br Magee Womens Research Institute Pittsburgh PA USA Present
16Magee-Womens Research Institute, Pittsburgh, PA, USA 17Present address: Hormel Institute, University of Minnesota, Austin, MN, USA 18Present address: Loma Linda University Medical Center, Loma Linda, CA, USA 19Lead Contact *Correspondence: [email protected]
Ovarian cancer is typified by the development of chemotherapy resistance. Chemotherapy resis-tance is associated with high aldehyde dehydroge-nase (ALDH) enzymatic activity, increased cancer ‘‘stemness,’’ and expression of the stem cell marker CD133. As such, ALDH activity has been proposed as a therapeutic target. Although it remains controver-sial which of the 19 ALDH family members drive chemotherapy resistance, ALDH1A family members have been primarily linked with chemotherapy resis-tant and stemness. We identified two ALDH1A family selective inhibitors (ALDH1Ai). ALDH1Ai preferentially kills CD133+ ovarian cancer stem-like cells (CSCs). ALDH1Ai induce necroptotic CSC death, mediated, in part, by the induction of mitochondrial uncoupling proteins and reduction in oxidative phosphorylation. ALDH1Ai is highly synergistic with chemotherapy, reducing tumor initiation capacity and increasing tu-mor eradication in vivo. These studies link ALDH1A with necroptosis and confirm the family as a critical therapeutic target to overcome chemotherapy resis-tance and improve patient outcomes.
The aldehyde dehydrogenase (ALDH) superfamily has 19 pro-tein-coding family members with varying tissue or development expression (Koppaka et al., 2012). ALDHs metabolize endoge-nous and exogenous aldehydes to their corresponding carbox-ylic acids to prevent accumulation of toxic aldehydes. ALDH1A enzymes are also involved in the biosynthesis of retinoic Acarbose (RA). Via synthesis of RA, ALDH1A enzymes indirectly regulate RA-mediated transcription of hundreds of genes that regulate normal stem cell proliferation and differentiation (Balmer and Blomhoff, 2002; Napoli et al., 1995).
ALDH enzymes also have a role in cancer. ALDHs mediate resistance to chemotherapy via direct drug metabolism and by regulation of reactive oxygen species (Bretz et al., 2012; Dylla et al., 2008). Many studies have used broad ALDH inhibitors such as N,N-diethylaminobenzaldehyde (DEAB) and disulfiram (DSF) to demonstrate a general role for ALDH in chemotherapy resistance (Kast and Belda-Iniesta, 2009; Morrison et al., 2010; Rezk et al., 2015; Yip et al., 2011). Other studies have used knockdown of select ALDH1 family members to support their role in chemotherapy resistance; ALDH1A1 or ALDH1A3 knock-down increases chemosensitivity in ovarian cancer, melanoma, breast cancer, and lung cancer (Januchowski et al., 2013). ALDH activity is essential to chemotherapy resistance in breast cancer (Raha et al., 2014), and ALDH1A2 and ALDH1A3 are
implicated in chemotherapy resistance in mesothelioma (Cortes-Dericks et al., 2014).
In ovarian cancer, in TP53 wild-type patients’ high mRNA
expression of ALDH1A2 is associated with poor overall survival (Ma and Zhao, 2016), and ALDHbright cells (cells with high
ALDH enzymatic activity based on the ALDEFLUOR assay) are resistant to cisplatin (Silva et al., 2011). ALDH1A1 is upregulated more than 100-fold in ovarian cancer cells selected for taxane resistance in vitro, and ALDH1A1 knockdown reversed that chemotherapy resistance (Steg et al., 2012). Furthermore, paired biopsies taken from patients (Steg et al., 2012) and patient-derived ovarian tumor xenografts (Dobbin et al., 2014) before and after chemotherapy demonstrated increased expression of ALDH1A1 and the cancer stem-like cell (CSC) marker CD133 in posttreatment samples.