Structural insights of cyclin dependent kinases: Implications in design of selective inhibitors

A Cdk5 inhibitor restores cognitive function and alleviates type 2 diabetes in mice

Type 2 diabetes (T2D) is a metabolic disorder commonly linked with cognitive decline, increasing patients' susceptibility to dementia. Alzheimer's disease (AD) has a strong connection with hyperglycemia and insulin dysregulation. Interestingly, certain anti-diabetic drugs have shown potential in reducing T2D-induced cognitive impairment. Previous studies, including ours, have highlighted the dysregulation of cyclin-dependent kinase 5 (Cdk5) activity in both T2D and AD, which may contribute to pathological changes in these conditions. Thus, targeting the Cdk5 kinase could offer a therapeutic approach for T2D and cognitive deterioration. Our research identifies Cdk5 as a key link between T2D and cognitive decline. By screening the KINACore library, we discovered two new brain-penetrant Cdk5 inhibitors, BLINK11 and BLINK15. In a high-fat diet-induced T2D model, these inhibitors improved blood glucose levels, obesity, and cognitive function. BLINK11, in particular, shows promise as a therapeutic candidate for treating cognitive impairment associated with T2D.

Design and Synthesis of Topoisomerases-Histone Deacetylase Dual Targeted Quinoline-Bridged Hydroxamates as Anticancer Agents

The multifactorial nature of cancer requires treatment that involves simultaneous targeting of associated overexpressed proteins and cell signaling pathways, possibly leading to synergistic effects. Herein, we present a systematic study that involves the simultaneous inhibition of human topoisomerases (hTopos) and histone deacetylases (HDACs) by multitargeted quinoline-bridged hydroxamic acid derivatives. These compounds were rationally designed considering pharmacophoric features and catalytic sites of the cross-talk proteins, synthesized, and assessed for their anticancer potential. Our findings revealed that the compound 5c significantly produced anticancer effects in vitro and in vivo by reducing the tumor growth and its size in the A549 cell-induced lung cancer xenograft model through multiple mechanisms, primarily by multi-inhibition of hTopoI/II and HDACs, especially HDAC1 via atypical binding. The present paper discusses detailed mechanistic biological investigations, structure-activity effects supported by computational docking studies, and DMPK studies and provides future scope for lead optimization and modification.

Targeting cyclin-dependent kinase 11: a computational approach for natural anti-cancer compound discovery

Cancer, a leading global cause of death, presents considerable treatment challenges due to resistance to conventional therapies like chemotherapy and radiotherapy. Cyclin-dependent kinase 11 (CDK11), which plays a pivotal role in cell cycle regulation and transcription, is overexpressed in various cancers and is linked to poor prognosis. This study focused on identifying potential inhibitors of CDK11 using computational drug discovery methods. Techniques such as pharmacophore modeling, virtual screening, molecular docking, ADMET predictions, molecular dynamics simulations, and binding free energy analysis were applied to screen a large natural product database. Three pharmacophore models were validated, leading to the identification of several promising compounds with stronger binding affinities than the reference inhibitor. ADMET profiling indicated favorable drug-like properties, while molecular dynamics simulations confirmed the stability and favorable interactions of top candidates with CDK11. Binding free energy calculations further revealed that UNPD29888 exhibited the strongest binding affinity. In conclusion, the identified compound shows potential as a CDK11 inhibitor based on computational predictions, suggesting their future application in cancer treatment by targeting CDK11. These computational findings encourage further experimental validation as anti-cancer agents.

CDK14 regulates the development and repair of lung

Cyclin-dependent kinases (CDK) 14 regulates cell cycle, tumor expansion by influencing the downstream targets of the canonical Wnt signaling pathway. However, the function of CDK14 during organ development and regeneration has not been investigated in genetically-modified animals. Here, we found that genetic ablation of Cdk14 influenced pulmonary vascular endothelial cells and alveolar epithelial cells during mice embryonic development as well as repair of lung after bleomycin or lipopolysaccharide induced injury. Genetic knockout of Cdk14 and the CDK14 covalent inhibitor FMF-04-159-2 resulted in reduction of pulmonary vessel covered area and epithelial cell number, exhibiting increased mortality and more severe lung damage after injury. Mechanistically, Cdk14 ablation inhibited the proliferation of epithelial and vascular endothelial cells, inducing cell cycle arrest at the G2/M phase. Through RNA-seq analysis of both endothelial and epithelial cells, we found that knockdown of Cdk14 controls the expression of signal transducers and activator of transcription 1 (STAT1) as well as associated genes in interferon signaling. Disruption of Cdk14 interferes with IFN-γ induced lung repair in vivo, suggesting potential crosstalk of CDK14 signaling and IFN-γ pathway. Our work highlights the importance of Cdk14 in lung development and regenerative repair through an uncharacterized CDK14- IFN-γ signaling axis.

A decade of pyridine-containing heterocycles in US FDA approved drugs: a medicinal chemistry-based analysis

Heterocyclic scaffolds, particularly, pyridine-containing azaheterocycles, constitute a major part of the drugs approved in the past decade. In the present review, we explored the pyridine ring part of US FDA-approved small molecules (2014-2023). The analysis of the approved drugs bearing a pyridine ring revealed that a total of 54 drugs were approved. Among them, the significant number comprised the anticancer category (18 drugs, 33%), followed by drugs affecting the CNS system (11 drugs, 20%), which include drugs to treat migraines, Parkinsonism disorders, chemotherapeutic-induced nausea, insomnia, and ADHD or as CNS-acting analgesics or sedatives. Next, six drugs (11%) were also approved to treat rare conditions, followed by five drugs that affect the hematopoietic system. The analysis also revealed that drug approval was granted for antibiotics, antivirals, and antifungals, including drugs for the treatment of tropical and sub-tropical diseases. Primary drug targets explored were kinases, and the major metabolizing enzyme was CYP3A4. Further analysis of formulation types revealed that 50% of the approved drugs were tablets, followed by 17% capsules and 15% injections. Elemental analysis showed that most approved drugs contained sulfur, while fluorine was noted in 32 compounds. Therefore, the present review is a concerted effort to cover drugs bearing pyridine rings approved in the last decade and provide thorough discussion and commentary on their pharmacokinetics and pharmacodynamics aspects. Furthermore, in-depth structural and elemental analyses were explored, thus providing comprehensive guidance for medicinal chemists and scientists working in allied science domains.

Targeting cyclin-dependent kinases: From pocket specificity to drug selectivity

The development of selective modulators of cyclin-dependent kinases (CDKs), a kinase family with numerous members and functional variations, is a significant preclinical challenge. Recent advancements in crystallography have revealed subtle differences in the highly conserved CDK pockets. Exploiting these differences has proven to be an effective strategy for achieving excellent drug selectivity. While previous reports briefly discussed the structural features that lead to selectivity in individual CDK members, attaining inhibitor selectivity requires consideration of not only the specific structures of the target CDK but also the features of off-target members. In this review, we summarize the structure-activity relationships (SARs) that influence selectivity in CDK drug development and analyze the pocket features that lead to selectivity using molecular-protein binding models. In addition, in recent years, novel CDK modulators have been developed, providing more avenues for achieving selectivity. These cases were also included. We hope that these efforts will assist in the development of novel CDK drugs.

A patent review of small molecule CDK4/6 inhibitors in the treatment of cancer: 2020-present

INTRODUCTION

Cyclin-dependent protein kinase 4/6 (CDK4/6) is a class of serine/threonine protein kinases that plays a key role in the regulation of the cell cycle. CDK4/6 is highly expressed in cancers such as breast cancer, melanoma, and non-small cell lung cancer (NSCLC). Currently, a variety of CDK4/6 inhibitors have been developed, aiming to develop effective inhibitors to solve CDK4/6 resistance and toxicity.

AREAS COVERED

This article searches patents through Espacenet and reviews the development of widely studied CDK inhibitors and FDA-approved CDK4/6 inhibitors, as well as the latest progress of patented inhibitors with good inhibitory activity against CDK4/6 from 2020 to now.

EXPERT OPINION

CDK4/6 is highly expressed in many tumors and has become an important anti-tumor target. Among the patents from 2020 to the present, many inhibitors have good kinase inhibitory effects on CDK4/6 and also show great development potential in anti-tumor. However, there is still an urgent need to develop novel CDK4/6 inhibitors that address challenges such as drug resistance, toxicity, and selectivity.

PROTAC: Novel degradable approach for different targets to treat breast cancer

The revolutionary Proteolysis Targeting Chimera (PROTACs) have the exciting potential to reshape the pharmaceutical industry landscape by leveraging the ubiquitin-proteasome system for targeted protein degradation. Breast cancer, the most prevalent cancer in women, could be treated using PROTAC therapy. Although substantial work has been conducted, there is not yet a comprehensive overview or progress update on PROTAC therapy for breast cancer. Hence, in this article, we've compiled recent research progress focusing on different breast cancer target proteins, such as estrogen receptor (ER), BET, CDK, HER2, PARP, EZH2, etc. This resource aims to serve as a guide for future PROTAC-based breast cancer treatment design.

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.

Hit discovery of potential CDK8 inhibitors and analysis of amino acid mutations for cancer therapy through computer-aided drug discovery

Cyclin-dependent kinase 8 (CDK8) has emerged as a promising target for inhibiting cancer cell function, intensifying efforts towards the development of CDK8 inhibitors as potential cancer therapeutics. Mutations in CDK8, a protein kinase, are also implicated as a primary factor associated with tumor formation. In this study, we identified potential inhibitors through virtual screening for CDK8 and single amino acid mutations in CDK8, namely D173A (Aspartate 173 mutate to Alanine), D189N (Aspartate 189 mutate to Asparagine), T196A (Threonine 196 mutate to Alanine) and T196D (Threonine 196 mutate to Aspartate). Four databases (CHEMBEL, ZINC, MCULE, and MolPort) containing 65,209,131 molecules have been searched to identify new inhibitors for CDK8 and its single mutations. In the first step, structure-based pharmacophore modeling in the Pharmit server was used to select the compounds to know the inhibitors. Then molecules with better predicted drug-like molecule properties were selected. The final filter used to select more effective inhibitors among the previously selected molecules was molecular docking. Finally, 13 hits for CDK8, 11 hits for D173A, 11 hits for D189N, 15 hits for T196A, and 12 hits for T196D were considered potential inhibitors. A majority of the virtual screening hits exhibited satisfactorily predict pharmacokinetic characteristics and toxicity properties.

Design, Synthesis and Molecular Docking Studies of Pyrazoline Derivatives as PI3K Inhibitors

AIM

Design, synthesis and molecular docking studies of quinoline/naphthalene containing pyrazoline derivatives as PI3K inhibitors.

BACKGROUND

Phosphatidylinositol 3-kinases (PI3Ks) belong to the family of enzymes, which are associated with various cellular functions such as cell growth, proliferation, differentiation etc. Overexpression or any changes in these functions may result in various abnormalities, which in turn cause cancer.

OBJECTIVES

To perform synthesis and molecular docking studies of quinoline/naphthalene containing pyrazoline derivatives as PI3K inhibitors.

METHODS

2-Chloroquinoline-3-carbaldehyde was synthesized by a reaction of acetanilide and POCl3. The latter was reacted with substituted acetophenones to synthesize chalcones, which were reacted with substituted phenyl hydrazines to yield pyrazoline derivatives (Series I). Similarly, pchloro benzaldehyde was reacted with 2-acetonapthone to yield chalcone with substituted phenyl hydrazines to yield pyrazoline derivatives (Series II).

RESULTS

The synthetic compounds were subjected to molecular modelling experiments using Schrodinger 2016 software and evaluated in silico for their PI3K binding affinities. All the compounds had better docking scores than AMG-319 (-4.36 Kcal/mol) and comparable docking scores with PI-103 (-6.83 Kcal/mol).

CONCLUSION

Compounds 5 and 3 had the best docking scores (-7.85 and -7.17 Kcal/mol, respectively). The synthesized compounds have better docking scores than the reference drug AMG-319. As a result, they might be used as lead molecules in investigating PI3K inhibitors.

Synthesis and In Silico Studies of Quinazolinones as PARP-1 Inhibitors

BACKGROUND

Cancer is a leading threat to humankind, accounting for nearly one million deaths in 2018, and the expected number of cancer-related deaths in 2040 is more than 16 million. The most common causes of cancer deaths are lung, colorectal, stomach, liver and breast cancer, while the highest number of new cancer cases belong to lung, breast, colorectal, prostate, stomach and liver cancer.

INTRODUCTION

PARP-1 is an enzyme that plays an important role in DNA repair, cell propagation/survival and death due to its influence on numerous biological processes. Quinazolinones represent an important scaffold in medicinal chemistry and have a broad spectrum of biological activities.

METHODS

In this study, we have synthesized quinazolinones by reaction of 2-aminobenzamide and substituted aldehydes. Molecular docking studies of synthesized compounds were performed for their PARP-1 binding affinities using Schrodinger 2016 software. In silico ADME studies were also performed for the synthesized compounds using the QikProp tool of Schrodinger software.

RESULTS

Results of molecular docking studies indicated that synthesized quinazolinones had a good affinity towards active site of PARP-1 and compound 4 had the best docking score (-10.343). Results of ADME studies indicated the drug-like properties of synthesized compounds, which make them suitable drug candidates.

CONCLUSION

All the synthesized compounds have a better docking score than niraparib (-9.05). Further, the synthesized compounds have a favorable ADME profile. Therefore, they may serve as important leads in discovering PARP-1 inhibitors.

Recent Progress in CDK4/6 Inhibitors and PROTACs

Cell division in eukaryotes is a highly regulated process that is critical to the life of a cell. Dysregulated cell proliferation, often driven by anomalies in cell Cyclin-dependent kinase (CDK) activation, is a key pathological mechanism in cancer. Recently, selective CDK4/6 inhibitors have shown clinical success, particularly in treating advanced-stage estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer. This review provides an in-depth analysis of the action mechanism and recent advancements in CDK4/6 inhibitors, categorizing them based on their structural characteristics and origins. Furthermore, it explores proteolysis targeting chimers (PROTACs) targeting CDK4/6. We hope that this review could be of benefit for further research on CDK4/6 inhibitors and PROTACs.

CDK4/6 inhibitors: basics, pros, and major cons in breast cancer treatment with specific regard to cardiotoxicity - a narrative review

Breast cancer is characterized by the uncontrolled proliferation of breast cells, with a high incidence reported in 2020 to have affected over 2 million women. In recent years, the conventional methods of treating breast cancer have involved radiotherapy and chemotherapy. However, the emergence of CDK4/6 inhibitors has shown potential as a promising cancer therapy. Cyclin-dependent kinases (CDK) inhibitors are a class of molecules that impede the formation of an active kinase complex, thereby hindering its activity and consequently halting the progression of the cell cycle. It was discovered that they have a significant impact on impeding the progression of the cancer. This is evident with the Food and Drug Administration's approval of drugs such as palbociclib, ribociclib, and abemaciclib for hormone receptor-positive metastatic breast cancer in combination with specific endocrine therapies. In spite of enormous success in breast cancer treatment, certain obstacles have emerged, such as therapy resistance, side effects, and most of all, cardiotoxicity. Some of these drawbacks have been successfully overcome by dosage reduction, different combinations of the drugs, and the assessment of each patient's condition and suitability prior to treatment. Yet other drawbacks still require tenacious research, especially certain cases of cardiotoxicities. This article delves into the biological mechanisms of CDK4/6 in the cell cycle and cancer, as well as the clinical advantages and most common adverse events (AEs) associated with CDK4/6 inhibitors. The primary objective of this review is to provide a comprehensive analysis of cardiotoxic AEs and elucidate the underlying pathophysiological mechanisms responsible for the cardiotoxicity of CDK4/6 inhibitors.

Cyclin-dependent kinases: Masters of the eukaryotic universe

A family of structurally related cyclin-dependent protein kinases (CDKs) drives many aspects of eukaryotic cell function. Much of the literature in this area has considered individual members of this family to act primarily either as regulators of the cell cycle, the context in which CDKs were first discovered, or as regulators of transcription. Until recently, CDK7 was the only clear example of a CDK that functions in both processes. However, new data points to several "cell-cycle" CDKs having important roles in transcription and some "transcriptional" CDKs having cell cycle-related targets. For example, novel functions in transcription have been demonstrated for the archetypal cell cycle regulator CDK1. The increasing evidence of the overlap between these two CDK types suggests that they might play a critical role in coordinating the two processes. Here we review the canonical functions of cell-cycle and transcriptional CDKs, and provide an update on how these kinases collaborate to perform important cellular functions. We also provide a brief overview of how dysregulation of CDKs contributes to carcinogenesis, and possible treatment avenues. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Processing > 3' End Processing RNA Processing > Splicing Regulation/Alternative Splicing.

Development of allosteric and selective CDK2 inhibitors for contraception with negative cooperativity to cyclin binding

Compared to most ATP-site kinase inhibitors, small molecules that target an allosteric pocket have the potential for improved selectivity due to the often observed lower structural similarity at these distal sites. Despite their promise, relatively few examples of structurally confirmed, high-affinity allosteric kinase inhibitors exist. Cyclin-dependent kinase 2 (CDK2) is a target for many therapeutic indications, including non-hormonal contraception. However, an inhibitor against this kinase with exquisite selectivity has not reached the market because of the structural similarity between CDKs. In this paper, we describe the development and mechanism of action of type III inhibitors that bind CDK2 with nanomolar affinity. Notably, these anthranilic acid inhibitors exhibit a strong negative cooperative relationship with cyclin binding, which remains an underexplored mechanism for CDK2 inhibition. Furthermore, the binding profile of these compounds in both biophysical and cellular assays demonstrate the promise of this series for further development into a therapeutic selective for CDK2 over highly similar kinases like CDK1. The potential of these inhibitors as contraceptive agents is seen by incubation with spermatocyte chromosome spreads from mouse testicular explants, where they recapitulate Cdk2-/- and Spdya-/- phenotypes.

Genomic Profiling of Lower-Grade Gliomas Subtype with Distinct Molecular and Clinicopathologic Characteristics via Altered DNA-Damage Repair Features

Lower WHO grade II and III gliomas (LGGs) exhibit significant genetic and transcriptional heterogeneity, and the heterogeneity of DNA damage repair (DDR) and its relationship to tumor biology, transcriptome, and tumor microenvironment (TME) remains poorly understood. In this study, we conducted multi-omics data integration to investigate DDR alterations in LGG. Based on clinical parameters and molecular characteristics, LGG patients were categorized into distinct DDR subtypes, namely, DDR-activated and DDR-suppressed subtypes. We compared gene mutation, immune spectrum, and immune cell infiltration between the two subtypes. DDR scores were generated to classify LGG patients based on DDR subtype features, and the results were validated using a multi-layer data cohort. We found that DDR activation was associated with poorer overall survival and that clinicopathological features of advanced age and higher grade were more common in the DDR-activated subtype. DDR-suppressed subtypes exhibited more frequent mutations in IDH1. In addition, we observed significant upregulation of activated immune cells in the DDR-activated subgroup, which suggests that immune cell infiltration significantly influences tumor progression and immunotherapeutic responses. Furthermore, we constructed a DDR signature for LGG using six DDR genes, which allowed for the division of patients into low- and high-risk groups. Quantitative real-time PCR results showed that CDK1, CDK2, TYMS, SMC4, and WEE1 were significantly upregulated in LGG samples compared to normal brain tissue samples. Overall, our study sheds light on DDR heterogeneity in LGG and provides insight into the molecular pathways of DDR involved in LGG development.

Targeting Protein-Protein Interactions to Inhibit Cyclin-Dependent Kinases

Cyclin-dependent kinases (CDKs) play diverse and critical roles in normal cells and may be exploited as targets in cancer therapeutic strategies. CDK4 inhibitors are currently approved for treatment in advanced breast cancer. This success has led to continued pursuit of targeting other CDKs. One challenge has been in the development of inhibitors that are highly selective for individual CDKs as the ATP-binding site is highly conserved across this family of proteins. Protein-protein interactions (PPI) tend to have less conservation amongst different proteins, even within protein families, making targeting PPI an attractive approach to improving drug selectivity. However, PPI can be challenging to target due to structural and physicochemical features of these interactions. A review of the literature specific to studies focused on targeting PPI involving CDKs 2, 4, 5, and 9 was conducted and is presented here. Promising lead molecules to target select CDKs have been discovered. None of the lead molecules discovered have led to FDA approval; however, the studies covered in this review lay the foundation for further discovery and develop of PPI inhibitors for CDKs.

A review on cyclin-dependent kinase 5: An emerging drug target for neurodegenerative diseases

Cyclin-dependent kinase 5 (CDK5) is the serine/threonine-directed kinase mainly found in the brain and plays a significant role in developing the central nervous system. Recent evidence suggests that CDK5 is activated by specific cyclins regulating its expression and activity. P35 and p39 activate CDK5, and their proteolytic degradation produces p25 and p29, which are stable products involved in the hyperphosphorylation of tau protein, a significant hallmark of various neurological diseases. Numerous high-affinity inhibitors of CDK5 have been designed, and some are marketed drugs. Roscovitine, like other drugs, is being used to minimize neurological symptoms. Here, we performed an extensive literature analysis to highlight the role of CDK5 in neurons, synaptic plasticity, DNA damage repair, cell cycle, etc. We have investigated the structural features of CDK5, and their binding mode with the designed inhibitors is discussed in detail to develop attractive strategies in the therapeutic targeting of CDK5 for neurodegenerative diseases. This review provides deeper mechanistic insights into the therapeutic potential of CDK5 inhibitors and their implications in the clinical management of neurodegenerative diseases.

Lessons Learned from Past Cyclin-Dependent Kinase Drug Discovery Efforts

Inhibition of cyclin-dependent kinases (CDKs) has become an effective therapeutic strategy for treating various diseases, especially cancer. Over almost three decades, although great efforts have been made to discover CDK inhibitors, many of which have entered clinical trials, only four CDK inhibitors have been approved. In the process of CDK inhibitor development, many difficulties and misunderstandings have hampered their discovery and clinical applications, which mainly include inadequate understanding of the biological functions of CDKs, less attention paid to pan- and multi-CDK inhibitors, nonideal isoform selectivity of developed selective CDK inhibitors, overlooking the metabolic stability of early discovered CDK inhibitors, no effective resistance solutions, and a lack of available combination therapy and effective biomarkers for CDK therapies. After reviewing the mechanisms of CDKs and the research progress of CDK inhibitors, this perspective summarizes and discusses these difficulties or lessons, hoping to facilitate the successful discovery of more useful CDK inhibitors.

Discovery of a novel cyclin-dependent kinase 8 inhibitor with an oxindole core for anti-inflammatory treatment

Chronic inflammation is an underlying cause in a number of diseases. Cyclin-dependent kinase 8 (CDK8) has been implicated as an inflammatory mediator, indicating its potential as an anti-inflammatory target. Herein, we performed structure-based virtual screening (SBVS) to identify novel CDK8 inhibitors. The pharmacological interactions for CDK8 were identified and incorporated into a SBVS protocol. Selected compounds were tested in enzymatic assays, and one compound was confirmed to be a CDK8 inhibitor with a 50% inhibitory concentration (IC₅₀) value of 1684.4 nM. Comparing structural analogs identified a compound, F059-1017, with greater potency (IC₅₀ 558.1 nM). When tested in cell lines, the compounds displayed low cytotoxicity. Cellular assays revealed that the identified CDK8 inhibitors can reduce phosphorylation and expression of signaling mediators associated with inflammation. In addition, results of kinase profiling showed that compound F059-1017 is selective towards CDK8. These findings suggest that the new inhibitors have great potential as lead compounds for developing novel anti-inflammatory therapeutics.

The Renaissance of Cyclin Dependent Kinase Inhibitors

Cyclin-dependent kinases (CDK) regulate cell cycle progression. During tumor development, altered expression and availability of CDKs strongly contribute to impaired cell proliferation, a hallmark of cancer. In recent years, targeted inhibition of CDKs has shown considerable therapeutic benefit in a variety of tumor entities. Their success is reflected in clinical approvals of specific CDK4/6 inhibitors for breast cancer. This review provides a detailed insight into the molecular mechanisms of CDKs as well as a general overview of CDK inhibition. It also summarizes the latest research approaches and current advances in the treatment of head and neck cancer with CDK inhibitors. Instead of monotherapies, combination therapies with CDK inhibitors may especially provide promising results in tumor therapy. Indeed, recent studies have shown a synergistic effect of CDK inhibition together with chemo- and radio- and immunotherapy in cancer treatment to overcome tumor evasion, which may lead to a renaissance of CDK inhibitors.

Serine/Threonine Protein Phosphatase 2A Regulates the Transport of Axonal Mitochondria

Microtubule-based transport provides mitochondria to distant regions of neurons and is essential for neuronal health. To identify compounds that increase mitochondrial motility, we screened 1,641 small-molecules in a high-throughput screening platform. Indirubin and cantharidin increased mitochondrial motility in rat cortical neurons. Cantharidin is known to inhibit protein phosphatase 2A (PP2A). We therefore tested two other inhibitors of PP2A: LB-100 and okadaic acid. LB-100 increased mitochondrial motility, but okadaic acid did not. To resolve this discrepancy, we knocked down expression of the catalytic subunit of PP2A (PP2CA). This long-term inhibition of PP2A more than doubled retrograde transport of axonal mitochondria, confirming the importance of PP2A as a regulator of mitochondrial motility and as the likely mediator of cantharidin's effect.

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.

CDK4/6 inhibitors: a brief overview and prospective research directions

The discovery of cyclin-dependent kinases (CDK) and their mechanism in regulating the cell cycle process was considered a game-changer in cancer therapy. Cell cycle arrest and apoptosis were both triggered by their inhibition. The CDK4/6 complex acts as a checkpoint during the cell cycle transition from cell growth (G1) to DNA synthesis (S) phase and its deregulation or overexpression induces abnormal cell proliferation and cancer development. Consequently, targeting CDK4/6 has been proposed as a paradigm shift in the anticancer approach. The design and development of effective CDK4/6 inhibitors are increasingly becoming a promising cancer therapy evident with approved drugs such as palbociclib, ribociclib, and abemaciclib, etc. In this article, we explore the biological importance of CDK4/6 in cancer therapy, the development of resistance to monotherapy, and a short overview of PROTAC (Proteolysis Targeting Chimera), a unique and pioneering technique for degrading CDK4/6 enzymes. Overall, our prime focus is to discuss novel CDK4/6 inhibitors with diverse chemical classes and their correlation with computational studies.

The discovery of cyclin-dependent kinases (CDK) and their mechanism in regulating the cell cycle process was considered a game-changer in cancer therapy.

Cyclin-dependent kinases-based synthetic lethality: Evidence, concept, and strategy

Synthetic lethality is a proven effective antitumor strategy that has attracted great attention. Large-scale screening has revealed many synthetic lethal genetic phenotypes, and relevant small-molecule drugs have also been implemented in clinical practice. Increasing evidence suggests that CDKs, constituting a kinase family predominantly involved in cell cycle control, are synthetic lethal factors when combined with certain oncogenes, such as MYC, TP53, and RAS, which facilitate numerous antitumor treatment options based on CDK-related synthetic lethality. In this review, we focus on the synthetic lethal phenotype and mechanism related to CDKs and summarize the preclinical and clinical discoveries of CDK inhibitors to explore the prospect of CDK inhibitors as antitumor compounds for strategic synthesis lethality in the future.

Liquid Biopsy: A New Tool for Overcoming CDKi Resistance Mechanisms in Luminal Metastatic Breast Cancer

Breast cancer (BC) is the most common cancer diagnosed in women worldwide. Approximately 70% of BC patients have the luminal subtype, which expresses hormone receptors (HR+). Adjuvant endocrine treatments are the standard of care for HR+/HER2− BC patients. Over time, approximately 30% of those patients develop endocrine resistance and metastatic disease. Cyclin-dependent kinase inhibitors (CDKi), in combination with an aromatase inhibitor or fulvestrant, have demonstrated superior efficacies in increasing progression-free survival, with a safe toxicity profile, in HR+/HER2− metastatic BC patients. CDKi blocks kinases 4/6, preventing G1/S cell cycle transition. However, not all of the patients respond to CDKi, and those who do respond ultimately develop resistance to the combined therapy. Studies in tumour tissues and cell lines have tried to elucidate the mechanisms that underlie this progression, but there are still no conclusive data. Over the last few years, liquid biopsy has contributed relevant information. Circulating tumour materials are potential prognostic markers for determining patient prognosis in metastatic luminal BC, for monitoring disease, and for treatment selection. This review outlines the different studies performed using liquid biopsy in patients with HR+ metastatic BC treated with CDKi plus endocrine therapy. We mainly focus on those studies that describe the possible resistance mechanisms in circulating tumour-derived material.

Small Molecule CDK Inhibitors for the Therapeutic Management of Cancer

Cyclin-dependent kinases (CDKs) are a group of multifunctional enzymes consisting of catalytic and regulatory subunits. The regulatory subunit, cyclin, remains dissociated under normal circumstances, and complexation of cyclin with the catalytic subunit of CDK leads to its activation for phosphorylation of protein substrates. The primary role of CDKs is in the regulation of the cell cycle. Retinoblastoma protein (Rb) is one of the widely investigated tumor suppressor protein substrates of CDK, which prevents cells from entering into cell-cycle under normal conditions. Phosphorylation of Rb by CDKs causes its inactivation and ultimately allows cells to enter a new cell cycle. Many cancers are associated with hyperactivation of CDKs as a result of mutation of the CDK genes or CDK inhibitor genes. Therefore, CDK modulators are of great interest to explore as novel therapeutic agents against cancer and led to the discovery of several CDK inhibitors to clinics. This review focuses on the current progress and development of anti-cancer CDK inhibitors from preclinical to clinical and synthetic to natural small molecules.

An update of new small-molecule anticancer drugs approved from 2015 to 2020

A high incidence of cancer has given rise to the development of more anti-tumor drugs. From 2015 to 2020, fifty-six new small-molecule anticancer drugs, divided into ten categories according to their anti-tumor target activities, have been approved. These include TKIs (30 drugs), MAPK inhibitors (3 drugs), CDK inhibitors (3 drugs), PARP inhibitors (3 drugs), PI3K inhibitors (3 drugs), SMO receptor antagonists (2 drugs), AR antagonists (2 drugs), SSTR inhibitors (2 drugs), IDH inhibitors (2 drugs) and others (6 drugs). Among them, PTK inhibitors (30/56) have led to a paradigm shift in cancer treatment with less toxicity and more potency. Each of their structures, approval statuses, applications, SAR analyses, and original research synthesis routes have been summarized, giving us a more comprehensive map for further efforts to design more specific targeted agents for reducing cancer in the future. We believe this review will help further research of potential antitumor agents in clinical usage.

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 of CDK4/6 Inhibitors: A Five Years Update

The inhibition of cyclin dependent kinases 4 and 6 plays a role in aromatase inhibitor resistant metastatic breast cancer. Three dual CDK4/6 inhibitors have been approved for the breast cancer treatment that, in combination with the endocrine therapy, dramatically improved the survival outcomes both in first and later line settings. The developments of the last five years in the search for new selective CDK4/6 inhibitors with increased selectivity, treatment efficacy, and reduced adverse effects are reviewed, considering the small-molecule inhibitors and proteolysis-targeting chimeras (PROTACs) approaches, mainly pointing at structure-activity relationships, selectivity against different kinases and antiproliferative activity.

Angel or Devil ? - CDK8 as the new drug target

Cyclin-dependent kinase 8 (CDK8) plays an momentous role in transcription regulation by forming kinase module or transcription factor phosphorylation. A large number of evidences have identified CDK8 as an important factor in cancer occurrence and development. In addition, CDK8 also participates in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis, and drug resistance. Therefore, CDK8 is regarded as a promising target for cancer therapy. Most studies in recent years supported the role of CDK8 as a carcinogen, however, under certain conditions, CDK8 exists as a tumor suppressor. The functional diversity of CDK8 and its exceptional role in different types of cancer have aroused great interest from scientists but even more controversy during the discovery of CDK8 inhibitors. In addition, CDK8 appears to be an effective target for inflammation diseases and immune system disorders. Therefore, we summarized the research results of CDK8, involving physiological/pathogenic mechanisms and the development status of compounds targeting CDK8, provide a reference for the feasibility evaluation of CDK8 as a therapeutic target, and guidance for researchers who are involved in this field for the first time.

Inhibitors of Cyclin-Dependent Kinase 1/2 for Anticancer Treatment

BACKGROUND

The cell cycle is regulated by cyclin-dependent kinases (CDKs) and their cognate cyclins, along with their endogenous inhibitors (CDKIs). CDKs act as central regulators in this process. Different CDKs play relevant roles in different phases. Among all CDKs, CDK1 is indispensible, which can drive all events that are required in the cell cycle in the absence of interphase CDKs (CDK2, CDK3, CDK4 and CDK6). So, CDK1 is an attractive target for anticancer drug development.

METHODS

CDK1 and CDK2 have 89.19% similar residues and 74.32% identical residues, their structures especially the ATP-binding sites are of great similarity. So, it is difficult to inhibit CDK1 and CDK2 individually. In this review, recent advances about CDK1/2 inhibitors were summarized. The chemical structures of different classes of CDK1/2 inhibitors and their structure activity are presented.

RESULTS

19 kinds of CDK1/2 or CDK1 inhibitors with different scaffolds, including CDK2 allosteric inhibitors, were summarized. Some inhibitors are nature derived, for example, phenanthrene derivatives, nortopsentin derivatives, variolin B derivatives and meridians.

CONCLUSION

Nature products, especially marine ones are potential resources for CDK1 inhibitors development. The findings of CDK2 allosteric inhibitors open an avenue to the discovery of novel selective CDK1 or other CDKs allosteric inhibitors.

Mechanisms of CDK4/6 Inhibitor Resistance in Luminal Breast Cancer

As a new-generation CDK inhibitor, a CDK4/6 inhibitor combined with endocrine therapy has been successful in the treatment of advanced estrogen receptor-positive (ER+) breast cancer. Although there has been overall progress in the treatment of cancer, drug resistance is an emerging cause for breast cancer-related death. Overcoming CDK4/6 resistance is an urgent problem. Overactivation of the cyclin-CDK-Rb axis related to uncontrolled cell proliferation is the main cause of CDK4/6 inhibitor resistance; however, the underlying mechanisms need to be clarified further. We review various resistance mechanisms of CDK4/6 inhibitors in luminal breast cancer. The cell signaling pathways involved in therapy resistance are divided into two groups: upstream response mechanisms and downstream bypass mechanisms. Finally, we discuss possible strategies to overcome CDK4/6 inhibitor resistance and identify novel resistance targets for future clinical application.

A perspective on potential target proteins of COVID-19: Comparison with SARS-CoV for designing new small molecules

SARS-CoV-2 (COVID-19) epidemic has created an unprecedented medical and economic crisis all over the world. SARS-CoV-2 is found to have more contagious character as compared to MERS-CoV and is spreading in a very fast manner all around the globe. It has affected over 31 million people all over the world till date. This virus shares around 80% of genome similarity with SARS-CoV. In this perspective, we have explored three major targets namely; SARS-CoV-2 spike (S) protein, RNA dependent RNA polymerase, and 3CL or Mpro Protease for the inhibition of SARS-CoV-2. These targets have attracted attention of the medicinal chemists working on computer-aided drug design in developing new small molecules that might inhibit these targets for combating COVID-19 disease. Moreover, we have compared the similarity of these target proteins with earlier reported coronavirus (SARS-CoV). We have observed that both the coronaviruses share around 80% similarity in their amino acid sequence. The key amino acid interactions which can play a crucial role in designing new small molecule inhibitors against COVID-19 have been reported in this perspective. Authors believe that this study will help the medicinal chemists to understand the key amino acids essential for interactions at the active site of target proteins in SARS-CoV-2, based on their similarity with earlier reported viruses. In this review, we have also described the lead molecules under various clinical trials for their efficacy against COVID-19.

Is highly expressed ACE 2 in pregnant women "a curse" in times of COVID-19 pandemic?

Angiotensin-converting enzyme 2 (ACE 2) is a membrane-bound enzyme that cleaves angiotensin II (Ang II) into angiotensin (1-7). It also serves as an important binding site for SARS-CoV-2, thereby, facilitating viral entry into target host cells. ACE 2 is abundantly present in the intestine, kidney, heart, lungs, and fetal tissues. Fetal ACE 2 is involved in myocardium growth, lungs and brain development. ACE 2 is highly expressed in pregnant women to compensate preeclampsia by modulating angiotensin (1-7) which binds to the Mas receptor, having vasodilator action and maintain fluid homeostasis. There are reports available on Zika, H1N1 and SARS-CoV where these viruses have shown to produce fetal defects but very little is known about SARS-CoV-2 involvement in pregnancy, but it might have the potential to interact with fetal ACE 2 and enhance COVID-19 transmission to the fetus, leading to fetal morbidity and mortality. This review sheds light on a path of SARS-CoV-2 transmission risk in pregnancy and its possible link with fetal ACE 2.

Identification of novel CDK 9 inhibitors based on virtual screening, molecular dynamics simulation, and biological evaluation

AIMS

Cyclin-dependent kinase 9 (CDK9) is a member of the CDK subfamily and plays a major role in the regulation of transcriptional elongation. It has attracted widespread attention as a therapeutic target for cancer. Here, we aimed to explore novel CDK 9 inhibitors by using a hybrid virtual screening strategy.

MAIN METHODS

A hybrid virtual screening strategy was constructed with computer-aided drug design (CADD). First, compounds were filtered in accordance with Lipinski's rule of five and adsorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. Second, a 3D-QSAR pharmacophore model was built and used as a 3D query to screen the obtained hit compounds. Third, the hit compounds were subjected to molecular docking studies. Fourth, molecular dynamics (MD) simulations were performed on CDK9 in complex with the final hits to examine the structural stability. Finally, CDK9 kinase biochemical assay was performed to identify the biological activity of the hit compounds.

KEY FINDINGS

Seven hit compounds were screened out. These hit compounds showed drug-like properties in accordance with Lipinski's rule of five and ADMET. Complexes involving the six hit compounds bound to CDK9 exhibited good structural stability in the MD simulation. Furthermore, these six hit compounds had strong inhibitory activity against CDK9 kinase. In particular, hit 3 showed the most promising activity with the percentage of 71%.

SIGNIFICANCE

The six hit compounds may be promising novel CDK9 inhibitors, and the hybrid virtual screening strategy designed in this study provides an important reference for the design and synthesis of novel CDK9 inhibitors.

Challenges and Opportunities in Cancer Drug Resistance

There has been huge progress in the discovery of targeted cancer therapies in recent years. However, even for the most successful and impactful cancer drugs which have been approved, both innate and acquired mechanisms of resistance are commonplace. These emerging mechanisms of resistance have been studied intensively, which has enabled drug discovery scientists to learn how it may be possible to overcome such resistance in subsequent generations of treatments. In some cases, novel drug candidates have been able to supersede previously approved agents; in other cases they have been used sequentially or in combinations with existing treatments. This review summarizes the current field in terms of the challenges and opportunities that cancer resistance presents to drug discovery scientists, with a focus on small molecule therapeutics. As part of this review, common themes and approaches have been identified which have been utilized to successfully target emerging mechanisms of resistance. This includes the increase in target potency and selectivity, alternative chemical scaffolds, change of mechanism of action (covalents, PROTACs), increases in blood-brain barrier permeability (BBBP), and the targeting of allosteric pockets. Finally, wider approaches are covered such as monoclonal antibodies (mAbs), bispecific antibodies, antibody drug conjugates (ADCs), and combination therapies.

Novel CDKs inhibitors for the treatment of solid tumour by simultaneously regulating the cell cycle and transcription control

A novel series of cyclin-dependent kinases (CDKs) inhibitors, which play critical roles in the cell cycle control and regulation of cell transcription, were synthesised. A systematic study of enzymatic and cellular assays led to the identification of compound X22 with a nanomolar potency against CDK4 and CDK9 and potent antiproliferative activities against a panel of tumour cell lines. X22 could induce cell cycle arrest and cell apoptosis in cancer cell lines. X22 dose-dependently inhibits signalling pathways downstream of CDKs in cancer cells. In vivo antitumor activity assays, oral administration of X22 led to significant tumour regression in mouse model without obvious toxicity. Superior anti-cancer efficacy in vitro and in vivo of X22 demonstrated combined depletion of cell cycle and transcriptional CDK all contributed to antitumor activity. Taken together, concomitant inhibition of cell cycle and transcriptional CDK activities provided valuable guide for further structural optimisation.

Discovery of novel cyclin-dependent kinase (CDK) and histone deacetylase (HDAC) dual inhibitors with potent in vitro and in vivo anticancer activity

In the current study, we reported a series of novel 1-H-pyrazole-3-carboxamide-based inhibitors targeting histone deacetylase (HDAC) and cyclin-dependent kinase (CDK). The representative compounds N-(4-((2-aminophenyl)carbamoyl)benzyl)-4-(2,6-dichlorobenzamido)-1H-pyrazole-3-carboxamide (7c) and N-(4-(2-((2-aminophenyl)amino)-2-oxoethyl)phenyl)-4-(2,6-dichlorobenzamido)-1H-pyrazole-3-carboxamide (14a) with potent antiproliferative activities towards five solid cancer cell lines, showed excellent inhibitory activities against HDAC2 (IC₅₀ = 0.25 and 0.24 nM respectively) and CDK2 (IC₅₀ = 0.30 and 0.56 nM respectively). In addition, compounds 7c and 14a significantly inhibited the migration of A375 and H460 cells. Further studies revealed that compounds 7c and 14a could arrest cell cycle in G2/M phase and promote apoptosis in A375, HCT116, H460 and Hela cells, which was associated with increasing the intracellular reactive oxygen species (ROS) levels. More importantly, compound 7c possessed favorable pharmacokinetic properties with the intraperitoneal bioavailability of 63.6% in ICR mice, and potent in vivo antitumor efficacy in the HCT116 xenograft model. Our study demonstrated that compound 7c provides a promising strategy for the treatment of malignant tumors.

In-silico molecular design of heterocyclic benzimidazole scaffolds as prospective anticancer agents

Benzimidazole is a valuable pharmacophore in the field of medicinal chemistry and exhibit wide spectrum of biological activity. Molecular docking technique is routinely used in modern drug discovery for understanding the drug-receptor interaction. The selected data set of synthesized benzimidazole compounds was evaluated for its in vitro anticancer activity against cancer cell lines (HCT116 and MCF7) by sulforhodamine B (SRB) assay. Further, molecular docking study of data set was carried out by Schrodinger-Maestro v11.5 using CDK-8 (PDB code: 5FGK) and ER-alpha (PDB code: 3ERT) as possible target for anticancer activity. Molecular docking results demonstrated that compounds 12, 16, N9, W20 and Z24 displayed good docking score with better interaction within crucial amino acids and corelate to their anticancer results. ADME results indicated that compounds 16, N9 and W20 have significant results within the close agreement of the Lipinski's rule of five and Qikprop rule within the range and these compounds may be taken as lead molecules for the discovery of new anticancer agents.

Synthesis of Oridonin Derivatives via Mizoroki-Heck Reaction and Click Chemistry for Cytotoxic Activity

BACKGROUND

Natural products (NPs) are evolutionarily chosen "privileged structures" that have a profound impact upon the anticancer drug discovery and development progress. However, the search for new drugs based on structure modification of NPs has often been hindered due to the tedious and complicated synthetic pathways. Fortunately, Mizoroki-Heck reaction and copper-catalyzed alkyne-azide cycloaddition (CuAAC) could provide perfect strategies for selective modification on NPs even in the presence of liable functionalities.

OBJECTIVE

Here, we used oridonin, an ent-kaurane diterpenoid that showed a wide range of biological activities, as a parent molecule for the generation of analogues with anticancer activity.

METHODS

Derivatives of oridonin were generated based on the structure-activity relationship study of oridonin and synthesized via Mizoroki-Heck reaction and CuAAC. The cytotoxicity of new oridonin derivatives were evaluated on both cancer cells and normal cells. Furthermore, the apoptotic effect and cell cycle arrest effect of the selected potent analogue were evaluated by flow cytometry and western blotting analysis.

RESULTS

Two series of novel C-14 and C-17 modified derivatives of oridonin were obtained via Heck reaction and copper-catalyzed alkyne-azide cycloaddition (CuAAC), respectively. In vitro antiproliferative activities showed that the introduction of C-14 (2-triazole)acetoxyl- moiety could retain or enhance cytotoxicity, whereas the introduction of C-17 phenyl ring might exert negative effect. Further studies demonstrated that derivative 23 exhibited broad-spectrum antiproliferative activity, effectively overcame drug-resistance and showed weak cytotoxicity on non-cancer cells. Preliminary mechanistic studies indicated that 23 might cause G2/M phase arrest and induce apoptosis in PC-3 cells.

CONCLUSION

Mizoroki-Heck reaction and CuAAC are perfect strategies for structure modification of complex natural products. The introduction of C-14 (2-triazole)acetoxyl- moiety could retain or enhance the cytotoxicity of oridonin, the introduction of C-17 phenyl group might exert negative effect on its cytotoxicity.