Mediated Cell Cycle Arrest Research Articles

Ochratoxin A causes cell cycle arrest in G1 and G1/S phases through p53 in HK-2 cells

Ochratoxin A (OTA) is a toxic metabolite produced by Aspergillus and Penicillium fungus. OTA found in the human and animal tissues can contaminate many foods that we daily consume in our lives. It accumulates especially in kidney. Although OTA is known to cause cell cycle arrest, the molecular mechanisms underlying this effect have not been fully understood, yet. We aimed to investigate the molecular details of OTA induced inhibitory response in G1 – G1/S phase of cell cycle and also the regulatory role of p53 in OTA mediated cell cycle arrest in human proximal tubule epithelial cells, HK-2. For this purpose, Cyclin E1 and Cyclin D1 mRNA expressions and Cyclin D1, Cdk4 and Cdk2 protein expressions were evaluated in HK-2 cells transfected with either 50 nM control siRNA or p53 siRNA for 72 h in the absence or presence of OTA using RT-PCR and Western blot analyses, respectively. Our findings showed that mRNA expressions of Cyclin D1 and Cyclin E1 and protein expressions of Cyclin D1, Cdk4 and Cdk2 were inhibited in HK-2 cells treated with two different doses of OTA, 10 μM and 25 μM, for 24 h. However, the downregulation of p53 led to enhance OTA-mediated increase in mRNA expressions of Cyclin D1 and Cyclin E1 and protein expressions of Cyclin D1, Cdk4 and Cdk2 compared to control siRNA transfected HK-2 cells. Our findings strongly suggest that the cell cycle arresting effect of OTA also performs via a p53 mediated mechanism besides other possible mechanisms.

A novel topoisomerase I inhibitor DIA-001 induces DNA damage mediated cell cycle arrest and apoptosis in cancer cell.

DNA topoisomerase enzyme plays an essential role in controlling the DNA topology structure by binding to DNA and cutting the phosphate backbone of either one or both of the DNA strands. Here, we have identified a small molecule inhibitor, DIA-001, that directly binds to Topoisomerase 1 (Topo I) and promotes the Topo I-DNA adducts. In this study, we investigated the antitumor effects of DIA-001 using MTS assay and colony formation. We examined cell cycle of tumor cells with DIA-001 treatment in vitro by flow cytometry. And we investigated DNA damage and cell cycle marker protein after treatment with DIA-001 at different concentration and time point by western blot. Immunofluorescence was performance to detect the nuclear foci. The effects of DIA-001 on Topo I and Topo II activities were examined by DNA relaxation assays. We demonstrate that DIA-001 inhibit DNA replication and arrest cell cycle progression at the G2/M phase by directly binds to Topo I and promotes the Topo I-DNA adducts. In addition, DIA-001 can activate the DNA damage response signaling cascade, resulting in apoptosis in treated cells. Our findings show a novel compound for treatment of cancer cells with the potential as a chemotherapy candidate that is less toxic to normal cells.

Serine 319 phosphorylation is necessary and sufficient to induce a Cx37 conformation that leads to arrested cell cycling.

Connexin 37 (Cx37; protein product of GJA4) expression profoundly suppresses proliferation of rat insulinoma (Rin) cells in a manner dependent on gap junction channel (GJCh) functionality and the presence and phosphorylation status of its C-terminus (CT). In Rin cells, growth is arrested upon induced Cx37 expression and serine 319 (S319) is frequently phosphorylated. Here, we show that preventing phosphorylation at this site (alanine substitution; S319A) relieved Cx37 of its growth-suppressive effect whereas mimicking phosphorylation at this site (aspartate substitution; S319D) enhanced the growth-suppressive properties of Cx37. Like wild-type Cx37 (Cx37-WT), Cx37-S319D GJChs and hemichannels (HChs) preferred the closed state, rarely opening fully, and gated slowly. In contrast, Cx37-S319A channels preferred open states, opened fully and gated rapidly. These data indicate that phosphorylation-dependent conformational differences in Cx37 protein and channel function underlie Cx37-induced growth arrest versus growth-permissive phenotypes. That the closed state of Cx37-WT and Cx37-S319D GJChs and HChs favors growth arrest suggests that rather than specific permeants mediating cell cycle arrest, the closed conformation instead supports interaction of Cx37 with growth regulatory proteins that result in growth arrest.

Bcl-2/BCL2L12 mediated apoptosis and cell cycle arrest induced by Kaempferol through the suppression of PI3K/AKT signaling pathway in Hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly aggressive and third leading cancer-related death. PI3k/AKT and p53 signaling pathways play a vital role and regulate cellular proliferation, migration, cell cycle, apoptosis, and autophagy during cancer conditions. BCL2L12 is a bcl-2 family protein and encoded by the BCL2L12 gene, which is involved in the execution phase of apoptosis. However, the biological function of PI3K/AKT/Bcl-2 mediated BCL2L12, and its molecular mechanism in HCC is largely unknown. Herein, we investigated the effect of Kaempferol, on PI3K/AKT/Bcl-2/BCL2L12 expressions in HCC cells. The expression level of PI3K/AKT/Bcl-2/BCL2L12, and its target genes in polyphenolic flavonoid Kaempferol treated HCC cells analyzed by Quantitative Real-Time PCR and Western blotting. Subsequently, the effect of Kaempferol in HCC chemosensitivity, cell proliferation, migration, cell cycle, and apoptosis were analyzed using AO/EtBr staining, ROS staining, mitochondrial membrane potential assay, wound healing assay, Transwell migration assay, MTT assay, and PI Staining. We found that the downregulation of PI3-K, AKT, LC3A/B, MMP9, Bcl-2, and BCL2L12 and upregulation of PTEN, p53, p21, and caspase 3 in Kaempferol treated HCC cells. Subsequently, we observed that Kaempferol effectively inhibits cellular proliferation, migration and enhances apoptosis, cell cycle arrest, autophagy, and 5-Fluorouracil mediated chemosensitivity in HCC cells. Furthermore, Kaempferol has dominant role against HCC and inhibits 50-60% of cells after 24h treatment with 30μM in HepG2 and 40μM in Huh7 cells. Therefore, Kaempferol plays a promising role in cancer therapeutics by inhibiting PI3K/AKT/Bcl-2 mediated BCL2L12 expression in HCC.

BRF1 accelerates prostate tumourigenesis and perturbs immune infiltration

BRF1 is a rate-limiting factor for RNA Polymerase III-mediated transcription and is elevated in numerous cancers. Here, we report that elevated levels of BRF1 associate with poor prognosis in human prostate cancer. In vitro studies in human prostate cancer cell lines demonstrated that transient overexpression of BRF1 increased cell proliferation whereas the transient downregulation of BRF1 reduced proliferation and mediated cell cycle arrest. Consistent with our clinical observations, BRF1 overexpression in a Pten-deficient mouse (PtenΔ/ΔBRF1Tg) prostate cancer model accelerated prostate carcinogenesis and shortened survival. In PtenΔ/ΔBRF1Tg tumours, immune and inflammatory processes were altered, with reduced tumoral infiltration of neutrophils and CD4 positive T cells, which can be explained by decreased levels of complement factor D (CFD) and C7 components of the complement cascade, an innate immune pathway that influences the adaptive immune response. We tested if the secretome was involved in BRF1-driven tumorigenesis. Unbiased proteomic analysis on BRF1-overexpresing PC3 cells confirmed reduced levels of CFD in the secretome, implicating the complement system in prostate carcinogenesis. We further identify that expression of C7 significantly correlates with expression of CD4 and has the potential to alter clinical outcome in human prostate cancer, where low levels of C7 associate with poorer prognosis.

Antitumour effects of Liporaxel (oral paclitaxel) for canine melanoma in a mouse xenograft model.

Paclitaxel, a member of the taxane family, exhibits antitumour effects by targeting the microtubules in cancer cells. Recently, oral paclitaxel has been developed to overcome the side effects of intravenous paclitaxel administration in human patients. The objective of this study was to investigate the antitumour effects of oral paclitaxel in vitro and in vivo. Three weeks after inoculation, oral paclitaxel (25 and 50 mg/kg) or saline was administered every week for three consecutive weeks. To explore the underlying mechanism, tumour angiogenesis was examined by immunohistochemistry with an anti-CD31 antibody. Tumour cell apoptosis was detected by Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling assay, and cell cycle arrest was confirmed by western blot analysis. Oral paclitaxel treatment of canine melanoma cells exerted mediated antiproliferative effects and mediated cell cycle arrest in vitro. In animal experiments, after oral paclitaxel administration, the average tumour size decreased to approximately 30% of that in the control. Histologically, oral paclitaxel showed anti-angiogenic effects and induced the apoptosis in tumour tissues. Oral paclitaxel also downregulated the intratumoural expression of cyclin D1 and inhibited cell proliferation. The study findings support potential application of oral paclitaxel as a novel chemotherapeutic strategy to treat canine melanoma. This is the first study to investigate the potential of oral paclitaxel as a therapeutic drug against canine tumours.

SMR peptide antagonizes mortalin promoted release of extracellular vesicles and affects mortalin protection from complement-dependent cytotoxicity in breast cancer cells and leukemia cells.

Background: Mortalin/GRP-75/mt-hsp70 is a mitochondrial chaperone protein, found in the cytoplasm, endoplasmic reticulum and cytoplasmic vesicles. It functions in many cellular processes such as mitochondrial biogenesis, intracellular trafficking, cell proliferation, signaling, immortalization and tumorigenesis. Thus, inhibition of mortalin is a promising avenue for cancer therapy. Previous studies in our lab have suggested that mortalin contributes to breast cancer development and progression. We showed that tumor extracellular vesicle secretion was decreased by knockdown of mortalin expression using HIV-1 Nef SMR peptides. Specifically, these peptides can block extracellular vesicle secretion and mediate cell cycle arrest in MDA-MB-231 and MCF-7 breast cancer cells. Aims: This study aims to investigate further the function and mechanism of interaction of PEG-SMR-CLU and SMR-CPP peptides with the chaperone protein mortalin and to explore the effect of SMR-derived peptides and mortalin expression on extracellular vesicle release and complement dependent cell toxicity in human breast cancer and leukemia cell lines. Results: Our results demonstrated additional effects reversing the tumorigenicity of these cells. First, the modified SMRwt peptides reduced the expression of the mesenchymal marker vimentin (VIM). Second, exposure to the SMRwt peptide inhibited mortalin and complement C9 expression in MDA-MB-231, MCF-7 breast cancer cells and K562 leukemia cells as measured by the Western blot analysis. Third, the SMRwt peptides blocked the cancer cells’ ability to release extracellular vesicles, which we observed blocked extracellular vesicle-mediated release of complement, re-establishing complements mediated cell death in those peptide-treated cells. Methods: We developed a series of peptides derived from the Secretion Modification Region (SMR) of HIV-1 Nef protein, modified by the addition of either a cell-penetrating peptide (CPP), a positively charged arginine-rich peptide derived from HIV-1 regulatory protein Tat, or a Clusterin-binding peptide (CLU), a molecular chaperone involved in protein secretion. Both CPP and CLU peptide sequences were added at the C-terminus of the Nef SMR peptide. The CLU-containing peptides were also modified with polyethylene glycol (PEG) to enhance solubility. After treatment of cells with the peptides, we used the MTT cell viability and complement-mediated cytotoxicity assays to confirm the inhibitory role of modified SMRwt peptides on the proliferation of MDA-MB-231 and MCF-7 breast cancer cells and K562 leukemia cells. Flow cytometry was used to determine complement mediated cell apoptosis and death. Western blot analysis was used to track SMR peptides impact on expression of mortalin, vimentin and complement C9 and to measure the expression of extracellular vesicle proteins. NanoSight analysis and acetylcholinesterase (AChE) assay were used for measuring extracellular vesicles particle size and concentration and acetylcholinesterase. Conclusions: Mortalin promotes cell proliferation, metastasis, angiogenesis, downregulate apoptotic signaling. Thus, mortalin is a potential therapeutic target for cancer immunotherapy. The novel SMRwt peptides antagonize the functions of mortalin, blocking tumor extracellular vesicle release and extracellular vesicle-mediated release of complement. This leads to decreases in breast cancer cell metastasis and allows standard treatment of these late stage tumor cells, thus having important clinical implications for late stage breast cancer chemotherapy. These findings support further investigation into the therapeutic value of the SMR peptide in cancer metastasis.

Abstract 4682: TGFB signaling disruption in the formation of oral pre-neoplasia

Abstract In humans, tissue homeostasis has to be maintained for decades without significant loss of functionality. Epithelia such as the oral mucosa achieve this through the self-renewing capabilities of stem cells. These life-long residents of the oral mucosa maintain homeostasis of the epithelium and at the same time have to be able to protect themselves from the main threats to longevity, i.e., stem cell exhaustion and malignant conversion and carcinogenesis. A key pathway in mediating cell cycle arrest in oral keratinocytes is mediated by TGFB superfamily signaling. There is good evidence implicating TGFB signaling as a tumor suppressor pathway in oral cancer. We have previously shown that disruption of TGFB signaling and cell adhesion can lead to oral squamous cell carcinoma. In vitro using oral keratinocytes, we found that TGFB regulates the stem cell compartment, inducing gene expression of quiescent stem cell markers MECP2, XPC, ITGB1 and PDPN. Using multiplex immunofluorescence, we have stained a tissue microarray containing 28 cases of squamous cell carcinoma, 4 adenocarcinoma, 4 metastatic carcinoma, 6 hyperplasia, and 5 adjacent inflammatory as well as normal adjacent and normal tissues. The antibodies selected were MECP2, XPC, ITGB1 and K15 in combination with the proliferation marker ki67 to determine if TGFB signaling regulates markers of stem cell quiescence. This quiescent gene signature highlighted a basal niche for slow-cycling cells, reserve stem cells. During oral disease progression, marker expression was abandoned in favor of increased proliferation. In vivo, a mouse model in which KrasG12D expression was induced and the Smad4 gene deleted specifically in the adult epithelium showed invasive cancers in the oral cavity. These Smad4-negative tumors express Sox9, a marker of human OSCCs and a TGFB target, which we have also observed to be upregulated in human premalignant lesions. Sox9-positive areas in the mouse tumors are associated with a downregulation of quiescent oral stem cell markers Krt15 and Mecp2, same as we observed in immunostainings of human tissues. In conclusion, TGFB and SMAD4 regulate quiescent stem cells and loss of this pathways allows invasive cancers to develop in the setting of oncogene expression. Furthermore, we could show that MECP2 in combination with other markers identifies quiescent basal cells in the human oral mucosa and is lost as TGFB signaling is disrupted in tumorigenesis. Citation Format: Claudia D. Andl, Anna L. Means, James S. Lewis, Alexandra Rothaus, Thomas Andl. TGFB signaling disruption in the formation of oral pre-neoplasia [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 4682.

Abstract 2971: Ellagic acid and its metabolite Urolithin A induce prostate cancer cell death in p53 dependent and independent manner

Abstract Carcinoma of the prostate (CaP) is the most common cancer in men and the second leading cause of cancer-related death in men worldwide. Treatment of early stages of CaP often involves the surgical removal of all or part of the prostate gland; whereas malignant cases of advanced CaP generally requires a combination of therapies including removal of the entire prostate, radiotherapy and androgen deprivation. However, significant number of CaP patients relapse the CaP as the disease becomes hormonal independent. Therefore, it is important to target cell death pathways that function independently of androgen signaling. p53 is a common tumor suppressor that mediates apoptosis, cell cycle arrest and DNA repair. Inactivation of p53 is common in CaP cells and this repression of p53 function diminishes androgen receptor signaling. The most common negative regulator of p53 is MDM2, which is itself a target gene of p53 to form an autoregulatory negative feedback loop. MDM2 inhibits p53 transcriptional activity through the induction of p53 polyubiquitination and degradation in the proteasome. This loss of p53 may permit CaP cells to undergo uncontrolled cell growth and cancer progression. Previous studies have shown that certain polyphenols, derived from natural products, possess anticancer activity that may be attributed to their repression of MDM2 ligase activity and activation of p53. Pomegranates, berries, and walnuts contain several bioactive compounds, including the Ellagitannins (ETs). ETs are polyphenolic compounds that are hydrolyzed in the stomach to form Ellagic acid (EA) which is itself metabolized in the gut microbiota to Urolithin A (UA). The purpose of this study was to investigate the influence of EA and UA on the p53-MDM2 signaling pathway in CaP cells. Three models of CaP cell lines were used because each harbor different p53 genotypes: LNCaP (p53+/+), 22RV1(p53-/+) and PC3 (p53-/-). Here we found that, when 22RV1 and LNCaP were treated with EA and UA, the interaction between p53 and MDM2 was disrupted. As a result, both EA and UA caused an increase in p53 protein levels and increased the steady-state concentration of p21, a main downstream target gene of p53 that mediates cell cycle arrest. In addition, EA and UA increased the levels of PUMA and NOXA proteins, both target genes of p53 which confer p53’s pro-apoptotic function. Moreover, we confirmed UA inhibits MDM2-mediated polyubiquitination and degradation of p53. Finally, the data show that EA and UA induce apoptosis in PC3 cells (p53-/-), indicating p53 independent role of these compounds. These results suggest that EA and UA may have potential anti-neoplastic activity in CaP cells that may be at least partially attributed to the stabilization and activation of p53. Citation Format: Yasir I. Mohammed Saleem, Mustafa Selim. Ellagic acid and its metabolite Urolithin A induce prostate cancer cell death in p53 dependent and independent manner [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 2971.

Identification of a 3,3-difluorinated tetrahydropyridinol compound as a novel antitumor agent for hepatocellular carcinoma acting via cell cycle arrest through disturbing CDK7-mediated phosphorylation of Cdc2.

Tetrahydropyridinol derivatives were recently reported to exhibit good biological activities, and the incorporation of fluorine into organic molecules may have profound effects on their physical and biological properties. Therefore, we investigated the anticancer activities of six fluorinated tetrahydropyridinol derivatives that we synthesized previously. We found that only one compound, 3,3-difluoro-2,2-dimethyl-1,6-diphenyl-5-tosyl-1,2,3,6-tetrahydropyridin-4-ol, showed significant antiproliferative activity on human hepatocellular carcinoma HepG2 and HMCCLM3 cells (the IC50 values were 21.25 and 29.07μM, respectively). We also found that this compound mediated cell cycle arrest in the G0/G1 phase at 30-40μM. Western blot analysis demonstrated that the cell cycle arrest induced by this compound in HepG2 and HMCCLM3 cells was associated with a significant decrease in Cdc2 and cyclin B1, which led to the accumulation of the phosphorylated-Tyr15 (inactive) form of Cdc2 and low expression of M phase-promoting factor (cyclin B1/Cdc2). Moreover, cells treated with this compound exhibited decreased expression of cyclin-dependent kinase (CDK)-activating kinase (CDK7/cyclin H). This compound also induced cell apoptosis via activation of caspase-3. A xenograft model in nude mice demonstrated anti-liver cancer activity and the mechanism of action of this compound. These findings indicated that the anticancer effect of this compound was partially due to G0/G1 cell cycle arrest via inhibition of CDK7-mediated expression of Cdc2, and this compound may be a promising anticancer candidate for further investigation.

Emerging Role of the Nucleolar Stress Response in Autophagy.

Autophagy represents a conserved self-digestion program, which allows regulated degradation of cellular material. Autophagy is activated by cellular stress, serum starvation and nutrient deprivation. Several autophagic pathways have been uncovered, which either non-selectively or selectively target the cellular cargo for lysosomal degradation. Autophagy engages the coordinated action of various key regulators involved in the steps of autophagosome formation, cargo targeting and lysosomal fusion. While non-selective (macro)autophagy is required for removal of bulk material or recycling of nutrients, selective autophagy mediates specific targeting of damaged organelles or protein aggregates. By proper action of the autophagic machinery, cellular homeostasis is maintained. In contrast, failure of this fundamental process is accompanied by severe pathophysiological conditions. Hallmarks of neuropathological disorders are for instance accumulated, mis-folded protein aggregates and damaged mitochondria. The nucleolus has been recognized as central hub in the cellular stress response. It represents a sub-nuclear organelle essential for ribosome biogenesis and also functions as stress sensor by mediating cell cycle arrest or apoptosis. Thus, proper nucleolar function is mandatory for cell growth and survival. Here, I highlight the emerging role of nucleolar factors in the regulation of autophagy. Moreover, I discuss the nucleolar stress response as a novel signaling pathway in the context of autophagy, health and disease.

LAMB3 mediates apoptotic, proliferative, invasive, and metastatic behaviors in pancreatic cancer by regulating the PI3K/Akt signaling pathway

The poor prognosis of patients with pancreatic ductal adenocarcinoma (PDAC) is partially attributed to the invasive and metastatic behavior of this disease. Laminin subunit beta-3 (LAMB3) encodes one of the three subunits of LM-332, an extracellular matrix protein secreted by cultured human keratinocytes. In addition, LAMB3 is involved in the invasive and metastatic abilities of some types of cancer, including colon, pancreas, lung, cervix, stomach, and prostate cancer, but the role and mechanism of LAMB3 in PDAC have not been previously determined. Herein, we tentatively investigated the role of LAMB3 in the malignant biological behavior of PDAC. In this study, we demonstrated that LAMB3 is upregulated in PDAC. Inhibition of LAMB3 abrogated the tumorigenic outcomes of PI3K/Akt signaling pathway activation, including those involving cell cycle arrest, cell apoptosis, proliferation, invasion and migration in vitro, and tumor growth and liver metastasis in vivo. Our results showed that LAMB3 could mediate cell cycle arrest and apoptosis in PDAC cells and alter the proliferative, invasive, and metastatic behaviors of PDAC by regulating the PI3K/Akt signaling pathway. LAMB3 may be a novel therapeutic target for the treatment of PDAC in the future.

Abstract P4-15-06: Results of a randomized double blind trial of neoadjuvant anastrozole plus placebo vs anastrozole plus saracatinib for ER+ postmenopausal breast cancer

Abstract Antiestrogen mediated cell cycle arrest requires the CDK inhibitor, p27. Src kinase mediates p27 loss and antiestrogen resistance in ER+ breast cancer lines in vitro. In ER+ xenografts, the Src inhibitor, saracatinib, restored antiestrogen responses in resistant tumors. This led to a Phase I/randomized double-blind Phase II trial to test effects of saracatinib with anastrozole for ER+ and/or PR+ postmenopausal breast cancer. Phase I accrued 12 subjects and showed 175 mg po saracatinib is safely given with 1 mg po daily anastrozole with good PK . In Phase II, postmenopausal women with new ER+ and/or PR+, HER2- breast cancers ≥ 2 cm were randomized 2:1 to either neoadjuvant anastrozole with saracatinib or anastrozole/placebo over 6 months. Response was assayed by clinical 2D measurements each cycle and by MRI pre-study, at 10 weeks and prior to surgery. The Phase II primary endpoint was to test if tumor volume decrease (from 2D clinical measures) with dual therapy (dual) exceeded that of monotherapy (mono) by >20%. Secondary endpoints included tumor response by 3D MRI measures and by RECIST, PK and toxicity, and molecular predictors of drug efficacy in pre-/ post-therapy tumors. Of 58 subjects, 15% were Black, 5% Asian and 79% White. 61% were Hispanic. Dual therapy was well tolerated, with the following grade 1 toxicities: flu-like syndrome 20%, non-pruritic rash 48% (17% for mono), self-limited diarrhea in 55% (33% mono). Transaminasemia with dual therapy was 52.5% and 17% with mono. 6/59 stopped dual due to drug related AEs: 2 had gr 3 hepatitis, one gr 3 anemia, 3 had grade 3 urticarial rash. Dual Rx increased mean anastrozole levels to 50 ng/ml vs 38 ng/ml for mono (T test p= 5.45201 E-05). Mean saracatinib level, 269 ng/ml, was similar to prior studies. All of 50 evaluable subjects showed clinical and MRI tumor responses. 17% in both groups progressed, usually after 16 weeks. Mean tumor vol (calculated from 2D clinic measures) declined more rapidly (by 63% in dual vs 55% in mono at 8 weeks), but both groups showed an 89% mean tumor volume decrease by 20 weeks. Clinical RECIST showed size reductions of 61% in dual and 62% after monotherapy. Tumor volumes based on 3D MRI show a non-significant trend to greater response to dual therapy, with mean volume decreased by 64% vs 45% at the end of dual vs monotherapy. RECIST response by MRI also showed a trend to greater % decrease tumor size post treatment by 34% vs 25% in dual vs mono. Thus, clinical volumetric assessment of response to this neoadjuvant endocrine therapy may overestimate response compared to volumes calculated by MRI, while RECIST may underestimate it. Pathologic responses based on initial and residual tumor burden calculated from initial and final tumor volumes and % cellularity in biopsy and surgical specimens will be presented. Citation Format: Slingerland JM, Mark P, Hurley J, Net J, Collado-Mesa F, Lippman M, Avisar E, Yepes M, Jorda M, Gomez C. Results of a randomized double blind trial of neoadjuvant anastrozole plus placebo vs anastrozole plus saracatinib for ER+ postmenopausal breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-15-06.

CircLARP4 induces cellular senescence through regulating miR-761/RUNX3/p53/p21 signaling in hepatocellular carcinoma.

Circular RNAs (circRNAs), a novel class of non‐coding RNAs, have emerged as indispensable modulators in human malignancies. Aberrant cellular senescence is a phenotype observed in various cancers. The association of circRNAs with cellular senescence in tumors is yet to determined. Here, we investigated the role of circLARP4 in cellular senescence and cell proliferation in hepatocellular carcinoma (HCC). Downregulated circLARP4 level was observed in HCC tissues and cell lines. Low expression level of circLARP4 independently predicted poor survival outcome. Gain‐of‐function and loss‐of‐function assays demonstrated that circLARP4 suppressed HCC cell proliferation, mediated cell cycle arrest and induced senescence in vitro. Levels of p53 and p21, 2 key regulatory molecules in cellular senescence, were increased in circLARP4‐overexpressed HCC cells and decreased in circLARP4‐silenced HCC cells. In vivo experiments further confirmed the tumor‐suppressing activity of circLARP4. Further mechanistic studies showed that circLARP4 dampened HCC progression by sponging miR‐761, thereby promoting the expression level of RUNX3 and activating the downstream p53/p21 signaling. Our study revealed the role of circLARP4/miR‐761/RUNX3/p53/p21 signaling in HCC progression, providing a potential survival predictor and therapeutic candidate for HCC.

A High-Throughput Screening Approach to Identify Therapeutics for the Treatment of Diamond-Blackfan Anaemia

Diamond-Blackfan Anaemia (DBA) is a rare blood cell aplasia that presents clinically at approximately 2-3 months of age and its main characteristic is reduced erythroid precursors in the bone marrow, i.e. anemia. Mutations in different ribosomal protein (RP) genes have been associated with DBA, with mutations in RPS19 accounting for 20-25% of all cases. It has been proposed that RPS19 deficiency causes perturbations in ribosome biogenesis, thus activation of the p53-dependent Nucleolar Surveillance Pathway (NSP). In this context free RPs (predominantly L5 and L11) in a complex with 5S rRNA sequester the E3 ubiquitin ligase murine double minute 2 (MDM2), leading to the accumulation of p53 and subsequent activation of its transcriptional targets mediating cell cycle arrest or apoptosis. In DBA, one of the molecular mechanisms impairing the proliferation and thus reducing the number of erythroid progenitors that can progress to mature red blood cells is an elevation of p53 protein mediating activation of the NSP.In order to identify potential therapeutics that could be repurposed to prevent the activation of NSP in DBA patients, we have screened compound libraries of clinically approved therapeutics to identify pathways implicated in the p53-dependent NSP due to RPS19 deficiency. We quantitated both cell number and the level of p53 expression, identifying compounds that can result in low and high expression of p53, the latter for potential use in cancer therapy. Using an RPS19 depleted A549 cell line as a model system, the screen successfully identified different therapeutic groups. In the DBA context, we were most interested in the compounds that reduced p53 and had no negative effect on cell number. A selection of 22 molecules were re-evaluated in vitro, again using RPS19 depleted A549 cells, through the quantification of p53 protein expression and densitometry analysis. From this, 10candidates were evaluated ex vivofor their effects on proliferation using bone marrow obtained from an inducible Rps19 knockdown (DBA) mouse model.While we are currently testing a number of compounds in vivo using the Rps19 DBA mouse model (as described), one of the compounds tested thus far has demonstrated a partial rescue of the cKit+ population, no changes in erythroid precursors but interestingly a reversal of the defect in the Granulocyte-Monocyte Progenitor (GMP) population. Impairment in lineage progression in the GMP compartment has also been reported to present in bone marrow failure Shwachman-Diamond Syndrome. We are currently evaluating the mechanism by which this drug is rescuing the c-Kit+ and GMP populations in these mice.In summary, our high-throughput screening approach and follow up studies have identified a suite of novel therapies that may be beneficial for repurposing for the treatment of bone marrow failure by increasing hematopoietic progenitor cells. We plan to evaluate this, and potentially other therapies, in a clinical trial with DBA patients. DisclosuresFlygare:LU Holding: Patents & Royalties: Patent.

Toxic effect of microcystin-LR on blood vessel development

The effect of microcystin-LR (MC-LR) at 50–1000 nmol/L on blood vessel development of zebrafish embryos has been explored. Upon exposure 72-h-post-fertilization (hpf), the hatching rate was significantly reduced and malformation and fatality rates were increased in a dose-dependent manner. MC-LR induced cell cycle arrest in the G0/G1-phase and damaged DNA structure in a dose-dependent manner. In human umbilical vein endothelial cells (HUVECs), MC-LR led to decreased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) and increased lipid peroxidation. These findings indicated that MC-LR could cause oxidative DNA damage, which mediated cell cycle arrest and inhibited cell proliferation afterwards, and retarded the blood vessel development.

Effects of p21 on adult hippocampal neuronal development after irradiation

Inhibition of hippocampal neurogenesis is implicated in neurocognitive impairment after cranial irradiation. We recently demonstrated that disruption of neuronal development after DNA damage was regulated by p53. The cyclin-dependent kinase inhibitor 1 or p21, a downstream effector p53, mediates cell cycle arrest in response to DNA damage. There is evidence that p21 negatively regulates proliferation of neural progenitors (NPCs). Here we characterized the effects of p21 on disruption of neuronal development in the hippocampal dentate gyrus after irradiation. We irradiated young adult mice wild type (+/+) or knockout (−/−) of the Cdkn1a (p21) gene, and used different bromodeoxyuridine (BrdU) paradigms for cell fate mapping. The acute apoptotic response of NPCs in the subgranular zone of the dentate gyrus was independent of p21 after irradiation. In nonirradiated mice, p21 knockout resulted in an increase in neuroblast proliferation and neurogenesis. At 9 weeks after 5Gy, NPCs in the subgranular zone demonstrated increased p21 expression. Loss of newborn type-1 cells and disruption of hippocampal neurogenesis was evident at 9 weeks after irradiation, and these effects were independent of p21 genotype status. Within the developmental milestones of NPCs, irradiation resulted in loss of early intermediate NPCs (type-2a cells) in wild-type mice, whereas the principal effect of irradiation with p21 loss was culling of proliferating late intermediate (type-2b cells) and neuroblasts. These results suggest that p21 exerts differential effects on cell fate of NPCs after irradiation. p21 may serve to protect proliferating late NPCs but does not alter the ultimate inhibition of new neuron production after DNA damage.

Abstract 1869: Role of Nef secretion modification region (SMR) peptides and the chaperone mortalin in breast cancer and leukemia cells

Abstract BACKGROUND: Mortalin/GRP-75(mt-hsp70, HSPA9) is a mitochondrial chaperone protein, also found in the cytoplasm, endoplasmic reticulum and cytoplasmic vesicles. It functions in many cellular processes such as mitochondrial biogenesis, intracellular trafficking, cell proliferation, signaling, immortalization and tumorigenesis, Thus, inhibition of mortalin is a promising avenue for cancer therapy. Previous studies in our lab have suggested that mortalin contributes to breast cancer development and progression. We showed tumor exosome secretion was decreased by knockdown of mortalin expression using HIV-1 Nef peptides. Specifically, these peptides can block exosome secretion and also mediate cell cycle arrest in MDA-MB-231 and MCF-7 breast cancer cells. AIMS: This study aims to investigate further the function and mechanism of interaction of PEG- SMR-CLU peptide and SMR-CPP peptide, and chaperone mortalin and to explore the effect of SMR-derived peptides and mortalin on human breast cancer and leukemia cell lines. RESULTS: Our results demonstrate that the modified SMRwt peptides not only affect breast cancer cell proliferation and arrest breast cancer cell growth, but they also inhibit migration of breast cancer cells. SMRwt peptides also block exosome-mediated release of complement, and allow the cells to die via complement induced cell death, and reduced mortalin protein expression. We further determined that expression levels of the mesenchymal markers vimentin (VIM) was decreased in presence of SMRwt peptides and MKT-077. CONCLUSIONS: Mortalin may promote cell proliferation and invasion via induction of epithelial mesenchymal transition (EMT) of cancer cells, which has a potential therapeutic target in cancer immunotherapy. SMRwt peptides block tumor exosome release and reduce the expression of mortalin. This may be a means to decreases breast cancer cell invasion and metastasis, which may have important clinical applications for late stage breast cancer chemotherapy. Furthermore, SMRwt peptides and inhibition of mortalin suppressed the migration and invasive capacity of cancer cells and is associated with a diminished EMT. These findings support a role for SMR peptide and mortalin in the induction of EMT, prompting a further investigation into their therapeutic value in cancer metastasis. Citation Format: Ming B. Huang, Vinvent C. Bond. Role of Nef secretion modification region (SMR) peptides and the chaperone mortalin in breast cancer and leukemia cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1869.

Abstract LB-243: Protein kinase D1 induces cell cycle arrest independent from check point kinases

Abstract Introduction: Prostate cancer (PCa), one of the most common cancers among men, initially manifests as an androgen-dependent malignancy. PCa eventually and inevitably progresses into hormone refractory or castration-resistant condition. Relapse of castration-resistant prostate cancer (CRPC) is life threatening, and responsible for the majority of mortality among PCa patients. During the transition from the hormone naive disease into CRPC, there is an up regulation of cell cycle markers and a decline in the expression of tumor suppressors like protein kinase D1 (PrKD1). The role of PrKD1 as a tumor suppressor has been identified in regulating various cellular events including the inhibition of the mitogenic pathways induced by growth factors and androgens. However, the potential role of PrKD1 as a cell cycle regulator has not been explored in solid cancers including prostate. Therefore, the present study has been designed to investigate the role of PrKD1 as a cell cycle regulator in PCa cells. Methods: LNCaP cells with high expression of PrKD1 and its aggressive derivative C4-2 cells with low expression of PrKD1 were used in this study. To evaluate the direct effect of PrKD1, C4-2 cells were stably transfected with PrKD1 and used alongside the two other cell lines. Cells were cultured in the presence and absence of Bryostatin 1 (Bryo-1, a PrKD1 activator) for 30 hours and exposed to 10 Gray gamma radiation (IR) to induce DNA damage. After the treatment period, cell cycle was assessed using flow cytometry and the phosphorylation of Cdc25 phophatases were analyzed by western blot. All experiments were repeated after inhibiting check point kinase 1 and 2 (CHEK1 and CHEK2) with siRNA to evaluate the independency of PrKD1 action on cell cycle. Results: LNCaP cells underwent cell cycle arrest in both Bryo-1 and IR group, whereas non-transfected C4-2 cells responded only to IR, not to Bryo-1. However, C4-2 cells when transfected with PrKD1 were arrested at G1/S checkpoint in response to Bryo-1. Down regulation of CHEK1 and CHEK2 with SiRNA in C4-2 cells did not cause any significant cell cycle arrest in response to DNA damage due to IR. Over expression of PrKD1 in these cells rescued the effect of siRNA against CHEK1 and CHEK2. Western blot analysis showed that activation of PrKD1 with Bryo-1 causes phophorylation of Cdc25 C phophatase. Conclusion: Our study showed that PrKD1 phosphorylates CDC25C and induces cell cycle arrest in G1/S phase in response to DNA damage. The results suggest that PrKD1, like the two other Serine Threonine kinases (CHEK1 and CHEK2), mediates cell cycle arrest in response to DNA damage. Citation Format: Bita Nickkholgh, Sivanandane Sittadjody, Michael B. Rothberg, KC Balaji. Protein kinase D1 induces cell cycle arrest independent from check point kinases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-243.

Abstract 2814: Antitumor effects of WEE1 inhibitor, AZD1775 alone or in combination with PARP inhibitor in triple negative breast cancer cells

Abstract Background: Wee1 is a critical component of the G2/M cell cycle checkpoint control and mediates cell cycle arrest by regulating the phosphorylation of CDC2. Inhibition of Wee1 has been reported to enhance the cytotoxic effect of DNA damaging agents in different types of carcinomas. Especially, recent reports have shown that DNA replication stress and double strand breaks are induced by the activation of CDK1 following WEE1 inhibitor treatment. We investigated the effects and underlying mechanisms of WEE1 inhibitor, AZD1775, in Triple Negative Breast Cancer (TNBC). In addition, we examined whether AZD1775 would enhance the anti-tumor effect of PARP inhibitor in TNBC cells by modulating DNA repair activity. Methods: MTT assay was performed to investigate the antitumor effect of WEE1 inhibitor, AZD1775 alone or with PARP inhibitor in breast cancer cell lines. The regulation of DNA damage response activity by AZD1775 or/and PARP inhibitor was accessed by the comet and western blotting. The status of the S phase was evaluated by EdU-BrdU dual pulse labeling, and the drug effect was also confirmed in vivo by mouse xenograft model of TNBC. Results: AZD1775 showed heterogeneous antitumor effects among TNBC cells regardless of TP53 mutation statues. WEE1 inhibition led to accelerated S phase progression and mitotic entry in the sensitive MDA-MB-231 cells. In addition, increased DNA damage and caspase-3 dependent apoptosis were observed in sensitive cells following AZD1775 treatment. Furthermore, AZD1775 enhanced cellular sensitivity to PARP inhibitor through increase apoptosis and DNA damage accumulation. In a MDA-MB-231 xenograft model, AZD1775 impedes tumor growth as well. Conclusions: In the TNBC, the WEE1 inhibitor has a heterogeneous cytotoxic effect regardless of the p53 mutation status. In MDA-MB-231 cell, which is a sensitive TNBC cells to WEE1 inhibitor AZD1775, the progression of the cell cycle was accelerated and the aberrant DNA content was increased. This resulted in DNA damage, which led to cell death, and this effect could be applied in vivo. In addition, we investigated that WEE1 inhibition can increase PARP inhibitor sensitivity in TNBC cells via increasing accumulation of DNA damage. Our results provide a rationale for the future clinical trials of PARP inhibitor combined with WEE1 inhibition in triple negative breast cancer. Citation Format: Dong Hyeon Ha, Arrum Min, Seongyeong Kim, So Hyeon Kim, Hyemin Jang, Yu Jin Kim, Daeun Jung, YoonJung Park, Koung Jin Suh, Kyung-Hun Lee, Tae-Yong Kiim Kim, Seock-Ah Im. Antitumor effects of WEE1 inhibitor, AZD1775 alone or in combination with PARP inhibitor in triple negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2814.