Preclinical Development of LNA Antimir-155 (MRG-106) in Acute Myeloid Leukemia

Introduction

MicroRNAs (miRs) are deregulated in AML and play a key role in leukemogenesis. MiR-155 is one of the most frequently overexpressed miRs in AML. Higher expression of miR-155 is associated with FLT3 internal tandem duplication (FLT3-ITD) and is associated with worse outcome, independent of FLT3-ITD status. Preliminary data shows that silencing of miR-155 induces strong antileukemic effects in AML cell lines. Altogether these data support a therapeutic role for miR-155 antagonism in AML.  Here, we show the in vitro and in vivo activity of MRG-106, a novel LNA antimiR-155 compound that we are developing as a potential treatment for hematological malignancies.

Methods

Unconjugated, LNA-modified oligonucleotide against miR-155 (MRG-106) was developed by miRagen Therapeutics, Inc.  MRG-106 was evaluated in FLT3-ITD+ AML cell lines and primary FLT3-ITD+ AML samples for impact on apoptosis and cellular proliferation using Annexin V and MTS assays. Predicted and validated targets of miR-155 were measured by qPCR and Western Blotting to assess the efficacy of miR-155 silencing.  The in vivo antileukemic effect of MRG-106 was evaluated in NOD/SCID gamma mice engrafted with MV4-11 AML cells that have elevated miR-155 expression. One week after leukemic cell inoculation, the mice were separated in 3 cohorts and received either MRG-106 (n=12); LNA-scramble control (n=12); or saline (n=6).

Results

Inhibition of miR-155 decreased cell proliferation in MV-4-11 and MOLM-13 cells at 48hrs (Absorbance 450 nM (A450nM): 0.5 and 0.4 vs controls 2.4 and 2.5, respectively, p<0.01). These effects were associated with increased apoptosis (2-fold increase in Annexin staining) and re-expression of the validated miR-155 target WEE1 protein. MRG-106 produced a 4-6 fold increase in apoptosis in primary samples from 3 newly diagnosed AML patients with FLT3-ITD cytogenetically normal AML (p<0.01). In addition, inhibition of miR-155 reduced the colony forming ability of the primary blasts (average # of colonies; controls=90 vs. MRG-106=55,p<0.01). In an MV4-11 xenograft model, MRG-106 significantly increased survival compared to controls (p<0.01). Biodistribution studies confirmed adequate MRG-106 distribution to bone marrow. GLP preclinical safety studies have been completed in rats and non-human primates, demonstrating an acceptable safety profile for MRG-106. 

Conclusions

Inhibition of miR-155 in AML cell lines and primary AML samples in vitro and in vivo induces significant antileukemic effects.  These studies validate miR-155 as a therapeutic target in AML and support the testing of MRG-106 in AML patients in the context of a phase 1 clinical trial.