BMI-1 Targeting Interferes with Patient-Derived Tumor-Initiating Cell Survival and Tumor Growth in Prostate Cancer.

PURPOSE: Current prostate cancer management calls for identifying novel and more effective therapies. Self-renewing tumor-initiating cells (TICs) hold intrinsic therapy resistance and account for tumor relapse and progression. As BMI-1 regulates stem cell self-renewal, impairing BMI-1 function for TIC-tailored therapies appears to be a promising approach. EXPERIMENTAL DESIGN: We have previously developed a combined immunophenotypic and time-of-adherence assay to identify CD49b(hi)CD29(hi)CD44(hi) cells as human prostate TICs. We utilized this assay with patient-derived prostate cancer cells and xenograft models to characterize the effects of pharmacologic inhibitors of BMI-1. RESULTS: We demonstrate that in cell lines and patient-derived TICs, BMI-1 expression is upregulated and associated with stem cell-like traits. From a screened library, we identified a number of post-transcriptional small molecules that target BMI-1 in prostate TICs. Pharmacologic inhibition of BMI-1 in patient-derived cells significantly decreased colony formation in vitro and attenuated tumor initiation in vivo, thereby functionally diminishing the frequency of TICs, particularly in cells resistant to proliferation- and androgen receptor-directed therapies, without toxic effects on normal tissues. CONCLUSIONS: Our data offer a paradigm for targeting TICs and support the development of BMI-1-targeting therapy for a more effective prostate cancer treatment. Clin Cancer Res; 22(24); 6176-91. ©2016 AACR.