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The therapeutic landscape for hormone receptor-positive (HR+) breast carcinoma has undergone a significant transformation with the advent of cyclin-dependent kinase (CDK)4/6 inhibitors, particularly in combination with endocrine therapy as the primary regimen. However, the evolution of resistance mechanisms in response to CDK4/6 inhibitors in HR+ metastatic breast cancer presents substantial challenges in managing the disease. This review explores the diverse genomic landscape underlying resistance, including disturbances in the cell cycle, deviations in oncogenic signaling pathways, deficiencies in DNA damage response (DDR) mechanisms, and changes in the tumor microenvironment (TME). Additionally, it discusses potential strategies to surmount resistance, including advancements in endocrine therapy, targeted inhibition of cell cycle components, suppression of AKT/mTOR activation, exploration of the FGFR pathway, utilization of antibody-drug conjugates (ADCs), and integration of immune checkpoint inhibitors (ICIs) with endocrine therapy and CDK4/6 inhibitors, providing pathways for enhancing patient outcomes amidst treatment challenges., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Aims and Objectives: Although cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i) are a vital part of the treatment of hormone receptor (HR)-positive/HER-2-negative metastatic breast cancer (BC), individuals have different sensitivities to CDK4/6i, indicating the need for biomarkers. The fasting triglyceride glucose (TyG) index is an easily accessible surrogate marker of insulin resistance (IR). Herein, we investigated the prognostic significance of the fasting triglyceride glucose (TyG) index in HR+/HER2- metastatic BC patients treated with CDK4/6i plus endocrine therapy (ET)., Methods: About 333 patients with HR+/HER2-metastatic BC treated with CDK4/6i plus ET were analyzed retrospectively. The TyG index was calculated within 3 months before the initiation of CDK4/6i plus ET. The median value of 8.43 was taken as the cutoff for the TyG index., Results: The median overall survival (OS) was 73.6 months (95% CI, 66.0-81.1) in the whole cohort. The progression-free survival (PFS) was significantly longer in the low-TyG subgroup than in the high-TyG subgroup (30.1 vs. 21.3 months, multivariate adjusted [HR] = 0.666, 95% CI, 0.450-0.987, P = .043). While the median OS was not reached in the low TyG subgroup, it was 69.0 months in the high TyG subgroup (multivariate-adjusted HR = 0.513, 95% CI, 0.281-0.936, P = .030). Although the ORR and DCR were numerically greater in the low-TyG subgroup, no significant differences were observed between the low-TyG subgroup and high-TyG subgroup (28.1% vs. 24.7%, P = .476; 83.2% vs. 80.1%, P = .463, respectively)., Conclusions: These data imply that the TyG index could be a predictive biomarker for the therapeutic efficacy of CDK4/6is. Extensive prospective studies are needed to confirm these findings., Competing Interests: Disclosure The authors declare that they have no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Abemaciclib (ABM), a cyclin-dependent kinase 4/6 inhibitor, shows pharmacological effects in cell cycle arrest. Epithelial-mesenchymal transition is an important cellular event associated with pathophysiological states such as organ fibrosis and cancer progression. In the present study, we evaluated the contribution of factors associated with cell cycle arrest to ABM-induced epithelial-mesenchymal transition. Treatment with 0.6 µM ABM induced both cell cycle arrest and epithelial-mesenchymal transition-related phenotypic changes. Interestingly, the knockdown of cyclin-dependent kinase 4/6, pharmacological targets of ABM or cyclin D1, which forms complexes with cyclin-dependent kinase 4/6, resulted in cell cycle arrest at the G1-phase and induction of epithelial-mesenchymal transition, indicating that downregulation of cyclin-dependent kinase 4/6-cyclin D1 complexes would mimic ABM. In contrast, knockdown of the Rb protein, which is phosphorylated by cyclin-dependent kinase 4/6, had no effect on the expression level of α-smooth muscle actin, an epithelial-mesenchymal transition marker. Furthermore, ABM-induced epithelial-mesenchymal transition was not affected by Rb knockdown, suggesting that Rb is not involved in the transition process. Our study is the first to suggest that cyclin-dependent kinase 4/6-cyclin D1 complexes, as pharmacological targets of ABM, may contribute to ABM-induced epithelial-mesenchymal transition, followed by clinical disorders such as organ fibrosis and cancer progression. This study suggests that blocking epithelial-mesenchymal transition might be a promising way to prevent negative side effects caused by a medication (ABM) without affecting its ability to treat the disease., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In search of potential anticancer agents, we synthesized SNO-donor salicylaldimine main ligand-based Pt(II) complexes bearing NH 3 as co-ligand at trans-position (C1-C6). These complexes showed similarity in structure with transplatin as the two N donor atoms of the main ligand and NH 3 co-ligand were coordinated to Pt in trans position to each other. Each complex with different substituents on the main ligand was characterized thoroughly by detailed spectroscopic and spectrophotometric methods. Four of these complexes were studied in solid state by single crystal X-ray analysis. The stability of reference complex C1 was measured in solution state in DMSO‑d 6 or its mixture with D 2 O using 1 H NMR methods. These complexes were further investigated for their anticancer activity in triple-negative-breast (TNBC) cells including MDA-MB-231, MDA-MB-468 and MDA-MB-436 cells. All these complexes showed satisfactory cytotoxic effect as revealed by the MTT results. Importantly, the highly active complex C4 anticancer effect was compared to the standard chemotherapeutic agents including cisplatin, oxaliplatin and 5-fluorouracil (5-FU). Functionally, C4 suppressed invasion, spheroids formation ability and clonogenic potential of cancer cells. C4 showed synergistic anticancer effect when used in combination with palbociclib, JQ1 and paclitaxel in TNBC cells. Mechanistically, C4 inhibited cyclin-dependent kinase (CDK)4/6 pathway and targeted the expressions of MYC/STAT3/CCND1/CNNE1 axis. Furthermore, C4 suppressed the EMT signaling pathway that suggested a role of C4 in the inhibition of TNBC metastasis. Our findings may pave further in detailed mechanistic study on these complexes as potential chemotherapeutic agents in different types of human cancers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Over the past few decades, first-line therapy for treating advanced and metastatic HR+/HER2-breast cancer has transformed due to the introduction of adjuvant endocrine therapy with cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i). However, there is an unmet need for novel classes of endocrine therapy with superior efficacy to improve treatment outcomes and overcome CDK4/6i resistance. New generation selective estrogen receptor degraders (SERDs), orally administered and with higher bioavailability, could potentially be the novel compounds to meet this emerging need. In this paper, we review accredited clinical studies on the combining effects of CDK4/6 inhibitors and oral SERDs, report efficacy of treatment data when available, and provide a framework for future research focusing on these promising agents., Competing Interests: Declaration of competing interest FZ has received honoraria for lectures and have served in an advisory role for Astra-Zeneca, Daiichi, Eli- Lilly, Merck, MSD, Novartis, Pfizer, Genesis- Pharma, Roche and Gilead. MAD has received research funding, honoraria and consulting fees from BMS, Janssen, Amgen, Takeda, and Beigene.The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Bruceantinol (BOL), isolated from the dried fruit of the Brucea javanica (L.) Merr., exhibits cytotoxic effects on breast cancer cells. However, the underlying mechanism remains to be fully addressed. In this paper, the MCF-7 and MDA-MB-231 human breast cancer cell lines were used as experimental models to uncover how BOL inhibits breast cancer cell growth. The effects of BOL on cell growth, proliferation, the cell cycle, and apoptosis were investigated using the MTT assays, EdU incorporation assays, and flow cytometry, respectively. Bioinformatics techniques were applied to predict the key targets of BOL in breast cancer. Subsequent validation of these targets and the anti-breast cancer mechanism of BOL was conducted through Western blotting, RT-PCR, siRNA transfection, and molecular docking analysis. The results demonstrated that BOL dose- and time-dependently reduced the growth of both cell lines, impeded cell proliferation, disrupted the cell cycle, and induced necrosis in MCF-7 cells and apoptosis in MDA-MB-231 cells. Furthermore, CDK2/4/6 were identified as BOL targets, and their knockdown reduced cell sensitivity to BOL. BOL was found to potentially bind with CDK2/4/6 to facilitate protein degradation through the proteasome pathway. Additionally, BOL activated ERK in MDA-MB-231 cells, and this activation was required for BOL's functions in these cells. Collectively, BOL may act as an inhibitor of CDK2/4/6 to exert anti-breast cancer effects. Its effects on cell growth and CDK2/4/6 expression may also depend on ERK activation in HRs - HER2 - breast cancer cells. These results suggest the potential of using BOL for treating breast cancer., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Introduction/background: Hormone Receptor-positive (HR+) and Human Epidermal Growth Factor Receptor 2-negative (HER2-) breast cancer is the most common subtype, predominantly treated with endocrine therapy. The efficacy of CDK4/6 inhibitors combined with endocrine therapy in this context remains to be fully evaluated., Materials (or Patients) and Methods: This study compared the effectiveness of CDK4/6 inhibitors (palbociclib and ribociclib) in combination with an aromatase inhibitor or fulvestrant against endocrine therapy alone in patients with HR+/HER2- advanced breast cancer. The main focus was on progression-free survival (PFS) and overall survival (OS). The study involved a population treated exclusively with endocrine therapy for bone involvement, examining median OS and PFS, and adjusting for variables like stage, visceral metastasis, age, and treatment line., Results: The study found no significant OS difference between treatments with palbociclib, ribociclib, and endocrine therapy alone. However, ribociclib combined with letrozole significantly improved PFS over letrozole alone. Propensity score weighting indicated a potential 50 % reduction in death risk with ribociclib compared to palbociclib, though this was not confirmed by cox regression., Conclusion: CDK4/6 inhibitors, particularly ribociclib in combination with letrozole, show promise in improving outcomes for HR+/HER2- breast cancer patients. While palbociclib may not be superior to traditional endocrine therapy, the results underscore the need for further research. These findings could influence future treatment protocols, emphasizing the importance of personalized therapy in this patient group., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: This phase II study evaluated the impact of adding ribociclib to maintenance endocrine therapy (ET) treatment of physicians' choice following the first palliative chemotherapy in pre- and post-menopausal women with hormone receptor positive (HR+)/human epidermal growth factor 2 negative (HER2-) metastatic breast cancer (mBC)., Patients and Methods: The initial randomized study design was later amended into a single-arm study, and all subsequent patients received ribociclib and ET. The primary end point was locally assessed progression-free survival (PFS). Secondary end points included overall survival (OS), clinical benefit rate (CBR), safety, compliance, and quality of life (QoL)., Results: A total of 43 patients received ribociclib + ET and 10 patients received ET only. Median PFS was 12.4 months [95% CI 8.7-24.4] for patients who received ribociclib + ET and 4.75 months [95% CI 1.0-10.3] for those who received ET only. Median OS was not reached for patients who received ribociclib + ET, and 28 (65.1%) patients experienced clinical benefit [95% CI 49.1-79.0]. For patients who received ribociclib + ET, grade 3-4 hematological adverse events (AEs) occurred in 25 (58.1%) patients, and grade 3-4 non-hematological AEs occurred in 17 (39.5%) patients. During the study, 15 patients died - 14 of whom due to tumor-related reasons, and one patient due to pneumonia, which was not treatment-related., Conclusion: The results of the AMICA study show a promising efficacy and safety of maintenance treatment with ribociclib added to ET after at least stable disease following the first metastatic chemotherapy in patients with HR+/HER2-mBC., Trial Registration: Anti-hormonal Therapy With Ribociclib in HR-positive/HER2- Negative Metastatic Breast Cancer (AMICA), NCT03555877, https://clinicaltrials.gov/ct2/show/NCT03555877., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. T. Decker reports ad boards from Lilly, Novartis, and IOMEDICO. K. Luedtke-Heckenkamp reports personal fees from AstraZeneca, Gilead, Novartis, and Pfizer. She is on the advisory board of Daiichi Sankyo, Lilly, and Roche. K. Lübbe is on the advisory board of Genomic Health, Roche, Daiichy Sankyo, Lilly, MSD, EISAI, Seagen, and Novartis, and has received lecture fees from Novartis, AstraZeneca, Genomic Health, Roche, and Lilly. M. Schmidt reports personal fees from AstraZeneca, personal fees from BioNTech, personal fees from Daiichi Sankyo, personal fees from Eisai, personal fees from Lilly, personal fees from MSD, personal fees from Novartis, personal fees from Pfizer, personal fees from Pierre-Fabre, personal fees from Roche, and personal fees from SeaGen outside the submitted work; in addition, M. Schmidt has a patent for EP 2390370 B1: A method for predicting the response of a tumor in a patient suffering from or at risk of developing recurrent gynecologic cancer towards a chemotherapeutic agent issued and a patent for EP 2951317 B1: A method for predicting the benefit from inclusion of a taxane in a chemotherapy regimen in patients with breast cancer issued. C. Denkert reports grants from European Commission H2020, grants from German Cancer Aid Translational Oncology, grants from German Breast Group; personal fees from Novartis, Roche, MSD Oncology, Daiichi Sankyo, AstraZeneca, Lilly, Molecular Health, Merck, grants from Myriad to his institution, other from Sividon diagnostics (cofounder and former shareholder until 2016); In addition, C. Denkert has a patent VMScope digital pathology software with royalties paid, a patent WO2020109570A1 - cancer immunotherapy pending, and a patent WO2015114146A1 and WO2010076322A1- therapy response issued. V. Müller received speaker honoraria from Amgen, Astra Zeneca, Daiichi-Sankyo, Eisai, GSK, Pfizer, MSD, Medac, Novartis, Roche, Teva, Seagen, Onkowissen, high5 Oncology, Medscape, Gilead, and Pierre Fabre; consultancy honoraria from Hexal, Roche, Pierre Fabre, Amgen, ClinSol, Novartis, MSD, Daiichi-Sankyo, Eisai, Lilly, Sanofi, Seagen, and Gilead; institutional research support from Novartis, Roche, Seagen, and Genentech; and travel grants from Roche, Pfizer, Daiichi Sankyo, and Gilead. M. Thill is on the advisory boards of Agendia, Amgen, AstraZeneca, Aurikamed, Becton/Dickinson, Biom‘Up, ClearCut, Clovis, Daiichi Sankyo, Eisai, Exact Sciences, Gilead Science, Grünenthal, GSK, Lilly, MSD, Norgine, Neodynamics, Novartis, Onkowissen, Organon, Pfizer, pfm Medical, Pierre-Fabre, Roche, RTI Surgical, Seagen, Sirius Pintuition, and Sysmex. He has received support from Amgen, AstraZeneca, Celgene, ClearCut, Clovis, Daiichi Sanyko, Hexal, Neodynamics, Novartis, Pfizer, pfm medical, Roche, Servier, and Sirius Medical. He reports travels expenses from Amgen, Art Tempi, AstraZeneca, Clearcut, Clovis, Connect Medica, Daiichi Sankyo, Eisai, Exact Sciences, Hexal, I-Med-Institute, Lilly, MCI, Medtronic, MSD, Neodynamics, Norgine, Novartis, Pfizer, pfm Medical, Roche, RTI Surgical, and Seagen. He has received honoraria and funding from Amgen, Art Tempi, AstraZeneca, Biom’Up, Celgene, Clearcut, Clovis, Connect Medica, Eisai, Endomag, Exact Sciences, Gedeon Richter, Gilead Science, GSK, Hexal, I-Med-Institute, Jörg Eickeler, Laborarztpraxis Walther et al., Lilly, MCI, Medscape, MSD, Medtronic, Neodynamics, Novartis, Onkowissen, Pfizer, pfm medical, Roche, RTI Surgical, Seagen, StreamedUp, Sysmex, Vifor, and Viatris. N. Hirmas and N. Filmann declare to be GBG Forschungs GmbH employees. GBG Forschungs GmbH received funding for research grants from Abbvie, AstraZeneca, BMS, Daiichi-Sankyo, Gilead, Novartis, Pfizer, and Roche (paid to the institution); other (non-financial/medical writing) from Daiichi-Sankyo, Gilead, Novartis, Pfizer, Roche and Seagen (paid to the institution). GBG Forschungs GmbH has following royalties/patents: EP14153692.0, EP21152186.9, EP15702464.7, EP19808852.8 and VM Scope GmbH. S. Loibl reports grants or contracts paid to institute from Abbvie, AstraZeneca, DSI, Celgene, Gilead, Novartis, Pfizer, Roche, Molecular H; in addition, S. Loibl has royalties or licenses for Digital Ki67 Evaluator from VM Scope GmbH that were paid to institute; in addition, S. Loibl receives honorary for lectures paid to the institute from AstraZeneca, DSI, Gilead, Novartis, Pfizer, and Roche; non-financial for Medical Writing from DSI, Gilead, Novartis, Pfizer, Roche, and Seagen; in addition, S. Loibl has patent for EP14153692.0, EP21152186.9, EP15702464.7 and EP19808852.8, all patents via institute; in addition, S. Loibl declares participation on a Data Safety Monitoring Board or Advisory Board from Abbvie, Amgen, AstraZeneca, BMS, Celgene, DSI, Eirgenix, Eisai Europe, GSK, Gilead, Lilly, Merck, Novartis, Pfizer, Pierre Fabre, Relay Therapeutics, Roche, Sanofi, and Seagen, all paid to institute., (Copyright © 2023. Published by Elsevier Ltd.)

Background: The impact of some hasty medical decision made during the first wave of the Coronavirus Disease 2019 (COVID-19) remains unknown. We have evaluated the consequences of one of these precautionary measures: the withdrawal of the cyclin D-dependent kinases 4/6 inhibitor (CDK4/6i) in patients whose metastatic disease was controlled by a combination of endocrine treatment and CDK 4/6i., Method: This study was noninterventional, retrospective, multicentric, and included 60 patients with HR+ HER2- metastatic disease. Their disease was controlled with the combination of endocrine treatment and CDK 4/6i. The CDK 4/6i was stopped for two months during the first COVID-19 outbreak. A univariate analysis was performed to assess the risk factors associated with disease progression., Results: During this therapeutic break, 22 (37 %) patients had a radiological and/or clinical disease progression. Among them, the CDK 4/6i was re-introduced to 16 patients (n = 16/22; 73 %). A new line of treatment (chemotherapy or targeted therapy) was initiated due to the rapid symptomatic tumor progression in four patients (n = 4/22; 18 %). Two patients (n = 2/22) died in visceral crisis before another anti-tumoral treatment was introduced. In univariate analysis, the presence of liver metastases increased the risk of metastatic disease progression during the withdrawal of the CDK 4/6 (OR = 6.6; 95 % CI 1.87-23.22; P= .0033)., Conclusion: Progression was observed in 37% of patients during the two-month treatment interruption of the CDK 4/6i. A prolonged CDK 4/6i treatment interruption in patients with clinical benefit on endocrine treatment does not seem to be a reasonable option in light of these results., Competing Interests: Disclosures T.P. reports grants from Pfizer, Novartis, AstraZeneca, Lilly, and Pierre Fabre, but which were unrelated to the submitted work. Other authors declare no conflicts of interest related to this manuscript., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Selective CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, have been approved in combination with hormone therapy for the treatment of patients with HR+, HER2-negative advanced or metastatic breast cancer (mBC). Despite their promising activity, approximately 10 % of patients have de novo resistance, while the rest of them will develop acquired resistance after 24-28 months when used as first-line therapy and after a shorter period when used as second-line therapy. Various mechanisms of resistance to CDK4/6 inhibitors have been described, including cell cycle-related mechanisms, such as RB loss, p16 amplification, CDK6 or CDK4 amplification, and cyclin E-CDK2 amplification. Other bypass mechanisms involve the activation of FGFR or PI3K/AKT/mTOR pathways. Identifying the different mechanisms by which resistance to CDK4/6 inhibitors occurs may help to design new treatment strategies to improve patient outcomes. This review presents the currently available knowledge on the mechanisms of resistance to CDK4/6 inhibitors, explores possible treatment strategies that could overcome this therapeutic problem, and summarizes relevant recent clinical trials., Competing Interests: Declaration of competing interest The authors do not have any competing financial interest that could influence, or give the perception of such influence on the behavior or content in a way that could undermine the objectivity, integrity, or perceived value of this manuscript., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Background: Evaluation of health-related quality of life (HR-QoL) among cancer patients has gained an increasing importance and is now a key determinant of anticancer treatments' value. HR-QoL has been assessed in trials testing cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in breast cancer (BC), using various questionnaires at different timepoints. HR-QoL reports from BC patients treated with CDK4/6i in the real-world setting are also available., Methods: We systematically reviewed the literature, searching for full-length articles, and selected conference abstracts reporting data on HR-QoL in BC patients at any stage and of any molecular subtype treated with abemaciclib, palbociclib or ribociclib., Results: A total of 533 full-length articles and 143 abstracts were retrieved. After screening for eligibility, 38 records were included (31 clinical trials; 7 real-world reports). Assessment methods were heterogeneous across studies in terms of questionnaires, evaluation timepoints and endpoints. Overall, adding CDK4/6i to endocrine therapy did not worsen patients' HR-QoL, with a positive trend towards pain improvement. Gastrointestinal scores (diarrhea, nausea and appetite loss) statistically favored the control arm among metastatic BC patients receiving abemaciclib, whereas they were superimposable in the early setting. The combination of palbociclib and endocrine therapy showed similar HR-QoL outcomes compared with endocrine therapy alone, but determined better scores compared with chemotherapy. HR-QoL was specifically assessed in premenopausal patients treated with ribociclib, showing similar scores compared with postmenopausal patients., Conclusions: Despite methodological heterogeneity does not allow a proper comparison, HR-QoL was generally maintained with CDK4/6i. However, differences between abemaciclib, palbociclib and ribociclib exist and mainly rely on the distinct safety profiles of the compounds. These differences should be acknowledged and taken into account in the clinical practice., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Cyclin-dependent kinase 6 (EC 2.7.11.22) play significant roles in numerous biological processes and triggers cell cycle events. CDK6 controlled the transcriptional regulation. A dysregulated function of CDK6 is linked with the development of progression of multiple tumor types. Thus, it is considered as an effective drug target for cancer therapy. Based on the direct roles of CDK4/6 in tumor development, numerous inhibitors developed as promising anti-cancer agents. CDK4/6 inhibitors regulate the G1 to S transition by preventing Rb phosphorylation and E2F liberation, showing potent anti-cancer activity in several tumors, including HR+/HER2- breast cancer. CDK4/6 inhibitors such as abemaciclib, palbociclib, and ribociclib, control cell cycle, provoke cell senescence, and induces tumor cell disturbance in pre-clinical studies. Here, we discuss the roles of CDK6 in cancer along with the present status of CDK4/6 inhibitors in cancer therapy. We further discussed, how structural features of CDK4/6 could be implicated in the design and development of potential anti-cancer agents. In addition, the therapeutic potential and limitations of available CDK4/6 inhibitors are described in detail. Recent pre-clinical and clinical information for CDK4/6 inhibitors are highlighted. In addition, combination of CDK4/6 inhibitors with other drugs for the therapeutic management of cancer are discussed., Competing Interests: Declaration of competing interest All authors declare no conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Cancer is one of the major causes of global deaths and needs immediate therapeutic development. So far, several strategies have been undertaken to prevent cancer, including kinase targeting by small-molecule inhibitors. Cyclin dependent kinase 6 (CDK6) plays an essential role in cancer progression and development as its overexpression is associated with tumor development and progression. The present study demonstrated that Naringenin (NAG) binds strongly to CDK6 with a binding affinity of -7.51 kcal/mol. ATPase assay of CDK6 in the presence of NAG shows that it inhibits CDK6 with an IC 50  = 3.13 μM. Fluorescence and isothermal titration calorimetry studies demonstrated that NAG binds to CDK6 with the binding constant (K) values of 3.55 × 10 6  M -1 and 7.06 ± 2.70 × 10 6  M -1 , respectively. The cell-based functional studies showed that NAG decreases the cell viability of human cancer cell lines, induces apoptosis, and reduces their colonization ability. Outcomes of the present in silico and in vitro studies highlighted the significance of NAG for the development of anti-cancer leads in terms of CDK6 inhibitors and provided future implications for combinatorial anti-cancer therapies., (Copyright © 2022. Published by Elsevier B.V.)

CDK4/6 were attractive chemotherapeutic targets for the treatment of malignant tumors, CDK4/6 selective inhibitors have made outstanding contributions in the treatment of breast cancer. However, these inhibitors share a single skeleton of N-(pyridin-2-yl) pyrimidin-2-amine which cannot overcome the side effects in clinical application. In our previous study, an N'- acetylpyrrolidine-1-carbohydrazide was hit as the initial fragment by analyzing the active site characteristics of CDK6. Two series of N-(pyridin-3-yl) proline were obtained by fragment growth method. The QSAR study was carried out according to the in vitro activities data against CDK4/6, and two compounds 7c and 7p with potent inhibitory activities were found to interact with CDK4 in different binding conformation. They showed potential inhibition of cell proliferation against the breast cancer cell, and 7c exhibited promised anti-breast cancer effect in vivo., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Health-related quality of life (HRQOL) is increasingly recognized as important when evaluating cancer treatments. The use, reporting, and analysis of patient-reported outcome measures (PROMs), however, are not standardized in clinical trials and are often poorly implemented in clinical practice. We report the results of a systematic literature review (PubMed search: January 1, 2000 to August 15, 2020) of PROM use, reporting, and analysis in phase 3 clinical trials of hormone receptor-positive (HR+) advanced breast cancer (ABC). Further inspection of cyclin-dependent kinase 4/6 (CDK4/6) inhibitor publications was performed to examine PROMs in the HR+/human epidermal growth factor receptor 2-negative setting. A total of 88 results were identified in the initial search; 32 were included in the final analysis. Among included studies, most (66%) had been published in the last 5 years (2015 to 2020). CDK4/6 inhibitors (38%) were the most common agents reported. No clear standard for PROM use, reporting, or analysis was found. The most common PROMs were European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30; 59%) and the Functional Assessment of Cancer Therapy-Breast (FACT-B; 34%). Important differences, among studies that reported them, ranged from 5 to 10 points for the EORTC QLQ-C30 and 8 points for the FACT-B total score. This review showed that a lack of clear consistency remains for PROM use, reporting, and analysis in phase 3 clinical trials of HR+ ABC. However, HRQOL is of high interest in the literature, including for CDK4/6 inhibitors., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The formation of cyclinD-CDK4/6 complex plays vital roles in the cell cycle transition from G1 phase to S phase which is characterized by vigorous transcription and synthesis. Through cyclinD-CDK4/6-Rb axis, CDK4/6 inhibitors arrest the cell cycle in the G1 phase and block the proliferation of aggressive cells, exhibiting promising effects in containing the aggressiveness of breast cancers. To date, there are three CDK4/6 inhibitors approved by the U.S. Food and Drug Administration in treating advanced hormone receptor-positive breast cancer, including palbociclib, abemaciclib, and ribociclib. In fact, several preclinical experiments and clinical trials presented therapeutic effects of CDK4/6 inhibitor-based treatment in triple-negative breast cancer., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Introduction: Cyclin-dependent kinase (CDK)4/6 inhibitor is a first-line therapy for metastatic ER+/HER2-breast cancer. However, there are limited data on safety of combined radiotherapy (RT) and CDK4/6 inhibition., Methods: We conducted a retrospective study of women with metastatic breast cancer who received palliative RT within 14 days of CDK4/6 inhibitor use. The primary endpoint was toxicity per Common Terminology Criteria for Adverse Events v5. Secondary endpoints were pain response and local control based on clinical assessment and imaging., Results: Thirty patients underwent 36 RT courses with palbociclib (n = 34 courses, 94.4%) or abemaciclib (n = 2, 5.6%). RT was delivered before, concurrently or after CDK4/6 inhibitors in 7 (19.4%), 8 (22.2%), and 21 (58.3%) of cases with median 3.5 days from RT to closest CDK4/6 inhibitor administration. Median RT dose was 30Gy (range 8-40.05Gy). Treated sites included brain (n = 5, 11.6%), spine (n = 19, 44.2%), pelvis (n = 9, 20.9%), other bony sites (n = 6, 14.0%) and others (n = 4, 9.3%). No acute grade ≥3 non-hematologic toxicity occurred. No increased hematologic toxicity was attributable to RT with grade 3 hematologic toxicities rates 16.7%, 0%, and 6.7% before, during, and 2 weeks after RT completion. All but one patient (29/30) achieved symptom relief. Local control rates were 94.4%, 91.7% at 6 and 12 months., Conclusions: The use of RT within 2 weeks of CDK4/6 inhibitors had low acceptable toxicity and high efficacy, suggesting that it is safe for palliation of metastatic breast cancer., Competing Interests: Declaration of competing interest The authors have no conflict of interest to declare., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Undoubtedly, the development of COVID-19 vaccines displays a critical step towards ending this devastating pandemic, considering their protective benefits in the general population. Yet, data regarding their efficacy and safety in cancer patients are limited. Herein we provide the initial analysis of immune responses after the first dose of vaccination in 21 breast cancer patients receiving cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors. The levels of neutralizing antibodies post vaccination were similar to the matched healthy controls, whereas no safety issues have been raised. Further exploration is needed to reduce the uncertainty of SARS-CoV-2 immunity among cancer patients under treatment., Competing Interests: Declaration of competing interest The authors report no conflict of interest., (Copyright © 2021. Published by Elsevier Ltd.)

Background: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors and endocrine therapy (ET) deeply transformed the treatment landscape of hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer. Randomized clinical trials suggest that second progression-free survival (PFS2) was not compromised and time to subsequent chemotherapy (TTC) may be delayed. We carried out a meta-analysis to assess the benefit on PFS2 and on delaying the TTC., Methods: We conducted a systematic literature search of randomized clinical trials with CDK4/6 inhibitors and ET reporting PFS2 or TTC of HR+/HER2- pre- or postmenopausal metastatic breast cancer. We also reviewed abstracts and presentations from all major conference proceedings. We calculated the pooled hazard ratios (HR) for PFS2 and TTC using random-effects models with 95% confidence intervals (CI). I 2 was used to quantify heterogeneity between results of the studies., Results: Eight studies (MONALEESA-2/3/7, MONARCH-2/3, PALOMA-1/2/3) were included in this analysis (N = 4580 patients). PFS2 benefit was observed in patients who received CDK4/6 inhibitors plus ET (pooled HR = 0.68, 95% CI = 0.62-0.74, I 2  = 0%) and also a delay in subsequent TTC (pooled HR = 0.65, 95% CI = 0.60-0.71, I 2  = 0%). A benefit in terms of PFS (pooled HR = 0.55, 95% CI = 0.51-0.59, I 2  = 0%) and overall survival (pooled HR = 0.76, 95% CI = 0.69-0.84, I 2  = 0%) was also observed., Conclusions: CDK4/6 inhibitors plus ET compared with ET alone improve PFS2 and TTC. The delay of chemotherapy may postpone the start of a more toxic treatment option, delaying related toxicities and potentially maintaining a better quality of life for patients, for a longer time. The benefit in PFS2 may postpone the onset of endocrine resistance and help further validate this treatment approach., Competing Interests: Disclosure EMu has acted as a consultant to Pierre Fabre, Genomic Health and Eisai; EMo had consulting or advisory role from Pierre Fabre; MC has received a research grant from Roche. All other authors have declared no conflicts of interest., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

CDK4/6 have been validated as the cancer therapeutic targets. Here, we describe a series of pteridin-7(8H)-one analogues as potent CDK4/6 inhibitors. Among them, the most promising compound 7s demonstrated remarkable and broad-spectrum antiproliferative activities toward HCT116, HeLa, MDA-MB-231, and HT-29 cells with IC 50 values of 0.65, 0.70, 0.39, and 2.53 μM, respectively, which were more potent than that of the anticancer drug Palbociclib. Interestingly, 7s also manifested the greatest inhibitory activities toward both CDK4/cyclin D3 and CDK6/cyclin D3 (IC 50  = 34.0 and 65.1 nM, respectively), which was comparable with Palbociclib. Additionally, molecular simulation indicated that 7s bound efficiently at the ATPbindingsitesofCDK4 and CDK6. Further mechanistic studies revealed that compound 7s could concentration-dependently induce cell cycle arrest and apoptosis in HeLa cells. Takentogether, 7s represents a promising novel CDK4/6 inhibitor for the potential treatment of cancer., (Copyright © 2021 Elsevier Inc. All rights reserved.)

CDK4 & CDK6 are essential regulators of initial cell cycle phases and are always considered an exciting choice for anti-cancer therapy. In the present study, we presented the structure-based rational design & synthesis of a new class of 1,2,3-triazole tethered acridinedione derivatives (6a-l) as selective CDK4/6 inhibitors. Title molecules were prepared as a result of the rate-determining reaction between substituted derivatives of 1-Phenyl-1H-1,2,3-triazole-4-carbaldehydes and substituted dimedones, and the molecules were structurally characterized by IR, 1 H, 13 C NMR, and MS spectral data. All molecules were screened for in-vitro cytotoxic potential against a group of human breast tumor cell lines of distinct origin with differential Rb expression status. Out of entire series of conjugated hexahydro acridinediones, 6g showed potent cytotoxic effect against MCF-7, BT-474, and SK-BR3 cell lines with IC 50 values 0.173 ± 0.037, 0.117 ± 0.025, and 0.136 ± 0.027 μM, respectively. Further, CDK inhibition assays revealed that the compounds 6g and 6h selectively inhibit CDK4/6 over other CDK-parter complexes of the family against the selected cell line group except for MDA-MB468 cells. Furthermore, apoptotic evaluation and cell cycle analysis determined that compound 6g successfully triggered apoptosis in all examined cell lines except MDA-MB468 through blocking G1/S cell cycle transformation. In addition, compound 6g showed the highest in-vitro selectivity towards CDK4/6 inhibition, even compared with Abemaciclib, and it was also proved for favourable in-vivo pharmacokinetic properties in male albino mice. Furthermore, molecule 6g showed promising tumor growth suppression with lower adverse effects in MCF-7 xenograft mice models, which could competently be considered as a novel chemotherapeutic candidate for a further comprehensive preclinical study involving breast cancer therapy., (Copyright © 2021. Published by Elsevier Inc.)

The historical median survival of advanced luminal breast cancer does not exceed four years. The deciphering of the mechanisms of resistance to hormone therapy has led to the development of inhibitors of cyclin D dependent kinases (CDK4 and 6). Three drugs, palbociclib, ribociclib and abemaciclib, very similar pharmacologically, have been evaluated in the context of pivotal, randomized phase III trials. Strikingly and regardless of the endocrine therapy backbone, and in both hormone-sensitive and hormone-resistant patients, the addition of a CDK4 / 6 inhibitor doubles progression-free survival with a hazard ratio always around 0.55. The benefit in overall survival begins to be demonstrated. This review presents all published results, as well as the main safety data., (Copyright © 2021 Société Française du Cancer. Published by Elsevier Masson SAS. All rights reserved.)

Background: CDK4/6 inhibitors (CDK4/6i), in combination with aromatase inhibitors, are United States Food and Drug Administration-approved for the treatment of hormone receptor-positive (HR + )/human epidermal growth factor receptor 2-negative (HER2 - ) metastatic breast cancer (MBC). The effectiveness of continuing them beyond first disease progression (PD) is currently unknown. This retrospective study evaluated the impact of the continuation of CDK4/6i beyond first PD in HR + /HER2 - MBC using real-world experience., Patients and Methods: A single-institution retrospective review of patients with HR + MBC who received CDK4/6is from 2015 to 2018 and where CDK4/6is were continued beyond first PD. The primary outcome was progression-free survival (PFS) after initial PD on CDK4/6i therapy., Results: Thirty women with HR + /HER2 - MBC met eligibility criteria. Patients were identified from a prospective database of patients at the Cleveland Clinic Foundation who were prescribed CDK4/6is. The median age and follow-up duration were 47.5 years and 27 months, respectively. Most patients received palbociclib (PA)/letrozole as initial therapy (67%), followed by PA/fulvestrant (23%), and PA/other aromatase inhibitor (20%), and abemaciclib with either fulvestrant or letrozole (6%). As of January 31, 2019, 25 (83.3%) patients were still alive, and 19 (63%) patients had progressed. The estimated median PFS for continued CDK4/6i use beyond the first PD was 11.8 months (95% confidence interval, 5.34-13.13 months)., Conclusions: Among a small cohort of patients with HR + MBC in a non-clinical trial setting, continuation of CDK4/6i-endocrine treatment post initial PD was associated with a median PFS of about 12 months. Formal randomized clinical trials evaluating the continuation of CDK4/6is beyond the first PD are currently ongoing and will provide more answers to this important clinical question., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Introduction: The addition of palbociclib to endocrine therapy has been shown to improve progression free survival in hormone receptor positive metastatic breast cancer patients. This cyclin CDK4/6 inhibitor could expose patients to a grade 3-4 hematological toxicity, leading to treatment discontinuation or treatment interruption that is potentially associated with a lack of efficiency. The aim of this study was to identify predictive factors of severe early hematotoxicity (ESHT)., Methods: This retrospective cohort study included patients who started palbociclib in the Institut Sainte Catherine between December 1, 2016 and January 1, 2019 for the treatment of metastatic breast cancer. Individual data and hematological toxicity were collected from electronic medical records. ESHT was defined as the occurrence, during the first 3 cycles, of grade 4 or grade 3 hematological toxicity requiring palbociclib dose reduction., Results: In total, 181 patients (180 females) were included; median age was 67 years. Forty-six patients (25.4%) experienced an ESHT. Predictive factors of ESHT in multivariate analysis were a performance status (PS) of 2 or more (P=0.024) and an history of radiotherapy of bone metastasis in the previous year (P=0.003). Before palbociclib initiation, a neutrophil count below 3.37g/L was predictive of ESHT with a sensibility of 76% and a specificity of 71%., Conclusions: ECOG PS, bone radiotherapy within the year and low baseline neutrophils count are associated with ESHT in palbociclib-treated metastatic breast cancer patients. These elements could be useful for a careful monitoring leading to adapted therapy., (Copyright © 2021 Société Française du Cancer. Published by Elsevier Masson SAS. All rights reserved.)

Background: The combination of cyclin-dependent kinases 4/6 inhibitors (CDK4/6is) and endocrine therapy (ET) is standard of care for patients with hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (BC). However, studies evaluating adjuvant CDK4/6is provided contradictory results thus far., Materials and Methods: We conducted a systematic review and meta-analysis to assess if the addition of CDK4/6is to adjuvant ET impacts on survival's outcomes and safety of patients with HR+/HER2- early BC (EBC). This study was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines and was registered in the PROSPERO database (ID: CRD42020218597). A systematic review of PubMed, Cochrane and EMBASE databases and major conference proceedings was performed up to 15 December 2020. All randomized controlled trials including patients with HR+/HER2- EBC treated with CDK4/6is plus ET versus ET alone in the adjuvant setting were included. Pooled hazard ratios (HRs) and odds ratios (ORs) for survival and safety outcomes, respectively, were calculated with 95% confidence intervals (95% CIs) using random effect models., Results: With data available from three studies (N = 12 647), the addition of CDK4/6is to adjuvant ET showed a trend for a benefit in terms of invasive disease-free survival (IDFS; HR 0.85, 95% CI 0.71-1.01; P = 0.071). No significant improvement in distant relapse-free survival was observed (HR 0.83, 95% CI 0.58-1.19; P = 0.311). The risk of all-grade toxicities and early treatment discontinuation increased significantly with the addition of CDK4/6is to ET (OR 9.36, 95% CI 3.46-25.33, P < 0.001, and OR 22.11, 95% CI 9.45-51.69, P < 0.001, respectively)., Conclusion: The administration of adjuvant CDK4/6is to patients with HR+/HER2- EBC showed a trend for an IDFS benefit and an increase in the risk of toxicities and treatment discontinuation. The role of adjuvant CDK4/6is remains controversial and a longer follow-up of these randomized controlled trials is needed before supporting a straightforward change in clinical practice., Competing Interests: Disclosure RC received speaker honoraria from Boehringer Ingelheim, AstraZeneca and Janssen; and travel grants from AstraZeneca and Pfizer (outside the submitted work). ML acted as a consultant for Roche, AstraZeneca, Lilly and Novartis; and received honoraria from Sandoz, Takeda, Roche, Lilly, Pfizer and Novartis (outside the submitted work). NP acted as a consultant for Lilly; and has received honoraria from Roche, Lilly, Novartis and AstraZeneca (outside the submitted work). EdA has received honoraria and serves on the advisory board of Roche/GNE, Novartis, Seattle Genetics, Zodiacs, Libbs and Pierre Fabre; has received travel grants from Roche/GNE, GSK/Novartis; and has also received research grant for his institute from Roche/GNE, Astra-Zeneca, Novartis and Servier (outside the submitted work). All other authors have declared no conflicts of interest., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

CDK4/6 inhibitors (CDK4/6i) in combination with endocrine therapy are the mainstay of treatment for patients with hormone receptor-positive, HER2 negative (HR+/HER2neg) metastatic breast cancer. However, resistance - either de novo or acquired - invariably occurs, leading to treatment failure and cancer progression. Genomic alterations, gene expression data and circulating biomarkers have been correlated to response to treatment, but to date no biomarker has been approved to stratify patients. Treatment strategies after progression on CDK4/6i are yet to be standardized. Current approaches include endocrine therapy alone or in combination with target therapy, or chemotherapy. New agents are in clinical development based on potential mechanisms of acquired resistance. Here we will review recent advancements in biomarkers of response to CDK4/6i, and in post- treatment therapeutic strategies., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Competing Interests: Disclosure AM has no conflicts of interest to disclose. ML acted as a consultant for Roche, Novartis, Lilly and AstraZeneca, and received honoraria from Theramex, Takeda, Roche, Lilly, Pfizer, Novartis and Sandoz outside the submitted work.

Background: PI3K pathway hyperactivation due to PIK3CA mutations contributes to endocrine resistance, and PIK3CA is one of the most frequently mutated genes in breast cancer (BC), occurring approximately 40 % of HR+, HER2- advanced BC (ABC). Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have changed the treatment landscape of HR+, HER2- ABC. Putative mechanisms of resistance to CDK4/6i have been identified, but limited data are available on PI3K deregulation. The present study evaluates the impact of PIK3CA mutations on CDK4/6i plus hormone therapy and evaluates potential characteristics that may suggest for a PI3K screening in patients with ABC., Methods: ABC patients were enrolled, and 12 mL of blood were collected in EDTA tubes at baseline prior to CDK4/6i plus hormone therapy. Plasma was separated and circulating free DNA (cfDNA) was extracted. PIK3CA mutation analysis was performed on a ddPCR. Selected and analyzed mutations included: p.C420R, p.E542 K, p.E545A, p.E545D, p.E545G, p.E545K, p.Q546E, p.Q546R, p.H1047L, p.H1047R, p.H1047Y. Statistical analysis were performed to investigate the predictive power of such mutations and any association with clinical factors., Results: Thirty patients were enrolled. PIK3CA mutation status at baseline was independently associated with shorter median PFS (7.44 vs 12.9 months, p = 0.01) in subject receiving CDK4/6i plus hormone therapy. PIK3CA mutations were found to be associated to Ki67 expression in primary lesions (p = 0.006). Moreover, the probability to find a PI3K mutation improved considering also the therapeutic management in previous lines of treatment (McFadden's R 2 = 0.415, p = 0.004; AUC of the ROC curve = 0.914)., Conclusion: The findings of this pilot study suggest that the presence of a PI3K mutation in liquid biopsy correlates with a worse PFS in patients with ABC receiving CDK4/6i, and that liquid biopsy is a useful tool to suggests a better tailored pharmacological intervention., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Purpose: Treatment with CDK4/6 inhibitors and endocrine therapy (CDK4/6i + ET) is a standard for patients with advanced hormone receptor-positive, HER2-negative (HR + HER2-) breast cancer (BC). However, real-world data on the implementation of therapy usage, efficacy, and toxicity have not yet been reported., Methods: The PRAEGNANT registry was used to identify advanced HR + HER2- BC patients (n = 1136). The use of chemotherapy, ET, everolimus + ET, and CDK4/6i + ET was analyzed for first-line, second-line, and third-line therapy. Progression-free survival (PFS) and overall survival (OS) were also compared between patients treated with CDK4/6i + ET and ET monotherapy. Also toxicity was assessed., Results: CDK4/6i + ET use increased from 38.5% to 62.7% in the first 2 years after CDK4/6i treatment became available (November 2016). Chemotherapy and ET monotherapy use decreased from 2015 to 2018 from 42.2% to 27.2% and from 53% to 9.5%, respectively. In this early analysis no statistically significant differences were found comparing CDK4/6i + ET and ET monotherapy patients with regard to PFS and OS. Leukopenia was was seen in 11.3% of patients under CDK4/6i + ET and 0.5% under ET monotherapy., Conclusions: In clinical practice, CDK4/6i + ET has been rapidly implemented. A group of patients with a more unfavorable prognosis was possibly treated in the real-world setting than in the reported randomized clinical trials. The available data suggest that longer follow-up times and a larger sample size are required in order to identify differences in survival outcomes. Studies should be supported that investigate whether chemotherapy can be avoided or delayed in this patient population by using CDK4/6i + ET., Competing Interests: Declaration of competing interest A.S. received honoraria from Roche, AstraZeneca, Aurikamed GmbH, Celgene, ClinSol Research GmbH, Connectmedica Sp.Z o.o., Deutsche Gesellschaft für Senologie GmbH, if-kongress management gmbh, I-MED Institute GmbH, Lilly Deutschland GmbH, Medicultus GmbH, med publico GmbH, MSD Sharp & Dohme GmbH, onkowissen.de GmbH, Pfizer GmbH, Schattauer Verlag GmbH, Promedicis GmbH, Tesaro Bio Germany GmbH, W. Zuckschwerdt Verlag GmbH. J.E. received honoraria from AstraZeneca, Celgene, Novartis, Lilly, Pfizer, Pierre Fabre, Roche and TEVA and travel support from Celgene, Pfizer, TEVA, and Pierre Fabre. D.L. received honoraria from Amgen, AstraZeneca, Celgene, Lilly, Loreal, MSD, Novartis, Pfizer, Tesaro, Teva. M.W.B reports support from Novartis, Merck Sharp & Dohme, AstraZeneca, Roche, Amgen, Eisai, paid to his institution. E.B. received honoraria from Novartis, Celgene, Riemser, Pfizer, Hexal, Amgen, onkowissen.de for consulting, clinical research management or medical education activities. P.A.F. received honoraria from Novartis, Pfizer, Roche, Amgen, Celgene, Daiichi-Sankyo, AstraZeneca, Merck-Sharp & Dohme, Eisai, Puma and Teva. His institution conducts research with funding from Novartis and Biontech. T.N.F. reports personal fees from Roche, personal fees from Novartis, personal fees from Pfizer, personal fees from Daichii Sankyo, personal fees from Lilly, personal fees from MSD, outside the submitted work. P.H. received honoraria, unrestricted educational grants and research funding from Amgen, AstraZeneca, Eli Lilly, MSD, Novartis, Pfizer, and Roche. A.D.H. received honoraria from Teva, GenomicHealth, Celgene, AstraZeneca, Novartis, Pfizer, and Roche. C.H. received honoraria from Amgen, Celgene, Oncovis, Roche, and Pfizer. J.H. received honoraria from Astra Zeneca, MSD, Lilly, travel grants from Novartis and research grants from Novartis, Celgene. E.R. reports personal fees from Roche, Pfizer, Amgen, Novartis, Tesaro, Astra Zeneca, Celgene, Pierre Fabre and Riemer, non-financial support from Olympus GmbH, personal fees from Riemser, outside the submitted work. W.J. received research grants and honoroaria from Novartis, Pfizer, Amgen, Chugai, Roche, Genomic-Health, AstraZeneca, Lilly. H.-C.K. received honoraria from Carl Zeiss meditec, TEVA, Theraclion, Novartis, Amgen, AstraZeneca, Pfizer, Janssen-Cilag, GSK, LIV Pharma, and Genomic Health. C.M.K. received honoraria from Amgen, Axios, Roche, Teva, Novartis, MSD Sharp & Dohme, Mundipharma, NewCo, Pfizer, Riemser, and ZytoService, research grants from Amgen, Axios, Novartis, MSD Sharp & Dohme, NewCo, Pfizer, and ZytoService, and travel support from Amgen, Paxman Inc., PharmaMar, and Pfizer. M.P.L. has participated on advisory boards for AstraZeneca, MSD, Novartis, Pfizer, Eisai, Genomic Health, Tesaro and Roche and has received honoraria for lectures from MSD, Lilly, Roche, Novartis, Pfizer, Genomic Health, AstraZeneca, medac and Eisai. V.M. received speaker honoraria from Amgen, Astra Zeneca, Celgene, Daiichi-Sankyo, Eisai, Pfizer, Novartis, Roche, Teva, Janssen-Cilag and consultancy honoraria from Genomic Health, Hexal, Roche, Pierre Fabre, Amgen, Novartis, MSD, Daiichi-Sankyo, Eisai, Lilly, Tesaro and Nektar. N.N. received consultancy honoraria from Janssen-Cilag and travel support from Novartis. F.O. received speaker and consultancy honoraria from Amgen, AstraZeneca, Bayer, BMS, Boehringer, Celgene, Cellex, Chugai, Gilead, Hexal, Ipsen, Janssen-Cilag, Merck, MSD, Novartis, Riemser, Roche, Tesaro, Teva. H.T. received honoraria from Novartis, Roche, Celgene, TEVA, and Pfizer and travel support. F.-A. T. received honoraria from Astra Zeneca, Genomic Health and Novartis. C.T. received honoraria from Amgen, Astra-Zeneca, Celgene, Novartis, Pfizer, and Roche. M.U. reports support paid to his institution from Abbvie, Amgen GmbH München, Astra Zeneca, BMS, Celgene GmbH München, Daiji Sankyo, Eisai GmbH München, Janssen Cilag, Johnsen&Johnsen, Lilly Deutschland, Lilly Int., MSD Merck, Mundipharma, Myriad Genetics GmbH Zürich, Odonate, Pfizer GmbH Berlin, PUMA Biotechnology, Riemser, Roche Pharma AG, Grenzach Wyhlen, Sanofi Aventis Deutschland GmbH, Sividon Diagnostics Köln, TEVA Pharmaceuticals Ind. Ltd. und. Berlin(.)P.W. received honoraria from Amgen, AstraZeneca, Merck Sharp & Dohme, Novartis, Pfizer, PharmaMar, Roche, TEVA, Eisai Clovis and Tesaro. She participated in advisory boards of Amgen, AstraZeneca, Merck Sharp & Dohme, Novartis, Pfizer, PharmaMar, Roche, TEVA, Eisai Clovis and Tesaro. Her institution received research grants from Amgen, AstraZeneca, MSD, Novartis, Pfizer, Pharmamar, Clovis and Tesaro. R.W. received honoraria from Agendia, Amgen, Astra Zeneca, Boeringer Ingelheim, Carl Zeiss, Celgene, Daiichi-Sankyo, Esai, Genomic Health, Glaxo Smith Kline, Lilly, MSD, Mundipharma, Nanostring, Novartis, Odonate, Paxman, Palleos, Pfizer, Pierre Fabre, PumaBiotechnolgogy, Riemser, Roche, Sandoz/Hexal, Seattle Genetics, Tesaro Bio, Teva. M.W. received speaker honoraria from AstraZeneca, Celgene, and Novartis. S.Y.B. reports personal fees from Novartis and Pfizer, both outside the submitted work. All remaining authors (J.S., E.K., M.G., L.H., B.V., D.W.) have declared that they do not have any conflicts of interest., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Spontaneously occurring canine oral squamous cell carcinomas (COSCC) are viewed as a useful model for human head and neck squamous cell carcinomas (HNSCC). To date however, the molecular basis of COSCC remains poorly understood. To identify changes pertinent to cancer cells in COSCC, we specifically analyzed tumor cells and matched normal epithelium from clinical formalin-fixed paraffin-embedded specimens using laser-capture-microdissection coupled with RNA-sequencing (RNAseq). Our results identify strong contributions of epithelial-to-mesenchymal transition (EMT), classical tumor-promoting (such as E2F, KRAS, MYC, mTORC1, and TGFB1 signaling) and immune-related pathways in the tumor epithelium of COSCC. Comparative analyses of COSCC with 43 paired tumor/normal HNSCC from The Cancer Genome Atlas revealed a high homology in transcriptional reprogramming, and identified processes associated with cell cycle progression, immune processes, and loss of cellular differentiation as likely central drivers of the disease. Similar to HNSCC, our analyses suggested a ZEB2-driven partial EMT in COSCC and identified selective upregulation of KRT14 and KRT17 in COSCC. Beyond homology in transcriptional signatures, we also found therapeutic vulnerabilities strongly conserved between the species: these included increased expression of PD-L1 and CTLA-4, coinciding with EMT and revealing the potential for immune checkpoint therapies, and overexpression of CDK4/6 that sensitized COSCC to treatment with palbociclib. In summary, our data significantly extend the current knowledge of molecular aberrations in COSCC and underline the potential of spontaneous COSCC as a model for HNSCC to interrogate therapeutic vulnerabilities and support translation of novel therapies from bench to bedside., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) represent the standard treatment for hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer. Data about the balance between efficacy and toxicity of combined palliative radiotherapy (RT) and CDK4/6 inhibition are lacking., Patients and Methods: We undertook a review of 46 patients with metastatic breast cancer on systemic treatment with CDK4/6i who underwent 62 metastases-directed RT. Clinical, laboratory, and RT treatment planning data were collected. Statistical analyses included Student t test, paired sample t test, and logistic regression modeling., Results: Thirty patients (65.2%) received palbociclib, 15 (32.6%) received ribociclib, and one patient received abemaciclib (2.2%). Median total prescribed RT dose was 20 Gy (range, 8-63 Gy). Sites of RT were bone (n = 50; 80.7%), visceral (n = 7; 11.3%), or brain metastases (n = 3; 4.8%), as well as primary tumor of the breast (n = 2; 3.2%). Overall, the rates of grade 3 or higher adverse events (AEs) were 6.5%, 4.3%, 15.2%, and 23.9% before the start of RT, during RT, 2 and 6 weeks after RT completion, respectively. We found no correlation between dose distribution to organs at risk and the development of AEs. The local control rates for the entire cohort were 98% at 6 months and 90% at 12 months. Overall, pain relief (complete or partial) was experienced by 80% (24/30) of patients who initially reported pain at the treated metastatic site., Conclusion: We observed a modest increase in the rates of grade 3 or higher AEs after combined RT and CDK4/6i, with maintained efficacy of concomitant RT., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Cyclin-dependent kinase inhibitors (CDKIs) and endocrine therapy (ET) are the corner-stone of systemic therapy for patients with hormone-positive (HR+) HER2-negative metastatic breast cancer (MBC). However, limited data exist regarding rechallenge treatment strategies with CDKIs after limiting toxicity. In this report, we provide evidence of the safety and efficacy of sequential treatment with palbociclib or abemaciclib in 6 HR+/HER- MBC patients who experienced grade ≥3 ribociclib-induced hypertransaminasemia. Until results from large observational or randomized studies are communicated, empirical evidence may help make individualized decisions on CDKI rechallenge beyond ribociclib-induced unacceptable liver toxicity., (Copyright © 2020. Published by Elsevier Ltd.)

Pancreatic ductal adenocarcinoma (PDAC) is one of the most deadly solid tumors in the world. Aerobic glycolysis is among the characteristic features of pancreatic cancer. However, the regulatory process of aerobic glycolysis in pancreatic cancer is too complicated, and the underlying mechanism remains unexplained. Reportedly, CDK4/6 inhibitors repress breast cancer cell proliferation by modulating glucose metabolism. Here, we reveal that the CDK4/6 inhibitor, PD0332991 stabilized FBP1 to hinder aerobic glycolysis in pancreatic cancer. We also show that the CDK4/6-E2 F1 signaling pathway mediated an increase in MAGED1 expression, promoting FBP1 degradation in pancreatic cancer. We, therefore, might have identified a novel mechanism by which the CDK4/6 inhibitor, PD0332991 blocks the Warburg effect of pancreatic cancer by stabilizing FBP1., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Palbociclib, ribociclib and abemaciclib have all been approved in combination with endocrine therapy in hormone-receptor positive, HER2 negative metastatic breast cancer. While the efficacy of these drugs appears similar, differences in safety and tolerability are apparent., Methods: We searched PubMed and ASCO, ESMO and SABCS proceedings to identify randomized trials of palbociclib, ribociclib and abemaciclib. Data on common and serious adverse events (AE) were extracted for each approved drug. The odds ratio for each AE and the hazard ratio for progression-free survival were calculated relative to endocrine therapy alone. A network meta-analysis was then performed for each endocrine therapy backbone (aromatase inhibitor (AI) or fulvestrant) to compare ribociclib and abemaciclib to palbociclib., Results: 8 trials were included in the analysis and comprised 2799 patients receiving cyclin-dependent kinase 4/6 inhibitors palbociclib: 873 patients; ribociclib: 1153 patients; abemaciclib: 773 patients. In 5 trials (1524 patients), the endocrine therapy backbone was an AI and in 3 trials (1275 patients) it was fulvestrant. Compared to palbociclib, ribociclib and abemaciclib showed significantly lower grade 3-4 neutropenia, but significantly higher GI toxicity. Treatment discontinuation was higher with abemaciclib than other drugs. Efficacy of the 3 drugs was similar. Compared to palbociclib, for AI backbone, the HR for PFS for ribociclib was 0.98 and for abemaciclib 1.02. For fulvestrant backbone, the HR were 0.88 and 0.93 respectively., Conclusions: Palbociclib, ribociclib and abemaciclib have comparable efficacy, but differences in safety and tolerability. Abemaciclib has worse tolerability with significantly higher treatment discontinuation likely due to GI toxicity., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Radiotherapy combined with chemotherapy is a common modality in abdominal cancer treatment. However, intestinal syndrome induced by radiation is a main factor leading to the poor prognosis of radiotherapy. In this work, we found that miR-378a-3p was markedly up-regulated in the small intestines of mice after total abdominal irradiation. Knocking-down (or overexpression) of miR-378a-3p increased (or decreased) the radiosensitivity of the small intestine cells HIEC and FHs-74-Int. Comet assay and γ-H2AX staining demonstrated that miR-378a-3p exerted its radioprotective function by reducing the accumulation of DNA damage in the cells and tissues of the small intestines. Mechanistically, miR-378a-3p could interact with the 3' UTR of CDK6 through complementary sequences and thus inhibited CDK6 expression in the small intestine cells. Rescue experiments suggested that the repression of miR-378a-3p overexpression on cell radiosensitivity and DNA damage accumulation was abrogated by the forced expression of CDK6. In summary, our results revealed for the first time that miR-378a-3p regulated the radiosensitivity and DNA damage response of small intestines by targeting CDK6. MiR-378a-3p may serve as a promising biomarker and radioprotective target in abdominal cancer., Competing Interests: Declaration of competing interest The authors have declared no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Fusion proteins involving Nucleoporin 98 (NUP98) are recurrently found in acute myeloid leukemia (AML) and are associated with poor prognosis. Lack of mechanistic insight into NUP98-fusion-dependent oncogenic transformation has so far precluded the development of rational targeted therapies. We reasoned that different NUP98-fusion proteins deregulate a common set of transcriptional targets that might be exploitable for therapy. To decipher transcriptional programs controlled by diverse NUP98-fusion proteins, we developed mouse models for regulatable expression of NUP98/NSD1, NUP98/JARID1A, and NUP98/DDX10. By integrating chromatin occupancy profiles of NUP98-fusion proteins with transcriptome profiling upon acute fusion protein inactivation in vivo, we defined the core set of direct transcriptional targets of NUP98-fusion proteins. Among those, CDK6 was highly expressed in murine and human AML samples. Loss of CDK6 severely attenuated NUP98-fusion-driven leukemogenesis, and NUP98-fusion AML was sensitive to pharmacologic CDK6 inhibition in vitro and in vivo. These findings identify CDK6 as a conserved, critical direct target of NUP98-fusion proteins, proposing CDK4/CDK6 inhibitors as a new rational treatment option for AML patients with NUP98-fusions., (© 2020 by The American Society of Hematology.)

Cell cycle dysregulation, characterised by aberrant activation of cyclin dependent kinases (CDKs), is a hallmark of cancer. After years of research on the first and second generations of less selective CDK inhibitors with unfavourable clinical activity and toxicity profiles, CDK4/6 inhibitors become the first and only class of highly specific CDK inhibitors being approved for cancer treatment to date. CDK4/6 inhibitors have transformed the treatment paradigm of estrogen receptor-positive (ER+) breast cancer, dramatically improving the survival outcomes of these patients when incorporated with conventional endocrine therapies in both the first and later-line settings. Currently, the efficacies of CDK4/6 inhibitors in other breast cancer subtypes and cancers are being actively explored. All three CDK4/6 inhibitors have demonstrated very similar clinical efficacies. However, being the least similar structurally, abemaciclib is the only CDK4/6 inhibitor with single agent activity in refractory metastatic ER + breast cancer, the ability to cross the blood brain barrier efficiently, and a distinct toxicity profile of lower myelosuppression such that it can be dosed continuously. Here, we further discuss the distinguishing features of abemaciclib as compared to the other two CDK4/6 inhibitors, palbociclib and ribociclib. Besides being the most potent inhibitor of CDK4/6, abemaciclib exhibits a wider selectivity towards other CDKs and kinases, and functions through additional mechanisms of action besides inducing G1 cell cycle arrest, in a dose dependent manner. Hence, abemaciclib has the potential to act independently of the CDK4/6-cyclin D-RB pathway, resulting in crucial implications on the possibly expanded clinical indications and predictive biomarkers of abemaciclib, in contrast to the other CDK4/6 inhibitors. The current status of preclinical evidence and clinical studies of abemaciclib as a single agent and in combination treatment in breast and other cancers, together with its potential predictive biomarkers, is also summarised in this review., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest, (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Expression of the cell cycle regulatory gene CDK6 is required for Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) cell growth, whereas expression of the closely related CDK4 protein is dispensable. Moreover, CDK6 silencing is more effective than treatment with the dual CDK4/6 inhibitor palbociclib in suppressing Ph+ ALL in mice, suggesting that the growth-promoting effects of CDK6 are, in part, kinase-independent in Ph+ ALL. Accordingly, we developed CDK4/6-targeted proteolysis-targeting chimeras (PROTACs) that inhibit CDK6 enzymatic activity in vitro, promote the rapid and preferential degradation of CDK6 over CDK4 in Ph+ ALL cells, and markedly suppress S-phase cells concomitant with inhibition of CDK6-regulated phospho-RB and FOXM1 expression. No such effects were observed in CD34+ normal hematopoietic progenitors, although CDK6 was efficiently degraded. Treatment with the CDK6-degrading PROTAC YX-2-107 markedly suppressed leukemia burden in mice injected with de novo or tyrosine kinase inhibitor-resistant primary Ph+ ALL cells, and this effect was comparable or superior to that of the CDK4/6 enzymatic inhibitor palbociclib. These studies provide "proof of principle" that targeting CDK6 with PROTACs that inhibit its enzymatic activity and promote its degradation represents an effective strategy to exploit the "CDK6 dependence" of Ph+ ALL and, perhaps, of other hematologic malignancies. Moreover, they suggest that treatment of Ph+ ALL with CDK6-selective PROTACs would spare a high proportion of normal hematopoietic progenitors, preventing the neutropenia induced by treatment with dual CDK4/6 inhibitors., (© 2020 by The American Society of Hematology.)

The development and approval of cyclin-dependent kinase (CDK) 4 and 6 inhibitors for hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer represents a major milestone in cancer therapeutics. Three different oral CDK4/6 inhibitors, palbociclib, ribociclib, and abemaciclib, have significantly improved progression-free survival by a number of months when combined with endocrine therapy. More recently, improvement in overall survival has been reported with ribociclib and abemaciclib. The toxicity profile of all three drugs is well described and generally easily manageable with dose reductions when indicated. More myelotoxicity is observed with palbociclib and ribociclib, but more gastrointestinal toxicity is observed with abemaciclib. Emerging data is shedding light on the resistance mechanisms associated with CDK4/6 inhibitors, including cell cycle alterations and activation of upstream tyrosine kinase receptors. A number of clinical trials are exploring several important questions regarding treatment sequencing, combinatorial strategies, and the use of CDK4/6 inhibitors in the adjuvant and neoadjuvant settings, thereby further expanding and refining the clinical application of CDK4/6 inhibitors for patients with breast cancer., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with backbone endocrine therapy have markedly improved progression-free survival and overall survival over endocrine therapy alone in advanced hormone receptor-positive, HER2-negative (HR + /HER2 - ) breast cancer and are the standard of care in the first- or second-line setting. There are few data to drive decision making for subsequent treatment strategies after inevitable disease progression after CDK4/6i. Information about the genomic landscape of CDK4/6i-resistant disease is emerging. Resistance mechanisms appear to be varied, but mutations in PIK3CA and ESR1, which can be acquired while receiving treatment, are frequent. Activating PIK3CA mutations are present in up to 35% of patients and are now the most actionable genomic alteration in HR + /HER2 - advanced breast cancer with the recent approval of alpelisib and fulvestrant. Everolimus-based combinations and chemotherapy appear to have continued efficacy after progression while receiving CDK4/6i, although historical data on benefit include CDK4/6i-naive patients. Use of selective estrogen down-regulators over aromatase inhibitors is best once the patient has an acquired ESR1 mutation. Tumor biopsy with genomic sequencing and repeat biomarker analysis in patients with CDK4/6i- and endocrine-resistant disease will be integral to guide subsequent treatment strategies and to inform clinical trial eligibility. Promising novel therapeutics in CDK4/6i-resistant disease including oral selective estrogen down-regulators, fibroblast growth factor receptor antagonists, and immunotherapy will be discussed., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The mammalian cell cycle is driven by a complex of cyclins and their associated cyclin-dependent kinases (CDKs). Abnormal dysregulation of cyclin-CDK is a hallmark of cancer. D-type cyclins and their associated CDKs (CDK4 and CDK6) are key components of cell cycle machinery in driving G1 to S phase transition via phosphorylating and inactivating the retinoblastoma protein (RB). A body of evidence shows that the cyclin Ds-CDKs axis plays a critical role in cancer through various aspects, such as control of proliferation, senescence, migration, apoptosis, and angiogenesis. CDK4/6 dual-inhibitors show significant efficacy in pre-clinical or clinical cancer therapies either as single agents or in combination with hormone, chemotherapy, irradiation or immune treatments. Of note, as the associated partner of D-type cyclins, CDK6 shows multiple distinct functions from CDK4 in cancer. Depletion of the individual CDK may provide a therapeutic strategy for patients with cancer., (© 2020 Elsevier Inc. All rights reserved.)

Background: Selective cyclin-dependent kinases 4/6 inhibitors (CDKi) have become the standard of care in patients with hormone receptor (HR)-positive, HER2-negative advanced breast cancer (ABC). We performed retrospective analysis in patients treated with CDKi in the first year of their routine clinical use in Slovenia., Methods: The primary goals were time-to-treatment failure (TTF) and overall survival (OS), analysed via Kaplan-Meier method, the secondary goals were clinical benefit rate (CBR) and safety., Results: Overall, 218 patients' data were evaluated. The median age was 61.8 years (30.6-84.6). The median number of previous ET lines for ABC was 2 (range 0-5). At the time of inclusion, 128 patients (58.7%) had visceral metastases, 45 patients (20.6%) had bone-only disease. At the median follow-up of 15.2 months, disease progressed in 74 patients and 60 patients died. The median TTF was 8.3 months for the whole group, 19.3, 10.3 and 5.5 months for patients treated in the first-, second- and further lines of systemic therapy, respectively. The median OS from the start of CDKi treatment was not reached in any of the groups. CBR was 59.6% for the whole group, 42.7% for further lines of therapy. The most common grade 3/4 adverse event was neutropaenia in 108 patients (49.5%), followed by an increase of hepatic aminotransferases in 13 patients (6.0%)., Conclusions: Even in the diverse real-world population treatment with CDKi in combination with ET showed clinical benefit, most prominently in the first- and second lines of systemic therapy., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The landscape of therapeutic options for the treatment of hormone receptor (HR)-positive (HR + ) HER2 - breast cancer (BC) has been profoundly changed by the introduction of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors into the metastatic setting. Currently all CDK4/6 inhibitors are approved only in the metastatic setting by Food and Drug Administration (FDA) and European Medicine Agency (EMA), whereas their role in the neoadjuvant setting is still at an investigational stage. Exploitation of novel agents such as CDK4/6 inhibitors to improve the efficacy of neoadjuvant endocrine therapy (ET) or to overcome de novo resistance to ET is an area of research under active evaluation. We present a review of the currently available data and ongoing clinical trials that are evaluating the role of CDK4/6 inhibitors in neoadjuvant therapy of HR + HER2 - early BC, and also illustrate translational aspects, such as the potential biomarkers of response to these new therapeutic agents., (Copyright © 2019 Elsevier Inc. All rights reserved.)

In December 2017, ESMO Open-Cancer Horizons convened a round-table discussion on the background and latest data regarding cyclin-dependent kinase (CDK)4/6 inhibitors with endocrine therapy (ET) in the treatment of endocrine-sensitive breast cancer (BC). A review on this discussion was published in summer 2018 (https://esmoopen.bmj.com/content/3/5/e000368).Endocrine-sensitive BC with non-visceral disease and limited spread of the metastases.Endocrine-sensitive BC with non-life-threatening visceral involvement. Several open questions were identified, which led to a second ESMO Open discussion on CDK4/6 inhibitors, taking place in December 2018 and covered in this article. The panel discussed two important clinical scenarios and the pro and cons of a treatment approach with CDK4/6 inhibitors for each scenario:Endocrine-sensitive BC with non-visceral disease and limited spread of the metastases.Endocrine-sensitive BC with non-life-threatening visceral involvement. Regarding scenario 1, the panel agreed that CDK4/6 inhibitors should be recommended in first-line therapy for most patients if cost and practicality allow. However, the use of single-agent ET with an aromatase inhibitor in the first-line treatment of these patients is still a possibility for a small group of patients with very limited disease, such as one or two bone lesions or limited lymph node involvement. Regarding scenario 2, chemotherapy is the first approach for patients with endocrine-sensitive metastatic BC with life-threatening visceral involvement because of the need for a faster response. The therapeutic approaches for patients with non-life-threatening visceral involvement are still under debate. Nevertheless, CDK4/6 inhibitors are currently the treatment of choice for most patients with a close follow-up of tumour response. A treatment algorithm has been suggested at the round table., Competing Interests: Competing interests: MP: honoraria for lectures, consultation or advisory board participation from the following for-profit companies: Bayer, Bristol-Myers Squibb, Novartis, Gerson Lehrman Group (GLG), CMC Contrast, GlaxoSmithKline, Mundipharma, Roche, Astra Zeneca, AbbVie, Lilly, Medahead, Daiichi Sankyo and Merck Sharp & Dome. JG: research support from Eisai, Genomic Health, Novartis, Pfizer and Roche; travel grants from Eisai, Genomic Health, Novartis, Pfizer and Roche; honoraria for advisory boards and speaker fees from Daiichi, Eisai, Genomic Health, Ipsen, Macrogenics, MSD, Novartis, Onxeo, Pfizer and Roche. GJ: grants, personal fees and non-financial support from Novartis and Roche; personal fees and non-financial support from Pfizer, Lilly, Amgen, BMS, Astra-Zeneca; personal fees from Celgene, Puma Technology, Daiichi Sankyo and Abbvie. AA: advisory boards, travel grants, speaker fees: Novartis, Roche, Lilly, Amgen, Eisai, BMS, MSD, LeoPharma, Genomic Health and Ipsen. CS: honoraria for lectures, consultation or advisory board participation from the following for-profit companies: Novartis, Gerson Lehrman Group, Astra-Zeneca, Lilly, Roche, Amgen, Pfitzer, Merck KGaA, and Tesaro. CCZ: honoraria from Roche, Novartis, BMS, MSD, Imugene, Ariad, Pfizer, Merrimack, Merck KGaA, Fibrogen, AstraZeneca, Tesaro, Gilead, Servier and Shire., (© Author (s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. Published by BMJ on behalf of the European Society for Medical Oncology.)

Background: Chemotherapy-induced damage of hematopoietic stem and progenitor cells (HSPC) causes multi-lineage myelosuppression. Trilaciclib is an intravenous CDK4/6 inhibitor in development to proactively preserve HSPC and immune system function during chemotherapy (myelopreservation). Preclinically, trilaciclib transiently maintains HSPC in G1 arrest and protects them from chemotherapy damage, leading to faster hematopoietic recovery and enhanced antitumor immunity., Patients and Methods: This was a phase Ib (open-label, dose-finding) and phase II (randomized, double-blind placebo-controlled) study of the safety, efficacy and PK of trilaciclib in combination with etoposide/carboplatin (E/P) therapy for treatment-naive extensive-stage small-cell lung cancer patients. Patients received trilaciclib or placebo before E/P on days 1-3 of each cycle. Select end points were prespecified to assess the effect of trilaciclib on myelosuppression and antitumor efficacy., Results: A total of 122 patients were enrolled, with 19 patients in part 1 and 75 patients in part 2 receiving study drug. Improvements were seen with trilaciclib in neutrophil, RBC (red blood cell) and lymphocyte measures. Safety on trilaciclib+E/P was improved with fewer ≥G3 adverse events (AEs) in trilaciclib (50%) versus placebo (83.8%), primarily due to less hematological toxicity. No trilaciclib-related ≥G3 AEs occurred. Antitumor efficacy assessment for trilaciclib versus placebo, respectively, showed: ORR (66.7% versus 56.8%, P = 0.3831); median PFS [6.2 versus 5.0 m; hazard ratio (HR) 0.71; P = 0.1695]; and OS (10.9 versus 10.6 m; HR 0.87; P = 0.6107)., Conclusion: Trilaciclib demonstrated an improvement in the patient's tolerability of chemotherapy as shown by myelopreservation across multiple hematopoietic lineages resulting in fewer supportive care interventions and dose reductions, improved safety profile, and no detriment to antitumor efficacy. These data demonstrate strong proof-of-concept for trilaciclib's myelopreservation benefits., Clinical Trail Number: NCT02499770., (© The Author(s) 2019. Published by Oxford University Press on behalf of the European Society for Medical Oncology.)

CDK4/6 inhibitors are a new class of anticancer drugs used for the treatment of women with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced or metastatic breast cancer with disease progression following endocrine therapy. Polypharmacy is a well-known problem in advanced cancer causing potential drug-drug interactions (DDIs), which, in turn, may limit the therapeutic value of CDK4/6 inhibitors. Therefore, understanding the mechanisms underlying potential DDIs in patients taking CDK4/6 inhibitors may be useful in decision-making processes and represent an important step towards treatment personalization. The present review is aimed at describing the potential DDIs that might occur in breast cancer patients receiving CDK4/6 inhibitors based on direct evidence from the literature and mechanistic considerations tailored on specific class of drugs used in combination., (Copyright © 2019. Published by Elsevier Ltd.)

Cell cycle dysregulation is typical in human cancers, and CDK4/6 inhibitors targeting cell cycle have potential antiapoptosis effect. The aim of this work is to identify the regulatory effect of Palbociclib on apoptosis of H9c2 cells induced by high glucose (HG) and to elucidate the fundamental mechanisms. It was observed that Palbociclib decreased intracellular ROS production, augmented mitochondrial membrane potential and hindered apoptosis of H9c2 cells. Palbociclib increased the Bcl-2/Bax ratio, diminished the expressions of Bax and cleaved-caspase-3, and affected the RB phosphorylation and p53 expression. Altogether, the anti-apoptotic efficacy of Palbociclib could be attributed in part to the modulation of the mitochondria apoptotic pathway., (Copyright © 2019 Elsevier Inc. All rights reserved.)