title: Validation and characterization of monoclonal antibodies to target cancer stem cells and to develop new anti-cancer therapies
Creators: name: Müller, Sandra Rita
Publisher: name: UNSPECIFIED
Year: 2022

description: A fundamental challenge for therapy and long-term survival of cancer patients is tumor reoccurrence, which is often caused by cancer stem cells (CSC) with self-renewal capacities that are not effectively eliminated by chemo- or targeted therapies. In this work, unique, affine and specific mouse monoclonal antibodies from a mouse immunization with CSC membranes were characterized and found to be well suited for the detection of CSC surface proteins. The identification of these targets revealed HSD17B12 as a novel CSC marker, which was evaluated in this work. For the very first time HSD17B12 was found to be located at the cell surface of certain cell types and this opened up the opportunity to investigate the functional relevance of cell surface HSD17B12 for the respective cell types. HSD17B12 was found to contribute to the maintenance of CSC properties as deletion of HSD17B12 reduced cell proliferation, especially in 3D cell culture, and CSC markers such as aldehyde dehydrogenase activity. In line with the known role of HSD17B12 in lipid metabolism, loss of HSD17B12 function was shown to impair lipid droplet formation. Further, the loss of HSD17B12 resulted in a resistance mechanism to ferroptosis which is a special form of cell death triggered by oxidation of cellular lipids. Interestingly, ferroptosis is linked to CSC biology through the Hippo pathway and the activity of YAP and TAZ. It was demonstrated that loss of HSD17B12 impacts the Hippo pathway and leads to the inactivation of oncogenic YAP and TAZ. Conversely, modulation of YAP/TAZ activity impacts the cell surface expression of HSD17B12. Along with the analysis of relevant EMT markers, this led to the hypothesis that loss of HSD17B12 contributes to the differentiation of cells from a more mesenchymal CSC phenotype to an epithelial one. Cellular differentiation upon deletion of HSD17B12 was also found in leukemic HAP1 cells. Thus, the plasma membrane localization of HSD17B12 was hypothesized to fulfill a novel function in CSC, possibly in the interaction with the extracellular matrix. The novel finding that HSD17B12 is expressed on the cell surface offered the opportunity to investigate the effect of treating cancer cells with anti-HSD17B12 antibodies. It could be shown that the antibodies reduce the growth of certain cancer cells in 3D cell culture. It was also found that the HSD17B12 antibodies partially internalize and that an antibody-drug conjugate (ADC) approach would theoretically be possible. However, as HSD17B12 was also found on regular monocytes potential undesired side effects of an ADC approach would need to be examined in more detail. To follow up on this, it will be important to further characterize the function of HSD17B12 on the cell surface on normal and cancer cells in order to assess whether targeting of cell surface HSD17B12 alone could be therapeutically relevant. Given its function in the biology of CSC, HSD17B12 might be a potential drug target for combination with standard of care chemo- or targeted therapy to develop treatment options for cancer patients that offer more durable therapeutic benefits.