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Evaluation of an EZH2 inhibitor in patient-derived orthotopic xenograft models of pediatric brain tumors alone and in combination with chemo- and radiation therapies

Abstract

Brain tumors are the leading cause of cancer-related death in children. Tazemetostat is an FDA-approved enhancer of zeste homolog (EZH2) inhibitor. To determine its role in difficult-to-treat pediatric brain tumors, we examined EZH2 levels in a panel of 22 PDOX models and confirmed EZH2 mRNA over-expression in 9 GBM (34.6 ± 12.7-fold) and 11 medulloblastoma models (6.2 ± 1.7 in group 3, 6.0 ± 2.4 in group 4) accompanied by elevated H3K27me3 expression. Therapeutic efficacy was evaluated in 4 models (1 GBM, 2 medulloblastomas and 1 ATRT) via systematically administered tazemetostat (250 and 400 mg/kg, gavaged, twice daily) alone and in combination with cisplatin (5 mg/kg, i.p., twice) and/or radiation (2 Gy/day × 5 days). Compared with the untreated controls, tazemetostat significantly (Pcorrected < 0.05) prolonged survival times in IC-L1115ATRT (101% at 400 mg/kg) and IC-2305GBM (32% at 250 mg/kg, 45% at 400 mg/kg) in a dose-dependent manner. The addition of tazemetostat with radiation was evaluated in 3 models, with only one [IC-1078MB (group 4)] showing a substantial, though not statistically significant, prolongation in survival compared to radiation treatment alone. Combining tazemetostat (250 mg/kg) with cisplatin was not superior to cisplatin alone in any model. Analysis of in vivo drug resistance detected predominance of EZH2-negative cells in the remnant PDOX tumors accompanied by decreased H3K27me2 and H3K27me3 expressions. These data supported the use of tazemetostat in a subset of pediatric brain tumors and suggests that EZH2-negative tumor cells may have caused therapy resistance and should be prioritized for the search of new therapeutic targets.

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Fig. 1: Expression of EZH2 mRNA in a panel of xenograft mouse models of pediatric cancers.
Fig. 2: EZH2 overexpression in pediatric brain tumors.
Fig. 3: In vivo therapeutic efficacy of tazemetostat in PDOX models of childhood brain tumors.
Fig. 4: Histological changes induced by tazemetostat.
Fig. 5: Immunohistochemical staining of molecular targets of tazemetostat in vivo.

Data availability

Data are either presented in the manuscript or provided in the supplemental figures/tables.

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Acknowledgements

The authors wish to thank all the veterinarians and veterinary technicians of the Center of Comparative Medicine in Baylor College of Medicine and staff members of the Feigin Center animal facility at Texas Children’s Hospital for their excellent support of our animal experiments.

Funding

This work was funded by NIH/NCI grants RO1 CA185402 (X.N.L.), U01 CA217613 (X.N.L.), and U0 1 CA199222.

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X.N.L., M.S., and B.T. conceived the project, X.N.L. and M.S. led the experimental design, L.Q., H.L., M.K., Y.D., F.B., H.Z., S.X., S.Z., S.I., P.B., J.M.S., S.X., X.N.L. performed the in vivo studies and immunohistochemical staining, L.Q., Y.D., F.B. led the molecular sub-classification of PDOX models, L.G. and H.Z. performed the Western hybridization, S.W.E., E.J.E. performed the statistical analysis. X.N.L. and L.Q. wrote the manuscript and all authors reviewed the manuscript.

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Correspondence to Xiao-Nan Li.

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The patient tumor tissues were collected following our Institutional Review Board (IRB) approved protocols after obtaining consent from the parent(s) or legal guardian(s) of the childhood patients. All the animal experiments were conducted following Institutional Animal Care and Use Committee (IACUC) approved protocols.

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Qi, L., Lindsay, H., Kogiso, M. et al. Evaluation of an EZH2 inhibitor in patient-derived orthotopic xenograft models of pediatric brain tumors alone and in combination with chemo- and radiation therapies. Lab Invest 102, 185–193 (2022). https://doi.org/10.1038/s41374-021-00700-8

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