American Association for Cancer Research
00085472can183066-sup-209661_2_supp_5325290_pmkc72.pdf (23.03 MB)

Supplementary Figures S1-S7 from MDM2 and MDM4 Are Therapeutic Vulnerabilities in Malignant Rhabdoid Tumors

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journal contribution
posted on 2023-03-31, 03:06 authored by Thomas P. Howard, Taylor E. Arnoff, Melinda R. Song, Andrew O. Giacomelli, Xiaofeng Wang, Andrew L. Hong, Neekesh V. Dharia, Su Wang, Francisca Vazquez, Minh-Tam Pham, Ann M. Morgan, Franziska Wachter, Gregory H. Bird, Guillaume Kugener, Elaine M. Oberlick, Matthew G. Rees, Hong L. Tiv, Justin H. Hwang, Katherine H. Walsh, April Cook, John M. Krill-Burger, Aviad Tsherniak, Prafulla C. Gokhale, Peter J. Park, Kimberly Stegmaier, Loren D. Walensky, William C. Hahn, Charles W.M. Roberts

S1: RNAi data and CRISPR-Cas9 data divided by p53 status. S2: Expression of MDM2 and MDM4 in MRT and control cell lines. S3: CRISPR-Cas9 mediated inactivation of TP53 in MRT cell lines. S4: Immunoblots for p53 pathway activation upon MDM2 and MDM2/4 inhibition in MRT and control cell lines. S5: Cell counts, flow cytometry, and senescence assays in MRT cells following MDM2 and MDM2/4 inhibition. S6: Characterization of MRT cells expressing SMARCB1 or p16. S7: MRT xenograft growth characteristics and pharmacodynamic responses.






Malignant rhabdoid tumors (MRT) are highly aggressive pediatric cancers that respond poorly to current therapies. In this study, we screened several MRT cell lines with large-scale RNAi, CRISPR-Cas9, and small-molecule libraries to identify potential drug targets specific for these cancers. We discovered MDM2 and MDM4, the canonical negative regulators of p53, as significant vulnerabilities. Using two compounds currently in clinical development, idasanutlin (MDM2-specific) and ATSP-7041 (MDM2/4-dual), we show that MRT cells were more sensitive than other p53 wild-type cancer cell lines to inhibition of MDM2 alone as well as dual inhibition of MDM2/4. These compounds caused significant upregulation of the p53 pathway in MRT cells, and sensitivity was ablated by CRISPR-Cas9–mediated inactivation of TP53. We show that loss of SMARCB1, a subunit of the SWI/SNF (BAF) complex mutated in nearly all MRTs, sensitized cells to MDM2 and MDM2/4 inhibition by enhancing p53-mediated apoptosis. Both MDM2 and MDM2/4 inhibition slowed MRT xenograft growth in vivo, with a 5-day idasanutlin pulse causing marked regression of all xenografts, including durable complete responses in 50% of mice. Together, these studies identify a genetic connection between mutations in the SWI/SNF chromatin-remodeling complex and the tumor suppressor gene TP53 and provide preclinical evidence to support the targeting of MDM2 and MDM4 in this often-fatal pediatric cancer. This study identifies two targets, MDM2 and MDM4, as vulnerabilities in a deadly pediatric cancer and provides preclinical evidence that compounds inhibiting these proteins have therapeutic potential.