Hematopoietic-specific heterozygous loss of Dnmt3a exacerbates colitis-associated colon cancer

Clonal hematopoiesis (CH) is defined as clonal expansion of mutant hematopoietic stem cells absent diagnosis of a hematologic malignancy. Presence of CH in solid tumor patients, including colon cancer, correlates with shorter survival. We hypothesized that bone marrow-derived cells with heterozygous loss-of-function mutations of DNMT3A, the most common genetic alteration in CH, contribute to the pathogenesis of colon cancer. In a mouse model that combines colitis-associated colon cancer (CAC) with experimental CH driven by Dnmt3a+/Δ, we found higher tumor penetrance and increased tumor burden compared with controls. Histopathological analysis revealed accentuated colonic epithelium injury, dysplasia, and adenocarcinoma formation. Transcriptome profiling of colon tumors identified enrichment of gene signatures associated with carcinogenesis, including angiogenesis. Treatment with the angiogenesis inhibitor axitinib eliminated the colon tumor-promoting effect of experimental CH driven by Dnmt3a haploinsufficiency and rebalanced hematopoiesis. This study provides conceptually novel insights into non-tumor-cell-autonomous effects of hematopoietic alterations on colon carcinogenesis and identifies potential therapeutic strategies.

DNMT3A Harboring Leukemia-Associated Mutations Directs Sensitivity to DNA Damage at Replication Forks

PURPOSE

In acute myeloid leukemia (AML), recurrent DNA methyltransferase 3A (DNMT3A) mutations are associated with chemoresistance and poor prognosis, especially in advanced-age patients. Gene-expression studies in DNMT3A-mutated cells identified signatures implicated in deregulated DNA damage response and replication fork integrity, suggesting sensitivity to replication stress. Here, we tested whether pharmacologically induced replication fork stalling, such as with cytarabine, creates a therapeutic vulnerability in cells with DNMT3A(R882) mutations.

EXPERIMENTAL DESIGN

Leukemia cell lines, genetic mouse models, and isogenic cells with and without DNMT3A(mut) were used to evaluate sensitivity to nucleoside analogues such as cytarabine in vitro and in vivo, followed by analysis of DNA damage and signaling, replication restart, and cell-cycle progression on treatment and after drug removal. Transcriptome profiling identified pathways deregulated by DNMT3A(mut) expression.

RESULTS

We found increased sensitivity to pharmacologically induced replication stress in cells expressing DNMT3A(R882)-mutant, with persistent intra-S-phase checkpoint activation, impaired PARP1 recruitment, and elevated DNA damage, which was incompletely resolved after drug removal and carried through mitosis. Pulse-chase double-labeling experiments with EdU and BrdU after cytarabine washout demonstrated a higher rate of fork collapse in DNMT3A(mut)-expressing cells. RNA-seq studies supported deregulated cell-cycle progression and p53 activation, along with splicing, ribosome biogenesis, and metabolism.

CONCLUSIONS

Together, our studies show that DNMT3A mutations underlie a defect in recovery from replication fork arrest with subsequent accumulation of unresolved DNA damage, which may have therapeutic tractability. These results demonstrate that, in addition to its role in epigenetic control, DNMT3A contributes to preserving genome integrity during replication stress.

Abstract B93: Investigating the role of the hematopoietic-specific DNMT3A mutations in the aggressive phenotype of colon cancer

Clonal hematopoiesis (CH) is a nonmalignant condition characterized by clonal expansion of one or few hematopoietic stem cells. CH is associated with advanced age and presence of presumed leukemic driver mutations, such as in the DNMT3A gene. Clinical studies show that presence of CH mutations in the bone marrow in patients with solid tumors is associated with unfavorable prognosis and shorter survival. Moreover, CH mutations are enriched in tumor-infiltrating leukocytes compared to peripheral blood. While these observations have profound clinical implications, the understanding of the relationship between mutations in the blood system and aggressive phenotype of solid tumors is still lacking. We hypothesized that bone marrow-derived cells harboring alterations in DNMT3A contribute to tumor-promoting microenvironment through immune imbalance. To this end, we established a mouse model of CH driven by Dnmt3a alterations and are investigating its effect on a well-established colitis-associated colon cancer model (CAC) as a prototypical solid tumor. Wild-type recipient mice were transplanted with bone marrow from animals with: a) heterozygous loss of Dnmt3a (Dnmt3a+/−); b) Dnmt3a R878H point-mutation (Dnmt3aRH); c) wild-type controls (Dnmt3a+/+). Since inflammation is known to promote tumorigenesis, we are testing the sensitivity of engrafted mice to experimental colitis induced by 2.5% dextran sulfate sodium salt (DSS) in drinking water. Animals of all 3 experimental groups will be co-housed to control for cage-to-cage variability in microbiota. We will use total body weight loss, histopathology of harvested colons (swiss roll method)/colitis scores, colon size, and appearance of intestinal contents as a readout for colitis severity. Next, we will investigate AOM/DSS-induced tumorigenesis in CH model, including tumor burden and extent of inflammation between experimental groups. Finally, we will characterize tumor-infiltrating leukocytes that contribute to aggressive CAC phenotype to identify immune populations that engender this tumor-modulating function, including epigenetic and gene expression profiles. Our goal is to understand the relationship between mutations in the blood system and aggressive phenotype of nonhematologic cancers and to nominate potential targets for therapeutic intervention.

Citation Format: Yang Feng, Daniil E. Shabashvili, Luisa M. Posada, Kathryn I. Krajcik, Chamara Gunaratne, Olga A. Guryanova. Investigating the role of the hematopoietic-specific DNMT3A mutations in the aggressive phenotype of colon cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B93.