CHARACTERIZING GLYCOSAMINOGLYCAN AND GLYCOSAMINOGLYCAN-OLIGO INTERACTIONS WITH CANCER STEM CELLS AND THEIR REGULATORS

Tumor metastasis and recurrence account for more than 90% of cancer-associated deaths and are thought to occur due to a small subpopulation of neoplastic cells known as cancer stem cells (CSCs). Because CSCs are resistant to conventional chemotherapy, there is a critical need to develop CSC-targeting agents. Microenvironmental components, especially glycosaminoglycans (GAGs), play a key role in regulating CSC phenotype. GAGs such as heparan sulfate (HS) interact with hundreds of proteins and influence a variety of biological processes including tumor proliferation, angiogenesis, metastasis and stem cell biology. Recently, the Desai and Patel laboratories have demonstrated that a hexasaccharide form of HS, HS06, inhibits CSC self-renewal in multiple cancer cell lines, while shorter/longer chains are less potent. To explore potential mechanisms driving this phenomenon, this work aimed to devise a biophysical screening methodology to identify CSC-relevant protein targets of HS06. This was accomplished using fluorescence spectroscopy in combination with computational docking assays. Our methodology identified several new, CSC-relevant proteins that bound HS06 with nanomolar affinity. Furthermore, chain-length dependent patterns were observed for HS binding to IGF-1, IGF-1R and the IGF-1/IGF-1R complex (a key regulator of CSCs), providing a plausible explanation for prior cell-based observations that HS06 inhibits IGF-1R activation while longer chains enhance activation. The second aim of this work was to study HS06’s ability to target CSCs, both in vitro and in vivo, in comparison to 2-O,3-O-desulfated heparin (ODSH), a nonanticoagulant GAG-derivative currently in multiple cancer clinical trials. Using preliminary in vitro screens, we observed that HS06 inhibited CSCs while longer nonanticoagulant GAGs like ODSH did not. This was confirmed in vivo, where HS06 was more effective at inhibiting tumor growth and CSC self-renewal in an HT-29 xenograft mouse model compared to ODSH. In conclusion, despite little attention being paid towards the study of GAG-oligos in literature, our work demonstrates that such molecules demonstrate significant therapeutic promise. These preliminary results indicate that in contrast to longer polymers such as ODSH, GAG-oligos like HS06 warrant further attention in translational/clinical studies aimed at developing anti-CSC agents