Highly efficient elimination of Philadelphia leukemic cells by exposure to bcr/abl antisense oligodeoxynucleotides combined with mafosfamide

A Gene Transfer-Positive Cell Sorting System Utilizing Membrane-Anchoring Affinity Tag

Gene delivery efficiency is an essential limit factor in gene study and gene therapy, especially for cells that are hard for gene transfer. Here we develop an affinity cell sorting system that allows efficient enrichment of gene transfer-positive cells. The system expresses an enhanced green fluorescent protein (EGFP) fused with an N-terminal high-affinity Twin-Strep-Tag (TST) that will be anchored to the cell membrane at the out-surface through a glycosylphosphatidylinositol (GPI) membrane-anchoring structure. The EGFP permits microscopy and flow cytometry analysis of the gene transfer-positive cells, and the TST tag at the N terminal of EGFP allows efficient affinity sorting of the positive cells using Strep-Tactin magnetic beads. The cell sorting system enables efficient isolation of gene transfer-positive cells in a simple, convenient, and fast manner. Cell sorting on transfected K-562 cells resulted in a final positive cell percentage of up to 95.0% with a positive cell enrichment fold of 5.8 times. The applications in gene overexpression experiments could dramatically increase the gene overexpression fold from 10 times to 58 times, and in shRNA gene knockdown experiments, cell sorting increased the gene knockdown efficiency from 12% to 53%. In addition, cell sorting in CRISPR/Cas9 genome editing experiments allowed more significant gene modification, with an editing percentage increasing from 20% to 79%. The gene transfer-positive cell sorting system holds great potential for all gene transfer studies, especially on those hard-to-transfect cells.

Use of ribozymes and antisense oligodeoxynucleotides to investigate mechanisms of drug resistance

Chemotherapy can cure a number of human cancers but resistance (either intrinsic or acquired) remains a significant problem in many patients and in many types of solid tumour. Combination chemotherapy (using drugs with different cellular targets/mechanisms) was introduced in order to kill cells which had developed resistance to a specific drug, and to allow delivery of a greater total dose of anti-cancer chemicals by combining drugs with different side-effects (Pratt et al., 1994). Nearly all anti-cancer drugs kill tumour cells by activating an endogenous bio-chemical pathway for cell suicide, known as programmed cell death or apoptosis.

Chronic myelogenous leukemia: elements of conventional chemotherapy and an overview of autografting in the treatment of the chronic phase

Chronic myelogenous leukemia (CML) consists of a clonal malignancy that arises from a pluripotent hematopoietic stem call. In most cases, neoplastic cells are characterized by the formation of a shortened chromosome 22 called the Philadelphia chromosome. It results from a reciprocal translocation between long arms of chromosomes 9 and 22. A rearranged gene (bcr-abl) is the consequence of this translocation, and it may be considered as the first step toward leukemic transformation. Conventional chemotherapy of CML in the chronic phase is unable to suppress the Ph+ leukemic clone. The treatment with the IFNalpha may induce an overall cytogenetic response rate of 40-50% of patients. Autografting for patients with CML in chronic phase may induce a 53% overall cytogenetic response rate with a duration of disease-free time and survival from the autograft ranging, respectively, from 4 to 24 mo and from 8 to 40 mo.

New models to investigate mechanisms of disease genesis from primitive BCR-ABL(+) hematopoietic cells

Three years ago we described a novel autocrine IL-3/G-CSF mechanism active in the leukemic CD34(+) cells from chronic myeloid leukemia (CML) patients in chronic phase (PNAS 96: 12804-12809, [1999]). We also showed that exposure of the most primitive CD34(+) cells from normal human bone marrow to excess IL-3 stimulates not only the division of these cells but also their differentiation. In contrast, both IL-3 and G-CSF cause an expansion of the more mature types of normal CD34(+) progenitors. These findings suggested that the autocrine IL-3/G-CSF mechanism active in CML stem cells can compromise their self-renewal in spite of increasing their proliferative activity, which, in turn, might explain the paradoxically slow rate of expansion of this compartment over time in patients with latent disease. To investigate this hypothesis, we have begun to characterize the numbers and types of cells generated from chronic phase CML patients' cells transplanted into adult immunodeficient mice or fetal sheep, and also from transplants of primitive murine and human hematopoietic cells transduced with a retroviral BCR-ABL vector. Our findings to date using these models reinforce the importance of the autocrine IL-3/G-CSF mechanism in the development of CML. BCR-ABL appears to directly activate IL-3 and G-CSF production in primitive hematopoietic cells and this is important to their transplantable leukemogenic activity. However, the development in vivo of an overt leukemia from primitive BCR-ABL(+) hematopoietic cells can be very delayed. These models thus offer new opportunities for analyzing the molecular events that underlie the pathogenesis of human CML and the future testing of new therapeutic approaches.

BCR/ABL regulates response to DNA damage: the role in resistance to genotoxic treatment and in genomic instability

BCR/ABL regulates cell proliferation, apoptosis, differentiation and adhesion. In addition, BCR/ABL can induce resistance to cytostatic drugs and irradiation by modulation of DNA repair mechanisms, cell cycle checkpoints and Bcl-2 protein family members. Upon DNA damage BCR/ABL not only enhances reparation of DNA lesions (e.g. homologous recombination repair), but also prolongs activation of cell cycle checkpoints (e.g. G2/M) providing more time for repair of otherwise lethal lesions. Moreover, by modification of anti-apoptotic members of the Bcl-2 family (e.g. upregulation of Bcl-x(L)) BCR/ABL provides a cytoplasmic 'umbrella' protecting mitochondria from the 'rain' of apoptotic signals coming from the damaged DNA in the nucleus, thus preventing release of cytochrome c and activation of caspases. The unrepaired and/or aberrantly repaired (but not lethal) DNA lesions resulting from spontaneous and/or drug-induced damage can accumulate in BCR/ABL-transformed cells leading to genomic instability and malignant progression of the disease. Inhibition of BCR/ABL kinase activity by STI571 (Gleevec, imatinib mesylate) reverses drug resistance and, in combination with standard chemotherapeutics can exert strong anti-leukemia effect.

Phosphatidylinositol-3 kinase inhibitors enhance the anti-leukemia effect of STI571

BCR/ABL fusion tyrosine kinase is responsible for the initiation and maintenance of the Philadelphia chromosome (Ph(1))-positive chronic myelogenous leukemia (CML) and a cohort of acute lymphocytic leukemias (ALL). STI571 (Gleevec), a novel anti-leukemia drug targeting BCR/ABL kinase can induce remissions of the Ph(1)-positive leukemias. STI571 was recently combined with the standard cytostatic drugs to achieve better therapeutic results and to overcome emerging drug resistance mechanisms. We decided to search for a more specific partner compound for STI571. Our previous studies showed that a signaling protein phosphatidylinositol-3 kinase (PI-3k) is essential for the growth of CML cells, but not of normal hematopoietic cells (Blood, 86:726,1995). Therefore the anti- Ph(1)-leukemia effect of the combination of BCR/ABL kinase inhibitor STI571 and PI-3k inhibitor wortmannin (WT) or LY294002 (LY) was tested. We showed that STI571+WT exerted a synergistic effect against the Ph(1)-positive cell lines, but did not affect the growth of Ph(1)-negative cell line. Moreover, the combinations of STI571+WT or STI571+LY were effective in the inhibition of clonogenic growth of CML-chronic phase and CML-blast crisis patient cells, while sparing normal bone marrow cells. Single colony RT-PCR assay showed that colonies arising from the mixture of CML cells and normal bone marrow cells after treatment with STI571+WT were selectively depleted of BCR/ABL-positive cells. Biochemical analysis of the CML cells after the treatment revealed that combination of STI571+WT caused a more pronounced activation of caspase-3 and induced massive apoptosis, in comparison to STI571 and WT alone. In conclusion, combination of STI571+WT or STI571+LY may represent a novel approach against the Ph(1)-positive leukemias.

Oncogenic tyrosine kinases and the DNA-damage response

Oncogenic tyrosine kinases (OTKs) are involved in the induction of many types of tumour, including haematological malignancies and cancers of the breast, prostate, colon and lung. Neoplastic cells that express OTKs are usually resistant to apoptosis that is induced by DNA-damaging agents, such as cytostatic drugs and irradiation, and they display genomic instability. So, what are the mechanisms involved, and what is the potential for overcoming OTK-mediated resistance in the clinic?

Molecular measurement of minimal residual disease in Philadelphia-positive acute lymphoblastic leukaemia

The Philadelphia chromosome (Ph) is found in approximately 5-25% of acute lymphoblastic leukaemia (ALL) cases and is the harbinger of a poor outcome. Polymerase chain reaction (PCR) assays can detect leukaemia-specific genetic lesions down to a sensitivity approaching one leukaemia cell in a background of a million normal cells. In Ph(+) ALL, the unique BCR-ABL translocation is thus a specific target for the detection of minimal residual disease (MRD). After chemotherapy or transplantation the detection of residual BCR-ABL transcripts is associated with a high risk of subsequent relapse. With the advent of novel therapeutics that target the structure and function of BCR-ABL, the detection of MRD may allow for targeted therapy that could abort a potential relapse.

BCR-ABL as a target for novel therapeutic interventions

The BCR-ABL oncogene is the result of a reciprocal translocation between the long arms of chromosome 9 and 22 t(9; 22). There is good experimental evidence demonstrating that BCR-ABL is the single causative abnormality in chronic myeloid leukaemia (CML), making it a unique model for the development of molecular targets. In addition to CML, BCR-ABL transcripts can be found in a minority of acute lymphoblastic leukaemias and very rarely in acute myeloid leukaemia (AML). Elucidating the molecular mechanisms and downstream pathways of BCR-ABL has led to the design of several novel therapeutic approaches. In this review, molecular targeting of BCR-ABL will be discussed based on the inhibition of protein tyrosine kinase activity, antisense strategies and immunomodulation.

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

Philadelphia chromosome-positive acute lymphocytic leukemia

On a molecular and cellular level, Ph+ ALL seems to be a heterogeneous disease. Unfortunately, the unifying theme of Ph positivity is the poor outcome associated with its presence. Further characterization of molecular subtypes of Ph+ ALL may in the future distinguish those few patients with a potentially good outcome from the majority who face inevitable relapse. Also, novel targeted biologic therapy especially in combination with aggressive, early chemotherapy, may soon be able to temper the disease. Most patients who obtain a remission would be best served by transplantation during remission. For those without a donor, following the disease by PCR-based techniques may detect early relapse. For relapsed patients without the option of transplantation, investigative studies are appropriate.

Progressive changes in the leukemogenic signaling in BCR/ABL-transformed cells

Our previous study indicated that BCR/ABL SH2 domain and BCR/ABL SH3 domain+SH2 domain complex are required for immediate activation of the phosphatidylinositol-3 kinase PI-3k)--> Akt serine/threonine kinase pathway and of the signal transducer and activator of transcription 5 (STAT5), respectively, in hematopoietic cells. We show here that the defect in activation of PI-3k/Akt by BCR/ABL DeltaSH2 mutant (SH2 domain deleted) and of STAT5 by BCR/ABL DeltaSH3+DeltaSH2 mutant (SH3 and SH2 domains deleted) is not permanent and both Akt and STAT5 could be 're-activated' by in vitro culture. This phenomenon was responsible for increased resistance to apoptosis, growth factor-independent proliferation and leukemogenesis in SCID mice. Incubation of cells with BCR/ABL tyrosine kinase inhibitor STI571 abrogated the 're-activation' of Akt or STAT5 by BCR/ABL SH3+SH2 mutants in some clones, in the others Akt and STAT5 activation became independent on BCR/ABL kinase activity. The immediate upstream activators of Akt and STAT5 such as PI-3k and Jak-2 were also activated. In addition, the common beta subunit of IL-3/IL-5/GM-CSF receptor was tyrosine phosphorylated in the clones in which 're-activation' was dependent on the BCR/ABL kinase activity. These results suggested that 're-activation' of Akt and STAT5, in the absence of functional BCR/ABL SH3+SH2 domains, may be achieved by two different mechanisms: (i) BCR/ABL kinase-dependent activation of alternative pathway(s) and (ii) additional genetic changes stimulating Akt and STAT5 independently of BCR/ABL. Oncogene (2000) 19, 4117 - 4124

The role of FAS-mediated apoptosis in chronic myelogenous leukemia

Clinical observation and laboratory evidence suggest that immune mechanisms play an important role in the natural control of evolution of the Ph+ clone in chronic phase as well as during progression of chronic myelogenous leukemia (CML). The understanding of these mechanisms could facilitate development of innovative therapeutic approaches. Due to bcr-abl translocation, CML cells carry an intrinsic resistance to apoptotic signals. However, resistance to apoptosis is not absolute and can be overcome through enhancement of immune-mediated pathways, e.g., during graft vs. leukemia reaction after allogeneic bone marrow transplantation, or during interferon-alpha (IFN-alpha) therapy. Among the effector mechanisms, T-lymphocyte-mediated killing of target cells via Fas-receptor (Fas-R) triggering plays an important role in the elimination of malignant cells, including CML cells. Although CML Ph+ progenitor cells express Fas-R, the expression levels are variable and do not correlate with clinical parameters. In addition, CML progenitor cells also express functional Fas-ligand (Fas-L), which may be an important immune surveillance escape factor. IFN-alpha can greatly upmodulate Fas-R expression, an effect that seems to be more pronounced in CML compared to normal cells, while Fas-L expression levels are not affected by IFN-alpha, thereby improving their susceptibility to elimination by the immune system. Responsiveness to Fas-induced apoptosis following stimulation with IFN-alpha correlates with the clinical effects of IFN-alpha therapy. This effect seems to be associated with decreased bcr-abl protein levels, which are influenced by Fas via posttranscriptional modulation. In comparison to the chronic phase, CML cells derived from patients in blast crisis are refractory to Fas-mediated apoptosis, regardless of the expression levels of Fas, suggesting that an immune-mediated selection pressure could result in acquisition of Fas-resistance. In the future, enhancement of immunological recognition and elimination of CML cells may prove to be an effective therapeutic approach directed towards the cure of CML.

Effect of antisense oligonucleotides on CD34+ cells from chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a hematopoietic stem cell disorder characterized by a specific hybrid gene BCR-ABL (formed as a result of t(9;22)). This leads to two possible mRNA usually present in leukemic cells, either B2A2 or B3A2. Targeting these mRNA by antisense oligonucleotides (AS) might offer the opportunity to decrease leukemic growth. We have tested the ability of AS to inhibit the in vitro proliferation of CD34 positive (CD34+) blood cells from 16 patients with newly diagnosed CML. CD34+ cells were isolated by an immunomagnetic technique and incubated for 16 to 18 hours with an 18 mer AS (0.25 mM). Sense oligonucleotides served as controls. The effects of AS were evaluated by clonogenic test (production of CFU-GM). Moreover, colonies were picked out and studied by RT-PCR to analyse the presence of BCR-ABL transcript. For nine patients with B3A2 transcript, the median inhibition of CFU-GM formation at day 14 was 64.0 +/- 11.2% (68.0 +/- 11.4% at day 21) and for the seven patients with a B2A2 transcript: 59.0 +/- 11.4% (72.5 +/- 12.0% at day 21). AS showed no effect on CD34+ cells from three normal volunteer donor cells. However, for every patient studied, colonies picked out remained BCR-ABL positive with the RT-PCR technique.

Oligonucleotide therapeutics for hematologic disorders

During the last decade, the catalogue of known genes responsible for cell growth, development, and neoplastic transformation has expanded dramatically. Attempts to translate this information into new therapeutic strategies for both hematologic and non-hematologic diseases have accelerated at a rapid pace as well. Inserting genes into cells which either replace, or counter the effects of disease causing genes has been one of the primary ways in which scientists have tried to exploit this new knowledge. Strategies to directly downregulate gene expression have developed in parallel with this approach. The latter include triple helix forming oligonucleotides (ODN) and 'antisense' ODN. The latter have already entered clinical trials for a variety of disorders. In this monograph, we review the use of these materials in the treatment of hematologic diseases, particularly myelogenous leukemias. Problems and possible solutions associated with the use of ODN will be discussed as well.

Interferon-alpha and bcr-abl antisense oligodeoxynucleotides in combination enhance the antileukemic effect and the adherence of CML progenitors to preformed stroma

We have studied the in vitro effect of IFN-alpha and bcr-abl antisense oligodeoxynucleotides (As ODN) alone and in combination with the aim of enhancing the antileukemic activity of the two single agents and evaluating whether the two agents in combination might restore the adherence capacity of chronic myeloid leukemia (CML) progenitors to preformed stroma. We have also correlated the increased adhesion found after in vitro treatment with the expression of adhesion molecules on leukemic progenitors. Incubation of the BV173 cell line with escalating doses of IFN-alpha (100-10000 U/ml) showed a colony growth inhibition between 10 and 30%. IFN-alpha and junction-specific As ODN in combination showed a greater antiproliferative effect compared to that observed with the two agents used alone. In particular, As ODN at a concentration of 40 microg/ml in combination with IFN-alpha at 100 and 1000 U/ml showed a greater inhibitory effect compared to that obtained with IFN-alpha only. Addition of As ODN to IFN-alpha at 10000 U/ml did not result in a greater BV173 inhibition. In a further set of experiments, primary cells from 16 CML patients at diagnosis were incubated with 40 microg/ml of J-spec As ODN, several control ODNs and IFN-alpha at 1000 U/ml alone and in combination. A significantly greater elimination of CML progenitors was found after treatment with the combination of IFN-alpha and J-spec As ODN, compared to any other treatment group, confirmed also by a more marked effect on p210 expression. The deficient adhesion of CML progenitors on human preformed stroma was restored at levels similar to that of normal bone marrow cells after treatment with IFN-alpha and/or J-spec As ODN, while the phenotypic analysis showed that the combined treatment increased significantly the expression of CD49b and CD62L on CML CD34+ cells. However, when the expression of adhesion molecules was blocked with specific monoclonal antibodies, only CD49d (expressed on more than 90% of CML CD34+ cells) appeared to influence the functional activity of adhesion molecules. In conclusion, IFN-alpha and bcr-abl As ODN in combination exert a marked in vitro antileukemic activity and could be a useful approach for in vitro purging of CML cells prior to autologous transplantation.

Progress in cancer gene therapy

Many technical difficulties have to be overcome before effective gene therapy can be achieved. Strategies for gene therapy include 'suicide' gene therapy, transfer of a tumor suppressor gene, inhibition of activated oncogenes by antisense mechanisms, and cytokine gene transfer and tumor cell vaccination. Gene therapy will have a major impact on the healthcare of our population only when vectors are developed that can safely and efficiently be injected directly into patients as drugs. One of the most promising areas of vector development is that of non-viral vectors, which consist of liposomes, molecular conjugates, and naked DNA delivered by mechanical methods. Future research should be focused on modifying viral vectors to reduce toxicity and immunogenicity, increasing the transduction efficiency of non-viral vectors, enhancing vector targeting and specificity, regulating gene expression, and identifying synergies between gene-based agents and other cancer therapeutics. The evaluation of gene therapy combinations is another important area for future research. The identification of tumor rejection antigens from a variety of cancers and the immune response that is defective in cancer patients are important topics for future studies. A universal gene delivery system has yet to be identified, but the further optimization of each of these vectors should result in each having a unique application. Gene therapy has still a long way to go and requires the efforts of investigators in the basic and clinical sciences. Despite substantial progress, a number of key technical issues need to be resolved before gene therapy can be effectively applied in the clinic.

Cell cycle-dependent distribution and specific inhibitory effect of vectorized antisense oligonucleotides in cell culture

Factors limiting the use of antisense phosphodiester oligodeoxynucleotides (ODNs) as therapeutic agents are inefficient cellular uptake and intracellular transport to RNA target. To overcome these obstacles, ODN carriers have been developed, but the intracellular fate of ODNs is controversial and strongly depends on the means of vectorization. Polyamidoamine dendrimers are non-linear polycationic cascade polymers that are able to bind ODNs electrostatically. These complexes have been demonstrated to protect phosphodiester ODNs from nuclease degradation and also to increase their cellular uptake and pharmacological effectiveness. We studied the intracellular distribution of a fluorescein isothiocyanate-labeled ODN vectorized by a dendrimer vector and found that intracellular ODN distribution was dependent on the phase of the cell cycle, with a nuclear localization predominantly in the G2/M phase. In addition, in order to evaluate the relevance of ODN vectors in enhancing the inhibition of the targeted genes' expression, we developed a rapid screening system which measures the transient expression of two reporter genes, one used as target, the other as control and vice versa. This system was validated through investigating the effect of the dendrimer vector on ODN biological activity. Antisense sequence-specific inhibition of more than 70% of one reporter gene was obtained with a chimeric ODN containing four phosphorothioate groups, two at each end.

Inhibition of P-Glycoprotein and Recovery of Drug Sensitivity of Human Acute Leukemic Blast Cells by Multidrug Resistance Gene (mdr1) Antisense Oligonucleotides

To overcome the problem of multidrug resistance, we investigated the effectiveness of phosphrothioate antisense oligonucleotides (MDR1-AS) in suppressing multidrug resistance gene (mdr1) expression in drug-resistant acute myelogenous leukemia (AML) blast cells and the K562 adriamycin-resistant cell line K562/ADM. The percentage of cells with the mdr1 gene product P-glycoprotein (P-gp) was decreased from 100% to 26% by 20 μmol/L MDR1-AS in the K562/ADM cells, and from 48.1% to 10.2% by 2.5 μmol/L MDR1-AS in the AML blast cells. Western blot analysis also showed a decrease in the amount of P-gp in the MDR1-AS–treated K562/ADM cells. This effect was specific to MDR1-AS, and not observed with sense or random control oligonucleotides. The expression of mdr1 mRNA in K562/ADM and AML blast cells treated with MDR1-AS was decreased compared with the random control. Intracellular rhodamine retention and [3H]daunorubicin also increased after antisense treatment. Chemosensitivity to daunorubicin increased in MDR1-AS–treated blast cells up to 5.9-fold in the K562/ADM cells and 3.0- to 6.4-fold in the AML blast cells. The expression of mdr1mRNA derived from colony cells decreased in the MDR1-AS–treated groups. No inhibitory effect of the oligonucleotides on normal bone marrow progenitors was observed. These findings suggest that MDR1-AS is useful to overcome multidrug resistance in the treatment of leukemia.

Inhibition of P-Glycoprotein and Recovery of Drug Sensitivity of Human Acute Leukemic Blast Cells by Multidrug Resistance Gene (mdr1) Antisense Oligonucleotides

To overcome the problem of multidrug resistance, we investigated the effectiveness of phosphrothioate antisense oligonucleotides (MDR1-AS) in suppressing multidrug resistance gene (mdr1) expression in drug-resistant acute myelogenous leukemia (AML) blast cells and the K562 adriamycin-resistant cell line K562/ADM. The percentage of cells with the mdr1 gene product P-glycoprotein (P-gp) was decreased from 100% to 26% by 20 μmol/L MDR1-AS in the K562/ADM cells, and from 48.1% to 10.2% by 2.5 μmol/L MDR1-AS in the AML blast cells. Western blot analysis also showed a decrease in the amount of P-gp in the MDR1-AS–treated K562/ADM cells. This effect was specific to MDR1-AS, and not observed with sense or random control oligonucleotides. The expression of mdr1 mRNA in K562/ADM and AML blast cells treated with MDR1-AS was decreased compared with the random control. Intracellular rhodamine retention and [3H]daunorubicin also increased after antisense treatment. Chemosensitivity to daunorubicin increased in MDR1-AS–treated blast cells up to 5.9-fold in the K562/ADM cells and 3.0- to 6.4-fold in the AML blast cells. The expression of mdr1mRNA derived from colony cells decreased in the MDR1-AS–treated groups. No inhibitory effect of the oligonucleotides on normal bone marrow progenitors was observed. These findings suggest that MDR1-AS is useful to overcome multidrug resistance in the treatment of leukemia.

BCR-ABL Delays Apoptosis Upstream of Procaspase-3 Activation

The p210bcr-abl protein was shown to inhibit apoptosis induced by DNA damaging agents. Apoptotic DNA fragmentation is delayed in the bcr-abl+ K562 and KCL-22 compared with thebcr-abl− U937 and HL-60 cell lines when treated with etoposide concentrations that induce similar DNA damage in the four cell lines. By the use of a cell-free system, we show that nuclei from untreated cells that express p210bcr-abl remain sensitive to apoptotic DNA fragmentation induced by triton-soluble extracts from p210bcr-abl− cells treated with etoposide. In the four tested cell lines, apoptotic DNA fragmentation is associated with a decreased expression of procaspase-3 (CPP32/Yama/apopain) and its cleavage into a p17 active fragment, whereas the long isoform of procaspase-2 (ICH-1L) remains unchanged and the poly(adenosine diphosphate–ribose)polymerase protein is cleaved. These events are delayed in bcr-abl+ compared with bcr-abl− cell lines. The role of p210bcr-abl in this delay is confirmed by comparing the effect of etoposide on the granulocyte-macrophage colony-stimulating factor (GM-CSF)–dependent UT7 cells and thebcr-abl–transfected GM-CSF–independent UT7/9 clone. We conclude that the cytosolic pathway that leads to apoptotic DNA fragmentation in etoposide-treated leukemic cells is delayed upstream of procaspase-3–mediated events in bcr-abl+ cell lines.

BCR-ABL Delays Apoptosis Upstream of Procaspase-3 Activation

The p210bcr-abl protein was shown to inhibit apoptosis induced by DNA damaging agents. Apoptotic DNA fragmentation is delayed in the bcr-abl+ K562 and KCL-22 compared with thebcr-abl− U937 and HL-60 cell lines when treated with etoposide concentrations that induce similar DNA damage in the four cell lines. By the use of a cell-free system, we show that nuclei from untreated cells that express p210bcr-abl remain sensitive to apoptotic DNA fragmentation induced by triton-soluble extracts from p210bcr-abl− cells treated with etoposide. In the four tested cell lines, apoptotic DNA fragmentation is associated with a decreased expression of procaspase-3 (CPP32/Yama/apopain) and its cleavage into a p17 active fragment, whereas the long isoform of procaspase-2 (ICH-1L) remains unchanged and the poly(adenosine diphosphate–ribose)polymerase protein is cleaved. These events are delayed in bcr-abl+ compared with bcr-abl− cell lines. The role of p210bcr-abl in this delay is confirmed by comparing the effect of etoposide on the granulocyte-macrophage colony-stimulating factor (GM-CSF)–dependent UT7 cells and thebcr-abl–transfected GM-CSF–independent UT7/9 clone. We conclude that the cytosolic pathway that leads to apoptotic DNA fragmentation in etoposide-treated leukemic cells is delayed upstream of procaspase-3–mediated events in bcr-abl+ cell lines.

Autologous transplantation for the treatment of chronic myelogenous leukemia

There is evidence that benign, Ph-negative hematopoietic progenitors persist in the marrow and blood of some patients with chronic myelogenous leukemia (CML). A number of pilot studies using purged and unpurged marrow or peripheral blood autografts have demonstrated that autologous transplantation can result in transient cytogenetic responses in CML. Although not curative, this procedure may be associated with longer-than-expected patient survival and represents an alternative treatment for patients ineligible for allogeneic transplantation and not responding to interferon-alpha therapy. Several novel approaches are being developed to improve graft purging and eliminate residual leukemia post-transplantation. Such approaches may allow for long-term restoration of Ph-negative hematopoiesis following the procedure.

The SH3 Domain Contributes to BCR/ABL-Dependent Leukemogenesis In Vivo: Role in Adhesion, Invasion, and Homing

To determine the possible role of the BCR/ABL oncoprotein SH3 domain in BCR/ABL-dependent leukemogenesis, we studied the biologic properties of a BCR/ABL SH3 deletion mutant (▵SH3 BCR/ABL) constitutively expressed in murine hematopoietic cells. ▵SH3 BCR/ABL was able to activate known BCR/ABL-dependent downstream effector molecules such as RAS, PI-3kinase, MAPK, JNK, MYC, JUN, STATs, and BCL-2. Moreover, expression of ▵SH3 BCR/ABL protected 32Dcl3 murine myeloid precursor cells from apoptosis, induced their growth factor-independent proliferation, and resulted in transformation of primary bone marrow cells in vitro. Unexpectedly, leukemic growth from cells expressing ▵SH3 BCR/ABL was significantly retarded in SCID mice compared with that of cells expressing the wild-type protein. In vitro and in vivo studies to determine the adhesive and invasive properties of ▵SH3 BCR/ABL-expressing cells showed their decreased interaction to collagen IV- and laminin-coated plates and their reduced capacity to invade the stroma and to seed the bone marrow and spleen. The decreased interaction with collagen type IV and laminin was consistent with a reduced expression of α2 integrin by ▵SH3 BCR/ABL-transfected 32Dcl3 cells. Moreover, as compared with wild-type BCR/ABL, which localizes primarily in the cytoskeletal/ membrane fraction, ▵SH3 BCR/ABL was more evenly distributed between the cytoskeleton/membrane and the cytosol compartments. Together, the data indicate that the SH3 domain of BCR/ABL is dispensable for in vitro transformation of hematopoietic cells but is essential for full leukemogenic potential in vivo.

The SH3 Domain Contributes to BCR/ABL-Dependent Leukemogenesis In Vivo: Role in Adhesion, Invasion, and Homing

To determine the possible role of the BCR/ABL oncoprotein SH3 domain in BCR/ABL-dependent leukemogenesis, we studied the biologic properties of a BCR/ABL SH3 deletion mutant (▵SH3 BCR/ABL) constitutively expressed in murine hematopoietic cells. ▵SH3 BCR/ABL was able to activate known BCR/ABL-dependent downstream effector molecules such as RAS, PI-3kinase, MAPK, JNK, MYC, JUN, STATs, and BCL-2. Moreover, expression of ▵SH3 BCR/ABL protected 32Dcl3 murine myeloid precursor cells from apoptosis, induced their growth factor-independent proliferation, and resulted in transformation of primary bone marrow cells in vitro. Unexpectedly, leukemic growth from cells expressing ▵SH3 BCR/ABL was significantly retarded in SCID mice compared with that of cells expressing the wild-type protein. In vitro and in vivo studies to determine the adhesive and invasive properties of ▵SH3 BCR/ABL-expressing cells showed their decreased interaction to collagen IV- and laminin-coated plates and their reduced capacity to invade the stroma and to seed the bone marrow and spleen. The decreased interaction with collagen type IV and laminin was consistent with a reduced expression of α2 integrin by ▵SH3 BCR/ABL-transfected 32Dcl3 cells. Moreover, as compared with wild-type BCR/ABL, which localizes primarily in the cytoskeletal/ membrane fraction, ▵SH3 BCR/ABL was more evenly distributed between the cytoskeleton/membrane and the cytosol compartments. Together, the data indicate that the SH3 domain of BCR/ABL is dispensable for in vitro transformation of hematopoietic cells but is essential for full leukemogenic potential in vivo.

Anti-sense oligonucleotides directed against EGF-related growth factors enhance anti-proliferative effect of conventional anti-tumor drugs in human colon-cancer cells

We have demonstrated that anti-sense phosphorothioate oligodeoxynucleotides (AS S-oligos) directed against the EGF-like growth factors CRIPTO (CR), amphiregulin (AR) or transforming-growth-factor-alpha(TGFalpha) mRNA, are equipotent in their ability to inhibit the growth of human colon-carcinoma GEO cells. In this study, we evaluated the effect of combinations of these AS S-oligos and conventional anti tumor drugs, such as 5-fluorouracil (5-FU), adriamycin (ADR), mitomycin C (MIT) and cis-platinum (CDDP), on GEO cell growth. Dose-dependent growth inhibition was observed by treatment either with AS S-oligos or with anti-tumor drugs, using a clonogenic assay. Furthermore, an additive growth inhibitory effect occurred when GEO cells were exposed to the AS S-oligos after treatment with different concentrations of either 5-FU, MIT, ADR or CDDP. For example, treatment of GEO cells with a combination of low concentrations of 5-FU and any of the 3 AS S-oligos resulted in up to 70% growth inhibition. However, treatment of GEO cells with AS S-oligos before exposure to 5-FU or CDDP resulted in reduced efficacy of both drugs. Flow-cytometric analysis of DNA content demonstrated that treatment with the AS S-oligos caused a slight reduction of the percentage of cells in the S-phase of the cell cycle. These data suggest that combinations of AS S-oligos directed against EGF-related growth factors and of conventional anti-tumor drugs may result in efficient inhibition of colon-carcinoma cell growth.

Antisense Oligodeoxyribonucleotides Suppress Hematologic Cell Growth Through Stepwise Release of Deoxyribonucleotides

Antisense oligodeoxyribonucleotides (ODNs) are now being extensively investigated in an attempt to achieve cell growth suppression through specific targeting of genes related to cell proliferation, despite increasing evidence of non-antisense cytotoxic effects. In the context of anti-BCR/ABL antisense strategies in chronic myeloid leukemia, we have re-examined the antiproliferative effect of phosphodiester and phosphorothioate ODNs on the leukemic cell line BV173 and on CD34+ bone marrow cells in liquid culture. The 3′ sequences of the ODNs determine their effect. At concentrations of 10 μmol/L (for phosphorothioate ODNs) or 25 μmol/L (for phosphodiester ODNs), all the tested ODNs exert an antiproliferative activity, except those that contain a cytosine residue at either their two most terminal 3′ positions. We show that this antiproliferative effect is due to the toxicity of the d-NMPs (5′ monophosphate deoxyribonucleosides), the enzymatic hydrolysis products of the ODNs in culture medium. The toxicity of the d-NMPs on hematologic cells depends on their nature (d-CMP [2′deoxycytidine 5′-monophosphate] is not cytotoxic), on their concentration (d-GMP [2′-deoxyguanosine 5′-monophosphate], TMP [thymidine 5′-monophosphate], and d-AMP [2′-deoxyadenosine 5′-monophosphate] are cytotoxic at concentrations between 5 and 10 μmol/L), and on the coincident presence of other d-NMPs in the culture medium (d-CMP neutralizes the toxicity of d-AMP, d-GMP, or TMP). The antiproliferative activity of ODNs is thus restricted to conditions where the 3′ hydrolysis process by exonucleases generates significant amounts of d-NMPs with a low proportion of d-CMP. Our results reveal a novel example of a nonantisense effect of ODNs, which should be taken into account when performing any experiment using assumed antisense ODNs.

Antisense Oligodeoxyribonucleotides Suppress Hematologic Cell Growth Through Stepwise Release of Deoxyribonucleotides

Antisense oligodeoxyribonucleotides (ODNs) are now being extensively investigated in an attempt to achieve cell growth suppression through specific targeting of genes related to cell proliferation, despite increasing evidence of non-antisense cytotoxic effects. In the context of anti-BCR/ABL antisense strategies in chronic myeloid leukemia, we have re-examined the antiproliferative effect of phosphodiester and phosphorothioate ODNs on the leukemic cell line BV173 and on CD34+ bone marrow cells in liquid culture. The 3′ sequences of the ODNs determine their effect. At concentrations of 10 μmol/L (for phosphorothioate ODNs) or 25 μmol/L (for phosphodiester ODNs), all the tested ODNs exert an antiproliferative activity, except those that contain a cytosine residue at either their two most terminal 3′ positions. We show that this antiproliferative effect is due to the toxicity of the d-NMPs (5′ monophosphate deoxyribonucleosides), the enzymatic hydrolysis products of the ODNs in culture medium. The toxicity of the d-NMPs on hematologic cells depends on their nature (d-CMP [2′deoxycytidine 5′-monophosphate] is not cytotoxic), on their concentration (d-GMP [2′-deoxyguanosine 5′-monophosphate], TMP [thymidine 5′-monophosphate], and d-AMP [2′-deoxyadenosine 5′-monophosphate] are cytotoxic at concentrations between 5 and 10 μmol/L), and on the coincident presence of other d-NMPs in the culture medium (d-CMP neutralizes the toxicity of d-AMP, d-GMP, or TMP). The antiproliferative activity of ODNs is thus restricted to conditions where the 3′ hydrolysis process by exonucleases generates significant amounts of d-NMPs with a low proportion of d-CMP. Our results reveal a novel example of a nonantisense effect of ODNs, which should be taken into account when performing any experiment using assumed antisense ODNs.

Potent and selective gene inhibition using antisense oligodeoxynucleotides

The development of antisense technology as a generally useful tool relies on the use of potent agents and the utilization of many controls in experiments. Here we describe our experience using oligodeoxynucleotides (ODNs) containing C-5 propynyl pyrimidine and phosphorothioate modifications as broadly applicable gene inhibition agents in cell culture. Methods include selection of antisense sequences, synthesis and purification of ODNs, choice of controls, delivery methods (microinjection, cationic lipid transfection, and electroporation), and analysis of gene inhibition.

Stem cell kinetics

Chronic myeloid leukaemia (CML) is a transplantable multi-lineage disease. In its initial chronic phase, the leukaemic clone exhibits a hierarchical structure that closely resembles normal haematopoiesis. Thus assays for in vitro colony-forming cells (CFC) and their more primitive precursors identified as long-term culture-initiating cells (LTC-IC) detect subsets of Ph+/BCR-ABL+ cells which cannot be readily distinguished from their normal counterparts. The use of these assays to examine the numbers, properties, genotype, distribution and regulation of primitive progenitors in patients' blood and marrow samples have revealed a number of unique and unexpected findings. These suggest that the indolent nature of the chronic phase of the disease may be explained by competing effects of the BCR-ABL gene product on the commitment to differentiate, control of cell cycle progression and apoptosis. As a result, the amplification of BCR-ABL+ stem cells is constrained but the expansion of their progeny is enhanced and, on the granulocyte pathway, this expansion proceeds unchecked to the stage of mature end cell production resulting in the leukaemic picture observed.

Combination of antisense oligonucleotide and low-dose chemotherapy in hematological malignancies

Current conventional chemotherapy for the treatment of hematological malignancies, although quite effective, has associated toxicities to normal tissue and organs, which is still a major dose limiting factor. In addition, high dose chemotherapy followed by autologous stem cell transplantation is limited by tumor cell contamination in the stem cell harvest. The use of conventional chemotherapy alone to purge these tumor cell contaminants is known to damage normal hematopoietic progenitor cells, resulting in delayed engraftment. The combination of antisense oligodeoxynucleotides (ODN) and low doses of chemotherapy offer a potential regiment which may lower the doses of conventional therapeutics required to effectively combat disease, thus lowering cytotoxicity experienced by normal cells. Transient downregulation of genes by ODN treatment, which are involved in the transformation or perpetuation of the cancerous disease state, can remove the growth and survival advantages exploited by tumor cells. Many groups are currently investigating this combination and have produced intriguing results. This review article discusses the current research investigating the combination of antisense ODN therapy with conventional chemotherapy in the treatment of hematological malignancies. Although further improvements in this strategy are required, the results thus far support a future for this strategy in clinical management of hematological malignancy.

Treatment of Philadelphia leukemia in severe combined immunodeficient mice by combination of cyclophosphamide and bcr/abl antisense oligodeoxynucleotides

BACKGROUND

Philadelphia cells are human chronic myelogenous leukemia (CML) cells that contain the BCR/ABL oncogene (a fusion of the BCR and ABL genes). Selective eradication of these cells in vitro can be achieved by combined treatment with antisense phosphorothioate oligodeoxynucleotides ([S]ODNs) specifically targeted to this oncogene (bcr/abl [S]ODNs) and a suboptimal (for use as a single agent) dose of mafosfamide (the in vitro active form of cyclophosphamide).

PURPOSE

We evaluated the ability of bcr/abl antisense [S]ODNs, alone or subsequent to treatment with a single injection of cyclophosphamide, to suppress the leukemic process induced in severe combined immunodeficient (SCID) mice by Philadelphia cells (i.e., primary CML-blast crisis [CML-BC] cells). In addition, we studied potential mechanisms that might explain the efficacy of the bcr/abl antisense [S]ODN-mafosfamide combination against Philadelphia cells in vitro.

METHODS

The effects of treating leukemic mice with cyclophosphamide (25 mg/kg body weight; 25% of the dose required to eradicate evidence of leukemia in SCID mice) and/or bcr/abl antisense [S]ODNs were assessed by analysis of survival, by examination of bone marrow for the presence of leukemia cells (using a colony formation assay or using coupled reverse transcription and the polymerase chain reaction to screen for bcr/abl messenger RNA), and by examination of a variety of tissues for the presence of infiltrating leukemia cells. The induction of apoptosis (a cell death program) in vitro in primary CML-BC cells following treatment with bcr/abl antisense [S]ODNs plus or minus prior treatment with mafosfamide was monitored by use of a commercial assay. Relative cellular uptake of [S]ODNs by CML-BC cells treated in vitro with or without prior treatment with mafosfamide was determined by use of confocal microscopy and flow cytometry (for fluorescent [S]ODNs) or by use of blotting techniques that employed radioactively labeled probes (for extracted, unlabeled [S]ODNs). Levels of specific proteins in treated and untreated cells were determined by use of western blotting methods. Reported P values are two-sided.

RESULTS

The disease process in leukemic mice was retarded substantially by combination treatment with cyclophosphamide and specific bcr/abl antisense [S]ODNs (P < .001, relative to treatment with specific antisense [S]ODNs alone, cyclophosphamide alone, or cyclophosphamide plus nonspecific [i.e., control] antisense [S]ODNs); 50% of the mice treated with cyclophosphamide and specific antisense [S]ODNs appeared to be cured of leukemia. The combination treatment was associated with increased induction of apoptosis. In addition, cellular uptake of bcr/abl antisense [S]ODNs appeared to be increased twofold to sixfold by prior treatment with mafosfamide. This increased uptake of [S]ODNs was associated with enhanced suppression of p210bcr/abl protein levels.

CONCLUSIONS AND IMPLICATIONS

Combination therapy with antisense [S]ODNs targeted to specific oncogenes and less toxic doses of anticancer drugs may represent a rational strategy to purpose for the treatment of human leukemias.

Gene therapy strategies for leukemia

A number of diverse gene therapy strategies are being evaluated in the search for novel therapeutic approaches to leukemia. Antisense oligonucleotides, ribozymes and retroviral vectors are approaches directed at the molecular mechanisms of cancer. Transfer of genes encoding cytokines and human leukocyte antigens (HLAs) could also be used to elicit immunity against tumor cells. Gene marking strategies have been useful in elucidating the biology of disease relapse after autologous bone marrow transplantation. Suicide genes, such as the herpes simplex thymidine kinase gene, have been used to modulate graft-versus-host disease after allogeneic bone marrow transplantation. Although gene delivery remains a major challenge to gene therapy, some modifications have been implemented to overcome this issue. This review will summarize these gene therapy strategies aimed at increasing the survival of patients with leukemia.

Antisense strategy: biological utility and prospects in the treatment of hematological malignancies

The use of antisense oligonucleotides for the specific control of cellular genes expression has undergone rapid developments recently. Besides the antisense approach, which usually targets translation initiation or splicing sites, it is also possible to interfere specifically with transcription process through triple helix formation (anti-gene strategy) or through the titration of regulatory proteins (sense and aptamer approaches). Progresses in oligonucleotides chemistry have led to the synthesis of analogs with improved pharmacological properties, while their generation from recombinant vectors in situ has improved oligos deliver to their nuclear or cytoplasmic targets. Hematological malignancies provide an ideal paradigm for the development of antisense therapeutic strategies. Many disease-specific molecular lesions have been identified which provide suitable targets for systemic in vivo administration of oligonucleotides as well as for ex vivo bone marrow purging manipulation. However, oligonucleotides have also been shown to bind to unexpected cellular targets and to induce various unpredictable biological responses as well. In addition, the multi-stage nature of carcinogenesis may indicate that even if successful inhibition of a single gene by oligomer is achieved, it may still be insufficient to induce a major impact on a malignant clone. Thus, much more basic information about both the disease and antisense technology is still required before antisense strategy gains the status of an acceptable therapeutical approach.

Functional aspects of apoptosis in hematopoiesis and consequences of failure

Apoptosis is an internally directed, physiological method of cell destruction. Cellular components are dismantled within the confines of an intact cell membrane, and rapid ingestion by phagocytic cells prevents local inflammation. A variety of genes have now been identified as positive or negative regulators of apoptosis. Transfection experiments and studies of gene cooperation in viral transformation suggest that full cellular transformation requires not only the deregulation of proliferation, but also the inhibition of concomitant apoptosis programs. The regulation of apoptosis is fundamental to hematopoietic homeostasis. Stem cell renewal is continuously counterbalanced by apoptosis in functionally inactive or terminally differentiated cells. Extensive cell death in developing lymphocyte populations ensures that only cells recognizing non-self antigens are released into the periphery, and the finite lifespan of terminally differentiated cells enables the extensive cell turnover demanded by functional aspects of the hematopoietic system. The requirement of each hematopoietic sub-population for a specific sub-set of survival factors, provides a flexible mechanism for dictating the cellular composition of the mature population and for controlling population size. Surplus cell production and apoptosis are therefore normal features of hematopoiesis. The consequences of deregulated apoptosis are severe. Excessive apoptosis in lymphocyte populations plays a major role in the pathogenesis of acquired immunodeficiency syndrome (AIDS), whereas ineffective apoptosis has been associated with the development of inflammation, autoimmunity and hematological malignancies. The identification of various genetic abnormalities which influence apoptosis in leukaemic cells (e.g., mutant p53, Bcr-Abl and over-expression of Bcl-2), suggests that the acquisition of an anti-apoptotic lesions is an important event in the multi-step evolution of hematological malignancies. In addition, the nature of some leukaemias particularly the chronic leukemias, in which the leukemic cells are nonproliferative and long lived, suggests that anti-apoptotic lesions are early events in the pathogenesis of these diseases. It is likely that the utilization of mechanisms to evade apoptosis would facilitate disease progression in all leukemias and contribute to the development of multi-drug resistance. A better understanding of apoptosis mechanisms in hematopoietic cells, and their exploitation by leukemic cells should be useful in the development of improved cytotoxic regimes.

Blastic transformation of p53-deficient bone marrow cells by p210bcr/abl tyrosine kinase

Blastic transformation of chronic myelogenous leukemia (CML) is characterized by the presence of nonrandom, secondary genetic abnormalities in the majority of Philadelphia1 clones, and loss of p53 tumor suppressor gene function is a consistent finding in 25-30% of CML blast crisis patients. To test whether the functional loss of p53 plays a direct role in the transition of chronic phase to blast crisis, bone marrow cells from p53+/+ or p53-/- mice were infected with a retrovirus carrying either the wild-type BCR/ABL or the inactive kinase-deficient mutant, and were assessed for colony-forming ability. Infection of p53-/- marrow cells with wild-type BCR/ABL, but not with the kinase-deficient mutant, enhanced formation of hematopoietic colonies and induced growth factor independence at high frequency, as compared with p53+/+ marrow cells. These effects were suppressed when p53-/- marrow cells were coinfected with BCR/ ABL and wild-type p53. p53-deficient BCR/ABL-infected marrow cells had a proliferative advantage, as reflected by an increase in the fraction of S+G2 phase cells and a decrease in the number of apoptotic cells. Immunophenotyping and morphological analysis revealed that BCR/ABL-positive p53-/- cells were much less differentiated than their BCR/ABL-positive p53+/+ counterparts. Injection of immunodeficient mice with BCR/ABL-positive p53-/- cells produced a transplantable, highly aggressive, poorly differentiated acute myelogenous leukemia. In marked contrast, the disease process in mice injected with BCR/ABL-positive p53+/+ marrow cells was characterized by cell infiltrates with a more differentiated phenotype and was significantly retarded, as indicated by a much longer survival of leukemic mice. Together, these findings directly demonstrate that loss of p53 function plays an important role in blast transformation in CML.

A comparison of the effect of bcr/abl breakpoint specific phosphothiorate oligodeoxynucleotides on colony formation by bcr/abl positive and negative, CD34 enriched mononuclear cell populations

In chronic myeloid leukaemia, the expression by clonal cells, of a leukaemia specific bcr/abl chimeric mRNA, makes the condition suitable for the application of "antisense" strategies. Furthermore, the origin of the condition in a pluripotential progenitor allows enrichment of leukaemic clonogenic cells by selection for CD34 expression, together with a useful reduction in contaminating accessory cells. In a methylcellulose clonogenic assay system we incubated bcr/abl expressing (n = 9) and bcr/abl negative (n = 8), CD34 enriched progenitors with phosphothiorate oligodeoxynucleotides (PS oligomers), antisense and sense to the b3a2 and b2a2 chimeric bcr/abl junctional sequences. All samples were cloned in the presence of both antisense, and sense PS oligomers to provide appropriate controls. For bcr/abl positive progenitors, the mean number of colonies formed was reduced by 21 (39%) (P < 0.05) in the presence of the specific antisense oligomer, 11 (20%) (P < 0.05) with the antisense oligomer directed to the alternative junctional breakpoint, and colony formation was not significantly altered by either sense PS oligomer. Colony formation by bcr/abl negative progenitors was not reproducibly reduced by any of the PS oligomers. These results confirm that PS oligomers can have a sequence dependent inhibitory effect on a CD34 enriched progenitor population from patients with chronic myeloid leukaemia.

Antisense oncogene and tumor suppressor gene therapy of cancer

Rapid advances in cancer gene therapy are driven by an explosive development of gene transfer technology and a strong demand for seeking alternatives to unsatisfactory conventional cancer therapies. Discovery of the genetic basis of cancer has indicated that cancer is a disease of genes. Among a variety of approaches to gene therapy of cancer, antisense oncogene and tumor suppressor gene therapy of cancer are the two strategies that aim at correcting genetic disorders of cancer through suppression of the abnormal expression of the proliferative genes. The potential effectiveness of these approaches is promised by their precise targeting at the mechanisms of the disease. Examples of several preclinical studies of these types of approaches that led to the approval of clinical trials are reviewed. Limitation and future development of these approaches are also discussed.

Recent status of the antisense oligonucleotide approaches in oncology

Antisense oligonucleotides designed to complement a region of a particular messenger RNA may inhibit gene expression potentially through sequence-specific hybridization. Their inhibiting effect has been shown in a variety of in vitro and in vivo models in oncology, whereas much rarer clinical trials have been carried out. Rigorous demonstration of in vitro and in vivo specific effects upon their targets is mandatory before their use as drugs in cancer therapy.

[Chronic myeloid leukemia, biological aspects]

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder of a stem cell, involving myeloid, erythroid, megacaryocyte, lymphoid B-cells and "natural killer" cells. The hallmark of CML is the Philadelphia (Ph) chromosome which is a shortened chromosome 22 (22q-) resulting from a reciprocal translocation involving chromosome 9 and chromosome 22, designed t (9;22) (q34;q11). This translocation juxtaposes parts of two genes; ABL on chromosome 9 and BCR (breakpoint cluster region) on chromosome 22. Transcription of the BCR/ABL fusion gene results in an hybrid mRNA that is translated into a 210 kDa or 190 kDa protein, depending on the location of the breakpoint in the bcr region. This protein plays a key role in CML: its tyrosine-kinase activity, that differs from the normal ABL product, may be involved in leukemic cell growth. Nonetheless, the loss of the negative cell growth regulation by c-ABL, or BCR/ABL fusion protein interaction with other cellular genes (such as RAS or c-MYC) could also be involved in CML pathophysiology. A better understanding of the molecular mecanisms of CML could lead to specific treatment, such as tyrosine-kinase inhibitors, synthetic oligodeoxynucleotides, or site-specific DNA-binding proteins designed against BCR/ABL oncogenic fusion sequence.

Biology and treatment of adult acute lymphoblastic leukemia

The molecular analysis of acute lymphoblastic leukemia (ALL) has provided exciting insights into the pathogenesis of this disease. This disease is heterogenous and can be subtyped based on chromosomal, immunophenotypic, and structural criteria. The varying prognostic implications of different ALL subtypes markedly influence the treatment decisions in adults. Many patients with T-cell ALL can be cured with chemotherapy alone. In contrast, patients with early B-lineage ALL with certain chromosomal abnormalities, especially the Philadelphia chromosome, do not have durable responses to chemotherapy and should receive a bone marrow transplantation if an HLA-matched donor is available. Recent reports have shown improved results for adults with B-cell ALL (Burkitt's) after intensive alternating cycles of chemotherapy containing high doses of methotrexate and cyclophosphamide. Future clinical and laboratory investigation should lead to the development of novel and possibly more effective treatments specifically tailored for different subsets of ALL.