Amplification of chromosome band 11q13 and a role for cyclin D1 in human breast cancer

FADD amplification is associated with CD8+ T-cell exclusion and malignant progression in HNSCC

OBJECTIVE

This study aimed to clarify the relationship between FADD amplification and overexpression and the tumor immune microenvironment.

METHODS

Immunohistochemical staining and bioanalysis were used to analyze the association between FADD expression in tumor cells and cells in tumor microenvironment. RNA-seq analysis was used to detect the differences in gene expression upon FADD overexpression. Flow cytometry and multicolor immunofluorescence staining (mIHC) were used to detect the differences in CD8+ T-cell infiltration in FADD-overexpressed cells or tumor tissues.

RESULTS

Overexpression of FADD significantly promoted tumor growth. Cells with high FADD expression presented high expression of CD276 and FGFBP1 and low expression of proinflammatory factors (such as IFIT1-3 and CXCL8), which reduced the percentage of CD8+ T cells and created a "cold tumor" immune microenvironment, thus promoting tumor progression. In vivo and in vitro experiment confirmed that tumor tissues with excessive FADD expression exhibited CD8+ T-cell exclusion in the microenvironment.

CONCLUSION

Our preliminary investigation has discovered the association between FADD expression and the immunosuppressive microenvironment in HNSCC. Due to the high frequent amplification of the chromosomal region 11q13.3, where FADD is located, targeting FADD holds promise for improving the immune-inactive state of tumors, subsequently inhibiting HNSCC tumor progression.

E3 ligase MG53 suppresses tumor growth by degrading cyclin D1

Due to the essential role of cyclin D1 in regulating transition from G1 to S phase in cell cycle, aberrant cyclin D1 expression is a major oncogenic event in many types of cancers. In particular, the dysregulation of ubiquitination-dependent degradation of cyclin D1 contributes to not only the pathogenesis of malignancies but also the refractory to cancer treatment regiments with CDK4/6 inhibitors. Here we show that in colorectal and gastric cancer patients, MG53 is downregulated in more than 80% of tumors compared to the normal gastrointestinal tissues from the same patient, and the reduced MG53 expression is correlated with increased cyclin D1 abundance and inferior survival. Mechanistically, MG53 catalyzes the K48-linked ubiquitination and subsequent degradation of cyclin D1. Thus, increased expression of MG53 leads to cell cycle arrest at G1, and thereby markedly suppresses cancer cell proliferation in vitro as well as tumor growth in mice with xenograft tumors or AOM/DSS induced-colorectal cancer. Consistently, MG53 deficiency results in accumulation of cyclin D1 protein and accelerates cancer cell growth both in culture and in animal models. These findings define MG53 as a tumor suppressor via facilitating cyclin D1 degradation, highlighting the therapeutic potential of targeting MG53 in treating cancers with dysregulated cyclin D1 turnover.

[Biological, preclinical and clinical aspects of the association between radiation therapy and CDK4/6 inhibitors]

Several clinical studies have shown that CDK4/6 inhibitors (CDK4/6i) improve survival in patients with metastatic or locally advanced HR-positive, HER-2-negative breast cancer (BC). The aim of this review was to synthesize the biological, preclinical and clinical aspects of the treatment of BC with CDK4/6i, with a focus on the combination of CDK4/6i and radiotherapy. The DNA damage induced after exposure of cells to ionizing radiation activates control pathways that inhibit cell progression in the G1 and G2 phases and induce a transient delay in progression in the S phase. These checkpoints are in particular mediated by cyclin-dependent kinases (CDK) 4/6 activated by cyclin D1. Several preclinical studies have shown that CDK4/6i could be used as radiosensitizers in non-small cell lung cancer, medulloblastoma, brainstem glioma and breast cancer. CDK4/6 inhibition also protected against radiation-induced intestinal toxicities by inducing redistribution of quiescent intestinal progenitor cells, making them less radiosensitive. Clinical data on the combination of CDK inhibitors and radiotherapy for both locoregional and metastatic irradiation are based on retrospective data. Nevertheless, the most optimal therapeutic sequence would be radiotherapy followed by palbociclib. Pending prospective clinical trials, the concomitant combination of the two treatments should be done under close supervision.

Aberrant Cyclin D1 splicing in cancer: from molecular mechanism to therapeutic modulation

Cyclin D1 (CCND1), a crucial mediator of cell cycle progression, possesses many mutation types with different mutation frequencies in human cancers. The G870A mutation is the most common mutation in CCND1, which produces two isoforms: full-length CCND1a and divergent C-terminal CCND1b. The dysregulation of the CCND1 isoforms is associated with multiple human cancers. Exploring the molecular mechanism of CCND1 isoforms has offer new insight for cancer treatment. On this basis, the alterations of CCND1 gene are described, including amplification, overexpression, and mutation, especially the G870A mutation. Subsequently, we review the characteristics of CCND1 isoforms caused by G870A mutation. Additionally, we summarize cis-regulatory elements, trans-acting factors, and the splice mutation involved in splicing regulation of CCND1. Furthermore, we highlight the function of CCND1 isoforms in cell cycle, invasion, and metastasis in cancers. Importantly, the clinical role of CCND1 isoforms is also discussed, particularly concerning prognosis, chemotherapy, and radiotherapy. Last, emphasis is given to the corrective strategies that modulate the cancerous CCND1 isoforms. Thus, it is highlighting significance of aberrant isoforms of CCND1 as targets for cancer therapy.

CDK4: a master regulator of the cell cycle and its role in cancer

The cell cycle is regulated in part by cyclins and their associated serine/threonine cyclin-dependent kinases, or CDKs. CDK4, in conjunction with the D-type cyclins, mediates progression through the G₁ phase when the cell prepares to initiate DNA synthesis. Although Cdk4-null mutant mice are viable and cell proliferation is not significantly affected in vitro due to compensatory roles played by other CDKs, this gene plays a key role in mammalian development and cancer. This review discusses the role that CDK4 plays in cell cycle control, normal development and tumorigenesis as well as the current status and utility of approved small molecule CDK4/6 inhibitors that are currently being used as cancer therapeutics.

Clinical Impact of 11q13.3 Amplification on Immune Cell Infiltration and Prognosis in Breast Cancer

Introduction

Amplification of the 11q13.3 locus has been observed in various tumors. This study sought to determine the correlation of gene amplification at the 11q13.3 locus with the immune status and survival of breast cancer.

Methods

Amplification of the 11q13.3 locus was characterized by analyzing a publicly available database from the cBioPortal platform (TCGA). The correlation of amplified genes with immune cell infiltration in breast cancer was further analyzed using the TIMER2.0 platform. Immunohistochemical staining was used to determine the expression levels of Cyclin D1 (CCND1), Fas-associated death domain (FADD) and P53 in 156 clinical breast cancer samples.

Results

This study revealed that amplification of the 11q13.3 amplicon in breast cancer is likely more frequently detected in luminal B breast cancer. Moreover, high expression or amplification of CCND1, fibroblast growth factor 3 (FGF3), fibroblast growth factor 4 (FGF4), fibroblast growth factor 19 (FGF19) and FADD was inversely correlated with the abundance of CD4+ T cells and dendritic cell infiltration in breast cancer (P < 0.05). Data analysis also demonstrated that high expression of CCND1, FGF4 and FADD mRNA levels was closely correlated with shorter recurrence-free survival (RFS) in patients with breast cancer (P < 0.05). The results of immunohistochemical staining from clinical samples further confirmed that high expression of CCND1 and FADD was frequently detected in luminal B and high-grade breast cancer with shorter metastasis-free survival times (P < 0.05).

Conclusion

This study demonstrated that coamplification of genes located on the 11q13.3 amplicon is frequently detected in luminal B subtype breast cancer and is closely associated with worse survival in patients with breast cancer. Moreover, coamplification of the CCND1-FGF locus might decrease antitumor immune activity in breast cancer, indicating that coamplification of the 11q13.3 amplicon is likely to be a key determinant of therapeutic resistance and accelerate the aggressive evolution of breast cancer.

Keratin 19 interacts with GSK3β to regulate its nuclear accumulation and degradation of cyclin D3

Cyclin D3 regulates the G1/S transition and is frequently overexpressed in several cancer types including breast cancer, where it promotes tumor progression. Here we show that a cytoskeletal protein keratin 19 (K19) physically interacts with a serine/threonine kinase GSK3β and prevents GSK3β-dependent degradation of cyclin D3. The absence of K19 allowed active GSK3β to accumulate in the nucleus and degrade cyclin D3. Specifically, the head (H) domain of K19 was required to sustain inhibitory phosphorylation of GSK3β Ser9, prevent nuclear accumulation of GSK3β, and maintain cyclin D3 levels and cell proliferation. K19 was found to interact with GSK3β and K19–GSK3β interaction was mapped out to require Ser10 and Ser35 residues on the H domain of K19. Unlike wildtype K19, S10A and S35A mutants failed to maintain total and nuclear cyclin D3 levels and induce cell proliferation. Finally, we show that the K19–GSK3β-cyclin D3 pathway affected sensitivity of cells toward inhibitors to cyclin-dependent kinase 4 and 6 (CDK4/6). Overall, these findings establish a role for K19 in the regulation of GSK3β-cyclin D3 pathway and demonstrate a potential strategy for overcoming resistance to CDK4/6 inhibitors.

Oncogenic and Tumor Suppressive Components of the Cell Cycle in Breast Cancer Progression and Prognosis

Cancer, a disease of inappropriate cell proliferation, is strongly interconnected with the cell cycle. All cancers consist of an abnormal accumulation of neoplastic cells, which are propagated toward uncontrolled cell division and proliferation in response to mitogenic signals. Mitogenic stimuli include genetic and epigenetic changes in cell cycle regulatory genes and other genes which regulate the cell cycle. This suggests that multiple, distinct pathways of genetic alterations lead to cancer development. Products of both oncogenes (including cyclin-dependent kinase (CDKs) and cyclins) and tumor suppressor genes (including cyclin-dependent kinase inhibitors) regulate cell cycle machinery and promote or suppress cell cycle progression, respectively. The identification of cyclins and CDKs help to explain and understand the molecular mechanisms of cell cycle machinery. During breast cancer tumorigenesis, cyclins A, B, C, D1, and E; cyclin-dependent kinase (CDKs); and CDK-inhibitor proteins p16, p21, p27, and p53 are known to play significant roles in cell cycle control and are tightly regulated in normal breast epithelial cells. Following mitogenic stimuli, these components are deregulated, which promotes neoplastic transformation of breast epithelial cells. Multiple studies implicate the roles of both types of components-oncogenic CDKs and cyclins, along with tumor-suppressing cyclin-dependent inhibitors-in breast cancer initiation and progression. Numerous clinical studies have confirmed that there is a prognostic significance for screening for these described components, regarding patient outcomes and their responses to therapy. The aim of this review article is to summarize the roles of oncogenic and tumor-suppressive components of the cell cycle in breast cancer progression and prognosis.

CDK4/6 and MAPK-Crosstalk as Opportunity for Cancer Treatment

Despite the development of targeted therapies and novel inhibitors, cancer remains an undefeated disease. Resistance mechanisms arise quickly and alternative treatment options are urgently required, which may be partially met by drug combinations. Protein kinases as signaling switchboards are frequently deregulated in cancer and signify vulnerable nodes and potential therapeutic targets. We here focus on the cell cycle kinase CDK6 and on the MAPK pathway and on their interplay. We also provide an overview on clinical studies examining the effects of combinational treatments currently explored for several cancer types.

Validation of ORAOV1 as a new treatment target in hepatocellular carcinoma

PURPOSE

Chromosome 11q13.2, which contains genes cyclin D1 (CCND1), fibroblast growth factor 19 (FGF19), and Oral Cancer Overexpressed 1 (ORAOV1), is the most highly amplified peak in hepatocellular carcinoma (HCC). CCND1 and FGF19 have been already suggested as therapeutic targets of HCC, but the role of ORAOV1 in carcinogenesis of HCCs has not been reported.

METHODS

This retrospective study investigated ORAOV1 expression using immunohistochemistry performed on tissue microarray blocks obtained from 259 HCC patients with curative resection, between 2000 and 2006. We assessed the prognostic significance of ORAOV1 expression by Kaplan-Meier method with log-rank test and Cox proportional hazards model. Also, we performed invasion, migration, apoptosis, and cell cycle assays in HCC cell lines, and evaluated the tumorigenicity of HCC xenografts in nude mice, after knockdown of ORAOV1.

RESULTS

High expression of ORAOV1 protein was observed in 80% of HCC tissues. The ORAOV1 high expression group showed shorter recurrence free survival (RFS) (p < 0.001) and shorter disease-specific survival (DSS) than the low expression group. It was an independent prognostic factor for predicting early recurrence [Odds ratio 2.74 (95% confidence interval (CI) 1.27-5.93), p = 0.01] as well as short RFS [hazard ratio 2.23 (95% CI 1.40-3.54), p = 0.001] and DSS [hazard ratio 2.30 (95% CI 1.27-4.17), p = 0.006]. Knockdown of ORAOV1 induced significant decreases in migration, invasion, and tumorigenicity of HCC cells in in-vitro model, and inhibited the growth of HCC xenografts in nude mice.

CONCLUSION

We demonstrated unfavorable prognostic effect of ORAOV1 expression with supporting experimental data in HCC. ORAOV1 may be used as a biomarker for predicting HCC prognosis and is a potential candidate for targeted therapy.

Fbxl8 suppresses lymphoma growth and hematopoietic transformation through degradation of cyclin D3

Overexpression of D-type cyclins in human cancer frequently occurs as a result of protein stabilization, emphasizing the importance of identification of the machinery that regulates their ubiqutin-dependent degradation. Cyclin D3 is overexpressed in ~50% of Burkitt’s lymphoma correlating with a mutation of Thr-283. However, the E3 ligase that regulates phosphorylated cyclin D3 and whether a stabilized, phosphorylation deficient mutant of cyclin D3, has oncogenic activity are undefined. We describe the identification of SCF-Fbxl8 as the E3 ligase for Thr-283 phosphorylated cyclin D3. SCF-Fbxl8 poly-ubiquitylates p-Thr-283 cyclin D3 targeting it to the proteasome. Functional investigation demonstrates that Fbxl8 antagonizes cell cycle progression, hematopoietic cell proliferation, and oncogene-induced transformation through degradation of cyclin D3, which is abolished by expression of cyclin D3T283A, a non-phosphorylatable mutant. Clinically, the expression of cyclin D3 is inversely correlated with the expression of Fbxl8 in lymphomas from human patients implicating Fbxl8 functions as a tumor suppressor.

Fbxl8 suppresses cell division, cell proliferation, and tumorigenesis through phosphorylation-dependent degradation of cyclin D3.

Fbxl8 suppresses oncogene-induced transformation of hematopoietic cells and lymphoma cell proliferation through cyclin D3 degradation.

Multiple Functions of Fubp1 in Cell Cycle Progression and Cell Survival

The discovery of novel and critical genes implicated in malignant development is a topic of high interest in cancer research. Intriguingly, a group of genes named “double-agent” genes were reported to have both oncogenic and tumor-suppressive functions. To date, less than 100 “double-agent” genes have been documented. Fubp1 is a master transcriptional regulator of a subset of genes by interacting with a far upstream element (FUSE). Mounting evidence has collectively demonstrated both the oncogenic and tumor suppressive roles of Fubp1 and the debate regarding its roles in tumorigenesis has been around for several years. Therefore, the detailed molecular mechanisms of Fubp1 need to be determined in each context. In the present study, we showed that the Fubp1 protein level was enriched in the S phase and we identified that Fubp1 deficiency altered cell cycle progression, especially in the S phase, by downregulating the mRNA expression levels of Ccna genes encoding cyclin A. Although this Fubp1-cyclin A axis appears to exist in several types of tumors, Fubp1 showed heterogeneous expression patterns among various cancer tissues, suggesting it exhibits multiple and complicated functions in cancer development. In addition, we showed that Fubp1 deficiency confers survival advantages to cells against metabolic stress and anti-cancer drugs, suggesting that Fubp1 may play both positive and negative roles in malignant development.

Tumour kinome re-wiring governs resistance to palbociclib in oestrogen receptor positive breast cancers, highlighting new therapeutic modalities

Combination of CDK4/6 inhibitors and endocrine therapy improves clinical outcome in advanced oestrogen receptor (ER)-positive breast cancer, however relapse is inevitable. Here, we show in model systems that other than loss of RB1 few gene-copy number (CN) alterations are associated with irreversible-resistance to endocrine therapy and subsequent secondary resistance to palbociclib. Resistance to palbociclib occurred as a result of tumour cell re-wiring leading to increased expression of EGFR, MAPK, CDK4, CDK2, CDK7, CCNE1 and CCNE2. Resistance altered the ER genome wide-binding pattern, leading to decreased expression of ‘classical’ oestrogen-regulated genes and was accompanied by reduced sensitivity to fulvestrant and tamoxifen. Persistent CDK4 blockade decreased phosphorylation of tuberous sclerosis complex 2 (TSC2) enhancing EGFR signalling, leading to the re-wiring of ER. Kinome-knockdown confirmed dependency on ERBB-signalling and G2/M–checkpoint proteins such as WEE1, together with the cell cycle master regulator, CDK7. Noteworthy, sensitivity to CDK7 inhibition was associated with loss of ER and RB1 CN. Overall, we show that resistance to CDK4/6 inhibitors is dependent on kinase re-wiring and the redeployment of signalling cascades previously associated with endocrine resistance and highlights new therapeutic networks that can be exploited upon relapse after CDK4/6 inhibition.

SPH3643: A novel cyclin-dependent kinase 4/6 inhibitor with good anticancer efficacy and strong blood-brain barrier permeability

The cyclin‐dependent kinase (CDK)4/6‐cyclin D1‐Rb‐p16/ink4a pathway is responsible for regulating cell progression past the G₁ restriction point during the cell cycle. The development of a majority of human tumors is associated with dysregulation of this pathway, resulting in increased cancer cell proliferation. Both CDK4 and CDK6, well‐validated cancer drug targets, function primarily as catalytic enzymes that mediate the phosphorylation of retinoblastoma protein (Rb). Here, we determined that SPH3643 is a novel potent antiproliferative agent that inhibits CDK4/6 kinase activity. In biochemical assays, SPH3643 showed more potent inhibition of both CDK4 and CDK6 than did 2 published CDK4/6 inhibitors, LY2835219 and palbociclib, and had better selectivity than LY2835219. Further in vitro study revealed that SPH3643 blocked Cdk/Rb signaling by inhibiting the phosphorylation of Rb^Ser780 and arrested the MCF‐7 cancer cells at G₀/G₁ phase, resulting in marked inhibition of the proliferation of Rb‐positive cancer cell lines. In vivo SPH3643 treatment in mice bearing xenograft tumor models of breast cancer, colon cancer, acute myelocytic leukemia, and glioblastoma resulted in significant decreases in tumor growth. SPH3643 was able to particularly strongly inhibit glioblastoma (U87‐MG) cell growth in the brains of orthotopic carcinoma xenograft mice due to its high degree of intracerebral penetration and significant persistence in this setting. Together these results revealed that SPH3643 is a potent, orally active small‐molecule inhibitor of CDK4/6 with robust anticancer efficacy and a high degree of blood‐brain barrier permeability.

CDK4/6 inhibitors in breast cancer - from in vitro models to clinical trials

Background: Breast cancer (BC) is one of the leading causes of cancer-related deaths worldwide. Standard therapies aim to disrupt pathways that regulate the growth and survival of BC cells. Therapeutic agents such as endocrine therapy target hormone dependent cancer cells and have shown to be suitable approaches in BC treatment. However, in the case of metastatic BC, curative options are limited, thus strategies have been explored to improve survival and clinical benefit. In this review we provide an up to date overview of the development of anti-cancer agents, particularly the newly developed CDK4/6 inhibitors.Material and methods: A search of PubMed was conducted to identify preclinical data surrounding the development of endocrine therapy and CDK4/6 inhibitors in early and metastatic BC. Clinical data were also sought using PubMed and clinicaltrials.gov.Results: Agents targeting oestrogen and its receptor have demonstrated positive outcomes in clinical trial with improvements in objective responses and overall survival. However, patients do exhibit adverse effects and some will eventually fail to respond to endocrine therapy. Subsequently, the development and success of 3rd generation CDK4/6 inhibitors in preclinical studies has allowed their introduction in clinical studies. In patients with ER + BC, CDK4/6 have demonstrated dramatic improvements in progression free survival when used in combination with endocrine therapies. Similar findings were also observed in metastatic disease. Adverse effects were limited in CDK4/6 treated patients, demonstrating the safety of these agents.Conclusion: CDK4/6 inhibitors are highly specific making them a safe and viable therapeutic for BC and there is increasing evidence of their potential to improve survival, even in the metastatic setting. Although a number of trials have demonstrated this, as a lone therapy or in combination, optimisation of treatment scheduling are still required in further clinical investigations.

Mechanisms of resistance to estrogen receptor modulators in ER+/HER2- advanced breast cancer

Endocrine therapy represents a mainstay adjuvant treatment of estrogen receptor-positive (ER+) breast cancer in clinical practice with an overall survival (OS) benefit. However, the emergence of resistance is inevitable over time and is present in one-third of the ER+ breast tumors. Several mechanisms of endocrine resistance in ER+/HER2- advanced breast cancers, through ERα itself, receptor tyrosine signaling, or cell cycle pathway, have been identified to be pivotal in endocrine therapy. The epigenetic alterations also contribute to ensuring tumor cells' escape from endocrine therapies. The strategy of combined hormone therapy with targeted pharmaceutical compounds has shown an improvement of progression-free survival or OS in clinical practice, including three different classes of drugs: CDK4/6 inhibitors, selective inhibitor of PI3Kα and mTOR inhibitors. Many therapeutic targets of cell cycle pathway and cell signaling and their combination strategies have recently entered clinical trials. This review focuses on Cyclin D-CDK4/6-RB axis, PI3K pathway and HDACs. Additionally, genomic evolution is complex in tumors exposed to hormonal therapy. We highlight the genomic alterations present in ESR1 and PIK3CA genes to elucidate adaptive mechanisms of endocrine resistance, and discuss how these mutations may inform novel combinations to improve clinical outcomes in the future.

Noninvasive PET Imaging of CDK4/6 Activation in Breast Cancer

The cell cycle is a progression of 4 distinct phases (G1, S, G2, and M), with various cycle proteins being essential in regulating this process. We aimed to develop a radiolabeled cyclin-dependent kinase 4/6 (CDK4/6) inhibitor for breast cancer imaging. Our transfluorinated analog (¹⁸F-CDKi) was evaluated and validated as a novel PET imaging agent to quantify CDK4/6 expression in estrogen receptor (ER)-positive human epidermal growth factor receptor 2 (HER₂)-negative breast cancer. Methods: ¹⁸F-CDKi was synthesized and assayed against CDK4/6 kinases. ¹⁸F-CDKi was prepared with a 2-step automated synthetic strategy that yielded the final product with remarkable purity and molar activity. In vitro and in vivo biologic specificity was assessed in a MCF-7 cell line and in mice bearing MCF-7 breast tumors. Nonradioactive palbociclib was used as a blocking agent to investigate the binding specificity and selectivity of ¹⁸F-CDKi. Results: ¹⁸F-CDKi was obtained with an overall radiochemical uncorrected yield of 15% and radiochemical purity higher than 98%. The total time from the start of synthesis to the final injectable formulated tracer is 70 min. The retention time reported for ¹⁸F-CDKi and ¹⁹F-CDKi is 27.4 min as demonstrated by coinjection with ¹⁹F-CDKi in a high-pressure liquid chromatograph. In vivo blood half-life (weighted, 7.03 min) and octanol/water phase partition coefficient (1.91 ± 0.24) showed a mainly lipophilic behavior. ¹⁸F-CDKi is stable in vitro and in vivo (>98% at 4 h after injection) and maintained its potent targeting affinity to CDK4/6. Cellular uptake experiments performed on the MCF-7 breast cancer cell line (ER-positive and HER₂-negative) demonstrated specific uptake with a maximum intracellular concentration of about 65% as early as 10 min after incubation. The tracer uptake was reduced to less than 5% when cells were coincubated with a molar excess of palbociclib. In vivo imaging and ex vivo biodistribution of ER-positive, HER₂-negative MCF-7 breast cancer models showed a specific uptake of approximately 4% injected dose/g of tumor (reduced to ∼0.3% with a 50-fold excess of cold palbociclib). A comprehensive biodistribution analysis also revealed a significantly lower activation of CDK4/6 in nontargeting organs. Conclusion: ¹⁸F-CDKi represents the first ¹⁸F PET CDK4/6 imaging agent and a promising imaging agent for ER-positive, HER₂-negative breast cancer.

CDK4/6 inhibitors in the treatment of patients with breast cancer: summary of a multidisciplinary round-table discussion

This article is the result of a round-table discussion organised by ESMO Open in Vienna in December 2017. Its purpose is to discuss the background and advances in the evidence regarding cyclin-dependent kinase 4/6 inhibitors (palbociclib, ribociclib and abemaciclib) in the treatment of metastatic and early-stage breast cancer and to explore what the key open research questions are and next steps should be.

Cyclin D1 overexpression induces global transcriptional downregulation in lymphoid neoplasms

Cyclin D1 is an oncogene frequently overexpressed in human cancers that has a dual function as cell cycle and transcriptional regulator, although the latter is widely unexplored. Here, we investigated the transcriptional role of cyclin D1 in lymphoid tumor cells with cyclin D1 oncogenic overexpression. Cyclin D1 showed widespread binding to the promoters of most actively transcribed genes, and the promoter occupancy positively correlated with the transcriptional output of targeted genes. Despite this association, the overexpression of cyclin D1 in lymphoid cells led to a global transcriptional downmodulation that was proportional to cyclin D1 levels. This cyclin D1-dependent global transcriptional downregulation was associated with a reduced nascent transcription and an accumulation of promoter-proximal paused RNA polymerase II (Pol II) that colocalized with cyclin D1. Concordantly, cyclin D1 overexpression promoted an increase in the Poll II pausing index. This transcriptional impairment seems to be mediated by the interaction of cyclin D1 with the transcription machinery. In addition, cyclin D1 overexpression sensitized cells to transcription inhibitors, revealing a synthetic lethality interaction that was also observed in primary mantle cell lymphoma cases. This finding of global transcriptional dysregulation expands the known functions of oncogenic cyclin D1 and suggests the therapeutic potential of targeting the transcriptional machinery in cyclin D1-overexpressing tumors.

NF-κB-driven improvement of EHD1 contributes to erlotinib resistance in EGFR-mutant lung cancers

Acquired resistance to epidermal growth factor receptor-tyrosine-kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib, is a critical obstacle in the treatment of EGFR mutant-positive non-small cell lung cancer (NSCLC). EHD1, a protein of the C-terminal Eps15 homology domain-containing (EHD) family, plays a role in regulating endocytic recycling, but the mechanistic details involved in EGFR-TKI resistance and cancer stemness remain largely unclear. Here, we found that a lower EHD1 expression improved both EGFR-TKIs sensitivity, which is consistent with a lower CD133 expression, and progression-free survival in NSCLC patients. The overexpression of EHD1 markedly increased erlotinib resistance and lung cancer cell stemness in vitro and in vivo. Moreover, we demonstrated that miR-590 targeted the 3′-UTR of EHD1 and was regulated by NK-κB, resulting in downregulated EHD1 expression, increased erlotinib sensitivity and repressed NSCLC cancer stem-like properties in vitro and in vivo. We found that EHD1 was an important factor in EGFR-TKI resistance and the cancer stem-like cell phenotype of lung cancer, and these results suggest that targeting the NF-κB/miR-590/EHD1 pathway has potential therapeutic promise in EGFR-mutant NSCLC patients with acquired EGFR-TKI resistance.

Cyclin D3 deficiency inhibits skin tumor development, but does not affect normal keratinocyte proliferation

Rearrangement and amplification of the D-type cyclin genes have been reported in human cancer. Previous studies have demonstrated that Ras-mediated skin tumorigenesis depends on pathways that act through cyclin D1 and D2; however, the role of cyclin D3 remains unknown. The present study demonstrates that cyclin D3 ablation does not affect keratinocyte proliferation, but instead increases apoptosis levels in the bulge region of the hair follicle. Consequently, cyclin D3 ablation reduces skin papilloma development in a Ras-dependent carcinogenesis model. Previous results revealed that cyclin D3 preferentially binds to cyclin-dependent kinase 6 (CDK6) in mouse keratinocytes and transgenic expression of CDK6 (K5CDK6 mice) inhibits skin tumor development. Thus, we hypothesized that the inhibitory effect of CDK6 is dependent on cyclin D3 expression. To test this hypothesis, a mouse model that overexpresses CDK6 and does not express cyclin D3 (K5CDK6/cyclin D3-/− compound mouse) was developed. Biochemical analysis of the epidermis of K5CDK6/cyclin D3-/− mice revealed that cyclin D3 ablation resulted in increased expression of cyclin D1 protein, with a consequent elevation in the level of CDK6/cyclin D1 and CDK4/cyclin D1 complexes. These findings were concurrent with the increase skin papilloma malignant progression observed in K5CDK6/cyclin D3-/− mice. In summary the absence of cyclin D3 led to fewer number of papillomas in cyclin D3-ablated mice than in the wild-type owing to increased apoptosis, suggesting that alterations in cell survival are a crucial mechanism for crippling cellular defense against neoplasia. The results of the current study also suggest that although cyclin D3 expression does not alter the tumor suppressive role of CDK6 in skin carcinogenesis, the compensatory increase in cyclin D1 can shift the balance towards malignant progression.

AR Signaling in Breast Cancer

Androgen receptor (AR, a member of the steroid hormone receptor family) status has become increasingly important as both a prognostic marker and potential therapeutic target in breast cancer. AR is expressed in up to 90% of estrogen receptor (ER) positive breast cancer, and to a lesser degree, human epidermal growth factor 2 (HER2) amplified tumors. In the former, AR signaling has been correlated with a better prognosis given its inhibitory activity in estrogen dependent disease, though conversely has also been shown to increase resistance to anti-estrogen therapies such as tamoxifen. AR blockade can mitigate this resistance, and thus serves as a potential target in ER-positive breast cancer. In HER2 amplified breast cancer, studies are somewhat conflicting, though most show either no effect or are associated with poorer survival. Much of the available data on AR signaling is in triple-negative breast cancer (TNBC), which is an aggressive disease with inferior outcomes comparative to other breast cancer subtypes. At present, there are no approved targeted therapies in TNBC, making study of the AR signaling pathway compelling. Gene expression profiling studies have also identified a luminal androgen receptor (LAR) subtype that is dependent on AR signaling in TNBC. Regardless, there seems to be an association between AR expression and improved outcomes in TNBC. Despite lower pathologic complete response (pCR) rates with neoadjuvant therapy, patients with AR-expressing TNBC have been shown to have a better prognosis than those that are AR-negative. Clinical studies targeting AR have shown somewhat promising results. In this paper we review the literature on the biology of AR in breast cancer and its prognostic and predictive roles. We also present our thoughts on therapeutic strategies.

CDK4/6 inhibitors for the treatment of advanced hormone receptor positive breast cancer and beyond: 2016 update

INTRODUCTION

Breast cancer remains a major cause of morbidity and mortality worldwide. Given the central role of cyclin-dependent kinases in regulating cell division, there has been a longstanding interest in developing compounds which target the cyclin D1: CDK4/6 axis in breast cancer. The recent discovery of potent and selective CDK4/6 inhibitors (CDK4/6i) was an important breakthrough.

AREAS COVERED

There are three CDK4/6i in clinical development (palbociclib, ribociclib and abemaciclib). Phase II and III studies using palbociclib in combination with endocrine therapy demonstrated remarkable clinical activity in women with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer, resulting in two separate FDA approvals in 2015 and 2016. In this article, we review the preclinical and clinical development of these compounds as well as discussing the role for novel applications of these agents outside the arena of HR-positive, HER2-negative advanced breast cancer.

EXPERT OPINION

In combination with endocrine therapy, CDK4/6i have shown promising efficacy in patients with advanced HR-positive, HER2-negative advanced breast cancer. Numerous trials in a variety of clinical settings and in different tumor types are ongoing or planned.

Targeting CDK4/6 in patients with cancer

The cyclin D-cyclin dependent kinase (CDK) 4/6-inhibitor of CDK4 (INK4)-retinoblastoma (Rb) pathway controls cell cycle progression by regulating the G1-S checkpoint. Dysregulation of the cyclin D-CDK4/6-INK4-Rb pathway results in increased proliferation, and is frequently observed in many types of cancer. Pathway activation can occur through a variety of mechanisms, including gene amplification or rearrangement, loss of negative regulators, epigenetic alterations, and point mutations in key pathway components. Due to the importance of CDK4/6 activity in cancer cells, CDK4/6 inhibitors have emerged as promising candidates for cancer treatment. Moreover, combination of a CDK4/6 inhibitor with other targeted therapies may help overcome acquired or de novo treatment resistance. Ongoing studies include combinations of CDK4/6 inhibitors with endocrine therapy and phosphatidylinositol 3-kinase (PI3K) pathway inhibitors for hormone receptor-positive (HR+) breast cancers, and with selective RAF and MEK inhibitors for tumors with alterations in the mitogen activated protein kinase (MAPK) pathway such as melanoma. In particular, the combination of CDK4/6 inhibitors with endocrine therapy, such as palbociclib's recent first-line approval in combination with letrozole, is expected to transform the treatment of HR+ breast cancer. Currently, three selective CDK4/6 inhibitors have been approved or are in late-stage development: palbociclib (PD-0332991), ribociclib (LEE011), and abemaciclib (LY2835219). Here we describe the current preclinical and clinical data for these novel agents and discuss combination strategies with other agents for the treatment of cancer.

Targeting the cyclin-dependent kinases (CDK) 4/6 in estrogen receptor-positive breast cancers

Despite significant advances in early detection and treatment, breast cancer still remains a major cause of morbidity and mortality for women. Our understanding of the molecular heterogeneity of the disease has significantly expanded over the past decade and the role of cell cycle signaling in both breast cancer oncogenesis and anti-estrogen resistance has gained increasing attention. The mammalian cell cycle is driven by a complex interplay between cyclins and their associated cyclin-dependent kinase (CDK) partners, and dysregulation of this process is one of the hallmarks of cancer. Despite this, initial results with broadly acting CDK inhibitors were largely disappointing. However, recent preclinical and phase I/II clinical studies using a novel, oral, reversible CDK4/6 inhibitor, palbociclib (PD-0332991), have validated the role of CDK4/6 as a potential target in estrogen receptor-positive (ER+) breast cancers. This review highlights our current understanding of CDK signaling in both normal and malignant breast tissues, with special attention placed on recent clinical advances in inhibition of CDK4/6 in ER+ disease.

Knockdown of TMEM16A suppressed MAPK and inhibited cell proliferation and migration in hepatocellular carcinoma

TMEM16A plays an important role in cell proliferation in various cancers. However, less was known about the expression and role of TMEM16A in hepatocellular carcinoma. We screened the expression of TMEM16A in patients' hepatocellular carcinoma tissues, and also analyzed the biological function of hepatocellular carcinoma cells by knockdown of TMEM16A, as well as the expression of MAPK signaling proteins, including p38, p-p38, ERK1/2, p-ERK1/2, JNK, and p-JNK, and cell cycle regulatory protein cyclin D1 in TMEM16A siRNA-transfected SMMC-7721 cells by Western blot. Our results showed that TMEM16A was overexpressed in hepatocellular carcinoma tissues. Inhibition of TMEM16A suppressed the cell proliferation, migration, and invasion, and cell cycle progression but did not influence the cell apoptosis. TMEM16A siRNA-suppressed cancer cell proliferation and tumor growth were accompanied by a reduction of p38 and ERK1/2 activation and cyclin D1 induction, and were not influenced by other tested MAPK signaling proteins. In addition, inhibition of TMEM16A suppressed tumorigenicity in vivo. TMEM16A is overexpressed in hepatocellular carcinoma, and that inhibition of TMEM16A suppressed MAPK and growth of hepatocellular carcinoma. TMEM16A could be a potentially novel therapeutic target for human cancers, including hepatocellular carcinoma.

No difference in CCND1 gene expression between breast cancer patients with and without lymph node metastasis in a Southern Brazilian sample

The Cyclin D1 protein has been extensively studied over the last decades, for its various roles in physiological processes, both in normal and cancer cells. Gene amplifications and overexpression of CCND1 are frequently reported in several types of cancers, including breast carcinomas, showing the increasing relevance of Cyclin D1 in tumorigenesis. Little is known about the role of this protein in the metastatic process, and the main objective of this study was to evaluate the importance of the CCND1 as a potential marker of tumor progression in breast carcinomas, in a sample collected in Southern Brazil. We studied 41 samples of formalin-fixed paraffin-embedded tissue sections from invasive ductal breast carcinomas subdivided into metastatic (n = 19) and non-metastatic (n = 22) tumors. Gene expression analysis was performed through Quantitative Real-Time PCR and immunohistochemistry. In spite of the higher expression levels of CCND1 mRNA and protein in tumors when compared with the control samples, no differences were observed between the metastatic and non-metastatic groups, suggesting that, in these samples, the expression of CCND1 has no significant influence on the metastatic process. Further studies must be performed in an attempt to clarify the diagnostic and prognostic value of Cyclin D1 in breast cancers, as well as the mechanisms that trigger its overexpression in tumors.

Increased Expression of Eps15 Homology Domain 1 is Associated with Poor Prognosis in Resected Small Cell Lung Cancer

One of the great challenges of small cell lung cancer (SCLC) treatment is identifying patients at high risk for recurrence after surgical resection and chemotherapy. We examined Eps15 homology domain 1 (EHD1) protein expression in paraffin sections of 85 resected SCLC tissues, metastatic lymph nodes and normal bronchial epithelial tissues using immunohistochemistry to study the correlation between EHD1 expression and patient clinicopathological features. Within these variables, disease free survival (DFS) analyzed by the log-rank test was constructed using the multivariate Cox proportional hazards regression model and Kaplan-Meier analysis. Immunohistochemistry results showed that EHD1 protein was significantly increased in SCLC tissues compared with normal tissues (P < 0.001). Moreover, EHD1 expression was positively correlated with tumor size (P = 0.019). Multivariate Cox proportional hazards model analysis showed that EHD1 expression (P = 0.047; HR, 1.869; 95% CI, 1.008-3.466) and American Joint Committee on Cancer (AJCC) status (P < 0.001; HR, 1.412; 95% CI, 1.165-1.711) were independent prognostic indicators of DFS. In conclusion, these data demonstrated a remarkable correlation between the cytoplasmic expression of EHD1 protein and adverse prognosis in patients receiving early-stage cisplatin treatment for resected SCLC.

Resibufogenin Induces G1-Phase Arrest through the Proteasomal Degradation of Cyclin D1 in Human Malignant Tumor Cells

Huachansu, a traditional Chinese medicine prepared from the dried toad skin, has been used in clinical studies for various cancers in China. Resibufogenin is a component of huachansu and classified as bufadienolides. Resibufogenin has been shown to exhibit the anti-proliferative effect against cancer cells. However, the molecular mechanism of resibufogenin remains unknown. Here we report that resibufogenin induces G1-phase arrest with hypophosphorylation of retinoblastoma (RB) protein and down-regulation of cyclin D1 expression in human colon cancer HT-29 cells. Since the down-regulation of cyclin D1 was completely blocked by a proteasome inhibitor MG132, the suppression of cyclin D1 expression by resibufogenin was considered to be in a proteasome-dependent manner. It is known that glycogen synthase kinase-3β (GSK-3β) induces the proteasomal degradation of cyclin D1. The addition of GSK-3β inhibitor SB216763 inhibited the reduction of cyclin D1 caused by resibufogenin. These effects on cyclin D1 by resibufogenin were also observed in human lung cancer A549 cells. These findings suggest that the anti-proliferative effect of resibufogenin may be attributed to the degradation of cyclin D1 caused by the activation of GSK-3β.

Palbociclib for the Treatment of Estrogen Receptor-Positive, HER2-Negative Metastatic Breast Cancer

Palbociclib is a selective inhibitor of cyclin-dependent kinases 4 and 6 that acts by reducing phosphorylation of the tumor suppressor gene retinoblastoma. When added to the aromatase inhibitor letrozole in a randomized phase II trial for first-line therapy of estrogen receptor-positive, HER2-negative metastatic breast cancer, palbociclib significantly increased progression-free survival compared with letrozole alone [palbociclib + letrozole: 20.2 months; 95% confidence interval (CI), 13.8-27.5; letrozole: 10.2 months; 95% CI, 5.7-12.6; HR, 0.49; 95% CI, 0.32-0.75; P = 0.0004]. On the basis of these results, the drug was recently granted accelerated approval by the FDA, and confirmatory studies are ongoing. Because this drug has a rational target in an oncologic pathway, concurrent biomarker development is of interest. In breast cancer, the most useful predictive biomarkers identified thus far are estrogen receptor and HER2 receptor status, although additional studies are ongoing. In this article, we review the development of palbociclib and its use in treatment of hormone receptor-positive metastatic breast cancer in the context of other FDA-approved agents in this setting.

Ano1/TMEM16A Overexpression Is Associated with Good Prognosis in PR-Positive or HER2-Negative Breast Cancer Patients following Tamoxifen Treatment

The calcium-activated chloride channel Ano1 (TMEM16A) is overexpressed in many tumors. Although Ano1 overexpression is found in breast cancer due to 11q13 amplification, it remains unclear whether signaling pathways are involved in Ano1 overexpression during breast cancer tumorigenesis in vivo. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) have been known to contribute to breast cancer progression. It is unclear whether Ano1 is associated with clinical outcomes in breast cancer patients with different ER, PR and HER2 status. In the present study, we investigated the Ano1 expression in 431 patients with invasive ductal breast carcinoma and 46 patients with fibroadenoma, using immunohistochemistry, and analyzed the association between Ano1 expression and clinical characteristics and outcomes of breast cancer patients with different ER, PR, and HER2 status. Ano1 was overexpressed in breast cancer compared with fibroadenoma. Ano1 was significantly more associated with breast cancer with the lower clinical stage (stage I or II), or triple-negative status. Mostly importantly, Ano1 overexpression was associated with good prognosis in patients with the PR-positive or HER2-negative status, and in patients following tamoxifen treatment. Multivariate Cox regression analysis showed that Ano1 overexpression was a prognostic factor for longer overall survival in PR-positive or HER2-negative patients, and a predictive factor for longer overall survival in patients following tamoxifen treatment. Our findings suggest that Ano1 may be a potential marker for good prognosis in PR-positive or HER2-negative patients following tamoxifen treatment. The PR and HER2 status defines a subtype of breast cancer in which Ano1 overexpression is associated with good prognosis following tamoxifen treatment.

CDK 4/6 inhibitor palbociclib (PD0332991) in Rb+ advanced breast cancer: phase II activity, safety, and predictive biomarker assessment

PURPOSE

The G1-S checkpoint of the cell cycle is frequently dysregulated in breast cancer. Palbociclib (PD0332991) is an oral inhibitor of CDK4/6. Based upon preclinical/phase I activity, we performed a phase II, single-arm trial of palbociclib in advanced breast cancer.

EXPERIMENTAL DESIGN

Eligible patients had histologically confirmed, metastatic breast cancer positive for retinoblastoma (Rb) protein and measureable disease. Palbociclib was given at 125 mg orally on days 1 to 21 of a 28-day cycle. Primary objectives were tumor response and tolerability. Secondary objectives included progression-free survival (PFS) and assessment of Rb expression/localization, KI-67, p16 loss, and CCND1 amplification.

RESULTS

Thirty-seven patients were enrolled; 84% hormone-receptor (HR)(+)/Her2(-), 5% HR(+)/Her2(+), and 11% HR(-)/Her2(-), with a median of 2 prior cytotoxic regimens. Two patients had partial response (PR) and 5 had stable disease ≥ 6 months for a clinical benefit rate (CBR = PR + 6moSD) of 19% overall, 21% in HR(+), and 29% in HR(+)/Her2(-) who had progressed through ≥2 prior lines of hormonal therapy. Median PFS overall was 3.7 months [95% confidence interval (CI), 1.9-5.1], but significantly longer for those with HR(+) versus HR(-) disease (P = 0.03) and those who had previously progressed through endocrine therapy for advanced disease (P = 0.02). Grade 3/4 toxicities included neutropenia (51%), anemia (5%), and thrombocytopenia (22%). Twenty-four percent had treatment interruption and 51% had dose reduction, all for cytopenias. No biomarker identified a sensitive tumor population.

CONCLUSIONS

Single-agent palbociclib is well tolerated and active in patients with endocrine-resistant, HR(+), Rb-positive breast cancer. Cytopenias were uncomplicated and easily managed with dose reduction.

GSK-3 as potential target for therapeutic intervention in cancer

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) was initially identified and studied in the regulation of glycogen synthesis. GSK-3 functions in a wide range of cellular processes. Aberrant activity of GSK-3 has been implicated in many human pathologies including: bipolar depression, Alzheimer's disease, Parkinson's disease, cancer, non-insulin-dependent diabetes mellitus (NIDDM) and others. In some cases, suppression of GSK-3 activity by phosphorylation by Akt and other kinases has been associated with cancer progression. In these cases, GSK-3 has tumor suppressor functions. In other cases, GSK-3 has been associated with tumor progression by stabilizing components of the beta-catenin complex. In these situations, GSK-3 has oncogenic properties. While many inhibitors to GSK-3 have been developed, their use remains controversial because of the ambiguous role of GSK-3 in cancer development. In this review, we will focus on the diverse roles that GSK-3 plays in various human cancers, in particular in solid tumors. Recently, GSK-3 has also been implicated in the generation of cancer stem cells in various cell types. We will also discuss how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTORC1, Ras/Raf/MEK/ERK, Wnt/beta-catenin, Hedgehog, Notch and others.

Current status of hormone therapy in patients with hormone receptor positive (HR+) advanced breast cancer

The natural history of HR+ breast cancer tends to be different from hormone receptor-negative disease in terms of time to recurrence, site of recurrence and overall aggressiveness of the disease. The developmental strategies of hormone therapy for the treatment of breast cancer have led to the classes of selective estrogen receptor modulators, selective estrogen receptor downregulators, and aromatase inhibitors. These therapeutic options have improved breast cancer outcomes in the metastatic setting, thereby delaying the need for chemotherapy. However, a subset of hormone receptor-positive breast cancers do not benefit from endocrine therapy (intrinsic resistance), and all HR+ metastatic breast cancers ultimately develop resistance to hormonal therapies (acquired resistance). Considering the multiple pathways involved in the HR network, targeting other components of pathologically activated intracellular signaling in breast cancer may prove to be a new direction in clinical research. This review focuses on current and emerging treatments for HR+ metastatic breast cancer.

Update on adjuvant chemotherapy for early breast cancer

Breast cancer is the second most common cancer in women worldwide. Although most women are diagnosed with early breast cancer, a substantial number recur due to persistent micro-metastatic disease. Systemic adjuvant chemotherapy improves outcomes and has advanced from first-generation regimens to modern dose-dense combinations. Although chemotherapy is the cornerstone of adjuvant therapy, new biomarkers are identifying patients who can forego such treatment. Neo-adjuvant therapy is a promising platform for drug development, but investigators should recognize the limitations of surrogate endpoints and clinical trials. Previous decades have focused on discovering, developing, and intensifying adjuvant chemotherapy. Future efforts should focus on customizing therapy and reducing chemotherapy for patients unlikely to benefit. In some cases, it may be possible to replace chemotherapy with treatments directed at specific genetic or molecular breast cancer subtypes. Yet, we anticipate that chemotherapy will remain a critical component of adjuvant therapy for years to come.

Breast cancer: current and future endocrine therapies

Endocrine therapy forms a central modality in the treatment of estrogen receptor positive breast cancer. The routine use of 5 years of adjuvant tamoxifen has improved survival rates for early breast cancer, and more recently has evolved in the postmenopausal setting to include aromatase inhibitors. The optimal duration of adjuvant endocrine therapy remains an active area of clinical study with recent data supporting 10 years rather than 5 years of adjuvant tamoxifen. However, endocrine therapy is limited by the development of resistance, this can occur by a number of possible mechanisms and numerous studies have been performed which combine endocrine therapy with agents that modulate these mechanisms with the aim of preventing or delaying the emergence of resistance. Recent trial data regarding the combination of the mammalian target of rapamycin (mTOR) inhibitor, everolimus with endocrine therapy have resulted in a redefinition of the clinical treatment pathway in the metastatic setting. This review details the current endocrine therapy utilized in both early and advanced disease, as well as exploring potential new targets which modulate pathways of resistance, as well as agents which aim to modulate adrenal derived steroidogenic hormones.

Overview of cyclins D1 function in cancer and the CDK inhibitor landscape: past and present

INTRODUCTION

Intensive efforts, over the last decade, have been made to inhibit the kinase activity of cyclins that act as mediators during cell-cycle progression. Activation of the cyclin D1 oncogene, often by amplification or rearrangement, is a major driver of multiple types of human tumors including breast and squamous cell cancers, B-cell lymphoma, myeloma and parathyroid adenoma.

AREAS COVERED

In this review, the authors summarize the activity of cyclins and cyclin-dependent kinases in cell-cycle progression and transcription. They focus on cyclin D1/CDK4/CDK6, a central mediator in the transition from G1 to S phase. Furthermore, the authors discuss the first generation of pan-cyclin-dependent kinase inhibitors that failed to meet expectation and discuss, in detail, the second generation of highly specific cyclin D1/CDK4/CDK6 inhibitors that are proving to be more efficacious.

EXPERT OPINION

The mechanism by which cyclin D1 drives tumorigenesis may be dependent on kinase and kinase-independent functions. Further evidence is necessary to delineate the roles of cyclin D1 in early pre-neoplastic lesions where its overexpression may promote genomic instability in a kinase-independent manner.

Palbociclib (PD 0332991) : targeting the cell cycle machinery in breast cancer

INTRODUCTION

The cyclin D-cyclin-dependent kinases 4 and 6 (CDK4/6)-retinoblastoma (Rb) pathway, governing the cell cycle restriction point, is frequently altered in breast cancer and is a potentially relevant target for anticancer therapy. Palbociclib (PD 0332991) , a potent and selective inhibitor of CDK4 and CDK6, inhibits proliferation of several Rb-positive cancer cell lines and xenograft models.

AREAS COVERED

The basic features and abnormalities of the cell cycle in breast cancer are described, along with their involvement in estrogen signaling and endocrine resistance. The pharmacological features of palbociclib, its activity in preclinical models of breast cancer and the potential determinants of response are then illustrated, and its clinical development in breast cancer described. A literature search on the topic was conducted through PubMed and the proceedings of the main cancer congresses of recent years.

EXPERT OPINION

The combination of palbociclib with endocrine agents is a very promising treatment and Phase III clinical trials are ongoing to confirm its efficacy. Further, potentially useful combinations are those with drugs targeting mitogenic signaling pathways, such as HER2- and PI3K-inhibitors. Combination with chemotherapy seems more problematic, as antagonism has been reported in preclinical models. The identification of predictive factors, already explored in preclinical studies, must be further refined and validated in clinical trials.

CDK4: A Key Player in the Cell Cycle, Development, and Cancer

The cell cycle is regulated in part by cyclins and their associated serine/threonine cyclin-dependent kinases, or CDKs. CDK4, in conjunction with the D-type cyclins, mediates progression through the G1 phase when the cell prepares to initiate DNA synthesis. Although CDK4-null mutant mice are viable and cell proliferation is not significantly affected in vitro due to compensatory roles played by other CDKs, this gene plays a key role in mammalian development and cancer. This review discusses the role that CDK4 plays in cell cycle control, normal development, and tumorigenesis as well as how small molecule inhibitors of CDK4 can be used to treat disease.

Up-regulation of CacyBP/SIP during rat breast cancer development

Background

CacyBP/SIP (calcyclin binding protein/Siah-1 interacting protein) was originally discovered in Ehrlich ascities tumor cells but was later found also in many different tumors.

Methods

To better understand the function of CacyBP/SIP in carcinogenesis, we used immunohistochemistry, Western blotting, and RT-PCR assays to study the distribution and level of CacyBP/SIP in mammary tissues after tumor induction in rat with DMBA [(dimethylbenz[a]anthracene)]. Application of such a model allowed us to monitor changes in CacyBP/SIP level during development of breast cancer.

Results

We found that both the protein and mRNA levels of CacyBP/SIP gradually increased in pathologically changed tissues and were highest in tumors taken 8 weeks after DMBA treatment. Similar changes as for CacyBP/SIP were detected in the level of β-catenin.

Conclusion

Increase in CacyBP/SIP expression during development of breast cancer, observed early in the mammary tissues with only minimal pathological changes, might suggest an important role of this protein in the process of carcinogenesis.

Differential control of growth, apoptotic activity, and gene expression in human breast cancer cells by extracts derived from medicinal herbs Zingiber officinale

The present study aimed to examine the antiproliferative potentiality of an extract derived from the medicinal plant ginger (Zingiber officinale) on growth of breast cancer cells. Ginger treatment suppressed the proliferation and colony formation in breast cancer cell lines, MCF-7 and MDA-MB-231. Meanwhile, it did not significantly affect viability of nontumorigenic normal mammary epithelial cell line (MCF-10A). Treatment of MCF-7 and MDA-MB-231 with ginger resulted in sequences of events marked by apoptosis, accompanied by loss of cell viability, chromatin condensation, DNA fragmentation, activation of caspase 3, and cleavage of poly(ADP-ribose) polymerase. At the molecular level, the apoptotic cell death mediated by ginger could be attributed in part to upregulation of Bax and downregulation of Bcl-2 proteins. Ginger treatment downregulated expression of prosurvival genes, such as NF-κB, Bcl-X, Mcl-1, and Survivin, and cell cycle-regulating proteins, including cyclin D1 and cyclin-dependent kinase-4 (CDK-4). On the other hand, it increased expression of CDK inhibitor, p21. It also inhibited the expression of the two prominent molecular targets of cancer, c-Myc and the human telomerase reverse transcriptase (hTERT). These findings suggested that the ginger may be a promising candidate for the treatment of breast carcinomas.

11q13 is a susceptibility locus for hormone receptor positive breast cancer

A recent two-stage genome-wide association study (GWAS) identified five novel breast cancer susceptibility loci on chromosomes 9, 10, and 11. To provide more reliable estimates of the relative risk associated with these loci and investigate possible heterogeneity by subtype of breast cancer, we genotyped the variants rs2380205, rs1011970, rs704010, rs614367, and rs10995190 in 39 studies from the Breast Cancer Association Consortium (BCAC), involving 49,608 cases and 48,772 controls of predominantly European ancestry. Four of the variants showed clear evidence of association (P ≤ 3 × 10(-9) ) and weak evidence was observed for rs2380205 (P = 0.06). The strongest evidence was obtained for rs614367, located on 11q13 (per-allele odds ratio 1.21, P = 4 × 10(-39) ). The association for rs614367 was specific to estrogen receptor (ER)-positive disease and strongest for ER plus progesterone receptor (PR)-positive breast cancer, whereas the associations for the other three loci did not differ by tumor subtype.

MUC1-C oncoprotein as a target in breast cancer: activation of signaling pathways and therapeutic approaches

Mucin 1 (MUC1) is a heterodimeric protein formed by two subunits that is aberrantly overexpressed in human breast cancer and other cancers. Historically, much of the early work on MUC1 focused on the shed mucin subunit. However, more recent studies have been directed at the transmembrane MUC1-C-terminal subunit (MUC1-C) that functions as an oncoprotein. MUC1-C interacts with EGFR (epidermal growth factor receptor), ErbB2 and other receptor tyrosine kinases at the cell membrane and contributes to activation of the PI3KAKT and mitogen-activated protein kinase kinase (MEK)extracellular signal-regulated kinase (ERK) pathways. MUC1-C also localizes to the nucleus where it activates the Wnt/β-catenin, signal transducer and activator of transcription (STAT) and NF (nuclear factor)-κB RelA pathways. These findings and the demonstration that MUC1-C is a druggable target have provided the experimental basis for designing agents that block MUC1-C function. Notably, inhibitors of the MUC1-C subunit have been developed that directly block its oncogenic function and induce death of breast cancer cells in vitro and in xenograft models. On the basis of these findings, a first-in-class MUC1-C inhibitor has entered phase I evaluation as a potential agent for the treatment of patients with breast cancers who express this oncoprotein.

Effects of cyclin D1 gene amplification and protein expression on time to recurrence in postmenopausal breast cancer patients treated with anastrozole or tamoxifen: a TransATAC study

INTRODUCTION

Gene amplification of CCND1 is observed in a subgroup of breast cancers with poor prognosis, whereas overexpression of the protein cyclin D1 has been linked to both worse and better clinical outcome. CCND1 amplification and protein overexpression have also been associated with resistance to treatment with tamoxifen or even to a potentially detrimental effect of tamoxifen.

METHODS

To clarify these challenging and partly contrasting treatment predictive and prognostic links for cyclin D1 we analysed a large cohort of postmenopausal breast cancer patients randomised to receive either adjuvant anastrozole or tamoxifen, as part of the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial. The CCND1 amplification status and protein expression of cyclin D1 were assessed by chromogenic in situ hybridisation and immunohistochemistry, respectively, in 1,155 postmenopausal, oestrogen-receptor-positive breast cancer patients included in the TransATAC substudy.

RESULTS

Amplification of CCND1 was observed in 8.7% of the tumours and was associated with increased risk of disease recurrence (hazard ratio = 1.61; 95% confidence interval, 1.08 to 2.41) after adjustment for other clinicopathological parameters. In contrast, nuclear expression of cyclin D1 protein was associated with decreased recurrence rate (hazard ratio = 0.6; 95% confidence interval, 0.39 to 0.92). The intensity of nuclear or cytoplasmic expression was not of prognostic value. There was no significant interaction between cyclin D1 status and treatment efficacy, ruling out any major detrimental effect of tamoxifen in CCND1-amplified postmenopausal breast cancer.

CONCLUSIONS

In summary, CCND1 amplification and low nuclear expression of cyclin D1 predicted poor clinical outcome in postmenopausal breast cancer patients treated with either anastrozole or tamoxifen.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN18233230.