Targeting MDS and AML Stem Cells with AZD-9150 Mediated Inhibition of STAT3

Myelodysplastic syndrome (MDS) & Acute Myeloid Leukemia (AML) arise from a population of aberrant hematopoietic stem cells (HSCs) that have been altered by multiple genetic & epigenetic alterations. A preliminary genomewide transcriptomic and epigenomic analysis of stem and progenitor cells from MDS and AML patients revealed STAT3 upregulation with corresponding loss of promoter methylation in diseased samples (Will et al, Blood, 2012). We now demonstrate that STAT3 is overexpressed in highly purified FACS sorted disease initiating populations in MDS/AML. STAT3 expression was determined to be significantly higher in phenotypic LT-HSC (CD34+/CD38-/CD90+/Lin -ve), ST-HSC (CD34+/CD38-/CD90-/Lin -ve) and GMP (CD34+/CD38+/CD123+/CD45Ra+/Lin -ve) from 10 diseased and 6 control sorted samples. Transcriptomic data from another cohort of CD34+ cells from 183 MDS patients found significantly increased expression of STAT3 in MDS samples when compared to healthy controls and importantly, found that increased STAT3 expression was predictive of significantly adverse prognosis (P value < 0.01, median survival of 2.6 years compared to 5.8 years for group with lower STAT3). Clinical correlations revealed that MDS patients with higher STAT3 expression in stem/progenitor cells were significantly more anemic (Mean Hgb 9.4gm/dl vs 10.2gm/dl, P=0.002) and had higher blast counts (Mean Blast Count 7.1% vs 5.3%, P=0.02), further demonstrating STAT3 to be an adverse prognostic marker in MDS.

To functionally determine the role of STAT3 in MDS/AML pathogenesis, we used AZD9150, a Gen 2.5 Antisense Oligonucleotide (ASO) specific inhibitor of STAT3 (Hong et al, SciTM, 2015). This ASO has recently demonstrated safety and single-agent antitumor activity in patients with refractory lymphoma in a phase 1 dose-escalation study. We evaluated its efficacy in multiple leukemic cell lines and primary MDS/AML samples and used an inactive structural analogue oligonucleotide as control. AZD9150 treatment led to significantly decreased viability in numerous AML and MDS derived cell lines. (N=7, P < 0.01). Loss of viability was accompanied by dose dependent increase in apoptosis in leukemic cells. Specific inhibition of STAT3, but not STAT5, was seen in AZD9150 treated leukemic cells in luciferase reporter assays. AZD9150 treatment also led to decreased expression of important oncogenic downstream genes including not only STAT3 itself, but also IL8, IL6, CXCR2 and others. In vivo studies using a leukemia xenograft model in NSG mice demonstrated that treatment with AZD9150 at 50mg/kg/day led to significantly improved survival compared to control oligonucleotide (p-value: 0.004).

It is generally challenging to show uptake of oligonucleotide-based therapeutics by primary cancer samples. Here, we treated healthy stem cells and AML primary patient samples with AZD 9150 and determined by intracellular flow cytometry that the ASO were readily taken up by primary patient- or cord blood-derived HSCs, myeloid progenitors and lymphocytes in a time and dose-dependent manner. We then treated a cohort of MDS and AML primary samples (N= 7) with AZD9150 or control and found qualitatively decreased leukemic colony growth, enhanced erythroid colony formation, and increased myeloid differentiation following STAT3 inhibition.

In conclusion, we demonstrate that STAT3 is upregulated in highly purified stem and progenitor cells in MDS and AML and is an adverse prognostic marker. Importantly, a clinically applicable oligonucleotide inhibitor of STAT3 shows preclinical in vitro and in vivo efficacy in MDS and AML models, thereby providing a rationale for further development and clinical testing in MDS and AML.

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