Potent inhibition of CDC2 kinase activity by the flavonoid L86-8275

CDK4/6 Inhibitors in Pancreatobiliary Cancers: Opportunities and Challenges

Existing treatment strategies for pancreatobiliary malignancies are limited. Nowadays, surgery is the only path to cure these types of cancer, but only a small number of patients present with resectable tumors at the time of diagnosis. The notoriously poor prognosis, lack of diverse treatment options associated with pancreaticobiliary cancers, and their resistance to current therapies reflect the urge for the development of novel therapeutic targets. Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have emerged as an attractive therapeutic strategy in a number of cancers since their approval for treatment in patients with ER+/HER- breast cancer in combination with antiestrogens. In this article, we discuss the therapeutic potential of CDK4/6 inhibitors in pancreatobiliary cancers, notably cholangiocarcinoma and pancreatic ductal adenocarcinoma.

CDK regulators—Cell cycle progression or apoptosis—Scenarios in normal cells and cancerous cells

Serine/threonine kinases called cyclin-dependent kinases (CDKs) interact with cyclins and CDK inhibitors (CKIs) to control the catalytic activity. CDKs are essential controllers of RNA transcription and cell cycle advancement. The ubiquitous overactivity of the cell cycle CDKs is caused by a number of genetic and epigenetic processes in human cancer, and their suppression can result in both cell cycle arrest and apoptosis. This review focused on CDKs, describing their kinase activity, their role in phosphorylation inhibition, and CDK inhibitory proteins (CIP/KIP, INK 4, RPIC). We next compared the role of different CDKs, mainly p21, p27, p57, p16, p15, p18, and p19, in the cell cycle and apoptosis in cancer cells with respect to normal cells. The current work also draws attention to the use of CDKIs as therapeutics, overcoming the pharmacokinetic barriers of pan-CDK inhibitors, analyze new chemical classes that are effective at attacking the CDKs that control the cell cycle (cdk4/6 or cdk2). It also discusses CDKI's drawbacks and its combination therapy against cancer patients. These findings collectively demonstrate the complexity of cancer cell cycles and the need for targeted therapeutic intervention. In order to slow the progression of the disease or enhance clinical outcomes, new medicines may be discovered by researching the relationship between cell death and cell proliferation.

Targeting CDK4 and CDK6 in cancer

Cyclin-dependent kinase 4 (CDK4) and CDK6 are critical mediators of cellular transition into S phase and are important for the initiation, growth and survival of many cancer types. Pharmacological inhibitors of CDK4/6 have rapidly become a new standard of care for patients with advanced hormone receptor-positive breast cancer. As expected, CDK4/6 inhibitors arrest sensitive tumour cells in the G1 phase of the cell cycle. However, the effects of CDK4/6 inhibition are far more wide-reaching. New insights into their mechanisms of action have triggered identification of new therapeutic opportunities, including the development of novel combination regimens, expanded application to a broader range of cancers and use as supportive care to ameliorate the toxic effects of other therapies. Exploring these new opportunities in the clinic is an urgent priority, which in many cases has not been adequately addressed. Here, we provide a framework for conceptualizing the activity of CDK4/6 inhibitors in cancer and explain how this framework might shape the future clinical development of these agents. We also discuss the biological underpinnings of CDK4/6 inhibitor resistance, an increasingly common challenge in clinical oncology.

A review on breast cancer in Iraq and future therapies insights

Cancer is one of the most common diseases around the world and the second leading cause of death after cardiovascular disease. Breast cancer is the most prevalent cancer type among Iraqi women, as it represents the highest percentage of malignant tumors in women until 2018. Therefore, women should be aware of the aggravation of this disease, the importance of the periodic examination for early detection for breast cancer, and following the most appropriate means for the treatment to get recovered and, thus, to reduce mortality. To fight cancer, there is an urgent need to search for new effective anticancer therapies that alter the molecular biology of tumor cells, stimulate the immune system, or specifically deliver chemotherapy factors directly to cancer cells without affecting normal cells and reducing the side effects of treatments. In this context, this paper aimed to highlight the therapeutic approaches used in the current researches of breast cancer treatment. Accumulated evidence showed that medicinal plant extracts, and can serve as anticancer agents. The proposed mechanisms were discussed and presented in this review.

Activation of Smad2/3 signaling by low fluid shear stress mediates artery inward remodeling

Endothelial cell (EC) sensing of wall fluid shear stress (FSS) from blood flow governs vessel remodeling to maintain FSS at a specific magnitude or set point in healthy vessels. Low FSS triggers inward remodeling to restore normal FSS but the regulatory mechanisms are unknown. In this paper, we describe the signaling network that governs inward artery remodeling. FSS induces Smad2/3 phosphorylation through the type I transforming growth factor (TGF)-β family receptor Alk5 and the transmembrane protein Neuropilin-1, which together increase sensitivity to circulating bone morphogenetic protein (BMP)-9. Smad2/3 nuclear translocation and target gene expression but not phosphorylation are maximal at low FSS and suppressed at physiological high shear. Reducing flow by carotid ligation in rodents increases Smad2/3 nuclear localization, while the resultant inward remodeling is blocked by the EC-specific deletion of Alk5. The flow-activated MEKK3/Klf2 pathway mediates the suppression of Smad2/3 nuclear translocation at high FSS, mainly through the cyclin-dependent kinase (CDK)-2-dependent phosphosphorylation of the Smad linker region. Thus, low FSS activates Smad2/3, while higher FSS blocks nuclear translocation to induce inward artery remodeling, specifically at low FSS. These results are likely relevant to inward remodeling in atherosclerotic vessels, in which Smad2/3 is activated through TGF-β signaling.

Naturally Sourced CDK Inhibitors and Current Trends in Structure-Based Synthetic Anticancer Drug Design by Crystallography

Cyclin-dependent kinases (CDKs) are the chief regulators in cell proliferation; the kinase activities are largely regulated by their interactions with CDK inhibitors (CKIs) and Cyclins. The association of different CDKs with CDKIs and Cyclins at the cell-cycle checkpoints of different stages of mitotic cell cycle function act more likely as the molecular switches that regulate different transcriptional events required for progression through the cell cycle. A fine balance in response to extracellular and intracellular signals is highly maintained in the orchestrated function of CDKs along with Cyclins and CDKIs for normal cell proliferation. This fine-tuning in mitotic cell cycle progression sometimes gets lost due to dysregulation of CDKs. The aberrant functioning of the CDKIs is therefore studied for its contributions as a vital hallmark of cancers. It has attracted our focus to maneuver cancer therapy. Hence, several synthetic CDKIs and their crystallography-based drug design have been explained to understand their mode of action with CDKs. Since most of the synthetic drugs function by inhibiting the CDK4/6 kinases by competitively binding to their ATP binding cleft, these synthetic drugs are reported to attack the normal, healthy growing cells adjacent to the cancer cells leading to the decrease in the life span of the cancer patients. The quest for traditional natural medicines may have a great impact on the treatment of cancer. Therefore, in the present studies, a search for naturally sourced CDK inhibitors has been briefly focused. Additionally, some synthetic crystallography-based drug design has been explained to elucidate different avenues to develop better anticancer chemotherapeutics, converting natural scaffolds into inhibitors of the CDK mediated abnormal signal transduction with lesser side effects.

Discovery of New Coumarin-Based Lead with Potential Anticancer, CDK4 Inhibition and Selective Radiotheranostic Effect: Synthesis, 2D & 3D QSAR, Molecular Dynamics, In Vitro Cytotoxicity, Radioiodination, and Biodistribution Studies

Novel 6-bromo-coumarin-ethylidene-hydrazonyl-thiazolyl and 6-bromo-coumarin-thiazolyl-based derivatives were synthesized. A quantitative structure activity relationship (QSAR) model with high predictive power r² = 0.92, and RMSE = 0.44 predicted five compounds; 2b, 3b, 5a, 9a and 9i to have potential anticancer activities. Compound 2b achieved the best ΔG of –15.34 kcal/mol with an affinity of 40.05 pki. In a molecular dynamic study 2b showed an equilibrium at 0.8 Å after 3.5 ns, while flavopiridol did so at 0.5 Å after the same time (3.5 ns). 2b showed an IC₅₀ of 0.0136 µM, 0.015 µM, and 0.054 µM against MCF-7, A-549, and CHO-K1 cell lines, respectively. The CDK4 enzyme assay revealed the significant CDK4 inhibitory activity of compound 2b with IC₅₀ of 0.036 µM. The selectivity of the newly discovered lead compound 2b toward localization in tumor cells was confirmed by a radioiodination biological assay that was done via electrophilic substitution reaction utilizing the oxidative effect of chloramine-t. ¹³¹I-2b showed good in vitro stability up to 4 h. In solid tumor bearing mice, the values of tumor uptake reached a height of 5.97 ± 0.82%ID/g at 60 min p.i. ¹³¹I-2b can be considered as a selective radiotheranostic agent for solid tumors with promising anticancer activity.

Development and characterization of a novel flavopiridol formulation for treatment of acute myeloid leukemia

For more than 30 years, treatment of acute myeloid leukemia (AML) has remained largely unchanged and reliant on chemotherapeutic drug combinations, specifically cytarabine and daunorubicin (the 7 + 3 regimen). One broad spectrum drug, flavopiridol (also known as Alvocidib) has shown significant activity against AML through the inhibition of cyclin-dependent kinases. Flavopiridol is a semisynthetic flavonoid and our research team recently described methods to formulate another flavonoid, quercetin, through the ability of flavonoids to bind divalent metals. This method relies on use of copper-containing liposomes to enhance the apparent solubility of flavopiridol and to create formulations suitable for intravenous (i.v.) use. Similar to quercetin, flavopiridol is defined as an aqueous-insoluble compound (< 1 mg/mL in water) and this research sought to evaluate whether the copper-binding capabilities of flavopiridol could be used to prepare an injectable formulation that would exhibit enhanced exposure and improved efficacy. Flavopiridol powder was added directly to preformed copper-containing liposomes (DSPC:Chol or DSPC:DSPE-PEG2000) and the resulting formulations were characterized. Pharmacokinetic and efficacy studies were then conducted. The liposomal flavopiridol formulations were well-tolerated in mice following i.v. administration at a dose of 5 mg/kg with no apparent acute or chronic toxicities. In vivo pharmacokinetics of the optimized DSPC/DSPE-PEG2000 liposomal flavopiridol formulation demonstrated a 30-fold increase in AUC (0.804 μg-hr/mL versus 26.92 μg-hr/mL) compared to the free flavopiridol formulation. The resultant liposomal formulation also demonstrated significant therapeutic activity in MV4-11 and MOLM-13 subcutaneous AML models. Additional studies will be required to define whether formulation changes can be made to enhance flavopiridol retention in the selected composition. The results suggest that further increases in flavopiridol retention will result in improved therapeutic activity.

CDK7 inhibitors as anticancer drugs

Cyclin-dependent kinase 7 (CDK7), along with cyclin H and MAT1, forms the CDK-activating complex (CAK), which directs progression through the cell cycle via T-loop phosphorylation of cell cycle CDKs. CAK is also a component of the general transcription factor, TFIIH. CDK7-mediated phosphorylation of RNA polymerase II (Pol II) at active gene promoters permits transcription. Cell cycle dysregulation is an established hallmark of cancer, and aberrant control of transcriptional processes, through diverse mechanisms, is also common in many cancers. Furthermore, CDK7 levels are elevated in a number of cancer types and are associated with clinical outcomes, suggestive of greater dependence on CDK7 activity, compared with normal tissues. These findings identify CDK7 as a cancer therapeutic target, and several recent publications report selective CDK7 inhibitors (CDK7i) with activity against diverse cancer types. Preclinical studies have shown that CDK7i cause cell cycle arrest, apoptosis and repression of transcription, particularly of super-enhancer-associated genes in cancer, and have demonstrated their potential for overcoming resistance to cancer treatments. Moreover, combinations of CDK7i with other targeted cancer therapies, including BET inhibitors, BCL2 inhibitors and hormone therapies, have shown efficacy in model systems. Four CDK7i, ICEC0942 (CT7001), SY-1365, SY-5609 and LY3405105, have now progressed to Phase I/II clinical trials. Here we describe the work that has led to the development of selective CDK7i, the current status of the most advanced clinical candidates, and discuss their potential importance as cancer therapeutics, both as monotherapies and in combination settings. ClinicalTrials.gov Identifiers: NCT03363893; NCT03134638; NCT04247126; NCT03770494.

CDK9 activity is critical for maintaining MDM4 overexpression in tumor cells

The identification of the essential role of cyclin-dependent kinases (CDKs) in the control of cell division has prompted the development of small-molecule CDK inhibitors as anticancer drugs. For many of these compounds, the precise mechanism of action in individual tumor types remains unclear as they simultaneously target different classes of CDKs - enzymes controlling the cell cycle progression as well as CDKs involved in the regulation of transcription. CDK inhibitors are also capable of activating p53 tumor suppressor in tumor cells retaining wild-type p53 gene by modulating MDM2 levels and activity. In the current study, we link, for the first time, CDK activity to the overexpression of the MDM4 (MDMX) oncogene in cancer cells. Small-molecule drugs targeting the CDK9 kinase, dinaciclib, flavopiridol, roscovitine, AT-7519, SNS-032, and DRB, diminished MDM4 levels and activated p53 in A375 melanoma and MCF7 breast carcinoma cells with only a limited effect on MDM2. These results suggest that MDM4, rather than MDM2, could be the primary transcriptional target of pharmacological CDK inhibitors in the p53 pathway. CDK9 inhibitor atuveciclib downregulated MDM4 and enhanced p53 activity induced by nutlin-3a, an inhibitor of p53-MDM2 interaction, and synergized with nutlin-3a in killing A375 melanoma cells. Furthermore, we found that human pluripotent stem cell lines express significant levels of MDM4, which are also maintained by CDK9 activity. In summary, we show that CDK9 activity is essential for the maintenance of high levels of MDM4 in human cells, and drugs targeting CDK9 might restore p53 tumor suppressor function in malignancies overexpressing MDM4.

Cyclin-dependent kinase inhibitors in brain cancer: current state and future directions

Cyclin-dependent kinases (CDKs) are important regulatory enzymes in the normal physiological processes that drive cell-cycle transitions and regulate transcription. Virtually all cancers harbour genomic alterations that lead to the constitutive activation of CDKs, resulting in the proliferation of cancer cells. CDK inhibitors (CKIs) are currently in clinical use for the treatment of breast cancer, combined with endocrine therapy. In this review, we describe the potential of CKIs for the treatment of cancer with specific focus on glioblastoma (GBM), the most common and aggressive primary brain tumour in adults. Despite intense effort to combat GBM with surgery, radiation and temozolomide chemotherapy, the median survival for patients is 15 months and the majority of patients experience disease recurrence within 6-8 months of treatment onset. Novel therapeutic approaches are urgently needed for both newly diagnosed and recurrent GBM patients. In this review, we summarise the current preclinical and clinical findings emphasising that CKIs could represent an exciting novel approach for GBM treatment.

The Exploration of Chirality for Improved Druggability within the Human Kinome

Chirality is important in drug discovery because stereoselective drugs can ameliorate therapeutic difficulties including adverse toxicity and poor pharmacokinetic profiles. The human kinome, a major druggable enzyme class has been exploited to treat a wide range of diseases. However, many kinase inhibitors are planar and overlap in chemical space, which leads to selectivity and toxicity issues. By exploring chirality within the kinome, a new iteration of kinase inhibitors is being developed to better utilize the three-dimensional nature of the kinase active site. Exploration into novel chemical space, in turn, will also improve drug solubility and pharmacokinetic profiles. This perspective explores the role of chirality to improve kinome druggability and will serve as a resource for pioneering kinase inhibitor development to address current therapeutic needs.

Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells

Empirical and anecdotal evidence have associated stress with accelerated hair greying (formation of unpigmented hairs)^1,2, but the scientific evidence linking the two is scant. Here, we report that acute stress leads to hair greying through fast depletion of melanocyte stem cells (MeSCs). Combining adrenalectomy, denervation, chemogenetics^3,4, cell ablation, and MeSC-specific adrenergic receptor knockout, we found that stress-induced MeSC loss is independent of immune attack or adrenal stress hormones. Rather, hair greying results from activation of the sympathetic nerves that innervate the MeSC niche. Upon stress, sympathetic nerve activation leads to burst release of the neurotransmitter norepinephrine, which drives quiescent MeSCs into rapid proliferation, followed by differentiation, migration, and permanent depletion from the niche. Transient suppression of MeSC proliferation prevents stress-induced hair greying. Our studies demonstrate that acute stress-induced neuronal activity can drive rapid and permanent loss of somatic stem cells, and illustrate an example in which somatic stem cell maintenance is directly influenced by the overall physiological state of the organism.

Using the Four-Cell C. elegans Embryo to Study Contractile Ring Dynamics During Cytokinesis

Cytokinesis is the process that completes cell division by partitioning the contents of the mother cell between the two daughter cells. It involves the highly regulated assembly and constriction of an actomyosin contractile ring, whose function is to pinch the mother cell in two. Research on the contractile ring has particularly focused on the signaling mechanisms that dictate when and where the ring is formed. In vivo studies of ring constriction are however scarce and its mechanistic understanding is therefore limited. Here we present several experimental approaches for monitoring ring constriction in vivo, using the four-cell C. elegans embryo as model. These approaches allow for the ring to be perturbed only after it forms and include the combination of live imaging with acute drug treatments, temperature-sensitive mutants and rapid temperature shifts, as well as laser microsurgery. In addition, we explain how to combine these with RNAi-mediated depletion of specific components of the cytokinetic machinery.

Evaluation of Pyrano[3,2 C] Quinoline Analogues as Anticancer Agents

Background:

Quinoline analogues exhibited diversified biological activities depending on the structure type. A number of natural products with pyrano[3,2-c]quinolone structural motifs and patented chromenes were reported as promising cytotoxic agents.

Objective:

The present study is aimed to evaluate a new series of pyrano[3,2-c]quinoline scaffolds derived from the fusion of bioactive quinolone pharmacophore with structurally diverse aryl substituted chromene for its cytotoxicity.

Methods:

A library of pyrano[3,2-c]quinoline analogues was prepared from one-pot multi component synthesis using various aromatic aldehydes, malononitrile and 2,4-dihydroxy-1-methylquinoline. The new synthetics were primarily screened for its cytotoxicity (IC50) against different human cancer cell lines in vitro. The promising synthetics were further evaluated in vitro for their potency against different kinase activity. The promising compounds were finally tested for their in vivo efficacy in SCID type mice HCT-116 tumor model.

Results:

The screening results revealed that compounds 4c, 4f, 4i and 4j showed promising activity in in vitro study. However, compound 4c was found to be the most potent candidate with 23% tumor growth inhibition in HCT-116 tumor mice model.

Conclusion:

The structure activity relationship suggested that 3-substitution on the aryl ring at C4 position of the pyrano[3,2 c]quinolone moiety seems to have an important position for cytotoxicity activity. However, 3- chloro substitution at C4 aryl ring showed a significant alteration of the bioactive conformer of the parent scaffold and outcome with compound 4c as the most potent candidate of the series.

Cyclin dependent kinase (CDK) inhibitors as anticancer drugs: Recent advances (2015-2019)

Sustained proliferative capacity and gene dysregulation are hallmarks of cancer. In mammalian cells, cyclin-dependent kinases (CDKs) control critical cell cycle checkpoints and key transcriptional events in response to extracellular and intracellular signals leading to proliferation. Significant clinical activity for the treatment of hormone receptor positive metastatic breast cancer has been demonstrated by palbociclib, ribociclib and abemaciclib, dual CDK4/6 inhibitors recently FDA-approved. SY-1365, a CDK7 inhibitor has shown initial encouraging data in phase I for solid tumors treatment. These results have rejuvenated the CDKs research field. This review provides an overview of relevant advances on CDK inhibitor research since 2015 to 2019, with special emphasis on transcriptional CDK inhibitors, new emerging strategies such as target protein degradation and compounds under clinical evaluation.

Recent Treatment Advances and the Role of Nanotechnology, Combination Products, and Immunotherapy in Changing the Therapeutic Landscape of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia that is becoming more prevalent particularly in the older (65 years of age or older) population. For decades, "7 + 3" remission induction therapy with cytarabine and an anthracycline, followed by consolidation therapy, has been the standard of care treatment for AML. This stagnancy in AML treatment has resulted in less than ideal treatment outcomes for AML patients, especially for elderly patients and those with unfavourable profiles. Over the past two years, six new therapeutic agents have received regulatory approval, suggesting that a number of obstacles to treating AML have been addressed and the treatment landscape for AML is finally changing. This review outlines the challenges and obstacles in treating AML and highlights the advances in AML treatment made in recent years, including Vyxeos®, midostaurin, gemtuzumab ozogamicin, and venetoclax, with particular emphasis on combination treatment strategies. We also discuss the potential utility of new combination products such as one that we call "EnFlaM", which comprises an encapsulated nanoformulation of flavopiridol and mitoxantrone. Finally, we provide a review on the immunotherapeutic landscape of AML, discussing yet another angle through which novel treatments can be designed to further improve treatment outcomes for AML patients.

Myeloid cell leukemia-1 dependence in acute myeloid leukemia: a novel approach to patient therapy

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults, affecting approximately 21,000 people annually (nearly 11,000 deaths) in the United States. B-cell lymphoma 2 (BCL-2) family proteins, notably myeloid cell leukemia-1 (MCL-1), have been associated with both the development and persistence of AML. MCL-1 is one of the predominant BCL-2 family members expressed in samples from patients with untreated AML. MCL-1 is a critical cell survival factor for cancer and contributes to chemotherapy resistance by directly affecting cell death pathways. Here, we review the role of MCL-1 in AML and the mechanisms by which the potent cyclin-dependent kinase 9 inhibitor alvocidib, through regulation of MCL-1, may serve as a rational therapeutic approach against the disease.

Flavopiridol's effects on metastasis in KRAS mutant lung adenocarcinoma cells

BACKGROUND

There is still no clinically approved agent for mutant KRAS, which is the most common alteration in non-small-cell lung cancer (NSCLC). Flavopiridol is a semisynthetic flavonoid that inhibits cell growth through cyclin-dependent kinases in G1/S or G2/M of the cell cycle and induces apoptosis. In this study, we evaluated its effect on cellular apoptosis, survival, and metastasis mechanisms on KRAS mutant A549, Calu-1, and H2009 cell lines.

METHODS

The cytotoxic effects of flavopiridol on NSCLC cells were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability test. The cells were treated with 200 and 400 nM flavopiridol, and, then, apoptosis, survival, and metastasis-related protein expressions were determined by Western blot analysis. The antimetastatic effects of flavopiridol were assessed by wound healing and Galectin-3 activity assay.

RESULTS

Flavopiridol drastically affected toxicity in all KRAS mutant NSCLC cells at nanomolar concentrations. Also, it could efficiently inhibit wound healing and Galectin-3 activity in all the cells tested. However, the metastasis-related protein expressions did not reflect these obvious effects on blotting. p-Erk was activated as a cellular survival mechanism to escape apoptosis in all the cells tested.

CONCLUSION

Although there are many mechanisms that still need to be elucidated, flavopiridol can be used as a metastasis inhibitor and an apoptosis inducer in KRAS mutant NSCLC.

Sensitization of prostate cancer to radiation therapy: Molecules and pathways to target

Radiation therapy is used to treat cancer by radiation-induced DNA damage. Despite the best efforts to eliminate cancer, some cancer cells survive irradiation, resulting in cancer progression or recurrence. Alteration in DNA damage repair pathways is common in cancers, resulting in modulation of their response to radiation. This article focuses on the recent findings about molecules and pathways that potentially can be targeted to sensitize prostate cancer cells to ionizing radiation, thereby achieving an improved therapeutic outcome.

The cyclin-dependent kinase inhibitor flavopiridol (alvocidib) inhibits metastasis of human osteosarcoma cells

Osteosarcoma is the most common primary malignant neoplasm of bone and typically occurs in children and young adults. As a highly metastatic malignancy, 15–20% of osteosarcoma patients are diagnosed after the tumor has already metastasized (typically to the lungs), which translates to 5-year survival rates of <40%. Here, we tested the effect of the cyclin-dependent kinase (CDK) inhibitor flavopiridol (alvocidib) in U2OS, SaOS-2, SJSA-1, and 143B osteosarcoma tumor cells in vitro and in vivo. Our results show that flavopiridol can drastically decrease survival in these osteosarcoma cell lines at nanomolar concentrations and induce mitotic catastrophe in p53-null osteosarcomas. We also performed transcriptome analysis (RNA-seq) of flavopiridol-treated osteosarcoma cells, which revealed significant changes in genes coding for proteins involved in cell-cell and cell-matrix adhesions, including cadherin 3 (CDH3) and 4 (CDH4). These transcriptional changes translated to a striking reduction in the ability of osteosarcoma cells to migrate and invade in vitro. Further, in vivo assessment of the effects of flavopiridol on osteosarcoma metastasis resulted in a significant reduction in the number of lung metastases in mice treated with flavopiridol at concentrations that are physiologically tolerable. This study suggests that flavopiridol, likely in combination with other cytotoxic chemotherapeutic agents, may be a promising drug for the treatment of osteosarcoma.

Small molecule tools in mitosis research

Mitosis belongs to the most appealing cellular processes. Yet, the highly dynamic and complex nature of mitosis represents a major challenge when it comes to the functional dissection of mitotic proteins. Due to their fast and often reversible mode of action, small molecules have proven themselves as invaluable tools to dissect mitotic processes. In this chapter, we provide a broad overview of available compounds affecting mitosis. We discuss the different application fields of small molecules and important aspects that have to be considered when using them. Finally, we provide two detailed protocols for the application of small molecules to study mitosis in tissue culture cells.

Review of Three New Agents that Target Angiogenesis, Matrix Metalloproteinases, and Cyclin-Dependent Kinases

Background

Many potential new antineoplastic agents are currently in various stages of clinical development. Three areas of drug development include antiangiogenic compounds, agents that inhibit matrix metalloproteinases, and agents that modulate cyclin-dependent kinases.

Methods

The authors reviewed the available data for endostatin, COL-3, and flavopiridol, each of which is being developed with one of the above-mentioned proposed mechanisms of action. These agents are among the first drugs to reach clinical testing that is focusing on these novel targets.

Results

Endostatin has finished preclinical testing and the first human trials are about to be initiated. COL-3 is in phase I testing in several locations. Phase I studies for flavopiridol have been completed and several phase II studies are underway. It is unknown at this point if any of these agents will provide clinical benefit to patients at doses that do not cause unacceptable toxicity.

Conclusions

These agents are currently at various stages of clinical testing. Albeit promising as potential modulators in molecular and biochemical pathways, continued research is needed into the toxicities and clinical usefulness of these agents.

Investigational drugs targeting cyclin-dependent kinases for the treatment of cancer: an update on recent findings (2013-2016)

INTRODUCTION

Cell cycle and gene transcription are under the control of cyclin-dependent kinases (CDKs), whose activity depends on the binding with cyclins. Deregulated CDK activities have been reported in a majority of human cancers, representing potential therapeutic targets.

AREAS COVERED

This review provides preclinical and clinical (phase I/II) updates of promising therapeutic compounds targeting CDKs published between 2013 and 2016 EXPERT OPINION: First generation pan-CDK inhibitors showed marked toxicity in clinical trials and most compounds were discontinued. Despite their failure was ascribed also to inadequate patient selection rules, novel pan-CDK inhibitors have entered clinical trials with still poorly defined selection strategies. The most interesting results have been obtained with dual CDK4/6 inhibitors and through a more accurate evaluation of predictive biomarkers, suggesting the usefulness of CDK inhibitors for personalized treatment. The increased knowledge on the roles of CDKs in cell cycle and gene transcription suggests to review also the anticancer potential of first generation CDK inhibitors by defining more appropriate rules for patients engagement. Recent findings has highlighted CDK8 as a novel target for cancer treatment. Indeed some biomarkers for CDK8 inhibition sensitivity have already been proposed. CDK8 inhibition is also supposed to prevent cancer metastasis.

In silico study of porphyrin-anthraquinone hybrids as CDK2 inhibitor

Cyclin-Dependent Kinases (CDKs) are known to play crucial roles in controlling cell cycle progression of eukaryotic cell and inhibition of their activity has long been considered as potential strategy in anti-cancer drug research. In the present work, a series of porphyrin-anthraquinone hybrids bearing meso-substituents, i.e. either pyridine or pyrazole rings were designed and computationally evaluated for their Cyclin Dependent Kinase-2 (CDK2) inhibitory activity using molecular docking, molecular dynamics simulation, and binding free energy calculation. The molecular docking simulation revealed that all six porphyrin hybrids were able to bind to ATP-binding site of CDK2 and interacted with key residues constituted the active cavity of CDK2, while molecular dynamics simulation indicated that all porphyrins bound to CDK2 were stable for 6ns. The binding free energies predicted by MM-PBSA method showed that most compounds exhibited higher affinity than that of native ligand (4-anilinoquinazoline, DTQ) and the affinity of mono-H₂PyP-AQ was about three times better than that of DTQ, indicating its potential to be advanced as a new CDK2 inhibitor.

Centrosome - a promising anti-cancer target

The centrosome, an organelle discovered >100 years ago, is the main microtubule-organizing center in mammalian organisms. The centrosome is composed of a pair of centrioles surrounded by the pericentriolar material (PMC) and plays a major role in the regulation of cell cycle transitions (G1-S, G2-M, and metaphase-anaphase), ensuring the normality of cell division. Hundreds of proteins found in the centrosome exert a variety of roles, including microtubule dynamics, nucleation, and kinetochore–microtubule attachments that allow correct chromosome alignment and segregation. Errors in these processes lead to structural (shape, size, number, position, and composition), functional (abnormal microtubule nucleation and disorganized spindles), and numerical (centrosome amplification [CA]) centrosome aberrations causing aneuploidy and genomic instability. Compelling data demonstrate that centrosomes are implicated in cancer, because there are important oncogenic and tumor suppressor proteins that are localized in this organelle and drive centrosome aberrations. Centrosome defects have been found in pre-neoplasias and tumors from breast, ovaries, prostate, head and neck, lung, liver, and bladder among many others. Several drugs/compounds against centrosomal proteins have shown promising results. Other drugs have higher toxicity with modest or no benefits, and there are more recently developed agents being tested in clinical trials. All of this emerging evidence suggests that targeting centrosome aberrations may be a future avenue for therapeutic intervention in cancer research.

Potential Use of Flavopiridol in Treatment of Chronic Diseases

This chapter describes the potential use of flavopiridol, a CDK inhibitor with anti-inflammatory and anti-proliferative activities, in the treatment of various chronic diseases. Flavopiridol arrests cell cycle progression in the G1 or G2 phase by inhibiting the kinase activities of CDK1, CDK2, CDK4/6, and CDK7. Additionally, it binds tightly to CDK9, a component of the P-TEFb complex (CDK9/cyclin T), and interferes with RNA polymerase II activation and associated transcription. This in turn inhibits expression of several pro-survival and anti-apoptotic genes, and enhances cytotoxicity in transformed cells or differentiation in growth-arrested cells. Recent studies indicate that flavopiridol elicits anti-inflammatory activity via CDK9 and NFκB-dependent signaling. Overall, these effects of flavopiridol potentiate its ability to overcome aberrant cell cycle activation and/or inflammatory stimuli, which are mediators of various chronic diseases.

Discovery of small molecule inhibitors of xyloglucan endotransglucosylase (XET) activity by high-throughput screening

Small molecules (xenobiotics) that inhibit cell-wall-localised enzymes are valuable for elucidating the enzymes' biological roles. We applied a high-throughput fluorescent dot-blot screen to search for inhibitors of Petroselinum xyloglucan endotransglucosylase (XET) activity in vitro. Of 4216 xenobiotics tested, with cellulose-bound xyloglucan as donor-substrate, 18 inhibited XET activity and 18 promoted it (especially anthraquinones and flavonoids). No compounds promoted XET in quantitative assays with (cellulose-free) soluble xyloglucan as substrate, suggesting that promotion was dependent on enzyme-cellulose interactions. With cellulose-free xyloglucan as substrate, we found 22 XET-inhibitors - especially compounds that generate singlet oxygen ((1)O2) e.g., riboflavin (IC50 29 μM), retinoic acid, eosin (IC50 27 μM) and erythrosin (IC50 36 μM). The riboflavin effect was light-dependent, supporting (1)O2 involvement. Other inhibitors included tannins, sulphydryl reagents and triphenylmethanes. Some inhibitors (vulpinic acid and brilliant blue G) were relatively specific to XET, affecting only two or three, respectively, of nine other wall-enzyme activities tested; others [e.g. (-)-epigallocatechin gallate and riboflavin] were non-specific. In vivo, out of eight XET-inhibitors bioassayed, erythrosin (1 μM) inhibited cell expansion in Rosa and Zea cell-suspension cultures, and 40 μM mycophenolic acid and (-)-epigallocatechin gallate inhibited Zea culture growth. Our work showcases a general high-throughput strategy for discovering wall-enzyme inhibitors, some being plant growth inhibitors potentially valuable as physiological tools or herbicide leads.

Cyclin dependent kinase (CDK) inhibitors as anticancer drugs

Sustained proliferative capacity is a hallmark of cancer. In mammalian cells proliferation is controlled by the cell cycle, where cyclin-dependent kinases (CDKs) regulate critical checkpoints. CDK4 and CDK6 are considered highly validated anticancer drug targets due to their essential role regulating cell cycle progression at the G1 restriction point. This review provides an overview of recent advances on cyclin dependent kinase inhibitors in general with special emphasis on CDK4 and CDK6 inhibitors and compounds under clinical evaluation. Chemical structures, structure activity relationships, and relevant preclinical properties will be described.

Final results of EFC6663: a multicenter, international, phase 2 study of alvocidib for patients with fludarabine-refractory chronic lymphocytic leukemia

Early phase studies of alvocidib showed activity in relapsed CLL including patients with high risk genomic features and those refractory to fludarabine. A multi-center, international, phase II study of alvocidib in fludarabine refractory CLL was undertaken to validate these early results. Patients with fludarabine refractory CLL or prolymphocytic leukemia arising from CLL were treated with single agent alvocidib. The primary outcome measure was overall response rate, with secondary outcomes including survival, toxicity, and response duration. One hundred and sixty five patients were enrolled and 159 patients were treated. The median age was 61 years, the median number of prior therapies was 4, and 96% of patients were fludarabine refractory. The investigator-assessed overall response rate was 25%; the majority of responses were partial. Response rates were lower among patients with del(17p) (14%), but equivalent in patients with del(11q) or bulky lymphadenopathy. Median progression free and overall survival were 7.6 and 14.6 months, respectively. Tumor lysis occurred in 39 patients (25%), and 13 received hemodialysis. Diarrhea, fatigue, and hematologic toxicities were common. Alvocidib has clinical activity in patients with advanced, fludarabine refractory CLL. Future studies should focus on discovery of biomarkers of clinical response and tumor lysis, and enhanced supportive care measures.

Targeting cyclin-dependent kinases in human cancers: from small molecules to Peptide inhibitors

Cyclin-dependent kinases (CDK/Cyclins) form a family of heterodimeric kinases that play central roles in regulation of cell cycle progression, transcription and other major biological processes including neuronal differentiation and metabolism. Constitutive or deregulated hyperactivity of these kinases due to amplification, overexpression or mutation of cyclins or CDK, contributes to proliferation of cancer cells, and aberrant activity of these kinases has been reported in a wide variety of human cancers. These kinases therefore constitute biomarkers of proliferation and attractive pharmacological targets for development of anticancer therapeutics. The structural features of several of these kinases have been elucidated and their molecular mechanisms of regulation characterized in depth, providing clues for development of drugs and inhibitors to disrupt their function. However, like most other kinases, they constitute a challenging class of therapeutic targets due to their highly conserved structural features and ATP-binding pocket. Notwithstanding, several classes of inhibitors have been discovered from natural sources, and small molecule derivatives have been synthesized through rational, structure-guided approaches or identified in high throughput screens. The larger part of these inhibitors target ATP pockets, but a growing number of peptides targeting protein/protein interfaces are being proposed, and a small number of compounds targeting allosteric sites have been reported.

Fluorescent biosensors for drug discovery new tools for old targets--screening for inhibitors of cyclin-dependent kinases

Cyclin-dependent kinases play central roles in regulation of cell cycle progression, transcriptional regulation and other major biological processes such as neuronal differentiation and metabolism. These kinases are hyperactivated in most human cancers and constitute attractive pharmacological targets. A large number of ATP-competitive inhibitors of CDKs have been identified from natural substances, in high throughput screening assays, or through structure-guided approaches. Alternative strategies have been explored to target essential protein/protein interfaces and screen for allosteric inhibitors that trap inactive intermediates or prevent conformational activation. However this remains a major challenge given the highly conserved structural features of these kinases, and calls for new and alternative screening technologies. Fluorescent biosensors constitute powerful tools for the detection of biomolecules in complex biological samples, and are well suited to study dynamic processes and highlight molecular alterations associated with pathological disorders. They further constitute sensitive and selective tools which can be readily implemented to high throughput and high content screens in drug discovery programmes. Our group has developed fluorescent biosensors to probe cyclin-dependent kinases and gain insight into their molecular behaviour in vitro and in living cells. These tools provide a means of monitoring subtle alterations in the abundance and activity of CDK/Cyclins and can respond to compounds that interfere with the conformational dynamics of these kinases. In this review we discuss the different strategies which have been devised to target CDK/Cyclins, and describe the implementation of our CDK/Cyclin biosensors to develop HTS/HCS assays in view of identifying new classes of inhibitors for cancer therapeutics.

An unmet actin requirement explains the mitotic inhibition of clathrin-mediated endocytosis

Clathrin-mediated endocytosis (CME) is the major internalisation route for many different receptor types in mammalian cells. CME is shut down during early mitosis, but the mechanism of this inhibition is unclear. In this study, we show that the mitotic shutdown is due to an unmet requirement for actin in CME. In mitotic cells, membrane tension is increased and this invokes a requirement for the actin cytoskeleton to assist the CME machinery to overcome the increased load. However, the actin cytoskeleton is engaged in the formation of a rigid cortex in mitotic cells and is therefore unavailable for deployment. We demonstrate that CME can be ‘restarted’ in mitotic cells despite high membrane tension, by allowing actin to engage in endocytosis. Mitotic phosphorylation of endocytic proteins is maintained in mitotic cells with restored CME, indicating that direct phosphorylation of the CME machinery does not account for shutdown.

DOI:http://dx.doi.org/10.7554/eLife.00829.001

The plasma membrane that surrounds a cell acts as a protective barrier that regulates what can enter or exit the cell. However, large molecules and other ‘cargo’ can get into a cell in a variety of ways. One of these routes—known as clathrin-mediated endocytosis—involves a receptor on the outside of the membrane grabbing hold of the cargo while a protein called clathrin forms a ‘pit’ beneath the receptor. This pit becomes deeper and deeper until the cargo is completely surrounded by clathrin-lined membrane and is brought inside the cell.

This process has been studied over the past 50 years, and it is known that clathrin-mediated endocytosis is turned off when a cell begins to divide to produce new cells, and then turned back on when cell division has come to an end. However, there are competing theories as to exactly why this process stops when cell division starts.

Now, Kaur et al. have investigated these theories by looking at the role that another protein, called actin, plays in turning off clathrin-mediated endocytosis. Actin is a molecule that forms a sort of scaffolding within the cell (called the cytoskeleton), and it also guides the movement of molecules and larger structures within the cell. Further, when the cell membrane is being stretched, the actin cytoskeleton can assist the clathrin-mediated endocytosis machinery to pull cargo into the cell.

So why doesn’t actin help with endocytosis during cell division? The answer, Kaur et al. suggest, is that all the actin in the cell is needed by the cytoskeleton during cell division, so there is no actin available to perform other tasks such as clathrin-mediated endocytosis. Further experiments demonstrated that this form of endocytosis can be ‘restarted’ in dividing cells by treating the cells in a way that frees up some additional actin. The work of Kaur et al. also ruled out the theory that chemical changes to the endocytosis machinery disabled it during cell division. These findings have implications for the delivery of drugs, via endocytosis, to the rapidly dividing cells that are involved in diseases such as cancer.

DOI:http://dx.doi.org/10.7554/eLife.00829.002

Discovery of the antiviral activities of pharmacologic cyclin-dependent kinase inhibitors: from basic to applied science

'Owing to the strong potential as antivirals exhibited to date by PCIs, cellular proteins are now starting to be considered more often as valid targets for antiviral drugs'

Contribution of Bcl-2 phosphorylation to Bak binding and drug resistance

Bcl-2 is phosphorylated on Ser(70) after treatment of cells with spindle poisons. On the basis of effects observed in cells overexpressing Bcl-2 S70E or S70A mutants, various studies have concluded that Ser(70) phosphorylation either enhances or diminishes Bcl-2 function. In the present study, the ability of phosphorylated Bcl-2, as well as the S70E and S70A mutants, to bind and neutralize proapoptotic Bcl-2 family members under cell-free conditions and in intact cells was examined in an attempt to resolve this controversy. Surface plasmon resonance indicated that phosphorylated Bcl-2, Bcl-2 S70E, and Bcl-2 S70A exhibit enhanced binding to Bim and Bak compared with unmodified Bcl-2. This enhanced binding reflected a readily detectable conformation change in the loop domain of Bcl-2. Furthermore, Bcl-2 S70E and S70A bound more Bak and Bim than wild-type Bcl-2 in pull-downs and afforded greater protection against several chemotherapeutic agents. Importantly, binding of endogenous Bcl-2 to Bim also increased during mitosis, when Bcl-2 is endogenously phosphorylated, and disruption of this mitotic Bcl-2/Bim binding with navitoclax or ABT-199, like Bcl-2 downregulation, enhanced the cytotoxicity of paclitaxel. Collectively, these results provide not only a mechanistic basis for the enhanced antiapoptotic activity of phosphorylated Bcl-2, but also an explanation for the ability of BH3 mimetics to enhance taxane sensitivity.

A small-molecule inhibitor of Haspin alters the kinetochore functions of Aurora B

A chemical biology study characterizes the role of Haspin kinase in centromere recruitment of the chromosome passenger complex and in spindle assembly checkpoint function.

By phosphorylating Thr3 of histone H3, Haspin promotes centromeric recruitment of the chromosome passenger complex (CPC) during mitosis. Aurora B kinase, a CPC subunit, sustains chromosome bi-orientation and the spindle assembly checkpoint (SAC). Here, we characterize the small molecule 5-iodotubercidin (5-ITu) as a potent Haspin inhibitor. In vitro, 5-ITu potently inhibited Haspin but not Aurora B. Consistently, 5-ITu counteracted the centromeric localization of the CPC without affecting the bulk of Aurora B activity in HeLa cells. Mislocalization of Aurora B correlated with dephosphorylation of CENP-A and Hec1 and SAC override at high nocodazole concentrations. 5-ITu also impaired kinetochore recruitment of Bub1 and BubR1 kinases, and this effect was reversed by concomitant inhibition of phosphatase activity. Forcing localization of Aurora B to centromeres in 5-ITu also restored Bub1 and BubR1 localization but failed to rescue the SAC override. This result suggests that a target of 5-ITu, possibly Haspin itself, may further contribute to SAC signaling downstream of Aurora B.

Investigational cell cycle inhibitors in clinical trials for bladder cancer

INTRODUCTION

Cancer-related cell cycle defects are often mediated by alterations in activity of diverse cell cycle regulators. The development of cell cycle inhibitors has undergone a gradual evolution, and new investigational drugs have been extensively tested as a single agent or combination with conventional chemotherapeutic drugs.

AREAS COVERED

This review covers a broad perspective of how the cell cycle is deregulated in bladder cancer and discusses the clinical trials of cell cycle inhibitors.

EXPERT OPINION

Although diverse cell cycle inhibitors have been considered as relevant drug candidates for cancer therapy owing to their potential role in restoring control of the cell cycle, these inhibitors have not been yet widely tested in human bladder cancer. Numerous studies already reported that deregulation of cell cycle controls has been commonly observed in bladder cancer cells, thus warranting clinical trials of these inhibitors in advanced bladder cancer patients. In addition, nonmuscle invasive bladder cancer (NMIBC) and muscle invasive bladder cancer (MIBC) show different clinical and molecular biological characteristics, although ∼ 10 - 20% of NMIBC will progress to MIBC. Therefore, adequate cell cycle inhibitors have to be chosen for bladder cancer treatment based on the different genetic features between NMIBC and MIBC related to cell cycle regulators.

Testing the promiscuity of commercial kinase inhibitors against the AGC kinase group using a split-luciferase screen

Using a newly developed competitive binding assay dependent upon the reassembly of a split reporter protein, we have tested the promiscuity of a panel of reported kinase inhibitors against the AGC group. Many non-AGC targeted kinase inhibitors target multiple members of the AGC group. In general, structurally similar inhibitors consistently exhibited activity toward the same target as well as toward closely related kinases. The inhibition data was analyzed to test the predictive value of either using identity scores derived from residues within 6 Å of the active site or identity scores derived from the entire kinase domain. The results suggest that the active site identity in certain cases may be a stronger predictor of inhibitor promiscuity. The overall results provide general guidelines for establishing inhibitor selectivity as well as for the future design of inhibitors that either target or avoid AGC kinases.

Molecular targeted agents for gastric and gastroesophageal junction cancer

Despite recent improvements in surgical techniques and chemotherapy, advanced cancers of the stomach and gastroesophageal junction (GEJ) continue to have poor clinical outcomes. However, molecules intimately related to cancer cell proliferation, invasion, and metastasis have been studied as candidates for molecular targeted agents. Target molecules, such as the epidermal growth factor receptor, vascular endothelial growth factor receptor, and P13k/Akt/mTor pathway, as well as the insulin-like growth factor receptor, c-Met pathways, fibroblast growth factor receptor, and other pathways are considered to be promising candidates for molecular targeted therapy for gastric and GEJ cancer. In this review we focus on the recent developments in targeting relevant pathways in these types of cancer.

Transcription inhibition as a therapeutic target for cancer

During tumorigenesis the transformed cells lose their normal growth control mechanisms and become dependent on oncogenes' products and pathways for survival. Treatments tailored to block the expression or function of transforming genes have shown efficacy in eliminating neoplastic cells. The mRNAs of many oncogenes, as well as regulators of other key processes such as cell proliferation, angiogenesis, and apoptosis, typically have shorter half-lives. Agents that impede mRNA synthesis are expected to selectively hinder the expression of these genes and, therefore, be detrimental to neoplastic cells that are physiologically dependent on them. In addition to exploiting the tumor cells' dependency on short-lived transcripts, RNA-directed agents also take advantage of the differential sensitivity between transformed and non-transformed cells, as the cytotoxic effects of inhibiting RNA synthesis have not been seen in non-transformed cells. The abrogation of the formation of oncotranscripts provides a new concept in cancer therapeutics and numerous agents have been developed which are able to target transcription. The focus of this review is to give an overview of transcription and the different inhibitory strategies that target various aspects of the transcriptional process.