Clinical Management of Potential Toxicities and Drug Interactions Related to Cyclin-Dependent Kinase 4/6 Inhibitors in Breast Cancer: Practical Considerations and Recommendations

Clinical impact of drug-drug interactions on abemaciclib in the real-world experience of AB-ITALY study

Abemaciclib demonstrated clinical benefit in women affected by HR+/HER2- advanced breast cancer (aBC). Drug-drug interactions (DDIs) can lead to reduced treatment efficacy or increased toxicity. This retro-prospective study aimed to evaluate outcomes, DDIs' impact, and toxicities of abemaciclib combined with endocrine therapy in a real-world setting. Patients from 12 referral Italian hospitals with HR+/HER2- aBC who received abemaciclib were included. Clinical data about comorbidities, concurrent medications, outcomes, and adverse events (AE) were collected. Drug-PIN® (Personalized Interactions Network) is a tool recognizing the role of multiple interactions between active and/or pro-drug forms combined with biochemical and demographic patient data. The software was used to define the Drug-PIN score and Drug-PIN tier (green, yellow, dark yellow, and red) for each patient. Univariate and multivariate analyses were performed to identify predictors of patients' PFS or toxicity. One hundred seventy-three patients were included. 13% of patients had >75years. The overall response rate (ORR) was 63%. The general population's median PFS (mPFS) was 22 months (mo), while mOS were not reached. Patients treated with abemaciclib in combination with AI and fulvestrant had a mPFS of 36 and 19 mo, respectively. The most common toxicities were diarrhea, asthenia, and neutropenia detected in 63%,49%, and 49% of patients. The number of concomitant medications and comorbidities were not associated with survival outcomes (22 vs 17 mo, p = 0.068, p = 0.99). Drug-PIN tier from dark yellow to red and Drug-PIN score >12 were associated with shorter PFS compared to no/low-risk DDIs and score <12 (15 vs 23, p = 0.005, p = 0.0017). Drug interaction was confirmed as an independent biomarker in a multivariate model (p = 0.02). No difference in any grade AE, severe toxicities, and diarrhea were detected among different age subgroups. No association was found between Drug-PIN score or Drug-PIN tier and overall toxicity (p = 0.44), severe AEs (p = 0.11), or drug reduction (p = 0.27). The efficacy and safety of abemaciclib plus ET were confirmed in a real-world setting, even in the elderly population and patients with comorbidities. Evaluation of DDIs with Drug-PIN appears to be an independent predictor of PFS.

The marine-derived HIF-1α inhibitor, Yardenone 2, reduces prostate cancer cell proliferation by targeting HIF-1 target genes

BACKGROUND

Prostate cancer (PCa) ranks as the second most prevalent cancer in men, with advanced stages posing significant treatment challenges. Given its solid tumor nature, PCa is highly susceptible to hypoxia, a condition associated with resistance to radiation and chemotherapy, metastasis, and unfavorable patient outcomes. Hypoxia-inducible factors (HIFs) play a pivotal role in cancer cell adaptation to hypoxic environments, contributing to treatment resistance. Consequently, inhibitors targeting HIFs hold promise for cancer therapy.

METHODS

In this study, we aimed to characterize novel HIF-1α inhibitors including Sodwanones A (1), B (2), C (3), G (4) and Yardenone 2 (5) isolated from marine sponges belonging to the Axinella genus. Our investigation evaluated the impact of these compounds on various aspects of HIF-1α regulation, including stabilization, nuclear localization, expression of HIF-1 target genes (while sparing HIF-2 target genes), cellular metabolism, as well as cell proliferation and viability in prostate cells under hypoxic conditions.

RESULTS

Our findings revealed that among the compounds tested, Yardenone 2 exhibited notable effects in hypoxia: it destabilized HIF-1α at the protein level, decreased its nuclear localization, selectively altered the expression of HIF-1 target genes, and restrained cell proliferation in aggressive PC3 prostate cancer cells as well as in an MSK-PCa3 patient-derived organoid line. Moreover, it affected the morphology of these organoid. Yardenone 2 was also compared to Docetaxel, a specific microtubule inhibitor and a drug used in the treatment of prostate cancer. The comparison between the two compounds revealed notable differences, such as a lack of specificity to hypoxic cells of Docetaxel.

CONCLUSION

These results mark the first demonstration that Yardenone 2 functions as a cytostatic-like inhibitor impacting microtubules, specifically targeting hypoxic cancer cells. This discovery suggests a promising avenue for novel therapeutic interventions in prostate cancer.

Development of a Radiolabeled Cyclin-Dependent Kinases 4 and 6 (CDK4/6) Inhibitor for Brain and Cancer PET Imaging

The synthesis, biochemical evaluation and radiosynthesis of a cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor and radioligand was performed. NT431, a newly synthesized 4-fluorobenzyl-abemaciclib, exhibited high potency to CDK4/6 and against four cancer cell lines with IC50 similar to that of the parent abemaciclib. We performed a two-step one-pot radiosynthesis to produce [18F]NT431 with good radiochemical yield (9.6 ± 3%, n = 3, decay uncorrected), high radiochemical purity (>95%), and high molar activity (>370 GBq/µmol (>10.0 Ci/µmol). In vitro autoradiography confirmed the specific binding of [18F]NT431 to CDK4/6 in brain tissues. Dynamic PET imaging supports that both [18F]NT431 and the parent abemaciclib crossed the BBB albeit with modest brain uptake. Therefore, we conclude that it is unlikely that NT431 or abemaciclib (FDA approved drug) can accumulate in the brain in sufficient concentrations to be potentially effective against breast cancer brain metastases or brain cancers. However, despite the modest BBB penetration, [18F]NT431 represents an important step towards the development and evaluation of a new generation of CDK4/6 inhibitors with superior BBB penetration for the treatment and visualization of CDK4/6 positive tumors in the CNS. Also, [18F]NT431 may have potential application in peripheral tumors such as breast cancer and other CDK4/6 positive tumors.

Ribociclib-Induced Cutaneous Adverse Events in Metastatic HR+/HER2- Breast Cancer: Incidence, Multidisciplinary Management, and Prognostic Implication

BACKGROUND

Ribociclib is approved for hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer (ABC) treatment, in combination with endocrine therapy. Hematological, hepatic, and cardiac adverse events (AEs) emerged from pivotal trials, but little is known about cutaneous adverse events (CAEs).

PATIENTS AND METHODS

We report data from a retrospective cohort study of all patients with HR+/HER2- ABC treated with ribociclib at Humanitas Cancer Center between June 2017 and December 2022. We recorded clinical-pathological data, the incidence, and treatment of ribociclib-related CAEs. These were evaluated according to the NCI-CTCAE v5.0 classification. Progression-free survival (PFS) was estimated by Kaplan-Meier method and the log-rank test was used to analyze differences between groups.

RESULTS

Thirteen of 91 patients (14.3%) experienced treatment-related CAEs (mean time to the occurrence: 3.9 months). The most frequent CAEs were eczematous dermatitis (53.8%) and maculo-papular reaction (15.4%). Itch was reported by all 13 patients. The grade was G3 in 8 cases, G2 in 4, and G1 in 1. An integrated approach based on ribociclib dose modulation and dermatological interventions (oral antihistamine, moisturized cream, topical, and/or systemic steroids) could prevent ribociclib discontinuation in most patients. At a median follow-up of 20 months, the median PFS was 13 months (range, 1-66) with a better PFS curves for patients experiencing CAEs (P = .04).

CONCLUSION

We mapped frequency and types of ribociclib-induced CAEs. An interdisciplinary management of CAEs incorporated into routine care may reduce the rate of drug discontinuation thus potentially contributing to better long-term outcomes.

Hematological toxicity of cyclin-dependent kinase 4/6 inhibitors in patients with breast cancer: a network meta-analysis and pharmacovigilance study

OBJECTIVES

We aimed to evaluate and compare the risk of hematological adverse events (AEs) associated with CDK4/6 inhibitors using data from randomized controlled trials (RCTs) and Food and Drug Adverse Event Reporting System (FAERS) database.

METHODS

The PubMed, Embase, and Cochrane Library databases were searched for RCTs related to abemaciclib, palbociclib, and ribociclib. A network meta-analysis (NMA) was conducted to compare the risks of hematological AEs, and a disproportionality analysis was performed to detect signals of hematological AEs.

RESULTS

16 RCTs comprising 16,350 breast cancer patients were included. Palbociclib and ribociclib had similar risks for hematological AEs, except a higher risk of grade 3-4 leukopenia observed with palbociclib (risk ratio [RR]: 7.84, 95% confidence interval [95%CI]: 1.33-41.28). Abemaciclib had a higher risk of anemia than both ribociclib (grade 1-4: RR: 2.23, 95% CI: 1.25 - 3.96; grade 3-4: RR: 3.52, 95% CI: 1.59 - 8.11) and palbociclib (grade 1-4: RR: 1.65, 95%CI: 1.03 - 2.59), but a lower risk of grade 3-4 of both leukopenia (RR: 0.12, 95%CI: 0.02 - 0.49) and neutropenia (RR: 0.15, 95%CI: 0.04 - 0.52) compared with palbociclib. Signals indicating occurrence of leukopenia, neutropenia, anemia, and thrombocytopenia were identified for three CDK4/6 inhibitors.

CONCLUSION

Abemaciclib, palbociclib, and ribociclib showed significant but inconsistent hematological toxicity risks.

Post-marketing safety concerns with palbociclib: a disproportionality analysis of the FDA adverse event reporting system

OBJECTIVES

To explore the association between palbociclib and related adverse events (AEs) in the real world through U.S. Food and Drug Administration Adverse Event Reporting System (FAERS) database.

METHODS

The signal strength of palbociclib-related AEs was done by disproportionality analysis. Clinical priority of palbociclib-related AEs was scored and ranked by assessing five different features. Outcome analysis, time to onset analysis, dose-report /AEs number analysis, and stratification analysis were all performed.

RESULTS

There were 61,821 'primary suspected (PS)' reports of palbociclib and 195,616 AEs associated with palbociclib. The four algorithms simultaneously detected 18 positive signals at the SOC level, and 65 positive signals at the PT level. Bone marrow failure, neuropathy, peripheral, pleural effusion, myelosuppression, pulmonary edema, and pulmonary thrombosis were also found to have positive signals. Gender (female vs male, χ2 = 5.287, p = 0.022) and age showed significant differences in serious and non-serious reports. Palbociclib-related AEs had a median onset time of 79 days (interquartile range [IQR] 20-264 days).

CONCLUSIONS

The study identified potential Palbociclib-related AEs and offered warnings for special AEs, providing further data for palbociclib safety studies in breast cancer patients. Nonetheless, prospective clinical trials are needed to validate these results and explain their relationship.

Cyclin-Dependent Kinase 4/6 Inhibitors as Neoadjuvant Therapy of Hormone Receptor-Positive/HER2-Negative Early Breast Cancer: What do we Know so Far?

The introduction of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors to the treatment of hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer is regarded as one of the greatest achievements of the last decades in breast oncology. To date, palbociclib, abemaciclib and ribociclib are the 3 approved CDK4/6 inhibitors that combined with endocrine therapy are now considered as the standard first-line treatment of metastatic HR+/HER2- breast cancer. The great success of these drugs in the setting of metastatic disease and the need to combat the high risk of recurrence have paved the way for a number of clinical trials to explore the use of CDK4/6 inhibitors in the neoadjuvant treatment of early breast cancer. In this review, we summarize the main findings of clinical trials that examined the use of CDK4/6 inhibitors in combination with hormone therapy or chemotherapy as neoadjuvant treatment of hormone receptor-positive and HER2-negative breast cancer. Active clinical trials that investigate different treatment schemes are also briefly presented and current limitations and future goals are discussed.

Abemaciclib-Associated Skin, Hair, and Nail Toxicities: A Case Report

Abemaciclib is a cyclin-dependent kinase 4/6 inhibitor that is utilized to manage hormone-sensitive human epidermal growth factor receptor-2 positive metastatic breast cancer. Palbociclib and ribociclib are types of other orally administered CDK4/6i that share similar safety and tolerability compared with Abemaciclib. Reported side effects include reversible neutropenia of a lower grade, gastrointestinal toxicity, and anemia. CDK4/6i could induce dermatological side effects. Although less frequent, cutaneous adverse effects of CDK4/6i account for 25% of medication discontinuation. Frequent cutaneous adverse events are rash and pruritus; nonetheless, hair loss, nail changes, vitiligo, and photosensitivity reactions, were also reported to a lesser extent. Herein, we report a case of hair, nail, and pigmentary disorder that occurred 10 months after initiating abemaciclib treatment.

Recommendations for cyclin‑dependent kinase 4/6 inhibitor treatments in the context of co‑morbidity and drug interactions (Review)

Breast cancer is most frequently diagnosed among women aged 65-74 years and the prevalence of comorbidities in elderly patients with breast cancer is 32.2%. In addition, polypharmacy is quite common in these patients. Understanding the interaction between breast cancer treatment modalities and comorbidities is important, particularly in elderly patients, as comorbidities affect the choice of appropriate treatment and are independent risk factors for survival. A total of three oral cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i), palbociclib, ribociclib and abemaciclib, notably prolonged progression-free survival when combined with endocrine therapy (ET), compared with ET alone in patients with advanced breast cancer (ABC). The present review article therefore addressed the safety, tolerability and toxicity of CDK4/6i treatment in ABC management, compiled real-world data on how multiple clinical and pharmacological features may affect the choice of these drugs and provided practical recommendations for clinical approaches. Before starting treatment with CDK4/6i drugs, all ongoing medical conditions should be inventorized and re-graded, and examination should be performed for any additional disease that the patient may not be aware of. It is also important to obtain a detailed history of concomitant drugs, including prescription and over-the-counter drugs, vitamins, supplements and herbal products. In addition, patients should be advised to consult their oncologist before starting any new medication.

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.

Predicting drug-drug interactions in breast cancer patients treated with CDK4/6 inhibitors and forward planning

INTRODUCTION

Cyclin-dependent kinase (CDK) 4/6 inhibitors are cornerstones in the treatment of Hormone Receptor (HR) positive and Human Epidermal Growth factor (HER2) negative metastatic breast cancer. Given their widespread use in the metastatic setting and emerging use in the adjuvant setting, studying drug-drug interactions (DDI) of these medications is of utmost importance.

AREAS COVERED

This review provides key background information on the CDK4/6 inhibitors, palbociclib, ribociclib, and abemaciclib. We discuss drug-drug interactions including those with proton pump inhibitors as well as CYP3A substrates, inhibitors, and inducers. We describe the effect of these drugs on membrane transporters and their substrates as well as those drugs that increase risk of CDK4/6 toxicities. Finally, we explore future directions for strategies to minimize drug-drug interactions.

EXPERT OPINION

It is crucial to be mindful of medications that may interfere with drug absorption, such as proton pump inhibitors, as well as those that interfere with drug metabolism, such as CYP3A4 inhibitors and inducers. Additionally, special consideration should be given to populations at higher risk for polypharmacy, such as older patients with greater comorbidities. These interactions and patient characteristics should be considered when developing individual treatment plans with CDK4/6 inhibitors.

Recent progress of CDK4/6 inhibitors' current practice in breast cancer

Dysregulated cellular proliferation represents a hallmark feature across all cancers. Aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway, independent of mitogenic signaling, engenders uncontrolled breast cancer cell proliferation. Consequently, the advent of CDK4/6 inhibition has constituted a pivotal milestone in the realm of targeted breast cancer therapy. The combination of CDK4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) has emerged as the foremost therapeutic modality for patients afflicted with hormone receptor-positive (HR + )/HER2-negative (HER2-) advanced breast cancer. At present, the Food and Drug Administration (FDA) has sanctioned various CDK4/6i for employment as the primary treatment regimen in HR + /HER2- breast cancer. This therapeutic approach has demonstrated a substantial extension of progression-free survival (PFS), often amounting to several months, when administered alongside endocrine therapy. Within this comprehensive review, we systematically evaluate the utilization strategies of CDK4/6i across various subpopulations of breast cancer and explore potential therapeutic avenues following disease progression during application of CDK4/6i therapy.

Silencing geranylgeranyltransferase I inhibits the migration and invasion of salivary adenoid cystic carcinoma through RhoA/ROCK1/MLC signaling and suppresses proliferation through cell cycle regulation

Geranylgeranyltransferase type I (GGTase-I) significantly affects Rho proteins, such that the malignant progression of several cancers may be induced. Nevertheless, the effect and underlying mechanism of GGTase-I in the malignant progression of salivary adenoid cystic carcinoma (SACC) remain unclear. This study primarily aimed to investigate the role and mechanism of GGTase-I in mediating the malignant progression of SACC. The level of GGTase-I gene in cells was stably knocked down by short hairpin RNA-EGFP-lentivirus. The effects of GGTase-I silencing on the migration, invasion, and spread of cells were examined, the messenger RNA levels of GGTase-I and RhoA genes of SACC cells after GGTase-I knockdown were determined, and the protein levels of RhoA and RhoA membrane of SACC cells were analyzed. Moreover, the potential underlying mechanism of silencing GGTase-I on the above-mentioned aspects in SACC cells was assessed by examining the protein expression of ROCK1, MLC, p-MLC, E-cadherin, Vimentin, MMP2, and MMP9. Furthermore, the underlying mechanism of SACC cells proliferation was investigated through the analysis of the expression of cyclinD1, MYC, E2F1, and p21CIP1/WAF1 . Besides, the change of RhoA level in SACC tissues compared with normal paracancer tissues was demonstrated through quantitative reverse-transcription polymerase chain reaction and western blot experiments. Next, the effect after GGTase-I silencing was assessed through the subcutaneous tumorigenicity assay. As indicated by the result of this study, the silencing of GGTase-I significantly reduced the malignant progression of tumors in vivo while decreasing the migration, invasion, and proliferation of SACC cells and RhoA membrane, Vimentin, ROCK1, p-MLC, MMP2, MMP9, MYC, E2F1, and CyclinD1 expression. However, the protein expression of E-cadherin and p21CIP1/WAF1 was notably upregulated. Subsequently, no significant transform of RhoA and MLC proteins was identified. Furthermore, RhoA expression in SACC tissues was significantly higher than that in paracancerous tissues. As revealed by the results of this study, GGTase-I shows a correlation with the proliferation of SACC through the regulation of cell cycle and may take on vital significance in the migration and invasion of SACC by regulating RhoA/ROCK1/MLC signaling pathway. GGTase-I is expected to serve as a novel exploration site of SACC.

SIK2-positive tumor epithelial cells in breast cancer maybe potential anti-cancer messengers: A systematic analysis from a single-cell perspective

Breast cancer is the most common malignancy in the world and one of the leading causes of cancer death, which is a heterogeneous disease involving genetic and environmental factors. Breast cancer stem cells (BCSCs) are the main players in the aggressiveness of different tumors, at the same time, these cells are the main challenge for cancer treatment. There are multiple treatment options for breast cancer (BC) patients and the lack of understanding of prognostic and predictive biomarkers for breast cancer is a potential research direction for us to develop better treatments in the future. In this paper, we conducted a correlation analysis between SIK2 and clinical traits by searching numerous BRCA datasets in the GEO database. The model was constructed and validated by incorporating tumor samples from the TCGA-BRCA cohort. Surprisingly, we found differential expression of SIK2 gene in individual tumor samples from the UCSC database. Subsequently, we found significantly high expression of SIK2 in epithelial cells by comparing the differential expression of SIK2 in different cell subpopulations and performed subsequent immune infiltration and pathway correlation analysis. Differential genes in SIK2+ epithelial cells, which may be potential therapeutic targets for breast cancer. In conclusion, our results suggest that SIK2 may be a potential prognostic and predictive biomarker that could serve as an oncogenic messenger for breast cancer. This discovery of SIK2 may provide more valuable references for potential therapeutic tools for breast cancer.

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.

Osteonecrosis of the jaw under palbociclib: A case series description

INTRODUCTION

Cases of osteonecrosis of the jaw have been reported by dental surgeons to the pharmacovigilance center in Rennes, France, occurring among patients treated with palbociclib, a cyclin-dependent kinase 4/6 inhibitor. Although this event was not expected with the drug, a safety signal was raised. Describing a local case series, the aim of our study was to identify specific patterns that might suggest a triggering role for these drugs, and to discuss pathophysiological hypotheses.

MATERIALS AND METHODS

A retrospective case series of patients exposed to cyclin-dependent kinase 4/6 inhibitors between 2016 and 2020 with a diagnosis of osteonecrosis of the jaw at the Rennes Dental Care Center was analyzed. The descriptive analysis was conducted on patient demographics, breast cancer characteristics, osteonecrosis of the jaw, biological data, and exposure to cyclin-dependent kinase 4/6 inhibitors.

RESULTS

We identified eight cases, most of them at stages 0-1 (62.5%). Four patients were still exposed to palbociclib at the time of diagnosis and four had discontinued the treatment before the diagnosis. Chronological imputability could not be excluded given the drug's half-life and the variable intervals of dental monitoring from one patient to another. All patients had at least one dental osteonecrosis risk factor (including dental extraction, dentures, and denosumab exposure at the time of diagnosis). Neutropenia and mucositis were not systematically reported at the time of diagnosis. The anatomopathological characteristics were nonspecific.

CONCLUSION

We did not identify a specific pattern that could suggest a triggering role of palbociclib in the development of ONJ.

Risk of Cardiovascular Events with Cyclin-Dependent Kinases 4 and 6 (CDK 4/6) Inhibitors among Patients with Advanced Breast Cancer: A Systematic Review and Network Meta-Analysis

Background

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors have shown promising survival outcomes with additional treatments to the traditional endocrine therapy (ET) in patients with hormone receptor-positive (HR-positive) and human epidermal growth factor receptor type 2 negative (HER2-negative) advanced breast cancer (aBC). However, the head-to-head cardiovascular safety profile of these three agents (palbociclib, ribociclib, and abemaciclib) remains unclear. We summarized the incidence of major adverse cardiovascular events (MACE) and hypertension associated with the use of CDK4/6 inhibitor in randomized control trials (RCTs) and compared the risks of MACE and hypertension through network-meta analysis (NMA).

Methods

A systematic search through PubMed and Cochrane Library was performed to identify phase III RCTs reporting cardiovascular safety data of CDK4/6 inhibitors in patients with aBC. We qualitatively synthesized the incidence of MACE and hypertension associated with CDK4/6 inhibitor use within on-treatment or placebo-controlled duration. A Bayesian NMA with random-effects models was performed, and pairwise comparisons between treatment options were presented by odds ratio (OR). The probability of each treatment arm's relative ranking was reported using surface under the cumulative ranking curve (SUCRA) scores. A sensitivity analysis was conducted using the Mantel-Haenszel (MH) method.

Results

Nine RCTs with four unique treatment arms and event(s) in at least one arm were included in the NMA. A total of 5218 patients were analyzed for MACE outcomes. The overall incidence of MACE in the CDK4/6 inhibitors+ET arm was 0.8%, while the endocrine therapy alone group was 0.4%. Abemaciclib+ET ranked the best in reducing the risk of MACE (SUCRA = 0.90) as compared to ET alone (SUCRA = 0.67, OR = 0.45, 95% credible interval (CI) = 0.07-2.82), palbociclib+ET (SUCRA = 0.25, OR = 0.09, 95% CI = 0.00-2.39) and ribociclib+ET (SUCRA = 0.17, OR = 0.08, 95% CI = 0.00-1.18). The findings were similar in the MH network. However, abemaciclib+ET (OR = 0.11; 95% CI = 0.02-0.81) had a significantly lower risk of MACE than ribociclib+ET in the MH network. No statistically significant differences in hypertension were shown among all comparisons.

Conclusions

Abemaciclib+ET may have a lower risk of MACE for the treatment of aBC, while palbociclib+ET may reduce the risk of hypertension in this population. Our findings suggest a comparative cardiovascular safety trend among the three CDK4/6 inhibitors, but further research on direct comparisons is needed to guide treatment choice.

Real-world effectiveness of ribociclib in metastatic breast cancer patients: Does dose affect survival?

Introduction: Real-world data are critical to demonstrate the reproducibility of evidence and external generalizability of randomized clinical trials. The purpose of this study was to assess real-world security profile and management of adverse events (AEs) presented with ribociclib for the treatment of HR + /HER2- metastatic breast cancer (MBC). Our secondary objective was to provide real-world effectiveness of this treatment (measured with progression-free survival (PFS)) and to confirm the hypothesis that dose reductions are not related with disease progression. Material and methods: Observational retrospective study evaluating all females with MBC treated with ribociclib. Study period: January 2017 to September 2019. Follow-up was done until November 2021. Response was assessed through the PFS according to RECIST1.1 and National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) was used to classify AEs. Results: The most common AE was any grade neutropenia, documented in 37 of 53 patients (69.8%) during the course of treatment. By the end of the follow-up period, overall median PFS with ribociclib therapy was 27.3 months (95% confidence interval (CI) 20.8-71.8 months). In total, 50 patients (94.4%) initiated ribociclib at 600 mg dose, 28 patients (58%) required dose reductions. PFS of patients receiving ribociclib as first-line treatment was 28 (95% CI 15-41 months). Conclusions: Our results from patients treated in real-world clinical settings indicate that ribociclib is safe and their AEs are manageable with active monitoring, temporal suspension of treatment and dose reduction. Furthermore, our results indicate that dose reduction of ribociclib is not associated with a loss of efficacy.

Recent Developments in the Therapeutic Landscape of Advanced or Metastatic Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) disease is the most frequently diagnosed subtype of breast cancer. Among tumor subtypes, natural course of HR+ breast cancer is indolent with favorable prognosis compared to other subtypes such as human epidermal growth factor protein 2-positive disease and triple-negative disease. HR+ tumors are dependent on steroid hormone signaling and endocrine therapy is the main treatment option. Recently, the discovery of cyclin-dependent kinase 4/6 inhibitors and their synergistic effects with endocrine therapy has dramatically improved treatment outcome of advanced HR+ breast cancer. The demonstrated efficacy of additional nonhormonal agents, such as targeted therapy against mammalian target of rapamycin and phosphatidylinositol 3-kinase signaling, poly(ADP-ribose) polymerase inhibitors, antibody-drug conjugates, and immunotherapeutic agents have further expanded the available therapeutic options. This article reviews the latest advancements in the treatment of HR+ breast cancer, and in doing so discusses not only the development of currently available treatment regimens but also emerging therapies that invite future research opportunities in the field.

Hematological Events Potentially Associated with CDK4/6 Inhibitors: An Analysis from the European Spontaneous Adverse Event Reporting System

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are a recent targeted therapy approved for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer. Abemaciclib, palbociclib and ribociclib demonstrated great efficacy and safety during clinical studies. However, differences in their adverse-event profiles have been observed. This work aims to describe the suspected adverse drug reactions (ADRs), such as leukopenia and thrombocytopenia, reported for each CDK4/6 inhibitor in the EudraVigilance (EV) database. Data on individual case safety reports (ICSRs) were obtained by accessing the European spontaneous reporting system via the EV website. Information on concomitant drug therapy, including fulvestrant, letrozole, anastrozole and exemestane, was also analyzed. A total of 1611 ICSRs were collected from the EV database. Most reports of palbociclib and ribociclib were classified as serious cases for both suspected leukopenia and thrombocytopenia ADRs. However, most patients had their leukopenia and thrombocytopenia recovered/resolved. On the contrary, reports of abemaciclib were mostly characterized as non-serious cases. Abemaciclib and palbociclib were often combined with fulvestrant, while ribociclib was generally associated with letrozole. Pharmacovigilance studies are crucial for the early identification of potential ADRs and to better differentiate the toxicity profile of the different CDK4/6 inhibitors, particularly in a real-world setting.

An Overview of the Safety Profile and Clinical Impact of CDK4/6 Inhibitors in Breast Cancer-A Systematic Review of Randomized Phase II and III Clinical Trials

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6is) have transformed the treatment of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer over the last decade. These inhibitors are currently established as first- and second-line systemic treatment choices for both endocrine-sensitive and -resistant breast cancer populations alongside endocrine therapy (ET) or monotherapy. Data on targeted therapy continue to mature, and the number of publications has been constantly rising. Although these drugs have been demonstrated to prolong overall survival (as well as progression-free survival (PFS) in breast cancer patients), changing the paradigm of all current knowledge, they also cause important adverse events (AEs). This review provides the latest summary and update on the safety profile of the three CDK4/6 inhibitors, as it appears from all major phase II and III randomized clinical trials regarding palbociclib, ribociclib, and abemaciclib, including the most relevant 15 clinical trials.

Targeting cyclin-dependent kinases in rheumatoid arthritis and psoriasis - a review of current evidence

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with synovial proliferation and bone erosion, which leads to the structural and functional impairment of the joints. Immune cells, together with synoviocytes, induce a pro-inflammatory environment and novel treatment agents target inflammatory cytokines. Psoriasis is a chronic immune-mediated skin disease, and several cytokines are considered as typical mediators in the progression of the disease, including IL-23, IL-22, and IL-17, among others.

AREA COVERED

In this review, we try to evaluate whether cyclin-dependent kinases (CDK), enzymes that regulate cell cycle and transcription of various genes, could become novel therapeutic targets in RA and psoriasis. We present the main results of in vitro and in vivo studies, as well as scarce clinical reports.

EXPERT OPINION

CDK inhibitors seem promising for treating RA and psoriasis because of their multidirectional effects. CDK inhibitors may affect not only the process of osteoclastogenesis, thereby reducing joint destruction in RA, but also the process of apoptosis of neutrophils and macrophages responsible for the development of inflammation in both RA and psoriasis. However, assessing the efficacy of these drugs in clinical practice requires multi-center, long-term clinical trials evaluating the effectiveness and safety of CDK-blocking therapy in RA and psoriasis.

Adverse Cardiovascular Events Associated With Cyclin-Dependent Kinase 4/6 Inhibitors in Patients With Metastatic Breast Cancer

Background Cyclin-dependent kinase (CDK) 4 and 6 inhibitors have significantly improved survival in patients with hormone receptor-positive metastatic breast cancer. There are few data regarding the epidemiology of cardiovascular adverse events (CVAEs) with these therapies. Methods and Results Using the OneFlorida Data Trust, adult patients without prior cardiovascular disease who received at least 1 CDK4/6 inhibitor were included in the analysis. CVAEs identified from International Classification of Diseases, Ninth and Tenth Revisions (ICD-9/10) codes included hypertension, atrial fibrillation(AF)/atrial flutter (AFL), heart failure/cardiomyopathy, ischemic heart disease, and pericardial disease. Competing risk analysis (Fine-Gray model) was used to determine the association between CDK4/6 inhibitor therapy and incident CVAEs. The effect of CVAEs on all-cause death was studied using Cox proportional hazard models. Propensity-weight analyses were performed to compare these patients to a cohort of patients treated with anthracyclines. A total of 1376 patients treated with CDK4/6 inhibitors were included in the analysis. CVAEs occurred in 24% (35.9 per 100 person-years). CVAEs were slightly higher in patients who received CKD4/6 inhibitors compared with anthracyclines (P=0.063), with higher death rate associated with the development of AF/AFL or cardiomyopathy/heart failure in the CDK4/6 group. The development of cardiomyopathy/heart failure and AF/AFL was associated with increased all-cause death (adjusted hazard ratio [HR], 4.89 [95% CI, 2.98-8.05]; and 5.88 [95% CI, 3.56-9.73], respectively). Conclusions CVAEs may be more common with CDK4/6 inhibitors than previously recognized, with increased death rates in these patients who develop AF/AFL or heart failure. Further research is needed to definitively determine cardiovascular risk associated with these novel anticancer treatments.

Combination Therapy as a Promising Way to Fight Oral Cancer

Oral cancer is a highly aggressive tumor with invasive properties that can lead to metastasis and high mortality rates. Conventional treatment strategies, such as surgery, chemotherapy, and radiation therapy, alone or in combination, are associated with significant side effects. Currently, combination therapy has become the standard practice for the treatment of locally advanced oral cancer, emerging as an effective approach in improving outcomes. In this review, we present an in-depth analysis of the current advancements in combination therapies for oral cancer. The review explores the current therapeutic options and highlights the limitations of monotherapy approaches. It then focuses on combinatorial approaches that target microtubules, as well as various signaling pathway components implicated in oral cancer progression, namely, DNA repair players, the epidermal growth factor receptor, cyclin-dependent kinases, epigenetic readers, and immune checkpoint proteins. The review discusses the rationale behind combining different agents and examines the preclinical and clinical evidence supporting the effectiveness of these combinations, emphasizing their ability to enhance treatment response and overcome drug resistance. Challenges and limitations associated with combination therapy are discussed, including potential toxicity and the need for personalized treatment approaches. A future perspective is also provided to highlight the existing challenges and possible resolutions toward the clinical translation of current oral cancer therapies.

Risk Factors for Palbociclib-Induced Early Developing Neutropenia in Patients with Hormone Receptor-Positive Metastatic Breast Cancer

PURPOSE

This study aimed to determine the risk factors for palbociclib-induced grade 4 or grade 3 neutropenia (NP) requiring dose reduction or delayed treatment in patients with HR+/HER2-metastatic breast cancer in the first 3 cycles (early grade 3/4 NP) and whether the early developing grade 3/4 NP affects progression-free survival.

METHODS

A retrospective study using electronic medical records was conducted on patients who received palbociclib for metastatic breast cancer between January 2018 and August 2022. The early grade 3/4 NP risk factors were evaluated with univariate and multivariable logistic regression analyses. In addition, the Kaplan-Meier method was used to estimate the median progression-free survival (PFS) to analyze the effect of early grade 3/4 NP on treatment.

RESULTS

Out of the 264 patients included in this study, 173 (65.6%) experienced early grade 3/4 NP. A total of four models were applied for multivariable analysis to identify early grade 3/4 NP-developing factors. Low baseline ANC, WBC, PLT, and BSA were significant risk factors for early grade 3/4 NP; baseline ANC < 3700/mm³, WBC < 6.30 × 10⁹/mm³, PLT < 230 × 10⁹/mm³, and BSA < 1.58 m² increased the risk by approximately 4.0-fold, 3.7-4.0-fold, 2.1-fold, and 2.0-fold, respectively. Early grade 3/4 NP did not affect PFS (p = 0.710), although patients with early grade 3/4 NP had more frequent dose reductions or treatment delays.

CONCLUSIONS

Based on the results, low baseline ANC, WBC, PLT, and BSA were associated with early grade 3/4 NP. Patients with risk factors require careful monitoring, and this study is expected to help predict NP, which may appear in early treatment.

Discordant Humoral and T-Cell Response to mRNA SARS-CoV-2 Vaccine and the Risk of Breakthrough Infections in Women with Breast Cancer, Receiving Cyclin-Dependent Kinase 4 and 6 Inhibitors

Few data are available about the immune response to mRNA SARS-CoV-2 vaccines in patients with breast cancer receiving cyclin-dependent kinase 4/6 inhibitors (CDK4/6i). We conducted a prospective, single-center study of patients with breast cancer treated with CDK4/6i who received mRNA-1273 vaccination, as well as a comparative group of healthcare workers. The primary endpoint was to compare the rate and magnitude of humoral and T-cell response after full vaccination. A better neutralizing antibody and anti-S IgG level was observed after vaccination in the subgroup of women receiving CDK4/6i, but a trend toward a reduced CD4 and CD8 T-cell response in the CDK4/6i group was not statistically significant. There were no differences in the rate of COVID-19 after vaccination (19% vs. 12%), but breakthrough infections were observed in those with lower levels of anti-S IgG and neutralizing antibodies after the first dose. A lower rate of CD4 T-cell response was also found in those individuals with breakthrough infections, although a non-significant and similar level of CD8 T-cell response was also observed, regardless of breakthrough infections. The rate of adverse events was higher in patients treated with CDK4/6i, without serious adverse events. In conclusion, there was a robust humoral response, but a blunted T-cell response to mRNA vaccine in women receiving CDK4/6i, suggesting a reduced trend of the adaptative immune response.

Hepatotoxicity of Small Molecule Protein Kinase Inhibitors for Cancer

Small molecule protein kinase inhibitors (PKIs) have become an effective strategy for cancer patients. However, hepatotoxicity is a major safety concern of these drugs, since the majority are reported to increase transaminases, and few of them (Idelalisib, Lapatinib, Pazopanib, Pexidartinib, Ponatinib, Regorafenib, Sunitinib) have a boxed label warning. The exact rate of PKI-induced hepatoxicity is not well defined due to the fact that the majority of data arise from pre-registration or registration trials on fairly selected patients, and the post-marketing data are often based only on the most severe described cases, whereas most real practice studies do not include drug-related hepatotoxicity as an end point. Although these side effects are usually reversible by dose adjustment or therapy suspension, or by switching to an alternative PKI, and fatality is uncommon, all patients undergoing PKIs should be carefully pre-evaluated and monitored. The management of this complication requires an individually tailored reappraisal of the risk/benefit ratio, especially in patients who are responding to therapy. This review reports the currently available data on the risk and management of hepatotoxicity of all the approved PKIs.

Pan-Cancer landscape of protein activities identifies drivers of signalling dysregulation and patient survival

Genetic alterations in cancer cells trigger oncogenic transformation, a process largely mediated by the dysregulation of kinase and transcription factor (TF) activities. While the mutational profiles of thousands of tumours have been extensively characterised, the measurements of protein activities have been technically limited until recently. We compiled public data of matched genomics and (phospho)proteomics measurements for 1,110 tumours and 77 cell lines that we used to estimate activity changes in 218 kinases and 292 TFs. Co-regulation of kinase and TF activities reflects previously known regulatory relationships and allows us to dissect genetic drivers of signalling changes in cancer. We find that loss-of-function mutations are not often associated with the dysregulation of downstream targets, suggesting frequent compensatory mechanisms. Finally, we identified the activities most differentially regulated in cancer subtypes and showed how these can be linked to differences in patient survival. Our results provide broad insights into the dysregulation of protein activities in cancer and their contribution to disease severity.

Deciphering the Immunomodulatory Role of Cyclin-Dependent Kinase 4/6 Inhibitors in the Tumor Microenvironment

Cancer is characterized by persistent cell proliferation driven by aberrant cell cycle regulation and stimulation of cyclin-dependent kinases (CDKs). A very intriguing and potential approach for the development of antitumor medicines is the suppression of CDKs that lead to induction of apoptosis and cell cycle arrest. The shift of the cell cycle from the G0/G1 phase to the S phase, which is characterized by active transcription and synthesis, depends on the development of the cyclin D-CDK4/6 complex. A precise balance between anticancer activity and general toxicity is demonstrated by CDK inhibitors, which can specifically block CDK4/6 and control the cell cycle by reducing the G1 to S phase transition. CDK4/6 inhibitors have recently been reported to exhibit significant cell growth inhibition via modulating the tumour microenvironment in cancerous cells. One significant new understanding is that these inhibitors serve important functions in the interaction among tumour cells and the host immune system in addition to being cytostatic. Herein, we discuss the biological significance of CDK4/6 inhibitors in cancer therapeutics, as well as their biological impact on T cells and other important immune cells. Furthermore, we explore the integration of preclinical findings of these pharmaceuticals' ability to enhance antitumor immunity.

Adherence to the CDK 4/6 Inhibitor Palbociclib and Omission of Dose Management Supported by Pharmacometric Modelling as Part of the OpTAT Study

The cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) palbociclib is administered orally and cyclically, causing medication adherence challenges. We evaluated components of adherence to palbociclib, its relationship with pharmacokinetics (PK), and drug-induced neutropenia. Patients with metastatic breast cancer (MBC) receiving palbociclib, delivered in electronic monitors (EM), were randomized 1:1 to an intervention and a control group. The intervention was a 12-month interprofessional medication adherence program (IMAP) along with monthly motivational interviews by a pharmacist. Implementation adherence was compared between groups using generalized estimating equation models, in which covariates were included. Model-based palbociclib PK and neutrophil profiles were simulated under real-life implementation scenarios: (1) optimal, (2) 2 doses omitted and caught up at cycle end. At 6 months, implementation was slightly higher and more stable in the intervention (n = 19) than in the control (n = 19) group, 99.2% and 97.3% (Δ1.95%, 95% CI 1.1−2.9%), respectively. The impact of the intervention was larger in patients diagnosed with MBC for >2 years (Δ3.6%, 95% CI 2.1−5.4%), patients who received >4 cycles before inclusion (Δ3.1%, 95% CI 1.7−4.8%) and patients >65 (Δ2.3%, 95% CI 0.8−3.6%). Simulations showed that 25% of patients had neutropenia grade ≥3 during the next cycle in scenario 1 versus 30% in scenario 2. Education and monitoring of patient CDK4/6i cycle management and adherence along with therapeutic drug monitoring can help clinicians improve prescription and decrease toxicity.

Tolerability of palbociclib in younger and older patients with advanced breast cancer

INTRODUCTION

Palbociclib is a small-molecule cyclin-dependent kinase 4/6 inhibitor used to treat hormone receptor-positive, human epidermal growth factor receptor-2 negative advanced breast cancer. Patient-specific factors impacting dose reductions or discontinuations are unknown.

METHODS

The primary objective was to evaluate the association of age (<60 vs. ≥60 years) with palbociclib dose reductions or discontinuations secondary to neutropenia. This single-center, retrospective chart review included hormone receptor-positive, human epidermal growth factor receptor-2 negative advanced breast cancer patients ≥18 years treated with palbociclib between April 2015 and May 2020. Patients <60 years at the time of palbociclib initiation were in the younger group and patients ≥60 years were in the older group.

RESULTS

Among the 107 patients included, younger patients were less likely than older patients to have a palbociclib starting dose <125 mg (0% vs. 11.9%, p = 0.02). Differences in palbociclib dose reductions or treatment discontinuations secondary to neutropenia were not detected (35.4% vs. 42.4%, p = 0.55). Neither the total number of palbociclib dose reductions (none: 54.2% vs. 49.1%, one: 33.3% vs. 42.4%, two: 12.5% vs. 8.5%, p = 0.61), nor the final dose of palbociclib (125 mg: 54.2% vs. 40.7%, 100 mg: 29.2% vs. 27.1%, 75 mg: 16.7% vs. 32.2%, p = 0.17) differed between younger and older patients.

CONCLUSIONS

Age (<60 vs. ≥60 years) was not associated with the rate of palbociclib dose reductions or discontinuations secondary to neutropenia. Older (≥60 years) patients were more likely to start palbociclib at lower doses which may impact neutropenia and non-neutropenic intolerance.

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.

The Cyclin-Dependent Kinase 4/6 Inhibitor Abemaciclib Is Tolerated Better than Palbociclib by Advanced Breast Cancer Patients with High Serum Albumin Levels

The cyclin-dependent kinase (CDK) 4/6 inhibitors, palbociclib and abemaciclib, have been approved in Japan. However, the selection criteria for these drugs have not been established. Hence, we aimed to identify the risk factors for CDK4/6 inhibitor-induced intolerable adverse events requiring dose reduction or therapy cessation and to establish useful markers for choosing the appropriate CDK4/6 inhibitor, based on the incidence of the intolerable adverse events. This retrospective cohort analysis included patients with advanced breast cancer who received 125 mg/d palbociclib or 300 mg/d abemaciclib. We defined significant adverse events (SAEs) as side effects requiring dose reduction or therapy cessation. Thirty-six percent of the patients who received palbociclib (9/25) and 27.3% of those who received abemaciclib (9/33) experienced SAEs. In palbociclib and abemaciclib groups, baseline white blood cell (WBC) counts and serum albumin (ALB) levels, respectively, were significantly lower in patients who experienced SAEs than in those who did not (palbociclib: p = 0.007; abemaciclib: p = 0.004). According to the receiver operating characteristic curve analysis, the optimal cutoff values for baseline WBC count and ALB level were 5700/µL and 4.0 g/dL, respectively. Among patients with ALB levels >4.0 g/dL, the incidence of abemaciclib-induced SAEs was significantly lower than that of the palbociclib-induced SAEs (1/17 (5.9%) vs. 6/14 (42.9%), odds ratio: 11.0, 95% confidence interval: 1.07-583, p = 0.0281). Thus, a baseline WBC count ≤5700/µL and ALB level ≤4.0 g/dL may be risk factors for palbociclib and abemaciclib-induced SAEs, respectively. Also, high ALB levels can serve as a useful marker for choosing abemaciclib.

CDK 4/6 inhibitors for the treatment of meningioma

Meningiomas are the most common non-metastatic brain tumors, and although the majority are relatively slow-growing and histologically benign, a subset of meningiomas are aggressive and remain challenging to treat. Despite a standard of care that includes surgical resection and radiotherapy, and recent advances in meningioma molecular grouping, there are no systemic medical options for patients with meningiomas that are resistant to standard interventions. Misactivation of the cell cycle at the level of CDK4/6 is common in high-grade or molecularly aggressive meningiomas, and CDK4/6 has emerged as a potential target for systemic meningioma treatments. In this review, we describe the preclinical evidence for CDK4/6 inhibitors as a treatment for high-grade meningiomas and summarize evolving clinical experience with these agents. Further, we highlight upcoming clinical trials for patients meningiomas, and discuss future directions aimed at optimizing the efficacy of these therapies and selecting patients most likely to benefit from their use.

Prediction of allosteric druggable pockets of cyclin-dependent kinases

Cyclin-dependent kinase (Cdk) proteins play crucial roles in the cell cycle progression and are thus attractive drug targets for therapy against such aberrant cell cycle processes as cancer. Since most of the available Cdk inhibitors target the highly conserved catalytic ATP pocket and their lack of specificity often lead to side effects, it is imperative to identify and characterize less conserved non-catalytic pockets capable of interfering with the kinase activity allosterically. However, a systematic analysis of these allosteric druggable pockets is still in its infancy. Here, we summarize the existing Cdk pockets and their selectivity. Then, we outline a network-based pocket prediction approach (NetPocket) and illustrate its utility for systematically identifying the allosteric druggable pockets with case studies. Finally, we discuss potential future directions and their challenges.

Cyclin-dependent kinase inhibition and its intersection with immunotherapy in breast cancer: more than CDK4/6 inhibition

INTRODUCTION

Cyclin-dependent kinase (CDK) 4/6 inhibitors (CDK4/6i) have had clinical success in treating hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer. Notably, CDK4/6i have expanded to the neoadjuvant setting for early breast cancer and other cancer types and potently synergize with immunotherapy. Other CDKs, including CDK7, CDK9, and CDK12/13, mainly function in transcriptional processes as well as cell cycle regulation, RNA splicing, and DNA damage response. Inhibiting these CDKs aids in suppressing tumors, reversing drug resistance, increasing drug sensitivity, and enhancing anti-tumor immunity in breast cancer.

AREAS COVERED

We reviewed the applications of CDK4/6i, CDK7i, CDK9i and CDK12/13i for various breast cancer subtypes and their potentials for combination with immunotherapy. A literature search of PubMed, Embase, and Web of Science was conducted in April 2022.

EXPERT OPINION

The use of CDK4/6i represents a major milestone in breast cancer treatment. Moreover, transcription-related CDKs play critical roles in tumor development and are promising therapeutic targets for breast cancer. Some relevant clinical studies are underway. More specific and efficient CDKis will undoubtedly be developed and clinically tested. Characterization of their immune-priming effects will promote the development of combination therapies consisting of CDKi and immunotherapy.

Molecular dynamics simulation and in vitro evaluation of herb-drug interactions involving dietary polyphenols and CDK inhibitors in breast cancer chemotherapy

Dietary polyphenols such as quercetin and curcumin have been extensively administered to patients with cancer in the form of herbal supplements. They may have a synergistic anticancer effect; however, a risk of pharmacokinetic interactions with selective CDK-4/6 inhibitors that are metabolized by the CYP3A4 enzyme exists. Considering these pharmacokinetic aspects, the current study examined the effects of curcumin and quercetin on human CYP3A4 to ascertain CYP3A4-mediated herb-drug interactions with CDK inhibitors. In this study, using in silico methods and CYP3A4 inhibition kinetics in human liver microsomes and recombinant CYP3A4 enzymes, the effects of concentration-dependent inhibition of CYP3A4 by quercetin and curcumin on CDK inhibitors metabolism were examined. Based on our in-silico docking findings, curcumin and quercetin were considerably bound to CYP3A4 protein and displace CDK inhibitors from the CYP3A4 substrate binding domain. The IC₅₀ values of curcumin and quercetin were 16.10 and 0.05 μM, respectively, for CYP3A4-mediated 1'-hydroxylation of midazolam. The dietary polyphenols prolonged the in vitro half-life of palbociclib and ribociclib by 6.4-fold and decreased their intrinsic microsomal clearance by approximately 4.6 times. Our findings indicate that curcumin and quercetin effectively cause herb-drug interactions and should be cautiously used to avoid therapeutic failure.

Population Pharmacokinetics of Palbociclib and Its Correlation with Clinical Efficacy and Safety in Patients with Advanced Breast Cancer

Neutropenia is the most frequent dose-limiting toxicity reported in patients with metastatic breast cancer receiving palbociclib. The objective of this study was to investigate the pharmacokinetic–pharmacodynamic (PK/PD) relationships for toxicity (i.e., absolute neutrophil count, ANC) and efficacy (i.e., progression-free survival, PFS). A semi-mechanistic PK/PD model was used to predict neutrophils’ time course using a population approach (NONMEM). Influence of demographic and clinical characteristics was evaluated. Cox proportional hazards models were developed to evaluate the influence of palbociclib PK on PFS. A two-compartment model with first-order absorption and a lag time adequately described the 255 palbociclib concentrations provided by 44 patients. The effect of the co-administration of proton-pump inhibitors in fasting conditions increased palbociclib clearance by 56%. None of the tested covariates affected the PD parameters. Model-based simulations confirmed the concentration-dependent and non-cumulative properties of palbociclib-induced neutropenia, reversible after treatment withdrawal. The ANC nadir occurred approximately at day 24 of each cycle. Cox analyses revealed a trend for better PFS with increasing palbociclib exposure in older patients. By characterizing palbociclib-induced neutropenia, this model offers support to clinicians to rationally optimize treatment management through patient-individualized strategies.

Transcriptional coactivator MED1 in the interface of anti-estrogen and anti-HER2 therapeutic resistance

Breast cancer is one of the most common cancer and leading causes of death in women in the United States and Worldwide. About 90% of breast cancers belong to ER+ or HER2+ subtypes and are driven by key breast cancer genes Estrogen Receptor and HER2, respectively. Despite the advances in anti-estrogen (endocrine) and anti-HER2 therapies for the treatment of these breast cancer subtypes, unwanted side effects, frequent recurrence and resistance to these treatments remain major clinical challenges. Recent studies have identified ER coactivator MED1 as a key mediator of ER functions and anti-estrogen treatment resistance. Interestingly, MED1 is also coamplified with HER2 and activated by the HER2 signaling cascade, and plays critical roles in HER2-mediated tumorigenesis and response to anti-HER2 treatment as well. Thus, MED1 represents a novel crosstalk point of the HER2 and ER pathways and a highly promising new therapeutic target for ER+ and HER2+ breast cancer treatment. In this review, we will discuss the recent progress on the role of this key ER/HER2 downstream effector MED1 in breast cancer therapy resistance and our development of an innovative RNA nanotechnology-based approach to target MED1 for potential future breast cancer therapy to overcome treatment resistance.

Second-Degree Type 2 Atrioventricular Block Requiring Permanent Cardiac Pacing in Patients on CDK4/6 Inhibitors: Report of Two Cases

Introduction

A wide spectrum of cardiovascular (CV) toxicity is associated with anticancer treatment, and nearly all chemotherapeutic agents can elicit CV toxicity. Inhibitors of cyclin-dependent kinases 4/6 (CDK4/6Is) have become standard of care in the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer (MBC). CV side effects are uncommon with CDK4/6Is and only include QT prolongation, with a low incidence rate.

Case Presentation

This paper describes 2 cases of new-onset second-degree type 2 atrioventricular (AV) blocks requiring permanent cardiac pacing involving 2 women with MBC receiving ribociclib or abemaciclib. Both our patients had no known history or risk factors of cardiac disease and a normal 12-lead resting electrocardiogram (ECG) when diagnosed with breast adenocarcinoma. Both patients have been subjected to surveillance for cardiotoxicity with serial ECG and echocardiography. No left ventricular dysfunction or arrhythmia was found during the follow-up, and cardiac biomarkers were normal.

Conclusion

To our knowledge, these are the first cases reported in the literature of new-onset advanced AV blocks in patients under treatment with CDK4/6Is, suggesting the clinical relevance of a more frequent ECG monitoring, besides the QT interval, in these patients.

New Insights on the Toxicity on Heart and Vessels of Breast Cancer Therapies

Cardiovascular diseases are largely represented in patients with cancer and appear to be important side effects of cancer treatments, heavily affecting quality of life and leading to premature morbidity and death among cancer survivors. In particular, treatments for breast cancer have been shown to potentially play serious detrimental effects on cardiovascular health. This review aims to explore the available literature on breast cancer therapy-induced side effects on heart and vessels, illustrating the molecular mechanisms of cardiotoxicity known so far. Moreover, principles of cardiovascular risk assessment and management of cardiotoxicity in clinical practice will also be elucidated. Chemotherapy (anthracycline, taxanes, cyclophosphamide and 5-fluorouracil), hormonal therapy (estrogen receptor modulator and gonadotropin or luteinizing releasing hormone agonists) and targeted therapy (epidermal growth factor receptor 2 and Cyclin-dependent kinases 4 and 6 inhibitors) adverse events include arterial and pulmonary hypertension, supraventricular and ventricular arrhythmias, systolic and diastolic cardiac dysfunction and coronary artery diseases due to different and still not well-dissected molecular pathways. Therefore, cardiovascular prevention programs and treatment of cardiotoxicity appear to be crucial to improve morbidity and mortality of cancer survivors.

Interstitial lung disease in patients treated with Cyclin-Dependent Kinase 4/6 inhibitors: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Cyclin-Dependent Kinase (CDK) 4/6 inhibitors have shown significant clinical activity in cancer patients. However, some concerns regarding rare adverse events (AEs) have occurred including interstitial lung disease (ILD)/pneumonitis, for which data are deficient. The aim of this study was to evaluate the overall incidence and risk of ILD/pneumonitis related to CDK4/6 inhibitors in randomized controlled trials (RCTs).

METHODS

Electronic databases and ClinicalTrials.gov were searched from inception to October 1, 2021 for RCTs reporting the occurrence of LD/pneumonitis in cancer patients treated with CDK4/6 inhibitors. Peto odds ratios (Peto ORs) and 95% confidence intervals (CIs) were used to pool the study.

RESULTS

12 RCTs with a total of 16,060 patients were eligible. The overall incidence of all-grade ILD/pneumonitis was 1.6% (131/8407) in the treatment group compared with 0.7% (50/7349) in the control group. CDK4/6 inhibitors significantly increased the risk of all-grade ILD/pneumonitis with a pooled Peto OR of 2.12 (95% CI [1.57, 2.86], P < 0.00001) with no heterogeneity (I² = 0%, χ² P = 0.98). A higher incidence of grade 3 or higher ILD/pneumonitis was also observed in the treatment group (0.2%, 16/7087) compared with the control group (0.05%, 3/6617) with a Peto OR of 3.22 (95% CI [1.28, 8.09], P = 0.01) with no heterogeneity (I² = 0%, χ² P = 0.62). Two grade 5 pneumonitis were reported in the included studies. Subgroup analyses did not show any significant difference.

CONCLUSIONS

The risk of all-grade and grade 3 or higher ILD/pneumonitis was higher in patients treated with CDK4/6 inhibitors compared to controls. The awareness for these rare AEs in the application of CDK4/6 inhibitors should be enhanced. Further studies are required to validate the mechanisms and the risk factors of ILD/pneumonitis with CDK4/6 inhibitors.

The Impact of Real-World Alternative Dosing Strategies of Palbociclib on Progression-Free Survival in Patients with Metastatic Breast Cancer

Background: Palbociclib, a cyclin-dependent kinase 4 and 6 (CDK 4/6) inhibitor, in combination with letrozole or fulvestrant has been demonstrated to prolong the progression-free survival (PFS) in patients with hormone receptor-positive (HR+), human epidermal growth factor 2-negative (HER2-) metastatic breast cancer. In efforts to mitigate neutropenic toxicities, oncologists in real-world practice have prescribed alternative dosing strategies with palbociclib, yet the implication on PFS is unknown. Methods: We conducted a retrospective, observational chart review of all female patients at our clinics with HR+, HER2- metastatic breast cancer receiving palbociclib in combination with either letrozole or fulvestrant with a first dose initiated between June 2016 and December 2018 and followed their disease course until 30 April 2020. Results: The median PFS for all clinic patients receiving palbociclib and letrozole (n = 63) was 40.8 months (95% confidence interval (CI) 25.6–not estimable) and 16.97 months (95% CI 8.57–not estimable) for patients receiving palbociclib and fulvestrant (n = 11). We identified seven alternative dosing strategies prescribed by oncologists, the most prevalent being prescribing palbociclib for three weeks on and two weeks off (n = 8). The Kaplan–Meier curves for PFS in patients receiving letrozole and palbociclib prescribed alternative dosing strategies appear to diverge from monograph dosing early in the treatment. Many patients prescribed palbociclib using alternative dosing strategies continued to be observed even by the 18-month timepoint. The prevalence of grade 4 neutropenia was lower for patients on palbociclib with letrozole, suggesting a possible mitigation of severe neutropenia with alternative dosing strategies. Conclusions: We conclude that alternative dosing strategies used by oncologists such as prescribing palbociclib for three weeks on, two weeks off may achieve comparable disease control while mitigating neutropenic toxicities when compared to standard monograph dosing recommendations, prolonging treatment tolerability and adherence. Further large-scale studies are needed to confirm these results for future clinical adoption.

Therapeutic Targeting of Minimal Residual Disease to Prevent Late Recurrence in Hormone-Receptor Positive Breast Cancer: Challenges and New Approaches

While the majority of breast cancers are diagnosed at a curable stage, approximately 20% of women will experience recurrence at a distant site during their lifetime. These metastatic recurrences are incurable with current therapeutic approaches. Over the past decade, the biologic mechanisms underlying these recurrences have been elucidated, establishing the existence of minimal residual disease in the form of circulating micrometastases and dormant disease, primarily in the bone marrow. Numerous technologies are now available to detect minimal residual disease (MRD) after breast cancer treatment, but it is yet unknown how to best target and eradicate these cells, and whether clearance of detectable disease prior to the formation of overt metastases can prevent ultimate progression and death. Clinical trials to test this hypothesis are challenging due to the rare nature of MRD in the blood and bone marrow, resulting in the need to screen a large number of survivors to identify those for study. Use of prognostic molecular tools may be able to direct screening to those patients most likely to harbor MRD, but the relationship between these predictors and MRD detection is as yet undefined. Further challenges include the lack of a definitive assay for MRD with established clinical utility, difficulty in selecting potential interventions due to limitations in understanding the biology of MRD, and the emotional impact of detecting MRD in patients who have completed definitive treatment and have no evidence of overt metastatic disease. This review provides a roadmap for tackling these challenges in the design and implementation of interventional clinical trials aimed at eliminating MRD and ultimately preventing metastatic disease to improve survival from this disease, with a specific focus on late recurrences in ER+ breast cancer.

Pharmacoeconomic evaluations of CDK4/6 inhibitors plus endocrine therapy for advanced hormone receptor-positive (HR+) and human epidermal growth factor receptor-2 negative (HER2-) breast cancer: a systematic review

Background

Hormone receptor-positive (HR+) and human epidermal growth factor receptor-2 negative (HER2−) breast cancer is the most common molecular subtype of breast cancer in many countries, and endocrine therapy remains a mainstay in its treatment. Cyclin-dependent kinase (CDK) 4/6 inhibitors are a new class of targeted agents administered orally that are recommended being used in combination with endocrine therapy as first and second line treatments for advanced HR+/HER2− breast cancer. However, their high prices largely hinder using these drugs in real world settings. To offer a new basis for future research, we investigated the cost-effectiveness of combinations of CDK4/6 inhibitors with endocrine therapy in the treatment of advanced HR+/HER2− breast cancer.

Methods

We systematically searched several frequently used databases and identified economic evaluations published from February 2015 to April 2021. The systematic review was performed after retrieving the literatures and extracting data based on inclusion and exclusion criteria. The quality of each selected economic evaluation was assessed by the Consolidated Health Economic Evaluation Reporting Standards (CHEERS).

Results

The literature search yielded 161 articles, among which fourteen studies (15 articles) with CHEER scores ranging from 58.33% to 87.50% entered the final analysis. Markov models were used in most studies. Based on the currently available data, CDK4/6 inhibitors plus endocrine therapy were less cost-effective in first- or second-line treatment of patients with HR+/HER2− advanced breast cancer. However, ribociclib plus letrozole was more cost-effective than palbociclib plus letrozole in the first-line treatment of postmenopausal women. The economic impacts of CDK4/6 inhibitors plus endocrine therapy in non-postmenopausal patients or second-line therapy cannot be fully evaluated due to the limited number of studies. The three most common factors affecting economic outcomes were the prices of CDK4/6 inhibitors, hazard ratios for progression-free survival and overall survival, and health status utility values.

Discussion

CDK4/6 inhibitors plus endocrine therapy have shown significantly improved efficacy outcomes in HR+/HER2− metastatic breast cancer (mBC)/advancer breast cancer (ABC) first-line and second-line treatment for endocrine-sensitive and endocrine-resistant populations, while more potential fields including neoadjuvant and adjuvant settings are being identified to benefit a wider range of breast cancer patients. Meanwhile, risk of severe adverse events that more likely to happen in patients treated with CDK4/6 inhibitors can lead to reduced life quality and higher medical costs patients need to afford. The adverse drug reaction related cost in several economic burden studies were explored to be primarily driven by hospitalizations and outpatient, and assessment of cost associated with CDK4/6 inhibitors adverse events is worth further developing. Drug wastage costs were found higher in palbociclib regimen than ribociclib regimen due to different dosing patterns. Moreover, current economic evaluations showed that ribociclib plus letrozole had better economic benefits than palbociclib plus letrozole for first-line treatment of postmenopausal women with HR+/HER2− ABC.

Barriers and facilitators to taking CDK4/6 inhibitors among patients with metastatic breast cancer: a qualitative study

PURPOSE

Most studies of adherence to treatment for breast cancer have focused on early-stage patients. Findings from these studies may not generalize to patients with metastatic breast cancer (MBC). The objective of this study was to identify barriers and facilitators of adherence to cyclin-dependent kinase 4/6 (CDK4/6) inhibitors among patients with MBC, guided by the social ecologic model (SEM).

METHODS

Patients with MBC (N = 25), their caregivers (N = 9), and oncology providers (N = 13) completed semi-structured qualitative interviews exploring their experiences with CDK4/6 inhibitors. Interviews were audio-recorded, transcribed verbatim, and analyzed by three raters using a combined deductive and inductive approach.

RESULTS

Qualitative analysis identified barriers and facilitators of adherence at each SEM level. Intrapersonal and interpersonal factors were most frequently discussed. Intrapersonal factors included knowledge/beliefs about CDK4/6 inhibitors, side effects, and establishing a routine. Interpersonal factors included effective communication with/coordination by the care team, support from family and friends, and information from other patients with MBC. Although less frequently discussed, policy factors (i.e., cost of CDK4/6 inhibitors) were of great concern to patients, caregivers, and providers.

CONCLUSION

Barriers to adherence to CDK4/6 inhibitors exist at multiple levels. Our results underscore the potential value of a multilevel intervention (e.g., patient education, evidence-based strategies for symptom management, tips for open and assertive communication with providers, information about financial resources/support available, and so on) to support adherence in this population.

Incidence and Severity of Myelosuppression With Palbociclib After Palliative Bone Radiation in Advanced Breast Cancer: A Single Center Experience and Review of Literature

BACKGROUND

Palbociclib is a cyclin-dependent kinase (CDK) 4/6 inhibitor with a primary toxicity of myelosuppression, especially neutropenia, due to cytostatic CDK6 inhibition on bone marrow. Preclinical studies suggest palbociclib may enhance radiation toxicity, but this was only evaluated in limited case series of palliative radiotherapy and not specific to radiation targeting bony metastases.

PATIENTS AND METHODS

This was a single institution retrospective cohort study. We included female patients who initiated palbociclib for advanced breast cancer between 2015 and 2019. The primary exposure was receipt of palliative radiation to bony metastases within 1 year prior to starting palbociclib. The primary outcome was the incidence and severity of myelosuppression during cycle one. Secondary outcomes include treatment interruptions and cycle 2 dose reductions, with subgroup analysis of radiation timing, type, dose, and location.

RESULTS

Of the 247 patients, 47 received radiation to bone metastases. Only absolute lymphocyte count (ALC) after cycle one of palbociclib was significantly lower in the group receiving radiation (median ALC 0.84 vs. 1.10 K/mm³, P < .001), with similar rates of neutropenia, anemia, and thrombocytopenia. Patients who received ≥10 fractions radiation were more likely to have cycle one interrupted than those receiving shorter radiation courses (42.9% vs. 11.1%, P = .03). No radiation characteristics were associated with other hematologic toxicities or dose reduction.

CONCLUSION

Palliative bone radiation within 1 year prior to palbociclib initiation was associated with greater lymphopenia during the first cycle than patients unexposed to radiation, but not neutropenia, anemia, or thrombocytopenia that would modify treatment.