Successful Management of Cushing Syndrome From Ectopic ACTH Secretion in an Adolescent With Osilodrostat

A previously healthy 11-year-old male was found to have a mass in the pancreatic head after several months of abdominal pain and jaundice. Pathology was consistent with a World Health Organization grade 2 pancreatic neuroendocrine tumor. He developed refractory hypertension and was found to have Cushing syndrome from ectopic ACTH secretion, with oligometastatic liver disease. He underwent surgical resection of the pancreatic tumor and metastases. Postoperatively, his Cushing syndrome resolved, but it reemerged 1 year later in the setting of disease recurrence. He was not a candidate for bilateral adrenalectomy. Ketoconazole therapy was inadequate and he was started on metyrapone, lanreotide, cabergoline, and spironolactone. Although this regimen was well-tolerated, his Cushing syndrome recurred 4 months later as his metastatic disease burden increased. Osilodrostat was begun and the dose was gradually increased in response to his uncontrolled Cushing syndrome. Osilodrostat resulted in rapid improvement and eventual normalization of his urinary free cortisol at a dose of 18 mg twice daily. He had no adverse effects. This rare case highlights the successful off-label use of osilodrostat, a medication intended for refractory Cushing disease in adult patients, in a pediatric patient with Cushing syndrome caused by ectopic ACTH secretion.

Receptor tyrosine kinase inhibitors for the treatment of osteosarcoma and Ewing sarcoma

Adjuvant chemotherapy for osteosarcoma and Ewing sarcoma consists of conventional cytotoxic regimens that have changed little over the past decades. There is an urgent need for agents that are more effective and have less long-term toxicity. Receptor tyrosine kinases regulate cell growth and proliferation of these tumors, and small-molecule inhibitors for many of these kinases are now available. In this article, we review published phase II trials for patients with recurrent disease and highlight the pathways targeted by available agents, as well as the toxicity and efficacy results seen to date. We also discuss the difficulties in identifying biomarkers to facilitate rational patient selection, as well as published and proposed strategies for how these inhibitors can be combined with conventional chemotherapy or other targeted agents. It is hoped future trials can capitalize on this growing experience to optimize the use of this exciting class of agents.

A phase I trial of the CDK 4/6 inhibitor palbociclib in pediatric patients with progressive brain tumors: A Pediatric Brain Tumor Consortium study (PBTC-042)

BACKGROUND

Disruption of cell-cycle regulators is a potential therapeutic target for brain tumors in children and adolescents. The aim of this study was to determine the maximum tolerated dose (MTD) and describe toxicities related to palbociclib, a selective cyclin-dependent kinase 4/6 (CDK4/6) inhibitor in pediatric patients with progressive/refractory brain tumors with intact retinoblastoma protein.

METHODS

Palbociclib was administered orally starting at 50 mg/m² daily for the first 21 days of a 28-day course. Dose escalation was according to the Rolling-6 statistical design in less heavily (stratum I) and heavily pretreated (stratum II) patients, and MTD was determined separately for each group. Pharmacokinetic studies were performed during the first course, and pharmacodynamic studies were conducted to evaluate relationships between drug levels and toxicities.

RESULTS

A total of 21 patients were enrolled on stratum I and 14 patients on stratum II. The MTD for both strata was 75 mg/m² . Palbociclib absorption (mean T_max between 4.9 and 6.6 h) and elimination (mean half-life between 11.3 and 19.5 h) were assessed. The most common toxicity was myelosuppression. Higher palbociclib exposure was associated with grade 3/4 neutropenia and leukopenia. Dose limiting toxicities included grade 4 neutropenia and grade 3 thrombocytopenia and dehydration. No patients had an objective response to palbociclib therapy.

CONCLUSIONS

Palbociclib was safely administered to children and adolescents at a dosage of 75 mg/m² for 21 consecutive days followed by seven days of rest in both strata. Future studies will establish its optimal utilization in pediatric patients with brain tumors.

Molecular and phenotypic diversity of CBL-mutated juvenile myelomonocytic leukemia

Mutations in the CBL gene were first identified in adults with various myeloid malignancies. Some patients with juvenile myelomonocytic leukemia (JMML) were also noted to harbor mutations in CBL, but were found to have generally less aggressive disease courses compared to patients with other forms of Ras pathway-mutant JMML. Importantly, and in contrast to most reports in adults, the majority of CBL mutations in JMML patients are germline with acquired uniparental disomy occurring in affected marrow cells. Here, we systematically studied a large cohort of 33 JMML patients with CBL mutations and found that this disease is highly diverse in presentation and overall outcome. Moreover, we discovered somatically acquired CBL mutations in 15% of pediatric patients who presented with more aggressive disease. Neither clinical features nor methylation profiling were able to distinguish patients with somatic CBL mutations from those with germline CBL mutations, highlighting the need for germline testing. Overall, we demonstrate that disease courses are quite heterogeneous even among patients with germline CBL mutations. Prospective clinical trials are warranted to find ideal treatment strategies for this diverse cohort of patients.

NFB-09. ENROLLMENT AND CLINICAL CHARACTERISTICS OF NEWLY DIAGNOSED, NEUROFIBROMATOSIS TYPE 1 ASSOCIATED OPTIC PATHWAY GLIOMA (NF1-OPG): PRELIMINARY RESULTS FROM AN INTERNATIONAL MULTI-CENTER NATURAL HISTORY STUDY

INTRODUCTION

Because treatment and clinical management decisions for children with NF1-OPG remain challenging, we sought to establish evidence-based guidelines. We prospectively enrolled children with newly-diagnosed NF1-OPGs, and gathered standardized clinical neuro-oncology and ophthalmology assessments.

METHODS

Only children with NF1 and newly diagnosed OPGs, confirmed by central review, were eligible. Indications for obtaining the initial MRI, as well as factors associated with the decision to treat with chemotherapy or observe without treatment, were obtained. Quantitative visual acuity (VA), other ophthalmic features, and imaging were captured at standard time points. Goal enrollment is 250 subjects.

RESULTS

One-hundred thirty-three children (52% female) from 20 institutions met inclusion criteria, and were included in this preliminary analysis. Eighty-six percent of subjects were able to perform quantitative VA testing at enrollment. The most common reasons for the diagnostic MRI included screening related to NF1 diagnosis (36.8%), ophthalmologic concerns (29.3%), and non-ophthalmologic concerns (24.8%), such as headache. To date, twenty subjects have initiated treatment with chemotherapy, twelve (9%) at the time of the initial OPG diagnosis. Median age at OPG diagnosis was 3.1 years. Age and sex distribution were similar in subjects immediately entering the observation and treatment arms (median age 3.0 versus 3.5 years, respectively).

CONCLUSION

Most children with NF1-OPGs are observed at time of their initial OPG diagnosis, rather than treated. Importantly, a large proportion of children are able to complete quantitative VA testing at enrollment. Once enrollment is complete, these data will help to establish evidence-based guidelines for clinical management of NF1-OPGs.

EPCT-05. A PHASE I TRIAL OF THE CDK 4/6 INHIBITOR PALBOCICLIB IN PEDIATRIC PATIENTS WITH PROGRESSIVE OR REFRACTORY CNS TUMORS: A PEDIATRIC BRAIN TUMOR CONSORTIUM (PBTC) STUDY

PBTC-042 was a phase I trial of palbociclib to determine the maximum tolerated dose (MTD) and describe toxicities in children. Palbociclib is an oral, selective cyclin dependent kinase 4/6 inhibitor. METHODS: A rolling-6 design was utilized. Eligible patients were children ≥4 and ≤21 years-old with a progressive/refractory CNS tumor with intact retinoblastoma protein, measurable disease, and ability to swallow capsules. Pharmacokinetic studies were performed during the first course. Here, we report on the heavily pretreated stratum, which included patients who received >4 prior treatment regimens (either chemotherapy or biologic agent), and/or craniospinal irradiation, and/or myeloablative chemotherapy plus stem cell rescue. Palbociclib was initiated at 50 mg/m²/day for 21 consecutive days of a 28-day course. This was one dosage level below the MTD for the less heavily pretreated stratum (75 mg/m²). RESULTS: Fourteen eligible patients were enrolled (median age 12.8 years; male 79%). Eleven patients (79%) had either ependymoma or medulloblastoma. Four eligible and evaluable patients were enrolled at 50 mg/m² with no DLTs. This prompted a dosage increase to 75 mg/m². Ten eligible subjects were enrolled and 7 were evaluable for DLT assessment. One of 7 evaluable patients experienced a DLT (grade 3 thrombocytopenia). This established 75 mg/m² as the MTD for more heavily pretreated patients. Mean ± SD palbociclib apparent oral clearance was 34.6 ± 18.4 L/h/m2. CONCLUSION: The MTD for palbociclib on a 3 week on/1 week off schedule in children with brain tumors is 75 mg/m² and does not appear to be influenced by the degree of prior therapy.

Genitourinary manifestations of hereditary cancer predisposition syndromes in children

Several hereditary cancer predisposition syndromes are associated with genitourinary (GU) manifestations in children. The GU manifestation may be the first symptom of a more global syndrome to arise, which places the pediatric urologist in a unique position to impact the health of the child. Some GU manifestations are pathognomonic for a particular hereditary cancer predisposition syndrome, which can prompt genetic testing and enhanced surveillance for other features of the condition. In other cases, knowledge of an underlying hereditary cancer predisposition syndrome alters treatment decisions. This review focuses on hereditary cancer predisposition syndromes that impact the GU tract and are likely to be seen by a pediatric urologist.

Abstract A03: Generation of primary sarcoma mouse models through CRISPR/Cas9 mediated activation of Yap1

Soft tissue sarcomas (STSs) are rare heterogeneous cancers arising from diverse connective tissues. Undifferentiated pleomorphic sarcomas (UPSs), the most common sarcomas diagnosed in adult patients, are complex karyotypes of nonspecific genetic alterations. To date, the molecular mechanisms by which UPSs develop in patients are still poorly understood, which hinders precision medicine to treat the disease. Primary UPS mouse model generated by conditional activation of KrasG12D and mutation of Trp53 (KP mouse model) is currently used for studying sarcoma biology, imaging, and preclinical trials. However, Kras mutation is rarely identified in human UPSs. We recently showed that injury can replace KrasG12D to induce primary UPSs in mouse models of conditional mutation of Trp53. Furthermore, our whole-exome sequencing determined Yap1 amplification in some injury-induced sarcomas. Moreover, it is also shown that a subset of human UPSs may be driven by Hippo pathway. In addition, it is reported that activation of mutant Yap1 induced primary rhabdomyosarcomas (RMSs) in mouse models. CRISPR/Cas9-mediated genetic mutation has been applied to rapidly create mouse models of cancers, including sarcoma, with spatial and temporal control. However, rare studies have been performed to investigate whether CRISPR/Cas9-mediated activation of endogenous oncogenes could generate primary cancer models. Thus, we applied CRISPR/Cas9 technology to test whether activation of endogenous Yap1 can induce cell transformation or even generate primary UPSs in mouse models. Our results showed that CRISPR/dCas9-p300-mediated activation of endogenous Yap1 resulted in transformation of KrasG12D immortalized mouse embryonic fibroblasts (MEFs) as well as Trp53 knockout MEFs. Moreover, we are currently applying our recently developed in vivo CRISPR/Cas9 delivery method combined with Sleeping Beauty transposon system to investigate whether we are able to develop primary UPSs in mouse models by activating Yap1. If successful, it will further allow us to perform CRISPR/Cas9-mediated direct in vivo activation screen to identify other oncogene drivers for sarcomagenesis. In conclusion, primary sarcoma mouse models generated by CRISPR/Cas9-mediated activation will be an indispensable platform for studying sarcoma biology and precision medicine.

Citation Format: Jianguo Huang, Eric Xu, David Van Mater, David G Kirsch. Generation of primary sarcoma mouse models through CRISPR/Cas9 mediated activation of Yap1 [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A03.

Somatic Mosaicism of IDH1 R132H Predisposes to Anaplastic Astrocytoma: A Case of Two Siblings

Anaplastic astrocytomas are aggressive glial cancers that present poor prognosis and high recurrence. Heterozygous IDH1 R132H mutations are common in adolescent and young adult anaplastic astrocytomas. In a majority of cases, the IDH1 R132H mutation is unique to the tumor, although rare cases of anaplastic astrocytoma have been described in patients with mosaic IDH1 mutations (Ollier disease or Maffucci syndrome). Here, we present two siblings with IDH1 R132H mutant high grade astrocytomas diagnosed at 14 and 26 years of age. Analysis of IDH^R132H mutations in the siblings' tumors and non-neoplastic tissues, including healthy regions of the brain, cheek cells, and primary teeth indicate mosaicism of IDH^R132H. Whole exome sequencing of the tumor tissue did not reveal any other common mutations between the two siblings. This study demonstrates the first example of IDH1 R132H mosaicism, acquired during early development, that provides an alternative mechanism of cancer predisposition.

Mutational landscape in genetically engineered, carcinogen-induced, and radiation-induced mouse sarcoma

Cancer development is influenced by hereditary mutations, somatic mutations due to random errors in DNA replication, or external factors. It remains unclear how distinct cell-intrinsic and -extrinsic factors impact oncogenesis within the same tissue type. We investigated murine soft tissue sarcomas generated by oncogenic alterations (KrasG12D activation and p53 deletion), carcinogens (3-methylcholanthrene [MCA] or ionizing radiation), and in a novel model combining both factors (MCA plus p53 deletion). Whole-exome sequencing demonstrated distinct mutational signatures in individual sarcoma cohorts. MCA-induced sarcomas exhibited high mutational burden and predominantly G-to-T transversions, while radiation-induced sarcomas exhibited low mutational burden and a distinct genetic signature characterized by C-to-T transitions. The indel to substitution ratio and amount of gene copy number variations were high for radiation-induced sarcomas. MCA-induced tumors generated on a p53-deficient background showed the highest genomic instability. MCA-induced sarcomas harbored mutations in putative cancer-driver genes that regulate MAPK signaling (Kras and Nf1) and the Hippo pathway (Fat1 and Fat4). In contrast, radiation-induced sarcomas and KrasG12Dp53-/- sarcomas did not harbor recurrent oncogenic mutations, rather they exhibited amplifications of specific oncogenes: Kras and Myc in KrasG12Dp53-/- sarcomas, and Met and Yap1 for radiation-induced sarcomas. These results reveal that different initiating events drive oncogenesis through distinct mechanisms.

Management of recurrent Ewing sarcoma: challenges and approaches

Although many patients with newly diagnosed Ewing sarcoma can become long-term survivors, relapse remains an important clinical problem for which there is no standard approach. Several prognostic factors have been identified, and these may help guide patient counseling and therapy decisions. A variety of chemotherapy regimens have produced responses in patients with recurrent Ewing sarcoma, but no comparative studies have been completed to show superiority of any one particular approach. In addition, the optimum length of therapy for salvage regimens and use of local control measures remains unknown. The likelihood of cure remains low and the gaps in our knowledge are great, and so enrollment on clinical trials should be strongly encouraged for these patients when feasible. Because Ewing sarcoma is relatively rare, some pediatric and adult oncologists may be less familiar with the management of relapsed patients. In this review, we address common questions facing the clinician and patient, and provide an update on new strategies for therapy.

Injury promotes sarcoma development in a genetically and temporally restricted manner

Cancer results from the accumulation of genetic mutations in a susceptible cell of origin. We and others have also shown that injury promotes sarcoma development, but how injury cooperates with genetic mutations at the earliest stages of tumor formation is not known. Here, we utilized dual recombinase technology to dissect the complex interplay of the timing of KrasG12D activation, p53 deletion, and muscle injury in sarcomagenesis using a primary mouse model of soft tissue sarcoma. When mutations in oncogenic Kras and p53 are separated by 3 weeks, few sarcomas develop without injury. However, the transformation potential of these tumor-initiating cells can be unmasked by muscle injury. In the absence of Kras mutations, injury of the muscle with global deletion of p53 results in sarcomas with amplification of chromosomal regions encompassing the Met or Yap1 gene. These findings demonstrate a complex interplay between the timing of genetic mutations and perturbations in the tumor microenvironment, which provides insight into the earliest stages of sarcoma development.

Abstract A17: Generation and comparison of CRISPR/Cas9 and Cre-mediated genetically engineered mouse models of sarcoma

Genetically engineered mouse models (GEMMs) that employ site-specific recombinase (SSR) technology are important tools for cancer research, and recently the CRISPR/Cas9 system has been increasingly utilized to model cancer in mice. Here, we used CRISPR/Cas9 to generate two primary mouse models of sarcoma, undifferentiated pleomorphic sarcoma (UPS) in a GEMM, and malignant peripheral nerve sheath tumor (MPNST) in wild-type mice, to demonstrate the versatility of the system to generate multiple soft-tissue sarcoma subtypes. Because CRISPR technology is becoming more prevalent in cancer modeling, it is critical to thoroughly evaluate if these models are indeed comparable as tools to study cancer biology compared to conventional GEMMs initiated by recombinase technology. We used two Kras-driven sarcoma models of UPS generated with either Cre recombinase technology or CRISPR/Cas9 technology and compared the mutational profiles, histology, and growth kinetics of these models. KrasLSL-G12D/+; Rosa26LSL-Cas9-EGFP/+ (KC) mice received intramuscular delivery of an adenovirus expressing Cre recombinase and a single guide RNA (sgRNA) targeting Trp53. Cre-mediated expression of oncogenic Kras and Cas9, in combination with CRISPR/Cas9-mediated knockout of Trp53, was sufficient to generate primary soft-tissue sarcomas. Compared to the Cre/loxP model, we determined that sarcomas generated with CRISPR/Cas9 had similar growth kinetics, histology, copy number variation, and mutational load as assessed by whole-exome sequencing. We also demonstrated that off-target mutations in the sarcomas initiated by the Cas9 endonuclease were rare in tumors. Finally, we analyzed the Cas9-mediated indels present in tumors as genetic barcodes, which will enable future studies of tumor heterogeneity and clonality. These results show that sarcomas generated with CRISPR/Cas9 technology are similar to sarcomas generated with conventional modeling techniques. Ultimately this work corroborates CRISPR/Cas9-generated mouse models with traditional GEMMs phenotypically and genotypically, and expands the range of sarcoma mouse models available for research.

Citation Format: Jianguo Huang, Mark Chen, Melodi Javid Whitley, Hsuan-Cheng Kuo, Eric S. Xu, Andrea Walens, Yvonne M. Mowery, David Van Mater, William C. Eward, Diana M. Cardona, Lixia Luo, Yan Ma, Omar M. Lopez, Christopher E. Nelson, Jacqueline N. Robinson-Hamm, Anupama Reddy, Sandeep S. Dave, Charles A. Gersbach, Rebecca D. Dodd, David G. Kirsch. Generation and comparison of CRISPR/Cas9 and Cre-mediated genetically engineered mouse models of sarcoma [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr A17.

Generation and comparison of CRISPR-Cas9 and Cre-mediated genetically engineered mouse models of sarcoma

Genetically engineered mouse models that employ site-specific recombinase technology are important tools for cancer research but can be costly and time-consuming. The CRISPR-Cas9 system has been adapted to generate autochthonous tumours in mice, but how these tumours compare to tumours generated by conventional recombinase technology remains to be fully explored. Here we use CRISPR-Cas9 to generate multiple subtypes of primary sarcomas efficiently in wild type and genetically engineered mice. These data demonstrate that CRISPR-Cas9 can be used to generate multiple subtypes of soft tissue sarcomas in mice. Primary sarcomas generated with CRISPR-Cas9 and Cre recombinase technology had similar histology, growth kinetics, copy number variation and mutational load as assessed by whole exome sequencing. These results show that sarcomas generated with CRISPR-Cas9 technology are similar to sarcomas generated with conventional modelling techniques and suggest that CRISPR-Cas9 can be used to more rapidly generate genotypically and phenotypically similar cancers.

Bone marrow transplantation for CVID-like humoral immune deficiency associated with red cell aplasia

Patients with common variable immunodeficiency (CVID) have a higher incidence of autoimmune disease, which may mark the disease onset; however, anemia secondary to pure red cell aplasia is an uncommon presenting feature. Here, we describe a case of CVID-like humoral immune deficiency in a child who initially presented with red cell aplasia and ultimately developed progressive bone marrow failure. Although bone marrow transplantation (BMT) has been associated with high mortality in CVID, our patient was successfully treated with a matched sibling BMT and engrafted with >98% donor chimerism and the development of normal antibody titers to diphtheria and tetanus toxoids.

Methods to generate genetically engineered mouse models of soft tissue sarcoma

We discuss the generation of primary soft tissue sarcomas in mice using the Cre-loxP system to activate conditional mutations in oncogenic Kras and the tumor suppressor p53 (LSL-Kras(G12D/+); p53(flox/flox)). Sarcomas can be generated either by adenoviral delivery of Cre recombinase, activation of transgenic Cre recombinase with tamoxifen, or through transplantation of isolated satellite cells with Cre activation in vitro. Various applications of these models are discussed, including anticancer therapies, metastasis, in vivo imaging, and genetic requirements for tumorigenesis.

Acute tissue injury activates satellite cells and promotes sarcoma formation via the HGF/c-MET signaling pathway

Some patients with soft-tissue sarcoma (STS) report a history of injury at the site of their tumor. Although this phenomenon is widely reported, there are relatively few experimental systems that have directly assessed the role of injury in sarcoma formation. We recently described a mouse model of STS whereby p53 is deleted and oncogenic Kras is activated in muscle satellite cells via a Pax7(CreER) driver following intraperitoneal injection with tamoxifen. Here, we report that after systemic injection of tamoxifen, the vast majority of Pax7-expressing cells remain quiescent despite mutation of p53 and Kras. The fate of these muscle progenitors is dramatically altered by tissue injury, which leads to faster kinetics of sarcoma formation. In adult muscle, quiescent satellite cells will transition into an active state in response to hepatocyte growth factor (HGF). We show that modulating satellite cell quiescence via intramuscular injection of HGF increases the penetrance of sarcoma formation at the site of injection, which is dependent on its cognate receptor c-MET. Unexpectedly, the tumor-promoting effect of tissue injury also requires c-Met. These results reveal a mechanism by which HGF/c-MET signaling promotes tumor formation after tissue injury in a mouse model of primary STS, and they may explain why some patients develop a STS at the site of injury.

Abstract A64: A role for injury in sarcomagenesis

We developed a primary mouse model of embryonal rhabdomyosarcoma and discovered that tissue injury dramatically accelerates sarcoma formation at the site of injury. We were intrigued by this finding as many sarcoma patients anecdotally report a history of trauma prior to sarcoma development. We therefore utilized this mouse model system to explore the mechanism of injury-mediated sarcoma formation. Our preliminary findings suggest that the majority of muscle progenitor cells remain quiescent following mutation of genes with high transformation potential. However, tissue injury “flips a switch”, thereby pushing resting muscle progenitor cells into a proliferative phase. In the setting of a normal mouse, proliferation of muscle cells results in resolution of the injury in a matter of weeks. Conversely, when cells in the vicinity of injury harbor transformative gene mutations, the “switch” does not return to an off-state, and a tumor rapidly develops at the injury site.

Our novel mouse model of embryonal rhabdomyosarcoma provides temporospatial control over the deletion of p53 and activation of Kras in muscle progenitor cells. Specifically, Pax7-CreERT2 (P7) mice express a tamoxifen-inducible Cre downstream of the endogenous promoter for the satellite cell transcription factor Pax7. P7 mice were crossed to genetically engineered mice containing a lox-STOP-lox cassette upstream of oncogenic K-rasG12D (K) in addition to 2 floxed p53 alleles (P) to generate P7KP mice. P7KP mice were injected with systemic, intraperitoneal (IP) tamoxifen to mediate Cre-dependent recombination in Pax7-expressing cells. When treated in this manner, sarcomas arise throughout the animal with 100% penetrance with a median onset of 45 days. In contrast, tumor onset is dramatically accelerated when P7KP mice are injured with cardiotoxin, a component of cobra venom that causes myonecrosis. P7KP mice treated with IP tamoxifen along with concurrent intramuscular (IM) cardiotoxin develop sarcomas at the site of injury with a median onset of 15 days. Cardiotoxin was next injected into the gastrocnemius muscle at time points either before, concurrent, or after IP tamoxifen to better define the effect of injury on sarcoma formation. Cardiotoxin promoted highly efficient transformation when administered up to 3 days before and up to 21 days after IP tamoxifen administration. Lineage tracing studies showed no appreciable proliferation of recombined Pax7+ cells in the absence of cardiotoxin, suggesting that sarcoma formation requires factors in addition to loss of p53 and activation of K-ras to cause sarcoma.

In order to test the hypothesis that proliferating satellite cells are more prone to sarcoma formation, we treated P7KP mice in the gastrocnemius muscle with hepatocyte growth factor (HGF) along with systemic, IP tamoxifen. HGF has been shown to promote proliferation of resting satellite cells. Interestingly, 12/13 mice treated with IM HGF developed sarcomas at the injection site in a median of 37 days versus 3/12 of mice treated with vehicle control. Current experiments are aimed at dissecting the role of the immune system in the cardiotoxin response.

Our experiments support the role of tissue injury acting as a classic promoter in the initiator/promoter model of tumorigenesis. Thus perturbation of the microenvironment has a dramatic effect on sarcoma formation. While the majority of cancer therapeutics are directed against mutations within the tumor, our findings reveal alternative candidates to prevent sarcoma initiation and perhaps maintenance. We anticipate that an understanding of signaling events at the earliest stages of sarcoma formation will provide new drug targets to treat existing tumors and potentially prevent the outgrowth of micrometastases.

Citation Format: David Van Mater, Leonor Ano, Jordan Blum, David G. Kirsch. A role for injury in sarcomagenesis. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A64.

MicroRNA-182 drives metastasis of primary sarcomas by targeting multiple genes

Metastasis causes most cancer deaths, but is incompletely understood. MicroRNAs can regulate metastasis, but it is not known whether a single miRNA can regulate metastasis in primary cancer models in vivo. We compared the expression of miRNAs in metastatic and nonmetastatic primary mouse sarcomas and found that microRNA-182 (miR-182) was markedly overexpressed in some tumors that metastasized to the lungs. By utilizing genetically engineered mice with either deletion of or overexpression of miR-182 in primary sarcomas, we discovered that deletion of miR-182 substantially decreased, while overexpression of miR-182 considerably increased, the rate of lung metastasis after amputation of the tumor-bearing limb. Additionally, deletion of miR-182 decreased circulating tumor cells (CTCs), while overexpression of miR-182 increased CTCs, suggesting that miR-182 regulates intravasation of cancer cells into the circulation. We identified 4 miR-182 targets that inhibit either the migration of tumor cells or the degradation of the extracellular matrix. Notably, restoration of any of these targets in isolation did not alter the metastatic potential of sarcoma cells injected orthotopically, but the simultaneous restoration of all 4 targets together substantially decreased the number of metastases. These results demonstrate that a single miRNA can regulate metastasis of primary tumors in vivo by coordinated regulation of multiple genes.

Trilateral retinoblastoma in a patient with Peutz-Jeghers syndrome

Germline loss of function mutations in tumor suppressor genes RB1 and LKB1/STK11 are associated with the autosomal dominant cancer predisposing syndromes familial retinoblastoma and Peutz-Jeghers syndrome (PJS), respectively. We present a rare case of a young woman with trilateral retinoblastoma diagnosed as an infant who survived and was then diagnosed with PJS as a teenager. There was no family history of either disorder. Analysis of the LKB1/STK11 gene sequence identified a germline frameshift mutation (c.107del) leading to a nonsense mutation near the N-terminus of the protein, confirming a clinical diagnosis of Peutz-Jeghers syndrome. Extensive RB1 gene analysis failed to detect germline mutations or deletions, and immunohistochemical analysis of her ocular tumors demonstrated nuclear staining of immunoreactive pRB. This result suggests that the RB1 gene is intact. We estimate the chance of trilateral retinoblastoma and PJS occurring in the same individual at approximately 1 in 134 billion live births, and we discuss the possibility that this case could be explained by a putative modifier of pRB action that is associated with the LKB1/STK11 pathway.

Transient activation of beta -catenin signaling in cutaneous keratinocytes is sufficient to trigger the active growth phase of the hair cycle in mice

Wnts have key roles in many developmental processes, including hair follicle growth and differentiation. Stabilization of beta-catenin is essential in the canonical Wnt signaling pathway. We developed transgenic mice expressing a regulated form of beta-catenin in the skin. Chronic activation of beta-catenin in resting (telogen) hair follicles resulted in changes consistent with induction of an exaggerated, aberrant growth phase (anagen). Transient activation of beta-catenin produced a normal anagen. Our data lend strong support to the notion that a Wnt/beta-catenin signal operating on hair follicle precursor cells serves as a crucial proximal signal for the telogen-anagen transition.

ITF-2, a downstream target of the Wnt/TCF pathway, is activated in human cancers with beta-catenin defects and promotes neoplastic transformation

In many cancers, inactivation of the adenomatous polyposis coli (APC) or Axin tumor suppressor proteins or activating mutations in beta-catenin lead to elevated beta-catenin levels, enhanced binding of beta-catenin to T cell factor (TCF) proteins, and increased expression of TCF-regulated genes. We found that the gene for the basic helix-loop-helix transcription factor ITF-2 (immunoglobulin transcription factor-2) was activated in rat E1A-immortalized RK3E cells following neoplastic transformation by beta-catenin or ligand-induced activation of a beta-catenin-estrogen receptor fusion protein. Human cancers with beta-catenin regulatory defects had elevated ITF-2 expression, and ITF-2 was repressed by restoring wild-type APC function or inhibiting TCF activity. Of note, ITF-2 promoted neoplastic transformation of RK3E cells. We propose that ITF-2 is a TCF-regulated gene, which functions in concert with other TCF target genes to promote growth and/or survival of cancer cells with defects in beta-catenin regulation.

Identification of the yeast cytidine deaminase CDD1 as an orphan C-->U RNA editase

Yeast co-expressing rat APOBEC-1 and a fragment of human apolipoprotein B (apoB) mRNA assembled functional editosomes and deaminated C6666 to U in a mooring sequence-dependent fashion. The occurrence of APOBEC-1-complementing proteins suggested a naturally occurring mRNA editing mechanism in yeast. Previously, a hidden Markov model identified seven yeast genes encoding proteins possessing putative zinc-dependent deaminase motifs. Here, only CDD1, a cytidine deaminase, is shown to have the capacity to carry out C-->U editing on a reporter mRNA. This is only the second report of a cytidine deaminase that can use mRNA as a substrate. CDD1-dependent editing was growth phase regulated and demonstrated mooring sequence-dependent editing activity. Candidate yeast mRNA substrates were identified based on their homology with the mooring sequence-containing tripartite motif at the editing site of apoB mRNA and their ability to be edited by ectopically expressed APOBEC-1. Naturally occurring yeast mRNAs edited to a significant extent by CDD1 were, however, not detected. We propose that CDD1 be designated an orphan C-->U editase until its native RNA substrate, if any, can be identified and that it be added to the CDAR (cytidine deaminase acting on RNA) family of editing enzymes.