Cdc2 Protein Research Articles

The synthesis and anti‐tumour properties of novel 4-substituted phthalazinones as Aurora B kinase inhibitors

A series of novel 4-substituted phthalazinones as Aurora B kinase inhibitors was synthesized and evaluated the anti-proliferative activities against A549, HCT116, MCF-7 and HepG2 cells. 1-(4-(2-((4-Oxo-3,4-dihydrophthalazin-1-yl)amino)ethyl) phenyl)-3-(3-(trifluoromethyl)phenyl)urea (17b) exhibited the most potent anti-proliferative activity against HCT116 cells with IC50 value of 4.35 ± 1.21 μM, as well as the moderate Aurora B inhibitory activity with the IC50 value of 142 nM. Furthermore, 17b inhibited the phosphorylation of Aurora B on Thr232, leading to cell cycle arrest in the G2/M phase by down-regulating the expression of CyclinB1 and Cdc2 proteins, and apoptosis by up-regulating the expression of BAD and Bax proteins in HCT116 cells. In addition, a docking study revealed that 17b could form key hydrogen bonds with Ala173, Glu171 and Glu177 in Aurora B. All the results reveal that 17b is worthy of further development as an Aurora B kinase inhibitor.

Cdc13 is predominant over Stn1 and Ten1 in preventing chromosome end fusions.

Telomeres define the natural ends of eukaryotic chromosomes and are crucial for chromosomal stability. The budding yeast Cdc13, Stn1 and Ten1 proteins form a heterotrimeric complex, and the inactivation of any of its subunits leads to a uniformly lethal phenotype due to telomere deprotection. Although Cdc13, Stn1 and Ten1 seem to belong to an epistasis group, it remains unclear whether they function differently in telomere protection. Here, we employed the single-linear-chromosome yeast SY14, and surprisingly found that the deletion of CDC13 leads to telomere erosion and intrachromosome end-to-end fusion, which depends on Rad52 but not Yku. Interestingly, the emergence frequency of survivors in the SY14 cdc13Δ mutant was ~29 fold higher than that in either the stn1Δ or ten1Δ mutant, demonstrating a predominant role of Cdc13 in inhibiting telomere fusion. Chromosomal fusion readily occurred in the telomerase-null SY14 strain, further verifying the default role of intact telomeres in inhibiting chromosome fusion.

Conservation of Cdc14 phosphatase specificity in plant fungal pathogens: implications for antifungal development

Cdc14 protein phosphatases play an important role in plant infection by several fungal pathogens. This and other properties of Cdc14 enzymes make them an intriguing target for development of new antifungal crop treatments. Active site architecture and substrate specificity of Cdc14 from the model fungus Saccharomyces cerevisiae (ScCdc14) are well-defined and unique among characterized phosphatases. Cdc14 appears absent from some model plants. However, the extent of conservation of Cdc14 sequence, structure, and specificity in fungal plant pathogens is unknown. We addressed this by performing a comprehensive phylogenetic analysis of the Cdc14 family and comparing the conservation of active site structure and specificity among a sampling of plant pathogen Cdc14 homologs. We show that Cdc14 was lost in the common ancestor of angiosperm plants but is ubiquitous in ascomycete and basidiomycete fungi. The unique substrate specificity of ScCdc14 was invariant in homologs from eight diverse species of dikarya, suggesting it is conserved across the lineage. A synthetic substrate mimetic inhibited diverse fungal Cdc14 homologs with similar low µM Ki values, but had little effect on related phosphatases. Our results justify future exploration of Cdc14 as a broad spectrum antifungal target for plant protection.

DNA replication protein Cdc45 directly interacts with PCNA via its PIP box in Leishmania donovani and the Cdc45 PIP box is essential for cell survival.

DNA replication protein Cdc45 is an integral part of the eukaryotic replicative helicase whose other components are the Mcm2-7 core, and GINS. We identified a PIP box motif in Leishmania donovani Cdc45. This motif is typically linked to interaction with the eukaryotic clamp proliferating cell nuclear antigen (PCNA). The homotrimeric PCNA can potentially bind upto three different proteins simultaneously via a loop region present in each monomer. Multiple binding partners have been identified from among the replication machinery in other eukaryotes, and the concerted /sequential binding of these partners are central to the fidelity of the replication process. Though conserved in Cdc45 across Leishmania species and Trypanosoma cruzi, the PIP box is absent in Trypanosoma brucei Cdc45. Here we investigate the possibility of Cdc45-PCNA interaction and the role of such an interaction in the in vivo context. Having confirmed the importance of Cdc45 in Leishmania DNA replication we establish that Cdc45 and PCNA interact stably in whole cell extracts, also interacting with each other directly in vitro. The interaction is mediated via the Cdc45 PIP box. This PIP box is essential for Leishmania survival. The importance of the Cdc45 PIP box is also examined in Schizosaccharomyces pombe, and it is found to be essential for cell survival here as well. Our results implicate a role for the Leishmania Cdc45 PIP box in recruiting or stabilizing PCNA on chromatin. The Cdc45-PCNA interaction might help tether PCNA and associated replicative DNA polymerase to the DNA template, thus facilitating replication fork elongation. Though multiple replication proteins that associate with PCNA have been identified in other eukaryotes, this is the first report demonstrating a direct interaction between Cdc45 and PCNA, and while our analysis suggests the interaction may not occur in human cells, it indicates that it may not be confined to trypanosomatids.

Vanillic Acid Stimulates Anagen Signaling via the PI3K/Akt/ β-Catenin Pathway in Dermal Papilla Cells.

The hair cycle (anagen, catagen, and telogen) is regulated by the interaction between mesenchymal cells and epithelial cells in the hair follicles. The proliferation of dermal papilla cells (DPCs), mesenchymal-derived fibroblasts, has emerged as a target for the regulation of the hair cycle. Here, we show that vanillic acid, a phenolic acid from wheat bran, promotes the proliferation of DPCs via a PI3K/Akt/Wnt/β-catenin dependent mechanism. Vanillic acid promoted the proliferation of DPCs, accompanied by increased levels of cell-cycle proteins cyclin D1, CDK6, and Cdc2 p34. Vanillic acid also increased the levels of phospho(ser473)-Akt, phospho(ser780)-pRB, and phospho(thr37/46)-4EBP1 in a time-dependent manner. Wortmannin, an inhibitor of the PI3K/Akt pathway, attenuated the vanillic acid-mediated proliferation of DPCs. Vanillic acid-induced progression of the cell-cycle was also suppressed by wortmannin. Moreover, vanillic acid increased the levels of Wnt/β-catenin proteins, such as phospho(ser9)-glycogen synthase kinase-3β, phospho(ser552)-β-catenin, and phospho(ser675)-β-catenin. We found that vanillic acid increased the levels of cyclin D1 and Cox-2, which are target genes of β-catenin, and these changes were inhibited by wortmannin. To investigate whether vanillic acid affects the downregulation of β-catenin by dihydrotestosterone (DHT), implicated in the development of androgenetic alopecia, DPCs were stimulated with DHT in the presence and absence of vanillic acid for 24 h. Western blotting and confocal microscopy analyses showed that the decreased level of β-catenin after the incubation with DHT was reversed by vanillic acid. These results suggest that vanillic acid could stimulate anagen and alleviate hair loss by activating the PI3K/Akt and Wnt/β-catenin pathways in DPCs.

Cell division cycle proteinising prognostic biomarker of breast cancer.

Cell division cycle protein (CDC20) has been observed to be expressed higher in various kinds of human cancers and was associated with poor prognosis. However, studies on role of CDC20 in breast cancer are seldom reported till now, most of which are not systematic and conclusive. The present study was performed to analyze the expression pattern, potential function, and distinct prognostic effect of CDC20 in breast cancer using several online databases including Oncomine, bc-GenExMiner, PrognoScan, and UCSC Xena. To verify the results from databases, we compared the mRNA CDC20 expression in breast cancer tissues and adjacent normal tissues of patients by real-time PCR. We found that CDC20 was expressed higher in different types of breast cancer, comparing with normal tissues. Moreover, the patients with a more advanced stage of breast cancer tended to express higher level CDC20. CDC20 was expressed higher in breast cancer tissues than normal tissues from patients in our hospital, consistent with the results from databases. Estrogen receptor (ER) and progesterone receptor (PR) status were negatively correlated with CDC20 level. Conversely, Scarff–Bloom–Richardson (SBR) grade, Nottingham prognostic index (NPI), epidermal growth factor receptor-2 (HER-2) status, basal-like status, and triple-negative status were positively related to CDC20 expression in breast cancer patients with respect to normal individuals. Higher CDC20 expression correlated with worse survival. Finally, a positive correlation between CDC20 and Targeting protein for Xenopus kinesin-like protein 2 (TPX2) expression was revealed. CDC20 could be considered as a potential predictive indicator for prognosis of breast cancer with co-expressed TPX2 gene.

Fluorescence fluctuation analysis reveals PpV dependent Cdc25 protein dynamics in living embryos.

The protein phosphatase Cdc25 is a key regulator of the cell cycle by activating Cdk-cyclin complexes. Cdc25 is regulated by its expression levels and post-translational mechanisms. In early Drosophila embryogenesis, Cdc25/Twine drives the fast and synchronous nuclear cycles. A pause in the cell cycle and the remodeling to a more generic cell cycle mode with a gap phase are determined by Twine inactivation and destruction in early interphase 14, in response to zygotic genome activation. Although the pseudokinase Tribbles contributes to the timely degradation of Twine, Twine levels are controlled by additional yet unknown post-translational mechanisms. Here, we apply a non-invasive method based on fluorescence fluctuation analysis (FFA) to record the absolute concentration profiles of Twine with minute-scale resolution in single living embryos. Employing this assay, we found that Protein phosphatase V (PpV), the homologue of the catalytic subunit of human PP6, ensures appropriately low Twine protein levels at the onset of interphase 14. PpV controls directly or indirectly the phosphorylation of Twine at multiple serine and threonine residues as revealed by phosphosite mapping. Mutational analysis confirmed that these sites are involved in control of Twine protein dynamics, and cell cycle remodeling is delayed in a fraction of the phosphosite mutant embryos. Our data reveal a novel mechanism for control of Twine protein levels and their significance for embryonic cell cycle remodeling.

Interaction of yeast Rad51 and Rad52 relieves Rad52-mediated inhibition of de novo telomere addition.

DNA double-strand breaks (DSBs) are toxic forms of DNA damage that must be repaired to maintain genome integrity. Telomerase can act upon a DSB to create a de novo telomere, a process that interferes with normal repair and creates terminal deletions. We previously identified sequences in Saccharomyces cerevisiae (SiRTAs; Sites of Repair-associated Telomere Addition) that undergo unusually high frequencies of de novo telomere addition, even when the original chromosome break is several kilobases distal to the eventual site of telomerase action. Association of the single-stranded telomere binding protein Cdc13 with a SiRTA is required to stimulate de novo telomere addition. Because extensive resection must occur prior to Cdc13 binding, we utilized these sites to monitor the effect of proteins involved in homologous recombination. We find that telomere addition is significantly reduced in the absence of the Rad51 recombinase, while loss of Rad52, required for Rad51 nucleoprotein filament formation, has no effect. Deletion of RAD52 suppresses the defect of the rad51Δ strain, suggesting that Rad52 inhibits de novo telomere addition in the absence of Rad51. The ability of Rad51 to counteract this effect of Rad52 does not require DNA binding by Rad51, but does require interaction between the two proteins, while the inhibitory effect of Rad52 depends on its interaction with Replication Protein A (RPA). Intriguingly, the genetic interactions we report between RAD51 and RAD52 are similar to those previously observed in the context of checkpoint adaptation. Forced recruitment of Cdc13 fully restores telomere addition in the absence of Rad51, suggesting that Rad52, through its interaction with RPA-coated single-stranded DNA, inhibits the ability of Cdc13 to bind and stimulate telomere addition. Loss of the Rad51-Rad52 interaction also stimulates a subset of Rad52-dependent microhomology-mediated repair (MHMR) events, consistent with the known ability of Rad51 to prevent single-strand annealing.

Effect of bFGF on the growth and matrix turnover of stem cells from human apical papilla: Role of MEK/ERK signaling

Basic fibroblast growth factor (bFGF) exhibits multiple biological functions in various tissues. Stem cells from apical papilla (SCAP) can be isolated from human apical papilla tissues in developmental teeth of children. The purposes of this study were to investigate the expression of FGF receptors (FGFRs) and the effects of bFGF on SCAP and related MEK/ERK signaling. SCAP cells were treated under different concentrations of bFGF with or without U0126 (an inhibitor of MEK/ERK). Expression of FGFR1 and FGFR2 in SCAP was analyzed by RT-PCR. Cell proliferation was measured by MTT assay. The expressions of type I collagen, cdc 2, cyclin B1, TIMP-1 and p-ERK proteins were examined by Western blot. SCAP cells expressed FGFR1 and FGFR2. Exposure of SCAP to bFGF enhanced cell proliferation, and the expression cyclinB1, cdc 2, and TIMP-1, but not type I collagen. U0126 pretreatment and co-incubation attenuated the bFGF-induced proliferation, cdc2, cyclin B1 and TIMP-1 proteins' expression, but not type I collagen in SCAP. SCAP cells express FGFRs. bFGF may stimulate proliferation and affect the matrix turnover of SCAP cells, possibly via stimulation of FGFRs and MEK/ERK signaling pathway. These results are useful for clinical therapies for apexogenesis and regeneration of pulpo-dentin complex.

Circular RNA Profiling Reveals That circRNA_104433 Regulates Cell Growth by Targeting miR-497-5p in Gastric Cancer.

BackgroundThe role and mechanism of hsa_circRNA_104433 in gastric cancer (GC) are further elucidated.Materials and methodsCircRNA_104433 was selected by circRNA microarrays and GEO database. qRT-PCR was used to analyze the expression of circRNA_104433 in GC. The role of circRNA_104433 in GC cells was evaluated based on cell cycle progression, cell proliferation, cell apoptosis, and tumor xenograft experiment assay. To explore the mechanisms of circRNA_104433 in GC TCGA database, STRING version, qRT-PCR and luciferase assay were performed. Furthermore, the prognostic value of CDC25A in GC was determined based on the GEO database.ResultsThe level of circRNA_104433 showed upregulation in GC tissues, and the expression of it showed a positive correlation with the degree of differentiation and the size of the tumor. Knockdown of circRNA_104433 inhibited cell cycle transition, and cell proliferation, while promoted cell apoptosis in GC. CircRNA_104433 directly binds to miR-497-5p, which directly regulates CDC25A. The median survival period of GC patients with high expression levels of CDC25A was 21.3 months, which was shorter than those with low group expression of CDC25A (35.9 months). The cell cycle proteins CDK1, CDK2, CCNB1, PKMYT1, CDC20, CHEK1 and CDC25A were coexpressed with CDC25A.ConclusionThese findings suggested that knockdown of circRNA_104433 expression suppressed tumor development in GC.

The telomeric Cdc13 protein from yeast Hansenula polymorpha

Telomeres are special structures at the ends of chromosomes that play an important role in the protection of the genetic material. Telomere composition is very diverse; noticeable differences can often be observed even among closely related species. Here, we identify the homolog of telomeric protein Cdc13 in the thermotolerant yeast Hansenula polymorpha. We show that it can specifically bind single-stranded telomeric DNA, as well as interact with the Stn1 protein. In addition, we have uncovered an interaction between Cdc13 and TERT (one of the core components of the telomerase complex), which suggests that Cdc13 is potentially involved in telomerase recruitment to telomeres in H. polymorpha.

Cloning and Expression Analysis of Cdc25 Gene of <i>Sipunculus nudus</i> in Oocytes

Cell division cycle 25 (Cdc25) is an important dual specificity phosphatase, which plays an important role in regulating the process of oocyte meiosis and embryo development. In this study, the full-length cDNA of Sn-Cdc25 was cloned from S. nudus using RACE technology. The results show that Sn-Cdc25 is 4 130 bp in length, including 3′ UTR 1 849 bp and 5′ UTR 427 bp. The Open reading frame (ORF) is 1 854 bp and encodes 617 amino acids. Sequence analysis shows that the molecular weight of Sn-Cdc25 protein is 69.58 kD, with two typical Cdc25 protein domains: M-phase inducer phosphatase domain and Rhodanese-like domain, and the active site sequence HCX 5 R that can catalyze the dephosphorylation process. Multi-sequence alignment finds that the C-terminal homology is higher than the N-terminal. The tertiary structure prediction shows that the spatial conformation of Cdc25 homologous protein and its active site are highly conservative. A total of 5 Motifs are found in Motif analysis, of which Motif 1 and Motif 2 are Paxillin LD motif and MYND domain binding motif, respectively. Phylogenetic tree analysis shows that Cdc25 is clustered into two branches: invertebrates and vertebrates. RT-PCR results show that the expression of Sn-Cdc25 , with two peaks, is significantly different in different developmental stages of oocytes. The increase in the expression of Sn-Cdc25 from primary vitellogenic stage to the late of active vitellogenic stage (O1-O3) may be related to the process of Sn-Cdc25 promoting DNA replication. When the oocytes entering metanephridium from coelomic fluid, the rapid rise of Sn-Cdc25 expression may be beneficial to the activation of maturation promoting factor (MPF). The above results have accumulated basic data for further understanding of the developmental mechanism of Sipuncula oocytes and for optimization of artificial breeding techniques.

A novel strategy to block mitotic progression for targeted therapy.

BackgroundBlockade of mitotic progression is an ideal approach to induce mitotic catastrophe that suppresses cancer cell expansion. Cdc20 is a critical mitotic factor governing anaphase initiation and the exit from mitosis through recruiting substrates to APC/C for degradation. Results from recent TCGA (The Cancer Genome Atlas) and pathological studies have demonstrated a pivotal oncogenic role for Cdc20-APC/C in tumor progression as well as drug resistance. Thus, deprivation of the mitotic role for Cdc20-APC/C by either inhibition of Cdc20-APC/C activity or elimination of Cdc20 protein via induced protein degradation emerges as an effective therapeutic strategy to control cancer.MethodsWe designed a proteolysis targeting chimera, called CP5V, which comprises a Cdc20 ligand and VHL binding moiety bridged by a PEG5 linker that induces Cdc20 degradation. We characterized the effect of CP5V in destroying Cdc20, arresting mitosis, and inhibiting tumor progression by measuring protein degradation, 3D structure dynamics, cell cycle control, tumor cell killing and tumor inhibition using human breast cancer xenograft mouse model.FindingsResults from our study demonstrate that CP5V can specifically degrade Cdc20 by linking Cdc20 to the VHL/VBC complex for ubiquitination followed by proteasomal degradation. Induced degradation of Cdc20 by CP5V leads to significant inhibition of breast cancer cell proliferation and resensitization of Taxol-resistant cell lines. Results based on a human breast cancer xenograft mouse model show a significant role for CP5V in suppressing breast tumor progression.InterpretationCP5V-mediated degradation of Cdc20 could be an effective therapeutic strategy for anti-mitotic therapy.

Identification of highly potent and selective Cdc25 protein phosphatases inhibitors from miniaturization click-chemistry-based combinatorial libraries

Cell division cycle 25 (Cdc25) protein phosphatases play key roles in the transition between the cell cycle phases and their association with various cancers has been widely proven, which makes them ideal targets for anti-cancer treatment. Though several Cdc25 inhibitors have been developed, most of them displayed low activity and poor subtype selectivity. Therefore, it is extremely important to discover novel small molecule inhibitors with potent activities and significant selectivity for Cdc25 subtypes, not only served as drugs to treat cancer but also to probe its mechanism in transitions. In this study, miniaturized parallel click chemistry synthesis via CuAAC reaction followed by in situ biological screening were used to discover selective Cdc25 inhibitors. The bioassay results showed that compound M2N12 proved to be the most potent Cdc25 inhibitor, which also act as a highly selective Cdc25C inhibitor and was about 9-fold potent than that of NSC 663284. Moreover, M2N12 showed remarkable anti-growth activity against the KB-VIN cell line, equivalent to that of PXL and NSC 663284. An all-atom molecular dynamics (MD) simulation approach was further employed to probe the significant selectivity of M2N12 for Cdc25C relative to its structural homologs Cdc25A and Cdc25B. Overall, above results make M2N12 a promising lead compound for further investigation and structural modification.

Knockdown of Pyruvate Kinase M Inhibits Cell Growth and Migration by Reducing NF-kB Activity in Triple-Negative Breast Cancer Cells.

Altered genetic features in cancer cells lead to a high rate of aerobic glycolysis and metabolic reprogramming that is essential for increased cancer cell viability and rapid proliferation. Pyruvate kinase muscle (PKM) is a rate-limiting enzyme in the final step of glycolysis. Herein, we report that PKM is a potential therapeutic target in triple-negative breast cancer (TNBC) cells. We found that PKM1 or PKM2 is highly expressed in TNBC tissues or cells. Knockdown of PKM significantly suppressed cell proliferation and migration, and strongly reduced S phase and induced G2 phase cell cycle arrest by reducing phosphorylation of the CDC2 protein in TNBC cells. Additionally, knockdown of PKM significantly suppressed NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity by reducing the phosphorylation of p65 at serine 536, and also decreased the expression of NF-κB target genes. Taken together, PKM is a potential target that may have therapeutic implications for TNBC cells.

Arnicolide D exerts anti-melanoma effects and inhibits the NF-κB pathway

BackgroundMelanoma is a lethal cancer. NF-κB has been validated as a molecular target for melanoma treatment. Current therapies for melanoma have limitations. Novel targeted therapeutics are needed. Arnicolide D (Ar-D), a sesquiterpene lactone isolated from the dried whole plant of Centipeda minima (L.) A. Br. et Aschers., has been reported to inhibit NF-κB activity in colorectal cancer cells. PurposeTo investigate the anti-melanoma effects of Ar-D in vitro and in vivo; and to determine whether Ar-D inhibits the NF-κB pathway in melanoma cells. MethodsA B16F10 allograft mouse model and two melanoma cell lines (A375 and B16F10) were used to investigate the anti-melanoma effects of Ar-D in vivo and in vitro. Dacarbazine was used as a positive control. Cell viability was assessed by MTT and crystal violet staining assays. Cell cycle arrest and apoptosis were analyzed by flow cytometry. Protein levels were determined by Immunoblotting. ResultsIn vivo assays showed that the average tumor weight in Ar-D-treated group (4 mg/kg, i.p, 15 days) was reduced by 53.7%, when compared with the control group. In vitro studies demonstrated that Ar-D reduced cell viability, induced G2/M cell cycle arrest and apoptosis, elevated levels of cell cycle regulatory proteins p53 and p21, and lowered levels of G2/M checkpoint proteins Cdc2 and Cyclin B1 in melanoma cells. Mechanistically, Ar-D inhibited the activity of IKKα/β, the degradation of IκBα, and the phosphorylation and expression of NF-κB p65 in melanoma cells. ConclusionAr-D has anti-melanoma effects, and inhibition of the IKK/IκBα/NF-κB p65 pathway is involved in the effects.

Tanshinone IIA inhibits proliferation and induces apoptosis of human nasopharyngeal carcinoma cells via p53‑cyclin B1/CDC2

Tanshinone IIA exhibits natural antioxidative and antineoplastic activity. However, to the best of our knowledge, the effects of tanshinone IIA on human nasopharyngeal carcinoma cells remains unknown. The present study aimed to investigate whether tanshinone IIA inhibits proliferation and induces apoptosis of human nasopharyngeal carcinoma cells via p53-cyclin B1/cell division cycle gene 2 (CDC2). Cell proliferation, cytotoxicity and apoptosis of 13-9B cells were evaluated by an MTT assay, lactate dehydrogenase assay and flow cytometry, respectively. ELISA and western blot analysis were used to analyze caspase-3 activity and poly (ADP-ribose) polymerase (PARP), p53, cyclin B1 and CDC2 protein expression in 13-9B cells. Treatment of 13-9B cells with tanshinone IIA significantly suppressed cell proliferation and significantly induced cytotoxicity and apoptosis of 13-9B cells. Furthermore, tanshinone IIA significantly increased caspase-3 activity, and significantly increased the protein expression levels of PARP, p53, cyclin B1 and CDC2 in 13-9B cells. In summary, the current results indicate that tanshinone IIA inhibits proliferation and induces apoptosis of human nasopharyngeal carcinoma cells via PARP, p53, cyclin B1/CDC2 and caspase-3-mediated signaling.

<p>Rhein sensitizes human colorectal cancer cells to EGFR inhibitors by inhibiting STAT3 pathway</p>

BackgroundActivation of epidermal growth factor receptor (EGFR) has been reported in a variety of cancer types, including colorectal cancer (CRC), and represents a potential chemotherapeutic drug target. EGFR tyrosine kinase inhibitors (EGFR-TKIs) have been increasingly applied in the clinical treatment of CRC, but development of drug resistance during the treatment has greatly limited their application. Signal transducer and activator of transcription 3 (STAT3) and its mediated signal transduction pathway play an important role in the occurrence, development and metastasis of CRC, and are related to the development of EGFR-TKI resistance in CRC.MethodsCell viability, colony formation and cellular morphology were examined to evaluate the potent antiproliferative effect of the STAT3 inhibitor napabucasin, LY5 and rhein on the human CRC cell lines HCT116, SW620, RKO and DLD-1. Flow cytometry-based analysis was employed to determine whether rhein can affect the cell cycle and apoptosis. The expression level of phosphorylated STAT3 (P-STAT3), and cell cycle- and apoptosis-related proteins BCL2, CDC2 BAX, Cyclin D1 and Cyclin B1 were detected by Western blot analysis.ResultsThis study revealed that rhein can significantly reduce cell viability and stimulate apoptosis in human CRC cells in a dose-dependent manner. In addition, rhein induced cell cycle arrest at the G2/M phase in CRC cells and dose-dependently inhibited the expression of cell cycle-related proteins. Additionally, it was found that napabucasin, LY5 and rhein considerably sensitized cells to the EGFR-TKI erlotinib, thus suppressing CRC cell proliferation. Rhein also inhibited the phosphorylation of its downstream target STAT3. Inhibition of STAT3 and EGFR phosphorylation was also observed after treatment with a combination of rhein and EGFR inhibitors.ConclusionThis study confirmed the synergistic effect of STAT3 inhibitor and EGFR inhibitor in CRC cell lines. Additionally, we found that rhein sensitizes human CRC cells to EGFR-TKIs by inhibiting STAT3 pathway. When combined with EGFR-TKIs, rhein may be a novel STAT3 inhibitor in CRC.

Abstract LB-288: CDC7 kinase inhibition by SRA141 induces a potentially novel caspase-dependent tumor cell apoptosis associated with altered DNA replication and cell cycle dynamics

Abstract DNA replication is a tightly regulated process required for faithful duplication of the genome. Previous research in lower eukaryotes has demonstrated a requisite role for the CDC7 protein kinase in DNA replication origin firing through phosphorylation of the MCM2-7 helicase complex. Owing to its overexpression in various neoplasms, CDC7 has emerged as an attractive target for cancer treatment. We previously reported that SRA141, a potent and selective CDC7 inhibitor, is cytotoxic to multiple tumor cell lines in vitro and demonstrates robust anti-tumor efficacy in colorectal and leukemia xenograft models. Here, we explored the effects of SRA141 on DNA replication and cell cycle dynamics and how these effects relate to the mechanism of SRA141-induced cell death in colorectal cancer cell lines. SRA141 treatment caused a complete inhibition of MCM2 phosphorylation and reduced overall cellular DNA synthesis within 3 hours, with the greatest effects observed in late S-phase. Unexpectedly, DNA combing experiments indicated that SRA141 caused a 70-90% increase in the rate of replication fork progression. These findings suggest that SRA141 may indeed limit origin firing, but this effect is compensated for in part by increased replication fork rates. Despite delay, nucleotide analog pulse-chase experiments indicated that SRA141 treated cells ultimately finished S phase and transitioned into mitosis. In contrast to other reports, no evidence of replication fork collapse was observed, indicating that the main mechanism of SRA141 cytotoxicity is not mediated through replication fork collapse. Intriguingly, some of the most pronounced effects of SRA141 treatment were on progression through M phase, as evidenced by an accumulation of mitotic cells and increased Cyclin B levels following treatment. Moreover, inhibition of Aurora B kinase, which regulates mitotic progression, strongly synergized with SRA141 in caspase-dependent cancer cell killing. Taken together, our findings indicate that the mechanism of cytotoxicity of CDC7 inhibitors is distinct from agents that cause replication fork collapse or inhibit CDKs, and thus may define a new class of cancer therapeutic agents that synergize with drugs that target certain mitotic pathways. Citation Format: Veena Jagannathan, Snezana Milutinovic, Ryan Hansen, Bryan Strouse, Christian Hassig, Eric Brown. CDC7 kinase inhibition by SRA141 induces a potentially novel caspase-dependent tumor cell apoptosis associated with altered DNA replication and cell cycle dynamics [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 LB-288.

PB1691 CDC20 IS A NOVEL POTENTIAL THERAPEUTIC TARGET IN ACUTE MYELOID LEUKEMIA

Background:Cell‐division cycle protein 20 (Cdc20) is one activator of the anaphase‐promoting complex (APC) during mitosis. APC‐Cdc20 has been characterized to play a role in cell cycle progression through ubiquitination and proteolysis of several cell cycle regulatory targets, including securin and cyclin B1 (Holland. SEB Exp Biol Ser. 2008). Many sudies have shown that CDC20 may function as oncoprotein to promote cancer development and progression (Smolders. Expert Opin Ther Targets, 2011). We previously have shown that Cdc20 is overexpressed in aneuploid acute myeloid leukemia (AML) patients compared with euploid ones (Simonetti, Padella. Cancer, 2019). We hypothesize that CDC20 upregulation might favor the survival and division of AML cells.Aims:This study aims to clarify the consequences of Cdc20 inhibition on AML cell lines.Methods:Intracellular staining of Cdc20 was performed on primary AML sample at diagnosis on CD34+ cells. AML cell lines were treated for 48 h with two different APC‐Cdc20 inhibitors: Apcin and proTAME. Cell viability, apoptosis and cell cycle were evaluated by RalTime‐Glo assay, Annexin‐V and PI staining, respectively. Cell cycle synchronization was obtained through 72 h of serum starvation for G0/G1 phase, double thymidine block (3 μM) for S phase, and single thymidine block (1 μM) followed by nocodazole (50ng/mL) for G2/M phase. PI staining was performed to evaluate the synchronization level. Western blot analysis was performed to quantify the protein level of Cdc20 and its target.Results:CDC20 is expressed at variable levels both in proliferating and resting CD34+ stem‐progenitor cells and in blast cells isolated from bone marrow or peripheral blood of AML patients. Conversely, synchronization of AML cell lines in each of the three phases of cell cycle showed preferential expression of Cdc20 in G2/M phase, with very low levels in G0/G1 and S phases.To evaluate the effect of Cdc20 functional inhibition we treated two different AML cell lines, KG‐1 (TP53‐mutated) and MV‐4‐11 (t(4;11) and FLT3‐ITD), with Apcin or proTAME as single agent. KG‐1 being most sensitive with IC50 values of 37.6 μM for Apcin, and 5.16 μM for proTAME after 48 h of treatment. Whereas MV‐4‐11 showed an IC50 of 180 μM for Apcin and 11.6 μM for proTAME. Annexin V/PI staining performed after treatment with different concentration of two inhibitors (50‐100 μM for Apcin, and 5‐10‐20 μM for proTAME) showed a reduction of cell viability in a dosage‐dependent manner. In particular, the percentage of apoptotic cells was 45.7% and 66.8% in KG‐1 after 48 h of treatment with 50 and 100 μM of Apcin, and 15%, 16.8% and 23.5% after treatment with 5, 10 and 20 μM of proTAME. At the same condition of treatment MV‐4‐11 showed low level of apoptotic cells, with values of 4.6% and 5.6% after Apcin treatment, and 5%, 6% and 6.9% after proTAME treatment. Moreover we observed that both molecules caused a significant arrest in G2/M phase of the cell cycle only in KG‐1 cells, in line with APC‐Cdc20 inhibition effect. WB analysis showed a reduction of Cdc20 protein level, especially in KG‐1, without stabilization of securin and cyclin B1 which results down‐regulated in both cell lines after treatment.Summary/Conclusion:Our data showed that Cdc20 is expressed at different levels in AML patients’ blast and in AML cell lines. The different effect of Cdc20 functional inhibition on two tested AML cell lines suggests a potential mechanism of action related to a genetic‐driven control of cell cycle progression. Further investigations are on the way to better clarify the potential therapeutic role of Cdc20 in AML.