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Stover, Daniel G.

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Stover

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Daniel G.

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Stover, Daniel G.

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2015 - 20162

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Author's Publications: search.filters.isAuthorOfPublication.591b088e-5ae6-4ddd-8e90-766756c84310

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    Combination inhibition of PI3K and mTORC1 yields durable remissions in orthotopic patient-derived xenografts of HER2-positive breast cancer brain metastases
    (2016) Ni, Jing; Ramkissoon, Shakti H.; Xie, Shaozhen; Goel, Shom; Stover, Daniel G.; Guo, Hanbing; Luu, Victor; Marco, Eugenio; Ramkissoon, Lori A.; Kang, Yun Jee; Hayashi, Marika; Nguyen, Quang-De; Ligon, Azra; Du, Rose; Claus, Elizabeth; Alexander, Brian; Yuan, Guo-Cheng; Wang, Zhigang C.; Iglehart, J. Dirk; Krop, Ian; Roberts, Thomas; Winer, Eric; Lin, Nancy; Ligon, Keith; Zhao, Jean
    Brain metastases represent the greatest clinical challenge in treating HER2-positive breast cancer. We report the development of orthotopic patient-derived xenografts (PDXs) of HER2-expressing breast cancer brain metastases (BCBM), and their use for the identification of targeted combination therapies. Combined inhibition of PI3K and mTOR resulted in durable tumor regressions in three of five PDXs, and therapeutic response correlated with reduction of 4EBP1 phosphorylation. The two non-responding PDXs showed hypermutated genomes with enrichment of mutations in DNA repair genes, suggesting an association of genomic instability with therapeutic resistance. These findings suggest that a biomarker-driven clinical trial of PI3K inhibitor plus an mTOR inhibitor should be conducted for patients with HER2-positive BCBM.
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    Response and resistance to BET bromodomain inhibitors in triple negative breast cancer
    (2015) Shu, Shaokun; Lin, Charles Y.; He, Housheng Hansen; Witwicki, Robert; Tabassum, Doris P.; Roberts, Justin M.; Janiszewska, Michalina; Huh, Sung Jin; Liang, Yi; Ryan, Jeremy; Doherty, Ernest; Mohammed, Hisham; Guo, Hao; Stover, Daniel G.; Ekram, Muhammad B.; Brown, Jonathan; D'Santos, Clive; Krop, Ian; Dillon, Deborah; McKeown, Michael; Ott, Christopher; Qi, Jun; Ni, Min; Rao, Prakash K.; Duarte, Melissa; Wu, Shwu-Yuan; Chiang, Cheng-Ming; Anders, Lars; Young, Richard A.; Winer, Eric; Letai, Antony; Barry, William T.; Carroll, Jason S.; Long, Henry; Brown, Myles; Liu, X. Shirley; Meyer, Clifford; Bradner, James E; Polyak, Kornelia
    Triple negative breast cancer (TNBC) is a heterogeneous and clinically aggressive disease for which there is no targeted therapy1-3. BET bromodomain inhibitors, which have shown efficacy in several models of cancer4-6, have not been evaluated in TNBC. These inhibitors displace BET bromodomain proteins such as BRD4 from chromatin by competing with their acetyllysine recognition modules, leading to inhibition of oncogenic transcriptional programs7-9. Here we report the preferential sensitivity of TNBCs to BET bromodomain inhibition in vitro and in vivo, establishing a rationale for clinical investigation and further motivation to understand mechanisms of resistance. In paired cell lines selected for acquired resistance to BET inhibition from previously sensitive TNBCs, we failed to identify gatekeeper mutations, new driver events or drug pump activation. BET-resistant TNBC cells remain dependent on wild-type BRD4, which supports transcription and cell proliferation in a bromodomain-independent manner. Proteomic studies of resistant TNBC identify strong association with MED1 and hyper-phosphorylation of BRD4 attributable to decreased activity of PP2A, identified here as a principal BRD4 serine phosphatase. Together, these studies provide a rationale for BET inhibition in TNBC and present mechanism-based combination strategies to anticipate clinical drug resistance.