Abstract
Overexpression and persistent activation of STAT5 play an important role in the development and progression of acute lymphoblastic leukemia (ALL), the most common pediatric cancer. Small interfering RNA (siRNA)-mediated downregulation of STAT5 represents a promising therapeutic approach for ALL to overcome the limitations of current treatment modalities such as high relapse rates and poor prognosis. However, to effectively transport siRNA molecules to target cells, development of potent carriers is of utmost importance to surpass hurdles of delivery. In this study, we investigated the use of lipopolymers as non-viral delivery systems derived from low molecular weight polyethylenimines (PEI) substituted with lauric acid (Lau), linoleic acid (LA) and stearic acid (StA) to deliver siRNA molecules to ALL cell lines and primary samples. Among the lipid-substituted polymers explored, Lau- and LA-substituted PEI displayed excellent siRNA delivery to SUP-B15 and RS4;11 cells. STAT5A gene expression was downregulated (36–92%) in SUP-B15 and (32%) in RS4;11 cells using the polymeric delivery systems, which consequently reduced cell growth and inhibited the formation of colonies in ALL cells. With regard to ALL primary cells, siRNA-mediated STAT5A gene silencing was observed in four of eight patient cells using our leading polymeric delivery system, 1.2PEI-Lau8, accompanied by the significant reduction in colony formation in three of eight patients. In both BCR-ABL positive and negative groups, three of five patients demonstrated marked cell growth inhibition in both MTT and trypan blue exclusion assays using 1.2PEI-Lau8/siRNA complexes in comparison with their control siRNA groups. Three patient samples did not show any positive results with our delivery systems. Differential therapeutic responses to siRNA therapy observed in different patients could result from variable genetic profiles and patient-to-patient variability in delivery. This study supports the potential of siRNA therapy and the designed lipopolymers as a delivery system in ALL therapy.
Highlights
Acute lymphoblastic leukemia (ALL), the most common type of childhood cancer [1], is characterized by overproduction and accumulation of malignant lymphoid progenitor cells within the bone marrow
In ALL, various targets have been successfully silenced by RNA interference (RNAi), such as Polo-like kinase 1 (Plk1), CD22ΔE12, CSF1R, JAK1 and FLT3 [34,35,36], all of which highlights the versatility of using RNAi for ALL therapy
We have demonstrated a strong reduction in mRNA levels which led to a sharp decrease in live cell counts and colony formation in ALL cell lines
Summary
Acute lymphoblastic leukemia (ALL), the most common type of childhood cancer [1], is characterized by overproduction and accumulation of malignant lymphoid progenitor cells within the bone marrow. Transcription factors are one of the most promising molecular targets for siRNA-based cancer therapy, as multiple oncogenic signalling pathways converge on a limited group of transcription factors which promote cell growth and survival [9] One such key group of transcription factors is the Signal Transducer and Activator of Transcription (STAT) family proteins. A preclinical study in BCR-ABL+ and BCR-ABL-like B-ALL cell lines and primary cells derived from newly diagnosed and relapsed/TKI-resistant BCR-ABL-like ALL patients, found that STAT5 silencing suppressed cell growth, induced apoptosis, and inhibited leukemogenesis [3] These studies suggest that STAT5 signaling is a potentially attractive therapeutic target in high-risk B-ALL [3, 9, 20, 21]; targeted small molecule inhibitors of STAT5 are not currently available. We focused on the silencing activity of siRNA delivery in selected cell models as the physicochemical properties of the lipopolymers were earlier reported [30]
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