Cell Cycle Checkpoint Inhibitors Research Articles

Abstract 4664: Therapeutic targeting of TP53-mutated acute myeloid leukemia by inhibiting cell cycle checkpoint

Abstract Acute myeloid leukemia (AML) is a hematological malignancy characterized by various somatic mutations leading to abnormal proliferation and differentiation of hematopoietic cells. Mutations on the TP53 gene occur in 5% to 10% of patients with de novo AML, with higher frequency in patients with relapsed and refractory (R/R) AML. Patients with TP53-mutated AML typically exhibit a poor response to conventional induction therapy and have a short overall survival (OS) rate, with a median duration of 5-9 months. Although various target agents have been developed for the treatment of AML, treatment options for TP53-mutated AML remain limited. Here, we have discovered a novel drug combination that can enhance the efficacy of the conventional therapeutic regimen for TP53-mutated AML patients. For in vitro analysis, we used the human AML cell line Kasumi-1(AML-M2), which harbors a homozygous TP53 R248Q mutation. We treated kasumi-1 cells with a combination of cytarabine and Idarubicin to produce drug tolerant persisters (DTPs) which is a minor population that survived the drug treatment. The Kasumi-1 DTPs displayed temporal G2/M phase cell cycle arrest and significant resistance to further repeated drug treatment. To discover drug candidates targeting TP53-mutated DTPs, we first examined the differentially expressed genes (DEGs) of TP53-mutated AML patients using patients’ RNA expression data deposited in the cancer genome atlas (TCGA) database. Using selected DEGs, drug candidates potentially affecting TP53-mutated AML cells were extracted from the connectivity map (CMap build 02) database. In addition, through a literature search, drugs with the ability to reactivate mutant p53, drugs that directly target mutant p53, synthetic lethal partners with mutant p53, and drugs that target leukemia stem cells were selected as candidate groups. As a result, we selected 46 drug candidates that would be effective for TP53-mutated AML through in silico analysis and therapy strategies targeting p53. Using in vitro cytotoxicity assay, we screened 46 candidate compounds at multiple doses and confirmed several drugs that effectively eliminate DTPs. The drug screening showed that cell cycle checkpoint inhibitors not only resulted in a significant reduction of G2/M phase arrested cells but also induction of apoptotic cells at the subG1 phase. Furthermore, the zero interaction potency (ZIP) model of SynergyFinder (https://synergyfinder.fimm.fi) analysis showed that cell cycle checkpoint inhibitors synergistically enhanced the cytotoxic effect of cytarabine on Kasumi-1 DTPs. Collectively, this study suggests that novel combination treatment of cell cycle checkpoint inhibitors with conventional drugs selectively inhibits TP53-mutated AML DTPs. Citation Format: Daehyeon Gwak, Dongchan Kim, Heejun Jang, Jun Liu, Suji Min, Ja Min Byun, Youngil Koh, Junshik Hong, Sung-soo Yoon, Dong-Yeop Shin, Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea, Republic of. Therapeutic targeting of TP53-mutated acute myeloid leukemia by inhibiting cell cycle checkpoint [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4664.

Abstract 4562: Activity of PARP1-selective inhibitor SNV-001 in models of HRD cancers as monotherapy and in combination

Abstract Current FDA approved poly (ADP-ribose) polymerase inhibitors (PARPi) inhibit both PARP1 and PARP2. Genetic studies indicate that loss of PARP1 is synthetic lethal with homologous recombination deficiency (HRD), including BRCA1/2 mutations, and PARP2 depletion may be linked to hematologic toxicity. To date, no first generation PARPi has been successfully combined with standard of care (SoC) agents in the clinic without significant reduction in dosing intensity because of overlapping toxicities. A selective inhibitor could potentially improve the therapeutic index and provide additional opportunities in combination strategies especially with drugs that are prone to myelosuppression. SNV-001 potently and selectively inhibits PARP1 in biochemical and cellular assays. SNV-001 inhibits PARylation in the low nanomolar range with over 500-fold selectivity against PARP2. SNV-001 did not inhibit any other PARP family member tested up to 10 uM in biochemical assays confirming its selectivity for PARP1. In human erythroid and myeloid colony formation assays, the IC50s of SNV-001 for both lineages were approximately 100-times higher than the target efficacious concentration based on the IC95 for inhibition of DLD1 (BRCA2 -/-) colony formation. In a subcutaneous MDA-MB-436 (BRCA1mut) xenograft model, oral administration of SNV-001 once daily resulted in a dose-dependent tumor regression. SNV-001 showed greater efficacy at lower doses compared to olaparib at 100 mg/kg or at equivalent doses of AZD9574. SNV-001 showed promising synergy with SoC chemotherapies or DDR inhibitors in cell proliferation assays. SNV-001 enhanced cytotoxicity of the DNA-damaging agent topotecan or carboplatin in Capan-1 (BRCA2mut) and HCC1395 (BRCA1mut) cells. Synergy was seen between SNV-001 and cell cycle check point inhibitors camonsertib (ATRi) or adavosertib (WEE1i) in DLD1 (BRCA2 -/-) and UWB1.289 (BRCA1mut) cells, as DNA damage induced by PARP1 trapping relies on cell cycle modulation for repair. Combination of SNV-001 with polymerase theta inhibitor ART558 or USP1 inhibitor KSQ4279 exhibited synergistic effects in DLD1 (BRCA2 -/-) or UWB1.289 (BRCA1mut) cells. These results suggest that inhibition of microhomology-mediated end-joining and translesion synthesis pathways may further exacerbate SNV-001-induced DDR in certain cellular contexts.In summary, the PARP1 selective inhibitor SNV-001 demonstrates potent antitumor activity and shows promising synergy between SoC chemotherapies or DDR inhibitors. Current data highlight a potential strategy for improving treatment efficacy and overcoming resistance. Further clinical investigations are warranted to validate this combination strategy. Citation Format: Zhentian Li, Qipeng Fan, Mingming Gao, Jun Pan, Liangxing Wu, Wenqing Yao, Phillip C. Liu. Activity of PARP1-selective inhibitor SNV-001 in models of HRD cancers as monotherapy and in combination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4562.

HDAC11 mediates the ubiquitin-dependent degradation of p53 and inhibits the anti-leukemia effect of PD0166285.

Cytarabine-resistant acute myeloid leukemia (AML) is a common phenomenon, necessitating the search for new chemotherapeutics. WEE1 participates in cell cycle checkpoint signaling and inhibitors targeting WEE1 (WEE1i) constitute a potential novel strategy for AML treatment. HDAC (histone deacetylase) inhibitors have been shown to enhance the anti-tumor effects of WEE1i but molecular mechanisms of HDAC remain poorly characterized. In this study, the WEE1 inhibitor PD0166285 showed a relatively good anti-leukemia effect. Notably, PD0166285 can arise the expression of HDAC11 which was negatively correlated with survival of AML patients. Moreover, HDAC11 can reduced the anti-tumor effect of PD0166285 through an effect on p53 stability and the changes in phosphorylation levels of MAPK pathways. Overall, the cell cycle inhibitor, PD0166285, is a potential chemotherapeutic drug for AML. These fundings contribute to a functional understanding of HDAC11 in AML.

Effects of Combined Therapeutic Targeting of AXL and ATR on Pleural Mesothelioma Cells.

Few treatment options exist for pleural mesothelioma (PM), which is a progressive malignant tumor. However, the efficacy of molecular-targeted monotherapy is limited, and further therapeutic strategies are warranted to treat PM. Recently, the cancer cell-cycle checkpoint inhibitors have attracted attention because they disrupt cell-cycle regulation. Here, we aimed to establish a novel combinational therapeutic strategy to inhibit the cell-cycle checkpoint kinase, ATR in PM cells. The siRNA screening assay showed that anexelekto (AXL) knockdown enhanced cell growth inhibition when exposed to ATR inhibitors, demonstrating the synergistic effects of the ATR and AXL combination in some PM cells. The AXL and ATR inhibitor combination increased cell apoptosis via the Bim protein and suppressed cell migration when compared with each monotherapy. The combined therapeutic targeting of AXL and ATR significantly delayed regrowth compared with monotherapy. Thus, optimal AXL and ATR inhibition may potentially improve the PM outcome.

A Selective Nano Cell Cycle Checkpoint Inhibitor Overcomes Leukemia Chemoresistance (Small 25/2023)

Nano Cell Cycle Checkpoint Inhibitors In article number 2300736, Daishun Ling, Fangyuan Li, and co-workers demonstrate that ultra-small iron oxide nanoparticles (IONPs) can serve as a selective nano cell cycle checkpoint inhibitor (NCCI) to catalyze the intracellular H2O2 into abundant ·OH, cleave heat shock protein 90 (Hsp90), and thus induce the degradation of the client protein ATR/CHK1, leading to the dysfunction of the G2/M checkpoint in acute myeloid leukemia (AML) cells. As a result, NCCI can interfere with the chemotherapy-induced DNA damage repair, which effectively reverses the chemoresistance of acute myeloid leukemia.

A Selective Nano Cell Cycle Checkpoint Inhibitor Overcomes Leukemia Chemoresistance.

Cell cycle checkpoint activation promotes DNA damage repair, which is highly associated with the chemoresistance of various cancers including acute myeloid leukemia (AML). Selective cell cycle checkpoint inhibitors are strongly demanded to overcome chemoresistance, but remain unexplored. A selective nano cell cycle checkpoint inhibitor (NCCI: citric acid capped ultra-small iron oxide nanoparticles) that can catalytically inhibit the cell cycle checkpoint of AML to boost the chemotherapeutic efficacy of genotoxic agents is now reported. NCCI can selectively accumulate in AML cells and convert H2 O2 to • OH to cleave heat shock protein 90, leading to the degradation of ataxia telangiectasia and Rad3-related proteinand checkpoint kinase 1, and the subsequent dysfunction of the G2/M checkpoint. Consequently, NCCI revitalizes the anti-AML efficacy of cytarabine that is previously ineffective both in vitro and in vivo. This study offers new insights into designing selective cell cycle checkpoint inhibitors for biomedical applications.

Five decades of progress in surgical oncology: Breast.

Surgery remains the single most effective treatment for breast cancer but coincident with a deeper understanding of tumor biology and advances in multidisciplinary care (encompassing breast imaging, systemic adjuvant therapy, radiotherapy, and genomics) continues to de-escalate, supported by strong level I data. We have moved from mastectomy to breast conservation, and from routine axillary dissection to sentinel lymph node biopsy to selective omission of axillary node staging altogether. We have further de-escalated through consensus over margin width in breast conservation, through improvements in neoadjuvant therapy, and by demonstrating no benefit for upfront surgery in patients with stage IV disease. For patients with ipsilateral breast tumor recurrence, reconservation surgery and reirradiation are promising. Cell cycle and immune checkpoint inhibitors, when added to conventional systemic therapy, have now moved beyond stage IV disease to phase III trials in the adjuvant and neoadjuvant settings, promising even further de-escalation of surgery. Finally, with genomic profiling we are moving away from the primacy of axillary node status for prognostication and into a new era allowing prediction of response to therapy.

Abstract 5408: Targeting ATR and AKT pathways promotes cell death in PARP inhibitor-resistant ovarian cancer cells by increasing DNA damage and lethal replication stress

Abstract Poly (ADP-ribose) polymerase inhibitors (PARPis) have changed the treatment paradigm in the management of high-grade serous ovarian cancer (HGSOC). However, most HGSOC ultimately develops resistance to PARPi, leading to unmet medical needs for better therapeutic strategies. ATR-mediated G2/M cell cycle checkpoints are important for cell survival and DNA repair, especially in HGSOC due to its dysfunctional p53-mediated G1/S checkpoint, making them an attractive therapeutic target. However, only modest monotherapy activity of ATR inhibitors (ATRis) has been reported in patients with HGSOC, highlighting the need for combination treatment. We conducted a high-throughput drug combination screen of ATRi (ceralasertib) with 1,912 drugs in two PARPi-resistant BRCA2-mutant PEO1 (PEO1/OlaR and PEO1/OlaJR) HGSOC cell lines. In this screen, 234 drugs showed synergistic cytotoxicity with ATRi, including 31 (13.2%) cell cycle checkpoint inhibitors, 27 (11.5%) chemotherapeutic drugs, and 13 (5.6%) PI3K/AKT pathway inhibitors. We prioritized the PI3K/AKT pathway inhibitors for ATRi combination because the PI3K/AKT pathway is upregulated in >70% of HGSOC and associated with an aggressive phenotype. Moreover, PI3K/AKT signaling is found to be activated in HGSOC cells with PARPi resistance. We separately validated that an ATRi (ceralasertib < 1 μM) in combination with an AKT inhibitor (AKTi; capivasertib < 10 μM) yielded additive/synergistic cytotoxic effects (combination index < 1) in various HGSOC cell lines, including acquired and de novo PARPi-resistant (PEO1/OlaR, PEO1/OlaJR, and PEO4) and platinum-resistant HGSOC cell lines (OVCAR3), by XTT and colony formation assays. With clinically attainable concentrations of ATRi (1 μM) and AKTi (10 μM), the combination treatment increased cell apoptosis compared to ATRi (increased 2.1 to 95.2-fold; P < 0.001) or AKTi alone (increased 3.3 to 92.2-fold; P < 0.001) in both PARPi-sensitive and -resistant HGSOC cells. ATRi+AKTi treatment also showed greater DNA damage as evidenced by increased percentage of cells with ≥ 5 γH2AX foci relative to ATRi (increased 1.1 to 7.6-fold; not significant in PEO1 and P < 0.001 in PARPi-resistant cells) or AKTi (increased 2.3 to 6.2-fold; P < 0.001) in both PARPi-sensitive and -resistant cells. Furthermore, ATRi+AKTi treatment augmented replication stress as measured by increased phospho-RPA+/γH2AX+ populations compared with ATRi (increased 1.7 to 4.7-fold; P < 0.001) or AKTi (increased 3.7 to 12.0-fold; P < 0.001). Overall, our results suggest that dual inhibition of ATR and AKT pathways results in greater cell death by increasing DNA damage and replication stress in HGSOC cells with PARPi resistance. Citation Format: Tzu-Ting Huang, Chih-Yuan Chiang, Nitasha Gupta, Kelli Wilson, Ken Chih-Chien Cheng, Jung-Min Lee. Targeting ATR and AKT pathways promotes cell death in PARP inhibitor-resistant ovarian cancer cells by increasing DNA damage and lethal replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5408.

Cyclin-Dependent Kinase 6 Identified as the Target Protein in the Antitumor Activity of Tetrastigma hemsleyanum.

Background Tetrastigma hemsleyanum (T. hemsleyanum) is widely used as an adjuvant drug for tumor therapy but its antitumor therapeutic targets and molecular mechanisms have remained unclear. The prediction and analysis of natural products has previously used only network pharmacology methods to identify potential target proteins from public databases. In this study, we use comprehensive bioinformatics analysis and experimental verification to determine the antitumor mechanism of T. hemsleyanum.MethodsNetwork pharmacology analysis was used to predict the potential in vivo target proteins of T. hemsleyanum. The expression matrix and clinical data to perform an analysis of hub genes were collected from the TCGA and GTEx databases, specifically the analysis of expression, prognosis, tumor immune cell infiltration analysis, immune checkpoint genes, microsatellite instability, tumor mutational burden, tumor neoantigen, and immune microenvironment, which identify the roles and biological functions of the hub genes in pan-cancer. Finally, gene set enrichment analysis was used to verify the biological processes and signaling pathways involved in the pan-cancer expression profile.ResultsWe found 124 potential in vivo target proteins of T. hemsleyanum through network pharmacological analysis, and five hub genes (AKR1C1, MET, PTK2, PIK3R1, and CDK6) were then screened by protein–protein interaction (PPI) network analysis and molecular complex detection analysis (MCODE). Experimental intervention with an aqueous extract of T. hemsleyanum verified that these hub genes are the target proteins involved in the regulation of T. hemsleyanum in cells. A pan-cancer analysis then confirmed that CDK6 and MET are potential targets upon which T. hemsleyanum may exert antitumor action, especially in ACC, CESC, LGG, and PAAD. The CDK6 protein targeted by T. hemsleyanum is also involved in the immune and mutation process of pan-cancer, especially in the regulation of immune cell infiltration, immune checkpoint gene expression, microsatellite instability, tumor mutation burdens, and tumor neoantigens. Together, these analyses show that T. hemsleyanum affects tumor immune regulation and genomic stability. Finally, a gene set enrichment analysis confirmed that T. hemsleyanum regulates the cell cycle checkpoint.ConclusionsWe found that T. hemsleyanum can behave as an antitumor agent by acting as a potential cell cycle checkpoint inhibitor in CDK6-driven tumors, such as ACC, CESC, LGG, and PAAD, and that it acts as a tyrosine kinase receptor inhibitor that inhibits the expression of the proto-oncogene MET. Combined with an analysis of immune and mutation correlations in pan-cancer, we determined that T. hemsleyanum may function biologically as an immune regulator and interfere with the stability of the tumor genome, which is worthy of further study.

Research Progress of PARP Inhibitor Monotherapy and Combination Therapy for Endometrial Cancer.

Endometrial cancer is one of the three most common malignant tumors in the female reproductive system. Advanced and recurrent endometrial cancers have poor prognoses and lack effective treatments. Poly (ADP-ribose) polymerase (PARP) inhibitors have been applied to many different types of tumors, and they can selectively kill tumor cells that are defective in homologous recombination repair. Endometrial cancer is characterized by mutations in homologous recombination repair genes; accordingly, PARP inhibitors have achieved positive results in off-label treatments of endometrial cancer cases. Clinical trials of PARP inhibitors as monotherapies and within combination therapies for endometrial cancer are ongoing. For this review, we searched PubMed with "endometrial cancer" and "PARP inhibitor" as keywords, and we used "olaparib", "rucaparib", "niraparib" and "talazoparib" as search terms in clinicaltrials.gov for ongoing trials. The literature search ended in October 2020, and only English-language publications were selected. Multiple studies confirm that PARP inhibitors play an important role in killing tumor cells with defects in homologous recombination repair. Its combination with immune checkpoint inhibitors, PI3K/AKT/mTOR pathway inhibitors, cell cycle checkpoint inhibitors, and other drugs can improve the treatment of endometrial cancer.

The Cross-Talk between Epigenetic Gene Regulation and Signaling Pathways Regulates Cancer Pathogenesis.

Cancer begins due to uncontrolled cell division. Cancer cells are insensitive to the signals that control normal cell proliferation. This uncontrolled cell division is due to the accumulation of abnormalities in different factors associated with the cell division, including different cyclins, cell cycle checkpoint inhibitors, and cellular signaling. Cellular signaling pathways are aberrantly activated in cancer mainly due to epigenetic regulation and post-translational regulation. In this chapter, the role of epigenetic regulation in aberrant activation of PI3K/AKT, Ras, Wnt, Hedgehog, Notch, JAK/STAT, and mTOR signaling pathways in cancer progression is discussed. The role of epigenetic regulators in controlling the upstream regulatory proteins and downstream effector proteins responsible for abnormal cellular signaling-mediated cancer progression is covered in this chapter. Similarly, the role of signaling pathways in controlling epigenetic gene regulation-mediated cancer progression is also discussed. We have tried to ascertain the current status of potential epigenetic drugs targeting several epigenetic regulators to prevent different cancers.

Targeting the DNA damage response: PARP inhibitors and new perspectives in the landscape of cancer treatment.

Cancer derives from alterations of pathways responsible for cell survival, differentiation and proliferation. Dysfunctions of mechanisms protecting genome integrity can promote oncogenesis but can also be exploited as therapeutic target. Poly-ADP-Ribose-Polymerase (PARP)-inhibitors, the first approved targeted agents able to tackle DNA damage response (DDR), have demonstrated antitumor activity, particularly when homologous recombination impairment is present. Despite the relevant results achieved, a large proportion of patients fail to obtain durable responses. The development of innovative treatments, able to overcome resistance and ensure long-lasting benefit for a wider population is still an unmet need. Moreover, improvement in biomarker assays is necessary to properly identify patients who can benefit from DDR targeting agents. Here we summarize the main DDR pathways, explain the current role of PARP inhibitors in cancer therapy and illustrate new therapeutic strategies targeting the DDR, focusing on the combinations of PARP inhibitors with other agents and on cell-cycle checkpoint inhibitors.

The Clinical Challenges, Trials, and Errors of Combatting Poly(ADP-Ribose) Polymerase Inhibitors Resistance.

The use of poly(ADP-ribose) polymerase inhibitor (PARPi) exploits synthetic lethality in solid tumors with homologous recombination repair (HRR) defects. Significant clinical benefit has been established in breast and ovarian cancers harboring BRCA1/2 mutations, as well as tumors harboring characteristics of "BRCAness." However, the durability of treatment responses is limited, and emerging data have demonstrated the clinical challenge of PARPi resistance. With the expanding use of PARPi, the significance of PARP therapy in patients pretreated with PARPi remains in need of significant further investigation. Molecular mechanisms contributing to this phenomenon include restoration of HRR function, replication fork stabilization, BRCA1/2 reversion mutations, and epigenetic changes. Current studies are evaluating the utility of combination therapies of PARPi with cell cycle checkpoint inhibitors, antiangiogenic agents, phosphatidylinositol 3-kinase/AKT pathway inhibitors, MEK inhibitors, and epigenetic modifiers to overcome this resistance. In this review, we address the mechanisms of PARPi resistance supported by preclinical models, examine current clinical trials applying combination therapy to overcome PARPi resistance, and discuss future directions to enhance the clinical efficacy of PARPi.

Toward developing a metastatic breast cancer treatment strategy that incorporates history of response to previous treatments

BackgroundInformation regarding response to past treatments may provide clues concerning the classes of drugs most or least likely to work for a particular metastatic or neoadjuvant early stage breast cancer patient. However, currently there is no systematized knowledge base that would support clinical treatment decision-making that takes response history into account.MethodsTo model history-dependent response data we leveraged a published in vitro breast cancer viability dataset (84 cell lines, 90 therapeutic compounds) to calculate the odds ratios (log (OR)) of responding to each drug given knowledge of (intrinsic/prior) response to all other agents. This OR matrix assumes (1) response is based on intrinsic rather than acquired characteristics, and (2) intrinsic sensitivity remains unchanged at the time of the next decision point. Fisher’s exact test is used to identify predictive pairs and groups of agents (BH p < 0.05). Recommendation systems are used to make further drug recommendations based on past ‘history’ of response.ResultsOf the 90 compounds, 57 have sensitivity profiles significantly associated with those of at least one other agent, mostly targeted drugs. Nearly all associations are positive, with (intrinsic/prior) sensitivity to one agent predicting sensitivity to others in the same or a related class (OR > 1). In vitro conditional response patterns clustered compounds into five predictive classes: (1) DNA damaging agents, (2) Aurora A kinase and cell cycle checkpoint inhibitors; (3) microtubule poisons; (4) HER2/EGFR inhibitors; and (5) PIK3C catalytic subunit inhibitors. The apriori algorithm implementation made further predictions including a directional association between resistance to HER2 inhibition and sensitivity to proteasome inhibitors.ConclusionsInvestigating drug sensitivity conditioned on observed sensitivity or resistance to prior drugs may be pivotal in informing clinicians deciding on the next line of breast cancer treatments for patients who have progressed on their current treatment. This study supports a strategy of treating patients with different agents in the same class where an associated sensitivity was observed, likely after one or more intervening treatments.

Development of imidazolone based angiotensin II receptor type I inhibitor small molecule as a chemotherapeutic agent for cell cycle inhibition

Cell cycle inhibitors are considered as hallmark strategy for cancer treatment due to their relatively higher selectivity and efficacy on various cancer types in comparison to cytotoxic agents. Small molecules target dividing cells in G1/S, G2 or M phases of cells to arrest and eventually trigger cancer cells to enter apoptosis and/or inhibit tumor growth. Cell cycle arrest at G2/M phase is a widely used approach to inhibit proliferating cancer cells. We report a novel angiotensin II receptor type I (AT1R) antagonist that also targets CDC2 (CDK1) kinase thereby showing a putative anti-cancer activity. The molecule named 19D was tested in various cancer cell lines at different concentrations. Molecular mechanisms of action triggered by the treatment of 19D were investigated for anti-cancer activity at cellular and molecular level. 19D molecule showed a potent cell cycle arrest with anti-proliferation activity. Cells treated with 19D showed nuclear deteriorations and apoptotic induction on cancer cells. Moreover, the mechanism of cell cycle inhibition was revealed as G2/M arrest via suppressing the CDC2 kinase cell cycle check point inhibitor. In conclusion, 19D (an AT1R antagonist) is a novel small molecule/imidazolone derivative which has been demonstrated as a fairly potent anti-cancer molecule. Abbreviations: AT1R: angiotensin II receptor type 1; BSA: bovine serum albumine; CDC2: cyclin-dependent kinase 1; CDK: cyclin-dependent kinase; DMEM: Dulbecco’s modified eagle medium; DMSO: dimethylsulfoxide; EDTA: ethylenediaminetetraacetic acid; FBS: fetal bovine serum; HBSS: Hank’s balanced salt solution; IC50: half maximal inhibitory concentration; PBS-T: phosphate buffered saline – TritonX; PBS: phosphate buffered saline; PDB: protein data bank; SDS: sodium dodecyl sulfate; TBS-T: Tris buffered saline – TritonX

Combination of CHEK1/2 inhibition and ionizing radiation results in abscopal tumor response through increased micronuclei formation.

We explore a novel strategy of activating immune signaling through increased micronuclei formation utilizing a cell cycle checkpoint inhibitor to drive cell cycle progression following ionizing radiation. The Chk1/2 inhibitor AZD7762 is used to abrogate radiation therapy (RT)-induced G2/M cell cycle arrest in multiple cell lines and, we find that this therapeutic combination promotes increased micronuclei formation in vitro and subsequently drives increased type I interferon signaling and cytotoxic T-cell activation. In vivo studies using B16-F10 melanoma cancer cells implanted in C57/BL6 mice demonstrate improved rates of tumor control at the abscopal (unirradiated) site, located outside of the radiation field, only in the AZD7762+RT group, with a corresponding reduction in mean tumor volume, increase in the CD8 T-cell population, and immune activated gene signaling. Our results demonstrate that targeted inhibition of cell cycle checkpoint activation following ionizing radiation drives increased production of immunogenic micronuclei, leading to systemic tumor response with potential future clinical benefit.

Oxidation resistance 1 prevents genome instability through maintenance of G2/M arrest in gamma-ray-irradiated cells.

ABSTRACTHuman oxidation resistance 1 (OXR1) was identified as a protein that decreases genomic mutations in Escherichia coli caused by oxidative DNA damage. However, the mechanism by which OXR1 defends against genome instability has not been elucidated. To clarify how OXR1 maintains genome stability, the effects of OXR1-depletion on genome stability were investigated in OXR1-depleted HeLa cells using gamma-rays (γ-rays). The OXR1-depleted cells had higher levels of superoxide and micronucleus (MN) formation than control cells after irradiation. OXR1-overexpression alleviated the increases in reactive oxygen species (ROS) level and MN formation after irradiation. The increased MN formation in irradiated OXR1-depleted cells was partially attenuated by the ROS inhibitor N-acetyl-L-cysteine, suggesting that OXR1-depeletion increases ROS-dependent genome instability. We also found that OXR1-depletion shortened the duration of γ-ray-induced G2/M arrest. In the presence of the cell cycle checkpoint inhibitor caffeine, the level of MN formed after irradiation was similar between control and OXR1-depleted cells, demonstrating that OXR1-depletion accelerates MN formation through abrogation of G2/M arrest. In OXR1-depleted cells, the level of cyclin D1 protein expression was increased. Here we report that OXR1 prevents genome instability by cell cycle regulation as well as oxidative stress defense.

New strategies in ovarian cancer treatment.

Insights from basic science dissecting carcinogenesis in the fallopian tube and ovary have led to a deeper understanding of the origin, molecular characteristics, and types of ovarian cancers. This logically then has led to the development of novel approaches to treat ovarian cancer. Increasingly, novel agents are being developed to target the different growth pathways. The identification of molecular markers associated with different histopathologies has resulted in newer clinical trial designs to capture both clinical and translational endpoints. Unique molecular characteristics in DNA damage and repair pathways and unique cell surface markers have driven new drug development, yielding promise for both patients with platinum-sensitive and platinum-resistant ovarian cancers. Specific examples described include the histology-selective mutations, such as ARID1A in clear cell and endometrioid ovarian cancers; the rationale for using cell cycle checkpoint inhibitors when there already is a p53-mediated loss of cell cycle checkpoint regulation or combinations of agents that will both induce neoantigen formation and unleash immune modulators; and techniques to enhance the therapeutic delivery of known agents. A systematic and thoughtful approach to combining agents in clinical trials is needed so that irrespective of the trial outcomes, the results inform both clinical and translational endpoints.

Inhibition of ATR Overcomes Chemotherapy Resistance in p53 Deficient Myeloma Cells

In MM, as well as in most hematological malignancies, deficiency in p53 pathway (mainly because of TP53 deletion and/or mutation) is associated with resistance to treatments (Tessoulin Blood Reviews 2017; 31:251). Recent clinical studies have shown that deletion or mutation of TP53 are the most adverse prognostic values for patients (Thakurta Blood 2019;133:1217). Although these patients are easily identified, there is no dedicated therapies for them. p53 pathway is central for homeostasis and cell adaptation/response to many stresses, including DNA repair orchestration and survival regulation. In p53 deficient cells, DNA damaging drugs don't induce massive apoptosis and cells escape to death. In normal cells, DNA damaging drugs induce cell cycle arrest and DNA repair, mainly orchestrated by p53 target genes. Cell cycle arrest in S phase, which is critical for allowing homologous DNA repair, is activated by cell cycle check-point inhibitor such as Chk1, an ATR target. In p53 deficient cells, inhibiting check point inhibitor using ATR inhibitor should allow DNA damaged cells to progress into cell cycle despite the lack of repair and in fine induce replicative/mitotic catastrophe. The aim of this study was to assess whether inhibiting ATR in p53 deficient myeloma cells could overcome chemotherapy resistance. ATR inhibitor, VE-821, was assessed in 13 human myeloma cell lines (HMCLs) alone and in combination with DNA damaging agents, CX5461, a G quadruplex inhibitor, or melphalan, the « myeloma » alkylating drug. The HMCL cohort included 8 HMCLs, 5 TP53Abn and 5 TP53wt. Cell viability was assessed using Cell Titer Glo assay or using flow cytometry (loss of AnnexinV or CD138 staining in HMCLs or primary myeloma cells, respectively). In our cohort of 13 HMCLs and by contrast to previous results, CX5461 was more efficient in TP53wt than in TP53abn HMCLs (mean of death at 0.5mM was 43% versus 24%, p=0.04). Melphalan was also more potent in TP53wt than in TP53abn HMCLs (LD50 values were 26 mM versus 10 mM, p=0.008). By contrast, ATR inhibitor VE-821 (2.5mM) was efficient in both types of HMCLs (mean of death in TP53wt was 45% and 28% in TP53abn HMCLs, p=0.6). Combination of CX5641 (0.5mM) with VE-821 (2.5mM) was more efficient than each drug alone and efficacy was not dependent on TP53 status (mean of death in TP53wt was 69% versus 56% in TP53abn HMCLs, p=0.6): interestingly, combo was efficient in all TP53abn HMCLs, being either additive (n=5) or even synergistic (n=3). By contrast, combo was not efficient in all TP53wt HMCLs (either additive or antagonist). Combination of melphalan (10 mM) with VE-821 (2.5mM) was also synergistic in TP53abn HMCLs (mean of cell death was 9% with melphalan and 73% for combo, p&lt;0.05). Preliminary results of combos in 6 consecutive primary samples with MM or plasma cell leukemia (3 TP53wt and 3 TP53abn) demonstrated efficacy. Indeed, in the 3 TP53abn samples, both CX5641/VE-821 and melphalan/VE-821 combos displayed synergism or additivity: median of expected values versus observed values was 61% versus 74% for CX5641/VE-821, and 98% versus 89% for melphalan/VE-821, respectively. In the 3 TP53wt samples, combos displayed additivity or antagonism: median of expected versus observed values was 15% versus 15% for CX5641/VE-821, and 100% versus 62% for melphalan/VE-821, respectively. In normal peripheral blood cells (n=2), both combos were not cytotoxic (mean values of cell death were 0% with CX5641/VE-821 and 3% with melphalan/VE-821). To decipher the molecular pathway involved in cell response, we monitored cell cycle using BrdU/IP assay, replicative stress response using Chk1 phosphorylation and DNA double strand breaks using Comets assays in 3 TP53abn HMCLs. At 24h, CX5641 induced an increase of cells in S (mean of increase 12%) and G2M phases (11%), while VE-821 didn't modify cell cycle. Combination of CX5641 with VE-821 induced a dramatic increase of cells in G2M (20%) (and in subG2 phase), and a decrease of cells in S phase (10%), indicating that cells blocked in S phase by CX5641 were released by VE-821.CX5641 induced Chk1 phosphorylation, which was inhibited by addition of VE-821, confirming the CX5641/ATR/Chk1 signaling. Finally, CX5641 and VE-821 induced comets, confirming irreversible DNA double strand breaks. All these results show that inhibition of ATR after inducing DNA damage in TP53abn myeloma cells efficiently induces cell death, while preserving normal cells. Disclosures Moreau: Janssen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria.

Abstract 2556: Enhanced expression of human cyclin G1 (CCNG1) gene in metastatic cancer, a novel biomarker in development for CCNG1 inhibitor therapy

Abstract Background: Metastatic cancer is associated with, hitherto, an invariably fatal outcome. DeltaRex-G, a CCNG1 inhibitor, has induced long term (9-12 year-) survivorship in patients with metastatic melanoma, sarcoma, lymphoma and cancer of pancreas and breast. Purpose: To evaluate CCNG1 expression in tumors as a novel biomarker for identification of patients who are likely to benefit from CCNG1 inhibitor therapy. Methods: RNA sequence analysis was used to compare CCNG1 expression in tumor (TCGA, N=9161) versus normal tissues (TGCA, N=678 and GTEx, N=7187) from 20 organ sites, and in primary vs metastatic melanoma (N=106 &amp; 367 respectively). Using IHC staining, the significance of differences between the number of CCNG1+ and Ki-67+ cells in normal tissues vs tumors were evaluated using paired Student’s t test. Pearson’s coefficient of correlation was used to evaluate the relationship between the number of Ki-67+ vs CCNG1+ cells. Results: CCNG1 gene expression, by RNA sequence analysis, was significantly enhanced in melanoma, sarcoma, leukemia, and cancers of the lung, thyroid, brain, liver, prostate, testicle, head and neck, bladder, kidney, adrenal, cervix, and pancreas, compared to normal tissues (p = 0.006- 1.8E-58), and even greater, in metastatic vs primary melanoma. In a subset of melanoma tumors, there was overall positive correlation with progression/metastasis in both Ki67 and CCNG1 expression levels. Consistent with these findings, IHC showed significant differences when comparing CCNG1 nuclear staining percentages between analogous healthy and cancerous tissues (p = 0.002, df = 11). The nuclear staining percentages of CCNG1 and Ki-67 share a statistically significant, positive correlation (r = .936977, p &amp;lt; 0.00001). Further, in some patients, the level of CCNG1 expression by IHC fluctuated over time. Conclusion: Taken together, these data indicate that (1) CCNG1 expression, is frequently enhanced in cancerous tumors compared to their normal analogous counterparts, and (2) the level of CCNG1 expression may change over time, necessitating real time analysis in order to determine the optimal timing for CCNG1 inhibitor therapy. A Phase 2 basket study of DeltaRex-G cell cycle checkpoint inhibitor therapy is planned to correlate treatment outcome parameters with CCNG1 expression in patients’ tumors and circulating tumor cells. Citation Format: Erlinda M. Gordon, Christopher Szeto, Joshua R. Ravicz, Sandeep Reddy, Michael Morse, Sant Chawla, Frederick Hall. Enhanced expression of human cyclin G1 (CCNG1) gene in metastatic cancer, a novel biomarker in development for CCNG1 inhibitor therapy [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 2556.