Selective inhibition of leukemia cell proliferation by BCR-ABL antisense oligodeoxynucleotides

Frequent polymorphism in BCR exon b2 identified in BCR-ABL positive and negative individuals using fluorescent hybridization probes

Recently, a polymorphic base in exon 13 of the BCR gene (exon b2 of the major breakpoint cluster region) has been identified in the eighth position before the junctional region of BCR-ABL cDNA. Cytosine replaces thymidine; the corresponding triplets are AAT (T allele) and AAC (C allele), respectively, both coding for asparagine. Therefore, this polymorphism has no implication in the primary structure of BCR and BCR-ABL proteins. However, since the alteration is located close to the fusion region it may have a significant influence on the annealing of PCR primers, probes for real time PCR, and antisense oligonucleotides. We have developed a RT-PCR-based screening method to easily identify polymorphic BCR and BCR-ABL alleles in CML patients and normal individuals in order to estimate their frequency. After amplification from cDNA, a melting curve of a specific fluorogenic probe mapping to the 3' end of BCR exon b2 and spanning the polymorphism readily discriminates between normal and polymorphic BCR and BCR-ABL alleles. This reporter probe is 3' labeled with fluorescein and placed next to 5' LC Red640-labeled anchor probes mapping to the 5' ends of BCR exon b3 or ABL exon a2 so that resonance energy transfer occurs when the probes are hybridized (LightCycler technology). T and C alleles were discriminated by a melting temperature difference of the reporter probe of 3.2 K. We have investigated cDNAs derived from leukocytes from seven cell lines and a total of 229 individuals: normal donors, n = 15; BCR-ABL negative chronic myeloproliferative disorders, n=30; BCR-ABL negative acute leukemias, n= 11; b2a2BCR-ABL positive CML, n = 93; and b3a2BCR-ABL positive CML, n= 80. The frequency of the C allele was 33.0% in BCR-ABL negative individuals, 30.6% in b2a2BCR-ABL, and 23.8% in b3a2BCR-ABL positive CML. In CML patients, 27.7% of BCR-ABL and 27.2% of BCR alleles had the C allele (NS). In total, 132 of 458 (28.8%) exons b2 of BCR or BCR-ABL alleles demonstrated this polymorphism. We conclude that a thymidine/cytosine replacement occurs frequently in BCR exon b2. Probes for real time quantitative RT-PCR should be designed not to map to the critical region in order to avoid underestimation of the number of BCR-ABL transcripts.

Comparison and evaluation of gene therapy and epigenetic approaches for wound healing

During the past decade considerable evidence has mounted concerning the importance of growth factors in the wound healing process both for cell replication and for stimulating reparative cells to synthesize and secrete extracellular matrix components. During normal wound healing the growth factor concentration has to be maintained at a certain level. If the growth factor concentration is too low, normal healing fails to occur. Whereas if the growth factor concentration is too high due to either over-expression of the growth factor or too much growth factor being applied to the wound, aberrant wound healing will occur. One approach for controlling the amount of growth factor at the wound site during normal healing is through gene therapy and the titration of gene dosage. However if a narrow window exists between the beneficial therapeutic effect and toxic effects with increasing gene dosage, an agent may be necessary to give in combination with gene therapy to regulate the over-expression of growth factor. In addition to genetic approaches to regulate wound healing, epigenetic approaches also exist. Antisense oligodeoxynucleotides have been shown to regulate wound repair in certain model systems and to determine the protein(s) necessary for normal wound healing. A novel approach to regulate the activity of collagen genes, thereby affecting fibrosis, is to use a sense oligodeoxynucleotide having the same sequence of the cis element which regulates the promoter activity of a particular collagen gene. This exogenous oligodeoxynucleotide will compete with the cis element in the collagen gene for the trans-acting factor which regulates promoter activity. These epigenetic approaches afford the opportunity to regulate over-expression of growth factor and therefore preclude the potential toxic effects of gene therapy. Both genetic and epigenetic approaches for regulating the wound healing process, either normal or aberrant wound healing, have certain advantages and disadvantages which are discussed in the present article.

Synthetic oligonucleotides as therapeutics: the coming of age

Synthetic oligonucleotides (ODNs) are short nucleic acid chains that can act in a sequence specific manner to control gene expression. Significant progress has been made in the development of synthetic ODN therapeutics since the first demonstration of gene inhibition by antisense ODNs in a cell culture system two decades ago. This new class of therapeutic agents can potentially target any abnormally expressed genes in a broad range of diseases from viral infections to psychoneurological disorders. A number of "first" generation synthetic ODNs have entered into human clinical trials in the last few years. The eminent approval of the first ODN for the treatment of cytomaglovirus retinitis by the FDA in USA will provide much excitement that this new class of compounds holds great promise as a therapeutic "magic bullet". However, many obstacles still exist in the development of this technology. In this review, the current status of synthetic ODN chemistry, drug delivery methods, mechanisms of ODN action, potential clinical applications and its limitations in a wide range of human disorders will be described.

Antisense therapy in cancer

This review discusses laboratory and clinical studies of antisense oligodeoxynucleotides as potential treatments for haematological malignancies and solid tumours. Mechanisms of action, pharmacokinetics, toxicities and potential clinical applications of these agents are described.

Ribonuclease H attack of leukaemic fused transcripts AML1-MTG8 (ETO) by DNA/RNA chimeric hammerhead ribozymes

BACKGROUND

Catalytic anti-sense oligonucleotides might be useful tools for controlling specific gene expression. However, to obtain effective oligonucleotides of the desired function in vivo is still a difficult task.

RESULTS

To evaluate the usefulness of synthesized DNA/RNA hammerhead ribozymes targeting AML1-MTG8 (ETO) leukaemic fusion transcripts in vivo, we analysed their effects on cell growth and the mechanism of action using isolated cell nuclei. These ribozymes inhibited the growth of leukaemic cell lines expressing the AML1 -MTG8 and degraded AML1-MTG8 mRNA in isolated nuclei of these cells. However, the reactions gave rise to additional cleavage products. Systematic cleavage analyses using an anti-sense oligonucleotide array revealed that the cleavage was induced by endogenous RNase H at specific sites, in accordance with their calculated melting temperature (Tm) values. With suppression of RNase H by sulfhydryl agents, the DNA/RNA ribozyme had a ribozyme catalytic activity. In addition, the ribozymes and anti-sense oligonucleotides suppressed the AML1-MTG8 protein in the leukaemic cells.

CONCLUSIONS

The DNA/RNA ribozymes inhibited cell growth primarily via anti-sense effects, the main role of which was the activation of RNase H-digestion by their DNA arms. In addition, the isolated nuclei provided a useful assay system for modelling in vivo conditions for the quantitative evaluation of anti-sense/ribozyme activity.

Targeted therapies for the myeloid leukaemias

Although the standard approach to myeloid leukaemias remains chemotherapy, the agents currently available rarely result in cure. Recent advances in understanding the biology of these disorders have lead to the development of targeted treatment strategies. In acute promyelocytic leukaemia (APL), all-trans retinoic acid (ATRA), sodium phenylbutyrate and arsenic trioxide are agents which either induce differentiation or apoptosis and have been used to successfully achieve remission. The tyrosine kinase inhibitor, STI-571, antisense oligonucleotides, and bcr-abl vaccines are strategies which focus on the oncogenic events in chronic myelogenous leukaemia (CML). Two anti-CD33 monoclonal antibody conjugates, Y90-HuM195 and CMA-676, have been used in acute myelogenous leukaemia (AML) and have shown some efficacy. Although the preliminary results with these targeted therapies are promising, further studies are needed to establish them as effective, less toxic alternatives to the current standard of care.

Limited synergistic effect of antisense oligonucleotides against bcr-abl and transferrin receptor mRNA in leukemic cells in culture

The synergistic use of antisense oligonucleotides (ASOs) towards the bcr-abl and the transferrin receptor (TfR) mRNA was studied in a chronic myeloid leukemia (CML) cell line, aiming to improve the efficiency of individual ASO treatment. At 20 microM concentration, bcr-abl ASOs reduced cell growth by 40% and was specific for cells that have the translocation: there was a 34% reduction of BCR-ABL protein. The TfR ASO reduced cell growth by 20% and decreased TfR protein by 24%. The ASOs were more potent at reducing cell growth when used in combination (respectively, -20 and -17% than bcr-abl ASO and TfR ASO when used individually at the 10 microM concentration), thus we postulate that there is synergism of action. Cell cycle analysis also revealed that the sub-G1 peak was bigger in the synergistic treatment.

Antisense therapeutics in chronic myeloid leukaemia: the promise, the progress and the problems

DNA sequences which are complementary or 'antisense' to a target mRNA can inhibit expression of that mRNA's protein product. Antisense therapeutics has therefore received attention for inhibiting oncogenes in haematological malignancy, in particular in chronic myeloid leukaemia. However, it is now becoming clear that antisense therapeutics is considerably more problematic than was naively initially assumed. In this article, some of these difficulties are discussed, together with the achievements in CML so far. Considerable further research is required in order to define an optimal antisense therapeutics strategy for clinical use.

Arsenic induces apoptosis of multidrug-resistant human myeloid leukemia cells that express Bcr-Abl or overexpress MDR, MRP, Bcl-2, or Bcl-xL

We investigated the in vitro growth inhibitory and apoptotic effects of clinically achievable concentrations of As2O3 (0.5 to 2.0 μmol/L) against human myeloid leukemia cells known to be resistant to a number of apoptotic stimuli. These included chronic myelocytic leukemia (CML) blast crisis K562 and HL-60/Bcr-Abl cells, which contain p210 and p185 Bcr-Abl, respectively, and HL-60 cell types that overexpress Bcl-2 (HL-60/Bcl-2), Bcl-xL(HL-60/Bcl-xL), MDR (HL-60/VCR), or MRP (HL-60/AR) protein. The growth-inhibitory IC50 values for As2O3 treatment for 7 days against all these cell types ranged from 0.8 to 1.5 μmol/L. Exposure to 2 μmol/L As2O3 for 7 days induced apoptosis of all cell types, including HL-60/Bcr-Abl and K562 cells. This was associated with the cytosolic accumulation of cyt c and preapoptotic mitochondrial events, such as the loss of inner membrane potential (▵Ψm) and the increase in reactive oxygen species (ROS). Treatment with As2O3 (2 μmol/L) generated the activities of caspases, which produced the cleavage of the BH3 domain containing proapoptotic Bid protein and poly (ADP-ribose) polymerase. Significantly, As2O3-induced apoptosis of HL-60/Bcr-Abl and K562 cells was associated with a decline in Bcr-Abl protein levels, without any significant alterations in the levels of Bcl-xL, Bax, Apaf-1, Fas, and FasL. Although As2O3 treatment caused a marked increase in the expression of the myeloid differentiation marker CD11b, it did not affect Hb levels in HL-60/Bcr-Abl, K562, or HL-60/neo cells. However, in these cells, As2O3 potently induced hyper-acetylation of the histones H3 and H4. These findings characterize As2O3 as a growth inhibiting and apoptosis-inducing agent against a variety of myeloid leukemia cells resistant to multiple apoptotic stimuli.

In vivo inhibition by a site-specific catalytic RNA subunit of RNase P designed against the BCR-ABL oncogenic products: a novel approach for cancer treatment

One major obstacle to the effective treatment of cancer is to distinguish between tumor cells and normal cells. The chimeric molecules created by cancer-associated chromosomal abnormalities are ideal therapeutic targets because they are unique to the disease. We describe the use of a novel approach based on the catalytic RNA subunit of RNase P to destroy specifically the tumor-specific fusion genes created as a result of chromosome abnormalities. Using as a target model the abnormal BCR-ABL p190 and p210 products, we constructed M1-RNA with guide sequences that recognized the oncogenic messengers at the fusion point (M1-p190-GS and M1-p210-GS). To test the effectiveness and the specificity of M1-p190-GS and M1-p210-GS, we studied in vitro and in vivo effects of these RNA enzymes againstBCR-ABLp190 andBCR-ABLp210, bearing in mind that both fusion genes share the ABL sequence but differ in the sequence coming from the BCR gene. We showed that M1-p190-GS and M1-p210-GS can act as sequence-specific endonucleases and can exclusively cleave target RNA that forms a base pair with the guide sequence (GS). We also demonstrated that when M1-p190-GS and M1-p210-GS were expressed in proper mammalian cell models, they abolished the effect of BCR-ABL by specifically decreasing the amount of the target BCR-ABL mRNA and preventing the function of theBCR-ABL oncogenes. These data clearly demonstrate the usefulness of the catalytic activity of M1-GS RNA to cleave specifically the chimeric molecules created by chromosomal abnormalities in human cancer and to represent a novel approach to cancer treatment.

Antisense cancer therapy: the state of the science

Over the last few years, antisense technology has emerged as an exciting and promising strategy in the fight against cancer. The antisense concept is to selectively bind short, modified DNA or RNA molecules to messenger RNA in cells and prevent the synthesis of the encoded protein. As anticancer agents, these molecules can be targeted against a myriad of genes involved in cell transformation, cell survival, metastasis, and angiogenesis. Indeed, the list of possible antisense targets increases as the knowledge of the genetic basis of oncogenesis expands. One aim of this review is to focus on those antisense cancer drugs that have entered human clinical trials. At least four of these compounds are currently in phase II trials, including those targeting protein kinase C-alpha, bcl-2, c-raf, and the R1-alpha subunit of protein kinase A. A new development in antisense chemistry (peptide nucleic acids) is discussed, along with alternative antisense-related strategies (ribozymes and 2-5A-antisense) designed to overcome some of the challenges of this already encouraging technology.

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.

Genetic dissection of dome formation in a mammary cell line: identification of two genes with opposing action

In this work, we extend the study of the genes controlling the formation of domes in the rat mammary cell line LA7 under the influence of DMSO. The role of the rat8 gene has already been demonstrated. We have now studied two additional genes. The first, called 133, is the rat ortholog of the human epithelial membrane protein 3 (EMP3), a member of the peripheral myelin protein 22 (PMP22)/EMP/lens-specific membrane protein 20 (MP20) gene family that encodes for tetratransmembrane proteins; it is expressed in the LA7 line in the absence of DMSO but not in its presence. The second gene is the beta subunit of the amiloride-sensitive Na(+) channel. Studies with antisense oligonucleotides show that the formation of domes is under the control of all three genes: the expression of rat8 is required for both their formation and their persistence; the expression of the Na(+) channel beta subunit is required for their formation; and the expression of gene 133 blocks the expression of the Na(+) channel genes, thus preventing formation of the domes. The formation of these structures is also accompanied by the expression of alpha(6)beta(1) integrin, followed by that of E-cadherin and cytokeratin 8. It appears, therefore, that dome formation requires the activity of the Na(+) channel and the rat8-encoded protein and is under the negative control of gene 133. DMSO induces dome formation by blocking this control.

Inhibition of bcr-abl oncogene expression by novel deoxyribozymes (DNAzymes)

Deoxyribozymes, or DNA enzymes (DNAzymes), are novel nucleic acids that have the ability to bind to specific sequences of RNA, and to cleave the target site catalytically. DNAzymes are smaller and more efficient enzymatically than ribozymes (RZs), which are catalytic nucleic acids synthesized from ribonucleotides. We have designed three DNAzymes that specifically target the two variants of the p210 bcr-abl gene (splice 1, b3a2; splice 2, b2a2) and the p190 variant (ela2). The cleavage sites for these DNAzymes are located 5 nucleotides (nt) 5' from the fusion site for b3a2, and only 1 nt 5' from the fusion sites for b2a2 and e1a2. We have shown in cell-free in vitro cleavage assays that these DNAzymes efficiently cleave their respective substrates. Mutated DNAzymes, in which only one critical base has been altered, do not cleave these targets. We have used a serum-resistant cytofectin (GS 2888; Gilead) to transfect the DNAzymes into target K562 cells, which express p210bcr-abl. In short-term transfection assays, the DNAzymes specifically inhibited p210bcr-abl protein expression by K562 cells by about 40%, and inhibited cell growth by more than 50% in a 6-day liquid culture assay. We have also transfected freshly isolated CD34+ bone marrow cells from patients with CML with the DNAzymes, which specifically inhibited the growth of bcr-abl-positive CFU-Mix colonies by 53-80%. The potential advantages of anti-bcr-abl DNAzymes over RZs include the following: DNAzymes are much less expensive to synthesize; they are more resistant to serum; and the anti-b2a2 DNAzyme cleaves at a site only 1 nt away from the fusion site, whereas its hammerhead RZ counterpart cleaves this target at a site 8 nt 3' to the fusion site, well within abl exon 2. DNAzymes are novel RNA-cleaving molecules that may significantly improve our ability to inhibit bcr-abl oncogene expression in Ph-positive target cells.

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.

Implications for Src kinases in hematopoiesis: signal transduction therapeutics

Signal transduction therapeutics is now the dominant theme of drug discovery, and its most immediate impact will be in cancer therapeutics. Blood cell proliferation, differentiation, and activation are controlled by cytokines, whose receptors contain tyrosine kinase catalytic domains or recruit cytosolic tyrosine kinases. Among the most important cytosolic protein tyrosine kinases are the Src and Jak families. Receptor or cytosolic protein tyrosine kinases activate a similar set of intracellular signaling molecules. In blood cells, excessive tyrosine kinase activity is associated with either cancer or autoreactive diseases. Therefore, tyrosine kinases and their substrates serve as excellent candidates for drug intervention. Herceptin has been approved for use in breast cancer. Other agents, such as SU101 and CGP 57418B, are well into phase I-III trials. Newer, more selective tyrosine kinase inhibitors are being evaluated for future use in the treatment of hematologic and solid tumors as well as a wide range of inflammatory or autoimmune diseases.

Growth inhibition of cervical tumor cells by antisense oligodeoxynucleotides directed to the human papillomavirus type 16 E6 gene

Human papillomavirus type 16 (HPV-16) is the HPV type most frequently associated with cervical carcinomas. Based on our previous research with anti-HPV ribozymes, we developed a 16-nucleotide antisense oligodeoxynucleotide (AntiE6) able to direct RNase H activity on full-length HPV-16 E6/E7 mRNA. Although the precise mechanism is not completely understood, addition of 50 microM AntiE6 oligodeoxynucleotide in sterile water caused a significant decrease in the growth rate of CaSki and QGU cervical tumor cell lines. In contrast, addition of a mismatched mutant oligodeoxynucleotide (M7) did not affect cell growth after 72 hours. Treatment with AntiE6 resulted in down-regulation of E6/E7 mRNA and an increase in p53 levels in QGU cells. AntiE6 was also able to (>70%) inhibit significantly growth of transplanted cervical tumors in nude mice after 2 weeks treatment using constant delivery by osmotic pumps. These results indicate that the AntiE6 antisense oligodeoxynucleotides can act as a therapeutic agent against cervical carcinomas.

Myb targeted therapeutics for the treatment of human malignancies

For the past several years, we have been engaged in developing a therapeutically effective strategy for disrupting gene function with reverse complementary, or so called 'antisense', oligodeoxynucleotides (ODN). This pursuit has focused on finding appropriate diseases in which to apply this approach, and suitable gene targets. Of the genes that we have targeted for disruption using the antisense ODN strategy (Clevenger et al., 1995; Gewirtz and Calabretta, 1988; Ratajczak et al., 1992c; Small et al., 1994) one that has been of particular interest, and one where therapeutically motivated disruptions are now in clinical trial, is the myb gene (reviewed in Lyon et al., 1994). These trials involve treatment of human leukemias. These diseases are a logical choice for developing oncogene targeted therapies because of easy access to tissues, and the abundance of knowledge about the cell and molecular biology of these diseases. Nevertheless, as will be touched on below, other malignancies have also been examined as models for Myb targeted therapy with some surprisingly encouraging results. Finally, while we have focused our efforts on the ODN strategy, I will allude briefly to other strategies for disrupting Myb function with therapeutic intent.

The presence of the Rb c-box peptide in the cytoplasm inhibits p210bcr-abl transforming function

In order to test if the carboxyl terminal polypeptide of the Retinoblastoma (Rb) tumor suppressor protein, could be used to suppress the growth factor-independent growth phenotype of p210bcr-abl positive myeloid cells, we introduced a truncated form of the 3' end of the Rb cDNA encoding its last 173 amino acid residues (Rb C-box) which localize into the cytoplasm where the p210bcr-abl transforming protein is found, into myeloid cells (32D) which depends on the p210bcr-abl protein for IL3 growth factor-independent growth (32D-p210). The expression of the plasmid vectors carrying the Rb C-box cDNAs was shown to inhibit the abl tyrosine specific protein kinase activity of the p210(bcr-abl) oncoprotein and to suppress the IL3-independent growth phenotype of the 32D-p210 cells. The Rb C-box polypeptides did not suppress the growth of the untransfected 32D parental cell line in methylcellulose in the presence of IL3-conditioned medium. These results suggest that the cytoplasmic localization of the p210(bcr-abl) allows it to escape the effect of intranuclear proteins such as Rb which negatively regulate the p145(c-abl) kinase.

2′,5′-Oligoadenylate-Antisense Chimeras Cause RNase L to Selectively Degrade bcr/abl mRNA in Chronic Myelogenous Leukemia Cells

We report an RNA targeting strategy, which selectively degrades bcr/abl mRNA in chronic myelogenous leukemia (CML) cells. A 2′,5′-tetraadenylate activator (2-5A) of RNase L was chemically linked to oligonucleotide antisense directed against either the fusion site or against the translation start sequence in bcr/abl mRNA. Selective degradation of the targeted RNA sequences was demonstrated in assays with purified RNase L and decreases of p210bcr/abl kinase activity levels were obtained in the CML cell line, K562. Furthermore, the 2-5A-antisense chimeras suppressed growth of K562, while having substantially reduced effects on the promyelocytic leukemia cell line, HL60. Findings were extended to primary CML cells isolated from bone marrow of patients. The 2-5A-antisense treatments both suppressed proliferation of the leukemia cells and selectively depleted levels of bcr/abl mRNA without affecting levels of β-actin mRNA, determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The specificity of this approach was further shown with control oligonucleotides, such as chimeras containing an inactive dimeric form of 2-5A, antisense lacking 2-5A, or chimeras with altered sequences including several mismatched nucleotides. The control oligonucleotides had either reduced or no effect on CML cell growth and bcr/abl mRNA levels. These findings show that CML cell growth can be selectively suppressed by targeting bcr/abl mRNA with 2-5A-antisense for decay by RNase L and suggest that these compounds should be further explored for their potential as ex vivo purging agents of autologous hematopoietic stem cell transplants from CML patients.

2′,5′-Oligoadenylate-Antisense Chimeras Cause RNase L to Selectively Degrade bcr/abl mRNA in Chronic Myelogenous Leukemia Cells

We report an RNA targeting strategy, which selectively degrades bcr/abl mRNA in chronic myelogenous leukemia (CML) cells. A 2′,5′-tetraadenylate activator (2-5A) of RNase L was chemically linked to oligonucleotide antisense directed against either the fusion site or against the translation start sequence in bcr/abl mRNA. Selective degradation of the targeted RNA sequences was demonstrated in assays with purified RNase L and decreases of p210bcr/abl kinase activity levels were obtained in the CML cell line, K562. Furthermore, the 2-5A-antisense chimeras suppressed growth of K562, while having substantially reduced effects on the promyelocytic leukemia cell line, HL60. Findings were extended to primary CML cells isolated from bone marrow of patients. The 2-5A-antisense treatments both suppressed proliferation of the leukemia cells and selectively depleted levels of bcr/abl mRNA without affecting levels of β-actin mRNA, determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The specificity of this approach was further shown with control oligonucleotides, such as chimeras containing an inactive dimeric form of 2-5A, antisense lacking 2-5A, or chimeras with altered sequences including several mismatched nucleotides. The control oligonucleotides had either reduced or no effect on CML cell growth and bcr/abl mRNA levels. These findings show that CML cell growth can be selectively suppressed by targeting bcr/abl mRNA with 2-5A-antisense for decay by RNase L and suggest that these compounds should be further explored for their potential as ex vivo purging agents of autologous hematopoietic stem cell transplants from CML patients.

Synergistic cytotoxicity of bcl-2 antisense oligodeoxynucleotides and etoposide, doxorubicin and cisplatin on small-cell lung cancer cell lines

Expression of Bcl-2 is life-sustaining for small-cell lung cancer cells and associated with drug resistance. In the present study, the interactions between the bcl-2 antisense oligodeoxynucleotide 2009 and the chemotherapeutic agents etoposide, doxorubicin and cisplatin were investigated on small-cell lung cancer cell lines to search for synergistic combinations. The cell lines NCI-H69, SW2 and NCI-H82 express high, intermediate-high and low basal levels of Bcl-2, respectively, which are inversely correlated with the sensitivities of the cell lines to treatment with oligodeoxynucleotide 2009 and the chemotherapeutic agents alone. Moreover, differences were found in the responsiveness of the cell lines to treatment with combinations of oligodeoxynucleotide 2009 and the chemotherapeutic agents. In the cell lines NCI-H69 and SW2, all combinations resulted in synergistic cytotoxicity. In NCI-H69 cells, maximum synergy with a combination index of 0.2 was achieved with the combination of oligodeoxynucleotide 2009 and etoposide. In SW2 cells, the combination of oligodeoxynucleotide 2009 and doxorubicin was the most effective (combination index = 0.5). In the cell line NCI-H82, which expresses a low basal level of Bcl-2, most of the combinations were slightly antagonistic. Our data suggest the use of oligodeoxynucleotide 2009 in combination with chemotherapy for the treatment of small-cell lung cancer that overexpresses Bcl-2.

Clinical evaluation of biologically targeted drugs: obstacles and opportunities

Recent insights into the molecular mechanisms of cancer have indicated that a variety of fundamental cellular processes are dysregulated in malignant cells. These processes include cell cycle control, signal transduction pathways, apoptosis, telomere stability, angiogenesis, and interactions with the extracellular matrix. Remarkable advances in molecular genetics, enzymology, and medicinal chemistry have permitted the design of compounds that modulate some of these processes with specificity that was unimaginable a decade ago. As these novel, biologically targeted compounds enter the clinic, they will require a strategy for clinical evaluation and development different from that used commonly for cytotoxic antineoplastic agents. This review examines the development of cancer drugs directed against angiogenesis, metastasis, signal transduction, telomerase, and molecular message (antisense), outlines strategies for the clinical testing of agents directed at these processes, and contrasts these efforts with traditional approaches to cancer drug testing.

Chronic myelogenous leukaemia CD34+ cells exit G0/G1 phases of cell cycle more rapidly than normal marrow CD34+ cells

To investigate the mechanisms behind the leukaemic expansion of chronic myelogenous leukaemia (CML), we examined the cell cycle status and activation kinetics of purified subpopulations of CD34+ cells from normal and CML bone marrow (BM). Propidium iodide staining was used to assess cell cycle status of fresh cells or those stimulated with cytokines. Although the cell cycle status of fresh low-density cells from CML and normal BM was similar, a larger percentage of CML CD34+ cells were cycling than those from normal BM. The HLA-DR compartment of CML CD34+ cells, a fraction enriched for normal, non-leukaemic progenitors, contained a higher percentage of quiescent cells than the CD34+ HLA-DR+ fraction. When the activation of CD34+ cells was examined in response to SCF or IL-3 alone, or SCF+IL-3+IL-6, CML CD34+ cells exited GO/G1 more rapidly than normal CD34+ cells. Interestingly, although normal BM CD34+ cells failed to cycle in response to IL-6 alone, or in the absence of exogenous cytokines, 30% of CML cells cycled under these conditions. No differences in the degree of apoptosis were documented among CML and normal CD34+ cells in these cultures. These data suggest that enhanced cell cycle activation of CML CD34+ cells, by either autocrine stimuli or via enhanced sensitivity to exogenous stimuli, may be partially responsible for the pronounced cellular expansion characteristic of CML.

Improving the Intracellular Delivery and Molecular Efficacy of Antisense Oligonucleotides in Chronic Myeloid Leukemia Cells: A Comparison of Streptolysin-O Permeabilization, Electroporation, and Lipophilic Conjugation

The hybrid gene BCR-ABL that typifies chronic myeloid leukemia (CML) represents an attractive target for therapy with antisense oligodeoxyribonucleotides (ODN). A central obstacle in the therapeutic application of ODN is their poor cellular uptake. Adding various lipophilic conjugates to the ODN backbone has been reported to improve uptake, and electroporation of target cells has also been shown to enhance intracellular ODN delivery. We have shown that (1)BCR-ABL–directed ODN will specifically decrease the level ofBCR-ABL mRNA, provided that cells are first permeabilized with Streptolysin-O (SL-O), and (2) chimeric methylphosphonodiester:phosphodiester ODN directed against 9 bases either side of the BCR-ABL junction are more efficient ODN effectors than structures composed solely of phosphodiester or phosphorothioate linkages. In this study, we compared the efficacy of lipophilic conjugation, SL-O permeabilization and electroporation on the intracellular delivery and molecular effect ofBCR-ABL–directed ODN. b2a2- and b3a2-directed chimeric ODN were synthesized either unmodified or with one of the following groups at the 5′ end: cholesterol, vitamin E, polyethylene glycol of average molecular weight 2,000 or 5,000, N-octyl-oligo-oxyethylene, or dodecanol. ODN associated with Lipofectin was also studied. Comparison was made in untreated, electroporated, and SL-O permeabilized KYO1 cells. Uptake was examined by fluorescence microscopy and flow cytometry, using ODN structures that were 3′ labeled with fluorescein. The effect on target BCR-ABL mRNA expression was analyzed by Northern blotting. Several conjugated structures associated avidly with the cell membrane without achieving significant intracellular uptake or molecular effect. Similarly, ODN:Lipofectin complexes moderately increased cell association, without enhancing intracellular levels of ODN or inducing detectable molecular effect. In SL-O permeabilized or electroporated cells, uptake was approximately 1 to 2 logs greater than in untreated cells, and rapid nuclear localization was seen, especially with unmodified chimeric ODN. In SL-O permeabilized cells treated with ODN directed to the b2a2 and b3a2 junctions respectively, b2a2 BCR-ABL mRNA levels at 4 hours were reduced to 2.6% ± 2.1% and 38.4% ± 1.3% of control values. In cells permeabilized by electroporation, BCR-ABL mRNA levels were decreased to 4.0% ± 1.4% of control levels by b2a2 directed ODN, although very little nontargeted suppression was seen with b3a2-targeted ODN (93.4% ± 4.2% of control). Greater cell to cell variation in ODN uptake was seen for SL-O permeabilized cells when compared with electroporated cells, suggesting that, after SL-O permeabilization, relatively unpermeabilized and overpermeabilized populations may coexist. No structure had any effect on the level of irrelevant (p53, MYC, and GADPH) mRNA levels. We conclude that the conjugation of chimeric ODN with one of the above-mentioned lipophilic groups or the complexing of ODN with Liopfectin does not improve either intracellular delivery of ODN or the molecular effect. In contrast, both electroporation and SL-O permeabilization (1) considerably enhanced uptake of chimeric ODN (even for structures without a conjugate group) and (2) achieved significant suppression of target mRNA levels.

Improving the Intracellular Delivery and Molecular Efficacy of Antisense Oligonucleotides in Chronic Myeloid Leukemia Cells: A Comparison of Streptolysin-O Permeabilization, Electroporation, and Lipophilic Conjugation

The hybrid gene BCR-ABL that typifies chronic myeloid leukemia (CML) represents an attractive target for therapy with antisense oligodeoxyribonucleotides (ODN). A central obstacle in the therapeutic application of ODN is their poor cellular uptake. Adding various lipophilic conjugates to the ODN backbone has been reported to improve uptake, and electroporation of target cells has also been shown to enhance intracellular ODN delivery. We have shown that (1)BCR-ABL–directed ODN will specifically decrease the level ofBCR-ABL mRNA, provided that cells are first permeabilized with Streptolysin-O (SL-O), and (2) chimeric methylphosphonodiester:phosphodiester ODN directed against 9 bases either side of the BCR-ABL junction are more efficient ODN effectors than structures composed solely of phosphodiester or phosphorothioate linkages. In this study, we compared the efficacy of lipophilic conjugation, SL-O permeabilization and electroporation on the intracellular delivery and molecular effect ofBCR-ABL–directed ODN. b2a2- and b3a2-directed chimeric ODN were synthesized either unmodified or with one of the following groups at the 5′ end: cholesterol, vitamin E, polyethylene glycol of average molecular weight 2,000 or 5,000, N-octyl-oligo-oxyethylene, or dodecanol. ODN associated with Lipofectin was also studied. Comparison was made in untreated, electroporated, and SL-O permeabilized KYO1 cells. Uptake was examined by fluorescence microscopy and flow cytometry, using ODN structures that were 3′ labeled with fluorescein. The effect on target BCR-ABL mRNA expression was analyzed by Northern blotting. Several conjugated structures associated avidly with the cell membrane without achieving significant intracellular uptake or molecular effect. Similarly, ODN:Lipofectin complexes moderately increased cell association, without enhancing intracellular levels of ODN or inducing detectable molecular effect. In SL-O permeabilized or electroporated cells, uptake was approximately 1 to 2 logs greater than in untreated cells, and rapid nuclear localization was seen, especially with unmodified chimeric ODN. In SL-O permeabilized cells treated with ODN directed to the b2a2 and b3a2 junctions respectively, b2a2 BCR-ABL mRNA levels at 4 hours were reduced to 2.6% ± 2.1% and 38.4% ± 1.3% of control values. In cells permeabilized by electroporation, BCR-ABL mRNA levels were decreased to 4.0% ± 1.4% of control levels by b2a2 directed ODN, although very little nontargeted suppression was seen with b3a2-targeted ODN (93.4% ± 4.2% of control). Greater cell to cell variation in ODN uptake was seen for SL-O permeabilized cells when compared with electroporated cells, suggesting that, after SL-O permeabilization, relatively unpermeabilized and overpermeabilized populations may coexist. No structure had any effect on the level of irrelevant (p53, MYC, and GADPH) mRNA levels. We conclude that the conjugation of chimeric ODN with one of the above-mentioned lipophilic groups or the complexing of ODN with Liopfectin does not improve either intracellular delivery of ODN or the molecular effect. In contrast, both electroporation and SL-O permeabilization (1) considerably enhanced uptake of chimeric ODN (even for structures without a conjugate group) and (2) achieved significant suppression of target mRNA levels.

Cytotoxic T cell response against the chimeric p210 BCR-ABL protein in patients with chronic myelogenous leukemia

Human chronic myelogenous leukemia (CML) is characterized by a translocation between chromosomes 9 and 22 that results in a BCR-ABL fusion gene coding for chimeric proteins. The junctional region of the BCR-ABLb3a2 molecule represents a potential leukemia-specific antigen which could be recognized by cytotoxic T lymphocytes (CTL). In fact, we identified a junctional nonapeptide (SSKALQRPV) which binds to HLA-A2.1 molecules. This peptide, as well as those binding to HLA-A3, -A11, and -B8 molecules (previously identified by others), elicits primary CTL responses in vitro from PBLs of both healthy donors and CML patients. Such CTL recognize HLA-matched, BCR-ABL-positive leukemic cells, implying efficient natural processing and presentation of these junctional peptides. Specific CTL were found at high frequency in 5 of 21 CML patients, suggesting that these epitopes are, to some extent, immunogenic in vivo during the course of the disease. These peptides could be useful for the development of specific immunotherapy in CML patients.

BCR-ABL Antisense Oligodeoxynucleotide In Vitro Purging and Autologous Bone Marrow Transplantation for Patients With Chronic Myelogenous Leukemia in Advanced Phase

BCR-ABL antisense oligodeoxynucleotides (ODN) have provided evidence of antileukemia effect when tested in vitro against Philadelphia-positive (Ph-pos) cells and in vivo when injected into leukemic mice. On the basis of the results obtained in vitro at diagnosis, eight patients with chronic myelogenous leukemia (CML) were selected and submitted to autologous bone marrow transplantation (ABMT) with bone marrow (BM) cells purged in vitro with junction-specific (J-sp) BCR-ABL antisense ODN at the time of transformation in accelerated phase or during second chronic phase. Mononuclear BM cells were treated in vitro for 24 or 72 hours with 150 μg/mL of antisense ODN yielding a median recovery of 47.6% mononuclear cells, 48.8% CD34+ cells, and 20.3% clonogenic cells. After a conditioning regimen including busulphan and etoposide, the reinfused treated cells allowed engraftment and hematologic reconstitution in all patients. Evaluation of the antileukemic effect by standard cytogenetic analysis and fluorescence in situ hybridization showed a complete karyotypic response in two cases and a minimal or no response in the other six. The patient autografted in second chronic phase died in blast crisis 7 months after ABMT; of the seven patients autografted in transformation, three developed blast crisis 21 to 39 months after reinfusion, one died from unrelated BMT complications 30 months after ABMT, and three are in persistent second chronic phase 14 to 26 months after autograft. The low toxicity of the protocol and the hemopoietic reconstitution observed in all patients make this approach feasible; the marked karyotypic response observed in some patients and the duration of the second chronic phase show that ODN-mediated BM purging and autograft is a promising treatment for this high-risk group of CML.

Inhibition of BCR-ABL Expression With Antisense Oligodeoxynucleotides Restores β1 Integrin-Mediated Adhesion and Proliferation Inhibition in Chronic Myelogenous Leukemia Hematopoietic Progenitors

Chronic myelogenous leukemia (CML) is characterized by the continuous proliferation and abnormal circulation of malignant hematopoietic progenitors. This may be related to the unresponsiveness of CML progenitors to β1 integrin adhesion receptor-mediated inhibition of progenitor proliferation by the marrow microenvironment. In hematopoietic cell lines, the BCR-ABL oncogene product, p210BCR-ABL, interacts with a variety of cytoskeletal elements important for normal integrin signaling. We studied the role of p210BCR-ABL in abnormal integrin function in CML by evaluating the effect of inhibition of BCR-ABL expression with antisense oligodeoxynucleotides (AS-ODNs) on integrin-mediated adhesion and proliferation inhibition of malignant primary progenitors from CML marrow. Preincubation of CML CD34+HLA-DR+(DR+) cells with breakpoint-specific AS-ODNs significantly increased adhesion of CML progenitors to stroma and fibronectin (FN). Pretreatment with breakpoint-specific ODNs also resulted in significant inhibition of CML progenitor proliferation after ligand or antibody-mediated β1 integrin engagement. Breakpoint-specific ODNs were significantly more effective in restoring CML progenitor adhesion and proliferation inhibition than control ODNs. BCR-ABL mRNA and p210BCR-ABL levels in CML CD34+ cells were significantly reduced after incubation with breakpoint-specific AS-ODN. These studies indicate a role for BCR-ABL in abnormal circulation and defective integrin-dependent microenvironmental regulation of proliferation of CML hematopoietic progenitors.

Inhibition of BCR-ABL Expression With Antisense Oligodeoxynucleotides Restores β1 Integrin-Mediated Adhesion and Proliferation Inhibition in Chronic Myelogenous Leukemia Hematopoietic Progenitors

Chronic myelogenous leukemia (CML) is characterized by the continuous proliferation and abnormal circulation of malignant hematopoietic progenitors. This may be related to the unresponsiveness of CML progenitors to β1 integrin adhesion receptor-mediated inhibition of progenitor proliferation by the marrow microenvironment. In hematopoietic cell lines, the BCR-ABL oncogene product, p210BCR-ABL, interacts with a variety of cytoskeletal elements important for normal integrin signaling. We studied the role of p210BCR-ABL in abnormal integrin function in CML by evaluating the effect of inhibition of BCR-ABL expression with antisense oligodeoxynucleotides (AS-ODNs) on integrin-mediated adhesion and proliferation inhibition of malignant primary progenitors from CML marrow. Preincubation of CML CD34+HLA-DR+(DR+) cells with breakpoint-specific AS-ODNs significantly increased adhesion of CML progenitors to stroma and fibronectin (FN). Pretreatment with breakpoint-specific ODNs also resulted in significant inhibition of CML progenitor proliferation after ligand or antibody-mediated β1 integrin engagement. Breakpoint-specific ODNs were significantly more effective in restoring CML progenitor adhesion and proliferation inhibition than control ODNs. BCR-ABL mRNA and p210BCR-ABL levels in CML CD34+ cells were significantly reduced after incubation with breakpoint-specific AS-ODN. These studies indicate a role for BCR-ABL in abnormal circulation and defective integrin-dependent microenvironmental regulation of proliferation of CML hematopoietic progenitors.

BCR-ABL Antisense Oligodeoxynucleotide In Vitro Purging and Autologous Bone Marrow Transplantation for Patients With Chronic Myelogenous Leukemia in Advanced Phase

BCR-ABL antisense oligodeoxynucleotides (ODN) have provided evidence of antileukemia effect when tested in vitro against Philadelphia-positive (Ph-pos) cells and in vivo when injected into leukemic mice. On the basis of the results obtained in vitro at diagnosis, eight patients with chronic myelogenous leukemia (CML) were selected and submitted to autologous bone marrow transplantation (ABMT) with bone marrow (BM) cells purged in vitro with junction-specific (J-sp) BCR-ABL antisense ODN at the time of transformation in accelerated phase or during second chronic phase. Mononuclear BM cells were treated in vitro for 24 or 72 hours with 150 μg/mL of antisense ODN yielding a median recovery of 47.6% mononuclear cells, 48.8% CD34+ cells, and 20.3% clonogenic cells. After a conditioning regimen including busulphan and etoposide, the reinfused treated cells allowed engraftment and hematologic reconstitution in all patients. Evaluation of the antileukemic effect by standard cytogenetic analysis and fluorescence in situ hybridization showed a complete karyotypic response in two cases and a minimal or no response in the other six. The patient autografted in second chronic phase died in blast crisis 7 months after ABMT; of the seven patients autografted in transformation, three developed blast crisis 21 to 39 months after reinfusion, one died from unrelated BMT complications 30 months after ABMT, and three are in persistent second chronic phase 14 to 26 months after autograft. The low toxicity of the protocol and the hemopoietic reconstitution observed in all patients make this approach feasible; the marked karyotypic response observed in some patients and the duration of the second chronic phase show that ODN-mediated BM purging and autograft is a promising treatment for this high-risk group of CML.

Nuclease-resistant composite 2',5'-oligoadenylate-3', 5'-oligonucleotides for the targeted destruction of RNA: 2-5A-iso-antisense

A new modification of 2-5A-antisense, 2-5A-iso-antisense, has been developed based on a reversal of the direction of the polarity of the antisense domain of a 2-5A-antisense composite nucleic acid. This modification was able to anneal with its target RNA as well as the parental 2-5A-antisense chimera. The 2-5A-iso-antisense oligonucleotide displayed enhanced resistance to degradation by 3'-exonuclease enzyme activity such as that represented by snake venom phosphodiesterase and by that found in human serum. 2-5A-Iso-antisense was able to effect the degradation of a synthetic nontargeted substrate, [5'-32P]pC11U2C7, and two targeted RNAs, PKR and BCR mRNAs, in a cell-free system containing purified recombinant human 2-5A-dependent RNase L. These results demonstrated that the novel structural modification represented by 2-5A-iso-antisense provided a stabilized biologically active formulation of the 2-5A-antisense strategy.

Antisense therapy of hepatitis B virus infection

Chronic infection with the hepatitis B virus (HBV) is a major health problem worldwide. The only established therapy is interferon-a with an efficacy of only 30-40% in highly selected patients. The discovery of animal viruses closely related to the HBV has contributed to active research on antiviral therapy of chronic hepatitis B. The animal model tested and described in this article are Peking ducks infected with the duck hepatitis B virus (DHBV). Molecular therapeutic strategies aimed at blocking gene expression include antisense DNA. An antisense oligodeoxynucleotide directed against the 5'-region of the preS gene of DHBV inhibited viral replication and gene expression in vitro in primary duck hepatocytes and in vivo in Peking ducks. These results demonstrate the potential clinical use of antisense DNA as antiviral therapeutics.

Selecting optimal oligonucleotide composition for maximal antisense effect following streptolysin O-mediated delivery into human leukaemia cells

It is widely accepted that most cell types efficiently exclude oligonucleotides in vitro and require specific delivery systems, such as cationic lipids, to enhance uptake and subsequent antisense effects. Oligonucleotides are not readily transfected into leukaemia cell lines using cationic lipid systems and streptolysin O (SLO) is used to effect their delivery. We wished to investigate the optimal oligonucleotide composition for antisense efficacy and specificity following delivery into leukaemia cells using SLO. For this study the well characterised chronic myeloid leukaemia cell line KYO-1 was selected and oligonucleotides (20mers) were targeted to an empirically identified accessible site of c- myc mRNA. The efficiency and specificity of antisense effect was measured 4 and 24 h after SLO-mediated delivery of the oligonucleotides. C5-propyne phosphodiester and phosphorothioate compounds were found to present substantial non-specific effects at 20 microM but were inactive at 0.2 microM. Indeed, no antisense-specific effect was noted at any concentration at either time. All of the other oligonucleotides tested induced some measurable antisense effect, except 7 (chimeric, all-phosphorothioate, 2'-methoxyethoxy termini) which was essentially inactive at 20 microM. The rank efficiency order of the remaining antisense compounds was 4 = 3 >> 9 >> 10 = 8 = 5 = 6 > 11. The efficient antisense effects induced by the chimeric methylphosphonate-phosphodiester compounds were found to be highly specific. Increased phosphorothioate content in the oligonucleotide backbone correlated with reduced antisense activity (efficacy: 2'-methoxyethoxy series 9 >> 8 >> 7, 2'-methoxytriethoxy series 10 > 11). No consistent evidence was obtained for increased activity correlating with increased oligonucleotide-mRNA heteroduplex thermal stability. In conclusion, the chimeric methylphosphonate-phosphodiester oligodeoxynucleotides present the most favourable characteristics of the compounds tested, for efficient and specific antisense suppression of gene expression following SLO-mediated delivery.

The rat gene homologous to the human gene 9-27 is involved in the development of the mammary gland

We have developed a model system for studying differentiation in the mammary gland, by using two clonal cultures deriving from a rat breast adenocarcinoma. They differ in the ability to form domes, structures the significance of which is unknown. By using the subtractive cDNA library approach, we isolated a cDNA that is highly expressed in the dome-forming cells, and identical to the rat8 gene and highly homologous to the human 9-27 gene. Antisense treatment of the dome-forming cells specifically and reproducibly abolishes dome formation, while forced expression of the gene in non-dome-forming cells causes morphological changes suggestive of "flat" domes. In situ hybridization on rat tissues shows that the gene is expressed in epithelia, especially in those forming tubular structures, suggesting a relatedness between these structures and domes. Cytokeratin 8 and E cadherin are strongly expressed in the domes but not outside them, suggesting that the rat8 gene triggers the cells to express molecules that tighten the lateral connections between the cells; the process is likely to parallel that occurring during the differentiation of the mammary gland.

Ex vivo effects associated with the expression of a bcr-abl-specific ribozyme in a CML cell line

The bcr-abl chimeric gene is found in 95% of chronic myeloid leukemia (CML) patients and is thought to be seminal to the etiology of the disease. The possibility of using ribozymes to suppress bcr-abl gene expression and subsequently alter the malignant phenotype of hematopoietic cells may provide an alternative therapeutic approach to current regimens. A series of hammerhead ribozymes targeted to a b3a2 bcr-abl transcript has been developed and previously shown to be capable of cleaving the desired sequence with varying degrees of specificity. This study investigated the ex vivo effects of endogenous expression of these ribozymes in a CML cell line, K562. We demonstrated a 53% decrease in bcr-abl mRNA levels in a clone induced to express Rz8, compared with its uninduced control. Phenotypic analysis of this clone also revealed a 63% decrease in colony-forming ability and a 43% inhibition of cell proliferation following ribozyme expression. Morphologic analysis of cells showed there was a slight increase (2.5% to 15%) in the number of cells undergoing apoptosis. These results suggest that Rz8 was effective in suppressing bcr-abl gene expression within a cellular environment and altering the leukemic nature of a CML cell line.

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.

Establishment of a Reproducible Model of Chronic-Phase Chronic Myeloid Leukemia in NOD/SCID Mice Using Blood-Derived Mononuclear or CD34+ Cells

An animal model of chronic myeloid leukemia (CML) will help characterize leukemic and normal stem cells and also help evaluate experimental therapies in this disease. We have established a model of CML in the NOD/SCID mouse. Infusion of ≥4 × 107chronic-phase CML peripheral blood cells results in engraftment levels of ≥1% in the bone marrow (BM) of 84% of mice. Engraftment of the spleen was seen in 60% of mice with BM engraftment. Intraperitoneal injection of recombinant stem cell factor produced a higher level of leukemic engraftment without increasing Philadelphia-negative engraftment. Granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor did not increase the level of leukemic or residual normal engraftment. Assessment of differential engraftment of normal and leukemic cells by fluorescence in situ hybridization analysis with bcr and abl probes showed that a median of 35% (range, 5% to 91%) of engrafted cells present in the murine BM were leukemic. BM engraftment was multilineage with myeloid, B-cell, and T-cell engraftment, whereas T cells were the predominant cell type in the spleen. BM morphology showed evidence of eosinophilia and increased megakaryocytes. We also assessed the ability of selected CD34+ CML blood cells to engraft NOD/SCID mice and showed engraftment with cell doses of 7 to 10 × 106 cells. CD34− cells failed to engraft at cell doses of 1.2 to 5 × 107. CD34+ cells produced myeloid and B-cell engraftment with high levels of CD34+ cells detected. Thus, normal and leukemic stem cells are present in CD34+ blood cells from CML patients at diagnosis and lead to development of the typical features of CML in murine BM. This model is suitable to evaluate therapy in CML.