Cyclin D1 Cyclin-dependent Kinase Research Articles

Clinical considerations of CDK4/6 inhibitors in HER2 positive breast cancer.

Deregulation of cell cycles can result in a variety of cancers, including breast cancer (BC). In fact, abnormal regulation of cell cycle pathways is often observed in breast cancer, leading to malignant cell proliferation. CDK4/6 inhibitors (CDK4/6i) can block the G1 cell cycle through the cyclin D-cyclin dependent kinase 4/6-inhibitor of CDK4-retinoblastoma (cyclinD-CDK4/6-INK4-RB) pathway, thus blocking the proliferation of invasive cells, showing great therapeutic potential to inhibit the spread of BC. So far, three FDA-approved drugs have been shown to be effective in the management of advanced hormone receptor positive (HR+) BC: palbociclib, abemaciclib, and ribociclib. The combination strategy of CDK4/6i and endocrine therapy (ET) has become the standard therapeutic regimen and is increasingly applied to advanced BC patients. The present study aims to clarify whether CDK4/6i can also achieve a certain therapeutic effect on Human epidermal growth factor receptor 2 positive (HER2+) BC. Studies of CDK4/6i are not limited to patients with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced BC, but have also expanded to other types of BC. Several pre-clinical and clinical trials have demonstrated the potential of CDK4/6i in treating HER2+ BC. Therefore, this review summarizes the current knowledge and recent findings on the use of CDK4/6i in this type of BC, and provides ideas for the discovery of new treatment modalities.

Phase 1b/2 study of abemaciclib combined with chemoimmunotherapy in pediatric and young adult patients with relapsed/refractory neuroblastoma (JPCS Part C).

TPS10068 Background: Survival for high-risk neuroblastoma (NBL) remains poor with over 50% of patients experiencing disease relapse. The addition of dinutuximab (DIN) and granulocyte macrophage colony-stimulating factor (GM-CSF) to irinotecan (IRN) and temozolomide (TMZ) in patients with first relapse achieved an overall response rate of 42% in the study ANBL12211 and is now standard of care. However, there remains a significant unmet need to improve outcomes for children with relapsed/refractory NBL. Deregulation of the Cyclin D/cyclin-dependent kinase (CDK) 4 & 6 pathway has been observed in NBL, rendering CDK4 & 6 inhibition logical to explore. Abemaciclib is an orally administered, selective CDK4 & 6 inhibitor approved to treat breast cancer. JPCS (NCT04238819) is designed to assess the pharmacokinetics, safety, and tolerability of abemaciclib added to standard treatment regimens for relapsed/refractory pediatric solid tumors. Part A defined the recommended phase 2 dose (RP2D) of abemaciclib in combination with IRN and TMZ. In Part C, the addition of DIN + GM-CSF to the JPCS Part A regimen will be evaluated. The co-primary objectives of Part C are to determine the RP2D and to estimate the anti-tumor activity of abemaciclib added to the ANBL1221 chemoimmunotherapy backbone in patients with first relapse/refractory NBL. Methods: JPCS Part C is a two-stage, non-randomized, open-label, Phase 1b/2 study for patients < 21 years of age with first relapse/refractory NBL. Stage 1 aims to identify the maximum tolerated dose (MTD) of abemaciclib at a starting dose of 55 mg/m2 combined with DIN, GM-CSF, IRN and TMZ using a 3+3 design. One dose de-escalation (30 mg/m2) will be possible if the starting dose is not tolerated. Further tolerability and initial anti-tumor activity will be evaluated in an expansion cohort at the MTD. Up to 11 evaluable patients will enroll in Stage 1 at the MTD; the MTD will be declared the RP2D if adequate safety and tolerability are observed and ≥6 patients achieve minimal response or better per International Neuroblastoma Response Criteria (INRC). Following determination of the RP2D, Stage 2 will enroll 35 patients. If ≥26 of 46 total patients achieve an INRC minimum response or better, further investigation of this regimen could be warranted. As of 31 Jan 2023, Part C is open for enrollment at one site (US) and additional sites are being evaluated.

Small molecule ‘4ab’ induced autophagy and endoplasmic reticulum stress-mediated death of aggressive cancer cells grown under adherent and floating conditions

Metastasis is the leading cause of death in cancer patients and a major challenging aspect of cancer biology. Various adaptive molecular signaling pathways play a crucial role in cancer metastasis and later in the formation of secondary tumors. Aggressive cancer cells like triple negative breast cancer (TNBCs) are more inclined to undergo metastasis hence having a high recurrence rate and potential of micro-metastasis. Tumor cells in circulation known as circulating tumor cells (CTCs) offer an attractive drug target to treat metastatic disease. Cell cycle regulation and stress response of CTCs in blood has a crucial role in their survival and progression and thus may be considered therapeutically active hotspots. The cyclin D/cyclin-dependent kinase (CDK) pathway regulates cell cycle checkpoints, a process that is frequently dysregulated in cancer cells. Selective CDK inhibitors can limit the phosphorylation of cell cycle regulatory proteins by inducing cell cycle phase arrest, and thus may be an effective therapeutic strategy for aggressive cancer cells in their dividing phase at the primary or secondary site. However, during the floating condition, cancer cells halt their multiplication process and proceed through the various steps of metastasis. Current study showed that a novel CDK inhibitor 4ab induced autophagy and endoplasmic reticulum (ER) stress inagressive cancer cells grown under adherent and floating conditions resulting in paraptosis. Further, our results showed that 4ab efficiently induced cell death in aggressive cancer cells through ER stress-mediated activation of JNK signaling. Additionally,was observed that treatment of 4ab in tumor-bearing mice displayed a significant reduction in tumor burden and micro-metastasis. The outcome of these studies showed that 4ab can be a potential anti-tumor and anti-metastatic agent. Graphical representation of 4ab: image representing the effect of 4ab on death-inducing pathways in aggressive cancer cells. 4ab induces ER stress and activates autophagy leading to vacuolation of thereby causing apoptosisin aggressive cancer cells.

Prognostic Potential of Cyclin D1 Expression in Colorectal Cancer.

Cyclin D1 is mainly known as an oncogenic driver in cancers, and the dysregulated cyclin D1/cyclin-dependent kinase (CDK) 4/6 axis is considered an attractive target for cancer therapy. Recent studies have reported that tumors respond to therapeutic interventions targeting altered cyclin D1 expression via application of the CDK4/6 inhibitor. However, the prognostic and therapeutic contributions of cyclin D1 to colorectal cancer (CRC) remain controversial. Herein, we assessed the associations between cyclin D1 expression and clinicopathological factors, including patients' overall survival (OS) and recurrence-free survival (RFS), in 495 surgically resected primary CRCs. We also examined previous studies for cyclin D1 in CRCs. High expressions of cyclin D1 (cyclin D1High) was observed in 389 CRC cases (78.6%). Cyclin D1High consistently predicted better patient OS and RFS in CRCs. Based on multivariate analysis, cyclin D1High and young age of patients remained as independent prognosticators of higher OS rate, whereas cyclin D1High, females, chemotherapy, absence of nodal metastasis, and lower T-category remained as independent prognosticators of better RFS. Cyclin D1 is commonly overexpressed in CRCs, and its expression can be used as a favorable prognostic indicator in patients with CRCs; this may be important for predicting responses to subsequent CDK4/6 inhibitors.

Baicalin Coadministration with Lithium Chloride Enhanced Neurogenesis via GSK3β Pathway in Corticosterone Induced PC-12 Cells.

Accumulating studies suggest that hippocampal neurogenesis plays a crucial role in the pathological mechanism of depression. As a classic antidepressant, lithium chloride can play an antidepressant role by inhibiting glycogen synthase kinase 3β (GSK3β) and promoting neurogenesis. Correspondingly, baicalin is a compound extracted from natural plants, which shows potential antidepressant effect, however, whether baicalin exerts antidepressant effects by promoting neurogenesis still needs further investigation. In the current study, we established an in vitro depression model through corticosterone induced PC-12 cells, and explored the potential mechanism of baicalin's antidepressant effect by comparing it with lithium chloride alone and the coadministration with lithium chloride. We used Cell Counting Kit-8 (CCK-8) assay, 5-ethynil-2'-deoxyuridine (EdU) staining and cell cycle analysis to evaluate the state of cell survival and cell proliferation. The protein expression levels of neurodevelopmental related factors Doublecortin (DCX), brain-derived neurotrophic factor (BDNF), and the GSK3β pathway-related proteins and mRNA were detected by Western blot and Real-time PCR. The results showed that baicalin could decrease the expression level of GSK3β, while upregulate the expression level of DCX, BDNF, Cyclin D1-cyclin dependent kinase 4/6 (CDK4/6), thus promoted cell proliferation and survival in corticosterone (CORT) induced PC-12 cells. Moreover, this effect was enhanced when baicalin and lithium chloride were coadministration. Taking the above results together, we conclude that baicalin can promote the proliferation and development of PC-12 cells by regulating GSK3β pathway, so as to reverse the depressive-like pathological changes induced by corticosterone.

Synergistic combination of cytotoxic chemotherapy and cyclin-dependent kinase 4/6 inhibitors in biliary tract cancers.

Biliary tract cancers (BTCs) are uncommon, but highly lethal, gastrointestinal malignancies. Gemcitabine/cisplatin is a standard-of-care systemic therapy, but has a modest impact on survival and harbors toxicities, including myelosuppression, nephropathy, neuropathy, and ototoxicity. Whereas BTCs are characterized by aberrations activating the cyclinD1/cyclin-dependent kinase (CDK)4/6/CDK inhibitor 2a/retinoblastoma pathway, clinical use of CDK4/6 inhibitors as monotherapy is limited by lack of validated biomarkers, diffident preclinical efficacy, and development of acquired drug resistance. Emerging studies have explored therapeutic strategies to enhance the antitumor efficacy of CDK4/6 inhibitors by the combination with chemotherapy regimens, but their mechanism of action remains elusive. Here, we report in vitro and in vivo synergy in BTC models, showing enhanced efficacy, reduced toxicity, and better survival with a combination comprising gemcitabine/cisplatin and CDK4/6 inhibitors. Furthermore, we demonstrated that abemaciclib monotherapy had only modest efficacy attributable to autophagy-induced resistance. Notably, triplet therapy was able to potentiate efficacy through elimination of the autophagic flux. Correspondingly, abemaciclib potentiated ribonucleotide reductase catalytic subunit M1 reduction, resulting in sensitization to gemcitabine. As such, these data provide robust preclinical mechanistic evidence of synergy between gemcitabine/cisplatin and CDK4/6 inhibitors and delineate a path forward for translation of these findings to preliminary clinical studies in advanced BTC patients.

Potential Prospect of CDK4/6 Inhibitors in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is an aggressive, difficult-to-treat subtype of cancer with a poor prognosis; there is an urgent need for effective, targeted molecular therapies. The cyclin D/cyclin-dependent kinase (CDK)4/6–retinoblastoma protein (Rb) pathway plays a critical role in regulating cell cycle checkpoints, a process which is often disrupted in cancer cells. Selective CDK4/6 inhibitors can prevent retinoblastoma protein phosphorylation by invoking cell cycle arrest in the first growth phase (G1), and may therefore represent an effective treatment option. In this article, we review the molecular mechanisms and therapeutic efficacy of CDK4/6 inhibitors in combination with other targeted therapies for the treatment of triple-negative breast cancer. Three selective CDK4/6 inhibitors have so far received the approval of the Food and Drug Administration (FDA) for patients with estrogen receptor (ER)+/human epidermal growth factor receptor 2 (HER2) breast cancer. Trilaciclib, a small molecule short-acting inhibitor of CDK4/6, has also been approved recently for people with small cell lung cancer, and is also expected to be clinically effective against breast cancer. Although the efficacy of CDK4/6 inhibitors in patients with triple-negative breast cancer remains uncertain, their use in conjunction with other targeted therapies may improve outcomes and is therefore currently being explored. Identifying biomarkers for response or resistance to CDK4/6 inhibitor treatment may optimize the personalization of treatment strategies for this disease. Ongoing and future clinical trials and biomarker studies will shed further light on these topics, and help to realize the full potential of CDK4/6 inhibitor treatment in triple-negative breast cancer.

Molecular Modeling Studies on Biochanin-A as a Potential Dual inhibitor for VEGFR-2 and Cyclin D1-CDK-4 Complex

Biochanin-A is a known phytoestrogen that is mainly found in red clover. It has several biological activities including anticancer, anti-inflammatory and antioxidant effects. Preclinical studies showed that Biochanin-A has anticancer properties in different cancer models. This effect was found to happen through a diversity of mechanisms inducing cell cycle arrest, apoptosis and antiangiogenic effects. Moreover, despite being a promising nature-derived anticancer agent, there is a paucity of information regarding specific target validation studies for Biochanin-A. In this study we first predicted the physicochemical properties of Biochanin-A using two different online tools (SwissADME and pkCSM), and then we performed an in silico molecular docking studies for Biochanin-A as a potential dual inhibitor for Cyclin-D1-cyclin dependent kinase (CDK) 4 complex and vascular endothelial growth factor receptor (VEGFR-2) which are key molecular targets for cancer therapy. The results suggest that Biochanin-A interacts with both Cyclin D1-CDK4 complex and VEGFR-2 with a docking affinity that is comparable to their standard inhibitors. These results open the door for further follow up investigations.

SHetA2 Increases the Activity of Palbociclib in Cervical Cancer in vitro and in vivo

Introduction Cervical cancer is caused by high-risk human papillomavirus (HPV) and treated with conventional chemotherapy combined with surgery and/or radiation. HPV oncoproteins increase retinoblastoma (Rb) phosphorylation by cyclin D1/cyclin dependent kinase (CDK)4/6 complexes and cellular proliferation. We hypothesized that cyclin D1 degradation by the SHetA2 drug in combination with palbociclib inhibition of CDK4/6 activity synergistically reduces Rb phosphorylation and inhibits cervical cancer growth. Methods The effects of these drugs, alone, and in combination, were evaluated in cervical cancer cell lines using cell culture, western blots and ELISA, and in a SiHa xenograft model. Endpoints were compared by isobolograms, ANOVA, and Chi-Square. Results SHetA2 and palbociclib acted synergistically in three cervical cell lines (CI <0.5) in association with reduced Rb phosphorylation. Both drugs significantly reduced Rb phosphorylation and growth of SiHa xenograft tumors as single agents and acted additively when combined, with no evidence of toxicity. SHetA2, but not palbociclib, reduced cyclin D1 in cell cultures and tumors. Dilated CD31-negative blood vessels adjacent to, or within, areas of necrosis and apoptosis were observed in all drug-treated tumors. Conclusions The drug combination was synergistic in vitro and significantly effective in vivo. The mechanism of synergy appears to involve inhibition of Rb phosphorylation.

AMBRA1 regulates cyclin D to guard S-phase entry and genomic integrity.

Mammalian development, adult tissue homeostasis and the avoidance of severe diseases including cancer require a properly orchestrated cell cycle, as well as error-free genome maintenance. The key cell-fate decision to replicate the genome is controlled by two major signalling pathways that act in parallel-the MYC pathway and the cyclin D-cyclin-dependent kinase (CDK)-retinoblastoma protein (RB) pathway1,2. Both MYC and the cyclin D-CDK-RB axis are commonly deregulated in cancer, and this is associated with increased genomic instability. The autophagic tumour-suppressor protein AMBRA1 has been linked to the control of cell proliferation, but the underlying molecular mechanisms remain poorly understood. Here we show that AMBRA1 is an upstream master regulator of the transition from G1 to S phase and thereby prevents replication stress. Using a combination of cell and molecular approaches and in vivo models, we reveal that AMBRA1 regulates the abundance of D-type cyclins by mediating their degradation. Furthermore, by controlling the transition from G1 to Sphase, AMBRA1 helps to maintain genomic integrity during DNA replication, which counteracts developmental abnormalities and tumour growth. Finally, we identify the CHK1 kinase as a potential therapeutic target in AMBRA1-deficient tumours. These results advance our understanding of the control of replication-phase entry and genomic integrity, and identify the AMBRA1-cyclinD pathway as a crucial cell-cycle-regulatory mechanism that is deeply interconnected with genomic stability in embryonic development and tumorigenesis.

Physiologically Based Pharmacokinetic Modeling of Central Nervous System Pharmacokinetics of CDK4/6 Inhibitors to Guide Selection of Drug and Dosing Regimen for Brain Cancer Treatment.

A better understanding of the human central nervous system (CNS) pharmacokinetics is critical to the selection of the right drug and refinement of dosing regimen for more effective treatment of primary and metastatic brain cancer. Using the physiologically‐based pharmacokinetic (PBPK) modeling approach, we systematically compared the CNS pharmacokinetics of three cyclin D‐cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors (ribociclib, palbociclib, and abemaciclib) in patients with cancer. A PBPK model platform was developed and verified for predicting plasma and CNS pharmacokinetics. Target engagement ratio (TER), defined as the ratio of the average steady‐state unbound drug brain concentration to the in vitro half‐maximal inhibitory concentration (IC50) for CDK4/6 inhibition, was used as a crude predictor of efficacy. As compared with ribociclib and palbociclib, abemaciclib penetrated into the human brain to a larger extent, but at a slower rate, and was retained in the brain longer. Following the standard dosing regimens, the predicted CDK4/6 TERs were 26/5.2 for abemaciclib, 2.4/0.62 for ribociclib, and 0.36/0.27 for palbociclib. Simulations suggested that abemaciclib achieved comparable TERs following twice daily or daily dosing; ribociclib may sufficiently inhibit both CDK4 and CDK6 at the maximum tolerated dose; whereas, palbociclib achieved TERs < 0.5 even at a dose 50% higher than the standard dose. In conclusion, the PBPK modeling, supported by available preclinical and clinical evidence, suggests that abemaciclib is the best CDK4/6 inhibitor for brain cancer treatment, whereas palbociclib is not recommended. The model refined dosing regimen is 300 mg daily on a 4‐weeks‐on schedule for abemaciclib, and 900 mg daily on a 3‐weeks‐on/1‐week‐off schedule for ribociclib.

G Protein-Coupled Estrogen Receptor Mediates Cell Proliferation through the cAMP/PKA/CREB Pathway in Murine Bone Marrow Mesenchymal Stem Cells.

Estrogen is an important hormone to regulate skeletal physiology via estrogen receptors. The traditional estrogen receptors are ascribed to two nuclear estrogen receptors (ERs), ERα and ERβ. Moreover, G protein-coupled estrogen receptor-1 (GPER-1) was reported as a membrane receptor for estrogen in recent years. However, whether GPER-1 regulated osteogenic cell biology on skeletal system is still unclear. GPER-1 is expressed in growth plate abundantly before puberty but decreased abruptly since the very late stage of puberty in humans. It indicates GPER-1 might play an important role in skeletal growth regulation. GPER-1 expression has been confirmed in osteoblasts, osteocytes and chondrocytes, but its expression in mesenchymal stem cells (MSCs) has not been confirmed. In this study, we hypothesized that GPER-1 is expressed in bone MSCs (BMSC) and enhances BMSC proliferation. The cultured tibiae of neonatal rat and murine BMSCs were tested in our study. GPER-1-specific agonist (G-1) and antagonist (G-15), and GPER-1 siRNA (siGPER-1) were used to evaluate the downstream signaling pathway and cell proliferation. Our results revealed BrdU-positive cell counts were higher in cultured tibiae in the G-1 group. The G-1 also enhanced the cell viability and proliferation, whereas G-15 and siGPER-1 reduced these activities. The cAMP and phosphorylation of CREB were enhanced by G-1 but inhibited by G-15. We further demonstrated that GPER-1 mediates BMSC proliferation via the cAMP/PKA/p-CREB pathway and subsequently upregulates cell cycle regulators, cyclin D1/cyclin-dependent kinase (CDK) 6 and cyclin E1/CDK2 complex. The present study is the first to report that GPER-1 mediates BMSC proliferation. This finding indicates that GPER-1 mediated signaling positively regulates BMSC proliferation and may provide novel insights into addressing estrogen-mediated bone development.

Abstract CT165: An open label, multi-cohort, phase Ib study of xentuzumab and abemaciclib: Preliminary results from the advanced non-small cell lung cancer (NSCLC) cohort

Abstract Introduction: Insulin-like growth factor (IGF) signaling and the cyclin D-cyclin-dependent kinase (CDK) 4 &amp; 6-retinoblastoma pathway are implicated in cancer progression and treatment resistance. Activation of the IGF receptor results in upregulation of cyclin D1 and progression through the cell cycle. Dual inhibition of IGF and CDK 4 &amp; 6 should lead to decreased cell proliferation through disruption of cell-cycle progression. This phase Ib trial assessed safety and preliminary efficacy of xentuzumab, an IGF-ligand neutralizing antibody, in combination with abemaciclib, a CDK 4 &amp; 6 inhibitor. In a dose-finding cohort in patients (pts) with solid tumors, the recommended phase II dose was determined as xentuzumab 1000 mg weekly intravenously plus abemaciclib 150 mg every 12 hours (Q12h) orally. Here, we present data from an expansion cohort in pts with NSCLC. Methods: Eligible pts had stage IV NSCLC with measurable disease which had progressed after platinum-based chemotherapy and immunotherapy, and had either received 1-2 prior chemotherapies for advanced/metastatic disease or were judged ineligible for further standard second-line chemotherapy. Prior CDK 4 &amp; 6 inhibitor therapy was not permitted. Pts received xentuzumab 1000 mg weekly plus abemaciclib 150 mg Q12h until disease progression or intolerability of study medication. The primary endpoint was objective response defined as best overall response of complete response or partial response (PR) per RECIST 1.1. Secondary endpoints included progression-free survival (PFS). Results: 25 pts with NSCLC were treated (17 male [68%], median age 64 years [range 53-76]). 4 pts remained on treatment at time of analysis. Median treatment exposure was 1.6 months (range 0.5-19.7). Of 19 pts evaluable for response, 1 had a best overall response of PR (65% target lesion shrinkage), 9 had stable disease (duration ≥24 weeks in 3 pts) and 9 had progressive disease. Median PFS was 2.1 months (95% CI 1.2-5.3). All pts experienced adverse events (AEs) and 23 experienced treatment-related AEs (TRAEs), most commonly diarrhea (n=15; 60%), nausea (n=10; 40%) and platelet count decreased (n=8; 32%). The most common grade ≥3 TRAEs were thrombocytopenia (n=4; 16%) and neutropenia (n=3; 12%). No AEs of hyperglycemia or blood glucose increased were reported. Serious AEs were experienced by 13 pts (52%). 2 pts had fatal serious AEs due to disease progression and respiratory failure. Conclusion: The combination of xentuzumab and abemaciclib showed preliminary efficacy in pts with NSCLC who had progressed on chemotherapy and an immune checkpoint inhibitor. One PR was reported. The combination had a manageable safety profile. Citation Format: Patricia LoRusso, Javier García-Corbacho, Fadi S. Braiteh, Anthony Gonçalves, Francesco Ricci, Hiroji Iwata, Marta Capelán, Marie Paule Sablin, Aleix Prat, Molly Catherine Hardebeck, Marta Puig, Dennis Chin-Lun Huang, Mingchi Hsu, Douglas Yee. An open label, multi-cohort, phase Ib study of xentuzumab and abemaciclib: Preliminary results from the advanced non-small cell lung cancer (NSCLC) cohort [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT165.

Complementary Targeting of Rb Phosphorylation and Growth in Cervical Cancer Cell Cultures and a Xenograft Mouse Model by SHetA2 and Palbociclib.

Cervical cancer is caused by high-risk human papillomavirus (HPV) types and treated with conventional chemotherapy with surgery and/or radiation. HPV E6 and E7 proteins increase phosphorylation of retinoblastoma (Rb) by cyclin D1/cyclin dependent kinase (CDK)4/6 complexes. We hypothesized that cyclin D1 degradation by the SHetA2 drug in combination with palbociclib inhibition of CDK4/6 activity synergistically reduces phosphorylated Rb (phospho-Rb) and inhibits cervical cancer growth. The effects of these drugs, alone, and in combination, were evaluated in SiHa and CaSki HPV-positive and C33A HPV-negative cervical cancer cell lines using cell culture, western blots and ELISA, and in a SiHa xenograft model. Endpoints were compared by isobolograms, ANOVA, and Chi-Square. In all cell lines, combination indexes documented synergistic interaction of SHetA2 and palbociclib in association SHetA2 reduction of cyclin D1 and phospho-Rb, palbociclib reduction of phospho-Rb, and enhanced phospho-Rb reduction upon drug combination. Both drugs significantly reduced phospho-Rb and growth of SiHa xenograft tumors as single agents and acted additively when combined, with no evidence of toxicity. Dilated CD31-negative blood vessels adjacent to, or within, areas of necrosis and apoptosis were observed in all drug-treated tumors. These results justify development of the SHetA2 and palbociclib combination for targeting phospho-Rb in cervical cancer treatment.

CDK4/6 inhibitors in P16/HPV16-negative squamous cell carcinoma of the head and neck.

Addition of CDK4/6 inhibitors to a variety of established treatments in squamous cell carcinoma of the head and neck (SCCHN) has the potential to improve responses to other therapies and may help overcome treatment resistance. The SCCHN is a heterogeneous group of cancers of the oral cavity, the pharynx and the larynx with poor prognosis despite the aggressive multimodal therapies. In the past decade, significant advances were made in understanding of the molecular and genetic abnormalities leading to oncogenesis in SCCHN. Besides EGFR targeting agents, antiangiogenic agents have been shown to produce antitumor activity in these tumors. The cyclin D-cyclin-dependent kinase (CDK) 4/6-inhibitor of CDK4 (INK4)-retinoblastoma (Rb) pathway regulates cellular proliferation by controlling the G1 to S cell cycle checkpoint. In SCCHN, the Rb pathway is frequently altered through amplification of CCND1 (cyclin D1) or deletion of CDKN2A (cyclin-dependent kinase inhibitor 2A) coding for p16INK4A, and thus promoting proliferation. This article summarizes what we actually know of the place of CDK4/6 inhibitors in the therapeutic arsenal of SCCHN. CDK4/6 inhibitors could serve as a method to target these tumors, and both p16 loss and CCND1 amplification could be investigated as biomarkers.

Mechanism of inhibiting proliferation of hepatocellular carcinoma Hepa1-6 cells by embryonic stem cell-conditioned medium.

The present study aimed to investigate the antiproliferative effect of embryonic stem cell-conditioned medium (ESC-CM) on the mouse liver cancer Hepa1-6 cells in vitro. Furthermore, in order to elucidate the underlying molecular mechanism, the microRNAs (miRNAs) in ESC-CM associated with the inhibition of Hepa1-6 proliferation were identified. Following the co-culture of ESC-CM and Hepa1-6 in Transwell chambers, the proliferation, cell cycle, apoptosis and associated protein expression were determined in Hepal-6 cells. Moreover, miRNA array analysis was employed to identify differentially expressed miRNAs. Based on the differentially expressed miRNAs, the target genes and potential associated signaling pathways were determined. Finally, RT-qPCR was conducted to confirm the above results. The ESC-CM inhibited Hepal-6 cell proliferation and increased the percentage of cells at G1 phase and decreased the percentage of cells at the G2/M phase of the cell cycle. The expression of cyclin D1/cyclin-dependent kinase (CDK)4/CDK6 was decreased following co-culture, with no effect on cell apoptosis. Six significantly regulated miRNAs were identified and 423 putative target genes of these regulated miRNAs were predicted. Gene ontology analysis revealed the putative target genes to be associated with the ‘DNA replication (GO: 0006260)’ GO term, ‘apoptosis’ and ‘signal transduction’. The Kyoto Encyclopedia of Genes and Genomes analysis indicated that deregulated miRNAs were enriched in the Wnt signaling (KEGG entry: Map 04310) and Hippo signaling pathways (KEGG entry: Map 04390), pathways associated with cancer. Overall, the present study demonstrated the inhibition of Hepa1-6 cell line proliferation upon treatment with ESC-CM, by decreasing cell cycle-associated protein cyclin D1/CDK4/CDK6 expression and arresting cells in G1 phase of the cell cycle, with no effect on cell apoptosis. Furthermore, the inhibition of proliferation by ESC-CM may be mediated by miRNAs that affect cell cycle-associated mRNAs and the Wnt signaling pathway.

Chemokine signaling links cell-cycle progression and cilia formation for left-right symmetry breaking.

Zebrafish dorsal forerunner cells (DFCs) undergo vigorous proliferation during epiboly and then exit the cell cycle to generate Kupffer’s vesicle (KV), a ciliated organ necessary for establishing left–right (L–R) asymmetry. DFC proliferation defects are often accompanied by impaired cilia elongation in KV, but the functional and molecular interaction between cell-cycle progression and cilia formation remains unknown. Here, we show that chemokine receptor Cxcr4a is required for L–R laterality by controlling DFC proliferation and KV ciliogenesis. Functional analysis revealed that Cxcr4a accelerates G1/S transition in DFCs and stabilizes forkhead box j1a (Foxj1a), a master regulator of motile cilia, by stimulating Cyclin D1 expression through extracellular regulated MAP kinase (ERK) 1/2 signaling. Mechanistically, Cyclin D1–cyclin-dependent kinase (CDK) 4/6 drives G1/S transition during DFC proliferation and phosphorylates Foxj1a, thereby disrupting its association with proteasome 26S subunit, non-ATPase 4b (Psmd4b), a 19S regulatory subunit. This prevents the ubiquitin (Ub)-independent proteasomal degradation of Foxj1a. Our study uncovers a role for Cxcr4 signaling in L–R patterning and provides fundamental insights into the molecular linkage between cell-cycle progression and ciliogenesis.

Phase 1 Study Evaluating the Association of the Cyclin-Dependent Kinase 4/6 Inhibitor Ribociclib and Cetuximab in Recurrent/Metastatic p16-Negative Squamous Cell Carcinoma of the Head and Neck.

Background: The majority of human papillomavirus (HPV)-negative squamous cell carcinoma of the head and neck (SCCHN) present upregulation of the epidermal growth factor receptor (EGFR) and frequent alterations in the cyclin D1-cyclin dependent kinase (CDK) 4/6 (CDK 4/6)-retinoblastoma protein (pRb) pathway, resulting in cell cycle progression and tumor proliferation. This study investigated the combination of ribociclib, an orally highly selective inhibitor of CDK 4/6, and cetuximab in recurrent and/or metastatic (R/M) SCCHN.Methods: A phase I trial using a 3 + 3 design was performed to determine the dose limiting toxicity (DLT) and maximum tolerated dose (MTD) of ribociclib with standard dose of weekly cetuximab in HPV-negative patients with R/M SCCHN. Ribociclib was administered orally (3 weeks on/1 week off) at dose level 1 of 400 mg daily and dose level 2 of 600 mg daily. The MTD of ribocilib was then further evaluated in an expansion cohort.Results: 10 patients were enrolled in the escalation trial. No DLTs were observed at dose level 1 (n = 3); at dose level 2, one patient was replaced due to rapid disease progression, and one patient out of six evaluable patients experienced a DLT (grade 4 thrombocytopenia >7 days). Ribociclib 600 mg daily was thus determined to be the MTD. Eleven additional patients were enrolled in the expansion cohort. Diarrhea (52%), rash (52%), fatigue (43%), nausea (33%), and mucositis (28%) were the most frequent grade 1–2 adverse events (AE). Neutropenia was the most frequent grade 3–4 AE (20%). Median progression-free survival (PFS) was 3.5 months (range 0.4–17.3 months) and median overall survival (OS) was 8.3 months (range 0.4–24.1 months). Among the 19 radiologically evaluable patients, two (10.5%) achieved a partial response and 11 (58%) had stable disease.Conclusions: The MTD of ribociclib is 600 mg daily when administered in combination with standard dose cetuximab for 3 weeks on and 1 week off. This combination was safe and showed efficacy. Further clinical trials should be conducted to evaluate the antitumor effects of this combination.Trial Information: ClinicalTrials.gov: NCT02429089; Eudract number 2014-005371-83.

Selective cyclin-dependent kinase 4/6 inhibitors as anticancer drugs: Moving beyond hormone receptor-positive breast cancer

AbstractThe cyclin D-cyclin-dependent kinase (CDK) 4/6 pathway controls the cell cycle machinery by regulating the G1-to-S-phase transition. Dysregulation of this pathway, resulting in increased cellular proliferation, is frequently observed in a variety of human cancers. Activation of cyclin D-CDK 4/6 pathway can occur through different mechanisms, including gene amplification/rearrangement, loss of negative regulatory factors, epigenetic modifications, and point mutations of different components of this pathway. Quite conspicuously, CDK 4/6 inhibitors have emerged as promising anticancer agents in various tumors in which CDK 4/6 has a pivotal role in the G1-to-S-phase cell cycle transition. The clinical use of first-generation, nonselective pan-CDK inhibitors was not progressed beyond early phase trials, due to unacceptable toxicity and lack of efficacy noted with these agents. The emergence of selective CDK 4/6 inhibitors, including ribociclib, abemaciclib, and palbociclib, has enabled us to effectively target cyclin D-CDK 4/6 pathway, at the cost of acceptable toxicity. The results of landmark phase III trials investigating palbociclib and ribociclib in advanced hormone receptor (HR)-positive breast cancer have demonstrated a substantial clinical benefit with a well-tolerated toxicity profile. Mechanisms of acquired resistance to selective CDK 4/6 inhibitors are beginning to emerge. Clearly, a detailed understanding of these resistance mechanisms is very much essential for the rational development of post-CDK 4/6 inhibitor therapeutic strategies. Extending the use of selective CDK 4/6 inhibitors beyond HR-positive breast cancer is a challenging task and will likely require identification of clinically meaningful biomarkers to predict response and the use of combination approaches to optimize CDK 4/6 targeting.

Cyclin-dependent kinase 4/6 inhibitors in hormone receptor-positive early breast cancer: preliminary results and ongoing studies.

The cyclin D-cyclin-dependent kinase (CDK) 4/6-inhibitors (CDK4/6i) induce cell cycle arrest in the G1 phase what eventually can prevent the proliferation of cancer cells. The CDK4/6i have changed the landscape of treatment options for ER-positive, HER2-negative metastatic breast cancer. Currently, palbociclib, ribociclib, and abemaciclib are approved by the US Food and Drug Administration in this setting. This success encouraged the researchers to examine CDK4/6i activity in (neo)adjuvant setting. In this review, clinical data to date and ongoing clinical trials with palbociclib, ribociclib, and abemaciclib in the early breast cancer are discussed. A literature search of these topics was carried out using PubMed and data reported at international oncology meetings and clinicaltrials.gov were included. Currently, we have the early promising data from Phase II clinical trials of CDK4/6i efficacy in the neoadjuvant setting in women with HR-positive breast cancer. Moreover, there are numerous studies that are in progress today in (neo)adjuvant setting.