Comparison of 5-fluoro-2'-deoxyuridine with 5-fluorouracil and their role in the treatment of colorectal cancer

In Vitro, In Vivo, Ex Vivo Characterisation of Dihydroimidazotriazinones and Their Thermal Decomposition Course Studied by Coupled and Simultaneous Thermal Analysis Methods

The biological and thermal properties of a class of synthetic dihydroimidazotriazinones were disclosed in this article for the first time. Molecules 1-6-as potential innovative antimetabolites mimicking bicyclic aza-analogues of isocytosine-were evaluated for their in vitro anticancer activity. Moreover, in vivo, in vitro, and ex vivo toxicity profiles of all the compounds were established in zebrafish, non-tumour cell, and erythrocyte models, respectively. Their antihaemolytic activity was also evaluated. Additionally, the thermal decomposition mechanism, path, and key thermal properties of heterocycles 1-6 were analysed. It was found that all the studied compounds revealed significant antiproliferative activities against tumour cells of the lung, cervix, ovary, and breast, as well as acute promyelocytic leukaemia cells, superior or comparable to that of an anticancer agent gemcitabine. Most of them were less toxic to non-tumour cells than this standard drug, and none had a haemolytic effect on red blood cells. All the tested heterocycles proved to be safer for zebrafish than a standard drug pemetrexed. Some exhibited the ability to inhibit oxidative haemolysis, suggesting their protective action on erythrocytes. The differential scanning calorimetry (DSC) analyses confirmed that all molecules melted within one narrow temperature range, proving their purity. The melting points depended solely on the type of substituent and increased as follows: 4 (R = 3-ClPh) < 2 (R = 4-CH3Ph) = 3 (R = 4-OCH3Ph) < 5 (R = 4-ClPh) = 1 (R = Ph) < 6 (R = 3,4-Cl2Ph). The thermogravimetry/differential thermogravimetry (TG/DTG) studies confirmed high thermal stability of all the investigated heterocycles in inert (>230 °C) and oxidising (>260 °C) atmospheres, which depended directly on the R. The pyrolysis process included one main decomposition stage and was connected with the emission of NH3, HCN, CH3CN, HNCO, alkane, alkene, aromatic fragments, CO2 (for all the compounds), and HCl (for the molecule with 3,4-Cl2Ph), which was confirmed by FTIR and QMS analyses. In turn, the oxidative decomposition process of the tested polyazaheterocycles took place in two main stages connected with the formation of the same volatiles as those observed in an inert atmosphere and additionally with the release of N2, NO, CO, and H2O. These results proved that the pyrolysis and oxidative decomposition run through the radical mechanism connected with the additional reactions between radicals and oxygen in synthetic air. The favourable biological and thermal properties of this class of dihydroimidazotriazinones imply their usefulness as potential pharmaceutics.

Spatiotemporal-controllable ROS-responsive camptothecin nano-bomb for chemo/photo/immunotherapy in triple-negative breast cancer

Chemotherapy is still one of the major approaches in triple-negative breast cancer (TNBC) treatment. The development of new formulations for classic chemotherapeutic drugs remains interests in studies. Camptothecin (CPT) is powerful antitumor agents in TNBC treatment though its clinic applications are limited by its low water solubility and systemic toxicity. To prepare a spatiotemporal controllable CPT nano-formulation, we construct a ROS-responsive self-assembly nanoparticle by combining hydrophobic CPT and hydrophilic 5-floxuridine (FUDR). A ROS-sensitive thioketal (TK) linker is used to prepare CPT-TK-FUDR (CTF). Next, we introduced IR780-based phototherapy to elicit massive ROS regeneration due to the endogenous ROS is not sufficient. IR780 is modified with hyaluronic acid (HA) to prepare HA-modified IR780 (HAIR) for its biocompatibility and tumor targeting ability improvement. CTF and HAIR self-assemble to form an attractive nano-bomb (HAIR/CTF NPs). HA accurately guides the NPs to tumor sites via HA-receptor recognition on tumor cells. After internalization, overexpressed intracellular HAase in tumor cells disassembles the NPs to free the contents. Due to the presence of IR780 molecules, the scheduled irradiation of 808 nm laser induces massive reactive oxygen species (ROS) generation, which further result in the cleavage of TK linker for free drugs release. Additionally, ROS-mediated photodynamic therapy (PDT) and near-infrared laser-mediated photothermal therapy (PTT) synergistically worked to eradicate tumor cells. Then immunogenic cell death (ICD) was evoked by CPT and phototherapy to amplify antitumor immunity, thereby achieving primary and abscopal tumor inhibition. In conclusion, the HAIR/CTF nano-bomb realized spatiotemporal controllable drug release, exciting tumor eradication and attractive anti-metastasis efficacy via combination chemo/photo/immunotherapy, offering a valuable reference for the re-development of classic drug in future clinical practice.

ARID1A loss sensitizes colorectal cancer cells to floxuridine

The loss-of-function mutation of AT-rich interactive domain 1A (ARID1A) frequently occurs in various types of cancer, making it a promising therapeutic target. In the present study, we performed a screening of an FDA-approved drug library in ARID1A isogenic colorectal cancer (CRC) cells and discovered that ARID1A loss sensitizes CRC cells to floxuridine (FUDR), an antineoplastic agent used for treating hepatic metastases from CRC, both in vivo and in vitro. As a pyrimidine analogue, FUDR induces DNA damage by inhibiting thymidylate synthase (TS) activity. ARID1A, as a regulator of DNA damage repair, when lost, exacerbates FUDR-induced DNA damage, leading to increased cell apoptosis. Specifically, ARID1A deficiency impairs DNA damage repair by downregulating Chk2 phosphorylation, thereby sensitizing cancer cells to FUDR. Notably, we found that FUDR exhibited increased sensitivity in ARID1A-deficient cells compared to 5-fluorouracil (5-FU), a commonly used anticancer drug for CRC. This suggests that FUDR is superior to 5-FU in treating ARID1A-deficient CRC. In conclusion, ARID1A loss significantly heightens sensitivity to FUDR by promoting FUDR-induced DNA damage in CRC. These findings offer a novel therapeutic approach for the treatment of CRC characterized by ARID1A loss-of-function mutations.

Single G-quadruplex-based fluorescence method for the uracil-DNA glycosylase inhibitor screening

Uracil-DNA glycosylase (UDG) plays a pivotal role in the base repair system. Through bioinformatics, we found that the expression of the UDG enzyme in many cancer cells is increased, and its high expression is not conducive to the prognosis of lung cancer patients. The development of analytical techniques for the quantification of UDG activity and the identification of UDG inhibitors is of paramount importance. We found that when the T base in the G4 loop region mutated to uracil, the G4 structure was not disrupted and still retained the characteristics of a G4 structure (emitting strong fluorescence after binding with ThT (Thioflavin T). Inspired by this phenomenon, we developed a detection method for UDG and its inhibitors utilizing a single DNA strand engineered to form a G-quadruplex structure, containing uracil residues within the loop region, designated as G4-dU. The inclusion of uracil-DNA glycosylase (UDG) in the assay environment induces the removal of uracil, resulting in the formation of apurinic sites (AP) within the G4-dU sequence. Subsequent thermal denaturation leads to strand cleavage at AP sites, precluding the reformation of the G-quadruplex configuration and abrogating fluorescence emission. The detection process in this study can be completed in only 30 min to 1 h, offers a straightforward, expedient, and efficacious modality for assessing UDG activity and UDG inhibitor potency, thereby facilitating the discovery of novel therapeutic agents for cancer treatment.

Aptamer-Drug conjugates for a targeted and synergistic anticancer Response: Exploiting T30923-5-fluoro-2'-deoxyuridine (INT-FdU) derivatives

One of the most appealing approaches for cancer treatment is targeted therapy, which is based on the use of drugs able to target cancer cells without affecting normal ones. This strategy lets to overcome the major limitation of conventional chemotherapy, namely the lack of specificity of anticancer drugs, which often leads to severe side effects, decreasing the therapy effectiveness. Delivery of cell-killing substances to tumor cells is one-way targeted drug therapy can work. Generally, monoclonal antibodies are combined with chemotherapeutic drugs, allowing cellular uptake through the binding to their targets on the surface of cancer cells. Aptamer-drug conjugates represent a promising alternative solution to antibodies to minimize off-target effects, considering the remarkable selective binding capabilities of aptamers. In this study, to enhance the therapeutic efficacy of the antineoplastic agent 5-fluoro-2'-deoxyuridine (FdU) in various cancer cells, we focused on the development of a novel conjugate using the antiproliferative aptamer T30923 (INT) as a drug vehicle. Three derivatives composed of T30923 conjugated with a different number of FdU units were synthesized, and their structural and biological properties were thoroughly characterized, highlighting their potential for targeted and synergistic anticancer responses.

Revolutionizing cancer therapy using tetrahedral DNA nanostructures as intelligent drug delivery systems

DNA nanostructures have surfaced as intriguing entities with vast potential in biomedicine, notably in the drug delivery area. Tetrahedral DNA nanostructures (TDNs) have received worldwide attention from among an array of different DNA nanostructures due to their extraordinary stability, great biocompatibility, and ease of functionalization. TDNs could be readily synthesized, making them attractive carriers for chemotherapeutic medicines, nucleic acid therapeutics, and imaging probes. Their varied uses encompass medication delivery, molecular diagnostics, biological imaging, and theranostics. This review extensively highlights the mechanisms of functional modification of TDNs and their applications in cancer therapy. Additionally, it discusses critical concerns and unanswered problems that require attention to increase the future application of TDNs in developing cancer treatment.

A synergistic two-drug therapy specifically targets a DNA repair dysregulation that occurs in p53-deficient colorectal and pancreatic cancers

The tumor-suppressor p53 is commonly inactivated in colorectal cancer and pancreatic ductal adenocarcinoma, but existing treatment options for p53-mutant (p53Mut) cancer are largely ineffective. Here, we report a therapeutic strategy for p53Mut tumors based on abnormalities in the DNA repair response. Investigation of DNA repair upon challenge with thymidine analogs reveals a dysregulation in DNA repair response in p53Mut cells that leads to accumulation of DNA breaks. Thymidine analogs do not interrupt DNA synthesis but induce DNA repair that involves a p53-dependent checkpoint. Inhibitors of poly(ADP-ribose) polymerase (PARPis) markedly enhance DNA double-strand breaks and cell death induced by thymidine analogs in p53Mut cells, whereas p53 wild-type cells respond with p53-dependent inhibition of the cell cycle. Combinations of trifluorothymidine and PARPi agents demonstrate superior anti-neoplastic activity in p53Mut cancer models. These findings support a two-drug combination strategy to improve outcomes for patients with p53Mut cancer.

Quinacrine-CASIN combination overcomes chemoresistance in human acute lymphoid leukemia

Chemoresistance posts a major hurdle for treatment of acute leukemia. There is increasing evidence that prolonged and intensive chemotherapy often fails to eradicate leukemic stem cells, which are protected by the bone marrow niche and can induce relapse. Thus, new therapeutic approaches to overcome chemoresistance are urgently needed. By conducting an ex vivo small molecule screen, here we have identified Quinacrine (QC) as a sensitizer for Cytarabine (AraC) in treating acute lymphoblastic leukemia (ALL). We show that QC enhances AraC-mediated killing of ALL cells, and subsequently abrogates AraC resistance both in vitro and in an ALL-xenograft model. However, while combo AraC+QC treatment prolongs the survival of primary transplanted recipients, the combination exhibits limited efficacy in secondary transplanted recipients, consistent with the survival of niche-protected leukemia stem cells. Introduction of Cdc42 Activity Specific Inhibitor, CASIN, enhances the eradication of ALL leukemia stem cells by AraC+QC and prolongs the survival of both primary and secondary transplanted recipients without affecting normal long-term human hematopoiesis. Together, our findings identify a small-molecule regimen that sensitizes AraC-mediated leukemia eradication and provide a potential therapeutic approach for better ALL treatment.

Results with Floxuridine, Actinomycin D, Etoposide, and Vincristine in Gestational Trophoblastic Neoplasias with International Federation of Gynecology and Obstetrics Scores ≥5

BACKGROUND

5-fluorouracil-based multiagent chemotherapy has been used as the primary treatment for high-risk gestational trophoblastic neoplasia (GTN) in China for a few decades. This study aims to assess the efficacy and toxicity of floxuridine, actinomycin D, etoposide, and vincristine (FAEV) as a primary treatment for patients with GTN who had International Federation of Gynecology and Obstetrics (FIGO) scores ≥5.

MATERIALS AND METHODS

A total of 207 patients with GTN who had FIGO scores ≥5 were treated with FAEV as first-line chemotherapy at Peking Union Medical College Hospital between January 2002 and December 2017. Complete remission (CR), resistance, survival, toxicity, and reproductive outcomes were analyzed.

RESULTS

Of the 207 patients treated with FAEV, 9 (4.3%) required a change of chemotherapy owing to toxicity and 1 (0.5%) died of cerebral hernia 5 weeks after commencing treatment. The remaining 197 patients were assessable to determine the response to FAEV; among them, 168 (85.3%) achieved CR with FAEV and 29 (14.7%) developed resistance to FAEV. The 5-year overall survival rate of the entire cohort was 97.4%. Grade 3-4 neutropenia, thrombocytopenia, and anemia occurred in 28.4%, 6.8%, and 6.2% of cycles, respectively. No acute toxicity-related deaths occurred. Five patients developed acute myeloid leukemia 10-50 months after exposure to chemotherapy; another patient developed duodenal cancer 2 years after completing therapy. Sixty-one patients who preserved fertility wanted to become pregnant; 56 of them conceived.

CONCLUSION

The FAEV regimen is an effective primary treatment for patients with GTN who have FIGO scores ≥5 and has predictable and manageable toxicity.

IMPLICATIONS FOR PRACTICE

The most commonly used multiagent chemotherapy for high-risk gestational trophoblastic neoplasia (GTN) is etoposide, methotrexate and actinomycin D/cyclophosphamide and vincristine (EMA/CO) worldwide. However, 5-fluorouracil-based multiagent chemotherapy has been used as a primary treatment for high-risk GTN in China for a few decades. This study evaluated the efficacy and toxicity of floxuridine, actinomycin D, etoposide, and vincristine (FAEV) as a primary treatment for patients with GTN who have International Federation of Gynecology and Obstetrics (FIGO) scores ≥5. The study's data demonstrated that FAEV as a primary treatment achieved favorable outcomes for patients with FIGO scores ≥5. Toxicities that result from the FAEV regimen are predictable and manageable. The FAEV regimen may provide another option for the treatment of GTN.

Selective therapeutic strategy for p53-deficient cancer by targeting dysregulation in DNA repair

Breast carcinomas commonly carry mutations in the tumor suppressor p53, although therapeutic efforts to target mutant p53 have previously been unfruitful. Here we report a selective combination therapy strategy for treatment of p53 mutant cancers. Genomic data revealed that p53 mutant cancers exhibit high replication activity and express high levels of the Base-Excision Repair (BER) pathway, whereas experimental testing showed substantial dysregulation in BER. This defect rendered accumulation of DNA damage in p53 mutant cells upon treatment with deoxyuridine analogues. Notably, inhibition of poly (ADP-ribose) polymerase (PARP) greatly enhanced this response, whereas normal cells responded with activation of the p53-p21 axis and cell cycle arrest. Inactivation of either p53 or p21/CDKN1A conferred the p53 mutant phenotype. Preclinical animal studies demonstrated a greater anti-neoplastic efficacy of the drug combination (deoxyuridine analogue and PARP inhibitor) than either drug alone. This work illustrates a selective combination therapy strategy for p53 mutant cancers that will improve survival rates and outcomes for thousands of breast cancer patients.

Inhibition of Human Uracil DNA Glycosylase Sensitizes a Large Fraction of Colorectal Cancer Cells to 5-Fluorodeoxyuridine and Raltitrexed but Not Fluorouracil

Previous short-hairpin RNA knockdown studies have established that depletion of human uracil DNA glycosylase (hUNG) sensitizes some cell lines to 5-fluorodeoxyuridine (FdU). Here, we selectively inhibit the catalytic activity of hUNG by lentiviral transduction of uracil DNA glycosylase inhibitor protein into a large panel of cancer cell lines under control of a doxycycline-inducible promoter. This induced inhibition strategy better assesses the therapeutic potential of small-molecule targeting of hUNG. In total, 6 of 11 colorectal lines showed 6- to 70-fold increases in FdU potency upon hUNG inhibition ("responsive"). This hUNG-dependent response was not observed with fluorouracil (FU), indicating that FU does not operate through the same DNA repair mechanism as FdU in vitro. Potency of the thymidylate synthase inhibitor raltitrexed (RTX), which elevates deoxyuridine triphosphate levels, was only incrementally enhanced upon hUNG inhibition (<40%), suggesting that responsiveness is associated with incorporation and persistence of FdU in DNA rather than deoxyuridine. The importance of FU/A and FU/G lesions in the toxicity of FdU is supported by the observation that dT supplementation completely rescued the toxic effects of U/A lesions resulting from RTX, but dT only increased the IC50 for FdU, which forms both FU/A and FU/G mismatches. Contrary to previous reports, cellular responsiveness to hUNG inhibition did not correlate with p53 status or thymine DNA glycosylase expression. A model is suggested in which the persistence of FU/A and FU/G base pairs in the absence of hUNG activity elicits an apoptotic DNA damage response in both responsive and nonresponsive colorectal lines. SIGNIFICANCE STATEMENT: The pyrimidine base 5-fluorouracil is a mainstay chemotherapeutic for treatment of advanced colorectal cancer. Here, this study shows that its deoxynucleoside form, 5-fluorodeoxyuridine (FdU), operates by a distinct DNA incorporation mechanism that is strongly potentiated by inhibition of the DNA repair enzyme human uracil DNA glycosylase. The hUNG-dependent mechanism was present in over 50% of colorectal cell lines tested, suggesting that a significant fraction of human cancers may be sensitized to FdU in the presence of a small-molecule hUNG inhibitor.

Auger electron therapy of glioblastoma using [125I]5-iodo-2'-deoxyuridine and concomitant chemotherapy - Evaluation of a potential treatment strategy

INTRODUCTION

Treatment of glioblastomas (GBM) using the Auger electron emitting compound [125I]5-Iodo-2'-deoxyuridine ([125I]I-UdR), combined with the thymidylate synthase inhibitor methotrexate (MTX) and concomitant chemotherapy with temozolomide (TMZ) has recently shown very promising therapeutic effects in vitro and in vivo in animals. The aim of the current study was to investigate if the therapeutic effects of this multimodal treatment strategy could be further increased by the thymidylate synthase inhibitor, 5-fluoro-2'-deoxyuridine (F-UdR), in comparison to MTX, and if the co-treatment should be given in a neoadjuvant or adjuvant setting.

METHODS

A patient-derived GBM cancer stem cell (CSC)-enriched cell line, grown as neurospheres, was employed to evaluate DNA-incorporation of [125I]I-UdR, determined by a DNA precipitation assay, using either pre-treatment or co-treatment with MTX or F-UdR. The therapeutic effects in the CSC-enriched cell line after exposure to various combinations of MTX, F-UdR, TMZ and [125I]I-UdR were also investigated by a CellTiter-Blue assay.

RESULTS

The highest general increase in [125I]I-UdR incorporation was observed with F-UdR co-treatment, which resulted in approx. 2.5-fold increase in the DNA-associated activity. Also the cell viability was significantly decreased when F-UdR was combined with [125I]I-UdR compared to [125I]I-UdR alone at all activity concentrations tested. MTX was redundant when combined with 400 and 500 Bq/ml [125I]I-UdR. TMZ was effective in combination with either [125I]I-UdR alone or with both thymidylate synthase inhibitors combined with 50-100 Bq/ml [125I]I-UdR.

CONCLUSIONS

Overall, our study revealed a higher incorporation and therapeutic effect of [125I]I-UdR when GBM cells were co-treated with F-UdR compared to MTX. The therapeutic effects were further increased when TMZ was combined with [125I]I-UdR in combination with the thymidylate synthase inhibitors.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Auger electron therapy in combination with thymidylate synthase inhibition and concomitant chemotherapy has the potential to become a future therapeutic treatment option for patients with glioblastoma.

A Simple Differentiation Protocol for Generation of Induced Pluripotent Stem Cell-Derived Basal Forebrain-Like Cholinergic Neurons for Alzheimer's Disease and Frontotemporal Dementia Disease Modeling

The study of neurodegenerative diseases using pluripotent stem cells requires new methods to assess neurodevelopment and neurodegeneration of specific neuronal subtypes. The cholinergic system, characterized by its use of the neurotransmitter acetylcholine, is one of the first to degenerate in Alzheimer’s disease and is also affected in frontotemporal dementia. We developed a differentiation protocol to generate basal forebrain-like cholinergic neurons (BFCNs) from induced pluripotent stem cells (iPSCs) aided by the use of small molecule inhibitors and growth factors. Ten iPSC lines were successfully differentiated into BFCNs using this protocol. The neuronal cultures were characterised through RNA and protein expression, and functional analysis of neurons was confirmed by whole-cell patch clamp. We have developed a reliable protocol using only small molecule inhibitors and growth factors, while avoiding transfection or cell sorting methods, to achieve a BFCN culture that expresses the characteristic markers of cholinergic neurons.

Drug screening assay based on the interaction of intact Keap1 and Nrf2 proteins in cancer cells

BACKGROUND

The Nrf2-Keap1 interaction is the major regulatory pathway for cytoprotective responses against oxidative and electrophilic stresses. Keap1, a substrate protein of a Cul3-dependent E3 ubiquitin ligase complex, is a negative regulator of Nrf2. The use of chemicals to regulate the interaction between Keap1 and Nrf2 has been proposed as a strategy for the chemoprevention of degenerative diseases and cancers.

RESULTS

The interactions between Keap1 and Nrf2 in vitro and in vivo were investigated using fluorescence resonance energy transfer (FRET) and bimolecular fluorescence complementation (BiFC) strategies in our study. Nrf2 with its N-terminal fused to eGFP and Keap1 with its C-terminal fused to mCherry were expressed and purified in vitro. When purified eGFP-Nrf2 and Keap1-mChrry proteins were mixed together, a strong FRET signal could be detected, indicating an efficient energy transfer from eGFP to mCherry. Moreover, the FRET was detected in vivo using confocal microscopy in colon cancer HCT-116 cells that were co-transfected with eGFP-Nrf2 and Keap1-mCherry. Finally, using an eGFP BiFC approach, the Keap1-Nrf2 interaction was also detected in MCF7 cells by transfecting eGFP N-terminal fused to Nrf2 (eN158-Nrf2) and eGFP C-terminal fused to Keap1 (eC159-Keap1). Using the BiFC and FRET systems, we demonstrated that the prototypical Nrf2-activiting compound tBHQ and the antitumor drug F-dUrd might interfere with the intracellular interaction between Keap1 and Nrf2 whereas the 5-Fu have little role in activating the protective response of Nrf2 pathway in cancer cells.

CONCLUSIONS

By analyzing the perturbation of the energy transfer between the donor and acceptor fluorophores and the bimolecular fluorescence complementation of eGFP, we can screen potential inhibitors for the interaction between Keap1 and Nrf2.

Effects of neoadjuvant chemotherapy on the depth of total intravenous anesthesia in patients with breast cancer undergoing unilateral modified radical mastectomy: A prospective observational study

Toxic effects of neoadjuvant chemotherapy (NC) on nervous, hepatorenal, and pulmonary systems might affect general anesthesia depth. This study aimed to evaluate the effects of NC on depth of total intravenous anesthesia.This prospective observational study enrolled 60 patients undergoing elective unilateral modified radical mastectomy during total intravenous anesthesia with propofol and remifentanil (January-June 2015; Liaocheng People's Hospital, China): the NC group (n = 30) received NC, while the control group (n = 30) did not. Propofol and remifentanil dosages were adjusted according to indexes of consciousness (IoC1: sedation; IoC2: analgesia) to control fluctuations of blood pressure and heart rate within 20% of baseline values. Parameters reflecting propofol/remifentanil dosages, intraoperative adverse events, and quality of anesthetic recovery were recorded.The duration of propofol infusion (1.3 ± 0.4 vs 1.8 ± 0.5 hours, P < .05), mean propofol dosage (8.0 ± 1.0 vs 9.3 ± 1.5 mg kg h, P < .05), and adjustment frequency of target-controlled remifentanil infusion (2.9 ± 1.8 vs 4.4 ± 2.6 times/surgery, P < .05) were significantly lower in the NC group than in the control group; adjustment frequency of target-controlled propofol infusion was also numerically lower (2.0 ± 1.1 vs 2.7 ± 1.5 times/surgery, P = .053). Duration of remifentanil infusion, mean remifentanil dosage, voluntary eye opening, extubation time, and recovery score were not significantly different between groups. The incidence of tachycardia was lower in the NC group than in the control group (7.1% vs 37.0%, P < .05), but there was no significant difference in the incidence of total adverse events between groups.NC can enhance the sensitivity of breast cancer patients to the anesthetic effect of propofol.

Thymidine Kinase 1 Loss Confers Trifluridine Resistance without Affecting 5-Fluorouracil Metabolism and Cytotoxicity

Acquired resistance to therapeutic drugs is a serious problem for patients with cancer receiving systemic treatment. Experimentally, drug resistance is established in cell lines in vitro by repeated, continuous exposure to escalating concentrations of the drug; however, the precise mechanism underlying the acquired resistance is not always known. Here, it is demonstrated that the human colorectal cancer cell line DLD1 with acquired resistance to trifluridine (FTD), a key component of the novel, orally administered nucleoside analogue-type chemotherapeutic drug trifluridine/tipiracil, lacks functional thymidine kinase 1 (TK1) expression because of one nonsense mutation in the coding exon. Targeted disruption of the TK1 gene also conferred severe FTD resistance, indicating that the loss of TK1 protein expression is the primary cause of FTD resistance. Both FTD-resistant DLD1 cells and DLD1-TK1 ^-/- cells exhibited similar 5-fluorouracil (5-FU) sensitivity to that of the parental DLD1 line. The quantity of cellular pyrimidine nucleotides in these cells and the kinetics of thymidylate synthase ternary complex formation in 5-FU-treated cells is similar to DLD1 cells, indicating that 5-FU metabolism and cytotoxicity were unaffected. The current data provide molecular-based evidence that acquired resistance to FTD does not confer 5-FU resistance, implying that 5-FU-based chemotherapy would be effective even in tumors that become refractory to FTD during trifluridine/tipiracil treatment. Mol Cancer Res; 16(10); 1483-90. ©2018 AACR.

Photosensitizers in prostate cancer therapy

The search for new therapeutics for the treatment of prostate cancer is ongoing with a focus on the balance between the harms and benefits of treatment. New therapies are being constantly developed to offer treatments similar to radical therapies, with limited side effects. Photodynamic therapy (PDT) is a promising strategy in delivering focal treatment in primary as well as post radiotherapy prostate cancer. PDT involves activation of a photosensitizer (PS) by appropriate wavelength of light, generating transient levels of reactive oxygen species (ROS). Several photosensitizers have been developed with a focus on treating prostate cancer like mTHPC, motexafin lutetium, padoporfin and so on. This article will review newly developed photosensitizers under clinical trials for the treatment of prostate cancer, along with the potential advantages and disadvantages in delivering focal therapy.

Inhibition of uracil DNA glycosylase sensitizes cancer cells to 5-fluorodeoxyuridine through replication fork collapse-induced DNA damage

5-fluorodeoxyuridine (5-FdU, floxuridine) is active against multiple cancers through the inhibition of thymidylate synthase, which consequently introduces uracil and 5-FU incorporation into the genome. Uracil DNA glycosylase (UDG) is one of the main enzymes responsible for the removal of uracil and 5-FU. However, how exactly UDG mediates cellular sensitivity to 5-FdU, and if so whether it is through its ability to remove uracil and 5-FU have not been well characterized. In this study, we report that UDG depletion led to incorporation of uracil and 5-FU in DNA following 5-FdU treatment and significantly enhanced 5-FdU's cytotoxicity in cancer cell lines. Co-treatment, but not post-treatment with thymidine prevented cell death of UDG depleted cells by 5-FdU, indicating that the enhanced cytotoxicity is due to the retention of uracil and 5-FU in genomic DNA in the absence of UDG. Furthermore, UDG depleted cells were arrested at late G1 and early S phase by 5-FdU, followed by accumulation of sub-G1 population indicating cell death. Mechanistically, 5-FdU dramatically reduced DNA replication speed in UDG depleted cells. UDG depletion also greatly enhanced DNA damage as shown by γH2AX foci formation. Notably, the increased γH2AX foci formation was not suppressed by caspase inhibitor treatment, suggesting that DNA damage precedes cell death induced by 5-FdU. Together, these data provide novel mechanistic insights into the roles of UDG in DNA replication, damage repair, and cell death in response to 5-FdU and suggest that UDG is a target for improving the anticancer effect of this agent.

Investigation of C-5 alkynyl (alkynyloxy or hydroxymethyl) and/or N-3 propynyl substituted pyrimidine nucleoside analogs as a new class of antimicrobial agents

The resurgence of mycobacterial infections and the emergence of drug-resistant strains urgently require a new class of agents that are distinct than current therapies. A group of 5-ethynyl (6-10), 5-(2-propynyloxy) (16, 18, 20, 22, 24), 5-(2-propynyloxy)-3-N-(2-propynyl) (17, 19, 21, 23, 25) and 5-hydroxymethyl-3-N-(2-propynyl) (30-33) derivatives of pyrimidine nucleosides were synthesized and evaluated against mycobacteria [Mycobacterium tuberculosis (Mtb), Mycobacterium bovis (BCG) and Mycobacterium avium], gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis) and gram-negative bacteria (Escherichia coli, Salmonella typhimurium and Pseudomonas aeruginosa) alone and in combination with existing drugs in in vitro assays. Although several compounds exhibited marked inhibitory activity at a higher concentration against Mtb, M. bovis, S. aureus and E. faecalis, they displayed unexpected synergistic and additive interactions at their lower concentrations with antitubercular drugs isoniazid and rifampicin, and antibacterial drug gentamicin. The active analogues were also found to inhibit intracellular Mtb in a human monocytic cell line infected with H37Ra. Oral administration of 5-hydroxymethyl-3-N-(2-propynyl)-3'-azido-2',3'-dideoxyuridine (32) and 5-hydroxymethyl-3-N-(2-propynyl)-2',3'-dideoxyuridine (33) at a dose of 100mg/kg for two weeks showed promising in vivo effects in mice infected with Mtb (H37Ra). No in vitro cytotoxicity of the test compounds was observed up to the highest concentration tested (CC50>300μg/mL).

Cleavage of DNA containing 5-fluorocytosine or 5-fluorouracil by type II restriction endonucleases

A systematic study of the cleavage of DNA sequences containing 5-fluorocytosine or 5-fluorouracil by type II restriction endonucleases (REs) was performed and the results compared with the same sequences containing natural pyrimidine bases, uracil or 5-methylcytosine. The results show that some REs recognize fluorine as a hydrogen on cytosine and cleave the corresponding sequences where the presence of m5dC leads to blocking of the cleavage. However, on uracil, the same REs recognize the F as a methyl surrogate and cleave the sequences which are not cleaved if uracil is incorporated instead of thymine. These results are interesting for understanding the recognition of DNA sequences by REs and for manipulation of the specific DNA cutting.

The influence of p53 status on the cytotoxicity of fluorinated pyrimidine L-nucleosides

Fluorinated nucleoside analogues are a major class of cancer chemotherapy agents, and include the drugs 5-fluorouracil (5FU) and 5-fluoro-2'-deoxyuridine (FdUrd). The aim of this study was to examine the cellular toxicity of two novel fluorinated pyrimidine L-nucleosides that are enantiomers of D-nucleosides and may be able to increase selectivity for cancer cells as a result of their unnatural L-configuration. Two fluorinated pyrimidine L-nucleosides were examined in this study, L110 ([β-L, β-D]-5-fluoro-2'-deoxyuridine) and L117 (β-L-deoxyuridine:β-D-5'-fluoro-2'-deoxyuridine). The cytotoxicity of these L-nucleoside was determined in primary mouse fibroblasts and was compared with 5FU and FdUrd. In addition, the influence of p53 status on cytotoxicity was investigated. These cytotoxicity assays were performed on a matched set of primary mouse fibroblasts that were either wild type or null for the p53 tumour suppressor gene. It was found that cells lacking functional p53 were over 7500 times more sensitive to the drugs L110, L117 and FdUrd than cells containing wild type p53.

Palladium-mediated dealkylation of N-propargyl-floxuridine as a bioorthogonal oxygen-independent prodrug strategy

Herein we report the development and biological screening of a bioorthogonal palladium-labile prodrug of the nucleoside analogue floxuridine, a potent antineoplastic drug used in the clinic to treat advanced cancers. N-propargylation of the N3 position of its uracil ring resulted in a vast reduction of its biological activity (~6,250-fold). Cytotoxic properties were bioorthogonally rescued in cancer cell culture by heterogeneous palladium chemistry both in normoxia and hypoxia. Within the same environment, the reported chemo-reversible prodrug exhibited up to 1,450-fold difference of cytotoxicity whether it was in the absence or presence of the extracellular palladium source, underlining the precise modulation of bioactivity enabled by this bioorthogonally-activated prodrug strategy.

A fatal combination: a thymidylate synthase inhibitor with DNA damaging activity

2′-deoxy-5-ethynyluridine (EdU) has been previously shown to be a cell poison whose toxicity depends on the particular cell line. The reason is not known. Our data indicates that different efficiency of EdU incorporation plays an important role. The EdU-mediated toxicity was elevated by the inhibition of 2′-deoxythymidine 5′-monophosphate synthesis. EdU incorporation resulted in abnormalities of the cell cycle including the slowdown of the S phase and a decrease in DNA synthesis. The slowdown but not the cessation of the first cell division after EdU administration was observed in all of the tested cell lines. In HeLa cells, a 10 μM EdU concentration led to the cell death in the 100% of cells probably due to the activation of an intra S phase checkpoint in the subsequent S phase. Our data also indicates that this EdU concentration induces interstrand DNA crosslinks in HeLa cells. We suppose that these crosslinks are the primary DNA damage resulting in cell death. According to our results, the EdU-mediated toxicity is further increased by the inhibition of thymidylate synthase by EdU itself at its higher concentrations.

Synthesis and in vitro evaluation of bile acid prodrugs of floxuridine to target the liver

Floxuridine is often used to treat metastatic liver disease and is given as an infusion directly into the hepatic artery to increase the amount of intact drug that reaches the liver. The objective of this work was to design and synthesize prodrugs of floxuridine through conjugation to chenodeoxycholic acid (CDCA) to target the liver via the bile acid liver uptake transporter Na(+)/taurocholate cotransporting polypeptide (NTCP, SLC10A1). Two isomeric prodrugs of floxuridine were synthesized: floxuridine 3'glutamic acid-CDCA and floxuridine 5'-glutamic acid-CDCA. Both were potent inhibitors and substrates of NTCP. Floxuridine 3'glutamic acid-CDCA showed Ki=6.86±1.37 μM, Km=10.7±2.1 μM, and passive permeability=0.663(±0.121)×10(-7) cm/s while floxuridine 5'-glutamic acid-CDCA showed Ki=0.397±0.038 μM, Km=40.4±15.2 μM, and passive permeability=1.72(±0.18)×10(-7) cm/s. Floxuridine itself had a higher passively permeability of 7.54(±0.45)×10(-7) cm/s in the same cell line, indicating that both prodrugs have the potential for lower non-specific effects than the drug alone. Prodrugs were stable in rat plasma (t=3 h), but quickly released in rat liver s9 fraction, suggesting future in vivo evaluation.

Albumin-drug conjugates in the treatment of hepatic disorders

INTRODUCTION

This review deals with the use of serum albumin (SA) as a carrier for the selective delivery of drugs to liver cells.

AREAS COVERED

The synthesis and properties of the SA conjugates prepared to enhance the performance of the drugs used in the treatment of viral hepatitis, hepatocellular carcinoma (HCC), liver micrometastases and hepatic fibrosis are reported.

EXPERT OPINION

Studies in humans and laboratory animals demonstrated the capacity of SA conjugates to accomplish a liver targeting of the drugs, but at the same time underscored their limits and drawbacks, which can explain why to date these complexes did not reach a practical application. The major drawback is the need of administration by intravenous route, which prevents long-term daily treatments as required by some liver pathologies, such as chronic virus hepatitis and fibrosis. At present, only a conjugate carrying doxorubicin and addressed to the treatment of HCC showed in laboratory animals a solid potentiality to improve the value of the coupled drug. In the future, conjugation to SA could remain a successful strategy to permit the administration of drugs with rapid resolutive effects inside liver cells without causing severe extrahepatic adverse reactions.

UNG-initiated base excision repair is the major repair route for 5-fluorouracil in DNA, but 5-fluorouracil cytotoxicity depends mainly on RNA incorporation

Cytotoxicity of 5-fluorouracil (FU) and 5-fluoro-2′-deoxyuridine (FdUrd) due to DNA fragmentation during DNA repair has been proposed as an alternative to effects from thymidylate synthase (TS) inhibition or RNA incorporation. The goal of the present study was to investigate the relative contribution of the proposed mechanisms for cytotoxicity of 5-fluoropyrimidines. We demonstrate that in human cancer cells, base excision repair (BER) initiated by the uracil–DNA glycosylase UNG is the major route for FU–DNA repair in vitro and in vivo. SMUG1, TDG and MBD4 contributed modestly in vitro and not detectably in vivo. Contribution from mismatch repair was limited to FU:G contexts at best. Surprisingly, knockdown of individual uracil–DNA glycosylases or MSH2 did not affect sensitivity to FU or FdUrd. Inhibitors of common steps of BER or DNA damage signalling affected sensitivity to FdUrd and HmdUrd, but not to FU. In support of predominantly RNA-mediated cytotoxicity, FU-treated cells accumulated ~3000- to 15 000-fold more FU in RNA than in DNA. Moreover, FU-cytotoxicity was partially reversed by ribonucleosides, but not deoxyribonucleosides and FU displayed modest TS-inhibition compared to FdUrd. In conclusion, UNG-initiated BER is the major route for FU–DNA repair, but cytotoxicity of FU is predominantly RNA-mediated, while DNA-mediated effects are limited to FdUrd.

The achievement of mass balance by simultaneous quantification of floxuridine prodrug, floxuridine, 5-fluorouracil, 5-dihydrouracil, α-fluoro-β-ureidopropionate, α-fluoro-β-alanine using LC-MS

5-Fluoro-2'-deoxyuridine (floxuridine, 5-FdUrd) and 5-fluorouracil (5-FU) are widely used for the treatment of colorectal cancers. The mechanisms of action of 5-FdUrd and 5-FU, as well as the biochemical pathway responsible for their metabolism, are well understood. Identification of every metabolite and achieving mass balance by conventional UV absorption-based HPLC analysis are not feasible because the metabolites beyond 5-FU in the 5-FdUrd metabolic pathway are undetectable by UV light. We therefore established a mass spectrometry method, designed for fast and convenient analysis, for simultaneously measuring 5-FdUrd, 5-FU, and their metabolites. Linearity, precision and accuracy were validated in the concentration ranges studied for each compound. Hydrolysis studies of 5-FdUrd and amino acid mono ester prodrugs of 5-FdUrd in Capan-2 cell homogenates were carried out and the achievement of mass balance was established with this method (recovery of 5'-O-l-leucyl-FdUrd was 96.6-108.2% and that of 5-FdUrd was 79.4-117.4%). This simple LC-MS method achieves reliable quantitation and mass balance of 5-FdUrd, 5-FU, and their metabolites and can be effectively utilized for further kinetic studies.

Cellular pharmacology of multi- and duplex drugs consisting of ethynylcytidine and 5-fluoro-2'-deoxyuridine

Prodrugs can have the advantage over parent drugs in increased activation and cellular uptake. The multidrug ETC-L-FdUrd and the duplex drug ETC-FdUrd are composed of two different monophosphate-nucleosides, 5-fluoro-2'deoxyuridine (FdUrd) and ethynylcytidine (ETC), coupled via a glycerolipid or phosphodiester, respectively. The aim of the study was to determine cytotoxicity levels and mode of drug cleavage. Moreover, we determined whether a liposomal formulation of ETC-L-FdUrd would improve cytotoxic activity and/or cleavage. Drug effects/cleavage were studied with standard radioactivity assays, HPLC and LC-MS/MS in FM3A/0 mammary cancer cells and their FdUrd resistant variants FM3A/TK(-). ETC-FdUrd was active (IC(50) of 2.2 and 79 nM) in FM3A/0 and TK(-) cells, respectively. ETC-L-FdUrd was less active (IC(50): 7 nM in FM3A/0 vs 4500 nM in FM3A/TK(-)). Although the liposomal formulation was less active than ETC-L-FdUrd in FM3A/0 cells (IC(50):19.3 nM), resistance due to thymidine kinase (TK) deficiency was greatly reduced. The prodrugs inhibited thymidylate synthase (TS) in FM3A/0 cells (80-90%), but to a lower extent in FM3A/TK(-) (10-50%). FdUMP was hardly detected in FM3A/TK(-) cells. Inhibition of the transporters and nucleotidases/phosphatases resulted in a reduction of cytotoxicity of ETC-FdUrd, indicating that this drug was cleaved outside the cells to the monophosphates, which was verified by the presence of FdUrd and ETC in the medium. ETC-L-FdUrd and the liposomal formulation were neither affected by transporter nor nucleotidase/phosphatase inhibition, indicating circumvention of active transporters. In vivo, ETC-FdUrd and ETC-L-FdURd were orally active. ETC nucleotides accumulated in both tumor and liver tissues. These formulations seem to be effective when a lipophilic linker is used combined with a liposomal formulation.

Salvage combination chemotherapy with floxuridine, dactinomycin, etoposide, and vincristine (FAEV) for patients with relapsed/chemoresistant gestational trophoblastic neoplasia

BACKGROUND

Although most patients with gestational trophoblastic neoplasia (GTN) are cured by conventional chemotherapy, some develop drug resistance or relapse. The use of new combination drugs has been studied to treat those with resistant or relapsed disease. We evaluated the results of floxuridine, dactinomycin, etoposide, and vincristine (FAEV) chemotherapy in patients with relapsed/chemoresistant GTN.

PATIENTS AND METHODS

Clinical data and outcome of the patients with relapsed/chemoresistant GTN from 1 January 2005 to 30 June 2008 were retrospectively reviewed. Eligible patients had received at least one cycle of FAEV chemotherapy. The primary end points were response rate and toxicity of FAEV regimen; the secondary end point was assessment of clinical predictors of response.

RESULTS

In total, 91 patients were included. Fifty-five of these patients (60.4%) achieved serologic complete remission (SCR), 29 patients had no response, 7 patients experienced recurrent grade ≥3 or intolerable toxicity. SCR of FAEV chemotherapy was significantly associated with number of previous chemotherapy regimens (≤2) in multivariate analysis (P = 0.005). The most serious adverse events were greater than or equal to grade 3 neutropenia (26.4%), febrile neutropenia (6.6%), and greater than or equal to grade 3 thrombocytopenia (3.3%).

CONCLUSION

FAEV is an effective regimen with manageable toxicity for patients with relapsed/chemoresistant GTN. Further studies of this regimen are warranted.

Potent radiosensitizing agents: 5-methylselenyl- and 5-phenylselenyl-methyl-2'-deoxyuridine

This Letter describes the novel radiosensitizing agents based on nucleoside base modification. In addition to the known 5-phenylselenide derivative, 5-methylselenide modified thymidine, which has a van der Waals radius smaller than the phenyl group, was newly synthesized. The similar monomer activity of 5-methylselenide derivative under oxidation condition was confirmed by NMR experiments. The cytotoxicity tests and radiosensitizing experiments of both compounds were carried out using the H460 lung cancer cell line. Both the 5-phenylselenide and the 5-methylselenide derivatives showed a relatively low toxicity to the cells. However, in combination with γ-radiolysis, both exerted good radiosensitizing effects to the lung cancer cell lines in vitro. This result confirms that 5-methylselenide modified thymidine could be a useful candidate as a potential radiosensitizing agent in vivo.

Lactosaminated human albumin, a hepatotropic carrier of drugs

A selective delivery of drugs to liver can be obtained by conjugation with galactosyl terminating macromolecules. The conjugates selectively enter hepatocytes after interaction of the carrier galactose residues with the asialoglycoprotein receptor (ASGP-R) present only on these cells. Within hepatocytes the conjugates are transported to lysosomes where the drug is set free from the carrier, becoming concentrated in liver cells. The present article reviews the liver targeting of drugs obtained with lactosaminated albumin (L-SA), a neoglycoprotein exposing galactosyl residues. We report: (1) experiments which demonstrate the antiviral efficacy of the L-H(human)SA-ara-AMP conjugate in laboratory animals and in humans with viral hepatitis; (2) the property of a L-HSA conjugate with fluorodeoxyuridine to produce concentrations of the drug higher in hepatic sinusoids than in systemic circulation, with the potential of accomplishing a loco-regional, noninvasive treatment of liver micrometastases; (3) the increased anticancer activity of doxorubicin (DOXO) when coupled to L-HSA on all the forms of chemically induced rat hepatocellular carcinomas including those which do not express the ASGP-R.

DNA mismatch repair (MMR)-dependent 5-fluorouracil cytotoxicity and the potential for new therapeutic targets

The metabolism and efficacy of 5-fluorouracil (FUra) and other fluorinated pyrimidine (FP) derivatives have been intensively investigated for over fifty years. FUra and its antimetabolites can be incorporated at RNA- and DNA-levels, with RNA level incorporation provoking toxic responses in human normal tissue, and DNA-level antimetabolite formation and incorporation believed primarily responsible for tumour-selective responses. Attempts to direct FUra into DNA-level antimetabolites, based on mechanism-of-action studies, have led to gradual improvements in tumour therapy. These include the use of leukovorin to stabilize the inhibitory thymidylate synthase-5-fluoro-2'-deoxyuridine 5' monophoshate (FdUMP)-5,10-methylene tetrahydrofolate (5,10-CH(2)FH(4)) trimeric complex. FUra incorporated into DNA also contributes to antitumour activity in preclinical and clinical studies. This review examines our current state of knowledge regarding the mechanistic aspects of FUra:Gua lesion detection by DNA mismatch repair (MMR) machinery that ultimately results in lethality. MMR-dependent direct cell death signalling or futile cycle responses will be discussed. As 10-30% of sporadic colon and endometrial tumours display MMR defects as a result of human MutL homologue-1 (hMLH1) promoter hypermethylation, we discuss the use and manipulation of the hypomethylating agent, 5-fluorodeoxycytidine (FdCyd), and our ability to manipulate its metabolism using the cytidine or deoxycytidylate (dCMP) deaminase inhibitors, tetrahydrouridine or deoxytetrahydrouridine, respectively, as a method for re-expression of hMLH1 and re-sensitization of tumours to FP therapy.

Resistance to cytarabine induces the up-regulation of NKG2D ligands and enhances natural killer cell lysis of leukemic cells

Prolonged treatment of leukemic cells with chemotherapeutic agents frequently results in development of drug resistance. Moreover, selection of drug-resistant cell populations may be associated with changes in malignant properties such as proliferation rate, invasiveness, and immunogenicity. In the present study, the sensitivity of cytarabine (1-beta-D-arabinofuranosylcytosine, araC)-resistant and parental human leukemic cell lines (T-lymphoid H9 and acute T-lymphoblastic leukemia Molt-4) to natural killer (NK) cell-mediated killing was investigated. The results obtained demonstrate that araC-resistant H9 and Molt-4 (H9(r)ARAC(100) and Molt-4(r)ARAC(100)) cell lines are more sensitive to NK cell-mediated lysis than their respective parental cell lines. This increased sensitivity was associated with a higher surface expression of ligands for the NK cell-activating receptor NKG2D, notably UL16 binding protein-2 (ULBP-2) and ULBP-3 in H9(r)ARAC(100) and Molt-4(r)ARAC(100) cell lines. Blocking ULBP-2 and ULBP-3 or NKG2D with monoclonal antibody completely abrogated NK cell lysis. Constitutive phosphorylated extracellular signal-regulated kinase (ERK) but not pAKT was higher in araC-resistant cells than in parental cell lines. Inhibition of ERK using ERK inhibitor PD98059 decreased both ULBP-2/ULBP-3 expression and NK cell cytotoxicity. Furthermore, overexpression of constitutively active ERK in H9 parental cells resulted in increased ULBP-2/ULBP-3 expression and enhanced NK cell lysis. These results demonstrate that increased sensitivity of araC-resistant leukemic cells to NK cell lysis is caused by higher NKG2D ligand expression, resulting from more active ERK signaling pathway.

Nonpolar nucleoside mimics as active substrates for human thymidine kinases

We describe the use of nonpolar nucleoside analogues of systematically varied size and shape to probe the mechanisms by which the two human thymidine kinases (TK1 and TK2) recognize and phosphorylate their substrate, thymidine. Comparison of polar thymidine with a nonpolar isostere, 2,4-difluorotoluene deoxyriboside, as substrates for the two enzymes establishes that TK1 requires electrostatic complementarity to recognize the thymine base with high efficiency. Conversely, TK2 does not and phosphorylates the hydrophobic shape mimic with efficiency nearly the same as the natural substrate. To test the response to nucleobase size, thymidine-like analogues were systematically varied by replacing the 2,4 substituents on toluene with hydrogen and the halogen series (H, F, Cl, Br, I). Both enzymes showed a distinct preference for substrates having the natural size. To examine the shape preference, we prepared four mono- and difluorotoluene deoxyribosides with varying positions of substitutions. While TK1 did not accept these nonpolar analogues as substrates, TK2 did show varying levels of phosphorylation of the shape-varied set. This latter enzyme preferred toluene nucleoside analogues having steric projections at the 2 and 4 positions, as is found in thymine, and strongly disfavored substitution at the 3-position. Steady-state kinetics measurements showed that the 4-fluoro compound (7) had an apparent V(max)/K(m) value within 14-fold of the natural substrate, and the 2,4-difluoro compound (1), which is the closest isostere of thymidine, had a value within 2.5-fold. The results establish that nucleoside recognition mechanisms for the two classes of enzymes are very different. On the basis of these data, nonpolar nucleosides are likely to be active in the nucleotide salvage pathway in human cells, suggesting new designs for future bioactive molecules.

Radiation- and photo-induced activation of 5-fluorouracil prodrugs as a strategy for the selective treatment of solid tumors

5-Fluorouracil (5-FU) is used widely as an anticancer drug to treat solid cancers, such as colon, breast, rectal, and pancreatic cancers, although its clinical application is limited because 5-FU has gastrointestinal and hematological toxicity. Many groups are searching for prodrugs with functions that are tumor selective in their delivery and can be activated to improve the clinical utility of 5-FU as an important cancer chemotherapeutic agent. UV and ionizing radiation can cause chemical reactions in a localized area of the body, and these have been applied in the development of site-specific drug activation and sensitization. In this review, we describe recent progress in the development of novel 5-FU prodrugs that are activated site specifically by UV light and ionizing radiation in the tumor microenvironment. We also discuss the chemical mechanisms underlying this activation.

MLH1 deficiency enhances radiosensitization with 5-fluorodeoxyuridine by increasing DNA mismatches

The antitumor drug 5-fluoro-2'-deoxyuridine (FdUrd) also sensitizes tumor cells to ionizing radiation in vitro and in vivo. Although radiosensitization with FdUrd requires dTTP depletion and S-phase arrest, the exact mechanism by which these events produce radiosensitization remains unknown. We hypothesized that the depletion of dTTP produces DNA mismatches that, if not repaired before irradiation, would result in radiosensitization. We evaluated this hypothesis in mismatch repair (MMR)-deficient HCT116 0-1 cells that lack the expression of the required MMR protein MLH1 (inactive MLH1), and in MMR-proficient (wild-type MLH1) HCT116 1-2 cells. Although HCT116 0-1 cells were less sensitive to FdUrd (IC(50) = 3.5 microM) versus HCT116 1-2 cells (IC(50) = 0.75 microM), when irradiation followed FdUrd (IC(50)) the MLH1-inactivated cells exhibited greater radiosensitization compared with MMR-wild-type cells [radiation enhancement ratio (RER) = 1.8 +/- 0.28 versus 1.1 +/- 0.1, respectively] and an increase (> or =8-fold) in nucleotide misincorporations. In SW620 cells and HCT116 1-2 MLH1-wild-type cells, FdUrd (IC(50)) did not produce radiosensitization nor did it increase the mutation frequency, but after short hairpin RNA-directed suppression of MLH1 this concentration produced excellent radiosensitization (RER = 1.6 +/- 0.10 and 1.5 +/- 0.06, respectively) and an increase in nucleotide misincorporations (8-fold and 6-fold, respectively). Incubation with higher concentrations of FdUrd (IC(90)) after suppression of MLH1 produced a further increase in ionizing radiation sensitivity in both SW620 and HCT116 1-2 cells (RER = 1.8 +/- 0.03 and 1.7 +/- 0.13, respectively) and nucleotide misincorporations (>10-fold in both cell lines). These results demonstrate an important role for MLH1 and implicate mismatches in radiosensitization by FdUrd.

Enhanced cancer cell growth inhibition by dipeptide prodrugs of floxuridine: increased transporter affinity and metabolic stability

Dipeptide monoester prodrugs of floxuridine were synthesized, and their chemical stability in buffers, resistance to glycosidic bond metabolism, affinity for PEPT1, enzymatic activation and permeability in cancer cells were determined and compared to those of mono amino acid monoester floxuridine prodrugs. Prodrugs containing glycyl moieties were the least stable in pH 7.4 buffer ( t 1/2 < 100 min). The activation of all floxuridine prodrugs was 2- to 30-fold faster in cell homogenates than their hydrolysis in buffer, suggesting enzymatic action. The enzymatic activation of dipeptide monoester prodrugs containing aromatic promoieties in cell homogenates was 5- to 20-fold slower than that of other dipeptide and most mono amino acid monoester prodrugs ( t 1/2 approximately 40 to 100 min). All prodrugs exhibited enhanced resistance to glycosidic bond metabolism by thymidine phosphorylase compared to parent floxuridine. In general, the 5'-O-dipeptide monoester floxuridine prodrugs exhibited higher affinity for PEPT1 than the corresponding 5'-O-mono amino acid ester prodrugs. The permeability of dipeptide monoester prodrugs across Caco-2 and Capan-2 monolayers was 2- to 4-fold higher than the corresponding mono amino acid ester prodrug. Cell proliferation assays in AsPC-1 and Capan-2 pancreatic ductal cell lines indicated that the dipeptide monoester prodrugs were equally as potent as mono amino acid prodrugs. The transport and enzymatic profiles of 5'- l-phenylalanyl- l-tyrosyl-floxuridine, 5'- l-phenylalanyl- l-glycyl-floxuridine, and 5'- l-isoleucyl- l-glycyl-floxuridine suggest their potential for increased oral uptake, delayed enzymatic bioconversion and enhanced resistance to metabolism to 5-fluorouracil, as well as enhanced uptake and cytotoxic activity in cancer cells, attributes that would facilitate prolonged systemic circulation for enhanced therapeutic action.

Enhanced absorption and growth inhibition with amino acid monoester prodrugs of floxuridine by targeting hPEPT1 transporters

A series of amino acid monoester prodrugs of floxuridine was synthesized and evaluated for the improvement of oral bioavailability and the feasibility of target drug delivery via oligopeptide transporters. All floxuridine 5'-amino acid monoester prodrugs exhibited PEPT1 affinity, with inhibition coefficients of Gly-Sar uptake (IC50) ranging from 0.7 - 2.3 mM in Caco-2 and 2.0 - 4.8 mM in AsPC-1 cells, while that of floxuridine was 7.3 mM and 6.3 mM, respectively. Caco-2 membrane permeabilities of floxuridine prodrugs (1.01 - 5.31 x 10(-6 )cm/sec) and floxuridine (0.48 x 10(-6 )cm/sec) were much higher than that of 5-FU (0.038 x 10(-6) cm/sec). MDCK cells stably transfected with the human oligopeptide transporter PEPT1 (MDCK/hPEPT1) exhibited enhanced cell growth inhibition in the presence of the prodrugs. This prodrug strategy offers great potential, not only for increased drug absorption but also for improved tumor selectivity and drug efficacy.

Nucleoside analogues are activated by bacterial deoxyribonucleoside kinases in a species-specific manner

OBJECTIVES

To investigate the bactericidal activity of antiviral and anticancer nucleoside analogues against a variety of pathogenic bacteria and characterize the activating enzymes, deoxyribonucleoside kinases (dNKs).

METHODS

Several FDA-approved nucleoside analogue drugs were screened for their potential bactericidal activity against several clinical bacterial isolates and type strains. We identified and subcloned the genes coding for putative deoxyribonucleoside kinases in Escherichia coli, Pasteurella multocida, Salmonella enterica, Yersinia enterocolitica, Bacillus cereus, Clostridium perfringens and Listeria monocytogenes. These genes were tested for their ability to increase the susceptibility of a dNK-deficient E. coli strain to various analogues. We overexpressed, purified and characterized the substrate specificity and kinetic properties of the recombinant enzymes from S. enterica and B. cereus.

RESULTS

The tested Gram-negative bacteria were susceptible to 3'-azido-3'-deoxythymidine (AZT) in the concentration range 0.032-31.6 microM except for a single E. coli isolate and two Pseudomonas aeruginosa isolates which were resistant to the tested AZT concentrations. Purified recombinant S. enterica thymidine kinase phosphorylated AZT efficiently with a Km of 73.3 microM and k(cat)/Km of 6.6 x 10(4) s(-1) M(-1) and is the activator of this drug in vivo. 2',2'-Difluoro-2'-deoxycytidine (gemcitabine) was a potent antibiotic against Gram-positive bacteria in the concentration range between 0.001 and 1.0 microM. The B. cereus deoxyadenosine kinase had a Km for gemcitabine of 33.5 microM and k(cat)/Km of 5.1 x 10(3) s(-1) M(-1) and activates gemcitabine in vivo. S. enterica and B. cereus are now amongst the first bacteria with a completely characterized set of dNK enzymes.

CONCLUSIONS

Bacterial dNKs efficiently activate nucleoside analogues in a species-specific manner. Therefore, nucleoside analogues have a potential to be employed as antibiotics in the fight against emerging multiresistant bacteria.

The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer

INTRODUCTION

High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to microsatellite stable (MSS) cancers.

OBJECTIVE

This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC).

RESULTS AND DISCUSSION

5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed.

CONCLUSION

Available evidence suggests that MSI-H CRC have different behaviour patterns and response to chemotherapy compared with MSS CRC.