Reverse transcriptase in leukocytes of leukemic patients in remission

Selected Milestones in Antiviral Drug Development

This review article will describe the (wide) variety of approaches that I envisaged to develop a specific therapy for viral infections: (i) interferon and its inducers, (ii) HSV, VZV and CMV inhibitors, (iii) NRTIs (nucleoside reverse transcriptase inhibitors), NtRTIs (nucleotide reverse transcriptase inhibitors) and NNRTIs (non-nucleoside reverse transcriptase inhibitors) as HIV inhibitors, (iv) NtRTIs as HBV inhibitors, and finally, (v) the transition of an HIV inhibitor to a stem cell mobilizer, as exemplified by AMD-3100 (Mozobil®).

Prognostic effect of gender on outcome of treatment for adults with acute myeloid leukaemia

There are conflicting reports in the literature suggesting that one gender or the other has a better survival with acute myeloid leukaemia (AML). The present study was done in an attempt to resolve the issue. The effect of gender was examined on 3546 newly diagnosed patients with AML, including 548 patients with acute promyelocytic leukaemia (APL) enrolled in 10 multi-institutional treatment studies from March 1984 to November 2008. Kaplan-Meier estimates were used to estimate event-time distributions for survival and multivariate models were used to examine the gender effect after adjusting for multiple risk factors. P values were based on two-sided tests. Non-APL female patients had a significantly better overall (OS) but not disease-free survival (DFS) than males, irrespective of age, initial white blood cell count, or dose of daunorubicin. No differences were observed for obese or FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD)-positive patients. Female patients with APL had a significantly better OS and DFS than male patients with APL, and differences in survival were greater for patients with t(15;17) + other cytogenetic abnormalities compared with those with t(15;17) only. Gender is an independent prognostic variable in patients with AML. Whether these survival differences are due to hormonal, genetic or pharmacokinetic differences between the sexes or differential toxin exposure such as smoking is unknown. However, the former seems less likely as patient age did not influence the survival advantage for female patients.

Human endogenous retrovirus (HERV-K) particles in megakaryocytes cultured from essential thrombocythemia peripheral blood stem cells

OBJECTIVE

The aim of this study was to determine the extent of human endogenous retrovirus (HERV) gene translation in megakaryocytes cultured from peripheral blood stem cells of patients with essential thrombocythemia previously reported with platelet-associated HERV sequences and reverse transcriptase activity.

MATERIALS AND METHODS

Terminally differentiated megakaryocytes derived from circulating stem cells in serum-free medium supplemented with stem cell factor and thrombopoietin were processed for electron microscopic immunostaining using a monoclonal antibody against the gag protein of HERV-K10 and an electron dense gold-labeled secondary antibody.

RESULTS

We found that HERV-K gag protein was detected as clusters in the cytoplasm as well as associated with viral particles budding from the cell membrane and into intracellular vacuoles in megakaryocytes from two patients with essential thrombocythemia. None of these structures was observed in megakaryocytes from a normal control or from a patient with chronic myelocytic leukemia.

CONCLUSION

This is the first evidence of HERV-K protein synthesis (gene translation) in human tissue other than seminomas, placenta, or fetal tissue. Translation of the HERV-K gag gene with subsequent packaging of the protein product into viral particles adds a new and important dimension to future studies on the role of HERVs in the myeloproliferative diseases.

Characterization of conditions for the activation of endogenous guinea pig retrovirus in cultured cells by 5-bromo-2'-deoxyuridine

Human endogenous retroviral sequences recently have been shown to be associated with breast cancer and some leukemias. These retroviral sequences have similarities to an endogenous retrovirus expressed in guinea pigs. The conditions for activation of this guinea pig retrovirus (GPRV) in cultured guinea pig embryo (GPE) cells using 5-bromo-2'-deoxyuridine (BrdU) was investigated. These studies employed the reverse transcriptase activity (RT) assay and electron microscopy (EM), in conjunction with Northern blot analysis that utilized a 2.6 kb GPRV-specific cDNA probe. Contrary to published studies, dexamethasone at concentrations ranging from 10(-8) to 10(-5) M appeared to play a minimal role in enhancing the production of GPRV. Following a 6 hr incubation with BrdU, GPRV mRNA was present in cultured GPE cells. Extracellular virion release was also observed by EM 12 hr later, although RT activity was not detected. All three methods detected viral expression at 48 hr after the addition of the drug. Additionally, after 6 hr exposure to BrdU, detectable RT and mRNA levels were maintained through 44 days after the removal of BrdU in a stationary culture condition and through 31 days in cultures that were subcultured weekly in media not containing BrdU. Low levels of extracellular viruses were detected in these cultures by electron microscopy through 49 days. Therefore, after only a 6 hr exposure to BrdU was extracellular GPRV detected 12 hr after drug removal and virus production continued for up to 49 days. This study provides information about an animal endogenous retroviral system that may be used as a model for the study of human endogenous retroviruses.

Expression of human endogenous retrovirus (HERV-K) in chronic myeloid leukemia

We have previously demonstrated the presence of a reverse transcriptase-like enzyme in retroviral particles from patients with essential thrombocythemia, polycythemia vera, and chronic myelogenous leukemia. It was subsequently shown that the human genome contains 50 copies of HERV-K. HERV-K is a human endogenous class I retroviral element that contains gag, pol, and env open reading frames. Using both reverse transcriptase-polymerase chain reaction and ribonuclease protection assays, it is demonstrated that the HERV-K pol is expressed in human blood leukocytes. The data indicates that this expression is restricted in CML white cells and is the result of gene regulation.

Implications of retroviral and oncogene activity in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a stem cell disease which, on a clinical level, progresses from the release from growth control of normally differentiated cells (a preleukemic state) to an acute leukemia. On a molecular level, the evolution of CML to acute leukemia is a multistep process. We propose that an early step, at the stem cell level, is acquisition of the ability for gene movement, which allows subsequent submicroscopic and chromosomal rearrangements that cause changes in the growth characteristics and regulation of the stem cell. A specific platelet DNA polymerase (PDP - reverse transcriptase) may play a role in gene movement. The characteristic reciprocal translocation of chromosomes #9 and #22, causing the activation of the c-abl oncogene, appears to be responsible for the uncontrolled cellular growth. Yet, other growth factors (e.g., platelet derived growth factor) and activated oncogenes (e.g., c-sis) must be responsible for the stimulation, progression, and variability seen during the course of the disease. Because CML is a progressive disease with clinically definable stages, CML appears to be a model system for the study of the molecular basis of the progression of preleukemia to leukemia specifically, and preneoplasia to aggressive neoplasia in general.

Platelet DNA polymerase levels in CML: implications for oncogenesis

Partially purified platelet DNA polymerase (PDP) was able to synthesize DNA transcripts of platelet polyadenylated RNA. PDP was elevated in the earliest stages of CML and PV. In PV, successful chemotherapy resulted in rapid return of PDP to normal levels while in CML this was not the case. An hypothesis is presented proposing that PDP contributes to oncogenesis by regulating the expression of oncogenes.

2' and 3' ribonucleoside monophosphate in leukocytes of acute myeloid leukemia: markers for early diagnosis of relapse

Levels of 2' and 3' purine and pyrimidine ribonucleoside monophosphates (2'-, 3'-NMP) in leukocytes from blood and/or bone marrow were measured in three adult patients with acute non-lymphoblastic leukemias. The measurements of 2'-, 3'-NMP were made by high-performance liquid chromatography (HPLC) at various times in the course of the disease. Complete remission (CR) was obtained for all three patients but two of these have since died after relapsing at 8 and 9 months, respectively. The third patient remains in CR at 1 1/2 year. The levels of 2'-, 3'-NMP in the leukocytes of the patient remaining in remission have not changed since the beginning of his remission. However, in the patients who relapsed 2'- and 3'-NMP levels increased first in bone marrow than in blood leukocytes. These increases occurred about 3 months before the relapse was detected by morphological criteria. These data suggest that 2'-, 3'-NMP measurements may have a prognostic value if used to monitor patients with acute myeloid leukemia in CR.

Quantitation of RNA-dependent platelet DNA polymerase in patients with myeloproliferative disorders

Platelets from 28 patients with the myeloproliferative diseases (MPD) polycythaemia vera (9), essential thrombocythaemia (6), myelofibrosis with myeloid metaplasia (5) and chronic myelogenous leukaemia (8) were examined for an RNA-dependent DNA polymerase activity using standardized conditions permitting highly reproducible quantitation. Low levels of activity were detected in platelets of normal individuals, but platelets of nearly all MPD patients (25/28) possessed higher levels. The polymerase activity correlated with diagnosis (P = 0.001) and did not correlate with platelet counts (P greater than 0.2). Quantitation of this RNA-dependent DNA polymerase activity may be a useful parameter in the diagnosis of myeloproliferative disorders.

Early diagnosis of relapse in acute myeloblastic leukemia: Serologic detection of leukemia-associated antigens in human marrow

We tested serial bone-marrow samples from 47 adults with acute myeloblastic leukemia in remission for reactivity with heteroantiserums to leukemia-associated antigens, to determine whether imminent relapse could be detected in patients with acute leukemia. Of 26 patients who relapsed by standard morphologic criteria, 21 had increased immunoreactivity of bone marrow for one to six months (mean, 3.7 months) before relapse. High concordance was observed between a positive test and relapse during the period of study (chi-square = 27.53, P less than 0.001). The median time to relapse after a positive test was four months, as compared with the median remission duration of 19 months for the whole group (P less than 0.02, Peto's log-rank analysis). Serologic detection of leukemia-associated antigens in marrow may be a reliable indicator of imminent relapse in acute myeloblastic leukemia.

Persistence of inhibitory activity against normal bone-marrow cells during remission of acute leukemia

Bone-marrow cells from patients with acute leukemia in remission were tested for their capacity to produce a substance (leukemia-associated inhibitory activity, LIA) that inhibits the formation of granulocyte and macrophage colonies in cultures of normal, but not of leukemic, bone marrow. LIA was detected in extracts of whole marrow in only eight of 83 patients in remission. However, extracts of slowly sedimenting cells, separated by velocity sedimentation from the marrows of eight patients in remission whose whole marrow had produced no LIA, produced inhibitory material in all cases. Extracts of the more rapidly sedimenting cells from these marrows contained an inactivator of LIA. Three of six patients in remission whose unfractionated marrow was unresponsive to LIA had a subpopulation of colony-forming cells that was sensitive to the inhibitor. These observations suggest that certain cellular functions dot not completely return to normal during remission of acute leukemia.

On the presence of reverse transcriptase in myelo- and lymphoproliferative disorders

Buffy coats from 31 patients with a diagnosis of leukemia and 16 normal donors were tested for the presence of a viral-like reverse transcriptase. Eighty-five percent of fresh leukemic buffy coats were positive. Also tested were spleens from 16 patients with hematological disorders and 5 spleens from patients without history of hematological malignancy. The 5 normal spleens were negative. Also negative were 4 spleens from patients with Hairy cell leukemia. From the remaining 12 spleens 7 were positive. Reverse transcriptase measurements can be used to distinguish leukemic from normal buffy coats.

Dissimilar courses of twins with leukemia

Twin girls, genetically identical, probably experienced different leukemogenic events and presented with acute lymphocytic leukemia 6 years apart. Their clinical presentations were similar, but they received significantly different therapy. The first twin died 34 months after diagnosis following multiple remissions and relapses, having received single-drug maintenance. The second twin remains free of apparent disease 60 months after diagnosis, following vincristine and prednisone induction, 6-mercaptopurine maintenance, methotrexate and prednisone reinforcement, and central nervous system treatment of occult disease. Their dissimilar clinical courses may have been due to different leukemogenic events and/or markedly different therapeutic programs.