The proto-oncogene c-myc acts through the cyclin-dependent kinase (Cdk) inhibitor p27(Kip1) to facilitate the activation of Cdk4/6 and early G(1) phase progression

Novel covalent CDK7 inhibitor potently induces apoptosis in acute myeloid leukemia and synergizes with Venetoclax

INTRODUCTION

The emergence of resistance to the highly successful BCL2-directed therapy is a major unmet need in acute myeloid leukemia (AML), an aggressive malignancy with poor survival rates. Towards identifying therapeutic options for AML patients who progress on BCL2-directed therapy, we studied a clinical-stage CDK7 inhibitor XL102, which is being evaluated in solid tumors (NCT04726332).

MATERIALS AND METHODS

To determine the anti-proliferative effects of XL102, we performed experiments including time-resolved fluorescence resonance energy transfer, target occupancy, cell cycle and apoptosis-based assays. We also included genetically characterized primary myeloid blasts from de novo and relapsed/refractory AML patients. For mechanistic studies, CRISPR/Cas9 mediated knockout of CDK7 and c-Myc and immunoblotting were performed. NOD/SCID orthotropic and subcutaneous AML xenografts were used to determine anti-leukemic effects. To assess the synergistic effects of XL102 with Venetoclax, we performed RNA sequencing and gene set enrichment analysis using Venetoclax sensitive and resistant model systems.

RESULTS

XL102, a highly specific, orally bioavailable covalent inhibitor of CDK7. Inhibitory effect on CDK7 by XL102 in primary myeloid blasts (n = 54) was in nanomolar range (mean = 300 nM; range = 4.0-952 nM). XL102 treated AML cells showed a reduction in phosphorylation levels of Serine 2/5/7 at carboxy-terminal domain of RNA polymerase II. T-loop phosphorylation of CDK1(Thr161) and CDK2(Thr160) was inhibited by XL102 in dose-dependent manner leading to cell-cycle arrest. c-Myc downregulation and enhanced levels of p53 and p21 in XL102 treated cells were observed. Increased levels of p21 and activation of p53 by XL102 were mimicked by genetic ablation of CDK7, which supports that the observed effects of XL102 are due to CDK7 inhibition. XL102 treated AML xenografts showed remarkable reduction in hCD45 + marrow cells (mean = 0.60%; range = 0.04%-3.53%) compared to vehicle control (mean = 38.2%; range = 10.1%-78%), with corresponding increase in p53, p21 and decrease in c-Myc levels. The data suggests XL102 induces apoptosis in AML cells via CDK7/c-Myc/p53 axis. RNA-sequencing from paired Venetoclax-sensitive and Venetoclax-resistant cells treated with XL102 showed downregulation of genes involved in proliferation and apoptosis.

CONCLUSION

Taken together, XL102 with Venetoclax led to synergistic effects in overcoming resistance and provided a strong rationale for clinical evaluation of XL102 as a single agent and in combination with Venetoclax.

Therapeutic potential of CDK4/6 inhibitors in renal cell carcinoma

The treatment of advanced and metastatic kidney cancer has entered a golden era with the addition of more therapeutic options, improved survival and new targeted therapies. Tyrosine kinase inhibitors, mammalian target of rapamycin (mTOR) inhibitors and immune checkpoint blockade have all been shown to be promising strategies in the treatment of renal cell carcinoma (RCC). However, little is known about the best therapeutic approach for individual patients with RCC and how to combat therapeutic resistance. Cancers, including RCC, rely on sustained replicative potential. The cyclin-dependent kinases CDK4 and CDK6 are involved in cell-cycle regulation with additional roles in metabolism, immunogenicity and antitumour immune response. Inhibitors of CDK4 and CDK6 are now commonly used as approved and investigative treatments in breast cancer, as well as several other tumours. Furthermore, CDK4/6 inhibitors have been shown to work synergistically with other kinase inhibitors, including mTOR inhibitors, as well as with immune checkpoint inhibitors in preclinical cancer models. The effect of CDK4/6 inhibitors in kidney cancer is relatively understudied compared with other cancers, but the preclinical studies available are promising. Collectively, growing evidence suggests that targeting CDK4 and CDK6 in kidney cancer, alone and in combination with current therapeutics including mTOR and immune checkpoint inhibitors, might have therapeutic benefit and should be further explored.

MYC promotes tyrosine kinase inhibitor resistance in ROS1 fusion-positive lung cancer

Targeted therapy of ROS1 fusion-driven non-small cell lung cancer (NSCLC) has achieved notable clinical success. Despite this, resistance to therapy inevitably poses a significant challenge. MYC amplification was present in ~19% of lorlatinib-resistant ROS1-driven NSCLC. We hypothesized that MYC overexpression drives ROS1-TKI resistance. Using complementary approaches in multiple models, including a MYC-amplified patient-derived cell line and xenograft (LUAD-0006), we established that MYC overexpression induces broad ROS1 TKI resistance. Pharmacological inhibition of ROS1 combined with MYC knockdown were essential to completely suppress LUAD-0006 cell proliferation compared to either treatment alone. We interrogated cellular signaling in ROS1-TKI resistant LUAD-0006 and discovered significant differential regulation of targets associated with cell cycle, apoptosis, and mitochondrial function. Combinatorial treatment of mitochondrial inhibitors with crizotinib revealed inhibitory synergism, suggesting increased reliance on glutamine metabolism and fatty-acid synthesis in chronic ROS1-TKI treated LUAD-0006 cells. In vitro experiments further revealed that CDK4/6 and BET bromodomain inhibitors effectively mitigate ROS1 TKI resistance in MYC-overexpressing cells. Notably, in vivo studies demonstrate that tumor control may be regained by combining ROS1 TKI and CDK4/6 inhibition. Our results contribute to the broader understanding of ROS1-TKI resistance in NSCLC. Implications: This study functionally characterizes MYC overexpression as a novel form of therapeutic resistance to ROS1 tyrosine kinase inhibitors in non-small-cell lung cancer and proposes rational combination treatment strategies.

Role of Hypoxia in the Control of the Cell Cycle

The cell cycle is an important cellular process whereby the cell attempts to replicate its genome in an error-free manner. As such, mechanisms must exist for the cell cycle to respond to stress signals such as those elicited by hypoxia or reduced oxygen availability. This review focuses on the role of transcriptional and post-transcriptional mechanisms initiated in hypoxia that interface with cell cycle control. In addition, we discuss how the cell cycle can alter the hypoxia response. Overall, the cellular response to hypoxia and the cell cycle are linked through a variety of mechanisms, allowing cells to respond to hypoxia in a manner that ensures survival and minimal errors throughout cell division.

Arg-Gly-Asp-modified elastin-like polypeptide regulates cell proliferation and cell cycle proteins via the phosphorylation of Erk and Akt in pancreatic β-cell

Objective

Enhancement of β-cell proliferation plays an important role in maintaining β-cell mass and function, and in improving pancreatic β-cell survival before transplantation. Extracellular matrix (ECM) components increase the adhesion and proliferation of β-cells, and the RGD-modified elastin-like polypeptide (RGD-ELP, REP) has been described as a bioactive matrix. In this study, we investigated whether REP could enhance β-cell adhesion and proliferation and elucidated the signaling pathways involved.

Methods

We investigated the effect of REP on cell adhesion, proliferation and insulin secretion via assays using Rin-m and rat islets. Crystal violet, CCK-8, and BrdU assay, FACS, western blot, real time q-PCR analyses and insulin ELISA were examined. To explain the associated mechanisms, phosphorylation of Akt and extracellular signal-regulated kinase (Erk) were measured.

Results

REP more increased the adhesion, proliferation and survival of Rin-m cells compared to elastin-like poly peptide (ELP) without RGD-motif. The enhancement of β-cell proliferation by REP was associated with increased cyclin D1, cyclin D2 and cdk6, and decreased p27 levels. When β-cells were cultured on REP, Erk and the phosphatidylinositol 3-kinase (PI3-kinase) downstream effector, Akt was stimulated. Treatment with the Erk pathway inhibitor and PI3-kinase inhibitor decreased REP-induced β-cell adhesion and proliferation, and regulated REP-induced cell cycle proteins. Additionally, REP increased the mRNA and protein levels of insulin and its transcription factor, PDX-1, and insulin secretion.

Conclusions

Our results demonstrate that the up-regulation of the PI3K/Akt and Erk signaling pathways and the regulation of cell cycle proteins by REP could serve as effective strategies for improving pancreatic β-cell adhesion and proliferation.

c-myc regulates the sensitivity of breast cancer cells to palbociclib via c-myc/miR-29b-3p/CDK6 axis

Palbociclib, a CDK4/6 inhibitor, has been granted accelerated approval by US FDA for hormone receptor-positive HER2-negative metastatic breast cancer. To determine potential biomarkers of palbociclib sensitivity to assist in patient selection and clinical development, we investigated the effects of palbociclib in a panel of molecularly characterized breast cancer cell lines. We quantified palbociclib sensitivity and c-myc expression in 11 breast cancer cell lines, 124 breast cancer samples, and The Cancer Genome Atlas database. We found non-TNBC subtypes were more sensitive to palbociclib than TNBC. Activation of c-myc led to differential palbociclib sensitivities, and further inhibition of c-myc enhanced palbociclib sensitivity. Moreover, we identified for the first time a c-myc/miR-29b-3p/CDK6 axis in breast cancer that could be responsible for c-myc-induced palbociclib insensitivity, in which c-myc activation resulted in downregulation of miR-29b-3p, further activated CDK6 and inhibited cell-cycle arrest at G₁ phase. Moreover, downregulated (inactived) c-myc-induced oncogenic addiction could increase palbociclib efficacy, using both Xenograft model and patient-derived tumor xenograft (PDTX) model. Our finding extends the concept of combined blockade of the CDK4/6 and c-myc signaling pathways to increase palbociclib sensitivity, making c-myc a promising biomarker for palbociclib sensitivity in breast cancer.

(-)-Kusunokinin inhibits breast cancer in N-nitrosomethylurea-induced mammary tumor rats

Natural and synthetic (-)-kusunokinin inhibited breast cancer, colon cancer and cholangiocarcinoma cells at the G2/M phase and induced apoptosis. However, there is no report on the action and adverse effects of (-)-kusunokinin in animal models. In this study, we investigated the cytotoxic effect of (-)-kusunokinin from Piper nigrum on cancer cells. NMU-induced rat mammary tumors, an ER positive breast cancer model, were treated with (-)-kusunokinin. Proteins of interest related to cell cycle, angiogenesis, migration and signaling proteins were detected in tumor tissues. Results showed that (-)-kusunokinin exhibited strong cytotoxicity against breast, colon and lung cancer cells and caused low toxicity against normal fibroblast cells. For in vivo study, 7.0 mg/kg and 14.0 mg/kg of (-)-kusunokinin reduced tumor growth without side effects on body weight, internal organs and bone marrow. Combination of (-)-kusunokinin with a low effective dose of doxorubicin significantly inhibited tumor growth and provoked cell death in cancer tissues. Mechanistically, 14.0 mg/kg of (-)-kusunokinin decreased cell proliferation (c-Src, PI3K, Akt, p-Erk1/2 and c-Myc), cell cycle (E2f-1, cyclin B1 and CDK1), and metastasis (E-cadherin, MMP-2 and MMP-9) proteins in tumor tissues, which supports its anticancer effect. We further confirmed the antimigration effect of (-)-kusunokinin; the results show that this compound inhibited breast cancer cell (MCF-7) migration in a dose-dependent manner. In conclusion, the results suggest that 14 mg/kg of (-)-kusunokinin inhibited tumors through the reduction of signaling proteins and their downstream molecules. Therefore, (-)-kusunokinin becomes an intriguing candidate for cancer treatment as it provides a strong potency in cancer inhibition.

CDK7 Inhibition is Effective in all the Subtypes of Breast Cancer: Determinants of Response and Synergy with EGFR Inhibition

CDK7, a transcriptional cyclin-dependent kinase, is emerging as a novel cancer target. Triple-negative breast cancers (TNBC) but not estrogen receptor-positive (ER+) breast cancers have been reported to be uniquely sensitive to the CDK7 inhibitor THZ1 due to the inhibition of a cluster of TNBC-specific genes. However, bioinformatic analysis indicates that CDK7 RNA expression is associated with negative prognosis in all the major subtypes of breast cancer. To further elucidate the effects of CDK7 inhibition in breast cancer, we profiled a panel of cell lines representing different breast cancer subtypes. THZ1 inhibited cell growth in all subtypes (TNBC, HER2+, ER+, and HER2+/ER+) with no apparent subtype selectivity. THZ1 inhibited CDK7 activity and induced G1 arrest and apoptosis in all the tested cell lines, but THZ1 sensitivity did not correlate with CDK7 inhibition or CDK7 expression levels. THZ1 sensitivity across the cell line panel did not correlate with TNBC-specific gene expression but it was found to correlate with the differential inhibition of three genes: CDKN1B, MYC and transcriptional coregulator CITED2. Response to THZ1 also correlated with basal CITED2 protein expression, a potential marker of CDK7 inhibitor sensitivity. Furthermore, all of the THZ1-inhibited genes examined were inducible by EGF but THZ1 prevented this induction. THZ1 had synergistic or additive effects when combined with the EGFR inhibitor erlotinib, with no outward selectivity for a particular subtype of breast cancer. These results suggest a potential broad utility for CDK7 inhibitors in breast cancer therapy and the potential for combining CDK7 and EGFR inhibitors.

Ganoderiol F purified from Ganoderma leucocontextum retards cell cycle progression by inhibiting CDK4/CDK6

This study was designed to purify molecules possess anti-cancer cell activity from the fruit body of Ganoderma leucocontextum. Bio-activity-guided purification and chromatographic separation of Ganoderma leucocontextum extract led to the enrichment of bioactive fractions and isolation of a single compound. The purified compound was identified as Ganoderiol F, which induced cancer cell death. In the in vivo experiments, we founded ethanol extract and ethyl acetate fraction inhibited tumor growth in the mice injected with 4T1 cells. We found that Ganoderiol F-mediated suppression of breast cancer cell viability occurred through cell cycle arrest. Ganoderiol F down-regulated expression of cyclin D, CDK4, CDK6, cyclin E and CDK2 and inhibited cell cycle progression arresting the cells in G1 phase. In addition, Ganoderiol F up-regulated pro-apoptotic Foxo3, down-regulated anti-apoptotic c-Myc, Bcl-2 and Bcl-w leading to apoptosis in human breast cancer cells MDA-MB-231. These results showed that c-Myc, cyclin D-CDK4/CDK6 and cyclin E-CDK2 are the central components of Ganoderiol F regulation of cell cycle progression. Hence Ganoderiol F may serve as a potential CDK4/CDK6 inhibitor for breast cancer therapy. Abbreviations: GLE: Ganoderma leucocontextum ethanol extract; GLEA: Ganoderma leucocontextum ethyl acetate fraction; GLPE: Ganoderma leucocontextum petroleum ether fraction; RP-HPLC: reversed-phase high-performance liquid chromatograph; DMEM: Dulbecco's modified Eagle's medium; FBS: fetal bovine serum; PAGE: polyacrylamide gel electrophoresis.

Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy

Neutrophils form an essential part of innate immunity against infection. Cancer chemotherapy-induced neutropenia (CCIN) is a condition in which the number of neutrophils in a patient's bloodstream is decreased, leading to increased susceptibility to infection. Granulocyte colony-stimulating factor (GCSF) has been the only approved treatment for CCIN over two decades. To date, CCIN-related infection and mortality remain a significant concern, as neutrophils generated in response to administered GCSF are functionally immature and cannot effectively fight infection. This review summarizes the molecular regulatory mechanisms of neutrophil granulocytic differentiation and innate immunity development, dissects the biology of GCSF in myeloid expansion, highlights the shortcomings of GCSF in CCIN treatment, updates the recent advance of a selective retinoid agonist that promotes neutrophil granulocytic differentiation, and evaluates the benefits of developing GCSF biosimilars to increase access to GCSF biologics versus seeking a new mode to fundamentally advance GCSF therapy for treatment of CCIN.

G1/S cell cycle regulators mediate effects of circadian dysregulation on tumor growth and provide targets for timed anticancer treatment

Circadian disruption has multiple pathological consequences, but the underlying mechanisms are largely unknown. To address such mechanisms, we subjected transformed cultured cells to chronic circadian desynchrony (CCD), mimicking a chronic jet-lag scheme, and assayed a range of cellular functions. The results indicated a specific circadian clock–dependent increase in cell proliferation. Transcriptome analysis revealed up-regulation of G1/S phase transition genes (myelocytomatosis oncogene cellular homolog [Myc], cyclin D1/3, chromatin licensing and DNA replication factor 1 [Cdt1]), concomitant with increased phosphorylation of the retinoblastoma (RB) protein by cyclin-dependent kinase (CDK) 4/6 and increased G1-S progression. Phospho-RB (Ser807/811) was found to oscillate in a circadian fashion and exhibit phase-shifted rhythms in circadian desynchronized cells. Consistent with circadian regulation, a CDK4/6 inhibitor approved for cancer treatment reduced growth of cultured cells and mouse tumors in a time-of-day–specific manner. Our study identifies a mechanism that underlies effects of circadian disruption on tumor growth and underscores the use of treatment timed to endogenous circadian rhythms.

A study of “jet-lagged” cells reveals a specific molecular mechanism regulating cell proliferation that it impacted by circadian disruption, underscoring the importance of administering anti-cancer treatment at a specific time of day.

Circadian misalignment caused by altered sleep–wake cycles, shift work, or frequent jet lag increases susceptibility to several disorders, including cancer. However, the mechanisms by which circadian disruption contributes to disease are not well understood, and so we addressed this issue by investigating the molecular, cellular, and biochemical consequences of chronic circadian desynchronization. Our studies using cancer cell or tumor tissue models show that chronic circadian desynchronization induces multiple oncogenic pathways to promote cell proliferation. In particular, chronic circadian desynchronization promotes phosphorylation of the retinoblastoma (RB) protein, thereby favoring G1/S phase cell cycle progression. Consistent with these findings, the antiproliferative activity of a selective inhibitor of the enzyme that phosphorylates RB has time-of-day–specific effects on cancer cells and mouse tumors, but this time dependence is abrogated by chronic jet-lag conditions. These data suggest a circadian regulation of G1/S cell cycle progression and provide an important molecular rationale for time-of-day–specific treatment of cancer patients, also known as chronotherapy.

MYC Oncogene Contributions to Release of Cell Cycle Brakes

Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.

Network-Based Combinatorial CRISPR-Cas9 Screens Identify Synergistic Modules in Human Cells

Tumorigenesis is a complex process that is driven by a combination of networks of genes and environmental factors; however, efficient approaches to identifying functional networks that are perturbed by the process of tumorigenesis are lacking. In this study, we provide a comprehensive network-based strategy for the systematic discovery of functional synergistic modules that are causal determinants of inflammation-induced tumorigenesis. Our approach prioritizes candidate genes selected by integrating clinical-based and network-based genome-wide gene prediction methods and identifies functional synergistic modules based on combinatorial CRISPR-Cas9 screening. On the basis of candidate genes inferred de novo from experimental and computational methods to be involved in inflammation and cancer, we used an existing TGFβ1-induced cellular transformation model in colonic epithelial cells and a new combinatorial CRISPR-Cas9 screening strategy to construct an inflammation-induced differential genetic interaction network. The inflammation-induced differential genetic interaction network that we generated yielded functional insights into the genes and functional module combinations, and showed varied responses to the inflammation agents as well as active traditional Chinese medicine compounds. We identified opposing differential genetic interactions of inflammation-induced tumorigenesis: synergistic promotion and suppression. The synergistic promotion state was primarily caused by deletions in the immune and metabolism modules; the synergistic suppression state was primarily induced by deletions in the proliferation and immune modules or in the proliferation and metabolism modules. These results provide insight into possible early combinational targets and biomarkers for inflammation-induced tumorigenesis and highlight the synergistic effects that occur among immune, proliferation, and metabolism modules. In conclusion, this approach deepens the understanding of the underlying mechanisms that cause inflammation to potentially increase the cancer risk of colonic epithelial cells and accelerate the translation into novel functional modules or synergistic module combinations that modulate complex disease phenotypes.

RNAm expression profile of cancer marker genes in HepG2 cells treated with different concentrations of a new indolin-3-one from Pseudomonas aeruginosa

The present study tested the effects of a newly identified indolin-3-one compound (compound 1), produced by Pseudomonas aeruginosa, on HepG2 cells. The MTT assays demonstrated decreased metabolic activities in HepG2 cells treated with compound 1, with dose- and time-dependent intensifying effect, starting at a concentration of 40 µM. The IC₅₀ after 24, 48, 72, and 96 h treatments were 41.35, 52.7, 92.79 and 66.65 μM of compound 1, respectively. Below 80 µM, no significative damage on erythrocytes membranes was observed by the hemolytic assays. The RT-qPCR revealed that the compound modulated key genes involved in carcinogenesis process, indicating possible indolin-3-one mechanisms of action. The data showed that gene expression alterations promoted by compound 1, in concentrations up to 60 μM after 48 h, led to a decrease in cellular progression and there was no direct cellular damage. In addition, non-cytotoxic concentrations of compound 1 halved the concentration of the chemotherapeutic doxorubicin, maintaining similar therapeutic effect against HepG2 cells. The novelty of the molecule and the biological activities observed in the present study emphasize the potential of the compound 1 in cancer therapy research.

Developmental therapeutics for inflammatory breast cancer: Biology and translational directions

Inflammatory breast cancer (IBC) is a rare and aggressive form of breast cancer, which accounts for approximately 3% of cases of breast malignancies. Diagnosis relies largely on its clinical presentation, and despite a characteristic phenotype, underlying molecular mechanisms are poorly understood. Unique clinical presentation indicates that IBC is a distinct clinical and biological entity when compared to non-IBC. Biological understanding of non-IBC has been extrapolated into IBC and targeted therapies for HER2 positive (HER2+) and hormonal receptor positive non-IBC led to improved patient outcomes in the recent years. This manuscript reviews recent discoveries related to the underlying biology of IBC, clinical progress to date and suggests rational approaches for investigational therapies.

Inhibition of CDK4/6 by Palbociclib Significantly Extends Survival in Medulloblastoma Patient-Derived Xenograft Mouse Models

Purpose: Bioinformatics analysis followed by in vivo studies in patient-derived xenograft (PDX) models were used to identify and validate CDK 4/6 inhibition as an effective therapeutic strategy for medulloblastoma, particularly group 3 MYC-amplified tumors that have the worst clinical prognosis.Experimental Design: A protein interaction network derived from a Sleeping Beauty mutagenesis model of medulloblastoma was used to identify potential novel therapeutic targets. The top hit from this analysis was validated in vivo using PDX models of medulloblastoma implanted subcutaneously in the flank and orthotopically in the cerebellum of mice.Results: Informatics analysis identified the CDK4/6/CYCLIN D/RB pathway as a novel "druggable" pathway for multiple subgroups of medulloblastoma. Palbociclib, a highly specific inhibitor of CDK4/6, was found to inhibit RB phosphorylation and cause G₁ arrest in PDX models of medulloblastoma. The drug caused rapid regression of Sonic hedgehog (SHH) and MYC-amplified group 3 medulloblastoma subcutaneous tumors and provided a highly significant survival advantage to mice bearing MYC-amplified intracranial tumors.Conclusions: Inhibition of CDK4/6 is potentially a highly effective strategy for the treatment of SHH and MYC-amplified group 3 medulloblastoma. Clin Cancer Res; 23(19); 5802-13. ©2017 AACR.

Interplay between cancer cell cycle and metabolism: Challenges, targets and therapeutic opportunities

A growing interest has emerged in the field of studying the cross-talk between cancer cell cycle and metabolism. In this review, we aimed to present how metabolism and cell cycle are correlated and how cancer cells get energy to drive cell cycle. Cell proliferation and cell death largely depend on the metabolic activity of the cell. Cell cycle proteins, e.g. cyclin D, cyclin dependent kinase (CDK), some pro-apoptotic and anti-apoptotic proteins, and P53 have been shown to be regulated by metabolic crosstalk. Dysregulation of this cross-talk between metabolism and cell cycle leads to degenerative disorder(s) and cancer. It is not fully understood the actual reason of aberration between metabolism and cell cycle, but it is a hallmark of cancer research. Herein, we discussed the role of some regulatory molecules relative of cell cycle and metabolism and highlight how they control the function of each other. We also pointed out, current therapeutic opportunities and some additional crucial therapeutic targets on these fields that could be a breakthrough in cancer research.

TW-01, a piperazinedione-derived compound, inhibits Ras-mediated cell proliferation and angioplasty-induced vascular restenosis

PURPOSE

Vascular smooth muscle cell (VSMC) proliferation plays a critical role in the pathogenesis of atherosclerosis and restenosis. This study investigated piperazinedione derived compound TW-01-mediated inhibitory effects on VSMC proliferation and intimal hyperplasia.

METHODS

Cell proliferation was determined using [(3)H]-thymidine incorporation and MTT assay; cell cycle distribution was measured using flow cytometry; proteins and mRNA expression were determined using western blotting and RT-PCR analyses; DNA binding activity of nuclear factor-κB (NF-κB), as measured using enzyme-linked immunosorbent assays (ELISA); in vivo effects of TW-01 were determined using balloon angioplasty in the rat.

RESULTS

TW-01 significantly inhibited cell proliferation. At the concentrations used, no cytotoxic effects were observed. Three predominant signaling pathways were inhibited by TW-01: (a) extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase (MAPK) activation and its downstream effectors of c-fos, c-jun, and c-myc; (b) DNA binding activity of nuclear factor-κB (NF-κB); and, (c) Akt/protein kinase B (PKB) and cell cycle progression. Furthermore, TW-01 also inhibited Ras activation, a shared upstream event of each of these signaling cascades. In vascular injury studies, oral administration of TW-01 significantly suppressed intimal hyperplasia induced by balloon angioplasty.

CONCLUSION

The present study suggests that TW-01 might be a potential candidate for atherosclerosis treatment.

Structurally diverse c-Myc inhibitors share a common mechanism of action involving ATP depletion

The c-Myc (Myc) oncoprotein is deregulated in a large proportion of diverse human cancers. Considerable effort has therefore been directed at identifying pharmacologic inhibitors as potential anti-neoplastic agents. Three such groups of small molecule inhibitors have been described. The first is comprised of so-called “direct” inhibitors, which perturb Myc's ability to form productive DNA-binding heterodimers in association with its partner, Max. The second group is comprised of indirect inhibitors, which largely function by targeting the BET-domain protein BRD4 to prevent the proper formation of transcriptional complexes that assemble in response to Myc-Max DNA binding. Thirdly, synthetic lethal inhibitors cause the selective apoptosis of Myc over-expressing either by promoting mitotic catastrophe or altering Myc protein stability. We report here a common mechanism by which all Myc inhibitors, irrespective of class, lead to eventual cellular demise. This involves the depletion of ATP stores due to mitochondrial dysfunction and the eventual down-regulation of Myc protein. The accompanying metabolic de-regulation causes neutral lipid accumulation, cell cycle arrest, and an attempt to rectify the ATP deficit by up-regulating AMP-activated protein kinase (AMPK). These responses are ultimately futile due to the lack of functional Myc to support the requisite anabolic response. Finally, the effects of Myc depletion on ATP levels, cell cycle arrest, differentiation and AMPK activation can be mimicked by pharmacologic inhibition of the mitochondrial electron transport chain without affecting Myc levels. Thus, all Myc inhibitors promote a global energy collapse that appears to underlie many of their phenotypic consequences.

CDK-dependent phosphorylation of PHD1 on serine 130 alters its substrate preference in cells

PHD1 (also known as EGLN2) belongs to a family of prolyl hydroxylases (PHDs) that are involved in the control of the cellular response to hypoxia. PHD1 is also able to regulate mitotic progression through the regulation of the crucial centrosomal protein Cep192, establishing a link between the oxygen-sensing and the cell cycle machinery. Here, we demonstrate that PHD1 is phosphorylated by CDK2, CDK4 and CDK6 at S130. This phosphorylation fluctuates with the cell cycle and can be induced through oncogenic activation. Functionally, PHD1 phosphorylation leads to increased induction of hypoxia-inducible factor (HIF) protein levels and activity during hypoxia. PHD1 phosphorylation does not alter its intrinsic enzymatic activity, but instead decreases the interaction between PHD1 and HIF1α. Interestingly, although phosphorylation of PHD1 at S130 lowers its activity towards HIF1α, this modification increases the activity of PHD1 towards Cep192. These results establish a mechanism by which cell cycle mediators, such as CDKs, temporally control the activity of PHD1, directly altering the regulation of HIF1α and Cep192.

Summary: CDK-mediated phosphorylation of PHD1 at serine 130 controls target specificity and confers cell cycle regulation of PHD1.

Cyproheptadine exhibits antitumor activity in urothelial carcinoma cells by targeting GSK3β to suppress mTOR and β-catenin signaling pathways

Cyproheptadine, a serotonin antagonist, has recently been reported to function as a novel therapeutic agent by inhibiting PI3K/AKT signaling in several human cancers. However, the therapeutic effect of cyproheptadine in urothelial carcinoma (UC) has never been explored. In this study, we determined the effect of cyproheptadine on the growth of five human UC cell lines and an in vivo xenograft model. The results showed that cyproheptadine exerted an inhibitory effect on the proliferation of UC cells both in vitro and in vivo. Cyproheptadine also induced cell cycle arrest in the G1 phase, subsequently followed by apoptosis and necrosis. The underlying mechanisms of cell cycle arrest were associated with the reduction of c-Myc, induction of p21 and p27, and the stabilization of Rb expression. In addition, the suppression of the GSK3β/TSC2/mTOR pathway and deregulation of the GSK3β/β-catenin signaling were observed in cyproheptadine-treated UC cells. Furthermore, cyproheptadine-induced apoptosis was associated with ANGPTL4 expression followed by activation of caspase3 and PARP in UC cells. Our experimental results provide evidence that cyproheptadine is a suitable therapeutic agent for the treatment of UC.

A New Double Stranded RNA Suppresses Bladder Cancer Development by Upregulating p21 (Waf1/CIP1) Expression

We have previously demonstrated that miR-1180-5p has potent ability to upregulate p21 expression by targeting promoter and inhibit bladder cancer. This prompted us to conjecture that a candidate dsRNA (dsP21-397) with perfect complementarity to the miR-1180-5p target site of p21 promoter may also trigger p21 expression. Transfection of dsP21-397 into T24 and EJ cells significantly activated p21 expression at 72 h and the activation presented in a time-course and dose-dependent manner. Moreover, the p21-activated activities of dsP21-397 and miR-1180-5p are not significantly different. Overexpression of p21 downregulated Cyclin D1, CDK4/6, and Cyclin A2 expression, and thereby induced cell cycle arrest and inhibited proliferation. Moreover, dsP21-397 suppressed bladder cancer largely depended on manipulating p21. In conclusion, our study identifies a pair of miRNA-dsRNA mediating endogenous p21 overexpression.

MYC and the control of DNA replication

The MYC oncogene is a multifunctional protein that is aberrantly expressed in a significant fraction of tumors from diverse tissue origins. Because of its multifunctional nature, it has been difficult to delineate the exact contributions of MYC's diverse roles to tumorigenesis. Here, we review the normal role of MYC in regulating DNA replication as well as its ability to generate DNA replication stress when overexpressed. Finally, we discuss the possible mechanisms by which replication stress induced by aberrant MYC expression could contribute to genomic instability and cancer.

Myc and cell cycle control

Soon after the discovery of the Myc gene (c-Myc), it became clear that Myc expression levels tightly correlate to cell proliferation. The entry in cell cycle of quiescent cells upon Myc enforced expression has been described in many models. Also, the downregulation or inactivation of Myc results in the impairment of cell cycle progression. Given the frequent deregulation of Myc oncogene in human cancer it is important to dissect out the mechanisms underlying the role of Myc on cell cycle control. Several parallel mechanisms account for Myc-mediated stimulation of the cell cycle. First, most of the critical positive cell cycle regulators are encoded by genes induced by Myc. These Myc target genes include Cdks, cyclins and E2F transcription factors. Apart from its direct effects on the transcription, Myc is able to hyperactivate cyclin/Cdk complexes through the induction of Cdk activating kinase (CAK) and Cdc25 phosphatases. Moreover, Myc antagonizes the activity of cell cycle inhibitors as p21 and p27 through different mechanisms. Thus, Myc is able to block p21 transcription or to induce Skp2, a protein involved in p27 degradation. Finally, Myc induces DNA replication by binding to replication origins and by upregulating genes encoding proteins required for replication initiation. Myc also regulates genes involved in the mitotic control. A promising approach to treat tumors with deregulated Myc is the synthetic lethality based on the inhibition of Cdks. Thus, the knowledge of the Myc-dependent cell cycle regulatory mechanisms will help to discover new therapeutic approaches directed against malignancies with deregulated Myc. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

A novel role of proteasomal β1 subunit in tumorigenesis

p27^Kip1 is a key cell-cycle regulator whose level is primarily regulated by the ubiquitin–proteasome degradation pathway. Its β1 subunit is one of seven β subunits that form the β-ring of the 20S proteasome, which is responsible for degradation of ubiquitinated proteins. We report here that the β1 subunit is up-regulated in oesophageal cancer tissues and some ovarian cancer cell lines. It promotes cell growth and migration, as well as colony formation. β1 binds and degrades p27^Kip1directly. Interestingly, the lack of phosphorylation at Ser¹⁵⁸ of the β1 subunit promotes degradation of p27^Kip1. We therefore propose that the β1 subunit plays a novel role in tumorigenesis by degrading p27^Kip1.

Lentiviral vector-mediated siRNA knockdown of c-MYC: cell growth inhibition and cell cycle arrest at G2/M phase in Jijoye cells

Inhibition of c-MYC has been considered as a potential therapy for lymphoma treatment. We explored a lentiviral vector-mediated small interfering RNA (siRNA) expression vector to stably reduce c-MYC expression in B cell line Jijoye cells and investigated the effects of c-MYC downregulation on cell growth, cell cycle, and apoptosis in vitro. The expression of c-MYC mRNA and protein levels were inhibited significantly by c-MYC siRNA. The c-MYC downregulation resulted in the inhibition of cell proliferation and cell cycle arrest at G2/M phase, which was associated with decreased expression of cyclin B and cyclin-dependent kinase 1 (CDK1) and increased expression of CDK inhibitor p21 proteins. In addition, downregulation of c-MYC induced cell apoptosis characterized by DNA fragmentation and caspase-3 activation. Taken together, these results suggest that lentiviral vector-mediated siRNA for c-MYC may be a promising approach for targeting c-MYC in the treatment of Burkitt lymphoma.

Kruppel-like factor 1 (KLF1), KLF2, and Myc control a regulatory network essential for embryonic erythropoiesis

The Krüppel-like factor 1 (KLF1) and KLF2 positively regulate embryonic β-globin expression and have additional overlapping roles in embryonic (primitive) erythropoiesis. KLF1(-/-) KLF2(-/-) double knockout mice are anemic at embryonic day 10.5 (E10.5) and die by E11.5, in contrast to single knockouts. To investigate the combined roles of KLF1 and KLF2 in primitive erythropoiesis, expression profiling of E9.5 erythroid cells was performed. A limited number of genes had a significantly decreasing trend of expression in wild-type, KLF1(-/-), and KLF1(-/-) KLF2(-/-) mice. Among these, the gene for Myc (c-Myc) emerged as a central node in the most significant gene network. The expression of the Myc gene is synergistically regulated by KLF1 and KLF2, and both factors bind the Myc promoters. To characterize the role of Myc in primitive erythropoiesis, ablation was performed specifically in mouse embryonic proerythroblast cells. After E9.5, these embryos exhibit an arrest in the normal expansion of circulating red cells and develop anemia, analogous to KLF1(-/-) KLF2(-/-) embryos. In the absence of Myc, circulating erythroid cells do not show the normal increase in α- and β-like globin gene expression but, interestingly, have accelerated erythroid cell maturation between E9.5 and E11.5. This study reveals a novel regulatory network by which KLF1 and KLF2 regulate Myc to control the primitive erythropoietic program.

Tricyclodecan-9-yl-xanthogenate (D609) mechanism of actions: a mini-review of literature

Tricyclodecan-9-yl-xanthogenate (D609) is known for its antiviral and antitumor properties. D609 actions are widely attributed to inhibiting phosphatidylcholine (PC)-specific phospholipase C (PC-PLC). D609 also inhibits sphingomyelin synthase (SMS). PC-PLC and/or SMS inhibition will affect lipid second messengers 1,2-diacylglycerol (DAG) and/or ceramide. Evidence indicates either PC-PLC and/or SMS inhibition affected the cell cycle and arrested proliferation, and stimulated differentiation in various in vitro and in vivo studies. Xanthogenate compounds are also potent antioxidants and D609 reduced Aß-induced toxicity, attributed to its antioxidant properties. Zn²⁺ is necessary for PC-PLC enzymatic activity; inhibition by D609 might be attributed to its Zn²⁺ chelation. D609 has also been proposed to inhibit acidic sphingomyelinase or down-regulate hypoxia inducible factor-1α; however these are down-stream events related to PC-PLC inhibition. Characterization of the mammalian PC-PLC is limited to inhibition of enzymatic activity (frequently measured using Amplex red assay with bacterial PC-PLC as a standard). The mammalian PC-PLC has not been cloned; sequenced and structural information is unavailable. D609 showed promise in cancer studies, reduced atherosclerotic plaques (inhibition of PC-PLC) and cerebral infarction after stroke (PC-PLC or SMS). D609 actions as an antagonist to pro-inflammatory cytokines have been attributed to PC-PLC. The purpose of this review is to comprehensively evaluate the literature and summarize the findings and relevance to cell cycle and CNS pathologies.

Antitumorigenic effect of brain proline rich polypeptide-1 in human chondrosarcoma

Proline rich polypeptide (PRP-1) produced by neurosecretory cells of the hypothalamus is one of the fragments of neurophysin-vasopressin-associated glycoprotein. The primary structure of the neuropeptide PRP-1 isolated from neurosecretory granules of bovine neurohypophysis. We investigated PRP-1 action on chondrosarcoma, the second most common malignancy in bone, which primarily affects the cartilage cells. This deadly disease does not have any effective treatment. Earlier we demonstrated MYC oncogene inactivating effect by 1 lg/ml concentration brain PRP-1 In the present study we observed reduced viable sarcoma JJ012 cell numbers in comparison with control (89% growth inhibition) when treated with low concentrations of PRP-1 (0.5–1 lg/ml). Higher concentrations did not exhibit inhibitory effect. We assume that PRP-1 in low concentration impedes cell cycle progression. The fact that low concentrations of PRP-1 abolished Myc activity prompts to think that the antitumorigenic effect of PRP-1 in low concentrations is mediated through oncogene inactivation.

Reviewing once more the c-myc and Ras collaboration: converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including "immortalization" and "transformation". In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.

Dipeptidyl peptidase 2 apoptosis assay determines the B-cell activation stage and predicts prognosis in chronic lymphocytic leukemia

OBJECTIVE

Dipeptidyl peptidase 2 (DPP2/DPP7) is a regulator of quiescence as inhibition of DPP2 results in apoptosis of resting, but not activated lymphocytes. The purpose of the present study was to investigate the prognostic value of DPP2 inhibition and the role of DPP2 in cell cycle in chronic lymphocytic leukemia (CLL).

MATERIALS AND METHODS

We screened 152 peripheral blood samples from patients with CLL in an apoptosis assay with AX8819, a DPP2-specific inhibitor. The apoptotic response was correlated with B-cell receptor signaling and cell cycle and molecular prognostic factors.

RESULTS

We categorized CLL into two prognostic subgroups. Inhibition of DPP2 induced apoptosis in 60% of CLL, while 40% were resistant to apoptosis. Resistance to apoptosis correlated with unmutated IgV(H) and increased ZAP-70 expression and was associated with unfavorable clinical outcomes. Sensitive CLL B cells expressed high p27, low c-Myc protein levels and decreased Syk phosphorylation, indicative of a resting phenotype. DPP2 inhibition in those cells resulted in apoptosis accompanied by enhanced phosphorylation of Syk, degradation of p27 and p130, and upregulation of c-Myc, indicative of activation and inappropriate cell cycle entry. Resistant CLL demonstrated baseline low p27 and high c-Myc protein levels and increased pSyk, indicative of an activated phenotype. Inhibition of heat shock protein 90 in this subset of CLL partially reversed apoptosis resistance.

CONCLUSIONS

The DPP2 apoptosis assay provides a reliable prognostic factor in CLL. CLL B cells sensitive to DPP2 inhibition are in true G(0), while resistant CLL B-cells are partially activated. DPP2 inhibition alone or with concomitant inhibition of heat shock protein 90 warrants investigation as a therapeutic modality in CLL.

Protection by D609 through cell-cycle regulation after stroke

Expressions of cell-cycle regulating proteins are altered after stroke. Cell-cycle inhibition has shown dramatic reduction in infarction after stroke. Ceramide can induce cell-cycle arrest by up-regulation of cyclin-dependent kinase (Cdk) inhibitors p21 and p27 through activation of protein phosphatase 2A (PP2A). Tricyclodecan-9-yl-xanthogenate (D609)-increased ceramide levels after transient middle cerebral artery occlusion (tMCAO) in spontaneously hypertensive rat (SHR) probably by inhibiting sphingomyelin synthase (SMS). D609 significantly reduced cerebral infarction and up-regulated Cdk inhibitor p21 and down-regulated phospho-retinoblastoma (pRb) expression after tMCAO in rat. Others have suggested bFGF-induced astrocyte proliferation is attenuated by D609 due to an increase in ceramide by SMS inhibition. D609 also reduced the formation of oxidized phosphatidylcholine (OxPC) protein adducts. D609 may attenuate generation of reactive oxygen species and formation of OxPC by inhibiting microglia/macrophage proliferation after tMCAO (please also see note added in proof: D609 may prevent mature neurons from entering the cell cycle at the early reperfusion, however may not interfere with later proliferation of microglia/ macrophages that are the source of brain derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF-1) in offering protection). It has been proposed that D609 provides benefit after tMCAO by attenuating hypoxia-inducible factor-1alpha and Bcl2/adenovirus E1B 19 kDa interacting protein 3 expressions. Our data suggest that D609 provides benefit after stoke through inhibition of SMS, increased ceramide levels, and induction of cell-cycle arrest by up-regulating p21 and causing hypophosphorylation of Rb (through increased protein phosphatase activity and/or Cdk inhibition).

Arginine deiminase originating from Lactococcus lactis ssp. lactis American Type Culture Collection (ATCC) 7962 induces G1-phase cell-cycle arrest and apoptosis in SNU-1 stomach adenocarcinoma cells

There are multiple lines of evidence that lactic acid bacteria (LAB) exert cancer-preventive effects. However, the underlying mechanisms are poorly understood. In the present study we found that the cytoplasmic fraction of Lactococcus lactis ssp. lactis American Type Culture Collection (ATCC) 7962 exerted the strongest antiproliferative effects (half-maximal inhibitory concentration (IC50) = 17 microg/ml) in SNU-1 human stomach cancer cells and arginine deiminase (ADI; EC 3.5.3.6) activity. We also cloned, expressed and purified ADI from L. lactis ssp. lactis ATCC 7962 (LADI). Both purified ADI from L. lactis (PADI; IC50 = 2 microg/ml) and recombinant ADI originating from LADI (IC50 = 0.6 microg/ml) inhibited the proliferation of SNU-1 cells. LADI induced G0/G1-phase arrest, sub-G1 accumulation, DNA condensation and DNA fragmentation in SNU-1 cells. 4',6-Diamidino-2-phenylindole (DAPI) staining and DNA fragmentation data provide evidence that LADI induces apoptosis in SNU-1 cells. LADI increased the expressions of p53 and p27Kip1, and decreased the expressions of cyclin D1, c-myc and Bcl-xL in SNU-1 cells. However, LADI had no effects on the expressions of p21Cip1 and Bcl-2. Collectively, these data indicate that ADI induces apoptosis and G0/G1-phase arrest of SNU-1 cells, which might contribute to the chemopreventive potential of LAB.

Differential regulation of cyclin-dependent kinase 4 (CDK4) and CDK6, evidence that CDK4 might not be activated by CDK7, and design of a CDK6 activating mutation

The homologous cyclin-dependent kinases (CDK) CDK4 and CDK6 integrate mitogenic and oncogenic signaling cascades with the cell cycle. Their activation requires binding to a D-type cyclin and then T-loop phosphorylation at T172 and T177 (respectively) by the only CDK-activating kinase identified in animal cells, cyclin H-CDK7. At odds with the existing data showing the constitutive activity of CDK7, we have recently identified the T172 phosphorylation of cyclin D-bound CDK4 as a crucial cell cycle regulatory target. Here we show that T172 phosphorylation of CDK4 is conditioned by its unique proline 173 residue. In contrast to CDK4, CDK6 does not contain such a proline and, unexpectedly, remained poorly phosphorylated and active in a variety of cells. Mutations of proline 173 did not adversely affect CDK4 activation by CDK7, but in cells they abolished CDK4 T172 phosphorylation and activity. Conversely, substituting a proline for the corresponding residue of CDK6 enforced its complete, apparently cyclin-independent T177 phosphorylation and dramatically increased its activity. These results lead us to propose that CDK4 might not be phosphorylated by CDK7 in intact cells but is more likely phosphorylated by another, presumably proline-directed kinase(s). Moreover, they provide a new model of a potentially oncogenic activating mutation of a CDK.

Adenovirus-mediated delivery of p27(KIP1) to prevent wound healing after experimental glaucoma filtration surgery

AIM

The aim of the study was to evaluate the outcome of adenovirus-mediated p27(KIP1) (Ad-p27) expression on wound healing after filtration surgery and to investigate the inhibition of cell proliferation induced by Ad-p27.

METHODS

We constructed the adenovirus recombinant vector Ad-p27 and administered it to a rabbit model of glaucoma filtration surgery by subconjunctival injection; phosphate-buffered saline (PBS) and mitomycin C (MMC) were used as controls. Intraocular pressure (IOP), bleb scores, and anterior chamber depths were observed during a 28-d period. Histological examinations, fluorescence observations and Western blot analyses were evaluated.

RESULTS

Ad-p27 enhanced the surgical outcome and inhibited cell proliferation when compared with PBS. Bleb scores in the Ad-p27-treated eyes were higher than those in the PBS-treated eyes on d 7 (P<0.01), 14 (P<0.01) and 21 (P<0.05). On d 28, IOP remained significantly decreased in the Ad-p27 group compared with the PBS group (P<0.05). However, no differences in bleb scores or IOPs were observed between the Ad-p27 and MMC groups. Histological analysis showed that total cell numbers were markedly reduced, and less scar tissue was observed at the surgical site in eyes treated with Ad-p27. The number of fibroblasts was decreased in Tenon's capsule in Ad-p27-treated eyes; however, a marked and diffuse signal from the green fluorescent protein (GFP) was observed in fibroblasts. Western blot analysis revealed a high level of p27(KIP1) expression in conjunctival epithelium (P<0.01), relatively high expression in superficial scleral stroma (P<0.01), and low expression in corneal epithelium in the Ad-p27 group.

CONCLUSIONS

Ad-p27 administration significantly improves the outcome of filtration surgery and inhibits postoperative proliferation in rabbit eyes. These findings suggest that p27(KIP1) is a potential adjunctive agent for inhibition of wound healing after filtration surgery.

Biological characterization of AT7519, a small-molecule inhibitor of cyclin-dependent kinases, in human tumor cell lines

Cyclin-dependent kinases (CDK), and their regulatory cyclin partners, play a central role in eukaryotic cell growth, division, and death. This key role in cell cycle progression, as well as their deregulation in several human cancers, makes them attractive therapeutic targets in oncology. A series of CDK inhibitors was developed using Astex's fragment-based medicinal chemistry approach, linked to high-throughput X-ray crystallography. A compound from this series, designated AT7519, is currently in early-phase clinical development. We describe here the biological characterization of AT7519, a potent inhibitor of several CDK family members. AT7519 showed potent antiproliferative activity (40-940 nmol/L) in a panel of human tumor cell lines, and the mechanism of action was shown here to be consistent with the inhibition of CDK1 and CDK2 in solid tumor cell lines. AT7519 caused cell cycle arrest followed by apoptosis in human tumor cells and inhibited tumor growth in human tumor xenograft models. Tumor regression was observed following twice daily dosing of AT7519 in the HCT116 and HT29 colon cancer xenograft models. We show that these biological effects are linked to inhibition of CDKs in vivo and that AT7519 induces tumor cell apoptosis in these xenograft models. AT7519 has an attractive biological profile for development as a clinical candidate, and the tolerability and efficacy in animal models compare favorably with other CDK inhibitors in clinical development. Studies described here formed the biological rationale for investigating the potential therapeutic benefit of AT7519 in cancer patients.

Myc's broad reach

The role of the myc gene family in the biology of normal and cancer cells has been intensively studied since the early 1980s. myc genes, responding to diverse external and internal signals, express transcription factors (c-, N-, and L-Myc) that heterodimerize with Max, bind DNA, and modulate expression of a specific set of target genes. Over the last few years, expression profiling, genomic binding studies, and genetic analyses in mammals and Drosophila have led to an expanded view of Myc function. This review is focused on two major aspects of Myc: the nature of the genes and pathways that are targeted by Myc, and the role of Myc in stem cell and cancer biology.

Identification of N-(4-piperidinyl)-4-(2,6-dichlorobenzoylamino)-1H-pyrazole-3-carboxamide (AT7519), a novel cyclin dependent kinase inhibitor using fragment-based X-ray crystallography and structure based drug design

The application of fragment-based screening techniques to cyclin dependent kinase 2 (CDK2) identified multiple (>30) efficient, synthetically tractable small molecule hits for further optimization. Structure-based design approaches led to the identification of multiple lead series, which retained the key interactions of the initial binding fragments and additionally explored other areas of the ATP binding site. The majority of this paper details the structure-guided optimization of indazole (6) using information gained from multiple ligand-CDK2 cocrystal structures. Identification of key binding features for this class of compounds resulted in a series of molecules with low nM affinity for CDK2. Optimisation of cellular activity and characterization of pharmacokinetic properties led to the identification of 33 (AT7519), which is currently being evaluated in clinical trials for the treatment of human cancers.

Growth inhibition of human hepatic carcinoma HepG2 cells by fucoxanthin is associated with down-regulation of cyclin D

Fucoxanthin, a major carotenoid in brown sea algae, has recently been demonstrated by us to inhibit the proliferation of colon cancer cells, and this effect was associated with growth arrest. These results, taken together with previous studies with fucoxanthin, suggest that it may be useful in chemoprevention of other human malignancies. The present study was designed to evaluate the molecular mechanisms of fucoxanthin against hepatic cancer using the human hepatocarcinoma HepG2 cell line (HepG2). Fucoxanthin reduced the viability of HepG2 cells accompanied with the induction of cell cycle arrest during the G0/G1 phase at 25 microM. This concentration of fucoxanthin inhibited the phosphorylation of the retinoblastoma protein (Rb) at Serine 780 (Ser780) position 18 h after treatment. The kinase activity of cyclin D and cdk4 complex, responsible for the phosphorylation of Rb Ser780 site, was down-regulated 18 h after the treatment. Western blotting analysis revealed that the expression of cyclin D-type protein was suppressed by treatment of fucoxanthin. This reduction was partially blocked by concurrent treatment with the proteasome inhibitor MG132, indicating the involvement of the proteasome-mediated degradation. In addition, RT-PCR analysis revealed that fucoxanthin also appeared to repress cyclin D mRNA. Thus, both the protein degradation and transcriptional repression seem to be responsible for suppressed cyclin D level in fucoxanthin-treated HepG2 cells which may be related to the antitumorgenic activity.

A small-molecule c-Myc inhibitor, 10058-F4, induces cell-cycle arrest, apoptosis, and myeloid differentiation of human acute myeloid leukemia

OBJECTIVE

The protooncogene c-Myc plays an important role in the control of cell proliferation, apoptosis, and differentiation, and its aberrant expression is frequently seen in multiple human cancers, including acute myeloid leukemia (AML). As c-Myc heterodimerizes with Max to transactivate downstream target genes in leukemogenesis. Inhibition of the c-Myc/Max heterodimerization by the recently identified small-molecule compound, 10058-F4, might be a novel antileukemic strategy.

MATERIALS AND METHODS

HL-60, U937, and NB4 cells and primary AML cells were used to examine the effects of 10058-F4 on apoptosis and myeloid differentiation.

RESULTS

We showed that 10058-F4 arrested AML cells at G0/G1 phase, downregulated c-Myc expression and upregulated CDK inhibitors, p21 and p27. Meanwhile, 10058-F4 induced apoptosis through activation of mitochondrial pathway shown by downregulation of Bcl-2, upregulation of Bax, release of cytoplasmic cytochrome C, and cleavage of caspase 3, 7, and 9. Furthermore, 10058-F4 also induced myeloid differentiation, possibly through activation of multiple transcription factors. Similarly, 10058-F4-induced apoptosis and differentiation could also be observed in primary AML cells.

CONCLUSION

Our study has shown that inhibition of c-Myc/Max dimerization with small-molecule inhibitors affects multiple cellular activities in AML cells and represents a potential antileukemic approach.

Differential modification of p27Kip1 controls its cyclin D-cdk4 inhibitory activity

Whether p27 is a cyclin D-cdk4/6 inhibitor or not is controversial, and how it might switch between these two modes is unknown. Arguing for a two-state mechanism, we show that p27 bound to cyclin D-cdk4 can be both inhibitory and noninhibitory, due to its differential-growth-state-dependent tyrosine phosphorylation. We found that p27 from proliferating cells was noninhibitory but that p27 from arrested cells was inhibitory, and the transition from a bound noninhibitor to a bound inhibitor was not due to an increase in p27 concentration. Rather, two tyrosine residues (Y88 and Y89) in p27's cdk interaction domain were phosphorylated preferentially in proliferating cells, which converted p27 to a noninhibitor. Concordantly, mutation of these sites rendered p27 resistant to phosphorylation and locked it into the bound-inhibitor mode in vivo and in vitro. Y88 was directly phosphorylated in vitro by the tyrosine kinase Abl, which converted p27 to a cdk4-bound noninhibitor. These data show that the growth-state-dependent tyrosine phosphorylation of p27 modulates its inhibitory activity in vivo.

Identification of differentially expressed genes in tobacco chewing-mediated oral cancer by differential display-polymerase chain reaction

BACKGROUND

Identification of changes in gene expression that occur in oral squamous cell carcinoma (OSCC), after sufficient characterization, may yield novel molecular markers that may be useful in the diagnosis and disease management of oral cancer.

MATERIALS AND METHODS

We used differential display-polymerase chain reaction (DD-PCR) to study critically the global gene expression profile of the oral tumour versus normal epithelium. The differential expression of fished out cDNA were confirmed by Northern blot and reverse transcription-PCR. The differentially expressed cDNA were cloned, sequenced and matched for homology in the GenBank database.

RESULTS

We identified 13 cDNA that showed differential expression. Out of these we selected four cDNA showing consistent reproducibility. One of the cDNA expressed exclusively in tumour had a homology to DEK, a putative oncogene, and is linked to leukaemia, various cancers, HIV infection and several autoimmune disorders. Another cDNA expressed only in tumour had homology to sorcin protein. Sorcin is a 22-kDa calcium-binding protein and is associated with drug resistance in various cell lines. Apparently, sorcin expression might be responsible for drug resistance of OSCC and poor prognosis. Another cDNA showing 10 times overexpression in cheek tumour as compared to normal had homology to CDK6 gene. Hence, it seems from our results that CDK6 is dysregulated during oral carcinogenesis. The fourth cDNA was overexpressed in normal as compared to cheek tumour, but did not show any match in BLAST search.

CONCLUSIONS

We conclude that there is an enormous significance of these differentially expressed cDNA in oral cancer progression as they can serve as cancer markers to be used for diagnosis and therapeutic intervention.

CDK4 and CDK6 delay senescence by kinase-dependent and p16INK4a-independent mechanisms

Replicative senescence of human diploid fibroblasts (HDFs) is largely implemented by the cyclin-dependent kinase (CDK) inhibitors p16(INK4a) and p21(CIP1). Their accumulation results in a loss of CDK2 activity, and cells arrest with the retinoblastoma protein (pRb) in its hypophosphorylated state. It has become standard practice to bypass the effects of p16(INK4a) by overexpressing CDK4 or a variant form that is unable to bind to INK4 proteins. Although CDK4 and CDK6 and their INK4-insensitive variants can extend the life span of HDFs, they also cause a substantial increase in the levels of endogenous p16(INK4a). Here we show that CDK4 and CDK6 can extend the life span of HDFs that have inactivating mutations in both alleles of INK4a or in which INK4a levels are repressed, indicating that overexpression of CDK4/6 is not equivalent to ablation of p16(INK4a). However, catalytically inactive versions of these kinases are unable to extend the replicative life span, suggesting that the impact of ectopic CDK4/6 depends on their ability to phosphorylate as yet unidentified substrates rather than to sequester CDK inhibitors. Since p16(INK4a) deficiency, CDK4 expression, and p53 or p21(CIP1) ablation have additive effects on replicative life span, our results underscore the idea that senescence is an integrated response to diverse signals.

Regulation of CDK4

Cyclin-dependent kinase (CDK)4 is a master integrator that couples mitogenic and antimitogenic extracellular signals with the cell cycle. It is also crucial for many oncogenic transformation processes. In this overview, we address various molecular features of CDK4 activation that are critical but remain poorly known or debated, including the regulation of its association with D-type cyclins, its subcellular location, its activating Thr172-phosphorylation and the roles of Cip/Kip CDK "inhibitors" in these processes. We have recently identified the T-loop phosphorylation of CDK4, but not of CDK6, as a determining target for cell cycle control by extracellular factors, indicating that CDK4-activating kinase(s) might have to be reconsidered.

Cyclophilin A is required for M-CSF-dependent macrophage proliferation

The immunosuppressor sanglifehrin A (SfA) is a member of a family of immunophilin cyclophilin A-binding molecules and does not inhibit calcineurin activity. Sanglifehrin A inhibits M-CSF-dependent macrophage proliferation by arresting the G1 phase of the cell cycle but does not affect cell viability. This immunosuppressor exerts its action on proliferation by inactivating cyclin-dependent kinase 2 (Cdk2) activity. Moreover, c-myc expression is also repressed. In the early steps of M-CSF signaling, SfA inhibits the phosphorylation of Raf-1 and the external regulated kinases (ERK)1/2 and mitogen-activated protein kinase phosphatase-1, which are required for proliferation. The effects of SfA are not related to a block of the proteosome activity. These data show that immunophilin contributes to M-CSF-dependent proliferation through activation of the Raf-1/MEK/ERK pathway and the regulation of Cdk activities, which is required for cell cycle progression.

Growth, differentiation, and malignant transformation of pre-B cells mediated by inducible activation of v-Abl oncogene

The nonreceptor tyrosine kinase, encoded by the v-Abl oncogene of Abelson murine leukemia virus induces transformation of progenitor B cells. The v-Abl oncogene promotes cell cycle progression and inhibits pre-B cell differentiation. The temperature-sensitive form of Abelson murine leukemia virus offers a reversible model to study the role of v-Abl in regulating growth and differentiation. Inactivation of v-Abl elevates p27 and Foxo3a levels and activates NF-kappaB/Rel, which leads to G1 arrest and induction of Ig L chain gene rearrangement, respectively. In turn, v-Abl reactivation reduces p27 and Foxo3a levels, thus permitting G1-arrested cells to reenter the cell cycle. However, the cell lines derived from SCID mice that are defective in the catalytic subunit of DNA-dependent protein kinase retain elevated levels of p27 and Foxo3a proteins despite reactivation of v-Abl. Consequently, these cells are locked in the G1 phase for an extended period of time. The few cells that manage to bypass the G1 arrest become tumorigenic and fail to undergo pre-B cell differentiation induced by v-Abl inactivation. Deregulation of p27, Foxo3a, c-myc, and NF-kappaB/Rel was found to be associated with the malignant transformation of SCID temperature-sensitive form of Abelson murine leukemia virus pre-B cells.

Regulated activating Thr172 phosphorylation of cyclin-dependent kinase 4(CDK4): its relationship with cyclins and CDK "inhibitors"

Cyclin-dependent kinase 4 (CDK4) is a master integrator of mitogenic and antimitogenic extracellular signals. It is also crucial for many oncogenic transformation processes. Various molecular features of CDK4 activation remain poorly known or debated, including the regulation of its association with D-type cyclins, its activating Thr172 phosphorylation, and the roles of Cip/Kip CDK "inhibitors" in these processes. Thr172 phosphorylation of CDK4 was reinvestigated using two-dimensional gel electrophoresis in various experimental systems, including human fibroblasts, canine thyroid epithelial cells stimulated by thyrotropin, and transfected mammalian and insect cells. Thr172 phosphorylation of CDK4 depended on prior D-type cyclin binding, but Thr172 phosphorylation was also found in p16-bound CDK4. Opposite effects of p27 on cyclin D3-CDK4 activity observed in different systems depended on its stoichiometry in this complex. Thr172-phosphorylated CDK4 was enriched in complexes containing p21 or p27, even at inhibitory levels of p27 that precluded CDK4 activity. Deletion of the p27 nuclear localization signal sequence relocalized cyclin D3-CDK4 in the cytoplasm but did not affect CDK4 phosphorylation. Within cyclin D3 complexes, T-loop phosphorylation of CDK4, but not of CDK6, was directly regulated, identifying it as a determining target for cell cycle control by extracellular factors. Collectively, these unexpected observations indicate that CDK4-activating kinase(s) should be reconsidered.