Phase 1 and pharmacodynamic studies of G3139, a Bcl-2 antisense oligonucleotide, in combination with chemotherapy in refractory or relapsed acute leukemia

Dysregulated innate immune signaling cooperates with RUNX1 mutations to transform an MDS-like disease to AML

Dysregulated innate immune signaling is linked to preleukemic conditions and myeloid malignancies. However, it is unknown whether sustained innate immune signaling contributes to malignant transformation. Here we show that cell-intrinsic innate immune signaling driven by miR-146a deletion (miR-146aKO), a commonly deleted gene in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), cooperates with mutant RUNX1 (RUNX1mut) to initially induce marrow failure and features of MDS. However, miR-146aKO hematopoietic stem and/or progenitor cells (HSPCs) expressing RUNX1mut eventually progress to a fatal AML. miR-146aKO HSPCs exhaust during serial transplantation, while expression of RUNX1mut restored their hematopoietic cell function. Thus, HSPCs exhibiting dysregulated innate immune signaling require a second hit to develop AML. Inhibiting the dysregulated innate immune pathways with a TRAF6-UBE2N inhibitor suppressed leukemic miR-146aKO/RUNX1mut HSPCs, highlighting the necessity of TRAF6-dependent cell-intrinsic innate immune signaling in initiating and maintaining AML. These findings underscore the critical role of dysregulated cell-intrinsic innate immune signaling in driving preleukemic cells toward AML progression.

Targeting apoptosis dysregulation in myeloid malignancies - The promise of a therapeutic revolution

In recent years, the therapeutic landscape of myeloid malignancies has been completely revolutionized by the introduction of several new drugs, targeting molecular alterations or pathways crucial for leukemia cells survival. Particularly, many agents targeting apoptosis have been investigated in both pre-clinical and clinical studies. For instance, venetoclax, a pro-apoptotic agent active on BCL-2 signaling, has been successfully used in the treatment of acute myeloid leukemia (AML). The impressive results achieved in this context have made the apoptotic pathway an attractive target also in other myeloid neoplasms, translating the experience of AML. Therefore, several drugs are now under investigation either as single or in combination strategies, due to their synergistic efficacy and capacity to overcome resistance. In this paper, we will review the mechanisms of apoptosis and the specific drugs currently used and under investigation for the treatment of myeloid neoplasia, identifying critical research necessities for the upcoming years.

Doxorubicin-conjugated siRNA lipid nanoparticles for combination cancer therapy

Evasion of apoptosis is a hallmark of cancer, attributed in part to overexpression of the anti-apoptotic protein B-cell lymphoma 2 (Bcl-2). In a variety of cancer types, including lymphoma, Bcl-2 is overexpressed. Therapeutic targeting of Bcl-2 has demonstrated efficacy in the clinic and is the subject of extensive clinical testing in combination with chemotherapy. Therefore, the development of co-delivery systems for Bcl-2 targeting agents, such as small interfering RNA (siRNA), and chemotherapeutics, such as doxorubicin (DOX), holds promise for enabling combination cancer therapies. Lipid nanoparticles (LNPs) are a clinically advanced nucleic acid delivery system with a compact structure suitable for siRNA encapsulation and delivery. Inspired by ongoing clinical trials of albumin-hitchhiking doxorubicin prodrugs, here we developed a DOX-siRNA co-delivery strategy via conjugation of doxorubicin to the surface of siRNA-loaded LNPs. Our optimized LNPs enabled potent knockdown of Bcl-2 and efficient delivery of DOX into the nucleus of Burkitts' lymphoma (Raji) cells, leading to effective inhibition of tumor growth in a mouse model of lymphoma. Based on these results, our LNPs may provide a platform for the co-delivery of various nucleic acids and DOX for the development of new combination cancer therapies.

Venetoclax in Acute Myeloid Leukemia: Molecular Basis, Evidences for Preclinical and Clinical Efficacy and Strategies to Target Resistance

Venetoclax is a BH3-mimetics agent specifically interacting with the antiapoptotic protein BCL-2, facilitating cytochrome c release from mitochondria, subsequent caspases activation, and cell death. Utilization of venetoclax has profoundly changed the landscape of treatment for the poor-prognosis category of AML patients unfit for intensive chemotherapy. In the phase III VIALE-A study, Venetoclax, in combination with the hypomethylating agent azacitidine, showed a 65% overall response rate and 14.7-month overall survival, in comparison with 22% and 8 months in the control arm. These results led to the widespread use of venetoclax in this indication. Other combination regimens, consisting of low-intensity, intensive, or targeted therapies are currently under evaluation. Despite promising results, preventing relapses or resistance to venetoclax is still an unmet clinical need. Numerous studies have been conducted to identify and overcome venetoclax resistance in preclinical models or in clinical trials, including the inhibition of other antiapoptotic proteins, the induction of proapoptotic BH3-only proteins, and/or the targeting of the mitochondrial metabolism and machinery.

Antisense Oligonucleotide-Mediated Splice Switching: Potential Therapeutic Approach for Cancer Mitigation

Splicing is an essential process wherein precursor messenger RNA (pre-mRNA) is reshaped into mature mRNA. In alternative splicing, exons of any pre-mRNA get rearranged to form mRNA variants and subsequently protein isoforms, which are distinct both by structure and function. On the other hand, aberrant splicing is the cause of many disorders, including cancer. In the past few decades, developments in the understanding of the underlying biological basis for cancer progression and therapeutic resistance have identified many oncogenes as well as carcinogenic splice variants of essential genes. These transcripts are involved in various cellular processes, such as apoptosis, cell signaling and proliferation. Strategies to inhibit these carcinogenic isoforms at the mRNA level are promising. Antisense oligonucleotides (AOs) have been developed to inhibit the production of alternatively spliced carcinogenic isoforms through splice modulation or mRNA degradation. AOs can also be used to induce splice switching, where the expression of an oncogenic protein can be inhibited by the induction of a premature stop codon. In general, AOs are modified chemically to increase their stability and binding affinity. One of the major concerns with AOs is efficient delivery. Strategies for the delivery of AOs are constantly being evolved to facilitate the entry of AOs into cells. In this review, the different chemical modifications employed and delivery strategies applied are discussed. In addition to that various AOs in clinical trials and their efficacy are discussed herein with a focus on six distinct studies that use AO-mediated exon skipping as a therapeutic strategy to combat cancer.

Phase 3 randomized trial of chemotherapy with or without oblimersen in older AML patients: CALGB 10201 (Alliance)

Overexpression of B-cell leukemia/lymphoma 2 (BCL2) renders acute myeloid leukemia (AML) cells resistant to chemotherapy and has been associated with unfavorable outcomes. Oblimersen (G3139) is a phosphorothioate 18-mer antisense oligonucleotide directed against the first 6 BCL2 codons. In a phase 1 study of AML patients treated with G3139, cytarabine, and daunorubicin induction with cytarabine consolidation, no antisense-related toxicity was reported, and BCL2 downregulation occurred in patients achieving complete remission. In this phase 3 trial, untreated older AML patients were randomized to cytarabine (100 mg/m2 per day on days 4-10) and daunorubicin (60 mg/m2 per day on days 4-6) followed by cytarabine consolidation (2000 mg/m2 per day on days 4-8) with (arm A) or without (arm B) G3139 (7 mg/m2 per day on days 1-10 [induction] or days 1-8 [consolidation]). A total of 506 patients were enrolled. No differences in toxicity were observed between arms. Estimated overall survival (OS) at 1 year was 43% for arm A and 40% for arm B (1-sided log rank P = .13), with no differences in disease-free (DFS; P = .26) or event-free survival (P = .80). Subgroup analyses showed patients age <70 years in arm A had improved OS by 1 month vs those in arm B (P = .04), and patients with secondary AML in arm A had better DFS vs those in arm B (P = .04). We conclude that addition of G3139 to chemotherapy failed to improve outcomes of older AML patients. However, more effective means of inhibiting BCL2 are showing promising results in combination with chemotherapy in AML. This trial was registered at www.clinicaltrials.gov as #NCT00085124.

Acute myeloid leukemia: Therapy resistance and a potential role for tetraspanin membrane scaffolds

Acute myeloid leukemia (AML) is characterized by the disruption of myeloid differentiation and accumulation of blast cells in the bone marrow. While AML patients respond favorably to induction chemotherapy, long-term outcomes remain poor due to a high rate of chemoresistance. Advances with targeted therapies, which can be used in combination with conventional chemotherapy, have expanded therapeutic options for patients. However, remission is often short-lived and followed by disease relapse and drug resistance. Therefore, there is a substantial need to improve treatment options by identifying novel molecular and cellular targets that regulate AML chemosensitivity. Membrane scaffolds such as the tetraspanin family of proteins often serve as signaling mediators, translating extracellular signaling cues into intracellular signaling cascades. In this review, we discuss the conventional and targeted treatment strategies for AML and review chemoresistance mechanisms with a focus on the tetraspanin family of membrane scaffold proteins.

Targeting Bcl-2 for cancer therapy

Apoptosis deficiency is one of the most important features observed in neoplastic diseases. The Bcl-2 family is composed of a subset of proteins that act as decisive apoptosis regulators. Research and clinical studies have both demonstrated that the hyperactivation of Bcl-2-related anti-apoptotic effects correlates with cancer occurrence, progression and prognosis, also having a role in facilitating the radio- and chemoresistance of various malignancies. Therefore, targeting Bcl-2 inactivation has provided some compelling therapeutic advantages by enhancing apoptotic sensitivity or reversing drug resistance. Therefore, this pharmacological route turned into one of the most promising routes for cancer treatment. This review discusses some of the well-defined and emerging roles of Bcl-2 as well as its potential clinical value in cancer therapeutics.

Evaluation of Pharmacokinetics and Metabolism of Phosphorothioate Antisense Oligonucleotide G3139 in Rat by Capillary Electrophoresis with Laser-Induced Fluorescence

A sensitive and specific capillary electrophoresis with laser-induced fluorescence (CE-LIF) and a simple extraction process was developed to simultaneously detect G3139 and its metabolites as a model of antisense oligonucleotides (ASOs). This method has shown excellent linearity within the tested concentration range for G3139 and its metabolites, with a detection limit of 3.0 pM and a recovery of >84.2%. Based on our developed plasma extraction method, we have evaluated the pharmacokinetics and metabolites from rat plasma after intravenous administration of G3139 at 0.76 mg/kg. The results showed that G3139 and its metabolites were successfully simultaneously detected and analyzed through a single run using CE-LIF with baseline separation until the 30-h test sampling time point. The half-life of G3139 and its metabolites was observed at 31 and 68 h, respectively. This study may provide an effective analytical method for the pharmacokinetic and metabolite evaluation required to develop ASOs to treat a variety of diseases.

Targeting Bcl-2 Proteins in Acute Myeloid Leukemia

B cell lymphoma 2 (BCL-2) family proteins play an important role in intrinsic apoptosis. Overexpression of BCL-2 proteins in acute myeloid leukemia can circumvent resistance to apoptosis and chemotherapy. Considering this effect, the exploration of anti-apoptotic BCL-2 inhibitors is considered to have tremendous potential for the discovery of novel pharmacological modulators in cancer. This review outlines the impact of BCL-2 family proteins on intrinsic apoptosis and the development of acute myeloid leukemia (AML). Furthermore, we will also review the new combination therapy with venetoclax that overcomes resistance to venetoclax and discuss biomarkers of treatment response identified in early-phase clinical trials.

Treatment of Acute Myeloid Leukemia in the Era of Genomics-Achievements and Persisting Challenges

Acute myeloid leukemia (AML) represents a malignant disorder of the hematopoietic system that is mainly characterized by rapid proliferation, dysregulated apoptosis, and impaired differentiation of leukemic blasts. For several decades, the diagnostic approach in AML was largely based on histologic characteristics with little impact on the treatment decision-making process. This perspective has drastically changed within the past years due to the advent of novel molecular technologies, such as whole genome next-generation sequencing (NGS), and the resulting knowledge gain in AML biology and pathogenesis. After more than four decades of intensive chemotherapy as a "one-size-fits-all" concept, several targeted agents have recently been approved for the treatment of AML, either as single agents or as part of combined treatment regimens. Several other compounds, directed against regulators of apoptotic, epigenetic, or microenvironmental pathways, as well as modulators of the immune system, are currently in development and being investigated in clinical trials. The constant progress in AML research has started to produce improved survival rates and fueled hopes that a once rapidly fatal disease can be transformed into a chronic condition. In this review, the authors provide a summary of recent advances in the development of targeted AML therapies and discuss persistent challenges.

From Bench to Bedside and Beyond: Therapeutic Scenario in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of clonal disorders characterized by abnormal proliferation of undifferentiated myeloid progenitors, impaired hematopoiesis, and variable response to therapy. To date, only about 30% of adult patients with AML become long-term survivors and relapse and/or disease refractoriness are the major cause of treatment failure. Thus, this is an urgent unmet clinical need and new drugs are envisaged in order to ameliorate disease survival outcomes. Here, we review the latest therapeutic approaches (investigational and approved agents) for AML treatment. A specific focus will be given to molecularly targeted therapies for AML as a representation of possible agents for precision medicine. We will discuss experimental and preclinical data for FLT3, IDH1, BCL-2, Hedgehog pathway inhibitors, and epitherapy.

Targeting Apoptotic Pathways in Acute Myeloid Leukaemia

Acute Myeloid Leukaemia is a devastating disease that continues to have a poor outcome for the majority of patients. In recent years, however, a number of drugs have received FDA approval, following on from successful clinical trial results. This parallels the characterization of the molecular landscape of Acute Myeloid Leukaemia (AML) over the last decade, which has led to the development of drugs targeting newly identified recurring mutations. In addition, basic biological research into the pathobiology of AML has identified aberrant programmed cell death pathways in AML. Following on from successful outcomes in lymphoid malignancies, drugs targeting the B Cell Lymphoma 2 (BCL-2) family of anti-apoptotic proteins have been explored in AML. In this review, we will outline the preclinical and clinical work to date supporting the role of drugs targeting BCL-2, with Venetoclax being the most advanced to date. We will also highlight rationale combinations using Venetoclax, ongoing clinical trials and biomarkers of response identified from the early phase clinical trials performed.

The Role of Inhibition of Apoptosis in Acute Leukemias and Myelodysplastic Syndrome

Avoidance of apoptosis is a key mechanism that malignancies, including acute leukemias and MDS, utilize in order to proliferate and resist chemotherapy. Recently, venetoclax, an inhibitor of the anti-apoptotic protein BCL-2, has been approved for the treatment of upfront AML in an unfit, elderly population. This paper reviews the pre-clinical and clinical data for apoptosis inhibitors currently in development for the treatment of AML, ALL, and MDS.

BCL-2 inhibition in AML: an unexpected bonus?

B-cell lymphoma 2 (BCL-2) was discovered at the breakpoint of the t(14;18) in follicular lymphoma >30 years ago. Although inhibition of BCL-2 first proved valuable in lymphoid malignancies, clinical progress in myeloid malignancies lagged. Here, we summarize the basic biology and preclinical results that spurred clinical BCL-2 inhibition in acute myeloid leukemia (AML). Response rates and toxicity for venetoclax in combination with standard AML agents, such as azacitidine, decitabine, and low-dose cytarabine, compare favorably with conventional induction chemotherapy. Durability of response requires further study.

Analysis of oligonucleotides by ion-pairing hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry

RATIONALE

Hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry (HILIC-LC/ESI-MS) has been proved to be useful for the quality control of oligonucleotides. However, the lack of separation for some oligonucleotides using HILIC-LC/MS has proved problematic. This study aimed to improve the resolving ability of HILIC-LC/MS.

METHODS

The study was performed on a Waters UPLC® system coupled to a Waters LCT premier XE ESI-TOF mass spectrometer using a Zorbax® RRHD HILIC column (2.1 mm × 100 mm, 1.8 μm). Buffer systems contained triethylammonium acetate (TEAA) and acetonitrile. The effects of the concentration of TEAA and the type of organic modifiers on the separation of oligonucleotides were investigated.

RESULTS

The results showed that the optimum concentration of TEAA is 10 mM and acetonitrile is a better organic solvent than methanol. The addition of TEAA in the HILIC mobile phase improved the separation of N from N + A significantly compared to the HILIC method buffered with ammonium acetate. The IP-HILIC chromatography has demonstrated that the separation of oligonucleotides is sequence dependent. In addition, the IP-HILIC method produces a much simpler mass spectrum of an oligonucleotide with very efficient desalting.

CONCLUSIONS

The HILIC-LC/MS method with the addition of TEAA at a MS-compatible concentration has improved the separation of oligonucleotides. The IP-HILIC-LC/MS method also produces very simple mass spectra with high desalting efficiency.

Targeted Therapy for Hematologic Malignancies

Background:

The introduction of monoclonal antibodies, either as native molecules or conjugated to radioisotopes or other toxins, has led to new therapeutic options for patients with hematologic malignancies. In addition, the use of small molecules against specific cell surface receptors, enzymes, and proteins has become an important strategy in the treatment of such disorders.

Methods:

The author reviewed the published clinical trials of monoclonal antibody and other targeted therapies in hematologic malignancies.

Results:

Results from several trials demonstrate a therapeutic benefit for the use of monoclonal antibodies (either native or conjugated) and other targeted therapies, used alone or in combination with standard cytotoxic chemotherapy.

Conclusions:

Targeted therapy of hematologic malignancies seems to be an effective and less toxic approach to the treatment of such disorders. Nevertheless, additional studies are needed to determine where and when such management fits into a therapeutic regimen for any given disorder, whether upfront or as salvage therapy, alone or in combination with chemotherapy (concurrent or sequential).

Apoptosis signaling and BCL-2 pathways provide opportunities for novel targeted therapeutic strategies in hematologic malignances

Apoptosis is an essential biological process involved in tissue homeostasis and immunity. Aberrations of the two main apoptotic pathways, extrinsic and intrinsic, have been identified in hematological malignancies; many of these aberrations are associated with pathogenesis, prognosis and resistance to standard chemotherapeutic agents. Targeting components of the apoptotic pathways, especially the chief regulatory BCL-2 family in the intrinsic pathway, has proved to be a promising therapeutic approach for patients with hematological malignances, with the expectation of enhanced efficacy and reduced adverse events. Continuous investigations regarding the biological importance of each of the BCL-2 family components and the clinical rationale to achieve optimal therapeutic outcomes, using either monotherapy or in combination with other targeted agents, have generated inspiring progress in the field. Genomic, epigenomic and biological analyses including BH3 profiling facilitate effective evaluation of treatment response, cancer recurrence and drug resistance. In this review, we summarize the biological features of each of the components in the BCL-2 apoptotic pathways, analyze the regulatory mechanisms and the pivotal roles of BCL-2 family members in the pathogenesis of major types of hematologic malignances, and evaluate the potential of apoptosis- and BCL-2-targeted strategies as effective approaches in anti-cancer therapies.

PP2A inhibition from LB100 therapy enhances daunorubicin cytotoxicity in secondary acute myeloid leukemia via miR-181b-1 upregulation

Patients with secondary acute myeloid leukemia (sAML) arising from myelodysplastic syndromes have a poor prognosis marked by an increased resistance to chemotherapy. An urgent need exists for adjuvant treatments that can enhance or replace current therapeutic options. Here we show the potential of LB100, a small-molecule protein phosphatase 2 A (PP2A) inhibitor, as a monotherapy and chemosensitizing agent for sAML using an in-vitro and in-vivo approach. We demonstrate that LB100 decreases cell viability through caspase activation and G2/M cell-cycle arrest. LB100 enhances daunorubicin (DNR) cytotoxicity resulting in decreased xenograft volumes and improved overall survival. LB100 profoundly upregulates miR-181b-1, which we show directly binds to the 3′ untranslated region of Bcl-2 mRNA leading to its translational inhibition. MiR-181b-1 ectopic overexpression further diminishes Bcl-2 expression leading to suppression of sAML cell growth, and enhancement of DNR cytotoxicity. Our research highlights the therapeutic potential of LB100, and provides new insights into the mechanism of LB100 chemosensitization.

Why anti-Bcl-2 clinical trials fail: a solution

The alteration in expression of B cell lymphoma-2 (Bcl-2) family of protein members in cancer is involved mainly in the regulation of apoptosis. Bcl-2 family proteins are currently used as major targets in the development of methods to improve treatment outcomes for cancer patients that underwent clinical trials. Although many agents have been developed for targeting Bcl-2 in the past decade, some previous attempts to target Bcl-2 have not resulted in beneficial clinical outcome for reasons unknown. Here, we propose that this was due in part for not considering the cellular level of a different antiapoptotic protein, i.e., galectin-3 (Gal-3). Gal-3 is a member of the β-galactoside binding protein family and a multifunctional oncogenic protein which regulates cell growth, cell adhesion, cell proliferation, angiogenesis, and apoptosis. Gal-3 is the sole protein that contains the NWGR anti-death motif of the Bcl-2 family and inhibits cell apoptosis induced by chemotherapeutic agents through phosphorylation, translocation and regulation of survival signaling pathways. It is now established that Gal-3 is a candidate target protein to suppress antiapoptotic activity and anticancer drug resistance. In this review, we describe the role and relevance of Gal-3 and Bcl-2 protein family in the regulation of apoptosis and propose a novel combination therapy modality. Combination therapy that targets Gal-3 could be essential for improvement of the efficacy of Bcl-2 targeting therapy in cancers and should be studied in future clinical trials. Otherwise, not considering Gal-3 cellular level could lead to trial failure.

Biology and Clinical Relevance of Acute Myeloid Leukemia Stem Cells

Evidence for the cancer stem cell model was first demonstrated in xenotransplanted blood and bone marrow samples from patients with acute myeloid leukemia (AML) almost two decades ago, supporting the concept that a rare clonal and mutated leukemic stem cell (LSC) population is sufficient to drive leukemic growth. The inability to eliminate LSCs with conventional therapies is thought to be the primary cause of disease relapse in AML patients, and as such, novel therapies with the ability to target this population are required to improve patient outcomes. An important step towards this goal is the identification of common immunophenotypic surface markers and biological properties that distinguish LSCs from normal hematopoietic stem and progenitor cells (HSPCs) across AML patients. This work has resulted in the development of a large number of potential LSC-selective therapies that target cell surface molecules, intracellular signaling pathways, and the bone marrow microenvironment. Here, we will review the basic biology, immunophenotypic detection, and clinical relevance of LSCs, as well as emerging biological and small-molecule strategies that either directly target LSCs or indirectly target these cells through modulation of their microenvironment.

Targeting bcr-abl transcripts with siRNAs in an imatinib-resistant chronic myeloid leukemia patient: challenges and future directions

Within the recent years, RNA interference (RNAi) has become an almost standard method for in vitro knockdown of any target gene of interest. Now, one major focus is to further explore its potential therapeutic use. From the mechanism, it becomes clear that small interfering RNAs (siRNAs) play a pivotal role in triggering RNAi. This chapter describes the in vivo application of targeted non-virally delivered synthetic bcr-abl siRNA in a female patient with recurrent Philadelphia chromosome positive chronic myeloid leukemia (CML) resistant to imatinib (Y253F mutation) and chemotherapy after allogeneic hematopoietic stem cell transplantation. A remarkable inhibition of the overexpressed bcr-abl oncogene resulting in increased apoptosis of CML cells was found. In vivo siRNA application was well tolerated without any clinically adverse events. The current findings imply that the clinical application of synthetic siRNA is feasible and safe and has real potential for genetic-based therapies using synthetic non-viral carriers.

Pediatric relapsed or refractory leukemia: new pharmacotherapeutic developments and future directions

Over the past 50 years, numerous advances in treatment have produced dramatic increases in the cure rates of pediatric leukemias. Despite this progress, the majority of children with relapsed leukemia are not expected to survive. With current chemotherapy regimens, approximately 15 % of children with acute lymphoblastic leukemia and 45 % of children with acute myeloid leukemia will have refractory disease or experience a relapse. Advances in the treatment of pediatric relapsed leukemia have not mirrored the successes of upfront therapy, and newer treatments are desperately needed in order to improve survival in these challenging patients. Recent improvements in our knowledge of cancer biology have revealed an extensive number of targets that have the potential to be exploited for anticancer therapy. These advances have led to the development of a number of new treatments that are now being explored in children with relapsed or refractory leukemia. Novel agents seek to exploit the same molecular aberrations that contribute to leukemia development and resistance to therapy. Newer classes of drugs, including monoclonal antibodies, tyrosine kinase inhibitors and epigenetic modifiers are transforming the treatment of patients who are not cured with conventional therapies. As the side effects of many new agents are distinct from those seen with conventional chemotherapy, these treatments are often explored in combination with each other or combined with conventional treatment regimens. This review discusses the biological rationale for the most promising new agents and the results of recent studies conducted in pediatric patients with relapsed leukemia.

Phase I study of GTI-2040, a ribonucleotide reductase antisense, with high dose cytarabine in patients with relapsed/refractory acute myeloid leukemia

We hypothesized that GTI-2040, a 20-mer oligonucleotide complementary to the R2 subunit mRNA of ribonucleotide reductase, combined with high dose cytarabine (HiDAC) would result in enhanced cytotoxicity by favoring Ara-CTP DNA incorporation. In a phase I dose escalation trial, adults (≥ 60 years) with refractory or relapsed acute myeloid leukemia (AML) received daily HiDAC plus infusional GTI-2040. Using a novel assay, evidence of intracellular drug accumulation and target R2 down-regulation was observed. GTI-2040/HiDAC can be administered safely. However, with no complete remissions observed, alternative doses and schedules may need to be investigated to achieve clinical activity in older patients with AML.

The BCL-2 protein in precursor B acute lymphoblastic leukemia in children

The BCL-2 protein plays an important role in controlling apoptosis. Disorders of this process can lead to the emergence and development of acute lymphoblastic leukemia (ALL) and can determine the resistance of leukemic cells to chemotherapy. The levels of BCL-2 mRNA were determined in 20 children with pre-B ALL using RT-polymerase chain reaction and the percentage of BCL-2+ cells in 51 patients using flow cytofluorometry. Similar levels of BCL-2 mRNA (P=0.18) with a higher percentage of cells BCL-2+ (P=0.04) were shown in the bone marrow of patients with pre-B ALL compared to normal peripheral blood mononuclear cells. We could not find any connection between the level of BCL-2 mRNA or the percentage of BCL-2+ cells and selected clinical features. A high percentage of BCL-2+ cells and high levels of BCL-2 mRNA did not affect the 5-year overall survival probability nor the 5-year relapse-free survival probability. These results may indicate a high activity of mechanisms promoting the development of the final form of the BCL-2 protein from mRNA in leukemic cells. A high BCL-2 level does not affect the clinical course or worsen the prognosis in children with ALL.

Successful treatment with low-dose decitabine in acute myelogenous leukemia in elderly patients over 80 years old: Five case reports

The incidence of acute myelogenous leukemia (AML) in patients over 80 years old is >20 times greater than that observed in younger patients. Previously, no standard treatment protocol for elderly patients with AML existed, however the development of hypomethylating agents, including decitabine, has brought about promising results in AML. In the present study, we report on the usage of a lower than routine dosage of decitabine in patients over 80 years old with AML. Since January 2010, 5 patients diagnosed with AML over the age of 80 years old received treatment with decitabine in our hospital. Decitabine was administered at a dose of 10–15 mg/m² and repeated every other day for a total of 5 days. This cycle was repeated for ∼6 weeks. The 5 patients received a total of 19 cycles of treatment with decitabine. No patient achieved complete or partial remission. An antileukemic effect was observed in 25% of courses (3/12). An increase in platelet count of >20×10⁹/l was observed in 26.3% (5/19) of cycles compared with previous treatment. An increase in hemoglobin concentration of >20 g/l was observed in 36.8% (7/19) of cycles in comparison to previous treatment, four of which achieved normal hemoglobin levels. One patient became red blood cell transfusion-independent. The median survival time was 19.8±4.8 months. Survival time from decitabine administration to mortality was 13.2±5.1 months. The main side-effect was bone marrow suppression with grade III–IV thrombocytopenia, grade III–IV leukocytopenia, grade III–IV neutropenia and anemia accounting for 94.7% (18/19), 47.4% (9/19), 89.5% (17/19) and 21.1% (4/19), respectively. Severe infection or bleeding was not observed and no patient stopped treatment due to adverse effects. In conclusion, extremely low-dose decitabine may be used safely in elderly patients and achieved longer survival times than reported previously in AML patients aged 80 and above. It is suggested that complete remission may not be the primary objective, while improvement of quality of life may be a better choice in AML patients over 80 years old. The cases observed in our study were limited, so more cases are required for further study.

Target mRNA inhibition by oligonucleotide drugs in man

Oligonucleotide delivery in vivo is commonly seen as the principal hurdle to the successful development of oligonucleotide drugs. In an analysis of 26 oligonucleotide drugs recently evaluated in late-stage clinical trials we found that to date at least half have demonstrated suppression of the target mRNA and/or protein levels in the relevant cell types in man, including those present in liver, muscle, bone marrow, lung, blood and solid tumors. Overall, this strongly implies that the drugs are being delivered to the appropriate disease tissues. Strikingly we also found that the majority of the drug targets of the oligonucleotides lie outside of the drugable genome and represent new mechanisms of action not previously investigated in a clinical setting. Despite the high risk of failure of novel mechanisms of action in the clinic, a subset of the targets has been validated by the drugs. While not wishing to downplay the technical challenges of oligonucleotide delivery in vivo, here we demonstrate that target selection and validation are of equal importance for the success of this field.

Determination of cellular uptake and intracellular levels of Cenersen (Aezea(®), EL625), a p53 antisense oligonucleotide in acute myeloid leukemia cells

TP53 encodes for tumor protein p53. The suppression of p53 protein results in interruption of DNA repair mechanisms in dividing malignant cells thereby increasing the DNA damage and activating p53-independent mechanisms of apoptosis. This ultimately may translate into enhanced cytotoxic effects of standard chemotherapy. Based on this rationale, Cenersen, a phosphorothioate oligonucleotide antisense to p53-mRNA was synthesized and tested in clinical trials for patients with acute myeloid leukemia (AML). An important component of Cenersen clinical development is to develop a sensitive and specific method to quantify plasma and intracellular levels of Cenersen in different biologic matrices in order to determine tissue and intracellular distribution of the parent compound and its metabolites. Ultimately, this will allow us to determine pharmacokinetic and pharmacodynamic relationship for dose-effect correlation and design effective regimen to be rapidly translate into the clinic. An ELISA-based assay was adapted for assay development and validation of Cenersen in mouse plasma and cell lysate. Cellular uptake of Cenersen was studied in MV4-11 and KASUMI-1 AML cell lines. Real-time RT-PCR was used to measure P53-mRNA expression changes in treated cells. The assay had a limit of quantification of 35pmol/L in mouse plasma. Within-day and between-day precision of <15% and accuracy nearly 100% were observed in a linear range of 10-2000pmol/L (R(2)=0.99) in AML cell lysate. The selectivity of this assay examined as cross-reactivity with its 3'N-1, 3'N-2-metabolites, was 16.8% and 0.4%, respectively, and with its mismatch and the scramble oligonucleotides was 0.06% and 0.4%, respectively. Cenersen was stable in mouse plasma up to 8h at 37°C. When exposed to 0.1-1μmol/L Cenersen, MV4-11 and KASUMI-1 cells showed intracellular concentration in the range of 9.97-45.34nmol/mg protein and 0.1-2.1nmol/mg protein, respectively. Successful downregulation of p53-mRNA expression was observed in Cenersen treated cells. This ELISA-based assay was applicable to plasma and intracellular concentration measurement of Cenersen. Assessment of achievable concentration of Cenersen in different biologic matrices will be useful to elucidate the biological and clinical activity of this promising drug and define its recommended dose in future clinical trials.

The Role of BCL2 Family of Apoptosis Regulator Proteins in Acute and Chronic Leukemias

The disturbance of apoptosis molecular signaling pathways is involved in carcinogenesis. BCL2 family of proteins is the hallmark of apoptosis regulation. In the last decade, new members of BCL2 gene family were discovered and cloned and were found to be differentially expressed in many types of cancer. BCL2 protein family, through its role in regulation of apoptotic pathways, is possibly related to cancer pathophysiology and resistance to conventional chemotherapy. It is well known that leukemias are haematopoietic malignancies characterized by biological diversity, varied cytogenetics, different immunophenotype profiles, and diverse outcome. Current research focuses on the prognostic impact and specific role of these proteins in the pathogenesis of leukemias. The understanding of the molecular pathways that participate in the biology of leukemias may lead to the design of new therapies which may improve patients' survival. In the present paper, we describe current knowledge on the role of BCL2 apoptosis regulator proteins in acute and chronic leukemias.

Long-term survival of a child with refractory anaplastic large cell lymphoma following therapy with an antisense oligonucleotide, topotecan, and vinblastine

Anaplastic large cell lymphoma includes a subset of highly aggressive tumours and has a relapse rate of 30% at 2 years. Relapsed patients often have poor clinical outcome. The use of antisense oligonucleotides to down-regulate Bcl-2 protein can reverse chemotherapy resistance. The authors describe an 11-year-old boy with recurrent anaplastic large cell lymphoma who had received double high-dose chemotherapy followed by autologous haematopoietic stem-cell transplantation, had refractory disease and then had achieved long-term remission with the use of an antisense oligonucleotides in combination with vinblastine and topotecan.

NUP98-HOXA9-transgenic zebrafish develop a myeloproliferative neoplasm and provide new insight into mechanisms of myeloid leukaemogenesis

NUP98-HOXA9 [t(7;11) (p15;p15)] is associated with inferior prognosis in de novo and treatment-related acute myeloid leukaemia (AML) and contributes to blast crisis in chronic myeloid leukaemia (CML). We have engineered an inducible transgenic zebrafish harbouring human NUP98-HOXA9 under the zebrafish spi1(pu.1) promoter. NUP98-HOXA9 perturbed zebrafish embryonic haematopoiesis, with upregulated spi1 expression at the expense of gata1a. Markers associated with more differentiated myeloid cells, lcp1, lyz, and mpx were also elevated, but to a lesser extent than spi1, suggesting differentiation of early myeloid progenitors may be impaired by NUP98-HOXA9. Following irradiation, NUP98-HOXA9-expressing embryos showed increased numbers of cells in G2-M transition compared to controls and absence of a normal apoptotic response, which may result from an upregulation of bcl2. These data suggest NUP98-HOXA9-induced oncogenesis may result from a combination of defects in haematopoiesis and an aberrant response to DNA damage. Importantly, 23% of adult NUP98-HOXA9-transgenic fish developed a myeloproliferative neoplasm (MPN) at 19-23 months of age. In summary, we have identified an embryonic haematopoietic phenotype in a transgenic zebrafish line that subsequently develops MPN. This tool provides a unique opportunity for high-throughput in vivo chemical modifier screens to identify novel therapeutic agents in high risk AML.

Pharmacokinetic evaluation of oblimersen sodium for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in the western hemisphere. Developing new therapies remains a priority as present treatment options do not offer a cure. BCL-2 overexpression in CLL is associated with aggressive disease features and resists chemotherapy. Oblimersen sodium (G3139) is a phosphorothioate oligonucleotide antisense drug targeting the BCL-2 mRNA and is the first antisense to reach advanced clinical testing in oncology. Preclinical evaluation has demonstrated good antineoplastic effect in B-cell cancers; several clinical trials have confirmed its safety and efficacy both alone and in combination with other therapeutics.

AREAS COVERED

This review focuses on the chemistry, pharmacodynamics, pharmacokinetics and clinical evaluation of oblimersen in CLL. PubMed and MEDLINE searches assisted in data collection.

EXPERT OPINION

Bcl-2 is an important target in CLL. Antisense therapy is a novel approach to target oncoproteins; this can be beneficial in the clinical setting. Oblimersen sodium demonstrates the clinical safety of the antisense therapeutic approach and, with chemotherapy, shows survival advantage in a subset of CLL patients. However, future approval of oblimersen sodium in CLL remains uncertain. Nevertheless, BCL-2 remains a critical target in drug development and is an area of high-priority research.

Folate-immunoglobulin G as an anticancer therapeutic antibody

Folate receptor-alpha (FR) is a promising cellular marker for tumor-specific drug delivery. Conjugation of folic acid to therapeutic and imaging agents has been shown to enhance their delivery to FR (+) cancer cells in vitro and in tumor-bearing mice via an FR-mediated cellular uptake mechanism. In this study, immunoglobulin G (IgG) was conjugated to folate and evaluated as a therapeutic antibody against folate receptor (FR)-positive tumors. Murine IgG (mIgG) was conjugated to folate via an amide bond to yield folate-conjugated mIgG (f-mIgG) that contained an average of approximately 2.6 folates per molecule. Selective uptake of f-IgG by FR (+) tumor cells was determined by fluorescence microscopy and by flow cytometry. Lysis of L1210JF cells by NK cells from murine donors was increased 1.4-9.0-fold at the effector:target (E:T) ratio of 25:1, relative to control mIgG. In mice bearing L1210JF tumors, f-mIgG was found to significantly inhibit tumor growth and to have prolonged the median survival time (MeST). Significantly, the antitumor efficacy of f-mIgG was greatly increased when combined with liposomal G3139, an 18-mer phosphorothioate oligonucleotide. In fact, the combination resulted in a 100% cure rate among the tumor-bearing mice. Injection of f-mIgG significantly increased serum INF-gamma and IL-6 level in mice compared with mIgG and dramatically increased serum INF-gamma and IL-6 level when combined with liposomal G3139. These results suggested that f-IgG, a novel immunotherapy agent, has potent activity as a therapeutic antibody to the FR-positive cancer, and the therapeutic activity is enhanced by immunomodulatory agents.

Remission induction, consolidation and novel agents in development for adults with acute myeloid leukaemia

Chemotherapy regimens used for remission induction in AML have not changed significantly over the last several decades. However the recognition of the prognostic value of cytogenetics and genomics has been a major advance which is helping clarify the most optimal post-remission consolidation strategy among various risk groups. We are not only beginning to realize the pitfalls of a 'one-fits-all' approach with intensive, cytarabine-based chemotherapy as the mainstay, but we are finally beginning to reap the rewards of decades of basic, translational, and clinical research. Developing individualized, 'targeted' therapy for each AML patient based on unique molecular features of disease remains a daunting goal yet one that we can now begin to envision. Hypothesis-based study designs-from pre-clinical/laboratory experiments to phase-I and subsequent efficacy trials-provide the foundation for advances in the diagnosis, risk stratification, and treatment for patients with AML. Here we critically review the literature for the management of AML, try to give recommendations regarding the appropriate induction and remission strategy, clarify the role of stem cell transplantation and discuss novel agents on the horizon.

Molecular targeted therapies for diffuse large B-cell lymphoma based on apoptosis profiles

Diffuse large B-cell lymphoma (DLBCL) is the most common type of adult non-Hodgkin lymphoma and is treated with chemotherapy in combination with rituximab. Despite this aggressive therapy, the disease is fatal in 30-40% of patients. Inhibition of the apoptosis signalling pathways is strongly related to response to chemotherapy and eventual clinical outcome. In order to survive, lymphoma cells depend on disruption of the apoptosis pathway by mutations in apoptosis inducing genes or by continuous expression of anti-apoptotic proteins. The development of molecules targeting these apoptosis inhibitors provides a very promising opportunity to specifically target tumour cells without toxicity to non-malignant cells in DLBCL patients. Sensitivity for most of these antagonists can be predicted based on biological markers, suggesting the possibility of pre-defining patients who will most likely benefit from these targeted therapies. Experimental therapies aimed at restoring the upstream apoptosis pathway or targeting apoptosis inhibitors are currently being tested in clinical trials and are expected to be effective particularly in chemotherapy-refractory DLBCL, providing hope for patients who are refractory to current therapies.

Phase I trial of oblimersen (Genasense®) and gemcitabine in refractory and advanced malignancies

BACKGROUND

Overexpression of Bcl-2 is associated with worse prognosis for a number of cancer types. The present study was designed to determine the maximum tolerated dose (MTD) of oblimersen (antisense Bcl-2) and gemcitabine when administered to patients with refractory malignancies.

MATERIALS AND METHODS

Sixteen patients with advanced solid tumors refractory to standard therapies were treated with escalating doses of oblimersen continuous, 120-h intravenous infusion given every 14 days, with a fixed-dose-rate intravenous infusion of gemcitabine administered on day 5 of each cycle. Serial plasma samples were collected to calculate the pharmacokinetics of oblimersen and gemcitabine, and also to measure the effect of oblimersen on Bcl-2 expression.

RESULTS

7 women and 9 men, median age 55 years (range 35-74 years), received a 5-day infusion of oblimersen at dose levels of 5 mg/kg/day (n = 4) or 7 mg/kg/day (n = 12). On the 5th day of the infusion, gemcitabine was given at 10 mg/m(2)/h for a total dose of 1,000 mg/m(2) (n = 7; cohorts I and II), 1,200 mg/m(2) (n = 3; cohort III), or 1,500 mg/m(2) (n = 6; cohort IV). Edema was the dose-limiting toxicity (DLT), necessitating expansion of cohort IV. No subsequent DLTs were noted. Thus, the maximum planned doses were well tolerated, and a formal MTD was not determined. Most hematologic toxicities were grade 1 or 2. There was low-grade fatigue, nausea/vomiting, and myalgias/arthralgias. Oblimersen C(ss) and AUC increased in relation to the dose escalation, but gemcitabine triphosphate levels did not correlate well with dose. There were no objective responses, though 5 patients had stable disease. A >75% reduction in Bcl-2 expression in peripheral blood mononuclear leucocytes was seen more frequently in patients who achieved stable disease than in progressing patients.

CONCLUSIONS

The maximal planned dose levels of oblimersen and gemcitabine in combination were well tolerated. Only one DLT (edema) occurred. There was a correlation between Bcl-2 reduction and stable disease. The recommended doses of the drugs for future studies are 7 mg/kg/day of oblimersen on days 1-5, and gemcitabine 1,500 mg/m(2) on day 5, every two weeks.

Targeting the Bcl-2

PURPOSE OF REVIEW

Members of the Bcl-2 family of proteins are critical components in regulating the intrinsic apoptotic pathway. Bcl-2 protein overexpression is associated with drug resistance and poor clinical outcome in cancer patients. Preclinical and clinical evaluations demonstrate that downregulation of Bcl-2 restores the intrinsic apoptotic pathways with antitumor effects. Thus, Bcl-2 is aggressively pursued as a therapeutic target in cancer with several new drugs undergoing clinical investigations. In this manuscript, we will review clinical information on some of the novel compounds specifically designed to target the Bcl-2 gene product(s).

RECENT FINDINGS

Extensive clinical evaluations using a Bcl-2-specific antisense have resulted in an overall disappointing experience. But new small molecule inhibitors of the Bcl-2 hold promise with high target affinity, ease of administration and improved toxicity profile. Early stage clinical trials of these agents are revealing promising results alone as well as in combination with existing anticancer therapeutics. Encouraging results from some of these clinical investigations are summarized in this review.

SUMMARY

Downregulation of Bcl-2 and restoration of a critical apoptotic pathway in cancer cells remains an important strategy. Novel Bcl-2 inhibitors have started to deliver the therapeutic promise of this target-specific quest.

New agents in acute myeloid leukemia: beyond cytarabine and anthracyclines

The standard therapeutic approaches for acute myeloid leukemia (AML) continue to be based on anthracyclines and cytarabine. However, the prognosis for AML remains poor, especially for patients with high-risk disease. During the past decade, promising novel agents that target DNA replication and repair, as well as cell cycling and apoptosis, have been developed and are being actively investigated in AML. Among these agents is flavopiridol, which interferes with key steps of the cell cycle and effectively promotes cell death, and voreloxin, an intercalating agent that also targets topoisomerase II. Also under clinical study in AML are oligonucleotide antisense constructs, which suppress the translation of proteins essential for leukemic blast survival and proliferation, and agents that target antiapoptotic cascades. In summary, it is hoped that novel therapies such as these will augment and/or supplant our current cytarabine- and anthracycline-based approaches, overcome active drug-resistance pathways, and eventually improve outcomes for patients with AML.

Exploiting cellular pathways to develop new treatment strategies for AML

The standard approaches to the treatment of acute myeloid leukemia (AML) have been predominantly based on cytarabine and anthracyclines. Yet, the outcomes associated with AML continue to be poor, especially for those patients who are older or carry higher-risk disease. In recent years, extensive research has led to the development and study of novel agents which target AML by diverse and varied mechanisms. Among these are targeted therapeutics such as kinase inhibitors and oligonucleotide constructs. These aim to suppress the production or activity of proteins, such as FLT3 and BCL2, among others, and thus disrupt related signaling cascades essential for leukemogenesis and proliferation. In addition, other agents like flavopiridol appear to target the myeloid blast by various mechanisms including suppression of cyclin-dependent kinases and interference with nucleotide synthesis. Another class of novel therapies includes inhibitors of histone deacetylase, which cause growth arrest and apoptosis through histone acetylation and resultant conformational changes. Clinical trials are now studying these and other agents alone and in combination with traditional cytotoxic therapies, with some encouraging results. In this review, we aim to provide a summary of the preclinical and clinical investigations of selected promising agents currently under study.

Synergistic effect of inhibiting translation initiation in combination with cytotoxic agents in acute myelogenous leukemia cells

We have previously shown that inhibition of translation initiation, using the small molecule inhibitor silvestrol, induces apoptosis in a pre-clinical murine lymphoma model when combined with daunorubicin. Silvestrol blocks ribosome recruitment by targeting the RNA helicase, eIF4A, which is required for this process. Here we investigate the sensitivity of acute myelogenous leukemia (AML) cell lines to protein synthesis inhibition in combination with the standard cytotoxic agents daunorubicin, etoposide, and cytarabine. Silvestrol shows synergy with standard-of-care agents in AML cell lines and synergizes with ABT-737, a small molecule inhibitor of Bcl-X(L) and Bcl-2. The in vitro synergy between silvestrol and the cytotoxic drugs used in AML therapy provides a basis for in vivo evaluation of these combinations.

Gene amplification in myeloid leukemias elucidated by fluorescence in situ hybridization

Gene amplification in hematologic malignancies is uncommon. When karyotyping leukemia cells, gene amplification is generally seen as double-minute (dmin) chromosomes and homogeneously staining regions (hsr). One of the more commonly amplified regions is MYC at 8q24.21, but amplification of MLL at 11q23 and regions on 9p, 19q, and elsewhere on 11q have been reported. Increased copy number of these genes has been associated with poor prognosis. Over an 11-year period, we identified 31 cases of possible gene amplification, 27 of which had enough sample material for further investigations. A total of 17 cases had dmin only, 13 cases had hsr only, and 1 case had both dmin and hsr in the karyotype. Fluorescence in situ hybridization (FISH) analysis identified amplification of MYC in 12 cases, all on dmin, and amplification of MLL in eight cases, all on hsr. Regions other than MYC and MLL were amplified in eight cases and, using multicolor FISH and multicolor banding, we identified a number of novel regions of amplification: 13q11 approximately q12.1, 15q26.1 approximately q26.3, and 17q12. We also identified one case where two different chromosomal regions were simultaneously amplified in the same cell line.

Acute myelogenous leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease with outcomes dependent upon several factors, including patient age, karyotype, mutational status, and comorbid conditions. For younger patients, approximately 60% to 80% achieve complete remission with standard therapy involving cytarabine and an anthracycline. However, only 20% to 30% have long-term disease-free survival. For adults older than 60 years of age, only 40% to 55% achieve a complete remission, with dismal long-term survival rates. Unfortunately, the median age at diagnosis for AML is 70 years. Significant advances in our understanding of the molecular biology of AML have led to newer therapies that specifically target molecular abnormalities. Examples of such therapies include the immunoconjugate gemtuzumab ozogamicin, FMS-like tyrosine kinase 3 inhibitors, farnesyl transferase inhibitors, histone deacetylase inhibitors, DNA hypomethylating agents, multidrug-resistance inhibitors, BCL-2 inhibitors, antiangiogenesis agents, and various nucleoside analogs. This review summarizes the standard treatments for AML and discusses the role of novel therapies.

Oxidative stress by targeted agents promotes cytotoxicity in hematologic malignancies

The past decade has seen an exponential increase in the number of cancer therapies with defined molecular targets. Interestingly, many of these new agents are also documented to raise levels of intracellular reactive oxygen species (ROS) in addition to inhibiting a biochemical target. In most cases, the exact link between the primary target of the drug and effects on cellular redox status is unknown. However, it is important to understand the role of oxidative stress in promoting cytotoxicity by these agents, because the design of multiregimen strategies could conceivably build on these redox alterations. Also, drug resistance mediated by antioxidant defenses could potentially be anticipated and circumvented with improved knowledge of the redox-related effects of these targeted agents. Given the large number of targeted chemotherapies, in this review, we focus on selected agents that have shown promise in hematologic malignancies: proteasome inhibitors, histone deacetylase inhibitors, Bcl-2-targeted agents, and a kinase inhibitor called adaphostin. Despite structural differences within classes of these compounds, a commonality of causing increased oxidative stress exists, which contributes to induction of cell death.

Therapeutic targeting of gene expression by siRNAs directed against BCR-ABL transcripts in a patient with imatinib-resistant chronic myeloid leukemia

Within the recent years, RNA interference (RNAi) has become an almost-standard method for in vitro knockdown of any target gene of interest. Now, one major focus is to further explore its potential in vivo, including the development of novel therapeutic strategies. From the mechanism, it becomes clear that small interfering RNAs (siRNAs) play a pivotal role in triggering RNAi. Thus, the efficient delivery of target gene-specific siRNAs is one major challenge in the establishment of therapeutic RNAi. Here we show that in vivo application of targeted nonvirally delivered synthetic bcr-abl siRNA in a female patient with recurrent Philadelphia chromosome positive chronic myeloid leukemia (CML) resistant to imatinib (Y253F mutation) and chemotherapy after allogeneic hematopoietic stem cell transplantation can silence the expression of bcr-abl gene. We found a remarkable inhibition of the overexpressed bcr-abl oncogene resulting in increased apoptosis of CML cells. In vivo siRNA application was well tolerated without any clinically adverse events. Our findings imply that the clinical application of synthetic siRNA is feasible, safe and has real potential for genetic-based therapies using synthetic nonviral carriers.