Design and syntheses of hyaluronan oligosaccharide conjugates as inhibitors of CD44-Hyaluronan binding

Combinatorial synthesis of a hyaluronan based polysaccharide library for enhanced CD44 binding

Hyaluronan (HA) plays important roles in a wide range of biological events. The principal receptor of HA in the human body is the Cluster of Differentiation 44 (CD44). To enhance the binding between HA and CD44, a new approach was designed to take advantage of the four-component Ugi reaction. By modifying the carboxyl group on HA with various amine, aldehyde, and isocyanide moieties through the Ugi reaction, 36 HA like polysaccharides were generated. Two lead compounds were identified with enhanced CD44 binding compared to unmodified HA, which was confirmed by surface plasmon resonance (SPR), cellular studies and an in vivo mouse tumor model. Ski-learn as a machine learning tool was applied to analyze library data and yield predictions with an accuracy over 80 %. In conclusion, modification of HA via the Ugi reaction can be a promising strategy to develop novel binders toward HA receptors such as CD44.

Inhibition of CD44 sensitizes cisplatin-resistance and affects Wnt/β-catenin signaling in HNSCC cells

CD44 is one of the key cancer stem-like cell (CSC) marker and may have a potential role in tumorigenesis. In this study, we investigated the role of CD44 in prognosis of HNSCC patients, its possible crosstalk with Wnt/β-catenin signaling and modulating cisplatin resistance. We observed increased expression of CD44 in the cut margin of recurrent HNSCC patients were associated with poor prognosis. We observed that inhibition of CD44 by using 1,2,3,4 tetrahydroisoquinoline (THIQ) modulates the expression of Wnt/ β-catenin signaling proteins and further silencing of β-catenin also decreases the expression of CD44. This led us to investigate the possible protein-protein interaction between CD44 and β-catenin. Co-immunoprecipitation study illustrated possible interaction between CD44 and β-catenin which was further confirmed by molecular docking and molecular dynamic (MD) simulation studies. Molecular docking study revealed that one interface amino acid residue Glu642 of β -catenin interacts with Lys92 of CD44 which was also present for 20% of simulation time. Furthermore, we observed that inhibition of CD44 chemosensitizes cisplatin-resistant HNSCC cells towards cisplatin. In conclusion, this study investigated the possible role of CD44 along with Wnt/ β-catenin signaling and their possible therapeutic role to abrogate cisplatin resistance.

Hyaluronan promotes TRPV4-induced chondrogenesis in ATDC5 cells

Hyaluronan (HA) is an extracellular matrix glycosaminoglycan essential for the homeostasis of cartilage-related tissues. Intracellular adhesion molecule-1 (ICAM-1) and CD44 have been identified as receptors for HA. Recently, transient receptor potential vanilloid 4 (TRPV4) has emerged as a potential research target in several areas of physiology. TRPV4 is a Ca²⁺-permeable, non-selective cation channel that appears to have mechanosensory or osmosensory roles in several musculoskeletal tissues. HA and TRPV4 play key roles in chondrogenesis; however, it has remained unclear whether they have interactive effects on chondrogenesis and, if so, how do they interact with each other? This study investigated the relationship between HA, its receptors ICAM-1 and CD44, and TRPV4 in the chondrogenic pathway using the ATDC5 cell line. It was found that the presence of HA is required for TRPV4-induced chondrogenesis. Loss of HA suppressed TRPV4-induced expression of the chondrogenic markers, SOX9 and Aggrecan. Moreover, HA affects TRPV4-induced chondrogenic development via each of ICAM-1 and CD44 partially. In conclusion, for the first time, the existence of an interaction between HA, its receptor ICAM-1 and CD44, and TRPV4-activity in chondrogenesis in the ATDC5 cell line was reported. TRPV4 is known to function as a mechanosensory channel in several musculoskeletal tissues. Therefore, findings of this study may suggest the existence of a molecular mechanism that underlies the interactive effects of HA and mechanical loading on joint chondrogenesis.

Atomistic fingerprint of hyaluronan-CD44 binding

Hyaluronan is a polyanionic, megadalton-scale polysaccharide, which initiates cell signaling by interacting with several receptor proteins including CD44 involved in cell-cell interactions and cell adhesion. Previous studies of the CD44 hyaluronan binding domain have identified multiple widespread residues to be responsible for its recognition capacity. In contrast, the X-ray structural characterization of CD44 has revealed a single binding mode associated with interactions that involve just a fraction of these residues. In this study, we show through atomistic molecular dynamics simulations that hyaluronan can bind CD44 with three topographically different binding modes that in unison define an interaction fingerprint, thus providing a plausible explanation for the disagreement between the earlier studies. Our results confirm that the known crystallographic mode is the strongest of the three binding modes. The other two modes represent metastable configurations that are readily available in the initial stages of the binding, and they are also the most frequently observed modes in our unbiased simulations. We further discuss how CD44, fostered by the weaker binding modes, diffuses along HA when attached. This 1D diffusion combined with the constrained relative orientation of the diffusing proteins is likely to influence the aggregation kinetics of CD44. Importantly, CD44 aggregation has been suggested to be a possible mechanism in CD44-mediated signaling.

Hyaluronan is a natural sugar polymer in our bodies. Besides acting as a space-filling agent for example in multiple connective tissues, it also functions as a cellular cue in cancer and inflammation. Our tissues sense hyaluronan through receptors—proteins that sit at the surface of cells and grab the molecules they are expected to recognize. Although the knowledge associated with hyaluronan and its receptors is constantly accumulating, the molecular-level insight is largely missing or incomplete due to the lack of techniques able to probe the dynamics of protein–carbohydrate interactions with sufficiently high resolution. In this work, we characterize the binding of hyaluronan to its receptor CD44 with atomistic precision. We achieve this level of precision by employing atomistic molecular dynamics simulations. This computational technique allows one to follow the movement of atoms of a virtual system at scales beyond the resolution of any experimental technique. Our work specifically focuses on the different stages of hyaluronan–CD44 binding, and we observe the process to involve three different binding modes, making it more versatile than previously thought. Our insights, therefore, promote the understanding of the interplay between hyaluronan and HA, thereby fostering development of new drugs or inhibitors to malignancies, such as cancer metastasis.

Hyaluronan as a therapeutic target in human diseases

Accumulation and turnover of extracellular matrix is a hallmark of tissue injury, repair and remodeling in human diseases. Hyaluronan is a major component of the extracellular matrix and plays an important role in regulating tissue injury and repair, and controlling disease outcomes. The function of hyaluronan depends on its size, location, and interactions with binding partners. While fragmented hyaluronan stimulates the expression of an array of genes by a variety of cell types regulating inflammatory responses and tissue repair, cell surface hyaluronan provides protection against tissue damage from the environment and promotes regeneration and repair. The interactions of hyaluronan and its binding proteins participate in the pathogenesis of many human diseases. Thus, targeting hyaluronan and its interactions with cells and proteins may provide new approaches to developing therapeutics for inflammatory and fibrosing diseases. This review focuses on the role of hyaluronan in biological and pathological processes, and as a potential therapeutic target in human diseases.