Spectrum and Degree of CDK Drug Interactions Predicts Clinical Performance

Radiosensitizing effects of CDK4/6 inhibitors in hormone receptor-positive and HER2-negative breast cancer mediated downregulation of DNA repair mechanism and NF-κB-signaling pathway

CDK4/6 inhibitors combined with endocrine therapy prolonged survival in hormone receptor (HR)-positive and HER2-negative advanced breast cancer. We investigated whether CDK4/6 inhibitors enhance radiosensitivity and their underlying mechanisms of this subtype of breast cancer. In vitro and in vivo experiments were conducted using two HR-positive and HER2-negative breast cancer cell lines (MCF-7 and T-47D), CDK4/6 inhibitors (ribociclib and palbociclib) and radiotherapy (RT) to assess the biological functions and mechanisms. The radiation-enhancing effect was assessed using clonogenic assays; γH2AX and 53BP1 levels were assessed by immunofluorescence to evaluate DNA damage. The levels of phospho (p)-ERK, c-Myc, and DNA-double strand break (DSB)-related molecules, p-DNA-PKcs, Rad51, and p-ATM, were assessed by western blotting. We used an NF-κB p65 transcription factor assay kit to evaluate NF-κB activity. We evaluated the antitumor effect of the combination of RT and ribociclib through the MCF-7 orthotopic xenograft model. The synergistic effects of combining RT with ribociclib and palbociclib pretreatment were demonstrated by clonogenic assay. CDK4/6 inhibitors synergistically increased the numbers of RT-induced γH2AX and 53BP1, downregulated the expression of p-DNA-PKcs, Rad51 and p-ATM activated by RT, and reduced RT-triggering p-ERK expression, NF-κB activation, and its down-streaming gene, c-Myc. Combined ribociclib and RT reduced the growth of MCF-7 cell xenograft tumors, and downregulated the immunohistochemical expression of p-ERK, p-NF-κB p65, and c-Myc compared to that in the control group. Combining CDK4/6 inhibitors enhanced radiosensitivity of HR-positive and HER2-negative breast cancer cells at least by reducing DNA-DSB repair and weakening the activation of ERK and NF-κB signaling by RT.

Targeting cyclin-dependent kinases: From pocket specificity to drug selectivity

The development of selective modulators of cyclin-dependent kinases (CDKs), a kinase family with numerous members and functional variations, is a significant preclinical challenge. Recent advancements in crystallography have revealed subtle differences in the highly conserved CDK pockets. Exploiting these differences has proven to be an effective strategy for achieving excellent drug selectivity. While previous reports briefly discussed the structural features that lead to selectivity in individual CDK members, attaining inhibitor selectivity requires consideration of not only the specific structures of the target CDK but also the features of off-target members. In this review, we summarize the structure-activity relationships (SARs) that influence selectivity in CDK drug development and analyze the pocket features that lead to selectivity using molecular-protein binding models. In addition, in recent years, novel CDK modulators have been developed, providing more avenues for achieving selectivity. These cases were also included. We hope that these efforts will assist in the development of novel CDK drugs.

Advances in SHP2 tunnel allosteric inhibitors and bifunctional molecules

SHP2 is a non-receptor tyrosine phosphatase encoded by PTPN11, which performs the functions of regulating cell proliferation, differentiation, apoptosis, and survival through removing tyrosine phosphorylation and modulating various signaling pathways. The overexpression of SHP2 or its mutations is related to developmental diseases and several cancers. Numerous allosteric inhibitors with striking inhibitory potency against SHP2 allosteric pockets have recently been identified, and several SHP2 tunnel allosteric inhibitors have been applied in clinical trials to treat cancers. However, based on clinical results, the efficacy of single-agent treatments has been proven to be suboptimal. Most clinical trials involving SHP2 inhibitors have adopted drug combination strategies. This review briefly discusses the research progress on SHP2 allosteric inhibitors and pathway-dependent drug combination strategies for SHP2 in cancer therapy. In addition, we summarize the current bifunctional molecules of SHP2 and elaborate on the design and structural optimization strategies of these bifunctional molecules in detail, offering further direction for the research on novel SHP2 inhibitors.

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

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

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.

FDA-approved small molecule kinase inhibitors for cancer treatment (2001-2015): Medical indication, structural optimization, and binding mode Part I

The dysregulation of kinases has emerged as a major class of targets for anticancer drug discovery given its node roles in the etiology of tumorigenesis, progression, invasion, and metastasis of malignancies, which is validated by the FDA approval of 28 small molecule kinase inhibitor (SMKI) drugs for cancer treatment at the end of 2015. While the preclinical and clinical data of these drugs are widely presented, it is highly essential to give an updated review on the medical indications, design principles and binding modes of these anti-tumor SMKIs approved by the FDA to offer insights for the future development of SMKIs with specific efficacy and safety.

Practical Guidance on Abemaciclib in Combination with Adjuvant Endocrine Therapy for Treating Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative High-Risk Early Breast Cancer

The most common subtype of breast cancer is hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, accounting for 65-70% of all breast cancer cases diagnosed in the United States. Until 2015, single-agent endocrine therapy (ET) was the recommended first-line treatment for metastatic HR-positive, HER2-negative breast cancer. However, the paradigm has since shifted, as targeted therapy is now recommended in combination with ET. The cyclin-dependent kinase (CDK) 4/6 inhibitors have revolutionized the treatment of this breast cancer subtype, and combining either palbociclib, ribociclib, or abemaciclib with ET is now the standard first-line treatment for metastatic disease. Results of clinical trials in the metastatic setting have demonstrated that treatment with the combination of a CDK4/6 inhibitor and ET rather than ET alone is associated with longer overall survival, longer progression-free survival, and better objective response rates. Each of the CDK4/6 inhibitors has been investigated in combination with ET in patients with early-stage HR-positive, HER2-negative breast cancer who are at high risk of relapse. In October 2021, abemaciclib was the first CDK4/6 inhibitor approved in combination with ET by the US Food and Drug Administration for adjuvant treatment of patients with HR-positive, HER2-negative, high-risk early breast cancer. Herein, we provide practical guidance on the use of abemaciclib in combination with ET for HR-positive, HER2-negative, high-risk early breast cancer to assist clinicians in their day-to-day practice, and we review clinically relevant topics of dosing, side effect management, sequencing and optimal timing for initiation, and patient selection.

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.

Comparative analysis of adverse events associated with CDK4/6 inhibitors based on FDA's adverse event reporting system: a case control pharmacovigilance study

BACKGROUND

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors marked a milestone in the breast cancer treatment. Due to the potential impact of adverse effects on treatment decisions and patient outcomes, careful consideration of the varying toxicities of CDK4/6 inhibitors is crucial, as three inhibitors-palbociclib, abemaciclib, and ribociclib-have been approved with differences in adverse event profiles. However, limitations in clinical trials call for urgent real-world safety studies to evaluate and compare the risk of adverse events (AEs) among these CDK4/6 inhibitors. Therefore, this study aimed to analyze AEs of CDK4/6 inhibitors and provide insights for clinical drug selection, using real world database.

METHODS

The AEs of CDK4/6 inhibitors in the FDA Adverse Event Reporting System (2015-2022) were analyzed. Four disproportionality methods were used to detect safety signals: reporting odds ratio (ROR), proportional reporting ratio, Bayesian Confidence Neural Network Propagation, and Multi-Item Gamma Poisson Shrinker. Venn analysis was used to compare and select common and specific AEs.

RESULTS

This study included 73,042 patients treated with palbociclib, 25,142 with ribociclib, and 7563 with abemaciclib. All three inhibitors had 27 common AEs. Palbociclib exhibited the highest ROR for hematologic toxicities, while ribociclib showed the highest ROR for macrocytosis, nail disorders, and hepatic lesions. Abemaciclib displayed the highest ROR for mucosal toxicity. Common signals for both palbociclib and ribociclib included hematologic toxicities, decreased immune responsiveness, and aphthous ulcers. Myelosuppression, oral pain, and pseudocirrhosis were common signals for palbociclib and abemaciclib. Anemia, hepatotoxicity, and pneumonitis were observed as common signals for ribociclib and abemaciclib. Furthermore, specific AEs associated with palbociclib included fatigue, alopecia, and stomatitis. For ribociclib, specific AEs included electrocardiogram QT prolongation, thrombocytopenia, and decreased hemoglobin. Abemaciclib was specifically linked to diarrhea, vomiting, and interstitial lung disease.

CONCLUSION

Our analysis revealed that palbociclib showed a higher risk of hematologic toxicity. Ribociclib showed higher risks of hepatotoxicity, nephrotoxicity, and QT prolongation. Abemaciclib showed higher risks of hepatotoxicity, gastrointestinal effects, interstitial lung disease, and thrombosis. These findings provide valuable insights for CDK4/6 inhibitor selection.

Discovery and preclinical evaluations of TQB3616, a novel CDK4-biased inhibitor

Among small-molecule CDK4/6 inhibitors (palbociclib, ribociclib, and abemaciclib) approved for metastatic breast cancers, abemaciclib has a more tolerable adverse effects in clinic. This is attributable to preferential inhibition of CDK4 over CDK6. In our search for a biased CDK4 inhibitor, we discovered a series of pyrimidine-indazole inhibitors. SAR studies led us to TQB3616 as a preferential CDK4 inhibitor. TQB3616 exhibited improvements in both enzymatic and cellular proliferation inhibitory potency when tested side-by-side with the FDA approved palbociclib and abemaciclib. TQB3616 also possessed favorable PK profile in multiple species. These differentiated properties, together with excellent GLP safety profile warranted TQB3616 moving to clinic. TQB3616 entered into clinical development in 2019 and currently in phase III clinical trials (NCT05375461, NCT05365178).

Homologous recombination proficient subtypes of high-grade serous ovarian cancer: treatment options for a poor prognosis group

Approximately 50% of tubo-ovarian high-grade serous carcinomas (HGSCs) have functional homologous recombination-mediated (HR) DNA repair, so-called HR-proficient tumors, which are often associated with primary platinum resistance (relapse within six months after completion of first-line therapy), minimal benefit from poly(ADP-ribose) polymerase (PARP) inhibitors, and shorter survival. HR-proficient tumors comprise multiple molecular subtypes including cases with CCNE1 amplification, AKT2 amplification or CDK12 alteration, and are often characterized as "cold" tumors with fewer infiltrating lymphocytes and decreased expression of PD-1/PD-L1. Several new treatment approaches aim to manipulate these negative prognostic features and render HR-proficient tumors more susceptible to treatment. Alterations in multiple different molecules and pathways in the DNA damage response are driving new drug development to target HR-proficient cancer cells, such as inhibitors of the CDK or P13K/AKT pathways, as well as ATR inhibitors. Treatment combinations with chemotherapy or PARP inhibitors and agents targeting DNA replication stress have shown promising preclinical and clinical results. New approaches in immunotherapy are also being explored, including vaccines or antibody drug conjugates. Many approaches are still in the early stages of development and further clinical trials will determine their clinical relevance. There is a need to include HR-proficient tumors in ovarian cancer trials and to analyze them in a more targeted manner to provide further evidence for their specific therapy, as this will be crucial in improving the overall prognosis of HGSC and ovarian cancer in general.

CDK4/6 inhibitors: The Devil is in the Detail

PURPOSE OF REVIEW

Update on the most recent clinical evidence on CDK4/6 inhibitors (CDK4/6i) in the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor (HER)2-negative breast cancer.

RECENT FINDINGS

Over the past decade, CDK4/6i have become part of the standard of care treatment of patients with both metastatic and high-risk early HR + /HER2- breast cancers. The three available CDK4/6i (palbociclib, ribociclib and abemaciclib) have been extensively studied in combination with endocrine therapy (ET) in metastatic breast cancer (mBC) with consistent prolongation of progression free survival; however, ribociclib has emerged as the preferred first line agent in mBC given overall survival benefit over endocrine monotherapy. In early BC, abemaciclib is the only currently approved agent while ribociclib has early positive clinical trial data. Toxicities and financial burden limit the use of CDK4/6i in all patients and resource-poor settings, and optimal timing of their use in mBC remains unclear. There is considerable evidence for the use of CDK4/6i in metastatic and early HR + /HER2- breast cancer, but knowledge gaps remain, and further research is necessary to better define their optimal use.

Abemaciclib pharmacology and interactions in the treatment of HR+/HER2- breast cancer: a critical review

Abemaciclib (ABE) in combination with endocrine therapy represents the mainstay treatment for either endocrine-resistant metastatic or high-risk early-stage HR+/HER2- breast cancer patients. Hence, an adequate knowledge of this agent pharmacodynamic, pharmacokinetic, and of its drug-drug interactions (DDIs) is crucial for an optimal patients management. Additionally, ABE interference with food and complementary/alternative medicines should be taken into account in the clinical practice. Several online tools allow to freely check DDIs and can be easily consulted before prescribing ABE. According to one of this instruments, ABE display the lowest number of interactions among the available cyclin-dependent kinase 4/6 inhibitors. Still, clinicians should be aware that online tools cannot replace the technical datasheet of the drug as well as a comprehensive clinical assessment for each patient. Here we critically review the main pharmacological features of ABE, then focusing on its potential interactions with drugs, food, and alternative medicine, in order to provide a guide for its optimal use in the treatment of HR+/HER2- breast cancer patients.

Ribociclib plus Endocrine Therapy in Early Breast Cancer

BACKGROUND

Ribociclib has been shown to have a significant overall survival benefit in patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. Whether this benefit in advanced breast cancer extends to early breast cancer is unclear.

METHODS

In this international, open-label, randomized, phase 3 trial, we randomly assigned patients with HR-positive, HER2-negative early breast cancer in a 1:1 ratio to receive ribociclib (at a dose of 400 mg per day for 3 weeks, followed by 1 week off, for 3 years) plus a nonsteroidal aromatase inhibitor (NSAI; letrozole at a dose of 2.5 mg per day or anastrozole at a dose of 1 mg per day for ≥5 years) or an NSAI alone. Premenopausal women and men also received goserelin every 28 days. Eligible patients had anatomical stage II or III breast cancer. Here we report the results of a prespecified interim analysis of invasive disease-free survival, the primary end point; other efficacy and safety results are also reported. Invasive disease-free survival was evaluated with the use of the Kaplan-Meier method. The statistical comparison was made with the use of a stratified log-rank test, with a protocol-specified stopping boundary of a one-sided P-value threshold of 0.0128 for superior efficacy.

RESULTS

As of the data-cutoff date for this prespecified interim analysis (January 11, 2023), a total of 426 patients had had invasive disease, recurrence, or death. A significant invasive disease-free survival benefit was seen with ribociclib plus an NSAI as compared with an NSAI alone. At 3 years, invasive disease-free survival was 90.4% with ribociclib plus an NSAI and 87.1% with an NSAI alone (hazard ratio for invasive disease, recurrence, or death, 0.75; 95% confidence interval, 0.62 to 0.91; P = 0.003). Secondary end points - distant disease-free survival and recurrence-free survival - also favored ribociclib plus an NSAI. The 3-year regimen of ribociclib at a 400-mg starting dose plus an NSAI was not associated with any new safety signals.

CONCLUSIONS

Ribociclib plus an NSAI significantly improved invasive disease-free survival among patients with HR-positive, HER2-negative stage II or III early breast cancer. (Funded by Novartis; NATALEE ClinicalTrials.gov number, NCT03701334.).

The multi-CDK inhibitor dinaciclib reverses bromo- and extra-terminal domain (BET) inhibitor resistance in acute myeloid leukemia via inhibition of Wnt/β-catenin signaling

Acute myeloid leukemia (AML) is a highly aggressive hematologic cancer with poor survival across a broad range of molecular subtypes. Development of efficacious and well-tolerable therapies encompassing the range of mutations that can arise in AML remains an unmet need. The bromo- and extra-terminal domain (BET) family of proteins represents an attractive therapeutic target in AML due to their crucial roles in many cellular functions, regardless of any specific mutation. Many BET inhibitors (BETi) are currently in pre-clinical and early clinical development, but acquisition of resistance continues to remain an obstacle for the drug class. Novel methods to circumvent this development of resistance could be instrumental for the future use of BET inhibitors in AML, both as monotherapy and in combination. To date, many investigations into possible drug combinations of BETi with CDK inhibitors have focused on CDK9, which has a known physical and functional interaction with the BET protein BRD4. Therefore, we wished to investigate possible synergy and additive effects between inhibitors of these targets in AML. Here, we describe combination therapy with the multi-CDK inhibitor dinaciclib and the BETi PLX51107 in pre-clinical models of AML. Dinaciclib and PLX51107 demonstrate additive effects in AML cell lines, primary AML samples, and in vivo. Further, we demonstrate novel activity of dinaciclib through inhibition of the canonical/β-catenin dependent Wnt signaling pathway, a known resistance mechanism to BETi in AML. We show dinaciclib inhibits Wnt signaling at multiple levels, including downregulation of β-catenin, the Wnt co-receptor LRP6, as well as many Wnt pathway components and targets. Moreover, dinaciclib sensitivity remains unaffected in a setting of BET resistance, demonstrating similar inhibitory effects on Wnt signaling when compared to BET-sensitive cells. Ultimately, our results demonstrate rationale for combination CDKi and BETi in AML. In addition, our novel finding of Wnt signaling inhibition could have potential implications in other cancers where Wnt signaling is dysregulated and demonstrates one possible approach to circumvent development of BET resistance in AML.

First-line CDK4/6 inhibitor-based combinations for HR+/HER2- advanced breast cancer: A Bayesian network meta-analysis

BACKGROUND

International guidelines recommend cyclin-dependent kinase 4/6 inhibitor (CDK4/6i)-based first-line therapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). However, direct drug comparisons are lacking. We aimed to identify the most effective and safe therapy through network meta-analysis (NMA).

METHODS

We searched PubMed, Embase, Web of Science, Cochrane Central Register of Controlled Trials, and OpenGrey up to September 30, 2023. Eligible studies included randomized controlled trials (RCTs) assessing endocrine therapy alone or in combination with CDK4/6i as first-line endocrine treatment for HR+/HER2- ABC patients. The hazard ratios for progression-free survival (PFS) and overall survival (OS) and relative risks for objective response rate and adverse events (AEs) were available in selected trials. We performed a Bayesian NMA following PRISMA guidelines.

RESULTS

Thirteen RCTs, involving 10 treatments, were included. Most studies were at low risk of bias. Regarding PFS, ribociclib+fulvestrant ranked first with a surface under the cumulative ranking curve (SUCRA) of 85.0%, followed by dalpiciclib+nonsteroidal aromatase inhibitor (NSAI) (SUCRA = 78.9%). Considering OS, the top three ranked treatments were ribociclib+fulvestrant (SUCRA = 94.1%), abemaciclib+NSAI (SUCRA = 69.9%), and ribociclib+NSAI (SUCRA = 68.5%). Out of four CDK4/6is, ribociclib minimized the grade 3/4 AEs, while dalpiciclib demonstrated the worst safety. Publication bias could not be ignored in our analyses, and the certainty of evidence was downgraded primarily due to imprecision.

CONCLUSIONS

Ribociclib+fulvestrant probably represents the best option in a first-line setting. When combined with NSAI, dalpiciclib likely showed the best efficacy but the worst safety. Abemaciclib+NSAI and ribociclib+NSAI could also be promising treatments, while palbociclib presented inferiority. (PROSPERO Registration No. CRD42022370271).

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.

Design, Synthesis, and Biological Evaluation for First GPX4 and CDK Dual Inhibitors

The coexistence of ferroptosis and other modes of death has great advantages in the treatment of cancers. A series of glutathione peroxidase 4 (GPX4) and cyclin-dependent kinase (CDK) dual inhibitors were designed and synthesized, given the synergistic anticancer effect of ML162 (GPX4 inhibitor) in combination with indirubin-3'-oxime (IO) (CDK inhibitor). Compound B9 exhibited the highest potential cytotoxic activity against all four cell lines and displayed excellent inhibitory activity against GPX4 (IC50 = 542.5 ± 0.9 nM) and selective inhibition of CDK 4/6 (IC50 = 191.2 ± 8.7, 68.1 ± 1.4 nM). Mechanism research showed that B9 could simultaneously induce ferroptosis and arrest cells at the G1 phase in both MDA-MB-231 cells and HCT-116 cells. Compared with ML162 and IO, B9 showed much stronger cancer cell growth inhibition in vivo. These results proved that developing potent GPX4/CDK dual inhibitors is a promising strategy for the malignant cancer therapy.

Large-scale characterization of drug mechanism of action using proteome-wide thermal shift assays

In response to an ever-increasing demand of new small molecules therapeutics, numerous chemical and genetic tools have been developed to interrogate compound mechanism of action. Owing to its ability to characterize compound-dependent changes in thermal stability, the proteome-wide thermal shift assay has emerged as a powerful tool in this arsenal. The most recent iterations have drastically improved the overall efficiency of these assays, providing an opportunity to screen compounds at a previously unprecedented rate. Taking advantage of this advance, we quantified 1.498 million thermal stability measurements in response to multiple classes of therapeutic and tool compounds (96 compounds in living cells and 70 compounds in lysates). When interrogating the dataset as a whole, approximately 80% of compounds (with quantifiable targets) caused a significant change in the thermal stability of an annotated target. There was also a wealth of evidence portending off-target engagement despite the extensive use of the compounds in the laboratory and/or clinic. Finally, the combined application of cell- and lysate-based assays, aided in the classification of primary (direct ligand binding) and secondary (indirect) changes in thermal stability. Overall, this study highlights the value of these assays in the drug development process by affording an unbiased and reliable assessment of compound mechanism of action.

Discovery of Novel Antitumor Small-Molecule Agent with Dual Action of CDK2/p-RB and MDM2/p53

Cell cycle-dependent kinase 2 (CDK2) is located downstream of CDK4/6 in the cell cycle and regulates cell entry into S-phase by binding to Cyclin E and hyper-phosphorylating Rb. Proto-oncogene murine double minute 2 (MDM2) is a key negative regulator of p53, which is highly expressed in tumors and plays an important role in tumorigenesis and progression. In this study, we identified a dual inhibitor of CDK2 and MDM2, III-13, which had good selectivity for inhibiting CDK2 activity and significantly reduced MDM2 expression. In vitro results showed that III-13 inhibited proliferation of a wide range of tumor cells, regardless of whether Cyclin E1 (CCNE1) was overexpressed or not. The results of in vivo experiments showed that III-13 significantly inhibited proliferation of tumor cells and did not affect body weight of mice. The results of the druggability evaluation showed that III-13 was characterized by low bioavailability and poor membrane permeability when orally administered, suggesting the necessity of further structural modifications. Therefore, this study provided a lead compound for antitumor drugs, especially those against CCNE1-amplified tumor proliferation.

CDK4/6 inhibition in hormone receptor-positive/HER2-negative breast cancer: Biological and clinical aspects

A dysregulated cell division, one of the key hallmarks of cancer, results in uncontrolled cellular proliferation. This aberrant process, mediated by a dysregulated cell-cycle machinery and overactivation of cyclin-dependent kinase (CDK) 4 and 6, can potentially promote tumorigenesis. The clinical application of CDK 4/6 inhibitors, developed to inhibit cell-cycle progression, in the treatment regimens of breast cancer (BC) patients is expanding. Currently, three agents, ribociclib, palbociclib, and abemaciclib, are approved for treating patients with hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic BC. In addition, abemaciclib is FDA and EMA-approved for patients with hormone receptor-positive HER2-negative, node-positive, early BC at high risk of recurrence. Emerging data suggest potential anti-tumor effects beyond cell cycle arrest, providing novel insights into the agent's mechanisms of action. As a result, a broader application of the CDK4/6 inhibitors in patients with cancer is achieved, contributing to enhanced optimized treatment in the adjuvant and neoadjuvant settings. Herein, the immunomodulatory activities of CDK4/6 inhibitors, their impact on the cell's metabolic state, and the effect on the decision of the cell to undergo quiescence or senescence are discussed. Moreover, this review provides an update on clinical trial outcomes and the differences in the underlying mechanisms between the distinct CDK4/6 inhibitors.

Novel indolyl 1,2,4-triazole derivatives as potential anti-proliferative agents: in silico studies, synthesis, and biological evaluation

A new series of indolyl 1,2,4-triazole scaffolds was designed, synthesised, and biologically evaluated for their inhibitory activity against both CDK4 and CDK6. The results ranged from 0.049 μM to 3.031 μM on CDK4 and from 0.075 μM to 1.11 μM on CDK6 when compared to staurosporine, with IC50 values of 1.027 and 0.402 μM, respectively. Moreover, all compounds were tested for their cytotoxicity against two breast cancer cell lines, MCF-7 and MDA-MB-231. All of the synthesised compounds showed promising anti-proliferative activity, with two compounds Vf (IC50 = 2.91 and 1.914 μM, respectively) and Vg (IC50 = 0.891 and 3.479 μM, respectively) having potent cytotoxic activity in comparison to the reference staurosporine (IC50 = 3.144 and 4.385 μM, respectively). Vf and Vg were also found to significantly induce apoptosis to 45.33% and 37.26% (control = 1.91%) where Vf arrested the cell cycle at the S phase while Vg arrested the cycle at the G0/G1 phase. The binding mode and interactions of all compounds were studied and found to mimic those of the FDA approved CDK4/6 inhibitor palbociclib that was used as a reference throughout the study.

The Role of CD4/6 Inhibitors in Breast Cancer Treatment

Over the last decade, treatment paradigms for breast cancer have undergone a renaissance, particularly in hormone-receptor-positive/HER2-negative breast cancer. These revolutionary therapies are based on the selective targeting of aberrancies within the cell cycle. This shift towards targeted therapies has also changed the landscape of disease monitoring. In this article, we will review the fundamentals of cell cycle progression in the context of the new cyclin-dependent kinase inhibitors. In addition to discussing the currently approved cyclin-dependent kinase inhibitors for breast cancer, we will explore the ongoing development and search for predictive biomarkers and modalities to monitor treatment.

Expanding the ligandable proteome by paralog hopping with covalent probes

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

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.

Kinase inhibitor pulldown assay (KiP) for clinical proteomics

Protein kinases are frequently dysregulated and/or mutated in cancer and represent essential targets for therapy. Accurate quantification is essential. For breast cancer treatment, the identification and quantification of the protein kinase ERBB2 is critical for therapeutic decisions. While immunohistochemistry (IHC) is the current clinical diagnostic approach, it is only semiquantitative. Mass spectrometry-based proteomics offers quantitative assays that, unlike IHC, can be used to accurately evaluate hundreds of kinases simultaneously. The enrichment of less abundant kinase targets for quantification, along with depletion of interfering proteins, improves sensitivity and thus promotes more effective downstream analyses. Multiple kinase inhibitors were therefore deployed as a capture matrix for kinase inhibitor pulldown (KiP) assays designed to profile the human protein kinome as broadly as possible. Optimized assays were initially evaluated in 16 patient derived xenograft models (PDX) where KiP identified multiple differentially expressed and biologically relevant kinases. From these analyses, an optimized single-shot parallel reaction monitoring (PRM) method was developed to improve quantitative fidelity. The PRM KiP approach was then reapplied to low quantities of proteins typical of yields from core needle biopsies of human cancers. The initial prototype targeting 100 kinases recapitulated intrinsic subtyping of PDX models obtained from comprehensive proteomic and transcriptomic profiling. Luminal and HER2 enriched OCT-frozen patient biopsies subsequently analyzed through KiP-PRM also clustered by subtype. Finally, stable isotope labeled peptide standards were developed to define a prototype clinical method. Data are available via ProteomeXchange with identifiers PXD044655 and PXD046169.

Intracellular Ellagic Acid Derived from Goat Urine DMSO Fraction (GUDF) Predicted as an Inhibitor of c-Raf Kinase

BACKGROUND

Dietary chemicals and their gut-metabolized products are explored for their anti-proliferative and pro-cell death effects. Dietary and metabolized chemicals are different from ruminants such as goats over humans.

METHODS

Loss of cell viability and induction of death due to goat urine DMSO fraction (GUDF) derived chemicals were assessed by routine in vitro assays upon MCF-7 breast cancer cells. Intracellular metabolite profiling of MCF-7 cells treated with goat urine DMSO fraction (GUDF) was performed using an in-house designed vertical tube gel electrophoresis (VTGE) assisted methodology, followed by LC-HRMS. Next, identified intracellular dietary chemicals such as ellagic acid were evaluated for their inhibitory effects against transducers of the c-Raf signaling pathway employing molecular docking and molecular dynamics (MD) simulation.

RESULTS

GUDF treatment upon MCF-7 cells displayed significant loss of cell viability and induction of cell death. A set of dietary and metabolized chemicals in the intracellular compartment of MCF-7 cells, such as ellagic acid, 2-hydroxymyristic acid, artelinic acid, 10-amino-decanoic acid, nervonic acid, 2,4-dimethyl-2-eicosenoic acid, 2,3,4'- Trihydroxy,4-Methoxybenzophenone and 9-amino-nonanoic acid were identified. Among intracellular dietary chemicals, ellagic acid displayed a strong inhibitory affinity (-8.7 kcal/mol) against c-Raf kinase. The inhibitory potential of ellagic acid was found to be significantly comparable with a known c-Raf kinase inhibitor sorafenib with overlapping inhibitory site residues (ARG450, GLU425, TRP423, VA403).

CONCLUSION

Intracellular dietary-derived chemicals such as ellagic acid are suggested for the induction of cell death in MCF-7 cells. Ellagic acid is predicted as an inhibitor of c-Raf kinase and could be explored as an anti-cancer drug.

HIt Discovery using docking ENriched by GEnerative Modeling (HIDDEN GEM): A novel computational workflow for accelerated virtual screening of ultra-large chemical libraries

Recent rapid expansion of make-on-demand, purchasable, chemical libraries comprising dozens of billions or even trillions of molecules has challenged the efficient application of traditional structure-based virtual screening methods that rely on molecular docking. We present a novel computational methodology termed HIDDEN GEM (HIt Discovery using Docking ENriched by GEnerative Modeling) that greatly accelerates virtual screening. This workflow uniquely integrates machine learning, generative chemistry, massive chemical similarity searching and molecular docking of small, selected libraries in the beginning and the end of the workflow. For each target, HIDDEN GEM nominates a small number of top-scoring virtual hits prioritized from ultra-large chemical libraries. We have benchmarked HIDDEN GEM by conducting virtual screening campaigns for 16 diverse protein targets using Enamine REAL Space library comprising 37 billion molecules. We show that HIDDEN GEM yields the highest enrichment factors as compared to state of the art accelerated virtual screening methods, while requiring the least computational resources. HIDDEN GEM can be executed with any docking software and employed by users with limited computational resources.

Network pharmacology, molecular docking and molecular dynamics simulation of chalcone scaffold-based compounds targeting breast cancer receptors

Compounds with a chalcone scaffold-based structure have demonstrated promising anticancer biological activity. However, the molecular interactions between chalcone scaffold-based compounds and breast cancer-associated proteins remain unclear. Through network pharmacology, molecular docking, and molecular dynamics (MD) simulation analyses, compounds with a chalcone scaffold-based structure were evaluated for their interaction with potential breast cancer targets. The compounds were retrieved from the ASINEX database, resulting in 575,302 compounds. A total of 342 compounds with chalcone scaffold-based structures were discovered. From the 342 compounds that was analysed, ten were chosen due to their adherence to Lipinski's rule, having an appropriate range of lipophilicity (LOGP), and topological polar surface area (TPSA), and absence of any toxicity. Based on target intersection, 50 target genes were found and subjected to protein-protein interaction (PPI), gene ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Four target genes were found to be involved in the breast cancer pathway. Consequently, molecular docking was utilised to analyse the molecular interactions between the compounds and four target protein receptors. Compound 211 exhibited the highest binding affinities for the epidermal growth factor receptor (EGFR), fibroblast growth factor receptor 1 (FGFR1), oestrogen receptor (ESR1), and cyclin dependent kinase 6 (CDK6) with values of -8.95 kcal/mol, -8.60 kcal/mol, -10.33 kcal/mol, and -9.90 kcal/mol, respectively. During MD simulation, compound 211 and its respective proteins were stable, compact, and had minimal flexibility. The findings provide foundations for future studies into the interaction underlying the anti-breast cancer potential of compounds with chalcone-based scaffold structures.Communicated by Ramaswamy H. Sarma.

Synthetic Approaches to Piperazine-Containing Drugs Approved by FDA in the Period of 2011-2023

The piperazine moiety is often found in drugs or in bioactive molecules. This widespread presence is due to different possible roles depending on the position in the molecule and on the therapeutic class, but it also depends on the chemical reactivity of piperazine-based synthons, which facilitate its insertion into the molecule. In this paper, we take into consideration the piperazine-containing drugs approved by the Food and Drug Administration between January 2011 and June 2023, and the synthetic methodologies used to prepare the compounds in the discovery and process chemistry are reviewed.

Peripheral blood lymphocytes predict clinical outcomes in hormone receptor-positive HER2-negative advanced breast cancer patients treated with CDK4/6 inhibitors

Background

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) combined with Endocrine Therapy (ET) are the standard treatment for patients with Hormone Receptor-positive/HER2-negative advanced breast cancer (HR+/HER2- aBC).

Objectives

While CDK4/6i are known to reduce several peripheral blood cells, such as neutrophils, lymphocytes and platelets, the impact of these modulations on clinical outcomes is unknown.

Design

A multicenter, retrospective-prospective Italian study.

Methods

We investigated the association between baseline peripheral blood cells, or their early modifications (i.e. 2 weeks after treatment initiation), and the progression-free survival (PFS) of HR+/HER2- aBC patients treated with ETs plus CDK4/6i. Random Forest models were used to select covariates associated with patient PFS among a large list of patient- and tumor-related variables.

Results

We evaluated 638 HR+/HER2- aBC patients treated with ET plus CDK4/6i at six Italian Institutions between January 2017 and May 2021. High baseline lymphocyte counts were independently associated with longer PFS [median PFS (mPFS) 20.1 versus 13.2 months in high versus low lymphocyte patients, respectively; adjusted Hazard Ratio (aHR): 0.78; 95% confidence interval (CI): 0.66-0.92; p = 0.0144]. Moreover, patients experiencing a lower early reduction of lymphocyte counts had significantly longer PFS when compared to patients undergoing higher lymphocyte decrease (mPFS 18.1 versus 14.5 months; aHR: 0.82; 95% CI: 0.73-0.93; p = 0.0037). Patients with high baseline lymphocytes and undergoing a lower reduction, or even an increase, of lymphocyte counts during CDK4/6i therapy experienced the longest PFS, while patients with lower baseline lymphocytes and undergoing a higher decrease of lymphocytes had the lowest PFS (mPFS 21.4 versus 11 months, respectively).

Conclusion

Baseline and on-treatment modifications of peripheral blood lymphocytes have independent prognostic value in HR+/HER2- aBC patients. This study supports the implementation of clinical strategies to boost antitumor immunity in patients with HR+/HER2- aBC treated with ETs plus CDK4/6i.

Targeting protein kinases for the treatment of Alzheimer's disease: Recent progress and future perspectives

Alzheimer's disease (AD) is a serious neurodegenerative disease characterized by memory impairment, mental retardation, impaired motor balance, loss of self-care and even death. Among the complex and diverse pathological changes in AD, protein kinases are deeply involved in abnormal phosphorylation of Tau proteins to form intracellular neuronal fiber tangles, neuronal loss, extracellular β-amyloid (Aβ) deposits to form amyloid plaques, and synaptic disturbances. As a disease of the elderly, the growing geriatric population is directly driving the market demand for AD therapeutics, and protein kinases are potential targets for the future fight against AD. This perspective provides an in-depth look at the role of the major protein kinases (GSK-3β, CDK5, p38 MAPK, ERK1/2, and JNK3) in the pathogenesis of AD. At the same time, the development of different protein kinase inhibitors and the current state of clinical advancement are also outlined.

CDK4/6 inhibitors in the treatment of metastatic breast cancer: Focus on toxicity and safety

The development of oral cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, including palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for patients with hormone-receptor-positive (HR+) and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (BC). When combined with an aromatase inhibitor or fulvestrant, these agents have been approved as first-line therapy in the metastatic setting. Abemaciclib has also gained FDA approval for patients with HR-positive, HER2-negative, node-positive, early BC at high risk of recurrence. Moreover, ribociclib has recently improved disease-free survival in patients with stage II or III HR+/HER2-negative early BC. CDK4/6 inhibitors have favorable safety profiles. However, the available agents have different toxicity profiles that must be clearly discussed with the patients for optimal clinical decisions. This manuscript aims to review CDK4/6 inhibitor-related treatment-associated adverse events, identify risk factors for intolerable adverse events, and assess their safety in special patient populations such as the elderly and those with renal insufficiency. Enhanced knowledge and understanding of CDK4/6 inhibitor-related toxicities can improve treatment strategies and ultimately enhance patient care.

The CDK4/6 inhibitors biomarker landscape: The most relevant biomarkers of response or resistance for further research and potential clinical utility

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6is) in combination with Endocrine Therapy (ET) represent the standard frontline therapy for patients with Hormone Receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic Breast Cancer (mBC). Clinical activity and efficacy of CDK4/6is-based therapies have been proven both in the endocrine sensitive and resistant settings. Therapy resistance eventually underpins clinical progression to any CDK4/6is-based therapies, yet there is a lack of validated molecular biomarkers predictive of either intrinsic or acquired resistance to CDK4/6is in clinical practice. As the "post-CDK4/6is" landscape for the management of HR-positive/HER2-negative mBC is rapidly evolving with the introduction of novel therapies, there is an urgent need for the definition of clinically relevant molecular biomarkers of intrinsic/acquired resistance mechanisms to CDK4/6is. This narrative review outlines the role of currently approved CDK4/6is-based therapies, describes the most relevant molecular biomarkers of CDK4/6is-resistance, and ultimately provides a perspective on the clinical and research scenario.

A review: FDA-approved fluorine-containing small molecules from 2015 to 2022

Fluorine-containing small molecules have occupied a special position in drug discovery research. The successful clinical use of fluorinated corticosteroids in the 1950s and fluoroquinolones in the 1980s led to an ever-increasing number of approved fluorinated compounds over the last 50 years. They have shown various biological properties such as antitumor, antimicrobial, and anti-inflammatory activities. Fluoro-pharmaceuticals have been considered a strong and practical tool in the rational drug design approach due to their benefits from potency and ADME (absorption, distribution, metabolism, and excretion) points of view. Herein, approved fluorinated drugs from 2015 to 2022 were reviewed.

Pooled ctDNA analysis of MONALEESA phase III advanced breast cancer trials

BACKGROUND

The phase III MONALEESA trials tested the efficacy and safety of the cyclin-dependent kinase (CDK)4/6 inhibitor ribociclib with different endocrine therapy partners as first- or second-line treatment of hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer (ABC). Using the largest pooled biomarker dataset of the CDK4/6 inhibitor ribociclib in ABC to date, we identified potential biomarkers of response to ribociclib.

PATIENTS AND METHODS

Baseline circulating tumour DNA from patients in the MONALEESA trials was assessed using next-generation sequencing. An analysis of correlation between gene alteration status and progression-free survival (PFS) was carried out to identify potential biomarkers of response to ribociclib.

RESULTS

Multiple frequently altered genes were identified. Alterations in ERBB2, FAT3, FRS2, MDM2, SFRP1, and ZNF217 were associated with a greater PFS benefit with ribociclib versus placebo. Patients with high tumour mutational burden (TMB) and with ANO1, CDKN2A/2B/2C, and RB1 alterations exhibited decreased sensitivity to ribociclib versus placebo.

CONCLUSIONS

Although exploratory, these results provide insight into alterations associated with the improved response to ribociclib treatment and may inform treatment sequencing in patients with actionable alterations following progression on CDK4/6 inhibitors. Validation of potential biomarkers identified here and development of prospective trials testing their clinical utility are warranted.

CLINICALTRIALS

GOV IDENTIFIERS

NCT01958021, NCT02422615, NCT02278120.

Abemaciclib Is Effective in Palbociclib-Resistant Hormone Receptor-Positive Metastatic Breast Cancers

Cyclin-dependent kinases 4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) is standard of care for patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC). However, resistance to CDK4/6is plus ET remains a clinical problem with limited therapeutic options following disease progression. Different CDK4/6is might have distinct mechanisms of resistance, and therefore using them sequentially or targeting their differentially altered pathways could delay disease progression. To understand pathways leading to resistance to the CDK4/6is palbociclib and abemaciclib, we generated multiple in vitro models of palbociclib-resistant (PR) and abemaciclib-resistant (AR) cell lines as well as in vivo patient-derived xenografts (PDX) and ex vivo PDX-derived organoids (PDxO) from patients who progressed on CDK4/6i. PR and AR breast cancer cells exhibited distinct transcriptomic and proteomic profiles that sensitized them to different classes of inhibitors; PR cells upregulated G2-M pathways and responded to abemaciclib, while AR cells upregulated mediators of the oxidative phosphorylation pathway (OXPHOS) and responded to OXPHOS inhibitors. PDX and organoid models derived from patients with PR breast cancer remained responsive to abemaciclib. Resistance to palbociclib while maintaining sensitivity to abemaciclib was associated with pathway-specific transcriptional activity but was not associated with any individual genetic alterations. Finally, data from a cohort of 52 patients indicated that patients with HR-positive/HER2-negative MBC who progressed on palbociclib-containing regimens can exhibit a meaningful overall clinical benefit from abemaciclib-based therapy when administered after palbociclib. These findings provide the rationale for clinical trials evaluating the benefit of abemaciclib treatment following progression on a prior CDK4/6i.

SIGNIFICANCE

Palbociclib-resistant breast cancers respond to abemaciclib and express pathway-specific signatures of sensitivity, providing a biomarker-driven therapeutic option for patients with metastatic breast cancer following disease progression on cyclin-dependent kinases 4/6 inhibitors.

Development of novel palbociclib-based CDK4/6 inhibitors exploring the back pocket behind the gatekeeper

CDK4/6 inhibitors plus endocrine therapy is a standard therapy for HR+/HER2- breast cancer. Herein, using structure-based drug design strategy, a novel series of palbociclib derivatives were designed and synthesized as CDK4/6 inhibitors, among which compound 17m exhibited more potent CDK4/6 inhibitory activity and in vitro antiproliferative activity against the phosphorylated Rb-positive cell line MDA-MB-453 than the approved drug palbociclib. Moreover, compound 17m possessed remarkable CDK4/6 selectivity over other CDK family members including CDK1, CDK2, CDK3, CDK5, CDK7 and CDK9. The potent and selective CDK4/6 inhibitory activity endowed compound 17m with robust G1 cell cycle arrest ability in MDA-MB-453 cells. The intracellular inhibition of CDK4/6 by 17m was confirmed by western blot analysis of the levels of phosphorylated Rb in MDA-MB-453 cells. With respect to the metabolic stability, compound 17m possessed longer half-life (t1/2) in mouse liver microsome than palbociclib.

Efficacy of probiotics and trimebutine maleate for abemaciclib-induced diarrhea: A randomized, open-label phase II trial (MERMAID, WJOG11318B)

BACKGROUND

Abemaciclib-induced diarrhea (AID) impairs quality of life (QOL) and treatment adherence in patients with breast cancer. Supportive treatment with loperamide is associated with constipation. We hypothesized that probiotics and trimebutine maleate (TM) would decrease the frequency of AID without causing constipation.

METHODS

Hormone receptor-positive, human epidermal growth factor 2-negative advanced breast cancer patients were randomized into the probiotic Bifidobacterium (A) or probiotic Bifidobacterium and TM (B) groups. Endocrine therapy, Abemaciclib and probiotic Bifidobacterium three times a day for 28 days, was administered to both arms. Arm B was treated with TM upon the onset of diarrhea. The primary endpoint was the percentage of patients who experienced grade ≥2 diarrhea. The secondary endpoints were safety, frequency, and duration of all-grade diarrhea; frequency of emesis and constipation; usage of loperamide; and health-related QOL/patient-reported outcome during the study. We evaluated whether the primary endpoint of each arm exceeded the predetermined threshold.

RESULTS

Fifty-one patients completed treatment. Grade 2 diarrhea occurred in 52% and 50% of patients in Arm A and Arm B, respectively. One patient experienced grade 3 diarrhea in each arm. The median duration of grade2 diarrhea was 2 and 2.5day, and only one patient required dose reduction. Grade ≥2 constipation was observed in 4% of Arm A and 3.6% of Arm B.

CONCLUSIONS

Probiotic Bifidobacterium or the combination of probiotic Bifidobacterium with TM did not decrease the incidence of grade 2 or greater diarrhea compared with historical control, although the grade 3 or greater diarrhea was reduced.

CLINICAL TRIAL REGISTRATION

jRCT (Japan registry of clinical trials). jRCTs031190154.

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.

Development of PROTAC degrader probe of CDK4/6 based on DCAF16

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

Combination strategies to overcome drug resistance in FLT+ acute myeloid leukaemia

BACKGROUND

Acute myeloid leukaemia (AML) remains difficult to treat despite the development of novel formulations and targeted therapies. Activating mutations in the FLT3 gene are common among patients and make the tumour susceptible to FLT3 inhibitors, but resistance to such inhibitors develops quickly.

METHODS

We examined combination therapies aimed at FLT3+-AML, and studied the development of resistance using a newly developed protocol. Combinations of FLT3, CDK4/6 and PI3K inhibitors were tested for synergism.

RESULTS

We show that AML cells express CDK4 and that the CDK4/6 inhibitors palbociclib and abemaciclib inhibit cellular growth. PI3K inhibitors were also effective in inhibiting the growth of AML cell lines that express FLT3-ITD. Whereas resistance to quizartinib develops quickly, the combinations overcome such resistance.

CONCLUSIONS

This study suggests that a multi-targeted intervention involving a CDK4/6 inhibitor with a FLT3 inhibitor or a pan-PI3K inhibitor might be a valuable therapeutic strategy for AML to overcome drug resistance. Moreover, many patients cannot tolerate high doses of the drugs that were studied (quizartinib, palbociclib and PI3K inhibitors) for longer periods, and it is therefore of high significance that the drugs act synergistically and lower doses can be used.

Differences in metabolic transport and resistance mechanisms of Abemaciclib, Palbociclib, and Ribociclib

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) play a crucial role in cancer treatment, particularly in breast cancer, and their mechanism of drug resistance is a topic of global interest in research. Hence, it is vital to comprehend the distinctions between various CDK4/6i, including their mechanisms of action and resistance mechanisms. This article aims to summarize the metabolic and transport variations as well as the differences in resistance among the three FDA-approved CDK4/6 inhibitors: Abemaciclib, Palbociclib, and Ribociclib. It also aims to discuss how these differences impact the effectiveness and safety of anticancer drugs. It was conducted in March 2023 to search PubMed, Embase, and Web of Science for literature related to this topic. Despite all being CDK4/6i, differences in their metabolism and transport were found, which are related to their chemical structure. Moreover, there are variations in preclinical pharmacology, pharmacokinetics, and clinical safety and efficacy of the different inhibitors. Genetic mutations, drug tolerance, and other factors may influence CDK4/6 resistance mechanisms. Currently, the resistance mechanisms differences of the three drugs remain largely unknown, and there are differences in the resistance mechanisms among them, necessitating further exploration and research.

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors: existing and emerging differences

The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors palbociclib, ribociclib, and abemaciclib are standard-of-care therapy for hormone receptor-positive advanced or metastatic breast cancer, based on randomized trials showing improved progression-free survival for all 3 drugs and overall survival for ribociclib and abemaciclib. Results in early breast cancer are discordant, with sustained improvement in invasive disease-free survival demonstrated for abemaciclib but not other CDK4/6 inhibitors to date. We review nonclinical studies exploring mechanistic differences between the drugs, the impact of continuous dosing on treatment effect, and translational research into potential resistance mechanisms and prognostic and predictive markers. We focus particularly on how emerging findings may help us understand similarities and differences between the available CDK4/6 inhibitors. Even at late-stage clinical development, there remains much to learn about how agents in this class exert their varying effects.

Firing of Replication Origins Is Disturbed by a CDK4/6 Inhibitor in a pRb-Independent Manner

Over the last decade, CDK4/6 inhibitors (palbociclib, ribociclib and abemaciclib) have emerged as promising anticancer drugs. Numerous studies have demonstrated that CDK4/6 inhibitors efficiently block the pRb-E2F pathway and induce cell cycle arrest in pRb-proficient cells. Based on these studies, the inhibitors have been approved by the FDA for treatment of advanced hormonal receptor (HR) positive breast cancers in combination with hormonal therapy. However, some evidence has recently shown unexpected effects of the inhibitors, underlining a need to characterize the effects of CDK4/6 inhibitors beyond pRb. Our study demonstrates how palbociclib impairs origin firing in the DNA replication process in pRb-deficient cell lines. Strikingly, despite the absence of pRb, cells treated with palbociclib synthesize less DNA while showing no cell cycle arrest. Furthermore, this CDK4/6 inhibitor treatment disturbs the temporal program of DNA replication and reduces the density of replication forks. Cells treated with palbociclib show a defect in the loading of the Pre-initiation complex (Pre-IC) proteins on chromatin, indicating a reduced initiation of DNA replication. Our findings highlight hidden effects of palbociclib on the dynamics of DNA replication and of its cytotoxic consequences on cell viability in the absence of pRb. This study provides a potential therapeutic application of palbociclib in combination with other drugs to target genomic instability in pRB-deficient cancers.

HR+/HER2- Advanced Breast Cancer Treatment in the First-Line Setting: Expert Review

The approval of CDK4/6 inhibitors has dramatically improved care for the treatment of HR+/HER2- advanced breast cancer, but navigating the rapidly-expanding treatment evidence base is challenging. In this narrative review, we provide best-practice recommendations for the first-line treatment of HR+/HER2- advanced breast cancer in Canada based on relevant literature, clinical guidelines, and our own clinical experience. Due to statistically significant improvements in overall survival and progression-free survival, ribociclib + aromatase inhibitor is our preferred first-line treatment for de novo advanced disease or relapse ≥12 months after completion of adjuvant endocrine therapy and ribociclib or abemaciclib + fulvestrant is our preferred first-line treatment for patients experiencing early relapse. Abemaciclib or palbociclib may be used when alternatives to ribociclib are needed, and endocrine therapy can be used alone in the case of contraindication to CDK4/6 inhibitors or limited life expectancy. Considerations for special populations-including frail and fit elderly patients, as well as those with visceral disease, brain metastases, and oligometastatic disease-are also explored. For monitoring, we recommend an approach across CDK4/6 inhibitors. For mutational testing, we recommend routinely performing ER/PR/HER2 testing to confirm the subtype of advanced disease at the time of progression and to consider ESR1 and PIK3CA testing for select patients. Where possible, engage a multidisciplinary care team to apply evidence in a patient-centric manner.

Cost Effectiveness of CDK4/6 Inhibitors in the First-Line Treatment of HR+/HER2- Metastatic Breast Cancer in Postmenopausal Women in the USA

BACKGROUND AND OBJECTIVE

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors improve progression-free survival when combined with endocrine therapies in patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer. However, the comparative cost effectiveness of utilizing three US Food and Drug Administration-approved CDK4/6 inhibitors is unknown. Therefore, we aimed to evaluate the cost effectiveness of individual CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib) with letrozole versus letrozole monotherapy in the first-line treatment of hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer in the USA.

METHODS

We constructed a Markov-based decision-analytic model to evaluate the cost effectiveness of CDK4/6 inhibitors plus endocrine therapies over a 40-year lifetime from a third-party payer perspective. The model incorporated health states (progression-free disease, progressive disease, and death), major adverse events (neutropenia), and cancer-specific and all-cause mortality. Using clinical efficacy and quality-of-life scores (utility) data from clinical trials, we estimated quality-adjusted life-years (QALYs) and incremental cost-effectiveness ratios using Medicare charges reported in US dollars per 2022 valuation and a discount rate of 3% applied to costs and outcomes. We performed deterministic and probabilistic sensitivity analyses to evaluate parametric and decision uncertainty.

RESULTS

Compared to letrozole, the model estimated an increase of 5.72, 5.87, and 6.39 in QALYs and costs of $799,178, $788,168, and $741,102 in combining palbociclib, ribociclib, and abemaciclib plus letrozole, respectively. Palbociclib or ribociclib plus letrozole were dominated by abemaciclib plus letrozole. Compared with letrozole, abemaciclib plus letrozole resulted in an incremental cost-effectiveness ratio of $457,538 per QALY with an incremental cost of $553,621 and an incremental QALY gain of 1.21. The results were sensitive to the cost of abemaciclib, disease progression utility, and patients' age.

CONCLUSIONS

At a willingness to pay of $100,000/QALY gained, our model predicts that combining CDK4/6 inhibitors plus letrozole is not cost effective with a marginal increase in QALYs at a high cost. Lowering the cost of these drugs or identifying patients who can receive maximal benefit from CDK4/6 inhibitors would improve the value of this regimen in patients.

Rationale and trial design of NATALEE: a Phase III trial of adjuvant ribociclib + endocrine therapy versus endocrine therapy alone in patients with HR+/HER2- early breast cancer

Background

Ribociclib has demonstrated a statistically significant overall survival benefit in pre- and postmenopausal patients with hormone receptor positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) advanced breast cancer. New Adjuvant Trial with Ribociclib [LEE011] (NATALEE) is a trial evaluating the efficacy and safety of adjuvant ribociclib plus endocrine therapy (ET) versus ET alone in patients with HR+/HER2- early nonmetastatic breast cancer (EBC).

Methods/design

NATALEE is a multicenter, randomized, open-label, Phase III trial in patients with HR+/HER2- EBC. Eligible patients include women, regardless of menopausal status, and men aged ⩾18 years. Select patients with stage IIA, stage IIB, or stage III disease (per the anatomic classification in the AJCC Cancer Staging Manual, 8th edition) with an initial diagnosis ⩽18 months prior to randomization are eligible. Patients receiving standard (neo)adjuvant ET are eligible if treatment was initiated ⩽12 months before randomization. Patients undergo 1:1 randomization to ribociclib 400 mg/day (3 weeks on/1 week off) +ET (letrozole 2.5 mg/day or anastrozole 1 mg/day [investigator's discretion] plus goserelin [men or premenopausal women]) or ET alone. Ribociclib treatment duration is 36 months; ET treatment duration is ⩾60 months. The primary end point is invasive disease-free survival.

Discussion

The 36-month treatment duration of ribociclib in NATALEE is extended compared with that in other adjuvant cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor trials and is intended to maximize efficacy due to longer duration of CDK4/6 inhibition. Compared with the 600-mg/day dose used in advanced breast cancer, the reduced ribociclib dose used in NATALEE may improve tolerability while maintaining efficacy. NATALEE includes the broadest population of patients with HR+/HER2- EBC of any Phase III trial currently evaluating adjuvant CDK4/6 inhibitor treatment.

Trial registration

ClinicalTrials.gov identifier: NCT03701334 (https://clinicaltrials.gov/ct2/show/NCT03701334).

Real-world treatment patterns of subsequent therapy after palbociclib in patients with advanced breast cancer in Japan

PURPOSE

The optimal treatment following endocrine therapy (ET) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) has not been established. We aimed to investigate treatment patterns and time to treatment failure (TTF) of subsequent therapy after palbociclib in a Japanese real-world setting.

METHDS

This retrospective observational study used de-identified data of patients with advanced breast cancer treated with palbociclib, using a nationwide claims database (April 2008 to June 2021). Measures included the type of subsequent therapies after palbociclib (endocrine-based therapy: ET alone, ET + CDK4/6i, and ET + mammalian target of rapamycin inhibitor [mTORi]; chemotherapy; chemotherapy + ET; and others) and their TTFs. The median TTF and 95% confidence interval (CI) were estimated using the Kaplan-Meier method.

RESULTS

Of 1170 patients treated with palbociclib, 224 and 235 received subsequent therapies after first- and second-line palbociclib treatment, respectively. Among them, 60.7% and 52.8% were treated with endocrine-based therapies as first subsequent therapy, including ET + CDK4/6i (31.2% and 29.8%, respectively). The median TTF (95% CI) of ET alone, ET + CDK4/6i, and ET + mTORi as first subsequent therapy after first-line palbociclib were 4.4 (2.8-13.7), 10.9 (6.5-15.6), and 6.1 (5.1-7.2) months, respectively. No apparent relationship between the treatment duration of prior ET + palbociclib and subsequent abemaciclib was observed.

CONCLUSION

This real-world study revealed that one-third of the patients received sequential CDK4/6i after ET + palbociclib, and treatment duration of ET + CDK4/6i following ET + palbociclib was the longest among the treatment options. Further data are awaited to determine whether ET + targeted therapy with CDK4/6i and mTORi provides acceptable treatment options following ET + palbociclib.