Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, including abemaciclib, have been approved for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced, and metastatic breast cancer. Despite the high therapeutic efficacy of CDK4/6 inhibitors, they are associated with various adverse effects, including potentially fatal interstitial lung disease. Therefore, a combination of CDK4/6 inhibitors with letrozole or fulvestrant has been attempted but has demonstrated limitations in reducing adverse effects, highlighting the need to develop new combination therapies. This study proposes a combination strategy using CDK4/6 inhibitors and tricyclic antidepressants to enhance the therapeutic outcomes of these inhibitors while reducing their side effects. The therapeutic efficacies of abemaciclib and desipramine were tested in different cancer cell lines (H460, MCF7, and HCT-116). The antitumor effects of the combined abemaciclib and desipramine treatment were evaluated in a xenograft colon tumor model. In vitro cell studies have shown the synergistic anticancer effects of combination therapy in the HCT-116 cell line. The combination treatment significantly reduced tumor size compared with control or single treatment without causing apparent toxicity to normal tissues. Although additional in vivo studies are necessary, this study suggests that the combination therapy of abemaciclib and desipramine may represent a novel therapeutic approach for treating solid tumors.

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

This study examines the biological effects of palbociclib and ribociclib in hormone receptor-positive breast cancer, pivotal to the HARMONIA prospective phase III clinical trial. We explore the downstream impacts of these CDK4/6 inhibitors, focusing on cell lines and patient-derived tumor samples. We treated HR+ breast cancer cell lines (T47D, MCF7, and BT474) with palbociclib or ribociclib (100 nM or 500 nM), alone or combined with fulvestrant (1 nM), over periods of 24, 72, or 144 h. Our assessments included PAM50 gene expression, RB1 phosphorylation, Lamin-B1 protein levels, and senescence-associated β-galactosidase activity. We further analyzed PAM50 gene signatures from the CORALLEEN and NeoPalAna phase II trials. Both CDK4/6 inhibitors similarly inhibited proliferation across the cell lines. At 100 nM, both drugs partially reduced p-RB1, with further decreases at 500 nM over 144 h. Treatment led to reduced Lamin-B1 expression and increased senescence-associated β-galactosidase activity. Both drugs enhanced Luminal A and reduced Luminal B and proliferation signatures at both doses. However, the HER2-enriched signature significantly diminished only at the higher dose of 500 nM. Corresponding changes were observed in tumor samples from the CORALLEEN and NeoPalAna studies. At 2 weeks of treatment, both drugs significantly reduced the HER2-enriched signature, but at surgery, this reduction was consistent only with ribociclib. Our findings suggest that while both CDK4/6 inhibitors effectively modulate key biological pathways in HR+/HER2- breast cancer, nuances in their impact, particularly on the HER2-enriched signature, are dose-dependent, influenced by the addition of fulvestrant and warrant further investigation.

Breast cancer (BC) cells have a high risk of metastasis due to epithelial-mesenchymal transition (EMT). Palbociclib (CDK4/6 inhibitor) is an approved drug for BC treatment. However, the drug resistance and metastasis can impair the treatment outcome of Palbociclib. Understanding the mechanisms of EMT and Palbociclib drug resistance in BC is conducive to the formulation of novel therapeutic strategy. Here, we investigated the role of circHIAT1/miR-19a-3p/CADM2 axis in modulating EMT and Palbociclib resistance in BC. circHIAT1 and CADM2 were down-regulated in BC tissues and cell lines, and miR-19a-3p showed an up-regulation. circHIAT1 could interact with miR-19a-3p and suppress its activity, while miR-19a-3p functioned to negatively regulate CADM2. Forced over-expression of circHIAT1 could impaired the EMT status and migratory ability of BC cells, and this effect was inhibited by miR-19a-3p mimic. In addition, we also generated Palbociclib resistant BC cells, and showed that circHIAT1 and CADM2 were down-regulated in the resistant BC cells while miR-19a-3p showed an up-regulation. Forced circHIAT1 over-expression re-sensitized BC cells to Palbociclib treatment. Quercetin, a bioactive flavonoid, could suppressed the migration and invasion of BC cells, and re-sensitized BC cells to Palbociclib. The anti-cancer effect of quercetin could be attributed to its regulatory effect on circHIAT1/miR-19a-3p/CADM2 axis. In vivo tumorigenesis experiment further revealed that quercetin administration enhanced the anti-cancer effect of Palbociclib, an effect was dependent on the up-regulation of circHIAT1 by quercetin. In summary, this study identified quercetin as a potential anti-cancer compound to reverse Palbociclib resistance and impair EMT in BC cells by targeting circHIAT1/miR-19a-3p/CADM2 axis.

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The aim of this study is to share real-life data on the increase in creatinine due to CDK 4/6 inhibitor treatment and patients diagnosed with HR+/HER2-MBC and treated with ribociclib or palbociclib combined with ET were included in the study. While creatinine increase was observed in 17.9% (n = 19) of the 106 patients in the study population, 8.5% (n = 9) had Grade 1, 8.5% (n = 8) had Grade 2, and % 0.9 (n = 1) had Grade 3 creatinine elevation. The increase in creatinine occurred in 25% (n = 12) of ribociclib users and 12.1% (n = 7) of palbociclib users. No patient required a dose reduction or discontinuation of treatment due to elevated creatinine. Of the patients with high creatinine levels, 36.8% (n = 7) were over 65 years of age. Those with multiple comorbidities, blood urea nitrogen (BUN) >13.5 mg/dl, creatinine >0.66 mg/dl, BUN/creatinine ratio >19.95, glomerular filtration rate (GFR) >96.05 ml/min, and uric acid >4.69mg/dl. It was observed that the increase in the creatinine level was statistically significant (p <0.001). In conclusion, this study revealed that the increase in the serum creatinine secondary to ribociclib and palbociclib treatments is associated with kidney function tests and the number of concomitant diseases. Key Words: CDK 4/6 inhibitor, Creatinine elevation, Palbociclib, Ribociclib.

OBJECTIVE: To evaluate the impact of CDK4/6 inhibitors on erythrocyte mean corpuscular volume (MCV) change and its possible correlation with progression-free survival (PFS) and overall survival (OS).
METHODS: Observational study. Place and Duration of the Study: Department of Medical Oncology, Kahramanmaras Necip Fazil City Hospital, Kahramanmaras, Turkiye, between January 2020 and 2023.
METHODS: The data of 74 patients with HR (+) HER2 (-) metastatic breast cancer were analysed retrospectively. MCV and other complete blood count metrics were noted before and after the treatment. The first post-treatment evaluation was performed at three months. The median ΔMCV values at the third month after treatment-baseline were calculated.
RESULTS: The patients were all females, with a median age of 55 years (between 35 and 80). Prior to the therapy, the baseline median MCV level was 90.4 (min-max: 77.3-113.2). After three months, the median MCV level was 95 (min-max: 84.3-115.3). Moreover, 7.15 was the median ΔMCV level. Regarding PFS (16.53 vs. 15.26 months) (p = 0.13) and OS (21.46 vs. 17.83 months) (p = 0.08), there was no statistically significant difference seen between the group with ΔMCV ≥7.15 and the group with ΔMCV <7.15.
CONCLUSIONS: CDK4/6 inhibitors led to an increase in MCV but there was no significant difference between PFS or OS and the increase in MCV. To figure out whether the rise in MCV represents a prognostic or predictive marker, further research is required.
BACKGROUND: Breast cancer, CDK4/6 inhibitors, Mean corpuscular volume, Prognosis.

OBJECTIVE: Retinal vascular endothelial cell (RVECs) injury is a major cause of morbidity and mortality among the patients with diabetes. RVECs dysfunction is the predominant pathological manifestation of vascular complication in diabetic retinopathy. N6-methyladenosine (m6A) serves as the most prevalent modification in eukaryotic mRNAs. However, the role of m6A RNA modification in RVECs dysfunction is still unclear.
METHODS: RT-qPCR analysis and western blot were conducted to detect the change of m6A RNA modification in diabetic retinopathy. CCK-8 assay, transwell experiment, wound healing assay, tube formation experiment, m6A-IP-qPCR were performed to determine the role of YTHDC1 in RVECs. Retinal trypsin digestion test and H&E staining were used to evaluate histopathological changes.
RESULTS: The levels of m6A RNA methylation were significantly up-regulated in HG-induced RVECs, which were caused by increased expression of YTHDC1. YTHDC1 regulated the viability, proliferation, migration and tube formation ability in vitro. YTHDC1 overexpression impaired RVECs function by repressing CDK6 expression, which was mediated by YTHDC1-dependent mRNA decay. Moreover, it showed sh-YTHDC1 inhibited CDK6 nuclear export. Sh-YTHDC1 promotes the mRNA degradation of CDK6 in the nucleus but does not affect the cytoplasmic CDK6 mRNA. In vivo experiments showed that overexpression of CDK6 reversed the protective effect of sh-YTHDC1 on STZ-induced retinal tissue damage.
CONCLUSIONS: YTHDC1-mediated m6A methylation regulates diabetes-induced RVECs dysfunction. YTHDC1-CDK6 signaling axis could be therapeutically targeted for treating DR.

Cyclin-dependent kinases 4 and 6 (CDK4/6) play a pivotal role in cell cycle and cancer development. Targeting CDK4/6 has demonstrated promising effects against breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i), such as palbociclib, remains a substantial challenge in clinical settings. Using high-throughput combinatorial drug screening and genomic sequencing, we find that the microphthalmia-associated transcription factor (MITF) is activated via O-GlcNAcylation by O-GlcNAc transferase (OGT) in palbociclib-resistant breast cancer cells and tumors. Mechanistically, O-GlcNAcylation of MITF at Serine 49 enhances its interaction with importin α/β, thus promoting its translocation to nuclei, where it suppresses palbociclib-induced senescence. Inhibition of MITF or its O-GlcNAcylation re-sensitizes resistant cells to palbociclib. Moreover, clinical studies confirm the activation of MITF in tumors from patients who are palbociclib-resistant or undergoing palbociclib treatment. Collectively, our studies shed light on the mechanism regulating palbociclib resistance and present clinical evidence for developing therapeutic approaches to treat CDK4/6i-resistant breast cancer patients.

CDK4/6 inhibitors are oral agents inhibiting key molecules of the cell cycle regulation. In patients with endocrine receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) breast cancer, the combination of CDK4/6 inhibitors with endocrine therapy is an effective treatment in the metastatic setting. Now, two studies in the adjuvant setting - MonarchE (2 years of abemaciclib) and NATALEE (3 years of ribociclib) - report positive invasive disease-free survival. Here, we re-evaluate these seminal trials. First, an excess drop-out or loss-to-follow up occurred early in the control arms of both studies. Since both trials are open-label, there is concern that the patients who drop-out do not do so at random but based on socioeconomic factors and alternative options. Is it possible that the results merely appear favorable due to loss to follow up? Based on re-constructed Kaplan-Meier curves, we concluded the results of these studies remain fragile, being prone to informative censoring. Secondly, adverse events were notably higher in both trials, and some of them, like COVID-19 related deaths in NATALEE, raise serious concerns. Third, the potential costs associated with CDK4/6 inhibition given as adjuvant therapy are unprecedented. The NATALEE strategy, in particular, could affect up to 35 % of patients with newly diagnosed breast cancer, which is the cancer with the highest incidence worldwide. Without confirmatory data based on a placebo-controlled trial, or better identification of patients that would benefit from the addition of CDK4/6 inhibitors in the adjuvant setting, we argue against their routine use as adjuvant therapy in ER+ /HER2- early breast cancer.