Abstract 2548: DNA damage response gene expression in CHK1 inhibitor responsive and resistant mouse models of MYC driven B-cell lymphoma

Abstract

Abstract Enhanced tumor replication stress and genomic instability can lead to disruption of the DNA damage response, leading to tumor survival and dependence on essential checkpoint controls. Drugs to target intact pathways, such as CHK1 inhibitors, are therefore desirable and currently in clinical trials as potential future anticancer therapies. The underlying mechanisms underpinning the response and resistance to CHK1 inhibitor treatment are still unclear. We have demonstrated that NF-κB can regulate the response to oncogene induced DNA replication stress in vivo through regulation of CLSPN (Claspin) gene expression. Claspin is an essential adaptor protein required for the phosphorylation and activation of CHK1 by ATR. Using the Eµ-MYC mouse model of B-cell lymphoma we have found that mutation of NF-κB subunits (knockout of c-Rel or a T505A transactivation domain mutation of RelA) leads to earlier lymphoma onset that correlates with loss of Clspnexpression and inhibition of CHK1 activity. Moreover, while wild type Eµ-MYC lymphomas are highly responsive to CHK1 inhibitor treatment, by contrast Eµ-MYC NF-κB mutant cRel-/- or RelAT505A lymphomas are resistant. To understand more about how MYC driven lymphoma cells respond to CHK1 inhibitor treatment, we have investigated changes in the expression of genes encoding members of DNA damage response pathways. Wild type mice reimplanted with Eµ-MYC lymphoma cells were treated with the CHK1 inhibitor CCT244747 and harvested at multiple fixed timepoints. Quantitative PCR analysis of mRNAs encoding proteins in the ATR/CHK1 and ATM/CHK2 pathways was performed, with RPL13A used as reference gene. Interestingly, while dramatic changes were seen in wild type Eµ-MYC cells, these were not seen in CHK1 inhibitor resistant cRel-/- lymphomas. We observed an upregulation of the DNA damage and cell cycle responsive genes in the CHK1 inhibitor sensitive wild-type Eµ-MYC mice. This is consistent with with previously published in vitro studies and suggests an S phase cell cycle arrest in response to CHK1 inhibitor induced DNA damage. This response, however, is absent in the CHK1 inhibitor resistant Eµ-MYC NF-κB mutant lymphomas. It is hoped that by understanding these differences in gene expression that biomarkers of CHK1 inhibitor response can be identified to help stratify future clinical candidates. Citation Format: Nicola L. Hannaway, Jill E. Hunter, Alastair Greystoke, Neil D. Perkins. DNA damage response gene expression in CHK1 inhibitor responsive and resistant mouse models of MYC driven B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2548.