Biochemical Studies of Lectins with Synthetic Glycoconjugates and the Cytotoxicity Studies of Metal ion Complexes

Part A: Lectins and glycoconjugates 

Lectins are useful as histochemical and cytochemical reagents for the detection of glycoconjugates in tissue sections, on cells and sub cellular organelles, and in the investigation of intracellular pathways of protein glycosylation.  It is always interesting to change the properties of lectins, and study the consequences of such changes in the context of cellular reactions.  Therefore, part A deals with the agglutination inhibition and binding aspects of lectins using aromatic-glyco-conjugates.  

Different lectins have been chosen to study the binding aspects toward glycoconjugates modified by connecting aromatic moieties through imine conjugation at their C1- or C2- position.  Naphthyl-imine-conjugates were found to be most effective towards agglutination inhibition, quenching fluorescence intensity and exhibit higher binding.  Changes in the secondary structures have been addressed by far- and near-UV CD spectroscopy.  The present studies demonstrated that conjugates bind at the carbohydrate recognition domain (CRD) mainly through polar interactions in addition to exhibiting nonpolar/hydrophobic interactions.  Binding of conjugates at CRD has been further demonstrated by rigid docking.

Part B: Metal ion complexes and cytotoxicity

Cancer is one of the life threatening diseases and the cancerous cells become resistant to natural drugs upon continuous treatment.  This shifts the interest to other side of drugs namely chemically synthesized metallodrugs such as cis-platin and carboplatin.  But their uses are restricted to narrow range of tumor, poor aqueous solubility and several toxicological problems.  This part deals with binding and cleavage of DNA and anti proliferative activity by metal complex of anthracenyl terpyridine-Cu(II).

Copper(II) complex of anthtracenyl terpyridine has been synthesized and stability at pH – 7.4  was monitored over a week.  This complex binds the CT-DNA primarily through intercalation.  While all the three forms of the plasmid DNA were present when the cleavage carried out under visible light, only closed and nicked circular forms were observed under UV light.  However, plasmid cleavage was spontaneous without exhibiting other forms when the cleavage carried out in dark.  A considerable low IC50 was observed in HPV infected (HeLa, SiHa, CaSki) as compared to non HPV infected cell lines (MCF–7, HepG2, H1299).  Granular structures were observed only with the HPV infected cells and not with others.  Significance of granular structure may be correlated with the involvement of HPV E6 oncoprotein.  The role of HPV has been further confirmed by transfecting the MCF–7 cells (originally not possessing HPV copy) with E6.  Apoptotic cell death induced by copper complex was supported by the western blot and FACS analysis.  To our knowledge this is the first copper complex that causes the cell death by interacting with HPV oncoprotein followed by exhibiting remarkable antiproliferative activity.