A Novel ALDH1A1 Inhibitor Targets Cells with Stem Cell Characteristics in Ovarian Cancer

Abstract

A small of population of slow cycling and chemo-resistant cells referred to as cancer stem cells (CSC) have been implicated in cancer recurrence. There is emerging interest in developing targeted therapeutics to eradicate CSCs. Aldehyde-dehydrogenase (ALDH) activity was shown to be a functional marker of CSCs in ovarian cancer (OC). ALDH activity is increased in cells grown as spheres versus monolayer cultures under differentiating conditions and in OC cells after treatment with platinum. Here, we describe the activity of CM37, a newly identified small molecule with inhibitory activity against ALDH1A1, in OC models enriched in CSCs. Treatment with CM37 reduced OC cells’ proliferation as spheroids under low attachment growth conditions and the expression of stemness-associated markers (OCT4 and SOX2) in ALDH+ cells fluorescence-activated cell sorting (FACS)-sorted from cell lines and malignant OC ascites. Likewise, siRNA-mediated ALDH1A1 knockdown reduced OC cells’ proliferation as spheres, expression of stemness markers, and delayed tumor initiation capacity in vivo. Treatment with CM37 promoted DNA damage in OC cells, as evidenced by induction of γH2AX. This corresponded to increased expression of genes involved in DNA damage response, such as NEIL3, as measured in ALDH+ cells treated with CM37 or in cells where ALDH1A1 was knocked down. By inhibiting ALDH1A1, CM37 augmented intracellular ROS accumulation, which in turn led to increased DNA damage and reduced OC cell viability. Cumulatively, our findings demonstrate that a novel ALDH1A1 small molecule inhibitor is active in OC models enriched in CSCs. Further optimization of this new class of small molecules could provide a novel strategy for targeting treatment-resistant OC.

Frizzled-7 Identifies Platinum Tolerant Ovarian Cancer Cells Susceptible to Ferroptosis

“…Given the possibility that CSCs would be more resistant to chemotherapy due to upregulated antiredox mechanisms (11) and considering a recently proposed association between oxidative stress and ferroptosis, a new form of cell death triggered by oxidized lipids, we examined a gene set related to "ferroptosis" (24) in platinum tolerant compared to parental OC cells. Clear differences including upregulated genes involved in glutathione metabolism and anti-oxidant defense mechanisms were observed in platinum-tolerant OC cells vs. chemotherapy-naïve cells (SKOV3,…”

“…glutathione peroxidase 4 (GPX4) tumor initiation capacity (TIC) (10). Importantly, ovarian CSCs possess a phenotype associated with drug resistance, including enhanced DNA repair, diminished apoptotic responses, increased efflux mechanisms and enhanced antioxidation defense (8,11), which allow them to escape from chemotherapy. The boundaries between stemness and chemotherapy tolerant phenotypes remain blurry and while an overlap exists, it is assumed that distinct pathways drive the two entities.…”

“…The findings reveal a novel therapeutic vulnerability of platinum tolerant cancer cells and provide new insight into a potential "persister cancer cell" phenotype.glutathione peroxidase 4 (GPX4) tumor initiation capacity (TIC) (10). Importantly, ovarian CSCs possess a phenotype associated with drug resistance, including enhanced DNA repair, diminished apoptotic responses, increased efflux mechanisms and enhanced antioxidation defense (8,11), which allow them to escape from chemotherapy. The boundaries between stemness and chemotherapy tolerant phenotypes remain blurry and while an overlap exists, it is assumed that distinct pathways drive the two entities.As platinum tolerant cancer cells drive tumor relapse, decreasing survival rate of women with OC, we aimed to identify specific markers, by using in vitro and in vivo models of repeated exposure to the cytotoxic agent.…”

Targeting Aldehyde Dehydrogenases to Eliminate Cancer Stem Cells in Gynecologic Malignancies

“…Using this HTS platform, 64,000 compounds were screened and a potent, highly selective, and novel ALDH1A1 inhibitor CM037 (A37) was identified [111] (Table 2). In OC cells, Matei and Hurley et al demonstrated that CM037 significantly inhibited tumorsphere formation and CSC viability [84]. In a subsequent study by the same group, CM037 treatment promoted DNA damage in OC cells with a corresponding increase in DNA damage response genes.…”

“…In OCSCs, of the 19 ALDH isoforms, ALDH1A1 was highly correlated with chemotherapy resistance [78,79,81,82,84,85]. Expression of ALDH1A1 was 100-fold higher in OC cells selected for taxane-resistance in vitro, and ALDH1A1 knockdown sensitized the resistant cells to chemotherapy [82].…”