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[Display omitted] • Compound A4 is an efficient DCAF16-based PROTACs that induces the degradation of CDK4/6. • Compound A4 exhibits 7 times lower toxicity than Palbociclib in non-tumor cells LO2. • Compound A4 capable of achieving antitumor activity in TNBC cell lines MDA-MB-231 both in vitro and in vivo. Treatment of breast cancer has greatly evolved during the last decades, but triple negative breast cancer (TNBC) with a higher degree of malignancy cannot be directly and effectively treated. Abnormal cell cycle is generally found in human breast cancer and other malignant tumors, and cyclin-dependent kinases (CDK) 4/6, a cell cycle-related regulatory nuclear protein, is deemed as an effective target for breast cancer treatment so far. Since DCAF16 E3 ligase is also mainly distributed in the nucleus, in this study, by combining Palbociclib and DCAF16 E3 ligase ligand KB02 with different linkers, a series of DCAF16 based CDK4/6 degraders were designed and synthesized. Among them, compound A4 showed potent inhibitory activity against CDK4/6, and decreased the level of CDK4/6 protein in MDA-MB-231 cells in a concentration- and time-dependent manner. Moreover, the toxicity of A4 in normal cells showed 7 times lower than that of Palbociclib, and A4 exhibits therapeutic potential in MDA-MB-231 xenograft models in vivo. These findings indicate that A4, as a novel CDK4/6 degrader based on DCAF16, is worthy of further investigating for the treatment of TNBC. [ABSTRACT FROM AUTHOR]

Chronic myeloid leukemia (CML) is a malignant tumor caused by the abnormal proliferation of hematopoietic stem cells. Among a new series of acridone derivatives previously synthesized, it was found that the methoxybenzyl 5-nitroacridone derivative 8q has nanomolar cytotoxicity in vitro against human chronic myelogenous leukemia K562 cells. In order to further explore the possible anti-leukemia mechanism of action of 8q on K562 cells, a metabolomics and molecular biology study was introduced. It was thus found that most of the metabolic pathways of the G1 phase of K562 cells were affected after 8q treatment. In addition, a concentration-dependent accumulation of cells in the G1 phase was observed by cell cycle analysis. Western blot analysis showed that 8q significantly down-regulated the phosphorylation level of retinoblastoma-associated protein (Rb) in a concentration-dependent manner, upon 48 h treatment. In addition, 8q induced K562 cells apoptosis, through both mitochondria-mediated and exogenous apoptotic pathways. Taken together, these results indicate that 8q effectively triggers G1 cell cycle arrest and induces cell apoptosis in K562 cells, by inhibiting the CDK4/6-mediated phosphorylation of Rb. Furthermore, the possible binding interactions between 8q and CDK4/6 protein were clarified by homology modeling and molecular docking. In order to verify the inhibitory activity of 8q against other chronic myeloid leukemia cells, KCL-22 cells and K562 adriamycin-resistant cells (K562/ADR) were selected for the MTT assay. It is worth noting that 8q showed significant anti-proliferative activity against these cell lines after 48 h/72 h treatment. Therefore, this study provides new mechanistic information and guidance for the development of new acridones for application in the treatment of CML.

Diffuse intrinsic pontine gliomas (DIPGs) are incurable childhood brain tumors, whereby the standard of care is focal radiation, a treatment that provides temporary relief for most patients. Surprisingly, decades of clinical trials have failed to identify additional therapies that can prolong survival in this disease. In this conference manuscript, we discuss how genetic engineered mouse modeling techniques with the use of a retroviral gene delivery system can help dissect the complex pathophysiology of this disease. With this approach, autochthonous murine DIPG models can be readily induced to (1) help interrogate the function of novel genetic alterations in tumorigenesis, (2) identify candidate cells of origin for this disease, (3) address how region-specific differences in the central nervous system influence the process of gliomagenesis, and (4) evaluate novel therapeutics in an immunocompetent model.

Cyclin-dependent kinases (CDKs), especially cyclin-dependent kinase 4/6 (CDK4/6), have been targets for the development of specific tumor imaging agents. Palbociclib is a highly selective CDK4/6 inhibitor. In this study, to develop a novel 18 F-labeled palbociclib derivative for specific tumor imaging, we designed and synthesized a ligand (NOTA-PBB) consisting of palbociclib as the targeted pharmacophore and NOTA as the macrocyclic bifunctional chelator. The corresponding [ 18 F]AlF-NOTA-PBB complex was prepared with high radiochemical purity (98.4 ± 0.15%) and yield (58.7 ± 4.5%) within 35 min without requiring HPLC purification through a simple one-step 18 F-labeling strategy of NOTA-AlF chelation chemistry. The radiotracer was lipophilic (log P = 0.095 ± 0.003) and had good stability in vitro and in vivo . The cellular uptake studies performed on the MCF-7 breast cancer cell line (ER-positive and HER2-negative) showed that radioactive uptake was blocked by preincubating with a molar dose of palbociclib and it had a nanomolar binding affinity to CDK4/6 (IC 50 = 16.23 ± 1.84 nM), demonstrating a CDK4/6-mediated uptake mechanism. Its ex vivo biodistribution in nude mice-bearing MCF-7 tumors showed obvious tumor uptake and a high tumor/muscle ratio of [ 18 F]AlF-NOTA-PBB, and tumor uptake was inhibited with 100 μg of palbociclib, demonstrating specific binding to CDK4/6. Radioactivity accumulation in MCF-7 tumors was observed in PET imaging with [ 18 F]AlF-NOTA-PBB. Based on the results of this work, [ 18 F]AlF-NOTA-PBB has the promising capability as a CDK4/6-targeted tumor imaging agent.

Pharmacologic inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) have recently entered the therapeutic armamentarium of clinical oncologists, and show promising activity in patients with breast and other cancers. Although their chief mechanism of action is inhibition of retinoblastoma (RB) protein phosphorylation and thus the induction of cell cycle arrest, CDK4/6 inhibitors alter cancer cell biology in other ways that can also be leveraged for therapeutic benefit. These include modulation of mitogenic kinase signaling, induction of a senescence-like phenotype, and enhancement of cancer cell immunogenicity. We describe here the less-appreciated effects of CDK4/6 inhibitors on cancer cells, and suggest ways by which they might be exploited to enhance the benefits of these agents for cancer patients. Highlights Selective pharmacologic inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) show immense promise as a treatment for a wide variety of cancers. The primary mechanism of CDK4/6 inhibitor activity is suppression of RB phosphorylation, enforcing G1 cell cycle arrest, and thus inhibiting proliferation. CDK4/6 inhibitors can also impact on other aspects of cancer cell behavior by inducing a senescence-like state, enhancing immunogenicity, and modulating kinase signaling. CDK4/6 inhibitors may also exert their activity through a direct effect on other cell types within tumors, including immune cells. Understanding the complex biological phenotypes induced by CDK4/6 inhibitors will ultimately allow the development of new therapeutic combinations to further benefit patients. [ABSTRACT FROM AUTHOR]

Cyclin-dependent kinases (CDKs) play a key role in cell cycle regulation, which makes them a clear therapeutic target to interfere with cell division and proliferation in cancer patients. Palbociclib, a specific inhibitor of CDK4/6 with outstanding clinical efficacy data and limited toxicity, has been recently approved for the treatment of hormone receptor (HR)-positive human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer, either in combination with an aromatase inhibitor or in combination with fulvestrant in women who have received prior endocrine therapy. This review describes the mechanism of action, preclinical experiences and clinical data of palbociclib, with a special focus on integrating this data with the positioning of palbociclib in the current clinical guidelines for advanced HR-positive/HER2-negative breast cancer. Aspects of the ongoing major studies are also presented, as well as future prospects in the development of palbociclib. [ABSTRACT FROM AUTHOR]

Fulvestrant is a steroidal selective estrogen receptor degrader that was approved by the US FDA in 2002 for treatment of ER-positive metastatic breast cancer (ER + MBC) post-progression on aromatase inhibitors. In 2017, the label was updated to include endocrine therapy naive ER + MBC. While initially fulvestrant was thought to be equivalent to aromatase inhibitors with monthly dose of 250 mg intramuscular injection, several postmarketing trials challenged this understanding. Subsequently, the recommended dose changed to 500 mg monthly plus loading dose, and this was proven to be superior to anastrozole in efficacy. Most recently the results of FALCON trial have further challenged the way fulvestrant is viewed and used. This report provides a historical perspective on this compound, its evolving role in management of ER + MBC and what the future may hold for this drug. [ABSTRACT FROM AUTHOR]

Background The cyclin-dependent kinase 4 (CDK4)/6 inhibitor Palbociclib is a new standard treatment in hormone-receptor positive breast cancer patients. No predictive biomarkers have been identified and no pharmacodynamics has properly been described so far. Patients and methods Patients with early-breast cancer were randomized 3 : 1 to oral palbociclib 125 mg daily for 14 days until the day before the surgery versus no treatment. Primary objective was antiproliferative response defined as a natural logarithm of Ki67 expression at day 15 below 1. Secondary end points were subgroups analyses and safety. Exploratory analyses included search for predictive biomarkers. Immunostainings (Ki67, RB, pRB, p16, pAKT, pER, pCDK2, CyclinD1), FISH (CCND1) and gene expression (GE) arrays were carried out at baseline and at surgery. In addition, activating PIK3CA and AKT1 mutations were assessed at baseline. Results 74 patients were allocated to palbociclib and 26 to control. Most patients (93%) were hormone-receptor (HR)-positive, whereas 8% were HER2-positive. Palbociclib led to significantly more antiproliferative responses when compared with control (58% versus 12%, P  <   0.001), and to a significantly higher Ki67 decrease (P  < 0.001). In the HR-positive/HER2-negative subgroup, this antiproliferative effect was even more marked in the palbociclib arm when compared with control (70% versus 9%, P  <   0.001). Palbociclib treatment led also to a significantly higher decrease from baseline in phospho-Rb when compared with control (P  <   0.001). Among treated patients, changes in Ki67 correlated with changes in phospho-Rb (Spearman rank r  = 0.41, P  <   0.0001). GE analyses confirmed a major effect on proliferation and cell cycle genes. Among treated patients, CCNE2 expression was significantly more decreased in antiproliferative responders versus nonresponders (P  =   0.006). Conclusion Short-term preoperative palbociclib decreases Ki67 in early-breast cancer patients. Early decrease of Rb phosphorylation correlates with drug’s effect on cell proliferation and could potentially identify patients with primary resistance. Clinical trial registration NCT02008734. [ABSTRACT FROM AUTHOR]

Hormone-receptor-positive breast cancer is the most common subtype of breast cancer among patients with both early-stage and metastatic disease. Recent advances in the understanding of its pathophysiology have led to the discovery and utilization of targeted inhibitors to cyclin-dependent kinases 4 and 6 (CDK4/6). There are currently three available CDK4/6 inhibitors available for use in USA: palbociclib, ribociclib, and abemaciclib. Their oral administration and tolerable toxicities make this class of agents appealing to both patients and health care providers. Abemaciclib, the most recently approved CDK4/6 inhibitor, has unique pharmacologic properties and potential toxicities. This review highlights the current understanding of abemaciclib and discusses its current and future roles in the treatment of breast cancer. [ABSTRACT FROM AUTHOR]

Purpose: The phase 3 MONALEESA-2 study demonstrated that addition of ribociclib (RIB) to letrozole (LET) significantly improved progression-free survival (PFS) in patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2−) advanced breast cancer (ABC). Here, we evaluated duration of response (DoR), tumor shrinkage, PFS by treatment-free interval (TFI), and health-related quality of life (HRQoL).Methods: Postmenopausal women (N = 668) with HR+ , HER2− ABC and no prior systemic therapy for ABC were randomized to RIB (600 mg/day; 3 weeks on/1 week off) plus LET (2.5 mg/day; continuous) or placebo (PBO) plus LET. Primary end point was PFS; HRQoL was the secondary end point; DoR was exploratory end point and PFS by TFI was post hoc analysis.Results: Of 501 pts with measurable disease and confirmed complete or partial response, median DoR was 26.7 months (95% CI, 24.0-NR) in the RIB arm versus 18.6 months (95% CI, 14.8-23.1) in the PBO arm. At 8 weeks, more pts in the RIB arm (32%) versus the PBO arm (17%) experienced best percentage change ≥ 60%. The average pain reduction was greater in the RIB arm (26%) versus the PBO arm (15%). PFS benefit was seen with RIB vs PBO, irrespective of TFI.Conclusion: RIB plus LET versus PBO plus LET is associated with earlier and more durable tumor response, greater degree of tumor shrinkage and pain reduction, and PFS benefit irrespective of TFI. These data further support RIB plus LET as a first-line treatment option for postmenopausal women with HR+ , HER2− ABC. [ABSTRACT FROM AUTHOR]

Diffuse intrinsic pontine gliomas (DIPGs) are incurable childhood brain tumors, whereby the standard of care is focal radiation, a treatment that provides temporary relief for most patients. Surprisingly, decades of clinical trials have failed to identify additional therapies that can prolong survival in this disease. In this conference manuscript, we discuss how genetic engineered mouse modeling techniques with the use of a retroviral gene delivery system can help dissect the complex pathophysiology of this disease. With this approach, autochthonous murine DIPG models can be readily induced to (1) help interrogate the function of novel genetic alterations in tumorigenesis, (2) identify candidate cells of origin for this disease, (3) address how region-specific differences in the central nervous system influence the process of gliomagenesis, and (4) evaluate novel therapeutics in an immunocompetent model. [ABSTRACT FROM AUTHOR]

Introduction: The emergence of cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors marked a significant advancement in the treatment of advanced breast cancer. Ribociclib is an orally bioavailable, highly selective inhibitor of CDK4/6. In combination with various endocrine therapies, ribociclib has demonstrated clinical activity as a first-line therapy for patients with HR+, HER2− advanced breast cancer, without compromising the favorable toxicity profile associated with endocrine therapy. Thus, ribociclib is now considered a new standard of care for HR+, HER2− advanced breast cancer. Areas covered: This review provides a concise overview of the preclinical and clinical development of ribociclib, including evidence of its clinical activity and safety profile when combined with endocrine therapy in HR+, HER2− advanced breast cancer. Expert commentary: CDK4/6 inhibition represents a promising treatment option for patients with HR+ metastatic breast cancer. Ribociclib significantly improved progression-free survival in patients receiving first-line endocrine therapy for HR+, HER2− advanced breast cancer. Planned and ongoing trials investigating ribociclib in combination with other endocrine therapies and in various clinical settings will help to determine the optimal treatment sequence for different patient populations. [ABSTRACT FROM PUBLISHER]

Introduction. Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have transformed the treatment of hormone receptorpositive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer over the last decade. These inhibitors are currently established as first- and second-line systemic treatment choices for both endocrine-sensitive and endocrine-resistant breast cancer populations, alongside endocrine therapy (ET) or monotherapy. Data on targeted therapy continue to mature, and the number of publications has been constantly rising. Although these drugs have been demonstrated to prolong overall survival (as well as progression-free survival in breast cancer patients), changing the paradigm of all current knowledge, they also cause important adverse events. This review provides the latest summary and update on the safety profile of the three CDK4/6 inhibitors, as it appears from all major phase II and III randomized clinical trials, regarding palbociclib, ribociclib and abemaciclib, including the most relevant 15 clinical trials. Aim and objectives. The greatest challenge in the research and development of CDK4/6 inhibitors might lie in dealing with the adverse effects and potential drug tolerance. Further, understanding the underlying mechanism and exploring the ideal combination therapy might help overcome the selectivity and drug tolerance of CDK inhibitors. Considering the similar efficacies and indications of palbociclib, ribociclib and abemaciclib, the evaluation of their toxicity profiles may facilitate treatment choice. This review explores the safety profiles of palbociclib, ribociclib and abemaciclib in all randomized phase II and III clinical trials. Materials and method. This systematic review was in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Extended systematic research was performed on ClinicalTrials.gov database clinical trials registries with results published or registered before July 2023. The keywords used were: palbociclib, ribociclib, abemaciclib, phase II and III, randomized, and available results. The last search was performed on the 8th of August 2023. The search returned 690 results. Literature articles were systematically assessed by searching in the PubMed Medline database from January 2016 until July 2023. The following keywords were used: CDK4/6 inhibitors, breast cancer, and toxicities. The inclusion criteria were: clinical studies on breast cancer patients, clinical phase II and III studies using currently approved doses for palbociclib (125 mg/day orally for three weeks, followed by one week off), ribociclib (200 mg X 3/day orally for three weeks, followed by one week off) or abemaciclib (150 mg X 2/day orally in combination with ET or 200 mg/day orally in monotherapy), and studies for which safety data or at least one adverse reaction were reported in the article in the form of the percentage or number of patients. Only free full-text articles were assessed. The exclusion criteria were: articles with unavailable abstracts, non-English written articles, conference presentations, metaanalyses and literature reviews, non-clinical studies, post-hoc or subgroup analyses, retrospective studies, and studies in which the adverse effects were not reported. In vivo and in vitro studies were also excluded. The search returned 130 results, all of which were already included in the first search on ClinicalTrials.gov. Conclusions. CDK4/6 inhibitors are generally well tolerated. The most common adverse reactions encountered on CDK4/6 inhibitors treatment include neutropenia, leukopenia, anemia, thrombocytopenia, fatigue, gastrointestinal side effects, hepatotoxicity and QTc prolongation. However, there are some distinctions between palbociclib, ribociclib and abemaciclib. The most prevalent adverse effect of palbociclib and ribociclib is neutropenia, while particular for ribociclib are the QTc prolongation and hepatobiliary toxicity, and for abemaciclib, the gastrointestinal toxicity. All these adverse reactions can be very well managed due to the possibility of multiple dosage decreases and adjustments. Therefore, in clinical practice, acknowledging a side effect is of paramount importance to best manage it. To the best of our knowledge, this is the latest and newest literature review compounding all phase II and III randomized clinical trials regarding the three CDK4/6 inhibitors’ toxicities. This review will hopefully be of real help to all clinicians in managing the adverse effects of CDK4/6 inhibitors, by providing an easier way to research the reported percentage of specific adverse reactions in consecrated clinical trials. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • CDK2 inhibition (CDK2i) causes rapid loss of kinase activity followed by a rebound • CDK2i unmasks CDK4/6 activity beyond G1, reinforcing Rb hyperphosphorylation • The Rb-E2F axis remains engaged under CDK2i, driving cyclin A and CDK2 activity • Co-inhibiting CDK2 and CDK4/6 presents a strategy to force durable cell-cycle exit Selective CDK2 inhibition initially blocks substrate phosphorylation. However, because of a potent positive feedback loop and reinforcement by CDK4/6 activity, cells can rapidly overcome CDK2 inhibition to complete the cell cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] Estrogen Receptor is the driving transcription factor in about 75% of all breast cancers, which is the target of endocrine therapies, but drug resistance is a common clinical problem. ESR1 point mutations at the ligand binding domain are frequently identified in metastatic tumor and ctDNA (Circulating tumor DNA) derived from ER positive breast cancer patients with endocrine therapies. Although endocrine therapy and CDK4/6 inhibitor therapy have demonstrated preclinical and clinical benefits for breast cancer, the development of resistance remains a significant challenge and the detailed mechanisms, and potential therapeutic targets in advanced breast cancer yet to be revealed. Since a crosstalk between tumor and tumor microenvironment (TME) plays an important role to grow tumor and metastasis, this effect could serve as key regulators in the resistance of endocrine therapy and the transition of breast cancer cells to metastasis. In this article, we have reviewed recent progress in endocrine therapy and the contribution of TME to ER positive breast cancer. [ABSTRACT FROM AUTHOR]

DNA replication of E1-deleted first-generation adenoviruses (AdV) in cultured cancer cells has been reported repeatedly and it was suggested that certain cellular proteins could functionally compensate for E1A, leading to the expression of the early region 2 (E2)-encoded proteins and subsequently virus replication. Referring to this, the observation was named E1A-like activity. In this study, we investigated different cell cycle inhibitors with respect to their ability to increase viral DNA replication of dl70-3, an E1-deleted adenovirus. Our analyses of this issue revealed that in particular inhibition of cyclin-dependent kinases 4/6 (CDK4/6i) increased E1-independent adenovirus E2-expression and viral DNA replication. Detailed analysis of the E2-expression in dl70-3 infected cells by RT-qPCR showed that the increase in E2-expression originated from the E2-early promoter. Mutations of the two E2F-binding sites in the E2-early promoter (pE2early-LucM) caused a significant reduction in E2-early promoter activity in trans-activation assays. Accordingly, mutations of the E2F-binding sites in the E2-early promoter in a virus named dl70-3/E2Fm completely abolished CDK4/6i induced viral DNA replication. Thus, our data show that E2F-binding sites in the E2-early promoter are crucial for E1A independent adenoviral DNA replication of E1-deleted vectors in cancer cells. IMPORTANCE E1-deleted AdV vectors are considered replication deficient and are important tools for the study of virus biology, gene therapy, and large-scale vaccine development. However, deletion of the E1 genes does not completely abolish viral DNA replication in cancer cells. Here, we report, that the two E2F-binding sites in the adenoviral E2-early promoter contribute substantially to the so-called E1A-like activity in tumor cells. With this finding, on the one hand, the safety profile of viral vaccine vectors can be increased and, on the other hand, the oncolytic property for cancer therapy might be improved through targeted manipulation of the host cell. [ABSTRACT FROM AUTHOR]

Cell cycle progression in cancer cells is highly activated, making CDK4/6 inhibition-based cell cycle arrest a potent cancer treatment strategy. To enhance therapeutic efficacy, it is crucial to explore CDK4/6 inhibition-based combination strategies. In this study, we found that combing CDK4/6 PROTAC with Chlorin e6-based photodynamic therapy produced a synergistic anti-cancer effect. This combination effect was mediated by mitochondria accumulation and activation, leading to increased production of reactive oxygen species and apoptosis. To promote clinical translation, we developed a self-assembled, carrier-free nanoparticle system to co-deliver these two molecules. The dual-drug nanoparticles not only induced higher apoptosis but also cooperatively induced immunogenic cell death and chemotaxis of immune cells, remodulating immunosuppressive tumor microenvironment to enhance anti-tumor immunity. This study provides a promising strategy to combine G1 cell cycle blockage and photodynamic therapy and advances the broad applications of PROTAC in clinical cancer treatment. [Display omitted] • CDK4/6 PROTAC-mediated G1 arrest sensitizes cancer cells to photodynamic therapy. • The combination effect is mediated by mitochondria biogenesis. • A self-assembled nanoparticle is developed to co-deliver these two therapeutic agents. • The nanoparticle remodulates immunosuppressive tumor microenvironment. [ABSTRACT FROM AUTHOR]

KRAS is one of the most commonly mutated oncogenes in non-small cell lung cancer (NSCLC). Resistance to MEK inhibitor monotherapy develops through a variety of mechanisms. CDK4 was reported to have a synthetic lethal interaction with KRAS. In this study, we demonstrated the combination effects of the MEK inhibitor selumetinib and the CDK4/6 inhibitor palbociclib in RAS-driven NSCLC. In vitro, cell lines with CDKN2A mutations were insensitive to selumetinib. We used siRNA and pharmacologic inhibition of CDK4 and found that the combination of selumetinib and palbociclib synergistically inhibited RAS-driven NSCLC cases with CDKN2A mutations but not those with wild type CDKN2A. The combination treatment potentiated growth inhibition and increased the population of cells in G1 phase. Selumetinib completely inhibited p-ERK but not p-RB. The addition of palbociclib markedly inhibited p-RB and downregulated survivin expression. In vivo, the combination treatment inhibited the growth of NSCLC xenografts, which correlated with decreased levels of p-RB, downregulated survivin and decreased Ki-67 staining. These data suggest that the combination treatment of palbociclib and selumetinib is effective in preclinical models of RAS-driven NSCLC with CDKN2A mutations. [ABSTRACT FROM AUTHOR]

Cyclin-dependent kinases (CDK) are rational cancer therapeutic targets fraught with the development of acquired resistance by tumor cells. Through metabolic and transcriptomic analyses, we show that the inhibition of CDK4/6 leads to a metabolic reprogramming associated with gene networks orchestrated by the MYC transcription factor. Upon inhibition of CDK4/6, an accumulation of MYC protein ensues which explains an increased glutamine metabolism, activation of the mTOR pathway and blunting of HIF- 1a-mediated responses to hypoxia. These MYC-driven adaptations to CDK4/6 inhibition render cancer cells highly sensitive to inhibitors of MYC, glutaminase or mTOR and to hypoxia, demonstrating that metabolic adaptations to antiproliferative drugs unveil new vulnerabilities that can be exploited to overcome acquired drug tolerance and resistance by cancer cells. [ABSTRACT FROM AUTHOR]

LC–MS/MS methods to measure ribociclib in mouse plasma and Ringer’s solution were successfully developed and validated. Reverse phase chromatography was performed with gradient elution using C18 (100A, 50 × 4.6 mm, 3 μ) and C8-A (50 × 2.0 mm, 5 μ) columns for plasma and Ringer’s samples, respectively. Mouse plasma samples were extracted using solid phase extraction method, whereas no extraction was required for the Ringer’s solution samples. Analytes were detected using positive ion MRM mode. The precursor to product ions (Q1 → Q3) selected for ribociclib and d6-ribociclib were ( m / z ) 435.2 → 252.1 and 441.2 → 252.1, respectively. The linear range of quantification of ribociclib was 62.5–10,000 ng/ml for plasma method and 0.1–100 ng/ml for Ringer’s solution method. The results for the inter-day and intra-day accuracy and precision of quality control samples were within the acceptable range. The lower limit of quantitation (LLOQ) for plasma and Ringer’s samples were 62.5 ng/ml (S/N > 30) and 0.1 ng/ml (S/N > 13), respectively, whereas the limit of detection (LOD) was 6.9 ng/ml (S/N > 7) and 0.05 ng/ml (S/N > 3), respectively. The developed methods were successfully applied to the analysis of ribociclib in mouse plasma and dialysate samples collected during a cerebral microdialysis study of ribociclib in a non-tumor bearing mouse. [ABSTRACT FROM AUTHOR]

PTEN is one of the most frequently mutated genes in human cancers. The frequency of PTEN alterations is particularly high in endometrial carcinomas. Loss of PTEN leads to dysregulation of cell division, and promotes the accumulation of cell cycle complexes such as cyclin D1-CDK4/6, which is an important feature of the tumour phenotype. Cell cycle proteins have been presented as key targets in the treatment of the pathogenesis of cancer, and several CDK inhibitors have been developed as a strategy to generate new anticancer drugs. Palbociclib ( PD-332991) specifically inhibits CDK4/6, and it has been approved for use in metastatic breast cancer in combination with letrazole. Here, we used a tamoxifen-inducible Pten knockout mouse model to assess the antitumour effects of cyclin D1 knockout and CDK4/6 inhibition by palbociclib on endometrial tumours. Interestingly, both cyclin D1 deficiency and palbociclib treatment triggered shrinkage of endometrial neoplasias. In addition, palbociclib treatment significantly increased the survival of Pten-deficient mice, and, as expected, had a general effect in reducing tumour cell proliferation. To further analyse the effects of palbociclib on endometrial carcinoma, we established subcutaneous tumours with human endometrial cancer cell lines and primary endometrial cancer xenografts, which allowed us to provide more translational and predictive data. To date, this is the first preclinical study evaluating the response to CDK4/6 inhibition in endometrial malignancies driven by PTEN deficiency, and it reveals an important role of cyclin D- CDK4/6 activity in their development. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Deregulation of the tyrosine kinase signalling is often associated with tumour progression and drug resistance, but its underlying mechanisms are only partly understood. In this study, we investigated the effects of the receptor tyrosine kinase AXL on the stability of the MDMX-MDM2 heterocomplex and the activity of p53 in melanoma cells. Our data demonstrated that AXL overexpression or activation through growth arrest-specific 6 (Gas6) ligand stimulation increases MDMX and MDM2 protein levels and decreases p53 activity. Upon activation, AXL stabilizes MDMX through a post-translational modification that involves phosphorylation of MDMX on the phosphosite Ser314, leading to increased affinity between MDMX and MDM2 and favouring MDMX nuclear translocation. Ser314 phosphorylation can also protect MDMX from MDM2-mediated degradation, leading to stabilization of the MDMX-MDM2 complex. We identified CDK4/6 and p38 MAPK as the two kinases mediating AXL-induced modulation of the MDMX-MDM2 complex, and demonstrated that suppression of AXL, either through siRNA silencing or pharmacological inhibition, increases expression levels of p53 target genes P21, MDM2, and PUMA, improves p53 pathway response to chemotherapy, and sensitizes cells to both Cisplatin and Vemurafenib. Our findings offer an insight into a novel signalling axis linking AXL to p53 and provide a potentially druggable pathway to restore p53 function in melanoma. [ABSTRACT FROM AUTHOR]

Background: Overexpression of cyclin D1 dependent kinases 4 and 6 (CDK4/6) is a common feature of many human cancers including leukemia. LEE011 is a novel inhibitor of both CDK4 and 6. To date, the molecular function of LEE011 in leukemia remains unclear. Methods: Leukemia cell growth and apoptosis following LEE011 treatment was assessed through CCK-8 and annexin V/propidium iodide staining assays. Cell senescence was assessed by β-galactosidase staining and p16INK4a expression analysis. Gene expression profiles of LEE011 treated HL-60 cells were investigated using an Arraystar Human LncRNA array. Gene ontology and KEGG pathway analysis were then used to analyze the differentially expressed genes from the cluster analysis. Results: Our studies demonstrated that LEE011 inhibited proliferation of leukemia cells and could induce apoptosis. Hoechst 33,342 staining analysis showed DNA fragmentation and distortion of nuclear structures following LEE011 treatment. Cell cycle analysis showed LEE011 significantly induced cell cycle G1 arrest in seven of eight acute leukemia cells lines, the exception being THP-1 cells. β-Galactosidase staining analysis and p16INK4a expression analysis showed that LEE011 treatment can induce cell senescence of leukemia cells. LncRNA microarray analysis showed 2083 differentially expressed mRNAs and 3224 differentially expressed lncRNAs in LEE011-treated HL-60 cells compared with controls. Molecular function analysis showed that LEE011 induced senescence in leukemia cells partially through downregulation of the transcriptional expression of MYBL2. Conclusions: We demonstrate for the first time that LEE011 treatment results in inhibition of cell proliferation and induction of G1 arrest and cellular senescence in leukemia cells. LncRNA microarray analysis showed differentially expressed mRNAs and lncRNAs in LEE011-treated HL-60 cells and we demonstrated that LEE011 induces cellular senescence partially through downregulation of the expression of MYBL2. These results may open new lines of investigation regarding the molecular mechanism of LEE011 induced cellular senescence. [ABSTRACT FROM AUTHOR]

Purpose of review: The purpose of this review is to describe the role of D-type cyclins and cyclin-dependent kinases (CDKs) 4 and 6 in breast cancer and to discuss potential biomarkers for sensitivity or resistance to CDK4/6 inhibitors. Recent findings: A small number of preclinical and clinical studies have explored potential mechanisms of CDK4/6 inhibitor response and resistance in breast cancer. Putative markers of response include estrogen receptor positivity, luminal patterns of gene expression, high cyclin D1 levels, and low p16 levels. Possible resistance mechanisms include loss of Rb function, overexpression/amplification of cyclin E, and CDK6 amplification. Most of these remain speculative and have not been validated in clinical specimens. Summary: If early successes with CDK4/6 inhibitors are to be capitalized upon, it is critical that our understanding of CDK4/6 biology in breast cancer extends beyond its current rudimentary state. Only then, we will be able to develop rational therapeutic combinations that further enhance the efficacy of these agents. [ABSTRACT FROM AUTHOR]

Background: Ewing sarcoma (EWS) is an aggressive sarcoma with few treatment options for patients with relapsed disease. Cyclin-dependent kinase 4 (CDK4) is a genomic vulnerability in EWS that is synergistic with IGF-1R inhibition in preclinical studies. We present the results of a phase 2 study combining palbociclib (CDK4/6 inhibitor) with ganitumab (IGF-1R monoclonal antibody) for patients with relapsed EWS., Patients and Methods: This open-label, non-randomized, phase 2 trial enrolled patients ≥12 years with relapsed EWS. All patients had molecular confirmation of EWS and RECIST measurable disease. Patients initially received palbociclib 125 mg orally on Days 1-21 and ganitumab 18 mg/kg intravenously on Days 1 and 15 of a 28-day cycle. The primary endpoints were objective response (complete or partial) per RECIST and toxicity by CTCAE. An exact one-stage design required ≥4 responders out of 15 to evaluate an alternative hypothesis of 40% response rate against a null of 10%. The study was closed following enrollment of the 10th patient due to discontinuation of ganitumab supply., Results: Ten evaluable patients enrolled [median age 25.7 years (range 12.3-40.1)]. The median duration of therapy was 2.5 months (range 0.9-10.8). There were no complete or partial responders. Three of 10 patients had stable disease for >4 cycles and 2 had stable disease at completion of planned therapy or study closure. Six-month progression-free survival was 30% (95% CI 1.6%-58.4%). Two patients had cycle 1 hematologic dose-limiting toxicities (DLTs) triggering palbociclib dose reduction to 100 mg daily for 21 days. Two subsequent patients had cycle 1 hematologic DLTs at the reduced dose. Eighty percent of patients had grade 3/4 AEs, including neutropenia (n = 8), white blood cell decreased (n = 7), and thrombocytopenia (n = 5). Serum total IGF-1 significantly increased (p = 0.013) and ctDNA decreased during the first cycle., Conclusions: This combination lacks adequate therapeutic activity for further study, though a subset of patients had prolonged stable disease., (© 2023 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Cancer chemotherapy relies on a high ratio of toxicity toward cancer cells vs. nonmalignant cells, making it desirable to protect normal cells. Among the nonmalignant cells, epithelia of the gut belong to the most vulnerable ones toward chemotherapeutics. Here, we use a murine intestinal organoid model to assess a strategy for protecting such epithelia against chemotherapy. Cell cycle progression was first stalled by palbociclib, a clinically established cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. Washout of the drug allowed subsequent outgrowth of gut organoids. This transient cell cycle arrest conferred near-complete protection of the cells toward the nucleoside analogue gemcitabine. Moreover, pre-treatment with palbociclib protected the organoids against SN-38, the topoisomerase I-inhibiting metabolite of irinotecan, which is otherwise known for its severe gastrointestinal toxicities. In contrast, RB1-mutated cancer cells were not protected against gemcitabine or SN-38 when pre-treated with palbociclib. Taken together, these results outline a strategy for protecting nonmalignant cells against the toxicities of chemotherapeutics commonly used to treat advanced colorectal and pancreatic cancer. We propose that this strategy is particularly promising to protect the gut when treating RB1-deficient tumors that fail to arrest the cell cycle in response to CDK4/6 inhibitors. [Figure: see text].

Background: Targeting CDK4/6 has advanced breast cancer treatment. Herein, new quinazolinones were synthesized with acetamide linkers as potential anti-breast cancer agents. Methods & results: In vitro ) to be of the highest potency. It showed good inhibitory activity on CDK4/6. Compound 5d ) to be of the highest potency. It showed good inhibitory activity on CDK4/6. Compound 5d arrested the cell cycle at the G1-phase, caused induction of early and late apoptosis in an Annexin V-FITC assay, led to an increase in the level of caspase-3 and upregulated Bax expression and downregulated Bcl-2 in MCF7 cells. Compound 5d This study introduces quinazolinone scaffolds as new CDK4/6 inhibitors for breast cancer.Conclusion: This study introduces quinazolinone scaffolds as new CDK4/6 inhibitors for breast cancer.

Background: In monarchE and Postoperative Therapy with Endocrine and TS-1 (POTENT) trials, abemaciclib and S-1 have, respectively, shown to be effective as adjuvant therapies for luminal breast cancer (BC), although whether patients who meet the criteria are at high risk of recurrence compared to non-eligible patients is still unknown. Here, we investigated recurrence risk according to the criteria of each trial in Japanese patients., Methods: We reviewed the records of 992 patients who received surgery at Chiba University Hospital for stage I-III BC from January 2017 to May 2022 and selected 553 analytic cohort patients and retrospectively analyzed the relapse-free survival of the patients as the primary endpoint. High-recurrence risk was defined according to monarchE trial and POTENT trial., Results: The 5-year RFS for monarchE cohort 1 and cohort 2 eligible patients were 77.78% and 89.33%, respectively, which were significantly lower than monarchE non-eligible patients (98.31%; p < 0.0001). However, the 5-year RFS rate for POTENT eligible patients (90.51%) was lower than for POTENT non-eligible patients (98.75%; p = 0.0001); excluding those who met the monarchE criteria, the prognosis of POTENT eligible patients had no significant differences from the prognosis of patients with POTENT non-eligible BC (p = 0.3100)., Conclusion: MonarchE criteria accurately identify patients who are prone to relapse. Moreover, although POTENT criteria also suggested a reasonable capacity for recurrence prediction, there was no significant difference in recurrence between POTENT non-eligible patients and the patients who were POTENT but not monarchE eligible. This might offer justification for reconsidering the use of S-1 in monarchE non-eligible patients., (© 2023 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.)

Resistance to standard endocrine therapies in hormone receptor-positive advanced breast cancer represents a significant clinical challenge. Different intracellular signaling pathways mediate independent activation of the estrogen receptor (ER), promoting tumor cell proliferation despite anti-hormonal treatment. Recently, the inhibition of cell cycle regulators, CDK4 and CDK6, has demonstrated to significantly enhance the effectiveness of endocrine therapy by overcoming or delaying resistance to estrogen blockade. Strategies such as inhibition of the PI3K/mTOR pathway or epigenetic modulation of ER-related gene expression are closely following the trail of CDK inhibitors. Here, we seek to review the most recent efforts to improve outcomes in these patients, in an attempt to extend endocrine treatment and defer the need for cytotoxic regimens. We also discuss future directions to be considered in the treatment of ER-positive disease, as mechanisms of resistance to these new agents arise. [ABSTRACT FROM AUTHOR]

Background: Anaplastic thyroid cancer (ATC) is an aggressive subtype of thyroid cancer, accounting for 1 to 2% of all cases. Deregulations of cell cycle regulatory genes including cyclins, cyclin-dependent kinases (CDKs), and endogenous inhibitors of CDKs (CKIs) are hallmarks of cancer cells and hence, studies indicate the inhibition of CDK4/6 kinases and cell cycle progression as potent therapeutic strategies. In this study, we investigated the anti-tumor activity of Abemaciclib, a CDK4 and CDK6 inhibitor, in ATC cell lines., Methods and Results: The ATC cell lines C643 and SW1736 were selected to study the antiproliferative effects of Abemaciclib using a cell proliferation assay and crystal violet staining assay. Annexin V/PI staining and cell cycle analysis by flow cytometry were also performed to examine the effects on apoptosis induction and cell cycle arrest. Wound healing assay and zymography analysis examined the effects of the drug on invasive abilities of ATC cells and Western blot analyses were applied to further study the anti-tumor mechanism of Abemaciclib, in addition to combination treatment with alpelisib. Our data demonstrated that Abemaciclib significantly inhibited cell proliferation and increased cellular apoptosis and cell cycle arrest in ATC cell lines, while considerably reducing cell migration and colony formation. The mechanism seemed to involve the PI3K pathway., Conclusion: Our preclinical data highlight CDK4/6 as interesting therapeutic targets in ATC and suggest CDK4/6-blockade therapies as promising strategies in this malignancy., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

The use of cell cycle inhibitors has necessitated a better understanding of the cell cycle in tumor biology to optimize the therapeutic approach. Cell cycle aberrations are common in cancers, and it is increasingly acknowledged that these aberrations exert oncogenic effects beyond the cell cycle. Multiple facets such as cancer metabolism, immunity and metastasis are also affected, all of which are beyond the effect of cell proliferation alone. This review comprehensively summarized the important recent findings and advances in these interrelated processes. In cancer metabolism, cell cycle regulators can modulate various pathways in aerobic glycolysis, glucose uptake and gluconeogenesis, mainly through transcriptional regulation and kinase activities. Amino acid metabolism is also regulated through cell cycle progression. On cancer metastasis, metabolic plasticity, immune evasion, tumor microenvironment adaptation and metastatic site colonization are intricately related to the cell cycle, with distinct regulatory mechanisms at each step of invasion and dissemination. Throughout the synthesis of current understanding, knowledge gaps and limitations in the literature are also highlighted, as are new therapeutic approaches such as combinational therapy and challenges in tackling emerging targeted therapy resistance. A greater understanding of how the cell cycle modulates diverse aspects of cancer biology can hopefully shed light on identifying new molecular targets by harnessing the vast potential of the cell cycle., (© 2022 UICC.)

Background: For many years, therapy for metastatic hormone-sensitive prostate cancer (mHSPC) was dominated by monotherapy using androgen deprivation therapy (ADT). With the demonstration of survival benefit with intensified systemic therapy from the CHAARTED and STAMPEDE trials, this has fundamentally changed. We analyzed the phase III trials that led to the change in therapy in mHSPC. In addition, we summarized ongoing trials in mHSPC., Objectives: The ongoing studies and current data on systemic therapy in mHSPC were analyzed., Results: Monotherapy with ADT is no longer considered the standard therapy for mHSPC. Combination therapy with ADT and novel androgen receptor targeting agents (ARTAs: abiraterone, apalutamide, enzalutamide) is now the established standard option. The added value of further intensification of therapy was demonstrated in the first trials of triple therapy with ADT + docetaxel + darolutamide or abiraterone in mHSPC. Current studies are also investigating new forms of therapy. Lutetium177-PSMA radioligand therapy is an established standard in metastatic castration-resistant prostate cancer (mCRPC) and is currently being evaluated in combination with ADT + ARTA in mHSPC. The use of PARP inhibitors (PARPi) have been established in mCRPC. Current studies are showing early evidence of benefit from novel combination therapies of PARPi + ARTA, which represent a further expansion of the therapeutic landscape. Experimental therapies are testing another combination, such as an AKT inhibitor with ARTA in patients with PTEN (phosphatase and tensin homolog) loss. Based on the proof of principle in mCRPC, this combination is now being evaluated in earlier stage mHSPC. Other experimental therapies in clinical testing include inhibitors of cyclin dependent kinases (CDK)., Conclusions: Combination therapies are the current standard of care for mHSPC, with the combination of ADT + ARTA dominating. Preliminary results underline the importance of further intensification of therapy by means of triple therapy. However, novel combinations with radioligand therapy or PARP inhibitors are also promising in the treatment of mHSPC. Preliminary results show the principle efficacy of AKT inhibitors in patients with PTEN loss, which similar to therapy with CDK4/6 inhibitors still have to prove their clinical relevance in randomized trials., (© 2023. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Purpose: Few targeted treatment options currently exist for patients with advanced, often recurrent breast cancers, both triple-negative breast cancer (TNBC) and hormone receptor-positive breast cancer. Forkhead box M1 (FOXM1) is an oncogenic transcription factor that drives all cancer hallmarks in all subtypes of breast cancer. We previously developed small-molecule inhibitors of FOXM1 and to further exploit their potential as anti-proliferative agents, we investigated combining FOXM1 inhibitors with drugs currently used in the treatment of breast and other cancers and assessed the potential for enhanced inhibition of breast cancer., Methods: FOXM1 inhibitors alone and in combination with other cancer therapy drugs were assessed for their effects on suppression of cell viability and cell cycle progression, induction of apoptosis and caspase 3/7 activity, and changes in related gene expressions. Synergistic, additive, or antagonistic interactions were evaluated using ZIP (zero interaction potency) synergy scores and the Chou-Talalay interaction combination index., Results: The FOXM1 inhibitors displayed synergistic inhibition of proliferation, enhanced G2/M cell cycle arrest, and increased apoptosis and caspase 3/7 activity and associated changes in gene expression when combined with several drugs across different pharmacological classes. We found especially strong enhanced effectiveness of FOXM1 inhibitors in combination with drugs in the proteasome inhibitor class for ER-positive and TNBC cells and with CDK4/6 inhibitors (Palbociclib, Abemaciclib, and Ribociclib) in ER-positive cells., Conclusion: The findings suggest that the combination of FOXM1 inhibitors with several other drugs might enable dose reduction in both agents and provide enhanced efficacy in treatment of breast cancer., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)