AZD5438, an inhibitor of Cdk1, 2, and 9, enhances the radiosensitivity of non-small cell lung carcinoma cells

Leveraging metabolic modeling and machine learning to uncover modulators of quiescence depth

Quiescence, a temporary withdrawal from the cell cycle, plays a key role in tissue homeostasis and regeneration. Quiescence is increasingly viewed as a continuum between shallow and deep quiescence, reflecting different potentials to proliferate. The depth of quiescence is altered in a range of diseases and during aging. Here, we leveraged genome-scale metabolic modeling (GEM) to define the metabolic and epigenetic changes that take place with quiescence deepening. We discovered contrasting changes in lipid catabolism and anabolism and diverging trends in histone methylation and acetylation. We then built a multi-cell type machine learning model that accurately predicts quiescence depth in diverse biological contexts. Using both machine learning and genome-scale flux simulations, we performed high-throughput screening of chemical and genetic modulators of quiescence and identified novel small molecule and genetic modulators with relevance to cancer and aging.

New spiro-indeno[1,2-b]quinoxalines clubbed with benzimidazole scaffold as CDK2 inhibitors for halting non-small cell lung cancer; stereoselective synthesis, molecular dynamics and structural insights

Despite the crucial role of CDK2 in tumorigenesis, few inhibitors reached clinical trials for managing lung cancer, the leading cause of cancer death. Herein, we report combinatorial stereoselective synthesis of rationally designed spiroindeno[1,2-b]quinoxaline-based CDK2 inhibitors for NSCLC therapy. The design relied on merging pharmacophoric motifs and biomimetic scaffold hopping into this privileged skeleton via cost-effective one-pot multicomponent [3 + 2] cycloaddition reaction. Absolute configuration was assigned by single crystal x-ray diffraction analysis and reaction mechanism was studied by Molecular Electron Density Theory. Initial MTT screening of the series against A549 cells and normal lung fibroblasts Wi-38 elected 6b as the study hit regarding potency (IC50 = 54 nM) and safety (SI = 6.64). In vitro CDK2 inhibition assay revealed that 6b (IC50 = 177 nM) was comparable to roscovitine (IC50 = 141 nM). Docking and molecular dynamic simulations suggested that 6b was stabilised into CDK2 cavity by hydrophobic interactions with key aminoacids.

A novel prognostic signature contributes to precision treatment in colon adenocarcinoma with KRAS mutation

BACKGROUND

Approximately 40% of colon cancer harbor Kirsten rat sarcoma viral oncogene ( KRAS ) mutations, but the prognostic value of KRAS mutations in colon cancer is still controversial.

METHODS

We enrolled 412 colon adenocarcinoma (COAD) patients with KRAS mutations, 644 COAD patients with KRAS wild-type and 357 COAD patients lacking information on KRAS status from five independent cohorts. A random forest model was developed to estimate the KRAS status. The prognostic signature was established using least absolute shrinkage and selection operator-Cox regression and evaluated by Kaplan-Meier survival analysis, multivariate-Cox analysis, receiver operating characteristic curve and nomogram. The expression data of KRAS -mutant COAD cell lines from the Cancer Cell Line Encyclopedia database and the corresponding drug sensitivity data from the Genomics of Drug Sensitivity in Cancer database were used for potential target and agent exploration.

RESULTS

We established a 36-gene prognostic signature classifying the KRAS -mutant COAD as high and low risk. High risk patients had inferior prognoses compared to those with low risk, while the signature failed to distinguish the prognosis of COAD with KRAS wild-type. The risk score was the independent prognostic factor for KRAS -mutant COAD and we further fabricated the nomograms with good predictive efficiency. Moreover, we suggested FMNL1 as a potential drug target and three drugs as potential therapeutic agents for KRAS -mutant COAD with high risk.

CONCLUSION

We established a precise 36-gene prognostic signature with great performance in prognosis prediction of KRAS -mutant COAD providing a new strategy for personalized prognosis management and precision treatment for KRAS -mutant COAD.

Double-strand DNA break repair: molecular mechanisms and therapeutic targets

Double-strand break (DSB), a significant DNA damage brought on by ionizing radiation, acts as an initiating signal in tumor radiotherapy, causing cancer cells death. The two primary pathways for DNA DSB repair in mammalian cells are nonhomologous end joining (NHEJ) and homologous recombination (HR), which cooperate and compete with one another to achieve effective repair. The DSB repair mechanism depends on numerous regulatory variables. DSB recognition and the recruitment of DNA repair components, for instance, depend on the MRE11-RAD50-NBS1 (MRN) complex and the Ku70/80 heterodimer/DNA-PKcs (DNA-PK) complex, whose control is crucial in determining the DSB repair pathway choice and efficiency of HR and NHEJ. In-depth elucidation on the DSB repair pathway's molecular mechanisms has greatly facilitated for creation of repair proteins or pathways-specific inhibitors to advance precise cancer therapy and boost the effectiveness of cancer radiotherapy. The architectures, roles, molecular processes, and inhibitors of significant target proteins in the DSB repair pathways are reviewed in this article. The strategy and application in cancer therapy are also discussed based on the advancement of inhibitors targeted DSB damage response and repair proteins.

Targeting CDK1 in cancer: mechanisms and implications

Cyclin dependent kinases (CDKs) are serine/threonine kinases that are proposed as promising candidate targets for cancer treatment. These proteins complexed with cyclins play a critical role in cell cycle progression. Most CDKs demonstrate substantially higher expression in cancer tissues compared with normal tissues and, according to the TCGA database, correlate with survival rate in multiple cancer types. Deregulation of CDK1 has been shown to be closely associated with tumorigenesis. CDK1 activation plays a critical role in a wide range of cancer types; and CDK1 phosphorylation of its many substrates greatly influences their function in tumorigenesis. Enrichment of CDK1 interacting proteins with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted to demonstrate that the associated proteins participate in multiple oncogenic pathways. This abundance of evidence clearly supports CDK1 as a promising target for cancer therapy. A number of small molecules targeting CDK1 or multiple CDKs have been developed and evaluated in preclinical studies. Notably, some of these small molecules have also been subjected to human clinical trials. This review evaluates the mechanisms and implications of targeting CDK1 in tumorigenesis and cancer therapy.

Molecular targets that sensitize cancer to radiation killing: From the bench to the bedside

Radiotherapy is a standard cytotoxic therapy against solid cancers. It uses ionizing radiation to kill tumor cells through damage to DNA, either directly or indirectly. Radioresistance is often associated with dysregulated DNA damage repair processes. Most radiosensitizers enhance radiation-mediated DNA damage and reduce the rate of DNA repair ultimately leading to accumulation of DNA damages, cell-cycle arrest, and cell death. Recently, agents targeting key signals in DNA damage response such as DNA repair pathways and cell-cycle have been developed. This new class of molecularly targeted radiosensitizing agents is being evaluated in preclinical and clinical studies to monitor their activity in potentiating radiation cytotoxicity of tumors and reducing normal tissue toxicity. The molecular pathways of DNA damage response are reviewed with a focus on the repair mechanisms, therapeutic targets under current clinical evaluation including ATM, ATR, CDK1, CDK4/6, CHK1, DNA-PKcs, PARP-1, Wee1, & MPS1/TTK and potential new targets (BUB1, and DNA LIG4) for radiation sensitization.

Therapeutic efficacy of cyclin-dependent kinase inhibition in combination with ionizing radiation for lung cancer

PURPOSE

To evaluate the therapeutic efficacy of cyclin-dependent kinase (CDK) inhibition in combination with ionizing radiation for lung cancer.

MATERIALS AND METHODS

Human lung adenocarcinoma (A549) and squamous cell carcinoma (H520) cells were used to evaluate the therapeutic efficacy of CDK inhibition in combination with ionizing radiation in vitro using colony formation assay, γH2AX immunofluorescence staining, western blotting, and cell cycle phase analysis. We also performed in vivo evaluations of ectopic tumor growth.

RESULTS

In vitro pretreatment with the CDK inhibitor, seliciclib, before irradiation significantly decreased the survival of A549 and H520 cells in a dose-dependent manner. Although CDK inhibition alone did not increase the intensity of γH2AX foci, its combination with ionizing radiation increased DNA double-strand breaks, as shown by γH2AX immunofluorescence staining and western blotting. The combination of CDK inhibition and ionizing radiation-induced G2/M arrest and increased apoptosis, as evidenced by the increased proportion of cells in G2/M arrest, subG1 apoptotic population, and expression of apoptotic markers (cleaved PARP-1 and cleaved caspase-3). Mechanistic studies showed reduced expression of cyclin A with combined treatment, indicating cell cycle shifting effects. An in vivo xenograft model showed that the combination of CDK inhibition and ionizing radiation delayed xenograft tumor growth, and increased the proportion of cleaved PARP-1- and cleaved caspase-3-positive cells, compared to either treatment alone.

CONCLUSIONS

We provide preclinical tumoricidal evidence that the combination of CDK inhibition and ionizing radiation is an efficacious treatment for lung cancer.

Radiotherapy as a tool to elicit clinically actionable signalling pathways in cancer

A variety of targeted anticancer agents have been successfully introduced into clinical practice, largely reflecting their ability to inhibit specific molecular alterations that are required for disease progression. However, not all malignant cells rely on such alterations to survive, proliferate, disseminate and/or evade anticancer immunity, implying that many tumours are intrinsically resistant to targeted therapies. Radiotherapy is well known for its ability to activate cytotoxic signalling pathways that ultimately promote the death of cancer cells, as well as numerous cytoprotective mechanisms that are elicited by cellular damage. Importantly, many cytoprotective mechanisms elicited by radiotherapy can be abrogated by targeted anticancer agents, suggesting that radiotherapy could be harnessed to enhance the clinical efficacy of these drugs. In this Review, we discuss preclinical and clinical data that introduce radiotherapy as a tool to elicit or amplify clinically actionable signalling pathways in patients with cancer.

THZ531 Induces a State of BRCAness in Multiple Myeloma Cells: Synthetic Lethality with Combination Treatment of THZ 531 with DNA Repair Inhibitors

Multiple myeloma (MM) is a hematological disease marked by abnormal growth of B cells in bone marrow. Inherent chromosomal instability and DNA damage are major hallmarks of MM, which implicates an aberrant DNA repair mechanism. Studies have implicated a role for CDK12 in the control of expression of DNA damage response genes. In this study, we examined the effect of a small molecule inhibitor of CDK12–THZ531 on MM cells. Treatment of MM cells with THZ531 led to heightened cell death accompanied by an extensive effect on gene expression changes. In particular, we observed downregulation of genes involved in DNA repair pathways. With this insight, we extended our study to identify synthetic lethal mechanisms that could be exploited for the treatment of MM cells. Combination of THZ531 with either DNA-PK inhibitor (KU-0060648) or PARP inhibitor (Olaparib) led to synergistic cell death. In addition, combination treatment of THZ531 with Olaparib significantly reduced tumor burden in animal models. Our findings suggest that using a CDK12 inhibitor in combination with other DNA repair inhibitors may establish an effective therapeutic regimen to benefit myeloma patients.

The Renaissance of Cyclin Dependent Kinase Inhibitors

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

Identification of Novel Drug Candidate for Epithelial Ovarian Cancer via In Silico Investigation and In Vitro Validation

Epithelial ovarian cancer (EOC) has a poor prognosis and high mortality rate; patients are easy to relapse with standard therapies. So, there is an urgent need to develop novel drugs. In this study, differentially expressed genes (DEGs) of EOC were identified in The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Enrichment and protein–protein interaction (PPI) analyses were performed. The drug candidate which has the possibility to treat EOC was predicted by Connectivity Map (CMAP) databases. Moreover, molecular docking was selected to calculate the binding affinity between drug candidate and hub genes. The cytotoxicity of drug candidates was assessed by MTT and colony formation analysis, the proteins coded by hub genes were detected by Western blots, and apoptosis analysis was evaluated by flow cytometry. Finally, 296 overlapping DEGs (|log 2 fold change|>1; q-value <0.05), which were principally involved in the cell cycle (p < 0.05), and cyclin-dependent kinase 1 (CDK1) were screened as the significant hub gene from the PPI network. Furthermore, the 21 drugs were extracted from CMAPs; among them, piperlongumine (PL) showed a lower CMAP score (-0.80, -62.92) and was regarded as the drug candidate. Furthermore, molecular docking results between PL and CDK1 with a docking score of –8.121 kcal/mol were close to the known CDK1 inhibitor (–8.24 kcal/mol). Additionally, in vitro experiments showed that PL inhibited proliferation and induced apoptosis via targeting CDK1 in EOC SKOV3 cells. Our results reveal that PL may be a novel drug candidate for EOC by inhibiting cell cycle.

Upregulated expression of MTFR2 as a novel biomarker predicts poor prognosis in hepatocellular carcinoma by bioinformatics analysis

Aim: The authors investigated the clinical role of MTFR2 in hepatocellular carcinoma (HCC) progression. Results: MTFR2 expression and methylation were abnormal in HCC tissues, and HCC patients with increased MTFR2 expression or methylation had poor or better overall survival, respectively. In addition, increased MTFR2 expression was correlated with age, grade, cancer stage and T stage. MTFR2 was an independent predictor of dismal prognosis in HCC patients. MTFR2 was involved in HCC progression by modulating the cell cycle, homologous recombination, DNA replication, p53 signaling pathway, etc. The ten hub genes were overexpressed in HCC tissues and were linked to cancer stage and dismal prognosis in HCC patients. Conclusion: MTFR2 could be a prospective biomarker of poor prognosis in individuals with HCC.

Evaluation of clinical value and potential mechanism of MTFR2 in lung adenocarcinoma via bioinformatics

Background

Mitochondrial fission regulator 2 (MTFR2) was involved in the progression and development of various cancers. However, the relationship between MTFR2 with lung adenocarcinoma (LUAD) had not been reported. Herein, this study analyzed the clinical significance and potential mechanisms of MTFR2 in LUAD via bioinformatics tools.

Results

We found that the level of MTFR2 was increased, and correlated with sex, age, smoking history, neoplasm staging, histological subtype and TP53 mutation status in LUAD patients. Kaplan-Meier survival analysis showed LUAD patients with increased MTFR2 had a poor prognosis. In addition, univariate COX regression analysis showed neoplasm staging, T stage, distant metastasis and MTFR2 level were risk factors for the prognosis of LUAD. A total of 1127 genes were coexpressed with MTFR2, including 840 positive and 208 negative related genes. KEGG and GSEA found that MTFR2 participated in the progression of LUAD by affecting cell cycle, DNA replication, homologous recombination, p53 signaling pathway and other mechanisms. The top 10 coexpressed genes, namely CDK1, CDC20, CCNB1, PLK1, CCNA2, AURKB, CCNB2, BUB1B, MAD2L1 and BUB1 were highly expressed, and were associated with poor prognosis in LUAD.

Conclusions

Consequently, we elucidated MTFR2 was a biomarker for diagnosis and poor prognosis in LUAD, and might participate in the progression of LUAD via affecting cell cycle, DNA replication, homologous recombination and p53 signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08378-3.

CDK1 inhibitor controls G2/M phase transition and reverses DNA damage sensitivity

CDK1 plays key roles in cell cycle progression through the G2/M phase transition and activation of homologous recombination (HR) DNA repair pathway. Accordingly, various CDK1 inhibitors have been developed for cancer therapy that induce prolonged G2 arrest and/or sensitize cells to DNA damaging agents in tumor cells, resulting in cell death. However, CDK1 inhibition can induce resistance to DNA damage in certain conditions. The mechanism of different DNA damage sensitivity is not completely understood. We performed immunofluorescence and flow cytometry analysis to investigate DNA damage responses in human tumor cells during low and high dose treatments with RO-3306, a selective CDK1 inhibitor. This comparative investigation demonstrated that RO-3306-induced G2 arrest prevented cells with DNA double-strand breaks from transitioning into the M-phase and that the cells maintained their DNA repair capacity in G2-phase, even under RO-3306 dose-dependent DNA repair inhibition. These findings reveal that CDK1 inhibitor-induced DNA repair inhibition and cell cycle control, which regulate each other during the G2/M phase transition determine the cellular sensitivity to DNA damage, providing insight useful for developing clinical strategies targeting CDK1 inhibition in tumor cells.

LncRNA SNHG12 regulates the radiosensitivity of cervical cancer through the miR-148a/CDK1 pathway

Background

Radiation resistance is a major obstacle to the prognosis of cervical cancer (CC) patients. Many studies have confirmed that long non-coding RNAs (lncRNAs) are involved in the regulation of radiosensitivity of cancers. However, whether small nucleolar RNA host gene 12 (SNHG12) regulates the radiosensitivity of CC remains unknown.

Methods

Quantitative real-time polymerase chain reaction was used to measure the expression levels of SNHG12 and microRNA-148a (miR-148a). The radiosensitivity of cells was evaluated by clonogenic assay. Flow cytometry and caspase-3 activity assay were performed to assess the apoptosis ability and cell cycle distribution of cells. Besides, dual-luciferase reporter and RNA immunoprecipitation assay were used to verify the interaction between miR-148a and SNHG12 or cyclin-dependent kinase 1 (CDK1). Also, the protein levels of CDK1, CCND1 and γ-H2AX were detected by western blot analysis. Furthermore, in vivo experiments were conducted to verify the effect of SNHG12 on CC tumor growth. Ki-67 and TUNEL staining were employed to evaluate the proliferation and apoptosis rates in vivo. The hematoxylin and eosin (HE) staining were employed to evaluate the tumor cell morphology.

Results

SNHG12 was upregulated in CC tissues and cells, and its knockdown improved the radiosensitivity by promoting the radiation-induced apoptosis and cell cycle arrest of CC cells. Also, miR-148a could be sponged by SNHG12 and could target CDK1. MiR-148a inhibitor or CDK1 overexpression could invert the promotion effect of silenced-SNHG12 on CC radiosensitivity. Meanwhile, SNHG12 interference reduced the tumor growth of CC, increased miR-148a expression, and inhibited CDK1 level in vivo.

Conclusion

LncRNA SNHG12 promoted CDK1 expression to regulate the sensitivity of CC cells to radiation through sponging miR-148a, indicating that SNHG12 could be used as a potential biomarker to treat the radiotherapy resistance of CC patients.

Identification of therapeutic targets and mechanisms of tumorigenesis in non-small cell lung cancer using multiple-microarray analysis

Lung cancer is the most commonly occurring cancer attributed to the leading cause of cancer-related deaths globally. Non-small cell lung cancer (NSCLC) comprises 85% to 90% of lung cancers. The survival rate of patients with advanced stage NSCLC is in months. Moreover, the underlying molecular mechanisms still remain to be understood.We used 2 sets of microarray data in combination with various bioinformatic approaches to identify the differentially expressed genes (DEGs) in NSCLC patients.We identified a total of 419 DEGs using the Limma package. Gene set enrichment analysis demonstrated that "Citrate cycle (TCA cycle)," "RNA degradation," and "Pyrimidine metabolism" pathways were significantly enriched in the NSCLC samples. Gene Ontology annotations of the 419 DEGs primarily comprised "glycosaminoglycan binding," "cargo receptor activity," and "organic acid binding." Kyoto Encyclopedia of Genes and Genomes analysis revealed that DEGs were enriched in pathways related to "Malaria," "Cell cycle," and "IL-17 signaling pathway." Protein protein interaction network analysis showed that the hub genes constituted of CDK1, CDC20, BUB1, BUB1B, TOP2A, CCNA2, KIF20A, CCNB1, KIF2C, and NUSAP1.Taken together, the identified hub genes and pathways will help understand NSCLC tumorigenesis and develop prognostic markers and therapeutic targets against NSCLC.

Restricted suitability of BODIPY for caging in biological applications based on singlet oxygen generation

Recent studies report the boron-dipyrromethene (BODIPY) moiety to be interesting for caging applications in photopharmacology based on its response to irradiation with wavelengths in the biooptical window. Thus, in a model study, we investigated the meso-methyl-BODIPY caged CDK2 inhibitor AZD5438 and aimed to assess the usability of BODIPY as a photoremovable protecting group in photoresponsive kinase inhibitor applications. Photochemical analysis and biological characterisation in vitro revealed significant limitations of the BODIPY-caged inhibitor concept regarding solubility and uncaging in aqueous solution. Notably, we provide evidence for BODIPY-caged compounds generating singlet oxygen/radicals upon irradiation, followed by photodegradation of the caged compound system. Consequently, instead of caging, a non-specific induction of necrosis in cells suggests the potential usage of BODIPY derivatives for photodynamic approaches.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.

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.

Treatment May Be Harmful: Mechanisms/Prediction/Prevention of Drug-Induced DNA Damage and Repair in Multiple Myeloma

Multiple myeloma (MM) is a malignancy characterized by accumulation of malignant plasma cells within the bone marrow (BM). MM is considered mostly without definitive treatment because of the inability of standard of care therapies to overcome drug-resistant relapse. Genotoxic agents are used in the treatment of MM and exploit the fact that DNA double-strand breaks are highly cytotoxic for cancer cells. However, their mutagenic effects are well-established and described. According to these effects, chemotherapy could cause harmful DNA damage associated with new driver genomic abnormalities providing selective advantage, drug resistance, and higher relapse risk. Several mechanisms associated with MM cell (MMC) resistance to genotoxic agents have been described, underlining MM heterogeneity. The understanding of these mechanisms provides several therapeutic strategies to overcome drug resistance and limit mutagenic effects of treatment in MM. According to this heterogeneity, adopting precision medicine into clinical practice, with the development of biomarkers, has the potential to improve MM disease management and treatment.

EBV encoded miRNA BART8-3p promotes radioresistance in nasopharyngeal carcinoma by regulating ATM/ATR signaling pathway

Resistance to radiotherapy is one of the main causes of treatment failure in patients with nasopharyngeal carcinoma (NPC). Epstein-Barr virus (EBV) infection is an important factor in the pathogenesis of NPC, and EBV-encoded microRNAs (miRNAs) promote NPC progression. However, the role of EBV-encoded miRNAs in the radiosensitivity of NPC remains unclear. Here, we investigated the effects of EBV-miR-BART8-3p on radiotherapy resistance in NPC cells in vitro and in vivo, and explored the underlying molecular mechanisms. Inhibitors of ataxia telangiectasia mutated (ATM)/ataxia telangiectasia mutated and Rad3-related (ATR) (KU60019 and AZD6738, respectively) were used to examine radiotherapy resistance. We proved that EBV-miR-BART8-3p promoted NPC cell proliferation in response to irradiation in vitro and associated with the induction of cell cycle arrest at the G2/M phase, which was a positive factor for the DNA repair after radiation treatment. Besides, EBV-miR-BART8-3p could increase the size of xenograft tumors significantly in nude mice. Treatment with KU60019 or AZD6738 increased the radiosensitivity of NPC by suppressing the expression of p-ATM and p-ATR. The present results indicate that EBV-miR-BART8-3p promotes radioresistance in NPC by modulating the activity of ATM/ATR signaling pathway.

Cyclin-dependent kinase inhibitors AZD5438 and R547 show potential for enhancing efficacy of daunorubicin-based anticancer therapy: Interaction with carbonyl-reducing enzymes and ABC transporters

Daunorubicin (DAUN) has served as an anticancer drug in chemotherapy regimens for decades and is still irreplaceable in treatment of acute leukemias. The therapeutic outcome of DAUN-based therapy is compromised by its cardiotoxicity and emergence of drug resistance. This phenomenon is often caused by pharmacokinetic mechanisms such as efflux of DAUN from cancer cells through ATP-binding cassette (ABC) transporters and its conversion to less cytostatic but more cardiotoxic daunorubicinol (DAUN-OL) by carbonyl reducing enzymes (CREs). Here we aimed to investigate, whether two cyclin-dependent kinase inhibitors, AZD5438 and R547, can interact with these pharmacokinetic mechanisms and reverse DAUN resistance. Using accumulation assays, we revealed AZD5438 as potent inhibitor of ABCC1 showing also weaker inhibitory effect to ABCB1 and ABCG2. Combination index analysis, however, shown that inhibition of ABCC1 does not significantly contribute to synergism between AZD5438 and DAUN in MDCKII-ABCC1 cells, suggesting predominant role of other mechanism. Using pure recombinant enzymes, we found both tested drugs to inhibit CREs with aldo-keto reductase 1C3 (AKR1C3). This interaction was further confirmed in transfected HCT-116 cells. Moreover, these cells were sensitized to DAUN by both compounds as Chou-Talalay combination index analysis showed synergism in AKR1C3 transfected HCT-116, but not in empty vector transfected control cell line. In conclusion, we propose AZD5438 and R547 as modulators of DAUN resistance that can prevent AKR1C3-mediated DAUN biotransformation to DAUN-OL. This interaction could be beneficially exploited to prevent failure of DAUN-based therapy as well as the undesirable cardiotoxic effect of DAUN-OL.

Identification of critically carcinogenesis-related genes in basal cell carcinoma

Background

Basal cell carcinoma (BCC) is a frequent malignant tumor of skin cancers with high morbidity. The objective of this study was to identify critical genes and pathways related to the carcinogenesis of BCC and gain more insights into the underlying molecular mechanisms of BCC.

Materials and methods

The gene expression profiles of GSE7553 and GSE103439 were downloaded from the Gene Expression Omnibus database with 19 tumors and 6 normal skin tissues. Differentially expressed genes (DEGs) were screened between BCC samples and normal tissues, followed by gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. Subsequently, protein–protein interaction (PPI) network was constructed for these DEGs, and module analysis was performed.

Results

A total of 313 DEGs were obtained. Among them, 222 genes were upregulated and 91 genes were downregulated. Enrichment analysis indicated that the upregulated genes were significantly enriched in cell cycle and mitosis, while the downregulated genes were mainly associated with unsaturated fatty acid metabolic process and cell differentiation. In addition, TOP2A, CDK1, and CCNB1 were identified as the top three hub genes ranked by degrees in the PPI network. Meanwhile, three subnetworks were derived, which indicated that these DEGs were significantly enriched in pathways, including “cell cycle”, “extracellular matrix–receptor interaction”, “basal cell carcinoma”, and “hedgehog signaling pathway”.

Conclusions

The novel critical DEGs and pathways identified in this study may serve pivotal roles in the carcinogenesis of BCC and indicate more molecular targets for the treatment of BCC.

Vicenin-2: a potential radiosensitizer of non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) is a major form of cancer and is resistant to chemo- and radio-therapy. Vicenin-2 (VCN-2) is a flavonoid obtained from Ocimum sanctum L. and it has been reported to have radioprotective and anti-cancer properties. This study was conducted to check for the radiosensitizing potential of VCN-2 in the NSCLC cell line, NCI-H23. NCI-H23 cells were exposed to VCN-2 singularly, and to X-rays with and without prior VCN-2 treatment. Cytotoxicity assay, cell proliferation assay, caspase-3 activity assay, DNA fragmentation assay and Western blotting for Rad50, MMP-2 and p21 were performed to investigate the radiosensitizing properties of VCN-2. Fibroblast survival assay was performed using HEK293T cells to check for any adverse effects of VCN-2 on normal fibroblast cell line. VCN-2 singularly and in combination with radiation reduced the surviving cancer cells, increased caspase-3 activity, increased DNA fragmentation, increased the levels of Rad50 and lowered levels of MMP-2 and p21 proteins while being non-toxic and radioprotective to the fibroblast cells. VCN-2 showed a potent radiosensitizing property while also showing a chemotherapeutic property against NSCLC cell line NCI-H23.

Targeting Cyclin-Dependent Kinases for Treatment of Gynecologic Cancers

Ovarian, uterine/endometrial, and cervical cancers are major gynecologic malignancies estimated to cause nearly 30,000 deaths in 2018 in US. Defective cell cycle regulation is the hallmark of cancers underpinning the development and progression of the disease. Normal cell cycle is driven by the coordinated and sequential rise and fall of cyclin-dependent kinases (CDK) activity. The transition of cell cycle phases is governed by the respective checkpoints that prevent the entry into the next phase until cellular or genetic defects are repaired. Checkpoint activation is achieved by p53- and ATM/ATR-mediated inactivation of CDKs in response to DNA damage. Therefore, an aberrant increase in CDK activity and/or defects in checkpoint activation lead to unrestricted cell cycle phase transition and uncontrolled proliferation that give rise to cancers and perpetuate malignant progression. Given that CDK activity is also required for homologous recombination (HR) repair, pharmacological inhibition of CDKs can be exploited as a synthetic lethal approach to augment the therapeutic efficacy of PARP inhibitors and other DNA damaging modalities for the treatment of gynecologic cancers. Here, we overview the basic of cell cycle and discuss the mechanistic studies that establish the intimate link between CDKs and HR repair. In addition, we present the perspective of preclinical and clinical development in small molecule inhibitors of CDKs and CDK-associated protein targets, as well as their potential use in combination with hormonal therapy, PARP inhibitors, chemotherapy, and radiation to improve treatment outcomes.

CDK1 inhibition sensitizes normal cells to DNA damage in a cell cycle dependent manner

Cyclin-dependent kinase 1 (CDK1) orchestrates the transition from the G2 phase into mitosis and as cancer cells often display enhanced CDK1 activity, it has been proposed as a tumor specific anti-cancer target. Here we show that the effects of CDK1 inhibition are not restricted to tumor cells but can also reduce viability in non-cancer cells and sensitize them to radiation in a cell cycle dependent manner. Radiosensitization by the specific CDK1 inhibitor, RO-3306, was determined by colony formation assays in three tumor lines (HeLa, T24, SQ20B) and three non-cancer lines (HFL1, MRC-5, RPE). Initial results showed that CDK1 inhibition radiosensitized tumor cells, but did not sensitize normal fibroblasts and epithelial cells in colony formation assays despite effective inhibition of CDK1 signaling. Further investigation showed that normal cells were less sensitive to CDK1 inhibition because they remained predominantly in G1 for a prolonged period when plated in colony formation assays. In contrast, inhibiting CDK1 a day after plating, when the cells were going through G2/M phase, reduced their clonogenic survival both with and without radiation. Our finding that inhibition of CDK1 can damage normal cells in a cell cycle dependent manner indicates that targeting CDK1 in cancer patients may lead to toxicity in normal proliferating cells. Furthermore, our finding that cell cycle progression becomes easily stalled in non-cancer cells under normal culture conditions has general implications for testing anti-cancer agents in these cells.

Anticancer and radiosensitizing effects of the cyclin-dependent kinase inhibitors, AT7519 and SNS‑032, on cervical cancer

Cyclin-dependent kinases (CDK) are considered to be potential targets of anticancer drugs that can interrupt the uncontrolled division of cancer cells. In this study, we selected two selective CDK inhibitors, AT7519 and SNS‑032, from current clinical trials and examined their anticancer and radiosensitizing effects in a cervical cancer model. SNS‑032 was found to be more potent than AT7519, with a lower half maximal inhibitory concentration (IC50) value. Both AT7519 and SNS‑032 induced the apoptosis, premature senescence and cytostasis of cervical cancer cells, which led to the attenuation of tumor growth in vivo. Moreover, using these CDK inhibitors together with radiation synergistically inhibited tumor growth in a human xenograft tumor model. The concomitant activation of the p53 tumor suppressor and the suppression of cell cycle checkpoint responses mediated by Chk1 led to the cytostasis of cervical cancer cells. Finally, AT7519 and SNS‑032 inhibited cancer cell migration, invasion and angiogenesis in vitro, and suppressed lung metastases in a spontaneous metastasis model. On the whole, the findings of this study indicate that the utilization of AT7519 and SNS‑032 as part of an adjuvant treatment may help control cervical cancer progression.

Cyclin-dependent kinase 1 targeting improves sensitivity to radiation in BRAF V600E colorectal carcinoma cells

OBJECTIVES

Preoperative chemoradiation is currently the standard of care in locally advanced rectal carcinoma, even though a subset of rectal tumors does not achieve major clinically meaningful responses upon neoadjuvant chemoradiation. At present, no molecular biomarkers are available to predict response to neoadjuvant chemoradiation and select resistant tumors willing more intense therapeutic strategies. Thus, BRAF mutational status was investigated for its role in favoring resistance to radiation in colorectal carcinoma cell lines and cyclin-dependent kinase 1 as a target to improve radiosensitivity in BRAF V600E colorectal tumor cells.

METHODS

Colony-forming assay and apoptotic rates were evaluated to compare the sensitivity of different colon carcinoma cell lines to ionizing radiation and their radiosensitivity upon exposure to BRAF and/or cyclin-dependent kinase 1 inhibitory/silencing strategies. Cyclin-dependent kinase 1 expression/subcellular distribution was studied by immunoblot analysis.

RESULTS

Colon carcinoma BRAF V600E HT29 cells exhibited poor response to radiation compared to BRAF wild-type COLO320 and HCT116 cells. Interestingly, neither radiosensitizing doses of 5-fluoruracil nor BRAF inhibition/silencing significantly improved radiosensitivity in HT29 cells. Of note, poor response to radiation correlated with upregulation/relocation of cyclin-dependent kinase 1 in mitochondria. Consistently, cyclin-dependent kinase 1 inhibition/silencing as well as its targeting, through inhibition of HSP90 quality control pathway, significantly inhibited the clonogenic ability and increased apoptotic rates in HT29 cells upon exposure to radiation.

CONCLUSION

These data suggest that BRAF V600E colorectal carcinoma cells are poorly responsive to radiation, and cyclin-dependent kinase 1 represents a target to improve radiosensitivity in BRAF V600E colorectal tumor cells.

The emerging picture of CDK9/P-TEFb: more than 20 years of advances since PITALRE

CDK9 is a prominent member of the transcriptional CDKs subfamily, a group of kinases whose function is to control the primary steps of mRNA synthesis and processing by eukaryotic RNA polymerase II. As a cyclin-dependent kinase, CDK9 activation in vivo depends upon its association with T-type cyclins to assemble the positive transcription elongation factor (P-TEFb). Although CDK9/P-TEFb phosphorylates the C-terminal domain of RNAP II in the same positions targeted by CDK7 (TFIIH) and CDK8 (Mediator), the former does not participate in the transcription initiation, but rather plays a unique role by driving the polymerase to productive elongation. In addition to RNAP II CTD, the negative transcription elongation factors DSIF and NELF also represent major CDK9 substrates, whose phosphorylation is required to overcome the proximal pause of the polymerase. CDK9 is recruited to specific genes through proteins that interact with both P-TEFb and distinct elements in DNA, RNA or chromatin, where it modulates the activity of individual RNAP II transcription complexes. The regulation of CDK9 function is an intricate network that includes post-translational modifications (phosphorylation/dephosphorylation and acetylation/deacetylation of key residues) as well as the association of P-TEFb with various proteins that can stimulate or inhibit its kinase activity. Several cases of CDK9 deregulation have been linked to important human diseases, including various types of cancer and also AIDS (due to its essential role in HIV replication). Not only HIV, but also many other human viruses have been shown to depend strongly on CDK9 activity to be transcribed within host cells. This review summarizes the main advances made on CDK9/P-TEFb field in more than 20 years, introducing the structural, functional and genetic aspects that have been elucidated ever since.

Parthenogenetic activation and somatic cell nuclear transfer of porcine oocytes activated by an electric pulse and AZD5438 treatment

We examined the in vitro developmental competence of parthenogenetic activation (PA) oocytes activated by an electric pulse (EP) and treated with various concentrations of AZD5438 for 4 h. Treatment with 10 µM AZD5438 for 4 h significantly improved the blastocyst formation rate of PA oocytes in comparison with 0, 20, or 50 µM AZD5438 treatment (46.4% vs. 34.5%, 32.3%, and 24.0%, respectively; P 0.05). Furthermore, 66.67% of blastocysts derived from these AZD5438-treated PA oocytes had a diploid karyotype. The blastocyst formation rate of PA and somatic cell nuclear transfer (SCNT) embryos was similar between oocytes activated by an EP and treated with 2 mM 6-dimethylaminopurine for 4 h and those activated by an EP and treated with 10 µM AZD5438 for 4 h (11.11% vs. 13.40%, P > 0.05). In addition, the level of maturation-promoting factor (MPF) was significantly decreased in oocytes activated by an EP and treated with 10 µM AZD5438 for 4 h. Finally, the mRNA expression levels of apoptosis-related genes (Bax and Bcl-2) and pluripotency-related genes (Oct4, Nanog, and Sox2) were checked by RT-PCR; however, there were no differences between the AZD5438-treated and non-treated control groups. Our results demonstrate that porcine oocyte activation via an EP in combination with AZD5438 treatment can lead to a high blastocyst formation rate in PA and SCNT experiments.

RPA3 is a potential marker of prognosis and radioresistance for nasopharyngeal carcinoma

Radioresistance-induced residual and recurrent tumours are the main cause of treatment failure in nasopharyngeal carcinoma (NPC). Thus, the mechanisms of NPC radioresistance and predictive markers of NPC prognosis and radioresistance need to be investigated and identified. In this study, we identified RPA3 as a candidate radioresistance marker using RNA-seq of NPC samples. In vitro studies further confirmed that RPA3 affected the radiosensitivity of NPC cells. Specifically, the overexpression of RPA3 enhanced radioresistance and the capacity for DNA repair of NPC cells, whereas inhibiting RPA3 expression sensitized NPC cells to irradiation and decreased the DNA repair capacity. Furthermore, the overexpression of RPA3 enhanced RAD51 foci formation in NPC cells after irradiation. Immunohistochemical assays in 104 NPC specimens and 21 normal epithelium specimens indicated that RPA3 was significantly up-regulated in NPC tissues, and a log-rank test suggested that in patients with NPC, high RPA3 expression was associated with shorter overall survival (OS) and a higher recurrence rate compared with low expression (5-year OS rates: 67.2% versus 86.2%; 5-year recurrence rates: 14.8% versus 2.3%). Moreover, TCGA data also indicated that high RPA3 expression correlated with poor OS and a high recurrence rate in patients with head and neck squamous cell carcinoma (HNSC) after radiotherapy. Taken together, the results of our study demonstrated that RPA3 regulated the radiosensitivity and DNA repair capacity of NPC cells. Thus, RPA3 may serve as a new predictive biomarker for NPC prognosis and radioresistance to help guide the diagnosis and individualized treatment of patients with NPC.

Long Noncoding RNA GAS5 Inhibits Tumorigenesis and Enhances Radiosensitivity by Suppressing miR-135b Expression in Non-Small Cell Lung Cancer

Growth arrest-specific transcript 5 (GAS5) has been demonstrated to correlate with clinicopathological characteristics and serve as a tumor suppressor in non-small cell lung cancer (NSCLC). However, the underlying mechanism of the competing endogenous RNA (ceRNA) regulatory network involving GAS5 in NSCLC remains to be elucidated. In this study, qRT-PCR results showed that GAS5 was downregulated and miR-135b was upregulated in NSCLC tissues and cells. The expressions of GAS5 and miR-135b changed inversely in response to irradiation. Gain-of-function experiments revealed that GAS5 overexpression and miR-135b downregulation significantly suppressed tumorigenesis by repressing cell proliferation and invasion, and enhanced the radiosensitivity of NSCLC cells by reducing colony formation rates. Luciferase reporter assay confirmed that GAS5 could directly target miR-135b and negatively regulate its expression. Moreover, rescue experiments demonstrated that miR-135b upregulation markedly abolished GAS5 overexpression-induced tumorigenesis inhibition and radiosensitivity improvement. Furthermore, xenograft model analysis validated that GAS5 overexpression suppressed tumor growth and improved radiosensitivity of NSCLC cells in vivo. Taken together, GAS5 inhibits tumorigenesis and enhances radiosensitivity by suppressing miR-135b expression in NSCLC cells, deepening our understanding of the mechanism of miRNA-lncRNA interaction and providing a novel therapeutic strategy for NSCLC.

Recent progress of cyclin-dependent kinase inhibitors as potential anticancer agents

Deregulation of the cell cycle is a common feature in human cancer. The inhibition of cyclin-dependent kinases (CDKs), which play a crucial role in control of the cell cycle, has always been one of the most promising areas in cancer chemotherapy. This review first summarizes the biology of CDKs and then focuses on the recent advances in both broad-range and selective CDK inhibitors during the last 5 years. The design rationale, structural optimization and structure–activity relationships analysis of these small molecules have been discussed in detail and the key interactions with the amino-acid residues of the most important compounds are highlighted. Future perspectives for CDKs inhibitors will be defined in the development of highly selective CDK inhibitors, an accurate knowledge of gene control mechanism and further predictive biomarker research.

Downregulation of a novel human gene, ROGDI, increases radiosensitivity in cervical cancer cells

ROGDI is a protein that contains a leucine zipper domain and may be involved in cell proliferation. In addition, ROGDI is associated with genome stability by regulating the activity of a DNA damage marker, γ-H2AX. The role of ROGDI in tumor radiosensitization has not been investigated. Previous studies have indicated that radiosensitivity is associated with DNA repair and the cell cycle. In general, the G2/M DNA damage checkpoint is more sensitive to radiation, whereas the G1/S phase transition is more resistant to radiation. Inhibition of cyclin-dependent kinases (CDKs) can lead to a halt of cell cycle progression and a stay at different phases or checkpoints. Our data show that the downregulation of ROGDI led to a decreased expression of CDK 1, 2, cyclin A, B and resulted in a G2/M phase transition block. In addition, the downregulation of ROGDI increased cell accumulation at the G2 phase as detected using flow cytometry and decreased cell survival as revealed by clonogenic assay in HeLa and C33A cells following irradiation. These findings suggest that the downregulation of ROGDI can mediate radiosensitivity by blocking cells at G2/M, the most radiosensitive phase of the cell cycle, as well as exerting deleterious effects in the form of DNA damage, as shown by increased γ-H2AX activation.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

NSCLC cells demonstrate differential mode of cell death in response to the combined treatment of radiation and a DNA-PKcs inhibitor

The current standard of care for lung cancer consists of concurrent chemotherapy and radiation. Several studies have shown that the DNA-PKcs inhibitor NU7441 is a highly potent radiosensitizer, however, the mechanism of NU7441's anti-proliferation effect has not been fully elucidated. In this study, the combined effect of NU7441 and ionizing radiation (IR) in a panel of non-small cell lung cancer cell lines (A549, H460 and H1299) has been investigated. We found that NU7441 significantly enhances the effect of IR in all cell lines. The notable findings in response to this combined treatment are (i) prolonged delay in IR-induced DNA DSB repair, (ii) induced robust G2/M checkpoint, (iii) increased aberrant mitosis followed by mitotic catastrophe specifically in H1299, (iv) dramatically induced autophagy in A549 and (v) IR-induced senescence specifically in H460. H1299 cells show greater G2 checkpoint adaptation after combined treatment, which can be attributed to higher expression level of Plk1 compared to A549 and H460. The enhanced autophagy after NU7441 treatment in A549 is possibly due to the higher endogenous expression of pS6K compared to H1299 and H460 cells. In conclusion, choice of cell death pathway is dependent on the mutation status and other genetic factors of the cells treated.

A Cyclin-Dependent Kinase Inhibitor, Dinaciclib, Impairs Homologous Recombination and Sensitizes Multiple Myeloma Cells to PARP Inhibition

PARP1/2 are required for single-strand break repair, and their inhibition causes DNA replication fork collapse and double-strand break (DSB) formation. These DSBs are primarily repaired via homologous recombination (HR), a high-fidelity repair pathway. Should HR be deficient, DSBs may be repaired via error-prone nonhomologous end-joining mechanisms, or may persist, ultimately resulting in cell death. The combined disruption of PARP and HR activities thus produces synthetic lethality. Multiple myeloma cells are characterized by chromosomal instability and pervasive DNA damage, implicating aberrant DNA repair. Cyclin-dependent kinases (CDK), upstream modulators of HR, are dysregulated in multiple myeloma. Here, we show that a CDK inhibitor, dinaciclib, impairs HR repair and sensitizes multiple myeloma cells to the PARP1/2 inhibitor ABT-888. Dinaciclib abolishes ABT-888-induced BRCA1 and RAD51 foci and potentiates DNA damage, indicated by increased γH2AX foci. Dinaciclib treatment reduces expression of HR repair genes, including Rad51, and blocks BRCA1 phosphorylation, a modification required for HR repair, thus inhibiting HR repair of chromosome DSBs. Cotreatment with dinaciclib and ABT-888 in vitro resulted in synthetic lethality of multiple myeloma cells, but not normal CD19(+) B cells, and slowed growth of multiple myeloma xenografts in SCID mice almost two-fold. These findings support combining dinaciclib with PARP inhibitors for multiple myeloma therapy. Mol Cancer Ther; 15(2); 241-50. ©2015 AACR.

Prognostic significance of G2/M arrest signaling pathway proteins in advanced non-small cell lung cancer patients

The aim of the present study was to retrospectively assess the correlation between the expression levels of proteins involved in G2/M arrest signaling pathways in non-small cell lung cancer (NSCLC) tissue, as determined by immunohistochemical (IHC) methods, and the overall survival of patients with advanced stage NSCLC. IHC analysis of advanced NSCLC specimens was used to determine the expression levels of proteins involved in G2/M arrest signaling pathways, including ataxia telangiectasia mutated (ATM) kinase, ataxia telangiectasia and Rad3-related (ATR) kinase, checkpoint kinase (Chk) 1, Chk2, cell division cycle 25C (Cdc25C), total cyclin-dependent kinase 1 (Cdk1) and active Cdk1 signaling pathways, the latter of which refers to dephospho-Cdk1 (Tyr15) and phospho-Cdk1 (Thr161). Patients were enrolled continuously and followed up for ≥2 years. Univariate analysis demonstrated that the protein expression levels of dephospho-Cdk1 (P=0.015) and phospho-Cdk1 (P=0.012) exhibited prognostic significance, while the expression of the other proteins was not significantly associated with patient survival (ATM, P=0.843; ATR, P=0.245; Chk1, P=0.341; Chk2, P=0.559; Cdc25C, P=0.649; total Cdk1, P=0.093). Furthermore, the patients with tumors exhibiting low expression levels of active Cdk1 survived significantly longer than those with tumors exhibiting high active Cdk1 expression levels (P<0.05). In addition, Cox regression analysis demonstrated that the expression of active Cdk1 [odds ratio (OR), 0.624; 95% confidence ratio (CI), 0.400–0.973; P=0.038] and the pathological tumor-node-metastasis stage (OR, 0.515; 95% CI, 0.297–0.894; P=0.018) were significant independent prognostic factors for NSCLC. Therefore, the results of the present study indicated that active Cdk1 protein is an independent prognostic factor for advanced NSCLC and may validate Cdk1 as a therapeutic target for advanced NSCLC patients.

Highlights of the Latest Advances in Research on CDK Inhibitors

Uncontrolled proliferation is the hallmark of cancer and other proliferative disorders and abnormal cell cycle regulation is, therefore, common in these diseases. Cyclin-dependent kinases (CDKs) play a crucial role in the control of the cell cycle and proliferation. These kinases are frequently deregulated in various cancers, viral infections, neurodegenerative diseases, ischemia and some proliferative disorders. This led to a rigorous pursuit for small-molecule CDK inhibitors for therapeutic uses. Early efforts to block CDKs with nonselective CDK inhibitors led to little specificity and efficacy but apparent toxicity, but the recent advance of selective CDK inhibitors allowed the first successful efforts to target these kinases for the therapies of several diseases. Major ongoing efforts are to develop CDK inhibitors as monotherapies and rational combinations with chemotherapy and other targeted drugs.

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.

Targeting homologous recombination-mediated DNA repair in cancer

INTRODUCTION

DNA is the target of many traditional non-specific chemotherapeutic drugs. New drugs or therapeutic approaches with a more rational and targeted component are mandatory to improve the success of cancer therapy. The homologous recombination (HR) pathway is an attractive target for the development of inhibitors because cancer cells rely heavily on HR for repair of DNA double-strand breaks resulting from chemotherapeutic treatments. Additionally, the discovery that poly(ADP)ribose polymerase-1 inhibitors selectively kill cells with genetic defects in HR has spurned an even greater interest in inhibitors of HR.

AREAS COVERED

HR drives the repair of broken DNA via numerous protein-mediated sequential DNA manipulations. Due to extensive number of steps and proteins involved, the HR pathway provides a rich pool of potential drug targets. This review discusses the latest developments concerning the strategies being explored to inhibit HR. Particular attention is given to the identification of small molecule inhibitors of key HR proteins, including the BRCA proteins and RAD51.

EXPERT OPINION

Current HR inhibitors are providing the basis for pharmaceutical development of more potent and specific inhibitors to be applied in mono- or combinatorial therapy regimes, while novel targets will be uncovered by experiments aimed to gain a deeper mechanistic understanding of HR and its subpathways.

The radiosensitizing effect of Paeonol on lung adenocarcinoma by augmentation of radiation-induced apoptosis and inhibition of the PI3K/Akt pathway

PURPOSE

To investigate the radiosensitizing effect and mechanism of action by the natural product Paeonol on lung adenocarcinoma both in vitro and in vivo.

MATERIALS AND METHODS

Two lung adenocarcinoma cell lines (human lung adenocarcinoma cell line A549 and mouse Lewis lung carcinoma (LLC) cell line) were chosen for this research. In order to select the experimental concentrations of Paeonol, cytotoxicity was determined using a MTT (3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide) assay. A clonogenic assay was performed to measure the radiosensitizing effects. Apoptosis was determined by the Tunel (terminal deoxynucleotidyl transferase-mediated dUTP nick and labeling) assay and flow cytometry. Protein expression was analyzed by Western blotting. To test the radiosensitizing effect in vivo, a transplanted tumor model was established.

RESULTS

The MTT assay showed that Paeonol inhibited proliferation of cells. Paeonol concentration ranged from an IC5 (5% inhibiting concentration) to an IC20 and was used at non-toxic concentrations for subsequent experiments. The clonogenic assay showed that Paeonol enhanced the radiosensitivity of cells. Data from the Tunel assay and flow cytometry verified that Paeonol enhanced radiation-induced apoptosis. Paeonol inhibited the activation of the PI3K/AKT (Phosphatidylinositol 3-kinase/ Protein Kinase B) pathway and down-regulated the expression of COX-2 (Cyclooxygenase-2) and Survivin. Paeonol (1718 mg/kg) combined with 10 Gy irradiation inhibited the growth of a transplanted tumor model in vivo, resulting in the longest tumor growth time, tumor growth delay and the highest inhibition ratio when compared with the radiotherapy alone group.

CONCLUSIONS

It is reported for the first time that Paeonol has a radiosensitizing effect on lung adenocarcinoma both in vitro and in vivo. This effect could be related to the augmentation of radiation-induced apoptosis and the inhibition of the PI3K/Akt signalling pathway and its downstream proteins: COX-2 and Survivin.