Efficacy and Safety of Abemaciclib, an Inhibitor of CDK4 and CDK6, for Patients with Breast Cancer, Non-Small Cell Lung Cancer, and Other Solid Tumors

Raddeanin A exerts potent efficacy against non-small cell lung cancer by inhibiting cyclin-dependent kinase 6

PURPOSE

The aim of this study was to investigate the anti-tumor effects and mechanisms of Raddeanin A in NSCLC in vitro and in vivo.

METHODS

The effects of Raddeanin A on cell cycle progression, proliferation, migration and invasion of NSCLC were assessed by flow cytometry and cell biological assays in multiple NSCLC cell lines. To identify possible targets of Raddeanin A in NSCLC, we employed a multifaceted approach incorporating network pharmacology, molecular docking, and molecular dynamics simulation, along with additional techniques such as SPR (Surface Plasmon Resonance), Co-IP (Co-Immunoprecipitation), and immunofluorescence. In vivo effects were investigated using a nude mouse xenograft tumor model.

RESULTS

Raddeanin A inhibits NSCLC cell survival, inhibits invasion and migration and causes cell cycle arrest in G1 phase. Raddeanin A impacts NSCLC cellular activity by inhibiting CDK6, leading to anti-tumor effects. Molecular analysis confirms that the tight binding between Raddeanin A and CDK6, facilitated by specific hydrogen bonds at binding sites including VAL-101, HIS-100, GLN-149, LYS-147, THR-182, VAL-180, and ALA-23, stabilizes within the 40-100 ns interval. In a nude mouse xenograft tumor model, Raddeanin A also demonstrated an inhibitory effect on NSCLC tumor growth.

CONCLUSIONS

Raddeanin A blocks the cell cycle in G1 phase by inhibiting CDK6. Raddeanin A is expected to be a novel antitumor agent against NSCLC.

Combination therapy and dual-target inhibitors based on cyclin-dependent kinases (CDKs): Emerging strategies for cancer therapy

Cyclin-dependent kinases (CDKs) are pivotal regulators of the cell cycle and transcriptional machinery, making them attractive targets for cancer therapy. While CDK inhibitors have demonstrated promising clinical outcomes, they also face challenges in enhancing efficacy, particularly in overcoming drug resistance. Combination therapies have emerged as a key strategy to augment the effectiveness of CDK inhibitors when used alongside other kinase inhibitors or non-kinase-targeted agents. Dual-target inhibitors that simultaneously inhibit CDKs and other oncogenic drivers are gaining attention, offering novel avenues to optimize cancer therapy. Based on the structural characterization and biological functions of CDKs, this review comprehensively examines the structure-activity relationship (SAR) of existing dual-target CDK inhibitors from a drug design perspective. We also thoroughly investigate the preclinical studies and clinical translational potential of combination therapies and dual-target inhibitors. Tailoring CDK inhibitors to specific cancer subtypes and therapeutic settings will inspire innovative approaches for the next generation of CDK-related therapies, ultimately improving patient survival.

Cyclin-dependent kinase 4 and 6 inhibitors in breast cancer treatment

Breast cancer is the second largest cancer in the world, and it has highest mortality rate in women worldwide. The aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway plays an important role in uncontrolled breast cancer cell proliferation. Therefore, targeting CDK4/6 to improve overall survival rates has been a strong interest in breast cancer therapeutics. Till date, four CDK4/6 inhibitors have been developed and approved for hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer therapies with great success. However, acquired resistance to CDK4/6 inhibitors has emerged and limits their effectiveness in breast cancer. In this review, we systematically discussed the mechanisms of resistance to CDK4/6 inhibitors including the cell cycle-specific and cell cycle-nonspecific mechanisms. Also, we analyzed combination strategies with other signaling inhibitors in clinical and preclinical settings that further expand the clinical application of CDK4/6 inhibitors in future breast cancer therapies.

Assessment of in vitro assays and quantitative determination of selectivity and modality of inhibitors targeting the cell cycle regulating, oncogenic cyclin-dependent kinases

At the heart of cancer pathology lies the dysregulated cell cycle, which is often driven by aberrant activities of the cell cycle regulating, cyclin-dependent kinases (CDKs). Efforts to harness the therapeutic potential of modulating CDK activities have led to the development of inhibitors with tailored CDK selectivity. However, uniformity in the methods used to evaluate CDK inhibitor selectivity has been lacking and consequently, direct comparison and interpretation of selectivity profiles determined under different assay conditions is difficult. Determination of the inhibition modalities crucial to profiling selectivity of a CDK inhibitor requires thorough kinetic analysis carried out under comparable assay conditions. In this study, we employed a streamlined series of in vitro assays for profiling CDK inhibitors wherein intrinsic inhibition constants and cellular binding parameters were measured by using strategically designed enzymatic inhibition and complementary biophysical assays. Our findings demonstrate the effectiveness of this strategy in determining and quantitatively analyzing the selectivity and inhibition modality of a set of representative CDK inhibitors towards the major oncogenic, cell cycle CDKs. In addition, the assay results provide insights into the inhibitor-target interactions that extend beyond potency and selectivity.

CDK4/6-mediated phosphorylation of DUB3 promotes YAP1 stability and hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies, frequently characterized by high expression and activation of Yes-associated protein 1 (YAP1), a key effector in the Hippo signaling pathway. Despite its crucial role in HCC progression, effective therapies directly targeting YAP1 remain challenging, underscoring the need to explore the regulatory mechanisms underlying its aberrant expression and activation. In this study, we identify cyclin-dependent kinase 4 and 6 (CDK4/6) as uncharacterized regulators of YAP1 in HCC. Genetic ablation or pharmacological inhibition of CDK4/6 significantly destabilizes YAP1 and attenuates its oncogenic functions both in vitro and in vivo. Furthermore, we establish DUB3 as a bona fide deubiquitinase of YAP1. Mechanistically, CDK4/6 directly phosphorylates DUB3, enhancing its deubiquitinase activity towards YAP1, which promotes tumor growth and contributes to chemo-resistance in HCC. Collectively, our findings unveil the previously unrecognized function and significance of the CDK4/6-DUB3 axis in stabilizing YAP1 and provide a rationale for potential therapeutic interventions in the treatment of HCC.

CDK4/6 inhibition in early and advanced hormone receptor-positive, HER2-negative breast cancer

INTRODUCTION

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibition in combination with endocrine therapy is the mainstay of treatment for hormone receptor-positive, HER2-negative (HR  +  /HER2-) advanced breast cancer; the CDK4/6 inhibitors abemaciclib and ribociclib are also approved for high-risk, early-stage, HR  +  /HER2- breast cancer. Numerous studies exploring CDK4/6 inhibitors in the early-stage setting are ongoing, as well as many more exploring novel combinations in the metastatic setting.

AREAS COVERED

Here, we review the basis of CDK4/6 inhibition for HR  +/HER2- breast cancer, the pivotal clinical trials which led to regulatory approval, and ongoing trials evaluating novel combinations to further improve outcomes for those with both early and advanced HR+/HER2- breast cancer. Current literature was reviewed by a comprehensive search of PubMed MEDLINE (1/1/2000-12/31/2024).

EXPERT OPINION

CDK4/6 inhibitors are integral in the management of both advanced and high-risk, early-stage HR  +  /HER2- breast cancer. Biomarkers predictive of CDK 4/6 inhibitor (CDK4/6i) benefit remain elusive, and clinical and pathological features remain key to identifying those who are candidates for CDK4/6 inhibition in the early-stage setting. Numerous trials evaluating the role of a CDK4/6i with novel endocrine therapy partners and other targeted agents are ongoing, with the goal of improving outcomes for those with HR  +  /HER2- disease.

Design, synthesis, and biological evaluation of novel CDK4/6 and BRD4 dual inhibitors for treatment of KRAS-mutant NSCLC

CDK4/6 is the candidate therapeutic target for KRAS-mutant NSCLC. However, its frequent primary and acquired resistance limits its potential clinical application. Recently it had been shown that BRD4 up-regulation induced conferred resistance of KRAS-mutant NSCLC cells to CDK4/6 inhibitor, and BRD4 inhibitor synergized with CDK4/6 inhibitor induced senescence in KRAS-mutant NSCLC tumors and cells, meanwhile, the combined therapy extended survival of the KRAS-mutant NSCLC mouse model. Thus, a series of CDK4/6 and BRD4 dual inhibitors were prepared to target KRAS-mutant NSCLC. Among these compounds, PJ2 exhibited potent antiproliferative effects against KRAS-mutant NSCLC cells NCI-H358 (IC50 = 0.34 ± 0.01 μM) and A549 (IC50 = 0.31 ± 0.04 μM), and had excellent inhibitory effects on CDK4, CDK6, BRD4(BD1) and BRD4(BD2), and IC50 values were 168.75 ± 46.32 nM, 292.45 ± 11.67 nM, 23.17 ± 3.61 nM and 3.12 ± 0.15 nM, respectively. Mechanism research indicated that PJ2 induced cell cycle arrest, senescence and apoptosis through ROS-mediated DNA damage. Furthermore, PJ2 could effectively suppress the migration and invasion of NCI-H358 cells. These results proved that developing potent CDK4/6 and BRD4 dual inhibitors was a promising strategy for the KRAS-mutant NSCLC therapy.

Differential Response and Resistance to KRAS-Targeted Therapy

KRAS is the most frequently mutated oncogene. In epithelial malignancies such as lung, colorectal, and pancreatic tumors, KRAS is mutated in 25 to above 90% cases. KRAS was considered undruggable for over three decades until the recent development of covalent inhibitors targeting the KRAS G12C mutant. The recent approval of the KRAS G12C inhibitors sotorasib and adagrasib has ushered in a new era of KRAS-targeted therapy. Despite this success, a major challenge in KRAS-targeted therapy is intrinsic and acquired resistance to KRAS inhibitors. Clinical studies have shown that many patients with KRAS G12C cancers did not respond to sotorasib and adagrasib. Colorectal cancer, in particular, has a markedly lower response rate to KRAS G12C inhibitors compared to non-small cell lung cancer. Furthermore, the therapeutic response to KRAS G12C inhibition was short-lived, with quick emergence of acquired resistance. In this review, we summarize several major themes that have emerged from recent clinical and preclinical studies on the mechanisms of intrinsic and acquired resistance to KRAS-targeted therapy in colorectal, lung, and pancreatic cancers. We also discuss various combination strategies for targeting these mechanisms to overcome resistance to KRAS inhibitors.

Potential Value of AURKA and CDK6 Amplification for the Response of Patients With Gastric Cancer to Neoadjuvant Chemotherapy

Many patients respond poorly to neoadjuvant chemotherapy (NACT), negatively affecting the surgical success rate. Identifying effective biomarkers and understanding the potential resistance mechanisms are urgently needed. Data of 18 patients with advanced stomach cancer who were treated with NACT categorized according to tumor regression grade into major histological response (MJHR) and nonhistological response (NHR) groups were retrospectively analyzed. Genomic signatures associated with the response to NACT were identified using whole-exome and RNA sequencing. Extraction of molecular signatures revealed increased deficient mismatch repair signature and tumor mutation levels in the NHR group. Compared to the MJHR group, the NHR group was also characterized by a greater number of copy number alterations (p = 0.08), which was further confirmed by RNA sequencing, and upregulation of aurora kinase A (AURKA) (p = 0.05) and cyclin-dependent kinase 6 (CDK6) (p = 0.049). Western blot analysis and immunohistochemical analyses further confirmed high CDK6 (p < 0.01/p < 0.0001) and AURKA (p < 0.01/p < 0.001) expression levels in the NHR group. Finally, palbociclib, an inhibitor of CDK4/6, effectively inhibited the proliferation (p < 0.05) and induced apoptosis of oxaliplatin-resistant gastric cancer cells (p < 0.01) in vitro. These findings support the potential value of AURKA and CDK6 amplification, as well as their effects on the tumor microenvironment, in predicting poor outcomes of NACT in patients with locally advanced gastric cancer. Thus, CDK4/6 inhibitors could be used to treat NACT-resistant patients with gastric cancer.

Recent Developments in Targeting the Cell Cycle in Melanoma

Melanoma is an aggressive cancer with rising incidence, particularly among older individuals. Despite advancements in targeted therapies for BRAF and MEK proteins and immunotherapies, many patients either fail to respond or develop resistance. For those progressing on immunotherapy, limited treatment options remain. The Cyclin D-CDK4/6-RB pathway is commonly dysregulated in melanoma, with up to 90% of cases showing alterations that activate it. Although targeting Cyclin-CDK complexes has shown promise in preclinical models, clinical responses have been suboptimal. This review explores the molecular mechanisms behind Cyclin-CDK dysregulation in melanoma and the challenges of targeting this pathway. It also discusses strategies to improve the efficacy of CDK4/6 inhibitors, including combination therapies to overcome resistance and enhance patient outcomes. Understanding these mechanisms can guide the development of more effective treatments for melanoma.

Bireociclib plus fulvestrant for HR+/HER2- advanced female breast cancer progressed on or after endocrine therapy: phase 3 BRIGHT-2 study interim analysis

The BRIGHT-2 study (NCT05077449) is a randomized, double-blind, placebo-controlled, phase 3 trial evaluating the efficacy and safety of bireociclib plus fulvestrant (BF) vs. placebo plus fulvestrant (F) in Chinese female patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) advanced breast cancer (ABC) who had progressed on or after prior endocrine therapy (ET). Interim results were analyzed after 70% of progression-free survival (PFS) events across 64 centers in China between December 8, 2021, and March 28, 2023. Patients were randomized (2:1) to receive BF or F, with stratification based on visceral involvement (yes/no) and resistance to prior primary or secondary ET. As the primary outcome, PFS was significantly prolonged in the BF group (n = 204) (12.94 months; 95% CI: 11.07-not reached) compared to 7.29 months (95% CI: 5.45-11.04) in the F group (n = 101) (hazard ratio, 0.56; 95% CI: 0.39-0.80; p = 0.001). The objective response rate in the BF group was 39.7% in the intention-to-treat population. Grade ≥3 adverse events were more frequent in the BF group (64.7%) than in the F group (18.8%), with neutropenia, leukopenia, and anemia being the most common. These findings suggest that BF is a promising therapeutic option for patients with HR+/HER2- ABC following ET failure.

Serial Circulating Tumor DNA Sequencing to Monitor Response and Define Acquired Resistance to Letrozole/Abemaciclib in Endometrial Cancer

PURPOSE

In a phase II study, letrozole/abemaciclib demonstrated an objective response rate of 30% and a median progression-free survival (PFS) of 9.1 months in recurrent estrogen receptor-positive endometrial cancer (EC). While tissue-based tumor profiling revealed several mechanistically relevant candidate baseline genomic predictors of response, circulating tumor DNA (ctDNA) is a less invasive alternative to monitor therapeutic efficacy and define acquired resistance.

METHODS

Serial plasma specimens were obtained at baseline, C2D1, C3D1, C8D1, the time of objective response, and the time of progression. Samples were analyzed using the Guardant Reveal assay to assess methylation-based tumor fraction (TF), with the Guardant360 assay providing genotyping of >700 genes in samples with detectable ctDNA. Treatment response was assessed using a measure of the relative change in TF pre- versus on-treatment.

RESULTS

A total of 99 of 102 (97%) samples from 28 patients were successfully analyzed. Patients with above median baseline TF exhibited worse median PFS (2.0 months v 16.5 months, P < .005, hazard ratio [HR], 24.1) and worse overall survival (OS) (10.7 months v not yet reached, P < .005, HR, 14.8). Patients with molecular response (MR) after the first or second cycle of letrozole/abemaciclib therapy had significantly better median PFS and OS regardless of the cutoff used for definition of MR. ctDNA analysis of postprogression specimens identified several acquired genomic alterations associated with resistance to letrozole/abemaciclib therapy in more than half of the patients, including PI3K pathway, receptor tyrosine kinase (FGFR1,2 and ERBB2 alterations), cell cycle pathway (RB1 and CCNE1 alterations), and ESR1 and MAPK pathway alterations. Two of the three patients with mismatch repair-deficient ECs acquired ESR1 mutations at the time of progression.

CONCLUSION

Baseline and on-treatment ctDNA dynamics may provide an early indication of benefit from letrozole/abemaciclib in EC. ctDNA at the time of progression may identify resistance alterations that may inform subsequent therapy.

Targeting CDK6 in hormone receptor-positive breast cancer: inhibitor discovery for precision oncology through dynamics study

CDK6 is a critical protein involved in the regulation of the cell cycle, playing an important role in the progression from the G1 to S phase. In breast cancer, dysregulation of this protein is involved in tumour development and progression, particularly in hormone receptor-positive (HR+) breast cancers. The upregulation of CDK6 have been observed in a subset of breast cancers, leading to uncontrolled progression of the cell cycle and increased proliferation of cells. The purpose of this abstract is to provide an outline of CDK6's role. In breast cancer and the therapeutic strategies targeting CDK6 using specific selected inhibitors. To discover viable therapeutic candidates after competitive inhibition of CDK6 with a small molecular drug complex, high throughput screening and docking studies were used. Further, we carried the compounds based on ADMET properties and prediction of activity spectra for substances analysis. Finally, two different compounds were selected to carry out MD simulations. CDK6-IMPHY002642 and CDK6-IMPHY005260 are the two compounds that were identified. Overall, our results suggest that the CDK6-IMPHY002642 and CDK6-IMPHY005260 complex was relatively stable during the simulation. The compounds that have been found can also be further examined as potential therapeutic possibilities. The combined findings suggest that CDK6, together with their genetic changes, can be investigated in therapeutic interventions for precision oncology, leveraging early diagnostics and target-driven therapy.

Pseudo acute kidney injury in patients receiving CDK4/6 inhibitors

INTRODUCTION

CDK4/6 inhibitors (CDK4/6i) improve progression-free survival in patients with advanced oestrogen-receptor-positive breast cancer. However, all CDK4/6i may increase creatinine levels, which can indicate kidney injury. In vitro research has shown that CDK4/6i can also inhibit tubular secretion of creatinine, thereby causing the phenomenon 'pseudo-acute kidney injury (pseudo-AKI)'. The incidence of pseudo-AKI is, however, unknown. We aimed to determine this incidence by assessing cystatin C, a protein filtered in the glomerulus without being subject to tubular secretion, in patients with creatinine increase during CDK4/6i treatment.

METHODS

In this retrospective single-centre cohort study patients with breast cancer who received CDK4/6 inhibitors between January 1st 2017 and December 29th 2023 were screened for the incidence of creatinine increases suggesting potential kidney injury in the first six months of treatment. A significant creatinine increase was defined as 1) a creatinine plasma level of >90 µmol/L in women or >115 µmol/L in men and >10% increase from baseline creatinine plasma level or 2) a creatinine plasma level >1.5 times baseline creatinine or 3) an increase in creatinine plasma level from baseline with >26 µmol/L. Pseudo-AKI was diagnosed if the estimated glomerular filtration rate (eGFR) using cystatin C at the moment of creatinine increase was 1) equal or higher than eGFR using creatinine at baseline and/or 2) at least 25% higher than eGFR using creatinine at the moment of creatinine increase. The primary endpoint was the percentage of patients with pseudo-AKI analysed by means of the binomial probability test.

RESULTS

Of the 234 patients treated with a CDK4/6i, 41 (17.5%) had creatinine levels indicating an AKI. From 22 of these 41 patients, cystatin C could be determined in retrospectively available serum. Pseudo-AKI was found in 16 out of 22 patients (73%, 95% CI 50-89%). In 5 out of 41 patients (12%) the CDK4/6i dose was unjustly adjusted or the drug was stopped due to creatinine increase.

CONCLUSION

Pseudo-AKI has a high incidence in patients treated with CDK4/6i. Determining an eGFR based on the cystatin C value should therefore be considered as the first step when creatinine increases during CDK4/6i treatment.

Abemaciclib Plus Fulvestrant in Advanced Breast Cancer After Progression on CDK4/6 Inhibition: Results From the Phase III postMONARCH Trial

PURPOSE

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are the standard first-line treatment for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC); however, disease progression occurs in almost all patients and additional treatment options are needed. Herein, we report outcomes of the postMONARCH trial investigating a switch in ET with/without CDK4/6 inhibition with abemaciclib after disease progression on CDK4/6i.

METHODS

This double-blind, randomized phase III study enrolled patients with disease progression on previous CDK4/6i plus aromatase inhibitor as initial therapy for advanced disease or recurrence on/after adjuvant CDK4/6i + ET. Patients were randomly assigned (1:1) to abemaciclib + fulvestrant or placebo + fulvestrant. The primary end point was investigator-assessed progression-free survival (PFS). Secondary end points included PFS by blinded independent central review, objective response rate (ORR), and safety.

RESULTS

This study randomly assigned 368 patients (abemaciclib + fulvestrant, n = 182 placebo + fulvestrant, n = 186). At the primary analysis (258 events), the hazard ratio (HR) was 0.73 (95% CI, 0.57 to 0.95; nominal P = .017), with median PFS 6.0 (95% CI, 5.6 to 8.6) versus 5.3 (95% CI, 3.7 to 5.6) months and 6-month PFS rates of 50% and 37% in the abemaciclib + fulvestrant and placebo + fulvestrant arms, respectively. These results were supported by BICR-assessed PFS (HR, 0.55 [95% CI, 0.39 to 0.77]; nominal P < .001). A consistent treatment effect was seen across major clinical and genomic subgroups, including with/without ESR1 or PIK3CA mutations. Among patients with measurable disease, investigator-assessed ORR was improved with abemaciclib + fulvestrant versus placebo + fulvestrant (17% v 7%; nominal P = .015). No new safety signals were observed, with findings consistent with the known safety profile of abemaciclib.

CONCLUSION

Abemaciclib + fulvestrant significantly improved PFS after disease progression on previous CDK4/6i + ET in patients with HR+, HER2- ABC, offering an additional targeted therapy option for these patients.

Models of Early Resistance to CDK4/6 Inhibitors Unveil Potential Therapeutic Treatment Sequencing

BACKGROUND

CDK4/6 inhibitors (CDK4/6i) combined with hormone therapies have demonstrated clinical benefit in HR+, HER2- breast cancer patients. However, the onset of resistance remains a concern and highlights a need for therapeutic strategies to improve outcomes. The objective of this study was to develop an in vitro model to better understand the mechanisms of resistance to CDK4/6i + hormone therapies and identify therapeutic strategies with potential to overcome this resistance.

METHODS

The HR+, HER2- T47D breast cancer cell line genetically modified with a Geminin-Venus reporter construct was treated with CDK4/6i (abemaciclib or palbociclib) in combination with 4-hydroxytamoxifen (tamoxifen). Resistant cells were identified by cell sorting for Geminin (%GEM+), a marker of the S/G2/M phases of the cell cycle, and confirmed by treatment with tamoxifen plus the CDK4/6i used to drive resistance. In resistant cells, following treatment with CDK4/6i + ET (tamoxifen or fulvestrant), the effects on cell proliferation (%GEM+) and viability, gene expression, and protein analysis to evaluate CDK4/6-cyclin D complex composition were examined.

RESULTS

Palbociclib + tamoxifen-resistant (PTxR) cells treated with abemaciclib + ET showed decreased %GEM+, %Ki67, and colony formation ability, compared to abemaciclib + tamoxifen-resistant (ATxR) cells treated with palbociclib + ET. Additionally, PTxR cells showed increased CDK4-p21 interaction, compared to ATxR. The CDK6 levels were greater in ATxR cells compared to PTxR cells, associated with CDK4/6i resistance. Additionally, abemaciclib + fulvestrant continued to robustly decrease pRb levels in PTxR models compared to palbociclib + fulvestrant in ATxR models. Transcriptome analysis revealed a depression of the cell cycle and E2F- and Rb-related genes in PTxR cells following treatment with abemaciclib + ET, not present in ATxR cells treated with palbociclib + ET. Both resistant models showed increased EGFR-related gene expression.

CONCLUSION

Taken together, we describe CDK4/6i-dependent mechanisms resulting in early-onset resistance to CDK4/6i + ET, using clinically relevant drug concentrations, in preclinical breast cancer cell models. The characterization of these preclinical models post progression on CDK4/6 inhibitor + ET treatment highlights the potential that the specific sequencing of CDK4/6 inhibitors could offer to overcome acquired resistance to CDK4/6i + ET. Abemaciclib + fulvestrant is currently under clinical investigation in patients with HR+, HER2- breast cancer and progression on prior CDK4/6i + ET (NCT05169567, postMONARCH).

Schisandrin B targets CDK4/6 to suppress proliferation and enhance radiosensitivity in nasopharyngeal carcinoma by inducing cell cycle arrest

Nasopharyngeal carcinoma (NPC) is notably prevalent in East and Southeast Asia, where despite advancements in radiotherapy leading to high control rates, challenges like radioresistance and collateral tissue damage remain significant. While Schisandrin B (SchB) has been demonstrated antitumor effects in various tumors, its efficacy in NPC remains unexplored. In this study, we explored the antitumor potential of Sch B on NPC, particularly its effects on cell proliferation and radiosensitivity. Our research demonstrates that Sch B effectively inhibits the proliferation of NPC cell lines HONE-1 and CNE-1 by inducing cell cycle G1 phase arrest, specifically through the down-regulation of cyclin-dependent kinase 4/6, without impacting the normal nasopharyngeal epithelial cell line NP69. This selective inhibitory effect positions Sch B as a targeted therapeutic agent, sparing healthy tissue from adverse effects. Furthermore, we observed that Sch B enhances the efficacy of radiotherapy in NPC cells by obstructing DNA double-strand break repair mechanisms, suggesting that a combined treatment regimen of Sch B and radiation could offer a superior therapeutic strategy. These findings propose Sch B not only as a potent inhibitor of NPC cell proliferation but also as an enhancer of radiosensitivity, providing a promising avenue for improving NPC treatment outcomes.

Physiologically Based Pharmacokinetic Model of Plasma and Intracranial Pharmacokinetics and CDK4/6 Occupancy of Abemaciclib to Optimizing Dosing Regimen for Brain Metastatic Patients

Objective: The study aimed to develop a physiologically based pharmacokinetic (PBPK) model to predict steady state trough concentrations (C min) and CDK4/6 occupancy in plasma and cerebrospinal fluid (CSF) for abemaciclib (ABE) and its three active metabolites. Additionally, a biomarker model was constructed to simulate changes in pRB and TOPO-IIα expression. Methods: The population PBPK and biomarker models of ABE were developed using physicochemical, pharmacokinetics (PK), CDK4/6 occupancy, biomarker, and physiological properties. These models were then validated using four clinical plasma PK studies, two CSF PK studies, and one clinically observed biomarker expression change in patients. Results: The PBPK model showed good consistency with observed data, with most prediction-to-observation ratios falling within the range of 0.5 to 2.0 for AUC, C max, C min in plasma and CSF. Key factors affecting C min and CDK4/6 occupancy for total analytes (sum of ABE and metabolites) were identified as CYP3A4, ABCB1, ABCG2 expression, and plasma albumin levels. PBPK simulations suggested that the optimal dosing regimen for ABE in brain metastatic breast cancer (MBC) is either 150 or 200 mg twice daily (BID). Conclusions: The PBPK model successfully simulated the PK profiles and CDK4/6 occupancy for ABE and its three metabolites in plasma and CSD, and determined the optimal dosing in brain MBC. Overall,The PBPK model can provide important insights for personalized dosing strategies, contributing to improved treatment efficacy and safety for patients, particularly those with brain MBC.

Targeting CDK4/6 suppresses colorectal cancer by destabilizing YAP1

Colorectal cancer (CRC) is among the most prevalent and deadly cancers worldwide. The Yes-associated protein 1 (YAP1) is frequently dysregulated in cancers, contributing to cancer stemness, chemoresistance, and cancer-related death. However, strategies directly targeting YAP1 have not yet been successful because of the lack of active binding pockets and unregulated toxicity. In this study, our Food and Drug Administration (FDA)-approved drug screening reveals that abemaciclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, dramatically promotes the proteasome-dependent degradation of YAP1, thereby inhibiting tumor progression in CRC cells and patient-derived xenograft models. We further identify deubiquitinating enzyme 3 (DUB3) as the bona fide deubiquitinase of YAP1 in CRC. Mechanistically, CDK4/6 directly phosphorylates DUB3 at Ser41, activating DUB3 to deubiquitinate and stabilize YAP1. Conversely, loss of Ser41 phosphorylation by CDK4/6 inhibition or Ser41A mutation, promotes YAP1 degradation and suppresses YAP1-driven tumor progression. Histological analysis shows a positive correlation between DUB3 and YAP1 expression in CRC specimens. Collectively, our study uncovers a novel oncogenic role of the CDK4/6-DUB3 pathway, which promotes YAP1 stabilization and tumor-promoting function, highlighting that targeting CDK4/6 offers a potential therapeutic strategy for CRC with aberrantly upregulated DUB3 and YAP1.

Cell cycle dysregulation in cancer

Cancer is a systemic manifestation of aberrant cell cycle activity and dysregulated cell growth. Genetic mutations can determine tumor onset by either augmenting cell division rates or restraining normal controls such as cell cycle arrest or apoptosis. As a result, tumor cells not only undergo uncontrolled cell division but also become compromised in their ability to exit the cell cycle accurately. Regulation of cell cycle progression is enabled by specific surveillance mechanisms known as cell cycle checkpoints, and aberrations in these signaling pathways often culminate in cancer. For instance, DNA damage checkpoints, which preclude the generation and augmentation of DNA damage in the G1, S, and G2 cell cycle phases, are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Notably, tumors have evolved to become dependent on checkpoints for their survival. For example, checkpoint pathways such as the DNA replication stress checkpoint and the mitotic checkpoint rarely undergo mutations and remain intact because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation leading to cell death. In this review, we initially focus on cell cycle control pathways and specific functions of checkpoint signaling involved in normal and cancer cells and then proceed to examine how cell cycle control and checkpoint mechanisms can provide new therapeutic windows that can be exploited for cancer therapy. SIGNIFICANCE STATEMENT: DNA damage checkpoints are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Conversely, DNA replication stress and mitotic checkpoints rarely undergo mutations because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation, leading to cancer cell death. This review focuses on the checkpoint signaling mechanisms involved in cancer cells and how an emerging understanding of these pathways can provide new therapeutic opportunities for cancer therapy.

Targeting cyclin-dependent kinase 2 (CDK2) interactions with cyclins and Speedy 1 (Spy1) for cancer and male contraception

The review discusses progress in discovering cyclin-dependent kinase 2 (CDK2) inhibitors for cancer treatment and their potential for male contraception. It summarizes first-, second-, and third-generation CDK inhibitors and selective CDK2 inhibitors currently in clinical trials for cancer. Novel strategies to discover allosteric inhibitors, covalent inhibitors, and degraders are also discussed.

Abemaciclib-associated kidney injuries: A retrospective analysis of the United States Food and Drug Administration adverse events reporting system

BackgroundAbemaciclib, an oral kinase inhibitor, is used to treat hormone receptor-positive and HER2-negative breast cancer patients. However, there has been a decrease in studies reporting adverse reactions to abemaciclib-related kidney injuries. Thus, this study was aimed at assessing its safety profile using a large-scale pharmacovigilance database.MethodsAbemaciclib-related adverse drug reaction reports from the Food and Drug Administration Adverse Event Reporting System were obtained and scrutinized, and adverse drug reactions were selected using reporting odds ratio, the proportional reporting ratio methods, empirical Bayes geometric mean and UK Medicines and Healthcare products Regulatory Agency methods.ResultsWe selected 10,757 matched reports associated with abemaciclib, among which we found eight adverse reactions about kidney injuries correlated with abeamciclib, such as increased blood creatinine, renal disorder, decreased glomerular filtration rate, increased blood urea, hydronephrosis, abnormal renal function test, increased creatinine renal clearance and increased cystatin C. A demographic analysis of reported cases of abemaciclib-associated renal injury revealed that the majority were female, aged ≥46 years and had taken the drug ≥30 days.ConclusionThis study highlights the characteristics of adverse reactions with abemaciclib and those associated with renal damage, which are crucial for safety studies on the clinical use of this drug.

Mechanistic Modeling of Spatial Heterogeneity of Drug Penetration and Exposure in the Human Central Nervous System and Brain Tumors

Direct measurement of spatial-temporal drug penetration and exposure in the human central nervous system (CNS) and brain tumors is difficult or infeasible. This study aimed to develop an innovative mechanistic modeling platform for quantitative prediction of spatial pharmacokinetics of systemically administered drugs in the human CNS and brain tumors. A nine-compartment CNS (9-CNS) physiologically-based pharmacokinetic model was developed to account for general anatomical structure and pathophysiological heterogeneity of the human CNS and brain tumors. Drug distribution into and within the CNS and tumors is driven by plasma concentration-time profiles and governed by drug properties and CNS pathophysiology. The model was validated by comparisons of model predictions and clinically observed data of six drugs (abemaciclib, ribociclib, pamiparib, olaparib, temuterkib, and ceritinib) in glioblastoma patients. As rigorously validated, the 9-CNS model allows reliable prediction of spatial pharmacokinetics in different regions of the brain parenchyma (i.e., parenchyma adjacent to CSF and deep parenchyma), tumors (i.e., tumor rim, bulk tumor, and tumor core), and CSF (i.e., ventricular CSF, cranial and spinal subarachnoid CSF). By considering inter-individual plasma pharmacokinetic variability and CNS/tumor heterogeneity, the model well predicts the inter-individual variability and spatial heterogeneity of drug exposure in the CNS and tumors as observed for all six drugs in glioblastoma patients. The 9-CNS model is a first-of-its kind, mechanism-based computational modeling platform that enables early reliable prediction of spatial CNS and tumor pharmacokinetics based on plasma concentration-time profiles. It provides a valuable tool to assist rational drug development and treatment for brain cancer.

Targeting tGLI1, a novel mediator of tumor therapeutic resistance, using Ketoconazole sensitizes glioblastoma to CDK4/6 therapy and chemoradiation

Glioblastoma (GBM) remains the most aggressive primary brain tumor in adults, with no effective treatments. While cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) show clinical promise in some cancers, they have not significantly improved survival in GBM patients. This lack of response is attributed to the treatment-resistant glioma stem cell (GSC) population. We previously identified truncated glioma-associated oncogene homolog 1 (tGLI1) as a novel transcription factor promoting GSCs; however, its role in CDK4/6i resistance has never been investigated in any cancer type. Here, we found positive correlations between tGLI1 and CDK4/6 therapeutic resistance in patient datasets and in vitro studies. Pharmacological inhibition of tGLI1 using FDA-approved ketoconazole (KCZ), a tGLI1-specific inhibitor, sensitized GBM and GSCs to CDK4/6is. KCZ+CDK4/6i combination therapy demonstrated synergistic anti-proliferative effects, significantly inhibiting GBM stemness and cell cycle progression while increasing apoptosis. The combination was more efficacious than monotherapies in two orthotopic GBM mouse models. tGLI1 promoted GBM resistance to radiation therapy and temozolomide, while KCZ potentiated effects of these treatments. Collectively, we report for the first time that tGLI1 is a novel mediator of GBM resistance to CDK4/6is, and KCZ sensitizes GBM to CDK4/6is, thereby supporting future clinical utility of novel KCZ+CDK4/6i combinatorial therapy for GBM patients.

Bruton's tyrosine kinase inhibition re-sensitizes multidrug-resistant DLBCL tumors driven by BCL10 gain-of-function mutants to venetoclax

Disparate pathogenic mechanisms complicate precision-medicine efforts to treat diffuse large B-cell lymphoma (DLBCL), the most common lymphoma diagnosis. Though potentially curable with frontline combination chemoimmunotherapy, DLBCL carries persistently poor prognosis for those with relapsed or refractory (rel/ref) disease, despite recent advances in immunotherapy. Here, we build on recent findings implicating gain-of-function mutations in the BCL10 signaling protein as drivers of resistance to Bruton's tyrosine kinase (BTK) inhibitors. We show mutant BCL10-driven DLBCL is resistant to multiple additional drug classes, demonstrating urgency to derive mechanistically rooted strategies to overcome undruggable BCL10 mutants that stabilize BTK-independent signaling filaments upstream of NF-kB activation. BCL10 mutants promote a cytokine-reinforced positive feedback loop of lymphomagenesis driving not just NF-kB but multiple additional pathways converging on diffuse activation of oncogenic transcription factors. Up-regulation of anti-apoptotic genes increases mitochondrial membrane potential, underlying multidrug resistance. Increased expression of BCL2, BCL2L1 (BCL-XL), and BCL2A1 (BFL1) drives resistance to venetoclax, but expression can be overcome by the potent non-covalent BTK inhibitor pirtobrutinib. Venetoclax plus pirtobrutinib synergized in overcoming resistance and potently killed BCL10-mutant lymphomas in vitro and in vivo. BTK therefore retains key roles protecting DLBCL from apoptosis even when downstream activation of the BCL10 signaling complex activates NF-kB independently.

TNG908 is a brain-penetrant, MTA-cooperative PRMT5 inhibitor developed for the treatment of MTAP-deleted cancers

TNG908 is a clinical stage PRMT5 inhibitor with an MTA-cooperative binding mechanism designed to leverage the synthetic lethal interaction between PRMT5 inhibition and MTAP deletion. MTAP deletion occurs in 10-15 % of all human cancer representing multiple histologies. MTA is a negative regulator of PRMT5 that accumulates as a result of MTAP deletion. In this study, we demonstrate that TNG908 selectively binds the PRMT5·MTA complex driving selective inhibition of PRMT5 in MTAP-null cancers, a mechanism that creates a large therapeutic index relative to first generation PRMT5 inhibitors that have alternative binding mechanisms that are not tumor-selective. Strong preclinical activity in multiple MTAP-deleted xenograft models, as well as demonstrated brain penetrance in preclinical models, support the potential for histology-agnostic clinical development of TNG908 in MTAP-deleted solid tumors, including CNS malignancies. TNG908 is being tested clinically in patients with MTAP-deleted tumors, including glioblastoma, in a Phase I/II clinical trial (NCT05275478).

Targeting CDK4/6 in breast cancer

Dysregulation of the cell cycle machinery, particularly the overactivation of cyclin-dependent kinases 4 and 6 (CDK4/6), is a hallmark of breast cancer pathogenesis. The introduction of CDK4/6 inhibitors has transformed the treatment landscape for hormone receptor-positive breast cancer by effectively targeting abnormal cell cycle progression. However, despite their initial clinical success, drug resistance remains a significant challenge, with no reliable biomarkers available to predict treatment response or guide strategies for managing resistant populations. Consequently, numerous studies have sought to investigate the mechanisms driving resistance to optimize the therapeutic use of CDK4/6 inhibitors and improve patient outcomes. Here we examine the molecular mechanisms regulating the cell cycle, current clinical applications of CDK4/6 inhibitors in breast cancer, and key mechanisms contributing to drug resistance. Furthermore, we discuss emerging predictive biomarkers and highlight potential directions for overcoming resistance and enhancing therapeutic efficacy.

Targeting the mitotic kinase NEK2 enhances CDK4/6 inhibitor efficacy by potentiating genome instability

Selective inhibitors that target cyclin-dependent kinases 4 and 6 (CDK4/6i) are approved by the U.S. Food and Drug Administration (FDA) for treatment of a subset of breast cancers and are being evaluated in numerous clinical trials for other cancers. Despite this advance, a subset of tumors are intrinsically resistant to these drugs and acquired resistance is nearly inevitable. Recent mechanistic evidence suggests that in addition to stalling the cell cycle, the antitumor effects of CDK4/6i involve the induction of chromosomal instability (CIN). Here, we exploit this mechanism by combining CDK4/6i with other instability-promoting agents to induce maladaptive CIN and irreversible cell fates. Specifically, dual targeting of CDK4/6 and the mitotic kinase NEK2 in vitro drives centrosome amplification and the accumulation of CIN that induces catastrophic mitoses, cell cycle exit, and cell death. Dual targeting also induces CIN in vivo and significantly decreases mouse tumor volume to a greater extent than either drug alone, without inducing overt toxicity. Importantly, we provide evidence that breast cancer cells are selectively dependent on NEK2, but nontransformed cells are not, in contrast with other mitotic kinases that are commonly essential in all cell types. These findings implicate NEK2 as a potential therapeutic target for breast cancer that could circumvent the dose-limiting toxicities that are commonly observed when blocking other mitotic kinases. Moreover, these data suggest that NEK2 inhibitors could be used to sensitize tumors to FDA-approved CDK4/6i for the treatment of breast cancers, improving their efficacy and providing a foundation for expanding the patient population that could benefit from CDK4/6i.

Advancing treatment choices: CDK4/6 inhibitor switching in HR+/HER2- metastatic breast cancer

PURPOSE

CDK4/6 inhibitors (CDK4/6i) use has revolutionized the treatment of hormone receptor-positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer. The choice of a specific CDK4/6i may be influenced by adverse events (AEs). Recently, the Italian Medicines Agency (AIFA) approved the possibility of switching between CDK4/6i for unacceptable toxicity. This study explores oncologists' experiences and future perspectives on CDK4/6 inhibitor switching following this new approval.

METHODS

With the support of the Italian Association of Medical Oncology (AIOM), we conducted a survey among 92 oncologists to assess the impact of AIFA's approval on patient management.

RESULTS

The survey showed that 48 % of participants were not surprised regarding AIFA's decision, with 76 % of respondents believing that this opportunity would significantly influence their treatment choices, enhancing AEs management for patients. Yet, 49 % of respondents emphasized the need for more real world evidence on CDK4/6i switch safety and efficacy. 96 % of respondents reported discontinuation rates between 0% and 25 % of patients, with constipation and hematological toxicity being the most frequent treatment discontinuation reasons. The oncologists prescribing CDK4/6i switch reported that most of these patients were in first line treatment (85 %) and the most common second CDK4/6i most frequently initiated was palbociclib (69 %), then abemaciclib (17 %) and ribociclib (14 %). Among those who started the second CDK4/6i at full dosage, 66 % of patients didn't require a dose reduction.

CONCLUSION

Our survey highlights the importance of allowing CDK4/6i switching, thus likely prompting oncologists to adapt their treatment choices, leading to better AEs management for improving patients' outcome.

An open-label, phase IB/II study of abemaciclib with paclitaxel for tumors with CDK4/6 pathway genomic alterations

BACKGROUND

Disruption of cyclin D-dependent kinases (CDKs), particularly CDK4/6, drives cancer cell proliferation via abnormal protein phosphorylation. This open-label, single-arm, phase Ib/II trial evaluated the efficacy of the CDK4/6 inhibitor, abemaciclib, combined with paclitaxel against CDK4/6-activated tumors.

PATIENTS AND METHODS

Patients with locally advanced or metastatic solid tumors with CDK4/6 pathway aberrations were included. Based on phase Ib, the recommended phase II doses were determined as abemaciclib 100 mg twice daily and paclitaxel 70 mg/m2 on days 1, 8, and 15, over 4-week-long cycles. The primary endpoint for phase II was the overall response rate (ORR). The secondary endpoints included the clinical benefit rate (CBR), progression-free survival (PFS), overall survival (OS), and safety. Tissue-based next-generation sequencing and exploratory circulating tumor DNA analyses were carried out.

RESULTS

Between February 2021 and April 2022, 30 patients received abemaciclib/paclitaxel (median follow-up: 15.7 months), and 27 were included in the efficacy analysis. CDK4/6 amplification (50%) and CCND1/3 amplification (20%) were common activating mutations. The ORR was 7.4%, with two partial responses, and the CBR was 66.7% (18/27 patients). The median OS and PFS were 9.9 months [95% confidence interval (CI) 5.7-14.0 months] and 3.5 months (95% CI 2.6-4.3 months), respectively. Grade 3 adverse events (50%, 21 events) were mainly hematologic. Genetic analysis revealed a 'poor genetic status' subgroup characterized by mutations in key signaling pathways (RAS, Wnt, PI3K, and NOTCH) and/or CCNE amplification, correlating with poorer PFS.

CONCLUSION

Abemaciclib and paclitaxel showed moderate clinical benefits for CDK4/6-activated tumors. We identified a poor genetic group characterized by bypass signaling pathway activation and/or CCNE amplification, which negatively affected treatment response and survival. Future studies with homogeneous patient groups are required to validate these findings.

Next-generation sequencing-based evaluation of the actionable landscape of genomic alterations in solid tumors: the "MOZART" prospective observational study

BACKGROUND

The identification of the most appropriate targeted therapies for advanced cancers is challenging. We performed a molecular profiling of metastatic solid tumors utilizing a comprehensive next-generation sequencing (NGS) assay to determine genomic alterations' type, frequency, actionability, and potential correlations with PD-L1 expression.

METHODS

A total of 304 adult patients with heavily pretreated metastatic cancers treated between January 2019 and March 2021 were recruited. The CLIA-/UKAS-accredit Oncofocus assay targeting 505 genes was used on newly obtained or archived biopsies. Chi-square, Kruskal-Wallis, and Wilcoxon rank-sum tests were used where appropriate. Results were significant for P < .05.

RESULTS

A total of 237 tumors (78%) harbored potentially actionable genomic alterations. Tumors were positive for PD-L1 in 68.9% of cases. The median number of mutant genes/tumor was 2.0 (IQR: 1.0-3.0). Only 34.5% were actionable ESCAT Tier I-II with different prevalence according to cancer type. The DNA damage repair (14%), the PI3K/AKT/mTOR (14%), and the RAS/RAF/MAPK (12%) pathways were the most frequently altered. No association was found among PD-L1, ESCAT, age, sex, and tumor mutational status. Overall, 62 patients underwent targeted treatment, with 37.1% obtaining objective responses. The same molecular-driven treatment for different cancer types could be associated with opposite clinical outcomes.

CONCLUSIONS

We highlight the clinical value of molecular profiling in metastatic solid tumors using comprehensive NGS-based panels to improve treatment algorithms in situations of uncertainty and facilitate clinical trial recruitment. However, interpreting genomic alterations in a tumor type-specific manner is critical.

bta-miR-484 Inhibits Bovine Intramuscular Adipogenesis by Regulating Mitotic Clonal Expansion via the MAP3K9/JNK/CCND1 Axis

Intramuscular fat (IMF) content is a critical indicator of the beef nutritional value and flavor. In this study, we focused on bta-miR-484, a microRNA that is differentially expressed during the adipogenic differentiation of bovine intramuscular adipocytes and is negatively correlated with the IMF content across different cattle breeds. Our findings demonstrate that bta-miR-484 inhibits adipogenic differentiation without altering the fatty acid composition of bovine intramuscular adipocytes. miRNA pull-down and dual-luciferase reporter assays confirmed that MAP3K9 is a target gene of bta-miR-484. Furthermore, bta-miR-484 suppresses the JNK signaling pathway by targeting MAP3K9, leading to decreased CCND1 expression, which impedes the mitotic clonal expansion (MCE) process and inhibits intramuscular adipocyte differentiation. In summary, this study uncovers a novel mechanism by which bta-miR-484 regulates bovine IMF content and provides the first exploration of MCE during intramuscular adipocyte adipogenic differentiation. These findings offer valuable theoretical insights into beef cattle breeding and molecular improvements.

Assay for the quantification of abemaciclib, its metabolites, and olaparib in human plasma by liquid chromatography-tandem mass spectrometry

An isotope-dilution bioanalytical assay for abemaciclib and its metabolites in combination with olaparib was developed and validated in human plasma K2 EDTA. For the quantitative assay, human plasma samples (or human plasma QC samples) were spiked with internal standard solution before a simple protein precipitation with methanol. The extract was injected onto a liquid chromatography-tandem mass spectrometry (LC-MS/MS) instrument where it was chromatographically separated by a polar end-capped reversed phase column and guard using gradient elution with water and methanol both modified with 0.2 % formic acid (v/v) as the mobile phases. The analytes and internal standards were measured by heated electrospray ionization (HESI) in positive polarity using selected reaction monitoring (SRM) on a triple quadrupole mass spectrometer. The assay was validated for linear ranges as follows: 0.4 - 1000 nM abemaciclib, 0.35 - 1000 nM M2 and M18, 0.5 - 1000 nM M20, and 0.75 - 1000 nM olaparib. The inter-day or between day precision for the quality controls (n = 18) was < 13 % and the accuracy was ± 12 %, for all analytes, including the lower limit of quantification (LLOQ). The intra-day or within day precision for the quality controls (n = 6) was ≤ 11 % and the accuracy was ± 12 % for low, mid, and high and < 19 % at LLOQ. The recovery in human plasma was determined to be between 92 % and 102 % for all analytes spanning the linear range. The validated, bioanalytical quantitative assay was designed to measure abemaciclib, its metabolites, and olaparib for pharmacokinetic evaluation of patients in clinical trials for breast, brain, and ovarian cancers.

Network Pharmacology Approach and Experimental Verification to Explore the Anti-NSCLC Mechanism of Grifolic Acid

Lung cancer is the leading cause of cancer-related death. Non-small cell lung cancer (NSCLC) accounts for 85% of all lung cancers and over 60% express wild-type EGFR (WT-EGFR); however, EGFR tyrosine kinase inhibitors (TKIs) have limited effect in most patients with WT-EGFR tumors. In this study, we applied network pharmacology screening and MTT screening of bioactive compounds to obtain one novel grifolic acid that may inhibit NSCLC through the EGFR-ERK1/2 pathway. Through the PPI network and machine learning, we identified two hub genes, EGFR and AKT1, as potential therapeutic targets. Molecular docking confirmed that the grifolic acid could effectively bind to the key target, EGFR. Using the NSCLC cell line NCI-H1781 as an in vitro model, we evaluated the effect of the drugs' combination on viability, apoptosis, and clonogenicity capacity. In vitro studies showed that combined treatment decreased cell viability, increased activation PARP, and caused cell cycle redistribution and significantly greater inhibition of pEGFR and pAKT. This study not only provides new insights into the mechanism of grifolic acid against NSCLC but also important information and new research ideas for the discovery of anti-NSCLC compounds from natural products.

Cyclin-dependent protein kinases and cell cycle regulation in biology and disease

Cyclin Dependent Kinases (CDKs) are closely connected to the regulation of cell cycle progression, having been first identified as the kinases able to drive cell division. In reality, the human genome contains 20 different CDKs, which can be divided in at least three different sub-family with different functions, mechanisms of regulation, expression patterns and subcellular localization. Most of these kinases play fundamental roles the normal physiology of eucaryotic cells; therefore, their deregulation is associated with the onset and/or progression of multiple human disease including but not limited to neoplastic and neurodegenerative conditions. Here, we describe the functions of CDKs, categorized into the three main functional groups in which they are classified, highlighting the most relevant pathways that drive their expression and functions. We then discuss the potential roles and deregulation of CDKs in human pathologies, with a particular focus on cancer, the human disease in which CDKs have been most extensively studied and explored as therapeutic targets. Finally, we discuss how CDKs inhibitors have become standard therapies in selected human cancers and propose novel ways of investigation to export their targeting from cancer to other relevant chronic diseases. We hope that the effort we made in collecting all available information on both the prominent and lesser-known CDK family members will help in identify and develop novel areas of research to improve the lives of patients affected by debilitating chronic diseases.

The continually evolving landscape of novel therapies in oncogene-driven advanced non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) is a highly heterogeneous disease that is frequently associated with a host of known oncogenic alterations. Advances in molecular diagnostics and drug development have facilitated the targeting of novel alterations such that the majority of NSCLC patients have driver mutations that are now clinically actionable. The goal of this review is to gain insights into clinical research and development principles by summary, analysis, and discussion of data on agents targeting known alterations in oncogene-driven, advanced NSCLC beyond those in the epidermal growth factor receptor (EGFR) and the anaplastic lymphoma kinase (ALK). A search of published and presented literature was conducted to identify prospective trials and integrated analyses reporting outcomes for agents targeting driver gene alterations (except those in EGFR and ALK) in molecularly selected, advanced NSCLC. Clinical efficacy data were extracted from eligible reports and summarized in text and tables. Findings show that research into alteration-directed therapies in oncogene-driven, advanced NSCLC is an extremely active research field. Ongoing research focuses on the expansion of new agents targeting both previously identified targets (particularly hepatocyte growth factor receptor (MET), human epidermal growth factor receptor 2 (HER2), and Kirsten rat sarcoma viral oncogene homolog (KRAS)) as well as novel, potentially actionable targets (such as neuregulin-1 (NRG1) and phosphatidylinositol 3-kinase (PI3K)). The refinement of biomarker selection criteria and the development of more selective and potent agents are allowing for increasingly specific and effective therapies and the expansion of clinically actionable alterations. Clinical advances in this field have resulted in a large number of regulatory approvals over the last 3 years. Future developments should focus on the continued application of alteration therapy matching principles and the exploration of novel ways to target oncogene-driven NSCLC.

The Metabolism of Creatinine and Its Usefulness to Evaluate Kidney Function and Body Composition in Clinical Practice

Serum creatinine levels are the most used clinical marker to estimate renal function as the glomerular function rate because it is simple, fast, and inexpensive. However, creatinine has limitations, as its levels can be influenced by factors such as advanced age, physical activity, protein-rich diets, male gender, medications, and ethnicity. Serum cystatin C and its combination with serum creatinine may serve as an alternative since these factors do not affect it. Most creatinine synthesis occurs in the muscles, making it a valuable marker for assessing lean body mass within body composition. This measurement is crucial for evaluating and monitoring nutritional status in patients with chronic kidney disease. This review aimed to discuss the literature on creatinine metabolism, its advantages and disadvantages in assessing renal function, and its utility in measuring lean body mass. The variability in the creatinine generation rate among individuals should be considered when assessing the glomerular function rate.

Efficacy and Safety of Abemaciclib in Combination With Endocrine Therapy for HR+/HER2- Advanced or Metastatic Breast Cancer: A Systematic Review and Meta-Analysis

OBJECTIVES

Breast cancer, particularly the hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) subtype, remains a major global health concern. Abemaciclib, a CDK4/6 inhibitor, has shown promising results in treating advanced cases. This study comprehensively assesses the efficacy and safety of abemaciclib in combination with endocrine therapy for HR+/HER2- advanced or metastatic breast cancer.

METHODS

Following PRISMA guidelines, a systematic review and meta-analysis was conducted. A thorough literature search was conducted on PubMed, EMBASE, Cochrane Library, and ClinicalTrials.gov til December 2023. Inclusion criteria encompassed randomized controlled trials and retrospective cohort studies reporting on abemaciclib in approved doses, either as monotherapy or in combination. Outcome assessments included progression-free survival (PFS), overall response rate (ORR), side effects/adverse effects (SE/AE), and overall survival (OS). Quality assessment utilized Cochrane's revised risk of bias tool and Newcastle-Ottawa scale.

RESULTS

Pooled results of 22 studies involving 14,010 patients revealed that abemaciclib significantly improved PFS (hazard ratio=0.53; 95% CI: 0.48-0.59; P =0.00; I 2 =0%), ORR (risk ratio=2.31; 95% CI: 1.93-2.75; P =0.00; I 2 =0%), and OS (risk ratio=0.76 (95% CI: 0.65-0.87; P =0.001; I 2 =0%). However, abemaciclib increased the risk of adverse events in the fulvestrant and nonsteroidal aromatase inhibitor (NSAI) combinations, respectively.

CONCLUSIONS

Abemaciclib, particularly in combination with fulvestrant, emerges as an effective therapeutic option for HR+/HER2- advanced or metastatic breast cancer, improving PFS and OS. The higher toxicity profile warrants cautious use, especially in treatment-naive patients.

Resistance mechanisms and therapeutic strategies of CDK4 and CDK6 kinase targeting in cancer

Cyclin-dependent kinases (CDKs) 4 and 6 (CDK4/6) are important regulators of the cell cycle. Selective CDK4/6 small-molecule inhibitors have shown clinical activity in hormonal receptor-positive (HR+) metastatic breast cancer, but their effectiveness remains limited in other cancer types. CDK4/6 degradation and improved selectivity across CDK paralogs are approaches that could expand the effectiveness of CDK4/6 targeting. Recent studies also suggest the use of CDK4/6-targeting agents in cancer immunotherapy. In this Review, we highlight recent advancements in the mechanistic understanding and development of pharmacological approaches targeting CDK4/6. Collectively, these developments pose new challenges and opportunities for rationally designing more effective treatments.

Sterile activation of RNA-sensing pathways in autoimmunity

RNA-sensing pathways play a pivotal role in host defense against pathogenic infections to maintain cellular homeostasis. However, in the absence of infection, certain endogenous RNAs can serve as the activators of RNA-sensing pathways as well. The inappropriate activation of RNA-sensing pathways by self-ligands leads to systemic inflammation and autoimmune diseases. In this review, we summarize current findings on the sterile activation of RNA sensors, as well as its implications in autoimmunity, inflammatory diseases, and therapeutics.

Using bioinformatics and artificial intelligence to map the cyclin-dependent kinase 4/6 inhibitor biomarker landscape in breast cancer

A cyclin-dependent kinase 4/6 (CDK4/6) inhibitor combined with endocrine therapy is the standard-of-care for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer. However, not all patients respond to the treatment, resistance often occurs and efficacy outcomes from early breast cancer trials have been mixed. To identify biomarkers associated with CDK4/6 inhibitor response or resistance, we combined bioinformatic-database analyses, artificial intelligence-assisted literature review, and manual literature review (Embase and OVID Medline; search window: January 2012-October 2022) to compile data to comprehensively describe the CDK4/6 inhibitor biomarker landscape. Based on these results, and validation by external experts, we identified 15 biomarkers of clinical importance (AR , AURKA, ERBB2, ESR1, CCNE1, CDKN1A/B, CDK2, CDK6, CDK7, CDK9, FGFR1/2, MYC, PIK3CA/AKT, RB1 and STAT3) that could guide future breast cancer research.

Evaluating Drug-Drug Interaction Risk Associated with Peptide Analogs Using advanced In Vitro Systems

Drug-drug interaction (DDI) assessment of therapeutic peptides is an evolving area. The industry generally follows DDI guidelines for small molecules, but the translation of data generated with commonly used in vitro systems to in vivo is sparse. In the current study, we investigated the ability of advanced human hepatocyte in vitro systems, namely HepatoPac, spheroids, and Liver-on-a-chip, to assess potential changes in regulation of CYP1A2, CYP2B6, CYP3A4, SLCO1B1, and ABCC2 in the presence of selected therapeutic peptides, proteins, and small molecules. The peptide NN1177, a glucagon and GLP-1 receptor co-agonist, did not suppress mRNA expression or activity of CYP1A2, CYP2B6, and CYP3A4 in HepatoPac, spheroids, or Liver-on-a-chip; these findings were in contrast to the data obtained in sandwich cultured hepatocytes. No effect of NN1177 on SLCO1B1 and ABCC2 mRNA was observed in any of the complex systems. The induction magnitude differed across the systems (e.g., rifampicin induction of CYP3A4 mRNA ranged from 2.8-fold in spheroids to 81.2-fold in Liver-on-a-chip). Small molecules, obeticholic acid and abemaciclib, showed varying responses in HepatoPac, spheroids, and Liver-on-a-chip, indicating a need for EC50 determinations to fully assess translatability data. HepatoPac, the most extensively investigated in this study (3 donors), showed high potential to investigate DDIs associated with CYP regulation by therapeutic peptides. Spheroids and Liver-on-a-chip were only assessed in one hepatocyte donor and further evaluations are required to confirm their potential. This study establishes an excellent foundation toward the establishment of more clinically-relevant in vitro tools for evaluation of potential DDIs with therapeutic peptides. SIGNIFICANT STATEMENT: At present, there are no guidelines for drug-drug interaction (DDI) assessment of therapeutic peptides. Existing in vitro methods recommended for assessing small molecule DDIs do not appear to translate well for peptide drugs, complicating drug development for these moieties. Here, we establish evidence that complex cellular systems have potential to be used as more clinically-relevant tools for the in vitro DDI evaluation of therapeutic peptides.

Successful use of Palbociclib combined with Venetoclax and Azacitidine in an adult with refractory/relapsed therapy-related acute myeloid leukemia

BACKGROUND

Therapy-related acute myeloid leukemia (t-AML) is considered high risk as it related to prior exposure to cytotoxic chemotherapy agents for solid tumors or hematologic malignancies. Compared with de novo AML, t-AML is associated with lower remission rates, inferior overall survival (OS) and higher relapse rates. Many efforts have been devoted to improving the overall but with limited success, and novel strategy is thus highly needed.

CASE DESCRIPTION

We reported one patient with refractory/relapsed t-AML was successfully treated with Palbociclib combined with Venetoclax and Azacytidine (AZA). In this case, a 47-year-old patient with t-AML recurred during Venetoclax in combination with AZA therapy. However, the patient achieved morphological, immunophenotypic and molecular complete remission again after Palbociclib combined with Venetoclax and AZA.

CONCLUSIONS

Although only one successful case is presented here, three-drug combination regimens should be considered as another treatment option for t-AML in the future.

Adverse event profiles of CDK4/6 inhibitors: data mining and disproportionality analysis of the FDA adverse event reporting system

Background

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are targeted therapies designed to selectively block CDK4/6, crucial regulators of the cell cycle. These inhibitors play a pivotal role in restoring cell cycle control, particularly in breast cancer cases marked by abnormal CDK regulation, ultimately inhibiting uncontrolled cell division and tumor growth.

Objectives

This analysis aimed to comprehensively examine adverse effects in CDK4/6 inhibitors using the United States Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database.

Design

Disproportionality analysis was conducted to analyze the adverse event (AE) reports related to CDK4/6 inhibitor submitted to the FAERS database.

Methods

We collected AE reports regarding palbociclib, ribociclib, abemaciclib, trilaciclib, and dalpiciclib submitted to the FAERS from 2015Q1 to 2023Q1. We used the system organ class and the Standardized MedDRA Query to perform a comprehensive search for AEs at the preferred term (PT) level, using case reports as our data source. After removing duplicate reports, we performed disproportionality analysis and sensitivity analysis to identify safety signals.

Results

A total of 85,635 reports encompassing 280,211 AEs were extracted for analysis. Among 3681 scrutinized PTs, approximately 484 were detected as statistically significant signals associated with CDK4/6 inhibitors. It was noteworthy that palbociclib and ribociclib had comparable safety profiles, whereas abemaciclib exhibited distinctive safety patterns. Notably, our analysis found novel safety signals linked to CDK4/6 inhibitors, including nail-related disorders such as onychoclasis, nail disorder, and nail discoloration, and psychiatric concerns, including eating disorders and emotional disorder.

Conclusion

Overall, the present study identified several new safety signals of CDK4/6 inhibitors, as well as differences among various drugs within the CDK4/6 category, through the use of the FDA FAERS, which deserve more careful monitoring in the clinic.

p16 Immunohistochemical Patterns in Triple-Negative Breast Cancer: Clinical and Genomic Similarities of the p16 Diffuse Pattern to pRB Deficiency

INTRODUCTION

Triple-negative breast cancer (TNBC) is associated with alterations in the retinoblastoma pathway. As a consequence of retinoblastoma protein (pRB) loss, compensatory upregulation of p16 occurs due to the loss of phosphorylated pRB-mediated negative feedback on p16 expression. The aim of this study is to investigate the clinicopathological and genomic characteristics associated with the diffuse pattern of p16 immunohistochemistry (IHC) in TNBC.

METHODS

The study analyzed surgically resected TNBC for whole-exome sequencing in 113 cases and for cDNA microarray in 144 cases. The p16 IHC results were classified into two patterns: diffuse and negative/mosaic.

RESULTS

In the entire cohort (n = 257), the diffuse pattern of p16 IHC was observed in 123 (47.9%) patients and the negative/mosaic pattern in 134 (52.1%). Biallelic RB1 inactivation was observed in 14.3% of patients with the diffuse pattern. The diffuse pattern of p16 IHC showed more frequent RB1 alterations and cell cycle progression signatures, a higher Ki-67 labeling index, more frequent chromosome segment copy number changes, a higher frequency of homologous recombination deficiency high, and immune-related signatures. PIK3CA mutations were more frequent in the negative/mosaic pattern. CCND1 amplification was identified in 5 cases, all with the negative/mosaic pattern.

CONCLUSION

In TNBC, the diffuse p16 pattern shows clinical and genomic similarities to pRB-deficient tumors, suggesting shared characteristics. This suggests that p16 IHC testing may provide new therapeutic approaches, underscoring its potential clinical importance.

INTRODUCTION

Triple-negative breast cancer (TNBC) is associated with alterations in the retinoblastoma pathway. As a consequence of retinoblastoma protein (pRB) loss, compensatory upregulation of p16 occurs due to the loss of phosphorylated pRB-mediated negative feedback on p16 expression. The aim of this study is to investigate the clinicopathological and genomic characteristics associated with the diffuse pattern of p16 immunohistochemistry (IHC) in TNBC.

METHODS

The study analyzed surgically resected TNBC for whole-exome sequencing in 113 cases and for cDNA microarray in 144 cases. The p16 IHC results were classified into two patterns: diffuse and negative/mosaic.

RESULTS

In the entire cohort (n = 257), the diffuse pattern of p16 IHC was observed in 123 (47.9%) patients and the negative/mosaic pattern in 134 (52.1%). Biallelic RB1 inactivation was observed in 14.3% of patients with the diffuse pattern. The diffuse pattern of p16 IHC showed more frequent RB1 alterations and cell cycle progression signatures, a higher Ki-67 labeling index, more frequent chromosome segment copy number changes, a higher frequency of homologous recombination deficiency high, and immune-related signatures. PIK3CA mutations were more frequent in the negative/mosaic pattern. CCND1 amplification was identified in 5 cases, all with the negative/mosaic pattern.

CONCLUSION

In TNBC, the diffuse p16 pattern shows clinical and genomic similarities to pRB-deficient tumors, suggesting shared characteristics. This suggests that p16 IHC testing may provide new therapeutic approaches, underscoring its potential clinical importance.

Establishment of a trastuzumab-resistant extramammary Paget disease model: loss of PTEN as a potential mechanism

BACKGROUND/OBJECTIVES

Extramammary Paget disease (EMPD) is a rare, cutaneous intraepithelial adenocarcinoma typically treated with wide local excision. Unfortunately, a number of patients with metastases show poor responses to chemotherapy. While some studies have explored trastuzumab's effectiveness against EMPD positive for human epidermal growth factor receptor 2 (HER2), trastuzumab resistance (TR) may emerge after anti-HER2 therapy.

METHODS/SUBJECTS

In this study, we established TR EMPD patient-derived xenografts (PDX) that replicated the histological and HER2 expression traits of naive EMPD tumours.

RESULTS

Cancer gene analyses revealed a loss of the PTEN gene in TR tumours, which was further confirmed by immunohistochemical staining and immunoblotting to test for protein expression levels. Reduced PTEN levels correlated with increased protein kinase B (Akt) phosphorylation and p27 downregulation, suggesting a potential mechanism for trastuzumab resistance in EMPD cells. In the trastuzumab-sensitive EMPD-PDX mouse model, PTEN inhibitors partially restored trastuzumab-mediated tumour regression. The TR EMPD-PDX responded favourably to targeted therapy (lapatinib, abemaciclib, palbociclib) and chemotherapy (eribulin, docetaxel, trastuzumab deruxtecan).

CONCLUSIONS

This study demonstrates an innovative TR EMPD-PDX model and introduces promising antineoplastic effects with various treatments for TR EMPD tumours.

Slower CDK4 and faster CDK2 activation in the cell cycle

Dysregulation of cyclin-dependent kinases (CDKs) impacts cell proliferation, driving cancer. Here, we ask why the cyclin-D/CDK4 complex governs cell cycle progression through the longer G1 phase, whereas cyclin-E/CDK2 regulates the shorter G1/S phase transition. We consider available experimental cellular and structural data including cyclin-E's high-level burst, sustained duration of elevated cyclin-D expression, and explicit solvent molecular dynamics simulations of the inactive monomeric and complexed states, to establish the conformational tendencies along the landscape of the distinct activation scenarios of cyclin-D/CDK4 and cyclin-E/CDK2 in the G1 phase and G1/S transition of the cell cycle, respectively. These lead us to propose slower activation of cyclin-D/CDK4 and rapid activation of cyclin-E/CDK2. We provide the mechanisms through which this occurs, offering innovative CDK4 drug design considerations. Our insightful mechanistic work addresses a compelling cell cycle regulation question and illuminates the distinct activation speeds between the G1 and the G1/S phases, which are crucial for function.

Therapeutic Monitoring of Palbociclib, Ribociclib, Abemaciclib, M2, M20, and Letrozole in Human Plasma: A Novel LC-MS/MS Method

BACKGROUND

Therapeutic drug monitoring (TDM) using cyclin-dependent kinase inhibitors (CDK4/6is) is a novel approach for optimizing treatment outcomes. Currently, palbociclib, ribociclib, and abemaciclib are the available CDK4/6is and are primarily coadministered with letrozole. This study aimed to develop and validate an LC-MS/MS method for the simultaneous analysis of CDK4/6is, 2 active metabolites of abemaciclib (M2 and M20), and letrozole in human plasma for use in TDM studies.

METHODS

Sample pretreatment comprised protein precipitation with methanol and dilution of the supernatant with an aqueous mobile phase. Chromatographic separation was achieved using a reversed-phase XBridge BEH C18 column (2.5 μm, 3.0 × 75 mm XP), with methanol serving as the organic mobile phase and pyrrolidine-pyrrolidinium formate (0.005:0.005 mol/L) buffer (pH 11.3) as the aqueous mobile phase. A triple quadrupole mass spectrometer was used for the detection, with the ESI source switched from negative to positive ionization mode and the acquisition performed in multiple reaction monitoring mode.

RESULTS

The complete validation procedure was successfully performed in accordance with the latest regulatory guidelines. The following analytical ranges (ng/mL) were established for the tested compounds: 6-300, palbociclib and letrozole; 120-6000, ribociclib; 40-800, abemaciclib; and 20-400, M2 and M20. All results met the acceptance criteria for linearity, accuracy, precision, selectivity, sensitivity, matrix effects, and carryover. A total of 85 patient samples were analyzed, and all measured concentrations were within the validated ranges. The percent difference for the reanalyzed samples ranged from -11.2% to 7.0%.

CONCLUSIONS

A simple and robust LC-MS/MS method was successfully validated for the simultaneous quantification of CDK4/6is, M2, M20, and letrozole in human plasma. The assay was found to be suitable for measuring steady-state trough concentrations of the analytes in patient samples.

Cancer takes many paths through G1/S

In the commonly accepted paradigm for control of the mammalian cell cycle, sequential cyclin-dependent kinase (CDK) and cyclin activities drive the orderly transition from G1 to S phase. However, recent studies using different technological approaches and examining a broad range of cancer cell types are challenging this established paradigm. An alternative model is evolving in which cell cycles utilize different drivers and take different trajectories through the G1/S transition. We are discovering that cancer cells in particular can adapt their drivers and trajectories, which has important implications for antiproliferative therapies. These studies have helped to refine an understanding of how CDK inhibition impinges on proliferation and have significance for understanding fundamental features of cell biology and cancer.

Clinical implications of the Drug-Drug Interaction in Cancer Patients treated with innovative oncological treatments

In the last two-decades, innovative drugs have revolutionized cancer treatments, demonstrating a significant improvement in overall survival. These drugs may present several pharmacokinetics interactions with non-oncological drugs, and vice versa, and, non-oncological drugs can modify oncological treatment outcome both with pharmacokinetic interaction and with an "off-target impact" on the tumor microenvironment or on the peripheral immune response. It's supposed that the presence of a drug-drug interaction (DDI) is associated with an increased risk of reduced anti-tumor effects or severe toxicities. However, clinical evidence that correlate the DDI presence with outcome are few, and results are difficult to compare because of difference in data collection and heterogeneous population. This review reports all the clinical evidence about DDI to provide an easy-to-use guide for DDI management and dose adjustment in solid tumors treated with inhibitors of the cyclin-dependent kinases CDK4-6, Antibody-drug conjugates, Poly ADPribose polymerase inhibitors, androgen-receptor targeted agents, or immunecheckpoints inhibitors.