Cyclin-dependent kinase inhibitor p27 as a prognostic biomarker and potential cancer therapeutic target

Cyclin-dependent kinase inhibitors for the treatment of lung cancer

INTRODUCTION

Cyclin-dependent kinases (CDKs) are critical regulators of cell cycle progression in both normal and malignant cells, functioning through complex molecular interactions. Deregulation of CDK-dependent pathways is commonly found in both non-small cell and small cell lung cancer, and these derangements suggest vulnerabilities that can be exploited for clinical benefit.

AREAS COVERED

In this review, the authors present an overview of the biology of CDKs in normal and malignant cells, with a focus on lung cancer, followed by an assessment of preclinical work that has demonstrated the vital role of CDKs in lung cancer development and progression, and the activity of CDK inhibitors in a variety of lung cancer models. Finally, the experience with clinical trials of CDK inhibitors in lung cancer is discussed along with the current status of these agents in cancer therapy.

EXPERT OPINION

Despite strong biological rationale and promising preclinical studies, the results of clinical trials of CDK inhibitors in lung cancer have thus far been disappointing. Further clinical development of CDK inhibitors in lung cancer will depend on the identification of predictive biomarkers and the design of combination regimens that take advantage of the unique molecular alterations that drive lung cancer growth and survival.

An insight into the emerging role of cyclin-dependent kinase inhibitors as potential therapeutic agents for the treatment of advanced cancers

Cancer denotes a pathological manifestation that is characterized by hyperproliferation of cells. It has anticipated that a better understanding of disease pathogenesis and the role of cell-cycle regulators may provide an opportunity to develop an effective cancer therapeutic agents. Specifically, the cyclin-dependent kinases (CDKs) which regulate the transition of cell-cycle through different phases; have been identified as fundamental targets for therapeutic advances. It is an evident from experimental studies that several events leading to tumor growth occur by exacerbation of CDK4/CDK6 in G1-phase of cell division cycle. Additionally, the characteristics of S- and G2/M-phase regulated by CDK1/CDK2 are pivotal events that may lead to abrupt the cell division. Although, previously reported CDK inhibitors have shown remarkable results in pre-clinical studies, but have not yielded appreciable clinical results yet. Therefore, the development of clinically potent CDK inhibitors has remained to be a challenging task. However, continuous efforts has led to the development of some novel CDKs inhibitors that have emerged as a potent strategy for the treatment of advanced cancers. In this article, we have summarized the role of CDKs in cell-cycle regulation and tumorigenesis and recent advances in the development of CDKs inhibitors as a promising therapy for the treatment of advanced cancer. In addition, we have also performed a comparison of crystallographic studies to get valuable insight into the interaction mode differences of inhibitors, binding to CDK isoforms with apparently similar binding sites. The knowledge of ligand-specific recognition towards a particular CDK isoform may be applied as a key tool in future for the designing of isoform-specific inhibitors.

FoxM1: Repurposing an oncogene as a biomarker

The past few decades have witnessed a tremendous progress in understanding the biology of cancer, which has led to more comprehensive approaches for global gene expression profiling and genome-wide analysis. This has helped to determine more sophisticated prognostic and predictive signature markers for the prompt diagnosis and precise screening of cancer patients. In the search for novel biomarkers, there has been increased interest in FoxM1, an extensively studied transcription factor that encompasses most of the hallmarks of malignancy. Considering the attractive potential of this multifarious oncogene, FoxM1 has emerged as an important molecule implicated in initiation, development and progression of cancer. Bolstered with the skill to maneuver the proliferation signals, FoxM1 bestows resistance to contemporary anti-cancer therapy as well. This review sheds light on the large body of literature that has accumulated in recent years that implies that FoxM1 neoplastic functions can be used as a novel predictive, prognostic and therapeutic marker for different cancers. This assessment also highlights the key features of FoxM1 that can be effectively harnessed to establish FoxM1 as a strong biomarker in diagnosis and treatment of cancer.

Upregulation of p27Kip1 by demethylation sensitizes cisplatin-resistant human ovarian cancer SKOV3 cells

Ovarian cancer has a poor prognosis due to its chemoresistance, and p27Kip1 (p27) has been implicated in tumor prognosis and drug-resistance. However, the regulatory mechanisms of p27 in drug‑resistance in ovarian cancer remain unknown. The current study successfully established chemoresistant cell lines using paclitaxel (TAX), cisplatin (DDP) and carboplatin (CBP) in SKOV3 ovarian cancer cells. The results indicated that the expression levels of p27 were dramatically downregulated in chemoresistant cells. However, 5-aza-2'-deoxycytidine (5-aza) treatment restored p27 expression in DDP-resistant cells, and increased their sensitivity to DDP. In addition, it was observed that the methylation of DDP‑resistant cells, which was downregulated by 5‑aza treatment, was significantly higher compared with SKOV3 cells. Additionally, the overexpression of p27 arrested the cell cycle in S phase and promoted an apoptotic response to DDP. In conclusion, p27 was involved in chemoresistance of SKOV3 cells. Upregulated p27 expression induced by demethylation may enhance sensitivity to DDP through the regulation of the cell cycle.

A Dynamical Framework for the All-or-None G1/S Transition

The transition from G1 into DNA replication (S phase) is an emergent behavior resulting from dynamic and complex interactions between cyclin-dependent kinases (Cdks), Cdk inhibitors (CKIs), and the anaphase-promoting complex/cyclosome (APC/C). Understanding the cellular decision to commit to S phase requires a quantitative description of these interactions. We apply quantitative imaging of single human cells to track the expression of G1/S regulators and use these data to parametrize a stochastic mathematical model of the G1/S transition. We show that a rapid, proteolytic, double-negative feedback loop between Cdk2:Cyclin and the Cdk inhibitor p27(Kip1) drives a switch-like entry into S phase. Furthermore, our model predicts that increasing Emi1 levels throughout S phase are critical in maintaining irreversibility of the G1/S transition, which we validate using Emi1 knockdown and live imaging of G1/S reporters. This work provides insight into the general design principles of the signaling networks governing the temporally abrupt transitions between cell-cycle phases.

The prognostic of p27(kip1) in ovarian cancer: a meta-analysis

PURPOSE

P27(kip1) is a negative cell cycle regulator that plays an important role in tumor suppression. Deregulation of p27(kip1) is commonly observed in many human cancers. Numerous studies about p27(kip1) are reported in clinical patients despite variable data for the prognostic of p27(kip1) expression. Here we report a meta-analysis of the association of p27(kip1) expression with the survival of ovarian cancer.

METHODS

PubMed and Web of science were searched for studies evaluating expression of p27(kip1) and prognostic in ovarian cancer. Published data were extracted and computed into odds ratios (ORs) for death at 3 and 5 years. Data were pooled using the random-effect model. All statistical tests were two-sided.

RESULTS

Analysis included 9 studies: six studies were reported in European, three studies were reported in American, and one study was reported in Asian. Loss of p27(kip1) was associated with worse overall survival (OS) at both 3 years [OR = 2.61, 95 % confidence interval (CI) 1.95-3.49, p < 0.05] and 5 years (OR = 3.01, 95 % CI 2.17-4.17, p < 0.05). Among studies with different ethnicity (European, American and Asian), the results showed a more significant association in European, including Italy, Germany, and Greece [for both 3-year OS (OR = 3.53, 95 % CI 2.37-5.26) and 5-year OS (OR = 3.66, 95 % CI 2.30-5.83)].

CONCLUSIONS

Loss of p27(kip1) is associated with worse survival in ovarian cancer. The development of strategies target p27(kip1) could be a reasonable therapeutic approach.

Prognostic role of the CDNK1B V109G polymorphism in multiple endocrine neoplasia type 1

CDKN1B encodes the cyclin-dependent kinase inhibitor p27/Kip1. CDKN1B mutations and polymorphisms are involved in tumorigenesis; specifically, the V109G single nucleotide polymorphism has been linked to different tumours with controversial results. Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant syndrome, characterized by the development of different types of neuroendocrine tumours and increased incidence of other malignancies. A clear genotype-phenotype correlation in MEN1 has not been established yet. In this study, we assessed whether the CDKN1B V109G polymorphism was associated with the development of aggressive tumours in 55 consecutive patients affected by MEN1. The polymorphism was investigated by PCR amplification of germline DNA followed by direct sequencing. Baseline and follow-up data of tumour types and their severity were collected and associated with the genetic data. MEN1-related aggressive and other malignant tumours of any origin were detected in 16.1% of wild-type and 33.3% of polymorphism allele-bearing patients (P = NS). The time interval between birth and the first aggressive tumour was significantly shorter in patients with the CDKN1B V109G polymorphism (median 46 years) than in those without (median not reached; P = 0.03). Similarly, shorter was the time interval between MEN1 diagnosis and age of the first aggressive tumour (P = 0.02). Overall survival could not be estimated as 96% patients were still alive at the time of the study. In conclusion, CDKN1B V109G polymorphism seems to play a role in the development of aggressive tumours in MEN1.

The history and future of targeting cyclin-dependent kinases in cancer therapy

Cancer represents a pathological manifestation of uncontrolled cell division; therefore, it has long been anticipated that our understanding of the basic principles of cell cycle control would result in effective cancer therapies. In particular, cyclin-dependent kinases (CDKs) that promote transition through the cell cycle were expected to be key therapeutic targets because many tumorigenic events ultimately drive proliferation by impinging on CDK4 or CDK6 complexes in the G1 phase of the cell cycle. Moreover, perturbations in chromosomal stability and aspects of S phase and G2/M control mediated by CDK2 and CDK1 are pivotal tumorigenic events. Translating this knowledge into successful clinical development of CDK inhibitors has historically been challenging, and numerous CDK inhibitors have demonstrated disappointing results in clinical trials. Here, we review the biology of CDKs, the rationale for therapeutically targeting discrete kinase complexes and historical clinical results of CDK inhibitors. We also discuss how CDK inhibitors with high selectivity (particularly for both CDK4 and CDK6), in combination with patient stratification, have resulted in more substantial clinical activity.

Progesterone enhances calcitriol antitumor activity by upregulating vitamin D receptor expression and promoting apoptosis in endometrial cancer cells

Human studies suggest that progesterone and calcitriol may prove beneficial in preventing or inhibiting oncogenesis, but the underlying mechanism is not fully understood. The current study investigates the effects of progesterone, calcitriol, and their combination on immortalized human endometrial epithelial cells and endometrial cancer cells and identifies their targets of action. Combination treatment with both agents enhanced vitamin D receptor expression and inhibited cell proliferation through caspase-3 activation and induction of G0-G1 cell-cycle arrest with associated downregulation of cyclins D1 and D3 and p27 induction. We used mass spectrometry-based proteomics to measure protein abundance differences between calcitriol-, progesterone-, or combination-exposed endometrial cells. A total of 117 proteins showed differential expression among these three treatments. Four proteins were then selected for validation studies: histone H1.4 (HIST1H1E), histidine triad nucleotide-binding protein 2 (HINT2), IFN-induced, double-stranded RNA-activated protein kinase (EIF2AK2), and Bcl-2-associated X protein (BAX). Abundance levels of selected candidates were low in endometrial cancer cell lines versus the immortalized endometrial epithelial cell line. All four proteins displayed elevated expression in cancer cells upon exposure to calcitriol, progesterone, or the combination. Further BAX analysis through gain- or loss-of-function experiments revealed that upregulation of BAX decreased cell proliferation by changing the BAX:BCL-2 ratio. Knockdown of BAX attenuated progesterone- and calcitriol-induced cell growth inhibition. Our results showed that progesterone and calcitriol upregulate the expression of BAX along with other apoptosis-related proteins, which induce inhibition of endometrial cancer cell growth by apoptosis and cell-cycle arrest.

miRNA-214 modulates radiotherapy response of non-small cell lung cancer cells through regulation of p38MAPK, apoptosis and senescence

Background:

Radio- and chemotherapy (RT/CT) resistance hampers success in combating small and non-small cell lung cancers (SCLC/NSCLC). The underlying molecular mechanisms of RT/CT resistance of LCs are multifactorial and have been understood in part hitherto. miRNAs, key regulators of mRNAs, are well-recognised oncomirs; however, their role in regulating RT response remains poorly understood.

Methods:

Six human NSCLC and five SCLC cell lines with different SF2 values were investigated. Using microarray we examined whether expression of miRNAs is linked to the RT resistance of NSCLCs or SCLCs. Obtained data were validated by quantitative real-time PCR. Apoptosis and senescence were analysed using siRNA transfection, western blot and flow cytometry.

Results:

miRNA-21, miRNA-1827, miRNA-214, miRNA-339-5p, miRNA-625, miRNA-768-3p, miRNA-523-3p, miRNA-1227, miRNA-324-5p, miRNA-423-3p, miRNA-1301 and miRNA-1249 are differentially expressed in LC cells. miRNA-214 is upregulated in RT-resistant NSCLC cells relative to radiosensitive counterparts. Considering miRNA-214 as a putative regulator of RT resistance, we demonstrate that knockdown of miRNA-214 in radioresistant NSCLCs sensitised them to RT by stimulation of senescence. Consistently, overexpression of miRNA-214 in radiosensitive NSCLCs protected against RT-induced apoptosis. Protection was mediated by p38MAPK, as downregulation of this kinase could reverse the miRNA-214 overexpression-induced resistance of NSCLC cells.

Conclusion:

miRNA profiling of LC revealed putative RT resistance signalling circuits, which might help in sensitisation of LC to RT.

Decreased skp2 expression is necessary but not sufficient for therapy-induced senescence in prostate cancer

Therapy-induced senescence (TIS), a cytostatic stress response in cancer cells, is induced inefficiently by current anticancer agents and radiation. The mechanisms that mediate TIS in cancer cells are not well defined. Herein, we characterize a robust senescence response both in vitro and in vivo to the quinone diaziquone (AZQ), previously identified in a high-throughput senescence-induction small-molecule screen. Using AZQ and several other agents that induce senescence, we screened a series of cyclin-dependent kinase inhibitors and found that p27(Kip1) was induced in all investigated prostate cancer cell lines. The ubiquitin-ligase Skp2 negatively regulates p27(Kip1) and, during TIS, is translocated to the cytoplasm before its expression is decreased in senescent cells. Overexpression of Skp2 blocks the effects of AZQ on senescence and p27(Kip1) induction. We also find that stable long-term short hairpin RNA knockdown of Skp2 decreases proliferation but does not generate the complete senescence phenotype. We conclude that Skp2 participates in regulating TIS but, alone, is insufficient to induce senescence in cancer cells.

p27(Kip1) V109G polymorphism and cancer risk: a systematic review and meta-analysis

Relationship between the p27Kip1 (here after referred to as p27) V109G polymorphism and cancer risk has been extensively studied; however, results from different studies were not fully consistent. Therefore, we carried out a meta-analysis to comprehensively assess the correlation between the p27V109G polymorphism and the cancer risk. Articles on the relationship of the p27V109G polymorphism with cancer risk were searched from Medline, Pub Med, and Web of science databases. A total of eight eligible studies with 3591 cases and 3799 controls were included in this meta-analysis. Overall, it seemed that the G allele was not associated with the elevated cancer risk (pooled odds ratio [OR]=0.98, 95% confidence interval [CI]: 0.88-1.09, p=0.68, fixed effects). Analyses in different populations revealed that no statistically significant associations between the G allele and cancer risk were demonstrated in Caucasians or Asians. When analyzed in different types of cancer that, from two studies, the G allele was found to be associated with a decreased risk of prostate cancer in a dominant genetic model (pooled OR=0.60, 95% CI=0.36-0.98, p=0.04, fixed effects), but did not alter the breast cancer risk from four studies. In conclusion, this meta-analysis indicated that the p27V109G polymorphism did not correlate with the overall cancer risk in the general population.

Inter-ethnic differences in lymphocyte sensitivity to glucocorticoids reflect variation in transcriptional response

Glucocorticoids (GCs) are steroid hormones widely used as pharmaceutical interventions, which act mainly by regulating gene expression levels. A large fraction of patients (~30%), especially those of African descent, show a weak response to treatment. To interrogate the contribution of variable transcriptional response to inter-ethnic differences, we measured in vitro lymphocyte GC sensitivity (LGS) and transcriptome-wide response to GCs in peripheral blood mononuclear cells (PBMCs) from African-American and European-American healthy donors. We found that transcriptional response after 8hrs treatment was significantly correlated with variation in LGS within and between populations. We found that NFKB1, a gene previously found to predict LGS within populations, was more strongly down-regulated in European-Americans on average. NFKB1 could not completely explain population differences, however, and we found an additional 177 genes with population differences in the average log₂ fold change (FDR<0.05), most of which also showed a weaker transcriptional response in African-Americans. These results suggest that inter-ethnic differences in GC sensitivity reflect variation in transcriptional response at many genes, including regulators with large effects (e.g. NFKB1) and numerous other genes with smaller effects.

Improved Statistical Analysis for Array CGH-Based DNA Copy Number Aberrations

Array-based comparative genomic hybridization (aCGH) allows measuring DNA copy number at the whole genome scale. In cancer studies, one may be interested in identifying DNA copy number aberrations (CNAs) associated with certain clinicopathological characteristics such as cancer metastasis. We proposed to define test regions based on copy number pattern profiles across multiple samples, using either smoothed log₂-ratio or discrete data of copy number gain/loss calls. Association test performed on the refined test regions instead of the probes has improved power due to reduced number of tests. We also compared three types of measurement of copy number levels, normalized log₂-ratio, smoothed log₂-ratio, and copy number gain or loss calls in statistical hypothesis testing. The relative strengths and weaknesses of the proposed method were demonstrated using both simulation studies and real data analysis of a liver cancer study.