Checkpoint Response Research Articles

Meiotic cells escape prolonged spindle checkpoint activity through kinetochore silencing and slippage.

To prevent chromosome mis-segregation, a surveillance mechanism known as the spindle checkpoint delays the cell cycle if kinetochores are not attached to spindle microtubules, allowing the cell additional time to correct improper attachments. During spindle checkpoint activation, checkpoint proteins bind the unattached kinetochore and send a diffusible signal to inhibit the anaphase promoting complex/cyclosome (APC/C). Previous work has shown that mitotic cells with depolymerized microtubules can escape prolonged spindle checkpoint activation in a process called mitotic slippage. During slippage, spindle checkpoint proteins bind unattached kinetochores, but the cells cannot maintain the checkpoint arrest. We asked if meiotic cells had as robust of a spindle checkpoint response as mitotic cells and whether they also undergo slippage after prolonged spindle checkpoint activity. We performed a direct comparison between mitotic and meiotic budding yeast cells that signal the spindle checkpoint through two different assays. We find that the spindle checkpoint delay is shorter in meiosis I or meiosis II compared to mitosis, overcoming a checkpoint arrest approximately 150 minutes earlier in meiosis than in mitosis. In addition, cells in meiosis I escape spindle checkpoint signaling using two mechanisms, silencing the checkpoint at the kinetochore and through slippage. We propose that meiotic cells undertake developmentally-regulated mechanisms to prevent persistent spindle checkpoint activity to ensure the production of gametes.

Abstract 6519: Haploinsufficiency for BRCA2 leads to common fragile site instability in human mammary epithelial cells

Abstract Individuals with germline heterozygous mutations of breast cancer susceptibility genes BRCA1 or BRCA2 have a 50 to 80% lifetime risk of developing breast cancer, yet the mechanisms of these cancers remain largely unknown. There is growing evidence that BRCA1 and BRCA2 heterozygosity confer haploinsufficiency in normal human mammary epithelial cells for their multiple known functions. Haploinsufficiency for BRCA1 leads to defects in differentiation, replication stress response, premature senescence and genomic instability in human mammary epithelial cells. Deficiencies in error-free DNA damage repair has been observed in genetically engineered cells as well as primary human mammary epithelial cells carrying BRCA1 heterozygous mutations. There is relatively less research on understanding the role of haploinsufficiency for BRCA2 in human mammary epithelial cells. It has been reported that haploinsufficiency for BRCA2 leads to genomic instability via unscheduled R-loops. We previously showed that accumulation of sub-chromosomal copy number variations (CNVs) and replication stress-induced DNA damage, together with attenuated checkpoint and apoptotic responses, constitute a haplo-insufficient phenotype in mammary epithelial cells of BRCA2 mutation carrier patients. Common fragile sites (CFS) are found in all individuals and represent a normal component of chromosome structure. Numerous studies have shown that CFSs are prone to deletions and rearrangements in many cancers, a situation referred as CFS instability. Importantly, Fanconi Anemia/BRCA pathway has been previously reported to have a role in regulating CFS instability. In this study, we further explored a link between BRCA2 haploinsufficiency and CFS instability. We induced replication stress with DNA polymerase inhibitor aphidicolin (APH) treatment in control and BRCA2- deficient human mammary epithelial cells. We then performed DAPI banding to map and score the cytogenic lesions in metaphase spreads cells, in the absence or presence of APH treatment. Our results demonstrated that BRCA2- deficient human mammary epithelial cells showed increased frequency of CFS regions such as FRA18B. Correspondingly, BRCA2-deficient cells exhibited a failure to activate CHK1, a central coordinator of the response to replication stress and DNA damage, in response to APH treatment, despite normal levels of total CHK1 protein. ATR/CHK1 pathway is a major regulator of CFS stability. Thus, our results provide support for BRCA2 haploinsufficiency leading to CFS instability in human mammary epithelial cells. These studies will yield unanticipated opportunities for improved risk assessment and prevention strategies in high-risk patients. Citation Format: Mihriban Karaayvaz, Kavya Vipparthi, Antony Caputo. Haploinsufficiency for BRCA2 leads to common fragile site instability in human mammary epithelial cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6519.

Abstract 4909: Molecular analysis of small cell lung cancer provides insights into mechanism of action underlying the novel drug combination of lurbinectedin and TIC10/ONC201

Abstract We previously explored the combination of novel imipridone TIC10/ONC201 and small molecule RNA polymerase inhibitor lurbinectedin as a potentially effective treatment regimen for small cell lung cancer (SCLC). Data from cell viability experiments demonstrated synergistic killing of SCLC cells with minimal death of healthy control cells. Analysis of intracellular proteins via Western blot indicated that combinatorial treatment induces the integrated stress response, DNA damage/cell cycle checkpoint responses, and increased apoptosis of tumor cells. We have utilized the Luminex 200 platform to perform analyses of cytokine levels in SCLC cell lines with various genetic alterations before and after ONC201 and lurbinectedin treatment. Our results revealed significant changes in cytokine levels following treatment indicating potential immunomodulatory and angioregulatory effects of ONC201 and lurbinectedin. CCL3, known to recruit and activate granulocytes, was found to be elevated by treatment with lurbinectedin, ONC201 and combination versus control. Angiopoietin 1, which contributes to blood vessel maturation, and angiopoietin 2, which promotes neovascularisation, were elevated by all drug treatments in H1882 SCLC cells. Our ongoing studies are further analysing the importance of specific cytokines in tumor vascularity and in recruitment and killing of SCLC cells by immune cells. Results from these experiments are helping to elucidate the molecular mechanisms underlying SCLC, its immune landscape, and treatment response. Citation Format: Ashley Sanchez Sevilla Uruchurtu, Nicholas Liguori, Leiqing Zhang, Kelsey Huntington, Lanlan Zhou, Young Lee, Abbas E. Abbas, Christopher G. Azzoli, Wafik S. El-Deiry. Molecular analysis of small cell lung cancer provides insights into mechanism of action underlying the novel drug combination of lurbinectedin and TIC10/ONC201. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4909.

Intratumoral CD8+ Tcells with a tissue-resident memory phenotype mediate local immunity and immune checkpoint responses in breast cancer.

CD8+ tumor-infiltrating lymphocytes with a tissue-resident memory T (TRM) cell phenotype are associated with favorable prognosis in patients with triple-negative breast cancer (TNBC). However, the relative contribution of CD8+ TRM cells to anti-tumor immunity and immune checkpoint blockade efficacy in breast cancer remains unknown. Here, we show that intratumoral CD8+ Tcells in murine mammary tumors transcriptionally resemble those from TNBC patients. Phenotypic and transcriptional studies established two intratumoral sub-populations: one more enriched in markers of terminal exhaustion (TEX-like) and the other with a bona fide resident phenotype (TRM-like). Treatment with anti-PD-1 and anti-CTLA-4 therapy resulted in expansion of these intratumoral populations, with the TRM-like subset displaying significantly enhanced cytotoxic capacity. TRM-like CD8+ Tcells could also provide local immune protection against tumor rechallenge and a TRM gene signature extracted from tumor-free tissue was significantly associated with improved clinical outcomes in TNBC patients treated with checkpoint inhibitors.

Fatty Acid Synthase Mutations Predict Favorable Immune Checkpoint Inhibitor Outcome and Response in Melanoma and Non-Small Cell Lung Cancer Patients.

Fatty acid synthase (FASN) acts as the central member in fatty acid synthesis and metabolism processes, which regulate oncogenic signals and tumor immunogenicity. To date, no studies have reported the connection of FASN mutations with ICI efficacy. In this study, from 631 melanoma and 109 NSCLC patients who received ICI treatments, we retrospectively curated multiomics profiles and ICI treatment data. We also explored the potential molecular biological mechanisms behind FASN alterations. In melanoma patients, FASN mutations were observed to associate with a preferable immunotherapeutic prognosis and response rate (both p < 0.01). These connections were further corroborated by the NSCLC patients (both p < 0.01). Further analyses showed that a favorable tumor immunogenicity and immune microenvironment were involved in FASN mutations. This work confirms the clinical immunotherapy implications of FASN mutation-mediated fatty acid metabolism and provides a possible indicator for immunotherapy prognosis prediction.

Intratumoral CD8+ T cells with a tissue-resident phenotype mediate local immunity and immune checkpoint responses in breast cancer

Intratumoral CD8+ T cells with a tissue-resident phenotype mediate local immunity and immune checkpoint responses in breast cancer

PTEN Loss Enhances Error-Prone DSB Processing and Tumor Cell Radiosensitivity by Suppressing RAD51 Expression and Homologous Recombination.

PTEN has been implicated in the repair of DNA double-strand breaks (DSBs), particularly through homologous recombination (HR). However, other data fail to demonstrate a direct role of PTEN in DSB repair. Therefore, here, we report experiments designed to further investigate the role of PTEN in DSB repair. We emphasize the consequences of PTEN loss in the engagement of the four DSB repair pathways-classical non-homologous end-joining (c-NHEJ), HR, alternative end-joining (alt-EJ) and single strand annealing (SSA)-and analyze the resulting dynamic changes in their utilization. We quantitate the effect of PTEN knockdown on cell radiosensitivity to killing, as well as checkpoint responses in normal and tumor cell lines. We find that disruption of PTEN sensitizes cells to ionizing radiation (IR). This radiosensitization is associated with a reduction in RAD51 expression that compromises HR and causes a marked increase in SSA engagement, an error-prone DSB repair pathway, while alt-EJ and c-NHEJ remain unchanged after PTEN knockdown. The G2-checkpoint is partially suppressed after PTEN knockdown, corroborating the associated HR suppression. Notably, PTEN deficiency radiosensitizes cells to PARP inhibitors, Olaparib and BMN673. The results show the crucial role of PTEN in DSB repair and show a molecular link between PTEN and HR through the regulation of RAD51 expression. The expected benefit from combination treatment with Olaparib or BMN673 and IR shows that PTEN status may also be useful for patient stratification in clinical treatment protocols combining IR with PARP inhibitors.

Integrin subunit alpha V is a potent prognostic biomarker associated with immune infiltration in lower-grade glioma

As a member of integrin receptor family, ITGAV (integrin subunit α V) is involved in a variety of cell biological processes and overexpressed in various cancers, which may be a potential prognostic factor. However, its prognostic value and potential function in lower-grade glioma (LGG) are still unclear, and in terms of immune infiltration, it has not been fully elucidated. Here, the expression preference, prognostic value, and clinical traits of ITGAV were investigated using The Cancer Genome Atlas database (n = 528) and the Chinese Glioma Genome Atlas dataset (n = 458). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses and gene set enrichment analysis (GSEA) were used to explore the biological function of ITGAV. Using R package "ssGSEA" analysis, it was found thatthe ITGAV mRNA expression level showed intense correlation with tumor immunity, such as tumor-infiltrating immune cells and multiple immune-related genes. In addition, ITGAV is associated with some immune checkpoints and immune checkpoint blockade (ICB) and response to chemotherapy. and the expression of ITGAV protein in LGG patients was verified via immunohistochemistry (IHC). ITGAV expression was higher in LGG tissues than in normal tissues (P < 0.001) and multifactor analysis showed that ITGAV mRNA expression was an independent prognostic factor for LGG overall survival (OS; hazard ratio = 2.113, 95% confidence interval = 1.393-3.204, P < 0.001). GSEA showed that ITGAV expression was correlated with Inflammatory response, complement response, KRAS signal, and interferon response. ssGSEA results showed a positive correlation between ITGAV expression and Th2 cell infiltration level. ITGAV mRNA was overexpressed in LGG, and high ITGAV mRNA levels were found to be associated with poor protein expression and poor OS. ITGAV is therefore a potential biomarker for the diagnosis and prognosis of LGG and may be a potential immunotherapy target.

Intratumoral neutrophil extracellular traps are associated with unfavorable clinical outcomes and immunogenic context in pancreatic ductal adenocarcinoma.

Extracellular traps (ETs) and tumor-infiltrating immune cells play crucial roles in tumor progression. However, little is known about the clinical significance of tumor-infiltrating neutrophils and macrophages and the related ETs in pancreatic ductal adenocarcinoma (PDAC). This study investigates the associations between neutrophil or macrophage infiltration or ET formation and the clinicopathological features, molecular characteristics, immune checkpoint molecules, clinical outcomes, and response to adjuvant chemotherapy (ACT) in PDAC. We performed multiplex immunofluorescence staining to detect ET formation by neutrophils or macrophages using tissue microarrays obtained from 205 patients, and analyzed the immunohistochemistry data for PD-L1, PD-L2, B7-H3, and B7-H4. The ET expression rates in macrophages and neutrophils were 23.9% and 45.4%, respectively. Patients with a high density of neutrophils or positive expression of neutrophil ETs exhibited poorer progression-free survival (PFS) and disease-specific survival (DSS), whereas macrophage ETs were not related to PFS and DSS. Neutrophil infiltration and ET formation were identified as independent prognostic predictors of DSS using univariate and multivariate Cox analyses. Patients with PDAC with lower neutrophil infiltration or negative staining for neutrophil ETs are more likely to benefit from ACT. Patients with PDAC were more accurately stratified based on the infiltration of neutrophils and presence of neutrophil ETs, and patients with low neutrophil infiltration and negative staining for neutrophil ETs showed the best survival. Patients with positive neutrophil ETs demonstrated inferior DSS compared to those with negative neutrophil ETs in the PD-L1 tumor proportion score (TPS) < 1% and PD-L1 IC < 1% subgroups. However, the positive expression of neutrophil ETs was not related to DSS in the PD-L1 TPS ≥ 1% or PD-L1 IC ≥ 1% subgroup. Our findings emphasize the potential of neutrophil infiltration and ETs as prognostic markers that could guide the formulation of more effective personalized treatments for PDAC.

Targeting DNA repair to enhance the efficacy of sorafenib in hepatocellular carcinoma.

The multityrosine kinase inhibitor sorafenib remains an important systemic treatment option for hepatocellular carcinoma (HCC). Signaling pathways, which are targeted by sorafenib, are involved in checkpoint and DNA repair response, RAD51 being a candidate protein. Here, we aim to evaluate the effect of the human RAD51 inhibitor B02 in combination with sorafenib in human HCC cells. Impact of RAD51 expression on HCC patient survival was evaluated by an in silico approach using Human Protein Atlas dataset. Cell viability of HUH7, AKH12, AKH13, and 3P was assessed by neutral red assay. To measure the cytotoxicity, we quantified loss of membrane integrity by lactate dehydrogenase release. We also employed colony formation assay and hanging drop method to assess clonogenic and invasive ability of HCC cell lines upon sorafenib and B02 treatment. Cell cycle distribution and characterization of apoptosis was evaluated by flow cytometry. In silico approach revealed that HCC patients with higher expression of RAD51 messenger RNA had a significantly shorter overall survival. The RAD51 inhibitor B02 alone and in combination with sorafenib significantly reduced viability, colony formation ability, and invasion capacity of HCC cells. Cell cycle analysis revealed that the combination of both agents reduces the proportion of cells in the G2/M phase while leading to an accumulating in the subG1 phase. The RAD51 inhibitor B02 seems to be a promising agent for HCC treatment and enhances the antitumor effects of sorafenib in vitro.

DNA polymerase delta interacting protein 3 facilitates the activation and maintenance of DNA damage checkpoint in response to replication stress.

BackgroundReplication stress response is crucial for the maintenance of a stable genome. POLDIP3 (DNA polymerase delta interacting protein 3) was initially identified as one of the DNA polymerase δ (Pol δ) interacting proteins almost 20 years ago. Using a variety of in vitro biochemical assays, we previously established that POLDIP3 is a key regulator of the enzymatic activity of Pol δ. However, the in vivo function of POLDIP3 in DNA replication and DNA damage response has been elusive.MethodsWe first generated POLDIP3 knockout (KO) cells using the CRISPR/Cas9 technology. We then investigated its biological functions in vivo using a variety of biochemical and cell biology assays.ResultsWe showed that although the POLDIP3‐KO cells manifest no pronounced defect in global DNA synthesis under nonstress conditions, they are sensitive to a variety of replication fork blockers. Intriguingly, we found that POLDIP3 plays a crucial role in the activation and maintenance of the DNA damage checkpoint in response to exogenous as well as endogenous replication stress.ConclusionOur results indicate that when the DNA replication fork is blocked, POLDIP3 can be recruited to the stalled replication fork and functions to bridge the early DNA damage checkpoint response and the later replication fork repair/restart.

PD-1 receptor blocker

PD-1 or the programmed cell death protein 1 plays a major role in eliciting the immune checkpoint response of T cells. They are the inhibitory receptors induced in activated T cells. The application of these receptors earns a great interest to investigate, in-depth, their mechanism of action and therapeutic success. The US FDA has successfully approved three categories of immune checkpoint inhibitors. These are PD-1 inhibitors (Nivolumab, Pembrolizumab, and Cemiplimab), PDL-1 inhibitors (Atezolimumab, Durvalumab and, Avelumab), and CTLA-4 inhibitor (Ipilimumab). But still there lie several limitations in using this mode of treatment. Unlikely, not all patients respond well to these drugs. Apart from these, anti PD-1 monoclonal antibody showed its miraculous activity in treating cancer. It showed a hundred percent cure in patients with colorectal cancer without any kind of major side effects following the treatment procedure. Anti PD-1 monoclonal antibody (Dostarlimab) has shown promising results in endometrial cancer, ovarian cancer, melanoma, head and neck cancer, and breast cancer therapy. The current review focuses on the literature regarding the mechanism of action of immune checkpoint inhibitors, their role in cancer treatment.

Emetine blocks DNA replication via proteosynthesis inhibition not by targeting Okazaki fragments.

DNA synthesis of the leading and lagging strands works independently and cells tolerate single-stranded DNA generated during strand uncoupling if it is protected by RPA molecules. Natural alkaloid emetine is used as a specific inhibitor of lagging strand synthesis, uncoupling leading and lagging strand replication. Here, by analysis of lagging strand synthesis inhibitors, we show that despite emetine completely inhibiting DNA replication: it does not induce the generation of single-stranded DNA and chromatin-bound RPA32 (CB-RPA32). In line with this, emetine does not activate the replication checkpoint nor DNA damage response. Emetine is also an inhibitor of proteosynthesis and ongoing proteosynthesis is essential for the accurate replication of DNA. Mechanistically, we demonstrate that the acute block of proteosynthesis by emetine temporally precedes its effects on DNA replication. Thus, our results are consistent with the hypothesis that emetine affects DNA replication by proteosynthesis inhibition. Emetine and mild POLA1 inhibition prevent S-phase poly(ADP-ribosyl)ation. Collectively, our study reveals that emetine is not a specific lagging strand synthesis inhibitor with implications for its use in molecular biology.

A novel senescence-associated LncRNA signature predicts the prognosis and tumor microenvironment of patients with colorectal cancer: a bioinformatics analysis

BackgroundAccumulating evidence suggests that cellular senescence promotes tumor formation and that long non-coding RNAs (lncRNAs) expression predicts tumor prognosis. However, senescence-related variables, particularly lncRNAs, are still largely unknown. Therefore, the present study developed a novel senescence-associated lncRNA signature to predict colorectal cancer (CRC) prognosis.MethodsA co-expression network of senescence-associated mRNAs and lncRNAs was built using RNA-sequence data from The Cancer Genome Atlas (TCGA). By using the prognosis outcomes data of overall survival (OS) and disease-free survival (DFS) from TCGA, we constructed a prognostic senescence-associated lncRNA signature (SenALSig). The OS and DFS were compared between the low- and high- risk groups defined by SenALSig. A single-sample gene set enrichment analysis (ssGSEA) and CIBERSORT algorithm were used to investigate the relationship between the predictive signature and immune status. Finally, the relationship between SenALSig and drug treatment options was investigated. An independent CRC cohort and three CRC cell lines were recruited to perform real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis to validate the results discovered in silico.ResultsA prognostic risk model consisting of six senescence-associated lncRNAs was constructed, including SNHG16, AL590483.1, ZEB1-AS1, AC107375.1, AC068580.3, and AC147067.1. High-risk scores according to the SenALSig were significantly associated with poor OS (hazard ratio =1.218, 95% confidence interval: 1.140–1.301; P<0.001). The model’s accuracy was further supported by receiver operating characteristic (ROC) curves (the area under the curve is 0.714) and a principal component analysis (PCA). In univariate and multivariate Cox regression analyses, SenALSig was further found to be a prognostic factor independent of other clinical factors. Furthermore, we discovered that immune checkpoint expression and response to chemotherapy and targeted therapy differed significantly between the SenALSig-stratified high- and low-risk groups. Finally, the qPCR results revealed that the expression levels of the six senescence-associated lncRNAs differed significantly between tumor and normal tissues and between the CRC cell lines and a normal human colon mucosal epithelial cell line.ConclusionsSenALSig can better predict survival and risk in CRC patients, as well as help develop new anti-cancer treatment strategies for CRC.

ATR Contributes More Than ATM in Intra-S-Phase Checkpoint Activation after IR, and DNA-PKcs Facilitates Recovery: Evidence for Modular Integration of ATM/ATR/DNA-PKcs Functions.

The intra-S-phase checkpoint was among the first reported cell cycle checkpoints in mammalian cells. It transiently slows down the rate of DNA replication after DNA damage to facilitate repair and thus prevents genomic instability. The ionizing radiation (IR)-induced intra-S-phase checkpoint in mammalian cells is thought to be mainly dependent upon the kinase activity of ATM. Defects in the intra-S-phase checkpoint result in radio-resistant DNA synthesis (RDS), which promotes genomic instability. ATM belongs to the PI3K kinase family along with ATR and DNA-PKcs. ATR has been shown to be the key kinase for intra-S-phase checkpoint signaling in yeast and has also been implicated in this checkpoint in higher eukaryotes. Recently, contributions of DNA-PKcs to IR-induced G2-checkpoint could also be established. Whether and how ATR and DNA-PKcs are involved in the IR-induced intra-S-phase checkpoint in mammalian cells is incompletely characterized. Here, we investigated the contributions of ATM, ATR, and DNA-PKcs to intra-S-phase checkpoint activation after exposure to IR of human and hamster cells. The results suggest that the activities of both ATM and ATR are essential for efficient intra-S-phase checkpoint activation. Indeed, in a wild-type genetic background, ATR inhibition generates stronger checkpoint defects than ATM inhibition. Similar to G2 checkpoint, DNA-PKcs contributes to the recovery from the intra-S-phase checkpoint. DNA-PKcs–deficient cells show persistent, mainly ATR-dependent intra-S-phase checkpoints. A correlation between the degree of DSB end resection and the strength of the intra-S-phase checkpoint is observed, which again compares well to the G2 checkpoint response. We conclude that the organization of the intra-S-phase checkpoint has a similar mechanistic organization to that of the G2 checkpoint in cells irradiated in the G2 phase.

Identification of Novel Tumor Microenvironment Regulating Factor That Facilitates Tumor Immune Infiltration in Cervical Cancer.

Cervical cancer is one of the most common gynecologic malignancies and one of the leading causes of cancer-related deaths in women worldwide. There are more than 30 categories of human papillomavirus infections in the genital tract. The recently discovered immune checkpoint suppression is a potential approach to improve clinical outcomes in these patients by altering immune cell function. However, many questions remain unanswered in terms of this method. For example, the proportion of responders is limited and the exact mechanism of action is uncertain. The tumor microenvironment (TME) has long been regarded as having nonnegligible influence on effectiveness of immunotherapy. The programmed cell death protein 1 (PD-1) pathway has received much attention due to its involvement in activating T-cell immune checkpoint responses. Since tumor cells may evade immune detection and become highly resistant to conventional treatments, anti-PD-1/PD-L1 antibodies are preferred as a kind of cancer treatment and many have just been licensed. To provide a theoretical basis for the development of new therapies, investigating the effect of tumor microenvironment on the prognosis of cervical cancer is necessary. In this work, immunological scores obtained from the ESTIMATE algorithm were used to differentiate between patients with high and low immune cell infiltration. We identified 11 immunologically significant differentially expressed genes (DEGs). For example, CXCR3 was found to be an important factor in CD8+ T cell recruitment and tumor immunological infiltration in cervical cancer. These results may lead to novel directions of understanding complex interactions between cancer cells and the tumor microenvironment, as well as new treatment options for cervical cancer.

P392: PHARMACOLOGICAL INHIBITION OF SYK CONFERS ANTI-PROLIFERATIVE AND NOVEL ANTI-TUMOR IMMUNE RESPONSES IN AML

Background: Spleen tyrosine kinase (SYK) acts as a key integrator of signals from cell surface receptors containing an immunoreceptor tyrosine-based activation motif to boost cellular proliferation. In acute myeloid leukemia (AML), SYK serves as a relay to an oncogenic transcriptional regulatory network linked to NPM1, HOXA9 and MEIS1. The selective, orally bioavailable SYK inhibitor entospletinib (ENTO) has demonstrated clinical activity and tolerability in HOXA9/MEIS1-driven AML. ENTO is currently being investigated in a global Phase 3 trial, AGILITY (NCT05020665), in combination with intensive induction/consolidation chemotherapy in patients (pts) with treatment-naive NPM1-mutated (NPM1m) AML. Lanraplenib (LANRA) is a next-generation SYK inhibitor with similar potency and selectivity to ENTO but with more favorable pharmacologic properties that is currently being evaluated in combination with gilteritinib in pts with relapsed or refractory FLT3-mutated AML (NCT05028751). Aims: To investigate the effects of ENTO and LANRA in T-cell responses in AML. Methods: All pt-derived bone marrow (BM) and peripheral blood samples were obtained in accordance with IRB (OHSU#004422) approval. Results from gene expression profiling studies (RNA sequence [RNA-seq]) in bone marrow/peripheral blood mononuclear cells (MNCs) derived from 152 pts with AML, for which matching NPM1 status and ex vivo sensitivity to ENTO was available, previously published by Tyner et al (2018), were reanalyzed using trimmed mean of M values normalization and differential expression using edgeR. ENTO/LANRA sensitivity was assessed ex vivo after 72 hours in culture at 37°C by MTS assay. T-cell functional assays were performed by culturing MNCs with anti-CD3 and treating with ENTO or LANRA, singly and in combination with anti-PD1. CD3+ T-cell proliferation as measured by Ki67 expression and pSYK activation were assessed by quantitative single-cell immunofluorescence microscopy. Six formalin-fixed, paraffin-embedded BM biopsies from newly diagnosed AML pts were assessed for spatial expression of mRNA using a digital spatial profiling method. Results: In AML, mutations in NPM1 with co-expression of HOXA9/MEIS1 at baseline predicted anti-proliferative activity to ENTO in ex vivo drug sensitivity studies. Accordingly, treatment of leukemic cells with either ENTO or LANRA inhibited SYK auto-phosphorylation in a dose-dependent manner. Pathway analysis of archival RNA-seq data from pts enrolled in the Leukemia and Lymphoma Society BEAT AML Master Protocol (NCT03013998 [BAML-16-001-S6]) revealed gene expression signatures at baseline associated with the observed sensitivity to ENTO, including significant enrichment in the expression of genes associated with leukemogenesis, myeloid differentiation and immune regulation. This was supported by T-cell functional studies, which demonstrated that ENTO and LANRA, singly as well as in combination with anti-PD1, could restore T-cell proliferation in primary AML pt samples that exhibited suppression. Lastly, Cancer Transcriptome Atlas analysis on archival BM biopsies obtained from these AML pts showed a strong correlation between immune checkpoint response and gene expression associated with immune pathway signaling. Summary/Conclusion: Inhibition of SYK is a promising therapeutic approach in NPM1m AML. Our studies illustrate that ENTO and LANRA may restore T-cell proliferation in a subset of AML pts with dysfunctional T-cell responses, suggesting a novel mechanism of action. Additional studies are required to fully understand the mechanism of SYK-mediated antitumor immune responses in AML.

Abstract 6129: Investigate the mechanism and treatment efficacy of regorafenib combined with anti-PD-L1 on bladder cancer

Abstract Bladder cancer is one of the most common cancer in urinary system in Taiwan. According to Ministry of Health and Welfare’s research, bladder cancer plays 15th leading causes of death in Taiwan in 2020. The patients who suffer from bladder cancer after undergoing resection surgery about 60% will relapse, and 80% of them will relapse in less than a year, 15% of the relapsing patients will aggravate and become invasive carcinoma spread all over the body. PD-L1 (Programmed death-ligand 1), also known as B7-H1 and CD274 is a transmembrane glycoprotein, which interacts with PD-1 (Programmed death-1) receptor on T cells to elicit the immune checkpoint response. Overexpression of PD-L1 suppresses the function of CD8+ T cells and facilitate tumor progression. Targeting tumor PD-L1 may be a possible treatment option; however, PD-L1 expression was only detected in small amount of population. Regorafenib is a multiple tyrosine kinase inhibitor, which has been approved by the US Food and Drug Administration to treat advanced HCC. In our research, we found that regorafenib may upregulation the surface PD-L1 expression in both mice and human cell line. Based on this finding, we suggested that regorafenib may show potential to enhance treatment efficacy anti-PD-L1. Therefore, we established MB-49 bearing animal model to identify the immune regulation and treatment efficacy of regorafenib combined with anti-PD-L1. In ours animal data we found that combination therapy effectively increased the tumor infiltrating population of NK cells and CD8+ lymphocytes which were determined by flow cytometry assay. Not only anti-tumoral leukocytes, we also detected the population of immune suppressor cells including regulatory T cells, MDSCs and M2 macrophage was suppressed by combination therapy. We also detected the tumor microenvironment related markers (VEGF, IDO-1, PD-L1, CD8, CD31, CD49b, FOXP3, granzyme B) to evaluate combination therapy effect by using immunohistochemistry staining. In conclusion, regorafenib may effectively enhance anti-PD-L1 efficacy via triggering positive immune regulation and increasing the interaction of anti-PD-L1 with tumor. Citation Format: Kai-Jen Pai, Yuan Chang, I-Tsang Chiang, Fei-Ting Hsu. Investigate the mechanism and treatment efficacy of regorafenib combined with anti-PD-L1 on bladder cancer [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 6129.

Prolyl Isomerization-Mediated Conformational Changes Define ATR Subcellular Compartment-Specific Functions.

ATR is a PI3K-like kinase protein, regulating checkpoint responses to DNA damage and replication stress. Apart from its checkpoint function in the nucleus, ATR actively engages in an antiapoptotic role at mitochondria following DNA damage. The different functions of ATR in the nucleus and cytoplasm are carried out by two prolyl isomeric forms of ATR: trans- and cis-ATR, respectively. The isomerization occurs at the Pin1 Ser428-Pro429 motif of ATR. Here, we investigated the structural basis of the subcellular location-specific functions of human ATR. Using a mass spectrometry-based footprinting approach, the surface accessibility of ATR lysine residues to sulfo-NHS-LC-biotin modification was monitored and compared between the cis- and the trans-isomers. We have identified two biotin-modified lysine residues, K459 and K469, within the BH3-like domain of cis-ATR that were not accessible in trans-ATR, indicating a conformational change around the BH3 domain between cis- and trans-ATR. The conformational alteration also involved the N-terminal domain and the middle HEAT domain. Moreover, experimental results from an array of complementary assays show that cis-ATR with the accessible BH3 domain was able to bind to tBid while trans-ATR could not. In addition, both cis- and trans-ATR can directly form homodimers via their C-terminal domains without ATRIP, while nuclear (trans-ATR) in the presence of ATRIP forms dimer–dimer complexes involving both N- and C-termini of ATR and ATRIP after UV. Structural characteristics around the Ser428-Pro429 motif and the BH3 domain region are also analyzed by molecular modeling and dynamics simulation. In support, cis conformation was found to be significantly more energetically favorable than trans at the Ser428-Pro429 bond in a 20-aa wild-type ATR peptide. Taken together, our results suggest that the isomerization-induced structural changes of ATR define both its subcellular location and compartment-specific functions and play an essential role in promoting cell survival and DNA damage responses.

KDM6B promotes PARthanatos via suppression of O6-methylguanine DNA methyltransferase repair and sustained checkpoint response.

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA damage sensor and contributes to both DNA repair and cell death processes. However, how PARP-1 signaling is regulated to switch its function from DNA repair to cell death remains largely unknown. Here, we found that PARP-1 plays a central role in alkylating agent-induced PARthanatic cancer cell death. Lysine demethylase 6B (KDM6B) was identified as a key regulator of PARthanatos. Loss of KDM6B protein or its demethylase activity conferred cancer cell resistance to PARthanatic cell death in response to alkylating agents. Mechanistically, KDM6B knockout suppressed methylation at the promoter of O6-methylguanine-DNA methyltransferase (MGMT) to enhance MGMT expression and its direct DNA repair function, thereby inhibiting DNA damage-evoked PARP-1 hyperactivation and subsequent cell death. Moreover, KDM6B knockout triggered sustained Chk1 phosphorylation and activated a second XRCC1-dependent repair machinery to fix DNA damage evading from MGMT repair. Inhibition of MGMT or checkpoint response re-sensitized KDM6B deficient cells to PARthanatos induced by alkylating agents. These findings provide new molecular insights into epigenetic regulation of PARP-1 signaling mediating DNA repair or cell death and identify KDM6B as a biomarker for prediction of cancer cell vulnerability to alkylating agent treatment.