A convenient thiazole orange fluorescence assay for the evaluation of DNA duplex hybridization stability

New ternary Fe(III)-8-hydroxyquinoline-reduced Schiff base complexes as selective anticancer drug candidates

Due to the growing prevalence of cancer diseases, new therapeutic options are urgently needed, and drugs based on metal ions other than platinum are alternatives with exciting possibilities. We report the synthesis, characterization and biological effect of mixed-ligand Fe(III)-aminophenolate complexes derived from salicylaldehyde and L-tryptophan with quinoline derivatives as co-ligands, namely 8-hydroxyquinoline (8HQ), [Fe(L)(8HQ)(H₂O)] (1) and its 5-cloro derivative (Cl8HQ), [Fe(L)(Cl8HQ)(H₂O)] (2). The complex bearing the aminophenolate and lacking the quinoline co-ligand, [Fe(L)(Cl)(H₂O)₂] (3), was prepared for comparison. The analytical and spectroscopic characterization revealed that 1 and 2 are octahedral Fe(III) complexes with the aminophenolate acting as a dianionic tridentate ligand and 8HQ co-ligands as bidentate chelates. Spectroscopic techniques and molecular docking studies were used to evaluate the ability of these complexes to bind bovine serum albumin (BSA) and calf thymus DNA. Complex 2 [Fe(L)(Cl8HQ)(H₂O)] was the one showing higher affinity for both biomolecules. Cell viability was assessed in breast, colorectal and bone human cancer cell lines. 1 and 2 were found to be more active than cisplatin in all cell lines tested. A non-tumoral fibroblast line (L929, mouse non-tumoral fibroblasts) was used to evaluate selectivity. The results evidence that 2 shows much higher selectivity than 1 in all cell lines tested, but particularly in bone cancer cells in which selectivity index (SI) values are 8.0 and 18.8 for 1 and 2, respectively.

Optical antisense tumor targeting in vivo with an improved fluorescent DNA duplex probe

Fluorescent conjugated DNA oligonucleotides for antisense targeting of mRNA has the potential of improving tumor/normal tissue ratios over that achievable by nuclear antisense imaging. By conjugating the Cy5.5 emitter to the 3' equivalent end of a 25 mer phosphorothioate (PS) antisense major DNA and hybridizing with a shorter 18 mer phosphodiester (PO) complementary minor DNA (cDNA) with the Black Hole inhibitor BHQ3 on its 5' end (i.e., PS DNA25-Cy5.5/PO cDNA18-BHQ3), we previously achieved antisense optical imaging in mice as a proof of this concept. In a process of optimization, we have now evaluated the stability of a small series of duplexes with variable-length minor strands. From these results, a new study anti-mdr1 antisense duplex was selected with a 10 mer minor strand (i.e., PS DNA25-Cy5.5/PO cDNA10-BHQ3). The new study duplex shows stability in serum environments at 37 degrees C and provides a dramatically enhanced fluorescence in KB-G2 (pgp++) cells when compared with KB-31 (pgp+/-) as evidence of antisense dissociation at its mdr1 mRNA target. The duplex was also administered to KB-G2 tumor bearing mice, and when compared to the duplex used previously, the fluorescence from the tumor thigh was more obvious and the tumor-to-background fluorescence ratio was improved. In conclusion, by a process designed to optimize the duplex for optical antisense tumor targeting, the fluorescence signal was improved both in cells and in tumored mice.