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

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

Accuracy assessment of NLCD 2011 impervious cover data for the Chesapeake Bay region, USA

The National Land Cover Database (NLCD) contains three eras (2001, 2006, 2011) of percentage urban impervious cover (%IC) at the native pixel size (30 m-×-30 m) of the Landsat Thematic Mapper satellite. These data are potentially valuable to environmental managers and stakeholders because of the utility of %IC as an indicator of watershed and aquatic condition, but lack an accuracy assessment because of the absence of suitable reference data. Recently developed 1 m2 land cover data for the Chesapeake Bay region makes it possible to assess NLCD %IC accuracy for a 262,000 km2 region based on a census rather than a sample of reference data. We report agreement between the two %IC datasets for watersheds and the riparian zones within watersheds and four additional square units. The areas of the six assessment units were 40 ha cell, 433 ha (riparian mean), 2756 ha cell, 5626 ha cell, 8569 ha (watershed mean) and 22,500 ha cell. Mean Absolute Deviation (MAD) and Mean Deviation (MD) were about 1.5% and -1.5%, respectively, for each of the assessment units except for the riparian unit, for which MAD and MD were 0.88 and 0.62, respectively. NLCD reliably reproduced %IC from the 1 m2 data with a small, consistent tendency for underestimation. Results were sensitive to assessment unit choice. The results for the four largest assessment units had very similar regression parameters, R2 values, and bias patterns. Results for the riparian assessment were different from those for the watershed unit and the other three larger units. MAD was about 50% less for the riparian zones than it was for the watersheds, the direction of bias was less consistent, and NLCD %IC was uniformly higher than 1 m2 %IC in urbanized riparian zones. For the smallest unit, bias patterns were more similar to the riparian unit and regression results were more similar to the four larger units. MAD and MD were also sensitive to the amount of urbanization, increasing as NLCD %IC increased. The low overall bias and positive relationship between bias and urbanization suggest that the benefits of obtaining 1 m2 IC data outside of urban areas may not outweigh the costs of obtaining such data.

With me or against me: Tumor suppressor and drug resistance activities of SAMHD1

Sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1) is a (deoxy)guanosine triphosphate (dGTP/GTP)-activated deoxyribonucleoside triphosphate (dNTP) triphosphohydrolase involved in cellular dNTP homoeostasis. Mutations in SAMHD1 have been associated with the hyperinflammatory disease Aicardi-Goutières syndrome (AGS). SAMHD1 also limits cells' permissiveness to infection with diverse viruses, including human immunodeficiency virus (HIV-1), and controls endogenous retroviruses. Increasing evidence supports the role of SAMHD1 as a tumor suppressor. However, SAMHD1 also can act as a resistance factor to nucleoside-based chemotherapies by hydrolyzing their active triphosphate metabolites, thereby reducing response of various malignancies to these anticancer drugs. Hence, informed cancer therapies must take into account the ambiguous properties of SAMHD1 as both an inhibitor of uncontrolled proliferation and a resistance factor limiting the efficacy of anticancer treatments. Here, we provide evidence that SAMHD1 is a double-edged sword for patients with acute myelogenous leukemia (AML). Our time-dependent analyses of The Cancer Genome Atlas (TCGA) AML cohort indicate that high expression of SAMHD1, even though it critically limits the efficacy of high-dose ara-C therapy, might be associated with more favorable disease progression.

SAMHD1 protects cancer cells from various nucleoside-based antimetabolites

Recently, we demonstrated that sterile α motif and HD domain containing protein 1 (SAMHD1) is a major barrier in acute myelogenous leukemia (AML) cells to the cytotoxicity of cytarabine (ara-C), the most important drug in AML treatment. Ara-C is intracellularly converted by the canonical dNTP synthesis pathway to ara-CTP, which serves as a substrate but not an allosteric activator of SAMHD1. Using an AML mouse model, we show here that wild type but not catalytically inactive SAMHD1 reduces ara-C treatment efficacy in vivo. Expanding the clinically relevant substrates of SAMHD1, we demonstrate that THP-1 CRISPR/Cas9 cells lacking a functional SAMHD1 gene showed increased sensitivity to the antimetabolites nelarabine, fludarabine, decitabine, vidarabine, clofarabine, and trifluridine. Within this Extra View, we discuss and build upon both these and our previously reported findings, and propose SAMHD1 is likely active against a variety of nucleoside analog antimetabolites present in anti-cancer chemotherapies. Thus, SAMHD1 may constitute a promising target to improve a wide range of therapies for both hematological and non-haematological malignancies.

SAMHD1 is a barrier to antimetabolite-based cancer therapies

The outcome of acute myelogenous leukemia (AML) therapy depends on the propensity of leukemic blasts to accumulate ara-CTP, the active triphosphate of cytarabine (ara-C). We identified sterile α motif and HD domain-containing protein 1 (SAMHD1) as an ara-CTPase that protects cancer cells from cytarabine-induced toxicity. Therefore, we propose targeting SAMHD1 as a strategy to potentiate cytarabine and possibly other antimetabolite-based therapies.

Targeting SAMHD1 with the Vpx protein to improve cytarabine therapy for hematological malignancies

The cytostatic deoxycytidine analog cytarabine (ara-C) is the most active agent available against acute myelogenous leukemia (AML). Together with anthracyclines, ara-C forms the backbone of AML treatment for children and adults. In AML, both the cytotoxicity of ara-C in vitro and the clinical response to ara-C therapy are correlated with the ability of AML blasts to accumulate the active metabolite ara-C triphosphate (ara-CTP), which causes DNA damage through perturbation of DNA synthesis. Differences in expression levels of known transporters or metabolic enzymes relevant to ara-C only partially account for patient-specific differential ara-CTP accumulation in AML blasts and response to ara-C treatment. Here we demonstrate that the deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAM domain and HD domain 1 (SAMHD1) promotes the detoxification of intracellular ara-CTP pools. Recombinant SAMHD1 exhibited ara-CTPase activity in vitro, and cells in which SAMHD1 expression was transiently reduced by treatment with the simian immunodeficiency virus (SIV) protein Vpx were dramatically more sensitive to ara-C-induced cytotoxicity. CRISPR-Cas9-mediated disruption of the gene encoding SAMHD1 sensitized cells to ara-C, and this sensitivity could be abrogated by ectopic expression of wild-type (WT), but not dNTPase-deficient, SAMHD1. Mouse models of AML lacking SAMHD1 were hypersensitive to ara-C, and treatment ex vivo with Vpx sensitized primary patient-derived AML blasts to ara-C. Finally, we identified SAMHD1 as a risk factor in cohorts of both pediatric and adult patients with de novo AML who received ara-C treatment. Thus, SAMHD1 expression levels dictate patient sensitivity to ara-C, providing proof-of-concept that the targeting of SAMHD1 by Vpx could be an attractive therapeutic strategy for potentiating ara-C efficacy in hematological malignancies.

The Early Bird Catches the Worm--Can Evolution Teach us Lessons in Fighting HIV?

BACKGROUND

Human immunodeficiency virus 1 (HIV-1) infection is the primary cause of the acquired immunodeficiency syndrome (AIDS). Worldwide, approximately 37 million people are infected (UNAIDS, 2014), most of them in developing countries. A vaccine is not available and current treatment strategies and diagnostics are expensive and require appropriate medical infrastructure. As a lentivirus of the family Retroviridae, HIV-1 reverse transcribes its RNA into double stranded DNA that integrates into the host genome during infection, establishing a stably integrated provirus that serves as a template for the production of progeny virus. The earliest steps during infection are critical for onset of disease, progression and clinical outcome.

METHODS

Here we review the current literature of known interactions between host cell factors and HIV-1 in the early infection steps and discuss them as possible targets for new treatment strategies.

RESULTS

Targeting the earliest interactions of the virus with host cell factors is an attractive way to prevent provirus formation, underlined by the evolution of multiple antiviral host cell barriers at this stage. HIV-1 has to overcome these restrictions by either counteracting them directly or by escape mutations. At the same time, viral fitness requires preservation of viral structures that interact with host components, thereby avoiding recognition of viral nucleic acids, like reverse transcription intermediates, by innate pattern recognition receptors.

CONCLUSION

Future drug development, improvement of existing drugs acting in the earliest stages of the HIV-1 replication cycle as well as specifically targeting interactions of viral components with host cell factors required for HIV-1 infection will likely advance current therapy strategies.

Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition

Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

The nucleocapsid domain of Gag is dispensable for actin incorporation into HIV-1 and for association of viral budding sites with cortical F-actin

Actin and actin-binding proteins are incorporated into HIV-1 particles, and F-actin has been suggested to bind the NC domain in HIV-1 Gag. Furthermore, F-actin has been frequently observed in the vicinity of HIV-1 budding sites by cryo-electron tomography (cET). Filamentous structures emanating from viral buds and suggested to correspond to actin filaments have been observed by atomic force microscopy. To determine whether the NC domain of Gag is required for actin association with viral buds and for actin incorporation into HIV-1, we performed comparative analyses of virus-like particles (VLPs) obtained by expression of wild-type HIV-1 Gag or a Gag variant where the entire NC domain had been replaced by a dimerizing leucine zipper [Gag(LZ)]. The latter protein yielded efficient production of VLPs with near-wild-type assembly kinetics and size and exhibited a regular immature Gag lattice. Typical HIV-1 budding sites were detected by using cET in cells expressing either Gag or Gag(LZ), and no difference was observed regarding the association of buds with the F-actin network. Furthermore, actin was equally incorporated into wild-type HIV-1 and Gag- or Gag(LZ)-derived VLPs, with less actin per particle observed than had been reported previously. Incorporation appeared to correlate with the relative intracellular actin concentration, suggesting an uptake of cytosol rather than a specific recruitment of actin. Thus, the NC domain in HIV-1 Gag does not appear to have a role in actin recruitment or actin incorporation into HIV-1 particles. Importance: HIV-1 particles bud from the plasma membrane, which is lined by a network of actin filaments. Actin was found to interact with the nucleocapsid domain of the viral structural protein Gag and is incorporated in significant amounts into HIV-1 particles, suggesting that it may play an active role in virus release. Using electron microscopy techniques, we previously observed bundles of actin filaments near HIV-1 buds, often seemingly in contact with the Gag layer. Here, we show that this spatial association is observed independently of the proposed actin-binding domain of HIV-1. The absence of this domain also did not affect actin incorporation and had a minor effect on the viral assembly rate. Furthermore, actin was not enriched in the virus compared to the average levels in the respective producing cell. Our data argue against a specific recruitment of actin to HIV-1 budding sites by the nucleocapsid domain of Gag.

A quantitative measure for alterations in the actin cytoskeleton investigated with automated high-throughput microscopy

The actin cytoskeleton modulates a large variety of physiological and disease-related processes in the cell. For example, actin has been shown to be a crucial host factor for successful infection by HIV-1, but the underlying mechanistic details are still unknown. Automated approaches open up the perspective to clarify such an issue by processing many samples in a high-throughput manner. To analyze the alterations in the actin cytoskeleton within an automated setting, large-scale image acquisition and analysis were established for JC-53 cells stained for actin. As a quantitative measure in such an automated approach, we suggest a parameter called image coherency. We successfully benchmarked our analysis by calculating coherency for both a biophysical model of the actin cytoskeleton and for cells whose actin architecture had been disturbed pharmacologically by latrunculin B or cytochalasin D. We then tested the influence of HIV-1 infection on actin coherency, but observed no significant differences between uninfected and infected cells.

Gender Differences in [123I]-ADAM Binding to Serotonin Transporters in Patients with Major Depression Before and After Treatment with Citalopram

Aims:

The aim was to determine the relation between characteristics of [123I]-ADAM binding to serotonin transporters (SERT) in several brain regions to different symptoms in patients diagnosed with major depressive disorder (MDD) and to analyze data for males and females separately. Differences of [123I]-ADAM binding in patients before and after treatment with Selective Serotonin Reuptake Inhibitor (SSRI) antidepressant Citalopram were assessed.

Method:

12 non medicated patients (5 females and 7 males) diagnosed with MDD were examined by SPECT with specific Serotonin transporter radioligand [123I]-ADAM before and after treatment with SSRI Citalopram. We administered the dose of 10 mg Citalopram per day intravenously at first day, followed by a 6 days period of oral application. After 7 days of treatment patients were examined for second time with SPECT. The relationships between [123I]-ADAM binding and different aspects of major depression represented by HAMD items, assessed twice by Hamilton Depression-Scale (HAMD) once at baseline and second after treatment period, were evaluated.

Results:

We found significant correlations with significant gender differences between singular sub items of HAMD and indices of [123I]-ADAM binding in midbrain before and after treatment. These findings points to the need of data analysis separately in males and females. No correlations between HAMD total scores at baseline and indices were found.

Conclusion:

SERT availability for 123-ADAM binding in the midbrain in drug naives as well as in treated patients with major depression disorder seems to be related to intensity of sub items in the HAMD and the outcome of treatment.

Imaging of serotonin transporters and its blockade by citalopram in patients with major depression using a novel SPECT ligand [123I]-ADAM

We studied the midbrain SERT availability in patients with major depression and assessed the relation of SERT occupancy by citalopram to the treatment response. 21 non-medicated patients with major depression and 13 healthy controls were examined by [(123)I]-ADAM SPECT. The midbrain SERT availability (SERT V(3)'') was calculated using individual MRI scans. In 13/21 patients SPECT was repeated 7 days after oral medication with citalopram (10 mg/day). We found no significant difference in the mean midbrain SERT availability between the studied patients with major depression and healthy controls (0.86 +/- 0.27 vs. 0.71 +/- 0.44, p = 0.069). The mean SERT occupancy accounted to 61%. The degree of SERT blockade by citalopram did not correlate with the reduction in HAMD total score. Treatment with low-dosed citalopram caused individually variable occupancy of the midbrain-SERT and a rapid clinical improvement in 54% of the investigated patients.

Fibrillar collagen assembled in the presence of glycosaminoglycans to constitute bioartificial stem cell niches in vitro

Fibrillar collagen was reconstituted from mixtures of monomeric tropocollagen and heparin or hyaluronic acid, respectively. Turbidity measurements were utilized to follow the fibrillar assembly and demonstrated the influence of the concentration of the glycosaminoglycan on the maximum optical densities. Thin film coatings of maleic anhydride copolymers were utilized for the covalent immobilization of the fibrillar assemblies to solid supports. Quantification of surface-bound collagen was accomplished by ellipsometry and HPLC-based amino acid analysis indicating that less collagen was immobilized in the presence of the glycosaminoglycans. SEM and AFM revealed various sizes and shapes of the immobilized fibrillar assemblies if collagen fibrils were prepared in the presence of heparin or hyaluronic acid. Human hematopoietic stem cells (HSCs) were cultivated on the surface-bound collagen fibrils and the migration of adherent cells was studied by time-lapse microscopy. Migration rates on fibrillar structures were significantly lower then on tropocollagen indicating a more intimate contact of HSCs to the fibrillar substrates.

A prospective comparison of wedge matrix resection with nail matrix phenolization for the treatment of ingrown toenail

In a prospective study, 110 patients with ingrown toenails were operated on, 55 with wedge matrix resection (WMR) and 55 with nail matrix phenolization (NMP). The patients were randomized on the basis of their address. All patients were reviewed by questionnaire 4 weeks postoperatively to establish the degree of pain, time of pain relief, walking and working ability, and the presence of infection. Furthermore, they were examined clinically at a median follow-up time of 11 months postoperatively to evaluate recurrence rate, rate of spicula formation, and patient satisfaction with regard to cosmesis and symptom relief. The data were tested for statistical significance using the chi-square test and Mann-Whitney rank sum test. The recurrence rate of ingrown toenail for the WMR group was 5.5% (3 patients) with a spicula rate of 36% (20 patients) and a reoperation rate of 20% (9 patients). In the NMP group, there were no recurrences (p = n.s.), the spicula rate was 7.3% (4 patients) (p < .005) and no patients were reoperated on (p < .016). Patient satisfaction with less pain and earlier pain relief was greatest in the NMP group. These results indicate that nail matrix phenolization is an efficient therapy for ingrown toenails and may be preferable to nail wedge resection.

Measurements of behavior in the naked mole-rat after intraperitoneal implantation of a radio-telemetry system

The naked mole-rat (Heterocephalus glaber) is a unique fossorial mammal that is eusocial, object blind, and virtually poikilothermic. This animal is an ideal model to examine questions pertaining to the thermoregulatory aspects of sleep/wake cycles and other circadian events. However, the monitoring of mammalian sleep usually involves implanting permanent electrodes into the skull which are linked to a counter-weighted cable apparatus. This is not a viable option for H. glaber because of the tunneled environments and sensitive social milieu. Instead, to monitor sleep, core temperature, and activity we have utilized intraperitoneal telemetry, a technique that transmits biopotential signals by radio waves. Here we describe the surgical procedure used to implant the device, the anesthesia technique developed, and the social reintroduction method devised for this novel animal model.

["Moon-cars" are dangerous]

We investigated the number and seriousness of moon-car accidents in our region (a moon-car is a toy-vehicle, see Fig. 1). The study was retrospective combined with a telephone-interview. Forty-seven patients were seen in the emergency room after a moon-car accident in the period 1/1 1990-31/12 95. There were 12 fractures, including five fractures of the tibial shaft and one supracondylar humeral fracture which was operated. There were 17 wounds, 14 of which were sutured. Seventeen patients had distorsions/contusions, three cases of head contusions (observed for concussion) and two with teeth damages. We found that the number of moon-car accidents is increasing (13 patients the last year), and that the accidents are not only minor. New rules in day care centres should be able to especially limit the number of more serious accidents.

[Lifet-threatening hemorrhage from a mandibular hemangioma]

A case of a nine year-old girl with a life-threatening episode of profuse bleeding after extraction of a loose deciduous molar is reported. An angiography confirmed the presence of a haemangioma in the right side of the mandible. The lesion was superselectively embolized. Two days later exploration of the haemangioma and resection of the bone was performed, and the bleeding stopped. Special concern must be exercised in cases with hypermobility of the teeth, and when episodes of spontaneous haemorrhage are encountered.

[Roller skating injuries]

The aim of this study was to investigate the number and types of accidents which occur in connection with roller-skates, and also to find out in which anatomical area the most injuries occurred. During the period 01.02.1995 to 31.08.1996, 389 patients sustained injuries in connection with roller-skates. Fifty-nine percent of all accidents happened on a public road. Out of 389 injuries, 174 sustained a fracture: 68% were forearm or distal radius/ulna fractures; 89% were upper extremity fractures. Thirty-three patients were admitted: four for observation due to concussion; 15 for reduction of fractures and application of plaster; and ten for osteosynthesis. Roller-skating accidents are extremely common. Possible prophylaxis includes protective equipment and restricted rinks for roller-skate enthusiast.

[Ultrasound examination of the liver in HELLP syndrome]

A 33-year-old multiparous woman in the 34th gestational week presented with severe upper abdominal pain, nausea and vomiting. Clinical examination revealed severe epigastric tenderness. Abdominal ultrasound examination showed geographical areas with increased echogenicity in the right lobe of the liver. Through haematological examination, we found severe thrombocytopenia and fibrinolysis. The diagnosis of HELLP syndrome was suspected and a caesarean section was performed. We suggest that obstetrical patients with upper abdominal pain and abnormal liver sonography should immediately be haematologically investigated to exclude the life-threatening condition of the HELLP syndrome.

Synovectomy and radial head excision in rheumatoid arthritis. 11 patients followed for 14 years

A radial head excision and partial synovectomy of the elbow through a lateral approach was performed in 24 patients suffering from rheumatoid arthritis. At follow-up examination of 11 patients (12 elbows) 14 years postoperatively, 10 patients were still satisfied with pain reduction and improved elbow motion. 2 elbows had been reoperated on. Radiographic destruction, assessed by the Larsen index, was, on average, 2.9 preoperatively and 3.8 at follow-up.