Relapse of acute myeloid leukemia (AML) is attributed to the persistence of leukemia stem cells (LSCs). Identifying and targeting LSCs is therefore crucial for curative therapy. The oncogenic protein MUC1 is highly expressed in AML LSCs as opposed to normal hematopoietic progenitors, in which MUC1 is absent, and CD34 negative AML cells, which express MUC1 at low levels.
Using large naïve phage-display antibody libraries,Wewehaveisolatedhighly specificrecombinantantibodies directed toward a MUC1-derived peptide or toward a peptide derived from another AML marker, WT1, presented on HLA-A2. As such, these antibodies display the specificity of a T-cell receptor (TCR), while retaining the biological and pharmacological simplicity of monoclonal antibodies. Using these TCR-like antibodies, we have found that MUC1 and WT1 presentation on HLA-A2+ LSCs is very low, but is markedly enhanced upon inhibition of MUC1 by a peptide inhibitor, GO-203. GO-203 has also been shown to promote terminal differentiation, necrosis and apoptosis of AML cells.
Our aim is to target both the pathophysiological function of MUC1 using GO-203, and exploit the enhanced presentation of MUC1 in GO-203 treated LSCs by targeting these cells with TCR-like antibodies. To enable efficient killing of target cells, a full length MUC1 TCR-like antibody, an Fc-mutated antibody with enhanced antibody dependent cell cytotoxicity capabilities, and a toxin-conjugated single chain Fv fragment will be constructed. We will examine the ability of these constructs to kill antigen presenting cells loaded with MUC1 peptides, AML cell lines, and finally, LSCs isolated from AML patients. The synergism of MUC1 inhibition and TCR-like antibodies will be determined by killing assays using each treatment separately versus their combination. Our approach will enable more efficient destruction of these cells, while allowing the use of reduced doses of each single agent.
