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

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.

CDK4/6 inhibitors have become the standard of care for HR-positive, HER2-negative advanced breast cancer. However, there is still a lack of standard recommendations for the subsequent treatment of patients with CDK4/6 inhibitor resistance, especially those with primary resistance or rapid progression. Currently, appropriate treatment strategies included re-challenge of CDK4/6 inhibitors, combination with PI3K/AKT/mTOR inhibitors, new antibody drug conjugate (ADC), novel endocrine therapy drugs, and chemotherapy. In addition, many new targeted drugs and new combination treatment strategies are also being explored. In the future, precise treatment strategies based on biomarkers should be established, as well as the optimal sequence of use of different therapies.

Breast cancer is a leading cause of cancer-related morbidity and mortality worldwide, with the highest incidence among women. Among the various subtypes of breast cancer, estrogen-receptor positive (ER+) is the most diagnosed. Estrogen upregulates cyclin D1, which in turn promotes the activity of CDK4/6 and facilitates cell cycle progression. To address this, the first-line treatment for ER+ breast cancer focuses on inhibiting estrogen production by targeting aromatase, the enzyme responsible for the rate-limiting step in estrogen synthesis. Thus, combining CDK4/6 inhibitors with aromatase inhibitors has emerged as a crucial treatment strategy for this type of breast cancer. This approach effectively suppresses estrogen biosynthesis and controls uncontrolled cell proliferation, significantly improving overall survival rates and delayed disease progression. This study aimed to identify compounds that are likely to inhibit CDK4/6 and aromatase simultaneously by using a structure-based drug design strategy. 12,432 approved and investigational drugs were prepared and docked into the active site of CDK6 using HTVS and XP docking modes of Glide resulting in 277 compounds with docking scores ≤ -7 kcal/mol. These compounds were docked into aromatase enzyme using XP mode to give seven drugs with docking scores≤ -6.001 kcal/mol. Furthermore, the shortlisted drugs were docked against CDK4 showing docking scores ranging from -3.254 to -8.254 kcal/mol. Moreover, MM-GBSA for the top seven drugs was calculated. Four drugs, namely ellagic acid, carazolol, dantron, and apomorphine, demonstrated good binding affinity to all three protein targets CDK4/6 and aromatase. Specifically, they exhibited favourable binding free energy with CDK6, with values of -51.92, -53.90, -50.22, and -60.97 kcal/mol, respectively. Among these drugs, apomorphine displayed the most favourable binding free energy with all three protein targets. To further evaluate the stability of the interaction, apomorphine was subjected to a 100 ns molecular dynamics simulation with CDK6. The results indicated the formation of a stable ligand-protein complex. While the results obtained from the MM-GBSA calculation of the binding free energies of the MD conformations of apomorphine showed less favourable binding free energy compared to that obtained post-docking. All these computational findings will provide better structural insight for the development of CDK4/6 and aromatase multi-target inhibitors., Competing Interests: he authors have declared that no competing interests exist., (Copyright: © 2023 yousif et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Cyclin-dependent kinases (CDKs), especially cyclin-dependent kinase 4/6 (CDK4/6), have been targets for the development of specific tumor imaging agents. Palbociclib is a highly selective CDK4/6 inhibitor. In this study, to develop a novel 18 F-labeled palbociclib derivative for specific tumor imaging, we designed and synthesized a ligand (NOTA-PBB) consisting of palbociclib as the targeted pharmacophore and NOTA as the macrocyclic bifunctional chelator. The corresponding [ 18 F]AlF-NOTA-PBB complex was prepared with high radiochemical purity (98.4 ± 0.15%) and yield (58.7 ± 4.5%) within 35 min without requiring HPLC purification through a simple one-step 18 F-labeling strategy of NOTA-AlF chelation chemistry. The radiotracer was lipophilic (log P = 0.095 ± 0.003) and had good stability in vitro and in vivo . The cellular uptake studies performed on the MCF-7 breast cancer cell line (ER-positive and HER2-negative) showed that radioactive uptake was blocked by preincubating with a molar dose of palbociclib and it had a nanomolar binding affinity to CDK4/6 (IC 50 = 16.23 ± 1.84 nM), demonstrating a CDK4/6-mediated uptake mechanism. Its ex vivo biodistribution in nude mice-bearing MCF-7 tumors showed obvious tumor uptake and a high tumor/muscle ratio of [ 18 F]AlF-NOTA-PBB, and tumor uptake was inhibited with 100 μg of palbociclib, demonstrating specific binding to CDK4/6. Radioactivity accumulation in MCF-7 tumors was observed in PET imaging with [ 18 F]AlF-NOTA-PBB. Based on the results of this work, [ 18 F]AlF-NOTA-PBB has the promising capability as a CDK4/6-targeted tumor imaging agent.

Background: The combination of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors and standard endocrine therapy (ET) in the adjuvant treatment of hormone receptor (HR)-positive/HER2-negative breast cancer (BC) has yielded conflicting results. We performed a pooled analysis of the adjuvant efficacy of CDK4/6 inhibitors by including data from the NATALEE trial, the most recent trial on this topic., Methods: We searched major databases and congress proceedings until 7 June 2023 to identify randomized controlled trials (RCT) comparing adjuvant CDK4/6 inhibitor plus ET combination versus ET in HR-positive/HER2-negative early-stage BC., Results: Four RCTs involving a total of 17,749 patients were included. According to the pooled analysis of these four studies, significant improvement in invasive disease-free survival (iDFS) was observed with the addition of CDK4/6 inhibitors to standard ET (HzR: 0.81, 95% CI 0.67-0.97). IDFS benefit was irrespective from menopausal status, Ki-67 index, tumor grade, and previous chemotherapy. CDK4/6 inhibitors plus ET had a significant improvement in iDFS in stage 3 whereas there was a trend toward better iDFS in stage 2 (HzR for stage 3: 0.67, 95% CI 0.58-0.78; HzR for stage 2: 0.74, 95% CI 0.55-1.01)., Conclusions: Addition of CDK4/6 inhibitors to standard ET in the adjuvant treatment of HR-positive/HER2-negative early-stage BC improves iDFS.

Treatment of breast cancer has greatly evolved during the last decades, but triple negative breast cancer (TNBC) with a higher degree of malignancy cannot be directly and effectively treated. Abnormal cell cycle is generally found in human breast cancer and other malignant tumors, and cyclin-dependent kinases (CDK) 4/6, a cell cycle-related regulatory nuclear protein, is deemed as an effective target for breast cancer treatment so far. Since DCAF16 E3 ligase is also mainly distributed in the nucleus, in this study, by combining Palbociclib and DCAF16 E3 ligase ligand KB02 with different linkers, a series of DCAF16 based CDK4/6 degraders were designed and synthesized. Among them, compound A4 showed potent inhibitory activity against CDK4/6, and decreased the level of CDK4/6 protein in MDA-MB-231 cells in a concentration- and time-dependent manner. Moreover, the toxicity of A4 in normal cells showed 7 times lower than that of Palbociclib, and A4 exhibits therapeutic potential in MDA-MB-231 xenograft models in vivo. These findings indicate that A4, as a novel CDK4/6 degrader based on DCAF16, is worthy of further investigating for the treatment of TNBC., 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 © 2023 Elsevier Inc. All rights reserved.)

Background: Cyclin-dependent kinase (CDK)4/6-inhibitors with endocrine therapy represent the standard of treatment of hormone receptor-positive(HR+)/human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC). Gut microbiota seems to predict treatment response in several tumour types, being directly implied in chemotherapy resistance and development of adverse effects. No evidence is available on gut microbiota impact on efficacy of HR+ breast cancer treatment., Patients and Methods: We assessed the potential association among faecal microbiota and therapeutic efficacy of CDK4/6-inhibitors on 14 MBC patients classified as responders (R) and non-responders (NR) according to progression-free survival. A stool sample was collected at baseline and V3-V4 16S targeted sequencing was employed to assess its bacterial composition. Statistical associations with R and NR were studied., Results: No significant differences were observed between R and NR in terms of α-/β-diversity at the phylum and species level. Machine-learning (ML) algorithms evidenced four bacterial species as a discriminant for R (Bifidobacterium longum, Ruminococcus callidus) and NR (Clostridium innocuum, Schaalia odontolytica), and an area under curve (AUC) of 0.946 after Random Forest modelling. Network analysis evidenced two major clusters of bacterial species, named Species Interacting Groups (SIG)1-2, with SIG1 harbouring 75% of NR-related bacterial species, and SIG2 regrouping 76% of R-related species (p < 0.001). Cross-correlations among several patients' circulating immune cells or biomarkers and bacterial species' relative abundances showed associations with potential prognostic implications., Conclusions: Our results provide initial insights into the gut microbiota involvement in sensitivity and/or resistance to CDK4/6-inhibitors + endocrine therapy in MBC. If confirmed in larger trials, several microbiota manipulation strategies might be hypothesised to improve response to CDK4/6-inhibitors., Competing Interests: Declaration of Competing Interest FS declares travel expenses by Novartis and Gilead and personal fees for educational events by Novartis, Daiichy-Sankyo and Gilead. DG declares personal fees for educational events by Novartis, Lilly, Pfizer, Daiichy-Sankyo, Roche; research funds from Astrazeneca, Novartis and LILT. GC declares reports advisory/consulting fees from Seagen, Roche, Novartis, Eli Lilly, Daiichi Sankyo, AstraZeneca, Pfizer, Sanofi, Pierre Fabre and Gilead, and fees for non-CME services (e.g. speakers' bureaus) from Eli Lilly, Pfizer Inc and Daiichi Sankyo. The other authors have nothing to declare., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have become the standard of care for hormone receptor-positive (HR + ) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer, improving survival outcomes compared to endocrine therapy alone. Abemaciclib and ribociclib, in combination with endocrine therapy, have demonstrated significant benefits in invasive disease-free survival for high-risk HR+/HER2- early breast cancer patients. Each CDK4/6i-palbociclib, ribociclib, and abemaciclib-exhibits distinct toxicity profiles. Radiation therapy (RT) can be delivered with a palliative or ablative intent, particularly using stereotactic body radiation therapy for oligometastatic or oligoprogressive disease. However, pivotal randomized trials lack information on concomitant CDK4/6i and RT, and existing preclinical and clinical data on the potential combined toxicities are limited and conflicting. As part of a broader effort to establish international consensus recommendations for integrating RT and targeted agents in breast cancer treatment, we conducted a systematic review and meta-analysis to evaluate the safety profile of combining CDK4/6i with palliative and ablative RT in both metastatic and early breast cancer settings., 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 © 2023 Elsevier Ltd. All rights reserved.)

Opinion Statement: Hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER-2-) metastatic breast cancer (MBC) is the most common subtype of breast cancer. Due to therapeutic advances with molecularly targeted therapies, the prognosis for patients with metastatic disease has improved significantly. The advent of CDK4/6 inhibitors (CDK4/6i) has changed the treatment paradigm for patients with HR+HER2-MBC. CDK4/6i allowed for marked improvement in overall survival, delaying the time to chemotherapy initiation, and improved quality of life for our patients. Efforts are now focused on the best approach(es) for patients after progression on CDK4/6i. Can we further harness the benefit of CDK4/6i in novel combinations at the time of progression? Should we continue CDK4/6i or proceed other novel agents or endocrine therapies? As we advance our treatment strategies for HR+HER2-MBC, there is no longer a one-size-fits-all model, but instead a multifaceted and personalized approach lending to improved outcomes for our patients., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Bladder cancer (BCa) is a urinary tumor with limited treatment options and high mortality. Liensinine (LIEN), a natural bisbenzylisoquinoline alkaloid, has shown excellent anti-tumor effects in numerous preclinical studies. However, the anti-BCa effect of LIEN remains unclear. To the best of our knowledge, this is the first study to investigate the molecular mechanism of LIEN in the management of BCa. First, we identified the treatment-related targets of BCa; those that repeatedly occur in more than two databases, including GeneCards, Online Mendelian Inheritance in Man, DisGeNET, Therapeutic Target Database, and Drugbank. The SwissTarget database was used to screen LIEN-related targets, and those with a probability >0 were possible LIEN targets. The prospective targets of LIEN in the treatment of BCa were then determined using a Venn diagram. Second, we discovered that the PI3K/AKT pathway and senescence mediated the anti-BCa action of LIEN by using GO and KEGG enrichment analysis to explore the function of LIEN therapeutic targets. A protein-protein interaction network was created using the String website, and six algorithms of the CytoHubba plug-in were then used in Cytoscape to assess the core targets of LIEN for the therapy of BCa. The outcomes of molecular docking and dynamics simulation demonstrated that CDK2 and CDK4 proteins were the direct targets of LIEN in the management of BCa, among which CDK2 was more stable in binding to LIEN than CDK4. Finally, in vitro experiments showed that LIEN inhibited the activity and proliferation of T24 cells. The expression of p-/AKT, CDK2, and CDK4 proteins progressively decreased, while the expression and fluorescence intensity of the senescence-related protein, γH2AX, gradually increased with increasing LIEN concentration in T24 cells. Therefore, our data suggest that LIEN may promote senescence and inhibit proliferation by inhibiting the CDK2/4 and PI3K/AKT pathways in BCa., 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 © 2023 Elsevier B.V. All rights reserved.)

Neuroblastoma (NB), the most frequent solid extracranial tumor in children, is not always cured by current aggressive therapies that have notable adverse effects; therefore, novel treatments are necessary. Phosphoinositide 3‑kinase (PI3K) and fibroblast growth factor receptor inhibitors exhibit synergistic effect in NB cell lines. In the present study, mono‑ and combination therapy of the United States Food and Drug Administration‑approved PI3K, cyclin‑dependent kinase‑4/6 (CDK4/6), poly‑ADP‑ribose‑polymerase (PARP) and WEE1 G2 checkpoint kinase (WEE1) inhibitors (BYL719, PD‑0332991, BMN673 and MK‑1775, respectively), were used to treat NB cell lines SK‑N‑AS, SK‑N‑BE(2)‑C, SK‑N‑DZ, SK‑N‑FI and SK‑N‑SH and viability (assessed by WST‑1 assay), proliferation (incucyte analysis) and cell cycle (FACS) changes were assessed. Treatments with all single drugs presented dose‑-dependent responses with decreased viability and proliferation and combining BYL719 with PD‑0332991 or BMN673 with MK‑1775 resulted in additive or synergistic effects in most cell lines., except for SK‑N‑SH for the former and for SK‑N‑AS for the latter. Moreover, combining MK‑1775 and BMN673 decreased the numbers of cells in S phase to a greater extent than either drug alone, while when combining PD‑0332991 and BYL719 the observed effect was close to that of PD‑0332991 alone. To summarize, PI3K and CDK4/6 or PARP and WEE1 exhibited synergistic anti‑NB effects and lower doses of the inhibitors could be utilized, thereby potentially reducing adverse side effects.

Purpose: Malignant peripheral nerve sheath tumors (MPNST) are lethal, Ras-driven sarcomas that lack effective therapies. We investigated effects of targeting cyclin-dependent kinases 4 and 6 (CDK4/6), MEK, and/or programmed death-ligand 1 (PD-L1) in preclinical MPNST models., Experimental Design: Patient-matched MPNSTs and precursor lesions were examined by FISH, RNA sequencing, IHC, and Connectivity-Map analyses. Antitumor activity of CDK4/6 and MEK inhibitors was measured in MPNST cell lines, patient-derived xenografts (PDX), and de novo mouse MPNSTs, with the latter used to determine anti-PD-L1 response., Results: Patient tumor analyses identified CDK4/6 and MEK as actionable targets for MPNST therapy. Low-dose combinations of CDK4/6 and MEK inhibitors synergistically reactivated the retinoblastoma (RB1) tumor suppressor, induced cell death, and decreased clonogenic survival of MPNST cells. In immune-deficient mice, dual CDK4/6-MEK inhibition slowed tumor growth in 4 of 5 MPNST PDXs. In immunocompetent mice, combination therapy of de novo MPNSTs caused tumor regression, delayed resistant tumor outgrowth, and improved survival relative to monotherapies. Drug-sensitive tumors that regressed contained plasma cells and increased cytotoxic T cells, whereas drug-resistant tumors adopted an immunosuppressive microenvironment with elevated MHC II-low macrophages and increased tumor cell PD-L1 expression. Excitingly, CDK4/6-MEK inhibition sensitized MPNSTs to anti-PD-L1 immune checkpoint blockade (ICB) with some mice showing complete tumor regression., Conclusions: CDK4/6-MEK inhibition induces a novel plasma cell-associated immune response and extended antitumor activity in MPNSTs, which dramatically enhances anti-PD-L1 therapy. These preclinical findings provide strong rationale for clinical translation of CDK4/6-MEK-ICB targeted therapies in MPNST as they may yield sustained antitumor responses and improved patient outcomes., (©2023 American Association for Cancer Research.)

Background: This network meta-analysis aimed to assess the comparative efficacy and safety of combinations involving three cyclin-dependent kinase 4/6 (CDK4/6) inhibitors and endocrine therapies (ETs) in patients with metastatic or advanced breast cancer (BC) who are hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-)., Methods: We initially identified relevant studies from previous meta-analyses and then conducted a comprehensive search of PubMed, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases to locate additional studies published between February 2020 and September 2021. Essential data were extracted, and a network meta-analysis was performed using R 4.1.1 software with a random-effects model. Furthermore, we assigned rankings to all available treatment combinations by calculating their cumulative probability., Results: Data analysis included ten reports from nine studies. Pooled results demonstrated that each treatment combination significantly reduced the hazard risk of progression-free survival (PFS) compared to treatment with an aromatase inhibitor (AI) or fulvestrant alone. However, there were no differences observed in PFS or overall survival (OS) among the different treatment combinations. Additionally, patients receiving palbociclib plus AI and abemaciclib plus AI or fulvestrant experienced more severe adverse events (AEs), with hazard ratios (HRs) of 10.83 (95% confidence interval [CI] = 2.3 to 52.51) and 4.8 (95%CI = 1.41 to 16.21), respectively. The HR for ribociclib plus AI was 9.45 (95%CI = 2.02 to 43.61), and the HR for palbociclib plus fulvestrant was 6.33 (95%CI = 1.03 to 39.86). Based on the ranking probabilities, palbociclib plus fulvestrant had the highest probability of achieving superior PFS (37.65%), followed by abemaciclib plus fulvestrant (28.76%). For OS, ribociclib plus fulvestrant ranked first (34.11%), with abemaciclib plus fulvestrant in second place (25.75%). In terms of safety, palbociclib plus AI (53.98%) or fulvestrant (51.37%) had the highest probabilities of being associated with adverse events., Conclusions: Abemaciclib plus fulvestrant or ribociclib plus AI appear to be effective and relatively safe for the treatment of HR+/HER2- metastatic or advanced BC patients. However, given the reliance on limited evidence, our findings require further validation through additional studies., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Background: This study sought to compare the benefits and safety of agents including Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitors, and histone deacetylase (HDAC) inhibitors as second-line treatments for these patients by conducting a comprehensive systematic review and network meta-analysis., Methods: The Medline, Embase and Cochrane Library databases were searched for randomized trials comparing CDK4/6 inhibitors, PI3K/mTOR inhibitors, or HDAC inhibitors vs. placebo with the addition of exemestane or fulvestrant as second-line treatments in patients with HR + advanced breast cancer up to December 16, 2021. Outcomes of interest were progression-free survival (PFS), overall response rate (ORR), overall survival (OS), clinical benefit rate (CBR), and grade 3-4 adverse drug events (ADEs). The present study was conducted according to the Cochrane Collaboration and PRISMA statements. The overall effect was pooled using the random effects model., Results: Seventeen studies with a total of 9,100 participants were included in the current study. Compared with placebo plus fulvestrant, PFS was significantly improved by CDK4/6 inhibitor plus fulvestrant, mTOR inhibitor plus fulvestrant, mTOR inhibitor plus exemestane, and PI3K inhibitor plus fulvestrant, but not HDAC inhibitor plus exemestane. While mTOR inhibitor plus exemestane was the best regimen (SUCRA value 89.5%), the mTOR inhibitor plus exemestane regimen induced more severe adverse events (SAEs) than the HDAC inhibitor plus exemestane regimen [OR, 95% CI: 2.40 (1.40-4.10)]., Conclusion: mTOR inhibitor and CDK4/6 inhibitor-based regimens demonstrated superior clinical efficacy and comparable safety profiles as second-line treatment in patients with HR-positive, HER2-negative advanced breast cancer., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Purpose: Cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) with endocrine therapy (ET) improves progression-free survival (PFS) and overall survival (OS) in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). Although preclinical and clinical data demonstrate a benefit in changing ET and continuing a CDK4/6i at progression, no randomized prospective trials have evaluated this approach., Methods: In this investigator-initiated, phase II, double-blind placebo-controlled trial in patients with HR+/HER2- MBC whose cancer progressed during ET and CDK4/6i, participants switched ET (fulvestrant or exemestane) from ET used pre-random assignment and randomly assigned 1:1 to the CDK4/6i ribociclib versus placebo. PFS was the primary end point, defined as time from random assignment to disease progression or death. Assuming a median PFS of 3.8 months with placebo, we had 80% power to detect a hazard ratio (HR) of 0.58 (corresponding to a median PFS of at least 6.5 months with ribociclib) with 120 patients randomly assigned using a one-sided log-rank test and significance level set at 2.5%., Results: Of the 119 randomly assigned participants, 103 (86.5%) previously received palbociclib and 14 participants received ribociclib (11.7%). There was a statistically significant PFS improvement for patients randomly assigned to switched ET plus ribociclib (median, 5.29 months; 95% CI, 3.02 to 8.12 months) versus switched ET plus placebo (median, 2.76 months; 95% CI, 2.66 to 3.25 months) HR, 0.57 (95% CI, 0.39 to 0.85); P = .006. At 6 and 12 months, the PFS rate was 41.2% and 24.6% with ribociclib, respectively, compared with 23.9% and 7.4% with placebo., Conclusion: In this randomized trial, there was a significant PFS benefit for patients with HR+/HER2- MBC who switched ET and received ribociclib compared with placebo after previous CDK4/6i and different ET.

Background/aim: Radiation pneumonitis is a known complication of radiotherapy. It is also a rare complication of CDK4/6 inhibitors, and it can be difficult to differentiate the two. This is a report of a case of pulmonary toxicity from a CDK4/6 inhibitor, which was initially ascribed to radiation pneumonitis., Case Report: A 77-year-old female was diagnosed with pneumonitis after receiving radiation to the thoracic spine. She had also been treated with abemaciclib. Upon review, the patient's lung mean dose was 11.54 Gy with a V20 of 17.02%, and the area of pneumonitis was largely outside of the treatment field. Abemaciclib was ceased. The patient was started on supportive oxygen as well as steroids. She no longer required oxygen and she was discharged from the hospital. Radiation pneumonitis is largely correlated with the volume of lung radiated and dose of radiation to the lung. CDK4/6 inhibitor pulmonary toxicity, while rare, is possible and will likely become more frequent with increasing use of these agents., Conclusion: Patients receiving CDK4/6 inhibitors are at an increased risk for pneumonitis. It can be confused with radiation pneumonitis and must be included in the differential diagnosis., (Copyright © 2023 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Hepatocellular carcinoma (HCC) is one of the most common cancerous tumors and one of the leading causes of death among cancer-related disorders. Chemotherapy is ineffective in HCC patients, and the number of drugs that are in use is limited. Thus, new molecules are needed that could increase the effectiveness of anti-HCC regimens. Here, we show that AT7519, a CDK inhibitor, exerts positive effects on HCC cells: it inhibits proliferation, migration and clonogenicity. Detailed analysis of the transcriptomes of cells treated with this compound indicated that AT7519 affects a substantial portion of genes that are associated with HCC development and progression. Moreover, we showed that the concomitant use of AT7519 with gefitinib or cabozantinib sensitized HCC cells to these drugs. Thus, our research indicates that AT7519 is worth considering in monotherapy for hepatocellular carcinoma patients or in combination with other drugs, e.g., gefitinib or cabozantinib., 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 © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Background: CDK4/6 inhibitors combined with endocrine therapy have significantly improved treatment outcomes for metastatic hormone receptor-positive (HR+) breast cancer patients. However, the impact of low HER2 expression on treatment response and progression-free survival (PFS) remains unclear., Methods: This multicenter retrospective study included 204 HR+ breast cancer patients treated with a combination of CDK4/6 inhibitor and endocrine therapy. HER2-zero disease was detected in 138 (68%) and HER2-low disease in 66 (32%) patients. Treatment-related characteristics and clinical outcomes were analyzed, with a median follow-up of 22 months., Results: The objective response rate (ORR) was 72.7% in the HER2 low group and 66.6% in the HER2 zero group (p = 0.54). Median PFS was not significantly different between the HER2-low and HER2 zero groups (19 months vs.18 months, p = 0.89), although there was a trend toward longer PFS in the HER2-low group for first-line treatment (24 months progression-free survival rate 63% vs 49%). In recurrent disease, the median PFS was 25 months in the HER2-low group and 12 months in the HER2-zero group (p = 0.08), while in de novo metastatic disease, the median PFS was 18 months in the HER2-low group and 27 months in the HER2-zero group (p = 0.16). The order of CDK4/6 inhibitor use and the presence of visceral metastasis were identified as independent variables affecting PFS., Conclusion: Low HER2 expression did not significantly impact treatment response or PFS in HR+ breast cancer patients treated with a CDK4/6 inhibitor and endocrine therapy. Because of the conflicting results in the literature, further prospective studies are needed to evaluate the clinical significance of HER2 expression in HR+ breast cancer., Competing Interests: Declaration of competing interest None., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: The optimal treatment following endocrine therapy (ET) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) has not been established. We aimed to investigate treatment patterns and time to treatment failure (TTF) of subsequent therapy after palbociclib in a Japanese real-world setting., Methds: This retrospective observational study used de-identified data of patients with advanced breast cancer treated with palbociclib, using a nationwide claims database (April 2008 to June 2021). Measures included the type of subsequent therapies after palbociclib (endocrine-based therapy: ET alone, ET + CDK4/6i, and ET + mammalian target of rapamycin inhibitor [mTORi]; chemotherapy; chemotherapy + ET; and others) and their TTFs. The median TTF and 95% confidence interval (CI) were estimated using the Kaplan-Meier method., Results: Of 1170 patients treated with palbociclib, 224 and 235 received subsequent therapies after first- and second-line palbociclib treatment, respectively. Among them, 60.7% and 52.8% were treated with endocrine-based therapies as first subsequent therapy, including ET + CDK4/6i (31.2% and 29.8%, respectively). The median TTF (95% CI) of ET alone, ET + CDK4/6i, and ET + mTORi as first subsequent therapy after first-line palbociclib were 4.4 (2.8-13.7), 10.9 (6.5-15.6), and 6.1 (5.1-7.2) months, respectively. No apparent relationship between the treatment duration of prior ET + palbociclib and subsequent abemaciclib was observed., Conclusion: This real-world study revealed that one-third of the patients received sequential CDK4/6i after ET + palbociclib, and treatment duration of ET + CDK4/6i following ET + palbociclib was the longest among the treatment options. Further data are awaited to determine whether ET + targeted therapy with CDK4/6i and mTORi provides acceptable treatment options following ET + palbociclib., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Palbociclib and endocrine therapy has been approved to treat hormone receptor-positive/human epidermal growth factor receptor 2-negative inoperable or recurrent breast cancer in Japan. However, this cotherapy imposes an economic burden on both patients and society because of its high cost. In this study, we assessed the cost-effectiveness of cotherapy with palbociclib and fulvestrant compared to fulvestrant monotherapy for inoperable or recurrent breast cancer., Methods: The three-state Markov model was built by taking into count health stats in inoperable or recurrent breast cancer. The clinical outcomes of the therapies were drawn from published randomized controlled trials. Total regimen cost was calculated from medical receipts of patients at the Yamagata University Hospital. The cost-effectiveness was evaluated by the incremental cost-effectiveness ratio(ICER), in case that it was below 400,000 Yen per month. Markov chain Monte Carlo simulation was performed to assess probability., Results: Acquisition cost of palbociclib and fulvestrant and fulvestrant monotherapy was 6,209,554 JPY and 780,870 JPY, and 25.7 and 22.8 months were achieved, respectively. ICER for the cotherapy was 1,847,721 JPY/quality adjusted life month(QALM)gained., Conclusions: The palbociclib and fulvestrant therapy provided better health outcomes than conventional fulvestrant monotherapy, but were costly and suggested to be less cost-effective.

The emergence of CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for hormone receptor-positive breast cancer. These agents have demonstrated significant clinical benefits in terms of both progression-free survival and overall survival. However, resistance to CDK4/6 inhibitors remains a challenge, limiting their long-term efficacy. Understanding the complex mechanisms driving resistance is crucial for the development of novel therapeutic strategies and the improvement of patient outcomes. Translational research efforts, such as preclinical models and biomarker studies, offer valuable insight into resistance mechanisms and may guide the identification of novel combination therapies. This review paper aims to outline the reported mechanisms underlying CDK4/6 inhibitor resistance, drawing insights from both clinical data and translational research in order to help direct the future of treatment for hormone receptor-positive metastatic breast cancer.

Objective: The addition of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) to endocrine therapy impressively improved the outcome of patients with hormone receptor-positive metastatic breast cancer. Despite their great efficacy, not all patients respond to treatment and many of them develop acquired resistance. The aim of this retrospective study was to assess the role of [18F]-FDG PET/CT in predicting PFS and OS in breast cancer patients treated with CDK4/6i., Methods: 114 patients who performed an [18F]-FDG PET/CT scan before (PET1) and 2-6 months (PET2) after starting treatment were retrospectively enrolled. Metabolic response was evaluated by EORTC, PERCIST and Deauville Score and correlated to PFS and OS., Results: In patients who did not progress at PET2 (n = 90), PFS rates were not significantly different between classes of response by EORTC and PERCIST. Conversely, patients showing a Deauville score ≤3 had a longer PFS (median PFS 42 vs 21.0 months; p = 0.008). A higher total metabolic tumor volume at PET1 (TMTV1) was also associated with a shorter PFS (median 18 vs 42 months; p = 0.0026). TMTV1 and Deauville score were the only independent prognostic factors for PFS at multivariate analysis and their combination stratified the population in four definite classes of relapse risk. Conversely, the above parameters did not affect OS which was only influenced by a progressive metabolic disease at PET2 (3-years survival rate 29.8 vs 84.9%; p<0.0001)., Conclusion: TMTV and metabolic response by Deauville score were significant prognostic factors for PFS in patients with breast cancer treated with CDK4/6i. Their determination could help physicians to select patients who may need a closer follow up., Competing Interests: The 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 © 2023 Annovazzi, Rea, Maccora, Pizzuti, Ferretti, Vici, Cappuzzo and Sciuto.)

Background: Survival outcomes in metastatic breast cancer (MBC) have improved due to novel agents such as CDK4/6 inhibitors (CDK4/6i). Nevertheless, Black patients and patients with lower socioeconomic status (SES) continue to bear a disproportionate mortality burden., Methods: We conducted a retrospective analysis of EHR-derived data from the Flatiron Health Database (FHD). A dataset was constructed to include Black/African-American (Black/AA) and White patients with hormone receptor (HR)-positive, HER2-negative MBC. Outcomes included CDK4/6i use (overall and first-line), and rates of leukopenia, dose reduction, and time on treatment for first-line CDK4/6i. Multivariable logistic regression was used to evaluate factors associated with use and outcomes., Results: A total of 6802 patients with MBC were included, of which 5187 (76.3%) received CDK4/6i. Of those, 3186 (61.4%) received CDK4/6i first-line. Overall, 86.7% of patients were categorized as White and 13.3% as Black/AA; 22.4% were > 75 years old; 12.6% were treated at an academic site; 3.3% had Medicaid insurance. In addition to advanced age and poorer performance status, lower use of CDK4/6i was associated with Black/AA vs White race (72.9% vs 76.8%; OR 0.83, 95% CI 0.70-0.99, p = 0.04) and Medicaid vs commercial insurance (69.6% vs 77.4%; OR: 0.68, 95% CI 0.49-0.95, p = 0.02). Odds of CDK4/6i use were twofold higher for patients treated at an academic center (p < 0.001). Rates of CDK4/6i-induced leukopenia and dose reductions did not differ significantly by race, insurance type, or treatment site. Time on CDK4/6i was significantly lower among Medicaid patients (395 days) than patients with commercial insurance (558 days) or Medicare (643 days) (p = 0.03)., Conclusion: This analysis of real-world data suggests that Black race and lower SES are associated with decreased CDK4/6i use. However, among patients treated with CDK4/6i, subsequent toxicity outcomes are similar. Efforts to ensure access to these life-prolonging medications are warranted., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Chemotherapy-induced diarrhea causes dehydration, debilitation, infection, and even death, but there are currently no Food and Drug Administration (FDA)-approved drugs for treatment of chemotherapy-induced diarrhea. It is generally believed that the timely regulation of intestinal stem cell (ISC) fate may provide a meaningful solution for intestinal injuries. However, the lineage plasticity of ISCs during and after chemotherapy remains poorly understood. Here, we demonstrated that palbociclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, regulated the fate of active or quiescent ISCs, provided multilineage protection from the toxicity of several different chemotherapeutics, and accelerated gastrointestinal epithelium recovery. Consistent with in vivo results, we determined that palbociclib enhanced intestinal organoid and ex vivo tissue survival after chemotherapy. Lineage tracing studies have shown that palbociclib protects active ISCs marked by Lgr5 and Olfm4 during chemotherapy and unexpectedly activates quiescent ISCs marked by Bmi1 to immediately participate in crypt regeneration after chemotherapy. Furthermore, palbociclib does not decrease the efficacy of cytotoxic chemotherapy in tumor grafts. The experimental evidence suggests that the combination of CDK4/6 inhibitors with chemotherapy could reduce damage to the gastrointestinal epithelium in patients. © 2023 The Pathological Society of Great Britain and Ireland., (© 2023 The Pathological Society of Great Britain and Ireland.)

Introduction: CDK4/6 inhibitors have changed the treatment paradigm of many patients living with metastatic and early-stage high-risk hormone receptor (HR)-positive breast cancer. Even though patients and clinicians are aware and learning how to manage common adverse events, such as bone marrow suppression and gastrointestinal toxicities, there are less common and potentially severe adverse events, such as interstitial lung disease (ILD), that require special consideration., Areas Covered: In this narrative review, we discuss the incidence, mechanism, and treatment of CDK4/6 inhibitor associated ILD., Expert Opinion: CDK4/6 inhibitors in combination with endocrine therapy (ET) are standard treatment for HR-positive, HER2-negative metastatic breast cancer and for selected patients with early stage HR-positive breast cancer. Common toxicities of these medications are often controlled with dose reductions, dose interruptions, and/or prophylactic medications, such as antidiarrheals. However, there are a small subset of patients at risk for less common and potentially severe toxicities, such as ILD. Individualized risk should be considered, including underlying lung disease, thrombosis risk and drug-drug interactions, in order to counsel patients about the risk of ILD.

Background: Outpatients treated with oral anti-cancer drugs, including selective cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), may benefit from a pharmacy practice setting adapted to support proper oral anti-cancer drug monitoring. This real-world study aimed to characterize patient-centered pharmacy practice aligned with American Society of Clinical Oncology (ASCO)/National Community Oncology Dispensing Association (NCODA) standards and to describe its impact on CDK4/6i treatment use., Methods: This retrospective study included women with confirmed hormone receptor-positive/human epidermal growth factor 2 negative locally advanced or metastatic breast cancer treated with either palbociclib, abemaciclib or ribociclib combined with letrozole or fulvestrant. Pharmacists collected patient characteristics, clinical activities, and treatment patterns using data from the pharmacy chart. CDK4/6i treatment adherence rates were estimated based on medication claims data. Time-to-treatment discontinuation, a proxy for time-to-event, was assessed using the Kaplan-Meier estimate., Results: Of the 195 patients assessed for eligibility, 65 were included in this study. The median observation duration was 13.6 months. An average of seven pharmaceutical care activities (range 2.8-21.7) per patient was documented for each treatment cycle. The mean proportion of days covered was 89.6%. The median time-to-treatment discontinuation was estimated at 44.2 months in patients treated with CDK4/6i + letrozole and 17.0 months in patients treated with CDK4/6i + fulvestrant. The average relative dose intensity was 85%, and the benefits of treatment were maintained regardless of the relative dose intensity levels., Conclusion: A structured patient-centered pharmacy practice model integrating the ASCO/NCODA patient-centered standards and ongoing communication with patients and healthcare providers ensure timely refills, close monitoring, and allows patients to achieve high adherence and persistence rates comparable to those reported in clinical trials.