Discovery of PF-06873600, a CDK2/4/6 Inhibitor for the Treatment of Cancer

Novel Fused Pyrimidines as Potent Cyclin-Dependent Kinases Inhibitor for Gastric Adenocarcinoma: Combined In Vitro, In Silico Anticancer Studies

Our research aims to design novel pyrimidine derivatives inspired by the common pyrimidine core found in many FDA-approved drugs. However, extensive prior research on the pyrimidine scaffold has made discovering new molecules more challenging. To overcome this obstacle, we employed a molecular hybridisation strategy, opting to hybridise tetralin and pyrimidine, recognising their potential in cancer therapeutics. The fused pyrimidine was synthesised through a base-mediated condensation of chalcone with amidine. The reaction conditions were further optimised for base, solvent, temperature and time to produce a series of 21 novel derivatives. These compounds were subsequently screened for anticancer activity against gastric adenocarcinoma cell lines using the MTT assay. Among the synthesised compounds, 2-(pyridin-3-yl)-4-(pyridin-3-yl)-5,6-dihydrobenzo[h]quinazoline 8b and 4-(2-(pyridin-3-yl)-5,6 dihydrobenzo[h]quinazolin-4-yl) phenol 5g exhibited potent anticancer activity compared to (R)-Roscovitine. Additionally, a molecular docking study was conducted to assess the reactivity of compound 5g, revealing that the presence of a phenolic hydroxyl group enables hydrogen bonding with CDKs and enhances anticancer activity. Furthermore, the efficacy of compound 5g was validated through an in vitro CDK2/cyclin A2 enzyme inhibition assay. Interestingly, the observed CDK2 inhibitory activity showed a good correlation with the corresponding value for the antiproliferative activity of the tested compounds.

Targeting CDK2 to combat drug resistance in cancer therapy

Drug resistance remains a major obstacle in cancer treatment, leading to treatment failures and high mortality rates. Despite advancements in therapies, overcoming resistance requires a deeper understanding of its mechanisms. This review highlights CDK2's pivotal role in both intrinsic and acquired resistance, and its potential as a therapeutic target. Cyclin E upregulation, which partners with CDK2, is linked to poor prognosis and resistance across various cancers. Specifically, amplifications of CCNE1/CCNE2 are associated with resistance to targeted therapies, immunotherapy, endocrine therapies and chemo/radiotherapy. Given CDK2's involvement in resistance mechanisms, investigating its role presents promising opportunities for developing novel strategies to combat resistance and improve treatment outcomes.

An allosteric cyclin E-CDK2 site mapped by paralog hopping with covalent probes

More than half of the ~20,000 protein-encoding human genes have paralogs. Chemical proteomics has uncovered many electrophile-sensitive cysteines that are exclusive to subsets of paralogous proteins. Here we explore whether such covalent compound-cysteine interactions can be used to discover ligandable pockets in paralogs lacking the cysteine. Leveraging the covalent ligandability of C109 in the cyclin CCNE2, we substituted the corresponding residue in paralog CCNE1 to cysteine (N112C) and found through activity-based protein profiling that this mutant reacts stereoselectively and site-specifically with tryptoline acrylamides. We then converted the tryptoline acrylamide-CCNE1-N112C interaction into in vitro NanoBRET (bioluminescence resonance energy transfer) and in cellulo activity-based protein profiling assays capable of identifying compounds that reversibly inhibit both the N112C mutant and wild-type CCNE1:CDK2 (cyclin-dependent kinase 2) complexes. X-ray crystallography revealed a cryptic allosteric pocket at the CCNE1:CDK2 interface adjacent to N112 that binds the reversible inhibitors. Our findings, thus, show how electrophile-cysteine interactions mapped by chemical proteomics can extend the understanding of protein ligandability beyond covalent chemistry.

Discovery of a potent CDKs/FLT3 PROTAC with enhanced differentiation and proliferation inhibition for AML

AML is an aggressive malignancy of immature myeloid progenitor cells. Discovering effective treatments for AML through cell differentiation and anti-proliferation remains a significant challenge. Building on previous studies on CDK2 PROTACs with differentiation-inducing properties, this research aims to enhance CDKs degradation through structural optimization to facilitate the differentiation and inhibit the proliferation of AML cells. Compound C3, featuring a 4-methylpiperidine ring linker, effectively degraded CDK2 with a DC50 value of 18.73 ± 10.78 nM, and stimulated 72.77 ± 3.51 % cell differentiation at 6.25 nM in HL-60 cells. Moreover, C3 exhibited potent anti-proliferative activity against various AML cell types. Degradation selectivity analysis indicated that C3 could be endowed with efficient degradation of CDK2/4/6/9 and FLT3, especially FLT3-ITD in MV4-11 cells. These findings propose that C3 combined targeting CDK2/4/6/9 and FLT3 with enhanced differentiation and proliferation inhibition, which holds promise as a potential treatment for AML.

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.

Inhibitors and PROTACs of CDK2: challenges and opportunities

INTRODUCTION

Abundant evidence suggests that the overexpression of CDK2-cyclin A/E complex disrupts normal cell cycle regulation, leading to uncontrolled proliferation of cancer cells. Thus, CDK2 has become a promising therapeutic target for cancer treatment. In recent years, insights into the structures of the CDK2 catalytic site and allosteric pockets have provided notable opportunities for developing more effective clinical candidates of CDK2 inhibitors.

AREA COVERED

This article reviews the latest CDK2 inhibitors that have entered clinical trials and discusses the design and discovery of the most promising new preclinical CDK2 inhibitors in recent years. Additionally, it summarizes the development of allosteric CDK2 inhibitors and CDK2-targeting PROTACs. The review encompasses strategies for inhibitor and PROTAC design, structure-activity relationships, as well as in vitro and in vivo biological assessments.

EXPERT OPINION

Despite considerable effort, no CDK2 inhibitor has yet received FDA approval for marketing due to poor selectivity and observed toxicity in clinical settings. Future research must prioritize the optimization of the selectivity, potency, and pharmacokinetics of CDK2 inhibitors and PROTACs. Moreover, exploring combination therapies incorporating CDK2 inhibitors with other targeted agents, or the design of multi-target inhibitors, presents significant promise for advancing cancer treatment strategies.

Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment

Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.

Mechanisms of resistance to tyrosine kinase inhibitor-targeted therapy and overcoming strategies

Tyrosine kinase inhibitor (TKI)-targeted therapy has revolutionized cancer treatment by selectively blocking specific signaling pathways crucial for tumor growth, offering improved outcomes with fewer side effects compared with conventional chemotherapy. However, despite their initial effectiveness, resistance to TKIs remains a significant challenge in clinical practice. Understanding the mechanisms underlying TKI resistance is paramount for improving patient outcomes and developing more effective treatment strategies. In this review, we explored various mechanisms contributing to TKI resistance, including on-target mechanisms and off-target mechanisms, as well as changes in the tumor histology and tumor microenvironment (intrinsic mechanisms). Additionally, we summarized current therapeutic approaches aiming at circumventing TKI resistance, including the development of next-generation TKIs and combination therapies. We also discussed emerging strategies such as the use of dual-targeted antibodies and PROteolysis Targeting Chimeras. Furthermore, we explored future directions in TKI-targeted therapy, including the methods for detecting and monitoring drug resistance during treatment, identification of novel targets, exploration of dual-acting kinase inhibitors, application of nanotechnologies in targeted therapy, and so on. Overall, this review provides a comprehensive overview of the challenges and opportunities in TKI-targeted therapy, aiming to advance our understanding of resistance mechanisms and guide the development of more effective therapeutic approaches in cancer treatment.

Sulfone Electrophiles in Cross-Electrophile Coupling: Nickel-Catalyzed Difluoromethylation of Aryl Bromides

Fluoroalkyl fragments have played a critical role in the design of pharmaceutical and agrochemical molecules in recent years due to the enhanced biological properties of fluorinated molecules compared to their non-fluorinated analogues. Despite the potential advantages conferred by incorporating a difluoromethyl group in organic compounds, industrial adoption of difluoromethylation methods lags behind fluorination and trifluoromethylation. This is due in part to challenges in applying common difluoromethyl sources towards industrial applications. We report here the nickel-catalyzed cross-electrophile coupling of (hetero)aryl bromides with difluoromethyl 2-pyridyl sulfone, a sustainably sourced, crystalline difluoromethylation reagent. The scope of this reaction is demonstrated with 24 examples (67 ± 16% average yield) including a diverse array of heteroaryl bromides and precursors to difluoromethyl-containing preclinical pharmaceuticals. This reaction can be applied to small-scale parallel synthesis and benchtop scale-up under mild conditions. As sulfone reagents are uncommon electrophiles in cross-electrophile coupling, the mechanism of this process was investigated. Studies confirmed the formation of •CF2H instead of difluorocarbene. A series of modified difluoromethyl sulfones revealed that sulfone reactivity does not correlate exclusively with reduction potential and that coordination of cations or nickel to the pyridyl group is essential to reactivity, setting out parameters for matching the reactivity of sulfones in cross-electrophile coupling.

Synthetic Approaches and Clinical Application of Representative Small-Molecule Inhibitors of Cyclin-Dependent Kinase for Cancer Therapy

The regulation of the cancer cell cycle heavily relies on cyclin-dependent kinases (CDKs). Targeting CDKs has been identified as a promising approach for effective cancer therapy. In recent years, there has been significant attention paid towards developing small-molecule CDK inhibitors in the field of drug discovery. Notably, five such inhibitors have already received regulatory approval for the treatment of different cancers, including breast tumors, lung malignancies, and hematological malignancies. This review provides an overview of the synthetic routes used to produce 17 representative small-molecule CDK inhibitors that have obtained regulatory approval or are currently being evaluated through clinical trials. It also discusses their clinical applications for treating CDK-related diseases and explores the challenges and limitations associated with their use in a clinical setting, which will stimulate the further development of novel CDK inhibitors. By integrating therapeutic applications, synthetic methodologies, and mechanisms of action observed in various clinical trials involving these CDK inhibitors, this review facilitates a comprehensive understanding of the versatile roles and therapeutic potential offered by interventions targeting CDKs.

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.

Tumor biomarkers for diagnosis, prognosis and targeted therapy

Tumor biomarkers, the substances which are produced by tumors or the body's responses to tumors during tumorigenesis and progression, have been demonstrated to possess critical and encouraging value in screening and early diagnosis, prognosis prediction, recurrence detection, and therapeutic efficacy monitoring of cancers. Over the past decades, continuous progress has been made in exploring and discovering novel, sensitive, specific, and accurate tumor biomarkers, which has significantly promoted personalized medicine and improved the outcomes of cancer patients, especially advances in molecular biology technologies developed for the detection of tumor biomarkers. Herein, we summarize the discovery and development of tumor biomarkers, including the history of tumor biomarkers, the conventional and innovative technologies used for biomarker discovery and detection, the classification of tumor biomarkers based on tissue origins, and the application of tumor biomarkers in clinical cancer management. In particular, we highlight the recent advancements in biomarker-based anticancer-targeted therapies which are emerging as breakthroughs and promising cancer therapeutic strategies. We also discuss limitations and challenges that need to be addressed and provide insights and perspectives to turn challenges into opportunities in this field. Collectively, the discovery and application of multiple tumor biomarkers emphasized in this review may provide guidance on improved precision medicine, broaden horizons in future research directions, and expedite the clinical classification of cancer patients according to their molecular biomarkers rather than organs of origin.

Discovery of macrocyclic CDK2/4/6 inhibitors with improved potency and DMPK properties through a highly efficient macrocyclic drug design platform

Cyclin-dependent kinases (CDKs) are critical cell cycle regulators that are often overexpressed in tumors, making them promising targets for anti-cancer therapies. Despite substantial advancements in optimizing the selectivity and drug-like properties of CDK inhibitors, safety of multi-target inhibitors remains a significant challenge. Macrocyclization is a promising drug discovery strategy to improve the pharmacological properties of existing compounds. Here we report the development of a macrocyclization platform that enabled the highly efficient discovery of a novel, macrocyclic CDK2/4/6 inhibitor from an acyclic precursor (NUV422). Using dihedral angle scan and structure-based, computer-aided drug design to select an optimal ring-closing site and linker length for the macrocycle, we identified compound 8 as a potent new CDK2/4/6 inhibitor with optimized cellular potency and safety profile compared to NUV422. Our platform leverages both experimentally-solved as well as generative chemistry-derived macrocyclic structures and can be deployed to streamline the design of macrocyclic new drugs from acyclic starting compounds, yielding macrocyclic compounds with enhanced potency and improved drug-like properties.

Discovery of novel macrocyclic derivatives as potent and selective cyclin-dependent kinase 2 inhibitors

Cyclin-dependent kinase 2 (CDK2) is a member of CDK family of kinases (CDKs) that regulate the cell cycle. Its inopportune or over-activation leads to uncontrolled cell cycle progression and drives numerous types of cancers, especially ovarian, uterine, gastric cancer, as well as those associated with amplified CCNE1 gene. However, developing selective lead compound as CDK2 inhibitors remains challenging owing to similarities in the ATP pockets among different CDKs. Herein, we described the optimization of compound 1, a novel macrocyclic inhibitor targeting CDK2/5/7/9, aiming to discover more selective and metabolically stable lead compound as CDK2 inhibitor. Molecular dynamic (MD) simulations were performed for compound 1 and 9 to gain insights into the improved selectivity against CDK5. Further optimization efforts led to compound 22, exhibiting excellent CDK2 inhibitory activity, good selectivity over other CDKs and potent cellular effects. Based on these characterizations, we propose that compound 22 holds great promise as a potential lead candidate for drug development.

Identification of a Novel Selective CDK9 Inhibitor for the Treatment of CRC: Design, Synthesis, and Biological Activity Evaluation

Cyclin-dependent kinase 9 (CDK9) is a member of the transcription CDK subfamily. In this work, we preliminarily demonstrated the feasibility of CDK9 as a potent target of treatment for colorectal cancer, and a series of novel CDK9 inhibitors were rationally designed and synthesized based on the structure of AZD5438 (a pan CDKs inhibitor reported by AstraZeneca). A novel selective CDK9 inhibitor named CLZX-205, which possessed significant CDK9 inhibitory activity (IC50 = 2.9 nM) with acceptable pharmacokinetic properties and antitumor efficacy in vitro and in vivo, was developed. Research on the mechanism indicated that CLZX-205 could induce apoptosis in the HCT116 cell line by inhibiting phosphorylation of RNA polymerase II at Ser2, which resulted in the inhibition of apoptosis-related genes and proteins expression, and these results were validated at the cellular and tumor tissue levels. Currently, CLZX-205 is undergoing further research as a promising candidate for CRC treatment.

A Highly Anticipated Selective Therapeutic Agent against CDK2: INX-315

SUMMARY

In this issue, Dietrich, Trub, and colleagues describe and characterize a novel selective CDK2 inhibitor: INX-315. This agent shows promise in CCNE1-amplified cancers and in CDK4/6 inhibitor-resistant breast cancers. See related article by Dietrich et al., p. 446 (8).

Discovery of (4-Pyrazolyl)-2-aminopyrimidines as Potent and Selective Inhibitors of Cyclin-Dependent Kinase 2

CDK2 is a critical regulator of the cell cycle. For a variety of human cancers, the dysregulation of CDK2/cyclin E1 can lead to tumor growth and proliferation. Historically, early efforts to develop CDK2 inhibitors with clinical applications proved unsuccessful due to challenges in achieving selectivity over off-target CDK isoforms with associated toxicity. In this report, we describe the discovery of (4-pyrazolyl)-2-aminopyrimidines as a potent class of CDK2 inhibitors that display selectivity over CDKs 1, 4, 6, 7, and 9. SAR studies led to the identification of compound 17, a kinase selective and highly potent CDK2 inhibitor (IC50 = 0.29 nM). The evaluation of 17 in CCNE1-amplified mouse models shows the pharmacodynamic inhibition of CDK2, measured by reduced Rb phosphorylation, and antitumor activity.

WWP2 binds to NKRF, enhances the NF-κB signaling, and promotes malignant phenotypes of acute myeloid leukemia cells

Acute myeloid leukemia (AML) is one of the hematological malignancies with a high recurrence rate. WW domain-containing E3 ubiquitin protein ligase 2 (WWP2) is identified as a pivotal regulator of tumor progression. This study aimed to assess the possible role of WWP2 in AML. Analysis of the GEPIA database indicated an elevated WWP2 expression in AML. We established stable WWP2-overexpressed or WWP2-silenced cells using lentivirus loaded with cDNA encoding WWP2 mRNA or shRNA targeting WWP2. Notably, WWP2 overexpression facilitated cell proliferation and cell cycle progression, which was manifested as the increase of colony formation number, S-phase percentage and cell cycle related protein levels. As observed, WWP2 knockdown presented opposite effects, leading to inhibition of tumorigenicity. Strikingly, WWP2 knockdown induced apoptosis, accompanied by upregulation of pro-apoptosis proteins cleaved caspase-9, Bax and cleaved caspase-3 and downregulation of anti-apoptosis protein Bcl-2. Functionally, we further confirmed that WWP2 overexpression enhanced the NF-κB signaling and upregulated the levels of downstream genes, which may contribute to aggravating the development of AML. More importantly, by co-immunoprecipitation assay, we verified that WWP2 bound to NF-κB-repressing factor (NKRF) and promoted NKRF ubiquitylation. Dramatically, NKRF overexpression abolished the role of WWP2 in facilitating the process of AML. Overall, our observations confirm that WWP2 exerts a critical role in the tumorigenicity of AML, and NKRF is regarded as an essential factor in the WWP2-mediated AML progression. WWP2 may be proposed as a promising target of AML.

Expanding the ligandable proteome by paralog hopping with covalent probes

More than half of the ~20,000 protein-encoding human genes have at least one paralog. Chemical proteomics has uncovered many electrophile-sensitive cysteines that are exclusive to a subset of paralogous proteins. Here, we explore whether such covalent compound-cysteine interactions can be used to discover ligandable pockets in paralogs that lack the cysteine. Leveraging the covalent ligandability of C109 in the cyclin CCNE2, we mutated the corresponding residue in paralog CCNE1 to cysteine (N112C) and found through activity-based protein profiling (ABPP) that this mutant reacts stereoselectively and site-specifically with tryptoline acrylamides. We then converted the tryptoline acrylamide-N112C-CCNE1 interaction into a NanoBRET-ABPP assay capable of identifying compounds that reversibly inhibit both N112C- and WT-CCNE1:CDK2 complexes. X-ray crystallography revealed a cryptic allosteric pocket at the CCNE1:CDK2 interface adjacent to N112 that binds the reversible inhibitors. Our findings thus provide a roadmap for leveraging electrophile-cysteine interactions to extend the ligandability of the proteome beyond covalent chemistry.

Inhibitory potential of furanocoumarins against cyclin dependent kinase 4 using integrated docking, molecular dynamics and ONIOM methods

Cyclin Dependent Kinase 4 (CDK4) is vital in the process of cell-cycle and serves as a G1 phase checkpoint in cell division. Selective antagonists of CDK4 which are in use as clinical chemotherapeutics cause various side-effects in patients. Furanocoumarins induce anti-cancerous effects in a range of human tumours. Therefore, targeting these compounds against CDK4 is anticipated to enhance therapeutic effectiveness. This work intended to explore the CDK4 inhibitory potential of 50 furanocoumarin molecules, using a comprehensive approach that integrates the processes of docking, drug-likeness, pharmacokinetic analysis, molecular dynamics simulations and ONIOM (Our own N-layered Integrated molecular Orbital and Molecular mechanics) methods. The top five best docked compounds obtained from docking studies were screened for subsequent analysis. The molecules displayed good pharmacokinetic properties and no toxicity. Epoxybergamottin, dihydroxybergamottin and notopterol were found to inhabit the ATP-binding zone of CDK4 with substantial stability and negative binding free energy forming hydrogen bonds with key catalytic residues of the protein. Notopterol exhibiting the highest binding energy was subjected to ONIOM calculations wherein the hydrogen bonding interactions were retained with significant negative interaction energy. Hence, through these series of computerised methods, notopterol was screened as a potent CDK4 inhibitor and can act as a starting point in successive processes of drug design.Communicated by Ramaswamy H. Sarma.

Thiazolo-pyridopyrimidines: An in silico evaluation as a lead for CDK4/6 inhibition, synthesis and cytotoxicity screening against breast cancer cell lines

Introduction

Pyridopyrimidines belong to a class of compounds characterized by the presence of nitrogen as heteroatoms. These compounds exhibit diverse biological effects, particularly showing promise as anticancer agents, including actions that inhibit CDK4/6.

Methods

We designed and synthesized a range of substituted thiazolo-pyridopyrimidines (4a-p). Computational ADME/T analysis and molecular docking were performed using the crystal structure of CDK4/6. Subsequently, we synthesized the top-scoring compounds, characterized them using IR, NMR, and Mass spectroscopy, and assessed their impact on MCF-7 and MDAMB-231 cell lines using the SRB assay. To further evaluate stability, molecular dynamics simulations were conducted for the two most promising compounds within the binding site.

Results

The docking scores indicated stronger interactions for compounds 4a, 4c, 4d, and 4g. As a result, these specific compounds (4a, 4c, 4d, and 4g) were chosen for synthesis and subsequent screening to assess their cytotoxic effects. Remarkably, compounds 4c and 4a exhibited the most promising activity in terms of their IC50 values across both tested cell lines. Furthermore, molecular dynamics simulation studies uncovered an elevated level of stability within the 4c-6OQO complex.

Conclusion

By integrating insights from computational, in vitro, and molecular dynamics simulation findings, compound 4c emerges as a leading candidate for future investigations. The presence of a polar hydroxyl group at the C2 position of the 8-phenyl substitution on the pyridopyrimidine rings appears to contribute to the heightened activity of the compound. Further enhancements to cytotoxic potential could be achieved through structural refinements.

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.

Oncogenic signals prime cancer cells for toxic cell overgrowth during a G1 cell cycle arrest

CDK4/6 inhibitors are remarkable anti-cancer drugs that can arrest tumor cells in G1 and induce their senescence while causing only relatively mild toxicities in healthy tissues. How they achieve this mechanistically is unclear. We show here that tumor cells are specifically vulnerable to CDK4/6 inhibition because during the G1 arrest, oncogenic signals drive toxic cell overgrowth. This overgrowth causes permanent cell cycle withdrawal by either preventing progression from G1 or inducing genotoxic damage during the subsequent S-phase and mitosis. Inhibiting or reverting oncogenic signals that converge onto mTOR can rescue this excessive growth, DNA damage, and cell cycle exit in cancer cells. Conversely, inducing oncogenic signals in non-transformed cells can drive these toxic phenotypes and sensitize the cells to CDK4/6 inhibition. Together, this demonstrates that cell cycle arrest and oncogenic cell growth is a synthetic lethal combination that is exploited by CDK4/6 inhibitors to induce tumor-specific toxicity.

Discovery of dual PARP and CDK6 inhibitors for triple-negative breast cancer with wild-type BRCA

Inhibition of PARP is synthetic lethal with defects in BRCA, which provide effective targeted therapy strategy for BRCA mutation type of TNBC patients. However, approximately 80% of TNBC patients do not have BRCA mutations. Recent studies have shown that CDK4/6 inhibitors can increase the sensitivity of wild-type BRCA cells to PARP inhibitors. We designed a series of dual PARP and CDK6 inhibitors, and the most promising compound, P4i, showed good inhibitory activity against PARP1 and CDK6 and good inhibitory effects on MDA-MB-231 (IC50 = 1.96 μM), MDA-MB-468 (IC50 = 2.81 μM) and BT-549 (IC50 = 2.37 μM) cells with wild-type BRCA. Compared with Olaparib, the inhibition capacity of the three BRCA wild-type (MDA-MB-231, MDA-MB-468 and BT-549) cells was about 10-20 times higher, and even better than the combination of Olaparib and Palbociclib. As a novel PARP multifunctional molecule, it is a potential compound for the treatment of BRCA wild-type TNBC.

Discovery of Selective Tertiary Amide Inhibitors of Cyclin-Dependent Kinase 2 (CDK2)

Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle and are frequently altered in cancer cells, thereby leading to uncontrolled proliferation. In this context, CDK2 has emerged as an appealing target for anticancer drug development. Herein, we describe the discovery of a series of selective small molecule inhibitors of CDK2 beginning with historical compounds from our ERK2 program (e.g., compound 6). Structure-based drug design led to the potent and selective tool compound 32, where excellent selectivity against ERK2 and CDK4 was achieved by filling the lipophilic DFG-1 pocket and targeting interactions with CDK2-specific lower hinge binding residues, respectively. Compound 32 demonstrated 112% tumor growth inhibition in mice bearing OVCAR3 tumors with 50 mg/kg bis in die (BID) oral dosing.

Cyclin E/CDK2 and feedback from soluble histone protein regulate the S phase burst of histone biosynthesis

Faithful DNA replication requires that cells fine-tune their histone pool in coordination with cell-cycle progression. Replication-dependent histone biosynthesis is initiated at a low level upon cell-cycle commitment, followed by a burst at the G1/S transition, but it remains unclear how exactly the cell regulates this burst in histone biosynthesis as DNA replication begins. Here, we use single-cell time-lapse imaging to elucidate the mechanisms by which cells modulate histone production during different phases of the cell cycle. We find that CDK2-mediated phosphorylation of NPAT at the restriction point triggers histone transcription, which results in a burst of histone mRNA precisely at the G1/S phase boundary. Excess soluble histone protein further modulates histone abundance by promoting the degradation of histone mRNA for the duration of S phase. Thus, cells regulate their histone production in strict coordination with cell-cycle progression by two distinct mechanisms acting in concert.

Rapid adaptation to CDK2 inhibition exposes intrinsic cell-cycle plasticity

CDK2 is a core cell-cycle kinase that phosphorylates many substrates to drive progression through the cell cycle. CDK2 is hyperactivated in multiple cancers and is therefore an attractive therapeutic target. Here, we use several CDK2 inhibitors in clinical development to interrogate CDK2 substrate phosphorylation, cell-cycle progression, and drug adaptation in preclinical models. Whereas CDK1 is known to compensate for loss of CDK2 in Cdk2-/- mice, this is not true of acute inhibition of CDK2. Upon CDK2 inhibition, cells exhibit a rapid loss of substrate phosphorylation that rebounds within several hours. CDK4/6 activity backstops inhibition of CDK2 and sustains the proliferative program by maintaining Rb1 hyperphosphorylation, active E2F transcription, and cyclin A2 expression, enabling re-activation of CDK2 in the presence of drug. Our results augment our understanding of CDK plasticity and indicate that co-inhibition of CDK2 and CDK4/6 may be required to suppress adaptation to CDK2 inhibitors currently under clinical assessment.

An Analysis of Successful Hit-to-Clinical Candidate Pairs

An analysis of 156 published clinical candidates from the Journal of Medicinal Chemistry between 2018 and 2021 was conducted to identify lead generation strategies most frequently employed leading to drug candidates. As in a previous publication, the most frequent lead generation strategies resulting in clinical candidates were from known compounds (59%) followed by random screening approaches (21%). The remainder of the approaches included directed screening, fragment screening, DNA-encoded library screening (DEL), and virtual screening. An analysis of similarity was also conducted based on Tanimoto-MCS and revealed most clinical candidates were distant from their original hits; however, most shared a key pharmacophore that translated from hit-to-clinical candidate. An examination of frequency of oxygen, nitrogen, fluorine, chlorine, and sulfur incorporation in clinical candidates was also conducted. The three most similar and least similar hit-to-clinical pairs from random screening were examined to provide perspective on changes that occur that lead to successful clinical candidates.

Synthesis and biological evaluation of novel pteridin-7(8H)-one derivatives as potent CDK2 inhibitors

Cyclin-dependent kinase 2 (CDK2) is considered as an important target in the research of antitumor drugs. Taking the CDK2/4/6 inhibitor Ebvaciclib as the positive control and an in-house library compound (23) as the lead compound, three classes of 30 target compounds with pteridin-7(8H)-one as the core structure were designed to establish structure-activity relationships (SAR). In general, SAR of pteridin-7(8H)-one CDK2 inhibitors is systematically described in this paper, resulting in the discovery of two compounds (KII-17 and KII-21) with further research value. After the above compounds were tested for CDK2/4/6 kinase selectivity, we found that compound KII-21 was about 3 and 4 times more selective to CDK2-cyclinE2 than CDK4-cyclinD1 and CDK6-cyclinD3, respectively. This work also provides a reference basis for the subsequent research on CDK2 inhibitors.

An Interpretable Multitask Framework BiLAT Enables Accurate Prediction of Cyclin-Dependent Protein Kinase Inhibitors

The cyclin-dependent protein kinases (CDKs) are protein-serine/threonine kinases with crucial effects on the regulation of cell cycle and transcription. CDKs can be a hallmark of cancer since their excessive expression could lead to impaired cell proliferation. However, the selectivity profile of most developed CDK inhibitors is not enough, which have hindered the therapeutic use of CDK inhibitors. In this study, we propose a multitask deep learning framework called BiLAT based on SMILES representation for the prediction of the inhibitory activity of molecules on eight CDK subtypes (CDK1, 2, 4-9). The framework is mainly composed of an improved bidirectional long short-term memory module BiLSTM and the encode layer of the Transformer framework. Additionally, the data enhancement method of SMILES enumeration is applied to improve the performance of the model. Compared with baseline predictive models based on three conventional machine learning methods and two multitask deep learning algorithms, BiLAT achieves the best performance with the highest average AUC, ACC, F1-score, and MCC values of 0.938, 0.894, 0.911, and 0.715 for the test set. Moreover, we constructed a targeted external data set CDK-Dec for the CDK family, which mainly contains bait values screened by 3D similarity with active compounds. This dataset was utilized in the subsequent evaluation of our model. It is worth mentioning that the BiLAT model is interpretable and can be used by chemists to design and synthesize compounds with improved activity. To further verify the generalization ability of the multitask BiLAT model, we also conducted another evaluation on three public datasets (Tox21, ClinTox, and SIDER). Compared with several currently popular models, BiLAT shows the best performance on two datasets. These results indicate that BiLAT is an effective tool for accelerating drug discovery.

The Evolving Nature of Biocatalysis in Pharmaceutical Research and Development

Biocatalysis is a highly valued enabling technology for pharmaceutical research and development as it can unlock synthetic routes to complex chiral motifs with unparalleled selectivity and efficiency. This perspective aims to review recent advances in the pharmaceutical implementation of biocatalysis across early and late-stage development with a focus on the implementation of processes for preparative-scale syntheses.

Aging microenvironment and antitumor immunity for geriatric oncology: the landscape and future implications

The tumor microenvironment (TME) has been extensively investigated; however, it is complex and remains unclear, especially in elderly patients. Senescence is a cellular response to a variety of stress signals, which is characterized by stable arrest of the cell cycle and major changes in cell morphology and physiology. To the best of our knowledge, senescence leads to consistent arrest of tumor cells and remodeling of the tumor-immune microenvironment (TIME) by activating a set of pleiotropic cytokines, chemokines, growth factors, and proteinases, which constitute the senescence-associated secretory phenotype (SASP). On the one hand, the SASP promotes antitumor immunity, which enhances treatment efficacy; on the other hand, the SASP increases immunosuppressive cell infiltration, including myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), M2 macrophages, and N2 neutrophils, contributing to TIME suppression. Therefore, a deeper understanding of the regulation of the SASP and components contributing to robust antitumor immunity in elderly individuals with different cancer types and the available therapies is necessary to control tumor cell senescence and provide greater clinical benefits to patients. In this review, we summarize the key biological functions mediated by cytokines and intercellular interactions and significant components of the TME landscape, which influence the immunotherapy response in geriatric oncology. Furthermore, we summarize recent advances in clinical practices targeting TME components and discuss potential senescent TME targets.

Hit discovery of novel 2-phenyl-substituted 4-amino-6,7-dihydro-5H-cyclopenta[d]pyrimidines as potential anti-glioblastoma therapeutics: Design, synthesis, biological evaluation, and computational screening

Glioblastoma multiforme (GBM) is a highly-aggressive, dreadful disease with poor prognosis and disappointing clinical success. There is an unmet medical need of molecularly-targeted therapeutics for GBM treatment. In the present work, a series of novel 2-phenyl-substituted 4-amino-6,7-dihydro-5H-cyclopenta[d]pyrimidines was designed, synthesized, purified, characterized, and evaluated for cytotoxicity against glioblastoma cell line U87-MG. The design process (virtual library enumeration around the core, physicochemical and molecular property prediction/calculation of the designs, filtering the undesirable ones, and the diversity analyses of the lead-like designs), was carefully curated so as to obtain a set of structurally-diverse, novel molecules (total 20), with a particular focus on the relatively unexplored core structure, 6,7-dihydro-5H-cyclopenta[d]pyrimidine. The preliminary screening was done using MTT assay at 10 and 100 μM concentrations of the title compounds F₁ -F₂₀ and positive control cisplatin, which yielded six hits (% inhibition at 10 μM: ~50%)-F₂ , F₃ , F₅ , F₇ , F₁₅ , and F₂₀ , which were taken up for IC₅₀ determination. The top hits F₂ and F₇ (IC₅₀  < 10 μM) were further used for computational studies such as target prediction, followed by their molecular docking in the binding sites of the top-3 predicted targets (epidermal growth factor receptor kinase domain, cyclin-dependent kinase 2 [CDK2]) /cyclin E, and anaplastic lymphoma kinase [ALK]). The docking pose analyses revealed interesting trends. The relatively planar core structure, presence of favorable hinge-binding substructures, basic groups, all added up, and culminated in appreciable cytotoxicity against GBM cell line.

2-Anilino-4-(1-methyl-1H-pyrazol-4-yl)pyrimidine-derived CDK2 inhibitors as anticancer agents: Design, synthesis & evaluation

Deregulation of cyclin-dependent kinase 2 (CDK2) and its activating partners, cyclins A and E, is associated with the pathogenesis of a myriad of human cancers and with resistance to anticancer drugs including CDK4/6 inhibitors. Thus, CDK2 has become an attractive target for the development of new anticancer therapies and for the amelioration of the resistance to CDK4/6 inhibitors. Bioisosteric replacement of the thiazole moiety of CDKI-73, a clinically trialled CDK inhibitor, by a pyrazole group afforded 9 and 19 that displayed potent CDK2-cyclin E inhibition (K_i = 0.023 and 0.001 μM, respectively) with submicromolar antiproliferative activity against a panel of cancer cell lines (GI₅₀ = 0.025-0.780 μM). Mechanistic studies on 19 with HCT-116 colorectal cancer cells revealed that the compound reduced the phosphorylation of retinoblastoma at Ser807/811, arrested the cells at the G2/M phase, and induced apoptosis. These results highlight the potential of the 2-anilino-4-(1-methyl-1H-pyrazol-4-yl)pyrimidine series in developing potent and selective CDK2 inhibitors to combat cancer.

Design, Synthesis, and Bioevaluation of Pyrido[2,3-d]pyrimidin-7-ones as Potent SOS1 Inhibitors

The use of small molecular modulators to target the guanine nucleotide exchange factor SOS1 has been demonstrated to be a promising strategy for the treatment of various KRAS-driven cancers. In the present study, we designed and synthesized a series of new SOS1 inhibitors with the pyrido[2,3-d]pyrimidin-7-one scaffold. One representative compound 8u showed comparable activities to the reported SOS1 inhibitor BI-3406 in both the biochemical assay and the 3-D cell growth inhibition assay. Compound 8u obtained good cellular activities against a panel of KRAS G12-mutated cancer cell lines and inhibited downstream ERK and AKT activation in MIA PaCa-2 and AsPC-1 cells. In addition, it displayed synergistic antiproliferative effects when used in combination with KRAS G12C or G12D inhibitors. Further modifications of the new compounds may give us a promising SOS1 inhibitor with favorable druglike properties for use in the treatment of KRAS-mutated patients.

Deregulated E2F Activity as a Cancer-Cell Specific Therapeutic Tool

The transcription factor E2F, the principal target of the tumor suppressor pRB, plays crucial roles in cell proliferation and tumor suppression. In almost all cancers, pRB function is disabled, and E2F activity is enhanced. To specifically target cancer cells, trials have been undertaken to suppress enhanced E2F activity to restrain cell proliferation or selectively kill cancer cells, utilizing enhanced E2F activity. However, these approaches may also impact normal growing cells, since growth stimulation also inactivates pRB and enhances E2F activity. E2F activated upon the loss of pRB control (deregulated E2F) activates tumor suppressor genes, which are not activated by E2F induced by growth stimulation, inducing cellular senescence or apoptosis to protect cells from tumorigenesis. Deregulated E2F activity is tolerated in cancer cells due to inactivation of the ARF-p53 pathway, thus representing a feature unique to cancer cells. Deregulated E2F activity, which activates tumor suppressor genes, is distinct from enhanced E2F activity, which activates growth-related genes, in that deregulated E2F activity does not depend on the heterodimeric partner DP. Indeed, the ARF promoter, which is specifically activated by deregulated E2F, showed higher cancer-cell specific activity, compared to the E2F1 promoter, which is also activated by E2F induced by growth stimulation. Thus, deregulated E2F activity is an attractive potential therapeutic tool to specifically target cancer cells.

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

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

Anti-cancer drug molecules targeting cancer cell cycle and proliferation

Cancer, a vicious clinical burden that potentiates maximum fatality for humankind, arises due to unregulated excessive cell division and proliferation through an eccentric expression of cell cycle regulator proteins. A set of evolutionarily conserved machinery controls the cell cycle in an extremely precise manner so that a cell that went through the cycle can produce a genetically identical copy. To achieve perfection, several checkpoints were placed in the cycle for surveillance; so, errors during the division were rectified by the repair strategies. However, irreparable damage leads to exit from the cell cycle and induces programmed cell death. In comparison to a normal cell, cancer cells facilitate the constitutive activation of many dormant proteins and impede negative regulators of the checkpoint. Extensive studies in the last few decades on cell division and proliferation of cancer cells elucidate the molecular mechanism of the cell-cycle regulators that are often targeted for the development of anti-cancer therapy. Each phase of the cell cycle has been regulated by a unique set of proteins including master regulators Cyclins, and CDKs, along with the accessory proteins such as CKI, Cdc25, error-responsive proteins, and various kinase proteins mainly WEE1 kinases, Polo-like kinases, and Aurora kinases that control cell division. Here in this chapter, we have analytically discussed the role of cell cycle regulators and proliferation factors in cancer progression and the rationale of using various cell cycle-targeting drug molecules as anti-cancer therapy.

Applications and mechanisms of the cyclin-dependent kinase 4/6 inhibitor, PD-0332991, in solid tumors

Abnormal CDK4/6-Rb-E2F signal transduction is a common finding in tumors and is a driving factor for the excessive proliferation of various tumor cells. PD-0332991, a highly specific, small molecule inhibitor for CDK4 and 6, has been shown to inhibit tumor growth by abrogating the phosphorylating capacity of CDK4/6 and suppressing Rb phosphorylation. It has been promoted for the treatment of breast cancer and potentially for other tumor types such as liver cancers, lung cancers and sarcomas. Due to the risk of monotherapy resistance, PD-0332991 is commonly used in combination with other drugs. Such combination treatments have proved able to inhibit tumor proliferation more effectively, induce stronger senescence and apoptosis, and enhance the efficiency of immunotherapy. Therefore, tumor cells with senescence induced by PD-0332991 are now used as ideal screening tools of cytolytic drugs with more efficient and thorough anti-tumor properties. With more extensive understandings about the branching points between senescence and apoptosis, it is possible to refine the dosage of PD-0332991. Better characterization of resistant cells, of inhibitors and of adverse effects such as leukopenia are needed to overcome obstacles in the use of PD-0332991. In this review of PD-0332991 research, we hope to provide guidance of transitions from laboratory findings to clinical applications of PD-0332991 and to facilitate PD-0332991-based multi-inhibitor combination therapies for various tumors.

Resistance to CDK4/6 inhibition: Mechanisms and strategies to overcome a therapeutic problem in the treatment of hormone receptor-positive metastatic breast cancer

Selective CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, have been approved in combination with hormone therapy for the treatment of patients with HR+, HER2-negative advanced or metastatic breast cancer (mBC). Despite their promising activity, approximately 10 % of patients have de novo resistance, while the rest of them will develop acquired resistance after 24-28 months when used as first-line therapy and after a shorter period when used as second-line therapy. Various mechanisms of resistance to CDK4/6 inhibitors have been described, including cell cycle-related mechanisms, such as RB loss, p16 amplification, CDK6 or CDK4 amplification, and cyclin E-CDK2 amplification. Other bypass mechanisms involve the activation of FGFR or PI3K/AKT/mTOR pathways. Identifying the different mechanisms by which resistance to CDK4/6 inhibitors occurs may help to design new treatment strategies to improve patient outcomes. This review presents the currently available knowledge on the mechanisms of resistance to CDK4/6 inhibitors, explores possible treatment strategies that could overcome this therapeutic problem, and summarizes relevant recent clinical trials.

Uncovering the degrader of D-type cyclins

AMBRA1 is identified as the long-sought, major controller of D-type cyclins

Discovery of 5,7-Dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-ones as Highly Selective CDK2 Inhibitors

A series of exceptionally selective CDK2 inhibitors are described. Starting from an HTS hit, we successfully scaffold hopped to a 5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one core structure, which imparted a promising initial selectivity within the CDK family. Extensive further SAR identified additional factors that drove selectivity to above 200× for CDKs 1/4/6/7/9. General kinome selectivity was also greatly improved. Finally, use of in vivo metabolite identification allowed us to pinpoint sulfonamide dealkylation as the primary metabolite, which was ameliorated through the deuterium effect.

Concurrent inhibition of CDK2 adds to the anti-tumour activity of CDK4/6 inhibition in GIST

BACKGROUND

Advanced gastrointestinal stromal tumour (GIST) is characterised by genomic perturbations of key cell cycle regulators. Oncogenic activation of CDK4/6 results in RB1 inactivation and cell cycle progression. Given that single-agent CDK4/6 inhibitor therapy failed to show clinical activity in advanced GIST, we evaluated strategies for maximising response to therapeutic CDK4/6 inhibition.

METHODS

Targeted next-generation sequencing and multiplexed protein imaging were used to detect cell cycle regulator aberrations in GIST clinical samples. The impact of inhibitors of CDK2, CDK4 and CDK2/4/6 was determined through cell proliferation and protein detection assays. CDK-inhibitor resistance mechanisms were characterised in GIST cell lines after long-term exposure.

RESULTS

We identify recurrent genomic aberrations in cell cycle regulators causing co-activation of the CDK2 and CDK4/6 pathways in clinical GIST samples. Therapeutic co-targeting of CDK2 and CDK4/6 is synergistic in GIST cell lines with intact RB1, through inhibition of RB1 hyperphosphorylation and cell proliferation. Moreover, RB1 inactivation and a novel oncogenic cyclin D1 resulting from an intragenic rearrangement (CCND1::chr11.g:70025223) are mechanisms of acquired CDK-inhibitor resistance in GIST.

CONCLUSIONS

These studies establish the biological rationale for CDK2 and CDK4/6 co-inhibition as a therapeutic strategy in patients with advanced GIST, including metastatic GIST progressing on tyrosine kinase inhibitors.

Visible-Light-Promoted bis(Difluoromethylation)/Cyclization of 2-Vinyloxy Arylalkynes to Prepare Benzofuran Derivatives

A visible-light-promoted difluoromethylation/cyclization of 2-vinyloxy arylalkynes was developed, providing a variety of bis(difluoromethyl)-substituted benzofurans in moderate to good yields. A plausible mechanism involving difluoromethyl radical cascade cyclization and solvent-promoted ionic addition was proposed. This protocol has the advantages of having mild reaction conditions, simple operation, and good functional group tolerance.

Reversible lysine-targeted probes reveal residence time-based kinase selectivity

The expansion of the target landscape of covalent inhibitors requires the engagement of nucleophiles beyond cysteine. Although the conserved catalytic lysine in protein kinases is an attractive candidate for a covalent approach, selectivity remains an obvious challenge. Moreover, few covalent inhibitors have been shown to engage the kinase catalytic lysine in animals. We hypothesized that reversible, lysine-targeted inhibitors could provide sustained kinase engagement in vivo, with selectivity driven in part by differences in residence time. By strategically linking benzaldehydes to a promiscuous kinase binding scaffold, we developed chemoproteomic probes that reversibly and covalently engage >200 protein kinases in cells and mice. Probe-kinase residence time was dramatically enhanced by a hydroxyl group ortho to the aldehyde. Remarkably, only a few kinases, including Aurora A, showed sustained, quasi-irreversible occupancy in vivo, the structural basis for which was revealed by X-ray crystallography. We anticipate broad application of salicylaldehyde-based probes to proteins that lack a druggable cysteine.

Stereocontrolled Pericyclic and Radical Cycloaddition Reactions of Readily Accessible Chiral Alkenyl Diazaborolidines

In this paper is described an easily synthesized chiral diazaborolidine that is inexpensive, stable, and provides excellent stereoselection across a number of reaction classes. These versatile compounds possess utility in four different classes of cycloaddition reactions, offering good yield and stereoselectivity. X-ray structure analysis provides insight about the origin of stereocontrol.

Exploiting senescence for the treatment of cancer

Senescence is a cellular response to a variety of stress signals that is characterized by a stable withdrawal from the cell cycle and major changes in cell morphology and physiology. While most research on senescence has been performed on non-cancer cells, it is evident that cancer cells can also mount a senescence response. In this Review, we discuss how senescence can be induced in cancer cells. We describe the distinctive features of senescent cancer cells and how these changes in cellular physiology might be exploited for the selective eradication of these cells (senolysis). We discuss activation of the host immune system as a particularly attractive way to clear senescent cancer cells. Finally, we consider the challenges and opportunities provided by a 'one-two punch' sequential treatment of cancer with pro-senescence therapy followed by senolytic therapy.