KDM 4 Inhibition Targets Breast Cancer Stem-like Cells

Introduction:

Breast cancer is the leading cause of cancer-related death among women worldwide. Among the subtypes of breast cancer, triple-negative disease is associated with a particularly poor prognosis and limited therapeutic options. During breast cancer treatment, therapy resistance and metastatic dissemination are the main problems that have to be faced. Breast cancer stem cells (BCSC) have been suggested to be responsible for both therapy resistance and metastatic dissemination. Until now, these resistant cancer stem cell populations have only been poorly characterized and targeted therapeutics have yet to be identified. It has been shown that alterations of epigenetic regulators such as the KDM 4 family members control tumor cell proliferation particularly in aggressive breast cancers and dysregulation of KDM 4 demethylases has been documented in a variety of cancers including breast cancer. The KDM 4 subfamily is comprised of KDM 4A, B, C, and D and belongs to the Jumonji C (JmjC) domain-containing family of histone demethylases. KDM 4 demethylases catalyze removal of the repressive H3K9me3 mark and that of H3K36me3, a mark linked to transcriptional elongation, thereby regulating a range of crucial pathways. These findings highlight KDM 4 demethylases as potential therapeutic targets for breast cancer treatment.

Methods:

Consequently, we set out to test potent and selective drug-like KDM 4 inhibitors. In order to validate inhibitors on cancer stem cells (CSC) from triple-negative breast cancer (TNBC), we established an efficient three-dimensional (3D) cultivation method allowing for growth of CSCs from patient tumor tissue without prior fluorescence-activated cell sorting (FACS) or murine xenografts to enrich for CSCs. We used defined conditions including a serum-free culture medium, a rho kinase inhibitor, Matrigel, and a low oxygen environment to isolate and enrich for BCSCs from individual patient tumors after neoadjuvant chemotherapy.

Results and discussion:

We present a novel method to isolate and propagate breast cancer stem-like cells (BCSC) from individual triple-negative tumors resected from patients after neoadjuvant chemotherapy. Limiting-dilution orthotopic xenografts of these BCSCs regenerated original patient tumor histology and gene expression. A member of the KDM 4 family of demethylases, KDM 4A, controls proliferation and xenograft tumor growth of BCSC cells. We describe an orally available, selective and potent KDM 4 inhibitor (QC6352) with unique preclinical characteristics. QC6352 blocked BCSC proliferation, sphere formation, and xenograft tumor formation. QC6352 also abrogated expression of EGFR, which drives the growth of therapy-resistant triple-negative breast cancer cells. Our findings validate a unique BCSC culture system for drug screening and offer preclinical proof of concept for KDM 4 inhibition as a new strategy to treat triple-negative breast cancer. Therefore, our models are ideal tools for the identification and validation of novel therapeutics.