P276-00, a cyclin-dependent kinase inhibitor, modulates cell cycle and induces apoptosis in vitro and in vivo in mantle cell lymphoma cell lines

Insights into the structural and functional activities of forgotten Kinases: PCTAIREs CDKs

In cells, signal transduction heavily relies on the intricate regulation of protein kinases, which provide the fundamental framework for modulating most signaling pathways. Dysregulation of kinase activity has been implicated in numerous pathological conditions, particularly in cancer. The druggable nature of most kinases positions them into a focal point during the process of drug development. However, a significant challenge persists, as the role and biological function of nearly one third of human kinases remains largely unknown.Within this diverse landscape, cyclin-dependent kinases (CDKs) emerge as an intriguing molecular subgroup. In human, this kinase family encompasses 21 members, involved in several key biological processes. Remarkably, 13 of these CDKs belong to the category of understudied kinases, and only 5 having undergone broad investigation to date. This knowledge gap underscores the pressing need to delve into the study of these kinases, starting with a comprehensive review of the less-explored ones.Here, we will focus on the PCTAIRE subfamily of CDKs, which includes CDK16, CDK17, and CDK18, arguably among the most understudied CDKs members. To contextualize PCTAIREs within the spectrum of human pathophysiology, we conducted an exhaustive review of the existing literature and examined available databases. This approach resulted in an articulate depiction of these PCTAIREs, encompassing their expression patterns, 3D configurations, mechanisms of activation, and potential functions in normal tissues and in cancer.We propose that this effort offers the possibility of identifying promising areas of future research that extend from basic research to potential clinical and therapeutic applications.

Cancer therapy by cyclin-dependent kinase inhibitors (CDKIs): bench to bedside

A major characteristic of cancer is dysregulated cell division, which results in aberrant growth of cells. Consequently, medicinal targets that prevent cell division would be useful in the fight against cancer. The primary regulator of proliferation is a complex consisting of cyclin and cyclin-dependent kinases (CDKs). The FDA has granted approval for CDK inhibitors (CDKIs) to treat metastatic hormone receptor-positive breast cancer. Specifically, CDK4/6 CDKIs block the enzyme activity of CDK4 and CDK6. Unfortunately, the majority of first-generation CDK inhibitors, also known as pan-CDK inhibitors because they target multiple CDKs, have not been authorized for clinical use owing to their serious side effects and lack of selection. In contrast to this, significant advancements have been created to permit the use of pan-CDK inhibitors in therapeutic settings. Notably, the toxicity and negative consequences of pan-CDK inhibitors have been lessened in recent years thanks to the emergence of combination therapy tactics. Therefore, pan-CDK inhibitors have renewed promise for clinical use when used in a combination regimen. The members of the CDK family have been reviewed and their primary roles in cell cycle regulation were covered in this review. Next, we provided an overview of the state of studies on CDK inhibitors.

Recent Discovery and Development of Inhibitors that Target CDK9 and Their Therapeutic Indications

CDK9 is a cyclin-dependent kinase that plays pivotal roles in multiple cellular functions including gene transcription, cell cycle regulation, DNA damage repair, and cellular differentiation. Targeting CDK9 is considered an attractive strategy for antitumor therapy, especially for leukemia and lymphoma. Several potent small molecule inhibitors, exemplified by TG02 (4), have progressed to clinical trials. However, many of them face challenges such as low clinical efficacy and multiple adverse reactions and may necessitate the exploration of novel strategies to lead to success in the clinic. In this perspective, we present a comprehensive overview of the structural characteristics, biological functions, and preclinical status of CDK9 inhibitors. Our focus extends to various types of inhibitors, including pan-inhibitors, selective inhibitors, dual-target inhibitors, degraders, PPI inhibitors, and natural products. The discussion encompasses chemical structures, structure-activity relationships (SARs), biological activities, selectivity, and therapeutic potential, providing detailed insight into the diverse landscape of CDK9 inhibitors.

New pyrrolidine-carboxamide derivatives as dual antiproliferative EGFR/CDK2 inhibitors

Cancer is one of the leading causes of mortality worldwide, making it a public health concern. A novel series of pyrrolidine-carboxamide derivatives 7a-q were developed and examined in a cell viability assay utilizing a human mammary gland epithelial cell line (MCF-10A), where all the compounds exhibited no cytotoxic effects and more than 85% cell viability at a concentration of 50 μM. Antiproliferative activity was evaluated in vitro against four panels of cancer cell lines A-549, MCF-7, Panc-1, and HT-29. Compounds 7e, 7g, 7k, 7n, and 7o were the most active as antiproliferative agents capable of triggering apoptosis. Compound 7g was the most potent of all the derivatives, with a mean IC50 of 0.90 μM compared to IC50 of 1.10 μM for doxorubicin. Compound 7g inhibited A-549 (epithelial cancer cell line), MCF-7 (breast cancer cell line), and HT-29 (colon cancer cell line) more efficiently than doxorubicin. EGFR inhibitory assay results of 7e, 7g, 7k, 7n, and 7o demonstrated that the tested compounds inhibited EGFR with IC50 values ranging from 87 to 107 nM in comparison with the reference drug erlotinib (IC50  = 80 nM). 7e, 7g, 7k, 7n, and 7o inhibited CDK2 efficiently in comparison to the reference dinaciclib (IC50  = 20 nM), with IC50 values ranging from 15 to 31 nM. The results of inhibitory activity assay against different CDK isoforms revealed that the tested compounds had preferential inhibitory activity against the CDK2 isoform.

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.

From Structure Modification to Drug Launch: A Systematic Review of the Ongoing Development of Cyclin-Dependent Kinase Inhibitors for Multiple Cancer Therapy

Herein, we discuss more than 50 cyclin-dependent kinase (CDK) inhibitors that have been approved or have undergone clinical trials and their therapeutic application in multiple cancers. This review discusses the design strategies, structure-activity relationships, and efficacy performances of these selective or nonselective CDK inhibitors. The theoretical basis of early broad-spectrum CDK inhibitors is similar to the scope of chemotherapy, but because their toxicity is greater than the benefit, there is no clinical therapeutic window. The notion that selective CDK inhibitors have a safer therapeutic potential than pan-CDK inhibitors has been widely recognized during the research process. Four CDK4/6 inhibitors have been approved for the treatment of breast cancer or for prophylactic administration during chemotherapy to protect bone marrow and immune system function. Furthermore, the emerging strategies in the field of CDK inhibitors are summarized briefly, and CDKs continue to be widely pursued as emerging anticancer drug targets for drug discovery.

Promising Anticancer Activity of Multitarget Cyclin Dependent Kinase Inhibitors against Human Colorectal Carcinoma Cells

Background:

Colorectal cancer (CRC) is the third leading cause of cancer death worldwide, and its incidence is steadily rising in developing nations. Cell cycle aberrations due to deregulation of cyclin dependent kinases (CDKs) and cyclins are common events during colorectal carcinogenesis. Yet, efficacy of multitarget CDK inhibitors as therapeutic agents has not been much explored against CRC.

Objective:

The anticancer potential of multitarget CDK inhibitor riviciclib (also known as P276-00), was investigated against CRC cell lines of varied genetic background.

Method:

Cytotoxicity of riviciclib - potent CDK1, CDK4 and CDK9-specific inhibitor was evaluated in vitro. Further, its effect on clonogenic potential, cell cycle, apoptosis and transcription was tested using colony forming assay, flow cytometry and western blot analysis respectively. Also, efficacy of riviciclib in combination with standard chemotherapeutic agents was assessed. Dependency of CRC cells on specific CDKs for their survival was confirmed using siRNA studies.

Results:

Riviciclib exerted significant cytotoxicity against CRC cells and inhibited their colony forming potential. It induced apoptosis along with inhibition of cell cycle CDKs and cyclins as well as transcriptional CDKs and cyclins. Moreover, dual combination of riviciclib with standard chemotherapeutic drugs exhibited synergism in CRC cells. siRNA studies indicated that CRC cells are dependent on specific CDKs for their survival which are targets of riviciclib.

Conclusion:

This study provides evidence that multitarget CDK inhibitors can serve as promising therapeutic agents against CRC alone or in combination.

CDK9 Inhibitors in Cancer Research

Cyclin dependent kinase 9 (CDK9) played an essential role in regulating transcriptional elongation. Aberrations in CDK9 activity have been observed in various cancers, which made CDK9 was an attractive therapeutic...

Analyzing the scaffold diversity of cyclin-dependent kinase inhibitors and revisiting the clinical and preclinical pipeline

Kinases have gained an important place in the list of vital therapeutic targets because of their overwhelming clinical success in the last two decades. Among various clinically validated kinases, the cyclin-dependent kinases (CDK) are one of the extensively studied drug targets for clinical development. Food and Drug Administration has approved three CDK inhibitors for therapeutic use, and at least 27 inhibitors are under active clinical development. In the last decade, research and development in this area took a rapid pace, and thus the analysis of scaffold diversity is essential for future drug design. Available reviews lack the systematic study and discussion on the scaffold diversity of CDK inhibitors. Herein we have reviewed and critically analyzed the chemical diversity present in the preclinical and clinical pipeline of CDK inhibitors. Our analysis has shown that although several scaffolds represent CDK inhibitors, only the amino-pyrimidine is a well-represented scaffold. The three-nitrogen framework of amino-pyrimidine is a fundamental hinge-binding unit. Further, we have discussed the selectivity aspects among CDKs, the clinical trial dose-limiting toxicities, and highlighted the most advanced clinical candidates. We also discuss the changing paradigm towards selective inhibitors and an overview of ATP-binding pockets of all druggable CDKs. We carefully analyzed the clinical pipeline to unravel the candidates that are currently under active clinical development. In addition to the plenty of dual CDK4/6 inhibitors, there are many selective CDK7, CDK9, and CDK8/19 inhibitors in the clinical pipeline.

Cyclin-Dependent Kinase Inhibitors in Hematological Malignancies-Current Understanding, (Pre-)Clinical Application and Promising Approaches

Simple Summary

Cyclin-dependent kinases are involved in the regulation of cancer-initiating processes like cell cycle progression, transcription, and DNA repair. In hematological neoplasms, these enzymes are often overexpressed, resulting in increased cell proliferation and cancer progression. Early (pre-)clinical data using cyclin-dependent kinase inhibitors are promising but identifying the right drug for each subgroup and patient is challenging. Certain chromosomal abnormalities and signaling molecule activities are considered as potential biomarkers. We therefore summarized relevant studies investigating cyclin-dependent kinase inhibitors in hematological malignancies and further discuss molecular mechanisms of resistance and other open questions.

Abstract

Genetically altered stem or progenitor cells feature gross chromosomal abnormalities, inducing modified ability of self-renewal and abnormal hematopoiesis. Cyclin-dependent kinases (CDK) regulate cell cycle progression, transcription, DNA repair and are aberrantly expressed in hematopoietic malignancies. Incorporation of CDK inhibitors (CDKIs) into the existing therapeutic regimens therefore constitutes a promising strategy. However, the complex molecular heterogeneity and different clinical presentation is challenging for selecting the right target and defining the ideal combination to mediate long-term disease control. Preclinical and early clinical data suggest that specific CDKIs have activity in selected patients, dependent on the existing rearrangements and mutations, potentially acting as biomarkers. Indeed, CDK6, expressed in hematopoietic cells, is a direct target of MLL fusion proteins often observed in acute leukemia and thus contributes to leukemogenesis. The high frequency of aberrancies in the retinoblastoma pathway additionally warrants application of CDKIs in hematopoietic neoplasms. In this review, we describe the preclinical and clinical advances recently made in the use of CDKIs. These include the FDA-approved CDK4/6 inhibitors, traditional and novel pan-CDKIs, as well as dual kinase inhibitors. We additionally provide an overview on molecular mechanisms of response vs. resistance and discuss open questions.

CDK inhibitors in cancer therapy, an overview of recent development

Dysregulated cell division, which leads to aberrant cell proliferation, is one of the key hallmarks of cancer. Therefore, therapeutic targets that block cell division would be effective for cancer treatment. Cell division is mainly controlled by a complex composed of cyclin and cyclin dependent kinases (CDKs). To date, the CDK inhibitors (CDKIs), specifically the ones that block the enzyme activity of CDK4 and CDK6 (CDK4/6), have been approved by FDA for the treatment of metastatic hormone receptor positive breast cancer. However, due to the non-selectivity and significant toxicity, most of the first generation CDK inhibitors (so called pan-CDK inhibitors that target several CDKs), have not been approved for clinical application. Despite this, great efforts and progress have been made to enable pan-CDK inhibitors application in the clinical setting. Notably, the development of combination therapy strategies in recent years has made it possible to reduce the toxicity and side effects of pan-CDK inhibitors. Thus, as a combination therapy approach, pan-CDK inhibitors regain great potential in clinical application. In this review, we introduced the CDK family members and discussed their major functions in cell cycle controlling. Then, we summarized the research progress regarding CDK inhibitors, especially those other than CDK4/6 inhibitors. We reviewed first-generation pan-CDKIs Flavopiridol and Roscovitine, and second-generation CDKIs Dinaciclib, P276-00, AT7519, TG02, Roniciclib, RGB-286638 by focusing on their developing stages, clinical trials and targeting cancers. The specific CDKIs, which targets to increase specificity and decrease the side effects, were also discussed. These CDKIs include CDK4/6, CDK7, CDK9, and CDK12/13 inhibitors. Finally, the efficacy and discrepancy of combination therapy with CDK inhibitors and PD1/PDL1 antibodies were analyzed, which might give insights into the development of promising strategy for cancer treatment.

Dinaciclib, a Bimodal Agent Effective against Endometrial Cancer

Endometrial cancer (EC) is the sixth most prevalent female cancer globally and although high rates of success are achieved when diagnosed at an early stage, the 5-year survival rate for cancers diagnosed at Stages II-IV is below 50%. Improving patient outcomes will necessitate the introduction of novel therapies to the clinic. Pan-cyclin-dependent kinase inhibitors (CDKis) have been explored as therapies for a range of cancers due to their ability to simultaneously target multiple key cellular processes, such as cell cycle progression, transcription, and DNA repair. Few studies, however, have reported on their potential for the treatment of EC. Herein, we examined the effects of the pan-CDKi dinaciclib in primary cells isolated directly from tumors and EC cell lines. Dinaciclib was shown to elicit a bimodal action in EC cell lines, disrupting both cell cycle progression and phosphorylation of the RNA polymerase carboxy terminal domain, with a concomitant reduction in Bcl-2 expression. Furthermore, the therapeutic potential of combining dinaciclib and cisplatin was explored, with the drugs demonstrating synergy at specific doses in Type I and Type II EC cell lines. Together, these results highlight the potential of dinaciclib for use as an effective EC therapy.

A review on kinases phosphorylating the carboxyl-terminal domain of RNA polymerase II-Biological functions and inhibitors

RNA polymerase II (RNA Pol II) plays a major role in gene transcription for eukaryote. One of the major modes of regulation in eukaryotes is the phosphorylation of the carboxyl-terminal domain (CTD) of RNA Pol II. The current study found that the phosphorylation of Ser2, Ser5, Ser7, Thr4 and Tyr1 among the heptapeptide repeats of CTD plays a key role in the transcription process. We therefore review the biological functions and inhibitors of kinases that phosphorylate these amino acid residues including transcriptional cyclin-dependent protein kinases (CDKs), bromodomain-containing protein 4 (BRD4), Polo-like kinases 3 (Plk3) and Abelson murine leukemia viral oncogene 1 and 2 (c-Abl1/2).

Emerging strategies to target the dysfunctional cohesin complex in cancer

INTRODUCTION

Mutations in cohesin genes have been described in numerous solid cancers and hematologic malignancies; subsequent experimental evidence has linked these mutations with carcinogenesis. Areas covered: In this review, we present current information about the physiological role of the cohesin complex in normal and malignant cells and describe current therapeutic strategies that are being explored in cohesin-mutated cancers. We discuss a range of targets and strategies that should be explored to develop targeted therapies for patients with aberrant cohesin. Expert opinion: Targeting of the cohesin complex is an underexplored area of drug development. There is a high frequency of cohesin mutations in multiple cancers, hence specific targeting strategies should be explored. Cohesins play a crucial role in cellular organization; therefore, we expect a narrow therapeutic window of direct inhibitors of cohesin components. Exploiting experimental approaches that correct dysfunctional cohesins and coupling them with current therapeutic strategies can provide novel, innovative and more effective treatment regimens.

Organocatalytic enantioselective direct alkylation of phloroglucinol derivatives: asymmetric total synthesis of (+)-aflatoxin B2

The organocatalytic enantioselective Friedel–Crafts alkylation of the phloroglucinol derivatives with enals is reported, providing general access to the benzylic chiral centers shown in a variety of phloroglucinol natural products.

An insight into the emerging role of cyclin-dependent kinase inhibitors as potential therapeutic agents for the treatment of advanced cancers

Cancer denotes a pathological manifestation that is characterized by hyperproliferation of cells. It has anticipated that a better understanding of disease pathogenesis and the role of cell-cycle regulators may provide an opportunity to develop an effective cancer therapeutic agents. Specifically, the cyclin-dependent kinases (CDKs) which regulate the transition of cell-cycle through different phases; have been identified as fundamental targets for therapeutic advances. It is an evident from experimental studies that several events leading to tumor growth occur by exacerbation of CDK4/CDK6 in G1-phase of cell division cycle. Additionally, the characteristics of S- and G2/M-phase regulated by CDK1/CDK2 are pivotal events that may lead to abrupt the cell division. Although, previously reported CDK inhibitors have shown remarkable results in pre-clinical studies, but have not yielded appreciable clinical results yet. Therefore, the development of clinically potent CDK inhibitors has remained to be a challenging task. However, continuous efforts has led to the development of some novel CDKs inhibitors that have emerged as a potent strategy for the treatment of advanced cancers. In this article, we have summarized the role of CDKs in cell-cycle regulation and tumorigenesis and recent advances in the development of CDKs inhibitors as a promising therapy for the treatment of advanced cancer. In addition, we have also performed a comparison of crystallographic studies to get valuable insight into the interaction mode differences of inhibitors, binding to CDK isoforms with apparently similar binding sites. The knowledge of ligand-specific recognition towards a particular CDK isoform may be applied as a key tool in future for the designing of isoform-specific inhibitors.

Discovery and Preclinical Development of IIIM-290, an Orally Active Potent Cyclin-Dependent Kinase Inhibitor

Rohitukine (1), a chromone alkaloid isolated from Indian medicinal plant Dysoxylum binectariferum, has inspired the discovery of flavopiridol and riviciclib, both of which are bioavailable only via intravenous route. With the objective to address the oral bioavailability issue of this scaffold, four series of rohitukine derivatives were prepared and screened for Cdk inhibition and cellular antiproliferative activity. The 2,6-dichloro-styryl derivative IIIM-290 (11d) showed strong inhibition of Cdk-9/T1 (IC₅₀ 1.9 nM) kinase and Molt-4/MIAPaCa-2 cell growth (GI₅₀ < 1.0 μM) and was found to be highly selective for cancer cells over normal fibroblast cells. It inhibited the cell growth of MIAPaCa-2 cells via caspase-dependent apoptosis. It achieved 71% oral bioavailability with in vivo efficacy in pancreatic, colon, and leukemia xenografts at 50 mg/kg, po. It did not have CYP/efflux-pump liability, was not mutagenic/genotoxic or cardiotoxic, and was metabolically stable. The preclinical data presented herein indicates the potential of 11d for advancement in clinical studies.

Mantle cell lymphoma in the era of precision medicine-diagnosis, biomarkers and therapeutic agents

Despite advances in the development of clinical agents for treating Mantle Cell Lymphoma (MCL), treatment of MCL remains a challenge due to complexity and frequent relapse associated with MCL. The incorporation of conventional and novel diagnostic approaches such as genomic sequencing have helped improve understanding of the pathogenesis of MCL, and have led to development of specific agents targeting signaling pathways that have recently been shown to be involved in MCL. In this review, we first provide a general overview of MCL and then discuss about the role of biomarkers in the pathogenesis, diagnosis, prognosis, and treatment for MCL. We attempt to discuss major biomarkers for MCL and highlight published and ongoing clinical trials in an effort to evaluate the dominant signaling pathways as drugable targets for treating MCL so as to determine the potential combination of drugs for both untreated and relapse/refractory cases. Our analysis indicates that incorporation of biomarkers is crucial for patient stratification and improve diagnosis and predictability of disease outcome thus help us in designing future precision therapies. The evidence indicates that a combination of conventional chemotherapeutic agents and novel drugs designed to target specific dysregulated signaling pathways can provide the effective therapeutic options for both untreated and relapse/refractory MCL.

Anticancer Alkaloids from Trees: Development into Drugs

Trees have made an enormous phytochemical contribution in anticancer drugs' development more than any other life form. The contributions include alkaloids that are biosynthesized in various ways and yield. Lead alkaloids isolated from the trees are taxol and camptothecins that currently have annual sales in billion dollars. Other important alkaloids isolated from these life forms include rohitukine, harringtonine, acronycine, thalicarpine, usambarensine, ellipticine, and matrines. Studies on their mechanism of action and target on the DNA and protein of cancerous cells aided the development of potent hemisynthesized congeners. The molecules and their congeners passed/are passing a long period of historical development before approved as antineoplastic drugs for cancer chemotherapy. Some of them did not find the application as anticancer drugs due to ineffectiveness in clinical trials; others are generating research interest in the antineoplastic activity at the present and have reached clinical trial stages. Potentials in antineoplastic molecules from trees are high and are hoped to be commensurate with cancer types afflicting human society in the future.

Cyclin Dependent Kinase 9 Inhibitors for Cancer Therapy

Cyclin dependent kinase (CDK) inhibitors have been the topic of intense research for nearly 2 decades due to their widely varied and critical functions within the cell. Recently CDK9 has emerged as a druggable target for the development of cancer therapeutics. CDK9 plays a crucial role in transcription regulation; specifically, CDK9 mediated transcriptional regulation of short-lived antiapoptotic proteins is critical for the survival of transformed cells. Focused chemical libraries based on a plethora of scaffolds have resulted in mixed success with regard to the development of selective CDK9 inhibitors. Here we review the regulation of CDK9, its cellular functions, and common core structures used to target CDK9, along with their selectivity profile and efficacy in vitro and in vivo.

Lipidoid nanoparticle mediated silencing of Mcl-1 induces apoptosis in mantle cell lymphoma

Conventional chemo-immunotherapy fails to cure the majority of mantle cell lymphoma patients and causes substantial toxicity. Resistant mantle cell lymphoma cells commonly overexpress and are dependent on the anti-apoptotic protein, Mcl-1, for survival. In this study, we use potent lipidoid nanoparticles to deliver siRNA to silence Mcl-1 expression. Studies were conducted using two different mantle cell lymphoma cell lines, a normal (JeKo-1) and an aggressive (MAVER-1) line, to assess the ability of lipidoid nanoparticles to be used broadly in the treatment of mantle cell lymphoma. Mcl-1 mRNA silencing and protein knockdown was observed as early as one day after treatment and the lipidoid nanoparticles achieved sustained silencing of Mcl-1 mRNA for at least four days in both JeKo-1 and MAVER-1 cells. Eighty percent silencing was achieved at three days post-transfection in JeKo-1 cells while 50% silencing was achieved in MAVER-1 cells, which are more resistant to transfection. Interestingly, silencing of Mcl-1 induced apoptosis in nearly 30% of both JeKo-1 and MAVER-1 cells three days post-transfection. Additionally, Mcl-1 silencing and the resultant apoptosis in mantle cell lymphoma cells were dose dependent. These data suggest that lipidoid nanoparticles siRNA therapy targeting Mcl-1 has potential as a new treatment modality for mantle cell lymphoma and many other cancers that overexpress Mcl-1. The combination of anti-Mcl-1 lipidoid nanoparticles with other forms of targeted therapy offers hope for reducing or replacing cytotoxic chemotherapy as standard treatment for mantle cell lymphoma.

NOD/SCID IL2Rγ-null mouse xenograft model of human p53-mutated chronic lymphocytic leukemia and ATM-mutated mantle cell lymphoma using permanent cell lines

Xenograft models represent a promising tool to study the pathogenesis of hematological malignancies. To establish a reliable and appropriate in vivo model of aggressive human B-cell leukemia and lymphoma we xenotransplanted four p53-mutated cell lines and one ATM-mutated cell line into immunodeficient NOD/SCID IL2Rγ-null mice. The cell lines MEC-1, SU-DHL-4, JEKO-1, REC-1, and GRANTA-519 were transplanted intraperitoneally or subcutaneously and the engraftment was investigated using immunohistochemistry and flow cytometry. We found significant differences in engraftment efficiency. MEC-1, JEKO-1 and GRANTA-519 cell lines engrafted most efficiently, while SU-DHL-4 cells did not engraft at all. MEC-1 and GRANTA-519 massively infiltrated organs and the whole intraperitoneal cavity showing very aggressive growth. In addition, GRANTA-519 cells massively migrated to the bone marrow regardless of the transplantation route. The MEC-1 and GRANTA-519 cells can be especially recommended for in vivo study of p53-mutated chronic lymphocytic leukemia and ATM-mutated mantle cell lymphoma, respectively.

Insights on Structural Characteristics and Ligand Binding Mechanisms of CDK2

Cyclin-dependent kinase 2 (CDK2) is a crucial regulator of the eukaryotic cell cycle. However it is well established that monomeric CDK2 lacks regulatory activity, which needs to be aroused by its positive regulators, cyclins E and A, or be phosphorylated on the catalytic segment. Interestingly, these activation steps bring some dynamic changes on the 3D-structure of the kinase, especially the activation segment. Until now, in the monomeric CDK2 structure, three binding sites have been reported, including the adenosine triphosphate (ATP) binding site (Site I) and two non-competitive binding sites (Site II and III). In addition, when the kinase is subjected to the cyclin binding process, the resulting structural changes give rise to a variation of the ATP binding site, thus generating an allosteric binding site (Site IV). All the four sites are demonstrated as being targeted by corresponding inhibitors, as is illustrated by the allosteric binding one which is targeted by inhibitor ANS (fluorophore 8-anilino-1-naphthalene sulfonate). In the present work, the binding mechanisms and their fluctuations during the activation process attract our attention. Therefore, we carry out corresponding studies on the structural characterization of CDK2, which are expected to facilitate the understanding of the molecular mechanisms of kinase proteins. Besides, the binding mechanisms of CDK2 with its relevant inhibitors, as well as the changes of binding mechanisms following conformational variations of CDK2, are summarized and compared. The summary of the conformational characteristics and ligand binding mechanisms of CDK2 in the present work will improve our understanding of the molecular mechanisms regulating the bioactivities of CDK2.

Targeting cell cycle regulators in hematologic malignancies

Hematologic malignancies represent the fourth most frequently diagnosed cancer in economically developed countries. In hematologic malignancies normal hematopoiesis is interrupted by uncontrolled growth of a genetically altered stem or progenitor cell (HSPC) that maintains its ability of self-renewal. Cyclin-dependent kinases (CDKs) not only regulate the mammalian cell cycle, but also influence other vital cellular processes, such as stem cell renewal, differentiation, transcription, epigenetic regulation, apoptosis, and DNA repair. Chromosomal translocations, amplification, overexpression and altered CDK activities have been described in different types of human cancer, which have made them attractive targets for pharmacological inhibition. Mouse models deficient for one or more CDKs have significantly contributed to our current understanding of the physiological functions of CDKs, as well as their roles in human cancer. The present review focuses on selected cell cycle kinases with recent emerging key functions in hematopoiesis and in hematopoietic malignancies, such as CDK6 and its role in MLL-rearranged leukemia and acute lymphocytic leukemia, CDK1 and its regulator WEE-1 in acute myeloid leukemia (AML), and cyclin C/CDK8/CDK19 complexes in T-cell acute lymphocytic leukemia. The knowledge gained from gene knockout experiments in mice of these kinases is also summarized. An overview of compounds targeting these kinases, which are currently in clinical development in various solid tumors and hematopoietic malignances, is presented. These include the CDK4/CDK6 inhibitors (palbociclib, LEE011, LY2835219), pan-CDK inhibitors that target CDK1 (dinaciclib, flavopiridol, AT7519, TG02, P276-00, terampeprocol and RGB 286638) as well as the WEE-1 kinase inhibitor, MK-1775. The advantage of combination therapy of cell cycle inhibitors with conventional chemotherapeutic agents used in the treatment of AML, such as cytarabine, is discussed.

A phase II, single-arm, open-label, multicenter study to evaluate the efficacy and safety of P276-00, a cyclin-dependent kinase inhibitor, in patients with relapsed or refractory mantle cell lymphoma

INTRODUCTION

Overexpression of cyclin D1 is a hallmark feature of mantle cell lymphoma (MCL). Many of the oncogenic effects of cyclin D1 are mediated through cyclin-dependent kinases (CDKs). P276-00 is a potent small molecule inhibitor of CDK4-D1, CDK1-B, and CDK9-T, with promising activity in preclinical models. In phase I studies of P276-00 in patients with refractory solid neoplasms, it was well-tolerated with a mild trend toward single-agent efficacy.

PATIENTS AND METHODS

A phase II study of P276-00 was conducted in patients with relapsed or refractory MCL at the recommended dose of 185 mg/m(2)/day from days 1 to 5 of a 21-day cycle. Thirteen patients were enrolled in the present study.

RESULTS

Of the 13 patients, 11 experienced disease progression, 1 patient was withdrawn because of an adverse event (AE), and 1 patient died. Also, 11 patients (84.6%) experienced a treatment-emergent AE deemed related to P276-00. Of the 13 patients, 9 (69.2%) received ≥ 2 cycles of treatment, which was the predefined threshold to be evaluable for efficacy. Treatment was discontinued early in 2 patients because of AEs (1 of which was attributed to P276-00 administration) and in 2 patients because of disease progression. Finally, 2 patients experienced stable disease for an estimated median duration of 60.5 days (range, 58-63 days). The estimated median time to progression for the predefined efficacy population was 43 days (range, 38-58 days).

CONCLUSION

Given the results observed in the present study, if evaluation of CDK inhibition in MCL continues, it should be considered earlier in the disease course or as a part of combination strategies for relapsed or refractory disease.

Remodelling of a polypyrimidine tract-binding protein complex during apoptosis activates cellular IRESs

Post-transcriptional control of gene expression is mediated by the interaction of RNA-binding proteins with their cognate mRNAs that specifically regulate their stability, localization and translation. mRNA-binding proteins are multifunctional and it has been proposed therefore that a combinatorial RNA-binding protein code exists that allows specific protein sub-complexes to control cytoplasmic gene expression under a range of pathophysiological conditions. We show that polypyrimidine tract-binding protein (PTB) is central to one such complex that forms in apoptotic cells. Thus, during apoptosis initiated by TNF-related apoptosis inducing ligand there is a change in the repertoire of RNA-binding proteins with which PTB interacts. We show that altering the cellular levels of PTB and its binding partners, either singly or in combination, is sufficient to directly change the rates of apoptosis with increased expression of PTB, YBX1, PSF and NONO/p54^nrb accelerating this process. Mechanistically, we show that these proteins post-transcriptionally regulate gene expression, and therefore apoptotic rates, by interacting with and stimulating the activity of RNA elements (internal ribosome entry segments) found in mRNAs that are translated during apoptosis. Taken together, our data show that PTB function is controlled by a set of co-recruited proteins and importantly provide further evidence that it is possible to dictate cell fate by modulating cytoplasmic gene expression pathways alone.

Potentiation of anticancer effect of valproic acid, an antiepileptic agent with histone deacetylase inhibitory activity, by the cyclin-dependent kinase inhibitor P276-00 in human non-small-cell lung cancer cell lines

BACKGROUND

P276-00 is a novel cyclin-dependent kinase (CDK) inhibitor is in Phase II clinical trials. Valproic acid (VPA), an antiepileptic agent has been associated with anticancer activity, through the inhibition of histone deacetylase I. Here we investigate the effect of the combination of VPA and P276-00, in non-small-cell lung cancer (NSCLC) cell lines.

MATERIALS AND METHODS

Cell growth inhibition was studied using the Propidium iodide (PI) assay. Cell cycle analysis and recovery were detected by flow cytometry. The expression levels of various proteins were detected by western blot. Inhibition of colony formation in H460 was checked in vitro. In vivo efficacy was studied in H460 xenograft model.

RESULTS

The combination of P276-00 and VPA showed synergistic effect on p53+ and p53- NSCLC cell lines in antiproliferative assay at both constant and non-constant ratio with marked decrease in colony forming potential. Flow cytometric analysis confirmed a significant time dependent increase in apoptosis with 64% apoptotic population at 96 h compared to VPA (1%) and P276-00 (28%) alone (p < 0.0001). Incubation of the cells after treatment, in fresh medium without drugs, led to the recovery of cells treated with P276-00 alone but not the cells treated with the combination of both the drugs. The combination treatment up-regulated tumor suppressor proteins like p53, p21 and p27 along with down-regulation of proliferation and survival proteins viz. cyclin D1 and Bcl-2. This was also associated with the upregulation of the pro-apoptotic protein Bax and significant accumulation of hyperacetylated histones in the combination treatment. Interestingly, VPA in combination with P276-00 was much more effective as an antitumor agent than alone, in the H460 xenograft tumor model in SCID mice.

CONCLUSIONS

This study indicates that the combination of HDAC inhibitor VPA with CDK inhibitor P276-00 is promising novel molecularly targeted therapeutic approach for NSCLC treatment.

Cyclin-dependent kinase inhibitor therapy for hematologic malignancies

INTRODUCTION

Cyclin-dependent kinases (CDKs) regulate cell cycle progression. Certain CDKs (e.g., CDK7, CDK9) also control cellular transcription. Consequently, CDKs represent attractive targets for anticancer drug development, as their aberrant expression is common in diverse malignancies, and CDK inhibition can trigger apoptosis. CDK inhibition may be particularly successful in hematologic malignancies, which are more sensitive to inhibition of cell cycling and apoptosis induction.

AREAS COVERED

A number of CDK inhibitors, ranging from pan-CDK inhibitors such as flavopiridol (alvocidib) to highly selective inhibitors of specific CDKs (e.g., CDK4/6), such as PD0332991, that are currently in various phases of development, are profiled in this review. Flavopiridol induces cell cycle arrest, and globally represses transcription via CDK9 inhibition. The latter may represent its major mechanism of action via down-regulation of multiple short-lived proteins. In early phase trials, flavopiridol has shown encouraging efficacy across a wide spectrum of hematologic malignancies. Early results with dinaciclib and PD0332991 also appear promising.

EXPERT OPINION

In general, the antitumor efficacy of CDK inhibitor monotherapy is modest, and rational combinations are being explored, including those involving other targeted agents. While selective CDK4/6 inhibition might be effective against certain malignancies, broad-spectrum CDK inhibition will likely be required for most cancers.

Targeting cell cycle regulation in cancer therapy

Cell proliferation is an essential mechanism for growth, development and regeneration of eukaryotic organisms; however, it is also the cause of one of the most devastating diseases of our era: cancer. Given the relevance of the processes in which cell proliferation is involved, its regulation is of paramount importance for multicellular organisms. Cell division is orchestrated by a complex network of interactions between proteins, metabolism and microenvironment including several signaling pathways and mechanisms of control aiming to enable cell proliferation only in response to specific stimuli and under adequate conditions. Three main players have been identified in the coordinated variation of the many molecules that play a role in cell cycle: i) The cell cycle protein machinery including cyclin-dependent kinases (CDK)-cyclin complexes and related kinases, ii) The metabolic enzymes and related metabolites and iii) The reactive-oxygen species (ROS) and cellular redox status. The role of these key players and the interaction between oscillatory and non-oscillatory species have proved essential for driving the cell cycle. Moreover, cancer development has been associated to defects in all of them. Here, we provide an overview on the role of CDK-cyclin complexes, metabolic adaptations and oxidative stress in regulating progression through each cell cycle phase and transitions between them. Thus, new approaches for the design of innovative cancer therapies targeting crosstalk between cell cycle simultaneous events are proposed.