Targeting Leukemia Initiating Cells by MUC1-C Subunit Inhibition
Authors: Stroopinsky Dina , Rosenblatt Jacalyn , Mills Heidi , Nardella Caterina , Ito Keisuke , Yin Li , Rajabi Hasan , Vasir Baldev , Kufe Turner , Luptakova Katarina , Arnason Jon E. , Levine James D. , Joyce Robin , Tzachanis Dimitrios , Boussiotis Vassiliki A. , Galinsky Ilene , Stone Richard M. , Reiter Yoram , Pandolfi Pier Paolo , Kufe Donald , Avigan David 
Published: October 2019

Abstract
Abstract 3583

Introduction:
Acute myeloid leukemia (AML) arises from a population of leukemia initiating cells (LICs) that exhibit chemotherapy resistance and serve as a reservoir for disease recurrence. We have demonstrated that the oncoprotein, MUC1, is expressed on LICs but not normal hematopoietic stem cells. We have developed an inhibitor of the MUC1-C subunit, designated GO-203, which blocks MUC1-C dimerization and its oncogenic function. In a murine NSG (NOD-scid IL2Rg) model, we examined whether MUC1high progenitors are more effective in inducing leukemic engraftment as compared to MUC1low progenitors and evaluated the capacity of GO-203 to eradicate disease.

Methods and results:
To confirm the hypothesis that LICs are contained within the MUChigh progenitor population, lineage−/MUC1high and lineage−/MUC1low cells were isolated from AML derived bone marrow mononuclear cells by flow cytometric sorting, and transplanted (1×106 cells/mouse) into sub-lethally irradiated NSG mice using retro orbital injections. Leukemia engraftment was observed in all recipient mice (6/6) inoculated with MUC1high cells, with no evidence of normal human engraftment as shown by immunophenotype, cell morphology, and presence of cytogenetic abnormality. In a cohort of 6 mice, treatment with GO-203 was initiated 8 weeks after challenge with MUC1high AML cells following the demonstration of circulating leukemia cells. Leukemia was eradicated in 5/6 mice treated with GO-203. In contrast, 6/6 mice inoculated with MUC1low cells demonstrated engraftment with normal human hematopoetic cells as demonstrated by immunophenotype, cell morphology and absence of cytogenetic abnormality by FISH analysis. Engraftment of normal hematopoietic cells was unaffected by treatment with GO-203 in 4/5 of mice inoculated with MUC1low cells, supporting that GO-203 does not affect non-malignant hematopoiesis. We further determined the effect of GO-203 treatment in a prevention model. NSG mice were treated with 21 days of GO-203 beginning 24 hours after inoculation with CD34+/lineage−/MUC1high cells isolated from patient derived bone marrow mononuclear cells. Treatment with GO-203 prevented leukemia engraftment in 4/5 animals with the 5th animal showing only 1.9% leukemia cells. In contrast, 4/5 animals inoculated with the CD34+/lineage-/MUC1high cells in the absence of GO-203 demonstrated evidence of extensive bone marrow infiltration with leukemia cells comprising a mean of 33% of the bone marrow mononuclear cells.

Conclusions:
The results demonstrate that LICs are contained within the MUC1high fraction of AML derived progenitors and that MUC1low progenitors contain normal hematopoietic stem cells capable of normal engraftment. Treatment with the MUC1-C inhibitor, GO-203, prevents engraftment of leukemia, and eradicates established disease in a murine model. Our work indicates that GO-203 is a novel therapeutic agent for AML that targets LICs and has the potential to improve disease outcomes.

Disclosures:
Kufe: Genus Oncology: Consultancy.