Anti-CD44 antibody, ARH460-16-2, binds to human AML CD34+CD38- cancer stem cells and demonstrates anti-tumor activity in an AML xenograft model

3976 The CD44 glycoprotein was first identified in cells of hematopoietic origin. CD44 has been found expressed in several hematologic malignancies including AML, ALL, CLL and multiple myeloma. Further, CD44 has been shown to be expressed on the CD34+CD38- cancer stem cells in these malignancies. These findings suggest that targeting CD44 in leukemia may be an effective therapeutic strategy. Using Arius’ FunctionFIRST™ platform, ARH460-16-2, a monoclonal antibody targeting CD44, was discovered. This antibody has potent anti-tumor activity in solid tumor models of breast (CD44+CD24-/lo), liver and prostate cancer. Using flow cytometry, chimeric ARH460-16-2 (chARH460-16-2) was shown to bind to cancer cells from patients with AML, CLL, ALL (B and T), multiple myelomas and to cells from patients with Monoclonal Gammopathies of Undetermined Significance (MGUS), albeit at varying levels of binding. chARH460-16-2 also bound to various leukemia, lymphoma and multiple myeloma cell lines including KG-1, HL-60, CCRF-CEM and OPM, respectively. To determine whether ARH460-16-2 also recognizes CD44 on hemopoietic stem cells, flow cytometry was carried out on peripheral blood samples from patients with AML. The results showed that the antibody bound to all AML CD34+CD38- cancer stem cells. While ARH460-16-2 also bound normal hematopoietic CD34+CD38- stem cells, albeit to a lower degree, these data raise the possibility that ARH460-16-2 can target AML cancer stem cells in a therapeutic setting. Consistent with this notion, a non-GLP cynomolgus dose-ranging toxicology study using chARH460-16-2, did not detect abnormalities in the hematopoietic compartment even though chARH460-16-2 bound to variety of blood cell types. To assess the therapeutic potential in hematologic cancers chARH460-16-2 was tested in two established in vivo subcutaneous models of promyelocytic leukemia (HL-60) and AML (KG-1) in SCID mice. In these experiments, chARH460-16-2 had significant dose-responsive tumor growth inhibition in the KG-1 model (57% at 10 mg/kg) and an increase in the median survival of 62 days compared to 49 days in the control group. The antibody did not have anti-tumor activity in the HL-60 model. Because the maximum levels of binding to KG-1and HL-60, as determined by flow cytometry, were 100 and 4.5 fold above isotype respectively, it is possible that the therapeutic activity of the antibody may directly correlate with CD44 levels.
 ARH460-16-2 is being developed as a therapeutic monoclonal antibody for solid tumors and hematologic malignancies based on its effectiveness in pre-clinical models. Its target, CD44, is expressed in a variety of hematologic malignancies and CD34+CD38- cancer stem cells in AML and extends its therapeutic utility.