Deoxycytidine kinase is overexpressed in poor outcome breast cancer and determines responsiveness to nucleoside analogs

Proteogenomic characterization of difficult-to-treat breast cancer with tumor cells enriched through laser microdissection

BACKGROUND

Breast cancer (BC) is the most commonly diagnosed cancer and the leading cause of cancer death among women globally. Despite advances, there is considerable variation in clinical outcomes for patients with non-luminal A tumors, classified as difficult-to-treat breast cancers (DTBC). This study aims to delineate the proteogenomic landscape of DTBC tumors compared to luminal A (LumA) tumors.

METHODS

We retrospectively collected a total of 117 untreated primary breast tumor specimens, focusing on DTBC subtypes. Breast tumors were processed by laser microdissection (LMD) to enrich tumor cells. DNA, RNA, and protein were simultaneously extracted from each tumor preparation, followed by whole genome sequencing, paired-end RNA sequencing, global proteomics and phosphoproteomics. Differential feature analysis, pathway analysis and survival analysis were performed to better understand DTBC and investigate biomarkers.

RESULTS

We observed distinct variations in gene mutations, structural variations, and chromosomal alterations between DTBC and LumA breast tumors. DTBC tumors predominantly had more mutations in TP53, PLXNB3, Zinc finger genes, and fewer mutations in SDC2, CDH1, PIK3CA, SVIL, and PTEN. Notably, Cytoband 1q21, which contains numerous cell proliferation-related genes, was significantly amplified in the DTBC tumors. LMD successfully minimized stromal components and increased RNA-protein concordance, as evidenced by stromal score comparisons and proteomic analysis. Distinct DTBC and LumA-enriched clusters were observed by proteomic and phosphoproteomic clustering analysis, some with survival differences. Phosphoproteomics identified two distinct phosphoproteomic profiles for high relapse-risk and low relapse-risk basal-like tumors, involving several genes known to be associated with breast cancer oncogenesis and progression, including KIAA1522, DCK, FOXO3, MYO9B, ARID1A, EPRS, ZC3HAV1, and RBM14. Lastly, an integrated pathway analysis of multi-omics data highlighted a robust enrichment of proliferation pathways in DTBC tumors.

CONCLUSIONS

This study provides an integrated proteogenomic characterization of DTBC vs LumA with tumor cells enriched through laser microdissection. We identified many common features of DTBC tumors and the phosphopeptides that could serve as potential biomarkers for high/low relapse-risk basal-like BC and possibly guide treatment selections.

Decitabine-induced DNA methylation-mediated transcriptomic reprogramming in human breast cancer cell lines; the impact of DCK overexpression

Decitabine (DAC), a DNA methyltransferase (DNMT) inhibitor, is tested in combination with conventional anticancer drugs as a treatment option for various solid tumors. Although epigenome modulation provides a promising avenue in treating resistant cancer types, more studies are required to evaluate its safety and ability to normalize the aberrant transcriptional profiles. As deoxycytidine kinase (DCK)-mediated phosphorylation is a rate-limiting step in DAC metabolic activation, we hypothesized that its intracellular overexpression could potentiate DAC’s effect on cell methylome and thus increase its therapeutic efficacy. Therefore, two breast cancer cell lines, JIMT-1 and T-47D, differing in their molecular characteristics, were transfected with a DCK expression vector and exposed to low-dose DAC (approximately IC20). Although transfection resulted in a significant DCK expression increase, further enhanced by DAC exposure, no transfection-induced changes were found at the global DNA methylation level or in cell viability. In parallel, an integrative approach was applied to decipher DAC-induced, methylation-mediated, transcriptomic reprogramming. Besides large-scale hypomethylation, accompanied by up-regulation of gene expression across the entire genome, DAC also induced hypermethylation and down-regulation of numerous genes in both cell lines. Interestingly, TET1 and TET2 expression halved in JIMT-1 cells after DAC exposure, while DNMTs’ changes were not significant. The protein digestion and absorption pathway, containing numerous collagen and solute carrier genes, ranking second among membrane transport proteins, was the top enriched pathway in both cell lines when hypomethylated and up-regulated genes were considered. Moreover, the calcium signaling pathway, playing a significant role in drug resistance, was among the top enriched in JIMT-1 cells. Although low-dose DAC demonstrated its ability to normalize the expression of tumor suppressors, several oncogenes were also up-regulated, a finding, that supports previously raised concerns regarding its broad reprogramming potential. Importantly, our research provides evidence about the involvement of active demethylation in DAC-mediated transcriptional reprogramming.

Homoharringtonine demonstrates a cytotoxic effect against triple-negative breast cancer cell lines and acts synergistically with paclitaxel

The lack of targeted therapies for triple-negative breast cancer (TNBC) contributes to their high mortality rates and high risk of relapse compared to other subtypes of breast cancer. Most TNBCs (75%) have downregulated the expression of CREB3L1 (cAMP-responsive element binding protein 3 like 1), a transcription factor and metastasis suppressor that represses genes that promote cancer progression and metastasis. In this report, we screened an FDA-approved drug library and identified four drugs that were highly cytotoxic towards HCC1806 CREB3L1-deficient TNBC cells. These four drugs were: (1) palbociclib isethionate, a CDK4/6 inhibitor, (2) lanatocide C (also named isolanid), a Na+/K+-ATPase inhibitor, (3) cladribine, a nucleoside analog, and (4) homoharringtonine (also named omacetaxine mepesuccinate), a protein translation inhibitor. Homoharringtonine consistently showed the most cytotoxicity towards an additional six TNBC cell lines (BT549, HCC1395, HCC38, Hs578T, MDA-MB-157, MDA-MB-436), and several luminal A breast cancer cell lines (HCC1428, MCF7, T47D, ZR-75-1). All four drugs were then separately evaluated for possible synergy with the chemotherapy agents, doxorubicin (an anthracycline) and paclitaxel (a microtubule stabilizing agent). A strong synergy was observed using the combination of homoharringtonine and paclitaxel, with high cytotoxicity towards TNBC cells at lower concentrations than when each was used separately.

Roles for hENT1 and dCK in gemcitabine sensitivity and malignancy of meningioma

Background

High-grade meningiomas are aggressive tumors with high morbidity and mortality rates that frequently recur even after surgery and adjuvant radiotherapy. However, limited information is currently available on the biology of these tumors, and no alternative adjuvant treatment options exist. Although we previously demonstrated that high-grade meningioma cells were highly sensitive to gemcitabine in vitro and in vivo, the underlying molecular mechanisms remain unknown.

Methods

We examined the roles of hENT1 (human equilibrative nucleoside transporter 1) and dCK (deoxycytidine kinase) in the gemcitabine sensitivity and growth of meningioma cells in vitro. Tissue samples from meningiomas (26 WHO grade I and 21 WHO grade II/III meningiomas) were immunohistochemically analyzed for hENT1 and dCK as well as for Ki-67 as a marker of proliferative activity.

Results

hENT1 and dCK, which play critical roles in the intracellular transport and activation of gemcitabine, respectively, were responsible for the high gemcitabine sensitivity of high-grade meningioma cells and were strongly expressed in high-grade meningiomas. hENT1 expression was required for the proliferation and survival of high-grade meningioma cells and dCK expression. Furthermore, high hENT1 and dCK expression levels correlated with stronger tumor cell proliferative activity and shorter survival in meningioma patients.

Conclusions

The present results suggest that hENT1 is a key molecular factor influencing the growth capacity and gemcitabine sensitivity of meningioma cells and also that hENT1, together with dCK, may be a viable prognostic marker for meningioma patients as well as a predictive marker of their responses to gemcitabine.

Zebularine elevates STING expression and enhances cGAMP cancer immunotherapy in mice

DNA methylation abnormality is closely related to tumor occurrence and development. Chemical inhibitors targeting DNA methyltransferase (DNMTis) have been used in treating cancer. However, the impact of DNMTis on antitumor immunity has not been well elucidated. In this study, we show that zebularine (a demethylating agent) treatment of cancer cells led to increased levels of interferon response in a cyclic guanosine monophosphate-AMP (cGAMP) synthase (cGAS)- and stimulator of interferon genes (STING)-dependent manner. This treatment also specifically sensitized the cGAS-STING pathway in response to DNA stimulation. Incorporation of zebularine into genomic DNA caused demethylation and elevated expression of a group of genes, including STING. Without causing DNA damage, zebularine led to accumulation of DNA species in the cytoplasm of treated cells. In syngeneic tumor models, administration of zebularine alone reduced tumor burden and extended mice survival. This effect synergized with cGAMP and immune checkpoint blockade therapy. The efficacy of zebularine was abolished in nude mice and in cGAS^-/- or STING^-/- mice, indicating its dependency on host immunity. Analysis of tumor cells indicates upregulation of interferon-stimulated genes (ISGs) following zebularine administration. Zebularine promoted infiltration of CD8 T cells and natural killer (NK) cells into tumor and therefore suppressed tumor growth. This study unveils the role of zebularine in sensitizing the cGAS-STING pathway to promote anti-tumor immunity and provides the foundation for further therapeutic development.

DCK is a promising prognostic biomarker and correlated with immune infiltrates in hepatocellular carcinoma

Background

Deoxycytidine kinase (DCK), an enzyme in the nucleoside biosynthetic pathway, can affect the development of immune cells. However, the relationships between the expression of DCK, patient prognosis, and tumor-infiltrating immune cells (TIICs) in hepatocellular carcinoma (HCC) are still unclear.

Methods

The expression of DCK in HCC was analyzed through the Oncomine and Tumor Immune Estimation Resource (TIMER) databases. The impact of DCK on clinical prognosis was investigated via the Kaplan-Meier plotter and verified in the Gene Expression Profiling Interactive Analysis (GEPIA) databases. The interrelationships between DCK expression and TIICs in HCC were analyzed by the TIMER database. Additionally, the relationship between DCK expression and immune cell gene markers was calculated through TIMER and GEPIA databases.

Results

Compared with the adjacent normal tissues, high expression of DCK was observed in HCC tissues. Also, the higher expression of DCK was correlated to poorer prognosis in HCC patients, and it was associated with decreased survival in those with early stage and grade. Moreover, DCK expression was positively correlated with TIICs, including CD4⁺ and CD8⁺ T cells, B cells, monocytes, tumor-associated macrophages (TAMs), M1 and M2 macrophages, neutrophils, natural killer cells, and dendritic cells. Specifically, DCK expression levels were significantly associated with diverse immune gene marker sets, including those of Tregs and exhausted T cells.

Conclusion

These findings suggest that DCK expression is correlated with patient outcomes and tumor infiltration cell levels in HCC patients. Additionally, the increased level of DCK was associated with marker genes of Tregs and exhaustion-related inhibitory receptors, suggesting the potential role of DCK in immunosuppression and immune escape. These findings suggest that DCK can function as a potential novel prognostic biomarker and reflect the immune infiltration status in HCC patients.

DCK is an Unfavorable Prognostic Biomarker and Correlated With Immune Infiltrates in Liver Cancer

BACKGROUND

The biological function of deoxycytidine kinase in tumor is not yet clear, and there are a few studies relating to the correlation of deoxycytidine kinase gene with the occurrence and development of liver cancer.

METHODS

The messenger RNA expression of deoxycytidine kinase was analyzed with the use of the UALCAN and GEPIA database. Moreover, we assessed the function of deoxycytidine kinase on clinical prognosis with Kaplan-Meier plotter database. The relationship between deoxycytidine kinase and cancer immune infiltrates was investigated via Tumor Immune Estimation Resource site. Furthermore, Tumor Immune Estimation Resource was also used to evaluate the correlations between the expression of deoxycytidine kinase and gene marker sets of immune infiltrates.

RESULTS

The deoxycytidine kinase messenger RNA level significantly upregulated in patients with liver cancer compared to normal liver samples. Moreover, the increased expression of deoxycytidine kinase messenger RNA was closely associated with reduced overall survival and disease-free survival in all liver cancers. In addition, deoxycytidine kinase expression displayed a strong correlation with infiltrating levels of macrophages, neutrophils, and dendritic cells in liver cancer, and deoxycytidine kinase expression was positively correlated with diverse immune marker sets in liver cancer.

CONCLUSIONS

All the above findings suggested that increased expression of deoxycytidine kinase was significantly related to unfavorable prognosis in patients with liver cancer. And deoxycytidine kinase is correlated with immune infiltrating levels, including those of B cells, macrophages, neutrophils, and dendritic cells in patients with liver cancer. These findings suggest that deoxycytidine kinase can be used as a prognostic biomarker for determining prognosis and immune infiltration in liver cancer. And deoxycytidine kinase is a potential target for liver cancer therapy, and these preliminary findings require further study to determine whether deoxycytidine kinase-targeting reagents might be developed for clinical application in liver cancer.

Recombinant deoxyribonucleoside kinase from Drosophila melanogaster can improve gemcitabine based combined gene/chemotherapy for targeting cancer cells

A recombinant deoxyribonucleoside kinase from Drosophila melanogaster with a deletion of the last 20 amino acid residues (named DmdNKΔC20) was hypothesized as a potential therapeutic tool for gene therapy due to its broad substrate specificity and better catalytic efficiency towards nucleosides and nucleoside analogs. This study was designed to evaluate the effect of DmdNKΔC20 for sensitizing human cancer cell lines to gemcitabine and to further investigate its role in reversal of acquired drug resistance in gemcitabine-resistant cancer cell line. The DmdNKΔC20 gene was delivered to three different cancer cell lines, including breast, colon and liver cancer cells, using lipid-mediated transfection reagent. After transfection, gene expression of DmdNKΔC20 was confirmed by quantitative reverse transcription PCR (qRT-PCR) and the combined effect of DmdNKΔC20 and gemcitabine based cytotoxicity was observed by cell viability assay. We further evolved a gemcitabine-resistant breast cancer cell line (named MCF7-R) through directed evolution in the laboratory, which showed 375-fold more resistance compared with parental MCF7 cells. Upon transfection with DmdNKΔC20 gene, MCF7-R cells showed 83-fold higher sensitivity to gemcitabine compared with the control group of MCF7-R cells. Moreover, we observed 79% higher expression of p21 protein in transfected MCF7-R cells, which may indicate induction of apoptosis. Our findings highlight the importance and therapeutic potential of DmdNKΔC20 in combined gene/chemotherapy approach to target a wide range of cancers, particularly gemcitabine-resistant cancers.

Novel Clofarabine-Based Combinations with Polyphenols Epigenetically Reactivate Retinoic Acid Receptor Beta, Inhibit Cell Growth, and Induce Apoptosis of Breast Cancer Cells

An epigenetic component, especially aberrant DNA methylation pattern, has been shown to be frequently involved in sporadic breast cancer development. A growing body of literature demonstrates that combination of agents, i.e. nucleoside analogues with dietary phytochemicals, may provide enhanced therapeutic effects in epigenetic reprogramming of cancer cells. Clofarabine (2-chloro-2′-fluoro-2′-deoxyarabinosyladenine, ClF), a second-generation 2′-deoxyadenosine analogue, has numerous anti-cancer effects, including potential capacity to regulate epigenetic processes. Our present study is the first to investigate the combinatorial effects of ClF (used at IC₅₀ concentration) with epigallocatechin-3-gallate (EGCG, tea catechin) or genistein (soy phytoestrogen), at physiological concentrations, on breast cancer cell growth, apoptosis, and epigenetic regulation of retinoic acid receptor beta (RARB) transcriptional activity. In MCF7 and MDA-MB-231 cells, RARB promoter methylation and expression of RARB, modifiers of DNA methylation reaction (DNMT1, CDKN1A, TP53), and potential regulator of RARB transcription, PTEN, were estimated using methylation-sensitive restriction analysis (MSRA) and quantitative real-time polymerase chain reaction (qPCR), respectively. The combinatorial exposures synergistically or additively inhibited the growth and induced apoptosis of breast cancer cells, followed by RARB hypomethylation with concomitant multiple increase in RARB, PTEN, and CDKN1A transcript levels. Taken together, our results demonstrate the ability of ClF-based combinations with polyphenols to promote cancer cell death and reactivate DNA methylation-silenced tumor suppressor genes in breast cancer cells with different invasive potential.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.

Effects of DCK knockdown on proliferation, apoptosis and tumorigenicity in vivo of cervical cancer HeLa cells

The present study explored the effect that deoxycytidine kinase (DCK) knockdown had on proliferation, apoptosis and tumorigenicity in vivo of cervical cancer HeLa cells. Human cervical cancer HeLa cells that had received no prior treatment were selected from the HeLa group. The HeLa-negative control (NC) group consisted of cells that had undergone an empty vector treatment, and finally the HeLa-short hairpin RNA (shRNA) group included cells that were treated by means of shRNA-DCK expression. DCK expressions were evaluated by quantitative real-time polymerase chain reaction in addition to western blotting assays. Cell proliferation was estimated using the Cell Counting Kit-8 (CCK-8) assay and cell cycle progression. Cell apoptosis was determined by flow cytometry. BALB/c nude mice (n=24) were selected to establish transplanted tumor models, with gross tumor volume measured every 3 days. The results in vitro were as follows: compared with the HeLa group, the HeLa-shRNA group exhibited downregulation of DCK expression and inhibition of cell proliferation at 48, 72 and 96 h. Additionally, more cells in the HeLa-shRNA group were arrested in G0/G1 stage and less in S and G2/M stages, as well as in promotion of cell apoptosis. In vivo results are as follows: when comparing the HeLa and HeLa-NC groups, the gross tumor volume of the transplanted tumor in nude mice in the HeLa-shRNA group was found to have decreased in 13, 16, 19 and 22 days. Based on these findings, our study suggests that DCK knockdown facilitates apoptosis while inhibiting proliferation and tumorigenicity in vivo of cervical cancer HeLa cells.

dCK Expression and Gene Polymorphism With Gemcitabine Chemosensitivity in Patients With Pancreatic Ductal Adenocarcinoma: A Strobe-Compliant Observational Study

The aim of this study was to investigate the relationship of deoxycytidine kinase (dCK) protein expression and gene single-nucleotide polymorphisms to gemcitabine chemosensitivity in patients with pancreatic ductal adenocarcinoma (PDAC).In total, 54 patients with resectable PDAC, who received postoperative gemcitabine-based therapy, were enrolled in this study, from January 2011 to April 2013. The dCK protein expression was measured retrospectively by immunohistochemistry. Furthermore, 5 single-nucleotide polymorphisms (C1205T, A9846G, A70G, C356G, and C364T) of the dCK gene were detected in PDAC cells by PCR amplification and sequencing.The dCK protein expression was found to be negatively correlated with age (P = 0.006), but correlated positively with overall survival (OS) (P = 0.000) and disease-free survival (DFS) (P = 0.003). The A9846G AA genotype in the dCK gene was significantly associated with reduced mortality compared with AG and GG genotypes. The OS and DFS were longer in patients with the A9846G AA genotype than the AG and GG genotypes. In univariate and multivariate analyses, we found that the dCK protein expression and A9846G genotype were significant predictors of both OS and DFS.Our study suggests that the dCK protein expression and A9846G genotype may act as prognostic biomarkers in identifying patients who are likely to benefit from postoperative gemcitabine therapy in PDAC.

Potent Sensitisation of Cancer Cells to Anticancer Drugs by a Quadruple Mutant of the Human Deoxycytidine Kinase

Identifying enzymes that, once introduced in cancer cells, lead to an increased efficiency of treatment constitutes an important goal for biomedical applications. Using an original procedure whereby mutant genes are generated based on the use of conditional lentivector genome mobilisation, we recently described, for the first time, the identification of a human deoxycytidine kinase (dCK) mutant (G12) that sensitises a panel of cancer cell lines to treatment with the dCK analogue gemcitabine. Here, starting from the G12 variant itself, we generated a new library and identified a mutant (M36) that triggers even greater sensitisation to gemcitabine than G12. With respect to G12, M36 presents an additional mutation located in the region that constitutes the interface of the dCK dimer. The simple presence of this mutation halves both the IC50 and the proportion of residual cells resistant to the treatment. Furthermore, the use of vectors with self-inactivating LTRs leads to an increased sensitivity to treatment, a result compatible with a relief of the transcriptional interference exerted by the U3 promoter on the internal promoter that drives the expression of M36. Importantly, a remarkable effect is also observed in treatments with the anticancer compound cytarabine (AraC), for which a 10,000 fold decrease in IC50 occurred. By triggering the sensitisation of various cancer cell types with poor prognosis to two commonly used anticancer compounds M36 is a promising candidate for suicide gene approaches.

Regulation of nucleotide metabolism by mutant p53 contributes to its gain-of-function activities

Mutant p53 (mtp53) is an oncogene that drives cancer cell proliferation. Here we report that mtp53 associates with the promoters of numerous nucleotide metabolism genes (NMG). Mtp53 knockdown reduces NMG expression and substantially depletes nucleotide pools, which attenuates GTP dependent protein (GTPase) activity and cell invasion. Addition of exogenous guanosine or GTP restores the invasiveness of mtp53 knockdown cells, suggesting that mtp53 promotes invasion by increasing GTP. Additionally, mtp53 creates a dependency on the nucleoside salvage pathway enzyme deoxycytidine kinase (dCK) for the maintenance of a proper balance in dNTP pools required for proliferation. These data indicate that mtp53 harboring cells have acquired a synthetic sick or lethal phenotype relationship with the nucleoside salvage pathway. Finally, elevated expression of NMG correlates with mutant p53 status and poor prognosis in breast cancer patients. Thus, mtp53’s control of nucleotide biosynthesis has both a driving and sustaining role in cancer development.

Facile method for determination of deoxycytidine kinase activity in biological milieus

A new analytical method for determining deoxycytidine kinase (dCK) activity in biological milieus using luminescence is reported here. This method, based on utilizing adenosine triphosphate (ATP) as the sole phosphate donor in the kinase reaction and monitoring ATP consumption via a luciferase-based chemiluminescence reaction, is capable of detecting dCK activity without the use of specific substrates or radioisotope techniques. Comparing with the reverse-phase high-performance liquid chromatography method, this new method is suggested to be efficient and sensitive. Further, application of the proposed method for profiling dCK activity in cultured cancer cells revealed that a cervix cell line exhibited the highest dCK activity to gemcitabine metabolism.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Hypoxia-induced deoxycytidine kinase expression contributes to apoptosis in chronic lung disease

Chronic obstructive pulmonary disease (COPD) is characterized by persistent inflammation and tissue remodeling and is a leading cause of death in the United States. Increased apoptosis of pulmonary epithelial cells is thought to play a role in COPD development and progression. Identification of signaling pathways resulting in increased apoptosis in COPD can be used in the development of novel therapeutic interventions. Deoxyadenosine (dAdo) is a DNA breakdown product that amplifies lymphocyte apoptosis by being phosphorylated to deoxyadenosine triphosphate (dATP). dAdo is maintained at low levels by adenosine deaminase (ADA). This study demonstrated that mice lacking ADA developed COPD manifestations in association with elevated dAdo and dATP levels and increased apoptosis in the lung. Deoxycitidine kinase (DCK), a major enzyme for dAdo phosphorylation, was up-regulated in mouse and human airway epithelial cells in association with air-space enlargement. Hypoxia was identified as a novel regulator of DCK, and inhibition of DCK resulted in diminished dAdo-mediated apoptosis in the lungs. Our results suggest that activating the dAdo-DCK-dATP pathway directly results in increased apoptosis in the lungs of mice with air-space enlargement and suggests a novel therapeutic target for the treatment of COPD.

Immunotherapy of cancer: reprogramming tumor-immune crosstalk

The advancement of cancer immunotherapy faces barriers which limit its efficacy. These include weak immunogenicity of the tumor, as well as immunosuppressive mechanisms which prevent effective antitumor immune responses. Recent studies suggest that aberrant expression of cancer testis antigens (CTAs) can generate robust antitumor immune responses, which implicates CTAs as potential targets for immunotherapy. However, the heterogeneity of tumor cells in the presence and quantity of CTA expression results in tumor escape from CTA-specific immune responses. Thus, the ability to modulate the tumor cell epigenome to homogenously induce expression of such antigens will likely render the tumor more immunogenic. Additionally, emerging studies suggest that suppression of antitumor immune responses may be overcome by reprogramming innate and adaptive immune cells. Therefore, this paper discusses recent studies which address barriers to successful cancer immunotherapy and proposes a strategy of modulation of tumor-immune cell crosstalk to improve responses in carcinoma patients.

Overcoming nucleoside analog chemoresistance of pancreatic cancer: a therapeutic challenge

Clinical refractoriness to nucleoside analogs (e.g., gemcitabine, capecitabine) is a major scientific problem and is one of the main reasons underlying the extremely poor prognostic state of pancreatic cancer. The drugs' effects are suboptimal partly due to cellular mechanisms limiting their transport, activation, and overall efficacy. Nonetheless, novel therapeutic approaches are presently under study to circumvent nucleoside analog resistance in pancreatic cancer. With these new approaches come additional challenges to be addressed. This review describes the determinants of chemoresistance in the gemcitabine cytotoxicity pathways, provides an overview of investigational approaches for overcoming chemoresistance, and discusses new challenges presented. Understanding the future directions of the field may assist in the successful development of novel treatment strategies for enhancing chemotherapeutic efficacy in pancreatic cancer.

Reexpression of tumor suppressor, sFRP1, leads to antitumor synergy of combined HDAC and methyltransferase inhibitors in chemoresistant cancers

Metastatic solid tumors are aggressive and mostly drug resistant, leading to few treatment options and poor prognosis as seen with clear cell renal cell carcinoma (ccRCC) and triple-negative breast cancer (TNBC). Therefore, the identification of new therapeutic regimes for the treatment of metastatic disease is desirable. ccRCC and TNBC cell lines were treated with the HDAC inhibitor romidepsin and the methyltransferase inhibitor decitabine, two epigenetic modifying drugs approved by the U.S. Food and Drug Administration for the treatment of various hematologic malignancies. Cell proliferation analysis, flow cytometry, quantitative PCR, and immunoblotting techniques were used to evaluate the antitumor synergy of this drug combination and identify the reexpression of epigenetically silenced tumor suppressor genes. Combinatorial treatment of metastatic TNBC and stage IV ccRCC cell lines with romidepsin/decitabine leads to synergistic inhibition of cell growth and induction of apoptosis above levels of individual drug treatments alone. Synergistic reexpression of the tumor suppressor gene secreted frizzled-related protein one (sFRP1) was observed in combinatorial drug-treated groups. Silencing sFRP1 (short hairpin RNA) before combinatorial drug treatment showed that sFRP1 mediates the growth inhibitory and apoptotic activity of combined romidepsin/decitabine. Furthermore, addition of recombinant sFRP1 to ccRCC or TNBC cells inhibits cell growth in a dose-dependent manner through the induction of apoptosis, identifying that epigenetic silencing of sFRP1 contributes to renal and breast cancer cell survival. Combinatorial treatment with romidepsin and decitabine in drug resistant tumors is a promising treatment strategy. Moreover, recombinant sFRP1 may be a novel therapeutic strategy for cancers with suppressed sFRP1 expression.

Correlated tissue expression of genes of cytoplasmic and mitochondrial nucleotide metabolisms in normal tissues is disrupted in transformed tissues

Cells maintain dual metabolic pathways to provide substrates for the replication of mitochondrial and nuclear DNA. These pathways involve two separate sets of genes in the nuclear DNA, with one set encoding proteins targeted to the mitochondrion. However, the cytoplasmic and mitochondrial metabolisms are capable of communication through the transport of deoxyribonucleosides and deoxyribonucleotides between the two subcellular compartments. Cytoplasmic and mitochondrial deoxyribonucleoside triphosphate concentrations are strongly correlated in normal cells but not in transformed cells. We were therefore interested in comparing the interactions in normal and transformed tissues between the corresponding cytoplasmic and mitochondrial metabolisms that produce deoxyribonucleoside triphosphates. We conducted an analysis of gene expression data in normal and transformed human tissues obtained from the UniGene database for a selected set of genes for proteins involved in nucleoside salvage in either the cytoplasm or mitochondria. We also included ribonucleotide reductase in our analysis due to its importance in generating deoxyribonucleoside triphosphates. This analysis revealed a large number of highly significant positive correlations between the tissue expression profiles of the genes of the mitochondrial and cytoplasmic pathways in normal tissues, indicating that in normal tissues, the two metabolisms coordinately generate deoxyribonucleoside triphosphates. In transformed tissues, this correlation structure was disrupted. Multiple correlations involving the mitochondrial nucleoside kinase gene DGUOK were statistically significantly different between normal and transformed tissues, suggesting that control of DGUOK expression relative to other cytoplasmic genes is important in transformed tissues.

Targeting the epigenome for treatment of cancer

Cancer genome analyses have revealed that the enzymes involved in epigenetic gene regulation are frequently deregulated in cancer. Here we describe the enzymes that control the epigenetic state of the cell, how they are affected in cancer and how this knowledge can be exploited to treat cancer with a new arsenal of selective therapies.