David Walterhouse

The Sonic Hedgehog–Patched–Gli Pathway in Human Development and Disease

Embryogenesis is regulated by a number of complex signaling cascades, which are critical for normal development. One such pathway begins with a secreted protein called “SONIC HEDGEHOG” (SHH [MIM 600725]), which sets off a chain of events in target cells, leading to the activation and repression of target genes by transcription factors in the Gli family. Dysregulation of the Sonic hedgehog–Patched–Gli (Shh-Ptch-Gli) pathway leads to several human diseases, including birth defects and cancers. Elements of the Shh-Ptch-Gli pathway are highly conserved, indicating its essential role in development. However, Shh signaling is also apparently susceptible to evolutionary pressures. Thus, Shh signaling has been adapted to serve tremendously diverse functions in a wide array of animal models, in both embryonic and adult life. Shh and the downstream molecules involved in signal transduction vary, to some extent, between animals, as well. Although a great deal can be learned from the study of animal models, it is essential to not assume that what is true in one model system is necessarily true in another. Thus, this review focuses specifically on our current understanding of the Shh-Ptch-Gli pathway and its clinical significance in humans.

Gene Expression Profiling Leads to Identification of GLI1-binding Elements in Target Genes and a Role for Multiple Downstream Pathways in GLI1-induced Cell Transformation

The zinc finger transcription factor GLI1, which mediates Sonic hedgehog signaling during development, is expressed in several human cancers, including basal cell carcinoma, medulloblastoma, and sarcomas. We identified 147 genes whose levels of expression were significantly altered in RNA obtained from cells demonstrating a transformed phenotype with stable GLI1 expression or stableHa-ras expression. Comparison of expression profiles fromGLI1- and Ha-ras-expressing cells established a set of genes unique to GLI1-induced cell transformation. Thirty genes were altered by stable GLI1 expression, and 124 genes were changed by stable Ha-ras expression. Seven genes had altered expression levels in both GLI1- andHa-ras-expressing cells. Genes whose expression was altered by GLI1 included cell cycle genes, cell adhesion genes, signal transduction genes, and genes regulating apoptosis. GLI1 consensus DNA-binding sequences were identified in the 5′ regions of cyclin D2, IGFBP-6, osteopontin, and plakoglobin, suggesting that these genes represent immediate downstream targets. Gel shift analysis confirmed the ability of the GLI1 protein to bind these sequences. Up-regulation of cyclin D2 and down-regulation of plakoglobin were demonstrated in GLI1-amplified compared with non-amplified human rhabdomyosarcoma cells. Many of theGLI1 targets with known function identified in this study increase cell proliferation, indicating that GLI1-induced cell transformation occurs through multiple downstream pathways.

Clear Cell Sarcoma of the Kidney: Up-regulation of Neural Markers with Activation of the Sonic Hedgehog and Akt Pathways

Purpose and Experimental Design: Clear cell sarcoma of the kidney (CCSK), the second most common renal tumor in children, poses significant diagnostic challenges. No positive diagnostic markers are available, and the pathogenesis of CCSK remains an enigma. To address these challenges, the gene expression patterns of 14 CCSKs were compared with 15 Wilms tumors and 3 fetal kidney samples using oligonucleotide arrays. Results: Using unsupervised methods, the gene expression profile of CCSK was distinctive: differentially expressed genes could largely be grouped into four categories: (a) a wide variety of neural markers, (b) members of the Sonic hedgehog pathway, (c) members of the phosphoinositide-3-kinase/Akt cell proliferation pathway, and (d) known therapeutic targets. Corresponding changes in critical proteins using Western blot and/or immunohistochemistry confirmed the up-regulation of these pathways and proteins. In particular, CD117 and epidermal growth factor receptor are up-regulated at the protein level in many CCSKs, providing potential therapeutic targets. One of the neural markers, nerve growth factor receptor, represents a promising diagnostic tool for CCSK. Conclusions: This study suggests that CCSKs arise within a renal mesenchymal cell that shows a wide variety of neural markers. As such, it seems to be susceptible to genetic changes also seen in a variety of other neuroectodermal and neuronal tumors, including activation of Sonic hedgehog and phosphoinositide-3-kinase/Akt pathways. Involvement of these pathways in CCSKs implicates their widening role in tumorigenesis.

Results of the Intergroup Rhabdomyosarcoma Study Group D9602 Protocol, Using Vincristine and Dactinomycin With or Without Cyclophosphamide and Radiation Therapy, for Newly Diagnosed Patients With Low-Risk Embryonal Rhabdomyosarcoma: A Report From the Soft Tissue Sarcoma Committee of the Children's Oncology Group

PURPOSE Patients with localized, grossly resected, or gross residual (orbital only) embryonal rhabdomyosarcoma (ERMS) had 5-year failure-free survival (FFS) rates of 83% and overall survival rates of 95% on Intergroup Rhabdomyosarcoma Study Group (IRSG) protocols III/IV. IRSG D9602 protocol (1997 to 2004) objectives were to decrease toxicity in similar patients by reducing radiotherapy (RT) doses and eliminating cyclophosphamide for the lowest-risk patients. PATIENTS AND METHODS Subgroup A patients (lowest risk, with ERMS, stage 1 group I/IIA, stage 1 group III orbit, stage 2 group I) received vincristine plus dactinomycin (VA). Subgroup B patients (ERMS, stage 1 group IIB/C, stage I group III nonorbit, stage 2 group II, stage 3 group I/II) received VA plus cyclophosphamide. Patients in group II/III received RT. Compared with IRS-IV, doses were reduced from 41.4 to 36 Gy for stage 1 group IIA patients and from 50 or 59 to 45 Gy for group III orbit patients. RESULTS Estimated 5-year FFS rates were 89% (95% CI, 84% to 92%) for subgroup A patients (n = 264) and 85% (95% CI, 74%, 91%) for subgroup B patients (n = 78); median follow-up: 5.1 years. Estimated 5-year FFS rates were 81% (95% CI, 68% to 90%) for patients with stage 1 group IIA tumors (n = 62) and 86% (95% CI, 76% to 92%) for patients with group III orbit tumors (n = 77). CONCLUSION Five-year FFS and OS rates were similar to those observed in comparable IRS-III patients, including patients receiving reduced RT doses, but were lower than in comparable IRS-IV patients receiving VA plus cyclophosphamide. Five-year FFS rates were similar among subgroups A and B patients.

N-myc Can Substitute for Insulin-Like Growth Factor Signaling in a Mouse Model of Sonic Hedgehog–Induced Medulloblastoma

Medulloblastoma is a malignant brain tumor that arises in the cerebellum in children, presumably from granule neuron precursors (GNP). Advances in patient treatment have been hindered by a paucity of animal models that accurately reflect the molecular pathogenesis of human tumors. Aberrant activation of the Sonic hedgehog (Shh) and insulin-like growth factor (IGF) pathways is associated with human medulloblastomas. Both pathways are essential regulators of GNP proliferation during cerebellar development. In cultured GNPs, IGF signaling stabilizes the oncogenic transcription factor N-myc by inhibiting glycogen synthase kinase 3beta-dependent phosphorylation and consequent degradation of N-myc. However, determinants of Shh and IGF tumorigenicity in vivo remain unknown. Here we report a high frequency of medulloblastoma formation in mice following postnatal overexpression of Shh in cooperation with N-myc. Overexpression of N-myc, alone or in combination with IGF signaling mediators or with the Shh target Gli1, did not cause tumors. Thus, Shh has transforming functions in addition to induction of N-myc and Gli1. This tumor model will be useful for testing novel medulloblastoma therapies and providing insight into mechanisms of hedgehog-mediated transformation.

Efficacy of Topotecan and Cyclophosphamide Given in a Phase II Window Trial in Children With Newly Diagnosed Metastatic Rhabdomyosarcoma: A Children’s Oncology Group Study

PURPOSE To determine the antitumor activity and toxicity of topotecan given immediately after cyclophosphamide as window therapy, then in combination with conventional agents in pediatric patients with newly diagnosed metastatic rhabdomyosarcoma (RMS). PATIENTS AND METHODS Sixty-one patients younger than 21 years with newly diagnosed metastatic RMS or undifferentiated sarcoma were assigned window therapy (weeks 0 to 6) with topotecan (0.75 mg/m(2) daily x 5 every 21 days) immediately after cyclophosphamide (250 mg/m(2) daily x 5 every 21 days; TC). We continued to give these agents in combination with vincristine (VTC) to patients who showed objective improvement, partial response (PR), or complete response (CR) to TC and alternated courses of VTC with vincristine, dactinomycin and cyclophosphamide (VAC) during weeks 6 to 41 (VTC/VAC). Those who showed no response or progressive disease after TC received only VAC. All patients received radiotherapy to sites of unresected disease (weeks 15 to 21). RESULTS The overall response rate (CR + PR) to TC was 47% (95% CI, 35% to 60%). Tumor size < or = 5 cm was associated with early response. Myelosuppression was the primary toxicity to TC. Overall 3-year disease-free survival and survival were estimated to be 10% (95% CI, 2% to 19%) and 20% (95% CI, 8% to 32%), respectively. Toxicity profiles for patients who received VTC/VAC or VAC alone were comparable. CONCLUSION Topotecan after cyclophosphamide is a combination that is active against newly diagnosed RMS, with an acceptable toxicity profile. Disease-free survival and overall survival, however, remain disappointing for children with metastatic RMS at diagnosis.

Ifosfamide and etoposide are superior to vincristine and melphalan for pediatric metastatic rhabdomyosarcoma when administered with irradiation and combination chemotherapy: A report from the intergroup rhabdomyosarcoma study group

Purpose This study was designed to estimate the partial and complete response rates (CR and PR) of two novel drug pairs (vincristine and melphalan vs. ifosfamide and etoposide) and to improve overall survival of previously untreated patients with metastatic rhabdomyosarcoma. Patients and Methods One hundred twenty-eight patients were randomly assigned to phase II window therapy consisting of vincristine and melphalan (VM-containing regimen) or ifosfamide and etoposide (IE-containing regimen). Brief window therapy (12 wks) was immediately followed-up by vincristine, dactinomycin, and cyclophosphamide (VAC), chemotherapy, surgery, and irradiation, with continuation of either VM or IE in patients with initial response. Major endpoints were initial CR and PR rates after the phase II window phase of therapy, failure-free survival (FFS), and survival. Results Patients who received the VM-containing regimen experienced significantly more anemia, neutropenia, thrombocytopenia, and had more cyclophosphamide dose reductions. The initial PR and CR rates were not significantly different for patients treated with either regimen (VM, 74%; IE, 79%;P = 0.428). However, FFS and overall survival (OS) at 3 years were significantly better with the IE-containing regimen (FFS: 33% vs. 19%;P = 0.043; OS: 55% vs. 27%;P = 0.012). Conclusions Although the VM-containing regimen produced a high response rate, inclusion of melphalan appeared to limit the cyclophosphamide dose that could be administered, and ultimately, this regimen was associated with a significantly worse outcome than was the IE-containing regimen. Also, the IE-containing regimen was associated with a gratifyingly high survival rate at 3 years (55%), which is significantly higher than has been observed on any previous Intergroup Rhabdomyosarcoma Study Group regimen for similar patients. We believe that this promising outcome indicates that this drug pair merits further randomized testing in metastatic rhabdomyosarcoma.

Optimal management strategies for rhabdomyosarcoma in children.

Rhabdomyosarcoma is the most common sarcoma of childhood. Fortunately, the goal of cure is realistic for the majority of patients with localized tumors. However, management of these patients remains challenging. The fact that the tumor arises in a wide variety of primary sites, some of which are associated with specific patterns of local invasion, regional lymph node spread, and therapeutic response, requires physicians to be familiar with site-specific staging and treatment details. In addition, rhabdomyosarcoma requires multimodality therapy that can be associated with significant acute toxicities and long-term effects, particularly when administered to young children. These factors sometimes present a dilemma as to the best approach to optimize the chance of cure, minimize toxicity, and respect quality of life.The purpose of this review is to discuss ‘optimal’ management of this complicated tumor. Since the tumor is relatively rare, requires highly specialized care, and important management questions remain to be answered, optimal management of rhabdomyosarcoma includes enrollment in clinical trials whenever possible. Appropriate management begins with establishing the correct pathologic diagnosis, histologic subtype, primary site, extent of disease (International Society of Pediatric Oncology [SIOP]-TNM-Union Internationale Contre le Cancer stage or Intergroup Rhabdomyosarcoma Study Group [IRSG] stage), and extent of resection (IRSG group). Cooperative groups throughout North America and Europe have defined risk-adapted treatment based on these factors; this treatment requires a coordinated management plan that includes surgery, chemotherapy, and usually radiotherapy.The surgical approach for rhabdomyosarcoma is to excise the primary tumor whenever possible without causing major functional or cosmetic deficits. Wide excision is difficult in some primary sites and can be complicated by the fact that the tumor grows in a locally infiltrative manner so that complete resection is often neither possible nor medically indicated. Incompletely resected tumors are generally treated with radiotherapy. The cooperative groups reduce the dose of radiation based on the response of the tumor to chemotherapy and delayed primary resection to differing degrees. Response-adjusted radiation administration may reduce the long-term effects of radiotherapy, such as bone growth arrest, muscle atrophy, bladder dysfunction, and induction of second malignant neoplasms; however, it may also be associated with an increased risk of tumor recurrence.All patients with rhabdomyosarcoma require chemotherapy. A backbone of vincristine and dactinomycin with either cyclophosphamide (VAC) or ifosfamide (IVA) has been established. Risk-adapted treatment involves reducing or eliminating the alklyating agent for patients with the most favorable disease characteristcs. Clinical trials are ongoing to improve outcomes for higher risk patients; newer agents, such as topotecan or irinotecan, in combination with VAC or use of agents in novel ways are being investigated. Acute and long-term toxicities associated with these chemotherapy regimens include myelosuppression, febrile neutropenia, hepatopathy, infertility, and second malignant neoplasms.A 5-year survival rate >70% has been achieved in recent trials for patients with localized rhabdomyosarcoma. However, the outcome for patients who present with metastatic disease remains poor. In the future, risk-adapted classification of rhabdomyosarcoma will likely be based on biologic features, such as the presence of chromosomal translocations or specific gene expression profiles. It is hoped that newer therapies directed at specific molecular genetic defects will benefit all patients with rhabdomyosarcoma.

Local control with reduced-dose radiotherapy for low-risk rhabdomyosarcoma: a report from the Children's Oncology Group D9602 study

PURPOSE To analyze the effect of reduced-dose radiotherapy on local control in children with low-risk rhabdomyosarcoma (RMS) treated in the Childrens Oncology Group D9602 study. METHODS AND MATERIALS Patients with low-risk RMS were nonrandomly assigned to receive radiotherapy doses dependent on the completeness of surgical resection of the primary tumor (clinical group) and the presence of involved regional lymph nodes. After resection, most patients with microscopic residual and uninvolved nodes received 36 Gy, those with involved nodes received 41.4 to 50.4 Gy, and those with orbital primary tumors received 45 Gy. All patients received vincristine and dactinomycin, with cyclophosphamide added for patient subsets with a higher risk of relapse in Intergroup Rhabdomyosarcoma Study Group III and IV studies. RESULTS Three hundred forty-two patients were eligible for analysis; 172 received radiotherapy as part of their treatment. The cumulative incidence of local/regional failure was 15% in patients with microscopic involved margins when cyclophosphamide was not part of the treatment regimen and 0% when cyclophosphamide was included. The cumulative incidence of local/regional failure was 14% in patients with orbital tumors. Protocol-specified omission of radiotherapy in girls with Group IIA vaginal tumors (n = 5) resulted in three failures for this group. CONCLUSIONS In comparison with Intergroup Rhabdomyosarcoma Study Group III and IV results, reduced-dose radiotherapy does not compromise local control for patients with microscopic tumor after surgical resection or with orbital primary tumors when cyclophosphamide is added to the treatment program. Girls with unresected nonbladder genitourinary tumors require radiotherapy for postsurgical residual tumor for optimal local control to be achieved.

Sonic Hedgehog-responsive Genes in the Fetal Prostate

The Hedgehog (Hh) signaling pathway plays an important role in prostate development and appears to play an equally important role in promoting growth of advanced prostate cancer. During prostate development, epithelial cells in the urogenital sinus (UGS) express Sonic Hedgehog (Shh) and secrete Shh peptide. The secreted Hh peptide acts on adjacent mesenchymal cells to activate the Hh signal transduction pathway and elicit paracrine effects on epithelial proliferation and differentiation. To identify mesenchymal targets of Shh signaling, we performed microarray analysis on a Shh-responsive, immortalized urogential sinus mesenchymal cell line. We found 68 genes that were up-regulated by Shh and 21 genes that were down-regulated. Eighteen of those were selected for further study with Ptc1 and Gli1 serving as reference controls. We found 10 of 18 were also Hh-regulated in primary UGS mesenchymal cells and 13 of 18 in the cultured UGS. Seven of 18 exhibited Shh-regulated expression in both assays (Igfbp-6, Igfbp-3, Fbn2, Ntrk3, Agpt4, Dmp1, and Mmp13). Three of the 18 genes contained putative Gli binding motifs that bound Gli1 peptide in electrophoretic mobility shift assays. With the exception of Tiam1, target gene expression generally showed no differences in the concentration dependence of ligand-induced expression, but we observed strikingly different responses to direct pathway activation by transfection with activated Smo, Gli1, and Gli2.