The CHD1 gene, encoding the chromo-domain helicase DNAbinding protein-1, is one of the most frequently deleted genes in prostate cancer. Here, we examined the role of CHD1 in DNA double-strand break (DSB) repair in prostate cancer cells. We show that CHD1 is required for the recruitment of CtIP to chromatin and subsequent end resection during DNA DSB repair. Our data support a role for CHD1 in opening the chromatin around the DSB to facilitate the recruitment of homologous recombination (HR) proteins. Consequently, depletion of CHD1 specifically affects HR-mediated DNA repair but not non-homologous end joining. Together, we provide evidence for a previously unknown role of CHD1 in DNA DSB repair via HR and show that CHD1 depletion sensitizes cells to PARP inhibitors, which has potential therapeutic relevance. Our findings suggest that CHD1 deletion, like BRCA1/2 mutation in ovarian cancer, may serve as a marker for prostate cancer patient stratification and the utilization of targeted therapies such as PARP inhibitors, which specifically target tumors with HR defects.

BackgroundDisruptor of telomeric silencing 1-like (DOT1L) is a non-SET domain containing methyltransferase known to catalyze mono-, di-, and tri-methylation of histone 3 on lysine 79 (H3K79me). DOT1L-mediated H3K79me has been implicated in chromatin-associated functions including gene transcription, heterochromatin formation, and DNA repair. Recent studies have uncovered a role for DOT1L in the initiation and progression of leukemia and other solid tumors. The development and availability of small molecule inhibitors of DOT1L may provide new and unique therapeutic options for certain types or subgroups of cancer.MethodsIn this study, we examined the role of DOT1L in DNA double-strand break (DSB) response and repair by depleting DOT1L using siRNA or inhibiting its methyltransferase activity using small molecule inhibitors in colorectal cancer cells. Cells were treated with different agents to induce DNA damage in DOT1L-depleted or -inhibited cells and analyzed for DNA repair efficiency and survival. Further, rectal cancer patient samples were analyzed for H3K79me3 levels in order to determine whether it may serve as a potential marker for personalized therapy.ResultsOur results indicate that DOT1L is required for a proper DNA damage response following DNA double-strand breaks by regulating the phosphorylation of the variant histone H2AX (γH2AX) and repair via homologous recombination (HR). Importantly, we show that small molecule inhibitors of DOT1L combined with chemotherapeutic agents that are used to treat colorectal cancers show additive effects. Furthermore, examination of H3K79me3 levels in rectal cancer patients demonstrates that lower levels correlate with a poorer prognosis.ConclusionsIn this study, we conclude that DOT1L plays an important role in an early DNA damage response and repair of DNA double-strand breaks via the HR pathway. Moreover, DOT1L inhibition leads to increased sensitivity to chemotherapeutic agents and PARP inhibition, which further highlights its potential clinical utility. Our results further suggest that H3K79me3 can be useful as a predictive and or prognostic marker for rectal cancer patients.Electronic supplementary materialThe online version of this article (10.1186/s13148-018-0601-1) contains supplementary material, which is available to authorized users.

Targeting DNA repair with small-molecule inhibitors is an attractive strategy for cancer therapy. Majority of DNA double-strand breaks in mammalian cells are repaired through nonhomologous end-joining (NHEJ). It has been shown that smallmolecule inhibitors of NHEJ can block efficient repair inside cancer cells, leading to cell death. Previously, we have reported that SCR7, an inhibitor of NHEJ can induce tumor regression in mice. Later studies have shown that different forms of SCR7 can inhibit DNA end-joining in Ligase IV-dependent manner. Recently, we have derivatized

Background: Toll-like receptor (TLR) proteins play key roles in immune responses against infection. TLRs are normally associated with multiple chronic inflammatory diseases. As chronic inflammation often leads to development of neoplasia, we hypothesize that TLRs may promote neoplasia in distinct organ types. Elevated expression of some TLRs has been reported in many tumor tissues and/or tumor cell lines. It is known that in pancreatic ductal adenocarcinoma (PDAC), chronic inflammatory conditions often precede the tumorigenesis process. However, in this context a comprehensive analysis of expression of TLRs in PDAC is currently unknown. Aim: To investigate the expression of multiple TLRs in PDAC cells. Methods and Results: Multiple PDAC cell lines including AsPC-1, MIA PaCa2, PANC-1, PANC-28, and SW1990 were used for TLR phenotyping. The expression of TLRs including TLR2, 3, 4, 7 and 9 were analyzed by Flow Cytometry and Western Blotting techniques. We found that the expression of TLR2, 3, 4, 7 and 9 can be detected in MIA PaCa2, PANC-1, PANC-28, and SW1990 cells. However, the expression of TLR4 and TLR7 are very low in SW1990 cells when compared to MIA PaCa2, PANC-1, and PANC-28 cells. In AsPC-1 cells, the expression of TLR2, 4, and 7 are below the detection levels while the expression of TLR9 and TLR3 can be readily detected. Conclusion: The expression profile of TLRs is distinct among multiple PDAC cells. Using the PDAC cell lines as a model system we are assessing potential predictive value of TLRs as biomarkers in cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 894. doi:10.1158/1538-7445.AM2011-894