Small-molecule cyclin-dependent kinase modulators

The Interplay between the DNA Damage Response (DDR) Network and the Mitogen-Activated Protein Kinase (MAPK) Signaling Pathway in Multiple Myeloma

The DNA damage response (DDR) network and the mitogen-activated protein kinase (MAPK) signaling pathway are crucial mechanisms for the survival of all living beings. An accumulating body of evidence suggests that there is crosstalk between these two systems, thus favoring the appropriate functioning of multi-cellular organisms. On the other hand, aberrations within these mechanisms are thought to play a vital role in the onset and progression of several diseases, including cancer, as well as in the emergence of drug resistance. Here, we provide an overview of the current knowledge regarding alterations in the DDR machinery and the MAPK signaling pathway as well as abnormalities in the DDR/MAPK functional crosstalk in multiple myeloma, the second most common hematologic malignancy. We also present the latest advances in the development of anti-myeloma drugs targeting crucial DDR- and MAPK-associated molecular components. These data could potentially be exploited to discover new therapeutic targets and effective biomarkers as well as for the design of novel clinical trials. Interestingly, they might provide a new approach to increase the efficacy of anti-myeloma therapy by combining drugs targeting the DDR network and the MAPK signaling pathway.

Triggering Breast Cancer Apoptosis via Cyclin-Dependent Kinase Inhibition and DNA Damage by Novel Pyrimidinone and 1,2,4-Triazolo[4,3-a]pyrimidinone Derivatives

Combinations of apoptotic inducers are common clinical practice in breast cancer. However, their efficacy is limited by the heterogeneous pharmacokinetic profiles. An advantageous alternative is merging their molecular entities in hybrid multitargeted scaffolds exhibiting synergistic activities and uniform distribution. Herein, we report apoptotic inducers simultaneously targeting DNA and CDK-2 (cyclin-dependent kinase-2) inspired by studies revealing that CDK-2 inhibition sensitizes breast cancer to DNA-damaging agents. Accordingly, rationally substituted pyrimidines and triazolopyrimidines were synthesized and assayed by MTT against MCF-7, MDA-MB231, and Wi-38 cells compared to doxorubicin. The N-(4-amino-2-((2-hydrazinyl-2-oxoethyl)thio)-6-oxo-1,6-dihydropyrimidin-5-yl)acetamide 5 and its p-nitrophenylhydrazone 8 were the study hits against MCF-7 (IC50 = 0.050 and 0.146 μM) and MDA-MB231 (IC50 = 0.826 and 0.583 μM), induced DNA damage at 10.64 and 30.03 nM, and inhibited CDK-2 (IC50 = 0.172 and 0.189 μM). 5 induced MCF-7 apoptosis by 46.75% and disrupted cell cycle during S phase. Docking and MD simulations postulated their stable key interactions.

Unveiling the therapeutic potential of natural-based anticancer compounds inducing non-canonical cell death mechanisms

In the Mid-19th century, Rudolf Virchow considered necrosis to be a prominent form of cell death; since then, pathologists have recognized necrosis as both a cause and a consequence of disease. About a century later, the mechanism of apoptosis, another form of cell death, was discovered, and we now know that this process is regulated by several molecular mechanisms that "programme" the cell to die. However, discoveries on cell death mechanisms are not limited to these, and recent studies have allowed the identification of novel cell death pathways that can be molecularly distinguished from necrotic and apoptotic cell death mechanisms. Moreover, the main goal of current cancer therapy is to discover and develop drugs that target apoptosis. However, resistance to chemotherapeutic agents targeting apoptosis is mainly responsible for the failure of clinical therapy and adverse side effects of the chemotherapeutic agents currently in use pose a major threat to the well-being and lives of patients. Therefore, the development of natural-based anticancer drugs with low cellular and organismal side effects is of great interest. In this comprehensive review, we thoroughly examine and discuss natural anticancer compounds that specifically target non-canonical cell death mechanisms.

An Overview of CDK Enzyme Inhibitors in Cancer Therapy

The ability to address the cell cycle in cancer therapy brings up new medication development possibilities. Cyclin-dependent kinases are a group of proteins that control the progression of the cell cycle. The CDK/cyclin complexes are activated when specific CDK sites are phosphorylated. Because of their non-selectivity and severe toxicity, most first-generation CDK inhibitors (also known as pan-CDK inhibitors) have not been authorized for clinical usage. Despite this, significant progress has been made in allowing pan-CDK inhibitors to be employed in clinical settings. Pan-CDK inhibitors' toxicity and side effects have been lowered in recent years because of the introduction of combination therapy techniques. As a result of this, pan-CDK inhibitors have regained a lot of clinical potential as a combination therapy approach. The CDK family members have been introduced in this overview, and their important roles in cell cycle control have been discussed. Then, we have described the current state of CDK inhibitor research, with a focus on inhibitors other than CDK4/6. We have mentioned first-generation pan-CDKIs, flavopiridol and roscovitine, as well as second-generation CDKIs, dinaciclib, P276-00, AT7519, TG02, roniciclib, and RGB-286638, based on their research phases, clinical trials, and cancer targeting. CDKIs are CDK4/6, CDK7, CDK9, and CDK12 inhibitors. Finally, we have looked into the efficacy of CDK inhibitors and PD1/PDL1 antibodies when used together, which could lead to the development of a viable cancer treatment strategy.

Cyclin-dependent kinases as potential targets for colorectal cancer: past, present and future

Colorectal cancer (CRC) is a common cancer in the world and its prevalence is increasing in developing countries. Deregulated cell cycle traverse is a hallmark of malignant transformation and is often observed in CRC as a result of imprecise activity of cell cycle regulatory components, viz. cyclins and cyclin-dependent kinases (CDKs). Apart from cell cycle regulation, some CDKs also regulate processes such as transcription and have also been shown to be involved in colorectal carcinogenesis. This article aims to review cyclin-dependent kinases as potential targets for CRC. Furthermore, therapeutic candidates to target CDKs are also discussed.

Therapeutic Potential of the Cyclin-Dependent Kinase Inhibitor Flavopiridol on c-Myc Overexpressing Esophageal Cancer

Tumors with elevated c-Myc expression often exhibit a highly aggressive phenotype, and c-Myc amplification has been shown to be frequent in esophageal cancer. Emerging data suggests that synthetic lethal interactions between c-Myc pathway activation and small molecules inhibition involved in cell cycle signaling can be therapeutically exploited to preferentially kill tumor cells. We therefore investigated whether exploiting elevated c-Myc expression is effective in treating esophageal cancer with the CDK inhibitor flavopiridol. We found frequent overexpression of c-Myc in human esophageal cancer cell lines and tissues. c-Myc overexpression correlated with accelerated esophageal cancer subcutaneous xenograft tumor growth. Esophageal cancer cells with elevated c-Myc expression were found preferentially more sensitive to induction of apoptosis by the CDK inhibition flavopiridol compared to esophageal cancer cells with lower c-Myc expression. In addition, we observed that flavopiridol alone or in combination with the chemotherapeutic agent nanoparticle albumin-bound paclitaxel (NPT) or in combinations with the targeted agent BMS-754807 significantly inhibited esophageal cancer cell proliferation and subcutaneous xenograft tumor growth while significantly enhancing overall mice survival. These results indicate that aggressive esophageal cancer cells with elevated c-Myc expression are sensitive to the CDK inhibitor flavopiridol, and that flavopiridol alone or in combination can be a potential therapy for c-Myc overexpressing esophageal cancer.

RAS/MAPK signaling functions in oxidative stress, DNA damage response and cancer progression

Mitogen-activated protein kinase (MAPK) signaling pathways organize a great constitution network that regulates several physiological processes, like cell growth, differentiation, and apoptotic cell death. Due to the crucial importance of this signaling pathway, dysregulation of the MAPK signaling cascades is involved in the pathogenesis of various human cancer types. Oxidative stress and DNA damage are two important factors which in common lead to carcinogenesis through dysregulation of this signaling pathway. Reactive oxygen species (ROS) are a common subproduct of oxidative energy metabolism and are considered to be a significant physiological modulator of several intracellular signaling pathways including the MAPK pathway. Studies demonstrated that the MAP kinases extracellular signal-regulated kinase (ERK) 1/2 and p38 were activated in response to oxidative stress. In addition, DNA damage is a partly common circumstance in cell life and may result in mutation, cancer, and even cell death. Recently, accumulating evidence illustrated that the MEK/ERK pathway is associated with the suitable performance of cellular DNA damage response (DDR), the main pathway of tumor suppression. During DDR, the MEK/ERK pathway is regularly activated, which contributes to the appropriate activation of DDR checkpoints to inhibit cell division. Therefore, the aim of this review is to comprehensively discuss the critical function of MAPK signaling in oxidative stress, DNA damage, and cancer progression.

Involvement of Akt in mitomycin C and its analog triggered cytotoxicity in MCF-7 and K562 cancer cells

Mitomycin C (MC) is a well-known DNA alkylating agent. MC analog, 10-decarbamoyl mitomycin C (DMC), unlike MC, has stronger effects on cancer with p53 mutation. We previously demonstrated that MC/DMC could activate p21WAF1/CIP1 in MCF-7 (p53-proficient) and K562 (p53-deficient) cells in a p53-independent mode. This study aimed to elucidate the upstream signaling pathway of p21WAF1/CIP1 activation triggered by MC/DMC. Besides p53, Akt plays an important role on deactivating p21WAF1/CIP1 . The results showed that MC/DMC inhibited Akt in MCF-7 cells, but not in K562 cells. By knocking down p53, the Akt inhibition in MCF-7 cells was alleviated. This implied that the deactivated Akt caused by MC/DMC was p53-dependent. With Akt activator (SC79), p21WAF1/CIP1 activation triggered by MC/DMC in MCF-7 cells was not reduced. This indicated that Akt inhibition triggered by MC/DMC was not associated with MC/DMC-induced p21WAF1/CIP1 activation. Label-free quantitative proteomic profiling analysis revealed that DMC has a stronger effect on down-regulating the PI3K/Akt signaling pathway in MCF-7 cells as compared to MC. No significant effect of MC/DMC on PI3K/Akt in K562 cells was observed. In summary, MC/DMC regulate Akt activation in a p53-dependent manner. This Akt deactivation is not associated with p21WAF1/CIP1 activation in response to MC/DMC.

S-allylcysteine suppresses ovarian cancer cell proliferation by DNA methylation through DNMT1

BACKGROUND

The anti-tumor effects of S-allylcysteine (SAC), a water-soluble garlic derivative, on human ovarian cancer cells have been previous studied in vitro and in vivo models but the precise epigenetic molecular mechanisms are still unclear. This study aimed to investigate the epigenetic mechanism of SAC.

METHODS

Human epithelial ovarian cancer cell line A2780 was selected. Cell proliferation and cell cycle was analyzed. DNA methylation, DNA methyltransferase (DNMT) activity, tumor suppressor gene expressions, as well as protein expression were analyzed.

RESULTS

SAC could inhibit the proliferation of A2780 cells in dose- and time-dependent manners (the IC₅₀ was 16.25 mmol/L and 5.25 mmol/L at 48 h and 72 h). Treatment of A2780 cells with SAC resulted in G1/S phase arrest. SAC treatment decreased global DNA methylation levels in A2780 cells in a dose-dependent manner. SAC decreased the levels of 5-methylcytosine, DNMT activity, messenger RNA (mRNA) and protein levels of DNMT1. Additionally, SAC treatment resulted in re-expression of the mRNA and proteins of silenced tumor suppressor gene CDKN1A accompany with reduced cell division control 2 expression.

CONCLUSION

Our data indicated the potential therapeutic effects of SAC on the human ovarian carcinoma cell line A2780 in vitro. The epigenetic mechanism of action of SAC may have important implications for epigenetic therapy.

The Tumor-Like Phenotype of Rheumatoid Synovium: Molecular Profiling and Prospects for Precision Medicine

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by destructive hyperplasia of the synovium. Fibroblast-like synoviocytes (FLS) are a major component of synovial pannus and actively participate in the pathologic progression of RA. How rheumatoid FLS acquire and sustain such a uniquely aggressive phenotype remains poorly understood. We describe the current state of knowledge of the molecular alterations in rheumatoid FLS at the genomic, epigenomic, transcriptomic, proteomic, and metabolomic levels, which offers a means to reconstruct the pathways leading to rheumatoid pannus. Such data provide new pathologic insight and suggest means to more sensitively assess disease activity and response to therapy, as well as support new avenues for therapeutic development.

Suppression of c-Myc enhances p21WAF1/CIP1 -mediated G1 cell cycle arrest through the modulation of ERK phosphorylation by ascochlorin

Numerous anti-cancer agents inhibit cell cycle progression via a p53-dependent mechanism; however, other genes such as the proto-oncogene c-Myc are promising targets for anticancer therapy. In the present study, we provide evidence that ascochlorin, an isoprenoid antibiotic, is a non-toxic anti-cancer agent that induces G1 cell cycle arrest and p21WAF1/CIP1 expression by downregulating of c-Myc protein expression. Ascochlorin promoted the G1 arrest, upregulated p53 and p21WAF1/CIP1 , and downregulated c-Myc in HCT116 cells. In p53-deficient cells, ascochlorin enhanced the expression of G1 arrest-related genes except p53. Small interfering RNA (siRNA) mediated c-Myc silencing indicated that the transcriptional repression of c-Myc was related to ascochlorin-mediated modulation of p21WAF1/CIP1 expression. Ascochlorin suppressed the stabilization of the c-Myc protein by inhibiting ERK and P70S6K/4EBP1 phosphorylation, whereas it had no effect on c-Myc degradation mediated by PI3K/Akt/GSK3β. The ERK inhibitor PD98059 and siRNA-mediated ERK silencing induced G1 arrest and p21WAF1/CIP1 expression by downregulating c-Myc in p53-deficient cells. These results indicated that ascochlorin-induced G1 arrest is associated with the repression of ERK phosphorylation and c-Myc expression. Thus, we reveal a role for ascochlorin in inhibiting tumor growth via G1 arrest, and identify a novel regulatory mechanism for ERK/c-Myc.

Regulation of the human papillomavirus type 16 late promoter by transcriptional elongation

Transcripts from the late promoter of human papillomavirus type 16 (HPV16) are upregulated upon host cell differentiation. Differentiation-dependent transcript regulation is thought to sequester viral antigens in the uppermost epithelial layers, facilitating immune evasion. The mechanisms regulating late promoter upregulation during differentiation are poorly characterized. We show that the late promoter is upregulated at the transcriptional level and that the viral enhancer stimulates promoter activity. Using kinase inhibition and chromatin immunoprecipitation analysis, we show evidence for differentiation-dependent enhancement of transcript elongation. Three factors that promote transcript elongation, cyclin dependent kinase 9 (CDK9), CDK8 (a subunit of the Mediator complex), and bromodomain containing protein 4 (Brd4) are recruited to viral genomes upon differentiation, and each plays a role in promoter activity. These results shed light on the transcriptional processes utilized by HPV16 for proper regulation of gene expression during the viral life cycle.

Targeting CDKs with Roscovitine Increases Sensitivity to DNA Damaging Drugs of Human Osteosarcoma Cells

Cyclin-dependent kinase 2 (CDK2) has been reported to be essential for cell proliferation in several human tumours and it has been suggested as an appropriate target to be considered in order to enhance the efficacy of treatment regimens based on the use of DNA damaging drugs. We evaluated the clinical impact of CDK2 overexpression on a series of 21 high-grade osteosarcoma (OS) samples profiled by using cDNA microarrays. We also assessed the in vitro efficacy of the CDKs inhibitor roscovitine in a panel of drug-sensitive and drug-resistant human OS cell lines. OS tumour samples showed an inherent overexpression of CDK2, and high expression levels at diagnosis of this kinase appeared to negatively impact on clinical outcome. CDK2 expression also proved to be relevant for in vitro OS cells growth. These findings indicated CDK2 as a promising candidate therapeutic marker for OS and therefore we assessed the efficacy of the CDKs-inhibitor roscovitine in both drug-sensitive and -resistant OS cell lines. All cell lines resulted to be responsive to roscovitine, which was also able to increase the activity of cisplatin and doxorubicin, the two most active DNA damaging drugs used in OS chemotherapy. Our results indicated that combined treatment with conventional OS chemotherapeutic drugs and roscovitine may represent a new candidate intervention approach, which may be considered to enhance tumour cell sensitivity to DNA damaging drugs.

Estrogen-related receptor γ is upregulated in liver cancer and its inhibition suppresses liver cancer cell proliferation via induction of p21 and p27

Orphan nuclear receptor estrogen-related receptor γ (ERRγ) regulates cell growth and tumorigenesis in various cancers. However, the clinical relevance of ERRγ to hepatocellular carcinoma (HCC) remains unclear. Here we examined the clinical significance of ERRγ in HCC and its potential as a therapeutic target. ERRγ levels in tissues from completely resected specimens from 190 HCC patients were examined immunohistochemically and their association with clinical stage and pathological grade was analyzed. Small interfering RNA (siRNA)-mediated knockdown of ERRγ (siRNA-ERRγ) or an ERRγ inverse agonist, GSK5182, were also used to examine the effects of ERRγ inhibition on the proliferation and growth of a human hepatoma cell line, PLC/PRF/5. Immunohistochemical analysis revealed that tumor tissues showed higher levels of ERRγ-positivity than adjacent non-tumor lesions. Tumors showing high levels of ERRγ immunoreactivity also had advanced tumor node metastasis (TNM) and Barcelona Clinic Liver Cancer stages and a higher Edmondson–Steiner grade. In addition, high-level expression of ERRγ in tumors of advanced TNM stage correlated with poorer overall survival. Treatment of PLC/PRF/5 cells with siRNA-ERRγ or GSK5182 inhibited proliferation through G1 arrest, increased expression of p21 and p27 and decreased expression of phosphorylated retinoblastoma protein. GSK5182-induced reactive oxygen species also suppressed the proliferation of PLC/PRF/5 cells. The present study showed that ERRγ expression is clinically significant in HCC; therefore, it can be considered a biomarker for HCC diagnosis. Moreover, the results provide a rationale for the use of ERRγ inhibitors such as GSK5182 as potential therapeutic agents.

Cell cycle regulation therapy combined with cytokine blockade enhances antiarthritic effects without increasing immune suppression

OBJECTIVE

Biological disease-modifying antirheumatic drugs (DMARDs) that inhibit aberrant immune reactions in rheumatoid arthritis (RA) cannot induce complete remission in all patients. Combination therapies using two biological DMARDs have failed to exert additive effects and increased serious infections. We have found that cell cycle inhibition of synovial fibroblasts with cyclin-dependent kinase (CDK) inhibitors ameliorated the disease in animal models of RA without attenuating acquired immunity. The objective of this study was to determine whether a clinically well-tolerated selective CDK 4/6 inhibitor (CDKI), palbociclib, is effective and whether combination with cytokine blockers acts additively without enhancing immune suppression.

METHODS

The effects of CDKI on haematopoiesis and physical and behavioural findings in mice were evaluated. Mice with collagen-induced arthritis (CIA) were treated with CDKI, etanercept or anti-interleukin (IL)-6 receptor antibody (MR16-1) alone or with a combination of CDKI with etanercept or MR16-1. Their clinical, histological and radiographic scores, serum anti-(type II collagen (CII)) antibody levels and proliferative responses of lymph node cells to CII were determined.

RESULTS

Although CDKI induced marginal myelosuppression, it was well tolerated and ameliorated CIA dose-dependently. The combinations of low-dose CDKI and either tumour necrosis factor-α or IL-6 blocker enhanced the antiarthritic effects additively. The addition of CDKI to either cytokine blocker did not affect the levels of anti-CII antibodies and proliferative responses of lymphocytes to CII.

CONCLUSIONS

A clinically well-tolerated CDK4/6 inhibitor exerted antiarthritic effects in this mouse model. By combining therapeutic agents targeting immune reaction and synovial proliferation, we have demonstrated for the first time that two molecular targeting treatments act additively and may not increase immune suppression.

Germ cell tumors overexpress the candidate therapeutic target cyclin B1 independently of p53 function

Germ cell tumors (GCTs) generally express wild-type p53 protein. Rare p53 mutations may be associated with cisplatin resistance. There is growing interest in the role of cyclins as targets for GCTs. Cyclin B1 is involved in G2/M transition and its overexpression has been reported in tumors carrying nonfunctional p53. Conversely, cyclin B1-specific small interfering RNAs have been shown to dramatically reduce tumor proliferation. We investigated whether a subset of chemotherapy-resistant GCTs overexpressed cyclin B1 as a result of nonfunctional p53, as this would make cyclin B1 a potential therapeutic target. Our data showed that GCTs consistently overexpressed cyclin B1 independently of their responsiveness to chemotherapy or the presence of p53 mutations. Cyclin B1 was overexpressed by GCT cell lines carrying functional p53. Cyclin B1-specific small interfering RNAs only slightly reduced the proliferation of JAR and JEG-3 placental choriocarcinoma cells. Further research into targeting cyclin B1 could provide a novel intervention for GCTs.

Derricin and derricidin inhibit Wnt/β-catenin signaling and suppress colon cancer cell growth in vitro

Overactivation of the Wnt/β-catenin pathway in adult tissues has been implicated in many diseases, such as colorectal cancer. Finding chemical substances that can prevent this phenomenon is an emerging problem. Recently, several natural compounds have been described as Wnt/β-catenin inhibitors and might be promising agents for the control of carcinogenesis. Here, we describe two natural substances, derricin and derricidin, belonging to the chalcone subclass, that show potent transcriptional inhibition of the Wnt/β-catenin pathway. Both chalcones are able to affect the cell distribution of β-catenin, and inhibit Wnt-specific reporter activity in HCT116 cells and in Xenopus embryos. Derricin and derricidin also strongly inhibited canonical Wnt activity in vitro, and rescued the Wnt-induced double axis phenotype in Xenopus embryos. As a consequence of Wnt/β-catenin inhibition, derricin and derricidin treatments reduce cell viability and lead to cell cycle arrest in colorectal cancer cell lines. Taken together, our results strongly support these chalcones as novel negative modulators of the Wnt/β-catenin pathway and colon cancer cell growth in vitro.

Cyclin-dependent kinase inhibitors and the treatment of gastrointestinal cancers

The cell cycle is a highly conserved and tightly regulated biological system that controls cellular proliferation and differentiation. The cell cycle regulatory proteins, which include the cyclins, the cyclin-dependent kinases (CDKs), and the CDK inhibitors, are critical for the proper temporal and spatial regulation of cellular proliferation. Conversely, alterations in cell cycle regulatory proteins, leading to the loss of normal cell-cycle control, are a hallmark of many cancers, including gastrointestinal cancers. Accordingly, overexpression of CDKs and cyclins and by contrast loss of CDK inhibitors, are all linked to gastrointestinal cancers and are often associated with less favorable prognoses and outcomes. Because of the importance that the cell cycle regulatory proteins play in tumorigenesis, currently there is a broad spectrum of cell-cycle inhibitors under development that, as a group, hold promise as effective cancer treatments. In support of this approach to cancer treatment, the growing availability of molecular diagnostics techniques may help in identifying patients who have driving abnormalities in the cell-cycle machinery and are thus more likely to respond to cell-cycle inhibitors. In this review, we discuss the prevalence of cell-cycle abnormalities in patients with gastrointestinal cancers and provide a preclinical and clinical overview of new agents that target cell-cycle abnormalities with a special emphasis on gastrointestinal cancers.

Staurosporine and extracellular matrix proteins mediate the conversion of small cell lung carcinoma cells into a neuron-like phenotype

Small cell lung carcinomas (SCLCs) represent highly aggressive tumors with an overall five-year survival rate in the range of 5 to 10%. Here, we show that four out of five SCLC cell lines reversibly develop a neuron-like phenotype on extracellular matrix constituents such as fibronectin, laminin or thrombospondin upon staurosporine treatment in an RGD/integrin-mediated manner. Neurite-like processes extend rapidly with an average speed of 10 µm per hour. Depending on the cell line, staurosporine treatment affects either cell cycle arrest in G2/M phase or induction of polyploidy. Neuron-like conversion, although not accompanied by alterations in the expression pattern of a panel of neuroendocrine genes, leads to changes in protein expression as determined by two-dimensional gel electrophoresis. It is likely that SCLC cells already harbour the complete molecular repertoire to convert into a neuron-like phenotype. More extensive studies are needed to evaluate whether the conversion potential of SCLC cells is suitable for therapeutic interventions.

Review of the molecular pathogenesis of osteosarcoma

Treating the osteosarcoma (OSA) remains a challenge. Current strategies focus on the primary tumor and have limited efficacy for metastatic OSA. A better understanding of the OSA pathogenesis may provide a rational basis for innovative treatment strategies especially for metastases. The aim of this review is to give an overview of the molecular mechanisms of OSA tumorigenesis, OSA cell proliferation, apoptosis, migration, and chemotherapy resistance, and how improved understanding might contribute to designing a better treatment target for OSA.

Cyclin E facilitates dysplastic hepatocytes to bypass G1/S checkpoint in hepatocarcinogenesis

BACKGROUND AND AIM

By array-comparative genomic hybridization, we demonstrated cyclin E as one of seven genes associated with hepatocellular carcinoma (HCC) development in Ku70 DNA repair-deficient mice. We therefore explored the hypothesis that during hepatocarcinogenesis, cyclin E kinase can overcome the inhibitory effects of p53 and establish whether abnormal miRNA(mi-R)-34, a co-regulator of cyclin E and p53, can account for their interactions as "drivers" of HCC.

METHODS

Dysplastic hepatocytes (DNs) and HCCs were generated from diethylnitrosamine (DEN)-injected C57BL/6 male mice at 3-12 months.

RESULTS

Cyclin E/cdk2 was barely expressed in normal liver, but was readily detected in dysplastic hepatocytes, localizing to glutathione-S transferase pi-form positive cells dissected by laser-dissection. Cyclin E kinase activity preceded cyclin D1, proliferating cell nuclear antigen expression in DNs and HCCs despite maximal p53 and p21 expression. We confirmed that cyclin E, rather than cyclin D1, is the proliferative driver in hepatocarcinogenesis by immunoprecipitation experiments demonstrating preferential binding of p21 to cyclin D1, allowing cyclin E-mediated "escape" from G1/S checkpoint. We then showed cyclin E was responsible for regulating wild-type p53 by knockdown experiments in primary HCC cells; cyclin E-knockdown increased p53 and p21, diminished anti-apoptotic Bcl-XL and reduced cell viability. Conversely, blocking p53 augmented cyclin E, Bcl-XL expression and increased proliferation. Physiological interactions between cyclin E/p53/p21 were confirmed in primary hepatocytes. miR-34a,c were upregulated in dysplastic murine, human liver and HCCs compared with normal liver, and appeared to be linked to cyclin E/p53.

CONCLUSION

Upregulation of functionally active cyclin E via miR34 with loss of p53 function is associated with cell-cycle checkpoint failure increasing proliferative drive that favors hepatocarcinogenesis.

Novel 1H-pyrrolo[2,3-b]pyridine derivative nortopsentin analogues: synthesis and antitumor activity in peritoneal mesothelioma experimental models

In this study, we describe the synthesis of new nortopsentin analogues, 1H-pyrrolo[2,3-b]pyridine derivatives and their biological effects in experimental models of diffuse malignant peritoneal mesothelioma (DMPM), a rare and rapidly fatal disease, poorly responsive to conventional therapies. The three most active compounds, 1f (3-[2-(5-fluoro-1-methyl-1H-indol-3-yl)-1,3-thiazol-4-yl]-1H-pyrrolo[2,3-b]pyridine), 3f (3-[2-(1H-indol-3-yl)-1,3-thiazol-4-yl]-1-methyl-1H-pyrrolo[2,3-b]pyridine), and 1l (3-[2-(5-fluoro-1-methyl-1H-indol-3-yl)-1,3-thiazol-4-yl]-1-methyl-1H-pyrrolo[2,3-b] pyridine), which were shown to act as cyclin-dependent kinase 1 inhibitors, consistently reduced DMPM cell proliferation and induced a caspase-dependent apoptotic response, with a concomitant reduction of the expression of the active Thr(34)-phosphorylated form of the antiapoptotic protein survivin. Moreover, the combined treatment of DMPM cells with 3f derivative and paclitaxel produced a synergistic cytotoxic effect, which was paralleled by an enhanced apoptotic response. In the mouse model, i.p. administration of 1f, 3f, and 1l derivatives was effective, resulting in a significant tumor volume inhibition of DMPM xenografts (range, 58-75%) at well-tolerated doses, and two complete responses were observed in each treatment group.

Deregulations in the cyclin-dependent kinase-9-related pathway in cancer: implications for drug discovery and development

The CDK9-related pathway is an important regulator of mammalian cell biology and is also involved in the replication cycle of several viruses, including the human immunodeficiency virus type 1. CDK9 is present in two isoforms termed CDK9-42 and CDK9-55 that bind noncovalently type T cyclins and cyclin K. This association forms a heterodimer, where CDK9 carries the enzymatic site and the cyclin partner functions as a regulatory subunit. This heterodimer is the main component of the positive transcription elongation factor b, which stabilizes RNA elongation via phosphorylation of the RNA pol II carboxyl terminal domain. Abnormal activities in the CDK9-related pathway were observed in human malignancies and cardiac hypertrophies. Thus, the elucidation of the CDK9 pathway deregulations may provide useful insights into the pathogenesis and progression of human malignancies, cardiac hypertrophy, AIDS and other viral-related maladies. These studies may lead to the improvement of kinase inhibitors for the treatment of the previously mentioned pathological conditions. This review describes the CDK9-related pathway deregulations in malignancies and the development of kinase inhibitors in cancer therapy, which can be classified into three categories: antagonists that block the ATP binding site of the catalytic domain, allosteric inhibitors, and small molecules that disrupt protein-protein interactions.

ATP-noncompetitive CDK inhibitors for cancer therapy: an overview

INTRODUCTION

Cyclin-dependent kinases (CDKs) are the key drivers of cell cycle progression and are often deregulated in cancer, therefore, targeting CDKs has long been pursued as a therapeutic strategy to tackle cancer. Unfortunately, however, none of the first-generation CDK inhibitors has yielded the expected efficacy to be successfully translated to the clinic mostly because, by targeting the very conserved kinase ATP-binding site resulted to be poorly specific and quite toxic.

AREAS COVERED

Here, the authors review recent approaches aimed at developing more specific CDK inhibitors mostly through the aid of computational drug design studies and report various small molecules and peptides, which resulted in promising CDK ATP-noncompetitive inhibitors.

EXPERT OPINION

Despite few successes, these new approaches still need additional considerations to generate effective antitumoral agents. The authors discuss some of the hurdles to overcome for a successful clinical translation.

Mammalian interphase cdks: dispensable master regulators of the cell cycle

Cyclin-dependent kinases (Cdks) drive cell cycle progression in all eukaryotes. Yeasts have a single major Cdk that mediates distinct cell cycle transitions via association with different cyclins. The closest homolog in mammals, Cdk1, drives mitosis. Mammals have additional Cdks-Cdk2, Cdk4, and Cdk6-that represent the major Cdks activated during interphase (iCdks). A large body of evidence has accrued that suggests that activation of iCdks dictates progression though interphase. In apparent contradiction, deficiency in each individual iCdk, respectively, in knockout mice proved to be compatible with live birth and in some instances fertility. Moreover, murine embryos could be derived with Cdk1 as the only functional Cdk. Thus, none of the iCdks is strictly essential for mammalian cell cycle progression, raising the possibility that Cdk1 is the dominant regulator in interphase. However, an absence of iCdks has been accompanied by major shifts in cyclin association to Cdk1, suggesting gain in function. After considerable tweaking, a chemical genetic approach has recently been able to examine the impact of acute inhibition of Cdk2 activity without marked distortion of cyclin/Cdk complex formation. The results suggest that, when expressed at its normal levels, Cdk2 performs essential roles in driving human cells into S phase and maintaining genomic stability. These new findings appear to have restored order to the cell cycle field, bringing it full circle to the view that iCdks indeed play important roles. They also underscore the caveat in knockdown and knockout approaches that protein underexpression can significantly perturb a protein interaction network. We discuss the implications of the new synthesis for future cell cycle studies and anti-Cdk-based therapy of cancer and other diseases.

Resolution of inflammation: mechanisms and opportunity for drug development

Inflammation is a beneficial host reaction to tissue damage and has the essential primary purpose of restoring tissue homeostasis. Inflammation plays a major role in containing and resolving infection and may also occur under sterile conditions. The cardinal signs of inflammation dolor, calor, tumor and rubor are intrinsically associated with events including vasodilatation, edema and leukocyte trafficking into the site of inflammation. If uncontrolled or unresolved, inflammation itself can lead to further tissue damage and give rise to chronic inflammatory diseases and autoimmunity with eventual loss of organ function. It is now evident that the resolution of inflammation is an active continuous process that occurs during an acute inflammatory episode. Successful resolution requires activation of endogenous programs with switch from production of pro-inflammatory towards pro-resolving molecules, such as specific lipid mediators and annexin A1, and the non-phlogistic elimination of granulocytes by apoptosis with subsequent removal by surrounding macrophages. These processes ensure rapid restoration of tissue homeostasis. Here, we review recent advances in the understanding of resolution of inflammation, highlighting the pharmacological strategies that may interfere with the molecular pathways which control leukocyte survival and clearance. Such strategies have proved beneficial in several pre-clinical models of inflammatory diseases, suggesting that pharmacological modulation of the resolution process may be useful for the treatment of chronic inflammatory diseases in humans.

Targeting cell cycle kinases and kinesins in anticancer drug development

The cell cycle is regulated by kinases such as the cyclin-dependent kinases (CDKs) and non-CDKs, which include Aurora and polo-like kinases, as well as checkpoint proteins. Mitotic kinesins are involved in the establishment of the mitotic spindle formation and function, and also play a role in cell cycle control. The disruption of the cell cycle is a hallmark of malignancy. Genetic or epigenetic events result in the upregulation of these kinases and mitotic kinesins in a myriad of tumour types, suggesting that their inhibition could result in preferential targeting of malignant cells. Such findings make the development of these inhibitors a rational and attractive new area for cancer therapeutics. Although challenges of potency and non-specificity have hampered their progress through the clinic, several novel compounds are presently in various phases of clinical trial evaluation.

Effects of Auraptene on IGF-1 Stimulated Cell Cycle Progression in the Human Breast Cancer Cell Line, MCF-7

Auraptene is being investigated for its chemopreventive effects in many models of cancer including skin, colon, prostate, and breast. Many mechanisms of action including anti-inflammatory, antiproliferative, and antiapoptotic effects are being suggested for the chemopreventive properties of auraptene. We have previously shown in the N-methylnitrosourea induced mammary carcinogenesis model that dietary auraptene (500 ppm) significantly delayed tumor latency. The delay in time to tumor corresponded with a significant reduction in cyclin D1 protein expression in the tumors. Since cyclin D1 is a major regulator of cell cycle, we further studied the effects of auraptene on cell cycle and the genes related to cell cycle in MCF-7 cells. Here we show that auraptene significantly inhibited IGF-1 stimulated S phase of cell cycle in MCF-7 cells and significantly changed the transcription of many genes involved in cell cycle.

Phase I and pharmacologic trial of cytosine arabinoside with the selective checkpoint 1 inhibitor Sch 900776 in refractory acute leukemias

PURPOSE

Incorporation of cytarabine into DNA activates checkpoint kinase 1 (Chk1), which stabilizes stalled replication forks, induces S-phase slowing, and diminishes cytarabine cytotoxicity. The selective Chk1 inhibitor SCH 900776 abrogates cytarabine-induced S-phase arrest and enhances cytarabine cytotoxicity in acute leukemia cell lines and leukemic blasts in vitro. To extend these findings to the clinical setting, we have conducted a phase I study of cytarabine and SCH 900776.

EXPERIMENTAL DESIGN

Twenty-four adults with relapsed and refractory acute leukemias received timed sequential, continuous infusion cytarabine 2 g/m(2) over 72 hours (667 mg/m(2)/24 hours) beginning on day 1 and again on day 10. SCH 900776 was administered as a 15- to 30-minute infusion on days 2, 3, 11, and 12. The starting dose of SCH 900776 was 10 mg/m(2)/dose.

RESULTS

Dose-limiting toxicities consisting of corrected QT interval prolongation and grade 3 palmar-plantar erythrodysesthesia occurred at 140 mg flat dosing (dose level 5, equivalent to 80 mg/m(2)). Complete remissions occurred in 8 of 24 (33%) patients, with 7 of 8 at 40 mg/m(2) or higher. SCH 900776 did not accumulate at any dose level. Marrow blasts obtained pretreatment and during therapy showed increased phosphorylation of H2Ax after SCH 900776 beginning at 40 mg/m(2), consistent with unrepaired DNA damage.

CONCLUSIONS

These data support a randomized phase II trial of cytarabine +/- SCH 900776 at a recommended flat dose of 100 mg (equivalent to 56 mg/m(2)) for adults with poor-risk leukemias. The trial (SP P05247) was registered at www.clinicaltrials.gov as NCT00907517.

The histone demethylase JMJD2B plays an essential role in human carcinogenesis through positive regulation of cyclin-dependent kinase 6

Histone methyltransferases and demethylases are known to regulate transcription by altering the epigenetic marks on histones, but the pathologic roles of their dysfunction in human diseases, such as cancer, still remain to be elucidated. Herein, we show that the histone demethylase JMJD2B is involved in human carcinogenesis. Quantitative real-time PCR showed notably elevated levels of JMJD2B expression in bladder cancers, compared with corresponding nonneoplastic tissues (P < 0.0001), and elevated protein expression was confirmed by immunohistochemistry. In addition, cDNA microarray analysis revealed transactivation of JMJD2B in lung cancer, and immunohistochemical analysis showed protein overexpression in lung cancer. siRNA-mediated reduction of expression of JMJD2B in bladder and lung cancer cell lines significantly suppressed the proliferation of cancer cells, and suppressing JMJD2B expression lead to a decreased population of cancer cells in S phase, with a concomitant increase of cells in G(1) phase. Furthermore, a clonogenicity assay showed that the demethylase activity of JMJD2B possesses an oncogenic activity. Microarray analysis after knockdown of JMJD2B revealed that JMJD2B could regulate multiple pathways which contribute to carcinogenesis, including the cell-cycle pathway. Of the downstream genes, chromatin immunoprecipitation showed that CDK6 (cyclin-dependent kinase 6), essential in G(1)-S transition, was directly regulated by JMJD2B, via demethylation of histone H3-K9 in its promoter region. Expression levels of JMJD2B and CDK6 were significantly correlated in various types of cell lines. Deregulation of histone demethylation resulting in perturbation of the cell cycle, represents a novel mechanism for human carcinogenesis and JMJD2B is a feasible molecular target for anticancer therapy.

Organometallic 3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines as potential anticancer agents

Six organometallic complexes of the general formula [M^IICl(η⁶-p-cymene)(L)]Cl, where M = Ru (11a, 12a, 13a) or Os (11b, 12b, 13b) and L = 3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines (L1–L3) have been synthesized. The latter are known as potential cyclin-dependent kinase (Cdk) inhibitors. All compounds have been comprehensively characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, UV–vis spectroscopy, ESI mass spectrometry, and X-ray crystallography (11b and 12b). The multistep synthesis of 3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines (L1–L3), which was reported by other researchers, has been modified by us essentially (e.g., the synthesis of 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylic acid (3) via 5-bromo-3-methyl-1H-pyrazolo[3,4-b]pyridine (2); the synthesis of 1-methoxymethyl-2,3-diaminobenzene (5) by avoiding the use of unstable 2,3-diaminobenzyl alcohol; and the activation of 1H-pyrazolo[3,4-b]pyridine-3-carboxylic acids (1, 3) through the use of an inexpensive coupling reagent, N,N′-carbonyldiimidazole (CDI)). Stabilization of the 7b tautomer of methoxymethyl-substituted L3 by coordination to a metal(II) center, as well as the NMR spectroscopic characterization of two tautomers 7b-L3 and 4b′-L3 in a metal-free state are described. Structure–activity relationships with regard to cytotoxicity and cell cycle effects in human cancer cells, as well as Cdk inhibitory activity, are also reported.

Three organic compounds L1−L3, known as potential Cdk inhibitors, and six novel complexes of the general formula [M^IICl(η⁶-p-cymene)(L)]Cl, where M = Ru (11a, 12a, 13a) or Os (11b, 12b, 13b) and L = L1−L3, correspondingly, have been synthesized and comprehensively characterized by elemental analysis, ESI mass-spectrometry, spectroscopic and X-ray diffraction methods. Structure−activity relationships, with regard to cytotoxicity and cell cycle effects, in human cancer cells, as well as Cdk inhibitory activity, are reported.

Interference with ER-α enhances the therapeutic efficacy of the selective CDK inhibitor roscovitine towards ER-positive breast cancer cells

In recent years many risk factors for the development of breast cancer that are linked to estrogens have been identified, and roscovitine (ROSC), a selective cyclin-dependent kinase (CDK) inhibitor, has been shown to be an efficient inhibitor of the proliferation of human breast cancer cells. Therefore, we have examined the possibility that interference with estrogen signaling pathways, using tamoxifen (TAM), a selective estrogen receptor modulator (SERM), could modulate the efficacy of treatment with ROSC. In conjunction with TAM, ROSC exhibited enhanced anti-proliferative activity and CDK inhibition, particularly in estrogen-dependent MCF-7 cells. The interaction between both drugs was synergistic. However, in ER-α-negative cells the interaction was antagonistic. Exposure of MCF-7 cells to ROSC abolished the activating phosphorylation of CDK2 and CDK7 at Ser(164/170). This in turn prevented the phosphorylation of the carboxyl-terminal repeat domain of RNA Polymerase II and ER-α at Ser(118), resulting in the down-regulation of the latter. Concomitantly, wt p53 was strongly activated by phosphorylation at Ser(46). Our results demonstrate that ROSC negatively affects the functional status of ER-α, making it potentially useful in the treatment of estrogen-dependent breast cancer cells.

Ibulocydine is a novel prodrug Cdk inhibitor that effectively induces apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is frequently associated with abnormalities in cell cycle regulation, leading to increased activity of cyclin-dependent kinases (Cdks) due to the loss, or low expression of, Cdk inhibitors. In this study, we showed that ibulocydine (an isobutyrate prodrug of the specific Cdk inhibitor, BMK-Y101) is a candidate anti-cancer drug for HCC. Ibulocydine has high activity against Cdk7/cyclin H/Mat1 and Cdk9/cyclin T. Ibulocydine inhibited the growth of HCC cells more effectively than other Cdk inhibitors, including olomoucine and roscovitine, whereas ibulocydine as well as the other Cdk inhibitors and BMK-Y101 minimally influenced the growth of normal hepatocyte cells. Ibulocydine induced apoptosis in HCC cells, most likely by inhibiting Cdk7 and Cdk9. In vitro treatment of HCC cells with ibulocydine rapidly blocked phosphorylation of the carboxyl-terminal domain (CTD) of the large subunit of RNA polymerase II, a process mediated by Cdk7/9. Anti-apoptotic gene products such as Mcl-1, survivin, and X-linked IAP (XIAP) are crucial for the survival of many cell types, including HCC. Following the inhibition of RNA polymerase II phosphorylation, ibulocydine caused rapid down-regulation of Mcl-1, survivin, and XIAP, thus inducing apoptosis. Furthermore, ibulocydine effectively induced apoptosis in HCC xenografts with no toxic side effects. These results suggest that ibulocydine is a strong candidate anti-cancer drug for the treatment of HCC.

The hallmarks of CDKN1C (p57, KIP2) in cancer

Cyclin-dependent kinase inhibitor 1C CDKN1C (p57(KIP2)) regulates several hallmarks of cancer, including apoptosis, cell invasion and metastasis, tumor differentiation and angiogenesis. p57(KIP2) is generally not mutated in cancer, but its expression is downregulated through epigenetic changes such as DNA methylation and repressive histone marks at the promoter. This opens up possibilities for therapeutic intervention through reactivation of p57(KIP2) gene expression. Furthermore, p57(KIP2) has been tested as a prognostic factor for many types of cancer, even differentiating between early and late stage cancer. In this review, the multifunctional tumor suppressor capabilities of p57(KIP2), the mechanisms of p57(KIP2) transcriptional repression in cancer, and the therapeutic potential of reactivation of p57(KIP2) protein expression will be discussed.

Novel agents for diffuse large B-cell lymphoma

INTRODUCTION

Although diffuse large B-cell lymphoma (DLBCL) is commonly considered as a cancer with a high cure rate with conventional therapies recent studies demonstrate that different biological variants of DBLCL exist, and that patients with one DLBCL variant and DLBCL patients who relapse early following rituximab-based therapy have markedly poorer outcomes with conventional management strategies. Over the last decade, there has been an increasing exploration of novel therapies derived from improved understanding of DLBCL biology and tumor-host interactions.

AREAS COVERED

This review examines the biological basis for novel therapeutic approaches in DLBCL and the early clinical data on compounds derived from this research. A description of the expanding options of novel agents and combination therapies for patients with poor risk DLBCL is provided.

EXPERT OPINION

Several promising novel agents and novel therapeutic combinations are under development for patients with poor risk DLBCL. Carefully designed clinical trials that build on our improved understanding of DLBCL biology and utilize tissue samples to examine the activity of novel combination therapies should expand treatment options for DLBCL patients in the future.

Fluorescent cyclin-dependent kinase inhibitors block the proliferation of human breast cancer cells

Inhibitors of cyclin-dependent kinases (CDKs) are an emerging class of drugs for the treatment of cancers. CDK inhibitors are currently under evaluation in clinical trials as single agents and as sensitizers in combination with radiation therapy and chemotherapies. Drugs that target CDKs could have important inhibitory effects on cancer cell cycle progression, an extremely important mechanism in the control of cancer cell growth. Using rational drug design, we designed and synthesized fluorescent CDK inhibitors (VMY-1-101 and VMY-1-103) based on a purvalanol B scaffold. The new agents demonstrated more potent CDK inhibitory activity, enhanced induction of G2/M arrest and modest apoptosis as compared to purvalanol B. Intracellular imaging of the CDK inhibitor distribution was performed to reveal drug retention in the cytoplasm of treated breast cancer cells. In human breast cancer tissue, the compounds demonstrated increased binding as compared to the fluorophore. The new fluorescent CDK inhibitors showed undiminished activity in multidrug resistance (MDR) positive breast cancer cells, indicating that they are not a substrate for p-glycoprotein. Fluorescent CDK inhibitors offer potential as novel theranostic agents, combining therapeutic and diagnostic properties in the same molecule.

A bioinformatical and functional approach to identify novel strategies for chemoprevention of colorectal cancer

Comparing normal colorectal mucosa and adenomas focusing on deregulated pathways obtains insight into the biological processes of early colorectal carcinogenesis. Publicly available microarray expression data from 26 normal mucosa and 47 adenoma samples were analyzed. Biological pathways enriched in adenomas were identified with Gene Set Enrichment Analysis (GSEA). The analysis revealed 10, 11 and 16 gene sets distinguishing adenomas from normal mucosa according to Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Map Annotator and Pathway Profiler (GenMAPP) and Biocarta databases, respectively. Biological pathways known to be involved in colon carcinogenesis such as cell cycle (P=0.002) and Wnt signaling (P=0.007) were enriched in adenomas. In addition, we found enrichment of novel pathways such as retinoblastoma (Rb) pathway (P=0.002), Src pathway (P=0.004), folate biosynthesis (P=0.019) and Hedgehog signaling (P=0.037) in adenomas. Microarray results for Rb and Src pathway genes were validated by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) on mRNA isolated from an independent set of adenoma and normal colon samples. A high correlation between microarray data and qRT-PCR expression data was found. The relevance of targeting of identified pathways was shown using the Rb pathway inhibitors roscovitine and PD-0332991 and the Src pathway inhibitor dasatinib. All inhibitors used induced cell growth reduction in adenoma cells. This study shows a bioinformatical and functional approach leading to potentially new options for chemoprevention of colorectal cancer.

Effects of an Indolocarbazole-Derived CDK4 Inhibitor on Breast Cancer Cells

Introduction: Cyclin D1 (D1) binds to cyclin-dependent kinases (CDK) 4 or 6 to form a holoenzyme that phosphorylates the Rb protein to promote cell cycle progression from G1 to S phase. Therefore, targeting CDK4/6 may be a good strategy for chemotherapy of cancer. We performed a proof-of-principle study to determine the effect of Naphtho [2, 1-α] pyrrolo [3, 4-c] carbazole-5, 7 (6H, 12H)-dione (NPCD), a novel CDK4 inhibitor, on breast cancer cell lines.

Methods: NPCD was synthesized and purified to over 99% purity verified by HPLC. MCF7, MB231, MCF15, T47D and GI101Ap human breast cancer cells were analyzed for the efficacy of NPCD with MTT and clonogenic assays, with FACS and staining for ethidium bromide and acridine orange for cell death and cell cycle profile. Western blot, reverse transcription and PCR were used for studies of gene expression, and co-immunoprecipitation for protein-complex formation.

Results: MTT assay showed that NPCD caused growth arrest and apoptosis of MCF7, MDA-MB231, T47D, MCF15 and GI101Ap cells with an IC50 ranging between 3 to 8 µM given as a single dose. The growth arrest persisted for many days after cessation of the treatment, as shown in a clonogenic assay. NPCD could induce or reduce the D1 and CDK4 protein levels, depending on the cell line, but this effect was not correlated with its efficacy. Phosphorylation of D1 at Thr286 was decreased but it unexpectedly did not correlate with the change in D1 level in the cell lines studied. Phosphorylation of the Rb protein was decreased as expected whereas the p27kip1 protein level was decreased unexpectedly. Protein levels of p21cip1, CDK2 and cyclin E were also decreased in some, but not all, of the cell lines, whereas the mRNA levels of D1, CDK4, cyclin E, CDK2, p27kip1 and p21cip1 were increased in different cell lines.

Conclusions: NPCD can cause long-lasting growth arrest and cell death of breast cancer cell lines at an IC50 of 3-8 µM. Decreased phosphorylation of Rb by D1-CDK4/6 and decreased p27kip1 protein level may be part of the underlying mechanism.

Role of the growth hormone-IGF-1 axis in cancer

A substantial body of evidence supports a role for the growth hormone (GH)-IGF-1 axis in cancer incidence and progression. This includes epidemiological evidence relating elevated plasma IGF-1 to cancer incidence as well as a lack of cancers in GH/IGF-1 deficiency. Rodent models lacking GH or its receptor are strikingly resistant to the induction of a wide range of cancers, and treatment with the GH antagonist pegvisomant slows tumor progression. While GH receptor expression is elevated in many cancers, autocrine GH is present in several types, and overexpression of autocrine GH can induce cell transformation. While the mechanism of autocrine action is not clear, it does involve both STAT5 and STAT3 activation, and probably nuclear translocation of the GH receptor. Development of a more potent GH receptor antagonist or secretion inhibitor is warranted for cancer therapy.

Design, synthesis, and testing of an 6-O-linked series of benzimidazole based inhibitors of CDK5/p25

Alzheimer's disease (AD) is a progressive neurodegenerative disease resulting in cognitive and behavioral impairment. The two classic pathological hallmarks of AD include extraneuronal deposition of amyloid β (Aβ) and intraneuronal formation of neurofibrillary tangles (NFTs). NFTs contain hyperphosphorylated tau. Tau is the major microtubule-associated protein in neurons and stabilizes microtubules (MTs). Cyclin dependent kinase 5 (CDK5), when activated by the regulatory binding protein p25, phosphorylates tau at a number of proline-directed serine/threonine residues, resulting in formation of phosphorylated tau as paired helical filaments (PHFs) then in subsequent deposition of PHFs as NFTs. Beginning with the structure of Roscovitine, a moderately selective CDK5 inhibitor, we sought to conduct structural modifications to increase inhibitory potency of CDK5 and increase selectivity over a similar enzyme, cyclin dependent kinase 2 (CDK2). The design, synthesis, and testing of a series of 1-isopropyl-4-aminobenzyl-6-ether-linked benzimidazoles is presented.

Cyclin T1 overexpression induces malignant transformation and tumor growth

Human PTE Fb is a protein kinase composed by CDK9 and Cyclin T that controls the elongation phase of RNA Pol II. This complex also affects the activation and differentiation program of lymphoid cells. In this study we found that several head and neck tumor cell lines overexpress PTE Fb. We also established that Cyclin T1 is able to induce transformation in vitro, as we determined by foci and colony formation assays. Nu/nu mice s.c. injected with stable transfected Cyclin T1 cells (NIH 3T3 Cyclin T1) developed tumors faster than animals injected with control cells (NIH 3T3 beta-gal). In vitro, NIH 3T3 Cyclin T1 cells show increased proliferation and CDK4-Rb phosphorylation. Even more, silencing E2F1 expression (shRNA E2F1) in NIH 3T3 cells resulted in a dramatic inhibition of Cyclin T1-induced foci. All these data demonstrate for the first time the Cyclin T1 oncogenic function and suggest a role for this protein in controlling cell cycle probably via Rb/E2F1 pathway.