CDK4/6 inhibitor resistance mechanisms and treatment strategies (Review)

TFAP2C-DDR1 axis regulates resistance to CDK4/6 inhibitor in breast cancer

Breast cancer is the predominant malignancy with the majority of cases are characterized as HR+/HER2-subtype. Although cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have shown remarkable efficacy in treating this subtype when combined with endocrine therapy, the development of resistance to these inhibitors remains a significant clinical obstacle. Hence, there is an urgent need to explore innovative therapies and decipher the underlying mechanisms of resistance to CDK4/6i. In this study, we employed quantitative high-throughput combination screening (qHTCS) and genomics/proteomics approaches to uncover the molecular mechanisms driving resistance to CDK4/6i (palbociclib) in breast cancer. The comprehensive analyses revealed DDR1 as a potential factor implicated in mediating resistance to CDK4/6i. Specifically, DDR1 inhibition in combination with palbociclib exhibited remarkable synergistic effects, reducing cell survival signaling and promoting apoptosis in resistant cells. In-vivo xenograft model further validated the synergistic effects, showing a significant reduction in the resistant tumor growth. Exploration into DDR1 activation uncovered TFAP2C as a key transcription factor regulating DDR1 expression in palbociclib resistant cells and inhibition of TFAP2C re-sensitized resistant cells to palbociclib. Gene set enrichment analysis (GSEA) in the NeoPalAna trial demonstrated a significant enrichment of the TFAP2C-DDR1 gene set from patitens after palbociclib treatment, suggesting the possible activation of the TFAP2C-DDR1 axis following palbociclib exposure. Overall, this study provides crucial insights into the novel molecular landscape of palbociclib resistance in breast cancer, suggesting TFAP2C-DDR1 axis inhibition as a promising strategy to overcome resistance.

Inhibition of METTL14 overcomes CDK4/6 inhibitor resistance driven by METTL14-m6A-E2F1-axis in ERα-positive breast cancer

CDK4/6i, the first-line drug for treating ERα-positive breast cancer, significantly improves clinical outcomes. However, CDK4/6i resistance often develops and remains a major hurdle, and the underlying mechanisms remain challenging to fully investigate. Here, we used Genome-wide CRISPR/Cas9 library screening combined with single-cell sequencing to screen for molecules mediating CDK4/6i resistance and identified METTL14 as a determinant of CDK4/6i sensitivity. Clinical samples and datasets were analyzed and in vitro and in vivo experiments were performed to confirm the critical function of METTL14 in CDK4/6i resistance. Mechanistically, METTL14 can induce an increase in E2F1 expression in breast cancer cells via an m6A IGF2BP2-dependent mechanism and thus promote CDK4/6i resistance. Furthermore, through a small molecule screen, a novel METTL14 inhibitor named WKYMVM, which can restore sensitivity to CDK4/6i in CDK4/6i-resistant breast cancer cells, was identified. Treatment with folate-conjugated liposomes targeting breast cancer cells that contained both a CDK4/6i and WKYMVM revealed the synergistic effect of METTL14 inhibition with CDK4/6i therapy in a CDK4/6i-resistant PDX model. Together, our findings reveal the mechanism of CDK4/6i resistance and provide a strategy for overcoming CDK4/6i resistance via METTL14 inhibition.

Effects of PPARG on the proliferation, apoptosis, and estrogen secretion in goat granulosa cells

As a member of peroxisome proliferator-activated receptor (PPAR) family, PPARG has been reported to be involved in glucolipid metabolism in various species. However, the function of PPARG in estradiol (E2) synthesis, apoptosis, and proliferation in goat ovarian granulosa cells (GCs) is unclear. In this study, we found that goat PPARG was expressed in GCs of all grades of follicles, and localized in the cytoplasm and nucleus of GCs. Transfection of small interfering RNA-PPARG2 (si-PPARG2) decreased E2 synthesis and the abundances of HSD3B and CYP19A1 mRNA and protein. It also promoted cell apoptosis with significant increases in the ratio of BAX/BCL-2 and Caspase3 mRNA and protein. Meanwhile, cell cycle was inhibited by si-PPARG2 transfection, accompanied by decreased mRNA levels of CDK4, CKD6, MYC, CCND1, CCND2, PCNA, and CCNB, increased mRNA level of P53, and decreased protein levels of CDK4, MYC, and CCND1. Furthermore, PPARG interference affected the mRNA and protein abundances of CREB as well as the phosphorylation of CREB but not PKA. In conclusion, our data suggest that PPARG plays an important role in regulating E2 synthesis, cell apoptosis, and proliferation of goat GCs, including the CREB expression and phosphorylation. These results provide evidences for the in-depth study of PPARG in the regulation of goat GCs function.

Acquired gene alterations in patients treated with ribociclib plus endocrine therapy or endocrine therapy alone using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials

BACKGROUND

A prior pooled analysis of the MONALEESA-2, -3, and -7 trials identified baseline markers predictive of sensitivity or resistance to ribociclib plus endocrine therapy (ET). We report the results of an analysis of paired baseline and end-of-treatment (EOT) circulating tumor DNA (ctDNA) samples across the MONALEESA trials.

PATIENTS AND METHODS

Paired baseline and EOT ctDNA samples from MONALEESA-2, -3, and -7 were sequenced using a targeted next-generation sequencing panel. Genes with an EOT alteration prevalence of >5% were included. A McNemar test was carried out on paired samples and adjusted for multiple testing to control the false discovery rate. A Bayesian mixed-effects model was used to adjust for ctDNA fraction at both time points and for study differences.

RESULTS

The analysis included 523 paired samples. At EOT, 21 genes had a >5% alteration prevalence. A trend for higher ctDNA fraction at EOT versus baseline (P = 0.08) was observed. Prevalence of alterations was higher at EOT versus baseline in RB1, SPEN, TPR, PCDH15, and FGFR2 in the ribociclib arm; PBRM1 in the placebo arm; and ESR1 in both arms. The mixed-effects model demonstrated that the same trends for increased prevalence of these alterations at EOT were observed after adjusting for ctDNA fraction and that the increased rate of RB1 and SPEN alterations at EOT were specific to ribociclib plus ET. Analysis of ESR1 indicated a similar increase at EOT in both arms. The most common acquired ESR1 mutations at EOT included Y537C/N/S/D, D538G, E380Q, and L536H/R/P/LC. The prevalence of PIK3CA hotspot mutations at baseline and EOT was similar.

CONCLUSIONS

This analysis identified acquired gene alterations in patients with hormone receptor-positive/human epidermal growth factor receptor-2 negative advanced breast cancer treated with ribociclib plus ET or placebo plus ET. These data may support further studies on acquired resistance mechanisms and inform future systemic interventions in the post-cyclin-dependent kinase 4/6 inhibitor setting.

Autophagic degradation of CDK4 is responsible for G0/G1 cell cycle arrest in NVP-BEZ235-treated neuroblastoma

BACKGROUND

CDK4 is highly expressed and associated with poor prognosis and decreased survival in advanced neuroblastoma (NB). Targeting CDK4 degradation presents a potentially promising therapeutic strategy compared to conventional CDK4 inhibitors. However, the autophagic degradation of the CDK4 protein and its anti-proliferation effect in NB cells has not been mentioned.

RESULTS

We identified autophagy as a new pathway for the degradation of CDK4. Firstly, autophagic degradation of CDK4 is critical for NVP-BEZ235-induced G0/G1 arrest, as demonstrated by the overexpression of CDK4, autophagy inhibition, and blockade of autophagy-related genes. Secondly, we present the first evidence that p62 binds to CDK4 and then enters the autophagy-lysosome to degrade CDK4 in a CTSB-dependent manner in NVP-BEZ235 treated NB cells. Similar results regarding the interaction between p62 and CDK4 were observed in the NVP-BEZ235 treated NB xenograft mouse model.

CONCLUSIONS

Autophagic degradation of CDK4 plays a pivotal role in G0/G1 cell cycle arrest in NB cells treated with NVP-BEZ235.

Self-assembled natural triterpenoids for the delivery of cyclin-dependent kinase 4/6 inhibitors to enhance cancer chemoimmunotherapy

Immunogenic cell death (ICD) has recently emerged as a promising strategy in reinforcing anti-PD-L1 blockade immunotherapy of triple-negative breast cancer (TNBC). The CDK4/6 inhibitor palbociclib (PAL), as a clinical star medicine targeting the cell cycle machinery, is an ideal candidate for fabricating a highly efficient ICD inducer for TNBC chemoimmunotherapy. However, the frequently observed chemoresistance and clinical adverse effects, as well as significant antagonistic effects when co-administered with certain chemotherapeutics, have seriously restricted the efficiency of PAL and the feasibility of combination strategies. Herein, we screened and identified six self-assembled natural pentacyclic triterpenoid (PT) molecules that can serve as competent co-administration nanoplatforms for the synergistic or combined delivery of PAL. Analysis of two representative PT-PAL nano-assemblies validated that PT-mediated co-assembly enhances the cytotoxicity and synergy of PAL by inhibiting the PI3K/AKT/mTOR signaling pathway, rather than directly targeting CDK4/6 proteins. Importantly, the PAL nanoassemblies exhibited multiple favorable therapeutic features and stronger accumulative ICD induction, ensuring highly efficient synergistic anti-PD-L1 chemoimmunotherapy by simultaneously facilitating T-cell immune response and reversing the immunosuppressive tumor microenvironment. This study offers possibilities for improving the anticancer efficacy of CDK4/6 inhibitors and potential avenues for clinical applications of chemoimmunotherapy in treating TNBC.

Enhancing therapeutic efficacy in homologous recombination-proficient pancreatic cancer via the combination of PARP1-PROTAC and a BRD4 inhibitor

Currently, poly (ADP-ribose) polymerase inhibitors (PARPi) have been approved by U.S. Food and Drug Administration for BRCA-mutated pancreatic cancer therapy. However, limited indications hinder their further application. Repression of bromodomain-containing protein 4 (BRD4) can block the homologous recombination (HR) repair pathway and has the potential to enhance the response to PARPi in HR-proficient pancreatic cancer therapy. In addition, proteolysis targeting chimeras (PROTACs) can hijack E3 ligase within the cell to ubiquitinate degradation-targeted proteins effectively and quickly, thus enhancing the therapeutic effect on tumors. In the present study, the LB23 compound, which induces PARP1 degradation, was employed in combination with the BRD4 inhibitor JQ1, confirming their synergistic effect in HR-proficient pancreatic cancer through various methods. Moreover, compared to the JQ1 and PARPi olaparib combination, PARP1-PROTAC and JQ1 had more notable synergistic effects. Further research into the synergistic mechanism demonstrated that combination therapy enhanced DNA damage and suppressed DNA repair by inducing cell cycle arrest and cell apoptosis. The present study therefore provides the experimental data for this type of combination therapy, which is expected to be an innovative approach for the treatment of HR-proficient pancreatic cancer.

Synergistic effect of bazedoxifene and abemaciclib co‑treatment in triple‑negative breast cancer cells in vitro

Triple-negative breast cancer (TNBC) is an aggressive disease with the capability of metastasizing quickly. However, treatment options for patients with TNBC still remain limited. CDK4/6 inhibitors have been approved by the U.S. Food and Drug Administration and are administered for the treatment of hormone receptor-positive breast cancer subtypes, but not yet for TNBC. Although pre-clinical research is being conducted on their efficacy in treating TNBC, acquired resistance to CDK4/6 inhibitors is now a growing clinical problem. One of the identified resistance mechanisms is through the IL-6/STAT3 signaling pathway. In the present study, the CDK4/6 inhibitor, abemaciclib, was tested in combination with the IL-6 inhibitor, bazedoxifene, on human (SUM159 and MDA-MB-231) and murine (4T1) TNBC cell lines. Both abemaciclib and bazedoxifene monotherapies inhibited cell cycle progression and cell viability, migration and invasion, and induced apoptosis; however, the combination treatment exerted a greater effect than either monotherapy. These findings support the concept of CDK4/6 and IL-6 dual inhibition as a novel targeted therapy against TNBC.

Advancements in breast cancer management: a comprehensive review of ribociclib combined with endocrine therapy

Background

In this review, the complicated landscape of breast cancer management is explored with a focus on the promising synergies between ribociclib and endocrine therapy. Ribociclib mainly acts as a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, which disrupts cell cycle progression necessary for tumor growth. This, in combination with endocrine therapy, aims to produce hormone receptor-positive breast cancers, which is a very relevant subtype with challenging therapeutics.

Methods

A comprehensive review was conducted using multiple databases, PubMed, Embase, Scopus, Cochrane Library, and Web of Science, covering the period from January 1990 to May 2024.

Results

Pharmacokinetic studies underscore the efficacy and tolerability of ribociclib, thus providing vital information for dose adjustments, particularly among patients with renal and hepatic impairments. Ribociclib's value in extending progression-free survival and improving overall survival has been shown by clinical trials such as the MONALEESA series. Quality of life considerations and patient-reported outcomes from these trials indicate that ribociclib has a broader effect on the well-being of the patients. However, despite the success experienced by this drug in clinical practice, it still has some side effects, including hematologic toxicity, hepatotoxicity, and thromboembolism associated with it. Ribociclib resistance mechanisms are multifaceted mixtures comprising genetic variations or mutations, compensatory signaling pathways, and epigenomic changes. While overcoming resistance remains challenging, ongoing research seeks to reconcile.

Conclusion

Ribociclib combined with endocrine therapy represents a significant advancement in breast cancer treatment, albeit with challenges that necessitate ongoing research and holistic patient care approaches.

Enhancing radiosensitivity in osteosarcoma via CDKN2C overexpression: A mechanism involving G1 phase arrest mediated by inhibition of CDK4 expression and Thr172 phosphorylation

BACKGROUND

The limited radiosensitivity of osteosarcoma poses a challenge in applying radiotherapy, necessitating the search for effective radiosensitizing targets.

METHODS

The lentiviral vectors were employed to establish CDKN2C-overexpressing (CDKN2C-OE) and CDKN2C-negative control (CDKN2C-NC) HOS and U2OS osteosarcoma cells. Cells were treated with or without irradiation (IR) to assess radiosensitization via viability, proliferation, apoptosis, and cell cycle analysis. A mouse model with subcutaneous tumors from CDKN2C-OE and CDKN2C-NC HOS cells evaluated tumor growth post-IR. Immunohistochemical staining and Western blot analysis were conducted to confirm model establishment and explore mechanisms.

RESULTS

CDKN2C-OE combined with IR inhibited cell viability and proliferation, promoting apoptosis in vitro and inhibiting tumor growth in vivo. CDKN2C-OE inhibited G1 phase progression post-IR by suppressing Cyclin-dependent kinase 4 (CDK4) expression and Thr172 phosphorylation, reducing retinoblastoma protein (RB) phosphorylation at Ser807/811. CDKN2C-OE did not primarily impact the cell cycle by regulating the expression of CDK6 and Cyclin D1. Furthermore, when CDKN2C-OE was combined with IR, the expression of BAX, Caspase-3, and its active cleavage product, cleaved Caspase-3, was upregulated.

CONCLUSIONS

Our research results indicate that overexpression of CDKN2C enhances radiosensitivity in osteosarcoma through the induction of G1 phase arrest and subsequent apoptosis. G1 phase arrest is mediated by the suppression of CDK4 expression and Thr172 phosphorylation, which consequently affects the expression of phosphorylated RB at the Ser807/811 sites.

Palbociclib as an Antitumor Drug: A License to Kill

Neoplastic cells are characterized by uncontrolled cell divisions caused by cell cycle dysregulation. Key regulatory proteins governing the transition from the G1 to the S phase are the CDK4 and CDK6 kinases, which are controlled by D-type cyclins. The CDK4/6 kinases enable the use of these proteins as targets for anticancer therapy because they prevent the growth and the development of malignant cells by inhibiting their activity. This paper surveys the clinical trial results concerning palbociclib, the first in-class FDA-approved anticancer drug for hormone-dependent breast cancer. It discusses the therapeutic applications in breast cancer as well as in solid tumors and hematopoietic malignancies. Additionally, the paper presents an analysis of palbociclib resistance acquired during therapy and explores new approaches, such as modifications to palbociclib that enhance its desired activity or open up new therapeutic possibilities (PROTACs).

Clinicopathogenomic analysis of PI3K/AKT/PTEN-altered luminal metastatic breast cancer in Japan

This rapid communication highlights the correlation between protein kinase B alpha (AKT1)-phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA)- phosphatase and tensin homolog (PTEN) alterations and clinicopathological factors in Japanese patients with metastatic recurrent breast cancer (mBC). This study analyzed 1967 patients with luminal-type breast cancer who underwent cancer gene panel testing. The results demonstrated that AKT pathway alterations, including PI3K/AKT/PTEN, occurred in 1038 (52.8%) cases. Patients with AKT pathway mutations were older (p = 0.002) and had a higher rate of invasive lobular carcinoma (ILC) histology (p = 0.001), progesterone receptor (PgR) positivity (p = 0.006), and bone metastases (p = 0.001), and a lower rate of germline BRCA2 (p < 0.001). Comprehensive genomic profile results demonstrated a higher tumor mutational burden (TMB) (< 0.001) and lower tumor BRCA1/2 expression (< 0.001) in patients with mutations in the AKT pathway. These results are crucial for characterizing candidates for AKT pathway-targeted molecular therapies and conceptualizing optimal treatment strategies. Clinical trial registration: This study is an observational study and is therefore not registered with the clinical trials registration.

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.

Protein biomarkers for subtyping breast cancer and implications for future research: a 2024 update

INTRODUCTION

Breast cancer subtyping is used clinically for diagnosis, prognosis, and treatment decisions. Subtypes are categorized by cell of origin, histomorphology, gene expression signatures, hormone receptor status, and/or protein levels. Categorizing breast cancer based on gene expression signatures aids in assessing a patient's recurrence risk. Protein biomarkers, on the other hand, provide functional data for selecting therapies for primary and recurrent tumors. We provide an update on protein biomarkers in breast cancer subtypes and their application in prognosis and therapy selection.

AREAS COVERED

Protein pathways in breast cancer subtypes are reviewed in the context of current protein-targeted treatment options. PubMed, Science Direct, Scopus, and Cochrane Library were searched for relevant studies between 2017 and 17 August 2024.

EXPERT OPINION

Post-translationally modified proteins and their unmodified counterparts have become clinically useful biomarkers for defining breast cancer subtypes from a therapy perspective. Tissue heterogeneity influences treatment outcomes and disease recurrence. Spatial profiling has revealed complex cellular subpopulations within the breast tumor microenvironment. Deciphering the functional relationships between and within tumor clonal cell populations will further aid in defining breast cancer subtypes and create new treatment paradigms for recurrent, drug resistant, and metastatic disease.

Capivasertib and fulvestrant for patients with hormone receptor-positive, HER2-negative advanced breast cancer (CAPItello-291): patient-reported outcomes from a phase 3, randomised, double-blind, placebo-controlled trial

BACKGROUND

CAPItello-291 is an ongoing phase 3 trial in which capivasertib-fulvestrant significantly improved progression-free survival versus placebo-fulvestrant in patients with hormone receptor-positive, HER2-negative advanced breast cancer who had relapse or disease progression during or after aromatase inhibitor treatment, in both the overall population and in patients with PIK3CA, AKT1, or PTEN-altered tumours. This study further explored patient-reported health-related quality of life (HRQOL), functioning, symptoms, and symptom tolerability in CAPItello-291.

METHODS

This phase 3, randomised, double-blind, placebo-controlled trial, which was conducted across 193 hospitals and cancer centres in 19 countries, enrolled women with any menopausal status or men, aged ≥18 years (≥20 years in Japan), with hormone receptor-positive, HER2-negative locally advanced or metastatic breast cancer who had relapse or disease progression during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase (CDK) 4 or 6 inhibitor therapy. Patients had an Eastern Cooperative Oncology Group/WHO performance score of 0 or 1 and could have received up to two previous lines of endocrine therapy and up to one previous line of chemotherapy for advanced disease. Patients were randomly assigned (1:1) using block randomisation (stratified according to the presence or absence of liver metastases, previous use of a CDK4/6 inhibitor [yes vs no], and geographical region) to receive oral capivasertib 400 mg (twice daily for 4 days, followed by 3 days off) plus intramuscular fulvestrant 500 mg (every 14 days for the first three injections, then every 28 days) or placebo with matching fulvestrant dosing. The dual primary endpoint of the trial was investigator-assessed progression-free survival assessed both in the overall population and among patients with PIK3CA, AKT1, or PTEN-altered tumours. The EORTC Quality of Life Questionnaire 30-item core module (QLQ-C30) and breast module (QLQ-BR23), Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE), and Patient Global Impression of Treatment Tolerability (PGI-TT) questionnaires were used to assess patient-reported outcomes. Evaluation of EORTC QLQ-C30 and EORTC QLQ-BR23 were secondary endpoints and evaluation of PRO-CTCAE and PGI-TT were pre-defined exploratory endpoints, and these endpoints are the subject of analysis in this Article. Data were collected at baseline and prespecified timepoints. Patient-reported outcomes were analysed in all randomly assigned patients with an evaluable baseline assessment and at least one evaluable post-baseline assessment. Change from baseline was assessed using mixed model with repeated measures for EORTC QLQ-C30 and summarised for QLQ-BR23. Time to deterioration was described using the Kaplan-Meier method. PGI-TT and PRO-CTCAE responses were summarised at each treatment cycle. Patient-reported outcomes were not prospectively powered for statistical comparison. The trial is registered with ClinicalTrials.gov, NCT04305496.

FINDINGS

Between June 2, 2020, and Oct 13, 2021, 901 patients were enrolled, of whom 708 patients were randomly assigned to receive capivasertib-fulvestrant (n=355) or placebo-fulvestrant (n=353). The median age of the patients was 59 years (IQR 51-67) in the capivasertib-fulvestrant group and 58 years (IQR 49-66) in the placebo-fulvestrant group. At data cutoff (Aug 15, 2022), the median duration of follow-up for progression-free survival in censored patients was 13·0 months (IQR 9·1-16·7) for capivasertib-fulvestrant and 12·7 months (IQR 2·0-16·4) for placebo-fulvestrant in the overall population. EORTC QLQ-C30 global health status/quality of life (GHS/QOL) scores were maintained from baseline and were similar between treatment groups throughout the study period (difference in mean change from baseline of -2·5 [95% CI -4·5 to -0·6] with capivasertib-fulvestrant vs -5·6 [-7·9 to -3·4] with placebo-fulvestrant; treatment difference 3·1 [95% CI 0·2 to 6·0]). Median time to deterioration in EORTC QLQ-C30 GHS/QOL was 24·9 months (95% CI 13·8 to not reached) in the capivasertib-fulvestrant group and 12·0 months (10·2 to 15·7) in the placebo-fulvestrant group (hazard ratio [HR] 0·70, 95% CI 0·53 to 0·92). Time to deterioration HRs for all EORTC QLQ-C30 and QLQ-BR23 subscale scores showed little difference between the treatment groups, except for diarrhoea, which was worse in the capivasertib-fulvestrant group than in the placebo-fulvestrant group (HR 2·75, 95% CI 2·01-3·81). In PRO-CTCAE symptom assessment, the proportion of patients reporting loose and watery stools "frequently" or "almost constantly" was 29% higher at cycle 1, day 15 in the capivasertib-fulvestrant group than in the placebo-fulvestrant group, decreasing at subsequent cycles. Other PRO-CTCAE-reported symptoms (rash, mouth or throat sores, itchy skin, and numbness or tingling in hands or feet) were absent or mild in most patients in both groups throughout treatment. According to the PGI-TT, most patients in both groups reported "not at all" or "a little bit" of bother from treatment side-effects.

INTERPRETATION

Patient-reported outcomes from CAPItello-291 demonstrated that capivasertib-fulvestrant delayed time to deterioration of GHS/QOL and maintained other dimensions of HRQOL (except symptoms of diarrhoea) similarly to fulvestrant. With the clinical efficacy and manageable safety profile, these exploratory results further support the positive benefit-risk profile of capivasertib-fulvestrant in this population.

FUNDING

AstraZeneca.

Breaking through therapeutic barriers: Insights into CDK4/6 inhibition resistance in hormone receptor-positive metastatic breast cancer

The therapeutic landscape for hormone receptor-positive (HR+) breast carcinoma has undergone a significant transformation with the advent of cyclin-dependent kinase (CDK)4/6 inhibitors, particularly in combination with endocrine therapy as the primary regimen. However, the evolution of resistance mechanisms in response to CDK4/6 inhibitors in HR+ metastatic breast cancer presents substantial challenges in managing the disease. This review explores the diverse genomic landscape underlying resistance, including disturbances in the cell cycle, deviations in oncogenic signaling pathways, deficiencies in DNA damage response (DDR) mechanisms, and changes in the tumor microenvironment (TME). Additionally, it discusses potential strategies to surmount resistance, including advancements in endocrine therapy, targeted inhibition of cell cycle components, suppression of AKT/mTOR activation, exploration of the FGFR pathway, utilization of antibody-drug conjugates (ADCs), and integration of immune checkpoint inhibitors (ICIs) with endocrine therapy and CDK4/6 inhibitors, providing pathways for enhancing patient outcomes amidst treatment challenges.

Capivasertib and fulvestrant for patients with hormone receptor-positive advanced breast cancer: characterization, time course, and management of frequent adverse events from the phase III CAPItello-291 study

BACKGROUND

Capivasertib is a potent, selective pan-AKT inhibitor. In CAPItello-291, the addition of capivasertib to fulvestrant resulted in a statistically significant (P < 0.001) improvement in progression-free survival over fulvestrant monotherapy in patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer and disease progression on or after aromatase inhibitor-based therapy. Characterization of the capivasertib-fulvestrant adverse event (AE) profile as managed in CAPItello-291 can inform future management guidance and optimize clinical benefit.

PATIENTS AND METHODS

Seven hundred and eight patients were randomized 1 : 1 to capivasertib (400 mg twice daily; 4 days on, 3 days off) or placebo, plus fulvestrant, on a 4-week cycle. Dose reductions/interruptions for capivasertib/placebo were permitted (up to two dose reductions). Safety analyses included exposure, AE, and clinical laboratory data and were conducted in patients who received at least one dose of capivasertib, fulvestrant, or placebo. Frequent AEs associated with phosphoinositide 3-kinase (PI3K)/protein kinase (AKT) pathway inhibition (diarrhea, rash, hyperglycemia) were characterized using group terms. AEs were summarized using descriptive statistics; time-to-event analyses were conducted.

RESULTS

Safety analyses included 705 patients: capivasertib-fulvestrant (n = 355) and placebo-fulvestrant (n = 350). Frequent any-grade AEs with capivasertib-fulvestrant were diarrhea (72.4%), rash (38.0%), and nausea (34.6%); frequent grade ≥3 AEs were rash (12.1%), diarrhea (9.3%), and hyperglycemia (2.3%). Diarrhea, rash, and hyperglycemia occurred shortly after starting capivasertib-fulvestrant [median days to onset (interquartile range) of any grade: 8 (2-22), 12 (10-15), and 15 (1-51), respectively], and were managed with supportive medications, dose reductions, interruptions, and/or discontinuation. Discontinuation rates were 2.0%, 4.5%, and 0.3%, respectively. Overall, 13.0% discontinued capivasertib due to AEs.

CONCLUSIONS

Frequent AEs associated with PI3K/AKT pathway inhibition occurred early and were manageable. The low rate of treatment discontinuations suggests that, when appropriately managed, these AEs do not pose a challenge to clinical benefit.

Real-World Data with CDK4/6 Inhibitors-A Single Center Experience from Croatia

BACKGROUND

There are limited real-world data (RWD) regarding the use of cyclin-dependent kinase (CDK) 4/6 inhibitors in western Balkan. The aim of our study was thus to analyze factors influencing progression-free survival (PFS) and overall survival (OS), along with the differences in adverse effects of CDK 4/6 therapy in a tertiary healthcare center in Croatia.

METHODS

We evaluated medical and demographic data for 163 consecutive patients with metastatic breast cancer treated with CDK4/6 inhibitors for at least one month, from October 2018, after the drug became available in Croatia. Eligible patients in our study were those patients who were treated with palbociclib, ribociclib, or abemaciclib.

RESULTS

The median PFS of CDK4/6 inhibitors treatment was 2.2 years (95% CI 1.8-3.3), with the longest ongoing treatment for 5.4 years. Treatment with CDK4/6 inhibitors in the first line was associated with a longer PFS compared to the second line or beyond (HR 0.50, 95% CI 0.3-0.9), and patients without liver metastasis exhibited longer survival compared to patients with liver metastasis (HR 0.46, 95% CI 0.2-0.8) (both p < 0.05). Regarding the choice of CDK4/6 inhibitors, ribociclib exhibited longer PFS compared to palbociclib (HR 0.49, 95% CI 0.29-0.82) (p = 0.0032), although the effect was not statistically significant when separating patients who were treated with CDK4/6 inhibitors in the first-line (HR 0.59, 95% CI 0.29-1.2), or second- or later-line therapy (0.49, 95% CI 0.15-1.55); the trend was present in both lines, however. The presence of liver metastasis (p = 0.04), initial luminal A grade (p = 0.039), and time to metastasis up to 5 years from the initial cancer (p = 0.002) were the only factors that remained statistically significant for PFS in multivariate analysis. Median OS since the diagnosis of metastatic disease was 4.5 years (95% CI 3.9-6.3), median OS since the start of CDK4/6 inhibitors treatment was 3.7 years (95% CI 3.4-4.4), while median OS from initial cancer diagnosis was 15.8 years (95% CI 13.8-18.3). There was no difference in OS based on the choice of CDK4/6 inhibitor (p = 0.44) or the adjuvant hormonal therapy (p = 0.12), although a nonsignificant trend for better OS with ribociclib was present for both regardless of whether it was in first- or second/later-line therapies (p > 0.05). In a multivariate analysis, only the presence of liver metastasis (p = 0.0003) and time to metastasis under 5 years from primary breast cancer (p = 0.03) were associated with a worse OS.

CONCLUSIONS

Our study provides the RWD with the use of CDK4/6 inhibitors in the treatment of metastatic HR+/HER2- breast cancer. To our best knowledge, there are limited RWD regarding CDK 4/6 inhibitors use in western Balkan; thus, our study provides valuable data from everyday clinical practice for this region of Europe, bridging the gap between randomized clinical trials and clinical reality in western Balkan.

Rationale for the Initiation, Outcomes, and Characteristics of Chemotherapy Following CDK4/6 Inhibitors in Breast Cancer: A Real-World Cohort Study

The standard therapy for hormone-receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer includes the use of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy. The optimal post-CDK4/6i treatment sequence is unclear. This cohort study evaluated the initiation, characteristics, and outcomes of chemotherapy following CDK4/6i-based treatment. Among the 227 patients who began CDK4/6i therapy, 114 completed it. Seventy-nine female patients received further treatment, including 55 receiving chemotherapy. The average age was 60.1 years. Post-CDK4/6i chemotherapy was typically (69.1%) first-line due to an impending visceral crisis. The median progression-free survival (mPFS) was 3.0 months (range 0.5-18.9), and the median overall survival (mOS) was 8.3 months (0.5-26.1). The median OS from the end of CDK4/6i treatment was 12.4 months (1.5-26.8). In univariate analysis, neither mPFS nor mOS was associated with age, tumor grade, receptor status, Ki67 status, time from diagnosis to CDK4/6i cessation, therapy line, or CDK4/6i type. Dose reduction occurred in 12 patients (21.8%), and chemotherapy was ceased due to adverse events in 8 patients (14.6%). Chemotherapy showed limited benefit regardless of the regimen. The role of chemotherapy may evolve with broader CDK4/6i use in adjuvant treatment.

Capivasertib in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative advanced breast cancer

PURPOSE

This review discusses the role and efficacy of Capivasertib in managing Hormone Receptor-Positive (HR+) breast cancer.

SUMMARY

Breast cancer is the most prevalent type of cancer among women worldwide. This article is an in-depth analysis of advanced therapeutic options involving Capivasertib in treating HR+ Breast Cancer. It focuses on the mode of action, efficacy, clinical trials, and comparison with fulvestrant alone. This review also highlights the therapy's precision in targeting specific cancer cells. Its mechanism of action involves preventing cancer cells from growing and having a cytotoxic effect on them. It improves progression-free survival while maintaining the quality of life. The side effects can be easily managed by dose reduction or discontinuation of the drug. This article sheds light on the ongoing trials and FDA recognition.

CONCLUSION

In conclusion, Capivasertib-fulvestrant therapy shows potential as an innovative therapeutic option for HR+ breast cancer but warrants additional research, especially in randomized control trials (RCT). It resulted in longer progression-free survival compared to fulvestrant alone. Its side effect profile is minimal.

Triglyceride-Glucose Index: A Candidate Prognostic Marker in HR-Positive/HER2-Negative Metastatic Breast Cancer Patients Treated With CDK4/6 Inhibitors

AIMS AND OBJECTIVES

Although cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i) are a vital part of the treatment of hormone receptor (HR)-positive/HER-2-negative metastatic breast cancer (BC), individuals have different sensitivities to CDK4/6i, indicating the need for biomarkers. The fasting triglyceride glucose (TyG) index is an easily accessible surrogate marker of insulin resistance (IR). Herein, we investigated the prognostic significance of the fasting triglyceride glucose (TyG) index in HR+/HER2- metastatic BC patients treated with CDK4/6i plus endocrine therapy (ET).

METHODS

About 333 patients with HR+/HER2-metastatic BC treated with CDK4/6i plus ET were analyzed retrospectively. The TyG index was calculated within 3 months before the initiation of CDK4/6i plus ET. The median value of 8.43 was taken as the cutoff for the TyG index.

RESULTS

The median overall survival (OS) was 73.6 months (95% CI, 66.0-81.1) in the whole cohort. The progression-free survival (PFS) was significantly longer in the low-TyG subgroup than in the high-TyG subgroup (30.1 vs. 21.3 months, multivariate adjusted [HR] = 0.666, 95% CI, 0.450-0.987, P = .043). While the median OS was not reached in the low TyG subgroup, it was 69.0 months in the high TyG subgroup (multivariate-adjusted HR = 0.513, 95% CI, 0.281-0.936, P = .030). Although the ORR and DCR were numerically greater in the low-TyG subgroup, no significant differences were observed between the low-TyG subgroup and high-TyG subgroup (28.1% vs. 24.7%, P = .476; 83.2% vs. 80.1%, P = .463, respectively).

CONCLUSIONS

These data imply that the TyG index could be a predictive biomarker for the therapeutic efficacy of CDK4/6is. Extensive prospective studies are needed to confirm these findings.

Quercetin inhibits the epithelial-mesenchymal transition and reverses CDK4/6 inhibitor resistance in breast cancer by regulating circHIAT1/miR-19a-3p/CADM2 axis

Breast cancer (BC) cells have a high risk of metastasis due to epithelial-mesenchymal transition (EMT). Palbociclib (CDK4/6 inhibitor) is an approved drug for BC treatment. However, the drug resistance and metastasis can impair the treatment outcome of Palbociclib. Understanding the mechanisms of EMT and Palbociclib drug resistance in BC is conducive to the formulation of novel therapeutic strategy. Here, we investigated the role of circHIAT1/miR-19a-3p/CADM2 axis in modulating EMT and Palbociclib resistance in BC. circHIAT1 and CADM2 were down-regulated in BC tissues and cell lines, and miR-19a-3p showed an up-regulation. circHIAT1 could interact with miR-19a-3p and suppress its activity, while miR-19a-3p functioned to negatively regulate CADM2. Forced over-expression of circHIAT1 could impaired the EMT status and migratory ability of BC cells, and this effect was inhibited by miR-19a-3p mimic. In addition, we also generated Palbociclib resistant BC cells, and showed that circHIAT1 and CADM2 were down-regulated in the resistant BC cells while miR-19a-3p showed an up-regulation. Forced circHIAT1 over-expression re-sensitized BC cells to Palbociclib treatment. Quercetin, a bioactive flavonoid, could suppressed the migration and invasion of BC cells, and re-sensitized BC cells to Palbociclib. The anti-cancer effect of quercetin could be attributed to its regulatory effect on circHIAT1/miR-19a-3p/CADM2 axis. In vivo tumorigenesis experiment further revealed that quercetin administration enhanced the anti-cancer effect of Palbociclib, an effect was dependent on the up-regulation of circHIAT1 by quercetin. In summary, this study identified quercetin as a potential anti-cancer compound to reverse Palbociclib resistance and impair EMT in BC cells by targeting circHIAT1/miR-19a-3p/CADM2 axis.

Targeting STAT3 potentiates CDK4/6 inhibitors therapy in head and neck squamous cell carcinoma

Anti-CDK4/6 therapy has been employed for the treatment for head and neck squamous cell carcinoma (HNSCC) with CDK4/6 hyperactivation, but the response rate is relatively low. In this study, we first showed that CDK4 and CDK6 was over-expressed and conferred poor prognosis in HNSCC. Moreover, in RB-positive HNSCC, STAT3 signaling was activated induced by CDK4/6 inhibition and STAT3 promotes RB deficiency by upregulation of MYC. Thirdly, the combination of Stattic and CDK4/6 inhibitor results in striking anti-tumor effect in vitro and in Cal27 derived animal models. Additionally, phospho-STAT3 level negatively correlates with RB expression and predicts poor prognosis in patients with HNSCC. Taken together, our findings suggest an unrecognized function of STAT3 confers to CDK4/6 inhibitors resistance and presenting a promising combination strategy for patients with HNSCC.

CD63+ cancer-associated fibroblasts confer CDK4/6 inhibitor resistance to breast cancer cells by exosomal miR-20

Cyclin-dependent kinase 4 (CDK4) and CDK6 inhibitors (CDK4/6i) have rapidly received Food and Drug Administration (FDA) approval as a new type of therapy for patients with advanced hormone receptor-positive breast cancer. However, with the widespread application of CDK4/6i, drug resistance has become a new challenge for clinical practice and has greatly limited the treatment effect. Here, the whole microenvironment landscape of ER+ breast cancer tumors was revealed through single-cell RNA sequencing, and a specific subset of cancer-associated fibroblasts (CD63+ CAFs) was identified as highly enriched in CDK4/6i resistant tumor tissues. Then, we found that CD63+ CAFs can distinctly promote resistance to CDK4/6i in breast cancer cells and tumor xenografts. In addition, it was discovered that miR-20 is markedly enriched in the CD63+ CAFs-derived exosomes, which are used to communicate with ER+ breast cancer cells, leading to CDK4/6i resistance. Furthermore, exosomal miR-20 could directly target the RB1 mRNA 3'UTR and negatively regulate RB1 expression to decrease CDK4/6i sensitivity in breast cancer cells. Most importantly, we designed and synthesized cRGD-miR-20 sponge nanoparticles and found that they can enhance the therapeutic effect of CDK4/6i in breast cancer. In summary, our findings reveal that CD63+ CAFs can promote CDK4/6i resistance via exosomal miR-20, which induces the downregulation of RB1 in breast cancer cells, and suggest that CD63+ CAFs may be a novel therapeutic target to enhance CDK4/6i sensitivity.

A retrospective study on the mechanism underlying quick transfer from response to resistance in a repeated recurrent chordoma patient with molecular alterations treated with Palbociclib

PURPOSE

There is no approved targeted therapy for chordoma at present. Although several preclinical studies have implied the potential applicability of CDK4/6 inhibitor for this rare tumor, no clinical evidence has been documented so far. The purpose of this study was to elucidate the therapeutic efficacy of CDK4/6 inhibitor for chordoma.

METHODS

The next generation sequencing (as for whole-exome sequencing, WES assay) and immunohistochemical (IHC) staining of the chordoma tissue from a patient with an advanced lesion were performed before treatment. Then, the patient was treated with Palbociclib for 4 months until progression occurred in the 5th month. Surgical resection was implemented and the tumor tissue was obtained postoperatively for assessment of molecular alterations.

RESULTS

Molecular features of the tumor before medical treatment suggested applicability of CDK4/6 inhibitor and the patient showed partial response (PR) according to Choi Criteria after 4 months treating with Palbociclib until progression occurred. Then, a drastic molecular alteration of the tumor as represented by emergence of dramatic E2F amplification, which is known to induce CDK4/6 independent cell-cycle entry and progression after treatment, was detected. The findings in this patient demonstrated tumor evolution under drug pressure.

CONCLUSION

The findings of the present study suggest the feasibility of Palbociclib for the clinical treatment of chordoma, and imply the necessity of combination therapies rather single drug administration due to the quick resistance of the tumor to Palbociclib treatment.

Identification of a Panel of miRNAs Associated with Resistance to Palbociclib and Endocrine Therapy

We investigated whether we could identify a panel of miRNAs associated with response to treatment in tumor tissues of patients with Hormone Receptor-positive/HER2-negative metastatic breast cancer treated with endocrine therapy (ET) and the CDK4/6 inhibitor (CDK4/6i)i palbociclib. In total, 52 patients were evaluated, with 41 receiving treatment as the first line. The overall median PFS was 20.8 months (range 2.5-66.6). In total, 23% of patients experienced early progression (<6 months). Seven miRNAs (miR-378e, miR-1233, miR-99b-5p, miR-1260b, miR-448, -miR-1252-5p, miR-324-3p, miR-1233-3p) showed a statistically significant negative association with PFS. When we considered PFS < 6 months, miR-378e, miR-99b-5p, miR-877-5p, miR-1297, miR-455-5p, and miR-4536-5p were statistically associated with a poor outcome. In the multivariate analysis, the first three miRNAs confirmed a significant and independent impact on PFS. The literature data and bioinformatic tools provide an underlying molecular rationale for most of these miRNAs, mainly involving the PI3K/AKT/mTOR pathway and cell-cycle machinery as cyclin D1, CDKN1B, and protein p27Kip1 and autophagy. Our findings propose a novel panel of miRNAs associated with a higher likelihood of early progression in patients treated with ET and Palbociclib and may contribute to shed some light on the mechanisms of de novo resistance to CDK4/6i, but this should be considered exploratory and evaluated in larger cohorts.

Efficacy of CDK4/6 inhibitors combined with endocrine therapy in HR+/HER2- breast cancer: an umbrella review

BACKGROUND

The use of Cyclin-Dependent kinase 4 and 6 (CDK4/6) inhibitors has profoundly changed the challenge of endocrine therapy (ET) resistance in hormone receptor-positive (HR+)/HER2-negative (HER2-) breast cancer. However, there is currently no comprehensive evaluation of the evidence for the efficacy of CDK4/6 inhibitors. We conducted an umbrella review to explore the impact of CDK4/6 inhibitor combined with ET on breast cancer by summarizing and assessing the meta-analysis (MA) and systematic review (SR) evidence.

METHODS

Cochrane, PubMed, Embase, and Web of Science databases were searched from inception to August 1st, 2022. Eligible studies were assessed for methodological quality, report quality, and evidence quality using the AMSTAR-2 scale, PRISMA 2020, and GRADE grading systems, respectively. We summarized all efficacy outcomes of CDK4/6 inhibitors for breast cancer and reported them in narrative form.

RESULTS

Our study included 24 MAs and SRs. The strongest evidence demonstrated that CDK4/6 inhibitor combined with ET significantly improved progression-free survival (PFS), overall survival (OS) in advanced breast cancer (ABC). A large body of moderate to high evidence showed a significant association between combination therapy and objective response rate (ORR), and clinical benefit response (CBR) benefit in ABC. Low evidence suggested some degree of benefit from combination therapy in second progression-free survival (PFS2) and time to subsequent chemotherapy (TTC) outcomes in ABC and invasive disease-free survival (IDFS) outcomes in early breast cancer.

CONCLUSIONS

Based on current evidence, CDK4/6 inhibitors combined with ET have great confidence in improving PFS, OS, ORR, and CBR outcomes in patients with ABC, which provides more rational and valid evidence-based medicine for CDK4/6 inhibitor promotion and clinical decision support.

The value of oral selective estrogen receptor degraders in patients with HR-positive, HER2-negative advanced breast cancer after progression on ≥ 1 line of endocrine therapy: systematic review and meta-analysis

BACKGROUND

Currently, the value of oral selective estrogen receptor degraders (SERDs) for hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (aBC) after progression on ≥ 1 line of endocrine therapy (ET) remains controversial. We conducted a meta-analysis to evaluate progression-free survival (PFS) and safety benefits in several clinical trials.

MATERIALS AND METHODS

Cochrane Library, Embase, PubMed, and conference proceedings (SABCS, ASCO, ESMO, and ESMO Breast) were searched systematically and comprehensively. Random effects models or fixed effects models were used to assess pooled hazard ratios (HRs) and 95% confidence intervals (CIs) for treatment with oral SERDs versus standard of care.

RESULTS

A total of four studies involving 1,290 patients were included in our analysis. The hazard ratio (HR) of PFS showed that the oral SERD regimen was better than standard of care in patients with HR+/HER2- aBC after progression on ≥ 1 line of ET (HR: 0.75, 95% CI: 0.62-0.91, p = 0.004). In patients with ESR1 mutations, the oral SERD regimen provided better PFS than standard of care (HR: 0.58, 95% CI: 0.47-0.71, p < 0.00001). Regarding patients with disease progression following previous use of CDK4/6 inhibitors, PFS benefit was observed in oral SERD-treatment arms compared to standard of care (HR: 0.75, 95% CI: 0.64-0.87, p = 0.0002).

CONCLUSIONS

The oral SERD regimen provides a significant PFS benefit compared to standard-of-care ET in patients with HR+/HER2- aBC after progression on ≥ 1 line of ET. In particular, we recommend oral SERDs as a preferred choice for those patients with ESR1m, and it could be a potential replacement for fulvestrant. The oral SERD regimen is also beneficial after progression on CDK4/6 inhibitors combined with endocrine therapy.

Potential Target of CDK6 Signaling Pathway for Cancer Treatment

BACKGROUND

Cancer involves uncontrolled cell growth due to genetic mutations. Tumors can form when CDK6, a gene essential for controlling cell growth, isn't working correctly. Researchers are investigating drugs that inhibit CDK6; some of them appear promising. Nevertheless, CDK6 is advantageous and harmful to cancer because it controls other cellular processes. By inhibiting CDK6 and CDK4, CDK4/6 inhibitors offer a novel therapeutic strategy that stops cell proliferation. The study investigates the function of CDK6 in cancer, the difficulties in targeting CDK6, and possible remedies.

OBJECTIVE

Scientists have developed drugs designed to block CDK6 and prevent it from altering other proteins. These drugs, also known as CDK6 inhibitors, help treat cancer. Finding the best drugs for CDK6 is still tricky, though. The drugs' selectivity, potency, and cost are some difficulties. These factors depend on CDK6's structure and interactions with other proteins. The structure of CDK6 and how it influences its function and regulation are explained in this review. It also describes CDK6's function in cancer and its interaction with other molecules and proteins, which is crucial for cell division. This review also discusses the present and upcoming therapies that target CDK6, as well as how CDK6 interacts with drugs that block it.

CONCLUSION

This review presents the structure, current research, and overview of CDK6. It also reviews the role of CDK6 in cancer, function, and regulation. Additionally, it explores its role in cancer signaling networks and its interaction with CDK6 inhibitors. Lastly, it discusses the current status and prospects of therapies targeting CDK6.

CDK4/6 inhibitors for hormone receptor-positive/human epidermal growth factor receptor 2 negative advanced breast cancer: A rapid health technology assessment

OBJECT

Based on the best available evidence, rapid health technology was used to assess 4 CDK4/6 inhibitors approved for marketing in China. This assessment aims to provide a reference basis for the selection of drugs by medical institutions in China and to promote the rational use of drugs in the clinic.

METHODS

Depending on the Rapid Guidelines for Drug Evaluation and Selection in Chinese Medical Institutions (the Second Edition), a percentage quantitative scoring approach was used to objectively score the pharmacological properties, efficacy, safety, economy, and other attributes of CDK4/6 inhibitors.

RESULTS

The composite score rankings were, in descending order, 78.09 points for abemaciclib, 78.04 points for palbociclib, 72.15 points for dalpiciclib, and 69.24 points for ribociclib by integrating the result of the 5 dimensions.

CONCLUSION

Until the clinical studies, guideline recommendations, prices, and many other aspects of this assessment are updated, abemaciclib and palbociclib, which have the top 2 scores, can be used as a priority recommendation for Chinese medical institutions to select CDK4/6 inhibitors and optimize the use of the drug catalog based on the scoring results of this assessment.

Progression after First-Line Cyclin-Dependent Kinase 4/6 Inhibitor Treatment: Analysis of Molecular Mechanisms and Clinical Data

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6iss) are widely used in first-line metastatic breast cancer. For patients with progression under CDK4/6is, there is currently no standard treatment recommended at the category 1 level in international guidelines. The purpose of this article is to review the cellular mechanisms underlying the resistance to CDK4/6is, as well as treatment strategies and the clinical data about the efficacy of subsequent treatments after CDK4/6is-based therapy. In the first part, this review mainly discusses cell-cycle-specific and cell-cycle-non-specific resistance to CDK4/6is, with a focus on early and late progression. In the second part, this review analyzes potential therapeutic approaches and the available clinical data on them: switching to other CDK4/6is, to another single hormonal therapy, to other target therapies (PI3K, mTOR and AKT) and to chemotherapy.

Long non-coding RNA H19 promotes proliferation in hepatocellular carcinoma cells via H19/miR-107/CDK6 axis

Hepatocellular carcinoma (HCC) is the leading cause of cancer death worldwide; nevertheless, current therapeutic options are limited or ineffective for many patients. Therefore, elucidation of molecular mechanisms in HCC biology could yield important insights for the intervention of novel therapies. Recently, various studies have reported dysregulation of long non-coding RNAs (lncRNAs) in the initiation and progression of HCC, including H19; however, the biological function of H19 in HCC remains unclear. Here, we show that knockdown of H19 disrupted HCC cell growth, impaired the G1-to-S phase transition, and promoted apoptosis, while overexpression of H19 yielded the opposite results. Screening for expression of cell cycle-related genes revealed a significant downregulation of CDK6 at both RNA and protein levels upon H19 suppression. Bioinformatic analysis of the H19 sequence and the 3' untranslated region (3' UTR) of CDK6 transcripts showed several binding sites for microRNA-107 (miR-107), and the dual luciferase reporter assay confirmed their direct interaction with miR-107. Consistently, blockage of miR-107 activity alleviated the growth suppression phenotypes induced by H19 downregulation, suggesting that H19 serves as a molecular sponge for miR-107 to promote CDK6 expression and cell cycle progression. Together, this study demonstrates a mechanistic function of H19 in driving the proliferation of HCC cells and suggests H19 suppression as a novel approach for HCC treatment.

Capivasertib in Hormone Receptor-Positive Advanced Breast Cancer

BACKGROUND

AKT pathway activation is implicated in endocrine-therapy resistance. Data on the efficacy and safety of the AKT inhibitor capivasertib, as an addition to fulvestrant therapy, in patients with hormone receptor-positive advanced breast cancer are limited.

METHODS

In a phase 3, randomized, double-blind trial, we enrolled eligible pre-, peri-, and postmenopausal women and men with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer who had had a relapse or disease progression during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor therapy. Patients were randomly assigned in a 1:1 ratio to receive capivasertib plus fulvestrant or placebo plus fulvestrant. The dual primary end point was investigator-assessed progression-free survival assessed both in the overall population and among patients with AKT pathway-altered (PIK3CA, AKT1, or PTEN) tumors. Safety was assessed.

RESULTS

Overall, 708 patients underwent randomization; 289 patients (40.8%) had AKT pathway alterations, and 489 (69.1%) had received a CDK4/6 inhibitor previously for advanced breast cancer. In the overall population, the median progression-free survival was 7.2 months in the capivasertib-fulvestrant group, as compared with 3.6 months in the placebo-fulvestrant group (hazard ratio for progression or death, 0.60; 95% confidence interval [CI], 0.51 to 0.71; P<0.001). In the AKT pathway-altered population, the median progression-free survival was 7.3 months in the capivasertib-fulvestrant group, as compared with 3.1 months in the placebo-fulvestrant group (hazard ratio, 0.50; 95% CI, 0.38 to 0.65; P<0.001). The most frequent adverse events of grade 3 or higher in patients receiving capivasertib-fulvestrant were rash (in 12.1% of patients, vs. in 0.3% of those receiving placebo-fulvestrant) and diarrhea (in 9.3% vs. 0.3%). Adverse events leading to discontinuation were reported in 13.0% of the patients receiving capivasertib and in 2.3% of those receiving placebo.

CONCLUSIONS

Capivasertib-fulvestrant therapy resulted in significantly longer progression-free survival than treatment with fulvestrant alone among patients with hormone receptor-positive advanced breast cancer whose disease had progressed during or after previous aromatase inhibitor therapy with or without a CDK4/6 inhibitor. (Funded by AstraZeneca and the National Cancer Institute; CAPItello-291 ClinicalTrials.gov number, NCT04305496.).

MYCN Amplification, along with Wild-Type RB1 Expression, Enhances CDK4/6 Inhibitors’ Efficacy in Neuroblastoma Cells

Neuroblastoma (NB) is one of the primary causes of death for pediatric malignancies. Given the high heterogeneity in NB’s mutation landscape, optimizing individualized therapies is still challenging. In the context of genomic alterations, MYCN amplification is the most correlated event with poor outcomes. MYCN is involved in the regulation of several cellular mechanisms, including cell cycle. Thus, studying the influence of MYCN overexpression in the G1/S transition checkpoint of the cell cycle may unveil novel druggable targets for the development of personalized therapeutical approaches. Here, we show that high expression of E2F3 and MYCN correlate with poor prognosis in NB despite the RB1 mRNA levels. Moreover, we demonstrate through luciferase reporter assays that MYCN bypasses RB function by incrementing E2F3-responsive promoter activity. We showed that MYCN overexpression leads to RB inactivation by inducing RB hyperphosphorylation during the G1 phase through cell cycle synchronization experiments. Moreover, we generated two MYCN-amplified NB cell lines conditionally knockdown (cKD) for the RB1 gene through a CRISPRi approach. Indeed, RB KD did not affect cell proliferation, whereas cell proliferation was strongly influenced when a non-phosphorylatable RB mutant was expressed. This finding revealed the dispensable role of RB in regulating MYCN-amplified NB’s cell cycle. The described genetic interaction between MYCN and RB1 provides the rationale for using cyclin/CDK complexes inhibitors in NBs carrying MYCN amplification and relatively high levels of RB1 expression.

The effects of Abemaciclib on cell cycle and apoptosis regulation in anaplastic thyroid cancer cells

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.

Mechanisms of Resistance to CDK4/6 Inhibitors and Predictive Biomarkers of Response in HR+/HER2-Metastatic Breast Cancer-A Review of the Literature

The latest and newest discoveries for advanced and metastatic hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer are the three cyclin-dependent kinases 4 and 6 inhibitors (CDK4/6i) in association with endocrine therapy (ET). However, even if this treatment revolutionized the world and continued to be the first-line treatment choice for these patients, it also has its limitations, caused by de novo or acquired drug resistance which leads to inevitable progression after some time. Thus, an understanding of the overview of the targeted therapy which represents the gold therapy for this subtype of cancer is essential. The full potential of CDK4/6i is yet to be known, with many trials ongoing to expand their utility to other breast cancer subtypes, such as early breast cancer, and even to other cancers. Our research establishes the important idea that resistance to combined therapy (CDK4/6i + ET) can be due to resistance to endocrine therapy, to treatment with CDK4/6i, or to both. Individuals' responses to treatment are based mostly on genetic features and molecular markers, as well as the tumor's hallmarks; therefore, a future perspective is represented by personalized treatment based on the development of new biomarkers, and strategies to overcome drug resistance to combinations of ET and CDK4/6 inhibitors. The aim of our study was to centralize the mechanisms of resistance, and we believe that our work will have utility for everyone in the medical field who wants to deepen their knowledge about ET + CDK4/6 inhibitors resistance.

Prognostic Parameters of Palbociclib in HR+/HER2- Advanced Breast Cancer: A Narrative Review

Recent studies have demonstrated that the combination of Cyclin-Dependent Kinase 4/6 Inhibitor (CDK4/6i) and endocrine therapy (ET) is more effective than ET alone and significantly improves progression-free survival (PFS) and overall survival (OS) in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor-2 negative (HER2-) breast cancer (BC). Palbociclib is the first CDK4/6i approved for use, and its clinical advantages have been shown. However, 30% of patients will continue to develop secondary drug resistance. Therefore, exploring the parameters that can predict the efficacy of Palbociclib and developing a clinical prediction model is essential for evaluating the prognosis of patients.

The Expression of Cell Cycle-Related Genes in USP8-Mutated Corticotroph Neuroendocrine Pituitary Tumors and Their Possible Role in Cell Cycle-Targeting Treatment

Protein deubiquitinases USP8 and USP48 are known driver genes in corticotroph pituitary neuroendocrine tumors (PitNETs). USP8 mutations have pleiotropic effects that include notable changes in genes' expression. Genes involved in cell cycle regulation were found differentially expressed in mutated and wild-type tumors. This study aimed to verify difference in the expression level of selected cell cycle-related genes and investigate their potential role in response to cell cycle inhibitors. Analysis of 70 corticotroph PitNETs showed that USP8-mutated tumors have lower CDKN1B, CDK6, CCND2 and higher CDC25A expression. USP48-mutated tumors have lower CDKN1B and CCND1 expression. A lower p27 protein level in mutated than in wild-type tumors was confirmed that may potentially influence the response to small molecule inhibitors targeting the cell cycle. We looked for the role of USP8 mutations or a changed p27 level in the response to palbociclib, flavopiridol and roscovitine in vitro using murine corticotroph AtT-20/D16v-F2 cells. The cells were sensitive to each agent and treatment influenced the expression of genes involved in cell cycle regulation. Overexpression of mutated Usp8 in the cells did not affect the expression of p27 nor the response to the inhibitors. Downregulating or upregulating p27 expression in AtT-20/D16v-F2 cells also did not affect treatment response.