Phosphorylation Of Retinoblastoma Protein Research Articles

Resveratrol attenuates hyperproliferation of vascular smooth muscle cells from spontaneously hypertensive rats: Role of ROS and ROS-mediated cell signaling

Resveratrol, a natural polyphenolic compound has been reported to attenuate angiotensin II -induced vascular smooth muscle cell (VSMC) hypertrophy; however, whether resveratrol could also inhibit hyperproliferation of VSMC from spontaneously hypertensive rats (SHR) is unexplored. The present study investigates the effect of resveratrol on hyperproliferation of VSMC from SHR and the underlying molecular mechanisms responsible for this response. For these studies, aortic VSMC from SHR and Wistar-Kyoto (WKY) rats were used. The proliferation of VSMC was determined by [3H] thymidine incorporation and the levels of proteins were determined by Western blotting. The enhanced proliferation exhibited by VSMC from SHR was attenuated by resveratrol. In addition, resveratrol attenuated the overexpression of cyclin D1, cyclin E, cyclin dependent kinase 4 (Cdk4), Cdk2, phosphorylated retinoblastoma protein (pRb), Giα proteins and enhanced phosphorylation of ERK1/2 and AKT in VSMC from SHR. Furthermore, the overproduction of superoxide anion, increased NADPH oxidase activity, overexpression of Nox2, Nox4 and p47phox proteins, increased phosphorylation of EGFR, IGF-IR, and c-Src were all abrogated by resveratrol. These results suggest that resveratrol attenuates the hyperproliferation of VSMC from SHR through the inhibition of ROS, c-Src, growth factor receptor activation, MAPK/PI3K, Giα and cell cycle proteins that are implicated in VSMC hyperproliferation.

Disruption of Interneuron Neurogenesis in Premature Newborns and Reversal with Estrogen Treatment.

Many Preterm-born children suffer from neurobehavioral disorders. Premature birth terminates the hypoxic in utero environment and supply of maternal hormones. As the production of interneurons continues until the end of pregnancy, we hypothesized that premature birth would disrupt interneuron production and that restoration of the hypoxic milieu or estrogen treatment might reverse interneuron generation. To test these hypotheses, we compared interneuronal progenitors in the medial ganglionic eminences (MGEs), lateral ganglionic eminences (LGEs), and caudal ganglionic eminences (CGEs) between preterm-born [born on embryonic day (E) 29; examined on postnatal day (D) 3 and D7] and term-born (born on E32; examined on D0 and D4) rabbits at equivalent postconceptional ages. We found that both total and cycling Nkx2.1+, Dlx2+, and Sox2+ cells were more abundant in the MGEs of preterm rabbits at D3 compared with term rabbits at D0, but not in D7 preterm relative to D4 term pups. Total Nkx2.1+ progenitors were also more numerous in the LGEs of preterm pups at D3 compared with term rabbits at D0. Dlx2+ cells in CGEs were comparable between preterm and term pups. Simulation of hypoxia by dimethyloxalylglycine treatment did not affect the number of interneuronal progenitors. However, estrogen treatment reduced the density of total and proliferating Nkx2.1+ and Dlx2+ cells in the MGEs and enhanced Ascl1 transcription factor. Estrogen treatment also reduced Ki67, c-Myc, and phosphorylation of retinoblastoma protein, suggesting inhibition of the G1-to-S phase transition. Hence, preterm birth disrupts interneuron neurogenesis in the MGE and estrogen treatment reverses interneuron neurogenesis in preterm newborns by cell-cycle inhibition and elevation of Ascl1. We speculate that estrogen replacement might partially restore neurogenesis in human premature infants.SIGNIFICANCE STATEMENT Prematurity results in developmental delays and neurobehavioral disorders, which might be ascribed to disturbances in the development of cortical interneurons. Here, we show that preterm birth disrupts interneuron neurogenesis in the medial ganglionic eminence (MGE) and, more importantly, that estrogen treatment reverses this perturbation in the population of interneuron progenitors in the MGE. The estrogen seems to restore neurogenesis by inhibiting the cell cycle and elevating Ascl1 expression. As preterm birth causes plasma estrogen level to drop 100-fold, the estrogen replacement in preterm infants is physiological. We speculate that estrogen replacement might ameliorate disruption in production of interneurons in human premature infants.

P-gp Inhibition by XL019, a JAK2 Inhibitor, Increases Apoptosis of Vincristine-treated Resistant KBV20C Cells with Increased p21 and pH2AX Expression.

The present study was designed to identify conditions that could increase the sensitivity of resistant cancer cells to antimitotic drugs. We investigated whether a Janus kinase 2 (JAK2) inhibitor used in clinical trials, XL019, sensitizes antimitotic drug-resistant KBV20C cells. XL019 reduced cellular viability and increased apoptosis in vincristine-treated KBV20C cells, independently of the JAK/signal transducer and activator of transcription (STAT) pathway. Based on the ATP-binding cassette protein B1 [ABCB1, P-glycoprotein (P-gp)] inhibitory assay, we demonstrated that XL019 functions as a P-gp inhibitor in drug-resistant KBV20C cells. Considering that another JAK2 inhibitor, CEP-33779, also inhibited P-gp and sensitized drug-resistant cancer cells in a previous study, we concluded that JAK2 inhibitors can be used as P-gp inhibitors in drug-resistant cancer cells. Fluorescence-activated cell sorting, western blot, and annexin V analyses were used to further investigate the mechanism of action of XL019 in vincristine-treated KBV20C cells. XL019 induced early apoptosis of KBV20C cells in response to vincristine treatment via increased G2 phase arrest. Moreover, G2 phase arrest and apoptosis of cells co-treated with vincristine and XL019 resulted from the up-regulation of phosphorylated retinoblastoma protein (pRb), p21, and the DNA-damage protein, phosphorylated H2A histone family, member X (pH2AX). Additionally, the P-gp-inhibitory effect of XL019 was less than that of CEP-33779, and a more than 2-fold higher dose was required to sensitize vincristine-treated KBV20C cells. Furthermore, lower doses of XL019 were required to sensitize KBV20C cells to a degree similar to that obtained with the established P-gp inhibitor verapamil, suggesting that XL019 has higher specificity than verapamil. Our results showed that JAK2 inhibitors inhibited P-gp action via a direct binding mechanism, which was similar to that of verapamil. These findings indicate that JAK2 inhibitors may be promising therapeutics for the treatment of cancer that is resistant to antimitotic drugs.

Recent advances of cyclin-dependent kinases as potential therapeutic targets in HR+/HER2- metastatic breast cancer: a focus on ribociclib.

In normal cell cycle progression, transition of G0/G1 phase to synthesis (S) phase for breast and other cells is regulated by association of cyclin D and cyclin-dependent kinases 4 and 6 (CDK4/6) that leads to phosphorylation of retinoblastoma (Rb) protein. Imbalance of this cyclin D-CDK4/6-inhibitors of CDK4/6-Rb phosphorylation pathway is associated with tumorigenesis of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) breast cancers. Despite effective first-line endocrine therapy, HR+/HER2− metastatic breast cancers remain still incurable. Currently, advances in understanding of cell cycle checkpoints are evolving as promising strategy to target in treatment of various types of cancers including breast cancer. Therapies that target this cell cycle machinery in HR+/HER2− breast cancers are getting approval by the US Food and Drug administration (FDA) including ribociclib (LEE011). Ribociclib got the first FDA approval in March 13, 2017, as an initial therapy for HR+/HER2− advanced or metastatic breast cancer in combination with an aromatase inhibitor. This review, therefore, addresses the role of selective CDK4/6 inhibitors in advanced or metastatic breast cancer with a specific focus on ribociclib. Some findings of clinical trials involving ribociclib found pivotal benefits of ribociclib in HR+/HER2− metastatic breast cancer in terms of prolonging progression-free survival and objective response rates. Daily dosage range of the drug for such benefits is 50–900 mg with common daily doses of 400 or 600 mg and 600 mg in early and advanced breast cancer therapies, respectively. Along with its therapeutic benefits, however, more incident but manageable dose-limiting grade 3 or 4 toxicities, primarily hematologic adverse events, are common in patients treated with ribociclib. Generally, there are several active clinical trials undergoing to investigate the clinical efficacy and toxicity profile of the drug in various cancerous conditions other than breast cancer and will likely benefit patients with other cancer types.

Cell Cycle Protein Expression in Neuroendocrine Tumors: Association of CDK4/CDK6, CCND1, and Phosphorylated Retinoblastoma Protein With Proliferative Index.

Dysregulation of the cell cycle has been observed and implicated as an etiologic factor in a range of human malignancies, but remains relatively unstudied in neuroendocrine tumors (NETs). We evaluated expression of key proteins involved in cell cycle regulation in a large cohort of NETs. We evaluated immunohistochemical expression of CDKN1B, CDKN1A, CDKN2A, CDK2, CDK4, CDK6, cyclin D1, cyclin E1, and phosphorylated retinoblastoma protein (phospho-RB1) in a cohort of 267 patients with NETs. We then explored associations between cell cycle protein expression, mutational status, histologic features, and overall survival. We found that high expression of CDK4, CDK6, CCND1, and phospho-RB1 was associated with higher proliferative index, as defined by MKI67. We additionally observed a trend toward shorter overall survival associated with low expression of CDKN1B. This association seemed strongest in SINETs (multivariate hazards ratio, 2.04; 95% confidence interval, 1.06-3.93; P = 0.03). We found no clear association between CDKN1B mutation and protein expression. Our results suggest that dysregulation and activation of the CDK4/CDK6-CCND1-phospho-RB1 axis is associated with higher proliferative index in NETs. Investigation of the therapeutic potential of CDK4/CDK6 inhibitors in higher grade NETs is warranted.

Cell Cycle Analysis by Mass Cytometry.

The regulated progression of cells through the cell cycle during proliferation is a critical factor in tumor progression, anti-neoplastic therapy response, immune system regulation, and developmental biology. While flow cytometric measurement of cell cycle progression is well established, mass cytometry assays allow the cell cycle to be measured along with up to 39 other antigens enabling characterization of the complex interactions between the cell cycle and a wide variety of cellular processes. This method describes the use of mass cytometry for the analysis of cell cycle state for cells from three different sources: in vitro cultured cell lines, ex vivo human blood or bone marrow, and in vivo labeling and ex vivo analysis of murine tissues. The method utilizes incorporation of 5-Iodo-2'-deoxyuridine (IdU), combined with measurement of phosphorylated retinoblastoma protein (pRb), cyclin B1, and phosphorylated histone H3 (p-HH3). These measurements can be integrated into a gating strategy that allows for clear separation of all five phases of the cell cycle.

Novel focal adhesion kinase 1 inhibitor sensitizes lung cancer cells to radiation in a p53-independent manner.

Focal adhesion kinase 1 (FAK1) is known to promote tumor progression and metastasis by controlling cell movement, invasion, survival and the epithelial-to-mesenchymal transition in the tumor microenvironment. As recent reports imply that FAK1 is highly associated with tumor cell development and malignancy, the inhibition of FAK1 activity could be an effective therapeutic approach for inhibiting the growth and metastasis of tumor cells. In this study, we aimed to determine the effect of a novel synthetic FAK1 inhibitor 2-[2-(2-methoxy-4-morpholin-4-yl-phenylamino)-5-trifluoromethyl-pyrimidin-4-ylamino]-N-methyl-benzamide, (MPAP) on lung cancer cells. MPAP suppressed cancer cell proliferation and the phosphorylation of FAK1. Combined treatment with MPAP and irradiation (IR) showed enhanced suppression of cancer cell proliferation in wild-type p53 cells and more intense suppression in p53-null cells. In addition, the combination treatment effectively induced G1 cell cycle arrest in a p53-independent manner. In an invivo tumor xenograft mouse model, treatment with both MPAP and IR reduced tumor growth more than the treatment with IR or MPAP alone. Overall, these data demonstrate that the radiosensitizing effect of MPAP is mediated by the regulation of retinoblastoma protein (RB) phosphorylation in a p53-independent manner.

Tumor microenvironment conditions alter Akt and Na+/H+ exchanger NHE1 expression in endothelial cells more than hypoxia alone: implications for endothelial cell function in cancer

BackgroundChronic angiogenesis is a hallmark of most tumors and takes place in a hostile tumor microenvironment (TME) characterized by hypoxia, low nutrient and glucose levels, elevated lactate and low pH. Despite this, most studies addressing angiogenic signaling use hypoxia as a proxy for tumor conditions. Here, we compared the effects of hypoxia and TME conditions on regulation of the Na+/H+ exchanger NHE1, Ser/Thr kinases Akt1–3, and downstream effectors in endothelial cells.MethodsHuman umbilical vein endothelial cells (HUVEC) and Ea.hy926 endothelial cells were exposed to simulated TME (1% hypoxia, low serum, glucose, pH, high lactate) or 1% hypoxia for 24 or 48 h, with or without NHE1 inhibition or siRNA-mediated knockdown. mRNA and protein levels of NHE1, Akt1–3, and downstream effectors were assessed by qPCR and Western blotting, vascular endothelial growth factor (VEGF) release by ELISA, and motility by scratch assay.ResultsWithin 24 h, HIF-1α level and VEGF mRNA level were increased robustly by TME and modestly by hypoxia alone. The NHE1 mRNA level was decreased by both hypoxia and TME, and NHE1 protein was reduced by TME in Ea.hy926 cells. Akt1–3 mRNA was detected in HUVEC and Ea.hy926 cells, Akt1 most abundantly. Akt1 protein expression was reduced by TME yet unaffected by hypoxia, while Akt phosphorylation was increased by TME. The Akt loss was partly reversed by MCF-7 human breast cancer cell conditioned medium, suggesting that in vivo, the cancer cell secretome may compensate for adverse effects of TME on endothelial cells. TME, yet not hypoxia, reduced p70S6 kinase activity and ribosomal protein S6 phosphorylation and increased eIF2α phosphorylation, consistent with inhibition of protein translation. Finally, TME reduced Retinoblastoma protein phosphorylation and induced poly-ADP-ribose polymerase (PARP) cleavage consistent with inhibition of proliferation and induction of apoptosis. NHE1 knockdown, mimicking the effect of TME on NHE1 expression, reduced Ea.hy926 migration. TME effects on HIF-1α, VEGF, Akt, translation, proliferation or apoptosis markers were unaffected by NHE1 knockdown/inhibition.ConclusionsNHE1 and Akt are downregulated by TME conditions, more potently than by hypoxia alone. This inhibits endothelial cell migration and growth in a manner likely modulated by the cancer cell secretome.

Chronic D609 treatment interferes with cell cycle and targets the expression of Olig2 in Glioma Stem like Cells

Glioma Stem-like Cells (GSCs) isolated from patient derived tumors have high metabolic activity and survive in the absence of exogenous growth factors. We recently demonstrated that acute D609 (Tricyclodecan-9-yl-xanthogenate), a PC-PLC inhibitor with anti-oxidative property, can decrease the ATP content & GADD45β protein in GSCs cultured without growth factors, but not in the presence of growth factors. In this study we examined the effect of chronic D609 treatment on GSCs cultured in complete medium containing growth factors. Our results show that chronic exposure of GSCs to D609 decreased the ATP content and reduced the expression of GADD45β protein. Furthermore, cyclin D1 content and the phosphorylation of retinoblastoma protein also diminished, resulting in the arrest of cells in G1 phase of cell cycle after D609 treatment. In addition, the expression of Olig2, a protein responsible for the progression of glioblastoma was reduced by D609. Together these results indicate that chronic D609 treatment can inhibit the growth of glioma cells by arresting cells in G1 phase of cell cycle and/or reducing Olig2 expression.

Serpine 1 induces alveolar type II cell senescence through activating p53-p21-Rb pathway in fibrotic lung disease.

SummarySenescence of alveolar type 2 (ATII) cells, progenitors of the alveolar epithelium, is implicated in the pathogeneses of idiopathic pulmonary fibrosis (IPF), an aging‐related progressive fatal lung disorder with unknown etiology. The mechanism underlying ATII cell senescence in fibrotic lung diseases, however, remains poorly understood. In this study, we report that ATII cells in IPF lungs express higher levels of serpine 1, also known as plasminogen activator inhibitor 1 (PAI‐1), and cell senescence markers p21 and p16, compared to ATII cells in control lungs. Silencing PAI‐1 or inhibition of PAI‐1 activity in cultured rat ATII (L2) cells leads to decreases in p53 serine 18 phosphorylation (p53S18P), p53 and p21 protein expressions; an increase in retinoblastoma protein phosphorylation (ppRb); and a reduction in the sensitivity to bleomycin‐ and doxorubicin‐induced senescence. Silencing p53, on the other hand, abrogates PAI‐1 protein‐stimulated p21 expression and cell senescence. In vivo studies, using ATII cell‐specific PAI‐1 conditional knockout mouse model generated recently in this laboratory, further support the role of PAI‐1 in the activation of p53‐p21‐Rb cell cycle repression pathway, ATII cell senescence, and lung fibrosis induced by bleomycin. This study reveals a novel function of PAI‐1 in regulation of cell cycle and suggests that elevation of PAI‐1 contributes importantly to ATII cell senescence in fibrotic lung diseases.

Abstract CT045: Ribociclib + letrozole for first-line treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC): efficacy by baseline tumor markers

Abstract Background: Cyclin D-cyclin-dependent kinase (CDK) 4/6 complexes promote cell proliferation through phosphorylation of retinoblastoma protein (Rb). In breast cancer, cyclin D-CDK4/6 activity can be increased through cyclin D gene (CCND1) amplification or loss of the CDK4/6 negative regulator p16. Here we present efficacy data from the Phase III MONALEESA-2 study of ribociclib (CDK4/6 inhibitor) + letrozole vs. placebo + letrozole for first-line treatment of HR+, HER2- ABC, assessed in baseline tumors by protein levels of Rb, p16, the cell proliferation marker Ki67, and by gene expression levels of CDKN2A (p16) and CCND1. Methods: Postmenopausal women with HR+, HER2- ABC with no prior systemic therapy for advanced disease were randomized 1:1 to receive ribociclib or placebo (600 mg/day 3-weeks-on/1-week-off) + letrozole (2.5 mg/day continuous). The primary endpoint was investigator-assessed progression-free survival (PFS). Provision of a representative baseline tumor biopsy or archival tissue at screening was mandatory if available. Baseline tumor tissue was evaluated for protein biomarkers (immunohistochemistry) and gene expression (NanoString nCounter® Human Cancer Reference panel). Results: Of 668 patients randomized, 479 were evaluable for total Rb, and 416 (87%) displayed high levels (H-score ≥100). p16 protein levels were evaluable in 405 patients; 165 (41%) had low (H-score <50), 182 (45%) medium (H-score ≥50-149), and 58 (14%) had high (H-score ≥150) p16 levels. Ki67 was detected in ≤14% of tumor cells in 216 (47%) patients and in >14% of cells in 247 (53%) patients. The median messenger RNA expression level was used as the cut-off to define patients with low or high baseline CDKN2A and CCND1 gene expression. An improved PFS was observed by the addition of ribociclib to letrozole in all the above patient subgroups, with hazard ratios ranging from 0.40 (high p16 by H-score; 95% confidence interval [CI] 0.16-1.0; p=0.06) to 0.64 (≤14% Ki67-positive cells; 95% CI 0.39-1.0; p=0.07). Patients with less or greater than 14% Ki67-positive cells, lower or higher p16 levels, Rb levels, or CDKN2A or CCND1 gene expression benefitted from the addition of ribociclib to letrozole to a similar extent. Conclusions: A consistent benefit from ribociclib + letrozole vs. placebo + letrozole was observed irrespective of baseline Rb, p16, and Ki67 levels or CDKN2A and CCND1 gene expression levels. Hormone receptor positivity remains the only established biomarker of response to CDK4/6 inhibitors. Citation Format: Fabrice Andre, Salomon M. Stemmer, Mario Campone, Katarina Petrakova, Shani Paluch-Shimon, Yoon-Sim Yap, Norbert Marschner, Arlene Chan, Cristian Villanueva, Lowell L. Hart, Carlos L. Arteaga, Gabe S. Sonke, Eva-Maria Grischke, Emilio Alba, Arnd Nusch, Denise A. Yardley, Erik Jakobsen, Sibel Blau, Sara M. Tolaney, Faye Su, Wei He, Caroline Germa, Gabriel N. Hortobagyi. Ribociclib + letrozole for first-line treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC): efficacy by baseline tumor markers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT045. doi:10.1158/1538-7445.AM2017-CT045

Abstract 128: The next-generation CDK2/9 inhibitor CYC065 elicits marked antineoplastic effects in lung cancer by engaging antimetastatic pathways

Abstract We previously reported CDK2 antagonism with the first generation CDK2/9/7 inhibitor seliciclib (CYC202; Cyclacel) triggered anaphase catastrophe. This occurred when genomically unstable cancer cells with supernumerary centrosomes (a hallmark of cancer) fail to cluster excessive centrosomes at mitosis. This causes multipolar cell division and apoptotic death. Anaphase catastrophe is conferred after CDK2 antagonism of aneuploid cancer cells, sparing bipolar normal cells with two centrosomes. CYC065 (Cyclacel) is a next-generation CDK2/9 inhibitor that is undergoing clinical trial. Here, we explored CYC065 activity against lung cancer cells, some with known high metastatic potential. CYC065 substantially inhibited growth, triggered apoptosis, and induced anaphase catastrophe in murine (ED1, LKR13, and 393P) and human (Hop62, A549, and H1299) lung cancer cells. In marked contrast, these effects were largely unseen in bipolar immortalized pulmonary epithelial (murine C10 and human BEAS-2B) cells. We sought to explore whether CYC065 antineoplastic effects engaged antimetastatic pathways. In vitro migration and invasion assays were performed. CYC065 markedly inhibited migration and invasion of lung cancer cells (murine: 344SQ and KC2; human: A549 and H1299). Reverse Phase Protein Arrays (RPPAs) interrogated nearly 300 growth-regulatory proteins in murine (344SQ and KC2) and human (A549 and H1299) lung cancer cells over time (6, 12, 24, and 48 hours) after CYC065 or vehicle treatments. These lung cancer cells have high metastatic as well migration or invasive potentials. When highlighted proteins were clustered after CYC065 treatment, some species were clustered as significantly up-regulated or down-regulated in all cells over studied time points. Not surprisingly, up-regulated proteins included those involved in DNA damage or apoptosis. In addition to known CDK targets like phosphorylated retinoblastoma protein, novel proteins were markedly down-regulated, including mTOR pathway and integrin pathway proteins such as FAK phosphorylation and Src phosphorylation. Affected pathways were identified using Ingenuity Pathway Analysis (IPA). IPA revealed up-regulation of pathways that engaged ATM signaling, G2/M DNA damage checkpoint regulation, or apoptosis signaling. Down-regulated pathways affected mTOR signaling, cyclins, cell cycle regulation, or integrin pathways. Mouse studies will be presented that examine in vivo effects of CYC065 in reducing metastases. Taken together, the next-generation CDK2/9 inhibitor, CYC065, elicits marked antineoplastic effects by antagonizing migration and invasion of lung cancer cells. Comprehensive RPPA and IPA studies found that distinct pathways trigger these effects. Citation Format: Masanori Kawakami, Jason Roszik, Lin Zheng, Jonathan Kurie, Lisa Maria Mustachio, Xi Liu, Ethan Dmitrovsky. The next-generation CDK2/9 inhibitor CYC065 elicits marked antineoplastic effects in lung cancer by engaging antimetastatic pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 128. doi:10.1158/1538-7445.AM2017-128

Abstract 2355: Palbociclib enhances the antitumor activity of taxanes by abrogating cell cycle checkpoints and alleviating hypoxia in squamous cell lung cancer

Abstract Lung cancer remains one of the leading causes of cancer-related mortality. Squamous cell lung cancer (SqCLC) is the second most common subtype of non-small cell lung cancer (NSCLC) and is responsible for ~100,000 deaths in the US and EU. Most SqCLC patients receive chemotherapy as 1st line treatments and have a high un-met medical need for new therapies. Therapeutic approaches that enhance the efficacy of chemotherapy would therefore improve clinical outcomes for this patient population. CDK inhibitors comprise a class of drugs that target the dysregulated cell cycle in malignant cells. Treatment of tumor cells with the CDK4/6 inhibitor palbociclib inhibits tumor growth by decreasing retinoblastoma (RB) protein phosphorylation and inducing cell cycle arrest at the G1/S phase transition. Based on promising clinical trial results, palbociclib in combination with letrozole was granted accelerated approval by the US FDA for the treatment of postmenopausal women with ER-positive, HER2-negative advanced breast cancer. Like hormone receptor positive breast cancer patients, the vast majority of SqCLC patients harbor wild type RB and thus may also benefit from palbociclib treatment. Previously, we reported robust cytotoxicity and antitumor effects of palbociclib plus taxanes, including nanoparticle albumin-bound paclitaxel (Nab-PTX) or docetaxel (DTX), in several preclinical models of SqCLC. In the present study, we extended our efficacy studies of this combination to additional RB+ SqCLC models with diverse molecular genetic backgrounds. In search of mechanisms of action underlying the observed combinatorial effects, we identified several novel mechanisms, including cell cycle checkpoint abrogation as well as reduction of hypoxia-inducible factor 1 alpha (HIF-1α). Decrease in HIF-1α protein led to strong modulation of downstream genes involved in angiogenesis, resulting in reduced blood vessel size in tumor vasculature. Our results suggest that palbociclib enhances the antitumor activity of taxanes by abrogating cell cycle checkpoints and alleviating hypoxia in SqCLC. Citation Format: Joan Cao, Zhou Zhu, Hui Wang, Tim Nichols, Edward Rosfjord, Christine Hopf, Erik Upeslacis, Paul Rejto, Scott Weinrich, Todd Vanarsdale, James Hardwick, Ping Wei. Palbociclib enhances the antitumor activity of taxanes by abrogating cell cycle checkpoints and alleviating hypoxia in squamous cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2355. doi:10.1158/1538-7445.AM2017-2355

Tightly controlled MRTF-A activity regulates epithelial differentiation during formation of mammary acini

BackgroundMyocardin-related transcription factors (MRTF) A and B link actin dynamics and mechanotransduction to gene expression. In mice, MRTF-A is involved in mammary gland differentiation, but its role in human mammary epithelial cells remains unclear.MethodsThree-dimensional cultures of human mammary epithelial MCF10A cells were used to model acinar morphogenesis. Stable MRTF-A knockdown, MRTF-A/B rescue and MRTF-A/B overexpression was established to characterize the functional role during morphogenesis using confocal microscopy and expression analysis. Breast cancer patient databases were analyzed for MRTF-A expression.ResultsWe showed that a precise temporal control of MRTFs is required for normal morphogenesis of MCF10A mammary acini. MRTF transcriptional activity, but not their protein amounts, is transiently induced during 3D acini formation. MRTF-A knockdown dramatically reduces acini size and prevents lumen formation. These effects are rescued by re-expression of MRTF-A, and partially by MRTF-B. Conversely, overexpression of MRTF-A and MRTF-B increases acini size, resulting in irregular spheroids without lumen and defective apico-basal polarity. These phenotypes correlate with deregulated expression of cell cycle inhibitors p21/Waf1, p27/Kip1 and altered phosphorylation of retinoblastoma protein. In MRTF overexpressing spheroids, proliferation and apoptosis are simultaneously increased at late stages, whilst neither occurs in control acini. MRTFs interfere with anoikis of the inner cells and cause an integrin switch from α6 to α5, repression of E-cadherin and induction of mesenchymal markers vimentin, Snai2 and Zeb1. Moreover, MRTF-overexpressing spheroids are insensitive to alteration in matrix stiffness. In two breast cancer cohorts, high expression of MRTF-A and known target genes was associated with decreased patient survival.ConclusionMRTF-A is required for proliferation and formation of mammary acini from luminal epithelial cells. Conversely, elevated MRTF activity results in pre-malignant spheroid formation due to defective proliferation, polarity loss and epithelial-mesenchymal transition.

Induction of p53-Independent Apoptosis and G1 Cell Cycle Arrest by Fucoidan in HCT116 Human Colorectal Carcinoma Cells.

It is well known that fucoidan, a natural sulfated polysaccharide present in various brown algae, mediates anticancer effects through the induction of cell cycle arrest and apoptosis. Nevertheless, the role of tumor suppressor p53 in the mechanism action of fucoidan remains unclear. Here, we investigated the anticancer effect of fucoidan on two p53 isogenic HCT116 (p53+/+ and p53−/−) cell lines. Our results showed that inhibition of cell viability, induction of apoptosis and DNA damage by treatment with fucoidan were similar in two cell lines. Flow cytometric analysis revealed that fucoidan resulted in G1 arrest in the cell cycle progression, which correlated with the inhibition of phosphorylation of retinoblastoma protein (pRB) and concomitant association of pRB with the transcription factor E2Fs. Furthermore, treatment with fucoidan obviously upregulated the expression of cyclin-dependent kinase (CDK) inhibitors, such as p21WAF1/CIP1 and p27KIP1, which was paralleled by an enhanced binding with CDK2 and CDK4. These events also commonly occurred in both cell lines, suggesting that fucoidan triggered G1 arrest and apoptosis in HCT116 cells by a p53-independent mechanism. Thus, given that most tumors exhibit functional p53 inactivation, fucoidan could be a possible therapeutic option for cancer treatment regardless of the p53 status.

The efficacy of the cyclin-dependent kinase 4/6 inhibitor in endometrial cancer.

BackgroundPD-0332991, the selective cyclin-dependent kinase 4/6 inhibitor palbociclib, causes cell cycle arrest by inhibiting phosphorylation of retinoblastoma (Rb) protein. The aim of this study was to evaluate the therapeutic potential of PD-0332991 in endometrial cancer.Methods and findingsFour human endometrial cancer cell lines, ECC, HEC1A, HEC108 and TEN, were treated with PD-0332991 and their function was evaluated. In vivo, the therapeutic efficacy was evaluated in a model of subcutaneous endometrial cancer. An immunohistochemical analysis was performed in 337 endometrial cancer specimens. A proliferation assay revealed that 2 of the 4 cell lines that expressed Rb were sensitive to PD-0332991 with an IC50 of 0.65 μM (HEC1A) and 0.58 μM (HEC108), respectively. Both cell lines had G0/G1 cell cycle arrest after treatment with PD-0332991 according to flow cytometry. In vivo, PD-0332991 had antitumoral efficacy with a reduction in the activity of Ki67 and phosphorylation of Rb. Immunohistochemical analyses revealed that the positive rate of Rb was 67.7%, however, there was no significant relationship between the expression levels of Rb and the tumor grade.ConclusionsPD-0332991 had therapeutic potential against endometrial cancer cell lines expressing Rb protein. Our immunohistochemical analysis revealed that approximately 70% of patients with endometrial cancer might have therapeutic indications for PD-0332991. Of note, the tumor grade had no impact on the indications for treatment.

Therapeutic potential of the antidiabetic drug metformin in small bowel adenocarcinoma.

Small bowel adenocarcinoma (SBAC) accounts for 3% of all gastrointestinal tract tumors and approximately 0.5% of all cancer cases. Recent studies have indicated that the use of metformin, one of the most commonly prescribed antidiabetic drugs, is associated with a better prognosis for certain malignant diseases. However, there have been no reports on the effect of metformin in SBAC. In the present study, we evaluated the effect of metformin on human SBAC cell proliferation invitro and in vivo and identified the microRNAs (miRNAs) associated with its antitumor effects. Metformin inhibited the proliferation of HuTu80 cells in a time- and dose-dependent manner. Importantly, metformin reduced the expression of cyclinD1, cyclinE, cyclin-dependent kinase 4, and phosphorylated retinoblastoma protein, which resulted in cell cycle arrest at the G0/G1 phase. This arrest was accompanied by activation of AMPKα and inhibition of mammalian target of rapamycin and p70s6k. Additionally, metformin reduced the levels of phosphorylated epidermal growth factor receptor and ROR2 as well as markedly altered miRNA expression in HuTu80 cells. Metformin also inhibited tumor growth invivo in a xenograft mouse model. Our data suggest that metformin might have therapeutic potential in SBAC.

Dietary fat/cholesterol‐sensitive PKCbeta‐RB signaling: Potential role in diet‐induced NASH/HCC axis

Hepatocellular carcinoma (HCC) is a frequent form of cancer with a poor prognosis. Recent studies suggest that abnormal lipid metabolism may play an essential role in nonalcoholic steatohepatitis (NASH) development and oncogenesis of HCC. Excess dietary cholesterol intake has been shown to cause development of experimental NASH in different animal models, especially in the setting of a concurrent high‐fat diet. Despite knowledge that Western‐style high‐fat and high‐cholesterol diet is a risk factor in the development of NASH and subsequent progression to HCC, diet‐induced signaling changes implicated in NASH/HCC axis are not well understood. Understanding molecular mechanisms altered by diet is crucial for developing preventive and therapeutic strategies. We previously assessed whether metabolic adaptation to high‐fat/cholesterol diet is associated with changes in hepatic PKCβ expression and also studied the consequence of PKCβ deficiency on diet‐induced hepatic cholesterol homeostasis. We reported that diets enriched with high‐fat and high‐cholesterol (with or without bile acid), shown to produce NASH and HCC, induce hepatic PKCβ expression, and a systemic loss of PKCβ promotes hepatic cholesterol accumulation in response to such diets. These results support the possibility that PKCβ is a physiological transducer of dietary fat/cholesterol and plays a critical role in hepatic adaptation to such diets. Here, we sought to determine how PKCβ and diet functionally interact during tumorigenesis. We examined effects of dietary fat/cholesterol on the PKCβ phosphorylation of retinoblastoma (RB) protein and family members, as well as compared PKCβ expression in human HCC versus normal tissue. We show that diet‐induced hepatic PKCβ expression is accompanied by increased phosphorylation of specific residues of RB protein in a time‐dependent manner. Intriguingly, PKCβ−/− livers exhibited reduced phospho‐RB and RB protein levels, which ultimately resulted in increased transcription of RB gene. It is also accompanied by reduced RBL‐1 with no significant effect on RBL‐2 protein level. To investigate the potential effect of PKCβ deficiency on DNA content of preneoplastic livers, flow cytometric analysis was conducted on hepatocytes obtained from high‐fat/cholesterol diet‐fed WT and PKCβ−/− mice. We also report reduced expression of PKCβ in HCC compared to an adjacent non‐tumorous liver in human patients. These results raise an interesting possibility that diet‐induced PKCβ activation represents an important mediator in the functional wiring of cholesterol metabolism and tumorigenesis through modulating stability of cell cycle‐associated proteins. Identification of PKCβ as a cellular relay in diet‐mediated change in RB functions can define the signaling events that could participate in diet‐induced oncogenesis.Support or Funding InformationThe Ohio State University College of Medicine Research Funds

MicroRNA-125b-5p mediates post-transcriptional regulation of hepatitis B virus replication via the LIN28B/let-7 axis

ABSTRACTMicroRNAs (miRNAs) are able to modulate hepatitis B virus (HBV) replication and play an important role in the pathogenesis of HBV infection. Recently, we have identified that serum miR-125b-5p levels correlated with HBV DNA levels and liver necroinflammation. In the present study, we addressed how miR-125b-5p regulated HBV replication at the different steps, inclduing viral transcription, assembly, and virion production and investigated the underlying mechanisms. We found that miR-125b-5p overexpression increased HBV replication without altering HBV transcription. This is the first demonstration of post-transcriptional miRNA regulation of HBV replication. In contrast, transfection of miR-125b-5p inhibitor resulted in downregulation of HBV replication in hepatoma cells. Further, miR-125b-5p inhibited the phosphorylation of retinoblastoma protein and blocked cell cycle progression at the G1/S phase in hepatoma cell lines. Our results indicate that certain miRNAs are able to arrest the cell cycle at G1 phase and may increase HBV replication. RNA sequencing revealed several liver-specific metabolic pathways regulated by miR-125b-5p, which was also found to suppress LIN28B and induce let-7 family members. Additional data demonstrated that miR-125b-5p targeted the LIN28B/let-7 axis to stimulate HBV replication at a post-transcriptional step.

CHK2 overexpression and mislocalisation within mitotic structures enhances chromosomal instability and hepatocellular carcinoma progression

ObjectiveChromosomal instability (CIN) is the most common form of genomic instability, which promotes hepatocellular carcinoma (HCC) progression by enhancing tumour heterogeneity, drug resistance and immunity escape. CIN per se is...