Ribonucleotide reductase R2 component is a novel malignancy determinant that cooperates with activated oncogenes to determine transformation and malignant potential

An NFATc1/SMAD3/cJUN Complex Restricted to SMAD4-Deficient Pancreatic Cancer Guides Rational Therapies

BACKGROUND & AIMS

The highly heterogeneous cellular and molecular makeup of pancreatic ductal adenocarcinoma (PDAC) not only fosters exceptionally aggressive tumor biology, but contradicts the current concept of one-size-fits-all therapeutic strategies to combat PDAC. Therefore, we aimed to exploit the tumor biological implication and therapeutic vulnerabilities of a clinically relevant molecular PDAC subgroup characterized by SMAD4 deficiency and high expression of the nuclear factor of activated T cells (SMAD4-/-/NFATc1High).

METHODS

Transcriptomic and clinical data were analyzed to determine the prognostic relevance of SMAD4-/-/NFATc1High cancers. In vitro and in vivo oncogenic transcription factor complex formation was studied by immunoprecipitation, proximity ligation assays, and validated cross model and species. The impact of SMAD4 status on therapeutically targeting canonical KRAS signaling was mechanistically deciphered and corroborated by genome-wide gene expression analysis and genetic perturbation experiments, respectively. Validation of a novel tailored therapeutic option was conducted in patient-derived organoids and cells and transgenic as well as orthotopic PDAC models.

RESULTS

Our findings determined the tumor biology of an aggressive and chemotherapy-resistant SMAD4-/-/NFATc1High subgroup. Mechanistically, we identify SMAD4 deficiency as a molecular prerequisite for the formation of an oncogenic NFATc1/SMAD3/cJUN transcription factor complex, which drives the expression of RRM1/2. RRM1/2 replenishes nucleoside pools that directly compete with metabolized gemcitabine for DNA strand incorporation. Disassembly of the NFATc1/SMAD3/cJUN complex by mitogen-activated protein kinase signaling inhibition normalizes RRM1/2 expression and synergizes with gemcitabine treatment in vivo to reduce the proliferative index.

CONCLUSIONS

Our results suggest that PDAC characterized by SMAD4 deficiency and oncogenic NFATc1/SMAD3/cJUN complex formation exposes sensitivity to a mitogen-activated protein kinase signaling inhibition and gemcitabine combination therapy.

Prognostic and Immunological Potential of Ribonucleotide Reductase Subunits in Liver Cancer

Background

Ribonucleotide reductase (RR) consists of two subunits, the large subunit RRM1 and the small subunit (RRM2 or RRM2B), which is essential for DNA replication. Dysregulations of RR were implicated in multiple types of cancer. However, the abnormal expressions and biologic functions of RR subunits in liver cancer remain to be elucidated.

Methods

TCGA, HCCDB, CCLE, HPA, cBioPortal, and GeneMANIA were utilized to perform bioinformatics analysis of RR subunits in the liver cancer. GO, KEGG, and GSEA were used for enrichment analysis.

Results

The expressions of RRM1, RRM2, and RRM2B were remarkably upregulated among liver cancer tissue both in mRNA and protein levels. High expression of RRM1 and RRM2 was notably associated with high tumor grade, high stage, short overall survival, and disease-specific survival. Enrichment analyses indicated that RRM1 and RRM2 were related to DNA replication, cell cycle, regulation of nuclear division, DNA repair, and DNA recombination. Correlation analysis indicated that RRM1 and RRM2 were significantly associated with several subsets of immune cell, including Th2 cells, cytotoxic cells, and neutrophils. RRM2B expression was positively associated with immune score and stromal score. Chemosensitivity analysis revealed that sensitivity of nelarabine was positively associated with high expressions of RRM1 and RRM2. The sensitivity of rapamycin was positively associated with high expressions of RRM2B.

Conclusion

Our findings demonstrated high expression profiles of RR subunits in liver cancer, which may provide novel insights for predicting the poor prognosis and increased chemosensitivity of liver cancer in clinic.

Comprehensive Landscape of RRM2 with Immune Infiltration in Pan-Cancer

Simple Summary

RRM2 is a crucial subunit of ribonucleotide reductase. In this article, we provided a comprehensive analysis of RRM2 with immune infiltration in pan-cancer. We focused on the hotspots of ferroptosis-related gene RRM2 and immunotherapy. Via bioinformatics analysis, multiple indicators suggested that RRM2 high expression may enhance immunotherapy sensitivity. For the first time, we systematically analyzed the role of RRM2 in pan-cancer. We provided the prospect of RRM2 and immunotherapy for pan-cancer. Additionally, we proved the expression pattern, clinical value, prognostic value and potential pathways of RRM2 with different platforms. In particular, we confirmed RRM2 expression and function in bladder cancer in our clinical samples and cell lines. Collectively, we found that RRM2 is a novel prognostic biomarker, and these findings may aid in an improved understanding of the role of RRM2 and its clinical application in human cancers.

Abstract

As a crucial subunit of ribonucleotide reductase, RRM2 plays a significant part in DNA synthesis. This study aimed to elucidate the comprehensive landscape of RRM2 in human cancers. With different bioinformatics platforms, we investigated the expression pattern, prognostic significance, mutational landscapes, gene interaction network, signaling pathways and immune infiltration of RRM2 in tumors. We found that RRM2 expression was predominantly up-expressed in tumor tissues in most tumors. Concurrently, RRM2 expression was significantly associated with worse prognosis and tumor stage across TCGA cancers. Moreover, RRM2 high levels were critically associated with the infiltration of natural killer T cells and immune scores. RRM2 was positively related to immune checkpoints, tumor mutation burden, microsatellite instability, neoantigen, and cytotoxic T lymphocyte in several cancers, predicting effective response to immunotherapy. Meanwhile, a strong co-expression of RRM2 with immune-related genes was observed. Additionally, multiple Cox regression analysis showed that RRM2 was an independent prognostic factor in bladder cancer (BLCA). Eventually, we verified that RRM2 was overexpressed in BLCA clinical samples and cell lines. Blocking RRM2 could suppress BLCA cells’ growth and proliferation while enhancing sensitivity to cisplatin. This study provided a new perspective for understanding RRM2 in cancers and new strategies for tumor immunotherapy.

RNA Sequencing and Bioinformatic Analysis on Retinoblastoma Revealing that Cell Cycle Deregulation Is a Key Process in Retinoblastoma Tumorigenesis

PURPOSE

Retinoblastoma (RB) is a primary pediatric ocular malignancy that can be fatal with inadequate treatment. While multimodal treatments are applied for eye salvage, vision loss and metastasis can occur in some patients. The present study aimed to explore key pathways and factors in RB pathogenesis, which could be potential targets for novel RB treatments.

METHODS

RNA sequencing was performed on three RB tissues and referenced with three normal retinas. Differentially expressed genes (DEGs) were identified from sequencing data and further analyzed with clustering analysis, function and pathway enrichment, protein-protein interaction (PPI), and data-mining analysis in order to screen for tumorigenic relevancy.

RESULTS

A total of 331 DEGs were identified by clustering analysis of RB tissues, and the expression patterns were significantly distinguishable from normal retinas. Function and pathway enrichment and PPI analysis together showed that cell cycle was the most prominently upregulated pathway found in RB tissues. Following comprehensive bioinformatic analyses, six key genes relevant to cell cycle regulation were identified, namely BUB1, RRM2, TPX2, UBE2C, NUSAP1, and DTL.

CONCLUSIONS

Cell cycle pathway and six relevant genes may be potential key factors in RB tumorigenesis and laying the foundation for prospective investigation on development of novel targeted therapies.

Potential tumor‑suppressive role of microRNA‑99a‑3p in sunitinib‑resistant renal cell carcinoma cells through the regulation of RRM2

Sunitinib is the most common primary molecular‑targeted agent for metastatic clear cell renal cell carcinoma (ccRCC); however, intrinsic or acquired sunitinib resistance has become a significant problem in medical practice. The present study focused on microRNA (miR)‑99a‑3p, which was significantly downregulated in clinical sunitinib‑resistant ccRCC tissues in previous screening analyses, and investigated the molecular network associated with it. The expression levels of miR‑99a‑3p and its candidate target genes were evaluated in RCC cells, including previously established sunitinib‑resistant 786‑o (SU‑R‑786‑o) cells, and clinical ccRCC tissues, using reverse transcription‑quantitative polymerase chain reaction. Gain‑of‑function studies demonstrated that miR‑99a‑3p significantly suppressed cell proliferation and colony formation in RCC cells, including the SU‑R‑786‑o cells, by inducing apoptosis. Based on in silico analyses and RNA sequencing data, followed by luciferase reporter assays, ribonucleotide reductase regulatory subunit‑M2 (RRM2) was identified as a direct target of miR‑99a‑3p in the SU‑R‑786‑o cells. Loss‑of‑function studies using small interfering RNA against RRM2 revealed that cell proliferation and colony growth were significantly inhibited via induction of apoptosis, particularly in the SU‑R‑786‑o cells. Furthermore, the RRM2 inhibitor Didox (3,4‑dihydroxybenzohydroxamic acid) exhibited anticancer effects in the SU‑R‑786‑o cells and other RCC cells. To the best of our knowledge, this is the first report demonstrating that miR‑99a‑3p directly regulates RRM2. Identifying novel genes targeted by tumor‑suppressive miR‑99a‑3p in sunitinib‑resistant RCC cells may improve our understanding of intrinsic or acquired resistance and facilitate the development of novel therapeutic strategies.

miR-211 regulates the expression of RRM2 in tumoral metastasis and recurrence in colorectal cancer patients with a k-ras gene mutation

Colorectal cancer (CRC) ranks as the third-leading cause of cancer-associated mortalities in Taiwan. The expression of ribonucleotide reductase M2 (RRM2) and p53R2 is associated with tumoral malignancy and progression in several types of cancer. The aim of the present study was to determine the association of p53R2/RRM2 with the upstream expression of microRNA (miR)-211 and the association of expression levels of p53, APC and k-ras with clinical outcomes in patients with CRC. The study consisted of 192 tumor tissue samples obtained from patients with CRC. Immunohistochemistry and direct sequencing of DNA were performed to analyze p53R2/RRM2 protein expression and p53/APC/k-ras gene mutations in these samples. The expression level of miR-211 was detected by reverse transcription-quantitative polymerase chain reaction. The results showed that the expression of p53R2 was lower and that of RRM2 was higher in patients with lymph node metastasis, distant metastasis, and late-stage CRC compared with patients without lymph node metastasis, distant metastasis and early-stage CRC. A high expression of RRM2 in patients had a negative effect on overall survival (OS) and disease-free survival (DFS) in CRC. Positive expression of RRM2 was detected in tumor tissues, and expression associated with the presence of k-ras gene mutation. Furthermore, it was detected that the upstream miR-211 expression was negatively associated with RRM2 expression in tumor tissues of patients with CRC. miR-211 expression was associated with survival and tumoral recurrence in patients with k-ras mutations. The present authors suggest that the downregulation of miR-211 and overexpression of RRM2 in tumor tissues of patients with CRC could be used to predict metastases and disease prognosis, particularly in patients with k-ras gene mutations.

Knockdown of TBRG4 affects tumorigenesis in human H1299 lung cancer cells by regulating DDIT3, CAV1 and RRM2

The transforming growth factor β regulator 4 (TBRG4) gene, located on the 7p14-p13 chromosomal region, is implicated in numerous types of cancer. However, the contribution(s) of TBRG4 in human lung cancer remains unknown. In the present study, the expression of TBRG4 mRNA was investigated in the H1299 lung cancer cell line using the quantitative polymerase chain reaction (qPCR) following the knockdown of TBRG4 by a lentivirus-mediated small interfering RNA (siRNA). Results identified that the expression of TBRG4 within H1299 cells was significantly suppressed (P<0.01) by RNA interference, and 586 genes were differentially expressed following TBRG4 silencing. Ingenuity Pathway Analysis (IPA) revealed that these genes were often associated with infectious diseases, organismal injury, abnormalities and cancer functional networks. Further IPA of these networks revealed that TBRG4 knockdown in H1299 cells deregulated the expression of 21 downstream genes, including the upregulation of DNA damage-inducible transcript 3 (DDIT3), also termed CCAAT/enhancer-binding protein homologous protein, and downregulation of caveolin 1 (CAV1) and ribonucleotide reductase regulatory subunit M2 (RRM2). Results were validated using qPCR and western blotting. Furthermore, immunohistochemical staining of TBRG4 protein identified that expression was markedly increased in carcinoma compared with in normal tissue. In conclusion, TBRG4 serves a role in the tumorigenesis of lung cancer via deregulation of DDIT3, CAV1 and RRM2. The results of the present study may be important in contributing to our understanding of TBRG4 as a target for lung cancer treatment.

Targeting Nucleotide Biosynthesis: A Strategy for Improving the Oncolytic Potential of DNA Viruses

The rapid growth of tumors depends upon elevated levels of dNTPs, and while dNTP concentrations are tightly regulated in normal cells, this control is often lost in transformed cells. This feature of cancer cells has been used to advantage to develop oncolytic DNA viruses. DNA viruses employ many different mechanisms to increase dNTP levels in infected cells, because the low concentration of dNTPs found in non-cycling cells can inhibit virus replication. By disrupting the virus-encoded gene(s) that normally promote dNTP biosynthesis, one can assemble oncolytic versions of these agents that replicate selectively in cancer cells. This review covers the pathways involved in dNTP production, how they are dysregulated in cancer cells, and the various approaches that have been used to exploit this biology to improve the tumor specificity of oncolytic viruses. In particular, we compare and contrast the ways that the different types of oncolytic virus candidates can directly modulate these processes. We limit our review to the large DNA viruses that naturally encode homologs of the cellular enzymes that catalyze dNTP biogenesis. Lastly, we consider how this knowledge might guide future development of oncolytic viruses.

p53R2 overexpression in cervical cancer promotes AKT signaling and EMT, and is correlated with tumor progression, metastasis and poor prognosis

p53R2 is a p53-inducible ribonucleotide reductase subunit involved in deoxyribonucleotide biosynthesis and DNA repair. Although p53R2 has been linked to human cancer, its role in cervical cancer remains unknown. In this study, we investigated the expression and clinical significance of p53R2 in early-stage cervical cancer. p53R2 expression is significantly upregulated at both mRNA and protein levels in cervical cancer cells and tissues, compared with that in matched normal cervical cells and tissues, respectively. p53R2 overexpression is associated with increased risk of pelvic lymph node metastasis (PLNM, p = 0.001) and cancer relapse (p = 0.009). Patients with high p53R2 expression have a shorter overall survival (OS) and disease-free survival (DFS). p53R2 is an independent factor for predicting OS and DFS of cervical cancer patients. We further show that p53R2 is important for oncogenic growth, migration and invasion in cervical cancer cells. Mechanistically, p53R2 promotes Akt signaling and epithelial-mesenchymal transition (EMT). In conclusion, our study demonstrates for the first time that p53R2 protein is overexpressed in early-stage cervical cancer and unravels some unconventional oncogenic functions of p53R2. p53R2 may be a useful prognostic biomarker and therapeutic target for cervical cancer.

Clinical pharmacology and clinical trials of ribonucleotide reductase inhibitors: is it a viable cancer therapy?

PURPOSE

Ribonucleotide reductase (RR) enzymes (RR1 and RR2) play an important role in the reduction of ribonucleotides to deoxyribonucleotides which is involved in DNA replication and repair. Augmented RR activity has been ascribed to uncontrolled cell growth and tumorigenic transformation.

METHODS

This review mainly focuses on several biological and chemical RR inhibitors (e.g., siRNA, GTI-2040, GTI-2501, triapine, gemcitabine, and clofarabine) that have been evaluated in clinical trials with promising anticancer activity from 1960's till 2016. A summary on whether their monotherapy or combination is still effective for further use is discussed.

RESULTS

Among the RR2 inhibitors evaluated, GTI-2040, siRNA, gallium nitrate and didox were more efficacious as a monotherapy, whereas triapine was found to be more efficacious as combination agent. Hydroxyurea is currently used more in combination therapy, even though it is efficacious as a monotherapy. Gallium nitrate showed mixed results in combination therapy, while the combination activity of didox is yet to be evaluated. RR1 inhibitors that have long been used in chemotherapy such as gemcitabine, cladribine, fludarabine and clofarabine are currently used mostly as a combination therapy, but are equally efficacious as a monotherapy, except tezacitabine which did not progress beyond phase I trials.

CONCLUSIONS

Based on the results of clinical trials, we conclude that RR inhibitors are viable treatment options, either as a monotherapy or as a combination in cancer chemotherapy. With the recent advances made in cancer biology, further development of RR inhibitors with improved efficacy and reduced toxicity is possible for treatment of variety of cancers.

E2F1 promote the aggressiveness of human colorectal cancer by activating the ribonucleotide reductase small subunit M2

As the ribonucleotide reductase small subunit, the high expression of ribonucleotide reductase small subunit M2 (RRM2) induces cancer and contributes to tumor growth and invasion. In several colorectal cancer (CRC) cell lines, we found that the expression levels of RRM2 were closely related to the transcription factor E2F1. Mechanistic studies were conducted to determine the molecular basis. Ectopic overexpression of E2F1 promoted RRM2 transactivation while knockdown of E2F1 reduced the levels of RRM2 mRNA and protein. To further investigate the roles of RRM2 which was activated by E2F1 in CRC, CCK-8 assay and EdU incorporation assay were performed. Overexpression of E2F1 promoted cell proliferation in CRC cells, which was blocked by RRM2 knockdown attenuation. In the migration and invasion tests, overexpression of E2F1 enhanced the migration and invasion of CRC cells which was abrogated by silencing RRM2. Besides, overexpression of RRM2 reversed the effects of E2F1 knockdown partially in CRC cells. Examination of clinical CRC specimens demonstrated that both RRM2 and E2F1 were elevated in most cancer tissues compared to the paired normal tissues. Further analysis showed that the protein expression levels of E2F1 and RRM2 were parallel with each other and positively correlated with lymph node metastasis (LNM), TNM stage and distant metastasis. Consistently, the patients with low E2F1 and RRM2 levels have a better prognosis than those with high levels. Therefore, we suggest that E2F1 can promote CRC proliferation, migration, invasion and metastasis by regulating RRM2 transactivation. Understanding the role of E2F1 in activating RRM2 transcription will help to explain the relationship between E2F1 and RRM2 in CRC and provide a novel predictive marker for diagnosis and prognosis of the disease.

T-type calcium channel antagonists, mibefradil and NNC-55-0396 inhibit cell proliferation and induce cell apoptosis in leukemia cell lines

Background

T-type Ca²⁺ channels are often aberrantly expressed in different human cancers and participate in the regulation of cell cycle progression, proliferation and death. Methods: RT-PCR, Q-PCR, western blotting and whole-cell patch-clamp recording were employed to assess the expression of T-type Ca²⁺ channels in leukemia cell lines. The function of T-type Ca²⁺ channels in leukemia cell growth and the possible mechanism of the effect of T-type Ca²⁺ channel antagonists on cell proliferation and apoptosis were examined in T-lymphoma cell lines.

Results

We show that leukemia cell lines exhibited reduced cell growth when treated with T-type Ca²⁺ channel inhibitors, mibefradil and NNC-55-0396 in a concentration-dependent manner. Mechanistically, these inhibitors played a dual role on cell viability: (i) blunting proliferation, through a halt in the progression to the G1-S phase; and (ii) promoting cell apoptosis, partially dependent on the endoplasmic reticulum Ca²⁺ release. In addition, we observed a reduced phosphorylation of ERK1/2 in MOLT-4 cells in response to mibefradil and NNC-55-0396 treatment.

Conclusions

These results indicate that mibefradil and NNC-55-0396 regulate proliferation and apoptosis in T-type Ca²⁺ channel expressing leukemia cell lines and suggest a potential therapeutic target for leukemia.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0171-4) contains supplementary material, which is available to authorized users.

The prognostic value of ribonucleotide reductase small subunit M2 in predicting recurrence for prostate cancers

PURPOSE

To investigate the prognostic significance of ribonucleotide reductase small subunit M2 (RRM2) in low- and intermediate-risk prostate cancer (PCa).

MATERIALS AND METHODS

A retrospective outcome study was conducted on 164 eligible PCa samples from the City of Hope (n = 90) and the Taipei Medical University (n = 74). The RRM2 protein levels were detected by immunohistochemistry. Biochemical recurrence was assessed using Kaplan-Meier and Cox proportional hazard analyses. Cell invasion assays, Ras/Raf, and matrix metallopeptidase 9 activities were determined to evaluate the role of RRM2 on invasiveness of PCa.

RESULTS

Expression of RRM2 was significantly increased in patients with higher Gleason score, who had advanced T stage, and who were margin/capsule positive (P<0.05). Analysis revealed that the expression of RRM2 positively associated with biochemical recurrence of PCa in the City of Hope set (hazard ratio = 5.26; 95% CI 1.50-24.71) and the Taipei Medical University set (hazard ratio = 2.55; 95% CI 1.30-9.22). In stratification analysis, RRM2 was significantly correlated with poor outcome in patients with lower-risk PCa, including those with Gleason score 4 to 7, margin(-), capsule(-), and stage T1-T2. In patients with Gleason score 4 to 7, the risk of recurrence was proportional to RRM2 protein levels. The prognostic performance of RRM2 was superior to that of pathoclinical factors, including margin/capsule status and T stage. An in vitro study demonstrated that RRM2 could promote tumor invasion activities in PCa cell lines. Suppression of RRM2 reduced the Ras/Raf and matrix metallopeptidase 9 activities.

CONCLUSION

RRM2 plays a critical role in proliferation and invasion of PCa. Adding RRM2 as a biomarker in clinical assessments may increase model precision in predicting recurrence in patients with low-risk PCa.

Ribonucleotide reductase and cancer: biological mechanisms and targeted therapies

Accurate DNA replication and repair is essential for proper development, growth and tumor-free survival in all multicellular organisms. A key requirement for the maintenance of genomic integrity is the availability of adequate and balanced pools of deoxyribonucleoside triphosphates (dNTPs), the building blocks of DNA. Notably, dNTP pool alterations lead to genomic instability and have been linked to multiple human diseases, including mitochondrial disorders, susceptibility to viral infection and cancer. In this review, we discuss how a key regulator of dNTP biosynthesis in mammals, the enzyme ribonucleotide reductase (RNR), impacts cancer susceptibility and serves as a target for anti-cancer therapies. Because RNR-regulated dNTP production can influence DNA replication fidelity while also supporting genome-protecting DNA repair, RNR has complex and stage-specific roles in carcinogenesis. Nevertheless, cancer cells are dependent on RNR for de novo dNTP biosynthesis. Therefore, elevated RNR expression is a characteristic of many cancers, and an array of mechanistically distinct RNR inhibitors serve as effective agents for cancer treatment. The dNTP metabolism machinery, including RNR, has been exploited for therapeutic benefit for decades and remains an important target for cancer drug development.

AKT-induced tamoxifen resistance is overturned by RRM2 inhibition

Acquired tamoxifen resistance develops in the majority of hormone-responsive breast cancers and frequently involves overexpression of the PI3K/AKT axis. Here, breast cancer cells with elevated endogenous AKT or overexpression of activated AKT exhibited tamoxifen-stimulated cell proliferation and enhanced cell motility. To gain mechanistic insight on AKT-induced endocrine resistance, gene expression profiling was performed to determine the transcripts that are differentially expressed post-tamoxifen therapy under conditions of AKT overexpression. Consistent with the biologic outcome, many of these transcripts function in cell proliferation and cell motility networks and were quantitatively validated in a larger panel of breast cancer cells. Moreover, ribonucleotide reductase M2 (RRM2) was revealed as a key contributor to AKT-induced tamoxifen resistance. Inhibition of RRM2 by RNA interference (RNAi)-mediated approaches significantly reversed the tamoxifen-resistant cell growth, inhibited cell motility, and activated DNA damage and proapoptotic pathways. In addition, treatment of tamoxifen-resistant breast cancer cells with the small molecule RRM inhibitor didox significantly reduced in vitro and in vivo growth. Thus, AKT-expressing breast cancer cells upregulate RRM2 expression, leading to increased DNA repair and protection from tamoxifen-induced apoptosis.

IMPLICATIONS

These findings identify RRM2 as an AKT-regulated gene, which plays a role in tamoxifen resistance and may prove to be a novel target for effective diagnostic and preventative strategies.

Phase I study of GTI-2040, a ribonucleotide reductase antisense, with high dose cytarabine in patients with relapsed/refractory acute myeloid leukemia

We hypothesized that GTI-2040, a 20-mer oligonucleotide complementary to the R2 subunit mRNA of ribonucleotide reductase, combined with high dose cytarabine (HiDAC) would result in enhanced cytotoxicity by favoring Ara-CTP DNA incorporation. In a phase I dose escalation trial, adults (≥ 60 years) with refractory or relapsed acute myeloid leukemia (AML) received daily HiDAC plus infusional GTI-2040. Using a novel assay, evidence of intracellular drug accumulation and target R2 down-regulation was observed. GTI-2040/HiDAC can be administered safely. However, with no complete remissions observed, alternative doses and schedules may need to be investigated to achieve clinical activity in older patients with AML.

Ribonucleotide reductase large subunit M1 predicts poor survival due to modulation of proliferative and invasive ability of gastric cancer

OBJECTIVES

We aimed to investigate the prognostic value of RRM1 in GC patients.

METHODS

A total of assessable 389 GC patients with clinicopathological and survival information were enrolled from City of Hope (COH, n = 67) and Zhejiang University (ZJU, n = 322). RRM1 protein expression was determined by immunohistochemistry on FFPE tissue samples. Kaplan-Meier and Cox analyses were used to measure survival. Ras/Raf activity and invasion assays were used to evaluate the role of RRM1 in GC cell lines.

RESULTS

In vitro experiments demonstrated RRM1 activated Ras/Raf/MAPK signal transduction and promoted GC cell proliferation. Meanwhile, RRM1 expression was significantly associated with lymph node involvement, tumor size, Ki67 expression, histological subtype and histological grade in the GC tissue samples (p<0.05). Kaplan-Meier analysis illustrated that high RRM1 expression predicted poor survival in GC patients in the COH and ZJU cohorts (log-rank p<0.01). In multivariate Cox analysis, the hazard ratios of RRM1 for overall survival were 2.55 (95% CI 1.27-5.15) and 1.51 (95% CI 1.07-2.13) in the COH and ZJU sets, respectively. In particular, RRM1 specifically predicted the outcome of advanced GCs with poor differentiation and high proliferative ability. Furthermore, inhibition of RRM1 by siRNA significantly reduced the dNTP pool, Ras/Raf and MMP-9 activities and the levels of p-MEK, p-ERK and NF-κB, resulting in growth retardation and reduced invasion in AGS and NCI-N87 cells.

CONCLUSIONS

RRM1 overexpression predicts poor survival in GC patients with advanced TNM stage. RRM1 could potentially serve as prognostic biomarker and therapeutic target for GCs.

RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy

PURPOSE

Ribonucleotide reductase subunit M2 (RRM2) plays an active role in tumor progression. Recently, we reported that depletion of RRM2 by systemic delivery of a nanoparticle carrying RRM2-specific siRNA suppresses head and neck tumor growth. The aim of this study is to clarify the underlying mechanism by which RRM2 depletion inhibits tumor growth.

EXPERIMENTAL DESIGN

siRNA-mediated gene silencing was carried out to downregulate RRM2. Immunoblotting, reverse-transcriptase PCR, confocal microscopy, tissue fractionation, gene overexpression and knockdown were employed to analyze critical apoptosis signaling. Conventional immunohistochemistry and quantum dot-based immunofluorescence were applied to detect RRM2 and Bcl2 expression and localization in tissue samples from patients and mice.

RESULTS

Knockdown of RRM2 led to apoptosis through the intrinsic pathway in head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) cell lines. We showed that Bcl-2 is a key determinant controlling apoptosis, both in vitro and in vivo, and that RRM2 depletion significantly reduces Bcl-2 protein expression. We observed that RRM2 regulates Bcl-2 protein stability, with RRM2 suppression leading to increased Bcl-2 degradation, and identified their colocalization in HNSCC and NSCLC cells. In a total of 50 specimens each from patients with HNSCC and NSCLC, we identified the colocalization of Bcl-2 and RRM2 and found a significant positive correlation between their expression in HNSCC (R = 0.98; P < 0.0001) and NSCLC (R = 0.92; P < 0.0001) tumor tissues.

CONCLUSIONS

Our novel findings add to the knowledge of RRM2 in regulating expression of the antiapoptotic protein Bcl-2 and reveal a critical link between RRM2 and Bcl-2 in apoptosis signaling.

Ribonucleotide reductase small subunit M2 serves as a prognostic biomarker and predicts poor survival of colorectal cancers

The overexpression of RRM2 [RR (ribonucleotide reductase) small subunit M2] dramatically enhances the ability of the cancer cell to proliferate and to invade. To investigate further the relevance of RRM2 and CRCs (colorectal cancers), we correlated the expression of RRM2 with the clinical outcome of CRCs. A retrospective outcome study was conducted on CRCs collected from the COH [(City of Hope) National Medical Center, 217 cases] and ZJU (Zhejiang University, 220 cases). IHC (immunohistochemistry) was employed to determine the protein expression level of RRM2, and quantitative real-time PCR was employed to validate. Multivariate logistic analysis indicated that the adjusted ORs (odds ratios) of RRM2-high for distant metastases were 2.06 [95% CI (confidence interval), 1.01-4.30] and 5.89 (95% CI, 1.51-39.13) in the COH and ZJU sets respectively. The Kaplan-Meier analysis displayed that high expression of RRM2 had a negative impact on the OS (overall survival) and PFS (progress-free survival) of CRC in both sets significantly. The multivariate Cox analysis further demonstrated that HRs (hazard ratios) of RRM2-high for OS were 1.88 (95% CI, 1.03-3.36) and 2.06 (95% CI, 1.10-4.00) in the COH and ZJU sets respectively. Stratification analysis demonstrated that the HR of RRM2 dramatically increased to 12.22 (95% CI, 1.62-258.31) in the MMR (mismatch repair) gene-deficient subgroup in the COH set. Meanwhile, a real-time study demonstrated that down-regulation of RRM2 by siRNA (small interfering RNA) could significantly and specifically reduce the cell growth and adhesion ability in HT-29 and HCT-8 cells. Therefore RRM2 is an independent prognostic factor and predicts poor survival of CRCs. It is also a potential predictor for identifying good responders to chemotherapy for CRCs.

Emerging roles of the ribonucleotide reductase M2 in colorectal cancer and ultraviolet-induced DNA damage repair

AIM

To investigate the roles of the ribonucleotide reductase M2 (RRM2) subunit in colorectal cancer (CRC) and ultraviolet (UV)-induced DNA damage repair.

METHODS

Immunohistochemical staining of tissue microarray was performed to detect the expression of RRM2. Seven CRC cell lines were cultured and three human colon cancer cell lines, i.e., HCT116, SW480 and SW620, were used. Reverse transcription polymerase chain reaction and Western blotting were performed to determine the mRNA and protein expression levels of RRM2, respectively. Cell proliferation assay, cell cycle analysis were performed. Cell apoptosis was evaluated by double staining with fluorescein isothiocyanate-conjugated Annexin V and propidium iodide (PI) using Annexin V/PI apoptosis kit. The motility and invasion of CRC cells were assessed by the Transwell chamber assay. Cells were irradiated with a 254 nm UV-C lamp to detect the UV sensitivity after RRM2 depletion.

RESULTS

Immunohistochemical staining revealed elevated RRM2 levels in CRC tissues. RRM2 overexpression was positively correlated with invasion depth (P < 0.05), poorly differentiated type (P = 0.0051), and tumor node metastasis stage (P = 0.0015). The expression of RRM2 in HCT116 cells was downregulated after transfection, and HCT116 cell proliferation was obviously suppressed compared to control groups (P < 0.05). In the invasion test, the number of cells that passed through the chambers in the RRM2-siRNA group was 81 ± 3, which was lower than that in the negative control (289 ± 7) and blank control groups (301 ± 7.2). These differences were statistically significant (P < 0.01). Our data suggest that RRM2 overexpression may be associated with CRC progression. RRM2 silencing by siRNA may inhibit the hyperplasia and invasiveness of CRC cells, suggesting that RRM2 may play an important role in the infiltration and metastasis of CRC, which is a potential therapeutic strategy in CRC. In addition, RRM2 depletion increased UV sensitivity.

CONCLUSION

These findings suggest that RRM2 may be a facilitating factor in colorectal tumorigenesis and UV-induced DNA damage repair.

Translational control gone awry: a new mechanism of tumorigenesis and novel targets of cancer treatments

Translational control is one of primary regulation mechanisms of gene expression. Eukaryotic translational control mainly occurs at the initiation step, the speed-limiting step, which involves more than ten translation initiation factors [eIFs (eukaryotic initiation factors)]. Changing the level or function of these eIFs results in abnormal translation of specific mRNAs and consequently abnormal growth of cells that leads to human diseases, including cancer. Accumulating evidence from recent studies showed that the expression of many eIFs was associated with malignant transformation, cancer prognosis, as well as gene expression regulation. In the present paper, we perform a critical review of recent advances in understanding the role and mechanism of eIF action in translational control and cancer as well as the possibility of targeting eIFs for therapeutic development.

Current progress of siRNA/shRNA therapeutics in clinical trials

Through a mechanism known as RNA interference (RNAi), small interfering RNA (siRNA) molecules can target complementary mRNA strands for degradation, thus specifically inhibiting gene expression. The ability of siRNAs to inhibit gene expression offers a mechanism that can be exploited for novel therapeutics. Indeed, over the past decade, at least 21 siRNA therapeutics have been developed for more than a dozen diseases, including various cancers, viruses, and genetic disorders. Like other biological drugs, RNAi-based therapeutics often require a delivery vehicle to transport them to the targeted cells. Thus, the clinical advancement of numerous siRNA drugs has relied on the development of siRNA carriers, including biodegradable nanoparticles, lipids, bacteria, and attenuated viruses. Most therapies permit systemic delivery of the siRNA drug, while others use ex vivo delivery by autologous cell therapy. Advancements in bioengineering and nanotechnology have led to improved control of delivery and release of some siRNA therapeutics. Likewise, progress in molecular biology has allowed for improved design of the siRNA molecules. Here, we provide an overview of siRNA therapeutics in clinical trials, including their clinical progress, the challenges they have encountered, and the future they hold in the treatment of human diseases.

Novel strategy with gemcitabine for advanced pancreatic cancer

5-fluorouracil (5-FU) is widely used in chemotherapy for gastric and colorectal cancer, but gemcitabine (GEM), and not 5-FU, is approved as a standard drug for use in pancreatic cancer. Interindividual variation in the enzyme activity of the GEM metabolic pathway can affect the extent of GEM metabolism and the efficacy of GEM chemotherapy. Human equilibrative nucleoside transporter 1 (hENT1) is recognized as a major transporter of GEM into cells. In addition, a factor that activates hENT1 is the inhibition of thymidylate synthase (TS), one of the 5-FU metabolic enzymes; TS inhibition mediates depleting intracellular nucleotide pools, resulting in the activation of the salvage pathway mediated through hENT1. In this paper, the role of 5-FU in GEM-based chemotherapy for pancreatic cancer is discussed with special emphasis on enzymes involved in the 5-FU and GEM metabolic pathways and in the correlation between GEM responsiveness and the expression of 5-FU and GEM metabolic enzymes.

Blockade of T-type Ca(2+) channels inhibits human ovarian cancer cell proliferation

Regulation of Ca(2+) channels has been implicated in the progression of tumor cells. We report here that T-type Ca(2+) channel expression in human ovarian cancer tissues is greatly increased compared to normal ovarian tissues. Blockade of T-type Ca(2+) channel with NNC 55-0396, mibefradil, or by specifically knocking down the expression of these proteins with siRNA-Ca(v)3.1/3.2 suppressed the proliferation of two ovarian cancer cell lines and increased G0/G1 phase distribution in the cell cycle. Furthermore, NNC 55-0396 slowed ovarian cancer formation in nude mice. Therefore the function of T-type Ca(2+) channels is important for the proliferation of human ovarian cancer cells.

Ribonucleotide reductase small subunit M2B prognoses better survival in colorectal cancer

Ribonucleotide reductase subunit RRM2B (p53R2) has been reported to suppress invasion and metastasis in colorectal cancer (CRC). Here, we report that high levels of RRM2B expression are correlated with markedly better survival in CRC patients. In a fluorescence-labeled orthotopic mouse xenograft model, we confirmed that overexpression of RRM2B in nonmetastatic CRC cells prevented lung and/or liver metastasis, relative to control cells that did metastasize. Clinical outcome studies were conducted on a training set with 103 CRCs and a validation set with 220 CRCs. All participants underwent surgery with periodic follow-up to determine survivability. A newly developed specific RRM2B antibody was employed to carry out immunohistochemistry for determining RRM2B expression levels on tissue arrays. In the training set, the Kaplan-Meier and multivariate Cox analysis revealed that RRM2B is associated with better survival of CRCs, especially in stage IV patients (HR = 0.40; 95% CI = 0.18-0.86, P = 0.016). In the validation set, RRM2B was negatively related to tumor invasion (OR = 0.45, 95% CI = 0.19-0.99, P = 0.040) and lymph node involvement (OR = 0.48, 95% CI = 0.25-0.92, P = 0.026). Furthermore, elevated expression of RRM2B was associated with better prognosis in this set as determined by multivariate analyses (HR = 0.48, 95% CI = 0.26-0.91, P = 0.030). Further investigations revealed that RRM2B was correlated with better survival of CRCs with advanced stage III and IV tumors rather than earlier stage I and II tumors. Taken together, our findings establish that RRM2B suppresses invasiveness of cancer cells and that its expression is associated with a better survival prognosis for CRC patients.

Preclinical toxicity and toxicokinetics of GTI-2040, a phosphorothioate oligonucleotide targeting ribonucleotide reductase R2

PURPOSE

GTI-2040, a 20-mer phosphorothioate oligonucleotide, was designed to hybridize to the mRNA sequence of human ribonucleotide reductase R2. GTI-2040 has been shown to inhibit human cancer cell proliferation by downregulation of R2 expression in vitro and to significantly inhibit tumor growth in xenograft models of human cancer in mice. As part of the safety evaluation for human clinical trials, the toxicity and toxicokinetics of GTI-2040 were determined in Sprague-Dawley rats and rhesus monkeys.

METHODS

GTI-2040 was administered to rats at 2, 10, and 50 mg/kg/day by bolus intravenous injection every second day for 21 days with a 21-day recovery. In monkeys, an acute study was performed with single, escalating doses of GTI-2040 ranging from 10 to 80 mg/kg given as a 24-h continuous intravenous infusion. As well, a 21-day, continuous intravenous infusion study with GTI-2040 was conducted in monkeys at 2, 10, and 50 mg/kg/day, with a 3-week recovery. Blood sampling was done to measure GTI-2040 plasma concentrations, metabolites, and pharmacokinetic parameters, and tissues were collected to assess the distribution of GTI-2040 and/or metabolites.

RESULTS

The toxicities of GTI-2040 in both rats and monkeys were typical for the phosphorothioate oligonucleotide class of compounds. In monkeys, there was a dose-related increase in GTI-2040 plasma levels with concomitant increase in complement activation and prolongation of activated partial thromboplastin time. In both rats and monkeys, the tissues having the highest concentrations of GTI-2040 (kidney, liver, spleen) had the largest dose-related toxic effects. Adverse effects were diminished or absent in the recovery animals.

CONCLUSIONS

GTI-2040 was well tolerated when infused over 24 h at doses up to 80 mg/kg in monkeys. In rats and monkeys, GTI-2040 was reasonably well tolerated and showed reversible toxicities when administered at doses up to 50 mg/kg/day for 21 days. The no observed adverse effect dose level for GTI-2040 in both animal species was 2 mg/kg/day. There were no apparent sequence-specific effects related to the interaction of GTI-2040 with the R2 component of the mRNA expressing ribonucleotide reductase.

Expression of ribonucleotide reductase M2 subunit in gastric cancer and effects of RRM2 inhibition in vitro

Ribonucleotide reductase M2 subunit is one of two subunits that constitute ribonucleotide reductase, the enzyme that catalyzes the conversion of ribonucleotide 5'-diphosphates into 2'-deoxyribonucleotides, which are required for DNA synthesis. This study was conducted to investigate the roles of ribonucleotide reductase M2 subunit in gastric cancer. The expression of ribonucleotide reductase M2 subunit protein was examined by immunohistochemistry. In normal gastric mucosa, ribonucleotide reductase M2 subunit expression was restricted to the neck regions of gastric pits and no expression was observed in the surface epithelium. Among 112 gastric cancer tissues, ribonucleotide reductase M2 subunit overexpression (≥10% cancer cells stained) was observed in 72 cases (64.3%). Ribonucleotide reductase M2 subunit overexpression was significantly associated with male sex (P = .015), presence of muscularis propria invasion (P = .020), presence of Epstein-Barr virus (P = .045), expression of survivin (P = .0014), and DNA methyltransferase 1 (P = .043), but not with age, histology, tumor size, lymph node metastasis or expression of phosphatase and tensin homolog, phosphorylated signal transducer, and activator of transcription 3 or p53. Suppression of ribonucleotide reductase M2 subunit synthesis, using small interfering RNA, inhibited the growth of 3 gastric cancer cell lines, MKN-1, MKN-7, and SNU-719. Our data suggest that ribonucleotide reductase M2 subunit overexpression could be associated with the gastric cancer progression and that suppression of its function is a potential therapeutic strategy in gastric cancer.

Ribonucleotide reductase is not limiting for mitochondrial DNA copy number in mice

Ribonucleotide reductase (RNR) is the rate-limiting enzyme in deoxyribonucleoside triphosphate (dNTP) biosynthesis, with important roles in nuclear genome maintenance. RNR is also essential for maintenance of mitochondrial DNA (mtDNA) in mammals. The mechanisms regulating mtDNA copy number in mammals are only being discovered. In budding yeast, RNR overexpression resulted in increased mtDNA levels, and rescued the disease phenotypes caused by a mutant mtDNA polymerase. This raised the question of whether mtDNA copy number increase by RNR induction could be a strategy for treating diseases with mtDNA mutations. We show here that high-level overexpression of RNR subunits (Rrm1, Rrm2 and p53R2; separately or in different combinations) in mice does not result in mtDNA copy number elevation. Instead, simultaneous expression of two RNR subunits leads to imbalanced dNTP pools and progressive mtDNA depletion in the skeletal muscle, without mtDNA mutagenesis. We also show that endogenous RNR transcripts are downregulated in response to large increases of mtDNA in mice, which is indicative of nuclear-mitochondrial crosstalk with regard to mtDNA copy number. Our results establish that RNR is not limiting for mtDNA copy number in mice, and provide new evidence for the importance of balanced dNTP pools in mtDNA maintenance in postmitotic tissues.

The translational regulator eIF3a: the tricky eIF3 subunit!

Regulation of gene expression is a fundamental step in cellular physiology as abnormalities in this process may lead to de-regulated growth and cancer. Translation of mRNA is mainly regulated at the rate-limiting initiation step, where many eukaryotic initiation factors (eIFs) are involved. The largest and most complex initiation factor is eIF3 which plays a role in translational regulation, cell growth and cancer. The largest subunit of eIF3 is eIF3a, although it is not required for the general function of eIF3 in translation initiation. However, eIF3a may play a role as a regulator of a subset of mRNAs and has been demonstrated to regulate the expression of p27(kip1), tyrosinated α-tubulin and ribonucleotide reductase M2 subunit. These molecules have a pivotal role in the regulation of the cell cycle. Moreover, the eIF3a mRNA is ubiquitously expressed in all tissues at different levels and is found elevated in a number of cancer types. eIF3a can modulate the cell cycle and may be a translational regulator for proteins important for entrance into S phase. The expression of eIF3a is decreased in differentiated cells in culture and the suppression of eIF3a expression can reverse the malignant phenotype and change the sensitivity of cells to cell cycle modulators. However, the role of eIF3a in cancer is still unclear. In fact, some studies have identified eIF3a to be involved in cancer development, while other results indicate that it could provide protection against evolution into higher malignancy. Together, these findings highlight the "tricky" and interesting nature of eIF3a.

p53R2 expression as a prognostic biomarker in early stage non-small cell lung cancer

p53R2 is a small subunit of ribonucleotide reductase (RR) which has 80% homology to hRRM2 and metastasis-suppressing potential. Previous reports suggested that the expression of p53R2 is used as a prognostic factor and chemotherapy response indicator in several types of cancer. This study aimed to elucidate the association of p53R2 expression and the clinicopathological characteristics of early stage non-small cell lung cancer (NSCLC). Immunohistochemistry was conducted on a tissue array including 92 early stage NSCLC samples. Correlations between p53R2 and clinicopathological factors, recurrence/metastasis and outcomes were analyzed. The analyses showed that there was no correlation between p53R2 expression and the clinicopathological factors. Among disease-free patients during follow-up, patients with p53R2(+) had a better outcome than those with p53R2(-) (P=0.022). By using Cox multivariate regression analysis, p53R2 (risk factor 3.801; 95% CI 1.004-9.454; P=0.044) served as a prognostic biomarker in the prediction of the survival rate for NSCLC patients. Detection of the RR subunit p53R2 may therefore be a useful prognostic marker in early stage NSCLC.

Targeted delivery of antisense oligodeoxynucleotide by transferrin conjugated pH-sensitive lipopolyplex nanoparticles: a novel oligonucleotide-based therapeutic strategy in acute myeloid leukemia

Therapeutic use of oligodeoxynucleotides (ODNs) that hybridize to and downregulate target mRNAs encoding proteins that contribute to malignant transformation has a sound rationale, but has had an overall limited clinical success in cancer due to insufficient intracellular delivery. Here we report a development of formulations capable of promoting targeted delivery and enhanced pharmacologic activity of ODNs in acute myeloid leukemia (AML) cell lines and patient primary cells. In this study, transferrin (Tf) conjugated pH-sensitive lipopolyplex nanoparticles (LPs) were prepared to deliver GTI-2040, an antisense ODN against the R2 subunit of ribonucleotide reductase that has been shown to contribute to chemoresistance in AML. LPs had an average particle size around 110 nm and a moderately positive zeta potential at approximately 10 mV. The ODN encapsulation efficiency of LPs was >90%. These nanoparticles could release ODNs at acidic endosomal pH and facilitate the cytoplasmic delivery of ODNs after endocytosis. In addition, Tf-mediated targeted delivery of GTI-2040 was achieved. R2 downregulation at both mRNA and protein levels was improved by 8-fold in Kasumi-1 cells and 2- to 20-fold in AML patient primary cells treated with GTI-2040-Tf-LPs, compared to free GTI-2040 treatment. Moreover, Tf-LPs were more effective than nontargeted LPs, with 10 to 100% improvement at various concentrations in Kasumi-1 cells and an average of 45% improvement at 3 microM concentration in AML patient primary cells. Treatment with 1 microM GTI-2040-Tf-LPs sensitized AML cells to the chemotherapy agent cytarabine, by decreasing its IC(50) value from 47.69 nM to 9.05 nM. This study suggests that the combination of pH sensitive LP formulation and Tf mediated targeting is a promising strategy for antisense ODN delivery in leukemia therapy.

Metabolic genes in cancer: their roles in tumor progression and clinical implications

Re-programming of metabolic pathways is a hallmark of physiological changes in cancer cells. The expression of certain genes that directly control the rate of key metabolic pathways including glycolysis, lipogenesis and nucleotide synthesis are drastically altered at different stages of tumor progression. These alterations are generally considered as an adaptation of tumor cells; however, they also contribute to the progression of tumor cells to become more aggressive phenotypes. This review summarizes the recent information about the mechanistic link of these genes to oncogenesis and their potential utility as diagnostic markers as well as for therapeutic targets. We particularly focus on three groups of genes; GLUT1, G6PD, TKTL1 and PGI/AMF in glycolytic pathway, ACLY, ACC1 and FAS in lipogenesis and RRM2, p53R2 and TYMS for nucleotide synthesis. All these genes are highly up-regulated in a variety of tumor cells in cancer patients, and they play active roles in tumor progression rather than expressing merely as a consequence of phenotypic change of the cancer cells. Molecular dissection of their orchestrated networks and understanding the exact mechanism of their expression will provide a window of opportunity to target these genes for specific cancer therapy. We also reviewed existing database of gene microarray to validate the utility of these genes for cancer diagnosis.

New agents in acute myeloid leukemia: beyond cytarabine and anthracyclines

The standard therapeutic approaches for acute myeloid leukemia (AML) continue to be based on anthracyclines and cytarabine. However, the prognosis for AML remains poor, especially for patients with high-risk disease. During the past decade, promising novel agents that target DNA replication and repair, as well as cell cycling and apoptosis, have been developed and are being actively investigated in AML. Among these agents is flavopiridol, which interferes with key steps of the cell cycle and effectively promotes cell death, and voreloxin, an intercalating agent that also targets topoisomerase II. Also under clinical study in AML are oligonucleotide antisense constructs, which suppress the translation of proteins essential for leukemic blast survival and proliferation, and agents that target antiapoptotic cascades. In summary, it is hoped that novel therapies such as these will augment and/or supplant our current cytarabine- and anthracycline-based approaches, overcome active drug-resistance pathways, and eventually improve outcomes for patients with AML.

E2F4 and ribonucleotide reductase mediate S-phase arrest in colon cancer cells treated with chlorophyllin

Chlorophyllin (CHL) is a water-soluble derivative of chlorophyll that exhibits cancer chemopreventive properties, but which also has been studied for its possible cancer therapeutic effects. We report here that human colon cancer cells treated with CHL accumulate in S-phase of the cell cycle, and this is associated with reduced expression levels of p53, p21, and other G(1)/S checkpoint controls. At the same time, E2F1 and E2F4 transcription factors become elevated and exhibit increased DNA binding activity. In CHL-treated colon cancer cells, bromodeoxyuridine pulse-chase experiments provided evidence for the inhibition of DNA synthesis. Ribonucleotide reductase (RR), a pivotal enzyme for DNA synthesis and repair, was reduced at the mRNA and protein level after CHL treatment, and the enzymatic activity was inhibited in a concentration-dependent manner both in vitro and in vivo. Immunoblotting revealed that expression levels of RR subunits R1, R2, and p53R2 were reduced by CHL treatment in HCT116 (p53(+/+)) and HCT116 (p53(-/-)) cells, supporting a p53-independent mechanism. Prior studies have shown that reduced levels of RR small subunits can increase the sensitivity of colon cancer cells to clinically used DNA-damaging agents and RR inhibitors. We conclude that by inhibiting R1, R2, and p53R2, CHL has the potential to be effective in the clinical setting, when used alone or in combination with currently available cancer therapeutic agents.

New approaches for cancer treatment: antitumor drugs based on gene-targeted nucleic acids

Currently, the main way to fight cancer is still chemotherapy. This method of treatment is at the height of its capacity, so, setting aside the need for further improvements in traditional treatments for neoplasia, it is vital to develop now approaches toward treating malignant tumors. This paper reviews innovational experimental approaches to treating malignant malformations based on the use of gene-targeted drugs, such as antisense oligonucleotides (asON), small interfering RNA (siRNA), ribozymes, and DNAzymes, which can all inhibit oncogene expression. The target genes for these drugs are thoroughly characterized, and the main results from pre-clinical and first-step clinical trials of these drugs are presented. It is shown that the gene-targeted oligonucleotides show considerable variations in their effect on tumor tissue, depending on the target gene in question. The effects range from slowing and stopping the proliferation of tumor cells to suppressing their invasive capabilities. Despite their similarity, not all the antisense drugs targeting the same region of the mRNA of the target-gene were equally effective. The result is determined by the combination of the drug type used and the region of the target-gene mRNA that it complements.

Ribonucleotide reductase small subunit p53R2 suppresses MEK-ERK activity by binding to ERK kinase 2

The p53-dependent RR small subunit (p53R2) protein, a newly identified member of the ribonucleotide reductase family, plays a key role in the p53-dependent cellular response to DNA. Several recent studies have suggested that p53R2 also plays an important role in suppressing the invasive potential of human cancer cells. However, the cellular mechanism that regulates invasiveness remains largely unknown. In this study, we show that p53R2 interacts with MEK2 (extracellular signal-regulated kinase (ERK) kinase 2-mitogen-activated protein kinase (MAPK) kinase 2), the molecule immediately upstream of ERK in the Ras-Raf-MAPK signaling cascade. In co-immunoprecipitation and immunofluorescence analyses, we found that p53R2 and MEK2 interact physically in cultured mammalian cells, and that the p53R2 segment comprising amino acids 161-206 is critical for this interaction. Moreover, serum-induced phosphorylation of MEK1/2 and ERK1/2 was greatly augmented in human cancer cells expressing small-interfering RNA against p53R2. On the other hand, phosphorylation of MEK1/2 and ERK1/2 in human cancer cells was markedly attenuated by overexpression of p53R2. Furthermore, MEK2 was required for p53R2 knockdown-induced enhancement of the invasive ability and anchorage-independent growth of human lung cancer H1299 cells. Taken together, these findings show that p53R2 negatively modulates serum-induced MEK-ERK activity and inhibits the MEK-ERK-mediated malignancy potential of human cancer cells.

Overexpression of RRM2 decreases thrombspondin-1 and increases VEGF production in human cancer cells in vitro and in vivo: implication of RRM2 in angiogenesis

Background

In addition to its essential role in ribonucleotide reduction, ribonucleotide reductase (RNR) small subunit, RRM2, has been known to play a critical role in determining tumor malignancy. Overexpression of RRM2 significantly enhances the invasive and metastatic potential of tumor. Angiogenesis is critical to tumor malignancy; it plays an essential role in tumor growth and metastasis. It is important to investigate whether the angiogenic potential of tumor is affected by RRM2.

Results

We examined the expression of antiangiogenic thrombospondin-1 (TSP-1) and proangiogenic vascular endothelial growth factor (VEGF) in two RRM2-overexpressing KB cells: KB-M2-D and KB-HURs. We found that TSP-1 was significantly decreased in both KB-M2-D and KB-HURs cells compared to the parental KB and mock transfected KB-V. Simultaneously, RRM2-overexpressing KB cells showed increased production of VEGF mRNA and protein. In contrast, attenuating RRM2 expression via siRNA resulted in a significant increased TSP-1 expression in both KB and LNCaP cells; while the expression of VEGF by the two cells was significantly decreased under both normoxia and hypoxia. In comparison with KB-V, overexpression of RRM2 had no significant effect on proliferation in vitro, but it dramatically accelerated in vivo subcutaneous growth of KB-M2-D. KB-M2-D possessed more angiogenic potential than KB-V, as shown in vitro by its increased chemotaxis for endothelial cells and in vivo by the generation of more vascularized tumor xenografts.

Conclusion

These findings suggest a positive role of RRM2 in tumor angiogenesis and growth through regulation of the expression of TSP-1 and VEGF.

Evaluation of mRNA by Q-RTPCR and protein expression by AQUA of the M2 subunit of ribonucleotide reductase (RRM2) in human tumors

PURPOSE

The purpose of this study was to evaluate baseline RRM2 protein and gene expression in tumors of patients receiving 3-AP.

METHODS

Tumor blocks from patients enrolled in phase I and II clinical studies using 3-AP, were evaluated for RRM2 gene and protein expression by quantitative real time polymerase chain reaction (Q-RTPCR) and automated quantitative analysis (AQUA).

RESULTS

Esophageal and gastric cancers overexpressed RRM2 protein when compared to prostate cancer (Z-score, 0.68 +/- 0.94 SD, vs 0.41 +/- 0.84 SD, respectively; p = 0.04). Esophageal and gastric cancers also overexpressed RRM2 mRNA when compared to prostate cancer (relative gene expression 2.56 +/- 1.49 SD, vs 0.29 +/- 0.20 SD, respectively; p = 0.02). Protein and gene expression were moderately associated (Spearman's rank correlation = 0.30; p = 0.12).

CONCLUSION

RRM2 gene and protein expression varies by tumor type.

Phase I study of GTI-2040, an antisense to ribonucleotide reductase, in combination with high-dose cytarabine in patients with acute myeloid leukemia

PURPOSE

Inhibition of ribonucleotide reductase reduces the availability of the endogenous pool of deoxycytidine and may increase cytarabine (AraC) cytotoxicity. We performed a phase I dose escalation trial of AraC combined with GTI-2040, a 20-mer antisense oligonucleotide shown in preclinical studies to decrease levels of the R2 subunit of ribonucleotide reductase, to determine the maximum tolerated dose in adults with relapsed/refractory acute myeloid leukemia.

EXPERIMENTAL DESIGN

Twenty-three adults (ages 18-59 years) were enrolled in this dose escalation phase I trial, receiving high-dose AraC twice daily combined with infusional GTI-2040. An ELISA-based assay measured plasma and intracellular concentrations of GTI-2040. R2 protein changes were evaluated by immunoblotting in pretreatment and post-treatment bone marrow samples.

RESULTS

The maximum tolerated dose was 5 mg/kg/d GTI-2040 (days 1-6) and 3 g/m2/dose AraC every 12 hours for 8 doses. Neurotoxicity was dose limiting. Eight patients (35%) achieved complete remission. Mean bone marrow intracellular concentration of GTI-2040 were higher at 120 hours than at 24 hours from the start of GTI-2040 (P = 0.002), suggesting intracellular drug accumulation over time. Reductions in bone marrow levels of R2 protein (>50%) were observed at 24 and 120 hours. Higher baseline R2 protein expression (P = 0.03) and reductions after 24 hours of GTI-2040 (P = 0.04) were associated with complete remission.

CONCLUSIONS

GTI-2040 and high-dose AraC were coadministered safely with successful reduction of the intended R2 target and encouraging clinical results. The clinical efficacy of this combination will be tested in an upcoming phase II study.

Broad overexpression of ribonucleotide reductase genes in mice specifically induces lung neoplasms

Ribonucleotide reductase (RNR) catalyzes the rate-limiting step in nucleotide biosynthesis and plays a central role in genome maintenance. Although a number of regulatory mechanisms govern RNR activity, the physiologic effect of RNR deregulation had not previously been examined in an animal model. We show here that overexpression of the small RNR subunit potently and selectively induces lung neoplasms in transgenic mice and is mutagenic in cultured cells. Combining RNR deregulation with defects in DNA mismatch repair, the cellular mutation correction system, synergistically increased RNR-induced mutagenesis and carcinogenesis. Moreover, the proto-oncogene K-ras was identified as a frequent mutational target in RNR-induced lung neoplasms. Together, these results show that RNR deregulation promotes lung carcinogenesis through a mutagenic mechanism and establish a new oncogenic activity for a key regulator of nucleotide metabolism. Importantly, RNR-induced lung neoplasms histopathologically resemble human papillary adenocarcinomas and arise stochastically via a mutagenic mechanism, making RNR transgenic mice a valuable model for lung cancer.

RNA interference targeting the R2 subunit of ribonucleotide reductase inhibits growth of tumor cells in vitro and in vivo

RNA interference, a posttranscriptional gene-silencing mechanism, has received considerable attention for its potential as a new therapeutic strategy to treat human diseases and conditions including cancer. Various studies have supported a role for the R2 subunit of ribonucleotide reductase in cancer progression and metastasis. Short interfering siRNA 1284 was designed to target R2. In vitro studies, in which three different human tumor cell lines (A498, HT-29 and A2058) were transfected with short interfering siRNA 1284, demonstrate sequence-specific down-regulation of R2, which coincides with a decrease in cell proliferation, and cell cycle inhibition. In vivo studies with xenograft mouse models, generated from the same tumor cell lines, indicate that treatment with short interfering siRNA 1284 leads to inhibition of tumor growth and this effect was found to be dose dependent. Taken together, these results suggest that short interfering siRNA 1284, targeting R2, has great potential to serve as a therapeutic agent towards the treatment of human cancers.

Ribonucleotide reductase subunits M2 and p53R2 are potential biomarkers for metastasis of colon cancer

BACKGROUND

Ribonucleoside diphosphate reductase plays a key role in converting ribonucleoside diphosphate to 2'-deoxyribonucleoside diphosphate, which is necessary for DNA repair and replication. To determine if human ribonucleotide reductase small subunit M2 (hRRM2) and p53-dependent human ribonucleotide reductase small subunit R2 (p53R2) play roles on invasion ability of cancer cells, the gene transferring technique was used to construct stable hRRM2 and p53R2 overexpression transfectants. Increase of hRRM2 dramatically enhanced the cell migration in KB and PC-3 cells, but p53R2 overexpression reduced cellular invasion potential to 50% and 40% in KB and PC-3 cells, respectively. Furthermore, hRRM2 enhanced cancer cells to induce the cell migration of Human Umbilical Vein Endothelial Cells, but p53R2 reduced this ability in transfectants.

PATIENTS AND METHODS

To further determine the role of human ribonucleotide reductase subunits on cancer metastasis, a tissue array, including 59 primary and 49 metastatic colon adenocarcinoma samples, was used. Immunohistochemistry was used to evaluate the relationship between human ribonucleotide reductase subunits and metastasis.

RESULTS

Univariate and multivariate analysis revealed that p53R2 is negatively related to the metastasis of colon adenocarcinoma samples (odds ratio, 0.23; P < 0.05); hRRM2 increases the risk of metastasis in colon cancer, but did not show significantly. Thus, opposing regulation of hRRM2 and p53R2 in invasion potential might play a critical role in determining the invasion and metastasis phenotype in cancer cells.

CONCLUSION

The expression level of ribonucleotide reductase small subunits could serve as biomarkers to predict the malignancy potential of human cancers in the future.

Phase I and pharmacokinetic study of Triapine, a potent ribonucleotide reductase inhibitor, in adults with advanced hematologic malignancies

Triapine, a potent inhibitor of ribonucleotide reductase, has demonstrated anti-leukemia activity in pre-clinical models. We conducted a Phase I study of Triapine administered as a 2 h infusion for 5 days in 25 adults with advanced leukemias. We established that Triapine at 96 mg/m2 once a day can be given safely on days 1-5 and 15-19 or 1-5 and 8-12 of a 4-week cycle. When administered twice a day on days 1-5 and 8-12, the maximum tolerated dose of Triapine appears to be 64 mg/m2, although the true criteria for DLT were not met by protocol definition. No CR or PR were observed, but 76% of patients had a >50% reduction in white blood cell counts. At all dose levels, the peak plasma concentration of Triapine (2.2-5.5 microM) was above levels required to achieve in vitro/in vivo leukemia growth inhibition. Based on these data, we conclude that Triapine warrants further investigation in hematologic malignancies.

Gemcitabine chemoresistance and molecular markers associated with gemcitabine transport and metabolism in human pancreatic cancer cells

To identify predictive molecular markers for gemcitabine resistance, we investigated changes in the expression of four genes associated with gemcitabine transport and metabolism during the development of acquired gemcitabine resistance of pancreatic cancer cell lines. The expression levels of human equilibrative nucleoside transporter-1 (hENT1), deoxycytidine kinase (dCK), RRM1, and RRM2 mRNA were analysed by real-time light cycler-PCR in various subclones during the development of acquired resistance to gemcitabine. Real-time light cycler-PCR demonstrated that the expression levels of either RRM1 or RRM2 progressively increased during the development of gemcitabine resistance. Expression of dCK was slightly increased in cells resistant to lower concentrations of gemcitabine, but was decreased below the undetectable level in higher concentration-resistant subclones. Expression of hENT1 was increased in the development of gemcitabine resistance. As acquired resistance to gemcitabine seems to correlate with the balance of these four factors, we calculated the ratio of hENT1 × dCK/RRM1 × RRM2 gene expression in gemcitabine-resistant subclones. The ratio of gene expression decreased progressively with development of acquired resistance in gemcitabine-resistant subclones. Furthermore, the expression ratio significantly correlated with gemcitabine sensitivity in eight pancreatic cancer cell lines, whereas no single gene expression level correlated with the sensitivity. These results suggest that the sensitivity of pancreatic cancer cells to gemcitabine is determined by the ratio of four factors involved in gemcitabine transport and metabolism. The ratio of the four gene expression levels correlates with acquired gemcitabine-resistance in pancreatic cancer cells, and may be useful as a predictive marker for the efficacy of gemcitabine therapy in pancreatic cancer patients.

Excess ribonucleotide reductase R2 subunits coordinate the S phase checkpoint to facilitate DNA damage repair and recovery from replication stress

Ribonucleotide reductase (RNR), which consists of R1 and R2 subunits, catalyzes a key step of deoxyribonucleoside triphosphate (dNTP) synthesis for DNA replication and repair. The R2 subunit is controlled in a cell cycle-specific manner for timely DNA synthesis and is negatively regulated by p53 in response to DNA damage. Herein we demonstrate that the presence of excess R2 subunits in p53(-/-) HCT-116 human colon cancer cells protects against DNA damage and replication stress. siRNA-mediated stable knockdown (>80%) of excess R2 subunits has no effect on proliferative growth but results in enhanced accumulation of gamma-H2Ax and delayed recovery from DNA lesions inflicted by exposure to cisplatin and Triapine. This accentuated induction of gamma-H2Ax in R2-knockdown cells is attributed to reduced ability to repair damaged DNA and overcome replication blockage. The lack of excess R2 subunits consequently augments chk1 activation and cdc25A degradation, causing impeded cell progression through the S phase and enhanced apoptosis in response to DNA damage and replication stress. In contrast, the level of R1 subunits appears to be limiting, since depletion of the R1 subunit directly activates the S phase checkpoint due to replication stress associated with impaired RNR activity. These findings suggest that excess R2 subunits facilitate DNA damage repair and recovery from replication stress through coordination with the S phase checkpoint in the absence of functional p53. Thus, the level of the R2 subunit constitutes an important determinant of the chemosensitivity of cancer cells and serves as a potential target for enhancement of DNA-damage based therapy.

Metastasis-suppressing potential of ribonucleotide reductase small subunit p53R2 in human cancer cells

PURPOSE

Previous gene transfection studies have shown that the accumulation of human ribonucleotide reductase small subunit M2 (hRRM2) enhances cellular transformation, tumorigenesis, and malignancy potential. The latest identified small subunit p53R2 has 80% homology to hRRM2. Here, we investigate the role of p53R2 in cancer invasion and metastasis.

EXPERIMENTAL DESIGN

The immunohistochemistry was conducted on a tissue array including 49 primary and 59 metastatic colon adenocarcinoma samples to determine the relationship between p53R2 expression and metastasis. A Matrigel invasive chamber was used to sort the highly invasive cells and to evaluate the invasion potential of p53R2.

RESULTS

Univariate and multivariate analyses revealed that p53R2 is negatively related to the metastasis of colon adenocarcinoma samples (odds ratio, 0.23; P<0.05). The decrease of p53R2 is associated with cell invasion potential, which was observed in both p53 wild-type (KB) and mutant (PC-3 and Mia PaCa-2) cell lines. An increase in p53R2 expression by gene transfection significantly reduced the cellular invasion potential to 54% and 30% in KB and PC-3 cells, respectively, whereas inhibition of p53R2 by short interfering RNA resulted in a 3-fold increase in cell migration.

CONCLUSIONS

Opposite regulation of hRRM2 and p53R2 in invasion potential might play a critical role in determining the invasion and metastasis phenotype in cancer cells. The expression level of ribonucleotide reductase small subunits may serve as a biomarker to predict the malignancy potential of human cancers in the future.