Abstract 3292: Therapeutic targeting of INI1 deficiency in pediatric ATRT: a preclinical study utilizing patient-derived orthotopic xenograft (PDOX) models

Abstract

Abstract Introduction: Atypical teratoid rhabdoid tumors (ATRTs) are a high grade pediatric brain malignancy with extremely poor survival outcomes. They are molecularly defined by deletions or mutations in the tumor suppressor gene INI1. INI1 deficiency causes dysfunction of chromatin-remodeling complexes, which normally function to oppose the epigenetic gene silencing protein EZH2. In the setting of INI1 deficiency, EZH2 is over-expressed, leading to ATRT oncogenesis. Consequently, using our novel patient derived orthotopic xenograft (PDOX) models, we investigated the pre-clinical utility of therapeutic EZH2 inhibition in ATRT using the drug DZNep. Methods: Two PDOX models were established, one from fresh surgical sample and the second (IC-L1115ATRT) from tumor tissue obtained at autopsy. Both tumors were pathologically documented to have INI1 deficiency. Tumor cells were directly implanted into mouse brains in the matched location with the patient tumor. For in vitro testing, ATRT cells harvested from xenograft tumors were exposed to an EZH2 inhibitor, DZNep, at doses ranging from 78 to 5000 nM for 2 weeks; cell viability was measured with the colorimetric CCK assay every 1- 3 days. For in vivo testing, 40 mice were divided into 4 treatment groups: control, DZNep treatment (5 mg/kg i.p. daily x 14 days), standard of care (cranial radiation therapy 2 Gy daily x 5 days, cisplatin 5 mg/kg i.p. on days 8 and 11), and combination therapy. Animals were euthanized once they developed neurologic deficits. Survival times were compared using log-rank analysis. Results: DZNep showed dose- and time-dependent in vitro inhibition of tumor cell viability in both ATRT models tested. One of these models (IC-L1115ATRT) was then subjected to in vivo studies. ATRT tumors were present at the time of xenograft death in all 4 treatment groups including DZNep- and combination therapy-treated animals. Survival time did not differ between the control- and DZNep-treated groups or the standard of care- and combination therapy-treated groups (P>0.05). Conclusions: While the EZH2 inhibitor DZNep is effective in vitro in killing ATRT tumor cells, it does not appear to have effects in vivo when tested in PDOX models of pediatric ATRT acting alone or in combination with combined chemo- and radio-therapies. Extensive further pre-clinical evidence should be obtained before an EZH2 inhibitor is brought into pediatric clinical trials. Citation Format: Holly B. Lindsay, Mari Kogiso, Lin Qi, Jeffrey C. Murray, Laszlo Perlaky, Jack MF Su, Patricia Baxter, Adekunle Adesina, Donald W. Parsons, Murali Chintagumpala, Xiao-Nan Li. Therapeutic targeting of INI1 deficiency in pediatric ATRT: a preclinical study utilizing patient-derived orthotopic xenograft (PDOX) models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3292. doi:10.1158/1538-7445.AM2015-3292