Targeting colorectal cancer stem cells with ALDH1B1 antagonists - Colorectal cancer is the third most common malignancy in the world, with approximately 1.4 million new cases and 700,000 deaths each year. Global incidence rates are expected to escalate 60% by 2030 as Western diets and lifestyles become more common, and colorectal cancer is afflicting increasing numbers of young adults. Despite preventative screening and surveillance, approximately 20% of colorectal cancer patients have metastatic disease at the time of diagnosis, and 40-50% of early-stage patients will relapse after treatment. Unfortunately standard colorectal cancer therapies such as anti-mitotic agents, epidermal growth factor receptor antagonists, and angiogenesis inhibitors are largely ineffectual against late-stage disease. As a result, the 5-year survival rates for these patients is only 12%. It is now widely believed that eliminating cancer stem cells (CSCs) is the key to durable clinical responses, as these self-renewing cells drive tumor relapse, chemoresistance, and metastasis. Our project strives to achieve this goal by investigating and pharmacologically targeting metabolic pathways that are unique to colorectal cancer CSCs. Our work builds on recent reports that aldehyde dehydrogenase 1B1 (ALDH1B1) is expressed in intestinal stem cell and required for the growth of colon cancer-derived spheroid cultures and xenografts. Our findings support a role for ALDH1B1 in colorectal CSC maintenance, and we have developed the first known ALDH1B1-selective antagonists. We have also solved the first X-ray crystal structures of ALDH1B1 and ALDH1B1-inhibitor complexes, uncovering the molecular basis of antagonist action and gaining insights for further compound development. Our latest lead compounds can inhibit the viability of colorectal cancer spheroids, with minimal effects on adherent cultures or non- cancerous cells. In addition, our preliminary studies indicate that ALDH1B1 inhibitors can suppress the growth of colon cancer xenografts in mice. We are now investigating the mechanisms by which ALDH1B1 promotes colorectal cancer (Aim 1). We will explore the potential roles of this mitochondrial enzyme in colorectal CSC maintenance, chemoresistance, and invasiveness, using cell lines that are representative of various colorectal cancer subtypes. We will also determine whether oncogenic ALDH1B1 function involves the oxidation of retinal and/or lipid peroxidation products, and we will elucidate the ALDH1B1-dependent transcriptome. In parallel with these mechanistic studies, we will use medicinal chemistry, biochemical assays, and cellular models to develop ALDH1B1 inhibitors with optimized potency, selectivity, and pharmacological properties (Aim 2). We will then evaluate the activities of ALDH1B1 inhibitors in colorectal cancer xenograft models (Aim 3). Together, these investigations will deepen our understanding of ALDH1B1 function and colorectal CSC biology. They will also generate new chemical tools for studying ALDH1B1-dependent pathways, reveal the therapeutic potential of pharmacological ALDH1B1 inhibition, and provide valuable leads for the development of ALDH1B1-targeting drugs.
