Synergistic inhibition of ErbB signaling by combined treatment with seliciclib and ErbB-targeting agents

Collateral-resistance to estrogen and HER-activated growth is associated with modified AKT, ERα, and cell-cycle signaling in a breast cancer model

Aim:

A model of progressively endocrine-resistant breast cancer was investigated to identify changes that can occur in signaling pathways after endocrine manipulation.

Methods:

The MCF7 breast cancer model is sensitive to estrogens and anti-estrogens while variant lines previously derived from wild-type MCF7 are either relatively 17β-estradiol (E₂ )-insensitive (LCC1) or fully resistant to estrogen and anti-estrogens (LCC9).

Results:

In LCC1 and LCC9 cell lines, loss of estrogen sensitivity was accompanied by loss of growth response to transforming growth factor alpha (TGFα), heregulin-beta and pertuzumab. LCC1 and LCC9 cells had enhanced AKT phosphorylation relative to MCF7 which was reflected in downstream activation of phospho-mechanistic target of rapamycin (mTOR), phospho-S6, and phospho-estrogen receptor alpha Ser167 [ERα(Ser167)]. Both AKT2 and AKT3 were phosphorylated in the resistant cell lines, but small interfering RNA (siRNA) knockdown suggested that all three AKT isoforms contributed to growth response. ERα(Ser118) phosphorylation was increased by E₂ and TGFα in MCF7, by E₂ only in LCC1, but by neither in LCC9 cells. Multiple alterations in E₂-mediated cell cycle control were identified in the endocrine-resistant cell lines including increased expression of MYC, cyclin A1, cyclin D1, cyclin-dependent kinase 1 (CDK1), CDK2, and hyperphosphorylated retinoblastoma protein (ppRb), whereas p21 and p27 were reduced. Estrogen modulated expression of these regulators in MCF7 and LCC1 cells but not in LCC9 cells. Seliciclib inhibited CDK2 activation in MCF7 cells but not in resistant variants; in all lines, it reduced ppRb, increased p53 associated responses including p21, p53 up-regulated modulator of apoptosis (PUMA), and p53 apoptosis-inducing protein 1 (p53AIP1), inhibited growth, and produced G2/M block and apoptosis.

Conclusions:

Multiple changes occur with progression of endocrine resistance in this model with AKT activation contributing to E₂ insensitivity and loss of ERα(Ser118) phosphorylation being associated with full resistance. Cell cycle regulation is modified in endocrine-resistant breast cancer cells, and seliciclib is effective in both endocrine-sensitive and resistant diseases.

Targeting apoptosis in cancer therapy

For over three decades, a mainstay and goal of clinical oncology has been the development of therapies promoting the effective elimination of cancer cells by apoptosis. This programmed cell death process is mediated by several signalling pathways (referred to as intrinsic and extrinsic) triggered by multiple factors, including cellular stress, DNA damage and immune surveillance. The interaction of apoptosis pathways with other signalling mechanisms can also affect cell death. The clinical translation of effective pro-apoptotic agents involves drug discovery studies (addressing the bioavailability, stability, tumour penetration, toxicity profile in non-malignant tissues, drug interactions and off-target effects) as well as an understanding of tumour biology (including heterogeneity and evolution of resistant clones). While tumour cell death can result in response to therapy, the selection, growth and dissemination of resistant cells can ultimately be fatal. In this Review, we present the main apoptosis pathways and other signalling pathways that interact with them, and discuss actionable molecular targets, therapeutic agents in clinical translation and known mechanisms of resistance to these agents.

Medical Treatment of Cushing's Disease: An Overview of the Current and Recent Clinical Trials

Cushing's disease (CD) is a serious endocrine disorder characterized by chronic hypercortisolism, or Cushing's syndrome (CS), caused by a corticotroph pituitary tumor, which induces an excessive adrenocorticotropic hormone (ACTH) and consequently cortisol secretion. CD presents a severe clinical burden, with impairment of the quality of life and increase in mortality. Pituitary surgery represents the first-line therapy, but it is non-curative in one third of patients, requiring additional treatments. Among second-line treatments, medical therapy is gradually gaining importance, although the current medical treatments are unable to reach optimal efficacy and safety profile. Therefore, new drugs and new formulations of presently available drugs are currently under clinical investigation in international clinical trials, in order to assess their efficacy and safety in CD, or in the general population of CS. Among pituitary-directed agents, pasireotide, in the twice-daily subcutaneous formulation, has been demonstrated to be an effective treatment both in clinical trials and in real-world studies, and extension studies of the phase II and III clinical trials reported evidence of long-term efficacy with general good safety profile, although associated with frequent hyperglycemia, which requires monitoring of glucose metabolism. Moreover, the most recent once-monthly intramuscular formulation, pasireotide long-acting release (LAR), showed similar efficacy and safety, but associated with potential better compliance profile in CD. Roscovitine is an experimental drug currently under investigation. Among adrenal-directed agents, metyrapone is the only historical agent currently under investigation in a prospective, multicenter, international clinical trial, that would likely clarify its efficacy and safety in a large population of patients with CS. Osilodrostat, a novel agent with a mechanism of action similar to metyrapone, seems to offer a rapid, sustained, and effective disease control of CD, according to recently completed clinical trials, whereas levoketoconazole, a different chemical formulation of the historical agent ketoconazole, is still under investigation in clinical trials, with preliminary evidences showing an effective and safe control of CS. ATR-101 is an experimental drug currently under investigation. Among glucocorticoid receptor-directed drugs, mifepristone has been demonstrated to improve clinical syndrome and comorbidities, especially hypertension and impairment of glucose metabolism, but the occurrence of hypokalemia and in women uterine disorders, due to the concomitant action on progestin receptor, requires caution, whereas the preliminary evidence on relacorilant, characterized by high selectivity for glucocorticoid receptor, suggested good efficacy in the control of hypertension and impairment of glucose metabolism, as well as a good safety profile, in CS. Finally, a limited experience has demonstrated that combination therapy might be an interesting approach in the management of CD. The current review provides a summary of the available evidences from current and recent clinical trials on CD, with a specific focus on preliminary data.

New Cell Cycle Inhibitors Target Aneuploidy in Cancer Therapy

Aneuploidy is a hallmark of cancer. Defects in chromosome segregation result in aneuploidy. Multiple pathways are engaged in this process, including errors in kinetochore-microtubule attachments, supernumerary centrosomes, spindle assembly checkpoint (SAC) defects, and chromosome cohesion defects. Although aneuploidy provides an adaptation and proliferative advantage in affected cells, excessive aneuploidy beyond a critical level can be lethal to cancer cells. Given this, enhanced chromosome missegregation is hypothesized to limit survival of aneuploid cancer cells, especially when compared to diploid cells. Based on this concept, proteins and pathways engaged in chromosome segregation are being exploited as candidate therapeutic targets for aneuploid cancers. Agents that induce chromosome missegregation and aneuploidy now exist, including SAC inhibitors, those that alter centrosome fidelity and others that are under active study in preclinical and clinical contexts. This review explores the therapeutic potentials of such new agents, including the benefits of combining them with other antineoplastic agents.

Engaging Anaphase Catastrophe Mechanisms to Eradicate Aneuploid Cancers

Cancer cells often have supernumerary centrosomes that promote genomic instability, a pathognomonic feature of cancer. During mitosis, cancer cells with supernumerary centrosomes undergo bipolar cell division by clustering centrosomes into two poles. When supernumerary centrosome clustering is antagonized, cancer cells are forced to undergo multipolar division leading to death of daughter cells. This proapoptotic pathway, called anaphase catastrophe, preferentially eliminates aneuploid cancer cells and malignant tumors in engineered mouse models. Anaphase catastrophe occurs through the loss or inhibition of the centrosomal protein CP110, a direct cyclin-dependent kinase 1 (CDK1) and CDK2 target. Intriguingly, CP110 is repressed by the KRAS oncoprotein. This sensitizes KRAS-driven lung cancers (an unmet medical need) to respond to CDK2 inhibitors. Anaphase catastrophe-inducing agents like CDK1 and CDK2 antagonists are lethal to cancer cells with supernumerary centrosomes, but can relatively spare normal cells with two centrosomes. This mechanism is proposed to provide a therapeutic window in the cancer clinic following treatment with a CDK1 or CDK2 inhibitor. Taken together, anaphase catastrophe is a clinically tractable mechanism that promotes death of neoplastic tumors with aneuploidy, a hallmark of cancer. Mol Cancer Ther; 17(4); 724-31. ©2018 AACR.

Roscovitine in cancer and other diseases

Roscovitine [CY-202, (R)-Roscovitine, Seliciclib] is a small molecule that inhibits cyclin-dependent kinases (CDKs) through direct competition at the ATP-binding site. It is a broad-range purine inhibitor, which inhibits CDK1, CDK2, CDK5 and CDK7, but is a poor inhibitor for CDK4 and CDK6. Roscovitine is widely used as a biological tool in cell cycle, cancer, apoptosis and neurobiology studies. Moreover, it is currently evaluated as a potential drug to treat cancers, neurodegenerative diseases, inflammation, viral infections, polycystic kidney disease and glomerulonephritis. This review focuses on the use of roscovitine in the disease model as well as clinical model research.

Immunohistochemical expression of cyclin D1 is higher in supratentorial ependymomas and predicts relapses in gross total resection cases

Ependymomas are tumors of the CNS. Although cyclin D1 overexpression has been related to several cancers, its prognostic value in ependymomas has not yet been fully established. We evaluated cyclin D1 expression by an immunohistochemistry analysis of 149 samples of ependymomas, including some relapses, corresponding to 121 patients. Eighty-one patients were adults, 60 were intracranial cases and 92 tumors were grade II. Gross total resection (GTR) was achieved in 62% of cases, and relapse was confirmed in 41.4% of cases. Cyclin D1 protein expression was analyzed by immunohistochemistry and scored with a labeling index (LI) calculated as the percentage of positively stained cells by intensity. We also analyzed expression of CCND1 and NOTCH1 in 33 samples of ependymoma by quantitative real-time PCR. A correlation between cyclin D1 LI score and anaplastic cases (P < 0.001), supratentorial location (P < 0.001) and age (P = 0.001) were observed. A stratified analysis demonstrated that cyclin D1 protein expression was strong in tumors with a supratentorial location, independent of the histological grade or age. Relapse was more frequent in cases with a higher cyclin D1 LI score (P = 0.046), and correlation with progression-free survival was observed in cases with GTR (P = 0.002). Only spinal canal tumor location and GTR were suggestive markers of PFS in multivarite analyses. Higher expression levels were observed in anaplastic cases for CCND1 (P = 0.002), in supratentorial cases for CCND1 (P = 0.008) and NOTCH1 (P = 0.011). There were correlations between the cyclin D1 mRNA and protein expression levels (P < 0.0001) and between CCND1 and NOTCH1 expression levels (P = 0.003). Higher cyclin D1 LI was predominant in supratentorial location and predict relapse in GTR cases. Cyclin D1 could be used as an immunohistochemical marker to guide follow-up and treatment in these cases.

Discovery and development of Seliciclib. How systems biology approaches can lead to better drug performance

Seliciclib (R-Roscovitine) was identified as an inhibitor of CDKs and has undergone drug development and clinical testing as an anticancer agent. In this review, the authors describe the discovery of Seliciclib and give a brief summary of the biology of the CDKs Seliciclib inhibits. An overview of the published in vitro and in vivo work supporting the development as an anti-cancer agent, from in vitro experiments to animal model studies ending with a summary of the clinical trial results and trials underway is presented. In addition some potential non-oncology applications are explored and the potential mode of action of Seliciclib in these areas is described. Finally the authors argue that optimisation of the therapeutic effects of kinase inhibitors such as Seliciclib could be enhanced using a systems biology approach involving mathematical modelling of the molecular pathways regulating cell growth and division.

Cell cycle inhibitors for the treatment of NSCLC

INTRODUCTION

Lung cancer remains to be the leading cause of cancer-related death worldwide. Treatment of lung cancer still poses a significant challenge. Cell cycle is a tightly integrated process and is frequently aberrant in lung cancer. Cell cycle inhibitors have emerged as novel therapeutics, in anticipation of overcoming the unrestricted cell division and growth in lung cancer.

AREAS COVERED

In this article, we first address the potential roles of cell cycle proteins and cell cycle deregulation in the development of lung cancer. The review then provides an overview for several major categories of cell cycle inhibitors with particular attention to their tolerability and disease control in early phases of lung cancer trials.

EXPERT OPINION

Targeted agents against different components of cell cycle regulation, such as cyclin-dependent kinase, polo-like kinase, checkpoint kinase and aurora kinase, are currently in clinical development for lung cancer management. Their clinical benefits remain to be defined. When evaluated as single agents in lung cancer, cell cycle inhibitors are often associated with limited clinical activity and tolerable toxicities. The key challenges in the drug development are to understand resistance mechanisms and to identify predictive biomarkers that can potentially guide patient selection and optimize the utility of these targeted inhibitors.

Anti-epidermal growth factor receptor therapy in head and neck squamous cell carcinoma: focus on potential molecular mechanisms of drug resistance

Targeted therapy against the epidermal growth factor receptor (EGFR) is one of the most promising molecular therapeutics for head and neck squamous cell carcinoma (HNSCC). EGFR is overexpressed in a wide range of malignancies, including HNSCC, and initiates important signal transduction pathways in HNSCC carcinogenesis. However, primary and acquired resistance are serious problems and are responsible for low single-agent response rate and tumor recurrence. Therefore, an improved understanding of the molecular mechanisms of resistance to EGFR inhibitors may provide valuable indications to identify biomarkers that can be used clinically to predict response to EGFR blockade and to establish new treatment options to overcome resistance. To date, no predictive biomarker for HNSCC is available in the clinic. Therapeutic resistance to anti-EGFR therapy may arise from mechanisms that can compensate for reduced EGFR signaling and/or mechanisms that can modulate EGFR-dependent signaling. In this review, we will summarize some of these molecular mechanisms and describe strategies to overcome that resistance.

Intrinsic caspase-8 activation mediates sensitization of erlotinib-resistant tumor cells to erlotinib/cell-cycle inhibitors combination treatment

Inhibitors of the tyrosine kinase activity of epidermal growth factor receptor, as erlotinib, have an established role in treating several cancer types. However, resistance to erlotinib, particularly in breast cancer cell lines, and erlotinib treatment-associated disorders have also been described. Also, methods and combination therapies that could reverse resistance and ameliorate non-desirable effects represent a clinical challenge. Here, we show that the ATP non-competitive CDK2/cyclin A inhibitor NBI1 sensitizes erlotinib-resistant tumor cells to the combination treatment (co-treatment) for apoptosis-mediated cell death. Furthermore, in erlotinib-sensitive cells, the effective dose of erlotinib was lower in the presence of NBI1. The analysis in the breast cancer MDA-MB-468 erlotinib-resistant and in lung cancer A549 cell lines of the molecular mechanism underlying the apoptosis induced by co-treatment highlighted that the accumulation of DNA defects and depletion of cIAP and XIAP activates the ripoptosome that ultimately activates caspases-8 and -10 and apoptosis. This finding could have significant implications for future treatment strategies in clinical settings.

The impact of multi-targeted cyclin-dependent kinase inhibition in breast cancer cells: clinical implications

INTRODUCTION

The progression of the mammalian cell cycle is driven by the transient activation of complexes consisting of cyclins and cyclin-dependent kinases (CDKs). Loss of control over the cell cycle results in accelerated cell division and malignant transformation and can be caused by the upregulation of cyclins, the aberrant activation of CDKs or the inactivation of cellular CDK inhibitors. For these reasons, cell cycle regulators are regarded as very promising therapeutic targets for the treatment of human malignancies.

AREAS COVERED

This review covers the structures and anti-breast cancer activity of selected pharmacological pan-specific CDK inhibitors. Multi-targeted CDK inhibitors affect CDKs involved in the regulation of both cell cycle progression and transcriptional control. The inhibition of CDK7/CDK9 has a serious impact on the activity of RNA polymerase II; when its carboxy-terminal domain is unphosphorylated, it is unable to recruit the cofactors required for transcriptional elongation, resulting in a global transcriptional block. Multi-targeted inhibition of CDKs represses anti-apoptotic proteins and thus promotes the induction of apoptosis. Moreover, the inhibition of CDK7 in estrogen receptor (ER)-positive breast cancer cells prevents activating phosphorylation of ER-α.

EXPERT OPINION

These diverse modes of action make multi-targeted CDK inhibitors promising drugs for the treatment of breast cancers.

Imatinib mesylate decreases the cytotoxic effect of roscovitine on human glioblastoma cells in vitro and the role of midkine

The purpose of the present study was to overcome resistance to imatinib (IM) by combining it with roscovitine (ROSC) and to investigate whether or not midkine (MK) had an effect on this combination in the treatment of glioblastoma (GBL). Human T98 GBL cells were used to evaluate the effects of IM (10 μM), ROSC (200 μM) and their combination on the cell proliferation index, apoptotic index, the apoptotic protein and anti-apoptotic protein levels, and ultrastructure. All applications decreased the cell proliferation index and increased the apoptotic index, but ROSC was the most efficient drug and the second most efficient drug was IM. Notably, ROSC increased anti-apoptotic proteins levels (PDGFR-α, AQP-4, hTERT), COX-1 activity and ribosome numbers. The effects of ROSC on hTERT, MK, AQP-4 and MRP-1 levels and COX-1 activity were reported for the first time. ROSC induced the highest increase in caspase-3 levels. Autophagy was not involved in the activity of ROSC in GBL spheroids. The combination of IM with ROSC showed an antagonist effect in the treatment of human GBL cells. The combination group decreased certain anti-apoptotic protein levels (PDGFR-α, EGFR, p-gp, MRP-1 and MK), cAMP levels, COX-1 activity and apoptotic protein levels (caspase-3). However, it induced the highest increase in hTERT levels and COX-2 activity. Ribosome numbers were much lower than those in the ROSC group and no autophagic vacuole was observed. In conclusion, more investigations are required to identify the key regulatory components that are responsible for this antagonism; however, the determination of this combination therapy as a failure therapy may be precautionary for oncologists in the treatment of GBL patients and potentially may contribute to the efficacy of new therapeutic regimens.

PPM1H is a p27 phosphatase implicated in trastuzumab resistance

The HER2 oncogene is overexpressed or amplified in 20% of breast cancers. HER2-positive cancer historically portends a poor prognosis, but the HER2-targeted therapy trastuzumab mitigates this otherwise ominous distinction. Nevertheless, some patients suffer disease recurrence despite trastuzumab, and metastatic disease remains largely incurable due to innate and acquired resistance. Thus, understanding trastuzumab resistance remains an unmet medical need. Through RNA interference screening, we discovered that knockdown of the serine/threonine phosphatase PPM1H confers trastuzumab resistance via reduction in protein levels of the tumor suppressor p27. PPM1H dephosphorylates p27 at threonine 187, thus removing a signal for proteasomal degradation. We further determined that patients whose tumors express low levels of PPM1H trend towards worse clinical outcome on trastuzumab. Identifying PPM1H as a novel p27 phosphatase reveals new insight into how cancer cells destabilize a well-recognized tumor suppressor. Furthermore, low PPM1H expression may identify a subset of HER2-positive tumors that are harder to treat.

Targeting NF-κB and HIF-1 pathways for the treatment of cancer: part I

The process of chronic inflammation is a common link which connects different kinds of environmental pollutants and infections with tumorigenesis. Transcription factor NF-κB is a common final target for many inflammatory and cell proliferation pathways, independent of the source of stimuli (e.g., cytokines, growth factors, environmental carcinogens, radiation, hypoxia, bacteria, and viruses). Over-activation of NF-κB has been confirmed in many tumors, resulting in worse prognosis for patient survival. Therefore, inhibition of cellular pathways for NF-κB activation is nowadays considered as a promising anti-cancer therapy and is extensively studied in clinical trials, or even has been adopted as an approved therapy in some kinds of cancer.

PNUTS knockdown potentiates the apoptotic effect of Roscovitine in breast and colon cancer cells

The phosphorylation state of Retinoblastoma protein (Rb) plays a role in cell proliferation and apoptosis. Within cells, cyclin dependent kinases (cdks) phosphorylate Rb in response to growth stimulatory signals, whereas protein phosphatase 1 (PP1) dephosphorylates Rb when cells stop proliferating or undergo apoptosis in response to anti-proliferative or stress signals. Stimulation of PP1 activity via siRNA mediated knockdown of its interacting protein PNUTS (Phosphatase Nuclear Targeting Subunit) leads to Rb dephosphorylation and apoptosis in cancer cells. We utilized two separate methods to modulate the phosphorylation state of Rb in cancer cells. Kinase activity toward Rb is inhibited by the clinically relevant cdk inhibitor, Roscovitine. In addition, siRNA mediated PNUTS knockdown stimulates phosphatase activity toward Rb. Either of these treatments in cancer cells causes a 2-fold stimulation of apoptosis. When activation of phosphatase activity is combined with inhibition of cdk activity toward Rb, however, cells exhibit a 4-fold increase in apoptosis. The mechanism by which PNUTS knockdown mediated PP1 activation leads to apoptosis was determined to be dependent on the activity of the transcription factor E2F1. The Rb phosphorylation profiles resulting from each treatment were analyzed and found to be similar but not identical. In addition, the two treatments differentially effect the expression of bcl-2 family proteins. Thus inhibition of cdk activity and activation of PP1 activity toward pRb are functionally distinct processes that together increase the apoptotic effect in cells.

Combination of sapacitabine and HDAC inhibitors stimulates cell death in AML and other tumour types

Background:

Alternative treatments are needed for elderly patients with acute myeloid leukaemia, as the disease prognosis is poor and the current treatment is unsuitable for many patients.

Methods:

In this study, we investigated whether combining the nucleoside analogue sapacitabine with histone deacetylase (HDAC) inhibitors could be an effective treatment. Synergy and mode-of-action analysis were studied in cultured cell lines and the efficacy of the combination was confirmed in a xenograft model.

Results:

CNDAC (1-(2-C-cyano-2-deoxy-β-D-arabino-pentofuranosyl)-cytosine), the active component of sapacitabine, synergised with vorinostat in cell lines derived from a range of tumour types. Synergy was not dependent on a specific sequence of drug administration and was also observed when CNDAC was combined with an alternative HDAC inhibitor, valproate. Flow cytometry and western blot analysis confirmed that the combination induced a significant increase in apoptosis. Mode-of-action analysis detected changes in Bcl-xl, Mcl-1, Noxa, Bid and Bim, which are all regulators of the apoptotic process. The sapacitabine/vorinostat combination demonstrated significant benefit compared with the single-agent treatments in an MV4-11 xenograft, in the absence of any observed toxicity.

Conclusion:

Sapacitabine and HDAC inhibitors are an effective drug combination that is worthy of clinical exploration.

Seliciclib in malignancies

Cyclins and cyclin-dependent kinases (CDK) form a key part of the regulatory proteins that govern the cell cycle. Aberrancy in their function can lead to uncontrolled growth and proliferation of the cells which forms the basis of many human diseases, especially cancers. Seliciclib (CYC202, R-roscovitine) is a second-generation CDK inhibitor that competes for ATP binding sites on these kinases, reducing tumor growth and inducing cell death. It is a direct inhibitor of cyclin E/CDK2 and also has inhibitory effects on cyclin H/CDK7 and cyclin T/CDK9. Seliciclib leads to growth arrest and apoptosis of cell lines through activation of the p53 gene, inhibition of RNA processing and blockage of the RNA polymerase II-dependent transcription, and reduction of anti-apoptotic proteins. Seliciclib has good oral bioavailability, although its absorption is slowed by food. It is distributed rapidly to the body tissues and metabolized rapidly to a carboxylated derivative that is excreted by the kidneys. The major adverse effects of seliciclib are electrolyte disturbances (hypokalemia, hyponatremia), gastrointestinal side effects (nausea, emesis, anorexia), fatigue, transient hyperglycemia, elevation of liver enzymes and reversible elevation of serum creatinine. At present, it is in Phase II trials for non-small cell lung cancer and nasopharyngeal carcinoma.

Targeting the cyclin E-Cdk-2 complex represses lung cancer growth by triggering anaphase catastrophe

PURPOSE

Cyclin-dependent kinases (Cdk) and their associated cyclins are targets for lung cancer therapy and chemoprevention given their frequent deregulation in lung carcinogenesis. This study uncovered previously unrecognized consequences of targeting the cyclin E-Cdk-2 complex in lung cancer.

EXPERIMENTAL DESIGN

Cyclin E, Cdk-1, and Cdk-2 were individually targeted for repression with siRNAs in lung cancer cell lines. Cdk-2 was also pharmacologically inhibited with the reversible kinase inhibitor seliciclib. Potential reversibility of seliciclib effects was assessed in washout experiments. Findings were extended to a large panel of cancer cell lines using a robotic-based platform. Consequences of cyclin E-Cdk-2 inhibition on chromosome stability and on in vivo tumorigenicity were explored as were effects of combining seliciclib with different taxanes in lung cancer cell lines.

RESULTS

Targeting the cyclin E-Cdk-2 complex, but not Cdk-1, resulted in marked growth inhibition through the induction of multipolar anaphases triggering apoptosis. Treatment with the Cdk-2 kinase inhibitor seliciclib reduced lung cancer formation in a murine syngeneic lung cancer model and decreased immunohistochemical detection of the proliferation markers Ki-67 and cyclin D1 in lung dysplasia spontaneously arising in a transgenic cyclin E-driven mouse model. Combining seliciclib with a taxane resulted in augmented growth inhibition and apoptosis in lung cancer cells. Pharmacogenomic analysis revealed that lung cancer cell lines with mutant ras were especially sensitive to seliciclib.

CONCLUSIONS

Induction of multipolar anaphases leading to anaphase catastrophe is a previously unrecognized mechanism engaged by targeting the cyclin E-Cdk-2 complex. This exerts substantial antineoplastic effects in the lung.

A cohort study of cyclin D1 expression and prognosis in 602 colon cancer cases

PURPOSE

Cyclin D1 and cyclin-dependent kinases (CDK) are commonly activated in colorectal cancer. The activity of cyclin D1 can be blocked by CDK inhibitors, including p27 (CDKN1B) and p21 (CDKN1A, which is induced by p53). However, prognostic significance of tumoral cyclin D1 remains uncertain, and no previous study has considered potential confounding effect of p53, p21, p27, and related molecular events [microsatellite instability (MSI), CpG island methylator phenotype, and LINE-1 hypomethylation].

EXPERIMENTAL DESIGN

Among 602 colon cancer patients (stage I-IV) in two prospective cohort studies, cyclin D1 overexpression was detected in 330 (55%) tumors by immunohistochemistry. Cox proportional hazard models computed hazard ratios (HR) of colon cancer-specific and overall mortalities, adjusted for patient characteristics and tumoral molecular features, including p53, p21, p27, cyclooxygenase-2, fatty acid synthase, LINE-1 methylation, CpG island methylator phenotype, MSI, BMI, KRAS, and BRAF.

RESULTS

Cyclin D1 overexpression was associated with a low cancer-specific mortality in Kaplan-Meier analysis (P = 0.006), and in both univariate Cox regression [unadjusted HR, 0.64; 95% confidence interval (CI), 0.47-0.88; P = 0.0063] and multivariate analyses (adjusted HR, 0.57; 95% CI, 0.39-0.84; P = 0.0048). Similar findings were observed for an overall mortality (adjusted HR, 0.74; 95% CI, 0.57-0.98; P = 0.036). Notably, the effect of cyclin D1 on survival might differ by MSI status (P(interaction) = 0.008). Compared with tumors that were both cyclin D1-negative and MSI-low/microsatellite stable, the presence of either cyclin D1 or MSI-high or both seemed to confer better clinical outcome (adjusted HR point estimates, 0.10-0.65).

CONCLUSIONS

Cyclin D1 overexpression is associated with longer survival in colon cancer.

Synergistic combinations of signaling pathway inhibitors: mechanisms for improved cancer therapy

Cancer cells contain multiple signal transduction pathways whose activities are frequently elevated due to their transformation, and that are often activated following exposure to established cytotoxic therapies including ionizing radiation and chemical DNA damaging agents. Many pathways activated in response to transformation or toxic stresses promote cell growth and invasion and counteract the processes of cell death. As a result of these findings many drugs, predominantly protein and lipid kinase inhibitors, of varying specificities, have been developed to block signaling by cell survival pathways in the hope of killing tumor cells and sensitizing them to toxic therapies. Unfortunately, due to the plasticity of signaling processes within a tumor cell, inhibition of any one growth factor receptor or signaling pathway frequently has only modest long-term effects on cancer cell viability, tumor growth, and patient survival. As a result of this realization, a greater emphasis has begun to be placed on rational combinations of drugs that simultaneously inhibit multiple inter-linked signal transduction/survival pathways. This, it is hoped, will limit the ability of tumor cells to adapt and survive because the activity within multiple parallel survival signaling pathways has been reduced. This review will discuss some of the approaches that have been taken to combine signal transduction modulatory agents to achieve enhanced tumor cell killing.