ChatGPT (GPT-3.5) as an assistant tool in microbial pathogenesis studies in Sweden: a cross-sectional comparative study

ChatGPT (GPT-3.5) has entered higher education and there is a need to determine how to use it effectively. This descriptive study compared the ability of GPT-3.5 and teachers to answer questions from dental students and construct detailed intended learning outcomes. When analyzed according to a Likert scale, we found that GPT-3.5 answered the questions from dental students in a similar or even more elaborate way compared to the answers that had previously been provided by a teacher. GPT-3.5 was also asked to construct detailed intended learning outcomes for a course in microbial pathogenesis, and when these were analyzed according to a Likert scale they were, to a large degree, found irrelevant. Since students are using GPT-3.5, it is important that instructors learn how to make the best use of it both to be able to advise students and to benefit from its potential.

Long term survival and abnormal liver fat accumulation in mice with specific thymidine kinase 2 deficiency in liver tissue

Deficiency in thymidine kinase 2 (TK2) causes mitochondrial DNA depletion. Liver mitochondria are severely affected in Tk2 complete knockout models and have been suggested to play a role in the pathogenesis of the Tk2 knockout phenotype, characterized by loss of hypodermal fat tissue, growth retardation and reduced life span. Here we report a liver specific Tk2 knockout (KO) model to further study mechanisms contributing to the phenotypic changes associated with Tk2 deficiency. Interestingly, the liver specific Tk2 KO mice had a normal life span despite a much lower mtDNA level in liver tissue. Mitochondrial DNA encoded peptide COXI did not differ between the Tk2 KO and control mice. However, the relative liver weight was significantly increased in the male Tk2 KO mouse model. Histology analysis indicated an increased lipid accumulation. We conclude that other enzyme activities can partly compensate Tk2 deficiency to maintain mtDNA at a low but stable level throughout the life span of the liver specific Tk2 KO mice. The lower level of mtDNA was sufficient for survival but led to an abnormal lipid accumulation in liver tissue.

Students’ performance of and perspective on an objective structured practical examination for the assessment of preclinical and practical skills in biomedical laboratory science students in Sweden: a 5-year longitudinal study

PURPOSE

It aims to find students’ performance of and perspectives on an objective structured practical examination (OSPE) for assessment of laboratory and preclinical skills in biomedical laboratory science (BLS). It also aims to investigate the perception, acceptability, and usefulness of OSPE from the students’ and examiners’ point of view.

METHODS

This was a longitudinal study to implement an OSPE in BLS. The student group consisted of 198 BLS students enrolled in semester 4, 2015–2019 at Karolinska University Hospital Huddinge, Sweden. Fourteen teachers evaluated the performance by completing a checklist and global rating scales. A student survey questionnaire was administered to the participants to evaluate the student perspective. To assess quality, 4 independent observers were included to monitor the examiners.

RESULTS

Almost 50% of the students passed the initial OSPE. During the repeat OSPE, 73% of the students passed the OSPE. There was a statistically significant difference between the first and the second repeat OSPE (P<0.01) but not between the first and the third attempt (P=0.09). The student survey questionnaire was completed by 99 of the 198 students (50%) and only 63 students responded to the free-text questions (32%). According to these responses, some stations were perceived as more difficult, albeit they considered the assessment to be valid. The observers found the assessment protocols and examiner’s instructions assured the objectivity of the examination.

CONCLUSION

The introduction of an OSPE in the education of biomedical laboratory scientists was a reliable, and useful examination of practical skills.

Development of an ELISA displaying similar reactivity with reduced and oxidized human Thioredoxin-1 (Trx1): The plasma level of Trx1 in early onset psychosis disorders

The plasma level of human thioredoxin-1 (Trx1) has been shown to be increased in various somatic diseases and psychiatric disorders. However, when comparing the reported plasma levels of Trx1, a great inter-study variability, as well as variability in study outcomes of differences between patients and control subjects has been observed, ultimately limiting the possibility to make comparative analyses. Trx1 is a highly redox active protein prone to form various redox forms, e.g. dimers, oligomers or Trx1-protein complexes. We have recently shown that ELISA systems may vary in reactivity to various Trx1 redox forms. The primary aim of the present study was to develop an ELISA system with similar reactivity to various Trx1 redox forms. By evaluating a panel of novel monoclonal antibodies (mAbs), in various paired combinations, three ELISA systems were generated, with observed large variability in reactivity to various Trx1 redox forms. Importantly, an ELISA system (capture mAb MT17R6 and detection mAb MT13X3-biotin), was identified that displayed similar reactivity to oxidized and DTT reduced Trx1. The ELISA system (MT17R6/MT13X3-biotin), was subsequently used to analyze the level of Trx1 in plasma from patients (<18 years) with early onset psychosis disorders (EOP). However, no significant (p > 0.7) difference in plasma Trx1 levels between patients with EOP (n = 23) and healthy age matched controls (HC) (n = 20) were observed. Furthermore, reliable measurement was shown to be dependent on the establishment of platelet poor plasma samples, enabled by rigorous blood sample centrifugation and by efficient blocking of potentially interfering heterophilic antibodies. In conclusion, we report the design and characterization of a Trx1 ELISA system with similar reactivity to various Trx1 redox forms. Importantly, data indicated that generated ELISA systems show large variability in reactivity to various redox forms with ultimate impact on measured levels of Trx1. Overall, results from this study suggests that future studies may be strongly improved by the use of Trx1 ELISA systems with characterized specificity to various redox forms.

Mitochondrial dysfunction is associated with lipid metabolism disorder and upregulation of angiotensin-converting enzyme 2

Thymidine kinase 2 (TK2) deficiency in humans leads to a myopathic form of mitochondrial DNA (mtDNA) deficiency. Here we present a skeletal and cardiac muscle specific TK2 knockout mouse (mTk2 KO). The mice showed dilated hearts and markedly reduced adipose tissue during week 12 to 16. A severe decrease of mtDNA was found only in skeletal muscle and heart tissue in mTk2 KO mice. Expression analysis of key metabolic genes of 16 weeks knockout mice showed significant changes of genes involved in lipid metabolism, with different patterns in heart and skeletal muscle. Our study further suggests that lipoprotein lipase (LPL) from liver supports the metabolism when heart and skeletal muscle were impaired due to mitochondrial dysfunction. The angiotensin-converting enzyme 2 (ACE2), which is involved in glucose homeostasis, was also affected by mtDNA deficiency in our study. Interestingly, both the gene and protein expression of ACE2 were increased in cardiac tissue of mTk2 KO mice. Since ACE2 is a receptor for the SARS-CoV-2 virus, its regulation in relation to mitochondrial function may have important clinical implications.

Coordinated pyruvate kinase activity is crucial for metabolic adaptation and cell survival during mitochondrial dysfunction

Deoxyguanosine kinase (DGUOK) deficiency causes mtDNA depletion and mitochondrial dysfunction. We reported long survival of DGUOK knockout (Dguok-/-) mice despite low (<5%) mtDNA content in liver tissue. However, the molecular mechanisms enabling the extended survival remain unknown. Using transcriptomics, proteomics and metabolomics followed by in vitro assays, we aimed to identify the molecular pathways involved in the extended survival of the Dguok-/- mice. At the early stage, the serine synthesis and folate cycle were activated but declined later. Increased activity of the mitochondrial citric acid cycle (TCA cycle) and the urea cycle and degradation of branched chain amino acids were hallmarks of the extended lifespan in DGUOK deficiency. Furthermore, the increased synthesis of TCA cycle intermediates was supported by coordination of two pyruvate kinase genes, PKLR and PKM, indicating a central coordinating role of pyruvate kinases to support the long-term survival in mitochondrial dysfunction.

Severe mtDNA depletion and dependency on catabolic lipid metabolism in DGUOK knockout mice

Deoxyguanosine kinase (DGUOK) provides guanosine and adenosine nucleotides for mitochondrial DNA (mtDNA) replication, and its deficiency in humans leads to hepatocerebral mtDNA depletion syndrome or to isolated hepatic disease. There are poor treatment options for DGUOK deficiency and the aim of this study was to generate a model for further studies of the disease that could reveal novel treatment strategies. We report a Dguok-deficient mouse strain that, similar to humans, is most severely affected in the liver. The Dguok complete knockout mice (Dguok-/-) were born normal, but began to lose weight at week 6. A change of fur color from black to blueish grey started at week 16 and was complete at week 20. The movements and behavior were indistinguishable compared to wild-type (wt) mice. A decrease of mtDNA copy number occurred in multiple tissues, with the liver being the most severely affected. The mtDNA-encoded protein cytochrome c oxidase was much lower in Dguok-/- liver tissue than in the wt, whereas the expression of the nuclear-encoded succinate dehydrogenase complex subunit A was unaffected. Histopathology showed severe alterations and immunohistochemistry showed signs of both oxidative stress and regeneration in Dguok-/- liver. The subcutaneous fat layer was undetectable in Dguok-/-, which, in addition to gene expression analysis, indicated an altered lipid metabolism. We conclude that Dguok has a major role for the synthesis of deoxyribonucleotides for mtDNA replication particularly in the liver, similar to the human disorder. Our data also show a catabolic lipid metabolism in liver tissue of Dguok-/-.

Inhibition of the thioredoxin system by PX-12 (1-methylpropyl 2-imidazolyl disulfide) impedes HIV-1 infection in TZM-bl cells

Human immunodeficiency virus (HIV-1) entry is initiated by the binding between the viral envelope glycoprotein gp120 and the host receptor CD4, and followed by reduction of structural disulfides of gp120 and CD4. The host thioredoxin-1 (Trx1) efficiently reduces disulfides of gp120 and CD4 in vitro, and recently CD4-dependent HIV-1 entry was shown to be inhibited by anti-Trx1-antibodies, indicating a central role for Trx1. 1-methylpropyl-2-imidazolyl disulfide (PX-12) is a reversible inhibitor of the Trx1 system that may also cause a slow irreversible thioalkylation of Trx1. It was developed as an antitumor agent, however, the current study aimed to determine if it also has an anti-HIV-1 effect. We show that PX-12 has anti-HIV-1(III_B) activity in TZM-bl cells, in fact, no virus was detected inside the cells in the presence of 10 µM PX-12. Moreover, PX-12 inhibited the enzymatic activity of Trx1 and the Trx1-dependent disulfide reduction of gp120. Microtubule polymerization and formation of acetylated microtubules were also inhibited, activities shown to be required for HIV-1 life cycle propagation. In conclusion, our data strengthens the notion that the early steps of the HIV-1 life cycle depends on the Trx1 system and indicate that the Trx1 system may be a rational drug target for HIV-1 treatment.

Metformin downregulates the mitochondrial carrier SLC25A10 in a glucose dependent manner

Metformin, a commonly used agent in the treatment of type 2 diabetes, is also associated with reduced risk of cancer development and improvement in cancer survival. Although much is known about metformin, the mechanisms behind its anti-cancer properties are not fully understood. In this study we addressed the role of a mitochondrial transporter commonly upregulated in cancer cells, SLC25A10, for cell survival and metabolism in the presence of metformin. SLC25A10 is a carrier in the mitochondrial inner membrane that transports malate and succinate out of the mitochondria, in exchange of phosphate and sulfate. We show that metformin treatment results in decreased gene expression of the SLC25A10 carrier both in lung cancer A549 mock cells and A549 SLC25A10 knockdown (siSLC25A10) cells. The decrease was even more pronounced when cells were grown at low glucose concentrations. The expression levels of key enzymes in glucose metabolism showed slightly altered mean values for all genes tested in both control cells and siSLC25A10 cells upon metformin treatment. The gene expression of the metabolic regulator glutamic-oxaloacetic transaminase 1 decreased in wild type cells upon metformin treatment whereas there was a trend of increased expression in the siSLC25A10 cells upon metformin treatment. In addition, the gene expression of the cyclin-dependent kinase inhibitor 1A was markedly increased in the siSLC25A10 compared to control A549 cells, and with even larger increases in the presence of metformin and at low glucose concentration. Our data show that in siSLC25A10 cell lines, metformin significantly alters the SLC25A10 carrier at both mRNA and protein levels and can thereby affect the supply of nutrients and the metabolic state of cancer cells.

Inhibition of glutamate oxaloacetate transaminase 1 in cancer cell lines results in altered metabolism with increased dependency of glucose

BACKGROUND

Glutamate oxaloacetate transaminase 1 (GOT1) regulates cellular metabolism through coordinating the utilization of carbohydrates and amino acids to meet nutrient requirements. KRAS mutated cancer cells were recently shown to rely on GOT1 to support long-term cell proliferation. The aim of the present study was to address the role of GOT1 in the metabolic adaption of cancer cells.

METHODS

GOT1-null and knockdown cell lines were established through CRISPR/Cas9 and shRNA techniques. The growth properties, colony formation ability, autophagy and selected gene expression profiles were analysed. Glucose deprivation decreased the viability of the GOT1-null cells and rescue experiments were conducted with selected intermediates. The redox NADH/NAD⁺ homeostasis as well as lactate secretion were determined. GOT1 expression levels and correlation with survival rates were analysed in selected tumor databases.

RESULTS

Inhibition of GOT1 sensitized the cancer cells to glucose deprivation, which was partially counteracted by oxaloacetate and phosphoenol pyruvate, metabolic intermediates downstream of GOT1. Moreover, GOT1-null cells accumulated NADH and displayed a decreased ratio of NADH/NAD⁺ with nutrient depletion. The relevance of GOT1 as a potential target in cancer therapy was supported by a lung adenocarcinoma RNA-seq data set as well as the GEO:GSE database of metastatic melanoma where GOT1 expression was increased. High levels of GOT1 were further linked to poor survival as analysed by the GEPIA web tool, in thyroid and breast carcinoma and in lung adenocarcinoma.

CONCLUSIONS

Our study suggests an important role of GOT1 to coordinate the glycolytic and the oxidative phosphorylation pathways in KRAS mutated cancer cells. GOT1 is crucial to provide oxaloacetate at low glucose levels, likely to maintain the redox homeostasis. Our data suggest GOT1 as a possible target in cancer therapy.

The mitochondrial carrier SLC25A10 regulates cancer cell growth

Dysregulation of cell metabolism is critical for the growth properties of cancer cells. The purpose of this study was to understand the role of substrate transport across the mitochondrial membrane to sustain the metabolic shift and redox defense in cancer cells. Mitochondrial carrier SLC25A10 is up-regulated in a variety of tumors and is involved in regulating intracellular levels of reactive oxygen species. We show that knockdown of SLC25A10 in A549 cells changed the growth properties to a less malignant phenotype and casued increased glutamine dependency and sensitivity to oxidative stress. The metabolic alteration was linked to an energy metabolic shift from glycolysis to mitochondrial oxidative phosphorylation illustrated by increased expression of glutamate dehydrogenase, decreased expression of lactate dehydrogenase due to down-regulation of hypoxia inducible factor 1α. We identified effects on NADPH production linked to the growth changes observed in SLC25A10 knockdown cells, demonstrated by decreased NADPH production in cells deprived of glutamine. The contribution of SLC25A10 to reprogram cell metabolism and to regulate cell growth suggests SLC25A10 as a novel target for anti-cancer strategies.

The Cellular Thioredoxin-1/Thioredoxin Reductase-1 Driven Oxidoreduction Represents a Chemotherapeutic Target for HIV-1 Entry Inhibition

Background

The entry of HIV into its host cell is an interesting target for chemotherapeutic intervention in the life-cycle of the virus. During entry, reduction of disulfide bridges in the viral envelope glycoprotein gp120 by cellular oxidoreductases is crucial. The cellular thioredoxin reductase-1 plays an important role in this oxidoreduction process by recycling electrons to thioredoxin-1. Therefore, thioredoxin reductase-1 inhibitors may inhibit gp120 reduction during HIV-1 entry. In this present study, tellurium-based thioredoxin reductase-1 inhibitors were investigated as potential inhibitors of HIV entry.

Results

The organotellurium compounds inhibited HIV-1 and HIV-2 replication in cell culture at low micromolar concentrations by targeting an early event in the viral infection cycle. Time-of-drug-addition studies pointed to virus entry as the drug target, more specifically: the organotellurium compound TE-2 showed a profile similar or close to that of the fusion inhibitor enfuvirtide (T-20). Surface plasmon resonance-based interaction studies revealed that the compounds do not directly interact with the HIV envelope glycoproteins gp120 and gp41, nor with soluble CD4, but instead, dose-dependently bind to thioredoxin reductase-1. By inhibiting the thioredoxin-1/thioredoxin reductase-1-directed oxidoreduction of gp120, the organotellurium compounds prevent conformational changes in the viral glycoprotein which are necessary during viral entry.

Conclusion

Our findings revealed that thioredoxin-1/thioredoxin reductase-1 acts as a cellular target for the inhibition of HIV entry.

Long term expression of Drosophila melanogaster nucleoside kinase in thymidine kinase 2-deficient mice with no lethal effects caused by nucleotide pool imbalances

Mitochondrial DNA depletion caused by thymidine kinase 2 (TK2) deficiency can be compensated by a nucleoside kinase from Drosophila melanogaster (Dm-dNK) in mice. We show that transgene expression of Dm-dNK in Tk2 knock-out (Tk2(-/-)) mice extended the life span of Tk2(-/-) mice from 3 weeks to at least 20 months. The Dm-dNK(+/-)Tk2(-/-) mice maintained normal mitochondrial DNA levels throughout the observation time. A significant difference in total body weight due to the reduction of subcutaneous and visceral fat in the Dm-dNK(+/-)Tk2(-/-) mice was the only visible difference compared with control mice. This indicates an effect on fat metabolism mediated through residual Tk2 deficiency because Dm-dNK expression was low in both liver and fat tissues. Dm-dNK expression led to increased dNTP pools and an increase in the catabolism of purine and pyrimidine nucleotides but these alterations did not apparently affect the mice during the 20 months of observation. In conclusion, Dm-dNK expression in the cell nucleus expanded the total dNTP pools to levels required for efficient mitochondrial DNA synthesis, thereby compensated the Tk2 deficiency, during a normal life span of the mice. The Dm-dNK(+/-) mouse serves as a model for nucleoside gene or enzyme substitutions, nucleotide imbalances, and dNTP alterations in different tissues.

Methodological aspects of ELISA analysis of thioredoxin 1 in human plasma and cerebrospinal fluid

Thioredoxin-1 (Trx1) is a protein antioxidant involved in major cellular processes. Increased plasma levels of Trx1 have been associated with human diseases suggesting that Trx1 is a marker for oxidative stress with putative clinical use. However, the reported mean levels of Trx1 in the control cohorts vary a hundred-fold between studies (0.8-87 ng/ml), possibly due to methodological differences between the capture ELISA used in the different studies. The aim of this study was to investigate methodological aspects related to the ELISA measurement of Trx1. ELISAs utilizing different capture and detection combinations of antibodies to Trx1 and as well as recombinant human (rh) Trx1 standards from two sources were characterized. The different ELISAs were subsequently used to measure Trx1 in human plasma and cerebrospinal fluid samples (CSF) from healthy donors and from patients with various neurological diagnoses. The Trx1 standards differed in their content of monomeric and oligomeric Trx1, which affected the ELISAs composed of different antibody combinations. Thus, the levels of Trx1 determined in human plasma and CSF samples varied depending on the antibody used in the ELISAs and on the rhTrx1 standard. Furthermore, the relevance of preventing interference by heterophilic antibodies (HA) in human plasma and CSF was investigated. The addition of a HA blocking buffer to human samples drastically reduced the ELISA signals in many samples showing that HA are likely to cause false positive results unless they are blocked. In conclusion, the study shows that the design of a Trx1 ELISA in regards to antibodies and standards used has an impact on the measured Trx1 levels. Importantly, analyses of human plasma and CSF without preventing HA interference may obscure the obtained data. Overall, the results of this study are crucial for the improvement of future studies on the association of Trx1 levels with various diseases.

Thymidine kinase 2 deficiency-induced mtDNA depletion in mouse liver leads to defect β-oxidation

Thymidine kinase 2 (TK2) deficiency in humans causes mitochondrial DNA (mtDNA) depletion syndrome. To study the molecular mechanisms underlying the disease and search for treatment options, we previously generated and described a TK2 deficient mouse strain (TK2^−/−) that progressively loses its mtDNA. The TK2^−/− mouse model displays symptoms similar to humans harboring TK2 deficient infantile fatal encephalomyopathy. Here, we have studied the TK2^−/− mouse model to clarify the pathological role of progressive mtDNA depletion in liver for the severe outcome of TK2 deficiency. We observed that a gradual depletion of mtDNA in the liver of the TK2^−/− mice was accompanied by increasingly hypertrophic mitochondria and accumulation of fat vesicles in the liver cells. The levels of cholesterol and nonesterified fatty acids were elevated and there was accumulation of long chain acylcarnitines in plasma of the TK2^−/− mice. In mice with hepatic mtDNA levels below 20%, the blood sugar and the ketone levels dropped. These mice also exhibited reduced mitochondrial β-oxidation due to decreased transport of long chain acylcarnitines into the mitochondria. The gradual loss of mtDNA in the liver of the TK2^−/− mice causes impaired mitochondrial function that leads to defect β-oxidation and, as a result, insufficient production of ketone bodies and glucose. This study provides insight into the mechanism of encephalomyopathy caused by TK2 deficiency-induced mtDNA depletion that may be used to explore novel therapeutic strategies.

Is trichloroacetic acid an insufficient sample quencher of redox reactions?

The global protein thiol pool has been reported to play a major role in the defense against oxidative stress as a redox buffer similar to glutathione. The present study uses a novel method to visualize cellular changes of the global protein thiol pool in response to induced oxidative stress. Unexpectedly, the results showed an uneven distribution of protein thiols in resting cells with no apparent change in their level or distribution in response to diamide as has been reported previously. Further analysis revealed that thiol pool oxidation is artificially high due to insufficient activity of the widely used sample quencher trichloroacetic acid (TCA). This suggests that previously published articles based on TCA as a quencher should be interpreted with caution as TCA could have caused similar artifacts. Overall, the results presented here question the major role for the global thiol pool in the defense against oxidative stress. Instead our hypothesis is that the fraction of proteins involved in response to oxidative stress is much smaller than previously anticipated in support of a fine-tuned cell signaling by redox regulation.

Transgene expression of Drosophila melanogaster nucleoside kinase reverses mitochondrial thymidine kinase 2 deficiency

A strategy to reverse the symptoms of thymidine kinase 2 (TK2) deficiency in a mouse model was investigated. The nucleoside kinase from Drosophila melanogaster (Dm-dNK) was expressed in TK2-deficient mice that have been shown to present with a severe phenotype caused by mitochondrial DNA depletion. The Dm-dNK(+/-) transgenic mice were shown to be able to rescue the TK2-deficient mice. The Dm-dNK(+/-)TK2(-/-) mice were normal as judged by growth and behavior during the observation time of 6 months. The Dm-dNK-expressing mice showed a substantial increase in thymidine-phosphorylating activity in investigated tissues. The Dm-dNK expression also resulted in highly elevated dTTP pools. The dTTP pool alterations did not cause specific mitochondrial DNA mutations or deletions when 6-month-old mice were analyzed. The mitochondrial DNA was also detected at normal levels. In conclusion, the Dm-dNK(+/-)TK2(-/-) mouse model illustrates how dTMP synthesized in the cell nucleus can compensate for loss of intramitochondrial dTMP synthesis in differentiated tissue. The data presented open new possibilities to treat the severe symptoms of TK2 deficiency.

Acute cytotoxicity of arabinofuranosyl nucleoside analogs is not dependent on mitochondrial DNA

The nucleoside analogs 9-beta-D-arabinofuranosylguanine (araG) and 1-beta-d-arabinofuranosylthymine (araT) are substrates of mitochondrial nucleoside kinases and have previously been shown to be predominantly incorporated into mtDNA of cells, but the pharmacological importance of their accumulation in mtDNA is not known. Here, we examined the role of mtDNA in the response to araG, araT and other anti-cancer and anti-viral agents in a MOLT-4 wild-type (wt) T-lymphoblastoid cell line and its petite mutant MOLT-4 rho(0) cells (lacking mtDNA). The mRNA levels and activities of deoxyguanosine kinase (dGK), deoxycytidine kinase (dCK), thymidine kinase 1 (TK1) and thymidine kinase 2 (TK2) were determined in the two cell lines. Compared to that in the MOLT-4 wt cells the mRNA level of the constitutively expressed TK2 was higher (p<0.01) in the rho(0) cells, whereas the TK1 mRNA level was lower (p<0.05). The enzyme activity of the S-phase restricted TK1 was also lower (p<0.05) in the MOLT-4 rho(0) cells, whereas the activities of dGK, dCK and TK2 were similar in MOLT-4 wt and rho(0) cell lines. The sensitivities to different cytotoxic nucleoside analogs were determined and compared between the two cell lines. Interestingly, we found that the acute cytotoxicity of araG, araT and other anti-viral and anti-cancer agents is independent of the presence of mtDNA in MOLT-4 T-lymphoblastoid cells.

Nelarabine: a new purine analog in the treatment of hematologic malignancies

GW506U78 or nelarabine (Glaxo-SmithKline) is a nucleoside analog that is rapidly converted by cells of lymphoid lineage to its corresponding arabinosylguanine nucleotide triphosphate (araGTP). The triphosphate form of araG acts as a substrate for DNA polymerases and araG gets incorporated into the DNA, resulting in inhibition of DNA synthesis and subsequent cytotoxicity. It has been shown that nelarabine has activity as a single agent in patients with T-cell malignancies that have relapsed or are refractory to other therapy. The ongoing research on nelarabine has earned fast-track status from the U.S. Food and Drug Administration (FDA) for treatment of patients with T-cell acute lymphoblastic leukemia and lymphoblastic lymphoma who have not responded to or whose disease has progressed during treatment with at least two standard regimens. It is likely that nelarabine will be a useful drug in the treatment of leukemic diseases in the future and therefore nelarabine is an interesting drug to study further. Here we present an overview of what is known about the mechanism of action of nelarabine and its status in clinical trials.

Human mitochondrial pyrophosphatase: cDNA cloning and analysis of the gene in patients with mtDNA depletion syndromes

Pyrophosphatases (PPases) catalyze the hydrolysis of inorganic pyrophosphate generated in several cellular enzymatic reactions. A novel human pyrophosphatase cDNA encoding a 334-amino-acid protein approximately 60% identical to the previously identified human cytosolic PPase was cloned and characterized. The novel enzyme, named PPase-2, was enzymatically active and catalyzed hydrolysis of pyrophosphate at a rate similar to that of the previously identified PPase-1. A functional mitochondrial import signal sequence was identified in the N-terminus of PPase-2, which targeted the enzyme to the mitochondrial matrix. The human pyrophosphatase 2 gene (PPase-2) was mapped to chromosome 4q25 and the 1.4-kb mRNA was ubiquitously expressed in human tissues, with highest levels in muscle, liver, and kidney. The yeast homologue of the mitochondrial PPase-2 is required for mitochondrial DNA maintenance and yeast cells lacking the enzyme exhibit mitochondrial DNA depletion. We sequenced the PPA2 gene in 13 patients with mitochondrial DNA depletion syndromes (MDS) of unknown cause to determine if mutations in the PPA2 gene of these patients were associated with this disease. No pathogenic mutations were identified in the PPA2 gene of these patients and we found no evidence that PPA2 gene mutations are a common cause of MDS in humans.

5-Fluoro-2'-deoxyuridine has effects on mitochondria in CEM T-lymphoblast cells

Fluoropyrimidines are useful anticancer agents and the compound 5-fluoro-2'-deoxyuridine (FdUrd) plays an important role in chemotherapy of colon cancers. Several nucleoside analogs, such as 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC), can be incorporated into and cause depletion of mitochondrial DNA (mtDNA). These drugs are known to cause mitochondrial toxicity after prolonged treatment in patients. In this study we demonstrate that FdUrd reduces the mtDNA content and the expression level of the mtDNA encoded cytochrome c oxidase (COX II) in a CEM T-lymphoblastic cell line.

The Drosophila melanogaster UMP-CMP kinase cDNA encodes an N-terminal mitochondrial import signal

Drosophila melanogaster cells express a multi-substrate deoxyribonucleoside kinase that phosphorylates both purine and pyrimidine deoxyribonucleosides. The subsequent phosphorylation step is catalyzed by nucleoside monophosphate kinases. We have cloned and characterized the D. melanogaster UMP-CMP kinase (Dm.UMP-CMP kinase) to further study the nucleotide metabolizing enzymes in these cells. The kinase, encoded by the dak1 gene, was approximately 60% similar to the human UMP-CMP kinase and predominantly phosphorylated CMP, dCMP, and UMP. Expression analysis showed that the Dm.UMP-CMP kinase mRNA was constitutively expressed throughout the Drosophila development. The open-reading frame of the Dm.UMP-CMP kinase cDNA was extended in the 5'-region compared to UMP-CMP kinases of other species. The extended region encoded an N-terminal sequence with properties characteristic of a mitochondrial import signal. Expression of the enzyme in fusion with the green fluorescent protein verified that the N-terminal signal targeted the enzyme to mitochondria. This is the first time a mitochondrial pyrimidine nucleoside monophosphate kinase has been cloned from any organism and we discuss the implication of this finding for deoxyribonucleoside salvage in both Drosophila and other organisms.

Effects of 9-beta-D-arabinofuranosylguanine on mitochondria in CEM T-lymphoblast leukemia cells

The nucleoside analog 9-beta-D-arabinofuranosylguanine (araG) is presently evaluated in clinical trials for therapy of T-cell lymphoid malignancies. AraG is a substrate for the mitochondrial deoxyguanosine kinase and we have recently shown that araG is predominantly incorporated into mitochondrial DNA (mtDNA). In this study we have investigated the effects of araG on mtDNA content and function. Although araG was incorporated into mtDNA, no decrease in mtDNA levels or effect on the expression of the mtDNA encoded cytochrome c oxidase was detected. Cells depleted of mtDNA were resistant to araG, but the mechanism of resistance was not specific for nucleoside analogs incorporated into mtDNA. Furthermore, the results suggest that the cells need to pass the S-phase in order for araG to induce caspase-dependent apoptosis. In summary, our findings suggest that the incorporation of araG into mtDNA does not cause the acute cytotoxicity of araG.

Dual mechanisms of 9-beta-D-arabinofuranosylguanine resistance in CEM T-lymphoblast leukemia cells

The guanine nucleoside analog araG is selectively toxic to T-lymphoblasts and has recently shown promise in treatment of lymphoid malignancies of T-cell origin. The molecular mechanism of this tissue-selective cytotoxicity is, however, yet unclear. AraG is phosphorylated, and thereby pharmacologically activated, by the mitochondrial deoxguanosine kinase and the cytosolic/nuclear deoxycytidine kinase. We have recently shown that araG is predominantly incorporated into mitochondrial DNA of cancer cell lines, which suggests a role of mitochondria as its pharmacological target. In the present study, we have generated araG-resistant CEM T-lymphoblast cell lines and show that araG resistance may occur by two separate molecular mechanisms that can occur sequentially. The first mechanism is associated with a decrease of araG incorporation into mitochondrial DNA, and the second event is associated with loss of dCK activity.