Abstract 4293: Evaluation of activated CD44 as a biological target in the eradication of breast cancer stem cells

Abstract

Abstract Introduction: Cancer therapies are designed to kill rapidly proliferating cells where initial therapeutic benefits are usually transient resulting in tumor relapse and metastatic disease. Current treatment failure is due to a small population of slow-growing and drug resistant cells known as cancer stem cells (CSCs). To effectively treat breast cancer it is necessary to develop anti-cancer agents that concomitantly kill the rapidly growing breast cancer cells and the dormant CSCs. CD44 is a protein over-expressed on rapidly dividing breast cancer cells where it plays a critical role in the formation and progression of the tumor. CD44 is used as a reliable marker for breast cancer stem cells, therefore, through the high expression of this protein on both rapidly proliferating and CSCs there is strong rationale to use CD44 as a therapeutic target. CD44 mediates the majority of its biological processes through its affinity for the polysaccharide hyaluronan (HA). HyACT® anti-cancer drugs (HA drug delivery vehicle containing cytotoxic drugs) are specifically designed to target and transport chemotherapeutic agents to activated intra-tumoral CD44, where preclinical studies have strongly correlated the efficacy of the HyACT® platform with enhanced therapeutic responsiveness in CD44-positive tumor cells. This study evaluated the activation status of CD44 on CSC and non-CSC breast cancer cell sub-populations and then validated it as a therapeutic target in the treatment of breast cancer CSC. Methodology: Four breast cancer cell lines were separated into CSC (CD44+CD24-ALDH+/−) and non-stem cell (CD44+CD24+ ALDH+/−, CD44-CD24+ ALDH+/−) sub-populations using FACS. Attachment and proliferation characteristics of the breast cancer sub-populations were established using real time electronic microsensory array assays. The activation status of CD44 was determined using a functional HA internalization assay. After confirming the CD44 activation status cell sub-populations were treated with two HyACT® drugs, HA/Doxorubicin or HA/Gemcitabine where efficacy was determined using clonogenic and microsensory array assays. Results: CD44s was the predominant CD44 isoform expressed on all CD44+ve breast cancer sub-populations but high levels of the CD4v6 and v9 variant isoforms were uniquely identified on CSC populations. All isoforms of CD44 were shown to be activated. When CSC and non-CSC breast cancer sub-populations were treated the CD44-targeted drugs, the EC50 was reduced 2 to 40-fold when compared to drug alone. This increase in efficacy was negated when CD44-ve breast cancer sub-populations were treated with the CD44-targeted drug. Conclusions: This preliminary study has demonstrated breast cancer CD44 variant isoforms to be valid targets for hyaluronan encapsulated chemotherapeutic drugs that can be used in the eradication of all CD44+ve breast cancer populations including cancer stem cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4293.