Background Relapsed pediatric sarcomas have a poor prognosis with no available curative options. Alpha-Tocopheryloxyacetic acid (a-TEA) is a redox-silent analog of alpha-tocopherol that induces apoptotic and immunogenic cell death of tumor cells at doses that are not harmful to healthy normal cells. In a first-in-human clinical trial, a-TEA was well tolerated in adults with advanced solid tumors (NCT02192346), but has not yet been studied in pediatric sarcoma. We used a murine model of rhabdomyosarcoma (M3-9-M RMS) to assess the in vitro and in vivo anti-tumor effects of a-TEA.
Methods In vitro studies were performed on the M3-9-M RMS cell line to measure a-TEA-mediated apoptosis using flow cytometry (Annexin V+/7AAD+ cells) and live cell imaging (Annexin V+ cells). In vivo studies involved orthotopic implantation of luciferase+ M3-9-M tumor cells into syngeneic C57BL/6 recipients. Once tumors were palpable, mice were randomized to a control diet or a-TEA-supplemented chow for 21 days and evaluated for bioluminescence, tumor growth and overall survival. Gene expression of tumor-infiltrating and splenic T cells were analyzed by bulk RNA-Seq and flow cytometry respectively.
Results M3-9-M RMS treatment with 2.5–100 uM a-TEA induced apoptosis in a dose-dependent manner within 24 hours (p < 0.05) as measured by flow cytometry and live cell imaging. In-vivo studies with the M3-9-M RMS mouse model showed that recipients of a-TEA chow had 30–40% reduced tumor growth (p<0.01) and bioluminescence (p<0.05), leading to prolonged survival (> 4 weeks) compared to recipients of matched control chow (p<0.05). Spleen cells isolated from a-TEA-fed tumor-bearing mice demonstrated increased levels of IFN??+ cells, CD4+ T-cells, Ki-67 proliferation, and decrease in splenic CD11b+ arginase-1+ (p<0.01) and PD-L1+ cells (p<0.05) compared to their counterparts on the control diet. Gene set enrichment analyses of excised RMS tumors after a-TEA treatment revealed increased gene expression of CD24, EP300, CXCR4, and c-Jun as compared to tumors from mice fed control chow.
Conclusions These data indicate that a-TEA mediates apoptosis of RMS in vitro and suppresses in vivo tumor growth, leading to prolonged survival likely via enhanced activation of adaptive immunity through CD4+ T cells and suppression of innate immunity through regulation of myeloid cell subsets. Furthermore, a-TEA may have direct effects on tumor cell proliferation through EP300 and c-Jun as well as indirect effects on tumor growth by regulation of immune cell recruitment through CD24 and CXCR4 gene expression. Administration of a-TEA as a potential salvage treatment for RMS is warranted.
Acknowledgements The study was supported by NIH TL1 TR002375 (FS), St. Baldrick’s Stand up to Cancer (SU2C) Pediatric Dream Team Translational Research Grant SU2C-AACR-DT-27-17, NIH/NCI R01 CA215461, American Cancer Society Research Scholar Grant RSG- 18-104-01-LIB, and the Midwest Athletes Against Childhood Cancer (MACC) Fund (CMC). SU2C is a division of the Entertainment Industry Foundation. Research grants are administered by the American Association for Cancer Research, the scientific partner of SU2C. The contents of this article do not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the US government.
Ethics Approval The University of Wisconsin-Madison Animal Care and Use Committee approved all protocols (M005915).
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