Breast cancer stem cells (CSCs) can be identified by increased Aldefluor activity which is primarily due to aldehyde dehydrogenase 1A3 (ALDH1A3) expression. In addition to being a CSC marker, ALDH1A3 regulates genes expression via inducing retinoic acid (RA) signaling and plays an important role in mediating progression of cancers, including breast, melanoma, lung and glioblastoma. Therefore, ALDH1A3 represents a novel druggable anti-cancer target of interest. There are no currently characterized inhibitors of the ALDH1A3 isoform, so twelve general ALDH inhibitors were tested for their effectiveness in targeting ALDH1A3 activity. Ability to directly inhibit ALDH activity was quantified with the Aldefluor assay on a patient tumor xenograft and on breast cancer cell lines with known ALDH isoform activity. Inhibition of RA signaling was quantified by measuring expression of the RA-inducible genes RARRES1 and RARβ. To investigate the anti-cancer properties of these compounds, apoptosis was quantified with the annexin V assay. Citral significantly reduced ALDH1A3- and ALDH2-associated Aldefluor activity in breast cancer cell lines and also reduced Aldefluor activity of a patient-derived xenograft. Citral reduced expression of RA-inducible genes through reducing ALDH1A3 activity. Citral induced apoptosis in vitro in an ALDH-independent manner in breast cancer cell lines and reduced proliferation in the MDA-MB-231 breast cancer cell line. Nanoparticle (NP)-encapsulated citral was generated for in vivo use and administered intravenously to female NOD/SCID mice harbouring MDA-MB-231 ALDH1A3-overexpression tumors. 10mg/kg NP-citral significantly decreased the growth of ALDH1A3-driven MDA-MB-231 tumors. Nanoparticle-encapsulated citral shows promise as an adjuvant therapy for patients with tumors that have a large population of high-ALDH1A3 CSCs.

Citation Format: Margaret L. Thomas, Roberto De Antueno, Krysta Coyle, Brianne Cruickshank, Michael Giacomantonio, Roy Duncan, Carman Giacomantonio, Paola Marcato. Citral reduces breast tumor growth by inhibiting cancer stem cell marker ALDH1A3. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2506.