In vitro spectroscopic studies of 9-amino-5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazine chloride with main carrier plasma proteins.

Current methods of cancer treatment, particularly chemotherapy, are associated with harmful side effects. For this reason, it is significant to study new substances with anticancer potential with the highest possible efficacy and the lowest possible side effects. The aim of the study was the spectroscopic analysis of the interaction between 9-amino-5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazine chloride (Salt3) and main carrier proteins, such as human serum albumin (HSA), α1 acid glycoprotein (AGP), human γ globulin (HGG) and controlled normal serum (CNS). The association constants (K [mol·L]) and the number of binding site classes (n) for the binding of Salt3 with studied carrier proteins and controlled normal serum were calculated using the Klotz equation. To study HSA and AGP high affinity binding sites, the fluorescent markers were used. Spectral parameter A and the second derivative of differential absorption spectra were used to assess environmental changes around aromatic amino acids residues. The changes in HSA and AGP secondary structure in the complexes with Salt3 were evaluated using the analysis using circular dichroism. Salt3 slightly binds to HSA, AGP, HGG molecules and CNS. In addition, Salt3 affects the tertiary structure of the studied proteins, while it does not damage the secondary structure of the main carrier proteins responsible for Salt3 distribution in the bloodstream. Because Salt3 binds weakly to model carrier proteins and normal control serum, it can lead to both strong therapeutic and toxic effects. Considering these preliminary spectroscopic studies, additional tests as well as expanding research to include other techniques seem justified.