Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment.

Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.

FAM83B promotes cell proliferation via regulating the expression of CDK4/CDK6/CCND1 complex in laryngeal squamous cell carcinoma.

FAM83B, as one of the FAM83 family members, has been closely involved in cell transformation, and a growing number of scholars have been studied its role in tumours over the years. Whereas the effect and potential mechanism of FAM83B in laryngeal squamous cell carcinoma (LSCC) have not been investigated. In this research, we discovered that the expression quantity of FAM83B was remarkably higher in LSCC tissues (79.65 ± 35.98) than in matched adjacent tissues (59.34 ± 32.59) by tissue microarrays and immunohistochemistry. Furthermore, expression of FAM83B was knocked down in HEP-2 and TU177 cell lines via lentivirus, and in the course of intracorporal and extracorporeal experiments, FAM83B knockdown showed the inhibition of tumour growth, migration, and invasion ability. Moreover, cell cycle assay showed that FAM83B knockdown leads to an apparent accumulation of cells in the G1 phase, indicating that FAM83B knockdown can inhibit cell proliferation. Meanwhile, western blotting (WB) demonstrated that FAM83B knockdown led to a significant reduction in CDK4/CDK6/CCND1 protein expression, which may have decelerated cell cycle progression. Collectively, this study demonstrates that FAM83B serves as an oncogene in LSCC, promoting cell proliferation by controlling the protein expression of CDK4, CDK6, and CCND1, thus inducing a transference of the G1 stage to S stage in cell-cycle of LSCC cells. These results provide an academic foundation for elucidating the mechanism of LSCC occurrence and evolution and for developing treatment strategies for LSCC.

CDK4/CDK6 Inhibitors Synergize with Midostaurin, Avapritinib, and Nintedanib in Inducing Growth Inhibition in KIT D816V+ Neoplastic Mast Cells.

In most patients with advanced systemic mastocytosis (AdvSM), neoplastic mast cells (MC) express KIT D816V. However, despite their disease-modifying potential, KIT D816V-targeting drugs, including midostaurin and avapritinib, may not produce long-term remissions in all patients. Cyclin-dependent kinase (CDK) 4 and CDK6 are promising targets in oncology. We found that shRNA-mediated knockdown of CDK4 and CDK6 results in growth arrest in the KIT D816V+ MC line HMC-1.2. The CDK4/CDK6 inhibitors palbociclib, ribociclib, and abemaciclib suppressed the proliferation in primary neoplastic MC as well as in all HMC-1 and ROSA cell subclones that were examined. Abemaciclib was also found to block growth in the drug-resistant MC line MCPV-1, whereas no effects were seen with palbociclib and ribociclib. Anti-proliferative drug effects on MC were accompanied by cell cycle arrest. Furthermore, CDK4/CDK6 inhibitors were found to synergize with the KIT-targeting drugs midostaurin, avapritinib, and nintedanib in inducing growth inhibition and apoptosis in neoplastic MCs. Finally, we found that CDK4/CDK6 inhibitors induce apoptosis in CD34+/CD38- stem cells in AdvSM. Together, CDK4/CDK6 inhibition is a potent approach to suppress the growth of neoplastic cells in AdvSM. Whether CDK4/CDK6 inhibitors can improve clinical outcomes in patients with AdvSM remains to be determined in clinical trials.

Real world incidence and management of adverse events in patients with HR+, HER2- metastatic breast cancer receiving CDK4 and 6 inhibitors in a United States community setting.

OBJECTIVE: To examine the real-world incidence and management of select adverse events (AEs) among female patients with hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), receiving a cyclin-dependent kinase 4 and 6 (CDK4 and 6) inhibitor (palbociclib, abemaciclib, or ribociclib). METHODS: This retrospective study analyzed data from the US Oncology Network iKnowMed electronic health record database for 396 patients with an initial MBC diagnosis on/after 1 January 2014 and receipt of first CDK4 and 6 regimen between 1 January 2017 and 31 December 2018. In this descriptive study, the proportion of patients who experienced select AEs and associated dose modifications or discontinuations were reported. The occurrence of select healthcare resource utilization categories was also reported. RESULTS: Median follow-up time was 451, 262, and 355 days for patients in the palbociclib, abemaciclib, and ribociclib cohorts, respectively. The most common AEs were neutropenia (palbociclib, 44.8%; abemaciclib, 10.6%; ribociclib, 36.3%), diarrhea (palbociclib, 8.0%; abemaciclib, 43.0%; ribociclib, 8.8%), and fatigue (palbociclib, 12.9%; abemaciclib, 17.6%; ribociclib, 16.5%). AEs resulted in a treatment hold among 91 (23.0%), a dose reduction among 86 (21.7%), and permanent discontinuation among 48 (12.1%) patients overall. CONCLUSIONS: This real-world study provides insight into the occurrence of AEs which varied by CDK4 and 6 inhibitor. Compared to clinical trials, frequencies of AEs were numerically lower but dose reductions due to AEs were numerically higher. It is possible these differences reflect proactive management of AEs on the part of clinicians to help patients remain on therapy.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4 and 6 inhibitors) have changed the landscape for the treatment of metastatic breast cancer (MBC) among patients who are hormone receptor positive (HR+) and human epidermal growth factor receptor 2 negative (HER2−). An understanding of the real-world management of adverse events (AEs) will help optimize treatment strategies. Here, data from the US Oncology Network electronic health record database for 396 HR+, HER2−, MBC patients receiving a CDK4 and 6 inhibitor were examined to describe the proportion of patients who experienced select AEs and the associated outcomes of these AEs. Compared to clinical trials, frequencies of AEs were numerically lower but dose reductions due to AEs were numerically higher. It is possible that these differences reflect a proactive management of AEs on the part of clinicians to help patients remain on therapy.

Cytokeratin 13 promotes radiotherapy sensitivity of nasopharyngeal carcinoma by downregulating the MEK/ERK pathway.

BACKGROUND: Radiation therapy is the first treatment choice for nasopharyngeal carcinoma (NPC), while radiation resistance and recurrence have become the primary factors and are associated with poor prognosis in the clinical treatment of NPC patients. The purpose of the present study was to explore the sensitivity and molecular basis of cytokeratin 13 (CK13) that regulates NPC radiotherapy. METHODS: HNE-3 or C666-1 cell line was used for overexpression and knockdown tests. Under radiotherapy conditions, CCK-8 assay, clone formation assay, and flow cytometry analyzed the effects of CK13 overexpression on cell proliferation, apoptosis, and cell cycle, respectively. In addition, Western blotting detected CK13-mediated downregulation of cell cycle-related genes. The mouse subcutaneous tumor-bearing experiment identified the effects of CK13 overexpression on the treatment of NPC in vivo. Further, Western blotting, CCK-8 assay, and flow cytometry investigated whether the CK13-mediated cell apoptosis involves the MEK/ERK signaling pathway. RESULTS: Overexpression of CK13 significantly inhibited the survival of HNE-3 cells under radiotherapy in vitro and in vivo, and there was a substantial decrease in cyclin-dependent kinase 4 and 6 (CDK4/6) levels promoting the cell percentage number in the G2/M phase and, subsequently, the ratio of the apoptotic cells. In contrast, the knockdown of CK13 showed the opposite partial regulatory effect. Interestingly, CK13 overexpression also showed a reduction in the survival of C666-1 cells and an increased ratio of the apoptotic cells under radiotherapy treatment. Furthermore, higher levels of CK13 downregulated the MEK/ERK signaling pathway, resulting in decreased HNE-3 cell proliferation and increased apoptosis. However, ERK activators were able to rescue the process partially. CONCLUSIONS: Together, these results showed that CK13 promoted the radiosensitivity of NPC cells by downregulating the MEK/ERK signaling pathway. Thus, targeting CK13 provided insights into the treatment of NPC radiotherapy.

The Renaissance of Cyclin Dependent Kinase Inhibitors.

Cyclin-dependent kinases (CDK) regulate cell cycle progression. During tumor development, altered expression and availability of CDKs strongly contribute to impaired cell proliferation, a hallmark of cancer. In recent years, targeted inhibition of CDKs has shown considerable therapeutic benefit in a variety of tumor entities. Their success is reflected in clinical approvals of specific CDK4/6 inhibitors for breast cancer. This review provides a detailed insight into the molecular mechanisms of CDKs as well as a general overview of CDK inhibition. It also summarizes the latest research approaches and current advances in the treatment of head and neck cancer with CDK inhibitors. Instead of monotherapies, combination therapies with CDK inhibitors may especially provide promising results in tumor therapy. Indeed, recent studies have shown a synergistic effect of CDK inhibition together with chemo- and radio- and immunotherapy in cancer treatment to overcome tumor evasion, which may lead to a renaissance of CDK inhibitors.

Differential Expression of PD-L1 during Cell Cycle Progression of Head and Neck Squamous Cell Carcinoma.

The expression of PD-L1 by tumor cells is mainly associated with its immunosuppressive effect. In fact, PD-1/PD-L1 immune checkpoint inhibitors demonstrated remarkable effects in advanced cancer patients including HNSCC. In this context, irradiation is currently being investigated as a synergistic treatment modality to immunotherapy. However, the majority of HNSCC patients still show little improvement or even hyperprogression. Interestingly, there is increasing evidence for additional cell-intrinsic functions of PD-L1 in tumor cells. In previous studies, we showed that PD-L1 has a strong influence on proliferation, migration, invasion, and survival after irradiation. We demonstrated that cellular expression and localization of PD-L1 differed depending on sensitivity to irradiation. Here, we show that PD-L1 is also differentially expressed during cell cycle progression of HNSCC. Furthermore, cellular localization of PD-L1 also changes depending on a particular cell cycle phase. Moreover, distinct observations occurred depending on the general differentiation status. Overall, the function of PD-L1 cannot be generalized. Rather, it depends on the differentiation status and microenvironment. PD-L1 expression and localization are variable, depending on different factors. These findings may provide insight into why differential response to PD-1/PD-L1 antibody therapy can occur. Detailed understanding of cell-intrinsic PD-L1 functions will further allow antibody-based immunotherapy to be optimized.

Real-world treatment patterns and outcomes of abemaciclib for the treatment of HR+, HER2- metastatic breast cancer.

OBJECTIVE: This retrospective observational study described baseline characteristics, real-world treatment patterns, and outcomes among patients with metastatic breast cancer treated with abemaciclib in the United States. METHODS: De-identified electronic health record-derived data were used to describe patients who began abemaciclib treatment on or after 30 June 2016 and ≥4 months before data cutoff (31 December 2018). Real-world response (rwR) and real-world progression assessments were abstracted from clinical documentation. Descriptive statistics were used to calculate the real-world best response. The Kaplan-Meier method estimated real-world time to first response (rwTTFR) and real-world progression-free survival (rwPFS). RESULTS: The median age of 118 female patients at abemaciclib initiation was 66.5 years (interquartile range, 57.0, 73.0). The breakdown of patients who received abemaciclib in first, second, third, or later lines was 28.8%, 21.2%, 20.3%, and 29.7%, respectively. Patients received abemaciclib as monotherapy (12.7%) or in combination with endocrine therapy: fulvestrant (59.3%); aromatase inhibitor (22.9%); aromatase inhibitor and fulvestrant (5.1%). There were 68 patients (57.6%) with ≥1 rwR assessment: 41.2% with a real-world complete response or real-world partial response. Median rwTTFR was 3.6 months (95% confidence interval, 3.5, 5.2). Twelve-month rwPFS probability was 61.7%. CONCLUSIONS: This study represents utilization and outcomes associated with abemaciclib approximately 1 year following FDA approval. Treatment patterns demonstrated heterogeneity and, as in clinical trials, patients appeared to benefit from abemaciclib treatment in the real world. More research investigating outcomes associated with abemaciclib treatment is needed, with larger samples and longer follow-up to enable closer evaluation by subgroup, regimen, and line of therapy.

Immunomodulation by targeted anticancer agents.

At odds with conventional chemotherapeutics, targeted anticancer agents are designed to inhibit precise molecular alterations that support oncogenesis or tumor progression. Despite such an elevated degree of molecular specificity, many clinically employed and experimental targeted anticancer agents also mediate immunostimulatory or immunosuppressive effects that (at least in some settings) influence therapeutic efficacy. Here, we discuss the main immunomodulatory effects of targeted anticancer agents and explore potential avenues to harness them in support of superior clinical efficacy.

Molecular homology between canine spontaneous oral squamous cell carcinomas and human head-and-neck squamous cell carcinomas reveals disease drivers and therapeutic vulnerabilities.

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

Trial watch: STING agonists in cancer therapy.

Stimulator of interferon response cGAMP interactor 1 (STING1, best known as STING) is an endoplasmic reticulum-sessile protein that serves as a signaling hub, receiving input from several pattern recognition receptors, most of which sense ectopic DNA species in the cytosol. In particular, STING ensures the production of type I interferon (IFN) in response to invading DNA viruses, bacterial pathogens, as well as DNA leaking from mitochondria or the nucleus (e.g., in cells exposed to chemotherapy or radiotherapy). As a type I IFN is critical for the initiation of anticancer immune responses, the pharmaceutical industry has generated molecules that directly activate STING for use in oncological indications. Such STING agonists are being tested in clinical trials with the rationale of activating STING in tumor cells or tumor-infiltrating immune cells (including dendritic cells) to elicit immunostimulatory effects, alone or in combination with a range of established chemotherapeutic and immunotherapeutic regimens. In this Trial Watch, we discuss preclinical evidence and accumulating clinical experience shaping the design of Phase I and Phase II trials that evaluate the safety and preliminary efficacy of STING agonists in cancer patients.

Caspase 2 and p53 Reunited in Tumor Control.

Recent findings (Tsabar et al.) demonstrate that human cancer cells that evade the cell cycle blockage normally imposed by DNA damage experience sustained p53 signaling upon MDM2 degradation by caspase 2. Such a response may be connected to the delivery of immunostimulatory signals to ensure the elimination of genetically instable cancer cells.

Lnc HAGLR Promotes Colon Cancer Progression Through Sponging miR-185-5p and Activating CDK4 and CDK6 in vitro and in vivo.

BACKGROUND/AIM: LncRNA plays a key role in tumor progression. HAGLR functions as an oncogene in many cancers. However, the molecular mechanism of HAGLR in colon cancer is still unclear. METHODS: qRT-PCR was used to measure the expression of HAGLR, miR-185-5p in colon cancer. The expression of CDK4 and CDK6 was detected by Western blot. CCK-8 assay, EdU staining, transwell and Annexin V-FITC/PI assay were used to analyze the effect of HAGLR and miR-185-5p on cell proliferation, invasion, migration and apoptosis. Bioinformatic analysis and luciferase were used to analyze the target genes of HAGLR and miR-185-5p. Nude mice were used to detect mouse tumor changes. RESULTS: Compared with normal colon cancer tissues and cells, the expression of HAGLR was increased in colon cancer tissues and cells. In addition, the expression of HAGLR down-regulation inhibited the growth, migration, and invasion of colon cancer cells. MiR-185-5p was reduced in colon cancer, and CDK4 and CDK6 acted as target genes of miR-185-5p to regulate the progress of colon cancer. And CDK4 and CDK6 were predicted as downstream targets of miR-185-5p. Finally, it was demonstrated that HAGLR regulated tumor progression in vivo. CONCLUSION: Lnc HAGLR promoted the development of colon cancer by miR-185-5p/CDK4/CDK6 axis, and lnc HAGLR might be potential target for colon cancer.

CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML.

PURPOSE: Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro. METHODS: Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and 3H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting. FINDINGS: HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1T315I-associated TKI resistance. INTERPRETATION: HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML. FUNDING: This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Ganoderiol F purified from Ganoderma leucocontextum retards cell cycle progression by inhibiting CDK4/CDK6.

This study was designed to purify molecules possess anti-cancer cell activity from the fruit body of Ganoderma leucocontextum. Bio-activity-guided purification and chromatographic separation of Ganoderma leucocontextum extract led to the enrichment of bioactive fractions and isolation of a single compound. The purified compound was identified as Ganoderiol F, which induced cancer cell death. In the in vivo experiments, we founded ethanol extract and ethyl acetate fraction inhibited tumor growth in the mice injected with 4T1 cells. We found that Ganoderiol F-mediated suppression of breast cancer cell viability occurred through cell cycle arrest. Ganoderiol F down-regulated expression of cyclin D, CDK4, CDK6, cyclin E and CDK2 and inhibited cell cycle progression arresting the cells in G1 phase. In addition, Ganoderiol F up-regulated pro-apoptotic Foxo3, down-regulated anti-apoptotic c-Myc, Bcl-2 and Bcl-w leading to apoptosis in human breast cancer cells MDA-MB-231. These results showed that c-Myc, cyclin D-CDK4/CDK6 and cyclin E-CDK2 are the central components of Ganoderiol F regulation of cell cycle progression. Hence Ganoderiol F may serve as a potential CDK4/CDK6 inhibitor for breast cancer therapy. Abbreviations: GLE: Ganoderma leucocontextum ethanol extract; GLEA: Ganoderma leucocontextum ethyl acetate fraction; GLPE: Ganoderma leucocontextum petroleum ether fraction; RP-HPLC: reversed-phase high-performance liquid chromatograph; DMEM: Dulbecco's modified Eagle's medium; FBS: fetal bovine serum; PAGE: polyacrylamide gel electrophoresis.

Metastases to extraocular muscles from breast cancer: case report and up-to-date review of the literature.

BACKGROUND: Unilateral or bilateral metastases to extraocular muscles are very rare in breast cancer. CASE PRESENTATION: We describe a case of inferior rectus extraocular muscle involved by ductal luminal B/Her-2 neu negative breast cancer, observed in a cohort of 580 patients. Our patient had received chemotherapy and hormonal therapy (tamoxifen for 3 years and letrozole in the following 3 years) for her primary cancer and developed an orbital metastasis while she was under aromatase inhibitor-based therapy. Diagnosis was confirmed by MRI and biopsy. Orbital radiotherapy, combined with fulvestrant, resulted in shrinking of the secondary mass. A third line hormonal therapy using palbociclib was then started. Twelve-months later, MRI showed no residual tumor mass. Currently, the patient is alive and in good general conditions after 20 months. CONCLUSIONS: Literature review yielded 57 patients with extraocular muscle metastases from breast cancer, mostly due to the invasive lobular subtype of carcinoma. In addition to the present case, only 4 other extraocular muscles metastases from invasive ductal carcinoma has been reported, pointing out to the rarity of ductal type spread to the orbit in the natural history of breast cancer. Surgery may be used as a single treatment, despite no improvement of symptoms. Radiotherapy alone or combined with chemotherapy, or with chemotherapy plus hormonal therapy are available options. Results are, however, missing or poor. The present case is the first one with complete and stable response after 20 months to radiotherapy, antiestrogen drug fulvestrant and selective inhibitor of CDK4 /CDK6 palbociclib. In this subset of patients, with unusual metastatic sites and frequent multi-organ metastatic impairment, a multidisciplinary approach is indicated in order to achieve the best therapeutic management and long-term surveillance.

A novel approach to eliminate therapy-resistant mantle cell lymphoma: synergistic effects of Vorinostat with Palbociclib.

Mantle cell lymphoma (MCL) represents an aggressive B-cell lymphoma with frequent relapse and poor survival. Recently, dysregulated histone-deacetylases (HDACs) and cell cycle CDK-Rb pathway have been shown to be commonly associated with MCL pathogenesis, and are considered promising targets for relapsed-lymphoma therapy. Therefore, we investigated the single agents and combination efficacy of HDACs inhibitor Vorinostat, CDK4/6 dual-inhibitor Palbociclib on MCL cell growth/survival and underlying molecular mechanism(s) using MCL cell lines including therapy-resistant MCL cell lines. Our results showed that both inhibitors as single agents or combined, significantly suppressed the cell growth and induced apoptosis in therapy-resistant and parental MCL lines. In addition, the combination of Vorinostat and Palbociclib significantly inhibited the activation of the key molecules of the CDK4/6-Rb pathway and HDAC activity and subsequently decreased the expression of Cyclin-D1 and Bcl-2. These studies demonstrated the potential for combining these two inhibitors as a novel therapeutic approach in refractory MCL therapy.

Molecular mcchanism of deguelin-induced apoptosis and cell cycle arrest in lung cancer cells in vitro / 中国药理学通报

Aim To explore whether deguelin can block cell cycle and cell migration, inhibit the proliferation of non-small cell lung cancer cells.Methods H1299 cells were treated with 1.562 5, 3.125, 6.25, 12.5, 25, 50 μmol·L-1 deguelin for different time(24, 48, 72 h); cell viability was detected by CCK-8 assay, and cell migration ability was tested by scratch assay.H1299 cells were treated with 1.5, 3, 6 μmol·L-1 deguelin for 24 h.Flow cytometry with PI single staining and Annexin V-FITC/PI double staining experiment were used to evaluate cell cycle and apoptosis.qPCR was used to detect the regulatory effects of deguelin and its carbamate derivative on the Cyclin D-CDK4/6 complex at the gene level.Results Deguelin inhibited cell growth and the IC50 value of deguelin was(5.47±0.97),(4.01±0.45),(2.86±0.19)μmol·L-1 when treated with 24, 48, 72 h respectively.Deguelin also inhibited the healing ability of H1299 cells and the migration of H1299 cells significantly(P<0.05).Deguelin could block H1299 cell cycle in G1 phase.Flow cytometry combined with Annexin V-FITC/PI double staining showed that deguelin could induce apoptosis of H1299 cells.qPCR experiments showed that deguelin could down-regulate the expression of CDK4, CDK6 and Cyclin D1 genes significantly(P<0.05).Conclusions Deguelin may regulate cell cycle by down-regulating CDK4, CDK6 and Cyclin D1 genes in the cell cycle regulation system, and reduce the migration ability of tumor cells to induce apoptosis.

Ribociclib, a Cdk4/Cdk6 kinase inhibitor, enhances glucocorticoid sensitivity in B-acute lymphoblastic leukemia (B-All).

Dysregulation of the cyclin D1-CDK4/CDK6 complex is frequently observed in almost all human cancer and contributes to aberrant cell proliferation and consequent tumorigenesis. Although many reports described the importance of CDK4/CDK6 in different set of human tumors, only few studies have been performed on leukemia. By gene expression analysis performed in a cohort of childhood patients affected by B-acute lymphoblastic leukemia (B-ALL) we found that both CDK4 and CDK6 are highly expressed. Moreover, reverse phase protein array (RPPA) analysis showed that cyclin D1 levels are higher in patients undergoing relapse. Starting from these considerations, we evaluated the effect of dual inhibition of CDK4/CDK6 in B-ALL and if this inhibition could enhance cytotoxic killing of leukemia cells after combination treatment with dexamethasone. We treated B-ALL cell lines with ribociclib, a highly specific CDK4/6 inhibitor. As expected, treatment with ribociclib induced growth inhibition of B-ALL cell lines, accompanied by strong cell cycle arrest in G1 phase, along with a dose-dependent decrease in phosphorylated retinoblastoma protein. Ribociclib exposure strongly synergizes with dexamethasone in SEM and RCH-ACV, two dexamethasone-resistant cell lines, along with a strong decrease in proliferation and a significant increase in apoptotic cell death. These results were also confirmed on primary cultures derived from bone marrow of pediatric patients affected by B-ALL. Immunoblot analysis showed a significant increase in glucocorticoid receptor (GR) along with some of its target genes, after combined treatment with ribociclib and dexamethasone. Altogether our findings support the concept that pharmacologic inhibition of CDK4/CDK6 may represent a useful therapeutic strategy to control cell proliferation in B-ALL and provide new insight in understanding potential mechanism of glucocorticoid resistance.