Absence of oncogenic canonical pathway mutations in aggressive pediatric rhabdoid tumors

BACKGROUND

Rhabdoid tumors (also called atypical teratoid/rhabdoid tumor (AT/RT) in the brain), are highly malignant, poor prognosis lesions arising in the kidneys, soft tissues, and central nervous system. Targeted therapy in this disease would benefit from advanced technologies detecting relevant actionable mutations.

PROCEDURE

Here we report on the evaluation of 25 tumors, all with known SMARCB1/INI1 alterations, for the presence of 983 different mutations in 115 oncogenes and tumor-suppressor genes using OncoMap, a mass spectrometric method of allele detection.

RESULTS

Other than mutations in SMARCB1, our results identified a single activating mutation in NRAS and complete absence of oncogenic mutations in all other genes tested.

CONCLUSION

The absence of mutations in canonical pathways critical for development and progression of adult cancers suggests that distinct mechanisms drive these highly malignant pediatric tumors. This may limit the therapeutic utility of available targeted therapies and require a refocusing toward developmental and epigenetic pathways.

Therapeutic Targeting of EZH2 and BET BRD4 in Pediatric Rhabdoid Tumors

Aberrant activity of the H3K27 modifiers EZH2 and BRD4 is an important oncogenic driver for atypical teratoid/rhabdoid tumor (AT/RT), and each is potentially a possible therapeutic target for treating AT/RT. We, therefore, determined whether targeting distinct histone modifier activities was an effective approach for treating AT/RT. The effects of EZH2 and BRD4 inhibition on histone modification, cell proliferation, and cell invasion were analyzed by immunoblotting, MTS assay, colony formation assay, and cell invasion assay. RNA- and chromatin immunoprecipitation-sequencing were used to determine transcriptional and epigenetic changes in AT/RT cells treated with EZH2 and BRD4 inhibitors. We treated mice bearing human AT/RT xenografts with EZH2 and BRD4 inhibitors. Intracranial tumor growth was monitored by bioluminescence imaging, and the therapeutic response was evaluated by animal survival. AT/RT cells showed elevated levels of H3K27 trimethylation (H3K27me3) and H3K27 acetylation (H3K27ac), with expression of EZH2 and BRD4, and lack of SMARCB1 proteins. Targeted inhibition of EZH2 and BRD4 activities reduced cell proliferation and invasiveness of AT/RT in association with decreasing H3K27me3 and H3K27ac. Differential genomic occupancy of H3K27me3 and H3K27ac regulated specific gene expression in response to EZH2 and BRD4 inhibitions. A combination of EZH2 and BRD4 inhibition increased the therapeutic benefit in vitro and in vivo, outperforming either monotherapy. Overall, histones H3K27me3 and H3K27ac were elevated in AT/RT cells and distributed in distinct chromatin regions to regulate specific gene expression and to promote AT/RT growth. Targeting EZH2 and BRD4 activity is, therefore, a potential combination therapy for AT/RT.

Delta-24-RGD, an Oncolytic Adenovirus, Increases Survival and Promotes Proinflammatory Immune Landscape Remodeling in Models of AT/RT and CNS-PNET

PURPOSE

Atypical teratoid/rhabdoid tumors (AT/RT) and central nervous system primitive neuroectodermal tumors (CNS-PNET) are pediatric brain tumors with poor survival and life-long negative side effects. Here, the aim was to characterize the efficacy and safety of the oncolytic adenovirus, Delta-24-RGD, which selectively replicates in and kills tumor cells.

EXPERIMENTAL DESIGN

Delta-24-RGD determinants for infection and replication were evaluated in patient expression datasets. Viral replication and cytotoxicity were assessed in vitro in a battery of CNS-PNET and AT/RT cell lines. In vivo, efficacy was determined in different orthotopic mouse models, including early and established tumor models, a disseminated AT/RT lesion model, and immunocompetent humanized mouse models (hCD34+-NSG-SGM3).

RESULTS

Delta-24-RGD infected and replicated efficiently in all the cell lines tested. In addition, the virus induced dose-dependent cytotoxicity [IC50 value below 1 plaque-forming unit (PFU)/cell] and the release of immunogenic markers. In vivo, a single intratumoral Delta-24-RGD injection (107 or 108 PFU) significantly increased survival and led to long-term survival in AT/RT and PNET models. Delta-24-RGD hindered the dissemination of AT/RTs and increased survival, leading to 70% of long-term survivors. Of relevance, viral administration to established tumor masses (30 days after engraftment) showed therapeutic benefit. In humanized immunocompetent models, Delta-24-RGD significantly extended the survival of mice bearing AT/RTs or PNETs (ranging from 11 to 27 days) and did not display any toxicity associated with inflammation. Immunophenotyping of Delta-24-RGD-treated tumors revealed increased CD8+ T-cell infiltration.

CONCLUSIONS

Delta-24-RGD is a feasible therapeutic option for AT/RTs and CNS-PNETs. This work constitutes the basis for potential translation to the clinical setting.

A Case of Adult-Onset Atypical Teratoid/Rhabdoid Tumor With Extracranial Metastasis

A 47-year-old woman visited a hospital with complaints of headache and epistaxis. A mass lesion was found in the sellar region, and the patient underwent partial removal via transsphenoidal surgery at the hospital. Pathological diagnosis revealed an atypical teratoid/rhabdoid tumor (AT/RT), and she was referred to our hospital for postoperative adjuvant therapy. Although chemotherapy with ifosfamide, carboplatin, and etoposide (ICE regimen) was administered, the residual tumor rapidly grew, and the patient presented with visual disturbance. Irradiation significantly reduced the tumor size. She was stable for 17 weeks; however, dissemination occurred in the left frontal lobe and lumbar spinal cord, and multiple metastases to the lungs occurred. The patient was treated with additional irradiation, oral temozolomide, intrathecal methotrexate, and intrathecal cytarabine; however, these treatments were ineffective. The patient died 34 weeks postoperatively. AT/RTs are rare malignant embryonal tumors that primarily occur in infants and children under three years of age. Due to its rarity, a standardized treatment has not been established. Adult-onset AT/RTs are extremely rare, with a limited number of reported cases. Extracranial metastases are also uncommon and have only been reported in a few cases. The accumulation of additional cases is necessary to establish a standardized treatment. Therefore, here, we report an adult case of extracranial metastasis to contribute to this effort.

Atypical Teratoid/Rhabdoid Tumor of the Sellar Region in an Adult Male: A Case Report

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare, fast-growing, aggressive tumor that is almost exclusively seen in the pediatric population; it has a poor prognosis despite aggressive treatment. Adult cases were thought to be exclusively of women, with a total of 23 cases reported worldwide. We herein report a case of a 35-year-old male who posed a unique clinical and diagnostic challenge. To the best of our knowledge, this is the third case of a male patient with sellar AT/RT in the world.