TLR9-mediated siRNA delivery for targeting of normal and malignant human hematopoietic cells in vivo

Abstract

• CpG(A)-siRNA oligonucleotides allow for targeting genes specifically in human TLR9 ϩ immune cells and blood cancer cells.• Tumoricidal and immunostimulatory properties of CpG(A)-STAT3 siRNA provide a novel therapeutic opportunity for hematologic malignancies.STAT3 operates in both cancer cells and tumor-associated immune cells to promote cancer progression. As a transcription factor, it is a highly desirable but difficult target for pharmacologic inhibition. We have recently shown that the TLR9 agonists CpG oligonucleotides can be used for targeted siRNA delivery to mouse immune cells. In the present study, we demonstrate that a similar strategy allows for targeted gene silencing in both normal and malignant human TLR9 ؉ hematopoietic cells in vivo. We have developed new human cell-specific CpG(A) - IntroductionThe proliferation and survival of the majority of hematologic cancers depends on constitutive activity of STAT transcription factors. 1,2 The first evidence linking STAT activity with human blood cancer was derived from studies on multiple myeloma (MM). Permanent activity of STAT3 observed in myeloma cells was critical for their survival because of up-regulation of antiapoptotic BCL-X L protein. 3 Later reports identified constitutive activation of STAT3 not only in myeloma but also in other hematologic malignancies, with the highest frequency in B-cell lymphoma (BCL) and acute myeloid leukemia (AML) patient blasts. 1,4,5 The presence of activated STAT3 in leukemic blasts was associated with decreased disease-free survival of AML patients. 4 As a point of convergence for downstream signaling from cytokine and growth factor receptors, STAT3 plays a critical role in mediating cross-talk within the tumor microenvironment, which promotes tumor immune tolerance, vascularization, and metastasis. 6 Because STAT3 operates in both cancer cells and nonmalignant tumorassociated cells, it represents a highly desirable target for cancer therapy. 6 These important findings instigated numerous attempts to develop STAT3 inhibitors; however, pharmacologic inhibition of a protein lacking enzymatic activity is challenging. 4,7 An additional complication is the close structural similarity between oncogenic STAT3 and functionally distinct STAT1, a transcriptional factor critical for generation of antitumor immunity by IFNs. 8,9 The tyrosine kinase inhibitors upstream from STAT3, such as JAK, SRC, c-KIT, and FLT3 in leukemia, gained attention as promising blood cancer therapeutics. 4 However, the effect of small-molecule drugs, including FLT3 inhibitors, in most clinical trials was short-lived. 10,11 Other conventional treatment regimens for hematologic malignancies are limited by the high toxicity to normal tissues, development of drug resistance, and low disease-free survival rates. For personal use only. on May 11, 2018. by guest www.bloodjournal.org FromThe emergence of therapeutic strategies based on RNA interference (RNAi) created a unique opportunity to silence any diseaserelated target gene. 13,14 The major obstacle ...

Regulation of adipose tissue T cell subsets by Stat3 is crucial for diet-induced obesity and insulin resistance

“…Being a transcription factor, Stat3 is a difficult target to inhibit in a cell-specific manner. However, recent approaches to inhibit Stat3 using targeted platforms to deliver siRNA to specific immune cells have been explored with therapeutic success by our group (16,36,37). Thus, in addition to more potent and innovative small molecule inhibitors of Stat3 signaling in the near future, targeting Stat3 specifically in T cells may be an ultimate goal for treating obesity and insulin resistance.…”

Leukemia cell–targeted STAT3 silencing and TLR9 triggering generate systemic antitumor immunity

“…16, 17 We later demonstrated that CpG-ODNs can be used for cell-specific small interfering RNA (siRNA) delivery as CpG-siRNA conjugate to silence genes in mouse and human TLR9-positive cells. [18][19][20] Here, we assessed whether systemically administered CpG-Stat3 siRNA would generate antitumor effects against a genetic mouse model of Cbfb-MYH11/Mpl 1 (CMM 1 )-induced leukemia, which closely mimics human AML with inv(16)(p13:q22) gene fusion in 10% of patients.…”

CTLA4 aptamer delivers STAT3 siRNA to tumor-associated and malignant T cells

“…We recently described a technology for efficient in vivo delivery of siRNA into immune cells by linking an siRNA to CpG oligonucleotide, which binds to its cognate receptor, TLR9 (21). TLR9 is expressed intracellularly in cells of myeloid lineage and B cells as well as tumor cells expressing TLR9, including human leukemic cells (21,22). However, the CpGsiRNA approach does not directly target T cells (21).…”