Ribociclib (LEE011): Mechanism of Action and Clinical Impact of This Selective Cyclin-Dependent Kinase 4/6 Inhibitor in Various Solid Tumors

Evaluating the simultaneous electrochemical determination of antineoplastic drugs using LaNiO3/g-C3N4@RGH nanocomposite material

A novel electrochemical sensor based on LaNiO3/g-C3N4@RGH nanocomposite material was developed to simultaneously determine Ribociclib (RIBO) and Alpelisib (ALPE). Ribociclib and Alpelisib are vital anticancer medications used in the treatment of advanced breast cancer. The sensor exhibited excellent electrocatalytic activity towards the oxidation of RIBO and ALPE, enabling their simultaneous detection. The fabricated sensor was characterized using various techniques, including energy dispersive X-ray (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), which confirmed the successful synthesis of the LaNiO3/g-C3N4@RGH composite material. Electrochemical characterization revealed enhanced conductivity and lower resistance of the modified electrode compared to the bare electrode. The developed sensor exhibited high repeatability, reproducibility, stability, and selectivity toward RIBO detection. Furthermore, the sensor displayed high sensitivity with low detection limits of 0.88 nM for RIBO and 6.1 nM for ALPE, and linear ranges of 0.05-6.2 μM and 0.5-6.5 μM, respectively. The proposed electrochemical sensor offers a promising approach for simultaneously determining RIBO and ALPE in pharmaceutical formulations and biological samples with recovery data of 98.7-102.0 %, providing a valuable tool for anticancer drug analysis and clinical research.

SLC7A11 protects luminal A breast cancer cells against ferroptosis induced by CDK4/6 inhibitors

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6 inhibitors) can significantly extend tumor response in patients with metastatic luminal A breast cancer, yet intrinsic and acquired resistance remains a prevalent issue. Understanding the molecular features of CDK4/6 inhibitor sensitivity and the potential efficacy of their combination with novel targeted cell death inducers may lead to improved patient outcomes. Herein, we demonstrate that ferroptosis, a form of regulated cell death driven by iron-dependent phospholipid peroxidation, partly underpins the efficacy of CDK4/6 inhibitors. Mechanistically, CDK4/6 inhibitors downregulate the cystine transporter SLC7A11 by inhibiting SP1 binding to the SLC7A11 promoter region. Furthermore, SLC7A11 is identified as critical for the intrinsic sensitivity of luminal A breast cancer to CDK4/6 inhibitors. Both genetic and pharmacological inhibition of SP1 or SLC7A11 enhances cell sensitivity to CDK4/6 inhibitors and synergistically inhibits luminal A breast cancer growth when combined with CDK4/6 inhibitors in vitro and in vivo. Our data highlight the potential of targeting SLC7A11 in combination with CDK4/6 inhibitors, supporting further investigation of combination therapy in luminal A breast cancer.

Role of specific CDKs in regulating DNA damage repair responses and replication stress

Cyclins along with their catalytic units, Cyclin-dependent kinases (CDKs) regulate the cell cycle transition and transcription; and are essentially known as 'master regulators' in modulating DNA damage response (DDR) and replication stress. In addition to influencing DNA repair and damage signaling, CDKs also play a pivotal role in cell division fidelity and the maintenance of genomic integrity after DNA damage. In this review, we focus on the intricate ways by which specific CDKs mainly CDK7, CDK9, and CDK12/13, regulate the cell cycle progression and transcription and how their modulation can lead to lethal effects on the integrity of the genome. With a better knowledge of how these CDKs control the DDR and replication stress, it is now possible to combine CDK inhibitors with chemotherapeutic drugs that damage DNA in ways that can be applied in clinical settings as successful therapeutic strategies.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Prophylaxis with abemaciclib delays tumorigenesis in dMMR mice by altering immune responses and reducing immunosuppressive extracellular vesicle secretion

BACKGROUND

The CDK4/6 inhibitor abemaciclib is an FDA-approved agent and induces T-cell-mediated immunity. Previously, we confirmed the therapeutic potential of abemaciclib on mismatch repair-deficient (dMMR) tumors in mice. Here, we applied a prophylactic administration/dosage setting using two preclinical mouse models of dMMR-driven cancer.

METHODS

Mlh1-/- and Msh2loxP/loxP mice received repeated prophylactic applications of abemaciclib mesylate (75 mg/kg bw, per oral) as monotherapy or were left untreated. Blood phenotyping and multiplex cytokine measurements were performed regularly. The tumor microenvironment was evaluated by immunofluorescence and Nanostring-based gene expression profiling. Numbers, size and immune composition and activity of extracellular vesicles (EVs) were studied at the endpoint.

FINDINGS

Prophylactic abemaciclib-administration delayed tumor development and significantly prolonged overall survival in both mouse strains (Mlh1-/-: 50.0 wks vs. control: 33.9 wks; Msh2loxP/loxP;TgTg(Vil1-cre: 58.4 wks vs. control 44.4 wks). In Mlh1-/- mice, pro-inflammatory cytokines (IL-2, IL-6) significantly increased, whereas IL-10 and IL-17A decreased. Circulating and splenic exhausted and regulatory T cell numbers were significantly lower in the abemaciclib groups. Deeper analysis of late-onset tumors revealed activation of the Hedgehog and Notch signaling in Mlh1-/- mice, and activation of the MAPK pathway in Msh2loxP/loxP;TgTg(Vil1-cre mice. Still, arising tumors had fewer infiltrating myeloid-derived suppressor cells (vs. control). Notably, prophylactic abemaciclib-administration prevented secretion of procoagulant EVs but triggered release of immunomodulatory EVs in Mlh1-/- mice.

INTERPRETATION

Prophylactic abemaciclib prolongs survival via global immunomodulation. Prophylactic use of abemaciclib should be considered further for individuals with inherited dMMR.

FUNDING

This work was supported by grants from the German research foundation [DFG grant number: MA5799/2-2] and the Brigitte und Dr. Konstanze Wegener-Stiftung to CM.

The effect of ribociclib on the expression levels of miR-141 and CDK4/6-USP51 signaling pathway genes in MCF-7 and MDA-MB-231 cells

INTRODUCTION

Patients with breast cancer, especially triple-negative breast cancer, have a poor prognosis. There is still no effective treatment for this disease. Due to resistance to traditional treatments such as chemotherapy and radiation therapy, there is a need to discover novel treatment strategies to treat this disease. Ribociclib is a selective CDK4/6 inhibitor. Approximately 20% of patients with HR+ breast cancer developed primary resistance to CDK4/6 inhibitors, and more than 30% experienced secondary resistance. Since most patients experience resistance during CDK4/6 inhibitor treatment, managing this disease is becoming more challenging. Many malignant tumors abnormally express microRNA (miR)-141, which participates in several cellular processes, including drug resistance, proliferation, epithelial-mesenchymal transition, migration, and invasion.

MATERIALS AND METHODS

In the present study, we cultured MDA-MB-231 and MCF-7 cells in DMEM-F12 medium. By performing MTT assay we determined the cytotoxic effects of ribociclib on breast cancer cells, as well as determining the IC50 of it. Then, we treated the cells with ribociclib at two time points: 24 h and 72 h. After that, RNA was isolated and reverse transcribed to cDNA. Finally, we performed qRT‒PCR to evaluate how ribociclib affects the expression level of desired genes.

RESULTS AND CONCLUSION

We found that ribociclib can inhibit cell growth in a dose- and time-dependent manner. We examined the mRNA expression of 4 genes. After ribociclib treatment, the mRNA expression of CDK6 and MYH10 decreased (p < 0.01, p < 0.05). The mRNA expression of CDON increased (p<0.05), but no significant changes were observed in ZEB1 mRNA expression. Furthermore, the qRT‒PCR results for miR-141 showed that the expression of miR-141 increased (p<0.01) after 72 h of treatment with ribociclib.

Integrative Analysis of Multi-Omics Data to Identify Deregulated Molecular Pathways and Druggable Targets in Chronic Lymphocytic Leukemia

Chronic Lymphocytic Leukemia (CLL) is the most common B-cell malignancy in the Western world, characterized by frequent relapses despite temporary remissions. Our study integrated publicly available proteomic, transcriptomic, and patient survival datasets to identify key differences between healthy and CLL samples. We exposed approximately 1000 proteins that differentiate healthy from cancerous cells, with 608 upregulated and 415 downregulated in CLL cases. Notable upregulated proteins include YEATS2 (an epigenetic regulator), PIGR (Polymeric immunoglobulin receptor), and SNRPA (a splicing factor), which may serve as prognostic biomarkers for this disease. Key pathways implicated in CLL progression involve RNA processing, stress resistance, and immune response deficits. Furthermore, we identified three existing drugs-Bosutinib, Vorinostat, and Panobinostat-for potential further investigation in drug repurposing in CLL. We also found limited correlation between transcriptomic and proteomic data, emphasizing the importance of proteomics in understanding gene expression regulation mechanisms. This generally known disparity highlights once again that mRNA levels do not accurately predict protein abundance due to many regulatory factors, such as protein degradation, post-transcriptional modifications, and differing rates of translation. These results demonstrate the value of integrating omics data to uncover deregulated proteins and pathways in cancer and suggest new therapeutic avenues for CLL.

Relationship between HER2-low status and efficacy of CDK4/6 inhibitors in advanced breast cancer: a real-world study

AIMS AND OBJECTIVES

Human epidermal growth factor receptor 2 (HER2)-low breast cancer (BC) is a new entity considered a biologically distinct subtype from HER2-zero BC. However, the importance of HER2 low expression on the activity of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) remains unclear.

METHODS/MATERIALS

We conducted a single-center retrospective study including hormone receptor-positive (HR +) /HER2- metastatic BC (mBC) patients treated with CDK4/6i plus endocrine treatment (ET) as first-line therapy. Clinical outcomes were analyzed according to HER2 expression.

RESULTS

258 women were analyzed with a median follow-up of 25.4 months; 39.9% had HER2 low, and 60.1% had HER2 zero BC. Median progression-free survival (mPFS) in the HER2-low group was 27.6 months compared with 44.3 months in the HER2-zero group (p = 0.341). In patients receiving ribociclib, the mPFS in the HER2-low group was 24.2 months compared with 53.1 months in the HER2-zero group (multivariate-adjusted HR: 1.981, 95 Cl 1.094-3.586; p = 0.024). The survival probabilities at 24, 36 and 48 months for the HER2 low and HER2 zero groups were 82%, 69%, 69% and 83%, 75% and 69%, respectively (p = 0.336). Objective response rate (p = 0.179) and disease control rate (p = 0.338) did not significantly differ between HER-2-low and HER-2-zero groups.

CONCLUSIONS

The mPFS in the Her2-zero group was almost twice that of the Her2-low group, but the difference was not statistically significant. mPFS was significantly longer in the HER2-zero group compared to the HER2-low group in patients receiving ribociclib. More prospective studies are needed to understand the actual consequences of this biomarker.

Assessing risks and knowledge gaps on the impact of systemic therapies in early breast cancer on female fertility: A systematic review of the literature

The therapeutic landscape for early breast cancer (eBC) has expanded by introducing novel anticancer agents into clinical practice. During their reproductive years, women with eBC should be informed of the potential risk of premature ovarian insufficiency (POI) and infertility with the proposed systemic therapy. Although the topic of female fertility is becoming increasingly relevant in patients with cancer, limited information is available on the gonadotoxicity of new agents available for eBC treatment. Analyses from clinical trials and prospective data on ovarian function biomarkers are lacking. The purpose of this systematic review is to report the available preclinical and clinical data on female fertility risk with the use of the new agents that are part of clinical practice use or under development for eBC management. This review highlights the clear need to perform additional research efforts to improve our understanding on the gonoadtoxicity of new anticancer agents.

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

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

Single nucleus transcriptomics, pharmacokinetics, and pharmacodynamics of combined CDK4/6 and mTOR inhibition in a phase 0/1 trial of recurrent high-grade glioma

Outcomes for adult patients with a high-grade glioma continue to be dismal and new treatment paradigms are urgently needed. To optimize the opportunity for discovery, we performed a phase 0/1 dose-escalation clinical trial that investigated tumor pharmacokinetics, pharmacodynamics, and single nucleus transcriptomics following combined ribociclib (CDK4/6 inhibitor) and everolimus (mTOR inhibitor) treatment in recurrent high-grade glioma. Patients with a recurrent high-grade glioma (n = 24) harboring 1) CDKN2A / B deletion or CDK4 / 6 amplification, 2) PTEN loss or PIK3CA mutations, and 3) wild-type retinoblastoma protein (Rb) were enrolled. Patients received neoadjuvant ribociclib and everolimus treatment and no dose-limiting toxicities were observed. The median unbound ribociclib concentrations in Gadolinium non-enhancing tumor regions were 170 nM (range, 65 - 1770 nM) and 634 nM (range, 68 - 2345 nM) in patients receiving 5 days treatment at the daily dose of 400 and 600 mg, respectively. Unbound everolimus concentrations were below the limit of detection (< 0.1 nM) in both enhancing and non-enhancing tumor regions at all dose levels. We identified a significant decrease in MIB1 positive cells suggesting ribociclib-associated cell cycle inhibition. Single nuclei RNAseq (snRNA) based comparisons of 17 IDH-wild-type on-trial recurrences to 31 IDH-wild-type standard of care treated recurrences data demonstrated a significantly lower fraction of cycling and neural progenitor-like (NPC-like) malignant cell populations. We validated the CDK4/6 inhibitor-directed malignant cell state shifts using three patient-derived cell lines. The presented clinical trial highlights the value of integrating pharmacokinetics, pharmacodynamics, and single nucleus transcriptomics to assess treatment effects in phase 0/1 surgical tissues, including malignant cell state shifts. ClinicalTrials.gov identifier: NCT03834740 .

Targeting oncogenic kinases: Insights on FDA approved tyrosine kinase inhibitors

Protein kinases play pivotal roles in various biological functions, influencing cell differentiation, promoting survival, and regulating the cell cycle. The disruption of protein kinase activity is intricately linked to pathways in tumor development. This manuscript explores the transformative impact of protein kinase inhibitors on cancer therapy, particularly their efficacy in cases driven by targeted mutations. Focusing on key tyrosine kinase inhibitors (TKIs) like Bcr-Abl, Epidermal Growth Factor Receptor (EGFR), and Vascular Endothelial Growth Factor Receptor (VEGFR), it targets critical kinase families in cancer progression. Clinical trial details of these TKIs offer insights into their therapeutic potentials. Learning from FDA-approved kinase inhibitors, the review dissects trends in kinase drug development since imatinib's paradigm-shifting approval in 2001. TKIs have evolved into pivotal drugs, extending beyond oncology. Ongoing clinical trials explore novel kinase targets, revealing the vast potential within the human kinome. The manuscript provides a detailed analysis of advancements until 2022, discussing the roles of specific oncogenic protein kinases in cancer development and carcinogenesis. Our exploration on PubMed for relevant and significant TKIs undergoing pre-FDA approval phase III clinical trials enriches the discussion with valuable findings. While kinase inhibitors exhibit lower toxicity than traditional chemotherapy in cancer treatment, challenges like resistance and side effects emphasize the necessity of understanding resistance mechanisms, prompting the development of novel inhibitors like osimertinib targeting specific mutant proteins. The review advocates thorough research on effective combination therapies, highlighting the future development of more selective RTKIs to optimize patient-specific cancer treatment and reduce adverse events.

Cardiovascular complications of ribociclib in breast cancer patients

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have unprecedentedly advanced hormone-dependent breast cancer treatment paradigm. In the metastatic setting, ribociclib has consistently demonstrated survival benefit in pre-, peri-, and postmenopausal patients, conjugating efficacy with health-related quality of life preservation. Accordingly, the emergence of cardiac and/or vascular adverse events related to this novel targeted agent is gaining significant interest. This narrative review provides an overview of the incidence and spectrum of cardiovascular toxicity, in both clinical trial framework and real-world evidence. The potential pathogenetic mechanism, along with the available diagnostic parameters including biomarkers, and proper management, are also summarized.

A low-cost voltammetric sensor based on multi-walled carbon nanotubes for highly sensitive and accurate determination of nanomolar levels of the anticancer drug Ribociclib in bulk and biological fluids

In this study, we present the development and comprehensive characterization of the first electrochemical sensor utilizing multi-walled carbon nanotubes (MWCNTs) for the sensitive and precise detection of Ribociclib (RIBO), an important anticancer drug. The sensor underwent systematic optimization, focusing on critical parameters such as pH, deposition potential, and cumulative time to enhance its electrocatalytic activity and expand the linear range for RIBO determination. The MWCNTs/GCE sensor exhibited excellent reproducibility and repeatability, ensuring reliable and consistent results. The applicability and feasibility of the sensor for real sample analysis were extensively evaluated by analyzing human serum, urine, and tablet samples using the standard addition method. The obtained percent recovery values demonstrated the sensor's exceptional accuracy and precision. Furthermore, interference studies revealed the sensor's remarkable selectivity, with minimal impact from common interfering substances. The developed sensor displayed a wide linear range of 0.01 μM to 5.0 μM, with a limit of detection (LOD) and limit of quantification (LOQ) calculated to be 0.69 nM and 2.31 nM, respectively, affirming its high sensitivity for detecting low RIBO concentrations. The MWCNTs/GCE sensor demonstrates substantial promise for diverse practical applications with its simplicity, cost-effectiveness, and excellent analytical performance.

Recent advances in multitarget-directed ligands via in silico drug discovery

To combat multifactorial refractory diseases, such as cancer, cardiovascular, and neurodegenerative diseases, multitarget drugs have become an emerging area of research aimed at 'synthetic lethality' (SL) relationships associated with drug-resistance mechanisms. In this review, we discuss the in silico design of dual and triple-targeted ligands, strategies by which specific 'warhead' groups are incorporated into a parent compound or scaffold with primary inhibitory activity against one target to develop one small molecule that inhibits two or three molecular targets in an effort to increase potency against multifactorial diseases. We also discuss the analytical exploration of structure-activity relationships (SARs), physicochemical properties, polypharmacology, scaffold feature extraction of US Food and Drug Administration (FDA)-approved multikinase inhibitors (MKIs), and updates regarding the clinical status of dual-targeted chemotypes.

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

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

Should the Use of Acid Reducing Agents in Conjunction with Ribociclib be Avoided? An Integrated QbD Approach for Assessment of pH-Mediated Interaction

The objective of the study was to evaluate the possible pH-dependent interaction of ribociclib succinate with acid-reducing agents, which are concomitantly administered as supportive care medicines in cancer. Quality by Design-based analytical method development for a weakly basic drug ribociclib succinate supposedly having the characteristic ability of pH-dependent solubility was carried out for analyzing micro-dissolution experiment samples in biorelevant media to study pH-dependent interaction. An accurate and robust analytical method was developed using a three-level three-factorial box-behnken design for quantification of ribociclib succinate in micro-dissolution samples by the implementation of the Analytical Quality by Design approach. Here, pH of aqueous mobile phase and flow rate proved to be critical process parameters. The gastric compartment solubility was found to be 814.05 μg/mL, which dropped down to 494.71 μg/mL after a pH shift from pH 1.2-6.5. In the intestinal compartment, initial solubility was 717.58 μg/mL, which reduced to 463.20 μg/mL after a pH shift from 6.5 to 6.8. Concluded results state that pH shift does not impact the solubility or the absorption of the drug to a significant extent in the presence of acid-reducing agents. However, the study would prove to be a practical approach for examination of the behavior of the drugs at the initial stages.

The CDK4/6 inhibitor revolution - a game-changing era for breast cancer treatment

Cyclin-dependent kinase (CDK) 4/6 inhibition in combination with endocrine therapy is the standard-of-care treatment for patients with advanced-stage hormone receptor-positive, HER2 non-amplified (HR+HER2-) breast cancer. These agents can also be administered as adjuvant therapy to patients with higher-risk early stage disease. Nonetheless, the clinical success of these agents has created several challenges, such as how to address acquired resistance, identifying which patients are most likely to benefit from therapy prior to treatment, and understanding the optimal timing of administration and sequencing of these agents. In this Review, we describe the rationale for targeting CDK4/6 in patients with breast cancer, including a summary of updated clinical evidence and how this should inform clinical practice. We also discuss ongoing research efforts that are attempting to address the various challenges created by the widespread implementation of these agents.

Efficacy, safety, and prognosis prediction in patients treated with ribociclib in combination with letrozole: Final results of phase 3b RIBECCA study in hormone receptor positive, human epidermal growth factor receptor-2 negative, locally advanced or metastatic breast cancer

BACKGROUND

In MONALEESA-2, addition of ribociclib to letrozole resulted in significantly longer progression-free survival (PFS) in postmenopausal women with HR+HER2- advanced breast cancer (ABC). RIBociclib for the treatment of advanCed breast CAncer (RIBECCA) study investigated ribociclib plus letrozole in a patient population reflecting routine clinical practice.

PATIENTS AND METHODS

In this multicenter, open-label, single-arm, phase 3b study, patients with HR+HER2- ABC not amenable to curative therapy and ECOG performance status ≤ 2 received ribociclib plus letrozole (cohort A: postmenopausal women and men in first-line; cohort B: pre-/perimenopausal women in first-line [B1], patients pretreated for advanced disease [B2]). The primary endpoint was clinical benefit rate (CBR) by week 24; secondary endpoints included overall response rate (ORR), PFS, overall survival (OS), and safety. Association of patient and tumor characteristics with PFS was analyzed by multivariable Cox regression analysis.

RESULTS

Overall, 487 patients were evaluable for efficacy, 502 for safety. By week 24, CBR was 60.8 % (95 % CI, 56.3-65.1), ORR was 19.3 % (95 % CI, 15.9-23.1). Median PFS was 21.8 months (95 % CI, 13.9-25.3) in first-line postmenopausal patients and 11.0 months (95 % CI, 8.2-16.4) in premenopausal and pretreated patients. Median OS was not reached. Higher baseline ECOG performance status, higher histological grade, and negative progesterone receptor status showed an unfavorable effect on PFS. Most common adverse events were neutropenia (50.0 %), nausea (42.0 %), and fatigue (39.2 %).

CONCLUSION

In this broad population of patients with HR+HER2- ABC, efficacy and safety results of ribociclib plus letrozole were similar to those observed in pivotal trials.

Molecules inducing specific cyclin-dependent kinase degradation and their possible use in cancer therapy

Cyclin-dependent kinases (CDKs) play an important role in the regulation of cell proliferation, and many CDK inhibitors were developed. However, pan-CDK inhibitors failed to be approved due to intolerant toxicity or low efficacy and the use of selective CDK4/6 inhibitors is limited by resistance. Protein degraders have the potential to increase selectivity, efficacy and overcome resistance, which provides a novel strategy for regulating CDKs. In this review, we summarized the function of CDKs in regulating the cell cycle and transcription, and introduced the representative CDK inhibitors. Then we made a detailed introduction about four types of CDKs degraders, including their action mechanisms, research status and application prospects, which could help the development of novel CDKs degraders.

Use of Pharmacokinetic and Pharmacodynamic Data to Develop the CDK4/6 Inhibitor Ribociclib for Patients with Advanced Breast Cancer

Ribociclib is an orally bioavailable, selective cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor. CDK4/6 inhibition by ribociclib leads to retinoblastoma tumor suppressor protein (Rb) reactivation, thereby restoring Rb-mediated cell cycle arrest. Ribociclib is approved for the treatment of patients with hormone receptor-positive/human epidermal growth factor receptor-2-negative (HR+/HER2-) advanced breast cancer (ABC), at the dose of 600 mg once daily (QD) during cycles of 21 days on/7 days off, with optional dose reduction to 400 mg and 200 mg. Ribociclib is rapidly absorbed with a median time to reach maximum plasma concentration of 2.4 h, mean half-life of 32.0 h and oral bioavailability of 65.8% at 600 mg. It is eliminated mainly by hepatic metabolism (~ 84% of total elimination), mostly by cytochrome P450 (CYP) 3A4. Age, body weight, race, baseline Eastern Cooperative Oncology Group status, food, mild hepatic impairment, mild-to-moderate renal impairment, proton pump inhibitors, and combination partners (non-steroidal aromatase inhibitors or fulvestrant) have no clinically relevant impact on ribociclib exposure. Ribociclib inhibits CYP3A at 600 mg leading to increased exposure of CYP3A substrates. Strong CYP3A inhibitors or inducers increase or decrease, respectively, ribociclib exposure. Exposure-safety and exposure-efficacy analyses support the clinical benefit of the 600 mg QD starting dose, with potential individualized dose reductions to 400 mg and 200 mg for effective management of the adverse events neutropenia and QTcF interval prolongation, while maintaining efficacy, in patients with HR+/HER2- ABC. Overall, these clinical pharmacology data informed ribociclib dose justification and clinical development, as well as its prescribing information for clinical use in advanced breast cancer patients.

Quantitative Assessment of Ribociclib Exposure-Response Relationship to Justify Dose Regimen in Patients with Advanced Breast Cancer

Ribociclib in combination with endocrine therapy (ET) is a globally approved treatment option for patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) and has demonstrated significantly improved overall survival (OS) in 3 phase 3 clinical trials. To justify the dose regimen and dose modification scheme for patients with ABC, the pharmacokinetic (PK), safety, and efficacy data of ribociclib were analyzed. The data of several phase 1-3 clinical studies were pooled and analyzed to characterize the relationship between exposure (dose or PK) and efficacy (progression-free survival (PFS), time to response, and OS) or safety (neutropenia and QT interval prolongation). The exposure-efficacy analysis showed no apparent relationship between ribociclib exposure and efficacy (PFS and OS), and efficacy analysis by dose reduction showed that patients with ABC continued to benefit from the treatment following dose reduction, supporting the starting dose of 600 mg as well as dose reductions to 400 and 200 mg. The exposure-safety analysis showed that neutropenia and QT prolongation are related to ribociclib exposure that can be effectively managed by individualized dose modification (dose reduction/interruption). Collective evidence from the exposure-response analyses for efficacy and safety support the use of ribociclib in combination with ET partners at the starting dose of 600 mg, and also the effectiveness of individualized dose reductions in managing safety, while maintaining efficacy, in patients with HR+/HER2- ABC. This analysis illustrates the utility of quantitative assessment in justifying dose selection and dose modification for oncology medicines.

Immune microenvironment heterogeneity reveals distinct subtypes in neuroblastoma: insights into prognosis and therapeutic targets

BACKGROUND

Neuroblastoma (NB) is a childhood cancer originating from immature nerve cells in the sympathetic nervous system. Current clinical and molecular subtyping methods for NB have limitations in providing accurate prognostic information and guiding treatment decisions.

RESULTS

To overcome these challenges, we explored the microenvironment of NB based on the knowledge-based functional gene expression signatures (Fges), which revealed heterogeneous subtypes. Consensus clustering of Fges activity scores identified three subtypes (Cluster 1, Cluster 2, and Cluster 3) that demonstrated significant differences in prognosis compared to mainstream subtypes. We assessed the immune infiltration, immunogenicity, CD8T cytotoxicity, and tumor purity of these subtypes, uncovering their distinct biological functions. Cluster 1 and Cluster 2 exhibited higher immunoreactivity, while Cluster 3 displayed higher tumor purity and poor prognosis. Gene ontology annotation and pathway analysis identified immune activation in Cluster 1, epithelial-mesenchymal transition (EMT) in Cluster 2, and cell cycle processes in Cluster 3. Notably, the impact of EMT activity on prognosis may vary across NB subtypes. A classification model using XGBoost accurately predicted subtypes in independent NB cohorts, with significant prognostic differences. GPR125, CDK4, and GREB1 emerged as potential therapeutic targets in Cluster 3. CD4K inhibitors showed subtype-specific responses, suggesting tailored treatment strategies. Single-cell analysis highlighted unfavorable clinical features in Cluster 3, including high-risk classification and reduced cytotoxicity. Suppressed interactions between monocytes, macrophages, and regulatory T cells were observed, affecting immune regulation and patient prognosis.

CONCLUSION

To summarize, we have identified a new independent prognostic factor in NB that underscores the significant correlation between tumor phenotype and immune contexture. These findings deepen our understanding of NB subtypes and immune cell interactions, paving the way for more effective treatment approaches.

Palbociclib releases the latent differentiation capacity of neuroblastoma cells

Neuroblastoma is the most common extracranial solid tumor in infants, arising from developmentally stalled neural crest-derived cells. Driving tumor differentiation is a promising therapeutic approach for this devastating disease. Here, we show that the CDK4/6 inhibitor palbociclib not only inhibits proliferation but induces extensive neuronal differentiation of adrenergic neuroblastoma cells. Palbociclib-mediated differentiation is manifested by extensive phenotypic and transcriptional changes accompanied by the establishment of an epigenetic program driving expression of mature neuronal features. In vivo palbociclib significantly inhibits tumor growth in mouse neuroblastoma models. Furthermore, dual treatment with retinoic acid resets the oncogenic adrenergic core regulatory circuit of neuroblastoma cells, further suppresses proliferation, and can enhance differentiation, altering gene expression in ways that significantly correlate with improved patient survival. We therefore identify palbociclib as a therapeutic approach to dramatically enhance neuroblastoma differentiation efficacy that could be used in combination with retinoic acid to improve patient outcomes.

Subacute cutaneous lupus erythematosus following ribociclib therapy for metastatic breast cancer

INTRODUCTION

Drug-induced subacute cutaneous lupus erythematosus (DI-SCLE) has been associated with drugs with different mechanisms of action, including anti-hypertensives, tumour necrosis factor-α inhibitors and even some chemotherapy medicines. In the last years, a few reports have been described in patients treated with cyclin-dependent kinase (CDK) 4/6 inhibitors, palbociclib and abemaciclib.

CASE REPORT

Here, we describe a case of DI-SCLE in association with ribociclib and exemestane in a woman diagnosed with metastatic breast cancer.

MANAGEMENT AND OUTCOME

Topical mometasone was prescribed for two weeks with complete resolution of lesions, also abemaciclib was substituted for ribociclib, and the patient had stable disease with no relapse of DI-SCLE.

DISCUSSION

To our knowledge, this is the first report of ribociclib-induced SCLE but based on the DI-SCLE reported cases associated others CDK4/6 inhibitors, the role of this family of drugs in dermatopathology must be further investigated.

Combined Mcl-1 and YAP1/TAZ inhibition for treatment of metastatic uveal melanoma

Uveal melanoma is the most common intraocular tumor in adults, representing approximately 5% of all melanoma cases. Up to 50% of uveal melanoma patients develop metastases that are resistant to most of the commonly used antineoplastic treatments. Virtually all uveal melanoma tumors harbor activating mutations in GNAQ or GNA11 , encoding Gαq and Gα11, respectively. Constant activity of these proteins causes deregulation of multiple downstream signaling pathways including PKC, MAPK and YAP1/TAZ. While the importance of YAP1 signaling for the proliferation of uveal melanoma has recently been demonstrated, much less is known about the paralog of YAP1 transcriptional coactivator, named TAZ; however, similar to YAP1, TAZ is expected to be a therapeutic target in uveal melanoma. We performed a small-scale drug screen to discover a compound synergistically inhibiting uveal melanoma proliferation/survival in combination with YAP1/TAZ inhibition. We found that the combination of genetic depletion of YAP1/TAZ together with Mcl-1 inhibition demonstrates a synergistic inhibitory effect on the viability of uveal melanoma cell lines. Similarly, indirect attenuation of the YAP1/TAZ signaling pathway with an inhibitor of the mevalonate pathway, that is, the geranyl-geranyl transferase inhibitor GGTI-298, synergizes with Mcl-1 inhibition. This combination could be potentially used as a treatment for metastatic uveal melanoma.

Abemaciclib restricts HCMV replication by suppressing pUL97-mediated phosphorylation of SAMHD1

Human cytomegalovirus (HCMV) is a herpesvirus that causes life-threatening infections in newborns or immunosuppressed patients. For viral replication, HCMV establishes a network of cellular interactions, among others cyclin-dependent kinases (CDK). Furthermore, HCMV encodes pUL97, a viral kinase, which is a CDK-homologue. HCMV uses pUL97 in order to phosphorylate and thereby antagonize SAMHD1, an antiviral host cell factor. Since HCMV has several mechanisms to evade restriction by SAMHD1, we first analyzed the kinetics of SAMHD1-inactivation and found that phosphorylation of SAMHD1 by pUL97 occurs directly after infection of macrophages. We hence hypothesized that inhibition of this process qualifies as efficient antiviral target and FDA approved CDK-inhibitors (CDKIs) might be potent antivirals that prevent the inactivation of SAMHD1. Indeed, Abemaciclib, a 2nd generation CDKI exhibited superior IC50s against HCMV in infected macrophages and the antiviral activity largely relied on its ability to block pUL97-mediated SAMHD1-phosphorylation. Altogether, our study highlights the therapeutic potential of clinically-approved CDKIs as antivirals against HCMV, sheds light on their mode of action and establishes SAMHD1 as a valid and highly potent therapeutic target.

Randomized Phase II Trial of Endocrine Therapy With or Without Ribociclib After Progression on Cyclin-Dependent Kinase 4/6 Inhibition in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: MAINTAIN Trial

PURPOSE

Cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) with endocrine therapy (ET) improves progression-free survival (PFS) and overall survival (OS) in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). Although preclinical and clinical data demonstrate a benefit in changing ET and continuing a CDK4/6i at progression, no randomized prospective trials have evaluated this approach.

METHODS

In this investigator-initiated, phase II, double-blind placebo-controlled trial in patients with HR+/HER2- MBC whose cancer progressed during ET and CDK4/6i, participants switched ET (fulvestrant or exemestane) from ET used pre-random assignment and randomly assigned 1:1 to the CDK4/6i ribociclib versus placebo. PFS was the primary end point, defined as time from random assignment to disease progression or death. Assuming a median PFS of 3.8 months with placebo, we had 80% power to detect a hazard ratio (HR) of 0.58 (corresponding to a median PFS of at least 6.5 months with ribociclib) with 120 patients randomly assigned using a one-sided log-rank test and significance level set at 2.5%.

RESULTS

Of the 119 randomly assigned participants, 103 (86.5%) previously received palbociclib and 14 participants received ribociclib (11.7%). There was a statistically significant PFS improvement for patients randomly assigned to switched ET plus ribociclib (median, 5.29 months; 95% CI, 3.02 to 8.12 months) versus switched ET plus placebo (median, 2.76 months; 95% CI, 2.66 to 3.25 months) HR, 0.57 (95% CI, 0.39 to 0.85); P = .006. At 6 and 12 months, the PFS rate was 41.2% and 24.6% with ribociclib, respectively, compared with 23.9% and 7.4% with placebo.

CONCLUSION

In this randomized trial, there was a significant PFS benefit for patients with HR+/HER2- MBC who switched ET and received ribociclib compared with placebo after previous CDK4/6i and different ET.

Ribociclib Hybrid Lipid-Polymer Nanoparticle Preparation and Characterization for Cancer Treatment

Ribociclib is a newly approved orally administered drug for breast cancer. This study aimed to prepare, characterize, and evaluate hybrid lipid-polymer nanoparticles (PLNs) of ribociclib to enhance its in vitro dissolution rate, pharmacokinetics, and anticancer efficacy. Ribociclib-loaded PLNs were prepared by solvent evaporation using the Box-Behnken design to optimize formulation variables. Particle size, entrapment efficiency, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), in vitro release cytotoxicity, molecular modeling, and pharmacokinetic studies were examined. The ribociclib-loaded PLN (formula 1, F1) was optimized in terms of particle size (266.9 ± 4.61 nm) and encapsulation efficiency (59.1 ± 2.57 mg/mL). DSC and thermogravimetric characterization showed the absence of a crystalline structure in the prepared PLNs, confirmed by FTIR, and showed no interactions between the components and the drug. AFM showed well-dispersed heterogeneously shaped nanoparticles. The in vitro release profile exhibited significant results for the optimized formula, reaching 100% at 600 and 90 min at pH 6.8 and 1.2, respectively. The low IC₅₀ obtained by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay suggests that optimized PLN might serve as an effective delivery vehicle for cancer treatment, especially breast and lung cancer. Molecular modeling revealed several hydrogen bonds. A pharmacokinetic study in rats showed that the ribociclib formula had a 6.5-fold increase in maximum concentration (C_max) and a 5.6-fold increase in area under the curve (AUC). Regarding the everted intestinal sac absorption, formula 1 increased ribociclib penetration relative to the physical combination and pure medication. In conclusion, optimized PLNs with enhanced physicochemical and cytotoxic properties and improved pharmacokinetic parameters were successfully prepared.

Targeting Human Proteins for Antiviral Drug Discovery and Repurposing Efforts: A Focus on Protein Kinases

Despite the great technological and medical advances in fighting viral diseases, new therapies for most of them are still lacking, and existing antivirals suffer from major limitations regarding drug resistance and a limited spectrum of activity. In fact, most approved antivirals are directly acting antiviral (DAA) drugs, which interfere with viral proteins and confer great selectivity towards their viral targets but suffer from resistance and limited spectrum. Nowadays, host-targeted antivirals (HTAs) are on the rise, in the drug discovery and development pipelines, in academia and in the pharmaceutical industry. These drugs target host proteins involved in the virus life cycle and are considered promising alternatives to DAAs due to their broader spectrum and lower potential for resistance. Herein, we discuss an important class of HTAs that modulate signal transduction pathways by targeting host kinases. Kinases are considered key enzymes that control virus-host interactions. We also provide a synopsis of the antiviral drug discovery and development pipeline detailing antiviral kinase targets, drug types, therapeutic classes for repurposed drugs, and top developing organizations. Furthermore, we detail the drug design and repurposing considerations, as well as the limitations and challenges, for kinase-targeted antivirals, including the choice of the binding sites, physicochemical properties, and drug combinations.

An Overview of CDK Enzyme Inhibitors in Cancer Therapy

The ability to address the cell cycle in cancer therapy brings up new medication development possibilities. Cyclin-dependent kinases are a group of proteins that control the progression of the cell cycle. The CDK/cyclin complexes are activated when specific CDK sites are phosphorylated. Because of their non-selectivity and severe toxicity, most first-generation CDK inhibitors (also known as pan-CDK inhibitors) have not been authorized for clinical usage. Despite this, significant progress has been made in allowing pan-CDK inhibitors to be employed in clinical settings. Pan-CDK inhibitors' toxicity and side effects have been lowered in recent years because of the introduction of combination therapy techniques. As a result of this, pan-CDK inhibitors have regained a lot of clinical potential as a combination therapy approach. The CDK family members have been introduced in this overview, and their important roles in cell cycle control have been discussed. Then, we have described the current state of CDK inhibitor research, with a focus on inhibitors other than CDK4/6. We have mentioned first-generation pan-CDKIs, flavopiridol and roscovitine, as well as second-generation CDKIs, dinaciclib, P276-00, AT7519, TG02, roniciclib, and RGB-286638, based on their research phases, clinical trials, and cancer targeting. CDKIs are CDK4/6, CDK7, CDK9, and CDK12 inhibitors. Finally, we have looked into the efficacy of CDK inhibitors and PD1/PDL1 antibodies when used together, which could lead to the development of a viable cancer treatment strategy.

A deep dive into CDK4/6 inhibitors: Evaluating real world toxicities and treatment paradigms in the elderly population

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors have become part of the standard of care in the treatment of hormone receptor positive, Her2Neu negative metastatic breast cancer. There is concern regarding the efficacy and potential increased cyclin-dependent kinase 4/6 inhibitors toxicity in the geriatric population in the community compared to the clinical trial population.

METHODS

We evaluated patients treated with cyclin-dependent kinase 4/6 inhibitors from 2015 to 2019 and stratified according to age ≥70 and <70 years. Complete blood count from the first two cycles was recorded. Rates of hematologic toxicities, dose interruptions and reductions, progression-free survival, and overall survival were compared between both groups. We sought to assess the hematologic toxicities between the age groups and the relationship between previous chemotherapy exposure, bone metastasis and starting cyclin-dependent kinase 4/6 inhibitors dose with progression-free survival and overall survival.

RESULTS

A total of 202 patients were included, 73 were ≥70 years and 129 were <70 years of age. There was no association between age group and grade of neutropenia or thrombocytopenia. There was a profound association between progression-free survival and overall survival and starting dose, where patients with recommended starting dose had higher progression-free survival and overall survival than those with a reduced dose (p = 0.0003 and p = 0.04).

CONCLUSIONS

Our study showed similar progression-free survival and overall survival between age groups without significant differences in neutropenia or thrombocytopenia toxicity. Nevertheless, we found an association between starting dose and progression-free survival and overall survival that has not been previously reported. Given the good tolerability across age groups and the improvement in progression-free survival and overall survival, patients should be treated at the cyclin-dependent kinase 4/6 inhibitors recommended dose and monitored appropriately.

Pyrrole-based EGFR inhibitors for the treatment of NCSLC: Binding modes and SARs investigations

The treatment of advanced non-small cell lung cancer (NSCLC) has made substantial progress due to the rapid development of small molecule targeted therapy, with dramatically prolonged survival. As an effective drug for the treatment of NSCLC, epidermal growth factor receptor (EGFR) inhibitors are currently experiencing issues like severe adverse events and drug resistance. It is urgent to develop novel types of EGFR inhibitors to overcome the abovementioned limitations. Pyrrole always works well as a probe for the creation of novel medication candidates for hard-to-treat conditions like lung cancer. Although the design, synthesis, and biological assays of pyrrole derivatives have been reported, their inhibitory actions against the receptor tyrosine kinase (RTK) EGFR have not been in-depthly studied. This review highlights the small molecule EGFR inhibitors containing pyrrole heterocyclic pharmacophores in recent years, and the research on their mechanism, biological activity, and structure-activity relationship (SAR).

Anti-cancer drug molecules targeting cancer cell cycle and proliferation

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

ACTR5 controls CDKN2A and tumor progression in an INO80-independent manner

Epigenetic dysregulation of cell cycle is a hallmark of tumorigenesis in multiple cancers, including hepatocellular carcinoma (HCC). Nonetheless, the epigenetic mechanisms underlying the aberrant cell cycle signaling and therapeutic response remain unclear. Here, we used an epigenetics-focused CRISPR interference screen and identified ACTR5 (actin-related protein 5), a component of the INO80 chromatin remodeling complex, to be essential for HCC tumor progression. Suppression of ACTR5 activated CDKN2A expression, ablated CDK/E2F-driven cell cycle signaling, and attenuated HCC tumor growth. Furthermore, high-density CRISPR gene tiling scans revealed a distinct HCC-specific usage of ACTR5 and its interacting partner IES6 compared to the other INO80 complex members, suggesting an INO80-independent mechanism of ACTR5/IES6 in supporting the HCC proliferation. Last, our study revealed the synergism between ACTR5/IES6-targeting and pharmacological inhibition of CDK in treating HCC. These results indicate that the dynamic interplay between epigenetic regulators, tumor suppressors, and cell cycle machinery could provide novel opportunities for combinational HCC therapy.

Antitumor response and quality of life: is there a need to sacrifice? Clinical observation: long-term and safe control of the disease using a combination of ribociclib with letrozole. Case report

Metastatic luminal B HER2-negative breast cancer (HR+/HER2- mBC) occupies a leading place in the global structure of morbidity and mortality among women. The current gold standard of first-line treatment is the combination of CDK4/6 inhibitors with aromatase inhibitors, among which ribociclib with letrozole is distinguished. According to the MONALEESA-2 study, the addition of ribociclib to letrozole significantly increased the median overall survival to 63.9 months, reducing the risk of death by 24%. The safety profile of the combination is manageable, and the development of adverse events led to the interruption of therapy only in 7.5% of cases. A study of the actual clinical practice of CompLEEment-1 also confirmed the safety and effectiveness of the combination. Maintaining and improving the quality of life is one of the main tasks in the treatment of patients with HR+/HER2- mBC. According to the MONALEESA-2 study, the addition of ribociclib significantly affects the maintenance of quality of life and leads to a decrease in the intensity of pain syndrome. The published data allowed us to assign a combination of ribociclib and letrozole 4 points on the ESMO-MCBS scale. The safety of long-term use of the combination in the first line of treatment illustrated by clinical observation. The patient's progression-free survival during therapy was 40 months, which significantly exceeds the data of the MONALEESA-2 and CompLEEment-1 studies. The maximum effect (partial response according to RECIST 1.1 -40%) achieved after 24 weeks and persisted for 24 months. Clinically, the patient noted a decrease in the severity of the pain syndrome after 8 weeks of therapy. Against the background of therapy, it was possible to maintain the quality of life without sacrificing antitumor efficacy.

The Renaissance of CDK Inhibitors in Breast Cancer Therapy: An Update on Clinical Trials and Therapy Resistance

Simple Summary

Cyclin-dependent kinase inhibitors (palbociclib (Ibrance), ribociclib (Kisqali), and abemaciclib (Verzenio)), targeting aberrant cell-cycle activity have been evaluated extensively in clinical trials. Significant delays in progression free survival and overall survival are now documented with each agent in estrogen receptor positive and human epidermal growth factor receptor two negative advanced breast cancer including luminal B breast cancer. Therapy resistance, driven by chromosomal instability, results in genomic rearrangements, activation of cell-cycle components (cyclin E/cdk2 in Rb⁻ tumors, cyclin D1 in growth factor activated pathways), and the immune response. Molecular analysis of therapy resistant tumors may provide the rational basis for new therapies (brivanib, CYC065, WEE1 kinase and other inhibitors). Luminal B breast cancer is enriched for cyclin D1 overexpression and the chromosomal instability gene signature. The molecular mechanisms governing chromosomal instability in luminal B breast cancer remain poorly understood. Co-targeting of chromosomal instability may potentially reduce the prevalent escape mechanisms that reduce the effectiveness of cyclin-dependent kinase inhibitors.

Abstract

Cyclin-dependent kinases (CDKs) govern cell-cycle checkpoint transitions necessary for cancer cell proliferation. Recent developments have illustrated nuanced important differences between mono CDK inhibitor (CDKI) treatment and the combination therapies of breast cancers. The CDKIs that are currently FDA-approved for breast cancer therapy are oral agents that selectively inhibit CDK4 and CDK6, include palbociclib (Ibrance), ribociclib (Kisqali), and abemaciclib (Verzenio). CDKI therapy is effective in hormone receptor positive (HR⁺), and human epidermal growth factor receptor two negative (HER2⁻) advanced breast cancers (ABC) malignancies, but remains susceptible due to estrogen and progesterone receptor overexpression. Adding a CDK4/6I to endocrine therapy increases efficacy and delays disease progression. Given the side effects of CDKI, identifying potential new treatments to enhance CDKI effectiveness is essential. Recent long-term studies with Palbociclib, including the PALLAS and PENELOPE B, which failed to meet their primary endpoints of influencing progression-free survival, suggest a deeper mechanistic understanding of cyclin/CDK functions is required. The impact of CDKI on the anti-tumor immune response represents an area of great promise. CDKI therapy resistance that arises provides the opportunity for specific types of new therapies currently in clinical trials.

Small-molecule inhibitors, immune checkpoint inhibitors, and more: FDA-approved novel therapeutic drugs for solid tumors from 1991 to 2021

The United States Food and Drug Administration (US FDA) has always been a forerunner in drug evaluation and supervision. Over the past 31 years, 1050 drugs (excluding vaccines, cell-based therapies, and gene therapy products) have been approved as new molecular entities (NMEs) or biologics license applications (BLAs). A total of 228 of these 1050 drugs were identified as cancer therapeutics or cancer-related drugs, and 120 of them were classified as therapeutic drugs for solid tumors according to their initial indications. These drugs have evolved from small molecules with broad-spectrum antitumor properties in the early stage to monoclonal antibodies (mAbs) and antibody‒drug conjugates (ADCs) with a more precise targeting effect during the most recent decade. These drugs have extended indications for other malignancies, constituting a cancer treatment system for monotherapy or combined therapy. However, the available targets are still mainly limited to receptor tyrosine kinases (RTKs), restricting the development of antitumor drugs. In this review, these 120 drugs are summarized and classified according to the initial indications, characteristics, or functions. Additionally, RTK-targeted therapies and immune checkpoint-based immunotherapies are also discussed. Our analysis of existing challenges and potential opportunities in drug development may advance solid tumor treatment in the future.

Phase I trial of ribociclib with platinum chemotherapy in recurrent ovarian cancer

BACKGROUND

New therapeutic combinations to improve the outcome of ovarian cancer patients are clearly needed. Preclinical studies with ribociclib (LEE-011), a CDK4/6 cell cycle checkpoint inhibitor, demonstrate a synergistic effect with platinum chemotherapy and efficacy as a maintenance therapy after chemotherapy. We tested the safety and initial efficacy of ribociclib in combination with platinum-based chemotherapy in recurrent ovarian cancer.

METHODS

This phase I trial combined weekly carboplatin and paclitaxel chemotherapy with ribociclib followed by ribociclib maintenance in patients with recurrent platinum-sensitive ovarian cancer. Primary objectives were safety and maximum tolerated dose (MTD) of ribociclib when given with platinum and taxane chemotherapy. Secondary endpoints were response rate (RR) and progression-free survival (PFS).

RESULTS

Thirty-five patients were enrolled. Patients had a mean 2.5 prior lines of chemotherapy, and 51% received prior maintenance therapy with Poly (ADP-ribose) polymerase inhibitors (PARPi) and/or Bevacizumab. The MTD was 400mg. The most common AEs included anemia (82.9%), neutropenia (82.9%), fatigue (82.9%), and nausea (77.1%). Overall RR was 79.3% with a stable disease (SD) rate of 18% resulting in a clinical benefit rate of 96.6%. The PFS was 11.4 months. RR and PFS did not differ based on number of lines of prior chemotherapy or prior maintenance therapy.

CONCLUSIONS

This work demonstrates the combination of ribociclib with chemotherapy in ovarian cancer is feasible and safe. With a clinical benefit rate of 97%, this work provides encouraging evidence of clinical efficacy in patients with recurrent platinum-sensitive disease.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT03056833.

FUNDING

This investigator-initiated trial was supported by Novartis who provided drug and funds for trial execution.

The Role of CDK Pathway Dysregulation and Its Therapeutic Potential in Soft Tissue Sarcoma

Soft tissue sarcomas (STSs) are tumors that are challenging to treat due to their pathologic and molecular heterogeneity and their tumor biology that is not yet fully understood. Recent research indicates that dysregulation of cyclin-dependent kinase (CDK) signaling pathways can be a strong driver of sarcogenesis. CDKs are enzyme forms that play a crucial role in cell-cycle control and transcription. They belong to the protein kinases group and to the serine/threonine kinases subgroup. Recently identified CDK/cyclin complexes and established CDK/cyclin complexes that regulate the cell cycle are involved in the regulation of gene expression through phosphorylation of critical components of transcription and pre-mRNA processing mechanisms. The current and continually growing body of data shows that CDKs play a decisive role in tumor development and are involved in the proliferation and growth of sarcoma cells. Since the abnormal expression or activation of large numbers of CDKs is considered to be characteristic of cancer development and progression, dysregulation of the CDK signaling pathways occurs in many subtypes of STSs. This review discusses how reversal and regulation can be achieved with new therapeutics and summarizes the current evidence from studies regarding CDK modulation for STS treatment.

Glioblastoma: Current Status, Emerging Targets, and Recent Advances

Glioblastoma (GBM) is a highly malignant brain tumor characterized by a heterogeneous population of genetically unstable and highly infiltrative cells that are resistant to chemotherapy. Although substantial efforts have been invested in the field of anti-GBM drug discovery in the past decade, success has primarily been confined to the preclinical level, and clinical studies have often been hampered due to efficacy-, selectivity-, or physicochemical property-related issues. Thus, expansion of the list of molecular targets coupled with a pragmatic design of new small-molecule inhibitors with central nervous system (CNS)-penetrating ability is required to steer the wheels of anti-GBM drug discovery endeavors. This Perspective presents various aspects of drug discovery (challenges in GBM drug discovery and delivery, therapeutic targets, and agents under clinical investigation). The comprehensively covered sections include the recent medicinal chemistry campaigns embarked upon to validate the potential of numerous enzymes/proteins/receptors as therapeutic targets in GBM.

Continuous treatment with abemaciclib leads to sustained and efficient inhibition of breast cancer cell proliferation

Abemaciclib is an oral, selective cyclin-dependent kinase 4 & 6 inhibitor (CDK4 & 6i), approved for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (ABC) as monotherapy for endocrine refractory disease, and with endocrine therapy (ET) for initial treatment and after progression on ET. Abemaciclib has also shown clinical activity in combination with ET in patients with high risk early BC (EBC). Here, we examined the preclinical attributes of abemaciclib and other CDK4 & 6i using biochemical and cell-based assays. In vitro, abemaciclib preferentially inhibited CDK4 kinase activity versus CDK6, resulting in inhibition of cell proliferation in a panel of BC cell lines with higher average potency than palbociclib or ribociclib. Abemaciclib showed activity regardless of HER2 amplification and phosphatidylinositol 3-kinase (PI3KCA) gene mutation status. In human bone marrow progenitor cells, abemaciclib showed lower impact on myeloid maturation than other CDK4 & 6i when tested at unbound concentrations similar to those observed in clinical trials. Continuous abemaciclib treatment provided profound inhibition of cell proliferation, and triggered senescence and apoptosis. These preclinical results support the unique efficacy and safety profile of abemaciclib observed in clinical trials.

Solubilization of a novel antitumor drug ribociclib in water and ten different organic solvents at different temperatures

OBJECTIVE

This study reports new solubility and physicochemical data for ribociclib (RCB) in water and ten organic solvents including "methanol (MeOH), ethanol (EtOH), isopropyl alcohol (IPA), n-butanol (n-BuOH), propylene glycol (PG), polyethylene glycol-400 (PEG-400), acetone, ethyl acetate (EA), Transcutol-HP (THP), and dimethyl sulfoxide (DMSO)" at 293.2-313.2 K and 101.1 kPa.

SIGNIFICANCE

The obtained data are useful for the industrial applications of RCB.

METHODS

The solubility of RCB was measured and regressed using "van't Hoff, Buchowski-Ksiazczak λh, the modified Apelblat, and Jouyban models."

RESULTS

The overall deviations of <4.0% were recorded for all four models. The maximum mole fraction solubility of RCB was 2.66 × 10^-2 in PEG-400 at 313.2 K, however, the lowest one was in the water. The RCB solubility increased with temperature and the order followed in the water and ten different organic solvents was PEG-400 (2.66 × 10^-2) > THP (1.00 × 10^-2) > PG (5.39 × 10^-3) > DMSO (5.00 × 10^-3) > n-BuOH (3.23 × 10^-3) > acetone (3.11 × 10^-3) > IPA (1.58 × 10^-3) > EA (1.41 × 10^-3) > EtOH (1.37 × 10^-3) > MeOH (8.10 × 10^-4) > water (2.38 × 10^-5) at 313.2 K. The maximum solute-solvent interactions were found in RCB-PEG-400 in comparison with other combination of RCB and solvents. "Apparent thermodynamic analysis" indicated an "endothermic and entropy-driven dissolution" of RCB in water and ten organic solvents.

CONCLUSIONS

Based on all these data and observations, PEG-400 can be used as the best co-solvent for RCB solubilization.

Combining a CDK4/6 Inhibitor With Pemetrexed Inhibits Cell Proliferation and Metastasis in Human Lung Adenocarcinoma

Background

Recent clinical trials of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in human lung adenocarcinoma (LUAD) have not achieved satisfactory results. The disappointing results of single-drug treatments have prompted studies about synergistic therapies of CDK4/6i with other drugs. We aimed to test the anti-tumor effect of ribociclib (a CDK4/6i) combined with pemetrexed on LUAD and the potential mechanisms.

Methods

Cell lines were exposed to ribociclib and pemetrexed at different doses. Antitumor effects were measured using growth inhibition. Cell cycle distribution and apoptosis were evaluated using flow cytometry. Cell migration and invasion were measured using wound healing and transwell invasion assays, respectively. The expression levels of proteins were analyzed using western blotting. Mice xenograft models were used for validation in vivo.

Results

Synergism was associated with a combination of cell cycle effects from both agents. Cell cycle analysis revealed that pemetrexed blocked cells in the S phase, whereas ribociclib arrested cells in the G1 phase. Concomitant treatment with pemetrexed and ribociclib resulted in a significantly stronger antitumor ability than treatment alone. We also found that ribociclib strongly enhanced the pro-apoptotic activity of pemetrexed via the caspase/bcl-2 signaling pathway. In addition, we report for the first time that combination treatment with ribociclib and pemetrexed significantly inhibits the migration and invasion of LUAD cells.

Conclusions

Combining ribociclib and pemetrexed showed a powerful ability to inhibit cancer proliferation, invasion, and metastasis, and it holds potential as a novel effective combinative therapy for patients with LUAD.

Targeting Cell Cycle Progression in HER2+ Breast Cancer: An Emerging Treatment Opportunity

The development of HER2-targeted therapies has dramatically improved patient survival and patient management and increased the quality of life in the HER2+ breast cancer patient population. Due to the activation of compensatory pathways, patients eventually suffer from resistance to HER2-directed therapies and develop a more aggressive disease phenotype. One of these mechanisms is the crosstalk between ER and HER2 signaling, especially the CDK4/6-Cyclin D-Rb signaling axis that is commonly active and has received attention for its potential role in regulating tumor progression. CDK 4/6 inhibitors interfere with the binding of cell-cycle-dependent kinases (CDKs) with their cognate partner cyclins, and forestall the progression of the cell cycle by preventing Rb phosphorylation and E2F release that consequentially leads to cancer cell senescence. CDK 4/6 inhibitors, namely, palbociclib, ribociclib, and abemaciclib, in combination with anti-estrogen therapies, have shown impressive outcomes in hormonal receptor-positive (HR+) disease and have received approval for this disease context. As an extension of this concept, preclinical/clinical studies incorporating CDK 4/6 inhibitors with HER2-targeted drugs have been evaluated and have shown potency in limiting tumor progression, restoring therapeutic sensitivity, and may improving the management of the disease. Currently, several clinical trials are examining the synergistic effects of CDK 4/6 inhibitors with optimized HER2-directed therapies for the (ER+/-) HER2+ population in the metastatic setting. In this review, we aim to interrogate the burden of HER2+ disease in light of recent treatment progress in the field and examine the clinical benefit of CDK 4/6 inhibitors as a replacement for traditional chemotherapy to improve outcomes in HER2+ breast cancer.

Super-Enhancers, Phase-Separated Condensates, and 3D Genome Organization in Cancer

3D chromatin organization plays an important role in transcription regulation and gene expression. The 3D genome is highly maintained by several architectural proteins, such as CTCF, Yin Yang 1, and cohesin complex. This structural organization brings regulatory DNA elements in close proximity to their target promoters. In this review, we discuss the 3D chromatin organization of super-enhancers and their relationship to phase-separated condensates. Super-enhancers are large clusters of DNA elements. They can physically contact with their target promoters by chromatin looping during transcription. Multiple transcription factors can bind to enhancer and promoter sequences and recruit a complex array of transcriptional co-activators and RNA polymerase II to effect transcriptional activation. Phase-separated condensates of transcription factors and transcriptional co-activators have been implicated in assembling the transcription machinery at particular enhancers. Cancer cells can hijack super-enhancers to drive oncogenic transcription to promote cell survival and proliferation. These dysregulated transcriptional programs can cause cancer cells to become highly dependent on transcriptional regulators, such as Mediator and BRD4. Moreover, the expression of oncogenes that are driven by super-enhancers is sensitive to transcriptional perturbation and often occurs in phase-separated condensates, supporting therapeutic rationales of targeting SE components, 3D genome organization, or dysregulated condensates in cancer.

Cost-effectiveness of Ribociclib in HER2- negative breast cancer: A synthesis of current evidence

Background

The main aim of this study was to investigate the cost-effectiveness of Ribociclib in the treatment of patients with breast cancer by assessing the published evidence.

Method

A systematic review of the published literature was conducted to identify the economic evaluations/cost-effectiveness study of Ribociclib. In this study, several databases were inspected, including PubMed, NHS Economic Evaluation, Cochran, and Scopus. Studies were eligible if they assessed the cost-effectiveness of Ribociclib and reported incremental cost-effectiveness ratio (ICER). The study was performed and conducted following the PRISMA reporting guidelines.

Results

Of 70 studies identified, 8 articles meet our inclusion criteria. The cost-effectiveness threshold varied from $24,144.18 in Spain to $198,000/QALY in the USA. Moreover, the result demonstrated that the mean ICER varied across different countries $1,863.47/QALY in Spain and $813,132/QALY in the USA.

Conclusion

Among all CDK4/6 inhibitors medications, current evidence indicated that the use of Ribociclib for HER2- negative breast cancer management was beneficial and considered to be cost-effective. Future research is needed to investigate the role of Ribociclib in long-term treatment.

Biomarkers for Cyclin-Dependent Kinase 4/6 Inhibitors in the Treatment of Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Advanced/Metastatic Breast Cancer: Translation to Clinical Practice

PURPOSE

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have emerged as effective treatments for patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced/metastatic breast cancer (mBC). Dedicated research efforts have been undertaken to find predictive biomarkers of response or resistance to these therapies although no molecular biomarkers for mBC have reached the clinic so far. This review aims to summarize and evaluate the performance of biomarkers in predicting progression-free survival in phase II and III clinical trials of CDK4/6 inhibitors in HR+/HER2- mBC.

METHODS

For this narrative review, a structured literature search of PubMed, Embase, and the Cochrane library (CENTRAL) was performed. Phase II or III clinical trials of a CDK4/6 inhibitor in patients with HR+/HER2- mBC reporting on at least one molecular biomarker analysis of progression-free survival were included. Publications and selected conference abstracts were included up until November 2021.

RESULTS

Twenty-two articles reporting biomarker results of 12 clinical trials were included. Retinoblastoma protein status and cyclin E1 mRNA expression were promising baseline biomarkers, whereas PIK3CA circulating tumor DNA ratio on treatment relative to baseline, change in plasma thymidine kinase activity, and circulating tumor cell count were potential dynamic biomarkers of response. A number of biomarkers were unsuccessful, despite a strong mechanistic rationale, and others are still being explored.

CONCLUSION

Our review of clinical trials showed that there are a number of promising biomarkers at baseline and several dynamic biomarkers that might predict response to CDK4/6 inhibitors. Validation of these findings and assessment of clinical utility are crucial to make the final translation to clinical practice. Better understanding of disease heterogeneity and further elucidation of resistance mechanisms could inform future studies of rationally selected biomarkers.

Structure-Based Design of 2-Aminopurine Derivatives as CDK2 Inhibitors for Triple-Negative Breast Cancer

Cyclin-dependent kinase 2 (CDK2) regulates the progression of the cell cycle and is critically associated with tumor growth. Selective CDK2 inhibition provides a potential therapeutic benefit against certain tumors. Purines and related heterocycle (e.g., R-Roscovitine) are important scaffolds in the development of CDK inhibitors. Herein, we designed a new series of 2-aminopurine derivatives based on the fragment-centric pocket mapping analysis of CDK2 crystal structure. Our results indicated that the introduction of polar substitution at the C-6 position of purine would be beneficial for CDK2 inhibition. Among them, compound 11l showed good CDK2 inhibitory activity (IC₅₀ = 19 nM) and possessed good selectivity against other CDKs. Further in vitro tests indicated that compound 11l possesses anti-proliferation activity in triple-negative breast cancer (TNBC) cells. Moreover, molecular dynamics simulation suggested the favorable binding mode of compound 11l, which may serve as a new lead compound for the future development of CDK2 selective inhibitors.