Mechanisms of apoptosis induction by nucleoside analogs

Synthesis and cytotoxicity of novel 6,8,9-trisubstituted purine analogs against liver cancer cells

A series of novel 6-(substituted phenyl piperazine)-8-(4-substituted phenyl)-9-cyclopentyl purines, 10-51, were synthesized by a four-step synthesis, achieving an overall yield of about 43 %. The reaction conditions were effectively optimized, and the final products were obtained with high purity and yield in all synthesis steps. The synthesized nucleobases were evaluated for their in vitro cytotoxic activities on selected human cancer cell lines (HUH7 (liver), HCT116 (colon), and MCF7 (breast)) using the Sulforhodamine B (SRB) assay. Among these analogs, compounds bearing 4-trifluoromethyl phenyl (19, 20 and 21), 4-methoxy phenyl (27) and 4-fluoro phenyl (34) substitutions at C-8 of purine were the most potent, and they were also analyzed in drug-resistance and drug-sensitive hepatocellular cancer cell (HCC) panels. Compound 19 displayed remarkable anticancer activities (IC50 = 2.9-9.3 μM) against Huh7, FOCUS, SNU475, SNU182, HepG2, and Hep3B cells compared to the positive control, Fludarabine. Additionally, the pharmacological properties and toxicity profiles of the molecules were investigated computationally by the Swiss-ADME and Pro-Tox II online tools, respectively. Results showed that our compounds have favorable physicochemical characteristics for oral bioavailability and do not reveal any toxicity endpoints such as carcinogenicity, immunotoxicity, mutagenicity, or cytotoxicity.

Construction of S100 family members prognosis prediction model and analysis of immune microenvironment landscape at single-cell level in pancreatic adenocarcinoma: a tumor marker prognostic study

Pancreatic adenocarcinoma characterized by a mere 10% five-year survival rate, poses a formidable challenge due to its specific anatomical location, making tumor tissue acquisition difficult. This limitation underscores the critical need for novel biomarkers to stratify this patient population. Accordingly, this study aimed to construct a prognosis prediction model centered on S100 family members. Leveraging six S100 genes and their corresponding coefficients, an S100 score was calculated to predict survival outcomes. The present study provided comprehensive internal and external validation along with power evaluation results, substantiating the efficacy of the proposed model. Additionally, the study explored the S100-driven potential mechanisms underlying malignant progression. By comparing immune cell infiltration proportions in distinct patient groups with varying prognoses, the research identified differences driven by S100 expression. Furthermore, the analysis explored significant ligand-receptor pairs between malignant cells and immune cells influenced by S100 genes, uncovering crucial insights. Notably, the study identified a novel biomarker capable of predicting the sensitivity of neoadjuvant chemotherapy, offering promising avenues for further research and clinical application.

Nucleoside Analogs: A Review of Its Source and Separation Processes

Nucleoside analogs play a crucial role in the production of high-value antitumor and antimicrobial drugs. Currently, nucleoside analogs are mainly obtained through nucleic acid degradation, chemical synthesis, and biotransformation. However, these methods face several challenges, such as low concentration of the main product, the presence of complex matrices, and the generation of numerous by-products that significantly limit the development of new drugs and their pharmacological studies. Therefore, this work aims to summarize the universal separation methods of nucleoside analogs, including crystallization, high-performance liquid chromatography (HPLC), column chromatography, solvent extraction, and adsorption. The review also explores the application of molecular imprinting techniques (MITs) in enhancing the identification of the separation process. It compares existing studies reported on adsorbents of molecularly imprinted polymers (MIPs) for the separation of nucleoside analogs. The development of new methods for selective separation and purification of nucleosides is vital to improving the efficiency and quality of nucleoside production. It enables us to obtain nucleoside products that are essential for the development of antitumor and antiviral drugs. Additionally, these methods possess immense potential in the prevention and control of serious diseases, offering significant economic, social, and scientific benefits to the fields of environment, biomedical research, and clinical therapeutics.

Conventional DNA-Damaging Cancer Therapies and Emerging cGAS-STING Activation: A Review and Perspectives Regarding Immunotherapeutic Potential

Many traditional cancer treatments such as radiation and chemotherapy are known to induce cellular DNA damage as part of their cytotoxic activity. The cGAS-STING signaling axis, a key member of the DNA damage response that acts as a sensor of foreign or aberrant cytosolic DNA, is helping to rationalize the DNA-damaging activity of these treatments and their emerging immunostimulatory capacity. Moreover, cGAS-STING, which is attracting considerable attention for its ability to promote antitumor immune responses, may fundamentally be able to address many of the barriers limiting the success of cancer immunotherapy strategies, including the immunosuppressive tumor microenvironment. Herein, we review the traditional cancer therapies that have been linked with cGAS-STING activation, highlighting their targets with respect to their role and function in the DNA damage response. As part of the review, an emerging "chemoimmunotherapy" concept whereby DNA-damaging agents are used for the indirect activation of STING is discussed as an alternative to the direct molecular agonism strategies that are in development, but have yet to achieve clinical approval. The potential of this approach to address some of the inherent and emerging limitations of cGAS-STING signaling in cancer immunotherapy is also discussed. Ultimately, it is becoming clear that in order to successfully employ the immunotherapeutic potential of the cGAS-STING axis, a balance between its contrasting antitumor and protumor/inflammatory activities will need to be achieved.

Resistance to Chemotherapeutic 5-Fluorouracil Conferred by Modulation of Heterochromatic Integrity through Ino80 Function in Fission Yeast

5-Fluorouracil (5-FU) is a conventional chemotherapeutic drug widely used in clinics worldwide, but development of resistance that compromises responsiveness remains a major hurdle to its efficacy. The mechanism underlying 5-FU resistance is conventionally attributed to the disruption of nucleotide synthesis, even though research has implicated other pathways such as RNA processing and chromatin dysregulation. Aiming to clarify resistance mechanisms of 5-FU, we tested the response of a collection of fission yeast (Schizosaccharomyces pombe) null mutants, which confer multiple environmental factor responsiveness (MER). Our screen identified disruption of membrane transport, chromosome segregation and mitochondrial oxidative phosphorylation to increase cellular susceptibility towards 5-FU. Conversely, we revealed several null mutants of Ino80 complex factors exhibited resistance to 5-FU. Furthermore, attenuation of Ino80 function via deleting several subunit genes reversed loss of chromosome-segregation fidelity in 5-FU in the loss-of-function mutant of the Argonaute protein, which regulates RNA interference (RNAi)-dependent maintenance of pericentromeric heterochromatin. Our study thus uncovered a critical role played by chromatin remodeling Ino80 complex factors in 5-FU resistance, which may constitute a possible target to modulate in reversing 5-FU resistance.

Metabolism in acute myeloid leukemia: mechanistic insights and therapeutic targets

Metabolic rewiring and cellular reprogramming are trademarks of neoplastic initiation and progression in acute myeloid leukemia (AML). Metabolic alteration in leukemic cells is often genotype specific, with associated changes in epigenetic and functional factors resulting in the downstream upregulation or facilitation of oncogenic pathways. Targeting abnormal or disease-sustaining metabolic activities in AML provides a wide range of therapeutic opportunities, ideally with enhanced therapeutic windows and robust clinical efficacy. This review highlights the dysregulation of amino acid, nucleotide, lipid, and carbohydrate metabolism in AML; explores the role of key vitamins and enzymes that regulate these processes; and provides an overview of metabolism-directed therapies currently in use or development.

Significance of Circulating Cell-Free DNA Biomarkers in HBeAg-Negative Chronic Hepatitis B Virus Infection and Their Changes after Treatment Initiation

Background: Chronic hepatitis B virus (HBV) infection is a common chronic liver disease that is closely associated with increased morbidity and mortality. Circulating cell-free DNA (cf-DNA) and global DNA methylation, expressed as circulating levels of 5-methyl-2′-deoxycytidine, are increasingly used to monitor chronic inflammatory diseases of several etiologies. This study attempts to investigate the serum levels of circulating cf-DNA and 5-methyl-2′-deoxycytidine in HBeAg-negative patients with chronic infection (carriers) and chronic hepatitis B (CHB), as well as their changes after treatment initiation in CHB. Methods: Serum samples from a total of 61 HBeAg-negative patients (30 carriers and 31 CHB patients) were included in order to quantify the levels of circulating cf-DNA and 5-methyl-2′-deoxycytidine. In addition, serum samples from 17 CHB patients in complete virological and biochemical remission after initiation of treatment with a nucleos(t)ide analogue were included. Results: Circulating cf-DNA concentration was significantly increased after the initiation of treatment (15 vs. 10 ng/mL, p = 0.022). There was a trend in higher mean levels of circulating 5-methyl-2′-deoxycytidine in carriers compared to CHB patients (211.02 vs. 175.66 ng/mL, p = 0.089), as well as a trend in increasing 5-methyl-2′-deoxycytidine levels after treatment initiation in CHB patients compared to pre-treatment levels (215 vs. 173 ng/mL, p = 0.079). Conclusions: Both circulating levels of cf-DNA and 5-methyl-2′-deoxycytidine might be useful biomarkers in order to monitor liver disease activity and response to antiviral treatment in HBeAg-negative chronic HBV patients, but further studies are essential in order to validate these intriguing findings.

Synthesis of new 1,2,3-triazolo-nucleoside analogues with 2-propargylamino pyrimidines via click reactions

In this study, it was reported that twelve nucleoside analogues were synthesized by click reactions. The reactions were carried out between the azide derivatives of D-glucopyranose, D-galactopyranose, D-ribofuranose and 2-propargylamino pyrimidine derivatives (5 and 7) that are synthesized via a different route for the first time. In the first step, N-propargyl guanidine was obtained with the reaction of 1H-pyrazole-1-carboxamidine hydrochloride and propargyl amine, then condensation of N-propargyl guanidine and β-diketone (4 and 6) resulted in 2-propargylamino pyrimidines (5 and 7) for the first time in good yields (85%). Finally, click reactions were performed with azidosugars (8a-8f) and 2-propargylamino pyrimidine derivatives and produced twelve new nucleoside analogues in good yields. (9a-9f, 10a-10f, 65-73% yields). The chemical structures of the new derivatives were elucidated spectroscopic techniques, such as FT-IR, ¹H NMR, ¹⁹F NMR, ¹³C NMR and TOF-ESI-MS.

A ferrocene-containing nucleoside analogue targets DNA replication in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is a disease that remains refractory to existing treatments including the nucleoside analogue gemcitabine. In the current study we demonstrate that an organometallic nucleoside analogue, the ferronucleoside 1-(S,Rp), is cytotoxic in a panel of PDAC cell lines including gemcitabine-resistant MIAPaCa2, with IC50 values comparable to cisplatin. Biochemical studies show that the mechanism of action is inhibition of DNA replication, S-phase cell cycle arrest and stalling of DNA-replication forks, which were directly observed at single molecule resolution by DNA-fibre fluorography. In agreement with this, transcriptional changes following treatment with 1-(S,Rp) include activation of three of the four genes (HUS1, RAD1, RAD17) of the 9-1-1 check point complex clamp and two of the three genes (MRE11, NBN) that form the MRN complex as well as activation of multiple downstream targets. Furthermore, there was evidence of phosphorylation of checkpoint kinases 1 and 2 as well as RPA1 and gamma H2AX, all of which are considered biochemical markers of replication stress. Studies in p53-deficient cell lines showed activation of CDKN1A (p21) and GADD45A by 1-(S,Rp) was at least partially independent of p53. In conclusion, because of its potency and activity in gemcitabine-resistant cells, 1-(S,Rp) is a promising candidate molecule for development of new treatments for PDAC.

Enhanced Cytotoxic Effects in Human Oral Squamous Cell Carcinoma Cells Treated with Combined Methyltransferase Inhibitors and Histone Deacetylase Inhibitors

Combined treatment of human oral squamous cell carcinoma (OSCCs) with DNA methyltransferase inhibitors (DNMTis), histone methyltransferase inhibitors (HMTis), and histone deacetylase inhibitors (HDACis), and the molecular mechanisms underlying their anticancer effects, have not been fully elucidated. Herein, we investigated the cytotoxic effects of combined DNMTis (5-Aza-deoxycytidine: 5-Aza-dC, RG108), HMTis (3-deazaneplanocin A: DZNep), and HDACis (trichostatin A: TSA) treatment on human OSCC cells and explored their molecular mechanisms. Combined 5-Aza-dC, or RG108, and TSA treatment significantly decreased HSC-2 and Ca9-22 cell viability. Combinatorial DZNep and TSA treatment also decreased Ca9-22 cell viability. Although caspase 3/7 activation was not observed in HSC-2 cells following combined treatment, caspase activity was significantly increased in Ca9-22 cells treated with DZNep and TSA. Moreover, combined treatment with 5-Aza-dC, RG108, and TSA increased the proportion of HSC-2 and Ca9-22 cells in the S and G2/M phases. Meanwhile, increased phosphorylation of the histone variant H2A.X, a marker of double-stranded DNA breaks, was observed in both cells after combination treatment. Hence, the decreased viability induced by combined treatment with epigenomic inhibitors results from apoptosis and cell cycle arrest in S and G2/M phases. Thus, epigenomic therapy comprising combined low concentrations of DNMTi, HMTi, and HDACi is effective against OSCC.

Targeting DNMT1 by demethylating agent OR-2100 increases tyrosine kinase inhibitors-sensitivity and depletes leukemic stem cells in chronic myeloid leukemia

ABL1 tyrosine kinase inhibitors (TKIs) dramatically improve the prognosis of chronic myeloid leukemia (CML), but 10-20% of patients achieve suboptimal responses with low TKIs sensitivity. Furthermore, residual leukemic stem cells (LSCs) are involved in the molecular relapse after TKIs discontinuation. Aberrant DNA hypermethylation contributes to low TKIs sensitivity and the persistence of LSCs in CML. DNMT1 is a key regulator of hematopoietic stem cells, suggesting that aberrant DNA hypermethylation targeting DNMT1 represents a potential therapeutic target for CML. We investigated the efficacy of OR-2100 (OR21), the first orally available single-compound prodrug of decitabine. OR21 exhibited anti-tumor effects as a monotherapy, and in combination therapy it increased TKI-induced apoptosis and induction of tumor suppressor genes including PTPN6 encoding SHP-1 in CML cells. OR21 in combination with imatinib significantly suppressed tumor growth in a xenotransplant model. OR21 and combination therapy decreased the abundance of LSCs and inhibited engraftment in a BCR-ABL1-transduced mouse model. These results demonstrate that targeting DNMT1 using OR21 exerts anti-tumor effects and impairs LSCs in CML. Therefore, combination treatment of TKIs and OR21 represents a promising treatment strategy in CML.

DNMT3A Harboring Leukemia-Associated Mutations Directs Sensitivity to DNA Damage at Replication Forks

PURPOSE

In acute myeloid leukemia (AML), recurrent DNA methyltransferase 3A (DNMT3A) mutations are associated with chemoresistance and poor prognosis, especially in advanced-age patients. Gene-expression studies in DNMT3A-mutated cells identified signatures implicated in deregulated DNA damage response and replication fork integrity, suggesting sensitivity to replication stress. Here, we tested whether pharmacologically induced replication fork stalling, such as with cytarabine, creates a therapeutic vulnerability in cells with DNMT3A(R882) mutations.

EXPERIMENTAL DESIGN

Leukemia cell lines, genetic mouse models, and isogenic cells with and without DNMT3A(mut) were used to evaluate sensitivity to nucleoside analogues such as cytarabine in vitro and in vivo, followed by analysis of DNA damage and signaling, replication restart, and cell-cycle progression on treatment and after drug removal. Transcriptome profiling identified pathways deregulated by DNMT3A(mut) expression.

RESULTS

We found increased sensitivity to pharmacologically induced replication stress in cells expressing DNMT3A(R882)-mutant, with persistent intra-S-phase checkpoint activation, impaired PARP1 recruitment, and elevated DNA damage, which was incompletely resolved after drug removal and carried through mitosis. Pulse-chase double-labeling experiments with EdU and BrdU after cytarabine washout demonstrated a higher rate of fork collapse in DNMT3A(mut)-expressing cells. RNA-seq studies supported deregulated cell-cycle progression and p53 activation, along with splicing, ribosome biogenesis, and metabolism.

CONCLUSIONS

Together, our studies show that DNMT3A mutations underlie a defect in recovery from replication fork arrest with subsequent accumulation of unresolved DNA damage, which may have therapeutic tractability. These results demonstrate that, in addition to its role in epigenetic control, DNMT3A contributes to preserving genome integrity during replication stress.

The Relevance of Aurora Kinase Inhibition in Hematological Malignancies

Aurora kinases are a family of serine/threonine protein kinases that play a central role in eukaryotic cell division. Overexpression of aurora kinases in cancer and their role as major regulators of the cell cycle quickly inspired the idea that their inhibition might be a potential pathway when treating oncologic patients. Over the past couple of decades, the search for designing and testing of molecules capable of inhibiting aurora activities fueled many pre-clinical and clinical studies. In this study, data from the past 10 years of in vitro and in vivo investigations, as well as clinical trials, utilizing aurora kinase inhibitors as therapeutics for hematological malignancies were compiled and discussed, aiming to highlight potential uses of these inhibitors as a novel monotherapy model or alongside conventional chemotherapies. While there is still much to be elucidated, it is clear that these kinases play a key role in oncogenesis, and their manageable toxicity and potentially synergistic effects still render them a focus of interest for future investigations in combinatorial clinical trials.

Ambivalent Effects of Tumor Necrosis Factor Alpha on Apoptosis of Malignant and Normal Human Keratinocytes

INTRODUCTION

Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that may paradoxically induce either apoptosis or cell survival. It mediates its activity through binding of TNF-receptor (TNFR) 1 or 2. TNFR1 is mainly responsible for transmitting apoptotic signals. The activation of apoptotic mechanisms can either be intrinsic (mitochondrial) or extrinsic (death receptors). Death ligands such as TNF-related apoptosis-inducing ligand (TRAIL) specifically induce extrinsic apoptosis, while cytostatic drugs such as 5-fluorouracil (5FU) induce intrinsic apoptosis.

OBJECTIVES

To investigate the effects of TNFα on apoptosis in malignant and normal human keratinocytes.

METHODS

Human cutaneous squamous cell carcinoma (SCC) cell line SCC-13 and immortalized human keratinocytes HaCaT as well as primary normal human keratinocytes (PNHK) were stimulated with TNFα and then treated either with TRAIL or 5FU. Cell viability and cell proliferation, DNA fragmentation, apoptosis, and cytotoxicity were determined by WST-1 proliferation assay, ELISA, flow cytometry, and colorimetric analysis of lactate dehydrogenase, respectively. In addition, Western blotting was performed for analysis of caspase-3.

RESULTS

TNFα affected viability of SCC-13 and HaCaT cells in combination with 5FU or TRAIL. In contrast, TNFα did not influence cell viability of PNHK. It enhanced the apoptotic effects of both extrinsic and intrinsic stimuli in SCC-13 and HaCaT. In clear contrast, TNFα protected PNHK against TRAIL- and 5FU-induced apoptosis. The effects were dose-dependent and TNFα-specific; furthermore, the apoptosis pathway was caspase-dependent.

CONCLUSIONS

In summary, opposing effects of TNFα in malignant versus normal human keratinocytes were observed with possibly relevant clinical implications, when patients are treated with TNFα inhibitors.

Response and Toxicity to Cytarabine Therapy in Leukemia and Lymphoma: From Dose Puzzle to Pharmacogenomic Biomarkers

Simple Summary

In this review, the authors propose a crosswise examination of cytarabine-related issues ranging from the spectrum of clinical activity and severe toxicities, through updated cellular pharmacology and drug formulations, to the genetic variants associated with drug-induced phenotypes. Cytarabine (cytosine arabinoside; Ara-C) in multiagent chemotherapy regimens is often used for leukemia or lymphoma treatments, as well as neoplastic meningitis. Chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. The individual variability in clinical response to Leukemia & Lymphoma treatments among patients appears to be associated with intracellular accumulation of Ara-CTP due to genetic variants related to metabolic enzymes. The review provides exhaustive information on the effects of Ara-C-based therapies, the adverse drug reaction will also be provided including bone pain, ocular toxicity (corneal pain, keratoconjunctivitis, and blurred vision), maculopapular rash, and occasional chest pain. Evidence for predicting the response to cytarabine-based treatments will be highlighted, pointing at their significant impact on the routine management of blood cancers.

Abstract

Cytarabine is a pyrimidine nucleoside analog, commonly used in multiagent chemotherapy regimens for the treatment of leukemia and lymphoma, as well as for neoplastic meningitis. Ara-C-based chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. Several studies suggest that the individual variability in clinical response to Leukemia & Lymphoma treatments among patients, underlying either Ara-C mechanism resistance or toxicity, appears to be associated with the intracellular accumulation and retention of Ara-CTP due to genetic variants related to metabolic enzymes. Herein, we reported (a) the latest Pharmacogenomics biomarkers associated with the response to cytarabine and (b) the new drug formulations with optimized pharmacokinetics. The purpose of this review is to provide readers with detailed and comprehensive information on the effects of Ara-C-based therapies, from biological to clinical practice, maintaining high the interest of both researcher and clinical hematologist. This review could help clinicians in predicting the response to cytarabine-based treatments.

Highly efficient chemical phosphorylation of 6-(4-phenylpiperazine-1-yl)-9-(β-D-ribofuranosyl)-9H-purine

Antimetabolites, which are metabolic antagonists used in the treatment of cancer and viral diseases by replacing metabolites, inhibit the action of metabolic enzymes and disrupt the pathways of synthesis of structural units necessary for the formation of nucleic acids. Purine antagonists, that are subunits of antimetabolites, reduce the production of purine bases, and hence, cause the nucleotide production to stop and bring about the death of cancer cells. Fludarabine (2-fluoro-ara-AMP), which is used in chemotherapy, is an antimetabolite of the purine class containing mono phosphate in its structure. In this study, a protocol was presented to effectively and efficiently synthesis of 6-(4-phenylpiperazine-1-yl)-9-(β-D-ribofuranosyl)-9H-purine-5'- O-phosphate compound in six steps and 25% overall yield starting with commercially available 6-chloropurine.

Supramolecular Architecture through Self-Organization of Janus-Faced Homoazanucleosides

Design of Janus-faced or double-headed homoazanucleosides with the possibility to undergo self-organization through base pairing has been conceptualized and accomplished. The synthetic strategy demonstrates the unique ability to introduce two similar or complementary nucleobases on opposite arms of a chiral polyhydroxypyrrolidine while also ensuring that their faces are anti to each other to allow only intermolecular interactions between the nucleobases, an essential requisite for self-assembly. Single-crystal X-ray structures were determined for all three types of homoazanucleosides, one possessing two adenine molecules, the other with two thymine moieties, and the third containing both adenine and thymine. The crystal structures of all three display noncovalent interactions, including Watson-Crick base pairing, Hoogsteen H-bonding, and π-π stacking, resulting in unusual supramolecular patterns. The most striking supramolecular motif among them, which emerged from the crystal structure of the homoazanucleoside containing both adenine and thymine, is a left-handed helix formed through Watson-Crick pairing between nucleobases. The present study thus forms a prelude to the design of Janus-faced building blocks to establish helical pillars as well as lateral branches that together define a three-dimensional (3D) lattice. The ready accessibility of these molecules is expected to spur the next generation of discoveries in the design of functional nanomaterials.

A Novel cytarabine analog evokes synthetic lethality by targeting MK2 in p53-deficient cancer cells

Most nucleoside anticancer drugs show a primary resistance to p53-deficient or p53-mutated cancer cells and are limited in the clinic to the treatment of hematological malignancies. However, 2'-fluoro-4'-seleno-ara-C (F-Se-Ara-C), a new generation of cytarabine (Ara-C) analogs, exhibited potent antitumor activity against the p53-deficient prostate cancer cell line PC-3. The distinct activity of F-Se-Ara-C was achieved by targeting the synthetic lethal interaction between p53 and mitogen-activated protein kinase-activated protein kinase-2 (MK2). MK2 is a checkpoint effector for DNA damage responses to drive cell cycle arrest and DNA repair in p53-deficient cancer cells. Therefore, targeting MK2 may be an effective therapeutic strategy that induces apoptosis for cancers deficient in p53. F-Se-Ara-C effectively induced anti-prostate cancer activity in vitro and in vivo by inhibition of MK2 activation in p53-deficient prostate cancer cells. Moreover, combining F-Se-Ara-C with cabozantinib, an anticancer drug currently in clinical use, induced synergistic antitumor activity in p53-deficient prostate cancer cells. Taken together, these data show that F-Se-Ara-C may become great anticancer drug candidate with its unique mechanism of action for overcoming the apoptotic resistance of p53-deficient cells by targeting the synthetic lethal interaction.

Sofosbuvir Activates EGFR-Dependent Pathways in Hepatoma Cells with Implications for Liver-Related Pathological Processes

Direct acting antivirals (DAAs) revolutionized the therapy of chronic hepatitis C infection. However, unexpected high recurrence rates of hepatocellular carcinoma (HCC) after DAA treatment became an issue in patients with advanced cirrhosis and fibrosis. In this study, we aimed to investigate an impact of DAA treatment on the molecular changes related to HCC development and progression in hepatoma cell lines and primary human hepatocytes. We found that treatment with sofosbuvir (SOF), a backbone of DAA therapy, caused an increase in EGFR expression and phosphorylation. As a result, enhanced translocation of EGFR into the nucleus and transactivation of factors associated with cell cycle progression, B-MYB and Cyclin D1, was detected. Serine/threonine kinase profiling identified additional pathways, especially the MAPK pathway, also activated during SOF treatment. Importantly, the blocking of EGFR kinase activity by erlotinib during SOF treatment prevented all downstream events. Altogether, our findings suggest that SOF may have an impact on pathological processes in the liver via the induction of EGFR signaling. Notably, zidovudine, another nucleoside analogue, exerted a similar cell phenotype, suggesting that the observed effects may be induced by additional members of this drug class.

Synthesis of new uracil derivatives and their sugar hydrazones with potent antimicrobial, antioxidant and anticancer activities

6-(4-Chloro-3-nitrophenyl)-4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carbonitrile (4) was prepared and was reacted with ethyl chloroacetate, hydrazine hydrate, 4-chloroaniline, formaldehyde, acetic anhydride, formic acid, carbon disulfide, 4-cyanobenzaldehyde, triethyl orthoformate, D-sugars, 4-aminoacetophenone, benzoyl choride and cyclohexanone to afford a series of new uracil derivatives (5-18). Examination of some of the prepared compounds for their antimicrobial, antioxidant and anticancer activities was conducted. Among the tested samples, compound 17 was the most active substance against the gram-positive bacteria and was more potent than the reference drug Cefoperazone. Moreover, the antibacterial activity of 17 was higher against gram-negative bacteria. Compounds 6 and 13 reached a higher scavenging ability toward DPPH radicals and are better candidates for antioxidant activity. Also, compounds 6 and 13 had no significant anticancer activity toward liver cancer (Hep G2) and breast cancer (MCF-7) cell lines.

Involvement of ribosomal protein L11 expression in sensitivity of gastric cancer against 5-FU

5-Fluorouracil (5-FU) is widely used in the treatment of various types of solid cancer. Our study showed that ribosomal protein L11 (RPL11) was a crucial factor affecting sensitivity of gastric cancer to 5-FU, implying that RPL11 expression is a potential biomarker for predicting 5-FU sensitivity. Kaplan-Meier survival analysis indicated that high RPL11 expression in gastric cancer patients treated with 5-FU was significantly associated with good prognosis. It was therefore investigated whether RPL11 affected the sensitivity of gastric cancer against 5-FU using four human gastric cancer cell lines, MKN45 (wild-type TP53 gene), NUGC4 (wild-type), MKN7 (mutated), and KE39 cells (mutated). In vitro assays demonstrated that RPL11 knockdown in gastric cancer cell lines carrying the TP53 wild-type gene attenuated 5-FU-induced cell growth suppression and activation of the P53 pathway, but not in cells carrying mutated TP53, suggesting that 5-FU suppresses tumor progression via RPL11-mediated activation of the P53 pathway in gastric cancer. The present study provides a potential therapeutic strategy for improving 5-FU resistance in gastric cancer by elevating RPL11 expression.

Genetic variants of nucleotide excision repair pathway and outcomes of induction therapy in acute myeloid leukemia

Aim: Acute myeloid leukemia (AML) is a heterogeneous disease in pathogenesis and response to therapy. Nucleotide excision repair (NER) pathway has a major role in the elimination of genotoxic effects of chemotherapeutic agents. We aimed to clarify the effects of selected variants of XPD, XPC, ERCC5 and ERCC1 genes on the outcomes of induction therapy. Materials & methods: The prevalence of NER genetic variants was evaluated in 67 subjects with AML and their effects on clinical outcomes were analyzed by χ² test. Results: The XPD 751 Lys variant was associated with improved response to chemotherapy compared with XPD 751 Gln and Lys/Gln variants (p = 0.023; odds ratio: 4.5; 95% CI: 1.14-17.73). There were no associations between other genotypes and any outcomes. Conclusion: Current findings suggest that XPD Lys751Gln variant could be considered as a prognostic factor in AML.

Enzymatic synthesis of novel purine nucleosides bearing a chiral benzoxazine fragment

A series of ribo- and deoxyribonucleosides bearing 2-aminopurine as a nucleobase with 7,8-difluoro- 3,4-dihydro-3-methyl-2H-[1,4]benzoxazine (conjugated directly or through an aminohexanoyl spacer) was synthesized using an enzymatic transglycosylation reaction. Nucleosides 3-6 were resistant to deamination under action of adenosine deaminase (ADA) Escherichia coli and ADA from calf intestine. The antiviral activity of the modified nucleosides was evaluated against herpes simplex virus type 1 (HSV-1, strain L2). It has been shown that at sub-toxic concentrations, nucleoside (S)-4-[2-amino-9-(β-D-ribofuranosyl)-purin-6-yl]-7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine exhibit significant antiviral activity (SI > 32) on the model of HSV-1 in vitro, including an acyclovir-resistant virus strain (HSV-1, strain L2/R).

Dual Targeting of Aurora Kinases with AMG 900 Exhibits Potent Preclinical Activity Against Acute Myeloid Leukemia with Distinct Post-Mitotic Outcomes

Aurora kinase A and B have essential and non-overlapping roles in mitosis, with elevated expression in a subset of human cancers, including acute myeloid leukemia (AML). In this study, pan-aurora kinase inhibitor (AKI) AMG 900 distinguishes itself as an anti-leukemic agent that is more uniformly potent against a panel of AML cell lines than are isoform-selective AKIs and classic AML drugs. AMG 900 inhibited AML cell growth by inducing polyploidization and/or apoptosis. AMG 900 and aurora-B-selective inhibitor AZD1152-hQPA showed comparable cellular effects on AML lines that do not harbor a FLT3-ITD mutation. AMG 900 was active against P-glycoprotein-expressing AML cells resistant to AZD1152-hQPA and was effective at inducing expression of megakaryocyte-lineage markers (CD41, CD42) on human CHRF-288-11 cells and mouse Jak2 V617F cells. In MOLM-13 cells, inhibition of p-histone H3 by AMG 900 was associated with polyploidy, extra centrosomes, accumulation of p53 protein, apoptosis, and cleavage of Bcl-2 protein. Co-administration of cytarabine (Ara-C) with AMG 900 potentiated cell killing in a subset of AML lines, with evidence of attenuated polyploidization. AMG 900 inhibited the proliferation of primary human bone marrow cells in culture, with a better proliferation recovery profile relative to classic antimitotic drug docetaxel. In vivo, AMG 900 significantly reduced tumor burden in a systemic MOLM-13 xenograft model where we demonstrate the utility of 3'-deoxy-3'-18F-fluorothymidine [18F]FLT positron emission tomographic (PET)-CT imaging to measure the antiproliferative effects of AMG 900 in skeletal tissues in mice.

PARP inhibitors synergize with gemcitabine by potentiating DNA damage in non-small-cell lung cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors have demonstrated great promise in the treatment of patients with deficiencies in homologous recombination (HR) DNA repair, such as those with loss of BRCA1 or BRCA2 function. However, emerging studies suggest that PARP inhibition can also target HR-competent cancers, such as non-small-cell lung cancer (NSCLC), and that the therapeutic effect of PARP inhibition may be improved by combination with chemotherapy agents. In our study, it was found that PARP inhibitors talazoparib (BMN-673) and olaparib (AZD-2281) both had synergistic activity with the common first-line chemotherapeutic gemcitabine in a panel of lung cancer cell lines. Furthermore, the combination demonstrated significant in vivo antitumor activity in an H23 xenograft model of NSCLC compared to either agent as monotherapy. This synergism occurred without loss of HR repair efficiency. Instead, the combination induced synergistic single-strand DNA breaks, leading to accumulation of toxic double-strand DNA lesions in vitro and in vivo. Our study elucidates the underlying mechanisms of synergistic activity of PARP inhibitors and gemcitabine, providing a strong motivation to pursue this combination as an improved therapeutic regimen.

Gemcitabine resistance mediated by ribonucleotide reductase M2 in lung squamous cell carcinoma is reversed by GW8510 through autophagy induction

Although chemotherapeutic regimen containing gemcitabine is the first-line therapy for advanced lung squamous cell carcinoma (LSCC), gemcitabine resistance remains an important clinical problem. Some studies suggest that overexpressions of ribonucleotide reductase (RNR) subunit M2 (RRM2) may be involved in gemcitabine resistance. We used a novel RRM2 inhibitor, GW8510, as a gemcitabine sensitization agent to investigate the therapeutic utility in reversing gemcitabine resistance in LSCC. Results showed that the expressions of RRM2 were increased in gemcitabine intrinsic resistant LSCC cells upon gemcitabine treatment. GW8510 not only suppressed LSCC cell survival, but also sensitized gemcitabine-resistant cells to gemcitabine through autophagy induction mediated by RRM2 down-regulation along with decrease in dNTP levels. The combination of GW8510 and gemcitabine produced a synergistic effect on killing LSCC cells. The synergism of the two agents was impeded by addition of autophagy inhibitors chloroquine (CQ) or bafilomycin A1 (Baf A1), or knockdown of the autophagy gene, Bcl-2-interacting protein 1 (BECN1). Moreover, GW8510-caused LSCC cell sensitization to gemcitabine through autophagy induction was parallel with impairment of DNA double-strand break (DSB) repair and marked increase in cell apoptosis, revealing a cross-talk between autophagy and DNA damage repair, and an interplay between autophagy and apoptosis. Finally, gemcitabine sensitization mediated by autophagy induction through GW8510-caused RRM2 down-regulation was demonstrated in vivo in gemcitabine-resistant LSCC tumor xenograft, further indicating that the sensitization is dependent on autophagy activation. In conclusion, GW8510 can reverse gemcitabine resistance in LSCC cells through RRM2 downregulation-mediated autophagy induction, and GW850 may be a promising therapeutic agent against LSCC as it combined with gemcitabine.

Bufalin and 5-fluorouracil synergistically induce apoptosis in colorectal cancer cells

5-fluorouracil (5-FU) has been used in the treatment of colorectal cancer for >50 years. However, drug resistance remains an obstacle in the application of 5-FU-based chemotherapy. Bufalin, a type of steroid with anti-tumor activity, may be purified from the skin and parotid venom glands of toads. In order to improve the anti-tumor effect of 5-FU, the present study examined the combined effects of bufalin with 5-FU on human colorectal cancer HCT116 cells. Following treatment, cell proliferation was quantified using MTT assay and apoptotic cell percentage was assessed by flow cytometry. The apoptosis-associated protein expression was evaluated by western blotting. It was observed that bufalin enhanced the cytotoxicity of 5-FU in HCT116 cells via the induction of the mitochondrial apoptotic pathway. Additionally, bufalin combined with 5-FU reduced the expression levels of anti-apoptotic proteins, such as Mcl-1, XIAP and Bcl-2 and upregulated the levels of the pro-apoptotic proteins, Bax and Bad. To verify the role of Bax, RNA interference was used to knock-down Bax. It was determined that the synergistic effect between 5-FU and bufalin was diminished following the silencing of Bax. In summary, bufalin in combination with 5-FU may induce a higher level of apoptosis compared with monotherapy, and the combination mat be a potential therapeutic strategy for the treatment of colorectal cancer.

Cancer chemotherapeutics in rheumatoid arthritis: A convoluted connection

Chemotherapy is one of the most popular therapeutic strategies to treat cancer. However, cancer chemotherapeutics have often been associated with impairment of the immune system, which might consequently lead to an augmented risk of autoimmune disorders, such as rheumatoid arthritis. Though the accurate mechanistic facets of rheumatoid arthritis induction have not been interpreted yet, a conglomeration of genetic and environmental factors might promote its etiology. What makes the scenario more challenging is that patients with rheumatoid arthritis are at a significantly elevated risk of developing various types of cancer. It is intriguing to note that diverse cancer chemotherapy drugs are also commonly used to treat symptoms of rheumatoid arthritis. However, a colossal multitude of such cancer therapeutics has demonstrated highly varied results in rheumatoid arthritis patients, including both beneficial and adverse effects. Herein, we attempt to present a holistic account of the variegated modalities of this complex tripartite cross-talk between cancer, rheumatoid arthritis and chemotherapy drugs in order to decode the sinuous correlation between these two appalling pathological conditions.

Glycodendrimer Nanocarriers for Direct Delivery of Fludarabine Triphosphate to Leukemic Cells: Improved Pharmacokinetics and Pharmacodynamics of Fludarabine

Fludarabine, a nucleoside analogue antimetabolite, has complicated pharmacokinetics requiring facilitated transmembrane transport and intracellular conversion to triphosphate nucleotide form (Ara-FATP), causing it to be susceptible to emergence of drug resistance. We are testing a promising strategy to improve its clinical efficacy by direct delivery of Ara-FATP utilizing a biocompatible glycodendrimer nanocarrier system. Here, we present results of a proof-of-concept experiment in several in vitro-cultured leukemic cell lines (CCRF, THP-1, U937) using noncovalent complexes of maltose-modified poly(propyleneimine) dendrimer and fludarabine triphosphate. We show that Ara-FATP has limited cytotoxic activity toward investigated cells relative to free nucleoside (Ara-FA), but complexation with the glycodendrimer (which does not otherwise influence cellular metabolism) drastically increases its toxicity. Moreover, we show that transport via hENT1 is a limiting step in Ara-FA toxicity, while complexation with dendrimer allows Ara-FATP to kill cells even in the presence of a hENT1 inhibitor. Thus, the use of glycodendrimers for drug delivery would allow us to circumvent naturally occurring drug resistance due to decreased transporter activity. Finally, we demonstrate that complex formation does not change the advantageous multifactorial intracellular pharmacodynamics of Ara-FATP, preserving its high capability to inhibit DNA and RNA synthesis and induce apoptosis via the intrinsic pathway. In comparison to other nucleoside analogue drugs, fludarabine is hereby demonstrated to be an optimal candidate for maltose glycodendrimer-mediated drug delivery in antileukemic therapy.

Synthesis of novel 6-substituted amino-9-(β-d-ribofuranosyl)purine analogs and their bioactivities on human epithelial cancer cells

New nucleoside derivatives with nitrogen substitution at the C-6 position were prepared and screened initially for their in vitro anticancer bioactivity against human epithelial cancer cells (liver Huh7, colon HCT116, breast MCF7) by the NCI-sulforhodamine B assay. N⁶-(4-trifluoromethylphenyl)piperazine analog (27) exhibited promising cytotoxic activity. The compound 27 was more cytotoxic (IC₅₀ = 1-4 μM) than 5-FU, fludarabine on Huh7, HCT116 and MCF7 cell lines. The most potent nucleosides (11, 13, 16, 18, 19, 21, 27, 28) were further screened for their cytotoxicity in hepatocellular cancer cell lines. The compound 27 demonstrated the highest cytotoxic activity against Huh7, Mahlavu and FOCUS cells (IC₅₀ = 1, 3 and 1 μM respectively). Physicochemical properties, drug-likeness, and drug score profiles of the molecules showed that they are estimated to be orally bioavailable. The results pointed that the novel derivatives would be potential drug candidates.

Epigenome-Based Precision Medicine in Lung Cancer

Lung cancer is the leading cause of cancer-related deaths in the world. Despite significant advances in the early detection and treatment of the disease, the prognosis remains poor, with an overall 5-year survival rate ranging from 15% to 20%. This poor prognosis results largely from early micrometastatic spread of cancer cells to nearby lymph nodes or tissues and partially from early recurrence after curative surgical resection. Recently, precision medicines that target potential oncogenic driver mutations have been approved to treat lung cancer. However, some lung cancer patients do not have targetable mutations, and many patients develop resistance to targeted therapy. Tumor heterogeneity and mutational density are also challenges in treating lung cancer, which underscores the need for developing alternative therapeutic strategies for treating lung cancer. Epigenetic therapy may circumvent the problems of tumor heterogeneity and drug resistance by affecting the expression of several hundred target genes. This review highlights precision medicine using an innovative approach of epigenetic priming prior to conventional standard therapy or targeted cancer therapy in lung cancer.

Suppression of the FA pathway combined with CHK1 inhibitor hypersensitize lung cancer cells to gemcitabine

The combination of platinum and gemcitabine is one of the standard regimens in the treatment of advanced lung squamous carcinoma (LSC). Resistance to gemcitabine is main barrier to the successful treatment of LSC. In this study, we showed that suppression of the Fanconi anemia (FA) pathway increased the sensitivity of two LSC cell lines SK-MES-1 and KLN205 to gemcitabine. Moreover, we found that the CHK1 pathway and the FA pathway are functionally compensatory in the repair of DNA damage in the LSC cell lines. Inactivation of one of the two pathways led to DNA damage, triggering compensatory activation of other pathway. Furthermore, we demonstrated that FANCD2 depletion combined with CHK1 inhibitor MK-8776 significantly potentiated the cytotoxicity of gemcitabine to the two LSC cell lines, compared to individual FANCD2 depletion or MK-8776 treatment. The enhanced effect of gemcitabine-chemosensitization was accompanied by loss of DNA repair function and accumulation of DNA single strand breaks and double strand breaks, in parallel with obvious increase of caspase-3 dependent apoptosis. Our results indicate that the enhancement effect of FANCD2 depletion combined with CHK1 inhibitor in sensitizing the LCS cells to gemcitabine supports the FA pathway and CHK1 as two therapeutic targets for improvement of anti-tumor regimens in treatment of LSC.

PARPi potentiates with current conventional therapy in MLL leukemia

Acute myeloid leukemias driven by MLL fusion proteins are commonly associated with poor prognosis and refractory treatment. Here, we provide evidence that olaparib can potentiate sensitivity of MLL leukemia cells to conventional chemotherapy and DNMT inhibitors offering new potential therapeutic strategies for MLL rearranged leukemias Using the primary mouse leukemia cells and human MLL-AF9 leukemic cell line, we demonstrate that treatment of MLL-AF9 leukemic cells with DNMT inhibitors or chemotherapies in combination with olaparib results in significant reduction in colony formation or cell growth while the single agent treatments had little impacts. Combining olaparib with DNMT inhibitor induce cell cycle block and apoptosis. Furthermore, we observe a significant increase in proportion of cells with >10 γH2AX DNA damage foci and double stranded breaks when treated with DNMT inhibitors or chemotherapy agents in combination with olaparib, thus providing possible mechanistic insights for the synergism.

Synthesis and Functional Investigations of Computer Designed Novel Cladribine-Like Compounds for the Treatment of Multiple Sclerosis

Cladribine (2-CdA) is used as an anti-cancer drug but is currently studied as a potential treatment for use in relapsing-remitting multiple sclerosis (MS). In this study, we computer designed, synthesized, and characterized two novel derivatives of 2-CdA, K1-5d and K2-4c, and investigated their underlying mechanism of beneficial effect using the CCRF-CEM and RAJI cell lines. For this purpose, we first determined their effect on MS and DNA damage and repair-related gene expression profiles using custom arrays along with 2-CdA treatment at non-toxic doses. Then, we determined whether cells underwent apoptosis after treatment with 2-CdA, K1-5d, and K2-4c in CCRF-CEM and RAJI cells, using the DNA fragmentation assay. It was found that both derivatives modulated the expression of the pathway-related genes that are important in inflammatory signaling, apoptosis, ATM/ATR, double-strand break repair, and the cell cycle. Furthermore, 2-CdA, K1-5d, and K2-4c significantly activated apoptosis in both cell lines. In summary, our data demonstrate that although both derivatives act as anti-inflammatory and apoptotic agents, inducing the accumulation of DNA strand breaks and activating the ultimate tumor suppressor p53 in T and B lymphocytes, the K1-5d derivative has shown more promising activities for further studies.

Solvatochromic Effects on the Absorption Spectrum of 2-Thiocytosine

The solvatochromic effects of six different solvents on the UV absorption spectrum of 2-thiocytosine have been studied by a combination of experimental and theoretical techniques. The steady-state absorption spectra show significant shifts of the absorption bands, where in more polar solvents the first absorption maximum shifts to higher transition energies and the second maximum to lower energies. The observed solvatochromic shifts have been rationalized using three popular solvatochromic scales and with high-level multireference quantum chemistry calculations including implicit and explicit solvent effects. It has been found that the dipole moments of the excited states account for some general shifts in the excitation energies, whereas the explicit solvent interactions explain the differences in the spectra recorded in the different solvents.

Checkpoint kinase inhibitor AZD7762 strongly sensitises urothelial carcinoma cells to gemcitabine

Background

More effective chemotherapies are urgently needed for bladder cancer, a major cause of morbidity and mortality worldwide. We therefore explored the efficacy of the combination of gemcitabine and AZD7762, a checkpoint kinase 1/2 (CHK1/2) inhibitor, for bladder cancer.

Methods

Viability, clonogenicity, cell cycle distribution and apoptosis were assessed in urothelial cancer cell lines and various non-malignant urothelial cells treated with gemcitabine and AZD7762. DNA damage was assessed by γH2A.X and 53-BP1 staining and checkpoint activation was followed by Western blotting. Pharmacological inhibition of CHK1 and CHK2 was compared to downregulation of either CHK1 or CHK2 using siRNAs.

Results

Combined use of gemcitabine and AZD7762 synergistically reduced urothelial carcinoma cell viability and colony formation relative to either single treatment. Non-malignant urothelial cells were substantially less sensitive to this drug combination. Gemcitabine plus AZD7762 inhibited cell cycle progression causing cell accumulation in S-phase. Moreover, the combination induced pronounced levels of apoptosis as indicated by an increase in the fraction of sub-G1 cells, in the levels of cleaved PARP, and in caspase 3/7 activity. Mechanistic investigations showed that AZD7762 treatment inhibited the repair of gemcitabine-induced double strand breaks by interference with CHK1, since siRNA-mediated depletion of CHK1 but not of CHK2 mimicked the effects of AZD7762.

Conclusions

AZD7762 enhanced sensitivity of urothelial carcinoma cells to gemcitabine by inhibiting DNA repair and disturbing checkpoints. Combining gemcitabine with CHK1 inhibition holds promise for urothelial cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0473-1) contains supplementary material, which is available to authorized users.

DCTPP1 attenuates the sensitivity of human gastric cancer cells to 5-fluorouracil by up-regulating MDR1 expression epigenetically

Gastric cancer (GC) is among the most malignant cancers with high incidence and poor prognoses worldwide as well as in China. dCTP pyrophosphatase 1 (DCTPP1) is overexpressed in GC with a poor prognosis. Given chemotherapeutic drugs share similar structures with pyrimidine nucleotides, the role of DCTPP1 in affecting the drug sensitivity in GC remains unclear and is worthy of investigation. In the present study, we reported that DCTPP1-knockdown GC cell line BGC-823 exhibited more sensitivity to 5-fluorouracil (5-FU), demonstrated by the retardation of cell proliferation, the increase in cell apoptosis, cell cycle arrest at S phase and more DNA damages. Multidrug resistance 1 (MDR1) expression was unexpectedly down-regulated in DCTPP1-knockdown BGC-823 cells together with more intracellular 5-FU accumulation. This was in large achieved by the elevated methylation in promoter region of MDR1 gene. The intracellular 5-methyl-dCTP level increased in DCTPP1-knockdown BGC-823 cells as well. More significantly, the strong correlation of DCTPP1 and MDR1 expression was detectable in clinical GC samples. Our results thus imply a novel mechanism of chemoresistance mediated by the overexpression of DCTPP1 in GC. It is achieved partially through decreasing the concentration of intracellular 5-methyl-dCTP, which in turn results in promoter hypomethylation and hyper-expression of drug resistant gene MDR1. Our study suggests DCTPP1 as a potential indicative biomarker for the predication of chemoresistance in GC.

DNA replication stress mediates APOBEC3 family mutagenesis in breast cancer

BACKGROUND

The APOBEC3 family of cytidine deaminases mutate the cancer genome in a range of cancer types. Although many studies have documented the downstream effects of APOBEC3 activity through next-generation sequencing, less is known about their upstream regulation. In this study, we sought to identify a molecular basis for APOBEC3 expression and activation.

RESULTS

HER2 amplification and PTEN loss promote DNA replication stress and APOBEC3B activity in vitro and correlate with APOBEC3 mutagenesis in vivo. HER2-enriched breast carcinomas display evidence of elevated levels of replication stress-associated DNA damage in vivo. Chemical and cytotoxic induction of replication stress, through aphidicolin, gemcitabine, camptothecin or hydroxyurea exposure, activates transcription of APOBEC3B via an ATR/Chk1-dependent pathway in vitro. APOBEC3B activation can be attenuated through repression of oncogenic signalling, small molecule inhibition of receptor tyrosine kinase signalling and alleviation of replication stress through nucleoside supplementation.

CONCLUSION

These data link oncogene, loss of tumour suppressor gene and drug-induced replication stress with APOBEC3B activity, providing new insights into how cytidine deaminase-induced mutagenesis might be activated in tumourigenesis and limited therapeutically.

Dihydropyrimidine Dehydrogenase Is a Prognostic Marker for Mesenchymal Stem Cell-Mediated Cytosine Deaminase Gene and 5-Fluorocytosine Prodrug Therapy for the Treatment of Recurrent Gliomas

We investigated a therapeutic strategy for recurrent malignant gliomas using mesenchymal stem cells (MSC), expressing cytosine deaminase (CD), and prodrug 5-Fluorocytosine (5-FC) as a more specific and less toxic option. MSCs are emerging as a novel cell therapeutic agent with a cancer-targeting property, and CD is considered a promising enzyme in cancer gene therapy which can convert non-toxic 5-FC to toxic 5-Fluorouracil (5-FU). Therefore, use of prodrug 5-FC can minimize normal cell toxicity. Analyses of microarrays revealed that targeting DNA damage and its repair is a selectable option for gliomas after the standard chemo/radio-therapy. 5-FU is the most frequently used anti-cancer drug, which induces DNA breaks. Because dihydropyrimidine dehydrogenase (DPD) was reported to be involved in 5-FU metabolism to block DNA damage, we compared the survival rate with 5-FU treatment and the level of DPD expression in 15 different glioma cell lines. DPD-deficient cells showed higher sensitivity to 5-FU, and the regulation of DPD level by either siRNA or overexpression was directly related to the 5-FU sensitivity. For MSC/CD with 5-FC therapy, DPD-deficient cells such as U87MG, GBM28, and GBM37 showed higher sensitivity compared to DPD-high U373 cells. Effective inhibition of tumor growth was also observed in an orthotopic mouse model using DPD- deficient U87MG, indicating that DPD gene expression is indeed closely related to the efficacy of MSC/CD-mediated 5-FC therapy. Our results suggested that DPD can be used as a biomarker for selecting glioma patients who may possibly benefit from this therapy.

Inhibitory effect of extracellular purine nucleotide and nucleoside concentrations on T cell proliferation

The release of nucleic acids and derivatives after tissue-injury may affect cellular immune-response. We studied the impact of extracellular ribo-, desoxyribonucleotides and nucleosides on T-cell immunity. Peripheral-blood-mononuclear-cells (PBMCs) or isolated CD3⁺T-cells obtained from 6 healthy donors were stimulated via CD3/CD28 Dynabeads or dendritic cells (DCs) in the presence or absence of pyrimidine-, purine-nucleotides and -nucleosides (range 2-200µM). Addition of deoxy-, guanosine-triphosphate (dGTP, GTP) and guanosine resulted concentration dependent in a complete, adenosine-triphosphate (ATP) in a partial inhibition of the induced T-cell-proliferation. Deoxyadenosine-triphosphate (dATP), adenosine and the pyrimidine-ribo- and -deoxyribonucleotides displayed no inhibitory capacity. Inhibitory effects of dGTP and GTP, but not of guanosine and ATP were culture-media-dependent and could be almost abrogated by use of the serum-free lymphocyte-culture-media X-Vivo15 instead of RPMI1640 with standard-supplementation. In contrast to RPMI1640, X-Vivo15 resulted in a significant down-regulation of the cell-surface-located ectonucleotidases CD39 (Ecto-Apyrase) and CD73 (Ecto-5'-Nucleotidase), critical for the extracellular nucleotides-hydrolysis to nucleosides, explaining the loss of inhibition mediated by dGTP and GTP, but not Guanosine. In line with previous findings ATP was found to exert immunosuppressive effects on T-cell-proliferation. Purine-nucleotides, dGTP and GTP displayed a higher inhibitory capacity, but seem to be strictly dependent on the microenvironmental conditions modulating the responsiveness of the respective T-lymphocytes. Further evaluation of experimental and respective clinical settings should anticipate these findings.

5-Fluorouracil sensitizes colorectal tumor cells towards double stranded DNA breaks by interfering with homologous recombination repair

Malignant tumors of the rectum are treated by neoadjuvant radiochemotherapy. This involves a combination of 5-fluorouracil (5-FU) and double stranded DNA-break (DSB)-inducing radiotherapy. Here we explored how 5-FU cooperates with DSB-induction to achieve sustainable DNA damage in colorectal cancer (CRC) cells. After DSB induction by neocarzinostatin, phosphorylated histone 2AX (γ-H2AX) rapidly accumulated but then largely vanished within a few hours. In contrast, when CRC cells were pre-treated with 5-FU, gammaH2AX remained for at least 24 hours. GFP-reporter assays revealed that 5-FU decreases the efficiency of homologous recombination (HR) repair. However, 5-FU did not prevent the initial steps of HR repair, such as the accumulation of RPA and Rad51 at nuclear foci. Thus, we propose that 5-FU interferes with the continuation of HR repair, e. g. the synthesis of new DNA strands. Two key mediators of HR, Rad51 and BRCA2, were found upregulated in CRC biopsies as compared to normal mucosa. Inhibition of HR by targeting Rad51 enhanced DNA damage upon DSB-inducing treatment, outlining an alternative way of enhancing therapeutic efficacy. Taken together, our results strongly suggest that interfering with HR represents a key mechanism to enhance the efficacy when treating CRC with DNA-damaging therapy.