Abstract Introduction: Inhibition of poly(ADP-ribose) polymerase (PARP) induces synthetic lethality in cells exhibiting defects in homologous repair (HR) pathways, such as BRCA1 and BRCA2-mutated breast or ovarian cancers, and 4 different PARP inhibitors (PARPi) are currently approved by the FDA. While HR-deficient cancers usually respond well to single agent PARPi, HR-proficient cancers are generally less sensitive to the treatment. Acquired resistance to PARPi due to activating mutations in BRCA genes are also not uncommon. In this work, we have examined strategies for enhancing PARPi activity in a HR-proficient context and identified histone deacetylases (HDACs) as targets for pharmacological synthetic lethality in the context of PARPi. Materials and methods: PARP1 and PARP2 activity were measured using Trevigen Universal Colorimetric PARP Assay Kit, BPS Bioscience PARP2 Colorimetric PARP2 Assay Kit, and PARylation assay. HDAC activity was measured using HeLa cell nuclear extracts and a fluorogenic peptide-based biochemical assay. Cell survival EC50 were determined using CellTiter Glo viability assay. Cell cycle analysis was performed by flow cytometry with propidium iodide staining. DNA damage was investigated by immunoblotting and immunofluorescence using gamma-H2AX antibodies, and comet assays for confirmation of double-strand breaks. Spheroid assays were performed using the Incucyte® S3 spheroid analysis module. In vivo metastasis formations were examined using the pulmonary metastasis assay (PuMA). Results and discussion: Combinations of PARP and HDAC inhibitors in HR-proficient tumor cells demonstrated that HDACi could enhance the efficacy of PARPi in vitro. This was associated with increased acute and sustained DNA-damage distinct cell cycle profiles showing activity in both S- and G2/M-phases. Importantly, dual single-molecule PARP-HDAC inhibitors showed potent inhibition of PARP1 and PARP2 activity and PAR synthesis, comparable to olaparib, as well as inhibition of HDAC with IC50 values in the low µM range. Dual PARP-HDAC inhibition decreased survival of HR-proficient cells in both 2D cultures and 3D spheroid assays with lower EC50 values than olaparib or vorinostat alone. Importantly, lung metastasis formation was significantly impaired by dual PARP-HDAC inhibition. Conclusion: Combination of PARP inhibition and HDAC inhibition showed increased efficacy compared to single agent PARP inhibition in HR-proficient cells. Development of bifunctional inhibitors may provide a novel therapeutic opportunity for tumors with limited response rates to single agent PARPi. Citation Format: Sarah Truong, Louise Ramos, Beibei Zhai, Fariba Ghaidi, Mona Marzban, Hans Adomat, Xiaoqi Chen, John Langlands, Dennis Brown, Jeffrey Bacha, Colin Collins, Poul H. Sorensen, Wang Shen, Mads Daugaard. Pharmacological synthetic lethality by co-inhibition of PARP and HDAC enzymes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB273.
Sorafenib is a multikinase inhibitor for the treatment of hepatocellular carcinoma. However, most patients who initially respond to sorafenib become refractory. In a previous study, we demonstrated that sphere-forming cells derived from liver cancer cell lines possess the properties of liver cancer stem cells (LCSCs). In the present study, we found that successive passages of LCSCs were more resistant to sorafenib, and LCSCs treated with sorafenib showed an increase in spheroid formation with a lower inhibition rate. MK2206, but not various other inhibitors of cell signaling pathways, enhanced their sensitivity to sorafenib, increased the apoptotic rate, and suppressed the growth of LCSC xenografts in vivo (P < 0.01); sorafenib treatment decreased the level of active phosphorylated (p)Akt (Thr308) and reduced the levels of active pAkt (Ser473) and extracellular signal-regulated kinase (ERK) in LCSCs, whereas MK2206 reduced pAkt expression and increased pERK expression. Cotreatment with sorafenib and MK2206 reduced pAkt and pERK expression in LCSCs and xenografted tumors (P < 0.01). Treatment with either sorafenib or MK2206 decreased the expression of EpCAM and CD133 in LCSCs, which was more evident after combined treatment. Based on these results, we conclude that resistance to sorafenib is associated with weak ERK signaling and strong Akt signaling in LCSCs. By inhibition of Akt and upregulation of ERK, MK2206 overcomes the resistance of LCSCs to sorafenib.
<div>AbstractPurpose:<p>Histone deacetylase (HDAC) inhibition has been shown to induce pharmacologic “BRCAness” in cancer cells with proficient DNA repair activity. This provides a rationale for exploring combination treatments with HDAC and PARP inhibition in cancer types that are insensitive to single-agent PARP inhibitors (PARPi). Here, we report the concept and characterization of a novel bifunctional PARPi (kt-3283) with dual activity toward PARP1/2 and HDAC enzymes in Ewing sarcoma cells.</p>Experimental Design:<p>Inhibition of PARP1/2 and HDAC was measured using PARP1/2, HDAC activity, and PAR formation assays. Cytotoxicity was assessed by IncuCyte live cell imaging, CellTiter-Glo, and spheroid assays. Cell-cycle profiles were determined using propidium iodide staining and flow cytometry. DNA damage was examined by γH2AX expression and comet assay. Inhibition of metastatic potential by kt-3283 was evaluated via <i>ex vivo</i> pulmonary metastasis assay (PuMA).</p>Results:<p>Compared with FDA-approved PARP (olaparib) and HDAC (vorinostat) inhibitors, kt-3283 displayed enhanced cytotoxicity in Ewing sarcoma models. The kt-3283-induced cytotoxicity was associated with strong S and G2–M cell-cycle arrest in nanomolar concentration range and elevated DNA damage as assessed by γH2AX tracking and comet assays. In three-dimensional spheroid models of Ewing sarcoma, kt-3283 showed efficacy in lower concentrations than olaparib and vorinostat, and kt-3283 inhibited colonization of Ewing sarcoma cells in the <i>ex vivo</i> PuMA model.</p>Conclusions:<p>Our data demonstrate the preclinical justification for studying the benefit of dual PARP and HDAC inhibition in the treatment of Ewing sarcoma in a clinical trial and provides proof-of-concept for a bifunctional single-molecule therapeutic strategy.</p></div>
1,2:5,6-Dianhydrogalactitol (DAG) is a bi-functional DNA-targeting agent currently in phase II clinical trial for treatment of temozolomide-resistant glioblastoma (GBM). In the present study, we investigated the cytotoxic activity of DAG alone or in combination with common chemotherapy agents in GBM and prostate cancer (PCa) cells, and determined the impact of DNA repair pathways on DAG-induced cytotoxicity. We found that DAG produced replication-dependent DNA lesions decorated with RPA32, RAD51, and γH2AX foci. DAG-induced cytotoxicity was unaffected by MLH1, MSH2, and DNA-PK expression, but was enhanced by knockdown of BRCA1. Acting in S phase, DAG displayed selective synergy with topoisomerase I (camptothecin and irinotecan) and topoisomerase II (etoposide) poisons in GBM, PCa, and lung cancer cells with no synergy observed for docetaxel. Importantly, DAG combined with irinotecan treatment enhanced tumor responses and prolonged survival of tumor-bearing mice. This work provides mechanistic insight into DAG cytotoxicity in GBM and PCa cells and offers a rational for exploring combination regimens with topoisomerase I/II poisons in future clinical trials.
The fluorescence behaviors and applications of two water‐soluble imidazolium analogs TPI‐1 and TPI‐2 with D‐π‐A structures have been studied. Compound TPI‐1 possessed the aggregation‐induced emission (AIE) effect, but TPI‐2 not. Moreover, compound TPI‐1 could serve as a fluorescence turn‐on probe for detecting uridine‐5'‐triphosphate (UTP) in living cells by AIE mechanism, while TPI‐2 was able to penetrate into the cell membranes and light up the living cells.
ABSTRACT Alternative polyadenylation of pre-mRNA has been recently shown to play important roles in development and cancer. Activating mutations in the Ras oncogene are common drivers of many human cancers but the mechanisms by which they cooperate with alternative polyadenylation are not known. By exploiting the genetics of C. elegans , we identified cfim-1/CFIm25 , a subunit of the alternative polyadenylation machine, as a key determinant of hyperactive Ras function. Ablation of cfim-1 increased penetrance of multivulva phenotype in let-60/Ras gain-of-function (gf) mutant through shortening of transcripts at the 3’ untranslated region, including p21 activated kinase pak-1/PAK1 and multidrug transporter mrp-5/ABCC1 . Depletion of CFIm25 in human KRAS-driven cancer cells resulted in a similar shortening of 3’ untranslated regions in the PAK1 and ABCC1 transcripts, which caused an epithelial-to-mesenchymal transition and increased cell migration. Exploiting the mechanisms by which alternative polyadenylation affects activated oncogene output could offer novel approaches for the treatment of Ras-driven tumors.
<div>Abstract<p>Purpose: Histone deacetylase (HDAC) inhibition has been shown to induce pharmacological “BRCAness” in cancer cells with proficient DNA repair activity. This provides a rationale for exploring combination treatments with HDAC and poly-(ADP-ribose)-polymerase (PARP) inhibition in cancer types that are insensitive to single-agent PARP inhibitors. Here, we report the concept and characterization of a novel bi-functional PARP inhibitor (kt-3283) with dual activity towards PARP1/2 and HDAC enzymes in Ewing sarcoma cells. Experimental Design: Inhibition of PARP1/2 and HDACs was measured using PARP1/2, HDAC activity, and PAR formation assays. Cytotoxicity was assessed by IncuCyte live cell imaging, CellTiter-Glo®, and spheroid assays. Cell cycle profiles were determined using propidium iodide staining and flow cytometry. DNA damage was examined by γH2AX expression and comet assay. Inhibition of metastatic potential by kt-3283 was evaluated via ex vivo pulmonary metastasis assay (PuMA). Results: Compared to FDA-approved PARP (olaparib) and HDAC (vorinostat) inhibitors, kt-3283 displayed enhanced cytotoxicity in Ewing sarcoma models. The kt-3283-induced cytotoxicity was associated with strong S and G2/M cell cycle arrest in nanomolar concentration range and elevated DNA damage as assessed by γH2AX tracking and comet assays. In three-dimensional spheroid models of Ewing sarcoma, kt-3283 showed efficacy in lower concentrations than olaparib and vorinostat and kt-3283 inhibited colonization of Ewing sarcoma cells in the ex vivo PuMA model. Conclusion: Our data demonstrates the preclinical justification for studying the benefit of dual PARP and HDAC inhibition in the treatment of Ewing sarcoma in a clinical trial and provides proof-of-concept for a bi-functional single-molecule therapeutic strategy.</p></div>
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