. The median time to relapse was 6.5 months. At the time of analysis eight patients were alive and four had died. Four cases, under palliative care at last check-up, were lost to follow-up.

CONCLUSION

BT provided an acceptable local control rate, but the poor regional control of these cases may suggest a need for more aggressive management of cervical regional lymph node regions in RMS of the nasolabial fold.

Primary cilia control hedgehog signaling during muscle differentiation and are deregulated in rhabdomyosarcoma

The primary cilium acts as a cellular antenna, transducing diverse signaling pathways, and recent evidence suggests that primary cilia are important in development and cancer. However, a role for cilia in normal muscle development and rhabdomyosarcoma (RMS) has not been explored. Here we implicate primary cilia in proliferation, hedgehog (Hh) signaling, and differentiation of skeletal muscle cells. Cilia and Hh signaling are highly dynamic during the differentiation of myoblasts. We show that cilia are assembled during the initial stages of myogenic differentiation but disappear as cells progress through myogenesis, concomitant with the destruction of proteins critical for cilia assembly and shortly after the Hh effector, Gli3, leaves the cilium. Importantly, we show that ablation of primary cilia strongly suppresses Hh signaling and myogenic differentiation while enhancing proliferation. Interestingly, our data further indicate that both cilia assembly and Hh signaling are deregulated in RMS, and cilia respond to Hh ligand in certain subsets of RMS cells but not others. Together, these findings provide evidence for an essential role for both primary cilia assembly and disassembly in the control of Hh signaling and early differentiation in muscle cells. We suggest that the temporally orchestrated destruction of centrosomal and ciliary proteins is a necessary antecedent for removal of the primary cilium and cessation of Hh signaling during myogenic differentiation. Additionally, our results further stratify RMS populations and highlight cilia assembly and disassembly as potential RMS drug targets.

Pituitary metastasis of rhabdomyosarcoma: a case report and review of the literature

INTRODUCTION

The pituitary gland is an uncommon site for metastases, in particular from rhabdomyosarcoma. Some authors have reported a recent increase in the incidence of metastases at infrequent sites, such as brain or bone, probably due to the expanded treatment options and the resulting improved survival. Treatment options are limited, but must be discussed and adapted to the patient profile.

CASE PRESENTATION

We report the case of a 17-year-old Arabic man, diagnosed with alveolar rhabdomyosarcoma of the left shoulder, who, after several cycles of chemotherapy, presented symptoms and signs of pituitary dysfunction. To the best of our knowledge, it is the first case described.

CONCLUSIONS

Pituitary metastasis of rhabdomyosarcoma is a rare situation, which must be actively researched to have access to an optimal therapeutic approach.

miR-203, a tumor suppressor frequently down-regulated by promoter hypermethylation in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma found in children and young adults. It is characterized by the expression of a number of skeletal muscle-specific proteins, including MyoD and muscle α-actin. However, unlike normal myoblasts, RMS cells differentiate poorly both in vivo and in culture. As microRNAs are known to regulate tumorigenesis, intensive efforts have been made to identify microRNAs that are involved in RMS development. In this work, we found that miR-203 was frequently down-regulated by promoter hypermethylation in both RMS cell lines and RMS biopsies and could be reactivated by DNA-demethylating agents. Re-expression of miR-203 in RMS cells inhibited their migration and proliferation and promoted terminal myogenic differentiation. Mechanistically, miR-203 exerts its tumor-suppressive effect by directly targeting p63 and leukemia inhibitory factor receptor in RMS cells, which promotes myogenic differentiation by inhibiting the Notch and the JAK1/STAT1/STAT3 pathways, respectively. Our work reveals that miR-203 functions as a tumor suppressor in RMS development.

Pan-mammalian target of rapamycin (mTOR) inhibitor AZD8055 primes rhabdomyosarcoma cells for ABT-737-induced apoptosis by down-regulating Mcl-1 protein

The PI3K/mammalian Target of Rapamycin (mTOR) pathway is often aberrantly activated in rhabdomyosarcoma (RMS) and represents a promising therapeutic target. Recent evaluation of AZD8055, an ATP-competitive mTOR inhibitor, by the Preclinical Pediatric Testing Program showed in vivo antitumor activity against childhood solid tumors, including RMS. Therefore, in the present study, we searched for AZD8055-based combination therapies. Here, we identify a new synergistic lethality of AZD8055 together with ABT-737, a BH3 mimetic that antagonizes Bcl-2, Bcl-xL, and Bcl-w but not Mcl-1. AZD8055 and ABT-737 cooperate to induce apoptosis in alveolar and embryonal RMS cells in a highly synergistic fashion (combination index < 0.2). Synergistic induction of apoptosis by AZD8055 and ABT-737 is confirmed on the molecular level, as AZD8055 and ABT-737 cooperate to trigger loss of mitochondrial membrane potential, activation of caspases, and caspase-dependent apoptosis that is blocked by the pan-caspase inhibitor Z-VAD-fmk. Similar to AZD8055, the PI3K/mTOR inhibitor NVP-BEZ235, the PI3K inhibitor NVP-BKM120 and Akt inhibitor synergize with ABT-737 to trigger apoptosis, whereas no cooperativity is found for the mTOR complex 1 inhibitor RAD001. Interestingly, molecular studies reveal a correlation between the ability of different PI3K/mTOR inhibitors to potentiate ABT-737-induced apoptosis and to suppress Mcl-1 protein levels. Importantly, knockdown of Mcl-1 increases ABT-737-induced apoptosis similar to AZD8055/ABT-737 cotreatment. This indicates that AZD8055-mediated suppression of Mcl-1 protein plays an important role in the synergistic drug interaction. By identifying a novel synergistic interaction of AZD8055 and ABT-737, our findings have important implications for the development of molecular targeted therapies for RMS.

Characterization of Wnt/β-catenin signaling in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and accounts for about 5% of all malignant paediatric tumours. β-Catenin, a multifunctional nuclear transcription factor in the canonical Wnt signaling pathway, is active in myogenesis and embryonal somite patterning. Dysregulation of Wnt signaling facilitates tumour invasion and metastasis. This study characterizes Wnt/β-catenin signaling and functional activity in paediatric embryonal and alveolar RMS. Immunohistochemical assessment of paraffin-embedded tissues from 44 RMS showed β-catenin expression in 26 cases with cytoplasmic/membranous expression in 9/14 cases of alveolar RMS, and 15/30 cases of embryonal RMS, whereas nuclear expression was only seen in 2 cases of embryonal RMS. The potential functional significance of β-catenin expression was tested in four RMS cell lines, two derived from embryonal (RD and RD18) RMS and two from alveolar (Rh4 and Rh30) RMS. Western blot analysis demonstrated the expression of Wnt-associated proteins including β-catenin, glycogen synthase kinase-3β, disheveled, axin-1, naked, LRP-6 and cadherins in all cell lines. Cell fractionation and immunofluorescence studies of the cell lines (after stimulation by human recombinant Wnt3a) showed reduced phosphorylation of β-catenin, stabilization of the active cytosolic form and nuclear translocation of β-catenin. Reporter gene assay demonstrated a T-cell factor/lymphoid-enhancing factor-mediated transactivation in these cells. In response to human recombinant Wnt3a, the alveolar RMS cells showed a significant decrease in proliferation rate and induction of myogenic differentiation (myogenin, MyoD1 and myf5). These data indicate that the central regulatory components of canonical Wnt/β-catenin signaling are expressed and that this pathway is functionally active in a significant subset of RMS tumours and might represent a novel therapeutic target.

Management and outcome of 239 adolescent and adult rhabdomyosarcoma patients

Adult rhabdomyosarcoma (RMS) is a rare tumor that has inferior outcome compared to younger patient population. The present work aims to study the age-related differences in management of adolescents and adults with RMS. Under an institutional review board-approved protocol, we retrospectively analyzed 239 patients, 10 years of age and greater, diagnosed with RMS at MD Anderson Cancer Center from 1957 through 2003. Of the 239 patients, 163 patients were nonmetastatic with a median overall survival (OS) of 3.8 years (95% CI 2.8-7.6). In the multivariate analysis, age >50 was significantly associated with shorter OS and recurrence-free survival (RFS) for primary patients. Metastases were present in 76 patients, the median OS was 1.4 years. Approximately 13% of metastatic patients <50 years old had a long-term survival exceeding 15 years. Multimodality therapy, including surgery, radiotherapy, and chemotherapy was significantly associated with longer OS in primary and metastatic patients. Use of bi- and triple modality treatment decreased in metastatic patients over 50 years of age compared to younger patients. RMS in adolescents and adults has a poor outcome compared with younger individuals. Increased use of multidisciplinary therapy may improve older patient clinical outcome.

Obatoclax (GX15-070) triggers necroptosis by promoting the assembly of the necrosome on autophagosomal membranes

Obatoclax (GX15-070), a small-molecule inhibitor of antiapoptotic Bcl-2 proteins, has been reported to trigger cell death via autophagy. However, the underlying molecular mechanisms have remained elusive. Here, we identify GX15-070-stimulated assembly of the necrosome on autophagosomal membranes as a key event that connects GX15-070-stimulated autophagy to necroptosis. GX15-070 predominately induces a non-apoptotic form of cell death in rhabdomyosarcoma cells, as evident by lack of typical apoptotic features such as DNA fragmentation or caspase activation and by insensitivity to the broad-range caspase inhibitor zVAD.fmk. Instead, GX15-070 triggers massive accumulation of autophagosomes, which are required for GX15-070-induced cell death, as blockade of autophagosome formation by silencing of Atg5 or Atg7 abolishes GX15-070-mediated cell death. Co-immunoprecipitation studies reveal that GX15-070 stimulates the interaction of Atg5, a constituent of autophagosomal membranes, with components of the necrosome such as FADD, RIP1 and RIP3. This GX15-070-induced assembly of the necrosome on autophagosomes occurs in a Atg5-dependent manner, as knockdown of Atg5 abrogates formation of this complex. RIP1 is necessary for GX15-070-induced cell death, as both genetic and pharmacological inhibition of RIP1 by shRNA-mediated knockdown or by the RIP1 inhibitor necrostatin-1 blocks GX15-070-induced cell death. Similarly, RIP3 knockdown rescues GX15-070-mediated cell death and suppression of clonogenic survival. Interestingly, RIP1 or RIP3 silencing has no effect on GX15-070-stimulated autophagosome formation, underlining that RIP1 and RIP3 mediate cell death downstream of autophagy induction. Of note, GX15-070 significantly suppresses tumor growth in a RIP1-dependent manner in the chorioallantoic membrane model in vivo. In conclusion, GX15-070 triggers necroptosis by promoting the assembly of the necrosome on autophagosomes. These findings provide novel insights into the molecular mechanisms of GX15-070-induced non-apoptotic cell death.

Synthetic lethal interaction between PI3K/Akt/mTOR and Ras/MEK/ERK pathway inhibition in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) frequently exhibits concomitant activation of the PI3K/Akt/mTOR and the Ras/MEK/ERK pathways. Therefore, we investigated whether pharmacological cotargeting of these two key survival pathways suppresses RMS growth. Here, we identify a synthetic lethal interaction between PI3K/Akt/mTOR and Ras/MEK/ERK pathway inhibition in RMS. The dual PI3K/mTOR inhibitor PI103 and the MEK inhibitor UO126 synergize to trigger apoptosis in several RMS cell lines in a highly synergistic manner (combination index <0.1), whereas either agent alone induces minimal cell death. Similarly, genetic knockdown of p110α and MEK1/2 cooperates to induce apoptosis. Molecular studies reveal that cotreatment with PI103/UO126 cooperates to suppress PI3K/Akt/mTOR and Ras/MEK/ERK signaling, whereas either compound alone is not only less effective to inhibit signaling, but even cross-activates the other pathway. Accordingly, PI103 alone increases ERK phosphorylation, while UO126 enhances Akt phosphorylation, consistent with negative crosstalks between these two signaling pathways. Furthermore, PI103/UO126 cotreatment causes downregulation of several antiapoptotic proteins such as XIAP, Bcl-xL and Mcl-1 as well as increased expression and decreased phosphorylation of the proapoptotic protein BimEL, thus shifting the balance towards apoptosis. Consistently, PI103/UO126 cotreatment cooperates to trigger Bax activation, loss of mitochondrial membrane potential, caspase activation and caspase-dependent apoptosis. This identification of a synthetic lethal interaction between PI3K/mTOR and MEK inhibitors has important implications for the development of novel treatment strategies in RMS.

Rhabdomyosarcoma in adrenal region of a child with hypertension and fever: a case report and literature review

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children but rarely involves the adrenal. We describe a case of alveolar rhabdomyosarcoma (ARMS) of the right adrenal in a 5-year-old boy with a characteristic history of hypertension and recurrent fever. On surveillance imaging, a right adrenal mass was incidentally detected, and a right adrenalectomy was subsequently performed. After the surgery, the fever disappeared simultaneously, and the blood pressure gradually returned to normal level. This is the first reported case in children.

A Comparative Review of Canine and Human Rhabdomyosarcoma With Emphasis on Classification and Pathogenesis

Rhabdomyosarcomas are a diverse group of malignant mesenchymal neoplasms exhibiting variable levels of differentiation toward skeletal myocytes. Neoplastic cells may resemble relatively undifferentiated myoblasts, satellite cells, or more differentiated elongated spindle cells and multicellular myotubes. In veterinary medicine, classification into subtypes and variants is based on an outdated system derived from human pathology and is solely based on histologic characteristics. In contrast, classification of human rhabdomyosarcoma is based on histologic, immunohistochemical, and molecular diagnostic techniques, and subclassification has clinical and prognostic relevance. Relevance of tumor subtyping has not been established in veterinary medicine. Recent discoveries of components of the molecular pathogenesis and genomes of human rhabdomyosarcomas have led to new diagnostic techniques and revisions of the human classification system. The current classification system in veterinary medicine is reviewed in light of these changes. Diagnosis of rhabdomyosarcoma using histopathology, electron microscopy, and the clinical aspects of human and canine rhabdomyosarcomas is compared. The clinical features and biologic behavior of canine rhabdomyosarcomas are compared with canine soft tissue sarcomas.

Investigation of PAX3/7-FKHR fusion genes and IGF2 gene expression in rhabdomyosarcoma tumors

The purpose of our study was to investigate the prevalence of the PAX3/7-FKHR fusion genes and quantify the IGF2 gene expression in rhabdomyosarcoma (RMS) samples. Soft tissue sarcomas account 5% of childhood cancers and 50% of them are RMS. Morphological evaluation of pediatric RMS has defined two histological subtypes, embryonal (ERMS) and alveolar (ARMS). Chromosomal analyses have demonstrated two translocations associated with ARMS, resulting in the PAX3/7-FKHR rearrangements. Reverse transcriptase-polymerase chain reaction (RT-PCR) is extremely useful in the diagnosis of ARMS positive for these rearrangements. Additionally, several studies have shown a significant involvement of IGF pathway in the pathogenesis of RMS. The presence of PAX3/7-FKHR gene fusions was studied in 25 RMS samples from patients attending the IOP-GRAACC/UNIFESP and three RMS cell lines by RT-PCR. IGF2 gene expression was quantified by qPCR and related with clinic pathological parameters. Of the 25 samples, nine (36%) were ARMS and 16 (64%) were ERMS. PAX3/7-FKHR gene fusions expression was detected in 56% of ARMS tumor samples. IGF2 overexpression was observed in 80% of samples and could indicate an important role of this pathway in RMS biology.

Genitourinary rhabdomyosarcoma: lessons from a developing-world series

OBJECTIVE

The objective was to retrospectively review a large series of pediatric patients with genitourinary rhabdomyosarcoma from a developing country.

METHODS

A total of 49 children were treated over a 47-year period (1961-2008). Analysis of the clinical presentation, demographics, surgical records, histological results, and oncological management was performed. The patients were analyzed as a whole and also in 2 separate groups (pre- and post-1992).

RESULTS

The median age at clinical presentation was 3½ years. The majority (59%) of patients were Intergroup Rhabdomyosarcoma Study group 3, with locally advanced disease at presentation. Twenty (41%) of the 49 patients presented with primary tumors greater than 10 cm in diameter. Sixteen (33%) of the 49 patients had positive regional lymph nodes at presentation. The overall survival of the series was 30 (65%) of 46. The survival for those treated after 1992 in Intergroup Rhabdomyosarcoma Study group 3 was superior (P = .04) to those treated before 1992 (80% vs 56%).

CONCLUSION

Children in this large African series of genitourinary rhabdomyosarcoma present with greater locally advanced disease (node positive and bulky disease) when compared with the developed world. Improvements in the last 2 decades in local surgical and oncological care have led to an improvement in survival in children with locally advanced disease.

RIP1 protein-dependent assembly of a cytosolic cell death complex is required for inhibitor of apoptosis (IAP) inhibitor-mediated sensitization to lexatumumab-induced apoptosis

Searching for new strategies to trigger apoptosis in rhabdomyosarcoma (RMS), we investigated the effect of two novel classes of apoptosis-targeting agents, i.e. monoclonal antibodies against TNF-related apoptosis-inducing ligand (TRAIL) receptor 1 (mapatumumab) and TRAIL receptor 2 (lexatumumab) and small-molecule inhibitors of inhibitor of apoptosis (IAP) proteins. Here, we report that IAP inhibitors synergized with lexatumumab, but not with mapatumumab, to reduce cell viability and to induce apoptosis in several RMS cell lines in a highly synergistic manner (combination index <0.1). Cotreatment-induced apoptosis was accompanied by enhanced activation of caspase-8, -9, and -3; loss of mitochondrial membrane potential; and caspase-dependent apoptosis. In addition, IAP inhibitor and lexatumumab cooperated to stimulate the assembly of a cytosolic complex containing RIP1, FADD, and caspase-8. Importantly, knockdown of RIP1 by RNA interference prevented the formation of the RIP1·FADD·caspase-8 complex and inhibited subsequent activation of caspase-8, -9, and -3; loss of mitochondrial membrane potential; and apoptosis upon treatment with IAP inhibitor and lexatumumab. In addition, RIP1 silencing rescued clonogenic survival of cells treated with the combination of lexatumumab and IAP inhibitor, thus underscoring the critical role of RIP1 in cotreatment-induced apoptosis. By comparison, the TNFα-blocking antibody Enbrel had no effect on IAP inhibitor/lexatumumab-induced apoptosis, indicating that an autocrine TNFα loop is dispensable. By demonstrating that IAP inhibitors and lexatumumab synergistically trigger apoptosis in a RIP1-dependent but TNFα-independent manner in RMS cells, our findings substantially advance our understanding of IAP inhibitor-mediated regulation of TRAIL-induced cell death.

Rhabdomyosarcoma of the trachea: first reported case treated with proton beam therapy

Objective:

We report a case of rhabdomyosarcoma of the trachea in a 14-month-old child, and we present the first reported use of proton beam therapy for this tumour.

Case report:

A 14-month-old girl presented acutely with a seven-day history of biphasic stridor. Emergency endoscopic debulking of a posterior tracheal mass was undertaken. Histological examination revealed an embryonal rhabdomyosarcoma with anaplasia. Multimodality therapy with surgery and chemotherapy was administered in the UK, and proton beam therapy in the USA.

Conclusion:

Only three cases of rhabdomyosarcoma of the trachea have previously been reported in the world literature. This is the first reported case of treatment of this tumour with proton beam therapy. Compared with conventional radiotherapy, proton beam therapy may confer improved long-term outcome in children, with benefits including reduced irradiation of the spinal cord.

Rhabdomyosarcoma: review of the Children's Oncology Group (COG) Soft-Tissue Sarcoma Committee experience and rationale for current COG studies

The prognosis for children and adolescents with rhabdomyosarcoma (RMS) has improved with refinements in multi-modal therapy. Since 1972, the Intergroup Rhabdomyosarcoma Study Group (now the Children's Oncology Group Soft-Tissue Sarcoma Committee) has conducted serial studies for RMS. This review describes the IRSG and COG experience with RMS, presents the current risk stratification definitions, and provides rationale for the current generation of COG RMS studies.

Application of proteomics to soft tissue sarcomas

Soft tissue sarcomas are rare and account for less than 1% of all malignant cancers. Other than development of intensive therapies, the clinical outcome of patients with soft tissue sarcoma remains very poor, particularly when diagnosed at a late stage. Unique mutations have been associated with certain soft tissue sarcomas, but their etiologies remain unknown. The proteome is a functional translation of a genome, which directly regulates the malignant features of tumors. Thus, proteomics is a promising approach for investigating soft tissue sarcomas. Various proteomic approaches and clinical materials have been used to address clinical and biological issues, including biomarker development, molecular target identification, and study of disease mechanisms. Several cancer-associated proteins have been identified using conventional technologies such as 2D-PAGE, mass spectrometry, and array technology. The functional backgrounds of proteins identified were assessed extensively using in vitro experiments, thus supporting expression analysis. These observations demonstrate the applicability of proteomics to soft tissue sarcoma studies. However, the sample size in each study was insufficient to allow conclusive results. Given the low frequency of soft tissue sarcomas, multi-institutional collaborations are required to validate the results of proteomic approaches.

Intensity modulated radiation therapy with dose painting to treat rhabdomyosarcoma

PURPOSE

To examine local control and patterns of failure in rhabdomyosarcoma patients treated with intensity modulated radiation therapy (RT) with dose painting (DP-IMRT).

PATIENTS AND METHODS

A total of 41 patients underwent DP-IMRT with chemotherapy for definitive treatment. Nineteen also underwent surgery with or without intraoperative RT. Fifty-six percent had alveolar histologic features. The median interval from beginning chemotherapy to RT was 17 weeks (range, 4-25). Very young children who underwent second-look procedures with or without intraoperative RT received reduced doses of 24-36 Gy in 1.4-1.8-Gy fractions. Young adults received 50.4 Gy to the primary tumor and lower doses of 36 Gy in 1.8-Gy fractions to at-risk lymph node chains.

RESULTS

With 22 months of median follow-up, the actuarial local control rate was 90%. Patients aged ≤7 years who received reduced overall and fractional doses had 100% local control, and young adults had 79% (P=.07) local control. Three local failures were identified in young adults whose primary target volumes had received 50.4 Gy in 1.8-Gy fractions.

CONCLUSIONS

DP-IMRT with lower fractional and cumulative doses is feasible for very young children after second-look procedures with or without intraoperative RT. DP-IMRT is also feasible in adolescents and young adults with aggressive disease who would benefit from prophylactic RT to high-risk lymph node chains, although dose escalation might be warranted for improved local control. With limited follow-up, it appears that DP-IMRT produces local control rates comparable to those of sequential IMRT in patients with rhabdomyosarcoma.

Activating Death Receptor DR5 as a Therapeutic Strategy for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. It is believed to arise from skeletal muscle progenitors, preserving the expression of genes critical for embryonic myogenic development such as MYOD1 and myogenin. RMS is classified as embryonal, which is more common in younger children, or alveolar, which is more prevalent in elder children and adults. Despite aggressive management including surgery, radiation, and chemotherapy, the outcome for children with metastatic RMS is dismal, and the prognosis has remained unchanged for decades. Apoptosis is a highly regulated process critical for embryonic development and tissue and organ homeostasis. Like other types of cancers, RMS develops by evading intrinsic apoptosis via mutations in the p53 tumor suppressor gene. However, the ability to induce apoptosis via the death receptor-dependent extrinsic pathway remains largely intact in tumors with p53 mutations. This paper focuses on activating extrinsic apoptosis as a therapeutic strategy for RMS by targeting the death receptor DR5 with a recombinant TRAIL ligand or agonistic antibodies directed against DR5.

Rhabdomyosarcoma treatment and outcome at a multidisciplinary pediatric cancer center in Lebanon

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Outcome of patients treated on standard protocols, in a multidisciplinary cancer center setting outside of clinical trials, is not well reported. We reviewed characteristics and outcome of 23 pediatric patients treated at a single, multidisciplinary cancer center in Lebanon, between April 2002 and December 2010. Median follow-up was 41 months. The most commonly affected primary site was the head and neck (48%, n = 11). Nineteen tumors (82.6%) were of embryonal histology. Tumor size was ≥5 cm in eight (34.8%) patients. Sixteen patients (69.6%) had localized disease, and one (4.4%) had metastatic disease. Fifteen (65.2%) had Group III tumors. All patients received chemotherapy, for a duration ranging 21-51 weeks. Upfront surgical resection was performed in 10 patients (43.5%). Eighteen patients (78.3%) received radiation therapy. The 5-year overall and disease-free survival rates were 83% and 64%, respectively. Relapse correlated with absence of surgery. Treatment of childhood RMS in a multidisciplinary cancer center in Lebanon results in similar survival to that in developed countries when similar protocols are applied. There was a higher incidence of local relapse, but those were salvageable with further therapy and surgical local control.

AKT and PAX3-FKHR cooperation enforces myogenic differentiation blockade in alveolar rhabdomyosarcoma cell

The chimeric PAX3-FKHR transcription factor is present in a majority of alveolar rhabdomyosarcoma (ARMS), an aggressive skeletal muscle cancer of childhood. PAX3-FKHR-mediated aberrant myogenic gene expression resulting in escape from terminal differentiation program is believed to contribute in ARMS development. In skeletal muscle differentiation, activation of AKT pathway leads to myogenic gene activation and terminal differentiation. Here, we report that AKT acts, in part, by modulating PAX3-FKHR transcriptional activity via phosphorylation in the maintenance of the myogenic differentiation blockade in established mouse models of ARMS cells. We observed that low levels of AKT activity are associated with elevated levels of PAX3-FKHR transcriptional activity, and AKT hyperactivation results in PAX3-FKHR phosphorylation coupled with decreased activity once cells are under differentiation-permissible conditions. Subsequent data shows that attenuated AKT activity-associated PAX3-FKHR activity is required to suppress the function of MyoD, a key myogenic regulator of muscle differentiation. Conversely, decreased PAX3-FKHR activity results in the eradication of MyoD expression and subsequent suppression of the myogenic differentiation. Thus, AKT regulation of the PAX3- FKHR suppresses myogenic gene expression in ARMS cells, causing a failure in differentiation. Evidence is presented that provides a novel molecular link between AKT and PAX3-FKHR in maintaining myogenic differentiation blockade in ARMS.

Calcitriol inhibits hedgehog signaling and induces vitamin d receptor signaling and differentiation in the patched mouse model of embryonal rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Aberrant Hedgehog (Hh) signaling is characteristic of the embryonal subtype (ERMS) and of fusion-negative alveolar RMS. In the mouse, ERMS-like tumors can be induced by mutations in the Hh receptor Patched1 (Ptch). As in humans these tumors show increased Hh pathway activity. Here we demonstrate that the treatment with the active form of vitamin D₃, calcitriol, inhibits Hh signaling and proliferation of murine ERMS in vivo and in vitro. Concomitantly, calcitriol activates vitamin D receptor (Vdr) signaling and induces tumor differentiation. In addition, calcitriol inhibits ERMS growth in Ptch-mutant mice, which is, however, a rather late response. Taken together, our results suggest that exogenous supply of calcitriol could be beneficial in the treatment of RMS, especially in those which are associated with aberrant Hh signaling activity.

Heme oxygenase-1 inhibits myoblast differentiation by targeting myomirs

AIMS

Heme oxygenase-1 (HMOX1) is a cytoprotective enzyme degrading heme to biliverdin, iron ions, and carbon monoxide, whose expression is induced in response to oxidative stress. Its overexpression has been suggested as a strategy improving survival of transplanted muscle precursors.

RESULTS

Here we demonstrated that HMOX1 inhibits differentiation of myoblasts and modulates miRNA processing: downregulates Lin28 and DGCR8, lowers the total pool of cellular miRNAs, and specifically blocks induction of myomirs. Genetic or pharmacological activation of HMOX1 in C2C12 cells reduces the abundance of miR-1, miR-133a, miR-133b, and miR-206, which is accompanied by augmented production of SDF-1 and miR-146a, decreased expression of MyoD, myogenin, and myosin, and disturbed formation of myotubes. Similar relationships between HMOX1 and myomirs were demonstrated in murine primary satellite cells isolated from skeletal muscles of HMOX1(+/+), HMOX1(+/-), and HMOX1(-/-) mice or in human rhabdomyosarcoma cell lines. Inhibition of myogenic development is independent of antioxidative properties of HMOX1. Instead it is mediated by CO-dependent inhibition of c/EBPδ binding to myoD promoter, can be imitated by SDF-1, and partially reversed by enforced expression of miR-133b and miR-206. Control C2C12 myoblasts injected to gastrocnemius muscles of NOD-SCID mice contribute to formation of muscle fibers. In contrast, HMOX1 overexpressing C2C12 myoblasts form fast growing, hyperplastic tumors, infiltrating the surrounding tissues, and disseminating to the lungs.

INNOVATION

We evidenced for the first time that HMOX1 inhibits differentiation of myoblasts, affects the miRNA processing enzymes, and modulates the miRNA transcriptome.

CONCLUSION

HMOX1 improves the survival of myoblasts, but concurrently through regulation of myomirs, may act similarly to oncogenes, increasing the risk of hyperplastic growth of myogenic precursors.

Cell death pathways as therapeutic targets in rhabdomyosarcoma

Resistance of rhabdomyosarcoma to current therapies remains one of the key issues in pediatric oncology. Since the success of most cytotoxic therapies in the treatment of cancer, for example, chemotherapy, depends on intact signaling pathways that mediate programmed cell death (apoptosis), defects in apoptosis programs in cancer cells may result in resistance. Evasion of apoptosis in rhabdomyosarcoma may be caused by defects in the expression or function of critical mediators of apoptosis or in aberrant expression of antiapoptotic proteins. Therefore, the identification of the molecular mechanisms that confer primary or acquired resistance to apoptosis in rhabdomyosarcoma presents a critical step for the rational development of molecular targeted drugs. This approach will likely open novel perspectives for the treatment of rhabdomyosarcoma.

Oral alveolar rhabdomyosarcoma: a case report with immunohistochemical analysis

Rhabdomyosarcomas are among the most common soft-tissue tumors in children. These tumors are derived from mesenchymal tissue with a tendency toward myogenic differentiation that probably originates from immature and highly invasive satellite cells associated with the embryogenesis of skeletal muscle. Some of these tumors are associated with high rates of recurrence and metastasis. The diagnosis is made by microscopic analysis and auxiliary techniques such as immunohistochemistry, electron microscopy, cytogenetic analysis, and molecular biology. We report a case of 28-year-old man who presented with a painless progressive swelling of gingiva since 3 months, which was gradually increasing in size without any systemic symptoms or signs of any metastatic spread. An incisional biopsy was done and histopathology reported an alveolar variant of rhabdomyosarcoma. Immunohistochemistry with panel of markers was done which showed positivity for CD99, vimentin and negative for desmin and myogenin. So the characteristic immunohistological expression was negative in present case. Hence we conclude that haematoxylin and eosin morphology and ultrastructure are needed to classify rhabdomyosarcoma and immunohistochemistry act only as an auxiliary.

Alveolar Rhabdomyosarcoma in a Juvenile Labrador Retriever: Case Report and Literature Review

A 7 mo old Labrador retriever presented for evaluation of facial swelling associated with a 5 cm oral mass extending caudally from the upper third premolar on the left side. Cytology revealed an atypical population of round cells of undetermined origin. A diagnosis of alveolar rhabdomyosarcoma (RMS) was reached via histopathology and confirmed with positive immunohistochemical staining for desmin. In humans, RMSs have a well-described round cell cytologic appearance. Few descriptions of veterinary cases of RMS exist. This report describes the cytologic appearance of alveolar RMS in a young dog and both summarizes and compares findings throughout the veterinary and human literature.

Inhibition of the Notch-Hey1 axis blocks embryonal rhabdomyosarcoma tumorigenesis

PURPOSE

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and remains refractory to combined-modality therapy in patients with high risk disease. In skeletal myogenesis, Notch signaling prevents muscle differentiation and promotes proliferation of satellite cell progeny. Given its physiologic role in myogenesis and oncogenic role in other human cancers, we hypothesized that aberrant Notch signaling may contribute to RMS tumorigenesis and present novel therapeutic opportunities.

EXPERIMENTAL DESIGN

Human RMS cell lines and tumors were evaluated by immunoblot, IHC, and RT-PCR to measure Notch ligand, receptor, and target gene expression. Manipulation of Notch signaling was accomplished using genetic and pharmacologic approaches. In vitro cell growth, proliferation, and differentiation were assessed using colorimetric MTT and BrdU assays, and biochemical/morphologic changes after incubation in differentiation-promoting media, respectively. In vivo tumorigenesis was assessed using xenograft formation in SCID/beige mice.

RESULTS

Notch signaling is upregulated in human RMS cell lines and tumors compared with primary skeletal muscle, especially in the embryonal (eRMS) subtype. Inhibition of Notch signaling using Notch1 RNAi or γ-secretase inhibitors reduced eRMS cell proliferation in vitro. Hey1 RNAi phenocopied Notch1 loss and permitted modest myogenic differentiation, while overexpression of an activated Notch moiety, ICN1, promoted eRMS cell proliferation and rescued pharmacologic inhibition. Finally, Notch inhibition using RNAi or γ-secretase inhibitors blocked tumorigenesis in vivo.

CONCLUSIONS

Aberrant Notch-Hey1 signaling contributes to eRMS by impeding differentiation and promoting proliferation. The efficacy of Notch pathway inhibition in vivo supports the development of Notch-Hey1 axis inhibitors in the treatment of eRMS.

High IGFBP2 expression correlates with tumor severity in pediatric rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common childhood sarcoma and is identified as either the embryonal or alveolar (ARMS) subtype. In approximately 75% of cases, ARMSs are characterized by specific chromosomal translocations that involve PAX and FKHR genes. ARMS gene expression signatures vary, depending on the presence or absence of the translocations. Insulin-like growth factor-binding protein 2 (IGFBP2) is strongly overexpressed in translocation-negative RMS. Because IGFBP2 is associated with tumorigenesis, we investigated its functional role in RMS. An analysis of IGFBP2 distribution in RMS cell lines revealed a strong accumulation in the Golgi complex, in which morphological characteristics appeared peculiarly modified. After silencing IGFBP2 expression, our microarray analysis revealed mostly cell cycle and actin cytoskeleton gene modulations. In parallel, IGFBP2-silenced cells showed reduced cell cycle and rates of invasion and decreased seeding in the lungs after tail vein injections in immunodeficient mice. An analysis of IGFBP2 mRNA and protein localization in human tumors showed abnormal protein accumulation in the Golgi complex, mostly in PAX/FKHR-negative RMS. Moreover, an analysis of patients with RMS revealed the presence of conspicuous circulating levels of IGFBP2 proteins in children with highly aggressive RMS tumors. Taken together, our data provide evidence that IGFBP2 contributes to tumor progression and that it could be used as a marker to better classify clinical and biological risks in RMS.

Undifferentiated sarcoma of the sellar region

Malignancies lacking specific features of cellular maturation are termed "undifferentiated" and represent 5-10% of all human tumors. They are encountered at a variety of sites but do not, as a rule, arise in the sellar region. A 39-year-old male with a history of testicular seminoma and an unsuccessful biopsy of a third ventricular neoplasm, presented with visual disturbances and memory loss. Light microscopically, the tumor consisted entirely of undifferentiated spindle cells. No germ cell component was noted. An exhaustive immunohistochemical study found immunoreactivity for vimentin and desmin, but for no other myoid markers. Polymerase chain reaction showed no X;18 translocation. Based upon these studies, a diagnosis of "undifferentiated sarcoma" was made. Our case, being highly unusual among reported sellar neoplasms, underscores the difficulties inherent in the differential diagnosis of undifferentiated neoplasms.

Drozitumab, a human antibody to death receptor 5, has potent antitumor activity against rhabdomyosarcoma with the expression of caspase-8 predictive of response

PURPOSE

Rhabdomyosarcoma (RMS) is a common pediatric soft-tissue tumor. In this study, we evaluated the efficacy and selectivity of drozitumab, a death receptor DR5-targeted therapeutic antibody, in RMS preclinical models.

EXPERIMENTAL DESIGN

A panel of 11 RMS cell lines was used for in vitro studies. The molecular marker predictive of response to drozitumab was interrogated. Selected RMS cell lines were injected into the gastrocnemius muscle of mice for in vivo assessment of the potency and selectivity of drozitumab.

RESULTS

We report that DR5, but not DR4, persisted at high levels and on the surface of all RMS cell lines. DR5 antibody drozitumab was effective in vitro against the majority of RMS cell lines. There was a strong correlation between caspase-8 expression and the sensitivity to drozitumab, which induced the rapid assembly of the death-induced signaling complex and the cleavage of caspase-8 only in sensitive cells. More importantly, caspase-8 catalytic activity was both necessary and sufficient for mediating the sensitivity to drozitumab. Furthermore, drozitumab had potent antitumor activity against established RMS xenografts with a specificity predicted from the in vitro analysis and with tumor-free status in half of the treated mice.

CONCLUSION

Our study provides the first preclinical evaluation of the potency and selectivity of a death receptor antibody in RMS. Drozitumab is effective, in vitro, against the majority of RMS cell lines that express caspase-8 and, in vivo, may provide long-term control of RMS.