Oncogenic stress sensitizes murine cancers to hypomorphic suppression of ATR
David W. Schoppy, … , J. Alan Diehl, Eric J. Brown
David W. Schoppy, … , J. Alan Diehl, Eric J. Brown
Published December 1, 2011
Citation Information: J Clin Invest. 2012;122(1):241-252. https://doi.org/10.1172/JCI58928.
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Research Article

Oncogenic stress sensitizes murine cancers to hypomorphic suppression of ATR

Abstract

Oncogenic Ras and p53 loss-of-function mutations are common in many advanced sporadic malignancies and together predict a limited responsiveness to conventional chemotherapy. Notably, studies in cultured cells have indicated that each of these genetic alterations creates a selective sensitivity to ataxia telangiectasia and Rad3-related (ATR) pathway inhibition. Here, we describe a genetic system to conditionally reduce ATR expression to 10% of normal levels in adult mice to compare the impact of this suppression on normal tissues and cancers in vivo. Hypomorphic suppression of ATR minimally affected normal bone marrow and intestinal homeostasis, indicating that this level of ATR expression was sufficient for highly proliferative adult tissues. In contrast, hypomorphic ATR reduction potently inhibited the growth of both p53-deficient fibrosarcomas expressing H-rasG12V and acute myeloid leukemias (AMLs) driven by MLL-ENL and N-rasG12D. Notably, DNA damage increased in a greater-than-additive fashion upon combining ATR suppression with oncogenic stress (H-rasG12V, K-rasG12D, or c-Myc overexpression), indicating that this cooperative genome-destabilizing interaction may contribute to tumor selectivity in vivo. This toxic interaction between ATR suppression and oncogenic stress occurred without regard to p53 status. These studies define a level of ATR pathway inhibition in which the growth of malignancies harboring oncogenic mutations can be suppressed with minimal impact on normal tissue homeostasis, highlighting ATR inhibition as a promising therapeutic strategy.

Authors

David W. Schoppy, Ryan L. Ragland, Oren Gilad, Nishita Shastri, Ashley A. Peters, Matilde Murga, Oscar Fernandez-Capetillo, J. Alan Diehl, Eric J. Brown

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Figure 3

ATR hypomorphic suppression is more limiting to MLL-ENL– and N-rasG12D–transformed AMLs than to normal bone marrow cells.

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ATR hypomorphic suppression is more limiting to MLL-ENL– and N-rasG12D–t...
(A) The amount of correctly spliced ATR transcript from the ATRseckel allele. Transcript levels relative to the murine ATRfl allele are shown. These levels were quantified through qRT-PCR as described in Figure 1 and Methods. Data represent mean ± SEM. (B) Experimental approach to suppressing ATR expression in murine AML. AML cells were transplanted from a primary recipient to secondary recipients, and tamoxifen was given upon detection of substantial representation (>20%) of GFP+ AML cells in peripheral white blood cells. (C) ATR hypomorphic suppression is competitively disadvantageous to AMLs to a greater degree than to normal bone marrow. tamoxifen-treated secondary (AML) recipient mice were sacrificed at various days following initiation of treatment. Genomic DNA was isolated from leukemic bone marrow, and Cre-mediated ATRfl recombination (ATRΔ) was quantified through qPCR. For comparison, bone marrow from systemically treated ATRfl/seckel mice was quantified similarly for the persistence of ATRΔ/seckel cells. No significant differences were observed between p53+/+ and p53–/– backgrounds. Data represent mean ± SEM.