Efficient Silencing of bcr/abl Oncogene by Single- and Double-Stranded siRNAs Targeted against b2a2 Transcripts

ASP210: a potent oligonucleotide-based inhibitor effective against TKI-resistant CML cells

Clinical experience with tyrosine kinase inhibitors (TKIs) over the past two decades has shown that, despite the apparent therapeutic benefit, nearly 30% of patients with chronic myelogenous leukemia (CML) display primary resistance or intolerance to TKIs, and approximately 25% of those treated are forced to switch TKIs at least once during therapy due to acquired resistance. Safe and effective treatment modalities targeting leukemic clones that escape TKI therapy could hence be game changers in the professional management of these patients. Here, we aimed to investigate the efficacy of a novel therapeutic oligonucleotide of unconventional design, called ASP210, to reduce BCR-ABL1 mRNA levels in TKI-resistant CML cells, with the assumption of inducing their apoptosis. Imatinib- and dasatinib-resistant sublines of BCR-ABL1-positive MOLM-7 and CML-T1 cells were established and exposed to 0.25 and 2.5 µM ASP210 for 10 days. RT-qPCR showed a remarkable reduction of the target mRNA level by >99% after a single application. Cell viability was monitored daily by trypan blue staining. In response to the lack of driver oncoprotein BCR-ABL1, TKI-resistant CML cells underwent apoptosis regardless of the presence of the clinically relevant T315I mutation by day 5 after redosing with ASP210. The effect was selective for cancer cells, indicating a favorable safety profile for this therapeutic modality. Furthermore, the spontaneous uptake and high intracellular concentrations of ASP210 suggest its potential to be effective at relatively low doses. The present findings suggest that ASP210 is a promising therapeutic avenue for patients with CML who fail to respond to TKI therapy.NEW & NOTEWORTHY Effective treatment modalities targeting leukemic clones that escape tyrosine kinase inhibitor (TKI) therapy could be game changers in the professional management of patients displaying primary resistance, intolerance, or acquired resistance to TKIs. Although delivering authentic innovations today is more complex than ever, we developed a highly potent and safe oligonucleotide-based modality against BCR-ABL1 mRNA named ASP210 that effectively induces cell death in BCR-ABL1-positive TKI-resistant cells while sparing BCR-ABL1-negative healthy cells.

Asymmetric Hairpins DNA Encapsulated Silver Nanoclusters for In Situ Fluorescence Imaging of Fusion Gene Isoforms in Bone Marrow

Rapid and accurate imaging of the BCR/ABL fusion gene isoforms (e.g., e13a2, e14a2 and co-expression type) of chronic myeloid leukemia (CML) is of vital importance to first-line drug selection, but there is no assay that meets clinical needs (e.g., clinical kits > 18 h without isoforms information). Herein, an in situ imaging platform is developed for the rapid and accurate detection of CML fusion gene isoforms using asymmetric sequence-enhanced hairpins DNA encapsulated silver nanoclusters (ADHA) and catalyzed hairpin assembly (CHA). The specific detection of e13a2 and e14a2 fusion gene isoforms with detection limits of 19.2 am (11.558 copies µL-1 ) and 32.56 am (19.601 copies µL-1 ) in one-pot is achieved. The feasibility of the developed assay for real-world applications are demonstrated by one-step fluorescence imaging (40 min) of e13a2, e14a2 and co-expression type in bone marrow quantitatively (International Standard: 15.66%-168.878%) and further validated by cDNA-sequencing. This work suggests that the developed imaging platform holds great potential for rapid identification of the fusion gene isoforms and isoform related treatment monitoring.

One-Pot Identification of BCR/ABLp210 Transcript Isoforms Based on Nanocluster Beacon

The BCR/ABL^p210 fusion gene is a classic biomarker of chronic myeloid leukemia, which can be divided into e13a2 and e14a2 isoforms according to different breakpoints. These two isoforms showed distinct differences in clinical manifestation, treatment effect, and prognosis risk. Herein, a strategy based on nanocluster beacon (NCB) fluorescence was developed to identify the e13a2 and e14a2 isoforms in one-pot. Because the fluorescence of AgNCs can be activated when they are placed in proximity to the corresponding enhancer sequences, thymine-rich (T-rich) or guanine-rich (G-rich). In this work, we explored an ideal DNA-AgNCs template as an excellent molecular reporter with a high signal-to-noise ratio. After recognition with the corresponding isoforms, the AgNCs can be pulled closer to the T-rich or G-rich sequences to form a three-way junction structure and generate fluorescence with corresponding wavelengths. Therefore, by distinguishing the corresponding wavelengths of AgNCs, we successfully identified two isoforms in one tube with the limitation of 16 pM for e13a2 and 9 pM for e14a2. Moreover, this strategy also realized isoform identification in leukemia cells and newly diagnosed CML patients within 40 min, which provides a powerful tool to distinguish fusion gene subtypes at the same time.

Highly sensitive fluorescence biosensing of BCR-ABL1 fusion gene based on exponential transcription-triggered hemin catalysis

Simple, sensitive and specific detection of the transcription level of BCR-ABL1 mRNA possesses vital clinical significance in diagnosis and treatment of chronic myeloid leukemia (CML). In this study, an innovative fluorescence biosensing methodology has been developed for sensitive and specific detection of BCR-ABL1 mRNA by integrating high-efficiency of exponential transcription and superior catalytic performance of DNA-grafted hemin. Exponential transcription was triggered by BCR-ABL1 mRNA to produce plenty of RNA products. They can specifically hybridize with circular dual-labeled hemin (DLH) probe to dissociate the intramolecular hemin dimmers into highly active hemin monomers for catalyzing fluorescence substrate tyramine. This exponential transcription-triggered hemin catalysis (ET-HC) strategy showed highly sensitive and specific for BCR-ABL1 detection with a limit of detection at 0.5 aM and a good linear range from 2 aM to 200 fM. This method was successfully applied to directly detect as low as 0.001% e13a2 transcript isoforms from complex genomic RNA extraction. Compared with clinical routine, the overall process is a thermostatic reaction and eliminates additional reverse transcription operation. Therefore, the developed ET-HC strategy might provide a promising alternative tool for precise diagnosis and personalized treatment of CML.

Design and self-assembly of siRNA-functionalized RNA nanoparticles for use in automated nanomedicine

Individual genes can be targeted with siRNAs. The use of nucleic acid nanoparticles (NPs) is a convenient method for delivering combinations of specific siRNAs in an organized and programmable manner. We present three assembly protocols to produce two different types of RNA self-assembling functional NPs using processes that are fully automatable. These NPs are engineered based on two complementary nanoscaffold designs (nanoring and nanocube), which serve as carriers of multiple siRNAs. The NPs are functionalized by the extension of up to six scaffold strands with siRNA duplexes. The assembly protocols yield functionalized RNA NPs, and we show that they interact in vitro with human recombinant Dicer to produce siRNAs. Our design strategies allow for fast, economical and easily controlled production of endotoxin-free therapeutic RNA NPs that are suitable for preclinical development.

Antisense locked nucleic acids efficiently suppress BCR/ABL and induce cell growth decline and apoptosis in leukemic cells

Chronic myeloid leukemia (CML) develops when a hematopoietic stem cell acquires the Philadelphia chromosome carrying the BCR/ABL fusion gene. This gives the transformed cells a proliferative advantage over normal hematopoietic cells. Silencing the BCR/ABL oncogene by treatment with specific drugs remains an important therapeutic goal. In this work, we used locked nucleic acid (LNA)-modified oligonucleotides to silence BCR/ABL and reduce CML cell proliferation, as these oligonucleotides are resistant to nucleases and exhibit an exceptional affinity for cognate RNA. The anti-BCR/ABL oligonucleotides were designed as LNA-DNA gapmers, consisting of end blocks of 3/4 LNA monomers and a central DNA stretch of 13/14 deoxyribonucleotides. The gapmers were complementary to the b2a2 and b3a2 mRNA junctions with which they form hybrid duplexes that have melting temperatures of 79 degrees C and 75 degrees C, respectively, in a 20 mmol/L NaCl-buffered (pH 7.4) solution. Like DNA, the designed LNA-DNA gapmers were capable of activating RNase H and promote cleavage of the target b2a2 and b3a2 BCR/ABL mRNAs. The treatment of CML cells with junction-specific antisense gapmers resulted in a strong and specific reduction of the levels of BCR/ABL transcripts ( approximately 20% of control) and protein p210(BCR/ABL) ( approximately 30% of control). Moreover, the antisense oligonucleotides suppressed cell growth up to 40% of control and induced apoptosis, as indicated by the increase of caspase-3/7 activity in the treated cells. Finally, the b2a2-specific antisense gapmer used in combination with STI571 (imatinib mesylate), a tyrosine kinase inhibitor of p210(BCR/ABL), produced an enhanced antiproliferative effect in KYO-1 cells, which compared with K562 cells are refractory to STI571. The data of this study support the application of BCR/ABL antisense LNA-DNA gapmers, used either alone or in combination with STI571, as potential antileukemic agents.

Targeting leukemic fusion proteins with small interfering RNAs: recent advances and therapeutic potentials

RNA interference has become an indispensable research tool to study gene functions in a wide variety of organisms. Because of their high efficacy and specificity, RNA interference-based approaches may also translate into new therapeutic strategies to treat human diseases. In particular, oncogenes such as leukemic fusion proteins, which arise from chromosomal translocations, are promising targets for such gene silencing approaches, because they are exclusively expressed in precancerous and cancerous tissues, and because they are frequently indispensable for maintaining the malignant phenotype. This review summarizes recent developments in targeting leukemia-specific genes and discusses problems and approaches for possible clinical applications.