Targeting Aberrant Glycosylation In Colon And Prostate Cancer With An Improved Synthetic Lectin Array

Cancers of the colon and prostate, though treatable, necessitate early detection to improve patient outcomes. Current diagnostics, (visual methods or biopsies) besides being invasive, are subjective towards interpretation, thus decreasing accuracy. Alternatively, blood-based tests involving measuring of specific biomarkers (like CEA and PSA for colon and prostate cancers, respectively) are associated with high false-positive rates and are more useful for monitoring post-treatment patient health, thus driving efforts to identify better screening and diagnostic techniques. Abnormal glycosylation of integral membrane and secreted glycoproteins is known to take place at the onset of many diseases, including cancer, and presents as the over, under or new occurrence of certain glycans. The aim of this study is to design synthetic lectins (SLs) that could discriminate cancer-associated glycans (CAGs) and to investigate global glycosylation changes associated with colon and prostate cancers. Further, the ability of an array of SLs to discriminate cells based upon their metastatic potential, demonstrates an alternative approach to detect colon and prostate cancers by looking at aberrant glycosylation changes rather than hunting for a specific biomarker. Chapter 1 details on abnormal protein glycosylations. An account of how diols in glycans can be investigated using boronic acids mediated glycan sensors in the past. This follows introduction to Lavigne group peptide-boronic acid conjugates (Synthetic Lectins). A discussion of SL-array platform and its utility at discriminating proteins extracted from colon cell lines Chapter 2 describes various chemical modifications done to the SLs (peptide sequences and boronic acid moieties) in order to establish structure and activity relationships against purified glycoprotein analytes. Purified glycoproteins were used since the glycans displayed in them are also present in CAGs and have a positive disease correlation. The aim of these experiments is to gain an insight on chemical basis of SL-glycoprotein interactions. Several hypothesis were drawn on the design of new SLs. Positive charges on SLs helped pre-organization of SL-glycoprotein interaction. Chapter 3 aims at incorporating new SLs into the pre-existing SL array to investigate colon and prostate cancer in vitro. The chemical make-up of the SLs that statistically contributed the most to discriminate cancer is evaluated. An extended SL array (combining old and new SLs), can discriminate normal, low metastatic and high metastatic states from secreted proteins of different prostate and colon cells with \u3e99% accuracy. Metastatic potential of colon and prostate correlate with variation in i). number of Arginine (R) residues and ii). number of phenyl rings in SL peptide sequences. Chapter 4 details on quantifying sialic acid content in vitro and investigating any correlations with the metastatic potential of colon and prostate cell lines. Further, several CAGs were classified using SL array with \u3e99% accuracy. The positively charged amino acids (e.g., Arg) and those containing phenyl ring residues (e.g., Tyr, Phe) appear to be the principal factors involved in discriminating CAGs. Based on the relative importance that charged amino acids and phenyl boronic acids in SLs have at evaluating metastatic potential; several tissue specific SLs were found and their peptide sequence homology was studied